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Sample records for buried tunnel junction

  1. Magnetic tunnel junctions (MTJs)

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    We review the giant tunnel magnetoresistance (TMR) in ferromagnetic-insulator-ferromagnetic junctions discovered in recent years, which is the magnetoresistance (MR) associated with the spin-dependent tunneling between two ferromagnetic metal films separated by an insulating thin tunnel barrier. The theoretical and experimental results including junction conductance, magnetoresistance and their temperature and bias dependences are described.

  2. Confocal Annular Josephson Tunnel Junctions

    Science.gov (United States)

    Monaco, Roberto

    2016-09-01

    The physics of Josephson tunnel junctions drastically depends on their geometrical configurations and here we show that also tiny geometrical details play a determinant role. More specifically, we develop the theory of short and long annular Josephson tunnel junctions delimited by two confocal ellipses. The behavior of a circular annular Josephson tunnel junction is then seen to be simply a special case of the above result. For junctions having a normalized perimeter less than one, the threshold curves in the presence of an in-plane magnetic field of arbitrary orientations are derived and computed even in the case with trapped Josephson vortices. For longer junctions, a numerical analysis is carried out after the derivation of the appropriate motion equation for the Josephson phase. We found that the system is modeled by a modified and perturbed sine-Gordon equation with a space-dependent effective Josephson penetration length inversely proportional to the local junction width. Both the fluxon statics and dynamics are deeply affected by the non-uniform annulus width. Static zero-field multiple-fluxon solutions exist even in the presence of a large bias current. The tangential velocity of a traveling fluxon is not determined by the balance between the driving and drag forces due to the dissipative losses. Furthermore, the fluxon motion is characterized by a strong radial inward acceleration which causes electromagnetic radiation concentrated at the ellipse equatorial points.

  3. Josephson tunnel junction microwave attenuator

    DEFF Research Database (Denmark)

    Koshelets, V. P.; Shitov, S. V.; Shchukin, A. V.

    1993-01-01

    A new element for superconducting electronic circuitry-a variable attenuator-has been proposed, designed, and successfully tested. The principle of operation is based on the change in the microwave impedance of a superconductor-insulator-superconductor (SIS) Josephson tunnel junction when dc bias...

  4. Electronic thermometry in tunable tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Maksymovych, Petro

    2016-03-15

    A tunable tunnel junction thermometry circuit includes a variable width tunnel junction between a test object and a probe. The junction width is varied and a change in thermovoltage across the junction with respect to the change in distance across the junction is determined. Also, a change in biased current with respect to a change in distance across the junction is determined. A temperature gradient across the junction is determined based on a mathematical relationship between the temperature gradient, the change in thermovoltage with respect to distance and the change in biased current with respect to distance. Thermovoltage may be measured by nullifying a thermoelectric tunneling current with an applied voltage supply level. A piezoelectric actuator may modulate the probe, and thus the junction width, to vary thermovoltage and biased current across the junction. Lock-in amplifiers measure the derivatives of the thermovoltage and biased current modulated by varying junction width.

  5. Predictive modelling of ferroelectric tunnel junctions

    Science.gov (United States)

    Velev, Julian P.; Burton, John D.; Zhuravlev, Mikhail Ye; Tsymbal, Evgeny Y.

    2016-05-01

    Ferroelectric tunnel junctions combine the phenomena of quantum-mechanical tunnelling and switchable spontaneous polarisation of a nanometre-thick ferroelectric film into novel device functionality. Switching the ferroelectric barrier polarisation direction produces a sizable change in resistance of the junction—a phenomenon known as the tunnelling electroresistance effect. From a fundamental perspective, ferroelectric tunnel junctions and their version with ferromagnetic electrodes, i.e., multiferroic tunnel junctions, are testbeds for studying the underlying mechanisms of tunnelling electroresistance as well as the interplay between electric and magnetic degrees of freedom and their effect on transport. From a practical perspective, ferroelectric tunnel junctions hold promise for disruptive device applications. In a very short time, they have traversed the path from basic model predictions to prototypes for novel non-volatile ferroelectric random access memories with non-destructive readout. This remarkable progress is to a large extent driven by a productive cycle of predictive modelling and innovative experimental effort. In this review article, we outline the development of the ferroelectric tunnel junction concept and the role of theoretical modelling in guiding experimental work. We discuss a wide range of physical phenomena that control the functional properties of ferroelectric tunnel junctions and summarise the state-of-the-art achievements in the field.

  6. Characterization of magnetic tunnel junction test pads

    DEFF Research Database (Denmark)

    Østerberg, Frederik Westergaard; Kjær, Daniel; Nielsen, Peter Folmer

    2015-01-01

    We show experimentally as well as theoretically that patterned magnetic tunnel junctions can be characterized using the current-in-plane tunneling (CIPT) method, and the key parameters, the resistance-area product (RA) and the tunnel magnetoresistance (TMR), can be determined. The CIPT method...... on square tunnel junction pads with varying sizes and analyze the measured data using both the original and the modified CIPT model. Thus, we determine in which sample size range the modified CIPT model is needed to ensure validity of the extracted sample parameters, RA and TMR. In addition, measurements...... as a function of position on a square tunnel junction pad are used to investigate the sensitivity of the measurement results to probe misalignment....

  7. Modelling of Dual-Junction Solar Cells including Tunnel Junction

    Directory of Open Access Journals (Sweden)

    Abdelaziz Amine

    2013-01-01

    Full Text Available Monolithically stacked multijunction solar cells based on III–V semiconductors materials are the state-of-art of approach for high efficiency photovoltaic energy conversion, in particular for space applications. The individual subcells of the multi-junction structure are interconnected via tunnel diodes which must be optically transparent and connect the component cells with a minimum electrical resistance. The quality of these diodes determines the output performance of the solar cell. The purpose of this work is to contribute to the investigation of the tunnel electrical resistance of such a multi-junction cell through the analysis of the current-voltage (J-V characteristics under illumination. Our approach is based on an equivalent circuit model of a diode for each subcell. We examine the effect of tunnel resistance on the performance of a multi-junction cell using minimization of the least squares technique.

  8. Inelastic tunneling in superconducting junctions

    Energy Technology Data Exchange (ETDEWEB)

    Hlobil, Patrik Christian

    2016-06-10

    In this dissertation a theoretical formalism of elastic and inelastic tunneling spectroscopy is developed for superconductors. The underlying physical processes behind the different two tunneling channels and their implications for the interpretation of experimental tunneling data are investigated in detail, which can explain the background conductance seen in the cuprate and iron-based superconductors. Further, the properties of the emitted light from a superconducting LED are investigated.

  9. Microscopic tunneling theory of long Josephson junctions

    DEFF Research Database (Denmark)

    Grønbech-Jensen, N.; Hattel, Søren A.; Samuelsen, Mogens Rugholm

    1992-01-01

    We present a numerical scheme for solving a nonlinear partial integro-differential equation with nonlocal time dependence. The equation describes the dynamics in a long Josephson junction modeled by use of the microscopic theory for tunneling between superconductors. We demonstrate...

  10. Cooling of suspended nanostructures with tunnel junctions

    OpenAIRE

    Koppinen, P. J.; Maasilta, I. J.

    2009-01-01

    We have investigated electronic cooling of suspended nanowires with SINIS tunnel junction coolers. The suspended samples consist of a free standing nanowire suspended by four narrow ($\\sim$ 200 nm) bridges. We have compared two different cooler designs for cooling the suspended nanowire. We demonstrate that cooling of the nanowire is possible with a proper SINIS cooler design.

  11. Josephson tunnel junctions with ferromagnetic interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Weides, M.P.

    2006-07-01

    Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al{sub 2}O{sub 3} tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or {pi} coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, {pi}) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-{pi} Josephson junction. At a certain temperature this 0-{pi} junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum {phi}{sub 0}. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T {yields} 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)

  12. Fabrication of magnetic tunnel junctions with epitaxial and textured ferromagnetic layers

    Science.gov (United States)

    Chang, Y. Austin; Yang, Jianhua Joshua

    2008-11-11

    This invention relates to magnetic tunnel junctions and methods for making the magnetic tunnel junctions. The magnetic tunnel junctions include a tunnel barrier oxide layer sandwiched between two ferromagnetic layers both of which are epitaxial or textured with respect to the underlying substrate upon which the magnetic tunnel junctions are grown. The magnetic tunnel junctions provide improved magnetic properties, sharper interfaces and few defects.

  13. Brownian refrigeration by hybrid tunnel junctions

    OpenAIRE

    Peltonen, J. T.; Helle, M.; Timofeev, A. V.; Solinas, P.; Hekking, F. W. J.; Pekola, Jukka P.

    2011-01-01

    Voltage fluctuations generated in a hot resistor can cause extraction of heat from a colder normal metal electrode of a hybrid tunnel junction between a normal metal and a superconductor. We extend the analysis presented in Phys. Rev. Lett. 98, 210604 (2007) of this heat rectifying system, bearing resemblance to a Maxwell’s demon. Explicit analytic calculations show that the entropy of the total system is always increasing. We then consider a single-electron transistor configuration with two ...

  14. Superconducting Tunnel Junction Arrays for UV Photon Detection Project

    Data.gov (United States)

    National Aeronautics and Space Administration — An innovative method is described for the fabrication of superconducting tunnel junction (STJ) detector arrays offering true "three dimensional" imaging throughout...

  15. Fully magnetic manganite spin filter tunnel junctions

    Science.gov (United States)

    Prasad, Bhagwati; Blamire, Mark G.

    2016-09-01

    In this paper we demonstrate spintronic devices which combine magnetic tunnel junctions with a spin-filtering tunnel barrier. These consist of an ultrathin ferromagnetic insulating barrier, Sm0.75Sr0.25MnO3, sandwiched between two ferromagnetic half-metallic manganite electrodes, La0.7Sr0.3MnO3 and La0.7Ca0.3MnO3, in a nanopillar structure. Depending on the relative magnetic configurations of barrier and electrode layers, three resistance states are well defined, which therefore represent a potential three-state memory concept. These results open the way for the development of spintronic devices by exploiting the many degrees of freedom of perovskite manganite heterostructure systems.

  16. Resonant tunnel magnetoresistance in a double magnetic tunnel junction

    KAUST Repository

    Useinov, Arthur

    2011-08-09

    We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FML/I/FMW/I/FMR, where the magnetization of the middle ferromagnetic metal layer FMW can be aligned parallel or antiparallel with respect to the fixed magnetizations of the left FML and right FMR ferromagnetic electrodes. The transmission coefficients for components of the spin-dependent current, and TMR are calculated as a function of the applied voltage. As a result, we found a high resonant TMR. Thus, DMTJ can serve as highly effective magnetic nanosensor for biological applications, or as magnetic memory cells by switching the magnetization of the inner ferromagnetic layer FMW.© Springer Science+Business Media, LLC 2011.

  17. Annealing free magnetic tunnel junction sensors

    Science.gov (United States)

    Knudde, S.; Leitao, D. C.; Cardoso, S.; Freitas, P. P.

    2017-04-01

    Annealing is a major step in the fabrication of magnetic tunnel junctions (MTJs). It sets the exchange bias between the pinned and antiferromagnetic layers, and helps to increase the tunnel magnetoresistance (TMR) in both amorphous and crystalline junctions. Recent research on MTJs has focused on MgO-based structures due to their high TMR. However, the strict process control and mandatory annealing step can limit the scope of the application of these structures as sensors. In this paper, we present AlOx-based MTJs that are produced by ion beam sputtering and remote plasma oxidation and show optimum transport properties with no annealing. The microfabricated devices show TMR values of up to 35% and using NiFe/CoFeB free layers provides tunable linear ranges, leading to coercivity-free linear responses with sensitivities of up to 5.5%/mT. The top-pinned synthetic antiferromagnetic reference shows a stability of about 30 mT in the microfabricated devices. Sensors with linear ranges of up to 60 mT are demonstrated. This paves the way for the integration of MTJ sensors in heat-sensitive applications such as flexible substrates, or for the design of low-footprint on-chip multiaxial sensing devices.

  18. MgB2 tunnel junctions and SQUIDs

    NARCIS (Netherlands)

    Brinkman, A.; Rowell, J.M.

    2007-01-01

    Recent advances in the realization and understanding of MgB2 tunnel junctions and SQUIDs are surveyed. High quality MgB2 junctions with suitable tunnel barriers have been realized based on both oriented and epitaxial thin MgB2 films. Multiband transport properties, such as the existence of two energ

  19. Parametric excitation of plasma oscillations in a Josephson tunnel junction

    DEFF Research Database (Denmark)

    Bak, Christen Kjeldahl; Kofoed, Bent; Pedersen, Niels Falsig

    1975-01-01

    Experimental evidence for subharmonic parametric excitation of plasma oscillations in Josephson tunnel junctions is presented. The experiments described are performed by measuring the microwave power necessary to switch a Josephson−tunnel junction biased in the zero−voltage state to a finite−volt......−voltage state. Journal of Applied Physics is copyrighted by The American Institute of Physics....

  20. Gamma Radiation Tolerance of Magnetic Tunnel Junctions

    Science.gov (United States)

    Ren, Fanghui; Jander, Albrecht; Dhagat, Pallavi; Nordman, Cathy

    2011-10-01

    Determining the radiation tolerance of magnetic tunnel junctions (MTJ), which are the storage elements of non-volatile magnetoresistive random access memories (MRAM), is important for investigating their potential application in space. In this effort, the effect of gamma radiation on MTJs with MgO tunnel barriers was studied. Experimental and control groups of samples were characterized by ex situ measurements of the magnetoresistive hysteresis loops and I-V curves. The experimental group was exposed to gamma rays from a ^60Co source. The samples initially received a dose of 5.9 Mrad (Si) after which they were again characterized electrically and magnetically. Irradiation was then continued for a cumulative dose of 10 Mrad and the devices re-measured. The result shows no change in magnetic properties such as coercivity or exchange coupling due to irradiation. After correcting for differences in temperature at the time of testing, the tunneling magnetoresistance was also found to be unchanged. Thus, it has been determined that MgO-based MTJs are highly tolerant of gamma radiation, particularly in comparison to silicon field-effect transistors which have been shown to degrade with gamma ray exposure even as low as 100 Krad [Zhiyuan Hu. et al., IEEE trans. on Nucl. Sci., vol. 58, 2011].

  1. Magnetic interaction between spatially extended superconducting tunnel junctions

    DEFF Research Database (Denmark)

    Grønbech-Jensen, Niels; Samuelsen, Mogens Rugholm

    2002-01-01

    A general description of magnetic interactions between superconducting tunnel junctions is given. The description covers a wide range of possible experimental systems, and we explicitly explore two experimentally relevant limits of coupled junctions. One is the limit of junctions with tunneling...... been considered through arrays of superconducting weak links based on semiconductor quantum wells with superconducting electrodes. We use the model to make direct interpretations of the published experiments and thereby propose that long-range magnetic interactions are responsible for the reported...

  2. Planar Josephson tunnel junctions in a transverse magnetic field

    DEFF Research Database (Denmark)

    Monacoa, R.; Aarøe, Morten; Mygind, Jesper

    2007-01-01

    Traditionally, since the discovery of the Josephson effect in 1962, the magnetic diffraction pattern of planar Josephson tunnel junctions has been recorded with the field applied in the plane of the junction. Here we discuss the static junction properties in a transverse magnetic field where...... demagnetization effects imposed by the tunnel barrier and electrodes geometry are important. Measurements of the junction critical current versus magnetic field in planar Nb-based high-quality junctions with different geometry, size, and critical current density show that it is advantageous to use a transverse...

  3. Zero-voltage nondegenerate parametric mode in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Pedersen, Niels Falsig

    1976-01-01

    A new parametric mode in a Josephson tunnel junction biased in the zero-voltage mode is suggested. It is a nondegenerate parametric excitation where the junction plasma resonance represents the input circuit, and a junction geometrical resonance represents the idler circuit. This nondegenerate mo...... for such a coupling. Journal of Applied Physics is copyrighted by The American Institute of Physics....

  4. Superpoissonian shot noise in organic magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Cascales, Juan Pedro; Martinez, Isidoro; Aliev, Farkhad G., E-mail: farkhad.aliev@uam.es [Dpto. Fisica Materia Condensada C3, Instituto Nicolas Cabrera (INC), Condensed Matter Physics Institute (IFIMAC), Universidad Autonoma de Madrid, Madrid 28049 (Spain); Hong, Jhen-Yong; Lin, Minn-Tsong, E-mail: mtlin@phys.ntu.edu.tw [Department of Physics, National Taiwan University, Taipei 10617, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Szczepański, Tomasz; Dugaev, Vitalii K. [Department of Physics, Rzeszów University of Technology, al. Powstańców Warszawy 6, 35-959 Rzeszów (Poland); Barnaś, Józef [Faculty of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland and Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179 Poznań (Poland)

    2014-12-08

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here, we investigate conductance and shot noise in magnetic tunnel junctions with 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10% and 40%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5–2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers.

  5. Operating modes of superconducting tunnel junction device

    Energy Technology Data Exchange (ETDEWEB)

    Maehata, Keisuke [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering

    1998-07-01

    In the Electrotechnical Laboratory, an Nb type superconducting tunnel junction (STJ) device with 200 x 200 sq. micron in area and super high quality was manufactured. By using 55-fe source, response of this large area STJ to X-ray was measured. In this measurement, two action modes with different output wave height from front amplifier were observed. Then, in this study, current-voltage feature of the element in each action mode was analyzed to elucidate a mechanism to form such two action modes. The feature was analyzed by using first order approximate solution on cavity resonance mode of Sine-Gordon equation. From the analytical results, it could be supposed that direction and magnitude of effective magnetic field penetrating into jointed area changed by an induction current effect owing to impressing speed of the magnetic field, which brings two different current-voltage features to make possible to observe two action modes with different pulse wave height. (G.K.)

  6. Tantalum oxide barrier in magnetic tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Guanghua Yu; Tingting Ren; Wei Ji; Jiao Teng; Fengwu Zhu

    2004-01-01

    Tantalum as an insulating barrier can take the place of Al in magnetic tunnel junctions (MTJs). Ta barriers in MTJs were fabricated by natural oxidation. X-ray photoelectron spectroscopy (XPS) was used to characterize the oxidation states of Ta barrier.The experimental results show that the chemical state of tantalum is pure Ta5+ and the thickness of the oxide is 1.3 nm. The unoxidized Ta in the barrier may chemically reacted with NiFe layer which is usually used in MTJs to form an intermetallic compound,NiTa2. A magnetic "dead layer" could be produced in the NiFe/Ta interface. The "dead layer" is likely to influence the spinning electron transport and the magnetoresistance effect.

  7. Development of superconducting tunnel junction radiation detectors

    Energy Technology Data Exchange (ETDEWEB)

    Katagiri, Masaki; Kishimoto, Maki; Ukibe, Masahiro; Nakamura, Tatsuya; Nakazawa, Masaharu [Japan Atomic Energy Research Inst., Tokyo (Japan); Kurakado, Masahiko; Ishibashi, Kenji; Maehata, Keisuke

    1998-07-01

    Study on development of high energy resolution X-ray detector using superconducting tunnel junction (STJ) for radiation detection was conducted for 5 years under cooperation of University of Tokyo group and Kyushu University group by Quantum measurement research group of Advanced fundamental research center of JAERI. As the energy resolution of STJ could be obtained better results than that of Si semiconductor detector told to be actually best at present, this study aimed to actualize an X-ray detector usable for the experimental field and to elucidate radiation detection mechanism due to STJ. The STJ element used for this study was the one developed by Kurakado group of Nippon Steel Corp. As a results, some technical problems were almost resolved, which made some trouble when using the STJ element to detection element of X-ray spectrometer. In order to make the X-ray detector better, it is essential to manufacture a STJ element and develop serial junction type STJ element on the base of optimization of the element structure and selection and single crystallization of new superconducting materials such as Ta and others, activating the research results. (G.K.)

  8. Seebeck effect in magnetic tunnel junctions.

    Science.gov (United States)

    Walter, Marvin; Walowski, Jakob; Zbarsky, Vladyslav; Münzenberg, Markus; Schäfers, Markus; Ebke, Daniel; Reiss, Günter; Thomas, Andy; Peretzki, Patrick; Seibt, Michael; Moodera, Jagadeesh S; Czerner, Michael; Bachmann, Michael; Heiliger, Christian

    2011-10-01

    Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, that is, the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge-based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In this respect, it is the analogue to the tunnelling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configurations are of the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. The geometric centre of the electronic density of states relative to the Fermi level determines the size of the Seebeck effect. Experimentally, we realized 8.8% magneto-Seebeck effect, which results from a voltage change of about -8.7 μV K⁻¹ from the antiparallel to the parallel direction close to the predicted value of -12.1 μV K⁻¹. In contrast to the spin-Seebeck effect, it can be measured as a voltage change directly without conversion of a spin current.

  9. Tunneling electroresistance of MgZnO-based tunnel junctions

    Science.gov (United States)

    Belmoubarik, Mohamed; Al-Mahdawi, Muftah; Obata, Masao; Yoshikawa, Daiki; Sato, Hideyuki; Nozaki, Tomohiro; Oda, Tatsuki; Sahashi, Masashi

    2016-10-01

    We investigated the tunneling electroresistance (TER) in metal/wurtzite-MgZnO/metal junctions for applications in nonvolatile random-access memories. A resistive switching was detected utilizing an electric-field cooling at ±1 V and exhibited a TER ratio of 360%-490% at 2 K. The extracted change in the average barrier height between the two resistance states gave an estimation of the MgZnO electric polarization at 2.5 μC/cm2 for the low-temperature limit. In addition, the temperature-dependent TER ratio and the shift of the localized states energies at the barrier interface supported the ferroelectric behavior of the MgZnO tunnel-barrier. From the first-principles calculations, we found a similar effect of the barrier height change coming from the reversal of ZnO electric polarization. The possibility of using metal electrodes and lower growth temperatures, in addition to the ferroelectric property, make the ZnO-based memory devices suitable for CMOS integration.

  10. Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

    Science.gov (United States)

    Parui, Subir; Ribeiro, Mário; Atxabal, Ainhoa; Bedoya-Pinto, Amilcar; Sun, Xiangnan; Llopis, Roger; Casanova, Fèlix; Hueso, Luis E.

    2016-08-01

    The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al2O3/NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

  11. Terahertz Detection with Twin Superconductor-Insulator-Superconductor Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    LI Jing; WANG Ming-Jye; SHI Sheng-Cai; Hiroshi Mat-suo

    2007-01-01

    Terahertz detection with twin superconductor-insulator-superconductor (SIS) tunnel junctions, which are connected in parallel via an inductive thin-film superconducting microstrip line, is mainly studied. Firstly, we investigate the direct-detection response of a superconducting twin-junction device by means of a Fourier transform spectrometer. Secondly, we construct a direct-detection model of twin SIS tunnel junctions. The superconducting twin-junction device is then simulated in terms of the constructed model. The simulation result is found to be in good agreement with the measured one. In addition, we observe that the direct-detection response of the device is consistent with the noise temperature behaviour.

  12. An Effective Method for Borehole Imaging of Buried Tunnels

    Directory of Open Access Journals (Sweden)

    Loreto Di Donato

    2012-01-01

    Full Text Available Detection and imaging of buried tunnels is a challenging problem which is relevant to both geophysical surveys and security monitoring. To comply with the need of exploring large portions of the underground, electromagnetic measurements carried out under a borehole configuration are usually exploited. Since this requires to drill holes in the soil wherein the transmitting and receiving antennas have to be positioned, low complexity of the involved apparatus is important. On the other hand, to effectively image the surveyed area, there is the need for adopting efficient and reliable imaging methods. To address these issues, in this paper we investigate the feasibility of the linear sampling method (LSM, as this inverse scattering method is capable to provide almost real-time results even when 3D images of very large domains are built, while not requiring approximations of the underlying physics. In particular, the results of the reported numerical analysis show that the LSM is capable of performing the required imaging task while using a quite simple measurement configuration consisting of two boreholes and a few number of multiview-multistatic acquisitions.

  13. Parallel Quantum Circuit in a Tunnel Junction

    Science.gov (United States)

    Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian

    2016-07-01

    Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N2 power law is preserved for Ωab(N) and for Vab(N).

  14. Parallel Quantum Circuit in a Tunnel Junction.

    Science.gov (United States)

    Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian

    2016-07-25

    Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N(2) power law is preserved for Ωab(N) and for Vab(N).

  15. Determination of Relaxation Time of a Josephson Tunnel Junction

    Institute of Scientific and Technical Information of China (English)

    WEN Xue-Da; YU Yang

    2008-01-01

    We propose a non-stationary method to measure the energy relaxation time of Josephson tunnel junctions from microwave enhanced escape phenomena.Compared with the previous methods,our method possesses simple and accurate features.Moreover,having determined the energy relaxation time,we can further obtain the coupling strength between the microwave source and the junction by changing the microwave power.

  16. Study of the geometrical resonances of superconducting tunnel junctions

    DEFF Research Database (Denmark)

    Sørensen, O. Hoffmann; Finnegan, T.F.; Pedersen, Niels Falsig

    1973-01-01

    The resonant cavity structure of superconducting Sn-Sn-oxide-Sn tunnel junctions has been investigated via photon-assisted quasiparticle tunneling. We find that the temperature-dependent losses at 35 GHz are determined by the surface resistance of the Sn films for reduced temperatures between 0...

  17. Shot noise in magnetic tunnel junctions from first principles

    Science.gov (United States)

    Liu, Kai; Xia, Ke; Bauer, Gerrit E. W.

    2012-07-01

    We compute the shot noise in ballistic and disordered Fe|MgO|Fe tunnel junctions by a wave-function-matching method. For tunnel barriers with ≲5 atomic layers we find a suppression of the Fano factor as a function of the magnetic configuration. In the antiparallel configuration the shot noise is full up to a threshold bias that indicates the onset of resonant tunneling. We find excellent agreement with recent experiments when interface disorder is taken into account.

  18. Tunnel Field-Effect Transistor with Epitaxially Grown Tunnel Junction Fabricated by Source/Drain-First and Tunnel-Junction-Last Processes

    Science.gov (United States)

    Morita, Yukinori; Mori, Takahiro; Migita, Shinji; Mizubayashi, Wataru; Tanabe, Akihito; Fukuda, Koichi; Masahara, Meishoku; Ota, Hiroyuki

    2013-04-01

    We fabricate p- and n-channel Si tunnel field-effect transistors (TFETs) with an epitaxially grown tunnel junction. In a novel source/drain-first and tunnel-junction-last fabrication process, a thin epitaxial undoped Si channel (epichannel) is deposited on a preferentially fabricated p- or n-type source area. The epichannel sandwiched by a gate insulator and a highly doped source well acts as a parallel-plate tunnel capacitor, which effectively multiplies drain current with an enlarged tunnel area. On the basis of its simple structure and easy fabrication, symmetric n- and p-transistor and complementary metal oxide semiconductor inverter operations were successfully demonstrated.

  19. Nonequilibrium and relaxation effects in tunnel superconducting junctions

    Science.gov (United States)

    Bezuglyi, E. V.; Vasenko, A. S.; Bratus', E. N.

    2017-02-01

    The specific property of a planar tunnel junction with thin-film diffusive plates and long enough leads is an essential enhancement of its transmission coefficient compared to the bare transparency of the tunnel barrier [1, 2]. In voltage-biased junctions, this creates favorable conditions for strong nonequilibrium of quasiparticles in the junction plates and leads, produced by multiparticle tunneling. We study theoretically the interplay between the nonequilibrium and relaxation processes in such junctions and found that nonequilibrium in the leads noticeably modifies the current-voltage characteristic at {eV}> 2{{Δ }}, especially the excess current, whereas strong diffusive relaxation restores the result of the classical tunnel model. At {eV}≤slant 2{{Δ }}, the diffusive relaxation decreases the peaks of the multiparticle currents. The inelastic relaxation in the junction plates essentially suppresses the n-particle currents (n> 2) by the factor n for odd and n/2 for even n. The results may be important for the problem of decoherence in Josephson-junction based superconducting qubits.

  20. Spin-valley filter and tunnel magnetoresistance in asymmetrical silicene magnetic tunnel junctions

    Science.gov (United States)

    Wang, Dali; Huang, Zeyuan; Zhang, Yongyou; Jin, Guojun

    2016-05-01

    The spin and valley transports and tunnel magnetoresistance are studied in a silicene-based asymmetrical magnetic tunnel junction consisting of a ferromagnetic tunnel barrier, sandwiched between a ferromagnetic electrode and a normal electrode. For such an asymmetrical silicene junction, a general formulism is established. The numerical results show that the spin-valley resolved conductances strongly depend on the magnetization orientation of the ferromagnetic tunnel barrier, and the fully spin-valley polarized current can be realized by tuning a perpendicularly applied electric field. We also find that the tunnel magnetoresistance in this case can be effectively modified by the external electric field when the conductance is fully spin-valley polarized. In particular, the exchange field in the ferromagnetic electrode can further substantially enhance the tunnel magnetoresistance of the system. Our work provides a practical method for electric and magnetic manipulation of valley/spin polarization and tunnel magnetoresistance.

  1. GaInN-based tunnel junctions with graded layers

    Science.gov (United States)

    Takasuka, Daiki; Akatsuka, Yasuto; Ino, Masataka; Koide, Norikatsu; Takeuchi, Tetsuya; Iwaya, Motoaki; Kamiyama, Satoshi; Akasaki, Isamu

    2016-08-01

    We demonstrated low-resistivity GaInN-based tunnel junctions using graded GaInN layers. A systematic investigation of the samples grown by metalorganic vapor phase epitaxy revealed that a tunnel junction consisting of a 4 nm both-sides graded GaInN layer (Mg: 1 × 1020 cm-3) and a 2 nm GaN layer (Si: 7 × 1020 cm-3) showed the lowest specific series resistance of 2.3 × 10-4 Ω cm2 at 3 kA/cm2 in our experiment. The InN mole fraction in the 4 nm both-sides graded GaInN layer was changed from 0 through 0.4 to 0. The obtained resistance is comparable to those of standard p-contacts with Ni/Au and MBE-grown tunnel junctions.

  2. High energy high resolution photoemission from Heusler compounds in half tunnelling-junctions

    Energy Technology Data Exchange (ETDEWEB)

    Gloskovskii, Andrei; Balke, Benjamin; Ouardi, Siham; Fecher, Gerhard H.; Felser, Claudia [Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg - University, Mainz (Germany); Yamamoto, Masafumi [Graduate School of Informatic Science and Technology, Hokkaido University, Sapporo (Japan)

    2008-07-01

    This work reports on high resolution photoelectron spectroscopy from the valence band of buried Co{sub 2}MnSi thin films excited by photons of about 5.9 keV energy. The measurements were performed on Co{sub 2}MnSi thin films covered by MgO(z)/AlO{sub x}(1 nm) with different thickness z from 2 nm to 20 nm of the MgO interlayer. The film structure corresponds to half a tunnelling magnetoresistive (TMR) junction. It is shown that the high energy spectra reveal the bulk electronic structure of the Heusler compound close to the Fermi energy even through the MgO layer. The high resolution measurements of the valence band close to the Fermi energy indicate a very large electron mean free path of the electrons through the MgO layer. The spectra of the buried thin films agree well with previous measurements from bulk samples.

  3. Advanced Metrology for Characterization of Magnetic Tunnel Junctions

    DEFF Research Database (Denmark)

    Kjær, Daniel

    solutions to take products to the next node and the field of memory technology is no exception. Over the past decade research and development in a novel, non-volatile memory type known as MRAM has intensified, and commercial MRAM devices are now available. MRAM holds an extremely favorable position......-plane tunneling (CIPT) for characterization of magnetic tunnel junctions (MTJs), which constitutes the key component not only in MRAM but also the read-heads of modern hard disk drives. MTJs are described by their tunnel magnetoresistance (TMR), which is the relative difference of the resistance area products (RA...... the turn-around time for measurements on magnetic tunnel junctions shortened dramatically from two days to one or two minutes. As one happy user put it, it was like going from a tricycle to a Ferrari in one step, and the tool is now in use in all major memory companies throughout the world. However...

  4. Millikelvin cooling by heavy-fermion-based tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Prest, Martin; Min, Gao, E-mail: Min@cardiff.ac.uk [School of Engineering, Cardiff University, Cardiff CF24 3AA (United Kingdom); Whall, Terry [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2015-12-28

    This paper addresses a high-performance electron-tunneling cooler based on a novel heavy-fermion/insulator/superconductor junction for millikelvin cooling applications. We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/superconductor junction. The calculation, based on typical parameters, indicates that, for a bath temperature of 300 mK, the minimum cooling temperature of an electron tunneling refrigerator is reduced from around 170 mK to below 50 mK if a heavy-fermion metal is employed in place of the normal metal. The improved cooling is attributed to an enhancement in electron tunneling due to the existence of a resonant density of states at the Fermi level.

  5. Magnetoresistance of galfenol-based magnetic tunnel junction

    Science.gov (United States)

    Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Panaccione, G.; Eddrief, M.; Marangolo, M.; Torelli, P.

    2015-12-01

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe1-xGax) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  6. Magnetic tunnel junction based spintronic logic devices

    Science.gov (United States)

    Lyle, Andrew Paul

    The International Technology Roadmap for Semiconductors (ITRS) predicts that complimentary metal oxide semiconductor (CMOS) based technologies will hit their last generation on or near the 16 nm node, which we expect to reach by the year 2025. Thus future advances in computational power will not be realized from ever-shrinking device sizes, but rather by 'outside the box' designs and new physics, including molecular or DNA based computation, organics, magnonics, or spintronic. This dissertation investigates magnetic logic devices for post-CMOS computation. Three different architectures were studied, each relying on a different magnetic mechanism to compute logic functions. Each design has it benefits and challenges that must be overcome. This dissertation focuses on pushing each design from the drawing board to a realistic logic technology. The first logic architecture is based on electrically connected magnetic tunnel junctions (MTJs) that allow direct communication between elements without intermediate sensing amplifiers. Two and three input logic gates, which consist of two and three MTJs connected in parallel, respectively were fabricated and are compared. The direct communication is realized by electrically connecting the output in series with the input and applying voltage across the series connections. The logic gates rely on the fact that a change in resistance at the input modulates the voltage that is needed to supply the critical current for spin transfer torque switching the output. The change in resistance at the input resulted in a voltage margin of 50--200 mV and 250--300 mV for the closest input states for the three and two input designs, respectively. The two input logic gate realizes the AND, NAND, NOR, and OR logic functions. The three input logic function realizes the Majority, AND, NAND, NOR, and OR logic operations. The second logic architecture utilizes magnetostatically coupled nanomagnets to compute logic functions, which is the basis of

  7. Dependence of transport properties in tunnel junction on boron doping

    Energy Technology Data Exchange (ETDEWEB)

    Shi, M.J.; Zeng, X.B.; Liu, S.Y.; Peng, W.B; Xiao, H.B; Liao, X.B.; Wang, Z.G.; Kong, G.L. [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China)

    2010-04-15

    Boron-doped hydrogenated silicon films with different gaseous doping ratio (B{sub 2}H{sub 6}/SiH{sub 4}) were fabricated as recombination p layers in tunnel junctions. The measurements of I-V characteristics of the junctions and transparency spectra of p layer indicated that the best gaseous doping ratio of the recombination layer is 0.04, which is correlated to the degradation of short range order (SRO) in the inserted p thin film. The junction with such recombination layer has small resistance, near ohmic contact. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Bias dependent inversion of tunneling magnetoresistance in Fe/GaAs/Fe tunnel junctions

    OpenAIRE

    Moser, J.; Zenger, M.; Gerl, C.; Schuh, D.; Meier, R.; Chen, P.; Bayreuther, G.; Wegscheider, W.; Weiss, D; Lai, C. -H.; Huang, R. -T.; Kosuth, M.; Ebert, H.

    2006-01-01

    We investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions. The tunneling magnetoresistance effect (TMR) was probed for different types of Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is increased and observable at room temperature. If an epitaxial Fe/GaAs(001) interface is involved, the tunnel junction exhibits a bias dependent inversion of the TMR effect. This is a first experimental signature for band structure effects at a Fe/GaAs interfac...

  9. Flicker (1/f) noise in tunnel junction DC SQUIDS

    Energy Technology Data Exchange (ETDEWEB)

    Koch, R.H.; Clarke, J.; Goubau, W.M.; Martinis, J.M.; Pegrum, C.M.; Van Harlingen, D.J.

    1983-04-01

    We have measured the spectral density of the 1/f voltage noise in current-biased resistively shunted Josephson tunnel junctions and dc SQUIDs. A theory in which fluctuations in the temperature give rise to fluctuations in the critical current and hence in the voltage predicts the magnitude of the noise quite accurately for junctions with areas of about 2 x 10/sup 4/ ..mu..m/sup 2/, but significantly overestimates the noise for junctions with areas of about 6 ..mu..m/sup 2/. DC SQUIDs fabricated from these two types of junctions exhibit substantially more 1/f voltage noise than would be predicted from a model in which the noise arises from critical current fluctuations in the junctions. This result was confirmed by an experiment involving two different bias current and flux modulation schemes, which demonstrated that the predominant 1/f voltage noise arises not from critical current fluctuations, but from some unknown source that can be regarded as an apparent 1/f flux noise. Measurements on five different configurations of dc SQUIDs fabricated with thin-film tunnel junctions and with widely varying areas, inductances, and junction capacitances show that the spectral density of the 1/f equivalent flux noise is roughtly constant, within a factor of three of (10/sup -10//f)phi/sup 2//sub 0/Hz/sup -1/. It is emphasized that 1/f flux noise may not be the predominant source of 1/f noise in SQUIDS fabricated with other technologies.

  10. CMOS buried quad p-n junction photodetector for multi-wavelength analysis.

    Science.gov (United States)

    Richard, Charles; Courcier, Thierry; Pittet, Patrick; Martel, Stéphane; Ouellet, Luc; Lu, Guo-Neng; Aimez, Vincent; Charette, Paul G

    2012-01-30

    This paper presents a buried quad p-n junction (BQJ) photodetector fabricated with a HV (high-voltage) CMOS process. Multiple buried junction photodetectors are wavelength-sensitive devices developed for spectral analysis applications where a compact integrated solution is preferred over systems involving bulk optics or a spectrometer due to physical size limitations. The BQJ device presented here is designed for chip-based biochemical analyses using simultaneous fluorescence labeling of multiple analytes such as with advanced labs-on-chip or miniaturized photonics-based biosensors. Modeling and experimental measurements of the spectral response of the device are presented. A matrix-based method for estimating individual spectral components in a compound spectrum is described. The device and analysis method are validated via a test setup using individually modulated LEDs to simulate light from 4-component fluorescence emission.

  11. Multiband model for tunneling in MgB2 junctions

    NARCIS (Netherlands)

    Brinkman, A.; Golubov, A.A.; Rogalla, H.; Dolgov, O.V.; Kortus, J.; Kong, Y.; Jepsen, O.; Andersen, O.K.

    2002-01-01

    A theoretical model for quasiparticle and Josephson tunneling in multiband superconductors is developed and applied to MgB2-based junctions. The gap functions in different bands in MgB2 are obtained from an extended Eliashberg formalism, using the results of band structure calculations. The temperat

  12. Thermally induced dynamics in ultrathin magnetic tunnel junctions

    NARCIS (Netherlands)

    Ogrodnik, P.; Bauer, G.E.W.; Xia, K.

    2013-01-01

    We consider the magnetization dynamics induced by thermally induced spin transfer torques in thin Fe|MgO|Fe tunnel junctions. The magnetization dynamics is described by the Landau-Lifshitz-Gilbert equation, including the thermal torques as computed from first principles. We show that the angular ske

  13. Fluxon dynamics in long annular Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Martucciello, N.; Mygind, Jesper; Koshelets, V.P.

    1998-01-01

    Single-fluxon dynamics has been experimentally investigated in high-quality Nb/Al-AlOx/Nb annular Josephson tunnel junctions having a radius much larger than the Josephson penetration depth. Strong evidence of self-field effects is observed. An external magnetic field in the barrier plane acts...

  14. Measuring the momentum of a nanomechanical oscillator using tunnel junctions

    Science.gov (United States)

    Doiron, Charles; Trauzettel, Bjoern; Bruder, Christoph

    2008-03-01

    We present a way to measure the momentum p of a nanomechanical oscillatorootnotetextC. B. Doiron, B. Trauzettel, C. Bruder. arXiv:0707.2709.. The momentum detector is based on two tunnel junctions in an Aharonov-Bohm-type setup, where one of the tunneling amplitudes depends on the motion of the oscillator and the other one does not. The coupling between the first tunnel junction and the oscillator is assumed to be linear in the position x of the oscillator t(x) = t0+ t1x. However, the presence of two junctions can, under certain conditions, lead to an effective imaginary coupling t(x) = t0+ i t1x. By calculating the equation-of-motion for the density matrix of the coupled (oscillator+tunnel junction) systemootnotetextA.A Clerk, S. Girvin. Phys. Rev. B 70, 121303 (2004)., we show that in this case the finite-frequency current noise of the detector is proportional to the momentum spectrum of the oscillator.

  15. Fluxon propagation and Fiske steps in long Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Erné, S. N.; Ferrigno, A.; Parmentier, R. D.

    1983-01-01

    The dynamical behavior of fluxons propagating in the presence of an applied magnetic field on an overlap-geometry Josephson tunnel junction of length 5λJ having a McCumber βc=5π is studied by numerical integration of the circuit equations of a 50-section lumped RSJ-type (resistive shunted junctio...

  16. Josephson tunnel junctions in a magnetic field gradient

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Koshelets, V.P.

    2011-01-01

    We measured the magnetic field dependence of the critical current of high-quality Nb-based planar Josephson tunnel junctions in the presence of a controllable nonuniform field distribution. We found skewed and slowly changing magnetic diffraction patterns quite dissimilar from the Fraunhofer-like...... be suppressed by an asymmetric magnetic field profile. © 2011 American Institute of Physics....

  17. Direct detection at submillimetre wavelengths using superconducting tunnel junctions

    NARCIS (Netherlands)

    Withington, S; Isaak, KG; Kovtonyuk, SA; Panhuyzen, RA; Klapwijk, TM

    1995-01-01

    Superconducting tunnel-junction direct detectors are considered in some detail. For frequencies below twice that of the gap there is some bias voltage for which the input impedance is real, the responsivity quantum limited, and the dynamic range high. A susperconducting detector saturates for two re

  18. Spin-transfer torque in spin filter tunnel junctions

    KAUST Repository

    Ortiz Pauyac, Christian

    2014-12-08

    Spin-transfer torque in a class of magnetic tunnel junctions with noncollinear magnetizations, referred to as spin filter tunnel junctions, is studied within the tight-binding model using the nonequilibrium Green\\'s function technique within Keldysh formalism. These junctions consist of one ferromagnet (FM) adjacent to a magnetic insulator (MI) or two FM separated by a MI. We find that the presence of the magnetic insulator dramatically enhances the magnitude of the spin-torque components compared to conventional magnetic tunnel junctions. The fieldlike torque is driven by the spin-dependent reflection at the MI/FM interface, which results in a small reduction of its amplitude when an insulating spacer (S) is inserted to decouple MI and FM layers. Meanwhile, the dampinglike torque is dominated by the tunneling electrons that experience the lowest barrier height. We propose a device of the form FM/(S)/MI/(S)/FM that takes advantage of these characteristics and allows for tuning the spin-torque magnitudes over a wide range just by rotation of the magnetization of the insulating layer.

  19. Tunnel junctions for InP-on-Si solar cells

    Science.gov (United States)

    Keavney, C.; Vernon, S.; Haven, V.

    1991-01-01

    Growing, by metalorganic chemical vapor deposition, a tunnel junction is described, which makes possible and ohmic back contact in an n-on-p InP solar cell on a silicon substrate. The junction between heavily doped layers of p-type InGaAs and n-type InP shows resistance low enough not to affect the performance of these cells. InP solar cells made on n-type Si substrates with this structure were measured with an efficiency of 9.9 percent. Controls using p-type GaAs substrates showed no significant difference in cell performance, indicating that the resistance associated with the tunnel junction is less than about 0.1 ohm/sq cm.

  20. Fabrication of High-Quality Niobium Superconducting Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    XU Qin-Yin; CAO Chun-Hai; LI Meng-Yue; JIANG Yi; ZHA Shi-Tong; KANG Lin; XU Wei-Wei; CHEN Jian; WU Pei-Heng

    2011-01-01

    @@ For high-quality superconducting tunnel junctions(STJS), it is necessary to reduce leakage current as much as possible.We describe the fabrication of niobium STJs using the selective niobium(Nb) etching process and various ways to minimize the leakage current.The experiment shows that the leakage current mainly comes from shorts in the tunnel barrier layer rather than those around the junction edges.Through systematic analysis of the thin film stress, surface morphology and modified junction structures, we fabricate high-quality Nb STJs with a gap voltage of 2.8 mV and a leakage current at 1 m V as low as 8.1 % and 0.023% at 4.2K and 0.3 K, respectively.

  1. Spatial dependence of plasma oscillations in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Holst, Thorsten; Hansen, Jørn Bindslev

    1991-01-01

    We report on direct measurements of the plasma oscillations in Josephson tunnel junctions of various spatial dimensions. The effect of the spatial variation of the Cooper-pair phase difference (the Josephson phase) on the dynamics of the junction was investigated by application of a static magnetic...... field threading the tunneling barrier. We compare measurements where the plasma frequency was tuned either by applying a magnetic field or by raising the temperature. A crossover from short- to long-junction behavior of the functional dependence of the plasma oscillations was observed in the case...... of an applied magnetic field. Numerical simulations of the governing partial-differential sine-Gordon equation were performed and compared to the experimental results and a perturbation analysis. The theoretical results support the experiments and allow us to interpret the observed crossover as due...

  2. Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

    Science.gov (United States)

    Gajewski, Krzysztof; Piasecki, Tomasz; Kopiec, Daniel; Gotszalk, Teodor

    2017-03-01

    Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown.

  3. Soliton excitations in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Lomdahl, P. S.; Sørensen, O. H.; Christiansen, Peter Leth

    1982-01-01

    on the Nth ZFS yields the frequency Nf1 Coexistence of two adjacent frequencies is found on the third ZFS of the longer junction (L / λJ=6) in a narrow range of bias current as also found in the experiments. Small asymmetries in the experimental environment, a weak magnetic field, e.g., is introduced via...

  4. All-carbon molecular tunnel junctions.

    Science.gov (United States)

    Yan, Haijun; Bergren, Adam Johan; McCreery, Richard L

    2011-11-30

    This Article explores the idea of using nonmetallic contacts for molecular electronics. Metal-free, all-carbon molecular electronic junctions were fabricated by orienting a layer of organic molecules between two carbon conductors with high yield (>90%) and good reproducibility (rsd of current density at 0.5 V carbon devices exhibit current density-voltage (J-V) behavior similar to those with metallic Cu top contacts. However, the all-carbon devices display enhanced stability to bias extremes and greatly improved thermal stability. Completed carbon/nitroazobenzene(NAB)/carbon junctions can sustain temperatures up to 300 °C in vacuum for 30 min and can be scanned at ±1 V for at least 1.2 × 10(9) cycles in air at 100 °C without a significant change in J-V characteristics. Furthermore, these all-carbon devices can withstand much higher voltages and current densities than can Cu-containing junctions, which fail upon oxidation and/or electromigration of the copper. The advantages of carbon contacts stem mainly from the strong covalent bonding in the disordered carbon materials, which resists electromigration or penetration into the molecular layer, and provides enhanced stability. These results highlight the significance of nonmetallic contacts for molecular electronics and the potential for integration of all-carbon molecular junctions with conventional microelectronics.

  5. In situ experiments on width and evolution characteristics of excavation damaged zone in deeply buried tunnels

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The seven long tunnels of Jinping II hydropower station are deeply buried.The width and evolution characteristics of excavation damaged zone(EDZ) are the key problem to the design of tunnels excavation and supports.In order to study this problem,several specific experimental tunnels with different overburden and geometric sizes were excavated at this site.Digital borehole camera,sliding micrometer,cross-hole acoustic wave equipment and acoustic emission apparatus were adopted.This paper introduced the comprehensive in situ experimental methods through pre-installed facilities and pre-drilled boreholes.Typical properties of the surrounding rock mass,including cracks,deformation,elastic wave and micro fractures,were measured during the whole process of the tunnel excavation.The width and characteristics of formation and evolution of tunnels EDZ were analyzed under different construction methods involving of TBM and drilling and blasting,the test tunnels were excavated by full-face or two benches.The relationships between EDZ and tunnel geometry sizes,overburden and excavation method were described as well.The results will not only contribute a great deal to the analysis of rock mass behavior in deeply buried rock mass,but also provide direct data for support design and rockburst prediction.

  6. Seebeck Effect in Magnetic Tunnel Junctions

    OpenAIRE

    Walter, Marvin; Walowski, Jakob; Zbarsky, Vladyslav; Münzenberg, Markus; Schäfers, Markus; Ebke, Daniel; Reiss, Günter; Thomas, Andy; Peretzki, Patrick; Seibt, Michael; Moodera, Jagadeesh S.; Czerner, Michael; Bachmann, Michael; Heiliger, Christian

    2011-01-01

    Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, i.e., the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel j...

  7. InAs/Si Hetero-Junction Nanotube Tunnel Transistors

    KAUST Repository

    Hanna, Amir

    2015-04-29

    Hetero-structure tunnel junctions in non-planar gate-all-around nanowire (GAA NW) tunnel FETs (TFETs) have shown significant enhancement in ‘ON’ state tunnel current over their all-silicon counterpart. Here we show the unique concept of nanotube TFET in a hetero-structure configuration that is capable of much higher drive current as opposed to that of GAA NW TFETs.Through the use of inner/outer core-shell gates, a single III-V hetero-structured nanotube TFET leverages physically larger tunneling area while achieving higher driver current (ION) and saving real estates by eliminating arraying requirement. Numerical simulations has shown that a 10 nm thin nanotube TFET with a 100 nm core gate has a 5×normalized output current compared to a 10 nm diameter GAA NW TFET.

  8. Asymmetric voltage behavior of the tunnel magnetoresistance in double barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2012-06-01

    In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.

  9. Development of suspended normal-metal-type tunneling junction refrigerator

    Science.gov (United States)

    Kashiwaya, Satoshi; Kashiwaya, Hiromi; Koyanagi, Masao; Tanaka, Yukio

    2016-09-01

    We have developed a suspended normal-metal-type superconducting-normal metal-superconductor tunneling junction refrigerator for the cooling of highly sensitive sensors operating at ultralow temperatures. The performance of the refrigerator is evaluated by comparing the experimental conductance with the numerical results of a theoretical formulation. The lowest temperature of 0.093 K at a bath temperature of 0.334 K indicates the successful operation of the refrigerator. The maximum cooling power of the present refrigerator estimated on the basis of the nonequilibrium stationary state model is 213 pW for a junction area of 40 × 7 µm2.

  10. Investigation of 1/f noise in tunnel junction dc SQUIDS

    Energy Technology Data Exchange (ETDEWEB)

    Koch, R.; Clarke, J.; Goubau, W.; Harlingen; Martinis, J.; Pegrum, C.

    1983-05-01

    The authors describe two methods of measuring the 1/f noise in a dc SQUID. One is sensitive only to 1/f noise in the critical currents of the junctions, and the other is sensitive only to 1/f flux noise that is not associated with critical current fluctuations. From measurements on a planar thin-film dc SQUID incorporating Josephson tunnel junctions the authors conclude that the predominant source of 1/f noise is not noise in the critical currents, but rather an apparent flux noise of unknown origin.

  11. Tunneling Conductance in Normal Metal/Insulator/Triplet Superconductor Junction

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Wei

    2005-01-01

    Tunneling conductance in normal metal/insulator/triplet superconductor junctions is studied theoretically as a function of the bias voltage at zero temperature and finite temperature. The results show there are zero-bias conductance peak, zero-bias conductance dip and double-minimum structures in the spectra for p-wave superconductor junctions. The existence of such structures in the conductance spectrum can be taken as evidence that the pairing symmetry of Sr2RuO4 is p-wave symmetry.

  12. Engineering ferroelectric tunnel junctions through potential profile shaping

    Energy Technology Data Exchange (ETDEWEB)

    Boyn, S.; Garcia, V., E-mail: vincent.garcia@thalesgroup.com; Fusil, S.; Carrétéro, C.; Garcia, K.; Collin, S.; Deranlot, C.; Bibes, M.; Barthélémy, A. [Unité Mixte de Physique CNRS/Thales, 1 Av. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay (France); Xavier, S. [Thales Research and Technology, 1 Av. Fresnel, 91767 Palaiseau (France)

    2015-06-01

    We explore the influence of the top electrode materials (W, Co, Ni, Ir) on the electronic band profile in ferroelectric tunnel junctions based on super-tetragonal BiFeO{sub 3}. Large variations of the transport properties are observed at room temperature. In particular, the analysis of current vs. voltage curves by a direct tunneling model indicates that the metal/ferroelectric interfacial barrier height increases with the top-electrode work function. While larger metal work functions result in larger OFF/ON ratios, they also produce a large internal electric field which results in large and potentially destructive switching voltages.

  13. Engineering ferroelectric tunnel junctions through potential profile shaping

    Directory of Open Access Journals (Sweden)

    S. Boyn

    2015-06-01

    Full Text Available We explore the influence of the top electrode materials (W, Co, Ni, Ir on the electronic band profile in ferroelectric tunnel junctions based on super-tetragonal BiFeO3. Large variations of the transport properties are observed at room temperature. In particular, the analysis of current vs. voltage curves by a direct tunneling model indicates that the metal/ferroelectric interfacial barrier height increases with the top-electrode work function. While larger metal work functions result in larger OFF/ON ratios, they also produce a large internal electric field which results in large and potentially destructive switching voltages.

  14. Spin transfer torque with spin diffusion in magnetic tunnel junctions

    KAUST Repository

    Manchon, Aurelien

    2012-08-09

    Spin transport in magnetic tunnel junctions in the presence of spin diffusion is considered theoretically. Combining ballistic tunneling across the barrier and diffusive transport in the electrodes, we solve the spin dynamics equation in the metallic layers. We show that spin diffusion mixes the transverse spin current components and dramatically modifies the bias dependence of the effective spin transfer torque. This leads to a significant linear bias dependence of the out-of-plane torque, as well as a nonconventional thickness dependence of both spin torque components.

  15. Electric field modulation of tunneling anisotropic magnetoresistance in tunnel junctions with antiferromagnetic electrodes

    Science.gov (United States)

    Goto, Minori; Nawaoka, Kohei; Miwa, Shinji; Hatanaka, Shohei; Mizuochi, Norikazu; Suzuki, Yoshishige

    2016-08-01

    We present electric field modulation of tunneling anisotropic magnetoresistance (TAMR) in MnIr|MgO|Ta tunnel junctions. TAMR enables direct observation of the antiferromagnetic spin direction at the MnIr|MgO interface. We found that the shape of magnetoresistance (MR) curve can be modulated by an electric field, which can be explained by electric field modulation of the interfacial magnetic anisotropy at MnIr|MgO.

  16. Shot Noise in Ferromagnetic Superconductor Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this paper, the superconducting order parameter and the energy spectrum of the Bogoliubov excitations are obtained from the Bogoliubov-de Gennes (BdG) equation for a ferromagnetic superconductor (FS). Taking into account the rough interface scattering effect, we calculate the shot noise and the differential conductance of the normal- metal insulator ferromagnetic superconductor junction. It is shown that the exchange energy Eh in FS can lead to splitting of the differential shot noise peaks and the conductance peaks. The energy difference between the two splitting peaks is equal to 2Eh. The rough interface scattering strength results in descent of conductance peaks and the shot noise-to-current ratio but increases the shot noise.

  17. Magnetoresistance of galfenol-based magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Gobaut, B., E-mail: benoit.gobaut@elettra.eu [Sincrotrone Trieste S.C.p.A., S.S. 14 Km 163.5, Area Science Park, 34149 Trieste (Italy); Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Rafaqat, H. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); ICTP, Trieste (Italy); Roddaro, S. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127 Pisa (Italy); Rossi, G. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano (Italy); Eddrief, M.; Marangolo, M. [Sorbonne Universités, UPMC Paris 06, CNRS-UMR 7588, Institut des Nanosciences de Paris, 75005, Paris (France)

    2015-12-15

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe{sub 1-x}Ga{sub x}) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  18. Room Temperature Magnetic Barrier Layers in Magnetic Tunnel Junctions

    Energy Technology Data Exchange (ETDEWEB)

    Nelson-Cheeseman, B. B.; Wong, F. J.; Chopdekar, R. V.; Arenholz, E.; Suzuki, Y.

    2010-03-09

    We investigate the spin transport and interfacial magnetism of magnetic tunnel junctions with highly spin polarized LSMO and Fe3O4 electrodes and a ferrimagnetic NiFe2O4 (NFO) barrier layer. The spin dependent transport can be understood in terms of magnon-assisted spin dependent tunneling where the magnons are excited in the barrier layer itself. The NFO/Fe3O4 interface displays strong magnetic coupling, while the LSMO/NFO interface exhibits clear decoupling as determined by a combination of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. This decoupling allows for distinct parallel and antiparallel electrode states in this all-magnetic trilayer. The spin transport of these devices, dominated by the NFO barrier layer magnetism, leads to a symmetric bias dependence of the junction magnetoresistance at all temperatures.

  19. FeGa based tunneling magnetoresistance junctions and strain sensors

    OpenAIRE

    Thajudin, Ahmed Fazir

    2012-01-01

    Tunnel magnetoresistance (TMR) and inverse magnetostriction based strain gauges have gained immense importance due to their high spatial resolution and extremely high gauge factors. A TMR junction comprises of two ferromagnetic electrodes separated by an insulating barrier layer. One of the ferromagnetic layer is soft magnetic which is free to rotate its magnetization under external magnetic field, the other ferromagnet is hard magnetic and is stable under the same external field. An intentio...

  20. Simulation of Tunnel Junction in Cascade Solar Cell (GaAs/Ge Using AMPS-1D

    Directory of Open Access Journals (Sweden)

    Benmoussa Dennai

    2014-11-01

    Full Text Available The development of the tunnel junction interconnect was key the first two-terminal monolithic, multi-junction solar cell development. This paper describes simulation for the tunnel junction (GaAs between top cell (GaAs and bottom cell (Ge. This solar cell cascade was simulated when using one dimensional simulation program called analysis of microelectronic and photonic structures (AMPS-1D. In the simulation, the thickness of the tunnel junction layer was varied from 10 to 50 nm. By varying thickness of tunnel junction layer the simulated device performance was demonstrate in the form of current-voltage(I-V characteristics and quantum efficiency (QE.

  1. Prediction of Collapse Scope of Deep-Buried Tunnels Using Pressure Arch Theory

    Directory of Open Access Journals (Sweden)

    Yingchao Wang

    2016-01-01

    Full Text Available Tunnel collapse remains a serious problem in practice. Effective prediction methods on tunnel collapse are necessary for tunnel engineering. In this study, systematic study on the pressure arch was presented to predict tunnel collapse. Multiple factors under different conditions were considered. First, the pressure arch was described as a certain scope in comparison with the lowest pressure arch line. Then, a deep-buried circular tunnel was selected as the investigated object. Its collapse scope was analyzed using the lowest pressure arch line. Meanwhile, the main influence from the ground stress field was considered. Different modes of ground stress fields were investigated in detail. The results indicate that the collapse scope varies with different ground stress fields. Determination on the collapse scope is strongly affected by the judgment standard of the pressure arch. Furthermore, a selected case was analyzed with the pressure arch. The area and the height of tunnel collapse were calculated with multiple factors, including ground stress field, judgment standard, and lateral pressure coefficient. Finally, selected results were compared with relevant previous researches, and reasonable results were obtained. The present results are helpful for further understanding of the tunnel collapse and could provide suitable guidance for tunnel projects.

  2. Scale invariance of a diode-like tunnel junction

    Science.gov (United States)

    Cabrera, Hugo; Zanin, Danilo Andrea; de Pietro, Lorenzo Giuseppe; Michaels, Thomas; Thalmann, Peter; Ramsperger, Urs; Vindigni, Alessandro; Pescia, Danilo

    2013-03-01

    In Near Field-Emission SEM (NFESEM), electrostatic considerations favor a diode-like tunnel junction consisting of an atomic-sized source mounted at the apex of a thin wire placed at nanometric distances from a collector. The quantum mechanical tunnel process, instead, can provide a barrier toward miniaturization. In the first place, it deteriorates the generation of electrons by introducing non-linearities within the classically forbidden zone that exponentially increase with decreasing sizes. In addition, in the direct tunnelling regime, i.e. when the distance between emitter and collector d approaches the subnanometer range, a characteristic length appears, making the cross-over from the (almost) scale-invariant electric-field assisted regime to the essentially different STM-regime. We have observed that the experimental data relating the current I to the two experimental variables V (bias voltage between tip and collector) and d can be made (almost) collapse onto a ``scaling curve'' relating I to the single variable V .d-λ , λ being some exponent that depends solely on the geometry of the junction. This scaling property can be used to highlight non-linear aspects of the quantum mechanical tunnelling process.

  3. Theoretical Approach to Electroresistance in Ferroelectric Tunnel Junctions

    Science.gov (United States)

    Chang, Sou-Chi; Naeemi, Azad; Nikonov, Dmitri E.; Gruverman, Alexei

    2017-02-01

    In this paper, a theoretical approach comprising the nonequilibrium Green's function method for electronic transport and the Landau-Khalatnikov equation for electric polarization dynamics is presented to describe polarization-dependent tunneling electroresistance (TER) in ferroelectric tunnel junctions. Using appropriate contact, interface, and ferroelectric parameters, the measured current-voltage characteristic curves in both inorganic (Co /BaTi O3/La0.67Sr0.33 MnO3 ) and organic (Au /PVDF /W ) ferroelectric tunnel junctions can be well described by the proposed approach. Furthermore, under this theoretical framework, the controversy of opposite TER signs observed experimentally by different groups in Co /BaTi O3/La0.67Sr0.33 MnO3 systems is addressed by considering the interface termination effects using the effective contact ratio defined through the effective screening length and dielectric response at the metal-ferroelectric interfaces. Finally, our approach is extended to investigate the role of a CoOx buffer layer at the Co /BaTi O3 interface in a ferroelectric tunnel memristor. It is shown that in order to have a significant memristor behavior not only the interface oxygen vacancies but also the CoOx layer thickness may vary with the applied bias.

  4. Coexistence of tunneling magnetoresistance and Josephson effects in SFIFS junctions

    Science.gov (United States)

    Vávra, O.; Soni, R.; Petraru, A.; Himmel, N.; Vávra, I.; Fabian, J.; Kohlstedt, H.; Strunk, Ch.

    2017-02-01

    We demonstrate an integration of tunneling magnetoresistance and the Josephson effects within one tunneling junction. Several sets of Nb-Fe-Al-Al2O3-Fe-Nb wafers with varying Al and Fe layers thickness were prepared to systematically explore the competition of TMR and Josephson effects. A coexistence of the critical current IC(dFe) and the tunneling magnetoresistance ratio T M R(dFe) is observed for iron layer dFe thickness range 1.9 and 2.9 nm. Further optimization such as thinner Al2O3 layer leads to an enhancement of the critical current and thus to an extension of the coexistence regime up to dFe≃3.9 nm Fe.

  5. FeGa/MgO/Fe/GaAs(001) magnetic tunnel junction: Growth and magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Gobaut, B., E-mail: benoit.gobaut@elettra.eu [Sincrotrone Trieste S.C.p.A., S.S. 14-km 163.5, Area Science Park, 34012 Trieste (Italy); Ciprian, R.; Salles, B.R.; Krizmancic, D. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy); Rossi, G. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy); Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano (Italy); Panaccione, G. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy); Eddrief, M.; Marangolo, M. [Sorbonne Universites, UPMC Univ Paris 06, UMR 7588, INSP, 4 place Jussieu, 75005 Paris (France); CNRS, UMR 7588, Institut des NanoSciences de Paris, 4 place Jussieu, 75005 Paris (France); Torelli, P. [Laboratorio TASC, IOM-CNR, S.S. 14-km 163.5, Basovizza, 34149 Trieste (Italy)

    2015-06-01

    Research on spintronics and on multiferroics leads now to the possibility of combining the properties of these materials in order to develop new functional devices. Here we report the integration of a layer of magnetostrictive material into a magnetic tunnel junction. A FeGa/MgO/Fe heterostructure has been grown on a GaAs(001) substrate by molecular beam epitaxy (MBE) and studied by X-ray magnetic circular dichroism (XMCD). The comparison between magneto optical Kerr effect (MOKE) measurements and hysteresis performed in total electron yield allowed distinguishing the ferromagnetic hysteresis loop of the FeGa top layer from that of the Fe buried layer, evidencing a different switching field of the two layers. This observation indicates an absence of magnetic coupling between the two ferromagnetic layers despite the thickness of the MgO barrier of only 2.5 nm. The in-plane magnetic anisotropy has also been investigated. Overall results show the good quality of the heterostructure and the general feasibility of such a device using magnetostrictive materials in magnetic tunnel junction.

  6. Experimental realization of single electron tunneling diode based on vertical graphene two-barrier junction

    OpenAIRE

    Xu, Rui; Bai, Ke-Ke; Nie, Jia-Cai; He, Lin

    2012-01-01

    Usually, graphene is used in its horizontal directions to design novel concept devices. Here, we report a single electron tunneling diode based on quantum tunneling through a vertical graphene two-barrier junction. The junction is formed by positioning a scanning tunnelling microscopy (STM) tip above a graphene nanoribbon that was deposited on a graphite surface. Because of the asymmetry of the two-barrier junction, the electrons can unidirectional transfer from the tip to the graphene nanori...

  7. Thermopower of molecular junctions: Tunneling to hopping crossover in DNA

    Science.gov (United States)

    Korol, Roman; Kilgour, Michael; Segal, Dvira

    2016-12-01

    We study the electrical conductance G and the thermopower S of single-molecule junctions and reveal signatures of different transport mechanisms: off-resonant tunneling, on-resonant coherent (ballistic) motion, and multi-step hopping. These mechanisms are identified by studying the behavior of G and S while varying molecular length and temperature. Based on a simple one-dimensional model for molecular junctions, we derive approximate expressions for the thermopower in these different regimes. Analytical results are compared to numerical simulations, performed using a variant of Büttiker's probe technique, the so-called voltage-temperature probe, which allows us to phenomenologically introduce environmentally induced elastic and inelastic electron scattering effects, while applying both voltage and temperature biases across the junction. We further simulate the thermopower of GC-rich DNA sequences with mediating A:T blocks and manifest the tunneling-to-hopping crossover in both the electrical conductance and the thermopower, in accord with measurements by Li et al. [Nat. Commun. 7, 11294 (2016)].

  8. Direct detection at submillimetre wavelengths using superconducting tunnel junctions

    Science.gov (United States)

    Withington, S.; Isaak, K. G.; Kovtonyuk, S. A.; Panhuyzen, R. A.; Klapwijk, T. M.

    1995-12-01

    Superconducting tunnel-junction direct detectors are considered in some detail. For frequencies below twice that of the gap there is some bias voltage for which the input impedance is real, the responsivity quantum limited, and the dynamic range high. A susperconducting detector saturates for two reasons: intrinsic saturation due to the relative increase in two-photon tunnelling processes, and extrinsic saturation due to the input match changing with bias voltage. The responsivity of a detector with a resistive RF source is least sensitive to bias-voltage changes and has the greatest dynamic range when operating with a sloping load line. In the case of an inductive source, the dynamic range can be higher than the intrinsic saturation rate would suggest. Ideally, superconducting tunnel-junction detectors should be biased in a constant-voltage mode. If the responsivity is to be depressed by no more than a few percent, the photon step should have a height which is no more than one quarter of the total current turn-on at the gap. Superconducting direct detectors can be used to make precise and well-calibrated optical measurements at submillimetre wavelengths.

  9. Anomalous Tunnel Magnetoresistance and Spin Transfer Torque in Magnetic Tunnel Junctions with Embedded Nanoparticles

    Science.gov (United States)

    Useinov, Arthur; Ye, Lin-Xiu; Useinov, Niazbeck; Wu, Te-Ho; Lai, Chih-Huang

    2015-12-01

    The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature.

  10. Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

    KAUST Repository

    Useinov, A. N.

    2011-08-24

    We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.

  11. Finite element simulation of shallow-buried and mining tunnelling in adjacent frame structures

    Directory of Open Access Journals (Sweden)

    Chun-lai Chen

    2014-05-01

    Full Text Available By using three dimensional software MIDAS/GTS, the interactions among structures-soil-tunnel system is considered in this paper, and the working condition of shallow-buried underground excavation is simulated in the foundation of frame structures with the short-pile. The loadings and deformations of structures are studied before and after the tunnelling, and the influences of the following factors, including the horizontal position of tunnel and building, the height of building and the soil property, are analyzed. It is indicated that when the horizontal distance L equals zero (the distance between building axis to the tunnel axis, the building settlement increases gradually and shows a normal distribution during and after the tunnelling. Due to the small stiffness of frame structures with short-pile foundations, the building has large nonuniform settlement. When the distance of excavation is no less than 1.8 times of the thickness of overburden soil, the building settlement becomes stable, and the first principal stress P1 and maximum deformation rate E1 generally show a trend of decrease. With the increasing L, P1 and E1 will decrease accordingly, and the buildings tend to be inclined toward the tunnel. For a relatively larger distance, the building is nearly not affected.

  12. Probing momentum distributions in magnetic tunnel junctions via hot-electron decay

    NARCIS (Netherlands)

    Jansen, R.; Banerjee, T.; Park, B.G.; Lodder, J.C.

    2007-01-01

    The tunnel momentum distribution in a (magnetic) tunnel junction is probed by analyzing the decay of the hot electrons in the Co metal anode after tunneling, using a three-terminal transistor structure in which the hot-electron attenuation is sensitive to the tunnel momentum distribution. Solid stat

  13. Electronic transport through EuO spin filter tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Jutong, Nuttachai; Eckern, Ulrich [Institut fuer Physik, Universitaet Augsburg, 86135 Augsburg (Germany); Rungger, Ivan; Sanvito, Stefano [School of Physics and CRANN, Trinity College Dublin, Dublin (Ireland); Schwingenschloegl, Udo [KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia (Saudi Arabia)

    2012-07-01

    Spin filter tunnel junctions based on europium monoxide (EuO), a ferromagnetic semiconductor, are investigated by means of density functional theory. In particular, the spin transport of Cu/EuO/Cu junctions is investigated by using the self-consistent ab-initio electron transport code SMEAGOL. The dependence of the transmission coefficient on the interface spacing and on the EuO thickness is studied, and explained in terms of the density of states and the complex band structure of EuO. Our calculation indicates that EuO epitaxially grown on Cu can act as a perfect spin filter, with polarization close to 100%, which is related mainly to the Eu-4f states. The transmission coefficient is sensitive to the interface spacing, since this spacing determines the charge transfer between EuO and the Cu leads.

  14. Tunneling transport in d-wave superconductor-silicene junction

    Science.gov (United States)

    Hajati, Y.; Vosoughi nia, S.; Rashedi, G.

    2017-02-01

    We theoretically study the tunneling conductance of a normal/d-wave superconductor silicene junction using Blonder-Tinkham-Klapwijk (BTK) formalism. We discuss in detail how the conductances spectra are affected by inducing d-wave superconducting pairing symmetry in the buckled silicene. It is obtained that the amplitude of the spin/valley-dependent Andreev reflection and subgap conductance of the junction can be strongly modulated by the orientation angle of superconductive gap (β) and perpendicular electric field (EZ), suggesting that one may experimentally tune the transport properties of the junction through changing β and EZ. We demonstrate that the subgap conductance exhibits an oscillatory behavior as a function of the orientation angle of superconductive gap (β) with a period of π / 2 and by increasing the insulating gap of silicene, the charge conductance oscillations suppress. Remarkably, due to the buckled structure of silicene at the maximum orientation angle of the d-wave superconducting β = π / 4 , we found a very distinct behavior from the graphene-based NS junction where the charge conductance is insensitive to the bias energy. In addition, the Andreev reflection and subgap conductance can be switched on and off by applying electric field.

  15. Radiation Detection Measurements with a New 'Buried Junction' Silicon Avalanche Photodiode

    CERN Document Server

    Lecomte, R; Rouleau, D; Dautet, H; McIntyre, R J; McSween, D; Webb, P

    1999-01-01

    An improved version of a recently developed 'Buried Junction' avalanche photodiode (APD), designed for use with scintillators, is described and characterized. This device, also called the 'Reverse APD', is designed to have a wide depletion layer and thus low capacitance, but to have high gain only for e-h pairs generated within the first few microns of the depletion layer. Thus it has high gain for light from scintillators emitting in the 400-600 nm range, with relatively low dark current noise and it is relatively insensitive to minimum ionizing particles (MIPs). An additional feature is that the metallurgical junction is at the back of the wafer, leaving the front surface free to be coupled to a scintillator without fear of junction contamination. The modifications made in this device, as compared with the earlier diode, have resulted in a lower excess noise factor, lower dark current, and much-reduced trapping. The electrical and optical characteristics of this device are described and measurements of ener...

  16. Ferroelectric control of anisotropic damping in multiferroic tunnel junctions

    Science.gov (United States)

    Wang, Yan; Zhang, Ning; Berakdar, Jamal; Jia, Chenglong

    2015-10-01

    The magnetoelectric effect on nonlocal magnetization dynamics is theoretically investigated in normal-metal/ferroelectric-insulator/ferromagnetic tunnel junctions. In addition to the Rashba spin-orbit interaction (SOI) originating from loss of parity symmetry at the interfaces, the topology of interfacial spiral spins triggered by ferroelectric polarization acts with an effective SOI that is electrically controllable. These spin-dependent interactions result in an anisotropic Gilbert damping with C2 v symmetry. The findings are of a direct relevance for the utilization of composite multiferroics for devices that rely on electrically controlled magnetic switching.

  17. Neural coding using telegraphic switching of magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Suh, Dong Ik; Bae, Gi Yoon; Oh, Heong Sik; Park, Wanjun, E-mail: wanjun@hanyang.ac.kr [Department of Electronic Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2015-05-07

    In this work, we present a synaptic transmission representing neural coding with spike trains by using a magnetic tunnel junction (MTJ). Telegraphic switching generates an artificial neural signal with both the applied magnetic field and the spin-transfer torque that act as conflicting inputs for modulating the number of spikes in spike trains. The spiking probability is observed to be weighted with modulation between 27.6% and 99.8% by varying the amplitude of the voltage input or the external magnetic field. With a combination of the reverse coding scheme and the synaptic characteristic of MTJ, an artificial function for the synaptic transmission is achieved.

  18. Quasiparticle tunneling in a periodically driven bosonic Josephson junction

    Science.gov (United States)

    Gertjerenken, Bettina; Holthaus, Martin

    2014-11-01

    A resonantly driven bosonic Josephson junction supports stable collective excitations, or quasiparticles, which constitute analogs of the Trojan wave packets previously explored with Rydberg atoms in strong microwave fields. We predict a quantum beating effect between such symmetry-related many-body Trojan states taking place on time scales which are long in comparison with the driving period. Within a mean-field approximation, this quantum beating can be regarded as a manifestation of dynamical tunneling. On the full N -particle level, the beating phenomenon leads to an experimentally feasible, robust strategy for probing highly entangled mesoscopic states.

  19. NbN/MgO/NbN SIS tunnel junctions for submm wave mixers

    Science.gov (United States)

    Stern, J. A.; Hunt, B. D.; Leduc, H. G.; Judas, A.; Mcgrath, W. R.; Cypher, S. R.; Khanna, S. K.

    1989-01-01

    The authors report on the fabrication and testing of all-refractory NbN/MgO/NbN SIS (superconductor-insulator-superconductor) tunnel junctions for use as high-frequency mixers. Progress in the development of techniques for the fabrication of submicron-area tunnel junctions is described. Junction structures which have been investigated include mesa, crossline, and edge geometries. Using reactive sputtering techniques, NbN tunnel junctions with critical currents in excess of 104 A/sq cm have been fabricated with Vm values as high as 65 mV and areas down to 0.1 sq micron. Specific capacitance measurements on NbN/MgO/NbN mesa-type tunnel junctions give values in the range 60-90 fF/sq micron. These SIS tunnel junctions have been integrated with antennas and coupling structures for mixer tests in a waveguide receiver at 207 GHz. Preliminary mixer results are reported.

  20. A Review of the CMOS Buried Double Junction (BDJ Photodetector and its Applications

    Directory of Open Access Journals (Sweden)

    Gabriel Vasilescu

    2008-10-01

    Full Text Available A CMOS Buried Double Junction PN (BDJ photodetector consists of two vertically-stacked photodiodes. It can be operated as a photodiode with improved performance and wavelength-sensitive response. This paper presents a review of this device and its applications. The CMOS implementation and operating principle are firstly described. This includes the description of several key aspects directly related to the device performances, such as surface reflection, photon absorption and electron-hole pair generation, photocurrent and dark current generation, etc. SPICE modelling of the detector is then presented. Next, design and process considerations are proposed in order to improve the BDJ performance. Finally, several BDJ-detector-based image sensors provide a survey of their applications.

  1. Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions.

    Energy Technology Data Exchange (ETDEWEB)

    Ozyuzer, L.

    1998-10-27

    Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV = 2A as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d{sub x{sup 2}-y{sup 2}} (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T{sub c} = 62 K, the Josephson current is measured as a function of junction resistance, R{sub n}, which varied by two orders of magnitude (1 k{Omega} to 100 k{Omega}). I{sub c}R{sub n} product is proportional to the 0.47 power of I{sub c} and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T{sub c} = 62 K) to the underdoped regime (T{sub c} = 70 K), the average I{sub c}R{sub n} product increases as does the quasiparticle gap. The maximum I{sub c}R{sub n} is {approximately} 40% of the {Delta}/e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.

  2. Experimental investigation on parametric excitation of plasma oscillations in Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Bak, Christen Kjeldahl; Kofoed, Bent; Pedersen, Niels Falsig;

    1975-01-01

    Experimental evidence for subharmonic, parametric excitation of plasma oscillations in Josephson tunnel junctions is presented. The experiments described are performed by measuring the microwave power necessary to switch a Josephson tunnel junction biased in the zero voltage state to a finite...

  3. Giant thermal spin torque assisted magnetic tunnel junction switching

    Science.gov (United States)

    Pushp, Aakash

    Spin-polarized charge-currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer-torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin-currents from temperature gradients, and their associated thermal-spin-torques (TSTs) have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge-currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe. Reference: A. Pushp*, T. Phung*, C. Rettner, B. P. Hughes, S.-H. Yang, S. S. P. Parkin, 112, 6585-6590 (2015).

  4. Synthesis of magnetic tunnel junctions with full in situ atomic layer and chemical vapor deposition processes

    Energy Technology Data Exchange (ETDEWEB)

    Mantovan, R., E-mail: roberto.mantovan@mdm.imm.cnr.it [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Vangelista, S.; Kutrzeba-Kotowska, B.; Cocco, S.; Lamperti, A.; Tallarida, G. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (MB) (Italy); Mameli, D. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Dipartimento di Scienze Chimiche, Universita di Cagliari, Cittadella Universitaria, 09042 Monserrato, Cagliari (Italy); Fanciulli, M. [Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20864 Agrate Brianza (Italy); Dipartimento di Scienza dei Materiali, Universita degli studi Milano-Bicocca, Via R Cozzi 53, 20125 Milano (Italy)

    2012-05-01

    Magnetic tunnel junctions, i.e. the combination of two ferromagnetic electrodes separated by an ultrathin tunnel oxide barrier, are core elements in a large variety of spin-based devices. We report on the use of combined chemical vapor and atomic layer deposition processes for the synthesis of magnetic tunnel junctions with no vacuum break. Structural, chemical and morphological characterizations of selected ferromagnetic and oxide layers are reported, together with the evidence of tunnel magnetoresistance effect in patterned Fe/MgO/Co junctions.

  5. Edge-Geometry NbN/MgO/NbN Tunnel Junctions

    Science.gov (United States)

    Hunt, Brian D.; Leduc, Henry G.

    1991-01-01

    Superconductor/insulator/superconductor (SIS) tunnel junctions fabricated with base and counter electrodes of NbN separated by thin layers of MgO. Useful as submillimeter-wave mixers and fast switches. Use of edge geometry to define small junction makes possible to fabricate junction by process including conventional photolithography.

  6. Supersymmetric phase transition in Josephson-tunnel-junction arrays

    Energy Technology Data Exchange (ETDEWEB)

    Foda, O.

    1988-08-31

    The fully frustrated XY model in two dimensions exhibits a vortex-unbinding as well as an Ising transition. If the Ising transition overlaps with the critical line that ends on the vortex transition: T/sub I/less than or equal toT/sub V/, then the model is equivalent, at the overlap temperature, to a free massless field theory of 1 boson and 1 Majorana fermion, which is a superconformal field theory, of central charge c=3/2. The model is experimentally realized in terms of an array of Josephson-tunnel junctions in a transverse magnetic field. The experiment reveals a phase transition consistent with T/sub I/=T/sub V/. Thus, at the critical temperature, the array provides a physical realization of a supersymmetric quantum field theory.

  7. Superconducting tunnel junction detectors for soft x-ray astrophysics

    Science.gov (United States)

    Verhoeve, P.; Hijmering, R. A.; Martin, D. D. E.; Jerjen, I.; Peacock, A.; Venn, R.

    2006-06-01

    The requirement on energy resolution for detectors in future X-ray satelite missions such as XEUS (X-ray Evolving Universe Spectroscopy mission) is 80%. In addition, the requirements for field of view and angular resolution demand a detector array of typically 150x150 micron sized pixels in a 30x30 pixel format. DROIDs (Distributed Read Out Imaging Devices), consisting of a superconducting absorber strip with superconducting tunnel junctions (STJs) as read-out devices on either end, can fulfill these requirements. The amplitudes of the two signals from the STJs provide information on the absorption position and the energy of the incoming photon in the absorber. In this paper we present the development status of Ta/Al 1-D DROIDs, as well as the the short term development program that should result in a full size XEUS array.

  8. Superconducting tunnel junctions as direct detectors for submillimeter astronomy

    Science.gov (United States)

    Teufel, John Daniel

    This thesis presents measurements on the of performance of superconducting tunnel junctions (STJ) as direct detectors for submillimeter radiation. Over the past several decades, STJ's have been successfully implemented as energy-resolving detectors of X-ray and optical photons. This work extends their application to ultra-sensitive direct detection of photons near 100 GHz. The focus of this research is to integrate the detector with a readout that is sensitive, fast, and able to be scaled for use in large format arrays. We demonstrate the performance of a radio frequency single electron transistor (RF-SET) configured as a transimpedance current amplifier as one such readout. Unlike traditional semiconductor amplifiers, the RF-SET is compatible with cryogenic operation and naturally lends itself to frequency domain multiplexing. This research progressed to the invention of RF-STJ, whereby the same RF reflectometry as used in the RF-SET is applied directly to the detector junction. This results in a greatly simplified design that preserves many of the advantages of the RF-SET while achieving comparable sensitivity. These experiments culminate in calibration of the detector with an on-chip, mesoscopic noise source. Millimeter wave Johnson noise from a gold microbridge illuminates the detector in situ. This allows for direct measurement of the "optical" properties of the detector and its RF readout, including the response time, responsivity and sensitivity.

  9. Chaos and related nonlinear noise phenomena in Josephson tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Miracky, R.F.

    1984-07-01

    The nonlinear dynamics of Josephson tunnel junctions shunted by a resistance with substantial self-inductance have been thoroughly investigated. The current-voltage characteristics of these devices exhibit stable regions of negative differential resistance. Very large increases in the low-frequency voltage noise with equivalent noise temperatures of 10/sup 6/ K or more, observed in the vicinity of these regions, arise from switching, or hopping, between subharmonic modes. Moderate increases in the noise, with temperatures of about 10/sup 3/ K, arise from chaotic behavior. Analog and digital simulations indicate that under somewhat rarer circumstances the same junction system can sustain a purely deterministic hopping between two unstable subharmonic modes, accompanied by excess low-frequency noise. Unlike the noise-induced case, this chaotic process occurs over a much narrower range in bias current and is destroyed by the addition of thermal noise. The differential equation describing the junction system can be reduced to a one-dimensional mapping in the vicinity of one of the unstable modes. A general analytical calculation of switching processes for a class of mappings yields the frequency dependence of the noise spectrum in terms of the parameters of the mapping. Finally, the concepts of noise-induced hopping near bifurcation thresholds are applied to the problem of the three-photon Josephson parametric amplifier. Analog simulations indicate that the noise rise observed in experimental devices arises from occasional hopping between a mode at the pump frequency ..omega../sub p/ and a mode at the half harmonic ..omega../sub p//2. The hopping is induced by thermal noise associated with the shunt resistance. 71 references.

  10. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Science.gov (United States)

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-01

    Heulser alloys Fe2Cr1-xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  11. USING GROUND PENETRATING RADAR TO DETERMINE THE TUNNEL LOCATION BURIED UNDER THE GLACIER

    Directory of Open Access Journals (Sweden)

    Deryuga Andrey Mikhaylovich

    2013-09-01

    Full Text Available The works were carried out with the help of ground penetrating radar “Grot-10”. Doublet broadband antennas with the central frequency of 100 MHz were used. Georadar measures the speed of EM waves v in ice-saturated soil and then the value ε′ is calculated. The radargrams received as a result of georadar survey, which represents stacked data (the two-way time is indicated on vertical scale, were transformed into depth sections, which reflect the space structure located below ground. The distance between the bottom landing and buried mountain road near the north tunnel portal is 78,5 m (profile # 1, and the distance from the upper landing is 84,5 m (profile no. 2. Later, in the April 2003 during the hole boring with the diameter 1,2 m the vertical distance between the upper landing, where ground penetrating works were carried out, and the carpet road of the tunnel was calculated. This distance appeared to be 83 m, that means, the discrepancy between boring and georadar data (84,5 m was only 1,5 m. Thus, the results of ground penetrating investigations helped the workers of glacier to make the correct conclusion on time about the location and burial depth of the tunnel.

  12. Effect of Barrier Width on Bias-Dependent Tunnelling in Ferromagnetic Junctions

    Institute of Scientific and Technical Information of China (English)

    LI Fei-Fei; XIAO Ming-Wen; LI Zheng-Zhong; HU An; XU Wang

    2004-01-01

    @@ We present a finite temperature theory for bias-dependent tunnelling in ferromagnetic tunnelling junctions. The effects of the barrier width d on the tunnelling magnetoresistance (TMR) and its sign change behaviour are discussed with this theory. Numerical results show that both the zero-bias TMR and the critical voltage Vc at which the TMR changes its sign decrease with the increasing barrier width for a considerably thick barrier junction. Furthermore, it is found that a minimum exists in the curve of Vc versus d if a composite junction is under oxidized.

  13. Electrical switching in Fe /Cr/MgO/Fe magnetic tunnel junctions

    Science.gov (United States)

    Halley, D.; Majjad, H.; Bowen, M.; Najjari, N.; Henry, Y.; Ulhaq-Bouillet, C.; Weber, W.; Bertoni, G.; Verbeeck, J.; Van Tendeloo, G.

    2008-05-01

    Hysteretic resistance switching is observed in epitaxial Fe /Cr/MgO/Fe magnetic tunnel junctions under bias voltage cycling between negative and positive values of about 1V. The junctions switch back and forth between high- and low-resistance states, both of which depend on the device bias history. A linear dependence is found between the magnitude of the tunnel magnetoresistance and the crafted resistance of the junctions. To explain these results, a model is proposed that considers electron transport both by elastic tunneling and by defect-assisted transmission.

  14. Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

    Science.gov (United States)

    Rashid, H.; Desmaris, V.; Pavolotsky, A.; Belitsky, V.

    2016-04-01

    In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.

  15. Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

    Directory of Open Access Journals (Sweden)

    H. Rashid

    2016-04-01

    Full Text Available In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.

  16. Experimental study on similarity materials for soft rock of deep-buried tunnels

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yu; PENG Hai-you

    2011-01-01

    When every parameter is properly scaled down in accordance with some similarity coefficients, it is possible to study the physical-mechanical properties of rock mass with a scale model. To identify the key mechanisms of soft rock in deep buried tunnels, the proper sand, binder and ratio were selected. During the process, the model manufacture technology was introduced and typical tests were done and the results were presented. The physical and mechanical properties effects caused by each composition were discussed. It is shown that the physical and mechanical properties of chosen ratio material such as uniaxial compressive strength tests, elasticity modulus, tensile strength, internal frictional angle, and Poisson's ratio meet with similarity relationship well. The physical and mechanical properties of deep soft rock are simulated successfully.

  17. Output voltage calculations in double barrier magnetic tunnel junctions with asymmetric voltage behavior

    KAUST Repository

    Useinov, Arthur

    2011-10-22

    In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR-V curves, output voltages and I-V characteristics for negative and positive values of applied voltages were carried out using MTJs with CoFeB/MgO interfaces as an example. Asymmetry of the experimental TMR-V curves is explained by different values of the minority and majority Fermi wave vectors for the left and right sides of the tunnel barrier, which arises due to different annealing regimes. Electron tunneling in DMTJs was simulated in two ways: (i) Coherent tunneling, where the DMTJ is modeled as one tunnel system and (ii) consecutive tunneling, where the DMTJ is modeled by two single barrier junctions connected in series. © 2012 Elsevier B.V. All rights reserved.

  18. Time-resolved measurement of the tunnel magneto-Seebeck effect in a single magnetic tunnel junction.

    Science.gov (United States)

    Boehnke, Alexander; Walter, Marvin; Roschewsky, Niklas; Eggebrecht, Tim; Drewello, Volker; Rott, Karsten; Münzenberg, Markus; Thomas, Andy; Reiss, Günter

    2013-06-01

    Recently, several groups have reported spin-dependent thermoelectric effects in magnetic tunnel junctions. In this paper, we present a setup for time-resolved measurements of thermovoltages and thermocurrents of a single micro- to nanometer-scaled tunnel junction. An electrically modulated diode laser is used to create a temperature gradient across the tunnel junction layer stack. This laser modulation technique enables the recording of time-dependent thermovoltage signals with a temporal resolution only limited by the preamplifier for the thermovoltage. So far, time-dependent thermovoltage could not be interpreted. Now, with the setup presented in this paper, it is possible to distinguish different Seebeck voltage contributions to the overall measured voltage signal in the μs time regime. A model circuit is developed that explains those voltage contributions on different sample types. Further, it will be shown that a voltage signal arising from the magnetic tunnel junction can only be observed when the laser spot is directly centered on top of the magnetic tunnel junction, which allows a lateral separation of the effects.

  19. Coexistance of Giant Tunneling Electroresistance and Magnetoresistance in an All-Oxide Composite Magnetic Tunnel Junction

    KAUST Repository

    Caffrey, Nuala Mai

    2012-11-30

    We propose, by performing advanced abinitio electron transport calculations, an all-oxide composite magnetic tunnel junction, within which both large tunneling magnetoresistance (TMR) and tunneling electroresistance (TER) effects can coexist. The TMR originates from the symmetry-driven spin filtering provided by an insulating BaTiO3 barrier to the electrons injected from the SrRuO3 electrodes. Following recent theoretical suggestions, the TER effect is achieved by intercalating a thin insulating layer, here SrTiO3, at one of the SrRuO3/BaTiO3 interfaces. As the complex band structure of SrTiO3 has the same symmetry as that of BaTiO3, the inclusion of such an intercalated layer does not negatively alter the TMR and in fact increases it. Crucially, the magnitude of the TER also scales with the thickness of the SrTiO3 layer. The SrTiO3 thickness becomes then a single control parameter for both the TMR and the TER effect. This protocol offers a practical way to the fabrication of four-state memory cells. © 2012 American Physical Society.

  20. Large influence of capping layers on tunnel magnetoresistance in magnetic tunnel junctions

    Science.gov (United States)

    Zhou, Jiaqi; Zhao, Weisheng; Wang, Yin; Peng, Shouzhong; Qiao, Junfeng; Su, Li; Zeng, Lang; Lei, Na; Liu, Lei; Zhang, Youguang; Bournel, Arnaud

    2016-12-01

    It has been reported in experiments that capping layers, which enhance the perpendicular magnetic anisotropy (PMA) of magnetic tunnel junctions (MTJs), induce a great impact on the tunnel magnetoresistance (TMR). To explore the essential influence caused by the capping layers, we carry out ab initio calculations on TMR in the X(001)|CoFe(001)|MgO(001)|CoFe(001)|X(001) MTJ, where X represents the capping layer material, which can be tungsten, tantalum, or hafnium. We report TMR in different MTJs and demonstrate that tungsten is an ideal candidate for a giant TMR ratio. The transmission spectrum in Brillouin zone is presented. It can be seen that in the parallel condition of MTJ, sharp transmission peaks appear in the minority-spin channel. This phenomenon is attributed to the resonant tunnel transmission effect, and we explained it by the layer-resolved density of states. In order to explore transport properties in MTJs, the density of scattering states was studied from the point of band symmetry. It has been found that CoFe|tungsten interface blocks scattering states transmission in the anti-parallel condition. This work reports TMR and transport properties in MTJs with different capping layers and proves that tungsten is a proper capping layer material, which would benefit the design and optimization of MTJs.

  1. Charge and spin current oscillations in a tunnel junction induced by magnetic field pulses

    Science.gov (United States)

    Dartora, C. A.; Nobrega, K. Z.; Cabrera, G. G.

    2016-08-01

    Usually, charge and spin transport properties in tunnel junctions are studied in the DC bias regime and/or in the adiabatic regime of time-varying magnetic fields. In this letter, the temporal dynamics of charge and spin currents in a tunnel junction induced by pulsed magnetic fields is considered. At low bias voltages, energy and momentum of the conduction electrons are nearly conserved in the tunneling process, leading to the description of the junction as a spin-1/2 fermionic system coupled to time-varying magnetic fields. Under the influence of pulsed magnetic fields, charge and spin current can flow across the tunnel junction, displaying oscillatory behavior, even in the absence of DC bias voltage. A type of spin capacitance function, in close analogy to electric capacitance, is predicted.

  2. Characterization of Magnetic Tunnel Junctions For Spin Transfer Torque Magnetic Random Access Memory

    Science.gov (United States)

    Dill, Joshua Luchay

    This thesis details two experimental methods for quantifying magnetic tunnel junction behavior, namely write error rates and field modulated spin-torque ferromagnetic resonance. The former examines how reliably an applied spin-transfer torque can excite magnetization dynamics that lead to a reversal of magnetization direction while the latter studies steady state dynamics provided by an oscillating spin-transfer torque. These characterization techniques reveal write error rate behavior for a particular composition magnetic tunnel junction that qualitatively deviates from theoretical predictions. Possible origins of this phenomenon are also investigated with the field modulated spin-torque ferromagnetic resonance technique. By understanding the dynamics of magnetic moments predicted by theory, one can experimentally confirm or disprove these theories in order to accurately model and predict tunnel junction behavior. By having a better model for what factors are important in magnetization dynamics, one can optimize these factors in terms of improving magnetic tunnel junctions for their use as computer memory.

  3. Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    You, Chun-Yeol [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of)

    2014-01-28

    We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.

  4. Second order anisotropy contribution in perpendicular magnetic tunnel junctions.

    Science.gov (United States)

    Timopheev, A A; Sousa, R; Chshiev, M; Nguyen, H T; Dieny, B

    2016-06-01

    Hard-axis magnetoresistance loops were measured on perpendicular magnetic tunnel junction pillars of diameter ranging from 50 to 150 nm. By fitting these loops to an analytical model, the effective anisotropy fields in both free and reference layers were derived and their variations in temperature range between 340 K and 5 K were determined. It is found that a second-order anisotropy term of the form -K2cos(4)θ must be added to the conventional uniaxial -K1cos(2)θ term to explain the experimental data. This higher order contribution exists both in the free and reference layers. At T = 300 K, the estimated -K2/K1 ratios are 0.1 and 0.24 for the free and reference layers, respectively. The ratio is more than doubled at low temperatures changing the ground state of the reference layer from "easy-axis" to "easy-cone" regime. The easy-cone regime has clear signatures in the shape of the hard-axis magnetoresistance loops. The existence of this higher order anisotropy was also confirmed by ferromagnetic resonance experiments on FeCoB/MgO sheet films. It is of interfacial nature and is believed to be due to spatial fluctuations at the nanoscale of the first order anisotropy parameter at the FeCoB/MgO interface.

  5. Switching Properties of sub-100 nm Perpendicular Magnetic Tunnel Junctions

    Science.gov (United States)

    Tryputen, Larysa; Piotrowski, Stephan; Bapna, Mukund; Chien, Chia-Ling; Wang, Weigang; Majetich, Sara; Ross, Caroline

    2015-03-01

    Perpendicular magnetic tunnel junctions (p-MTJs) have great potential for realizing high-density non-volatile memory and logic devices. It is critical to solve scalability problem to implement such devices, to achieve low resistance area and to reduce switching current density while maintaining thermal stability. We present our recent results on fabrication of high resolution Ta/CoFeB/MgO/CoFeB/Ta p-MTJ devices and characterization of their switching properties as well as topography and current mapping by using nanoscale Conductive Atomic Force Microscopy. Our patterning method is based on using hydrogen silsesquioxane resist mask combined with ion beam etching. It allows to fabricate p-MTJ devices down to 40 nm in diameter while maintaining the magnetic quality of the multilayers. Repeatable, consistent switching behaviour has been observed in the obtained p-MTJ devices of 500 nm down to 40 nm with 10 - 800 mV voltage applied. Switching field increased as device diameter decreased, from 580 Oe at 500 nm (MR = 10%) to 410 Oe at 80 nm (MR = 9%). We discuss the effect of device sizes on the switching properties. This work was supported in part by C-SPIN, one of the six centers of STARnet, a Semiconductor Research Corporation Program sponsored by MARCO and DARPA and in part through the National Science Foundation through NCN-Needs Program, Contract 12207020-EEC.

  6. Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges

    Directory of Open Access Journals (Sweden)

    Mengxing Wang

    2015-08-01

    Full Text Available Magnetic tunnel junction (MTJ, which arises from emerging spintronics, has the potential to become the basic component of novel memory, logic circuits, and other applications. Particularly since the first demonstration of current induced magnetization switching in MTJ, spin transfer torque magnetic random access memory (STT-MRAM has sparked a huge interest thanks to its non-volatility, fast access speed, and infinite endurance. However, along with the advanced nodes scaling, MTJ with in-plane magnetic anisotropy suffers from modest thermal stability, high power consumption, and manufactural challenges. To address these concerns, focus of research has converted to the preferable perpendicular magnetic anisotropy (PMA based MTJ, whereas a number of conditions still have to be met before its practical application. This paper overviews the principles of PMA and STT, where relevant issues are preliminarily discussed. Centering on the interfacial PMA in CoFeB/MgO system, we present the fundamentals and latest progress in the engineering, material, and structural points of view. The last part illustrates potential investigations and applications with regard to MTJ with interfacial PMA.

  7. AlGaAs/GaAs tunnel junctions in a 4-J tandem solar cell

    Institute of Scientific and Technical Information of China (English)

    Lü Siyu; Qu Xiaosheng

    2011-01-01

    The Ⅲ-Ⅴ compound tandem solar cell is a third-generation new style solar cell with ultra-high efficiency.The energy band gaps of the sub-cells in a GaInP/GaAs/InGaAs/Ge 4-J tandem solar cell are 1.8,1.4,1.0and 0.7 eV,respectively.In order to match the currents between sub-cells,tunnel junctions are used to connect the sub-cells.The characteristics of the tunnel junction,the material used in the tunnel junction,the compensation of the tunnel junction to the overall cell's characteristics,the tunnel junction's influence on the current density of sub-cells and the efficiency increase are discussed in the paper.An A1GaAs/GaAs tunnel junction is selected to simulate the cell's overall characteristics by PC 1 D,current densities of 16.02,17.12,17.75 and 17.45 mA/cm2 are observed,with a Voc of 3.246 V,the energy conversion efficiency under AM0 is 33.9%.

  8. Bottom-Up Molecular Tunneling Junctions Formed by Self-Assembly

    NARCIS (Netherlands)

    Zhang, Yanxi; Zhao, Zhiyuan; Fracasso, Davide; Chiechi, Ryan C

    2014-01-01

    This Minireview focuses on bottom-up molecular tunneling junctions - a fundamental component of molecular electronics - that are formed by self-assembly. These junctions are part of devices that, in part, fabricate themselves, and therefore, are particularly dependent on the chemistry of the molecul

  9. Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

    DEFF Research Database (Denmark)

    Pedersen, Niels Falsig; Sørensen, O. H.; Mygind, Jesper

    1978-01-01

    The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature Tc of the Sn films. The temperature dependence of the cosφ conductance is determined from the resonant response at the junction plasma frequency fp...... of the experiment....

  10. Noncovalent Self-Assembled Monolayers on Graphene as a Highly Stable Platform for Molecular Tunnel Junctions.

    Science.gov (United States)

    Song, Peng; Sangeeth, C S Suchand; Thompson, Damien; Du, Wei; Loh, Kian Ping; Nijhuis, Christian A

    2016-01-27

    Monolayer graphene is used as the bottom electrode to fabricate stable and high-quality self-assembled monolayer (SAM)-based tunnel junctions. The SAMs are formed on graphene via noncovalent bonds without altering the structure of the graphene. This work paves the way to new types of molecular electronic junctions based on 2D materials.

  11. Comparison of the magneto-Peltier and magneto-Seebeck effects in magnetic tunnel junctions

    NARCIS (Netherlands)

    Shan, J.; Dejene, F. K.; Leutenantsmeyer, J. C.; Flipse, J.; Munzenberg, M.; van Wees, B. J.

    2015-01-01

    Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction v

  12. Measured Temperature Dependence of the cos-phi Conductance in Josephson Tunnel Junctions

    DEFF Research Database (Denmark)

    Sørensen, O. H.; Mygind, Jesper; Pedersen, Niels Falsig

    1977-01-01

    The temperature dependence of the cosϕ conductance in Sn-O-Sn Josephson tunnel junctions has been measured just below the critical temperature, Tc. From the resonant microwave response at the junction plasma frequency as the temperature is decreased from Tc it is deduced that the amplitude...

  13. Static properties of small Josephson tunnel junctions in an oblique magnetic field

    DEFF Research Database (Denmark)

    Monaco, Roberto; Aarøe, Morten; Mygind, Jesper;

    2009-01-01

    We have carried out a detailed experimental investigation of the static properties of planar Josephson tunnel junctions in presence of a uniform external magnetic field applied in an arbitrary orientation with respect to the barrier plane. We considered annular junctions, as well as rectangular j...

  14. Thermal Spin Transfer in Fe-MgO-Fe Tunnel Junctions

    NARCIS (Netherlands)

    Jia, X.; Xia, K.; Bauer, G.E.W.

    2011-01-01

    We compute thermal spin transfer (TST) torques in Fe-MgO-Fe tunnel junctions using a first principles wave-function-matching method. At room temperature, the TST in a junction with 3 MgO monolayers amounts to 10-7  J/m2/K, which is estimated to cause magnetization reversal for temperature difference

  15. Fabrication of tunnel junctions on thick X-ray absorbing substrates of Nb and Ta

    NARCIS (Netherlands)

    Hamster, A.W.; Ferrari, E.; Adelerhof, D.J.; Brons, G.C.S.; Schoofs, I.J.E.; Flokstra, J.; Rogalla, H.; Bruijn, M.P.; Kiewiet, F.; Luiten, O.J.; Korte, de P.A.J.

    1996-01-01

    X-ray detectors based on absorber-junction combinations can combine a large detector area with position resolution and good energy resolution. We plan to use a thick, single crystal Nb or Ta absorber with readout tunnel junctions integrated on top as our next generation X-ray detector. The thickness

  16. Effect of Anti-Diffusion Oxide Layer on Enhanced Thermal Stability of Magnetic Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zong-Zhi; ZHAO Hui; Cardoso S.; Freitas P. P.

    2006-01-01

    @@ Magnetic tunnel junctions (MTJs) with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance (TMR) signals as high as 39% after anneal at 380℃ .

  17. Effect of the electromagnetic environment on current fluctuations in driven tunnel junctions

    Science.gov (United States)

    Frey, Moritz; Grabert, Hermann

    2016-07-01

    We examine current fluctuations in tunnel junctions driven by a superposition of a constant and a sinusoidal voltage source. In standard setups, the external voltage is applied to the tunneling element via an impedance providing an electromagnetic environment of the junction. The modes of this environment are excited by the time-dependent voltage and are the source of Johnson-Nyquist noise. We determine the autocorrelation function of the current flowing in the leads of the junction in the weak tunneling limit up to terms of second order in the tunneling Hamiltonian. The driven modes of the electromagnetic environment are treated exactly by means of a unitary transformation introduced recently. Particular emphasis is placed on the spectral function of the current fluctuations. The spectrum is found to comprise three contributions: a term arising from the Johnson-Nyquist noise of the environmental impedance, a part due to the shot noise of the tunneling element, and a third contribution which comes from the cross correlation between fluctuations caused by the electromagnetic environment and fluctuations of the tunneling current. All three parts of the spectral function occur already for devices under dc bias. The spectral function of ac driven tunneling elements can be determined from the result for a dc bias by means of a photoassisted tunneling relation of the Tien-Gordon type. Specific results are given for an Ohmic environment and for a junction driven through a resonator.

  18. Electrical properties of graphene tunnel junctions with high-κ metal-oxide barriers

    Science.gov (United States)

    Feng, Ying; Trainer, Daniel J.; Chen, Ke

    2017-04-01

    An insulating barrier is one of the key components in electronic devices that makes use of quantum tunneling principles. Many metal-oxides have been used as a good barrier material in a tunnel junction for their large band gap, stable chemical properties and superb properties for forming a thin and pin-hole-free insulating layer. The reduced dimensions of transistors have led to the need for alternative, high dielectric constant (high-κ) oxides to replace conventional silicon-based dielectrics to reduce the leaking current induced by electron tunneling. On the other hand, a tunnel junction with one or both electrodes made of graphene may lead to novel applications due to the massless Dirac fermions from the graphene. Here we have fabricated sandwich-type graphene tunnel junctions with high-κ metal-oxides as barriers, including Al2O3, HfO2, ZrO2, and TiO2. Tunneling properties are investigated by observing the temperature and time dependences of the tunneling spectra. Our results show the potential for applications of high-κ oxides in graphene tunnel junctions and bringing new opportunities for memory and logic electronic devices.

  19. Detecting Current Noise with a Josephson Junction in the Macroscopic Quantum Tunneling Regime

    OpenAIRE

    Peltonen, J. T.; Timofeev, A. V.; Meschke, M.; Pekola, J.P.

    2006-01-01

    We discuss the use of a hysteretic Josephson junction to detect current fluctuations with frequencies below the plasma frequency of the junction. These adiabatic fluctuations are probed by switching measurements observing the noise-affected average rate of macroscopic quantum tunneling of the detector junction out of its zero-voltage state. In a proposed experimental scheme, frequencies of the noise are limited by an on-chip filtering circuit. The third cumulant of current fluctuations at the...

  20. Magnetoresistance in Co/AlO sub x /Co tunnel junction arrays

    CERN Document Server

    Urech, M; Haviland, D B

    2002-01-01

    Lateral arrays of Co/AlO sub x /Co junctions with dimensions down to 60 nm and inter-junction separations approx 60-100 nm have been fabricated and analyzed for possible coherent tunneling effects. Extra attention is paid to avoid uncertainties due to inconsistencies in switching and/or resistance of successive barriers. We observe approx 10% magnetoresistance enhancement at moderate bias in double junctions that cannot be accounted for by a simple model of two resistsors in series.

  1. Current distribution effects in patterned non-linear magnetoresistive tunnel junctions

    CERN Document Server

    Montaigne, F; Schuhl, A

    2000-01-01

    To be used in submicronic devices like magnetic memories, magnetic tunnel junctions require low resistances. Four-probe measurements of such resistances are often altered by non-uniformity of the current distribution in the junction. The measured resistance is decreased by localised preferential conduction and increased by voltage drop in the measure electrode. Competition between these two effects is investigated as a function of the geometry. The non-linear conduction of tunnel junctions amplifies dramatically these phenomena and can modify by more than 50% the measured resistance.

  2. Nb/NiCu bilayers in single and stacked superconductive tunnel junctions: preliminary results

    Science.gov (United States)

    Pepe, G. P.; Ruotolo, A.; Parlato, L.; Peluso, G.; Ausanio, G.; Carapella, G.; Latempa, R.

    2004-05-01

    We present preliminary experimental results concerning both single and stacked tunnel junctions in which one of the electrodes was formed by a superconductor/ferromagnet (S/F) bi-layer. In particular, in the stacked configuration a Nb/NiCu bi-layer was used as the intermediate electrode, and it was probed by tunneling on both sides. Tunnel junctions have been characterized in terms of current-voltage characteristics (IVC), and differential conductance. Preliminary steady-state injection-detection measurements performed in the stacked devices at T=4.2K are also presented and discussed.

  3. Nb/NiCu bilayers in single and stacked superconductive tunnel junctions: preliminary results

    Energy Technology Data Exchange (ETDEWEB)

    Pepe, G.P. E-mail: ruotolo_antonio@tin.it; Ruotolo, A.; Parlato, L.; Peluso, G.; Ausanio, G.; Carapella, G.; Latempa, R

    2004-05-01

    We present preliminary experimental results concerning both single and stacked tunnel junctions in which one of the electrodes was formed by a superconductor/ferromagnet (S/F) bi-layer. In particular, in the stacked configuration a Nb/NiCu bi-layer was used as the intermediate electrode, and it was probed by tunneling on both sides. Tunnel junctions have been characterized in terms of current-voltage characteristics (IVC), and differential conductance. Preliminary steady-state injection-detection measurements performed in the stacked devices at T=4.2 K are also presented and discussed.

  4. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Pu, E-mail: Vicky-sg1015@hotmail.com [Department of Electrical and Computer Engineering, National University of Singapore (Singapore); Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Lim, Sze-Ter; Han, Gu-Chang, E-mail: HAN-Guchang@dsi.a-star.edu.sg [Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Teo, Kie-Leong, E-mail: eleteokl@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore (Singapore)

    2015-12-21

    Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  5. Inter-band phase fluctuations in macroscopic quantum tunneling of multi-gap superconducting Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Asai, Hidehiro, E-mail: hd-asai@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Ota, Yukihiro [CCSE, Japan Atomic Energy Agency, Kashiwa, Chiba 277-8587 (Japan); Kawabata, Shiro [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Nori, Franco [CEMS, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, MI 48109-1040 (United States)

    2014-09-15

    Highlights: • We study MQT in Josephson junctions composed of multi-gap superconductors. • We derive a formula of the MQT escape rate for multiple phase differences. • We investigate the effect of inter-band phase fluctuation on MQT. • The MQT escape rate is significantly enhanced by the inter-band phase fluctuation. - Abstract: We theoretically investigate macroscopic quantum tunneling (MQT) in a hetero Josephson junction formed by a conventional single-gap superconductor and a multi-gap superconductor. In such Josephson junctions, phase differences for each tunneling channel are defined, and the fluctuation of the relative phase differences appear which is referred to as Josephson–Leggett’s mode. We take into account the effect of the fluctuation in the tunneling process and calculate the MQT escape rate for various junction parameters. We show that the fluctuation of relative phase differences drastically enhances the escape rate.

  6. Tunnel anisotropic magnetoresistance in CoFeB|MgO|Ta junctions

    Energy Technology Data Exchange (ETDEWEB)

    Hatanaka, S.; Miwa, S., E-mail: miwa@mp.es.osaka-u.ac.jp; Matsuda, K.; Nawaoka, K.; Tanaka, K.; Morishita, H.; Goto, M.; Mizuochi, N.; Shinjo, T.; Suzuki, Y. [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)

    2015-08-24

    We found that CoFeB|MgO|Ta tunnel junctions exhibit tunnel anisotropic magnetoresistance (TAMR) at room temperature. The tunnel junctions exhibit positive magnetoresistance with the application of a magnetic field normal to the film plane. The dependencies on the applied magnetic field angle and MgO thickness reveal that the magnetoresistance originates from the TAMR, caused by the spin polarization and the spin-orbit interaction at the CoFeB|MgO interface. We also found that the TAMR can be used to detect ferromagnetic resonance in the CoFeB. This detection method could be useful for the characterization of nanomagnets that are free from the spin-transfer effect and the stray field of a reference layer, unlike conventional magnetic tunnel junctions.

  7. Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier

    Science.gov (United States)

    Althammer, Matthias; Vikam Singh, Amit; Keshavarz, Sahar; Kenan Yurtisigi, Mehmet; Mishra, Rohan; Borisevich, Albina Y.; LeClair, Patrick; Gupta, Arunava

    2016-12-01

    We experimentally investigate the structural, magnetic, and electrical transport properties of La0.67 Sr0.33 MnO3 based magnetic tunnel junctions with a SrSnO3 barrier. Our results show that despite the high density of defects in the strontium stannate barrier, due to the large lattice mismatch, the observed tunnel magnetoresistance (TMR) is comparable to tunnel junctions with a better lattice matched SrTiO3 barrier, reaching values of up to 350 % at T =5 K . Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease of the TMR with increasing bias voltage. In addition, the observed TMR vanishes for T >200 K . Our results suggest that by employing a better lattice matched ferromagnetic electrode, and thus reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future.

  8. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

    Directory of Open Access Journals (Sweden)

    Takeo Ohno and Yutaka Oyama

    2012-01-01

    Full Text Available In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE, in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor.

  9. The importance of Fe surface states for spintronic devices based on magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Chantis, Athanasios N [Los Alamos National Laboratory

    2008-01-01

    In this article we give a review of our recent theoretical studies of the influence of Fe(001) surface (interface) states on spin-polarized electron transport across magnetic tunnel junctions with Fe electrodes. We show that minority-spin surface (interface) states are responsible for at least two effects which are important for spin electronics. First, they can produce a sizable tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a single Fe electrode. The effect is driven by a Rashba shift of the resonant surface band when the magnetization changes direction. This can introduce a new class of spintronic devices, namely, tunneling magnetoresistance junctions with a single ferromagnetic electrode. Second, in Fe/GaAs(001) magnetic tunnel junctions minority-spin interface states produce a strong dependence of the tunneling current spin polarization on applied electrical bias. A dramatic sign reversal within a voltage range of just a few tenths of an eV is predicted. This explains the observed sign reversal of spin polarization in recent experiments of electrical spin injection in Fe/GaAs(001) and related reversal of tunneling magnetoresistance through vertical Fe/GaAs/Fe trilayers.

  10. Tunnel magnetoresistance in thermally robust Mo/CoFeB/MgO tunnel junction with perpendicular magnetic anisotropy

    Directory of Open Access Journals (Sweden)

    B. Fang

    2015-06-01

    Full Text Available We report on tunnel magnetoresistance and electric-field effect in the Mo buffered and capped CoFeB/MgO magnetic tunnel junctions (MTJs with perpendicular magnetic anisotropy. A large tunnel magnetoresistance of 120% is achieved. Furthermore, this structure shows greatly improved thermal stability and stronger electric-field-induced modulation effect in comparison with the Ta/CoFeB/MgO-based MTJs. These results suggest that the Mo-based MTJs are more desirable for next generation spintronic devices.

  11. Submicron area NbN/MgO/NbN tunnel junctions for SIS mixer applications

    Science.gov (United States)

    Leduc, H. G.; Judas, A.; Cypher, S. R.; Bumble, B.; Hunt, B. D.

    1991-01-01

    The development of submicron area mixer elements for operation in the submillimeter wave range is discussed. High-current-density NbN/MgO/NbN tunnel junctions with areas down to 0.1 sq microns have been fabricated in both planar and edge geometries. The planar junctions were fabricated from in situ deposited trilayers using electron-beam lithography to pattern submicron area mesas. Modifications of fabrication techniques used in larger-area NbN tunnel junctions are required and are discussed. The NbN/MgO/NbN edge junction process using sapphire substrates has been transferred to technologically important quartz substrates using MgO buffer layers to minimize substrate interactions. The two junction geometries are compared and contrasted in the context of submillimeter wave mixer applications.

  12. Four-state non-volatile memory in a multiferroic spin filter tunnel junction

    Science.gov (United States)

    Ruan, Jieji; Li, Chen; Yuan, Zhoushen; Wang, Peng; Li, Aidong; Wu, Di

    2016-12-01

    We report a spin filter type multiferroic tunnel junction with a ferromagnetic/ferroelectric bilayer barrier. Memory functions of a spin filter magnetic tunnel junction and a ferroelectric tunnel junction are combined in this single device, producing four non-volatile resistive states that can be read out in a non-destructive manner. This concept is demonstrated in a LaNiO3/Pr0.8Ca0.2MnO3/BaTiO3/La0.7Sr0.3MnO3 all-oxide tunnel junction. The ferromagnetic insulator Pr0.8Ca0.2MnO3 serves as the spin filter and the ferromagnetic metal La0.7Sr0.3MnO3 is the spin analyzer. The ferroelectric polarization reversal in the BaTiO3 barrier switches the tunneling barrier height to produce a tunneling electroresistance. The ferroelectric switching also modulates the spin polarization and the spin filtering efficiency in Pr0.8Ca0.2MnO3.

  13. Junction size dependence of ferroelectric properties in e-beam patterned BaTiO{sub 3} ferroelectric tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Singh, A. V.; Gupta, A. [Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama 35487 (United States); Althammer, M. [Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama 35487 (United States); Walther-Meissner-Institut, Bayerische Akdademie der Wissenschaften, Garching 85748 (Germany); Rott, K.; Reiss, G. [Thin Films and Physics of Nanostructures, Department of Physics and Center for Spinelectronic Materials and Devices, Bielefeld University, Bielefeld 33615 (Germany)

    2015-09-21

    We investigate the switching characteristics in BaTiO{sub 3}-based ferroelectric tunnel junctions patterned in a capacitive geometry with circular Ru top electrode with diameters ranging from ∼430 to 2300 nm. Two different patterning schemes, viz., lift-off and ion-milling, have been employed to examine the variations in the ferroelectric polarization, switching, and tunnel electro-resistance resulting from differences in the pattering processes. The values of polarization switching field are measured and compared for junctions of different diameter in the samples fabricated using both patterning schemes. We do not find any specific dependence of polarization switching bias on the size of junctions in both sample stacks. The junctions in the ion-milled sample show up to three orders of resistance change by polarization switching and the polarization retention is found to improve with increasing junction diameter. However, similar switching is absent in the lift-off sample, highlighting the effect of patterning scheme on the polarization retention.

  14. Using tunnel junctions to grow monolithically integrated optically pumped semipolar III-nitride yellow quantum wells on top of electrically injected blue quantum wells.

    Science.gov (United States)

    Kowsz, Stacy J; Young, Erin C; Yonkee, Benjamin P; Pynn, Christopher D; Farrell, Robert M; Speck, James S; DenBaars, Steven P; Nakamura, Shuji

    2017-02-20

    We report a device that monolithically integrates optically pumped (20-21) III-nitride quantum wells (QWs) with 560 nm emission on top of electrically injected QWs with 450 nm emission. The higher temperature growth of the blue light-emitting diode (LED) was performed first, which prevented thermal damage to the higher indium content InGaN of the optically pumped QWs. A tunnel junction (TJ) was incorporated between the optically pumped and electrically injected QWs; this TJ enabled current spreading in the buried LED. Metalorganic chemical vapor deposition enabled the growth of InGaN QWs with high radiative efficiency, while molecular beam epitaxy was leveraged to achieve activated buried p-type GaN and the TJ. This initial device exhibited dichromatic optically polarized emission with a polarization ratio of 0.28. Future improvements in spectral distribution should enable phosphor-free polarized white light emission.

  15. Dynamical image-charge effect in molecular tunnel junctions

    DEFF Research Database (Denmark)

    Jin, Chengjun; Thygesen, Kristian Sommer

    2014-01-01

    When an electron tunnels between two metal contacts it temporarily induces an image charge (IC) in the electrodes which acts back on the tunneling electron. It is usually assumed that the IC forms instantaneously such that a static model for the image potential applies. Here we investigate how...

  16. Response of an on-chip coil-integrated superconducting tunnel junction to x-rays

    CERN Document Server

    Maehata, K; Taino, T

    2003-01-01

    An on-chip coil-integrated superconducting tunnel junction (OC sup 2 -STJ) was irradiated by X-rays emitted from an sup 5 sup 5 Fe source to the examine the performance of X-ray detection by applying a magnetic field produced by a superconducting microstrip coil integrated into the junction chip. Response characteristics were obtained for a diamond-shaped Nd-based tunnel junction with a sensitive area of 100 x 100 mu m sup 2 in the OC sup 2 -STJ chip. Two kinds of stable operation modes with different pulse heights were observed by changing the magnetic flux density in the barrier region of the junction. In the low-pulse-height mode, the pulse height distribution exhibits two full-energy peaks corresponding to signals created in the top and base electrodes. Stable operation of the OC sup 2 -STJ was demonstrated without using conventional external electromagnets. (author)

  17. Direct detection of the parametrically generated half-harmonic voltage in a Josephson tunnel junction

    DEFF Research Database (Denmark)

    Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.

    1976-01-01

    The first direct observation of the parametrically generated half-harmonic voltage in a Josephson tunnel junction is reported. A microwave signal at f=17.25 GHz is applied to the junction dc current biased at zero voltage such that the Josephson plasma resonance fp=f/2. Under these conditions a l...... a large-amplitude microwave signal is emitted at fp provided the input power exceeds a threshold value. The results are compared to existing theory. Applied Physics Letters is copyrighted by The American Institute of Physics.......The first direct observation of the parametrically generated half-harmonic voltage in a Josephson tunnel junction is reported. A microwave signal at f=17.25 GHz is applied to the junction dc current biased at zero voltage such that the Josephson plasma resonance fp=f/2. Under these conditions...

  18. Tunneling conductance studies in the ion-beam sputtered CoFe/Mg/MgO/NiFe magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Braj Bhusan; Chaudhary, Sujeet [Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)

    2013-06-03

    Magnetic tunnel junctions consisting of CoFe(10 nm)/Mg(1 nm)/MgO(3.5 nm)/NiFe(10 nm) are grown at room temperature using dual ion beam sputtering via in-situ shadow masking. The effective barrier thickness and average barrier height are estimated to be 3.5 nm (2.9 nm) and 0.69 eV (1.09 eV) at 290 K (70 K), respectively. The tunnel magnetoresistance value of 0.2 % and 2.3 % was observed at 290 K and 60 K, respectively. The temperature dependence of tunneling conductance revealed the presence of localized states present within the forbidden gap of the MgO barrier leading to finite inelastic spin independent tunneling contributions, which degrade the TMR value.

  19. Tunneling Conductance in Quantum-Wire/Ferromagnetic-Insulator/d-Wave Superconductor Junction

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Wei

    2008-01-01

    We have studied the quasiparticle transport in quantum-wire /ferromagnetic-insulator/d wave super-conductor Junction (q/FI/d) in the framework of the Blonder Tinkham-Klapwijk model We calculate the tunneling conductance in q/FI/d as a function of the bias voltage at zero temperature and finite temperature based on Bogoliubov-de Gennes equations. Different from the case in normal-metal/insulator/d wave superconductor Junctions, the zero-bias conductance peaks vanish for the single-mode case. The tunneling conductance spectra depend on the magnitude of the exchange interaction at the ferromagnetic-insulator.

  20. Evidence for two-band superconductivity from break-junction tunneling on MgB2.

    Science.gov (United States)

    Schmidt, H; Zasadzinski, J F; Gray, K E; Hinks, D G

    2002-03-25

    Superconductor-insulator-superconductor tunnel junctions have been fabricated on MgB2 that display Josephson and quasiparticle currents. These junctions exhibit a gap magnitude, Delta approximately 2.5 meV, that is considerably smaller than the BCS value, but which clearly and reproducibly closes near the bulk T(c). In conjunction with fits of the conductance spectra, these results are interpreted as direct evidence of two-band superconductivity.

  1. A Far-Infrared Laser Study of Small-Area Superconducting Tunnel Junctions.

    Science.gov (United States)

    1983-10-01

    line, and also served as one end mirror. The output coupling mirror was mounted on a 4. piezo -electric transducer (PZT) stack for fine tuning of the...lower voltages, possibly subharmonic gap structure. 120 More power is coupled into this low ac , non-hysteretic junction, and a total of five steps are... subharmonic step. The presence of this step may be due to the much higher capaci- tance of the tunnel junction as compared to the point contact. It may

  2. Giant piezoelectric resistance effect of nanoscale zinc oxide tunnel junctions: first principles simulations.

    Science.gov (United States)

    Zhang, Genghong; Luo, Xin; Zheng, Yue; Wang, Biao

    2012-05-21

    Based on first principles simulations and quantum transport calculations, we have investigated in the present work the effect of the mechanical load on transport characteristics and the relative physical properties of nanoscale zinc oxide (ZnO) tunnel junctions, and verified an intrinsic giant piezoelectric resistance (GPR) effect. Our results show that the transport-relevant properties, e.g., the piezoelectric potential (piezopotential), built-in electric field, conduction band offset and electron transmission probability of the junction etc., can obviously be tuned by the applied strain. Accordingly, it is inspiring to find that the current-voltage characteristics and tunneling electro-resistance of the ZnO tunnel junction can significantly be adjusted with the strain. When the applied strain switches from -5% to 5%, an increase of more than 14 times in the tunneling current at a bias voltage of 1.1 V can be obtained. Meanwhile, an increase of up to 2000% of the electro-resistance ratio with respect to the zero strain state can be reached at the same bias voltage and with a 5% compression. According to our investigations, the giant piezoelectric resistance effect of nanoscale ZnO tunnel junctions exhibits great potential in exploiting tunable electronic devices. Furthermore, the methodology of strain engineering revealed in this work may shed light on the mechanical manipulations of electronic devices.

  3. Negative tunnelling magnetoresistance in spin filtering magnetic junctions with spin-orbit coupling

    Institute of Scientific and Technical Information of China (English)

    Li Yun

    2011-01-01

    We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer-Büttiker formalism and taking into account the spin-orbit coupling (SOC). It is shown that spin-flip scattering induced by SOC is stronger in parallel alignment of magnetization of the ferromegnet barrier (FB) and the ferromagnetic electrode than that in antiparallel case. The increase of negative tunnelling magnetoresistance with bias is in agreement with recent experimental observation.

  4. All-electric-controlled spin current switching in single-molecule magnet-tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Zhang Zheng-Zhong; Shen Rui; Sheng Li; Wang Rui-Qiang; Wang Bai-Gen; Xing Ding-Yu

    2011-01-01

    A single-molecule magnet (SMM)coupled to two normal metallic electrodes can both switch spin-up and spindown electronic currents within two different windows of SMM gate voltage. Such spin current switching in the SMM tunnel junction arises from spin-selected single electron resonant tunneling via the lowest unoccupied molecular orbit of the SMM. Since it is not magnetically controlled but all-electrically controlled, the proposed spin current switching effect may have potential applications in future spintronics.

  5. Quantum-limited detection of millimeter waves using superconducting tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Mears, C.A.

    1991-09-01

    The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus_minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker`s theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.

  6. Quantum-limited detection of millimeter waves using superconducting tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Mears, C.A.

    1991-09-01

    The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker's theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.

  7. Chemical beam epitaxy growth of AlGaAs/GaAs tunnel junctions using trimethyl aluminium for multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, B.; DeVita, M.; Turala, A.; Kolhatkar, G.; Boucherif, A.; Jaouad, A.; Aimez, V.; Arès, R. [Institut Interdisciplinaire d' Innovation Technologique (3IT), Université de Sherbrooke, Sherbrooke, Québec (Canada); Wilkins, M.; Wheeldon, J. F.; Walker, A. W.; Hinzer, K. [Centre for Research in Photonics, University of Ottawa, Ottawa, ON (Canada); Fafard, S. [Cyrium Technologies Inc., Ottawa, ON (Canada)

    2013-09-27

    AlGaAs/GaAs tunnel junctions for use in high concentration multijunction solar cells were designed and grown by chemical beam epitaxy (CBE) using trimethyl aluminium (TMA) as the p-dopant source for the AlGaAs active layer. Controlled hole concentration up to 4⋅10{sup 20} cm{sup −3} was achieved through variation in growth parameters. Fabricated tunnel junctions have a peak tunneling current up to 6140 A/cm{sup 2}. These are suitable for high concentration use and outperform GaAs/GaAs tunnel junctions.

  8. Enhancement of thermal spin transfer torque by double-barrier magnetic tunnel junctions with a nonmagnetic metal spacer

    Science.gov (United States)

    Chen, C. H.; Tseng, P.; Yang, Y. Y.; Hsueh, W. J.

    2017-01-01

    Enhancement of thermal spin transfer torque in a double-barrier magnetic tunnel junction with a nonmagnetic-metal spacer is proposed in this study. The results indicate that, given the same temperature difference, thermal spin transfer torque and charge current density for the proposed double barrier magnetic tunnel junction configuration can be approximately twice as much as that of the traditional single-barrier magnetic tunnel junctions. This enhancement can be attributed to the resonant tunneling mechanism in the double-barrier structure.

  9. Magnetic tunneling junctions with permalloy electrodes: a study of barrier, thermal annealing, and interlayer coupling

    Energy Technology Data Exchange (ETDEWEB)

    Liu Xiaoyong E-mail: xiaoyong_liu@brown.edu; Ren Cong; Ritchie, Lance; Schrag, B.D.; Xiao Gang; Li Laifeng

    2003-11-01

    Magnetic properties of Ni{sub 81}Fe{sub 19}/Al{sub 2}O{sub 3}/Ni{sub 81}Fe{sub 19} tunneling junctions are studied for different Al thicknesses and plasma oxidation times. A maximal magnetoresistance of 34% is obtained with Al thickness of 20 A. Magnetometry reveals large exchange bias fields ({approx}400 Oe) over a wide range of barrier thicknesses, indicating junctions of high quality. Transport measurements conducted on junctions before and after thermal annealing show a dramatic improvement in barrier quality after annealing. Interlayer coupling fields have been measured as a function of barrier thickness for different oxidation times.

  10. Realization of Primary Thermometer from Electrical Shot Noise in a Metal-Insulator-Metal Tunnel Junction

    Energy Technology Data Exchange (ETDEWEB)

    Park, J. H.; Rehman, M.; Choi, J. S.; Song, W.; Chong, Y. [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Khim, Z. G. [Dept. of Physics and Astronomy, Seoul National University, Seoul (Korea, Republic of); Ryu, S. W. [Dept. of Physics, Chonnam National University, Gwangju (Korea, Republic of)

    2010-04-15

    We measured electrical shot noise in a metal-insulator-metal tunnel junction, which was made by using electron-beam lithography and double-angle evaporation technique. Since the dependence of the shot noise on bias voltage and temperature is theoretically well known, we can determine the temperature of the junction by measuring the noise as the voltage across the junction is changed. A cryogenic low noise amplifier was used to amplify the noise signal in the frequency range of 600-800 MHz, which enabled fast measurement of noise signal and thus temperature. With further study, this method could be useful for primary thermometry in cryogenic temperatures.

  11. Coherent quantum transport in normal-metal/d-wave superconductor/normal-metal double tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    DONG; Zhengchao; FU; Hao

    2004-01-01

    Taking into account the effects of quantum interference and interface scattering, combining the electron current with hole current contribution to tunnel current,we study the coherent quantum transport in normal-metal/d-wave superconductor/normal-metal (NM/d-wave SC/NM) double tunnel junctions by using extended Blonder-Tinkham-Klapwijk (BTK) approach. It is shown that all quasiparticle transport coefficients and conductance spectrum exhibit oscillating behavior with the energy, in which periodic vanishing of Andreev reflection (AR) above superconducting gap is found.In tunnel limit for the interface scattering strength taken very large, there are a series of bound states of quasiparticles formed in SC.

  12. Light emission and finite-frequency shot noise in molecular junctions: from tunneling to contact

    DEFF Research Database (Denmark)

    Lu, Jing Tao; Christensen, Rasmus Bjerregaard; Brandbyge, Mads

    2013-01-01

    Scanning tunneling microscope induced light emission from an atomic or molecular junction has been probed from the tunneling to contact regime in recent experiments. There, the measured light emission yields suggest a strong correlation with the high-frequency current/charge fluctuations. We show...... that this is consistent with the established theory in the tunneling regime, by writing the finite-frequency shot noise as a sum of inelastic transitions between different electronic states. Based on this, we develop a practical scheme to perform calculations on realistic structures using nonequilibrium Green's functions...

  13. Optically controlled electroresistance and electrically controlled photovoltage in ferroelectric tunnel junctions.

    Science.gov (United States)

    Jin Hu, Wei; Wang, Zhihong; Yu, Weili; Wu, Tom

    2016-02-29

    Ferroelectric tunnel junctions (FTJs) have recently attracted considerable interest as a promising candidate for applications in the next-generation non-volatile memory technology. In this work, using an ultrathin (3 nm) ferroelectric Sm0.1Bi0.9FeO3 layer as the tunnelling barrier and a semiconducting Nb-doped SrTiO3 single crystal as the bottom electrode, we achieve a tunnelling electroresistance as large as 10(5). Furthermore, the FTJ memory states could be modulated by light illumination, which is accompanied by a hysteretic photovoltaic effect. These complimentary effects are attributed to the bias- and light-induced modulation of the tunnel barrier, both in height and width, at the semiconductor/ferroelectric interface. Overall, the highly tunable tunnelling electroresistance and the correlated photovoltaic functionalities provide a new route for producing and non-destructively sensing multiple non-volatile electronic states in such FTJs.

  14. Optically controlled electroresistance and electrically controlled photovoltage in ferroelectric tunnel junctions

    KAUST Repository

    Jin Hu, Wei

    2016-02-29

    Ferroelectric tunnel junctions (FTJs) have recently attracted considerable interest as a promising candidate for applications in the next-generation non-volatile memory technology. In this work, using an ultrathin (3 nm) ferroelectric Sm0.1Bi0.9FeO3 layer as the tunnelling barrier and a semiconducting Nb-doped SrTiO3 single crystal as the bottom electrode, we achieve a tunnelling electroresistance as large as 105. Furthermore, the FTJ memory states could be modulated by light illumination, which is accompanied by a hysteretic photovoltaic effect. These complimentary effects are attributed to the bias- and light-induced modulation of the tunnel barrier, both in height and width, at the semiconductor/ferroelectric interface. Overall, the highly tunable tunnelling electroresistance and the correlated photovoltaic functionalities provide a new route for producing and non-destructively sensing multiple non-volatile electronic states in such FTJs.

  15. Magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy

    Science.gov (United States)

    Ning, Keyu; Liu, Houfang; Ju, Zhenyi; Fang, Chi; Wan, Caihua; Cheng, Jinglei; Liu, Xiao; Li, Linsen; Feng, Jiafeng; Wei, Hongxiang; Han, Xiufeng; Yang, Yi; Ren, Tian-Ling

    2017-01-01

    As one invigorated filed of spin caloritronics combining with spin, charge and heat current, the magneto-Seebeck effect has been experimentally and theoretically studied in spin tunneling thin films and nanostructures. Here we analyze the tunnel magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy (p-MTJs) under various measurement temperatures. The large tunnel magneto-Seebeck (TMS) ratio up to -838.8% for p-MTJs at 200 K is achieved, with Seebeck coefficient S in parallel and antiparallel states of 6.7 mV/K and 62.9 mV/K, respectively. The temperature dependence of the tunnel magneto-Seebeck can be attributed to the contributing transmission function and electron states at the interface between CoFeB electrode and MgO barrier.

  16. Magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy

    Directory of Open Access Journals (Sweden)

    Keyu Ning

    2017-01-01

    Full Text Available As one invigorated filed of spin caloritronics combining with spin, charge and heat current, the magneto-Seebeck effect has been experimentally and theoretically studied in spin tunneling thin films and nanostructures. Here we analyze the tunnel magneto-Seebeck effect in magnetic tunnel junctions with perpendicular anisotropy (p-MTJs under various measurement temperatures. The large tunnel magneto-Seebeck (TMS ratio up to −838.8% for p-MTJs at 200 K is achieved, with Seebeck coefficient S in parallel and antiparallel states of 6.7 mV/K and 62.9 mV/K, respectively. The temperature dependence of the tunnel magneto-Seebeck can be attributed to the contributing transmission function and electron states at the interface between CoFeB electrode and MgO barrier.

  17. Static properties of small Josephson tunnel junctions in a transverse magnetic field

    DEFF Research Database (Denmark)

    Monaco, R.; Aarøe, Morten; Mygind, Jesper;

    2008-01-01

    The magnetic field distribution in the barrier of small planar Josephson tunnel junctions is numerically simulated in the case when an external magnetic field is applied perpendicular to the barrier plane. The simulations allow for heuristic analytical solutions for the Josephson static phase pro...

  18. Testing the kibble-zurek scenario with annular josephson tunnel junctions

    Science.gov (United States)

    Kavoussanaki; Monaco; Rivers

    2000-10-16

    In parallel with Kibble's description of the onset of phase transitions in the early Universe, Zurek has provided a simple picture for the onset of phase transitions in condensed matter systems, supported by agreement with experiments in 3He and superconductors. We show how experiments with annular Josephson tunnel junctions can, and do, provide further support for this scenario.

  19. Electron tunneling through alkanedithiol self-assembled monolayers in large-area molecular junctions

    NARCIS (Netherlands)

    Akkerman, Hylke B.; Naber, Ronald C. G.; Jongbloed, Bert; van Hal, Paul A.; Blom, Paul W. M.; de Leeuw, Dago M.; de Boer, Bert

    2007-01-01

    The electrical transport through self-assembled monolayers of alkanedithiols was studied in large-area molecular junctions and described by the Simmons model [Simmons JIG (1963) J Appi Phys 34:1793-1803 and 2581-2590] for tunneling through a practical barrier, i.e., a rectangular barrier with the im

  20. Macroscopic quantum tunneling in π Josephson junctions with insulating ferromagnets and its application to phase qubits

    NARCIS (Netherlands)

    Kawabata, Shiro; Golubov, Alexander A.

    2007-01-01

    We theoretically investigate macroscopic quantum tunneling (MQT) in a current-biased π junction with a superconductor (S) and an insulating ferromagnet (IF). By using the functional integral method and the instanton approximation, the influence of the quasiparticle dissipation on MQT is found to be

  1. Anisotropic Magnetoresistance and Anisotropic Tunneling Magnetoresistance due to Quantum Interference in Ferromagnetic Metal Break Junctions

    DEFF Research Database (Denmark)

    Bolotin, Kirill; Kuemmeth, Ferdinand; Ralph, D

    2006-01-01

    We measure the low-temperature resistance of permalloy break junctions as a function of contact size and the magnetic field angle in applied fields large enough to saturate the magnetization. For both nanometer-scale metallic contacts and tunneling devices we observe large changes in resistance...

  2. Magnetic Tunnel Junctions Incorporating a Near-Zero-Moment Ferromagnetic Semiconductor

    Science.gov (United States)

    Warring, H.; Trodahl, H. J.; Plank, N. O. V.; Natali, F.; Granville, S.; Ruck, B. J.

    2016-10-01

    We present a fully semiconductor-based magnetic tunnel junction that uses spin-orbit coupled materials made of intrinsic ferromagnetic semiconductors. Unlike more common approaches, one of the electrodes consists of a near-zero magnetic-moment ferromagnetic semiconductor, samarium nitride, with the other electrode composed of the more conventional ferromagnetic semiconductor gadolinium nitride. Fabricated tunnel junctions show a magnetoresistance as high as 200%, implying strong spin polarization in both electrodes. In contrast to conventional tunnel junctions, the resistance is largest at high fields, a direct result of the orbital-dominant magnetization in samarium nitride that requires that the spin in this electrode must align opposite to that in the gadolinium nitride when the magnetization is saturated. The magnetoresistance at intermediate fields is controlled by the formation of a twisted magnetization phase in the samarium nitride, a direct result of the orbital-dominant ferromagnetism. Thus, an alternative type of functionality can be brought to magnetic tunnel junctions by the use of different electrode materials, in contrast to the usual focus on tuning the barrier properties.

  3. CMOS Interface Circuits for Spin Tunneling Junction Based Magnetic Random Access Memories

    Energy Technology Data Exchange (ETDEWEB)

    Ganesh Saripalli

    2002-12-31

    Magneto resistive memories (MRAM) are non-volatile memories which use magnetic instead of electrical structures to store data. These memories, apart from being non-volatile, offer a possibility to achieve densities better than DRAMs and speeds faster than SRAMs. MRAMs could potentially replace all computer memory RAM technologies in use today, leading to future applications like instan-on computers and longer battery life for pervasive devices. Such rapid development was made possible due to the recent discovery of large magnetoresistance in Spin tunneling junction devices. Spin tunneling junctions (STJ) are composite structures consisting of a thin insulating layer sandwiched between two magnetic layers. This thesis research is targeted towards these spin tunneling junction based Magnetic memories. In any memory, some kind of an interface circuit is needed to read the logic states. In this thesis, four such circuits are proposed and designed for Magnetic memories (MRAM). These circuits interface to the Spin tunneling junctions and act as sense amplifiers to read their magnetic states. The physical structure and functional characteristics of these circuits are discussed in this thesis. Mismatch effects on the circuits and proper design techniques are also presented. To demonstrate the functionality of these interface structures, test circuits were designed and fabricated in TSMC 0.35{micro} CMOS process. Also circuits to characterize the process mismatches were fabricated and tested. These results were then used in Matlab programs to aid in design process and to predict interface circuit's yields.

  4. Feasibility of a Frequency-Multiplexed TES Read-Out Using Superconducting Tunnel Junctions

    NARCIS (Netherlands)

    de Lange, G.

    2014-01-01

    We describe a feasibility study of a frequency multiplexed read-out scheme for large number transition edge sensor arrays. The read-out makes use of frequency up- and down-conversion and RF-to-DC conversion with superconducting-isolator-superconducting tunnel junctions operating at GHz frequencies,

  5. Thermoelectricity and disorder of FeCo/MgO/FeCo magnetic tunnel junctions

    NARCIS (Netherlands)

    Wang, S.Z.; Xia, K.; Bauer, G.E.W.

    2014-01-01

    We compute the thermoelectric transport parameterized by the Seebeck coefficient and thermal/electric conductance of random-alloy FeCo/MgO/FeCo(001) magnetic tunnel junctions (MTJs) from first principles using a generalized Landauer-Büttiker formalism. The thermopower is found to be typically smalle

  6. Anisotropic Magnetoresistance and Anisotropic Tunneling Magnetoresistance due to Quantum Interference in Ferromagnetic Metal Break Junctions

    DEFF Research Database (Denmark)

    Bolotin, Kirill; Kuemmeth, Ferdinand; Ralph, D

    2006-01-01

    We measure the low-temperature resistance of permalloy break junctions as a function of contact size and the magnetic field angle in applied fields large enough to saturate the magnetization. For both nanometer-scale metallic contacts and tunneling devices we observe large changes in resistance w...

  7. Zurek-Kibble domain structures: The dynamics of spontaneous vortex formation in annular Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Rivers, R.J.

    2002-01-01

    Phase transitions create a domain structure with defects, which has been argued by Zurek and Kibble (ZK) to depend in a characteristic way on the quench rate. We present an experiment to measure the ZK scaling exponent sigma. Using long symmetric Josephson tunnel junctions, for which the predicted...

  8. CMOS Interface Circuits for Spin Tunneling Junction Based Magnetic Random Access Memories

    Energy Technology Data Exchange (ETDEWEB)

    Saripalli, Ganesh [Iowa State Univ., Ames, IA (United States)

    2002-01-01

    Magneto resistive memories (MRAM) are non-volatile memories which use magnetic instead of electrical structures to store data. These memories, apart from being non-volatile, offer a possibility to achieve densities better than DRAMs and speeds faster than SRAMs. MRAMs could potentially replace all computer memory RAM technologies in use today, leading to future applications like instan-on computers and longer battery life for pervasive devices. Such rapid development was made possible due to the recent discovery of large magnetoresistance in Spin tunneling junction devices. Spin tunneling junctions (STJ) are composite structures consisting of a thin insulating layer sandwiched between two magnetic layers. This thesis research is targeted towards these spin tunneling junction based Magnetic memories. In any memory, some kind of an interface circuit is needed to read the logic states. In this thesis, four such circuits are proposed and designed for Magnetic memories (MRAM). These circuits interface to the Spin tunneling junctions and act as sense amplifiers to read their magnetic states. The physical structure and functional characteristics of these circuits are discussed in this thesis. Mismatch effects on the circuits and proper design techniques are also presented. To demonstrate the functionality of these interface structures, test circuits were designed and fabricated in TSMC 0.35μ CMOS process. Also circuits to characterize the process mismatches were fabricated and tested. These results were then used in Matlab programs to aid in design process and to predict interface circuit's yields.

  9. Experimental investigations of SiO{sub 2} based ferrite magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Ravi, S., E-mail: sravi@mepcoeng.ac.in [Department of Physics, Mepco Schlenk Engineering College, Sivakasi (India); Karthikeyan, A. [Department of Physics, Mepco Schlenk Engineering College, Sivakasi (India); Aravindan, V. [Energy Research Institute, Nanyang Technological University (Singapore); Pugazhvadivu, K.S.; Tamilarasan, K. [Department of Physics, Kongu Engineering College, Perundurai (India)

    2013-09-01

    Highlights: • CoFe{sub 2}O{sub 4}/SiO{sub 2}/Co–NiFe{sub 2}O{sub 4} magnetic junction was fabricated using RF/DC sputtering. • Spin transport through nanostructure silicon oxide with ferrite as free and pinned layer is our first report. • Magnetization studies were done to justify the free layer and pinned layer for our multilayer. • Magnetoresistance behavior shows a sharp discriminating between parallel and antiparallel alignment with TMR value of 16%. -- Abstract: We report experimental results of ferrite based magnetic tunnel junction. Ferrite junction and spin transport through SiO{sub 2} were interesting since they can readily replace the conventional electronics. We fabricated a cobalt ferrite/SiO{sub 2}/cobalt nickel ferrite based magnetic tunnel junction over a copper coated n-silicon substrate using a RF/DC magnetron sputtering. The tunneling magnetoresistance shows a very good response to applied field and we achieved a TMR of about 16%. Although theoretically it was predicted infinite TMR for half metallic ferromagnetic junction, the deviation was explained on the basis of incoherent scattering along the interfaces.

  10. Ratiometric, filter-free optical sensor based on a complementary metal oxide semiconductor buried double junction photodiode.

    Science.gov (United States)

    Yung, Ka Yi; Zhan, Zhiyong; Titus, Albert H; Baker, Gary A; Bright, Frank V

    2015-07-16

    We report a complementary metal oxide semiconductor integrated circuit (CMOS IC) with a buried double junction (BDJ) photodiode that (i) provides a real-time output signal that is related to the intensity ratio at two emission wavelengths and (ii) simultaneously eliminates the need for an optical filter to block Rayleigh scatter. We demonstrate the BDJ platform performance for gaseous NH3 and aqueous pH detection. We also compare the BDJ performance to parallel results obtained by using a slew scanned fluorimeter (SSF). The BDJ results are functionally equivalent to the SSF results without the need for any wavelength filtering or monochromators and the BDJ platform is not prone to errors associated with source intensity fluctuations or sensor signal drift.

  11. Reinventing the PN Junction: Dimensionality Effects on Tunneling Switches

    Science.gov (United States)

    2012-05-11

    Transistors," Physical Review Letters , vol. 93, p. 196805, 2004. [10] R. Gandhi , et al., "CMOS-Compatible Vertical-Silicon-Nanowire Gate-All-Around... Letters , vol. 28, pp. 743-745, Aug 2007. [5] K. Jeon, et al., "Si tunnel transistors with a novel silicided source and 46mV/dec swing," presented at...p- Type Tunneling FETs With <= 50-mV/decade Subthreshold Swing," Ieee Electron Device Letters , vol. 32, pp. 1504-1506, Nov 2011. [11] G. Dewey, et

  12. Fabrication of high-quality submicron Nb/Al-AlOx/Nb tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Yu Hai-Feng; Cao Wen-Hui; Zhu Xiao-Bo; Yang Hai-Fang; Yu Hong-Wei; Ren Yu-Feng; Gu Chang-Zhi; Chen Geng-Hua; Zhao Shi-Ping

    2008-01-01

    Nb/Al-AlOx/Nb tunnel junctions are often used in the studies of macroscopic quantum phenomena and supercon-ducting qubit applications of the Josepheon devices. In this work, we describe a convenient and reliable process using electron beam lithography for the fabrication of high-quality, submicron-sized Nb/Al-AlOx/Nb Josephson junctions.The technique follows the well-known selective Nb etching process and produces high-quality junctions with Vm=100 mV at 2.3 K for the typical critical current density of 2.2 kA/cm2, which can be adjusted by controlling the oxygen pressure and oxidation time during the formation of the tunnelling barrier. We present the results of the temperature depen-dence of the sub-gap current and in-plane magnetic-field dependence of the critical current, and compare them with the theoretical predictions.

  13. NbN/MgO/NbN edge-geometry tunnel junctions

    Science.gov (United States)

    Hunt, B. D.; Leduc, H. G.; Cypher, S. R.; Stern, J. A.; Judas, A.

    1989-01-01

    The fabrication and low-frequency testing of the first edge-geometry NbN/MgO/NbN superconducting tunnel junctions are reported. The use of an edge geometry allows very small junction areas to be obtained, while the all-NbN electrodes permit operation at 8-10 K with a potential maximum operating frequency above 1 THz. Edge definition in the base NbN film was accomplished utilizing Ar ion milling with an Al2O3 milling mask, followed by a lower energy ion cleaning step. This process has produced all-refractory-material tunnel junctions with areas as small as 0.1 sq micron, resistance-area products less than 21 ohm sq micron, and subgap to normal state resistance ratios larger than 18.

  14. Giant amplification of tunnel magnetoresistance in a molecular junction: Molecular spin-valve transistor

    Energy Technology Data Exchange (ETDEWEB)

    Dhungana, Kamal B.; Pati, Ranjit, E-mail: patir@mtu.edu [Department of Physics, Michigan Technological University, Houghton, Michigan 49931 (United States)

    2014-04-21

    Amplification of tunnel magnetoresistance by gate field in a molecular junction is the most important requirement for the development of a molecular spin valve transistor. Herein, we predict a giant amplification of tunnel magnetoresistance in a single molecular spin valve junction, which consists of Ru-bis-terpyridine molecule as a spacer between two ferromagnetic nickel contacts. Based on the first-principles quantum transport approach, we show that a modest change in the gate field that is experimentally accessible can lead to a substantial amplification (320%) of tunnel magnetoresistance. The origin of such large amplification is attributed to the spin dependent modification of orbitals at the molecule-lead interface and the resultant Stark effect induced shift in channel position with respect to the Fermi energy.

  15. Electrical control of memristance and magnetoresistance in oxide magnetic tunnel junctions

    KAUST Repository

    Zhang, Kun

    2015-01-01

    Electric-field control of magnetic and transport properties of magnetic tunnel junctions has promising applications in spintronics. Here, we experimentally demonstrate a reversible electrical manipulation of memristance, magnetoresistance, and exchange bias in Co/CoO–ZnO/Co magnetic tunnel junctions, which enables the realization of four nonvolatile resistance states. Moreover, greatly enhanced tunneling magnetoresistance of 68% was observed due to the enhanced spin polarization of the bottom Co/CoO interface. The ab initio calculations further indicate that the spin polarization of the Co/CoO interface is as high as 73% near the Fermi level and plenty of oxygen vacancies can induce metal–insulator transition of the CoO1−v layer. Thus, the electrical manipulation mechanism on the memristance, magnetoresistance and exchange bias can be attributed to the electric-field-driven migration of oxygen ions/vacancies between very thin CoO and ZnO layers.

  16. Radio-frequency shot-noise measurement in a magnetic tunnel junction with a MgO barrier

    Energy Technology Data Exchange (ETDEWEB)

    Rehman, Mushtaq; Park, Junghwan; Song, Woon; Chong, Yonuk [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Lee, Yeonsub; Min, Byoungchul; Shin, Kyungho [Korea Institute of Science and Technology, Seoul (Korea, Republic of); Ryu, Sangwan [Chonnam National University, Gwangju (Korea, Republic of); Khim, Zheong [Seoul National University, Seoul (Korea, Republic of)

    2010-10-15

    We measured the noise power of a magnetic tunnel junction in the frequency range of 710 {approx} 1200 MHz. A low-noise cryogenic HEMT amplifier was used to measure the small noise signal at a high frequency with wide bandwidth. The MgO-barrier tunnel junction showed large tunnel magnetoresistance ratio of 215% at low temperature, which indicates electronic transport through the tunnel barrier without any significant spin-flip scattering. In the bias-dependent noise measurement, however, the zero-bias shot noise was enhanced compared to the value expected from a perfect tunnel barrier or the value observed from a good Al-AlO{sub x}-Al tunnel junction. We assume that this enhanced noise comes from inelastic tunneling processes through the barrier, which may be related to the observed zero-bias anomaly in the differential resistance of the tunnel junctions. We present a simple phenomenological model for how the inelastic scattering process can enhance the zero-bias noise in a tunnel junction.

  17. InGaN/GaN Tunnel Junctions For Hole Injection in GaN Light Emitting Diodes

    OpenAIRE

    Krishnamoorthy, Sriram; Akyol, Fatih; Rajan, Siddharth

    2014-01-01

    InGaN/GaN tunnel junction contacts were grown on top of an InGaN/GaN blue (450 nm) light emitting diode wafer using plasma assisted molecular beam epitaxy. The tunnel junction contacts enable low spreading resistance n-GaN top contact layer thereby requiring less top metal contact coverage on the surface. A voltage drop of 5.3 V at 100 mA, forward resistance of 2 x 10-2 ohm cm2 and a higher light output power are measured in tunnel junction LED. A low resistance of 5 x 10-4 ohm cm2 was measur...

  18. Voltage-driven versus current-driven spin torque in anisotropic tunneling junctions

    KAUST Repository

    Manchon, Aurelien

    2011-10-01

    Nonequilibrium spin transport in a magnetic tunnel junction comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is studied theoretically. The interfacial SOI generates a spin torque of the form T=T∥ M×(z× M)+T⊥ z× M, even in the absence of an external spin polarizer. For thick and large tunnel barriers, the torque reduces to the perpendicular component T⊥, which can be electrically tuned by applying a voltage across the insulator. In the limit of thin and low tunnel barriers, the in-plane torque T∥ emerges, proportional to the tunneling current density. Experimental implications on magnetic devices are discussed. © 2011 IEEE.

  19. Light amplification by stimulated emission from an optically pumped molecular junction in a scanning tunneling microscope

    CERN Document Server

    Braun, K; Wang, X; Adler, H; Peisert, H; Chasse, T; Zhang, D; Meixner, A J

    2013-01-01

    Here, we introduce and experimentally demonstrate optical amplification and stimulated emission from a single optically pumped molecular tunneling junction of a scanning tunneling microscope. The gap between a sharp gold tip and a flat gold substrate covered with a self-assembled monolayer of 5-chloro-2-mercaptobenzothiazole molecules forms an extremely small optical gain medium. When electrons tunnel from the molecules highest occupied molecular orbital to the tip, holes are left behind. These can be repopulated by hot electrons induced by the laser-driven plasmon oscillation on the metal surfaces enclosing the cavity. Solving the laser-rate equations for this system shows that the repopulation process can be efficiently stimulated by the gap modes near field, TERS scattering from neighboring molecules acting as an optical seed. Our results demonstrate how optical enhancement inside the plasmonic cavity can be further increased by a stronger localization via tunneling through molecules. We anticipate that st...

  20. Magnetic tunnel junction on a magnetostrictive substrate: An ultrasensitive magnetic-field sensor

    Science.gov (United States)

    Pertsev, N. A.

    2016-09-01

    The concept of a magnetic tunnel junction (MTJ) fabricated on an active substrate made of a highly magnetostrictive ferromagnetic material is described theoretically. It is shown that, under certain conditions, such hybrid device exhibits strongly enhanced sensitivity of the tunnel current to the external magnetic field. This feature results from the field-induced substrate deformations, which create lattice strains in the MTJ due to the interfacial mechanical interaction. If the free electrode of MTJ is made of a cubic ferromagnet like Co40Fe60 having strong magnetoelastic coupling between the magnetization and strains, the field-induced magnetization reorientation here may be enhanced by the strain effect drastically. This reorientation should lead to a change in the junction's electrical conductance because the magnetization of the reference electrode may be pinned by adjacent antiferromagnetic layer to keep its initial direction. Taking into account additional strain effects on the height and width of the tunnel barrier and the effective mass of tunneling electrons, we performed numerical calculations of the conductance magnetosensitivity for the CoFe/MgO/CoFeB junctions mechanically coupled to the FeGaB film grown on Si and found that such hybrid device is promising as an ultrasensitive room-temperature magnetic-field sensor.

  1. Spin-transfer torque switched magnetic tunnel junctions in magnetic random access memory

    Science.gov (United States)

    Sun, Jonathan Z.

    2016-10-01

    Spin-transfer torque (or spin-torque, or STT) based magnetic tunnel junction (MTJ) is at the heart of a new generation of magnetism-based solid-state memory, the so-called spin-transfer-torque magnetic random access memory, or STT-MRAM. Over the past decades, STT-based switchable magnetic tunnel junction has seen progress on many fronts, including the discovery of (001) MgO as the most favored tunnel barrier, which together with (bcc) Fe or FeCo alloy are yielding best demonstrated tunnel magneto-resistance (TMR); the development of perpendicularly magnetized ultrathin CoFeB-type of thin films sufficient to support high density memories with junction sizes demonstrated down to 11nm in diameter; and record-low spin-torque switching threshold current, giving best reported switching efficiency over 5 kBT/μA. Here we review the basic device properties focusing on the perpendicularly magnetized MTJs, both in terms of switching efficiency as measured by sub-threshold, quasi-static methods, and of switching speed at super-threshold, forced switching. We focus on device behaviors important for memory applications that are rooted in fundamental device physics, which highlights the trade-off of device parameters for best suitable system integration.

  2. Backhopping effect in magnetic tunnel junctions: Comparison between theory and experiment

    Energy Technology Data Exchange (ETDEWEB)

    Skowroński, Witold, E-mail: skowron@agh.edu.pl; Wrona, Jerzy; Stobiecki, Tomasz [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Krakow (Poland); Ogrodnik, Piotr, E-mail: piotrogr@if.pw.edu.pl [Faculty of Physics, Warsaw University of Technology, Ul. Koszykowa 75, 00-662 Warsaw (Poland); Institute of Molecular Physics, Polish Academy of Sciences, Ul. Smoluchowskiego 17, 60-179 Poznań (Poland); Świrkowicz, Renata [Faculty of Physics, Warsaw University of Technology, Ul. Koszykowa 75, 00-662 Warsaw (Poland); Barnaś, Józef [Institute of Molecular Physics, Polish Academy of Sciences, Ul. Smoluchowskiego 17, 60-179 Poznań (Poland); Reiss, Günter [Thin Films and Physics of Nanostructures, Bielefeld University, 33615 Bielefeld (Germany); Dijken, Sebastiaan van [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland)

    2013-12-21

    We report on magnetic switching and backhopping effects due to spin-transfer-torque in magnetic tunnel junctions. Experimental data on current-induced switching in junctions with a MgO tunnel barrier reveal random back-and-forth switching between magnetization states, which appears when the current direction favors the parallel magnetic configuration. The effect depends on the barrier thickness t{sub b} and is not observed in tunnel junctions with very thin MgO tunnel barriers, t{sub b} < 0.95 nm. The switching dependence on bias voltage and barrier thickness is explained in terms of the macrospin model, with the magnetization dynamics described by the modified Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the competition between in-plane and out-of-plane torque components can result in a non-deterministic switching behavior at high bias voltages, in agreement with experimental observations. When the barrier thickness is reduced, the overall coupling between the magnetic layers across the barrier becomes ferromagnetic, which suppresses the backhopping effect.

  3. Direct optical determination of interfacial transport barriers in molecular tunnel junctions.

    Science.gov (United States)

    Fereiro, Jerry A; McCreery, Richard L; Bergren, Adam Johan

    2013-07-03

    Molecular electronics seeks to build circuitry using organic components with at least one dimension in the nanoscale domain. Progress in the field has been inhibited by the difficulty in determining the energy levels of molecules after being perturbed by interactions with the conducting contacts. We measured the photocurrent spectra for large-area aliphatic and aromatic molecular tunnel junctions with partially transparent copper top contacts. Where no molecular absorption takes place, the photocurrent is dominated by internal photoemission, which exhibits energy thresholds corresponding to interfacial transport barriers, enabling their direct measurement in a functioning junction.

  4. On exploration for ultra-shallow-buried bias section of road tunnels%公路隧道超浅埋偏压段技术探讨

    Institute of Scientific and Technical Information of China (English)

    张艳做

    2012-01-01

    结合忻州至阜平高速公路火焰山隧道实际施工经验,有针对性地提出一些超浅埋偏压段隧道处理措施,且应用效果良好,能够确保隧道建设及运营的安全,为今后超浅埋偏压隧道施工提供了经验。%Combining with the factual construction experience in Huoyanshan tunnel along Xinzhou-Fuping expressway,the paper points out some treatment measures for some ultra-shallow-buried bias section of road tunnels,and proves it has better application effect and ensures the operation and safety of the tunnel construction,so as to provide the experience for the construction of the ultra-shallow-buried bias section of road tunnels in future.

  5. Zeeman effects on the coherent tunnelling conductance in normal-metal / superconductor / normal-metal double tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Dong Zheng-Chao

    2005-01-01

    The coherent quantum transport is investigated in normal-metal/superconductor/normal-metal (N/S/N) double tunnel junctions under a Zeeman magnetic field on the S. Taking simultaneously into account the electron-injected current from one N electrode and the hole-injected current from the other N electrode, we derive a general formula for the differential conductance in the N/S/N system. It is shown that the conductance spectrum exhibits oscillatory behaviour with the bias voltage, and the oscillation amplitude is reduced with increasing temperature and Zeeman magnetic field, the Zeeman energy can lead to the Zeeman splitting of conductance peaks. In the tunnel limit, a series of bound states of quasiparticles will form in the S.

  6. TUNNEL MAGNETORESISTANCE IN THE FERROMAGNETIC TUNNEL JUNCTION WITH FERROMAGNETIC LAYERS OF FINITE THICKNESS SUBJECTED TO AN ELECTRIC FIELD

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    Based on the two-band model, we investigate the tunnel magnetoresistance(TMR) in ferromagnet/insulator(semiconductor)/ferromagnet(FM/I(S)/FM) tunnel junction covered on both sides by nonmagnetic metal layers subjected to an electric field. Our results show that TMR oscillates with the thickness of ferromagnetic layers owing to the quantum-size effect and can reach very large value under suitable conditions, which may in general not be reached in FM/I(S)/FM with infinitely thick ferromagnetic layer. Although the electric field causes the change of the oscillation period, phase and amplitude of the TMR, a large TMR is still obtained in some situations with the electric field. Furthermore, the electric field does not change the feature that TMR varies monotonously with the change of magnetization angle of the middle ferromagnetic layer.

  7. Fabrication and characterization of high current-density, submicron, NbN/MgO/NbN tunnel junctions

    Science.gov (United States)

    Stern, J. A.; Leduc, Henry G.; Judas, A. J.

    1992-01-01

    At near-millimeter wavelengths, heterodyne receivers based on SIS tunnel junctions are the most sensitive available. However, in order to scale these results to submillimeter wavelengths, certain device properties should be scaled. The tunnel-junction's current density should be increased to reduce the RC product. The device's area should be reduced to efficiently couple power from the antenna to the mixer. Finally, the superconductor used should have a large energy gap to minimize RF losses. Most SIS mixers use Nb or Pb-alloy tunnel junctions; the gap frequency for these materials is approximately 725 GHz. Above the gap frequency, these materials exhibit losses similar to those in a normal metal. The gap frequency in NbN films is as-large-as 1440 GHz. Therefore, we have developed a process to fabricate small area (down to 0.13 sq microns), high current density, NbN/MgO/NbN tunnel junctions.

  8. Spin transport in nanoscale spin valves and magnetic tunnel junctions

    Science.gov (United States)

    Patibandla, Sridhar

    Spintronics or electronics that utilizes the spin degree of freedom of a single charge carrier (or an ensemble of charge carriers) to store, process, sense or communicate data and information is a rapidly burgeoning field in electronics. In spintronic devices, information is encoded in the spin polarization of a single carrier (or multiple carriers) and the spin(s) of these carrier(s) are manipulated for device operation. This strategy could lead to devices with low power consumption. This dissertation investigates spin transport in one dimensional and two dimensional semiconductors, with a view to applications in spintronic devices. This dissertation is arranged as follows: Chapter 1 gives a detailed introduction and necessary background to understand aspects of spin injection into a semiconductor from a spin polarized source such as a ferromagnet, and spin polarized electron transport in the semiconductor. Chapter 2 discusses the nanoporous alumina technique that is employed to fabricate nanowires and nanowire spin valves for the investigation of spin transport in 1D semiconductors. Chapter 3 investigates the spin transport in quasi one-dimensional spin valves with germanium spacer layer. These spin valves with 50nm in diameter and 1 mum length were fabricated using the porous alumina technique. Spin transport in nanoscale germanium spin valves was demonstrated and the spin relaxation lengths and the spin relaxation times were calculated. Chapter 4 discusses spin transport studies conducted in bulk high purity germanium with a view to comparing spin relaxation mechanisms in low mobility nanowires and high mobility bulk structures. Lateral spin valve with tunnel injectors were employed in this study and the spin transport measurements were conducted at various temperatures. The spin relaxation rates were measured as a function of temperature which allowed us to distinguish between two different mechanisms---D'yakonov-Perel' and Elliott-Yafet---that dominate spin

  9. Important issues facing model-based approaches to tunneling transport in molecular junctions

    CERN Document Server

    Baldea, Ioan

    2015-01-01

    Extensive studies on thin films indicated a generic cubic current-voltage $I-V$ dependence as a salient feature of charge transport by tunneling. A quick glance at $I-V$ data for molecular junctions suggests a qualitatively similar behavior. This would render model-based studies almost irrelevant, since, whatever the model, its parameters can always be adjusted to fit symmetric (asymmetric) $I-V$ curves characterized by two (three) expansion coefficients. Here, we systematically examine popular models based on tunneling barrier or tight-binding pictures and demonstrate that, for a quantitative description at biases of interest ($V$ slightly higher than the transition voltage $V_t$), cubic expansions do not suffice. A detailed collection of analytical formulae as well as their conditions of applicability are presented to facilitate experimentalists colleagues to process and interpret their experimental data by obtained by measuring currents in molecular junctions. We discuss in detail the limits of applicabili...

  10. Electric Field Control of the Resistance of Multiferroic Tunnel Junctions with Magnetoelectric Antiferromagnetic Barriers

    Science.gov (United States)

    Merodio, P.; Kalitsov, A.; Chshiev, M.; Velev, J.

    2016-06-01

    Based on model calculations, we predict a magnetoelectric tunneling electroresistance effect in multiferroic tunnel junctions consisting of ferromagnetic electrodes and magnetoelectric antiferromagnetic barriers. Switching of the antiferromagnetic order parameter in the barrier in applied electric field by means of the magnetoelectric coupling leads to a substantial change of the resistance of the junction. The effect is explained in terms of the switching of the orientations of local magnetizations at the barrier interfaces affecting the spin-dependent interface transmission probabilities. Magnetoelectric multiferroic materials with finite ferroelectric polarization exhibit an enhanced resistive change due to polarization-induced spin-dependent screening. These results suggest that devices with active barriers based on single-phase magnetoelectric antiferromagnets represent an alternative nonvolatile memory concept.

  11. Paramagnetic molecule induced strong antiferromagnetic exchange coupling on a magnetic tunnel junction based molecular spintronics device.

    Science.gov (United States)

    Tyagi, Pawan; Baker, Collin; D'Angelo, Christopher

    2015-07-31

    This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs) were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the tunnel junction's perimeter. These MTJMSDs exhibited molecule-induced strong antiferromagnetic coupling. We simulated the 3D atomic model analogous to the MTJMSD and studied the effect of molecule's magnetic couplings with the two FM electrodes. Simulations show that when a molecule established ferromagnetic coupling with one electrode and antiferromagnetic coupling with the other electrode, then theoretical results effectively explained the experimental findings. Our studies suggest that in order to align MTJMSDs' electrodes antiparallel to each other, the exchange coupling strength between a molecule and FM electrodes should be ∼50% of the interatomic exchange coupling for the FM electrodes.

  12. Enhanced voltage-controlled magnetic anisotropy in magnetic tunnel junctions with an MgO/PZT/MgO tunnel barrier

    Science.gov (United States)

    Chien, Diana; Li, Xiang; Wong, Kin; Zurbuchen, Mark A.; Robbennolt, Shauna; Yu, Guoqiang; Tolbert, Sarah; Kioussis, Nicholas; Khalili Amiri, Pedram; Wang, Kang L.; Chang, Jane P.

    2016-03-01

    Compared with current-controlled magnetization switching in a perpendicular magnetic tunnel junction (MTJ), electric field- or voltage-induced magnetization switching reduces the writing energy of the memory cell, which also results in increased memory density. In this work, an ultra-thin PZT film with high dielectric constant was integrated into the tunneling oxide layer to enhance the voltage-controlled magnetic anisotropy (VCMA) effect. The growth of MTJ stacks with an MgO/PZT/MgO tunnel barrier was performed using a combination of sputtering and atomic layer deposition techniques. The fabricated MTJs with the MgO/PZT/MgO barrier demonstrate a VCMA coefficient, which is ˜40% higher (19.8 ± 1.3 fJ/V m) than the control sample MTJs with an MgO barrier (14.3 ± 2.7 fJ/V m). The MTJs with the MgO/PZT/MgO barrier also possess a sizeable tunneling magnetoresistance (TMR) of more than 50% at room temperature, comparable to the control MTJs with an MgO barrier. The TMR and enhanced VCMA effect demonstrated simultaneously in this work make the MgO/PZT/MgO barrier-based MTJs potential candidates for future voltage-controlled, ultralow-power, and high-density magnetic random access memory devices.

  13. Millisecond dynamics of thermal expansion of mechanically controllable break junction electrodes studied in the tunneling regime

    Science.gov (United States)

    Kolesnychenko, O. Yu.; Toonen, A. J.; Shklyarevskii, O. I.; van Kempen, H.

    2001-10-01

    The thermal expansion dynamics of W, Pt-Ir, and Au mechanically controllable break junction electrodes was studied in the millisecond range. By measuring a transient tunnel current as a function of time, we found that, at low temperatures, the electrode elongation Δs˜t1/2 due to the large values of thermal diffusivity of metals. The magnitude of Δs varies in direct proportion to the power P dissipated in the electrodes.

  14. X-band singly degenerate parametric amplification in a Josephson tunnel junction

    DEFF Research Database (Denmark)

    Mygind, Jesper; Pedersen, Niels Falsig; Sørensen, O. H.

    1978-01-01

    Preliminary measurements on a (quasi-) degenerate parametric amplifier using a single Josephson tunnel junction as the active element is reported. The pump frequency is at 18 GHz and the signal and idler frequencies are both at about 9 GHz. A power gain of 16 dB in a 4-MHz 3-dB bandwidth is achie...... is achieved at the top of the cryostat. Applied Physics Letters is copyrighted by The American Institute of Physics....

  15. Analysis of mechanical behaviors of big pipe roof for shallow buried large-span tunnel

    Institute of Scientific and Technical Information of China (English)

    Li Jian; Tan Zhongsheng; Yu Yu; Guo Xiaohong

    2013-01-01

    A series of researches on mechanical behaviors of big pipe roof for shallow large-span loess tunnel were carried out based on the Wenxiang tunnel in Zhengzhou-Xi’an Special Passenger Railway. The longitudinal de-formations of the pipe roofs were monitored and the mechanical behaviors of the pipe roofs were analyzed at the test section. A new double-parameter elastic foundation beam model for pipe roof in shallow tunnels was put for-ward in Wenxiang tunnel. The measured values and the calculation results agreed well with each other,revealing the force-deformation law of big pipe roof in loess tunnel:At about 15 m in front of the excavating face,the pipe roof starts to bear the load;at about 15 m behind the excavating face,the force of the pipe roof tends to be stabi-lized;the longitudinal deformation of the whole pipe roofs is groove-shaped distribution,and the largest force of pipe roofs is at the excavating face. Simultaneously,the results also indicate that mechanical behaviors of pipe roof closely relate to the location of the excavation face,the footage of the tunnelling cycle and the mechanics pa-rameters of pipe roof and rock. The conclusions can be reference for the design parameter optimization and the con-struction scheme selection of pipe roofs,and have been verified by the result of numerical analysis software FLAC3D and deformation monitoring.

  16. Engineering double-well potentials with variable-width annular Josephson tunnel junctions

    Science.gov (United States)

    Monaco, Roberto

    2016-11-01

    Long Josephson tunnel junctions are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.

  17. An ARC less InGaP/GaAs DJ solar cell with hetero tunnel junction

    Science.gov (United States)

    Sahoo, G. S.; Nayak, P. P.; Mishra, G. P.

    2016-07-01

    Multi junction solar cell has not achieved an optimum performance yet. To acquire more conversion efficiency research on multi junction solar cell are in progress. In this work we have proposed a dual junction solar cell with conversion efficiency of 43.603%. Mainly the focus is given on the tunnel diode, window layer and back surface field (BSF) layer of the cell, as all of them plays important role on the cell performance. Here we have designed a hetero InGaP/GaAs tunnel diode which makes tunnel diode more transparent to the bottom cell as well as reduces the recombination at the interfaces. The thickness of the window and BSF layer are optimized to achieve higher conversion efficiency. The simulation is carried out using Silvaco ATLAS TCAD under 1000 sun of AM1.5G spectrum. Different performance parameters of the cell like short circuit current density (Jsc), open circuit voltage (Voc), external quantum efficiency (EQE), fill factor (FF), conversion efficiency (η), spectral response and photogeneration rate of the cell are examined and compared with previously reported literatures. For the proposed model a Voc of 2.7043 V, Jsc of 1898.52 mA/cm2, FF of 88.88% and η of 43.6% are obtained.

  18. Terahertz time domain interferometry of a SIS tunnel junction and a quantum point contact

    Energy Technology Data Exchange (ETDEWEB)

    Karadi, Chandu [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1995-09-01

    The author has applied the Terahertz Time Domain Interferometric (THz-TDI) technique to probe the ultrafast dynamic response of a Superconducting-Insulating-Superconducting (SIS) tunnel junction and a Quantum Point Contact (QPC). The THz-TDI technique involves monitoring changes in the dc current induced by interfering two picosecond electrical pulses on the junction as a function of time delay between them. Measurements of the response of the Nb/AlOxNb SIS tunnel junction from 75--200 GHz are in full agreement with the linear theory for photon-assisted tunneling. Likewise, measurements of the induced current in a QPC as a function of source-drain voltage, gate voltage, frequency, and magnetic field also show strong evidence for photon-assisted transport. These experiments together demonstrate the general applicability of the THz-TDI technique to the characterization of the dynamic response of any micron or nanometer scale device that exhibits a non-linear I-V characteristic.

  19. Investigation of inelastic electron tunneling spectra of metal-molecule-metal junctions fabricated using direct metal transfer method

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Hyunhak; Hwang, Wang-Taek; Kim, Pilkwang; Kim, Dongku; Jang, Yeonsik; Min, Misook; Park, Yun Daniel; Lee, Takhee, E-mail: tlee@snu.ac.kr [Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747 (Korea, Republic of); Xiang, Dong [Institute of Modern Optics, Nankai University, Tianjin 300071 (China); Song, Hyunwook [Department of Applied Physics, Kyung Hee University, Yongin-si, Gyeonggi-do 446–701 (Korea, Republic of); Jeong, Heejun, E-mail: hjeong@hanyang.ac.kr [Department of Applied Physics, Hanyang University, Ansan 426-791 (Korea, Republic of)

    2015-02-09

    We measured the inelastic electron tunneling spectroscopy (IETS) characteristics of metal-molecule-metal junctions made with alkanethiolate self-assembled monolayers. The molecular junctions were fabricated using a direct metal transfer method, which we previously reported for high-yield metal-molecule-metal junctions. The measured IETS data could be assigned to molecular vibration modes that were determined by the chemical structure of the molecules. We also observed discrepancies and device-to-device variations in the IETS data that possibly originate from defects in the molecular junctions and insulating walls introduced during the fabrication process and from the junction structure.

  20. Macroscopic quantum tunneling induced by a spontaneous field in intrinsic Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Chizaki, Y., E-mail: y.chizaki@aist.go.jp [Nanosystem Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)] [CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012 (Japan); Kashiwaya, H.; Kashiwaya, S. [Nanoelectronics Research Institute (NeRI), AIST, Tsukuba, Ibaraki 305-8568 (Japan); Koyama, T. [CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012 (Japan)] [Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577 (Japan); Kawabata, S. [Nanosystem Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)] [CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012 (Japan)

    2011-11-15

    Derivation of an effective Hamiltonian in the case that one of the capacitively coupled junctions is in the finite voltage state. Calculation of MQT rate by using the Hamiltonian. The MQT rate is resonantly enhanced and the enhancement is found even when the bias current is off the resonant point. Discussion of the validity of the two types of enhancement. We theoretically study macroscopic quantum tunneling (MQT) in capacitively coupled Josephson junctions in the case that one of the junctions is in the finite voltage state. We find that the system can be mapped into a one dimensional model with a spontaneous periodic perturbation and calculate the MQT rate by using the time-dependent WKB method. Then the MQT rate is found to be resonantly enhanced and the enhancement of MQT rate is found even off the resonant point.

  1. Gap state charge induced spin-dependent negative differential resistance in tunnel junctions

    Science.gov (United States)

    Jiang, Jun; Zhang, X.-G.; Han, X. F.

    2016-04-01

    We propose and demonstrate through first-principles calculation a new spin-dependent negative differential resistance (NDR) mechanism in magnetic tunnel junctions (MTJ) with cubic cation disordered crystals (CCDC) AlO x or Mg1-x Al x O as barrier materials. The CCDC is a class of insulators whose band gap can be changed by cation doping. The gap becomes arched in an ultrathin layer due to the space charge formed from metal-induced gap states. With an appropriate combination of an arched gap and a bias voltage, NDR can be produced in either spin channel. This mechanism is applicable to 2D and 3D ultrathin junctions with a sufficiently small band gap that forms a large space charge. It provides a new way of controlling the spin-dependent transport in spintronic devices by an electric field. A generalized Simmons formula for tunneling current through junction with an arched gap is derived to show the general conditions under which ultrathin junctions may exhibit NDR.

  2. Quantum critical points in tunneling junction of topological superconductor and topological insulator

    Energy Technology Data Exchange (ETDEWEB)

    Zuo, Zheng-Wei, E-mail: zuozw@163.com [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China); National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Kang, Da-wei [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China); Wang, Zhao-Wu [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China); National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Li, Liben [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China)

    2016-08-26

    The tunneling junction between one-dimensional topological superconductor and integer (fractional) topological insulator (TI), realized via point contact, is investigated theoretically with bosonization technology and renormalization group methods. For the integer TI case, in a finite range of edge interaction parameter, there is a non-trivial stable fixed point which corresponds to the physical picture that the edge of TI breaks up into two sections at the junction, with one side coupling strongly to the Majorana fermion and exhibiting perfect Andreev reflection, while the other side decouples, exhibiting perfect normal reflection at low energies. This fixed point can be used as a signature of the Majorana fermion and tested by nowadays experiment techniques. For the fractional TI case, the universal low-energy transport properties are described by perfect normal reflection, perfect Andreev reflection, or perfect insulating fixed points dependent on the filling fraction and edge interaction parameter of fractional TI. - Highlights: • Tunneling junctions between topological superconductor and topological insulator are investigated. • There is a non-trivial stable fixed point in integer topological insulator case at low energies. • The edge of topological insulator breaks up into two sections at the junction. • One side couples strongly to the Majorana fermion and exhibits perfect Andreev reflection. • The other side decouples and exhibits perfect normal reflection.

  3. Band structure of topological insulators from noise measurements in tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Cascales, Juan Pedro, E-mail: juanpedro.cascales@uam.es; Martínez, Isidoro; Aliev, Farkhad G., E-mail: farkhad.aliev@uam.es [Dpto. Fisica Materia Condensada C3, Instituto Nicolas Cabrera (INC), Condensed Matter Physics Institute (IFIMAC), Universidad Autonoma de Madrid, Madrid 28049 (Spain); Katmis, Ferhat; Moodera, Jagadeesh S. [Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Chang, Cui-Zu [Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Guerrero, Rubén [Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid (Spain)

    2015-12-21

    The unique properties of spin-polarized surface or edge states in topological insulators (TIs) make these quantum coherent systems interesting from the point of view of both fundamental physics and their implementation in low power spintronic devices. Here we present such a study in TIs, through tunneling and noise spectroscopy utilizing TI/Al{sub 2}O{sub 3}/Co tunnel junctions with bottom TI electrodes of either Bi{sub 2}Te{sub 3} or Bi{sub 2}Se{sub 3}. We demonstrate that features related to the band structure of the TI materials show up in the tunneling conductance and even more clearly through low frequency noise measurements. The bias dependence of 1/f noise reveals peaks at specific energies corresponding to band structure features of the TI. TI tunnel junctions could thus simplify the study of the properties of such quantum coherent systems that can further lead to the manipulation of their spin-polarized properties for technological purposes.

  4. Measuring the Momentum of a Nanomechanical Oscillator through the Use of Two Tunnel Junctions

    Science.gov (United States)

    Doiron, C. B.; Trauzettel, B.; Bruder, C.

    2008-01-01

    We propose a way to measure the momentum p of a nanomechanical oscillator. The p detector is based on two tunnel junctions in an Aharonov-Bohm-type setup. One of the tunneling amplitudes depends on the motion of the oscillator, the other one not. Although the coupling between the detector and the oscillator is assumed to be linear in the position x of the oscillator, it turns out that the finite-frequency noise output of the detector will in general contain a term proportional to the momentum spectrum of the oscillator. This is a true quantum phenomenon, which can be realized in practice if the phase of the tunneling amplitude of the detector is tuned by the Aharonov-Bohm flux Φ to a p-sensitive value.

  5. Large magnetocapacitance effect in magnetic tunnel junctions based on Debye-Fröhlich model

    Energy Technology Data Exchange (ETDEWEB)

    Kaiju, Hideo, E-mail: kaiju@es.hokudai.ac.jp; Takei, Masashi; Misawa, Takahiro; Nishii, Junji [Research Institute for Electronic Science, Hokkaido University, Sapporo, Hokkaido 001-0020 (Japan); Nagahama, Taro [School of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628 (Japan); Xiao, Gang [Department of Physics, Brown University, Providence, Rhode Island 02912 (United States)

    2015-09-28

    The frequency dependence of tunneling magnetocapacitance (TMC) in magnetic tunnel junctions (MTJs) is investigated theoretically and experimentally. According to the calculation based on Debye-Fröhlich model combined with Julliere formula, the TMC ratio strongly depends on the frequency and it has the maximum peak at a specific frequency. The calculated frequency dependence of TMC is in good agreement with the experimental results obtained in MgO-based MTJs with a tunneling magnetoresistance (TMR) ratio of 108%, which exhibit a large TMC ratio of 155% at room temperature. This calculation also predicts that the TMC ratio can be as large as about 1000% for a spin polarization of 87%, while the TMR ratio is 623% for the same spin polarization. These theoretical and experimental findings provide a deeper understanding on AC spin-dependent transport in the MTJs and will open up wider opportunities for device applications, such as highly sensitive magnetic sensors and impedance-tunable devices.

  6. Estimation of rectangular buried-section tunnel%矩形暗埋段隧道的估算

    Institute of Scientific and Technical Information of China (English)

    李梅

    2014-01-01

    以太原市南沙河沿岸中矩形暗埋段隧道为例,结合其场地岩土构成与工程特性,对建筑安装工程费(人工费、材料费、机械费)、工程建设其他费用以及基本预备费进行了估算预测,为项目决策提供了参考依据。%Taking the rectangular buried-section tunnel along Nansha river coast in Taiyuan city as an example, combining with the geotechnical structure of the field and the engineering characteristics, the paper estimates and predicts the building installation engineering cost ( labor cost, material cost, machinery cost) , engineering construction cost and basic preparation cost as well, which has provided some guidance for the pro-ject decision.

  7. Spatial inhomogeneities in the energy response of a tunnel junction detector due to penetration of Abrikosov vortices

    NARCIS (Netherlands)

    Grand, le J.B.; Martin, J.; Gross, R.; Hubener, R.P.; Hamster, A.W.; Brons, G.C.S.; Adelerhof, D.J.; Flokstra, J.; Korte, de P.A.J.

    1996-01-01

    For the application of superconductive tunnel junctions (STJs) as high resolution X-ray detectors the homogeneity of the detector response is of utmost importance. In this article it is shown how this homogeneity is degraded by the penetration of Abrikosov vortices (AVs) into the junction electrodes

  8. Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach.

    Science.gov (United States)

    Yang, Chao-Yao; Chang, Shu-Jui; Lee, Min-Han; Shen, Kuei-Hung; Yang, Shan-Yi; Lin, Horng-Ji; Tseng, Yuan-Chieh

    2015-11-24

    We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport.

  9. Valley and spin resonant tunneling current in ferromagnetic/nonmagnetic/ferromagnetic silicene junction

    Directory of Open Access Journals (Sweden)

    Yaser Hajati

    2016-02-01

    Full Text Available We study the transport properties in a ferromagnetic/nonmagnetic/ferromagnetic (FNF silicene junction in which an electrostatic gate potential, U, is attached to the nonmagnetic region. We show that the electrostatic gate potential U is a useful probe to control the band structure, quasi-bound states in the nonmagnetic barrier as well as the transport properties of the FNF silicene junction. In particular, by introducing the electrostatic gate potential, both the spin and valley conductances of the junction show an oscillatory behavior. The amplitude and frequency of such oscillations can be controlled by U. As an important result, we found that by increasing U, the second characteristic of the Klein tunneling is satisfied as a result of the quasiparticles chirality which can penetrate through a potential barrier. Moreover, it is found that for special values of U, the junction shows a gap in the spin and valley-resolve conductance and the amplitude of this gap is only controlled by the on-site potential difference, Δz. Our findings of high controllability of the spin and valley transport in such a FNF silicene junction may improve the performance of nano-electronics and spintronics devices.

  10. Edge geometry superconducting tunnel junctions utilizing an NbN/MgO/NbN thin film structure

    Science.gov (United States)

    Hunt, Brian D. (Inventor); Leduc, Henry G. (Inventor)

    1992-01-01

    An edge defined geometry is used to produce very small area tunnel junctions in a structure with niobium nitride superconducting electrodes and a magnesium oxide tunnel barrier. The incorporation of an MgO tunnel barrier with two NbN electrodes results in improved current-voltage characteristics, and may lead to better junction noise characteristics. The NbN electrodes are preferably sputter-deposited, with the first NbN electrode deposited on an insulating substrate maintained at about 250 C to 500 C for improved quality of the electrode.

  11. Effective description of tunneling in a time-dependent potential with applications to voltage switching in Josephson junctions

    DEFF Research Database (Denmark)

    Andersen, Christian Kraglund; Mølmer, Klaus

    2013-01-01

    variable: the phase change across a Josephson junction. The Josephson junction phase variable behaves as the position coordinate of a particle moving in a tilted washboard potential, and our general solution to the motion in such a potential with a time-dependent tilt reproduces a number of features......We propose to use a time-dependent imaginary potential to describe quantum mechanical tunneling through time-varying potential barriers. We use Gamow solutions for stationary tunneling problems to justify our choice of potential, and we apply our method to describe tunneling of a mesoscopic quantum...... associated with voltage switching in Josephson junctions. Apart from applications as artificial atoms in quantum information studies, the Josephson junction may serve as an electric field sensitive detector, and our studies provide a detailed understanding of how the voltage switching dynamics couples...

  12. Rectification in tunneling junctions: 2,2'-bipyridyl-terminated n-alkanethiolates.

    Science.gov (United States)

    Yoon, Hyo Jae; Liao, Kung-Ching; Lockett, Matthew R; Kwok, Sen Wai; Baghbanzadeh, Mostafa; Whitesides, George M

    2014-12-10

    Molecular rectification is a particularly attractive phenomenon to examine in studying structure-property relationships in charge transport across molecular junctions, since the tunneling currents across the same molecular junction are measured, with only a change in the sign of the bias, with the same electrodes, molecule(s), and contacts. This type of experiment minimizes the complexities arising from measurements of current densities at one polarity using replicate junctions. This paper describes a new organic molecular rectifier: a junction having the structure Ag(TS)/S(CH2)11-4-methyl-2,2'-bipyridyl//Ga2O3/EGaIn (Ag(TS): template-stripped silver substrate; EGaIn: eutectic gallium-indium alloy) which shows reproducible rectification with a mean r(+) = |J(+1.0 V)|/|J(-1.0 V)| = 85 ± 2. This system is important because rectification occurs at a polarity opposite to that of the analogous but much more extensively studied systems based on ferrocene. It establishes (again) that rectification is due to the SAM, and not to redox reactions involving the Ga2O3 film, and confirms that rectification is not related to the polarity in the junction. Comparisons among SAM-based junctions incorporating the Ga2O3/EGaIn top electrode and a variety of heterocyclic terminal groups indicate that the metal-free bipyridyl group, not other features of the junction, is responsible for the rectification. The paper also describes a structural and mechanistic hypothesis that suggests a partial rationalization of values of rectification available in the literature.

  13. Comparison of the magneto-Peltier and magneto-Seebeck effects in magnetic tunnel junctions

    Science.gov (United States)

    Shan, J.; Dejene, F. K.; Leutenantsmeyer, J. C.; Flipse, J.; Münzenberg, M.; van Wees, B. J.

    2015-07-01

    Understanding heat generation and transport processes in a magnetic tunnel junction (MTJ) is a significant step towards improving its application in current memory devices. Recent work has experimentally demonstrated the magneto-Seebeck effect in MTJs, where the Seebeck coefficient of the junction varies as the magnetic configuration changes from a parallel (P) to an antiparallel (AP) configuration. Here we report a study on its reciprocal effect, the magneto-Peltier effect, where the heat flow carried by the tunneling electrons is altered by changing the magnetic configuration of the MTJ. The magneto-Peltier signal that reflects the change in the temperature difference across the junction between the P and AP configurations scales linearly with the applied current in the small bias but is greatly enhanced in the large-bias regime, due to higher-order Joule heating mechanisms. By carefully extracting the linear response which reflects the magneto-Peltier effect, and comparing it with the magneto-Seebeck measurements performed on the same device, we observe results consistent with Onsager reciprocity. We estimate a magneto-Peltier coefficient of 13.4 mV in the linear regime using a three-dimensional thermoelectric model. Our result opens up the possibility of programmable thermoelectric devices based on the Peltier effect in MTJs.

  14. Effect of interface geometry on electron tunnelling in Al/Al2O3/Al junctions

    Science.gov (United States)

    Koberidze, M.; Feshchenko, A. V.; Puska, M. J.; Nieminen, R. M.; Pekola, J. P.

    2016-04-01

    We investigate how different interface geometries of an Al/Al2O3 junction, a common component of modern tunnel devices, affect electron transport through the tunnel barrier. We study six distinct Al/Al2O3 interfaces which differ in stacking sequences of the metal and the oxide surface atoms and the oxide termination. To construct model potential barrier profiles for each examined geometry, we rely on first-principles density-functional theory (DFT) calculations for the barrier heights and the shapes of the interface regions as well as on experimental data for the barrier widths. We show that even tiny variations in the atomic arrangement at the interface cause significant changes in the tunnel barrier parameters and, consequently, in electron transport properties. Especially, we find that variations in the crucial barrier heights and widths can be as large as 2 eV and 5 Å, respectively. Finally, to gain information about the average properties of the measured junction, we fit the conductance calculated within the Wentzel-Kramers-Brillouin approximation to the experimental data and interpret the fit parameters with the help of the DFT results.

  15. Control of City Shallow Buried Tunnel Blasting Hazard to Surface Buildings

    Directory of Open Access Journals (Sweden)

    Yang Deqiang

    2015-01-01

    Full Text Available Combining with the blasting test of an under-construction tunnel, this paper optimizes the overall blasting construction scheme. The optimized blasting scheme is used in the site construction test and the peak particle vibration velocity is strictly controlled under working conditions through blasting vibration monitoring to ensure the safety of surrounding buildings and structures in the construction process. The corresponding control measures are proposed to reduce the blasting vibration which brings certain guiding significance to the following construction project.

  16. Zeeman effects on d-wave superconductor and tunneling spectrum in normal-metal/d-wave superconductor tunnel junction

    Institute of Scientific and Technical Information of China (English)

    DONG Zhengchao

    2006-01-01

    We study the Zeeman effect on the d-wave superconductor and tunneling spectrum in normal-metal(N)/d-wave superconductor(S) junction by applying a Zeeman magnetic field to the S. It is shown that: (1) the Zeeman magnetic field can lead to the S gap decreasing, and with the increase in Zeeman energy, the superconducting state is changed to the normal state, exhibiting a first-order phase transition; (2) the Zeeman energy difference between the two splitting peaks in the conductance spectrum is equal to2h0 (h0 is the Zeeman energy); (3) both the barrier strength of interface scattering and the temperature can lower the magnitudes of splitting peaks, of which the barrier strength can lead to the splitting peaks becoming sharp and the temperature can smear out the peaks,however, neither of them can influence the Zeeman effect.

  17. Size and voltage dependence of effective anisotropy in sub-100-nm perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Piotrowski, Stephan K.; Bapna, Mukund; Oberdick, Samuel D.; Majetich, Sara A.; Li, Mingen; Chien, C. L.; Ahmed, Rizvi; Victora, R. H.

    2016-07-01

    Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The 1.23 -nm Co40Fe40B20 recording layer coercivity exhibits a size dependence which suggests single-domain behavior for diameters ≤100 nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy Keff using two different techniques. Keff is extracted both from distributions of the switching fields of the recording and reference layers and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that Keff increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that Keff can be controlled with a voltage down to the smallest size measured, 64 nm.

  18. Dual Control of Giant Field-like Spin Torque in Spin Filter Tunnel Junctions

    Science.gov (United States)

    Tang, Y.-H.; Chu, F.-C.; Kioussis, Nicholas

    2015-06-01

    We predict a giant field-like spin torque, , in spin-filter (SF) barrier tunnel junctions in sharp contrast to existing junctions based on nonmagnetic passive barriers. We demonstrate that has linear bias behavior, is independent of the SF thickness, and has odd parity with respect to the SF’s exchange splitting. Thus, it can be selectively controlled via external bias or external magnetic field which gives rise to sign reversal of via magnetic field switching. The underlying mechanism is the interlayer exchange coupling between the noncollinear magnetizations of the SF and free ferromagnetic electrode via the nonmagnetic insulating (I) spacer giving rise to giant spin-dependent reflection at the SF/I interface. These findings suggest that the proposed field-like-spin-torque MRAM may provide promising dual functionalities for both ‘reading’ and ‘writing’ processes which require lower critical current densities and faster writing and reading speeds.

  19. Inelastic electron tunneling through degenerate and nondegenerate ground state polymeric junctions

    Energy Technology Data Exchange (ETDEWEB)

    Golsanamlou, Z.; Bagheri Tagani, M., E-mail: m_bagheri@guilan.ac.ir; Rahimpour Soleimani, H.

    2015-05-01

    Highlights: • Current–voltage characteristics of two polymeric junctions are studied. • Current is reduced in phonon assistant tunneling regime. • Behavior of current is independent of temperature. • Elastic energy changes current drastically. - Abstract: The inelastic electron transport properties through two polymeric (trans-polyacetylene and polythiophene) molecular junctions are studied using Keldysh nonequilibrium Green function formalism. The Hamiltonian of the polymers is described via Su–Schrieffer–Heeger model and the metallic electrodes are modeled by the wide-band approximation. Results show that the step-like behavior of the current–voltage characteristics is deformed in presence of strong electron–phonon interaction. Also, the magnitude of current is slightly decreased in the phonon assistant electron transport regime. In addition, it is observed that the I–V curves are independent of temperature.

  20. Magnetism of Semiconductor-Based Magnetic Tunnel Junctions under Electric Field from First Principles

    Energy Technology Data Exchange (ETDEWEB)

    Kan, E.; Xiang, H.; Yang, J.; Whangbo, M. H.

    2009-06-01

    Semiconductor magnetic tunnel junctions (MTJs), composed of diluted magnetic semiconductors (DMSs) sandwiching a semiconductor barrier, have potential applications in spintronics but their development has been slow due to the difficulty of controlling the magnetism of DMSs. In terms of density functional calculations for model semiconductor MTJs, (Zn,Co)O/ZnO/(Zn,Co)O and (Ga,Mn)N/GaN/(Ga,Mn)N, we show that the magnetic coupling between the transition metal ions in each DMS electrode of such semiconductor MTJs can be switched from ferromagnetic to antiferromagnetic, or vice versa, under the application of external electric field across the junctions. Our results suggest a possible avenue for the application of semiconductor MTJs.

  1. Tetragonal Heusler-Like Mn-Ga Alloys Based Perpendicular Magnetic Tunnel Junctions

    Science.gov (United States)

    Ma, Qinli; Sugihara, Atsushi; Suzuki, Kazuya; Zhang, Xianmin; Miyazaki, Terunobu; Mizukami, Shigemi

    2014-10-01

    Films of the Mn-based tetragonal Heusler-like alloys, such as Mn-Ga, exhibit a large perpendicular magnetic anisotropy (PMA), small damping constant, small saturation magnetization and large spin polarizations. These properties are attractive for the application to the next generation high density spin-transfer-torque (STT) magnetic random access memory (STT-MRAM). We reviewed the structure, magnetic properties and Gilbert damping of the alloy films with large PMA, and the current status of research on tunnel magnetoresistance (TMR) in perpendicular magnetic tunnel junctions (p-MTJs) based on Mn-based tetragonal Heusler-like alloy electrode, and also discuss the issues for the application of those to STT-MRAM.

  2. Electron Holography of Barrier Structures in Co/ZrAlOx/Co Magnetic Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhe; ZHU Tao; SHEN Feng; SHENG Wen-Ting; WANG Wei-Gang; XIAO John Q; ZHANG Ze

    2005-01-01

    @@ We investigate the potential profiles and elemental distribution of barriers in Co/ZrAlOx/Co magnetic tunnel junctions (MTJs) using electron holography (EH) and scanning transmission electron microscopy. The MTJ barriers are introduced by oxidizing a bilayer consisting with a uniform 0.45-nm Al layer and a wedge-shaped Zr layer (0-2 nm). From the scanning transmission electron microscopy, AlOx and ZrOx layers are mixed together,indicating that compact AlOx layer cannot be formed in such a bilayer structure of barriers. The EH results reveal that there are no sharp interfaces between the barrier and magnetic electrodes, which may be responsible for a smaller tunnelling magnetoresistance compared with the MTJs of Co/AlOx/Co.

  3. Optical modulation of nano-gap tunnelling junctions comprising self-assembled monolayers of hemicyanine dyes

    Science.gov (United States)

    Pourhossein, Parisa; Vijayaraghavan, Ratheesh K.; Meskers, Stefan C. J.; Chiechi, Ryan C.

    2016-06-01

    Light-driven conductance switching in molecular tunnelling junctions that relies on photoisomerization is constrained by the limitations of kinetic traps and either by the sterics of rearranging atoms in a densely packed monolayer or the small absorbance of individual molecules. Here we demonstrate light-driven conductance gating; devices comprising monolayers of hemicyanine dyes trapped between two metallic nanowires exhibit higher conductance under irradiation than in the dark. The modulation of the tunnelling current occurs faster than the timescale of the measurement (~1 min). We propose a mechanism in which a fraction of molecules enters an excited state that brings the conjugated portion of the monolayer into resonance with the electrodes. This mechanism is supported by calculations showing the delocalization of molecular orbitals near the Fermi energy in the excited and cationic states, but not the ground state and a reasonable change in conductance with respect to the effective barrier width.

  4. Magnetic-Field-Modulated Resonant Tunneling in Ferromagnetic-Insulator-Nonmagnetic Junctions

    Science.gov (United States)

    Song, Yang; Dery, Hanan

    2014-07-01

    We present a theory for resonance-tunneling magnetoresistance (MR) in ferromagnetic-insulator-nonmagnetic junctions. The theory sheds light on many of the recent electrical spin injection experiments, suggesting that this MR effect rather than spin accumulation in the nonmagnetic channel corresponds to the electrically detected signal. We quantify the dependence of the tunnel current on the magnetic field by quantum rate equations derived from the Anderson impurity model, with the important addition of impurity spin interactions. Considering the on-site Coulomb correlation, the MR effect is caused by competition between the field, spin interactions, and coupling to the magnetic lead. By extending the theory, we present a basis for operation of novel nanometer-size memories.

  5. Molecular-Beam Epitaxially Grown MgB2 Thin Films and Superconducting Tunnel Junctions

    Directory of Open Access Journals (Sweden)

    Jean-Baptiste Laloë

    2011-01-01

    Full Text Available Since the discovery of its superconducting properties in 2001, magnesium diboride has generated terrific scientific and engineering research interest around the world. With a of 39 K and two superconducting gaps, MgB2 has great promise from the fundamental point of view, as well as immediate applications. Several techniques for thin film deposition and heterojunction formation have been established, each with its own advantages and drawbacks. Here, we will present a brief overview of research based on MgB2 thin films grown by molecular beam epitaxy coevaporation of Mg and B. The films are smooth and highly crystalline, and the technique allows for virtually any heterostructure to be formed, including all-MgB2 tunnel junctions. Such devices have been characterized, with both quasiparticle and Josephson tunneling reported. MgB2 remains a material of great potential for a multitude of further characterization and exploration research projects and applications.

  6. Degradation of magnetic tunnel junctions with thin AlOx barrier

    Directory of Open Access Journals (Sweden)

    Tadashi Mihara, Yoshinari Kamakura, Masato Morifuji and Kenji Taniguchi

    2007-01-01

    Full Text Available The degradation of magnetic tunnel junctions (MTJs with AlOx barrier was experimentally investigated. Constant voltage stress (CVS measurement was carried out to monitor the time evolution of the conductance and tunneling magnetoresistance (TMR of MTJs. The gradual increase of the stress-induced leakage current (SILC was observed prior to the breakdown, following a power law function of stress time with an exponent of about 0.2–0.4, which is similar to the case of the ultrathin gate oxide films in MOSFETs. The measured TMR for SILC suggests that the spin-dependent current component would be involved in the early stage of degradation, while spin-independent conduction becomes dominant before the breakdown resulting in a decrease of TMR.

  7. Behavioural model of Spin Torque Transfer Magnetic Tunnel Junction, Using Verilog-A

    Science.gov (United States)

    Garg, Rishubh; Kumar, Deepak; Jindal, Navneet; Negi, Nandita; Ahuja, Chetna

    2012-11-01

    A novel simple and efficient model of Spin Torque Transfer Magnetic Tunnel Junction (STT-MTJ) is presented. The model is implemented using Verilog-A. The model accurately emulates the main properties of an STT-MTJ which includes Tunnel Magneto resistance Ratio (TMR), its dependence on the voltage bias and the Critical switching current. The novelty of the model lies in the fact that the voltage dependence of TMR has been modeled using a single equation dividing it into three different operating regions. A register based on the model is also developed. The model can be used for faster simulations of hybrid Magnetic CMOS circuits and in various other wide range of applications. The models were verified using Synopsys Hspice 2010.

  8. Disorder Scattering in Magnetic Tunnel Junctions: Theory of Nonequilibrium Vertex Correction

    Science.gov (United States)

    Ke, Youqi; Xia, Ke; Guo, Hong

    2008-04-01

    We report a first principles formalism and its numerical implementation for treating quantum transport properties of nanoelectronic devices with atomistic disorder. We develop a nonequilibrium vertex correction (NVC) theory to handle the configurational average of random disorder at the density matrix level so that disorder effects to nonlinear and nonequilibrium quantum transport can be calculated from atomic first principles in a self-consistent and efficient manner. We implement the NVC into a Keldysh nonequilibrium Green’s function (NEGF) -based density functional theory (DFT) and apply the NEGF-DFT-NVC formalism to Fe/vacuum/Fe magnetic tunnel junctions with interface roughness disorder. Our results show that disorder has dramatic effects on the nonlinear spin injection and tunnel magnetoresistance ratio.

  9. Spontaneous fluxon production in annular Josephson tunnel junctions in the presence of a magnetic field

    DEFF Research Database (Denmark)

    Monaco, Roberto; Aarøe, Morten; Mygind, Jesper;

    2008-01-01

    We report on the spontaneous production of fluxons in annular Josephson tunnel junctions during a thermal quench in the presence of a symmetry-breaking magnetic field. The dependence on field intensity B of the probability (f) over bar (1) to trap a single defect during the N-S phase transition...... depends drastically on the sample circumferences. We show that this can be understood in the framework of the same picture of spontaneous defect formation that leads to the experimentally well attested scaling behavior of (f) over bar (1) with quench rate in the absence of an external field....

  10. Observation of Thermoelectric Currents in High-Field Superconductor-Ferromagnet Tunnel Junctions.

    Science.gov (United States)

    Kolenda, S; Wolf, M J; Beckmann, D

    2016-03-01

    We report on the experimental observation of spin-dependent thermoelectric currents in superconductor-ferromagnet tunnel junctions in high magnetic fields. The thermoelectric signals are due to a spin-dependent lifting of the particle-hole symmetry, and are found to be in excellent agreement with recent theoretical predictions. The maximum Seebeck coefficient inferred from the data is about -100  μV/K, much larger than commonly found in metallic structures. Our results directly prove the coupling of spin and heat transport in high-field superconductors.

  11. Development and process control of magnetic tunnel junctions for magnetic random access memory devices

    Science.gov (United States)

    Kula, Witold; Wolfman, Jerome; Ounadjela, Kamel; Chen, Eugene; Koutny, William

    2003-05-01

    We report on the development and process control of magnetic tunnel junctions (MTJs) for magnetic random access memory (MRAM) devices. It is demonstrated that MTJs with high magnetoresistance ˜40% at 300 mV, resistance-area product (RA) ˜1-3 kΩ μm2, low intrinsic interlayer coupling (Hin) ˜2-3 Oe, and excellent bit switching characteristics can be developed and fully integrated with complementary metal-oxide-semiconductor circuitry into MRAM devices. MTJ uniformity and repeatability level suitable for mass production has been demonstrated with the advanced processing and monitoring techniques.

  12. Temperature dependence of microwave oscillations in magnetic tunnel junctions with a perpendicularly magnetized free layer

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Peng; Feng, Jiafeng, E-mail: hxwei@iphy.ac.cn, E-mail: jiafengfeng@iphy.ac.cn; Wei, Hongxiang, E-mail: hxwei@iphy.ac.cn, E-mail: jiafengfeng@iphy.ac.cn; Han, Xiufeng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Fang, Bin; Zhang, Baoshun; Zeng, Zhongming [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Ruoshui Road 398, Suzhou 215123 (China)

    2015-01-05

    We experimentally study the temperature dependence of the spin-transfer-torque-induced microwave oscillations in MgO-based magnetic tunnel junction nanopillars with a perpendicularly magnetized free layer. We demonstrate that the oscillation frequency increases rapidly with decreasing temperature, which is mainly ascribed to the temperature dependence of both the saturation magnetization and the perpendicular magnetic anisotropy. We also find that a strong temperature dependence of the output power while a nonmonotonic temperature dependence of spectral linewidth are maintained for a constant dc bias in measured temperature range. Possible mechanisms leading to the different dependences of oscillation frequency, output power, and linewidth are discussed.

  13. All-optical detection of magnetization precession in tunnel junctions under applied voltage

    Science.gov (United States)

    Sasaki, Yuta; Suzuki, Kazuya; Sugihara, Atsushi; Kamimaki, Akira; Iihama, Satoshi; Ando, Yasuo; Mizukami, Shigemi

    2017-02-01

    An all-optical time-resolved magneto-optical Kerr effect measurement of a micron-sized tunnel junction with a CoFeB electrode was performed. The femtosecond (fs) laser-induced magnetization precession was clearly observed at various magnetic field angles. The frequency f and relaxation time τ of the magnetization precession varied with the voltage applied via a MgO barrier. The precession dynamics were in accordance with Kittel’s ferromagnetic resonance mode, and the voltage-induced changes in f and τ were well explained by the voltage-induced change in the perpendicular magnetic anisotropy of -36 fJ/Vm.

  14. On-chip measurement of the Brownian relaxation frequency of magnetic beads using magnetic tunneling junctions

    DEFF Research Database (Denmark)

    Donolato, M.; Sogne, E.; Dalslet, Bjarke Thomas

    2011-01-01

    We demonstrate the detection of the Brownian relaxation frequency of 250 nm diameter magnetic beads using a lab-on-chip platform based on current lines for exciting the beads with alternating magnetic fields and highly sensitive magnetic tunnel junction (MTJ) sensors with a superparamagnetic free...... layer. The first harmonic out-of-phase component of the MTJ response gives the imaginary part of the magnetic bead susceptibility, which peaks at the Brownian relaxation frequency. This work paves the way to on-chip implementation of Brownian magnetorelaxometry in innovative "lab-on-a-bead" assays...

  15. Electrical switching in Fe/V/MgO/Fe tunnel junctions

    Science.gov (United States)

    Najjari, N.; Halley, D.; Bowen, M.; Majjad, H.; Henry, Y.; Doudin, B.

    2010-05-01

    Bipolar hysteretic resistance switching in epitaxial Fe/V/MgO/Fe magnetic tunnel junctions is observed in highly reproducible I(V) curves and found to be modified by the frequency of the bias voltage sweep. Observation of slow relaxation of the resistance state values is reported. A model is proposed that takes into account the incidence of time-dependent electric-field-induced migration of atomic species on the effective barrier thickness. This model provides a good qualitative agreement with experimental data.

  16. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    Mingsen Deng

    2015-01-01

    Full Text Available The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS. Based on a model molecule of Bis-(4-mercaptophenyl-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  17. Charge filling factors in clean and disordered arrays of tunnel junctions.

    Science.gov (United States)

    Walker, Kelly A; Vogt, Nicolas; Cole, Jared H

    2015-12-02

    We simulate one-dimensional arrays of tunnel junctions using the kinetic Monte Carlo method to study charge filling behaviour in the large charging energy limit. By applying a small fixed voltage bias and varying the offset voltage, we investigate this behaviour in clean and disordered arrays (both weak and strong disorder effects). The offset voltage dependent modulation of the current is highly sensitive to background charge disorder and exhibits substantial variation depending on the strength of the disorder. We show that while small fractional charge filling factors are likely to be washed out in experimental devices due to strong background charge disorder, larger factors may be observable.

  18. Parametric amplification on rf-induced steps in a Josephson tunnel junction

    DEFF Research Database (Denmark)

    Sørensen, O.H.; Pedersen, Niels Falsig; Mygind, Jesper

    1979-01-01

    Parametric effects including amplification in a singly degenerate mode have been observed in Josephson tunnel junctions at dc bias points on rf-induced steps. Net gain at 9 GHz was achieved with a bias on the fundamental 18-GHz step and subharmonic self-oscillations were seen on 18 and 70-GHz rf-......-induced steps even at voltages approaching the energy gap. A qualitative explanation of the results is presented. Journal of Applied Physics is copyrighted by The American Institute of Physics....

  19. Magnetic tunnel junctions using Co/Pt multilayered free layers with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Machida, K; Funabashi, N; Aoshima, K; Kuga, K; Kikuchi, H; Shimidzu, N [Science and Technology Research Labs., Japan Broadcasting Corp. (NHK), 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan); Furukawa, K; Nakayama, T [Department of Electrical Engineering, Tokyo Denki University, 2-2 Kandanishikicho, Chiyoda-ku, Tokyo 101-8457 (Japan); Ishibashi, T, E-mail: machida.k-ge@nhk.or.jp [Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata 940-2188 (Japan)

    2011-07-06

    Co/Pt multilayered films with perpendicular magnetic anisotropy have a large magneto-optical Kerr effect. To use the films with a submicron magneto-optical light modulator driven by spin transfer switching, we fabricated two types of magnetic tunnel junctions (MTJs) with Co/Pt multilayered films for the free layers. One is an fcc-based MTJ, another is a bcc-based MTJ with CoFeB/MgO/CoFeB junction. The fcc-based MTJ with a Ag buffer layer on the bottom electrode showed a large coercive force of the pinned layer, a large Kerr rotation angle of 0.3 degree in the free layer and a tunnel magnetoresistance (TMR) ratio of 3.8%. In the CoFeB/MgO/CoFeB junction, an X-ray diffraction pattern of an MgO layer showed a large MgO(002)-orientation. However, the TMR ratio was less than 3 %. An MTJ with a Ta buffer layer between the CoFeB layer and the Co/Pt multilayered films in the free layer was prepared. The Ta buffer was used to alleviate a lattice mismatch between bcc-CoFeB/MgO/CoFeB and fcc-Co/Pt multilayer. The peak intensity of the MgO(002)-orientation was increased up to 2 times. This result suggests that the crystalline texture of the bcc-CoFeB/MgO/CoFeB junction is strongly influenced by the fcc-Co/Pt multilayered films.

  20. Multiferroic tunnel junctions and ferroelectric control of magnetic state at interface (invited)

    KAUST Repository

    Yin, Y. W.

    2015-03-03

    As semiconductor devices reach ever smaller dimensions, the challenge of power dissipation and quantum effect place a serious limit on the future device scaling. Recently, a multiferroic tunnel junction (MFTJ) with a ferroelectric barrier sandwiched between two ferromagnetic electrodes has drawn enormous interest due to its potential applications not only in multi-level data storage but also in electric field controlled spintronics and nanoferronics. Here, we present our investigations on four-level resistance states, giant tunneling electroresistance (TER) due to interfacial magnetoelectric coupling, and ferroelectric control of spin polarized tunneling in MFTJs. Coexistence of large tunneling magnetoresistance and TER has been observed in manganite/(Ba, Sr)TiO3/manganite MFTJs at low temperatures and room temperature four-resistance state devices were also obtained. To enhance the TER for potential logic operation with a magnetic memory, La0.7Sr0.3MnO3/BaTiO3/La0.5Ca0.5MnO3 /La0.7Sr0.3MnO3 MFTJs were designed by utilizing a bilayer tunneling barrier in which BaTiO3 is ferroelectric and La0.5Ca0.5MnO3 is close to ferromagnetic metal to antiferromagnetic insulator phase transition. The phase transition occurs when the ferroelectric polarization is reversed, resulting in an increase of TER by two orders of magnitude. Tunneling magnetoresistance can also be controlled by the ferroelectric polarization reversal, indicating strong magnetoelectric coupling at the interface.

  1. Noise and current correlations in tunnel junctions of quantum spin Hall edge states

    Science.gov (United States)

    Dolcini, Fabrizio

    2015-10-01

    The edge channels of two-dimensional topological systems are protected from elastic reflection and are noiseless at low temperature. Yet, noise and cross correlations can be induced when electron waves partly transmit to the opposite edge via tunneling through a constriction. In particular, in a quantum spin Hall (QSH) system tunneling occurs via both spin-preserving (p ) and spin-flipping (f ) processes, each fulfilling time-reversal symmetry. We investigate the current correlations of a four-terminal QSH setup in the presence of a tunneling region, both at equilibrium and out of equilibrium. We find that, although p and f processes do not commute and the generic current correlation depends on both, under appropriate conditions a direct detection of two types of partition noise is possible. In particular, while the spin-preserving partitioning can be probed for any arbitrary tunnel junction with a specific configuration of terminal biases, the spin-flipping partitioning can be directly detected only under suitably designed setups and conditions. We describe two setups where these conditions can be fulfilled, and both types of partitioning can be detected and controlled.

  2. Scanning tunneling microscope light emission: Effect of the strong dc field on junction plasmons

    Science.gov (United States)

    Kalathingal, Vijith; Dawson, Paul; Mitra, J.

    2016-07-01

    The observed energies of the localized surface plasmons (LSPs) excited at the tip-sample junction of a scanning tunneling microscope, as identified by spectral peaks in the light output, are very significantly redshifted with respect to calculations that use standard optical data for the tip and sample material, gold in this case. We argue that this anomaly depends on the extreme field in the sub-nm tunneling proximity of the tip and the sample, across which a dc bias (1-2 V) is applied. Finite element modeling analysis is presented of a gold nanosphere-plane (NS-P) combination in tunneling proximity and, crucially, in the presence of a high static electric field (˜109V /m ). It is argued that the strong dc field induces nonlinear corrections to the dielectric function of the gold via the effect of a large background polarizability through the nonlinear, χ(3 ) susceptibility contribution. When fed into the model system the modified optical data alters the LSP cavity modes of the NS-P system to indeed reveal a large redshift in energy compared to those of the virgin gold NS-P system. The net outcome may be regarded as equivalent to lowering the bulk plasmon energy, the physical interpretation being that the intense field of the tunneling environment leads to surface charge screening, effectively reducing the density of free electrons available to participate in the plasmon oscillations.

  3. Symmetry dependent spin injection from Fe/MgO in single crystal based magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Hehn, Michel; Greullet, Fanny; Bernos, Julien; Tiusan, Coriolan; Bellouard, Christine; Montaigne, Francois; Lacour, Daniel; Alnot, Marc; Lu, Yuan; Lengaigne, Gwladys [LPM, Vandoeuvre les Nancy (France); Halley, David; Weber, Wolfgang [IPCMS, 67 - Strasbourg (France)

    2009-07-01

    The transport in crystalline magnetic tunnel junctions (MTJ) attracted the interest of the international community after the theoretical predictions of Butler et al of giant tunnel magnetoresistance (TMR) effects. In these model systems the electrons are classified with respect to the symmetry of their associated electronic Bloch wave function. The large predicted TMR ratio is related to a symmetry dependent attenuation rate within the MgO single crystal barrier combined with a half metallic property of a specific symmetry in the Fe electrode. After a brief introduction to the physics of the transport in Fe/MgO/Fe MTJ, I show how to exploit the symmetry dependence of the tunnel conductivity to engineer novel MTJs functionalities. We demonstrate that, a suitably chosen Cr(001) epitaxial metallic spacer layer quenches the transmission of particular electronic states, therefore acting as an additional symmetry dependent tunnel barrier for electrons at the Fermi level. Moreover, we show that this ultrathin Cr metallic barrier can promote quantum well states in an adjacent Fe layer. These results confirm the transport mechanism proposed by Butler et al. Extension to other materials are also discussed.

  4. Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Weisheng Zhao

    2016-01-01

    Full Text Available Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., <1 nm to reduce the resistance area for the spin transfer torque switching in the nanopillar. These failure issues limit the research and development of STT-MRAM to widely achieve commercial products. In this paper, we give a full analysis of failure mechanisms for PMA-MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

  5. Tunneling electroresistance effect in ultrathin BiFeO3-based ferroelectric tunneling junctions

    Science.gov (United States)

    Yoong, Herng Yau; Wang, Han; Xiao, Juanxiu; Guo, Rui; Yang, Ping; Yang, Yi; Lim, Sze Ter; Wang, John; Venkatesan, T.; Chen, Jingsheng

    2016-12-01

    Tunneling electroresistance (TER) effect has been observed in high quality ultrathin BiFeO3 thin films. The growth quality of the ultrathin BiFeO3 films was confirmed using the synchrotron high resolution X-ray diffraction techniques as well as high-resolution transmission electron microscopy. Ferroelectric-based resistive switching behavior is observed down to 2 u.c. of BiFeO3 ultrathin film, which is way below the critical thickness of BiFeO3 thin films exhibiting ferroelectricity reported in the previous research works. Upon fitting mathematically using the direct tunneling model, it could be seen that there is an increase in the change in the average potential barrier height when the barrier thickness increases from 2 u.c. to 10 u.c., which also results in an increase in the TER ratio by one order of magnitude. These results are promising and pave the way for developing ultrathin BiFeO3 films to be adopted in the non-volatile memory applications.

  6. Electric-field manipulation of magnetization rotation and tunneling magnetoresistance of magnetic tunnel junctions at room temperature

    Science.gov (United States)

    Chen, Aitian; Li, Peisen; Li, Dalai; Zhao, Yonggang; Zhang, Sen; Yang, Lifeng; Liu, Yan; Zhu, Meihong; Zhang, Huiyun; Han, Xiufeng

    2015-03-01

    Recent studies on the electric-field control of tunneling magnetoresistance (TMR) have attracted considerable attention for low power consumption. So far two methods have been demonstrated for electric-field control of TMR. One method uses ferroelectric or multiferroic barriers, which is limited by low temperature. The other is nanoscale thin film magnetic tunnel junction (MTJ), but the assistance of a magnetic field is required. Therefore, electric-field control of TMR at room temperature without a magnetic field is highly desired. One promising way is to employ strain-mediated coupling in ferromagnetic/piezoelectric structure. Though MTJs/piezoelectric has been predicted by theory, experiment work is still lacking. We deposited CoFeB/AlOx/CoFeB on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric single crystal. Under external electric fields, PMN-PT will produce a piezostrain due to piezoelectric effect, and the piezostrain transfers to ferromagnetic film to change the magnetic anisotropy. We demonstrate a reversible, continuous magnetization rotation and manipulation of TMR at room temperature by electric fields without the assistance of a magnetic field.

  7. Large influence of capping layers on tunnel magnetoresistance in CoFe/MgO/CoFe magnetic tunnel junctions

    CERN Document Server

    Zhou, Jiaqi; Wang, Yin; Peng, Shouzhong; Qiao, Junfeng; Su, Li; Zeng, Lang; Lei, Na; Zhang, Youguang; Bournel, Arnaud

    2016-01-01

    We report the first-principles theoretical investigations of the tunnel magnetoresistance(TMR) effect in the symmetric capping layer/CoFe(001)/MgO(001)/CoFe(001)/capping layer magnetic tunnel junctions(MTJs) with Ta, Hf and Ir used as capping layer materials. Spin-resolved conductance and TMR ratios are shown and it is found that the TMR ratio is sensitive to the capping layer material. The spin polarization of s state in Co atom at the CoFe/capping layer interface is presented to explain the influence on TMR ratio caused by different capping layers, and we can obtain a high spin polarization value and a giant TMR ratio when Ir is used, demonstrating that Ir is an ideal capping layer material. We also study the spin-polarized transport properties in the Brillouin zone. In the parallel condition, a central broad peak is found in the majority-spin channel due to the {\\Delta}1 state, while sharp transmission probability peaks at some k||-points appear in the minority-spin channel. The sharp peak phenomenon is at...

  8. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Miwa, Shinji, E-mail: miwa@mp.es.osaka-u.ac.jp; Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Kotani, Yoshinori; Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198 (Japan)

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  9. Similarities between normal- and super-currents in topological insulator magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Soodchomshom, Bumned, E-mail: Bumned@hotmail.co [ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rd. Bangkok 10400 (Thailand); Chantngarm, Peerasak [Department of Electronics and Telecommunication Engineering, Faculty of Engineering, Pathumwan Institute of Technology, Bangkok 10330 (Thailand)

    2010-11-15

    This work compares the normal-current in a NM/Fi/NM junction with the super-current in a SC/Fi/SC junction, where both are topological insulator systems. NM and Fi are normal region and ferromagnetic region of thickness d with exchange energy m playing a role of the mass of the Dirac electrons and with the gate voltage V{sub G}, respectively. SC is superconducting region induced by a s-wave superconductor. We show that, interestingly, the critical super-current passing through a SC/Fi/SC junction behaves quite similar to the normal-current passing through a NM/Fi/NM junction. The normal-current and super-current exhibit N-peak oscillation, found when currents are plotted as a function of the magnetic barrier strength {chi} {approx} md/hv{sub F}. With the barrier strength Z {approx} V{sub G}d/hv{sub F}, the number of peaks N is determined through the relation Z {approx} N{pi} + {sigma}{pi} (with 0 < {sigma}{<=}1 for {chi} < Z). The normal- and the super-currents also exhibit oscillating with the same height for all of peaks, corresponding to the Dirac fermion tunneling behavior. These anomalous oscillating currents due to the interplay between gate voltage and magnetic field in the barrier were not found in graphene-based NM/Fi/NM and SC/Fi/SC junctions. This is due to the different magnetic effect between the Dirac fermions in topological insulator and graphene.

  10. Superluminescence from an optically pumped molecular tunneling junction by injection of plasmon induced hot electrons

    Directory of Open Access Journals (Sweden)

    Kai Braun

    2015-05-01

    Full Text Available Here, we demonstrate a bias-driven superluminescent point light-source based on an optically pumped molecular junction (gold substrate/self-assembled molecular monolayer/gold tip of a scanning tunneling microscope, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. A positive, steadily increasing bias voltage induces a step-like rise of the Stokes shifted optical signal emitted from the junction. This emission is strongly attenuated by reversing the applied bias voltage. At high bias voltage, the emission intensity depends non-linearly on the optical pump power. The enhanced emission can be modelled by rate equations taking into account hole injection from the tip (anode into the highest occupied orbital of the closest substrate-bound molecule (lower level and radiative recombination with an electron from above the Fermi level (upper level, hence feeding photons back by stimulated emission resonant with the gap mode. The system reflects many essential features of a superluminescent light emitting diode.

  11. Imaging soft x-ray spectrometers based on superconducting tunnel junctions

    Science.gov (United States)

    Verhoeve, P.; Martin, D. D. E.; Venn, R.

    2010-07-01

    X-ray detectors based on superconducting tunnel junctions (STJs) have demonstrated good energy resolution in the soft X-ray energy range 0.1-6 keV. In particular DROIDS (Distributed Read Out Imaging Devices), consisting of a superconducting absorber strip with superconducting tunnel junctions as read-out devices on either end, could combine this high resolving power with a large sensitive area and good soft X-ray detection efficiency. In this paper we present results on the spectroscopic performance of Al and Ta/Al DROIDs with different absorber materials (Ta, Re) and with variations in absorber configurations: our standard absorber integrated with the read-out structure is compared with absorbers deposited after definition of the read-out structure. The latter allows maximising the detection efficiency through thicker layers and different absorber materials. Also, absorbers which are electrically coupled to the readout structure are compared to insulated absorbers which couple to the readout structure by phonon exchange across a thin dielectric layer. New process routes have been designed for all new configurations. Whilst not all these structures have been fabricated successfully yet, our integrated absorber sofar exhibits the best performance, with 2.45 eV FWHM at 400 eV and 16.6 eV FWHM at 5.9 keV.

  12. Interface characterization of epitaxial Fe/MgO/Fe magnetic tunnel junctions.

    Science.gov (United States)

    Wang, S G; Ward, R C C; Hesjedal, T; Zhang, X G; Wang, C; Kohn, A; Ma, Q L; Zhang, Jia; Liu, H F; Han, X F

    2012-02-01

    Following predictions by first-principles theory of a huge tunnel magnetoresistance (TMR) effect in epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs), measured magnetoresistance (MR) ratios of about 200% at room temperature (RT) have been reported in MgO-based epitaxial MTJs. Recently, a MR ratio of about 600% has been reported at RT in MgO-based MTJs prepared by magnetron sputtering, using amorphous CoFeB as the ferromagnetic electrode. These MTJs show great potential for application in spintronic devices. Fully epitaxial MTJs are excellent model systems that enhance our understanding of the spin-dependent tunneling process as the interface is well defined and can be fully characterized. Both theoretical calculations and experimental results clearly indicate that the interfacial structure plays a crucial role in the coherent tunneling across a single crystal MgO barrier, especially in epitaxial MgO-based MTJs grown by molecular beam epitaxy (MBE). Surface X-ray diffraction, Auger electron spectroscopy, X-ray absorption spectra, and X-ray magnetic circular dichroism techniques have been reported previously for interface characterization. However, no consistent viewpoint has been reached on the interfacial structures (such as FeO layer formation at the bottom Fe/MgO interface), and it is still an open issue. In this article, our recent studies on the interface characterization of MgO-based epitaxial MTJs by X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and spin-dependent tunneling spectroscopy, will be presented.

  13. Spin asymmetry calculations of the TMR-V curves in single and double-barrier magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2011-10-01

    Spin-polarization asymmetry is the key parameter in asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) in magnetic tunnel junctions. In this paper, we study the value of the TMR as a function of the applied voltage Va in the single as well as double barrier magnetic tunnel junctions (SMTJ & DMTJ, which are constructed from CoFeB/MgO interfaces) and numerically estimate the possible difference of the TMR-V a curves for negative and positive voltages in the homojunctions. As a result, we found that AVB may help to determine the exact values of Fermi wave vectors for minority and majority conducting spin sub-bands. Moreover, significant asymmetry of the experimental TMR-Va curves, which arises due to different annealing regimes, is explained by different heights of the tunnel barriers and values of the spin asymmetry. The numerical TMR-V a data are in good agreement with experimental ones. © 2011 IEEE.

  14. Antenna-Coupled Superconducting Tunnel Junctions with Single-Electron Transistor Readout for Detection of Sub-mm Radiation

    Science.gov (United States)

    Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Stahle, C. M.; Wollack, E. J.; Schoelkopf, R. J.; Teufel, J.; Krebs, Carolyn (Technical Monitor)

    2002-01-01

    Antenna-coupled superconducting tunnel junction detectors have the potential for photon-counting sensitivity at sub-mm wavelengths. The device consists of an antenna structure to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure currents through tunnel junction contacts to the absorber volume. We will describe optimization of device parameters, and recent results on fabrication techniques for producing devices with high yield for detector arrays. We will also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

  15. Method for producing edge geometry superconducting tunnel junctions utilizing an NbN/MgO/NbN thin film structure

    Science.gov (United States)

    Hunt, Brian D. (Inventor); Leduc, Henry G. (Inventor)

    1992-01-01

    A method for fabricating an edge geometry superconducting tunnel junction device is discussed. The device is comprised of two niobium nitride superconducting electrodes and a magnesium oxide tunnel barrier sandwiched between the two electrodes. The NbN electrodes are preferably sputter-deposited, with the first NbN electrode deposited on an insulating substrate maintained at about 250 C to 500 C for improved quality of the electrode.

  16. Electronic transport through EuO spin-filter tunnel junctions

    KAUST Repository

    Jutong, Nuttachai

    2012-11-12

    Epitaxial spin-filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide (EuO) are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore, we also discuss the relation between the spin transport properties and the Cu-EuO interface geometry. The level alignment of the junction is sensitively affected by the interface spacing, since this determines the charge transfer between EuO and the Cu electrodes. Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect spin filter, with a spin polarization of the current close to 100%, and with both the Eu-5d conduction-band and the Eu-4f valence-band states contributing to the coherent transport. For epitaxial EuO on Cu, a symmetry filtering is observed, with the Δ1 states dominating the transmission. This leads to a transport gap larger than the fundamental EuO band gap. Importantly, the high spin polarization of the current is preserved up to large bias voltages.

  17. Tunneling Conductance in a Normal Metal/Ferromagnetic Superconductor Nano-Junction at a Finite Temperature

    Institute of Scientific and Technical Information of China (English)

    Hamidreza Emamipour; M.R. Abolhassani

    2011-01-01

    In this study, we investigate the tunneling conductance at a finite temperature in a normal metal/ferromagnetic superconductor nano-junction where the ferromagnetic superconductor (FS) is in three different cooper pairing states: spin singlet s-wave pairing (SWP), spin triplet opposite spin pairing (OSP), and spin triplet equal spin pairing (ESP) while including Fermi wave mismatch (FWM) and effective mass mismatch (EMM) in two sides of the nano-junction. We find that the conductance shows clearly different behaviors all depending on the symmetries of cooper pairing in a manner that the conductance spectra shows a gap-like structure, two interior dips structure and zero bias peak for SWP, OSP, and ESP, respectively. Also, the effective FS gap (Δeff) is a linear and decreasing function of exchange field. The slope of (Δeff) versus exchange field for OSP is twice the SWP. Thus, we can determine the spin polarization of N/FS nano-junction based on the dependence of (Δeff) to exchange field.

  18. Hybrid Tunnel Junction-Graphene Transparent Conductive Electrodes for Nitride Lateral Light Emitting Diodes.

    Science.gov (United States)

    Wang, Liancheng; Cheng, Yan; Liu, Zhiqiang; Yi, Xiaoyan; Zhu, Hongwei; Wang, Guohong

    2016-01-20

    Graphene transparent conductive electrode (TCE) applications in nitride light emitting diodes (LEDs) are still limited by the large contact resistance and interface barrier between graphene and p-GaN. We propose a hybrid tunnel junction (TJ)-graphene TCE approach for nitride lateral LEDs theoretically and experimentally. Through simulation using commercial advanced physical models of semiconductor devices (APSYS), we found that low tunnel resistance can be achieved in the n(+)-GaN/u-InGaN/p(+)-GaN TJ, which has a lower tunneling barrier and an enhanced electric field due to the polarization effect. Graphene TCEs and hybrid graphene-TJ TCEs are then modeled. The designed hybrid TJ-graphene TCEs show sufficient current diffusion length (Ls), low introduced series resistance, and high transmittance. The assembled TJ LED with the triple-layer graphene (TLG) TCEs show comparable optoelectrical performance (3.99 V@20 mA, LOP = 10.8 mW) with the reference LED with ITO TCEs (3.36 V@20 mA, LOP = 12.6 mW). The experimental results further prove that the TJ-graphene structure can be successfully incorporated as TCEs for lateral nitride LEDs.

  19. Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces

    Science.gov (United States)

    Ngo, Thach D. N.; Chang, Jung-Won; Lee, Kyujoon; Han, Seungju; Lee, Joon Sung; Kim, Young Heon; Jung, Myung-Hwa; Doh, Yong-Joo; Choi, Mahn-Soo; Song, Jonghyun; Kim, Jinhee

    2015-08-01

    Complex oxide systems have attracted considerable attention because of their fascinating properties, including the magnetic ordering at the conducting interface between two band insulators, such as LaAlO3 and SrTiO3. However, the manipulation of the spin degree of freedom at the LaAlO3/SrTiO3 heterointerface has remained elusive. Here, we have fabricated hybrid magnetic tunnel junctions consisting of Co and LaAlO3/SrTiO3 ferromagnets with the insertion of a Ti layer in between, which clearly exhibit magnetic switching and the tunnelling magnetoresistance effect below 10 K. The magnitude and sign of the tunnelling magnetoresistance are strongly dependent on the direction of the rotational magnetic field parallel to the LaAlO3/SrTiO3 plane, which is attributed to a strong Rashba-type spin-orbit coupling in the LaAlO3/SrTiO3 heterostructure. Our study provides a further support for the existence of the macroscopic ferromagnetism at LaAlO3/SrTiO3 heterointerfaces and opens a novel route to realize interfacial spintronics devices.

  20. Optimized electrode configuration for current-in-plane characterization of magnetic tunnel junction stacks

    Science.gov (United States)

    Cagliani, A.; Kjær, D.; Østerberg, F. W.; Hansen, O.; Nielsen, P. F.; Petersen, D. H.

    2017-02-01

    The current-in-plane tunneling technique (CIPT) has been a crucial tool in the development of magnetic tunnel junction stacks suitable for magnetic random access memories (MRAM) for more than a decade. The MRAM development has now reached the maturity to make the transition from the R&D phase to the pilot production phase. This will require an improvement in the repeatability of the CIPT metrology technique. Here, we present an analytical model that can be used to simulate numerically the repeatability of a CIPT measurement for an arbitrary MTJ stack prior to any CIPT measurement. The model describes mathematically the main sources of error arising when a micro multi-electrode probe is used to perform a CIPT measurement. The numerically simulated repeatability values obtained on four different MTJ stacks are verified by experimental data and the model is used to optimize the choice of electrodes on a multi-electrode probe to reach up to 36% improvement on the repeatability for the resistance area product and the tunneling magnetoresistance measurement, without any hardware modification.

  1. Vortex domain structures and dc current dependence of magneto-resistances in magnetic tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Wei Hong-Xiang; Lu Qing-Feng; Zhao Su-Fen; Zhang Xie-Qun; Feng Jia-Feng; Han Xiu-Feng

    2004-01-01

    Microfabrication and the magneto-transport characteristics of the magnetic tunnel junctions (MTJs) with a spin-valve-type structure of Ta (5nm)/Ni7gFe21 (25nm)/Ir22Mn78 (12nm)/Co75Fe25 (4nm)/Al(0.8nm) oxide/Co75Fe25(4nm)/Ni7gFe21 (20nm)/Ta(5nm) were investigated in this paper. A series of experimental data measured with a MTJ was used to verify a magnon-assisted tunnelling model and theory. Furthermore, a micromagnetics simulation shows that the butterfly-like vortex domain structures can be formed under a current-induced Oersted field, which decreases the net magnetization values of the ferromagnetic electrodes under a large dc current (i.e., in high voltage regimes). It is one of the main reasons for the tunnel magnetoresistance ratios to decrease significantly at high voltage biasing.

  2. A physics-based compact model of ferroelectric tunnel junction for memory and logic design

    Science.gov (United States)

    Wang, Zhaohao; Zhao, Weisheng; Kang, Wang; Bouchenak-Khelladi, Anes; Zhang, Yue; Zhang, Youguang; Klein, Jacques-Olivier; Ravelosona, Dafiné; Chappert, Claude

    2014-01-01

    Ferroelectric tunnel junction (FTJ) is able to store non-volatile data in the spontaneous polarization direction of ferroelectric tunnel barrier. Recent progress has demonstrated its great potential to build up the next generation non-volatile memory and logic (NVM and NVL) thanks to the high OFF/ON resistance ratio, fast operation speed, low write power, non-destructive readout and so on. In this paper, we present the first physics-based compact model for Co/BTO/LSMO FTJ nanopillar, which was reported experimentally to exhibit excellent NVM performance. This model integrates related physical models of tunnel resistance, static switching voltage and dynamic switching delay. Its accuracy is shown by the good agreement between numerical model simulation and experimental measurements. This compact model has been developed in Verilog-A language and validated by single-cell simulation on Cadence Virtuoso Platform. Hybrid simulations based on 40 nm-technology node of FTJ memory arrays and non-volatile full adder were performed to demonstrate the efficiency of our compact model for the simulation and analysis of CMOS/FTJ integrated circuits.

  3. Model for the fine structure of zero field steps in long Josephson tunnel junctions and its comparison with experiment

    DEFF Research Database (Denmark)

    Barbara, Paola; Monaco, R.; Ustinov, A. V.

    1996-01-01

    The single fluxon dynamics in the resonant regime has been investigated on high-quality low-loss Nb/Al–AlOx/Nb window Josephson tunnel junctions. A new model accounting for the fine structure of zero field steps in linear junctions is proposed. Depending on the fluxon velocity and on the junction...... simulations, and experiments. The presence of the idle region has been proved to play a determinant role for the occurrence of the fine structure. ©1996 American Institute of Physics....

  4. Sub-nanometer atomic layer deposition for spintronics in magnetic tunnel junctions based on graphene spin-filtering membranes.

    Science.gov (United States)

    Martin, Marie-Blandine; Dlubak, Bruno; Weatherup, Robert S; Yang, Heejun; Deranlot, Cyrile; Bouzehouane, Karim; Petroff, Frédéric; Anane, Abdelmadjid; Hofmann, Stephan; Robertson, John; Fert, Albert; Seneor, Pierre

    2014-08-26

    We report on the successful integration of low-cost, conformal, and versatile atomic layer deposited (ALD) dielectric in Ni–Al2O3–Co magnetic tunnel junctions (MTJs) where the Ni is coated with a spin-filtering graphene membrane. The ALD tunnel barriers, as thin as 0.6 nm, are grown layer-by-layer in a simple, low-vacuum, ozone-based process, which yields high-quality electron-transport barriers as revealed by tunneling characterization. Even under these relaxed conditions, including air exposure of the interfaces, a significant tunnel magnetoresistance is measured highlighting the robustness of the process. The spin-filtering effect of graphene is enhanced, leading to an almost fully inversed spin polarization for the Ni electrode of −42%. This unlocks the potential of ALD for spintronics with conformal, layer-by-layer control of tunnel barriers in magnetic tunnel junctions toward low-cost fabrication and down-scaling of tunnel resistances.

  5. 600 GHz resonant mode in a parallel array of Josephson tunnel junctions connected by superconducting microstrip lines

    DEFF Research Database (Denmark)

    Kaplunenko, V. K.; Larsen, Britt Hvolbæk; Mygind, Jesper;

    1994-01-01

    The high frequency properties of the one-dimensional transmission line consisting of a parallel array of resistively shunted Josephson tunnel junctions have been studied in the limit of relatively low damping where this nonlinear system exhibits new and interesting phenomena. Here we report...

  6. Self-assembled monolayers of terminal acetylenes as replacements for thiols in bottom-up tunneling junctions

    NARCIS (Netherlands)

    Fracasso, Davide; Kumar, Sumit; Rudolf, Petra; Chiechi, Ryan C.

    2014-01-01

    Why use thiols in Molecular Electronics? They stink, oxidize readily, poison catalysts, and often require nontrivial protection/deprotection chemistry. In this communication we demonstrate the fabrication of tunneling junctions formed by contact of self-assembled monolayers (SAMs) of terminal alkyne

  7. Field-induced inversion of resonant tunneling currents through single molecule junctions and the directional photo-electric effect

    Science.gov (United States)

    Kuperman, Maayan; Peskin, Uri

    2017-03-01

    It has been known for several decades that the electric current through tunneling junctions is affected by irradiation. In particular, photon-assisted currents by asymmetric irradiation of the two leads was demonstrated and studied extensively in tunneling junctions of different compositions and for different radiation wavelengths. In this work, this phenomenon is revisited in the context of single molecule junctions. Restricting the theoretical discussion to adiabatic periodic driving of one lead with respect to the other within a non-interacting electron formulation, the main features of specific molecules are encoded in the discrete electronic energy levels. The detailed level structure of the molecule is shown to yield new effects in the presence of asymmetric driving of the leads. In particular, when the field-free tunneling process is dominated by a single electronic level, the electric current can be suppressed to zero or flow against the direction of an applied static bias. In the presence of a second electronic level, a directional photo-electric effect is predicted, where not only the magnitude but also the direction of the steady state electric current through the tunneling junction can be changed by a monotonous increase of the field intensity. These effects are analyzed and explained by outlying the relevant theory, using analytic expressions in the wide-band limit, as well as numerical simulations beyond this limit.

  8. Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Yang, G.; Li, D. L.; Wang, S. G., E-mail: Sgwang@iphy.ac.cn; Ma, Q. L.; Liang, S. H.; Wei, H. X.; Han, X. F. [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Hesjedal, T.; Ward, R. C. C. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Kohn, A.; Elkayam, A.; Tal, N. [Department of Materials Engineering and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Zhang, X.-G. [Department of Physics and Quantum Theory Project, University of Florida, Gainesville, Florida 32611 (United States); Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493 (United States)

    2015-02-28

    Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.

  9. Tunneling conductance in quantum wire/insulator/d_(x~2-y~2)+id_(xy) mixed wave superconductor junctions

    Institute of Scientific and Technical Information of China (English)

    Wei Jian-Wen

    2009-01-01

    Using the extended Blonder-Tinkham-Klapwijk(BTK)theory, this paper calculates the tunnelling conductance in quantum wire/insulator/d_(x~2-y~2)+id_(xy) mixed wave superconductor(q/I/d_(x~2-y~2)+id_(xy))junctions That is different from the case in d-and p-wave superconductor junctions. When the angle α between a-axis of the d_(x~2-y~2) wave superconductor and the interface normal is π/4, there follows a rather distinctive tunnelling conductance. The zero-bias conductance peak(ZBCP)may or may not appear in the tunnelling conductance. Both the interface potential z and the quasi-particle lifetime factor [F]are smaller, there is no ZBCP. Otherwise, the ZBCP will appear. The position otbias conductance peak(BCP)depends strongly on the amplitude ratio of two components for d_(x~2-y~2)+id_(xy) mixed wave. The low and narrow ZBCP may coexist with the BCP in the tunnelling conductance. Using those features in the tunnelling conductance of q/I/d_(x~2-y~2)+id_(xy) junctions, it can distinguish d_(x~2-y~2)+id_(xy) mixed wave superconductor from d-and p-wave one.

  10. Magnetic Tunnel Junction-Based On-Chip Microwave Phase and Spectrum Analyzer

    Science.gov (United States)

    Fan, Xin; Chen, Yunpeng; Xie, Yunsong; Kolodzey, James; Wilson, Jeffrey D.; Simons, Rainee N.; Xiao, John Q.

    2014-01-01

    A magnetic tunnel junction (MTJ)-based microwave detector is proposed and investigated. When the MTJ is excited by microwave magnetic fields, the relative angle between the free layer and pinned layer alternates, giving rise to an average resistance change. By measuring the average resistance change, the MTJ can be utilized as a microwave power sensor. Due to the nature of ferromagnetic resonance, the frequency of an incident microwave is directly determined. In addition, by integrating a mixer circuit, the MTJ-based microwave detector can also determine the relative phase between two microwave signals. Thus, the MTJ-based microwave detector can be used as an on-chip microwave phase and spectrum analyzer.

  11. Probing the Influence of Thermal Spin Torque on Magnetic Tunnel Junction Switching

    Science.gov (United States)

    Phung, Timothy; Pushp, Aakash; Rettner, Charles; Hughes, Brian; Yang, See-Hun; Parkin, Stuart

    2013-03-01

    It has been established in the past few years that heat flow within a ferromagnet can induce a spin current and an associated voltage. This so called Spin Seebeck effect, initially reported in ferromagnetic metals, has also been observed in magnetic semiconductors, magnetic insulators as well as in strongly spin orbit coupled systems. An open question has been whether heat induced spin currents can be used in switching a magnetic tunnel junction (MTJ) via thermal spin torque (TST). In order to answer this question, we investigate the MTJ switching with TST induced by sharp temperature gradients on the order of 1-10 K/nm. We will describe our experimental setup and present data that show the various roles that temperature plays on the saturation magnetization of the material and on the induced spin currents that influence MTJ switching.

  12. Superconducting tunnel junction array development for high-resolution energy-dispersive x-ray spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Barfknecht, A. T.; Cramer, S. P; Frank, M.; Friedrich, S.; Hiller, L. J.; Labov, S. E.; Mears, C. A.; Niderost, B.

    1998-07-01

    Cryogenic energy-dispersive x-ray detectors are being developed because of their superior energy resolution ((less than or equal to) 10 eV FWHM for keV x rays) compared to semiconductor EDS systems. So far, their range of application is limited due to their comparably small size and low count rate. We present data on the development of superconducting tunnel junction (STJ) detector arrays to address both of these issues. A single STJ detector has a resolution around 10 eV below 1 keV and can be operated at count rates of order 10,000 counts/s. We show that the simultaneous operation of several STJ detectors does not diminish their energy resolution significantly, while increasing the detector area and the maximum count rate by a factor given by the total number of independent channels.

  13. Promising X-ray fluorescent tests for superconducting tunnel junction detector

    Energy Technology Data Exchange (ETDEWEB)

    Friedrich, Stephan; Robinson, Art

    2001-01-11

    Scientists in the Physical Biosciences Division of the Ernest Orlando Berkeley National Laboratory (Berkeley Lab) studying transition metals in proteins with fluorescence-detected L-edge absorption spectroscopy have found the measurements to be extremely challenging. The difficulty is that the metal centers are present in very dilute concentrations so that their weak fluorescence is often obscured by strong background signals from carbon and oxygen. To solve this problem, the Berkeley group has been working with researchers from the Advanced Detector Group at the Lawrence Livermore National Laboratory on an energy-dispersive superconducting tunnel junction x-ray detector. These devices in principle have the energy resolution needed to reveal the metal signal. The most recent results with the latest version of the detector on Beamline 4.0.1-2 at the Advanced Light Source (ALS) illustrate the promise of the cryogenic detector strategy not only for this application but also for spectroscopy of other types of dilute samples.

  14. Detection of HIV-1 antigen based on magnetic tunnel junction sensor and magnetic nanoparticles

    CERN Document Server

    Li, L; Zhou, Y; Pong, P W T

    2016-01-01

    In recent years, it is evidenced that the individuals newly infected HIV are transmitting the virus prior to knowing their HIV status. Identifying individuals that are early in infection with HIV antibody negative (window period) remains problematic. In the newly infected individuals, HIV antigen p24 is usually present in their serum or plasma 7-10 days before the HIV antibody. After antibody production initiates, the p24 antigen is bound into immune complexes. That means the detectable p24 antigens in serum/plasma are short-lived, and their amount is in the pg/ml range. Thus, a rapid quantitative bio-detection system with high-sensitivity is required to achieve early disease diagnosis. Magnetoresistive (MR) biosensor with ultra-high sensitivity possesses great potential in this area. In this study, a p24 detection assay using MgO-based magnetic tunnel junction (MTJ) sensor and 20-nm magnetic nanoparticles is reported.

  15. Bias dependence of the response of superconducting tunnel junctions used as photon detectors

    CERN Document Server

    Poelaert, A; Peacock, A; Kozorezov, A; Wigmore, J K

    2000-01-01

    In the last decade, several research groups have developed superconducting tunnel junctions (STJ) for photon detection in astronomy. Despite extensive studies, the behavior of multi-layered devices, subject to the superconducting proximity effect (proximized devices), has remained difficult to model. Recently, a new model has been presented, leading to a more realistic approach for the photon detection within an STJ. This model is based on the existence of local traps in the superconducting electrodes of the STJ. In this paper, we show that the new model is successful in predicting the bias dependence of the response of an STJ. The bias dependence also demonstrates that the quasiparticles, i.e. the charge carriers created as a result of the photon absorption process, cannot relax down to the superconducting energy gap. This result is important, since most theoretical developments to date (implicitly) assume that quasiparticle relax to the gap energy. crystal-structure; energy-levels; tantalum-; traps cooper-p...

  16. Analytical solution of the Boltzmann-Poisson equation and its application to MIS tunneling junctions

    Institute of Scientific and Technical Information of China (English)

    Zhang Li-Zhi; Wang Zheng-Chuan

    2009-01-01

    In order to consider quantum transport under the influence of an electron-electron (e-e) interaction in a mesoscopic conductor, the Boltzmann equation and Poisson equation are investigated jointly. The analytical expressions of the distribution function for the Boltzmann equation and the self-consistent average potential concerned with e-e interaction are obtained, and the dielectric function appearing in the self-consistent average potential is naturally generalized beyond the Thomas-Fermi approximation. Then we apply these results to the tunneling junctions of a metal-insulatorsemiconductor (MIS) in which the electrons are accumulated near the interface of the semiconductor, and we find that the e-e interaction plays an important role in the transport procedure of this system. The electronic density, electric current as well as screening Coulombic potential in this case are studied, and we reveal the time and position dependence of these physical quantities explicitly affected by the e-e interaction.

  17. Interfacial spin-orbit splitting and current-driven spin torque in anisotropic tunnel junctions

    KAUST Repository

    Manchon, Aurelien

    2011-05-17

    Spin transport in magnetic tunnel junctions comprising a single magnetic layer in the presence of interfacial spin-orbit interaction (SOI) is investigated theoretically. Due to the presence of interfacial SOI, a current-driven spin torque can be generated at the second order in SOI, even in the absence of an external spin polarizer. This torque possesses two components, one in plane and one perpendicular to the plane of rotation, that can induce either current-driven magnetization switching from an in-plane to out-of-plane configuration or magnetization precessions, similar to spin transfer torque in spin valves. Consequently, it appears that it is possible to control the magnetization steady state and dynamics by either varying the bias voltage or electrically modifying the SOI at the interface.

  18. Short-Term Plasticity and Long-Term Potentiation in Magnetic Tunnel Junctions: Towards Volatile Synapses

    Science.gov (United States)

    Sengupta, Abhronil; Roy, Kaushik

    2016-02-01

    Synaptic memory is considered to be the main element responsible for learning and cognition in humans. Although traditionally nonvolatile long-term plasticity changes are implemented in nanoelectronic synapses for neuromorphic applications, recent studies in neuroscience reveal that biological synapses undergo metastable volatile strengthening followed by a long-term strengthening provided that the frequency of the input stimulus is sufficiently high. Such "memory strengthening" and "memory decay" functionalities can potentially lead to adaptive neuromorphic architectures. In this paper, we demonstrate the close resemblance of the magnetization dynamics of a magnetic tunnel junction (MTJ) to short-term plasticity and long-term potentiation observed in biological synapses. We illustrate that, in addition to the magnitude and duration of the input stimulus, the frequency of the stimulus plays a critical role in determining long-term potentiation of the MTJ. Such MTJ synaptic memory arrays can be utilized to create compact, ultrafast, and low-power intelligent neural systems.

  19. Observation of thermal spin-transfer torque via ferromagnetic resonance in magnetic tunnel junctions

    Science.gov (United States)

    Zhang, Zhaohui; Bai, Lihui; Chen, Xiaobin; Guo, Hong; Fan, X. L.; Xue, D. S.; Houssameddine, D.; Hu, C.-M.

    2016-08-01

    The thermal spin-transfer torque (TSTT) in magnetic tunneling junctions (MTJs) was systematically studied using electrical detection of ferromagnetic resonance (FMR). Evidence for the existence of TSTT in MTJs is observed. A temperature difference was applied across an MTJ acting as a TSTT on the free layer of the MTJ. The FMR of the free layer was then excited by a microwave current and electrically detected as a dc voltage. We found that the FMR line shape was changed by the TSTT, indicated by the ratio of dispersive and Lorentz components of the FMR spectra (D /L ). D /L increases by increasing the temperature difference. In addition, we analyze the magnetization orientation dependence of TSTT and provide solid evidence that this dependence differs from the magnetization orientation dependence of spin-transfer torque driven by a dc bias.

  20. Fabrication of superconducting tunnel junctions with embedded coil for applying magnetic field

    Science.gov (United States)

    Yamaguchi, Kenji; Nakagawa, Hiroshi; Aoyagi, Masahiro; Naruse, Masato; Myoren, Hiroaki; Taino, Tohru

    2016-11-01

    We have proposed and demonstrated a superconducting tunnel junction (STJ) with an embedded coil for applying a magnetic field. The STJ was fabricated on the coil, which was embedded in a Si substrate. The coil in the Si substrate consists of superconducting microstrip lines and applies a magnetic field to the STJ to suppress the dc Josephson current. The embedded coil was designed with a line and space of 3 μm and a thickness of 120 nm. To planarize the coil, we employed chemical mechanical polishing (CMP) in our fabrication process. In this STJ, the maximum current of the embedded coil was 28 mA, which corresponded to the maximum magnetic field of 11.76 mT.

  1. Confined State and Electronic Transport in an Artificial Graphene-Based Tunnel Junction

    Institute of Scientific and Technical Information of China (English)

    袁建辉; 张建军; 曾奇军; 张俊佩; 成泽

    2011-01-01

    Artificial graphene structures embedded in semiconductors could open novel routes for studies of electron interactions in 1ow-dimensional systems. We propose a way to manipulate the transport properties of massless Dirac fermions in an artificial graphene-based tunnel junction. Velocity-modulation control of electron wave propagation in the different regions can be regarded as velocity barriers. Transmission probability of electron is affected profoundly by this velocity barrier. We find that there is no confinement for Dirac electron as the velocity ratio ζ is less than 1, but when the velocity ratio is larger than 1 the confined state appears in the continuum band. These localized Dirac electrons may lead to the decreasing of transmission probability.

  2. Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Clément, P.-Y.; Baraduc, C., E-mail: claire.baraduc@cea.fr; Chshiev, M.; Diény, B. [Univ. Grenoble Alpes, INAC-SPINTEC, F-38000 Grenoble (France); CNRS, INAC-SPINTEC, F-38000 Grenoble (France); CEA, INAC-SPINTEC, F-38000 Grenoble (France); Ducruet, C. [Crocus-Technology, 5, Place Robert Schuman, F-38054 Grenoble (France); Vila, L. [Univ. Grenoble Alpes, INAC-SP2M, F-38000 Grenoble, France and CEA, INAC-SP2M, F-38000 Grenoble (France)

    2015-09-07

    Magnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pave the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated.

  3. Novel handheld magnetometer probe based on magnetic tunnelling junction sensors for intraoperative sentinel lymph node identification.

    Science.gov (United States)

    Cousins, A; Balalis, G L; Thompson, S K; Forero Morales, D; Mohtar, A; Wedding, A B; Thierry, B

    2015-06-03

    Using magnetic tunnelling junction sensors, a novel magnetometer probe for the identification of the sentinel lymph node using magnetic tracers was developed. Probe performance was characterised in vitro and validated in a preclinical swine model. Compared to conventional gamma probes, the magnetometer probe showed excellent spatial resolution of 4.0 mm, and the potential to detect as few as 5 μg of magnetic tracer. Due to the high sensitivity of the magnetometer, all first-tier nodes were identified in the preclinical experiments, and there were no instances of false positive or false negative detection. Furthermore, these preliminary data encourage the application of the magnetometer probe for use in more complex lymphatic environments, such as in gastrointestinal cancers, where the sentinel node is often in close proximity to other non-sentinel nodes, and high spatial resolution detection is required.

  4. Magnetic tunnel junction design margin exploration for self-reference sensing scheme.

    Science.gov (United States)

    Sun, Z; Li, H; Wang, X

    2012-04-01

    This work investigates the magnetic tunnel junction (MTJ) design requirements for the application of nondestructive self-reference sensing scheme, a novel sensing scheme featuring high tolerance of process variations, fast sensing speed, and no impact on device reliability. Unlike the conventional sensing scheme that requires a large TMR ratio and the uniform antiparallel and parallel resistances for MTJs, the nondestructive self-reference sensing scheme is more sensitive to the roll-off slope of MTJ's R-I or R-V curve. Our purpose is to provide a guidance to facilitate MTJ design used in the nondestructive self-reference scheme. In this work, we comprehensively investigate and analyze the design matrix by considering MTJ device physical properties, such as bias voltage dependent conductance, spin torque, etc. The manuscript suggests the approaches to optimize MTJ design for better trade-off between device properties and circuit design.

  5. Tunneling Conductance in Ferromagnetic Metal/Normal Metal/Spin-Singlet -Wave Ferromagnetic Superconductor Junctions

    Directory of Open Access Journals (Sweden)

    Hamidreza Emamipour

    2013-01-01

    Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.

  6. Magneto Seebeck effect in Co-Fe-B/MgO/Co-Fe-B tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Walter, Marvin; Walowski, Jakob; Zbarsky, Vladyslav; Muenzenberg, Markus [I. Physikalisches Institut, Universitaet Goettingen (Germany); Drewello, Volker; Ebke, Daniel; Reiss, Guenter; Thomas, Andy [Department of Physics, Bielefeld University (Germany); Peretzki, Patrick; Seibt, Michael [IV. Physikalisches Institut, Universitaet Goettingen (Germany); Czerner, Michael; Bachmann, Michael; Heiliger, Christian [I. Physikalisches Institut, Universitaet Giessen (Germany)

    2011-07-01

    Co-Fe-B/MgO/Co-Fe-B devices showing a giant TMR effect are possible candidates for the generation of spin-currents by thermal heating. We present the observation of a magneto Seebeck effect in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions (MTJs). The effects could be used for thermal spin-injection and thermally driven spin-transfer torque. The samples presented in this work consist of a minimal pseudo-spin-valve stack with sputtered Ta and Co-Fe-B layers and an e-beam evaporated MgO barrier. The MTJs are heated by a diode laser which achieves powers of up to 100 mW and is focused onto the sample in a standard confocal microscope setup. The heating is simulated by finite element methods and the experimental results are compared with ab initio calculations of the magneto-thermoelectric power and of the spin-Seebeck coefficient.

  7. Giant electrocaloric effect in asymmetric ferroelectric tunnel junctions at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yang, E-mail: liuyangphy52@gmail.com; Infante, Ingrid C.; Dkhil, Brahim, E-mail: brahim.dkhil@ecp.fr [Laboratoire Structures, Propriétés et Modélisation des Solides, UMR 8580 CNRS-Ecole Centrale Paris, Grande Voie des Vignes, Châtenay-Malabry Cedex 92295 (France); Lou, Xiaojie [Multi-disciplinary Materials Research Center, Frontier Institute of Science and Technology, and State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)

    2014-02-24

    Room-temperature electrocaloric properties of Pt/BaTiO{sub 3}/SrRuO{sub 3} ferroelectric tunnel junctions (FTJs) are studied by using a multiscale thermodynamic model. It is found that there is a divergence in the adiabatic temperature change ΔT for the two opposite polarization orientations. This difference under a typical writing voltage of 3 V can reach over 1 K as the barrier thickness decreases. Thanks to the ultrahigh external stimulus, a giant electrocaloric effect (1.53 K/V) with ΔT being over 4.5 K can be achieved at room temperature, which demonstrates the perspective of FTJs as a promising solid-state refrigeration.

  8. Origins of large light induced voltage in magnetic tunnel junctions grown on semiconductor substrates

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Y.; Lin, W.; Petit-Watelot, S.; Hehn, M.; Rinnert, H.; Lu, Y.; Montaigne, F.; Lacour, D.; Andrieu, S.; Mangin, S., E-mail: stephane.mangin@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine- BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex (France)

    2016-01-14

    Recently, the study of interactions between electron spins and heat currents has given rise to the field of “Spin Caloritronics”. Experimental studies of these interactions have shown a possibility to combine the use of heat and light to power magnetic tunnel junction (MTJ) devices. Here we present a careful study of an MTJ device on Si substrate that can be powered entirely by light. We analyze the influence of the material properties, device geometry, and laser characteristics on the electric response of the sample. We demonstrate that by engineering the MTJ and its electrical contact, a large photovoltage reaching 100 mV can be generated. This voltage originates from the Si substrate and depends on the MTJ magnetic configuration. Finally, we discuss the origin of the photo-voltage in terms of Seebeck and photovoltaic effects.

  9. Tunnel Junctions between Metals and Magnetic Perovskites and their use in Spin Polarized Spectroscopy

    Science.gov (United States)

    Mieville, Laurent; Worledge, Daniel; Geballe, Theodore H.; Char, Kookrin

    1998-03-01

    The recently reported "colossal" magnetoresistance (CMR) effect in (La_1-xA_x)MnO3 (where A stands for alkaline earth element) has shed new light on the magnetic properties exhibited by some members of the perovskite family with the generic formula ABO_3. We have studied the interface resistance between metals (Al, Nb and Pd) and magnetic perovskites ((La_0.66Sr_0.34)MnO_3, SrRuO3 and (La_0.5Sr_0.5)CoO_3) thin films grown by pulsed laser deposition. Low temperature measurements of tunnel junctions which aim to measure directly the amount of spin polarized carriers present in these perovskites will be also reviewed.

  10. Nanoscale electroluminescence from n-type GaAs(110) in tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Guo, X L; Fujita, D; Niori, N; Keisuke, S; Onishi, K [Advanced Nanocharacterization Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)

    2007-05-16

    Nanoscale electroluminescence (EL) was induced from n-type GaAs(110) in tunnel junctions using an indium tin oxide (ITO)-coated optical fibre probe at both polarities, room temperature (RT), and 80 K. The quantum efficiency of photon emission at negative bias is much higher than at positive bias at both RT and 80 K. A high quantum efficiency of about {approx}10{sup -4}(photons/electron) was achieved at 80 K. The well-defined optical spectra exhibit two-peak features at 1.49 and 1.39 eV which are generated by the radiative recombination of hole-electron pairs over the direct band gap and surface states, respectively.

  11. Electronic band alignment and electron transport in Cr/BaTiO{sub 3}/Pt ferroelectric tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Zenkevich, A. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Minnekaev, M.; Matveyev, Yu.; Lebedinskii, Yu. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Bulakh, K.; Chouprik, A.; Baturin, A. [Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Maksimova, K. [Immanuel Kant Baltic Federal University, 236041 Kaliningrad (Russian Federation); Thiess, S.; Drube, W. [Deutsches Elektronen-Synchrotron DESY, D-22603 Hamburg (Germany)

    2013-02-11

    Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO{sub 3}(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO{sub 3}/Pt junctions with a sub-{mu}m Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of {approx}30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO{sub 3}/Pt (Cr/BaTiO{sub 3}) interface +0.42(-0.03) eV following downward to upward polarization reversal.

  12. Use of a Superconducting Tunnel Junction for X-Ray Fluorescence Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hiller, L

    2001-03-06

    A superconducting tunnel junction (STJ) in combination with a superconducting absorber of radiation may function as a highly resolving x-ray spectrometer. Electronic excitations, or quasiparticles, are created when a superconductor absorbs an x ray and are detected as an excess tunnel current through the junction. The number of quasiparticles created and the magnitude of the excess current is proportional to the energy of the absorbed x ray. This is similar to existing semiconductor-based spectrometers that measure electron-hole pairs, but with 1000 times more excitations. The energy measurement therefore can be up to 30 times more precise with a superconducting detector than with a semiconductor detector. This work describes the development and testing of an STJ spectrometer design for x-ray fluorescence applications. First, the basic principles of the STJ spectrometer are explained. This is followed by detailed simulations of the variance in the number of quasiparticles produced by absorption of an x ray. This variance is inherent in the detector and establishes an upper limit on the resolving power of the spectrometer. These simulations include effects due to the materials used in the spectrometer and to the multilayer structure of the device. Next, the spectrometer is characterized as functions of operating temperature, incident x-ray energy, and count rate. Many of these tests were performed with the spectrometer attached to a synchrotron radiation port. Finally, example x-ray fluorescence spectra of materials exposed to synchrotron radiation are presented. These materials are of interest to semiconductor processing and structural biology, two fields that will benefit immediately from the improved resolving power of the STJ spectrometer.

  13. BEOL compatible high tunnel magneto resistance perpendicular magnetic tunnel junctions using a sacrificial Mg layer as CoFeB free layer cap

    Energy Technology Data Exchange (ETDEWEB)

    Swerts, J., E-mail: Johan.Swerts@imec.be; Mertens, S.; Lin, T.; Couet, S.; Tomczak, Y.; Sankaran, K.; Pourtois, G.; Kim, W.; Meersschaut, J.; Souriau, L.; Radisic, D.; Van Elshocht, S.; Kar, G.; Furnemont, A. [imec, Kapeldreef 75, Leuven 3001 (Belgium)

    2015-06-29

    Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface of the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-induced damage during the Ta deposition. The Ta-capped CoFeB free layer using the sacrificial Mg interlayer has significantly better electrical and magnetic properties than the equivalent stack without protective layer. We demonstrate a tunnel magneto resistance increase up to 30% in bottom pinned magnetic tunnel junctions and tunnel magneto resistance values of 160% at resistance area product of 5 Ω.μm{sup 2}. Moreover, the free layer maintains perpendicular magnetic anisotropy after 400 °C annealing.

  14. BEOL compatible high tunnel magneto resistance perpendicular magnetic tunnel junctions using a sacrificial Mg layer as CoFeB free layer cap

    Science.gov (United States)

    Swerts, J.; Mertens, S.; Lin, T.; Couet, S.; Tomczak, Y.; Sankaran, K.; Pourtois, G.; Kim, W.; Meersschaut, J.; Souriau, L.; Radisic, D.; Van Elshocht, S.; Kar, G.; Furnemont, A.

    2015-06-01

    Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface of the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-induced damage during the Ta deposition. The Ta-capped CoFeB free layer using the sacrificial Mg interlayer has significantly better electrical and magnetic properties than the equivalent stack without protective layer. We demonstrate a tunnel magneto resistance increase up to 30% in bottom pinned magnetic tunnel junctions and tunnel magneto resistance values of 160% at resistance area product of 5 Ω.μm2. Moreover, the free layer maintains perpendicular magnetic anisotropy after 400 °C annealing.

  15. Perpendicular magnetic tunnel junctions with a synthetic storage or reference layer: A new route towards Pt- and Pd-free junctions

    Science.gov (United States)

    Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Prejbeanu, Ioan L.; Dieny, Bernard

    2016-02-01

    We report here the development of Pt and Pd-free perpendicular magnetic tunnel junctions (p-MTJ) for STT-MRAM applications. We start by studying a p-MTJ consisting of a bottom synthetic Co/Pt reference layer and a synthetic FeCoB/Ru/FeCoB storage layer covered with an MgO layer. We first investigate the evolution of RKKY coupling with Ru spacer thickness in such a storage layer. The coupling becomes antiferromagnetic above 0.5 nm and its strength decreases monotonously with increasing Ru thickness. This contrasts with the behavior of Co-based systems for which a maximum in interlayer coupling is generally observed around 0.8 nm. A thin Ta insertion below the Ru spacer considerably decreases the coupling energy, without basically changing its variation with Ru thickness. After optimization of the non-magnetic and magnetic layer thicknesses, it appears that such a FeCoB/Ru/FeCoB synthetic storage layer sandwiched between MgO barriers can be made stable enough to actually be used as hard reference layer in single or double magnetic tunnel junctions, the storage layer being now a single soft FeCoB layer. Finally, we realize Pt- or Pd-free robust perpendicular magnetic tunnel junctions, still keeping the advantage of a synthetic reference layer in terms of reduction of stray fields at small pillar sizes.

  16. Oscillatory behavior of the tunnel magnetoresistance due to thickness variations in Ta|CoFe|MgO magnetic tunnel junctions: A first-principles study

    Science.gov (United States)

    Sankaran, K.; Swerts, J.; Couet, S.; Stokbro, K.; Pourtois, G.

    2016-09-01

    To investigate the impact of both the CoFe ferromagnetic layer thickness and the capping paramagnetic layer on the tunnel magnetoresistance (TMR), we performed first-principles simulations on epitaxial magnetic tunnel junctions contacted with either CoFe or Ta paramagnetic capping layers. We observed a strong oscillation of the TMR amplitude with respect to the thickness of the ferromagnetic layer. The TMR is found to be amplified whenever the MgO spin tunnel barrier is thickened. Quantization of the electronic structure of the ferromagnetic layers is found to be at the origin of this oscillatory behavior. Metals such as Ta contacting the magnetic layer are found to enhance the amplitude of the oscillations due to the occurrence of an interface dipole. The latter drives the band alignment and tunes the nature of the spin channels that are active during the tunneling process. Subsequently, the regular transmission spin channels are modulated in the magnetic tunnel junction stack and other complex ones are being activated.

  17. Massive Dirac fermion transport in a gapped graphene-based magnetic tunnel junction

    Science.gov (United States)

    Soodchomshom, Bumned; Tang, I.-Ming; Hoonsawat, Rassmidara

    2009-08-01

    The spin transport in a graphene-based magnetic (NG/ferromagnetic barrier (FB)/NG) tunnel junction with the graphene sheet being grown on a SiC substrate is investigated. Zhou et al. [Nat. Mater. 6 (2007) 770] has shown that in these epitaxial grown graphene sheets, the electrons behave like massive relativistic particles with an energy gap of 2 Δ∼260 meV opening up in the energy spectrum of the massive relativistic electron. Basing on assumption that gap in graphene can occur under the influence of the magnetic field, we find that in the case of thick ferromagnetic graphene barriers, the electronic gap causes the barrier to behave as a strong insulator when the gate potential is in the range 400-130 meVswitched from a 100% spin up current to a 100% spin down current by small variation of V G from V G E f , the features of a perfect spin filtering electronic junction.

  18. Proximity effect in planar superconducting tunnel junctions containing Nb/NiCu superconductor/ferromagnet bilayers

    Science.gov (United States)

    Pepe, G. P.; Latempa, R.; Parlato, L.; Ruotolo, A.; Ausanio, G.; Peluso, G.; Barone, A.; Golubov, A. A.; Fominov, Ya. V.; Kupriyanov, M. Yu.

    2006-02-01

    We present experimental results concerning both the fabrication and characterization of superconducting tunnel junctions containing superconductor/ferromagnet (S/F) bilayers made by niobium (S) and a weak ferromagnetic Ni0.50Cu0.50 alloy. Josephson junctions have been characterized down to T=1.4K in terms of current-voltage I - V characteristics and Josephson critical current versus magnetic field. By means of a numerical deconvolution of the I - V data the electronic density of states on both sides of the S/F bilayer has been evaluated at low temperatures. Results have been compared with theoretical predictions from a proximity model for S/F bilayers in the dirty limit in the framework of Usadel equations for the S and F layers, respectively. The main physical parameters characterizing the proximity effect in the Nb/NiCu bilayer, such as the coherence length and the exchange field energy of the F metal, and the S/F interface parameters have been also estimated.

  19. Magnetotransport in MgO-based magnetic tunnel junctions grown by molecular beam epitaxy (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Andrieu, S., E-mail: stephane.andrieu@univ-lorraine.fr; Bonell, F.; Hauet, T.; Montaigne, F. [Institut Jean Lamour, Nancy University/CNRS, Bd des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy (France); Calmels, L.; Snoeck, E. [CEMES, CNRS and Toulouse University, 29 rue Jeanne Marvig, 31055 Toulouse (France); Lefevre, P.; Bertran, F. [Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette cedex (France)

    2014-05-07

    The strong impact of molecular beam epitaxy growth and Synchrotron Radiation characterization tools in the understanding of fundamental issues in nanomagnetism and spintronics is illustrated through the example of fully epitaxial MgO-based Magnetic Tunnel Junctions (MTJs). If ab initio calculations predict very high tunnel magnetoresistance (TMR) in such devices, some discrepancy between theory and experiments still exists. The influence of imperfections in real systems has thus to be considered like surface contaminations, structural defects, unexpected electronic states, etc. The influence of possible oxygen contamination at the Fe/MgO(001) interface is thus studied, and is shown to be not so detrimental to TMR as predicted by ab initio calculations. On the contrary, the decrease of dislocations density in the MgO barrier of MTJs using Fe{sub 1−x}V{sub x} electrodes is shown to significantly increase TMR. Finally, unexpected transport properties in Fe{sub 1−X}Co{sub x}/MgO/Fe{sub 1−X}Co{sub x} (001) are presented. With the help of spin and symmetry resolved photoemission and ab initio calculation, the TMR decrease for Co content higher than 25% is shown to come from the existence of an interface state and the shift of the empty Δ1 minority spin state towards the Fermi level.

  20. Analytical description of ballistic spin currents and torques in magnetic tunnel junctions

    KAUST Repository

    Chshiev, M.

    2015-09-21

    In this work we demonstrate explicit analytical expressions for both charge and spin currents which constitute the 2×2 spinor in magnetic tunnel junctions with noncollinear magnetizations under applied voltage. The calculations have been performed within the free electron model in the framework of the Keldysh formalism and WKB approximation. We demonstrate that spin/charge currents and spin transfer torques are all explicitly expressed through only three irreducible quantities, without further approximations. The conditions and mechanisms of deviation from the conventional sine angular dependence of both spin currents and torques are shown and discussed. It is shown in the thick barrier approximation that all tunneling transport quantities can be expressed in an extremely simplified form via Slonczewski spin polarizations and our effective spin averaged interfacial transmission probabilities and effective out-of-plane polarizations at both interfaces. It is proven that the latter plays a key role in the emergence of perpendicular spin torque as well as in the angular dependence character of all spin and charge transport considered. It is demonstrated directly also that for any applied voltage, the parallel component of spin current at the FM/I interface is expressed via collinear longitudinal spin current components. Finally, spin transfer torque behavior is analyzed in a view of transverse characteristic length scales for spin transport.

  1. Perpendicular magnetic tunnel junction with a strained Mn-based nanolayer.

    Science.gov (United States)

    Suzuki, K Z; Ranjbar, R; Okabayashi, J; Miura, Y; Sugihara, A; Tsuchiura, H; Mizukami, S

    2016-07-26

    A magnetic tunnel junction with a perpendicular magnetic easy-axis (p-MTJ) is a key device for spintronic non-volatile magnetoresistive random access memory (MRAM). Co-Fe-B alloy-based p-MTJs are being developed, although they have a large magnetisation and medium perpendicular magnetic anisotropy (PMA), which make it difficult to apply them to a future dense MRAM. Here, we demonstrate a p-MTJ with an epitaxially strained MnGa nanolayer grown on a unique CoGa buffer material, which exhibits a large PMA of more than 5 Merg/cm(3) and magnetisation below 500 emu/cm(3); these properties are sufficient for application to advanced MRAM. Although the experimental tunnel magnetoresistance (TMR) ratio is still low, first principles calculations confirm that the strain-induced crystal lattice distortion modifies the band dispersion along the tetragonal c-axis into the fully spin-polarised state; thus, a huge TMR effect can be generated in this p-MTJ.

  2. AlOx barrier growth in magnetic tunnel junctions for sensor applications

    Science.gov (United States)

    Knudde, S.; Farinha, G.; Leitao, D. C.; Ferreira, R.; Cardoso, S.; Freitas, P. P.

    2016-08-01

    Magnetic tunnel junction (MTJ) research has been focused on MgO-based crystalline structures due to high tunnel magnetoresistance (TMR), despite requiring a more severe process control than previous generations of MTJ stacks based on amorphous barriers (e.g. AlOx). In this work, we study the electrical transport properties in AlOx barriers in MTJ sensors fabricated using Ion beam sputtering and remote plasma oxidation. Amorphous barriers were prepared from oxidation of thin Al films, deposited in single step barrier (SSB-Al 1 nm/oxidation) or double step barrier (DSB-Al 0.5 nm/oxidation/Al 0.5 nm/oxidation) structures. We show tunable resistance-area products (RxA) ranging from ≈ 10 Ω μ m2 (suited for nano devices) up to ≈ 100 k Ω μ m2 (suited for large area sensors) with TMR above 30%. For all geometries studied, the structures have a coercivity free linear response and require none or one annealing step. This makes them very competitive for all industrial applications where the TMR level is not the dominant specification to meet.

  3. Cryogenic Phase-Locking Loop System Based on SIS Tunnel Junction

    Science.gov (United States)

    Khudchenko, A. V.; Koshelets, V. P.; Kalashnikov, K. V.

    An ultra-wideband cryogenic phase-locking loop (CPLL) system is a new cryogenic device. The CPLL is intended for phase-locking of a Flux-Flow Oscillator (FFO) in a Superconducting Integrated Receiver (SIR) but can be used for any cryogenic terahertz oscillator. The key element of the CPLL is Cryogenic Phase Detector (CPD), a recently proposed new superconducting element. The CPD is an innovative implementation of superconductor-insulator-superconductor (SIS) tunnel junction. All components of the CPLL reside inside a cryostat at 4.2 K, with the loop length of about 50 cm and the total loop delay 5.5 ns. Such a small delay results in CPLL synchronization bandwidth as wide as 40 MHz and allows phase-locking of more than 60% of the power emitted by the FFO even for FFO linewidth of about 10 MHz. This percentage of phase-locked power three times exceeds that achieved with conventional room-temperature PLLs. Such an improvement enables reducing the FFO phase noise and extending the SIR operation range.Another new approach to the FFO phase-locking has been proposed and experimentally verified. The FFO has been synchronized by a cryogenic harmonic phase detector (CHPD) based on the SIS junction. The CHPD operates simultaneously as the harmonic mixer (HM) and phase detector. We have studied the HM based on the SIS junction theoretically; in particular we calculated 3D dependences of the HM output signal power versus the bias voltage and the LO power. Results of the calculations have been compared with experimental measurements. Good qualitative and quantitative correspondence has been achieved. The FFO phase-locking by the CHPD has been demonstrated. Such a PLL system is expected to be extra wideband. This concept is very promising for building of the multi-pixel SIR array.

  4. Influence of the MgO barrier thickness on the lifetime characteristics of magnetic tunnelling junctions for sensors

    Science.gov (United States)

    Conca, A.; Casper, F.; Paul, J.; Lehndorff, R.; Jakob, G.; Kläui, M.; Hillebrands, B.; Leven, B.

    2016-06-01

    Magnetic tunnelling junctions increasingly enter the market for magnetic sensor applications. Thus, technological parameters such as the lifetime characteristics become more and more important. Here, an analysis of the lifetime characteristics of magnetic tunnelling junctions using the Weibull statistical distribution for CoFeB/MgO/CoFeB junctions is presented. The Weibull distribution is governed by two parameters, the characteristic lifetime η of the population and the shape parameter β, which gives information about the presence of an infant mortality. The suitability of the Weibull distribution is demonstrated for the description of dielectric breakdown processes in MgO-based tunnelling junctions at different voltages. A study of the dependence of the characteristic lifetime extrapolated to the low voltage regime, and the β parameter on the nominal barrier thickness and the resistance  ×  area product of the MgO barrier is shown. The influence of the RF deposition power for the MgO barrier and an annealing step on the Weibull parameters is also discussed.

  5. Unidirectional Spin-Dependent Molecule-Ferromagnet Hybridized States Anisotropy in Cobalt Phthalocyanine Based Magnetic Tunnel Junctions

    Science.gov (United States)

    Barraud, Clément; Bouzehouane, Karim; Deranlot, Cyrile; Fusil, Stéphane; Jabbar, Hashim; Arabski, Jacek; Rakshit, Rajib; Kim, Dong-Jik; Kieber, Christophe; Boukari, Samy; Bowen, Martin; Beaurepaire, Eric; Seneor, Pierre; Mattana, Richard; Petroff, Frédéric

    2015-05-01

    Organic or molecular spintronics is a rising field of research at the frontier between condensed matter physics and chemistry. It aims to mix spin physics and the richness of chemistry towards designing new properties for spin electronics devices through engineering at the molecular scale. Beyond the expectation of a long spin lifetime, molecules can be also used to tailor the spin polarization of the injected current through the spin-dependent hybridization between molecules and ferromagnetic electrodes. In this Letter, we provide direct evidence of a hybrid interface spin polarization reversal due to the differing hybridization between phthalocyanine molecules and each cobalt electrode in Co /CoPc /Co magnetic tunnel junctions. Tunnel magnetoresistance and anisotropic tunnel magnetoresistance experiments show that interfacial hybridized electronic states have a unidirectional anisotropy that can be controlled by an electric field and that spin hybridization at the bottom and top interfaces differ, leading to an inverse tunnel magnetoresistance.

  6. Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

    Directory of Open Access Journals (Sweden)

    Rui Sun

    2016-06-01

    Full Text Available We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100 substrates with a TiN buffer layer. A 50-nm-thick (200-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large IcRN product of 3.8 mV, a sharp quasiparticle current rise with a ΔVg of 0.4 mV, and a small subgap leakage current. The junction quality factor Rsg/RN was about 23 for the junction with a Jc of 47 A/cm2 and was about 6 for the junction with a Jc of 3.0 kA/cm2. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200-orientated TiN buffer layer and had a highly crystalline structure with the (200 orientation.

  7. Tunneling planer Hall effect in Ni81Fe19/Al2O3/Nix Fe1-x junction

    Institute of Scientific and Technical Information of China (English)

    陈慧余; 冯永嘉; 熊曹水

    1999-01-01

    Tunneling planer Hall (TPH) effect in Ni81Fe19/Al2O3/NixFe1-x trilayer junction is different from general planer Hall effect in single-layer film or two-layer junction. This effect concerns the spin-polarized transport, so that the TPH voltage depends on the angle between magnetic vectors of two ferromagnetic layers. The TPH effect is reported to be influenced by composition and magnetic properties of FM layers and the thickness of the insulating layer.

  8. Evidence of a Symmetry-Dependent Metallic Barrier in Fully Epitaxial MgO Based Magnetic Tunnel Junctions

    Science.gov (United States)

    Greullet, F.; Tiusan, C.; Montaigne, F.; Hehn, M.; Halley, D.; Bengone, O.; Bowen, M.; Weber, W.

    2007-11-01

    We report on the experimental observation of tunneling across an ultrathin metallic Cr spacer layer that is inserted at the interface of a Fe/MgO/Fe(001) junction. We show how this remarkable behavior in a solid-state device reflects a quenching in the transmission of particular electronic states, as expected from the symmetry-filtering properties of the MgO barrier and the band structure of the bcc Cr(001) spacer in the epitaxial junction stack. This ultrathin Cr metallic barrier can promote quantum well states in an adjacent Fe layer.

  9. Tunneling characteristics of YBa 2Cu 3O 7-δ-Pb window-type Josephson junctions

    Science.gov (United States)

    Frangi, F.; Dwir, B.; Pavuna, D.

    1992-02-01

    We present the results of tunneling measurements done on window-type, native-barrier YBa 2Cu 3O 7-δ-Pb junctions. We show features in the I-V curves which are related to the gap of YBa 2Cu 3O 7-δ, as well as to the Pb and YBa 2Cu 3O 7-δ phonon spectra. The nature of barrier in these structures is found to be semi-conducting. We can also see the asymmetry in the tunneling curves.

  10. Perpendicularly magnetized ferrimagnetic [Mn50Ga50/Co2FeAl] superlattice and the utilization in magnetic tunnel junctions

    Directory of Open Access Journals (Sweden)

    Q. L. Ma

    2015-08-01

    Full Text Available The ferrimagnetic superlattice (SL [MnGa/Co2FeAl]n exhibiting perpendicular magnetic anisotropy opened a new method for spintronics materials used in magnetic random access memory, because of the high anisotropy, small damping constant and tunable magnetization. In this work, we fabricated SLs with different MnGa composition and studied the MnGa composition dependence of the structure and magnetic properties of the SLs. Furthermore, we fabricated fully perpendicular magnetic tunnel junctions with SLs as both top and bottom electrodes. A clear tunnel magnetoresistance (TMR effect with TMR ratio of 1.3% at room temperature was observed.

  11. Generation of constant-amplitude radio-frequency sweeps at a tunnel junction for spin resonance STM

    Science.gov (United States)

    Paul, William; Baumann, Susanne; Lutz, Christopher P.; Heinrich, Andreas J.

    2016-07-01

    We describe the measurement and successful compensation of the radio-frequency transfer function of a scanning tunneling microscope over a wide frequency range (15.5-35.5 GHz) and with high dynamic range (>50 dB). The precise compensation of cabling resonances and attenuations is critical for the production of constant-voltage frequency sweeps for electric-field driven electron spin resonance (ESR) experiments. We also demonstrate that a well-calibrated tunnel junction voltage is necessary to avoid spurious ESR peaks that can arise due to a non-flat transfer function.

  12. Novel compact model for multi-level spin torque magnetic tunnel junctions

    Science.gov (United States)

    Prajapati, Sanjay; Verma, Shivam; Kulkarni, Anant Aravind; Kaushik, Brajesh Kumar

    2016-10-01

    Spin-transfer torque (STT) and spin-orbit torque (SOT) based magnetic tunnel junction (MTJ) devices are emerging as strong contenders for the next generation memories. Conventional STT magneto-resistive random access memory (MRAM) offers lower power, non-volatility and CMOS process compatibility. However, higher current requirement during the write operation leads to tunnel barrier reliability issues and larger access devices. SOT-MRAM eliminates the reliability issues with strong spin polarized current (100%) and separate read/write current paths; however, the additional two access transistors in SOT-MRAM results into increased cell area. Multilevel cell (MLC) structure paves a way to circumvent the problems related to the conventional STT/SOT based MTJ devices and provides enhanced integration density at reduced cost per bit. Conventional STT/SOT-MRAM requires a unit cell area of 10-60 F2 and reported simulations have been based on available single-level MTJ compact models. However, till date no compact model exists that can capture the device physics of MLC-MTJ accurately. Hence, a novel compact model is proposed in this paper to capture the accurate device physics and behaviour of the MLC-MTJs. It is designed for MLCs with different MTJ configurations demonstrated so far, such as series and parallel free layer based MLC-MTJs. The proposed model is coded in Verilog-A, which is compatible with SPICE for circuit level simulations. The model is in close agreement with the experimental results exhibiting an average error of less than 15%.

  13. Interfacial Nb-substitution induced anomalous enhancement of polarization and conductivity in BaTiO3 ferroelectric tunnel junctions

    Directory of Open Access Journals (Sweden)

    H. F. Li

    2014-12-01

    Full Text Available Using density functional theory (DFT method combined with non-equilibrium Green’s function approach, we systematically investigated the structural, ferroelectric and electronic transport properties of Pt/BaTiO3/Pt ferroelectric tunnel junctions (FTJ with the interface atomic layers doped by charge neutral NbTi substitution. It is found that interfacial NbTi substitution will produce several anomalous effects such as the vanishing of ferroelectric critical thickness and the decrease of junction resistance against tunneling current. Consequently, the thickness of the ferroelectric thin film (FTF in the FTJ can be reduced, and both the electroresistance effect and sensitivity to external bias of the FTJ are enhanced. Our calculations indicate that the enhancements of conductivity and ferroelectric distortion can coexist in FTJs, which should be important for applications of functional electronic devices based on FTJs.

  14. Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling

    Science.gov (United States)

    Chavent, A.; Ducruet, C.; Portemont, C.; Vila, L.; Alvarez-Hérault, J.; Sousa, R.; Prejbeanu, I. L.; Dieny, B.

    2016-09-01

    Understanding quantitatively the heating dynamics in magnetic tunnel junctions submitted to current pulses is very important in the context of spin-transfer-torque magnetic random-access memory development. Here we provide a method to probe the heating of magnetic tunnel junctions using the Ruderman-Kittel-Kasuya-Yoshida coupling of a synthetic ferrimagnetic storage layer as a thermal sensor. The temperature increase versus applied bias voltage is measured thanks to the decrease of the spin-flop field with temperature. This method allows distinguishing spin-transfer torque effects from the influence of temperature on the switching field. The heating dynamics is then studied in real time by probing the conductance variation due to spin-flop rotation during heating. This approach provides a method for measuring fast heating in spintronic devices, particularly magnetic random-access memory using thermally assisted or spin-transfer torque writing.

  15. Tunneling Hamiltonian description of the atomic-scale 0-{pi} transition in superconductor/ferromagnetic-insulator junctions

    Energy Technology Data Exchange (ETDEWEB)

    Kawabata, S., E-mail: s-kawabata@aist.go.jp [Nanosystem Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)] [CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012 (Japan); Tanaka, Y. [Department of Applied Physics, Nagoya University, Nagoya 464-8603 (Japan); Golubov, A.A. [Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Vasenko, A.S. [Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble (France); Kashiwaya, S. [Nanoelectronics Research Institute (NeRI), AIST, Tsukuba, Ibaraki 305-8568 (Japan); Asano, Y. [Department of Applied Physics, Hokkaido University, Sapporo 060-8628 (Japan)

    2011-11-15

    Josephson transport in a superconductor/ferromagnetic-insulator(FI)/superconductor junction is investigated analytically. By using the tunneling Hamiltonian method, we found that the spin-dependent {pi}-phase shift of the electron wave function in a FI layer gives the atomic scale 0-{pi} transition. This observation is consistent with previous numerical results. We show a perturbation theory of the Josephson transport through ferromagnetic insulators (FIs). Recently we have found that the appearance of the atomic scale 0-{pi} transition in such junctions based on numerical calculations. In order to explore the mechanism of this anomalous transition, we have analytically calculated the Josephson current using the tunneling Hamiltonian theory and found that the spin dependent {pi}-phase shift in the FI barrier gives the atomic scale 0-{pi} transition.

  16. The key technology of shallow buried tunnel through the debris flow gully%浅埋隧道穿越泥石流沟关键技术

    Institute of Scientific and Technical Information of China (English)

    侯敏

    2012-01-01

    为有效的控制浅埋段的围岩变形,将浅埋段开挖方法由两台阶改为三台阶七步法,并缩小施工步距;明洞段(泥石流沟)地质为砂质黄土,大开挖可能会导致边坡的坍塌和滑坡,将明洞段采用半挖方式和明洞暗作,为以后过泥石流段隧道施工积累了经验。%In order to effectively control the surrounding rock deformation of shallow buried section, this paper made the shallow section excava- tion method to three steps seven steps by two steps, and reduced the construction step, the open cut tunnel section (debris flow gully) geological was sandy loess, the large excavation may lead to slope collapse and landslide, made the open cut tunnel section using semi-incomplete cut meth- od and dark operation in open tunnel, accumulated experience for later tunnel construction of debris flow section.

  17. Temperature dependence of spin-dependent tunneling conductance of magnetic tunnel junctions with half-metallic C o2MnSi electrodes

    Science.gov (United States)

    Hu, Bing; Moges, Kidist; Honda, Yusuke; Liu, Hong-xi; Uemura, Tetsuya; Yamamoto, Masafumi; Inoue, Jun-ichiro; Shirai, Masafumi

    2016-09-01

    In order to elucidate the origin of the temperature (T ) dependence of spin-dependent tunneling conductance (G ) of magnetic tunnel junctions (MTJs), we experimentally investigated the T dependence of G for the parallel and antiparallel magnetization alignments, GP and GAP, of high-quality C o2MnSi (CMS)/MgO/CMS MTJs having systematically varied spin polarizations (P ) at 4.2 K by varying the Mn composition α in C o2M nαSi electrodes that exhibited giant tunneling magnetoresistance ratios. Results showed that GP normalized by its value at 4.2 K exhibited a notable, nonmonotonic T dependence although its variation with T was significantly smaller than that of GAP normalized by its value at 4.2 K, indicating that an analysis of the experimental GP(T ) is critical to revealing the origin of the T dependence of G . By analyzing the experimental GP(T ) , we clarified that both spin-flip inelastic tunneling via a thermally excited magnon and spin-conserving elastic tunneling in which P decays with increasing T play key roles. The experimental GAP(T ) , including its stronger T dependence for higher P at 4.2 K, was also consistently explained with this model. Our findings provide a unified picture for understanding the origin of the T dependence of G of MTJs with a wide range of P , including MTJs with high P close to a half-metallic value.

  18. Modeling of switching energy of magnetic tunnel junction devices with tilted magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Surawanitkun, C. [Science and Technology Program, Nongkhai Campus, Khon Kaen University, Nongkhai 43000 (Thailand); Kaewrawang, A. [KKU-Seagate Cooperation Research Laboratory, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002 (Thailand); Siritaratiwat, A., E-mail: apirat@kku.ac.th [KKU-Seagate Cooperation Research Laboratory, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002 (Thailand); Kruesubthaworn, A. [Science and Technology Program, Nongkhai Campus, Khon Kaen University, Nongkhai 43000 (Thailand); Sivaratana, R. [Seagate Technology, 1627, Teparak, Samutprakarn 10200 (Thailand); Jutong, N. [Institute of Physics, University of Augsburg, 86135 Augsburg (Germany); Mewes, C.K.A.; Mewes, T. [Department of Physics & Astronomy, MINT Center, University of Alabama, Tuscaloosa, AL 35487 (United States)

    2015-05-01

    For spin transfer torque (STT), the switching energy and thermal stability of magnetic tunnel junctions (MTJ) bits utilized in memory devices are important factors that have to be considered simultaneously. In this article, we examined the minimum energy for STT induced magnetization switching in MTJ devices for different in-plane angles of the magnetization in the free layer and the pinned layer with respect to the major axis of the elliptical cylinder of the cell. Simulations were performed by comparing the analytical solution with macrospin and full micromagnetic calculations. The results show good agreement of the switching energy calculated by using the three approaches for different initial angles of the magnetization of the free layer. Also, the low-energy location specifies the suitable value of both time and current in order to reduce the heat effect during the switching process. - Highlights: • Switching energy model was firstly examined with tiled magnetization in STT-RAM. • Simulation was performed by analytical solution, macrospin and micromagnetic models. • Low energy results from three models show agreement for tilt angle in free layer. • We also found an optimal tilt angle of the pinned layer. • Low-energy location specifies the suitable switching location to reduce heat effect.

  19. A Survey on the Modeling of Magnetic Tunnel Junctions for Circuit Simulation

    Directory of Open Access Journals (Sweden)

    Hyein Lim

    2016-01-01

    Full Text Available Spin-transfer torque-based magnetoresistive random access memory (STT-MRAM is a promising candidate for universal memory that may replace traditional memory forms. It is expected to provide high-speed operation, scalability, low-power dissipation, and high endurance. MRAM switching technology has evolved from the field-induced magnetic switching (FIMS technique to the spin-transfer torque (STT switching technique. Additionally, material technology that induces perpendicular magnetic anisotropy (PMA facilitates low-power operation through the reduction of the switching current density. In this paper, the modeling of magnetic tunnel junctions (MTJs is reviewed. Modeling methods and models of MTJ characteristics are classified into two groups, macromodels and behavioral models, and the most important characteristics of MTJs, the voltage-dependent MTJ resistance and the switching behavior, are compared. To represent the voltage dependency of MTJ resistance, some models are based on physical mechanisms, such as Landau-Lifshitz-Gilbert (LLG equation or voltage-dependent conductance. Some behavioral models are constructed by adding fitting parameters or introducing new physical parameters to represent the complex switching behavior of an MTJ over a wide range of input current conditions. Other models that are not based on physical mechanisms are implemented by simply fitting to experimental data.

  20. High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications

    Science.gov (United States)

    Chen, Jun-Yang; Lau, Yong-Chang; Coey, J. M. D.; Li, Mo; Wang, Jian-Ping

    2017-02-01

    The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices‘ robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications.

  1. Double-pinned magnetic tunnel junction sensors with spin-valve-like sensing layers

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Z. H.; Huang, L.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn; Wen, Z. C.; Li, D. L.; Han, X. F. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P. O. Box 603, Beijing 100190 (China); Nakano, Takafumi; Naganuma, Hiroshi, E-mail: naganuma@mlab.apph.tohoku.ac.jp [Department of Applied Physics, Tohoku University, Sendai, Miyagi 980-8579 (Japan); Yu, T. [Department of Applied Physics, Tohoku University, Sendai, Miyagi 980-8579 (Japan); College of Physical Science and Technology, Sichuan University, Chengdu 610064 (China)

    2015-08-07

    MgO magnetic tunnel junction (MTJ) sensors with spin-valve-like sensing layers of Ir{sub 22}Mn{sub 78} (6)/Ni{sub 80}Fe{sub 20} (t{sub NiFe} = 20–70)/Ru (0.9)/Co{sub 40}Fe{sub 40}B{sub 20} (3) (unit: nm) have been fabricated. A linear field dependence of magnetoresistance for these MTJ sensors was obtained by carrying out a two-step field annealing process. The sensitivity and linear field range can be tuned by varying the thickness of NiFe layer and annealing temperature, and a high sensitivity of 37%/mT has been achieved in the MTJ sensors with 70 nm NiFe at the optimum annealing temperature of 230 °C. Combining the spin-valve-like sensing structure and a soft magnetic NiFe layer, MTJ sensors with relatively wide field sensing range have been achieved and could be promising for showing high sensitivity magnetic field sensing applications.

  2. Perpendicular magnetic tunnel junction with thin CoFeB/Ta/Co/Pd/Co reference layer

    Energy Technology Data Exchange (ETDEWEB)

    Gan, Huadong, E-mail: huadong@avalanche-technology.com; Malmhall, Roger; Wang, Zihui; Yen, Bing K; Zhang, Jing; Wang, Xiaobin; Zhou, Yuchen; Hao, Xiaojie; Jung, Dongha; Satoh, Kimihiro; Huai, Yiming [Avalanche Technology, 46600 Landing Parkway, Fremont, California 94538 (United States)

    2014-11-10

    Integration of high density spin transfer torque magnetoresistance random access memory requires a thin stack (less than 15 nm) of perpendicular magnetic tunnel junction (p-MTJ). We propose an innovative approach to solve this challenging problem by reducing the thickness and/or moment of the reference layer. A thin reference layer structure of CoFeB/Ta/Co/Pd/Co has 60% magnetic moment of the conventional thick structure including [Co/Pd] multilayers. We demonstrate that the perpendicular magnetization of the CoFeB/Ta/Co/Pd/Co structure can be realized by anti-ferromagnetically coupling to a pinned layer with strong perpendicular anisotropy via Ruderman-Kittel-Kasuya-Yosida exchange interaction. The pMTJ with thin CoFeB/Ta/Co/Pd/Co reference layer has a comparable TMR ratio (near 80%) as that with thick reference layer after annealing at 280 °C. The pMTJ with thin reference layer has a total thickness less than 15 nm, thereby significantly increasing the etching margin required for integration of high density pMTJ array on wafers with form factor of 300 mm and beyond.

  3. Brief rapid thermal treatment effect on patterned CoFeB-based magnetic tunneling junctions

    Science.gov (United States)

    Wu, Kuo-Ming; Huang, Chao-Hsien; Wang, Yung-Hung; Kao, Ming-Jer; Tsai, Ming-Jinn; Wu, Jong-Ching; Horng, Lance

    2007-05-01

    The brief thermal treatment effects on the magnetoresistance of microstructured Co60Fe20B20-based magnetic tunneling junctions have been studied. The elliptical shape of devices with long/short axis of 4/2μm was patterned out of film stack of seed layer (20)/PtMn(15)/Co60Fe20B20(3)/Al(0.7)oxide/C60Fe20B20(20)/capping layer (48) (thickness unit in nanometers) combining conventional lithography and inductively coupled plasma reactive ion beam etching technologies. The thermal annealing was carried out with device loading into a furnace with preset temperatures ranging from 100to400°C for only 5min in the absence of any external magnetic field. The magnetoresistance was found to increase with increasing annealing temperatures up to 250°C and then decrease at higher annealing temperatures. In addition, the magnetoresistance ratio of around 35%, similar to that of as-fabricated devices, sustains up to annealing temperature of 350°C. This survival of magnetoresistance at higher annealing temperature is due to boron conservation in the amorphous CoFeB ferromagnetic layer at higher annealing temperature for only a short time, which is manifested using x-ray diffractometer technique.

  4. SPICE modelling of magnetic tunnel junctions written by spin-transfer torque

    Energy Technology Data Exchange (ETDEWEB)

    Guo, W; Prenat, G; De Mestier, N; Baraduc, C; Dieny, B [SPINTEC, UMR(8191), INAC, CEA/CNRS/UJF, 17 Av. des Martyrs, 38054 Grenoble Cedex 9 (France); Javerliac, V; El Baraji, M, E-mail: guillaume.prenat@cea.f [CROCUS Technology, 5 Place Robert Schuman, 38025 Grenoble (France)

    2010-06-02

    Spintronics aims at extending the possibility of conventional electronics by using not only the charge of the electron but also its spin. The resulting spintronic devices, combining the front-end complementary metal oxide semiconductor technology of electronics with a magnetic back-end technology, employ magnetic tunnel junctions (MTJs) as core elements. With the intent of simulating a circuit without fabricating it first, a reliable MTJ electrical model which is applicable to the standard SPICE (Simulation Program with Integrated Circuit Emphasis) simulator is required. Since such a model was lacking so far, we present a MTJ SPICE model whose magnetic state is written by using the spin-transfer torque effect. This model has been developed in the C language and validated on the Cadence Virtuoso Platform with a Spectre simulator. Its operation is similar to that of the standard BSIM (Berkeley Short-channel IGFET Model) SPICE model of the MOS transistor and fully compatible with the SPICE electrical simulator. The simulation results obtained using this model have been found in good accord with those theoretical macrospin calculations and results.

  5. High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications.

    Science.gov (United States)

    Chen, Jun-Yang; Lau, Yong-Chang; Coey, J M D; Li, Mo; Wang, Jian-Ping

    2017-02-02

    The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices' robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications.

  6. High Performance MgO-barrier Magnetic Tunnel Junctions for Flexible and Wearable Spintronic Applications

    Science.gov (United States)

    Chen, Jun-Yang; Lau, Yong-Chang; Coey, J. M. D.; Li, Mo; Wang, Jian-Ping

    2017-01-01

    The magnetic tunnel junction (MTJ) using MgO barrier is one of most important building blocks for spintronic devices and has been widely utilized as miniaturized magentic sensors. It could play an important role in wearable medical devices if they can be fabricated on flexible substrates. The required stringent fabrication processes to obtain high quality MgO-barrier MTJs, however, limit its integration with flexible electronics devices. In this work, we have developed a method to fabricate high-performance MgO-barrier MTJs directly onto ultrathin flexible silicon membrane with a thickness of 14 μm and then transfer-and-bond to plastic substrates. Remarkably, such flexible MTJs are fully functional, exhibiting a TMR ratio as high as 190% under bending radii as small as 5 mm. The devices‘ robustness is manifested by its retained excellent performance and unaltered TMR ratio after over 1000 bending cycles. The demonstrated flexible MgO-barrier MTJs opens the door to integrating high-performance spintronic devices in flexible and wearable electronics devices for a plethora of biomedical sensing applications. PMID:28150807

  7. Memristive behaviors in Pt/BaTiO{sub 3}/Nb:SrTiO{sub 3} ferroelectric tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Zheng [College of Physics, Qingdao University, Qingdao 266071 (China); National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China and Department of Materials Science and Engineering, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093 (China); Wu, Di, E-mail: diwu@nju.edu.cn; Li, Aidong [National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China and Department of Materials Science and Engineering, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093 (China)

    2014-08-04

    We demonstrate memristive behaviors in Pt/BaTiO{sub 3}/Nb:SrTiO{sub 3} metal/ferroelectric/semiconductor ferroelectric tunnel junctions, in which the semiconductor electrode can be switched between the accumulated and the depleted states by polarization reversal in the BaTiO{sub 3} barrier via the ferroelectric field effect. An extra barrier, against electron tunneling, forms in the depleted region of the Nb:SrTiO{sub 3} electrode surface, which together with the ferroelectric barrier itself modulate the tunneling resistance with the change of effective polarization. Continuous resistance modulation over four orders of magnitude is hence achieved by application of programmed voltage pulses with different polarity, amplitude, and repetition numbers, as a result of the development of the extra barrier.

  8. The effect of the ferromagnetic metal layer on tunnelling conductance and magnetoresistance in double magnetic planar junctions

    Institute of Scientific and Technical Information of China (English)

    谢征微; 李伯臧; 李玉现

    2002-01-01

    Based on the free-electron approximation, we investigate the effect of the ferromagnetic metal layer on the tunnelling magnetoresistance (TMR) and tunnelling conductance (TC) in the double magnetic tunnel junctions (DMTJs)of the structure NM/FM/Ⅰ(S)/NM/Ⅰ(S)/FM/NM, where FM, NM and Ⅰ(S) represent the ferromagnetic metal, nonmagnetic metal and insulator (semiconductor), respectively. The FM, Ⅰ(S) and inner NM layers are of finite thickness,while the thickness of the outer NM layer is infinite. The calculated results show that, due to the spin-dependent interfacial potential barriers caused by electronic band mismatch between the various magnetic and nonmagnetic layers,the dependences of the TMR and TC on the thicknesses of the FM layers exhibit oscillations, and a much higher TMR can be obtained for suitable thicknesses of FM layers.

  9. Dependency of Tunneling-Magnetoresistance Ratio on Nanoscale Spacer Thickness and Material for Double MgO Based Perpendicular-Magnetic-Tunneling-Junction.

    Science.gov (United States)

    Lee, Du-Yeong; Hong, Song-Hwa; Lee, Seung-Eun; Park, Jea-Gun

    2016-12-08

    It was found that in double MgO based perpendicular magnetic tunneling junction spin-valves ex-situ annealed at 400 °C, the tunneling magnetoresistance ratio was extremely sensitive to the material and thickness of the nanoscale spacer: it peaked at a specific thickness (0.40~0.53 nm), and the TMR ratio for W spacers (~134%) was higher than that for Ta spacers (~98%). This dependency on the spacer material and thickness was associated with the (100) body-centered-cubic crystallinity of the MgO layers: the strain enhanced diffusion length in the MgO layers of W atoms (~1.40 nm) was much shorter than that of Ta atoms (~2.85 nm) and the shorter diffusion length led to the MgO layers having better (100) body-centered-cubic crystallinity.

  10. Inelastic Tunneling Spectroscopy of Gold-Thiol and Gold-Thiolate Interfaces in Molecular Junctions: The Role of Hydrogen

    CERN Document Server

    Demir, Firuz

    2012-01-01

    It is widely believed that when a molecule with thiol (S-H) end groups bridges a pair of gold electrodes, the S atoms bond to the gold and the thiol H atoms detach from the molecule. However, little is known regarding the details of this process, its time scale, and whether molecules with and without thiol hydrogen atoms can coexist in molecular junctions. Here we explore theoretically how inelastic tunneling spectroscopy (IETS) can shed light on these issues. We present calculations of the geometries, low bias conductances and IETS of propanedithiol and propanedithiolate molecular junctions with gold electrodes. We show that IETS can distinguish between junctions with molecules having no, one or two thiol hydrogen atoms. We find that in most cases the single-molecule junctions in the IETS experiment of Hihath et al. [Nano Lett. 8, 1673 (2008)] had no thiol H atoms, but that a molecule with a single thiol H atom may have bridged their junction occasionally. We also consider the evolution of the IETS spectrum ...

  11. Very High Current Density Nb/AlN/Nb Tunnel Junctions for Low-Noise Submillimeter Mixers

    Science.gov (United States)

    Kawamura, Jonathan; Miller, David; Chen, Jian; Zmuidzinas, Jonas; Bumble, Bruce; LeDuc, Henry G.; Stern, Jeff A.

    2000-01-01

    We have fabricated and tested submillimeter-wave superconductor-insulator-superconductor (SIS) mixers using very high current density Nb/AlN/Nb tunnel junctions (J(sub c) approximately equal 30 kA/sq cm) . The junctions have low resistance-area products (R(sub N)A approximately 5.6 Omega.sq micron), good subgap to normal resistance ratios R(sub sg)/R(sub N) approximately equal 10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that omega.R(sub N)C = 1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlO(x)/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected receiver noise temperature of T(sub RX) = 110 K (DSB) at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing RF loss in the tuning circuits.

  12. A Single-Level Tunnel Model to Account for Electrical Transport through Single Molecule- and Self-Assembled Monolayer-based Junctions

    Science.gov (United States)

    Garrigues, Alvar R.; Yuan, Li; Wang, Lejia; Mucciolo, Eduardo R.; Thompon, Damien; Del Barco, Enrique; Nijhuis, Christian A.

    2016-05-01

    We present a theoretical analysis aimed at understanding electrical conduction in molecular tunnel junctions. We focus on discussing the validity of coherent versus incoherent theoretical formulations for single-level tunneling to explain experimental results obtained under a wide range of experimental conditions, including measurements in individual molecules connecting the leads of electromigrated single-electron transistors and junctions of self-assembled monolayers (SAM) of molecules sandwiched between two macroscopic contacts. We show that the restriction of transport through a single level in solid state junctions (no solvent) makes coherent and incoherent tunneling formalisms indistinguishable when only one level participates in transport. Similar to Marcus relaxation processes in wet electrochemistry, the thermal broadening of the Fermi distribution describing the electronic occupation energies in the electrodes accounts for the exponential dependence of the tunneling current on temperature. We demonstrate that a single-level tunnel model satisfactorily explains experimental results obtained in three different molecular junctions (both single-molecule and SAM-based) formed by ferrocene-based molecules. Among other things, we use the model to map the electrostatic potential profile in EGaIn-based SAM junctions in which the ferrocene unit is placed at different positions within the molecule, and we find that electrical screening gives rise to a strongly non-linear profile across the junction.

  13. Stability, sub-gap current, 1/f-noise, and elemental depth profiling of annealed Al:Mn-AlOX-Al normal metal-insulator-superconducting tunnel junctions

    Science.gov (United States)

    Julin, J. K.; Chaudhuri, S.; Laitinen, M.; Sajavaara, T.; Maasilta, I. J.

    2016-12-01

    In this paper we report a study of the effect of vacuum annealing at 400°C on the properties of normal metal-insulator-superconductor (NIS) tunnel junctions, with manganese doped aluminium (Al:Mn) as the normal metal, aluminum as the superconductor and amorphous aluminum oxide as the tunneling barrier (Al:Mn-AlOx-Al). The annealing treatment improves the stability of the junctions, increases their tunneling resistance and does not have a negative impact on the low-temperature current-voltage characteristics. The measured 1/f resistance noise of the junctions also changes after annealing, in the best case decreasing by over an order of magnitude. All these observations show that annealing is a viable route to improve NIS junction devices after the sample has been fabricated.

  14. Charge transport in molecular electronic junctions: compression of the molecular tunnel barrier in the strong coupling regime.

    Science.gov (United States)

    Sayed, Sayed Y; Fereiro, Jerry A; Yan, Haijun; McCreery, Richard L; Bergren, Adam Johan

    2012-07-17

    Molecular junctions are essentially modified electrodes familiar to electrochemists where the electrolyte is replaced by a conducting "contact." It is generally hypothesized that changing molecular structure will alter system energy levels leading to a change in the transport barrier. Here, we show the conductance of seven different aromatic molecules covalently bonded to carbon implies a modest range ( 2 eV range). These results are explained by considering the effect of bonding the molecule to the substrate. Upon bonding, electronic inductive effects modulate the energy levels of the system resulting in compression of the tunneling barrier. Modification of the molecule with donating or withdrawing groups modulate the molecular orbital energies and the contact energy level resulting in a leveling effect that compresses the tunneling barrier into a range much smaller than expected. Whereas the value of the tunneling barrier can be varied by using a different class of molecules (alkanes), using only aromatic structures results in a similar equilibrium value for the tunnel barrier for different structures resulting from partial charge transfer between the molecular layer and the substrate. Thus, the system does not obey the Schottky-Mott limit, and the interaction between the molecular layer and the substrate acts to influence the energy level alignment. These results indicate that the entire system must be considered to determine the impact of a variety of electronic factors that act to determine the tunnel barrier.

  15. High density processing electronics for superconducting tunnel junction x-ray detector arrays

    Energy Technology Data Exchange (ETDEWEB)

    Warburton, W.K., E-mail: bill@xia.com [XIA LLC, 31057 Genstar Road, Hayward, CA 94544 (United States); Harris, J.T. [XIA LLC, 31057 Genstar Road, Hayward, CA 94544 (United States); Friedrich, S. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States)

    2015-06-01

    Superconducting tunnel junctions (STJs) are excellent soft x-ray (100–2000 eV) detectors, particularly for synchrotron applications, because of their ability to obtain energy resolutions below 10 eV at count rates approaching 10 kcps. In order to achieve useful solid detection angles with these very small detectors, they are typically deployed in large arrays – currently with 100+ elements, but with 1000 elements being contemplated. In this paper we review a 5-year effort to develop compact, computer controlled low-noise processing electronics for STJ detector arrays, focusing on the major issues encountered and our solutions to them. Of particular interest are our preamplifier design, which can set the STJ operating points under computer control and achieve 2.7 eV energy resolution; our low noise power supply, which produces only 2 nV/√Hz noise at the preamplifier's critical cascode node; our digital processing card that digitizes and digitally processes 32 channels; and an STJ I–V curve scanning algorithm that computes noise as a function of offset voltage, allowing an optimum operating point to be easily selected. With 32 preamplifiers laid out on a custom 3U EuroCard, and the 32 channel digital card in a 3U PXI card format, electronics for a 128 channel array occupy only two small chassis, each the size of a National Instruments 5-slot PXI crate, and allow full array control with simple extensions of existing beam line data collection packages.

  16. Experimental demonstration of single electron transistors featuring SiO{sub 2} plasma-enhanced atomic layer deposition in Ni-SiO{sub 2}-Ni tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Karbasian, Golnaz, E-mail: Golnaz.Karbasian.1@nd.edu; McConnell, Michael S.; Orlov, Alexei O.; Rouvimov, Sergei; Snider, Gregory L. [Electrical Engineering Department, University of Notre Dame, Indiana 46556 (United States)

    2016-01-15

    The authors report the use of plasma-enhanced atomic layer deposition (PEALD) to fabricate single-electron transistors (SETs) featuring ultrathin (≈1 nm) tunnel-transparent SiO{sub 2} in Ni-SiO{sub 2}-Ni tunnel junctions. They show that, as a result of the O{sub 2} plasma steps in PEALD of SiO{sub 2}, the top surface of the underlying Ni electrode is oxidized. Additionally, the bottom surface of the upper Ni layer is also oxidized where it is in contact with the deposited SiO{sub 2}, most likely as a result of oxygen-containing species on the surface of the SiO{sub 2}. Due to the presence of these surface parasitic layers of NiO, which exhibit features typical of thermally activated transport, the resistance of Ni-SiO{sub 2}-Ni tunnel junctions is drastically increased. Moreover, the transport mechanism is changed from quantum tunneling through the dielectric barrier to one consistent with thermally activated resistors in series with tunnel junctions. The reduction of NiO to Ni is therefore required to restore the metal-insulator-metal (MIM) structure of the junctions. Rapid thermal annealing in a forming gas ambient at elevated temperatures is presented as a technique to reduce both parasitic oxide layers. This method is of great interest for devices that rely on MIM tunnel junctions with ultrathin barriers. Using this technique, the authors successfully fabricated MIM SETs with minimal trace of parasitic NiO component. They demonstrate that the properties of the tunnel barrier in nanoscale tunnel junctions (with <10{sup −15} m{sup 2} in area) can be evaluated by electrical characterization of SETs.

  17. Simulation Study on Understanding the Spin Transport in MgO Adsorbed Graphene Based Magnetic Tunnel Junction

    Science.gov (United States)

    Raturi, Ashish; Choudhary, Sudhanshu

    2016-11-01

    First principles calculations of spin-dependent electronic transport properties of magnetic tunnel junction (MTJ) consisting of MgO adsorbed graphene nanosheet sandwiched between two CrO2 half-metallic ferromagnetic (HMF) electrodes is reported. MgO adsorption on graphene opens bandgap in graphene nanosheet which makes it more suitable for use as a tunnel barrier in MTJs. It was found that MgO adsorption suppresses transmission probabilities for spin-down channel in case of parallel configuration (PC) and also suppresses transmission in antiparallel configuration (APC) for both spin-up and spin-down channel. Tunnel magneto-resistance (TMR) of 100% is obtained at all bias voltages in MgO adsorbed graphene-based MTJ which is higher than that reported in pristine graphene-based MTJ. HMF electrodes were found suitable to achieve perfect spin filtration effect and high TMR. I-V characteristics for both parallel and antiparallel magnetization states of junction are calculated. High TMR suggests its usefulness in spin valves and other spintronics-based applications.

  18. Niobium nano-SQUIDs based on sub-micron tunnel junction fabricated by three-dimensional Focused Ion Beam sculpting

    Science.gov (United States)

    Fretto, M.; Enrico, E.; De Leo, N.; Boarino, L.; Lacquaniti, V.; Granata, C.; Russo, R.; Vettoliere, A.

    2014-05-01

    A three dimensional nano-SQUID (Superconducting Quantum Interference Device) has been realized in a vertical configuration (with the loop in the same plane of Josephson Tunneling Junctions, JTJs). The loop area is 0.25 μm2 corresponding to a modulation period of about 5 mT, the square JTJs have a side length of 0.3 μm. Josephson junction's fabrication is carried out combining optical lithography to pattern trilayer and three dimensional (3D) Focused Ion Beam (FIB) sculpting technique to define the junctions' and the loop's areas. Two different ion etching processes were performed, perpendicular and parallel to the multilayer, resulting in a precise 3D structure. Finally, a standard anodization was performed to eliminate the unstructured surface material generated by the high energetic ion beam assuring high quality junctions. Electric transport characteristics of the nanodevice measured at T = 4.2 K are reported, in particular the current-voltage characteristics and critical current vs external magnetic field. The high modulation depth of the critical current (up to 70% of the Ic at zero magnetic flux) and the device reliability are very encouraging in view of nanoscience applications.

  19. Development of superconducting tunnel junction as photon counting detector in astronomy; Developpement de jonctions supraconductrices a effet tunnel pour le comptage de photons en astronomie

    Energy Technology Data Exchange (ETDEWEB)

    Jorel, C

    2004-12-15

    This work describes the development of S/Al-AlOx-Al/S Superconducting Tunnel Junctions (STJ) to count photons for astronomical applications in the near-infrared. The incoming light energy is converted into excited charges in a superconducting layer (S, either Nb or Ta) with a population proportional to the deposited energy. The photon energy can thus be evaluated by integrating the tunnel current induced in a voltage biased junction at a very low temperature (100 mK). The performance of STJ for light detection is discussed in the first chapter and compared with the best performances obtained with other techniques based on either superconductors. At the beginning of the thesis, a previous manufacturing process made it possible to obtain good quality Nb based junctions and preliminary results for photon counting. The objective of the thesis was to replace Nb as absorber with Ta, an intrinsically more sensitive material, and secondly to develop a new and more efficient manufacturing process. We first focused on the optimization of the Tantalum thin film quality. Structural analysis showed that these films can be grown epitaxially by magnetron sputtering onto an R-plane sapphire substrate heated to 600 Celsius degrees and covered by a thin Nb buffer layer. Electrical transport measurement from room to low temperatures gave excellent Relative Resistive Ratios of about 50 corresponding to mean free path of the order of 100 nm. Then, we conceived an original manufacturing process batch on 3 inch diameter sapphire substrate with five mask levels. These masks made it possible to produce single pixel STJ of different sizes (from 25*25 to 50*50 square microns) and shapes. We also produced multiple junctions onto a common absorber as well as 9-pixel arrays. Thanks to the development of this process we obtained a very large percentage of quality junctions (>90%) with excellent measured normal resistances of a few micro-ohm cm{sup 2} and low leakage currents of the order of one

  20. Temperature and bias voltage dependence of Co/Pd multilayer-based magnetic tunnel junctions with perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Kugler, Zoe, E-mail: zkugler@physik.uni-bielefeld.d [Bielefeld University, Department of Physics, Universitaetsstr. 25, 33615 Bielefeld (Germany); Drewello, Volker; Schaefers, Markus; Schmalhorst, Jan; Reiss, Guenter; Thomas, Andy [Bielefeld University, Department of Physics, Universitaetsstr. 25, 33615 Bielefeld (Germany)

    2011-01-15

    Temperature- and bias voltage-dependent transport measurements of magnetic tunnel junctions (MTJs) with perpendicularly magnetized Co/Pd electrodes are presented. Magnetization measurements of the Co/Pd multilayers are performed to characterize the electrodes. The effects of the Co layer thickness in the Co/Pd bilayers, the annealing temperature, the Co thickness at the MgO barrier interface, and the number of bilayers on the tunneling magneto resistance (TMR) effect are investigated. TMR-ratios of about 11% at room temperature and 18.5% at 13 K are measured and two well-defined switching fields are observed. The results are compared to measurements of MTJs with Co-Fe-B electrodes and in-plane anisotropy.

  1. Zero-field spin transfer oscillators based on magnetic tunnel junction having perpendicular polarizer and planar free layer

    Science.gov (United States)

    Fang, Bin; Feng, Jiafeng; Gan, Huadong; Malmhall, Roger; Huai, Yiming; Xiong, Rongxin; Wei, Hongxiang; Han, Xiufeng; Zhang, Baoshun; Zeng, Zhongming

    2016-12-01

    We experimentally studied spin-transfer-torque induced magnetization oscillations in an asymmetric MgO-based magnetic tunnel junction device consisting of an in-plane magnetized free layer and an out-of-plane magnetized polarizer. A steady auto-oscillation was achieved at zero magnetic field and room temperature, with an oscillation frequency that was strongly dependent on bias currents, with a large frequency tunability of 1.39 GHz/mA. Our results suggest that this new structure has a high potential for new microwave device designs.

  2. Zero-field spin transfer oscillators based on magnetic tunnel junction having perpendicular polarizer and planar free layer

    Directory of Open Access Journals (Sweden)

    Bin Fang

    2016-12-01

    Full Text Available We experimentally studied spin-transfer-torque induced magnetization oscillations in an asymmetric MgO-based magnetic tunnel junction device consisting of an in-plane magnetized free layer and an out-of-plane magnetized polarizer. A steady auto-oscillation was achieved at zero magnetic field and room temperature, with an oscillation frequency that was strongly dependent on bias currents, with a large frequency tunability of 1.39 GHz/mA. Our results suggest that this new structure has a high potential for new microwave device designs.

  3. High sensitivity microwave detection using a magnetic tunnel junction in the absence of an external applied magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Gui, Y. S.; Bai, L. H.; Hu, C.-M. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada); Xiao, Y.; Guo, H. [Department of Physics, Center for the Physics of Materials, McGill University, Montreal, Quebec H3A 2T8 (Canada); Hemour, S.; Zhao, Y. P.; Wu, K. [Ecole Polytechnique de Montreal, Montreal, Quebec H3T 1J4 (Canada); Houssameddine, D. [Everspin Technologies, 1347 N. Alma School Road, Chandler, Arizona 85224 (United States)

    2015-04-13

    In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5000 mV/mW.

  4. A compact model for magnetic tunnel junction (MTJ) switched by thermally assisted Spin transfer torque (TAS + STT)

    Science.gov (United States)

    Zhao, Weisheng; Duval, Julien; Klein, Jacques-Olivier; Chappert, Claude

    2011-12-01

    Thermally assisted spin transfer torque [TAS + STT] is a new switching approach for magnetic tunnel junction [MTJ] nanopillars that represents the best trade-off between data reliability, power efficiency and density. In this paper, we present a compact model for MTJ switched by this approach, which integrates a number of physical models such as temperature evaluation and STT dynamic switching models. Many experimental parameters are included directly to improve the simulation accuracy. It is programmed in the Verilog-A language and compatible with the standard IC CAD tools, providing an easy parameter configuration interface and allowing high-speed co-simulation of hybrid MTJ/CMOS circuits.

  5. Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    Directory of Open Access Journals (Sweden)

    J. Rogge

    2015-07-01

    Full Text Available We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs. By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR ratio of -10% is found for Co2FeAl (24 nm / BaO (5 nm / Fe (7 nm MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM, it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  6. Elliptic annular Josephson tunnel junctions in an external magnetic field: the statics

    DEFF Research Database (Denmark)

    Monaco, Roberto; Granata, Carmine; Vettoliere, Antonio

    2015-01-01

    symmetric electrodes a transverse magnetic field is equivalent to an in-plane field applied in the direction of the current flow. Varying the ellipse eccentricity we reproduce all known results for linear and ring-shaped JTJs. Experimental data on high-quality Nb/Al-AlOx/Nb elliptic annular junctions...... or in the perpendicular direction. We report a detailed study of both short and long elliptic annular junctions having different eccentricities. For junctions having a normalized perimeter less than one the threshold curves are derived and computed even in the case with one trapped Josephson vortex. For longer junctions...

  7. Influence of exchange bias on magnetic losses in CoFeB/MgO/CoFeB tunnel junctions

    Science.gov (United States)

    Stearrett, Ryan; Wang, W. G.; Kou, Xiaoming; Feng, J. F.; Coey, J. M. D.; Xiao, J. Q.; Nowak, E. R.

    2012-07-01

    The strength of the exchange bias field is found to influence the low-frequency magnetoresistive noise associated with the magnetic reference layer in sputtered-deposited and electron-beam-evaporated CoFeB/MgO/CoFeB tunnel junctions. The noise is due to magnetic losses arising in the reference layer. The losses are parameterized by a phase lag ɛ which exhibits a nontrivial dependence on the externally applied field. The general trend found among all devices is that the losses are largest in the antiparallel state. The effect of exchange bias on the reference layer's noise is investigated at a field corresponding to maximum resistance susceptibility, Href. Higher values for the phase lag at Href, ɛref, are found in devices having a large exchange bias field. We also observed that Href and ɛref are larger in devices having thicker seed layers. This characteristic is also evident in double-barrier magnetic tunnel junctions. Prolonged thermal annealing is found to decrease ɛref, reduce Href, and alter the field profile of the resistance susceptibility of the reference layer to resemble that of a more magnetically soft behavior. In addition to its impact on the magnetoresistive noise, the incorporation of exchange bias layers into the materials stack also affects the tunneling magnetoresistance ratio with higher values found at smaller exchange bias fields. We attribute the magnitude of the magnetic losses, and hence the magnetoresistive noise, from the reference layer to disorder in its magnetic microstructure. Our results indicate that the nature and degree of disorder are correlated to the strength of the exchange bias coupling. The origin of this correlation may be due to a competition between different microstructures among various layers, one that leads to coherent tunneling (large tunneling magnetoresistance) in MgO-based tunneling devices and the other which promotes strong exchange bias coupling. A decrease in the exchange bias either through degradation

  8. Microwave resonant activation in hybrid single-gap/two-gap Josephson tunnel junctions

    Science.gov (United States)

    Carabello, Steven; Lambert, Joseph G.; Mlack, Jerome; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Xi, X. X.; Ramos, Roberto C.

    2016-09-01

    Microwave resonant activation is a powerful, straightforward technique to study classical and quantum systems, experimentally realized in Josephson junction devices cooled to very low temperatures. These devices typically consist of two single-gap superconductors separated by a weak link. We report the results of the first resonant activation experiments on hybrid thin film Josephson junctions consisting of a multi-gap superconductor (MgB2) and a single-gap superconductor (Pb or Sn). We can interpret the plasma frequency in terms of theories both for conventional and hybrid junctions. Using these models, we determine the junction parameters including critical current, resistance, and capacitance and find moderately high quality factors of Q0˜ 100 for these junctions.

  9. Transport Properties of the Tunnel Junctions Al1-xCox/{Al1-xCox-oxide}/Al

    Institute of Scientific and Technical Information of China (English)

    X.F.Han; J. Murai; H.Kubota; Y.Ando; Q.Y.Wang; N.Tezuka; T.Miyazaki

    2000-01-01

    The oxides of Al1-xCox (x=0,0.25,0.5,0.75, and 1.0) alloys were chosen as barrier materials in this work. The tunnel junction consists of the bottom electrode Al1-xCox and the top electrode Al with an insulating layer { Al1-xCox-oxide} which was formed by natural oxidation in a baking-box at 333K. The oxidation time for forming an Al1-xCox-oxide layer on the surface of the bottom Al1-xCox layers were optimized.The resistance of Al1-xCox/{ Al1-xCox-oxide}/Al tunnel junctions varied between 101 and 106 Ω measured at 1 my and 4.2 K. The effective barrier height and width of insulating layers Al1-xCox-oxide ( x=0.25, 0.5, and 0.75 )varied between 0.6 and 2.7 eV and between 1.3 and 2.1 nm. It is shown that the thin oxide layer of Al1-xCox alloys can be chosen as barrier materials.

  10. Tunneling conductance study of a metal-superconductor junction in the presence of Rashba spin orbit coupling

    Science.gov (United States)

    Kapri, Priyadarshini; Basu, Saurabh

    2017-02-01

    The tunneling conductance for a junction device consisting of a normal metal and a singlet superconductor is studied with Rashba spin orbit coupling (RSOC) being present in the metallic lead and the interface separating the two regions via an extended Blonder-Tinkham-Klapwijk (BTK) formalism. Interesting interplay between the RSOC and a number of parameters that have experimental significance, and characterize either the junction or the superconducting leads, such as the barrier transparency, quasiparticle lifetime, Fermi wavevector mismatch, an in-plane magnetic field and their effects on the tunneling conductance are investigated in details for both a s-wave and a d-wave superconductor. In an opaque barrier, in presence of a quasiparticle lifetime, a Fermi wavevector mismatch or an external in-plane magnetic field, RSOC enhances the conductance corresponding to low biasing energies, that is, at energies lesser than the superconducting gap, while the reverse is noted for energies exceeding the magnitude of the gap. Further, there are exciting anomalies noted in the conductance spectrum for the d-wave gap which can be understood by incorporating the interplay between the superconducting gap and the angle of incident of the charge carriers.

  11. Impact of lattice strain on the tunnel magnetoresistance in Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 magnetic tunnel junctions

    KAUST Repository

    Useinov, Arthur

    2013-08-19

    The objective of this work is to describe the tunnel electron current in single-barrier magnetic tunnel junctions within an approach that goes beyond the single-band transport model. We propose a ballistic multichannel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single-crystal magnetic Fe(110) electrodes for Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 tunnel junctions, where the electronic band structures of Fe and La0.67Sr0.33MnO3 are derived by ab initio calculations.

  12. Tunnel magnetoresistance in full-epitaxial magnetic tunnel junctions with a top electrode consisting of a perpendicularly magnetized D022-Mn3Ge film

    Science.gov (United States)

    Sugihara, Atsushi; Suzuki, Kazuya; Miyazaki, Terunobu; Mizukami, Shigemi

    2015-07-01

    We grew a magnetic tunnel junction (MTJ) with a top electrode consisting of a Mn3Ge film using a thin Co-Fe alloy film as a seed layer. X-ray diffraction showed that the Mn3Ge had (001)-oriented D022 structure epitaxially grown on an MgO(001) substrate. Magnetic hysteresis loops suggested that the D022-Mn3Ge film possessed perpendicular magnetic anisotropy. A magnetoresistance (MR) ratio of 11.3% was observed in the microfabricated MTJ at room temperature. The resistance-field curve suggested that the top-Co-Fe and D022-Mn3Ge layer are weakly coupled antiferromagnetically. The optimization of top-Co-Fe composition would improve MR ratio.

  13. Low temperature tunneling magnetoresistance on (La,Sr)MnO3/Co junctions with organic spacer layers

    Science.gov (United States)

    Vinzelberg, H.; Schumann, J.; Elefant, D.; Gangineni, R. B.; Thomas, J.; Büchner, B.

    2008-05-01

    This paper concerns with giant magnetoresistance (MR) effects in organic spin valves, which are realized as layered (La,Sr)MnO3 (LSMO)-based junctions with tris-(8, hydroxyquinoline) aluminum (Alq3)-spacer and ferromagnetic top layers. The experimental work was focused on the understanding of the transport behavior in this type of magnetic switching elements. The device preparation was carried out in an ultrahigh vacuum chamber equipped with a mask changer by evaporation and sputtering on SrTiO3 substrates with LSMO stripes deposited by pulsed laser technique. The field and temperature dependences of the MR of the prepared elements are studied. Spin-valve effects at 4.2K have been observed in a broad resistance interval from 50Ω to MΩ range, however, without systematic dependence on spacer layer thickness and device area. In some samples, the MR changes sign as a function of the bias voltage. The observed similarity in the bias voltages dependences of the MR in comparison with conventional magnetic tunnel junctions with oxide barriers suggests a description of the found effects within the classical tunneling concept. This assumption is also confirmed by a similar switching behavior observed on ferromagnetically contacted carbon nanotube devices. The proposed model implies the realization of the transport via local Co chains embedded in the Alq3 layer and spin dependent tunneling over barriers at the interface Co grains/Alq3/LSMO. The existence of conducting Co chains within the organics is supported by transmission electron microscopic/electron energy loss spectroscopic studies on cross-sectional samples from analogous layer stacks.

  14. Graphene-SnO2 nanocomposites decorated with quantum tunneling junctions: preparation strategies, microstructures and formation mechanism.

    Science.gov (United States)

    Wang, Qingxiu; Wu, Xianzheng; Wang, Lijun; Chen, Zhiwen; Wang, Shilong

    2014-09-28

    Tin dioxide (SnO2) and graphene are versatile materials that are vitally important for creating new functional and smart materials. A facile, simple and efficient ultrasonic-assisted hydrothermal synthesis approach has been developed to prepare graphene-SnO2 nanocomposites (GSNCs), including three samples with graphene/Sn weight ratios = 1 : 2 (GSNC-2), 1 : 1 (GSNC-1), and graphene oxide/Sn weight ratio = 1 : 1 (GOSNC-1). Low-magnification electron microscopy analysis indicated that graphene was exfoliated and adorned with SnO2 nanoparticles, which were dispersed uniformly on both the sides of the graphene nanosheets. High-magnification electron microscopy analysis confirmed that the graphene-SnO2 nanocomposites presented network tunneling frameworks, which were decorated with the SnO2 quantum tunneling junctions. The size distribution of SnO2 nanoparticles was estimated to range from 3 to 5.5 nm. Comparing GSNC-2, GSNC-1, and GOSNC-1, GOSNC-1 was found to exhibit a significantly better the homogeneous distribution and a considerably smaller size distribution of SnO2 nanoparticles, which indicated that it was better to use graphene oxide as a supporting material and SnCl4·5H2O as a precursor to synthesize hybrid graphene-SnO2 nanocomposites. Experimental results suggest that the graphene-SnO2 nanocomposites with interesting SnO2 quantum tunneling junctions may be a promising material to facilitate the improvement of the future design of micro/nanodevices.

  15. Niobium tunnel junction fabrication using e-gun evaporation and SNAP

    Science.gov (United States)

    Kortlandt, J.; van der Zant, H. S. J.; Schellingerhout, A. J. G.; Mooij, J. E.

    1990-11-01

    We have fabricated high quality small area Nb-Al-Al 2O 3-Nb junctions with SNAP, making use of e-beam evaporation in a 10 -5 Pa diffusion pumped vacuum system. Nominal dimensions of the junctions are 8x8, 4x4 and 2x2 μm 2. We obtain typical current densities of 5-6 × 10 +2A/cm 2 and (critical current) x (subgap resistance) products of 40 mV.

  16. Direct Observation of Tunnelling through 100-nm-Wide All Metal Magnetic Junction into Si

    Institute of Scientific and Technical Information of China (English)

    Nam n. KIM; WANG Ke-Qiang; ZHANG Yu; WANG Jian-Qing

    2008-01-01

    @@ Nanoscaled spin-dependent tunnelling lines were patterned on doped Si and studied for tunnelling from the SDT ferromagnetic layer through an insulating barrier into Si. The injection contacts have the form of long strips with width and separation, ranging from 100 nm to 2 μm, and are patterned using e-beam lithography. The measured Ⅰ-Ⅴ characteristics versus temperature (80 to 300 K) on the 100 nm scaled devices between the layered-magnetic metals and the semiconductor clearly showed ballistic tunnelling, with weak dependence on the temperature.This is qualitatively different, at elevated temperatures, from 2-μm-wide scaled-up spin-dependent tunnelling structures, where thermal-ionic emission was observed to dominate carrier transport.

  17. Quantum Tunneling Model of a P-N Junction in Silvaco

    Science.gov (United States)

    2008-09-01

    September 1-5, 2008. [14] M. Shur, Physics of Semiconductor Devices, Prentice–Hall, Inc, 1990. [15] R. P. Feynman , The Feynman Lectures on Physics , Volume... physically based 2-D model was created in Silvaco Inc.’s ATLAS© software to model the quantum tunneling effect that is realized within a multi...photovoltaic cell. A physically based 2-D model was created in Silvaco Inc.’s software to model the quantum tunneling effect that is realized within a

  18. The manufacture and testing of magnetic tunnel junctions and a study of their switching characteristics Cobalt; Aluminium oxide; Permalloy; Sputtering; Thin films

    CERN Document Server

    Hughes, N D

    2002-01-01

    This thesis investigates the manufacture and switching characteristics of a series of cobalt/aluminium oxide/permalloy magnetic tunnel junctions. It describes the assembly and commissioning of the sputtering, magnetometry and electron transport measurement equipment required to manufacture and test the junctions. The junctions are made by sputtering thin films of the ferromagnetic materials and an ultra thin film of aluminium, which is oxidised by means of a DC glow discharge. The optimum oxidation conditions for the barrier are investigated and its characteristics determined by current-voltage modelling. The barrier thickness identified by the modelling is compared with that found by x-ray reflectometry. A simple single domain model is shown to give a reasonable fit to hysteresis and magneto-resistive data from the junctions and to provide a means to quantify the interlayer coupling. A comparative study of the magneto-resistive characteristics of junctions with ferromagnetic layers of 10nm and 100nm finds th...

  19. Numerical Optimization of Tunnel-recombination Junction and Optical Absorption Properties of a-Si:H/a-SiGe:H Double-junction Solar Cell

    Institute of Scientific and Technical Information of China (English)

    KE Shaoying; WANG Chong; PAN Tao; WANG Zhaoqing; YANG Jie; YANG Yu

    2015-01-01

    The tunnel-recombination junction (TRJ) and optical absorption properties of a-Si:H/a-SiGe:H dou-ble-junction solar cell were calculated by means of one dimensional simulator named AMPS-1D at the radiation of AM1.5G with a power density of 100 mW/cm2. Since the TRJ is the core component of the tandem solar cell, the optical absorption of the sub-cells and the electronic transport properties at the interface of the sub-cells are affected by the thickness and doping concentration of the TRJ. As a result, the TRJ parameters were optimized. The numerical results indicate that the maximum conversion efficiency (Ef) of 9.862% can be obtained when the thickness and doping con-centration of the TRJ are 10 nm and 5´1019 cm–3, respectively. Based on the analysis of the contour map of short circuit current density, the optimal current matching can be achieved for 130 nm-thick topi-layer and 250 nm-thick bottom i-layer. In addition, four kinds of TRJ structures were also simulated for the comparison purpose. According to the cal-culated resistivity and band structures of the four TRJs, the efficiency of the solar cell withn-typeμc-Si:H layer and p-type a-Si:H layer in TRJ structure is greater than that with other TRJ structures. It is assumed that the effect of the band offset that results in the formation of triangular barrier and backscattering behavior at the edge of the TRJ could be responsible to this phenomenon.

  20. Numerical Optimization of Tunnel-recombination Junction and Optical Absorption Properties of a-Si:H/a-SiGe:H Double-junction Solar Cell

    Institute of Scientific and Technical Information of China (English)

    KE; Shaoying; WANG; Chong; PAN; Tao; WANG; Zhaoqing; YANG; Jie; YANG; Yu

    2015-01-01

    The tunnel-recombination junction(TRJ) and optical absorption properties of a-Si:H/a-Si Ge:H double-junction solar cell were calculated by means of one dimensional simulator named AMPS-1D at the radiation of AM1.5G with a power density of 100 m W/cm2. Since the TRJ is the core component of the tandem solar cell, the optical absorption of the sub-cells and the electronic transport properties at the interface of the sub-cells are affected by the thickness and doping concentration of the TRJ. As a result, the TRJ parameters were optimized. The numerical results indicate that the maximum conversion efficiency(Eff) of 9.862% can be obtained when the thickness and doping concentration of the TRJ are 10 nm and 5*1019 cm–3, respectively. Based on the analysis of the contour map of short circuit current density, the optimal current matching can be achieved for 130 nm-thick top i-layer and 250 nm-thick bottom i-layer. In addition, four kinds of TRJ structures were also simulated for the comparison purpose. According to the calculated resistivity and band structures of the four TRJs, the efficiency of the solar cell with n-type μc-Si:H layer and p-type a-Si:H layer in TRJ structure is greater than that with other TRJ structures. It is assumed that the effect of the band offset that results in the formation of triangular barrier and backscattering behavior at the edge of the TRJ could be responsible to this phenomenon.

  1. Zurek-Kibble mechanism for the spontaneous vortex formation in Nb-Al/Al-ox/Nb Josephson tunnel junctions: New theory and experiment

    DEFF Research Database (Denmark)

    Monaco, R.; Mygind, Jesper; Aarøe, Morten

    2006-01-01

    New scaling behavior has been both predicted and observed in the spontaneous production of fluxons in quenched Nb-Al/Al-ox/Nb annular Josephson tunnel junctions (JTJs) as a function of the quench time, tau(Q). The probability f(1) to trap a single defect during the normal-metal-superconductor pha...

  2. MoRe-based and MgB{sub 2} -based tunnel junctions and their characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Shaternik, V; Noskov, V; Chubatyy, V [Kurdyumov Institute for Metal Physics of National Academy of Sciences of Ukraine, Vernadskii boulevard 36, 02142 Kiev (Ukraine); Larkin, S [Concern ' Nauka' , Dovnar-Zapol' skii street 2/20, 03116 Kiev (Ukraine); Belogolovskii, M, E-mail: shaternik@mail.r [Donetsk Institute for Physics and Engineering, National Academy of Sciences of Ukraine, 83114 Donetsk (Ukraine)

    2010-06-01

    Perspective Josephson Mo-Re alloy-oxide-Pb, MgB{sub 2}- oxide - Mo-Re alloy and Mo-Re alloy-normal metal-oxide- normal metal-Mo-Re alloy junctions have been fabricated and investigated. Thin ({approx}50-100 nm) MoRe superconducting films are deposited on Al{sub 2}O{sub 3} substrates by using a dc magnetron sputtering of MoRe target. Thin ({approx}50-100 nm) MgB{sub 2} superconducting films are deposited on Al{sub 2}O{sub 3} substrates by using e-beam evaporation of boron and thermal coevaporation of magnesium. To investigate a transparency spread for the fabricated junctions barriers the computer simulation of the measured quasiparticle I-V curves have been done in framework of the model of multiple Andreev reflections in double-barrier junction interfaces. It's demonstrated the investigated junctions can be described as highly asymmetric double-barrier Josephson junctions with great difference between the two barrier transparencies. Results of computer simulation of quasiparticles I-V curves of junctions are presented and discussed. The I{sub C}(T) characteristics, measured for Josephson heterostructures with different thickness of metal layer s and exposure dose E, essentially deviate from an Ambegaokar- Baratoff (A and B) I{sub C}(T) behavior and Kulik-Omelianchuck (K and O) curves, because of proximity effect caused by the comparatively high value of s (up to 100 nm).

  3. Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure

    Science.gov (United States)

    Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

    2016-09-01

    For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

  4. Long and narrow Josephson tunnel junctions of mixed overlap and inline character

    DEFF Research Database (Denmark)

    Olsen, O.H.; Samuelsen, Mogens Rugholm

    1983-01-01

    A model describing long Josephson junctions of mixed overlap and inline geometry is presented. The shape of the first zero field step is calculated for this model using a perturbation approach. The question of influence of external magnetic field on the maximum supercurrent is investigated for ov...... for overlap, inline, and mixed overlap-inline geometries. A linear dependence is found for the inline model and for mixed overlap-inline junctions in agreement with experiments. Journal of Applied Physics is copyrighted by The American Institute of Physics....

  5. Complementary Barrier Infrared Detector (CBIRD) with Double Tunnel Junction Contact and Quantum Dot Barrier Infrared Detector (QD-BIRD)

    Science.gov (United States)

    Ting, David Z.-Y; Soibel, Alexander; Khoshakhlagh, Arezou; Keo, Sam A.; Nguyen, Jean; Hoglund, Linda; Mumolo, Jason M.; Liu, John K.; Rafol, Sir B.; Hill, Cory J.; Gunapala, Sarath D.

    2012-01-01

    The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from approximately 4.2 micrometers to 6 micrometers, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225 K.

  6. Spin Transfer Torque Switching and Perpendicular Magnetic Anisotropy in Full Heusler Alloy Co2FeAl-BASED Tunnel Junctions

    Science.gov (United States)

    Sukegawa, H.; Wen, Z. C.; Kasai, S.; Inomata, K.; Mitani, S.

    2014-12-01

    Some of Co-based full Heusler alloys have remarkable properties in spintronics, that is, high spin polarization of conduction electrons and low magnetic damping. Owing to these properties, magnetic tunnel junctions (MTJs) using Co-based full Heusler alloys are potentially of particular importance for spintronic application such as magnetoresistive random access memories (MRAMs). Recently, we have first demonstrated spin transfer torque (STT) switching and perpendicular magnetic anisotropy (PMA), which are required for developing high-density MRAMs, in full-Heusler Co2FeAl alloy-based MTJs. In this review, the main results of the experimental demonstrations are shown with referring to related issues, and the prospect of MTJs using Heusler alloys is also discussed.

  7. Investigation of the Mn{sub 3−δ}Ga/MgO interface for magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    ViolBarbosa, C. E., E-mail: carlos.barbosa@cpfs.mpg.de; Ouardi, S.; Fecher, G. H.; Felser, C. [Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, 01187 Dresden (Germany); Kubota, T.; Mizukami, S.; Miyazaki, T. [WPI Advanced Institute for Materials Research, Tohoku University, 980-8577 Sendai (Japan); Kozina, X.; Ikenaga, E. [JASRI, SPring-8, Sayo-cho, Hyogo 679-5198 (Japan)

    2014-07-21

    The Mn{sub 3}Ga Heusler compound and related alloys are the most promising materials for the realization of spin-transfer-torque magnetoresistive memories. Mn–Ga films exhibits perpendicular magnetic anisotropy and high spin polarization and can be used to improve the performance of MgO-based magneto tunneling junctions. The interface between Mn–Ga and MgO films were chemically characterized by hard x-ray photoelectron spectroscopy. The experiment indicated the formation of Ga-O bonds at the interface and evidenced changes in the local environment of Mn atoms in the proximity of the MgO film. We show that the deposition of few monoatomic layers of Mg on top of Mn–Ga film, before the MgO deposition, strongly suppresses the oxidation of gallium.

  8. Simulation of electric-field and spin-transfer-torque induced magnetization switching in perpendicular magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiangli; Zhang, Zongzhi, E-mail: zzzhang@fudan.edu.cn [Department of Optical Science and Engineering, Shanghai Ultra-Precision Optical Engineering Center, Fudan University, Shanghai 200433 (China); Liu, Yaowen [School of Physical Science and Engineering, Tongji University, Shanghai 200092 (China); Jin, Q. Y. [State Key Laboratory of Precision Spectroscopy and Department of Physics, East China Normal University, Shanghai 200062 (China)

    2015-05-07

    Macrospin simulations are performed to model the magnetization switching driven by the combined action of electric-field and spin-polarized electric current (spin-transfer torque; STT) in MgO/CoFeB based magnetic tunnel junctions with interfacial perpendicular magnetic anisotropy. The results indicate that at low current case, the free layer magnetization shows a fast toggle-like switching, the final parallel or antiparallel magnetization state is determined by the electric-field effect, and the STT just helps or resists it to reach the final state depending on the current direction. However, with the increase of current strength, the contribution of STT effect gradually increases, which eventually achieves a deterministic magnetization switching state. Simulations further demonstrate that by appropriately tuning the parameters of applied electric-field and current the power consumption can be easily reduced by two orders of magnitude.

  9. A compact model for magnetic tunnel junction (MTJ switched by thermally assisted Spin transfer torque (TAS + STT

    Directory of Open Access Journals (Sweden)

    Zhao Weisheng

    2011-01-01

    Full Text Available Abstract Thermally assisted spin transfer torque [TAS + STT] is a new switching approach for magnetic tunnel junction [MTJ] nanopillars that represents the best trade-off between data reliability, power efficiency and density. In this paper, we present a compact model for MTJ switched by this approach, which integrates a number of physical models such as temperature evaluation and STT dynamic switching models. Many experimental parameters are included directly to improve the simulation accuracy. It is programmed in the Verilog-A language and compatible with the standard IC CAD tools, providing an easy parameter configuration interface and allowing high-speed co-simulation of hybrid MTJ/CMOS circuits.

  10. Investigation of magnetic sensor properties of magnetic tunnel junctions with superparamagnetic free layer at low frequencies for biomedical imaging applications

    Science.gov (United States)

    Ishikawa, Kyohei; Oogane, Mikihiko; Fujiwara, Kousuke; Jono, Junichi; Tsuchida, Masaaki; Ando, Yasuo

    2016-12-01

    The magnetic sensor properties of magnetic tunnel junctions (MTJs) with a superparamagnetic (SP) free layer were systematically investigated at low frequencies (<10 Hz). We prepared four varieties of MTJs with various SP properties by changing the annealing temperature. The temperature dependence of magnetoresistance curves and the signal/noise property at 285 K were evaluated. We found that the SP free layer has the advantage of detecting very small and low-frequency AC magnetic fields compared with a ferromagnetic free layer. The SP free layer strongly suppressed magnetic 1/f noise at low frequencies and expressed a very linear response to a small magnetic field. The obtained properties in MTJs with the SP free layer are suitable for detecting biomagnetic fields. The detectivity was 111 nT at low frequencies (from 0.1 to 10 Hz), which is one of the highest values in single-MTJ sensors.

  11. Origin of the broad three-terminal Hanle signals in Fe/SiO{sub 2}/Si tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Shoichi; Tanaka, Masaaki [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Nakane, Ryosho [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Institute for Innovation in International Engineering Education, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2015-07-20

    Lorentzian-shaped broader three-terminal Hanle (B-3TH) signals are observed in Fe/SiO{sub 2}/Si tunnel junction devices at 6–300 K. We propose a spin conducting model, which explains all the characteristics of our experimental results, such as field angle dependence and bias dependence of the B-3TH signals, as well as experimental results reported by other groups. It was found that the shape of the B-3TH signals is determined by the spin depolarization at the Fe/SiO{sub 2} interface caused by local magnetic fields, unlike the conventional understanding. The shape of the B-3TH signals, including narrower and inverted Hanle signals, reflects the magnetic order of an ultrathin paramagnetic layer formed at the Fe/SiO{sub 2} interface. Our model provides a unified explanation of the B-3TH signals observed in three-terminal Hanle measurements.

  12. Experimental Observation of Non-'S-Wave' Superconducting Behavior in Bulk Superconducting Tunneling Junctions of Yba2Cu3O7-δ

    Directory of Open Access Journals (Sweden)

    Leandro Jose Guerra

    1998-06-01

    Full Text Available Evidence of non-s-wave superconductivity from normal tunneling experiments in bulk tunneling junctions of YBa2Cu3O7-δ is presented. The I-V and dI/dV characteristics of bulk superconducting tunneling junctions of YBa2Cu3O7-δ have been measured at 77.0K and clear deviation from s-wave superconducting behavior has been observed. The result agrees with d-wave symmetry, and interpreting the data in this way, the magnitude of the superconducting energy gap, 2Δ, is found to be (0.038 ± 0.002 eV. Comparing this energy gap with Tc (2Δ/kB Tc = 5.735, indicates that these high-Tc superconductors are strongly correlated materials, which in contrast with BCS-superconductors are believed to be weakly correlated.

  13. Simulations of fine structures on the zero field steps of Josephson tunnel junctions

    DEFF Research Database (Denmark)

    Scheuermann, M.; Chi, C. C.; Pedersen, Niels Falsig;

    1986-01-01

    are generated by the interaction of the bias current with the fluxon at the junction edges. On the first zero field step, the voltages of successive fine structures are given by Vn=[h-bar]/2e(2omegap/n), where n is an even integer. Applied Physics Letters is copyrighted by The American Institute of Physics....

  14. A Novel Approach to Modeling Tunnel Junction Diodes Using Silvaco Atlas Software

    Science.gov (United States)

    2005-12-01

    Santa Clara, California, 2003. 2. A. S. Sedra , and K. C. Smith , Microelectronic Circuits, Oxford University Press, New York, 1998. 3. S. O. Kasap...Swartz, “In Perspective: The Tunnel Diode,” International Solid State Circuits Conference, pp. 278-280, 1986. 18. D. D. Smith , J. M. Gee, M. D

  15. Effect of annealing on the temperature dependence of inelastic tunneling contributions vis-à-vis tunneling magnetoresistance and barrier parameters in CoFe/MgO/NiFe magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Bhusan Singh, Braj; Chaudhary, Sujeet, E-mail: sujeetc@physics.iitd.ac.in [Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi-110 016 (India)

    2014-02-28

    The effect of annealing on the changes in the inelastic tunneling contributions in tunneling conductance of ion beam sputtered CoFe/MgO/NiFe magnetic tunnel junctions (MTJs) is investigated. The inelastic contributions are evaluated using hopping conduction model of Glazman and Matveev in the temperature range of 25–300 K. The hopping through number of series of localized states present in the barrier due to structural defects increases from 9 (in as deposited MTJ) to 18 after annealing (at 200 °C/1 h); although no changes in the interface roughness of CoFe-MgO and MgO-NiFe interfaces are observed as revealed by the x-ray reflectance studies on planar MTJs. The bias dependence of tunneling magnetoresistance (TMR) at 25 K is found to get improved after annealing as revealed by the value V{sub 1/2} (the bias value at which the TMR reaches to half of its value at nearly zero bias); which is 78 mV (in MTJ annealed at 200 °C/1 h) 2.5 times the value of 33 mV (in as deposited MTJ). At 25 K the inelastic tunneling spectra revealed the presence of zero bias anomaly and magnon excitations in the range of 10–15 mV. While the barrier height exhibited a strong temperature dependence with nearly 100% increase from the value at 300 K to 25 K, the temperature dependence of TMR becomes steep after annealing.

  16. A link between the coercivity and microstructure of high moment Fe films and their use in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Georgieva, M.T. [Institute for Materials Research, Maxwell Building, The University of Salford, Salford M5 4WT (United Kingdom)]. E-mail: milena.georgieva@mdm.infm.it; Telling, N.D. [Institute for Materials Research, Maxwell Building, The University of Salford, Salford M5 4WT (United Kingdom); Magnetic Spectroscopy Group, CCLRC Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Grundy, P.J. [Institute for Materials Research, Maxwell Building, The University of Salford, Salford M5 4WT (United Kingdom)

    2006-01-25

    Magnetron sputtered single Fe films have been 'softened' magnetically by controlled N-doping during the sputter deposition. This technique allows a reduction in grain size and coercivity of the Fe films, without decreasing the saturation magnetization and without the formation of any crystalline FeN phases. We describe this effect through a modification of the random magnetocrystalline anisotropy model, by taking the film thickness into account. The coercivities calculated in this way are in good agreement with those obtained experimentally. It is demonstrated that N-doping can be samples increased as to control the switching field of the 'free' layer in magnetic trilayer films of the MTJ type. It is thus possible to construct an all Fe-electrode magnetic tunnel junction (MTJ) that displays the tunneling magnetoresistance (TMR) effect by altering the switching field of one Fe layer using N-doping. The ability to control the magnetic softness of high magnetic moment materials is important in regard to their incorporation into TMR devices.

  17. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Science.gov (United States)

    Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, J.-Q.

    2016-11-01

    We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  18. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Directory of Open Access Journals (Sweden)

    Chao Zhang

    2016-11-01

    Full Text Available We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  19. Enhancement of electric-field-induced change of magnetic anisotropy by interface engineering of MgO magnetic tunnel junctions

    Science.gov (United States)

    Bonaedy, Taufik; Choi, Jun Woo; Jang, Chaun; Min, Byoung-Chul; Chang, Joonyeon

    2015-06-01

    Electric-field-induced modification of magnetic anisotropy is studied using tunnel magnetoresistance of the Co40Fe40B20/ MgO/ Co40Fe40B20 and Co40Fe40B20/ Hf (0.08 nm)/ MgO/ Co40Fe40B20 magnetic tunnel junctions. In both systems, the interfacial perpendicular magnetic anisotropy is increased with increasing electron density at the MgO interface. A quantitative comparison between the two systems reveals that the change of magnetic anisotropy energy with electric field is significantly enhanced in Co40Fe40B20/ Hf/ MgO/ Co40Fe40B20 compared to Co40Fe40B20/ MgO/ Co40Fe40B20. The sub-monolayer Hf insertion at the Co40Fe40B20/MgO interface turns out to be critical to the enhanced electric field control of the magnetic anisotropy, indicating the interface sensitive nature of the effect.

  20. MnGa-based fully perpendicular magnetic tunnel junctions with ultrathin Co2MnSi interlayers.

    Science.gov (United States)

    Mao, Siwei; Lu, Jun; Zhao, Xupeng; Wang, Xiaolei; Wei, Dahai; Liu, Jian; Xia, Jianbai; Zhao, Jianhua

    2017-02-24

    Because tetragonal structured MnGa alloy has intrinsic (not interface induced) giant perpendicular magnetic anisotropy (PMA), ultra-low damping constant and high spin polarization, it is predicted to be a kind of suitable magnetic electrode candidate in the perpendicular magnetic tunnel junction (p-MTJ) for high density spin transfer torque magnetic random access memory (STT-MRAM) applications. However, p-MTJs with both bottom and top MnGa electrodes have not been achieved yet, since high quality perpendicular magnetic MnGa films can hardly be obtained on the MgO barrier due to large lattice mismatch and surface energy difference between them. Here, a MnGa-based fully p-MTJ with the structure of MnGa/Co2MnSi/MgO/Co2MnSi/MnGa is investigated. As a result, the multilayer is with high crystalline quality, and both the top and bottom MnGa electrodes show well PMA. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. Ultrathin Co2MnSi films are used to optimize the interface quality between MnGa and MgO barrier. A strong antiferromagnetic coupling in MnGa/Co2MnSi bilayer is confirmed with the interfacial exchange coupling constant of -5erg/cm(2). This work proposes a novel p-MTJ structure for the future STT-MRAM progress.

  1. MnGa-based fully perpendicular magnetic tunnel junctions with ultrathin Co2MnSi interlayers

    Science.gov (United States)

    Mao, Siwei; Lu, Jun; Zhao, Xupeng; Wang, Xiaolei; Wei, Dahai; Liu, Jian; Xia, Jianbai; Zhao, Jianhua

    2017-01-01

    Because tetragonal structured MnGa alloy has intrinsic (not interface induced) giant perpendicular magnetic anisotropy (PMA), ultra-low damping constant and high spin polarization, it is predicted to be a kind of suitable magnetic electrode candidate in the perpendicular magnetic tunnel junction (p-MTJ) for high density spin transfer torque magnetic random access memory (STT-MRAM) applications. However, p-MTJs with both bottom and top MnGa electrodes have not been achieved yet, since high quality perpendicular magnetic MnGa films can hardly be obtained on the MgO barrier due to large lattice mismatch and surface energy difference between them. Here, a MnGa-based fully p-MTJ with the structure of MnGa/Co2MnSi/MgO/Co2MnSi/MnGa is investigated. As a result, the multilayer is with high crystalline quality, and both the top and bottom MnGa electrodes show well PMA. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. Ultrathin Co2MnSi films are used to optimize the interface quality between MnGa and MgO barrier. A strong antiferromagnetic coupling in MnGa/Co2MnSi bilayer is confirmed with the interfacial exchange coupling constant of −5erg/cm2. This work proposes a novel p-MTJ structure for the future STT-MRAM progress. PMID:28233780

  2. Superconducting Tunnel Junction Refrigerators for Sub-Kelvin Cooling of Electrons, Phonons, and Arbitrary, User-Supplied Payloads

    Science.gov (United States)

    Lowell, Peter Joseph

    Modern science often requires measurements at sub-Kelvin temperatures. Temperatures of 300 mK can be reached by using liquid 3He, but reaching lower temperatures requires the use of adiabatic demagnetization and dilution refrigerators which are complex, large, and costly. Normal-metalInsulatorSuperconductor (NIS) tunnel junctions provide an alternative refrigeration method that is simple to use, compact, and provides continuous cooling power that has the potential to expand the accessibility of these sub-Kelvin temperatures. When properly biased, the electron system in the normal metal of an NIS junction is cooled since the hottest electrons preferentially tunnel from the normal metal to the superconductor, transferring heat in the process. When the normal metal is extended onto a thermally isolated membrane, the cold electrons cool the phonons in the membrane through electron-phonon coupling. In previous work, NIS junctions have been used to cool detectors and bulk objects that were integrated with the membrane, but could not be considered a general-purpose refrigerator since they could not cool arbitrary objects. The goal of this work has been to demonstrate a general-purpose NIS refrigerator to which a user can attach arbitrary bulk objects. First, we discuss NIS refrigeration and then develop a model to predict phonon cooling. We fabricated and tested NIS refrigerators capable of cooling bulk objects and used the model to explain the results. The devices were able to cool phonons from 300 mK to 154 mK with 100 pW of cooling power at 200 mK. With these devices, we were able to cool a 2 cm3 piece of copper from 290 mK to 256 mK with 700 pW of cooling power at 290 mK. This demonstration marks the emergence of NIS refrigerators as a true, general-purpose refrigerator since users can attach arbitrary objects. Measurements of Andreev reflections in the devices and next-generation refrigerators that cool electrons from 100 mK to below 50 mK are also presented.

  3. Non-equilibrium tunneling in zigzag graphene nanoribbon break-junction results in spin filtering

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Liming [Centre for Neural Engineering, The University of Melbourne, 203 Bouverie Street, Carlton, Victoria 3053 (Australia); Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010 (Australia); National ICT Australia, The University of Melbourne, Parkville 3010 (Australia); Qiu, Wanzhi; Sharafat Hossain, Md; Al-Dirini, Feras; Skafidas, Efstratios, E-mail: sskaf@unimelb.edu.au [Centre for Neural Engineering, The University of Melbourne, 203 Bouverie Street, Carlton, Victoria 3053 (Australia); Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010 (Australia); Evans, Robin [Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010 (Australia)

    2016-02-07

    Spintronic devices promise new faster and lower energy-consumption electronic systems. Graphene, a versatile material and candidate for next generation electronics, is known to possess interesting spintronic properties. In this paper, by utilizing density functional theory and non-equilibrium green function formalism, we show that Fano resonance can be generated by introducing a break junction in a zigzag graphene nanoribbon (ZGNR). Using this effect, we propose a new spin filtering device that can be used for spin injection. Our theoretical results indicate that the proposed device could achieve high spin filtering efficiency (over 90%) at practical fabrication geometries. Furthermore, our results indicate that the ZGNR break junction lattice configuration can dramatically affect spin filtering efficiency and thus needs to be considered when fabricating real devices. Our device can be fabricated on top of spin transport channel and provides good integration between spin injection and spin transport.

  4. Charge transport in molecular junctions: From tunneling to hopping with the probe technique

    CERN Document Server

    Kilgour, Michael

    2015-01-01

    We demonstrate that a simple phenomenological approach can be used to simulate electronic conduction in molecular wires under thermal effects induced by the surrounding environment. This "Landauer-B\\"uttiker's probe technique" can properly replicate different transport mechanisms: phase coherent nonresonant tunneling, ballistic behavior, and hopping conduction, to provide results consistent with experiments. Specifically, our simulations with the probe method recover the following central characteristics of charge transfer in molecular wires: (i) The electrical conductance of short wires falls off exponentially with molecular length, a manifestation of the tunneling (superexchange) mechanism. Hopping dynamics overtakes superexchange in long wires demonstrating an ohmic-like behavior. (ii) In off-resonance situations, weak dephasing effects facilitate charge transfer. Under large dephasing the electrical conductance is suppressed. (iii) At high enough temperatures, $k_BT/\\epsilon_B>1/25$, with $\\epsilon_B$ as ...

  5. Interface study of FeMgOFe magnetic tunnel junctions using 3D Atom Probe

    CERN Document Server

    Mazumder, B; Vella, A; Vurpillot, F; Deconihout, B

    2011-01-01

    A detailed interface study was conducted on a Fe/MgO/Fe system using laser assisted 3D atom probe. It exhibits an additional oxide formation at the second interface of the multilayer structure independent of laser wavelength, laser fluence and the thickness of the tunnel barrier. We have shown with the help of simulation that this phenomena is caused by the field evaporation of two layers having two different evaporation

  6. GaInP/GaAs tandem solar cells with highly Te-and Mg-doped GaAs tunnel junctions grown by MBE

    Institute of Scientific and Technical Information of China (English)

    郑新和; 刘三姐; 夏宇; 甘兴源; 王海啸; 王乃明; 杨辉

    2015-01-01

    We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction (TJ) with using tellurium (Te) and magnesium (Mg) as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy (MBE) at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm2. The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 mA/cm2, but a low open-circuit voltage range of 1.4 V∼1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy (SIMS) analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended GaAs n++/p++junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of∼2.5 × 1020 in GaAs could cause a lattice strain of 10−3 in magnitude and thus a surface roughening, which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell.

  7. Fe3O4/MgO/Fe Heteroepitaxial Structures for Magnetic Tunnel Junctions

    Energy Technology Data Exchange (ETDEWEB)

    Orna, J. [University of Zaragoza, Spain; Morellon, Luis [University of Zaragoza, Spain; Algarabel, Pedro A. [University of Zaragoza, Spain; Pardo, J. A. [University of Zaragoza, Spain; Sangiao, S [Instituto de Nanociencia de Aragón, Universidad de Zaragoza, Zaragoza, 50009 Spain; Magen, C [Oak Ridge National Laboratory (ORNL); Snoeck, E. [CEMES-CNRS, Toulouse, France; De Teresa, J M [Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, Zaragoza, 50009 Spain; Ibarra, M. Ricardo [University of Zaragoza, Spain

    2008-01-01

    In this work we report the growth and structural and magnetic characterization of heteroepitaxial Fe O/MgO/Fe junctions. All three layers have been deposited by pulsed laser deposition. Combining High Resolution Transmission Electron Microscopy and X-ray results, we have obtained for the heterostructure the epitaxy relation MgO(001) [100]//Fe O(001)[100]/MgO(001) [100]/Fe(001)[110]. All interfaces appear very sharp with relatively small root-mean square (rms) roughness, 0.2 nm. The magnetic coupling between Fe O and Fe electrodes is also very small, 0.03 mJ/

  8. Coherence effects in S/I/N/I/FS tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Li Xiao-Wei

    2007-01-01

    The dc Josephson effect in superconductor/insulator/normal metal/insulator/ferromagnetic superconductor junctions has been studied. We calculate the dc Josephson current based on the Bogoliubov de Gennes equation. The Josephson current is derived as a function of exchange field in ferromagnetic superconductor, normal metal thickness and insulating barrier strength. It is found that there exists an oscillation relation between the critical Josephson current and the normal metal thickness. The oscillation amplitude decreases as the thickness of the normal metal increases or the exchange field augments.

  9. ``Hybrid'' multi-gap/single-gap Josephson junctions: Evidence of macroscopic quantum tunneling in superconducting-to-normal switching experiments on MgB2/I/Pb and MgB2/I/Sn junctions

    Science.gov (United States)

    Carabello, Steve; Lambert, Joseph; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Xi, X. X.; Ramos, Roberto

    We report results of superconducting-to-normal switching experiments on MgB2/I/Pb and MgB2/I/Sn junctions, with and without microwaves. These results suggest that the switching behavior is dominated by quantum tunneling through the washboard potential barrier, rather than thermal excitations or electronic noise. Evidence includes a leveling in the standard deviation of the switching current distribution below a crossover temperature, a Lorentzian shape of the escape rate enhancement peak upon excitation by microwaves, and a narrowing in the histogram of escape counts in the presence of resonant microwave excitation relative to that in the absence of microwaves. These are the first such results reported in ``hybrid'' Josephson tunnel junctions, consisting of multi-gap and single-gap superconducting electrodes.

  10. Voltage-controlled inversion of tunnel magnetoresistance in epitaxial nickel/graphene/MgO/cobalt junctions

    Energy Technology Data Exchange (ETDEWEB)

    Godel, F.; Doudin, B.; Henry, Y.; Halley, D., E-mail: halley@ipcms.unistra.fr, E-mail: dayen@ipcms.unistra.fr; Dayen, J.-F., E-mail: halley@ipcms.unistra.fr, E-mail: dayen@ipcms.unistra.fr [Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-UdS, 23 rue du Loess, 67034 Strasbourg (France); Venkata Kamalakar, M. [Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-UdS, 23 rue du Loess, 67034 Strasbourg (France); Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg (Sweden)

    2014-10-13

    We report on the fabrication and characterization of vertical spin-valve structures using a thick epitaxial MgO barrier as spacer layer and a graphene-passivated Ni film as bottom ferromagnetic electrode. The devices show robust and scalable tunnel magnetoresistance, with several changes of sign upon varying the applied bias voltage. These findings are explained by a model of phonon-assisted transport mechanisms that relies on the peculiarity of the band structure and spin density of states at the hybrid graphene|Ni interface.

  11. Voltage-controlled inversion of tunnel magnetoresistance in epitaxial nickel/graphene/MgO/cobalt junctions

    Science.gov (United States)

    Godel, F.; Venkata Kamalakar, M.; Doudin, B.; Henry, Y.; Halley, D.; Dayen, J.-F.

    2014-10-01

    We report on the fabrication and characterization of vertical spin-valve structures using a thick epitaxial MgO barrier as spacer layer and a graphene-passivated Ni film as bottom ferromagnetic electrode. The devices show robust and scalable tunnel magnetoresistance, with several changes of sign upon varying the applied bias voltage. These findings are explained by a model of phonon-assisted transport mechanisms that relies on the peculiarity of the band structure and spin density of states at the hybrid graphene|Ni interface.

  12. Modulation of interlayer exchange coupling strength in magnetic tunnel junctions via strain effect

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xin, E-mail: jiangxinyj@gmail.com; Li, Zhipeng; Zheng, Yuankai; Kaiser, Christian; Diao, Zhitao; Fang, Jason; Leng, Qunwen, E-mail: Qunwen.Leng@wdc.com [Western Digital Corporation, 44100 Osgood Road, Fremont, California 94539 (United States)

    2015-09-15

    Interlayer exchange coupling of two ferromagnetic electrodes separated by a thin MgO tunnel barrier is investigated using magneto-optical Kerr effect. We find that the coupling field can be reduced by more than 40% as the thickness of a top Ta capping layer increases from 0.5 to 1.2 nm. In contrast, a similar film stack with an additional 3 nm Ru capping layer displays no such dependence on Ta thickness. Transmission electron microscopy study shows that the oxidation of the exposed Ta capping layer induces changes in the crystalline structures of the underlying films, giving rise to the observed reduction of the interlayer coupling field.

  13. Tunneling conductance through normal metal - superconductor junctions: effects of Rashba spin orbit coupling and magnetic field

    Science.gov (United States)

    Kapri, Priyadarshini; Ganguly, Sudin; Basu, Saurabh

    2016-10-01

    In a system consisting of a metal-(s-wave) superconductor junction, we study the conductance characteristics in presence of Rashba spin orbit coupling (RSOC) and an external magnetic field applied along the plane of the sample. With a selective inclusion of the Rashba coupling either in the metallic or in both we note that there is a distinct effect with regard to the magnitude of the Andreev peak that occurs at a biasing voltage lower than the superconducting gap energy. The height of the peak is sensitive to the RSOC (increases with increase in RSOC) for RSOC to be present only in the metallic region, (same is true when RSOC is present throughout the junction), while the peak height is fairly independent when RSOC is solely present in the superconducting region. The in-plane magnetic field has very interesting effects which show up in the form of having a conductance peak at zero bias, thereby making it possible to realize a Majorana bound state.

  14. Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi; Kato, Daisuke; Kuga, Kiyoshi; Kikuchi, Hiroshi; Shimidzu, Naoki [Science and Technology Research Laboratories, Japan Broadcasting Corporation (NHK), Kinuta, Setagaya, Tokyo 157-8510 (Japan); Matsui, Koichi [Department of Green and Sustainable Chemistry, Tokyo Denki University, Adachi, Tokyo 120-8551 (Japan)

    2014-05-28

    Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

  15. Dynamical image-charge effect in molecular tunnel junctions: Beyond energy level alignment

    Science.gov (United States)

    Jin, Chengjun; Thygesen, Kristian S.

    2014-01-01

    When an electron tunnels between two metal contacts it temporarily induces an image charge (IC) in the electrodes which acts back on the tunneling electron. It is usually assumed that the IC forms instantaneously such that a static model for the image potential applies. Here we investigate how the finite IC formation time affects charge transport through a molecule suspended between two electrodes. For a single-level model, an analytical treatment shows that the conductance is suppressed by a factor Z2, where Z is the quasiparticle renormalization factor, compared to the static IC approximation. We show that Z can be expressed either in terms of the plasma frequency of the electrode or as the overlap between electrode wave functions corresponding to an empty and filled level, respectively. First-principles GW calculations for benzene-diamine connected to gold electrodes show that the dynamical corrections can reduce the conductance by more than a factor of two when compared to static GW or density functional theory where the molecular energy levels have been shifted to match the exact quasiparticle levels.

  16. A Novel Design and Fabrication of Magnetic Random Access Memory Based on Nano-ring-type Magnetic Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    X.F.Han; M. Ma; Y. Wang; Z.C. Wen; D.P. Liu; W.S.Zhan; H.X. Wei; Z.L.Peng; H.D. Yang; J.F. Feng; G.X.Du; Z.B.Sun; L.X. Jiang; Q.H. Qin

    2007-01-01

    Nano-ring-type magnetic tunnel junctions (NR-MTJs) with the layer structure of Ta(5)/Ir22Mn78(10)/Co75Fe25(2)/Ru(0.75)/Co60Fe20B20(3)/Al(0.6)-oxide/Co60Fe20B20(2.5)/Ta(3)/Ru(5) (thickness unit: nm)were nano-fabricated on the Si(100)/SiO2 substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography (EBL) and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunnelling magnetoresistance (TMR & R) versus driving current (I) loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co60Fe20B20 layer relative to the reference Co60Fe20B20 layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch2 even 6 Gbite/inch2 are possible using both 1 NR-MTJ+1 transistor structure and current switching mechanism based on based on our fabricated 4×4 MRAM demo devices.

  17. Correlation-driven transport asymmetries through coupled spins in a tunnel junction

    Science.gov (United States)

    Muenks, Matthias; Jacobson, Peter; Ternes, Markus; Kern, Klaus

    2017-01-01

    Spin-spin correlations can be the driving force that favours certain ground states and are key in numerous models that describe the behaviour of strongly correlated materials. While the sum of collective correlations usually lead to a macroscopically measurable change in properties, a direct quantification of correlations in atomic scale systems is difficult. Here we determine the correlations between a strongly hybridized spin impurity on the tip of a scanning tunnelling microscope and its electron bath by varying the coupling to a second spin impurity weakly hybridized to the sample surface. Electronic transport through these coupled spins reveals an asymmetry in the differential conductance reminiscent of spin-polarized transport in a magnetic field. We show that at zero field, this asymmetry can be controlled by the coupling strength and is related to either ferromagnetic or antiferromagnetic spin-spin correlations in the tip.

  18. From tunneling to contact: Inelastic signals in an atomic gold junction from first principles

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Lorente, N.; Paulsson, Magnus

    2007-01-01

    change in conductance is quantitatively well approximated by the simplest calculation where only the apex atoms are allowed to vibrate. Our study is completed by the application of a simplified model where the relevant parameters are obtained from the above DFT-based calculations.......The evolution of electron conductance in the presence of inelastic effects is studied as an atomic gold contact is formed evolving from a low-conductance regime (tunneling) to a high-conductance regime (contact). In order to characterize each regime, we perform density-functional theory (DFT......) calculations to study the geometric and electronic structures, together with the strength of the atomic bonds and the associated vibrational frequencies. The conductance is calculated by, first, evaluating the transmission of electrons through the system and, second, by calculating the conductance change due...

  19. Modulation of interlayer exchange coupling strength in magnetic tunnel junctions via strain effect

    Directory of Open Access Journals (Sweden)

    Xin Jiang

    2015-09-01

    Full Text Available Interlayer exchange coupling of two ferromagnetic electrodes separated by a thin MgO tunnel barrier is investigated using magneto-optical Kerr effect. We find that the coupling field can be reduced by more than 40% as the thickness of a top Ta capping layer increases from 0.5 to 1.2 nm. In contrast, a similar film stack with an additional 3 nm Ru capping layer displays no such dependence on Ta thickness. Transmission electron microscopy study shows that the oxidation of the exposed Ta capping layer induces changes in the crystalline structures of the underlying films, giving rise to the observed reduction of the interlayer coupling field.

  20. A comprehensive picture in the view of atomic scale on piezoelectricity of ZnO tunnel junctions: The first principles simulation

    Directory of Open Access Journals (Sweden)

    Genghong Zhang

    2016-06-01

    Full Text Available Piezoelectricity is closely related with the performance and application of piezoelectric devices. It is a crucial issue to understand its detailed fundamental for designing functional devices with more peculiar performances. Basing on the first principles simulations, the ZnO piezoelectric tunnel junction is taken as an example to systematically investigate its piezoelectricity (including the piezopotential energy, piezoelectric field, piezoelectric polarization and piezocharge and explore their correlation. The comprehensive picture of the piezoelectricity in the ZnO tunnel junction is revealed at atomic scale and it is verified to be the intrinsic characteristic of ZnO barrier, independent of its terminated surface but dependent on its c axis orientation and the applied strain. In the case of the ZnO c axis pointing from right to left, an in-plane compressive strain will induce piezocharges (and a piezopotential energy drop with positive and negative signs (negative and positive signs emerging respectively at the left and right terminated surfaces of the ZnO barrier. Meanwhile a piezoelectric polarization (and a piezoelectric field pointing from right to left (from left to right are also induced throughout the ZnO barrier. All these piezoelectric physical quantities would reverse when the applied strain switches from compressive to tensile. This study provides an atomic level insight into the fundamental behavior of the piezoelectricity of the piezoelectric tunnel junction and should have very useful information for future designs of piezoelectric devices.

  1. Alternating-Current InGaN/GaN Tunnel Junction Nanowire White-Light Emitting Diodes.

    Science.gov (United States)

    Sadaf, S M; Ra, Y-H; Nguyen, H P T; Djavid, M; Mi, Z

    2015-10-14

    The current LED lighting technology relies on the use of a driver to convert alternating current (AC) to low-voltage direct current (DC) power, a resistive p-GaN contact layer to inject positive charge carriers (holes) for blue light emission, and rare-earth doped phosphors to down-convert blue photons into green/red light, which have been identified as some of the major factors limiting the device efficiency, light quality, and cost. Here, we show that multiple-active region phosphor-free InGaN nanowire white LEDs connected through a polarization engineered tunnel junction can fundamentally address the afore-described challenges. Such a p-GaN contact-free LED offers the benefit of carrier regeneration, leading to enhanced light intensity and reduced efficiency droop. Moreover, through the monolithic integration of p-GaN up and p-GaN down nanowire LED structures on the same substrate, we have demonstrated, for the first time, AC operated LEDs on a Si platform, which can operate efficiently in both polarities (positive and negative) of applied voltage.

  2. Atomic-Scale Structure and Local Chemistry of CoFeB-MgO Magnetic Tunnel Junctions.

    Science.gov (United States)

    Wang, Zhongchang; Saito, Mitsuhiro; McKenna, Keith P; Fukami, Shunsuke; Sato, Hideo; Ikeda, Shoji; Ohno, Hideo; Ikuhara, Yuichi

    2016-03-09

    Magnetic tunnel junctions (MTJs) constitute a promising building block for future nonvolatile memories and logic circuits. Despite their pivotal role, spatially resolving and chemically identifying each individual stacking layer remains challenging due to spatially localized features that complicate characterizations limiting understanding of the physics of MTJs. Here, we combine advanced electron microscopy, spectroscopy, and first-principles calculations to obtain a direct structural and chemical imaging of the atomically confined layers in a CoFeB-MgO MTJ, and clarify atom diffusion and interface structures in the MTJ following annealing. The combined techniques demonstrate that B diffuses out of CoFeB electrodes into Ta interstitial sites rather than MgO after annealing, and CoFe bonds atomically to MgO grains with an epitaxial orientation relationship by forming Fe(Co)-O bonds, yet without incorporation of CoFe in MgO. These findings afford a comprehensive perspective on structure and chemistry of MTJs, helping to develop high-performance spintronic devices by atomistic design.

  3. State diagram of a perpendicular magnetic tunnel junction driven by spin transfer torque: A power dissipation approach

    Science.gov (United States)

    Lavanant, M.; Petit-Watelot, S.; Kent, A. D.; Mangin, S.

    2017-04-01

    The state diagram of a magnetic tunnel junction with perpendicularly magnetized electrodes in the presence of spin-transfer torques is computed in a macrospin approximation using a power dissipation model. Starting from the macrospin's energy we determine the stability of energy extremum in terms of power received and dissipated, allowing the consideration of non-conservative torques associated with spin transfer and damping. The results are shown to be in agreement with those obtained by direct integration of the Landau-Lifshitz-Gilbert-Slonczewski equation. However, the power dissipation model approach is faster and shows the reason certain magnetic states are stable, such as states that are energy maxima but are stabilized by spin transfer torque. Breaking the axial system, such as by a tilted applied field or tilted anisotropy, is shown to dramatically affect the state diagrams. Finally, the influence of a higher order uniaxial anisotropy that can stabilize a canted magnetization state is considered and the results are compared to experimental data.

  4. Voltage-induced magnetization dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions

    Science.gov (United States)

    Miura, Katsuya; Yabuuchi, Shin; Yamada, Masaki; Ichimura, Masahiko; Rana, Bivas; Ogawa, Susumu; Takahashi, Hiromasa; Fukuma, Yasuhiro; Otani, Yoshichika

    2017-02-01

    Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (Vrec) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions.

  5. Voltage-induced magnetization dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions

    Science.gov (United States)

    Miura, Katsuya; Yabuuchi, Shin; Yamada, Masaki; Ichimura, Masahiko; Rana, Bivas; Ogawa, Susumu; Takahashi, Hiromasa; Fukuma, Yasuhiro; Otani, Yoshichika

    2017-01-01

    Recent progress in magnetic tunnel junctions (MTJs) with a perpendicular easy axis consisting of CoFeB and MgO stacking structures has shown that magnetization dynamics are induced due to voltage-controlled magnetic anisotropy (VCMA), which will potentially lead to future low-power-consumption information technology. For manipulating magnetizations in MTJs by applying voltage, it is necessary to understand the coupled magnetization motion of two magnetic (recording and reference) layers. In this report, we focus on the magnetization motion of two magnetic layers in MTJs consisting of top layers with an in-plane easy axis and bottom layers with a perpendicular easy axis, both having perpendicular magnetic anisotropy. According to rectified voltage (Vrec) measurements, the amplitude of the magnetization motion depends on the initial angles of the magnetizations with respect to the VCMA direction. Our numerical simulations involving the micromagnetic method based on the Landau-Lifshitz-Gilbert equation of motion indicate that the magnetization motion in both layers is induced by a combination of VCMA and transferred angular momentum, even though the magnetic easy axes of the two layers are different. Our study will lead to the development of voltage-controlled MTJs having perpendicular magnetic anisotropy by controlling the initial angle between magnetizations and VCMA directions. PMID:28209976

  6. A novel low-cost high-throughput probe card scanner analyzer for characterization of magnetic tunnel junctions

    Science.gov (United States)

    Pong, Philip W. T.; Schmoueli, Moshe; Marcus, Eliezer; Egelhoff, William F., Jr.

    2007-09-01

    The advancement of the technology of magnetic tunnel junctions (MTJs) greatly hinges on the optimization of the magnetic materials, fabrication process, and annealing conditions which involve characterization of a large number of samples. As such, it is of paramount importance to have a rapid-turnaround characterization method since the characterization process can take even longer time than the fabrication. Conventionally, micropositioners and probe tips are manually operated to perform 4-point electrical measurement on each individual device which is a time-consuming, low-throughput process. A commercial automatic probe card analyzer can provide high turnaround; however, it is expensive and involves much cost and labor to install and maintain the equipment. In view of this, we have developed a novel low-cost, home-made, high-throughput probe card analyzer system for characterization of MTJs. It can perform fast 4-probe electrical measurements including current vs voltage, magnetoresistance, and bias dependence measurements with a high turnaround of about 500 devices per hour. The design and construction of the system is discussed in detail in this paper.

  7. Reactive ion etching of Nb thin films for Nb/Al-AlO[sub x]/Nb Josephson tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Popova, K. (Dept. of Physics and Applied Physics, Univ. of Strathclyde, Glasgow (United Kingdom)); Lea, W.F. (Dept. of Physics and Applied Physics, Univ. of Strathclyde, Glasgow (United Kingdom)); Hutson, D. (Dept. of Physics and Applied Physics, Univ. of Strathclyde, Glasgow (United Kingdom)); Sydow, J.P. (Dept. of Physics and Applied Physics, Univ. of Strathclyde, Glasgow (United Kingdom)); Pegrum, C.M. (Dept. of Physics and Applied Physics, Univ. of Strathclyde, Glasgow (United Kingdom))

    1994-03-01

    Reactive ion etching of both Nb and Nb/Al-AlO[sub x]/Nb trilayer has been optimised for the fabrication of Josephson tunnel junctions. Niobium thin films deposited by magnetron sputtering on silicon wafers have been patterned by a process using CF[sub 4] + O[sub 2]. The effect of main process parameters on photoresist mask etch anisotropy has been demonstrated by scanning electron microscopy (SEM) observations, and the influence of gas composition, total pressure and discharge power on etch rates has been evaluated by response surface methodology. A face-centred cubed experimental design with 17 trials has been performed and the data processed using multiple regression analysis. Second-order polynomial expressions (response surfaces) for Nb and Si etch rates as functions of process parameters have been obtained. A reliable and repeatable Nb etch process has been defined in the range 100-270 mTorr total pressure, 50-70 W input power and 0-10% by flow of O[sub 2] added to the CF[sub 4]. Maximum Nb and Si etch rates were obtained with 7% O[sub 2] in the gas mixture, and SEM showed that vertical etch profiles were produced at 50 mTorr CF[sub 4] + 5%O[sub 2]. (orig.)

  8. Comprehensive and Macrospin-Based Magnetic Tunnel Junction Spin Torque Oscillator Model- Part II: Verilog-A Model Implementation

    Science.gov (United States)

    Chen, Tingsu; Eklund, Anders; Iacocca, Ezio; Rodriguez, Saul; Malm, B. Gunnar; Akerman, Johan; Rusu, Ana

    2015-03-01

    The rapid development of the magnetic tunnel junction (MTJ) spin torque oscillator (STO) technology demands an analytical model to enable building MTJ STO-based circuits and systems so as to evaluate and utilize MTJ STOs in various applications. In Part I of this paper, an analytical model based on the macrospin approximation, has been introduced and verified by comparing it with the measurements of three different MTJ STOs. In Part II, the full Verilog-A implementation of the proposed model is presented. To achieve a reliable model, an approach to reproduce the phase noise generated by the MTJ STO has been proposed and successfully employed. The implemented model yields a time domain signal, which retains the characteristics of operating frequency, linewidth, oscillation amplitude and DC operating point, with respect to the magnetic field and applied DC current. The Verilog-A implementation is verified against the analytical model, providing equivalent device characteristics for the full range of biasing conditions. Furthermore, a system that includes an MTJ STO and CMOS RF circuits is simulated to validate the proposed model for system- and circuit-level designs. The simulation results demonstrate that the proposed model opens the possibility to explore STO technology in a wide range of applications.

  9. Final Scientific/Technical Report: Electronics for Large Superconducting Tunnel Junction Detector Arrays for Synchrotron Soft X-ray Research

    Energy Technology Data Exchange (ETDEWEB)

    Warburton, William K

    2009-03-06

    Superconducting tunnel junction (STJ) detectors offer a an approach to detecting soft x-rays with energy resolutions 4-5 times better and at rates 10 faster than traditions semiconductor detectors. To make such detectors feasible, however, then need to be deployed in large arrays of order 1000 detectors, which in turn implies that their processing electronics must be compact, fully computer controlled, and low cost per channel while still delivering ultra-low noise performance so as to not degrade the STJ's performance. We report on our progress in designing a compact, low cost preamplifier intended for this application. In particular, we were able to produce a prototype preamplifier of 2 sq-cm area and a parts cost of less than $30 that matched the energy resolution of the best conventional system to date and demonstrated its ability to acquire an STJ I-V curve under computer control, the critical step for determining and setting the detectors' operating points under software control.

  10. Bias-voltage dependence of perpendicular spin-transfer torque in asymmetric MgO-based magnetic tunnel junctions

    KAUST Repository

    Oh, Se Chung

    2009-10-25

    Spin-transfer torque (STT) allows the electrical control of magnetic states in nanostructures. The STT in magnetic tunnel junctions (MTJs) is of particular importance owing to its potential for device applications. It has been demonstrated that the MTJ has a sizable perpendicular STT (, field-like torque), which substantially affects STT-driven magnetization dynamics. In contrast to symmetric MTJs where the bias dependence of is quadratic, it is theoretically predicted that the symmetry breaking of the system causes an extra linear bias dependence. Here, we report experimental results that are consistent with the predicted linear bias dependence in asymmetric MTJs. The linear contribution is quite significant and its sign changes from positive to negative as the asymmetry is modified. This result opens a way to design the bias dependence of the field-like term, which is useful for device applications by allowing, in particular, the suppression of the abnormal switching-back phenomena. © 2009 Macmillan Publishers Limited. All rights reserved.

  11. Compact-device model development for the energy-delay analysis of magneto-electric magnetic tunnel junction structures

    Science.gov (United States)

    Sharma, N.; Bird, J. P.; Dowben, P. A.; Marshall, A.

    2016-06-01

    We discuss the application of a novel class of device, the magneto-electric magnetic tunnel junction (ME-MTJ) to realize a variety of computational functions, including majority logic and the XNOR/XOR gate. We also develop a compact model to describe the operation of these devices, which function by utilizing the phenomenon of ‘voltage-controlled magnetism’ to switch the operational state of MTJs. The model breaks down the switching process into three key stages of operation: electrical-to-magnetic conversion, magnetization transfer, and final-state readout. Estimates for the switching energy and delay of these devices, obtained from this compact model, reveal significant improvements in both of these parameters when compared to conventional MTJs switched by spin-transfer-torque. In fact, the capacity to use the ME-MTJ to implement complex logical operations within a single device allows its energy costs to even approach those of low-power CMOS. The added benefits of non-volatility and compact circuit footprint, combined with their potential for heterogeneous integration with CMOS, make the ME devices of considerable interest for post-CMOS technology.

  12. Nonlinear thermoelectric effects in high-field superconductor-ferromagnet tunnel junctions

    Directory of Open Access Journals (Sweden)

    Stefan Kolenda

    2016-11-01

    Full Text Available Background: Thermoelectric effects result from the coupling of charge and heat transport and can be used for thermometry, cooling and harvesting of thermal energy. The microscopic origin of thermoelectric effects is a broken electron–hole symmetry, which is usually quite small in metal structures. In addition, thermoelectric effects decrease towards low temperatures, which usually makes them vanishingly small in metal nanostructures in the sub-Kelvin regime.Results: We report on a combined experimental and theoretical investigation of thermoelectric effects in superconductor/ferromagnet hybrid structures. We investigate the dependence of thermoelectric currents on the thermal excitation, as well as on the presence of a dc bias voltage across the junction.Conclusion: Large thermoelectric effects are observed in superconductor/ferromagnet and superconductor/normal-metal hybrid structures. The spin-independent signals observed under finite voltage bias are shown to be reciprocal to the physics of superconductor/normal-metal microrefrigerators. The spin-dependent thermoelectric signals in the linear regime are due to the coupling of spin and heat transport, and can be used to design more efficient refrigerators.

  13. Correlation between Barrier Width, Barrier Height, and DC Bias Voltage Dependences on the Magnetoresistance Ratio in Ir-Mn Exchange Biased Single and Double Tunnel Junctions

    Science.gov (United States)

    Saito, Yoshiaki; Amano, Minoru; Nakajima, Kentaro; Takahashi, Shigeki; Sagoi, Masayuki; Inomata, Koichiro

    2000-10-01

    Dual spin-valve-type double tunnel junctions (DTJs) of Ir-Mn/CoFe/AlOx/Co90Fe10/AlOx/CoFe/Ir-Mn and spin-valve-type single tunnel junctions (STJs) of Ir-Mn/CoFe/AlOx/CoFe/Ni-Fe were fabricated using an ultrahigh vacuum sputtering system, conventional photolithography and ion-beam milling. The STJs could be fabricated with various barrier heights by changing the oxidization conditions during deposition and changing the annealing temperature after deposition, while the AlOx layer thickness remained unchanged. There was a correlation between barrier width, height estimated using Simmons’ expressions, and dc bias voltage dependence on the MR ratio. The VB dependence on the tunneling magnetoresistance (TMR) ratio was mainly related to the barrier width, and the decrease in the TMR ratio with increasing bias voltage is well explained, taking into account the spin-independent two-step tunneling via defect states in the barrier, as a main mechanism, at room temperature. Under optimized oxidization and annealing conditions, the maximum TMR ratio at a low bias voltage, and the dc bias voltage value at which the TMR ratio decreases in value by half (V1/2) were 42.4% and 952 mV in DTJs, and 49.0% and 425 mV in STJs, respectively.

  14. The role of Mg interface layer in MgO magnetic tunnel junctions with CoFe and CoFeB electrodes

    Directory of Open Access Journals (Sweden)

    Hyunsoo Yang

    2012-03-01

    Full Text Available The tunneling spin polarization (TSP is directly measured from reactively sputter deposited crystalline MgO tunnel barriers with various CoFe(B compositions using superconducting tunneling spectroscopy. We find that the Mg interface layer thickness dependence of TSP values for CoFeB/Mg/MgO junctions is substantially different from those for CoFe/Mg/MgO especially in the pre-annealed samples due to the formation of boron oxide at the CoFeB/MgO interface. Annealing depletes boron at the interface thus requiring a finite Mg interface layer to prevent CoFeOx formation at the CoFeB/MgO interface so that the TSP values can be optimized by controlling Mg thickness.

  15. Addressing the challenges of using ferromagnetic electrodes in the magnetic tunnel junction-based molecular spintronics devices

    Science.gov (United States)

    Tyagi, Pawan; Friebe, Edward; Baker, Collin

    2015-11-01

    Addressing the challenges of using high-Curie temperature ferromagnetic (FM) electrodes is critical for molecular spintronics devices (MSDs) research. Two FM electrodes simultaneously chemically bonded with a thiol-functionalized molecule can produce novel MSDs to exploring new quantum mechanical phenomenon and computer technologies. For developing a commercially viable MSD, it is crucial to developing a device fabrication scheme that carefully considers FM electrodes' susceptibility to oxidation, chemical etching, and stress-induced deformations during fabrication and usage. This paper studies NiFe, an alloy extensively used in present-day memory devices and high-temperature engineering applications, as a candidate FM electrode for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe oxidized aggressively after heating beyond 90 °C. The NiFe surfaces, aged for several months or heated for several minutes below 90 °C, exhibited remarkable electrochemical activity and were found suitable for chemical bonding with the thiol-functionalized molecular device elements. NiFe also demonstrated excellent etching resistance against commonly used solvents and lithography related chemicals. Additionally, NiFe mitigated the adverse effects of mechanical stress by subsiding the stress-induced deformities. A magnetic tunnel junction-based MSD approach was designed by carefully considering the merits and limitations of NiFe. The device fabrication protocol considers the safe temperature limit to avoiding irreversible surface oxidation, the effect of mechanical stresses, surface roughness, and chemical etching. This paper provides foundational experimental insights in realizing a versatile MSD allowing a wide range of transport and magnetic studies.

  16. Comparison of nonpolar III-nitride vertical-cavity surface-emitting lasers with tunnel junction and ITO intracavity contacts

    KAUST Repository

    Leonard, J. T.

    2016-03-01

    We report on the lasing of III-nitride nonpolar, violet, vertical-cavity surface-emitting lasers (VCSELs) with III-nitride tunnel-junction (TJ) intracavity contacts and ion implanted apertures (IIAs). The TJ VCSELs are compared to similar VCSELs with tin-doped indium oxide (ITO) intracavity contacts. Prior to analyzing device results, we consider the relative advantages of III-nitride TJs for blue and green emitting VCSELs. The TJs are shown to be most advantageous for violet and UV VCSELs, operating near or above the absorption edge for ITO, as they significantly reduce the total internal loss in the cavity. However, for longer wavelength III-nitride VCSELs, TJs primarily offer the advantage of improved cavity design flexibility, allowing one to make the p-side thicker using a thick n-type III-nitride TJ intracavity contact. This offers improved lateral current spreading and lower loss, compare to using ITO and p-GaN, respectively. These aspects are particularly important for achieving high-power CW VCSELs, making TJs the ideal intracavity contact for any III-nitride VCSEL. A brief overview of III-nitride TJ growth methods is also given, highlighting the molecular-beam epitaxy (MBE) technique used here. Following this overview, we compare 12 mu m aperture diameter, violet emitting, TJ and ITO VCSEL experimental results, which demonstrate the significant improvement in differential efficiency and peak power resulting from the reduced loss in the TJ design. Specifically, the TJ VCSEL shows a peak power of similar to 550 mu W with a threshold current density of similar to 3.5 kA/cm(2), while the ITO VCSELs show peak powers of similar to 80 mu W and threshold current densities of similar to 7 kA/cm

  17. Communication of Ca(2+) signals via tunneling membrane nanotubes is mediated by transmission of inositol trisphosphate through gap junctions.

    Science.gov (United States)

    Lock, Jeffrey T; Parker, Ian; Smith, Ian F

    2016-10-01

    Tunneling membrane nanotubes (TNTs) are thin membrane projections linking cell bodies separated by many micrometers, which are proposed to mediate signaling and even transfer of cytosolic contents between distant cells. Several reports describe propagation of Ca(2+) signals between distant cells via TNTs, but the underlying mechanisms remain poorly understood. Utilizing a HeLa M-Sec cell line engineered to upregulate TNTs we replicated previous findings that mechanical stimulation elicits robust cytosolic Ca(2+) elevations that propagate to surrounding, physically separate cells. However, whereas this was previously interpreted to involve intercellular communication through TNTs, we found that Ca(2+) signal propagation was abolished - even in TNT-connected cells - after blocking ATP-mediated paracrine signaling with a cocktail of extracellular inhibitors. To then establish whether gap junctions may enable cell-cell signaling via TNTs under these conditions, we expressed sfGFP-tagged connexin-43 (Cx43) in HeLa M-Sec cells. We observed robust communication of mechanically-evoked Ca(2+) signals between distant but TNT-connected cells, but only when both cells expressed Cx43. Moreover, we also observed communication of Ca(2+) signals evoked in one cell by local photorelease of inositol 1,4,5-trisphosphate (IP3). Ca(2+) responses in connected cells began after long latencies at intracellular sites several microns from the TNT connection site, implicating intercellular transfer of IP3 and subsequent IP3-mediated Ca(2+) liberation, and not Ca(2+) itself, as the mediator between TNT-connected, Cx43-expressing cells. Our results emphasize the need to control for paracrine transmission in studies of cell-cell signaling via TNTs and indicate that, in this cell line, TNTs do not establish cytosolic continuity between connected cells but rather point to the crucial importance of connexins to enable communication of cytosolic Ca(2+) signals via TNTs.

  18. Addressing the challenges of using ferromagnetic electrodes in the magnetic tunnel junction-based molecular spintronics devices

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, Pawan, E-mail: ptyagi@udc.edu; Friebe, Edward; Baker, Collin [University of the District of Columbia, Department of Mechanical Engineering (United States)

    2015-11-15

    Addressing the challenges of using high-Curie temperature ferromagnetic (FM) electrodes is critical for molecular spintronics devices (MSDs) research. Two FM electrodes simultaneously chemically bonded with a thiol-functionalized molecule can produce novel MSDs to exploring new quantum mechanical phenomenon and computer technologies. For developing a commercially viable MSD, it is crucial to developing a device fabrication scheme that carefully considers FM electrodes’ susceptibility to oxidation, chemical etching, and stress-induced deformations during fabrication and usage. This paper studies NiFe, an alloy extensively used in present-day memory devices and high-temperature engineering applications, as a candidate FM electrode for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe oxidized aggressively after heating beyond ∼90 °C. The NiFe surfaces, aged for several months or heated for several minutes below ∼90 °C, exhibited remarkable electrochemical activity and were found suitable for chemical bonding with the thiol-functionalized molecular device elements. NiFe also demonstrated excellent etching resistance against commonly used solvents and lithography related chemicals. Additionally, NiFe mitigated the adverse effects of mechanical stress by subsiding the stress-induced deformities. A magnetic tunnel junction-based MSD approach was designed by carefully considering the merits and limitations of NiFe. The device fabrication protocol considers the safe temperature limit to avoiding irreversible surface oxidation, the effect of mechanical stresses, surface roughness, and chemical etching. This paper provides foundational experimental insights in realizing a versatile MSD allowing a wide range of transport and magnetic studies.

  19. Magnetic tunneling junctions with the Heusler compound Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al

    Energy Technology Data Exchange (ETDEWEB)

    Conca Parra, A.

    2007-07-20

    Materials with large spin polarization are required for applications in spintronics devices. For this reason, major research efforts are directed to study the properties of compounds which are expected to be half metals, i.e. materials with 100% spin polarization. Half metals are expected to have a gap in the density of states at the Fermi energy for one spin band while the other spin band is metallic leading to a completely spin polarized current. The ferromagnetic full Heusler alloy Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al (CCFA) has attracted great interest in the field of spintronics. The high Tc (800 K) and the expected half metallicity make CCFA a good candidate for applications in spintronic devices such as magnetic tunneling junctions (MTJs). This thesis presents the results of the study of the electronic and structural properties of CCFA thin films. The films were implemented in magnetic tunneling junctions and the tunneling magnetoresistance effect (TMR) was investigated. The main objectives were the measurement of the spin polarisation of the CCFA alloy and to obtain information about its electronic structure. The influence of the deposition conditions on the thin film properties and on the surface crystalline order and their respective influence on the TMR ratio was investigated. Epitaxial CCFA thin films with two alternative growth orientations were deposited on different substrates and buffer layers. An annealing step was used to improve the crystalline properties of the thin films. In the tunneling junctions, Al{sub 2}O{sub 3} was used as a barrier material and Co was chosen as counter electrode. The multilayer systems were patterned in Mesa structures using lithographic techniques. In the framework of the Julliere model, a maximum spin polarisation of 54% at 4K was measured in tunneling junctions with epitaxial CCFA electrodes. A strong influence of the annealing temperature on the TMR ratio was determined. The increase of the TMR ratio could be correlated

  20. 深长隧道涌水量预测影响因素评价分析%Analysis on affecting factors in prediction of gushing water volume in deep-buried and long tunnel

    Institute of Scientific and Technical Information of China (English)

    李显伟

    2014-01-01

    The water inflow in tunnel is in concerned with its construction , its characteristics and the hydrogeological environment it locates in .In this light,an accurate prediction of the gushing water volume is premised on the wise selection and analysis of major influential factors .The paper reviews in detail the geological and hydrological environment the deep-buried and long tunnels in China surrounded by .Based on this,the analytic hierarchy process is used ,in the effort of building an assessment model to quantify all the influential factors that affect the gushing water volume in deep-buried and long tunnel .The results indicate that the lithologic characters and the water-rich property of the stratum , the type of the underground water , the geological structure , the topography , the annual average precipitation are all identified as key parameters .Hopefully , the paper can be of scientific use for the perdiction of gushing water volume in deep-buried and long tunnel .%隧道涌水不但与施工条件和隧道特征有关,而且受到水文地质条件的影响,对影响隧道涌水的主要因素的遴选和分析是准确进行隧道涌水量预测的前提。对我国深长隧道地质与水文地质条件进行详细分析,采用层次分析法建立深长隧道涌水量影响因素评价模型,定量确定了各因素的权重。研究结果表明:地层岩性、岩层富水性、地下水类型、地质构造、地形地貌和年均降水量是影响深长隧道涌水量的关键因素。本文分析结果为深长隧道涌水量预测分析提供了科学依据。

  1. Preparation and characterization of a ferrimagnetic amorphous alloy of GdCo entering the design of magnetic tunnel junctions: ionizing radiations hardness of magnetic tunnel junctions; preparation et caracterisation d'un alliage amorphe ferrimagnetique de GdCo entrant dans la conception de jonctions tunnel magnetiques. Resistance des jonctions tunnel magnetiques aux rayonnements ionisants

    Energy Technology Data Exchange (ETDEWEB)

    Conraux, Y

    2005-10-15

    The magnetic random access memories (MRAM) are on the way to supplant the other forms of random access memories using the states of electric charge, and this thanks to their many technical advantages: not-volatility, speed, low consumption power, robustness. Also, the MRAM are alleged insensitive with the ionizing radiations, which was not checked in experiments until now. The current architecture of the MRAM is based on the use of magnetic tunnel junctions (MTJ). These MRAM can present an important disadvantage, because they are likely of present errors of addressing, in particular when integration (density of memory cells) is increasingly thorough. The work undertaken during this thesis relates to these two points: - to check the functional reliability of the MRAM containing JTM exposed to high energy ionizing radiations; - to study a ferrimagnetic amorphous alloy, GdCo, likely to enter the composition of JTM and allowing to free from the possible errors of addressing by a process of thermal inhibition of the memory cells. This work of thesis showed that the MRAM containing JTM preserve their functional properties fully when they are subjected to intense ionizing radiations, and that GdCo is a very interesting material from the point of view of the solid state physics and magnetism, that its physical properties are very promising as for its applications, and that its integration in a JTM still claims technological developments. (author)

  2. Comparison of laser-induced and intrinsic tunnel magneto-Seebeck effect in CoFeB /MgAl2O4 and CoFeB/MgO magnetic tunnel junctions

    Science.gov (United States)

    Huebner, Torsten; Boehnke, Alexander; Martens, Ulrike; Thomas, Andy; Schmalhorst, Jan-Michael; Reiss, Günter; Münzenberg, Markus; Kuschel, Timo

    2016-06-01

    We present a comparison of the tunnel magneto-Seebeck effect for laser-induced and intrinsic heating. Therefore, Co40Fe40B20 /MgAl2O4 and Co25Fe55B20 /MgO magnetic tunnel junctions have been prepared. The TMS ratio of 3% in case of the MAO MTJ agrees well with ratios found for other barrier materials, while the TMS ratio of 23% of the MgO MTJ emphasizes the influence of the CoFe composition. We find results using the intrinsic method that differ in sign and magnitude in comparison to the results of the laser heating. The intrinsic contributions can alternatively be explained by the Brinkman model and the given junction properties. Especially, we are able to demonstrate that the symmetric contribution is solely influenced by the barrier asymmetry. Thus, we conclude that the symmetry analysis used for the intrinsic method is not suitable to unambiguously identify an intrinsic tunnel magneto-Seebeck effect.

  3. Progress Towards High-Sensitivity Arrays of Detectors of Sub-mm Radiation Using Superconducting Tunnel Junctions with Integrated Radio Frequency Single-Electron Transistors

    Science.gov (United States)

    Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Prober, D. E.; Rhee, K. W.; Schoelkopf, R. J.; Stahle, C. M.; Teufel, J.; Wollack, E. J.

    2004-01-01

    For high resolution imaging and spectroscopy in the FIR and submillimeter, space observatories will demand sensitive, fast, compact, low-power detector arrays with 104 pixels and sensitivity less than 10(exp -20) W/Hz(sup 0.5). Antenna-coupled superconducting tunnel junctions with integrated rf single-electron transistor readout amplifiers have the potential for achieving this high level of sensitivity, and can take advantage of an rf multiplexing technique. The device consists of an antenna to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure current through junctions contacting the absorber. We describe optimization of device parameters, and results on fabrication techniques for producing devices with high yield for detector arrays. We also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

  4. Ultra-low switching energy and scaling in electric-field-controlled nanoscale magnetic tunnel junctions with high resistance-area product

    Energy Technology Data Exchange (ETDEWEB)

    Grezes, C.; Alzate, J. G.; Cai, X.; Wang, K. L. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Ebrahimi, F.; Khalili Amiri, P. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Inston, Inc., Los Angeles, California 90024 (United States); Katine, J. A. [HGST, Inc., San Jose, California 95135 (United States); Langer, J.; Ocker, B. [Singulus Technologies AG, Kahl am Main 63796 (Germany)

    2016-01-04

    We report electric-field-induced switching with write energies down to 6 fJ/bit for switching times of 0.5 ns, in nanoscale perpendicular magnetic tunnel junctions (MTJs) with high resistance-area product and diameters down to 50 nm. The ultra-low switching energy is made possible by a thick MgO barrier that ensures negligible spin-transfer torque contributions, along with a reduction of the Ohmic dissipation. We find that the switching voltage and time are insensitive to the junction diameter for high-resistance MTJs, a result accounted for by a macrospin model of purely voltage-induced switching. The measured performance enables integration with same-size CMOS transistors in compact memory and logic integrated circuits.

  5. Reducing spin-torque switching current by incorporating an ultra-thin Ta layer with CoFeB free layer in magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, R. S., E-mail: liurs7204@yahoo.com; Meng, H.; Naik, V. B.; Sim, C. H.; Yap, S.; Luo, P. [Data Storage Institute, A*STAR (Agency for Science Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore)

    2014-12-15

    We studied the spin torque switching in dual MgO layer based magnetic tunnel junctions (MTJs) by incorporating an ultra-thin (0.5 nm) Ta layer at the CoFeB free layer/top MgO layer interface. The Ta incorporated MTJ showed a significant reduction (∼30%) in critical switching current density (J{sub C0} ) as compared to that of the control MTJ whilst maintaining the same tunneling magnetoresistance as well as thermal stability. The reduction of J{sub C0} can be attributed to the perpendicular magnetic anisotropy arising from the incorporation of an ultrathin Ta layer with the MgO|CoFeB structure. This scheme of reducing J{sub C0} without degrading other properties may contribute to the development of spin-transfer-torque magnetic random access memory for low power applications.

  6. First-principles study on magnetic tunneling junctions with semiconducting CuInSe2 and CuGaSe2 barriers

    Science.gov (United States)

    Masuda, Keisuke; Miura, Yoshio

    2017-02-01

    We theoretically investigate two magnetic tunneling junctions (MTJs) with different semiconductor barriers, CuInSe2 (CIS) and CuGaSe2 (CGS), sandwiched between Fe electrodes. We find that Δ1 wave functions provide dominant contributions to spin-dependent tunneling transport in both CIS- and CGS-based MTJs. We also find that the CGS-based MTJ has a much higher magnetoresistive (MR) ratio than the CIS-based MTJ, which indicates that a higher MR ratio is expected for a higher Ga concentration x in the recently reported CuIn1- x Ga x Se2-based MTJs. Furthermore, we show that the CIS- and CGS-based MTJs have much smaller resistance-area products (RA) than the conventional MgO-based MTJs.

  7. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    Science.gov (United States)

    Daqiq, Reza; Ghobadi, Nader

    2016-07-01

    We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching.

  8. In-situ grazing incidence X-ray diffraction measurements of relaxation in Fe/MgO/Fe epitaxial magnetic tunnel junctions during annealing

    Science.gov (United States)

    Eastwood, D. S.; Ali, M.; Hickey, B. J.; Tanner, B. K.

    2013-12-01

    The relaxation of Fe/MgO/Fe tunnel junctions grown epitaxially on (001) MgO substrates has been measured by in-situ grazing incidence in-plane X-ray diffraction during the thermal annealing cycle. We find that the Fe layers are fully relaxed and that there are no irreversible changes during annealing. The MgO tunnel barrier is initially strained towards the Fe but on annealing, relaxes and expands towards the bulk MgO value. The strain dispersion is reduced in the MgO by about 40% above 480 K post-annealing. There is no significant change in the "twist" mosaic. Our results indicate that the final annealing stage of device fabrication, crucial to attainment of high TMR, induces substantial strain relaxation at the MgO barrier/lower Fe electrode interface.

  9. In-plane magnetic field effect on switching voltage and thermal stability in electric-field-controlled perpendicular magnetic tunnel junctions

    Science.gov (United States)

    Grezes, C.; Rojas Rozas, A.; Ebrahimi, F.; Alzate, J. G.; Cai, X.; Katine, J. A.; Langer, J.; Ocker, B.; Khalili Amiri, P.; Wang, K. L.

    2016-07-01

    The effect of in-plane magnetic field on switching voltage (Vsw) and thermal stability factor (Δ) are investigated in electric-field-controlled perpendicular magnetic tunnel junctions (p-MTJs). Dwell time measurements are used to determine the voltage dependence of the energy barrier height for various in-plane magnetic fields (Hin), and gain insight into the Hin dependent energy landscape. We find that both Vsw and Δ decrease with increasing Hin, with a dominant linear dependence. The results are reproduced by calculations based on a macrospin model while accounting for the modified magnetization configuration in the presence of an external magnetic field.

  10. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    Science.gov (United States)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-01-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  11. Study of Temperature Field Affected by Blockage Ratio in a Deep Buried Long Tunnel%深埋长大高速铁路隧道阻塞比对温度影响研究

    Institute of Scientific and Technical Information of China (English)

    朱艳峰; 吴亚平

    2011-01-01

    Because of bad air ventilation, a significant amount of thermal energy from aerodynamic power, air conditioning and auxiliary equipment will not be driven out timely in deep buried long tunnel. As a consequence, the temperature in tunnel would be continual rising. For ensuring security and stability of tunnel structure and normal use of the facilities, a simulation of high-speed train traveling through a deep buried long tunnel has been made. The object of this paper is to present a generalized three-dimensional flow theory which is capable of modeling the effects of interested objects in the tunnel environment. According to the different cross-sectional area ratio of train to that of tunnel, the pressure drag between train nose and train tail, friction drag on train body and the quantity of heat produced by the energy-consuming for working of train against all resistance are evaluated in terms of different blockage ratio.The heating of train drag, train wall friction, auxiliary equipment, train equipment, train braking and pantograph electric arc etc. has also been comprehensively considered, and the energy loss of heat conduction introduced by tunnel wall has been taken into account. The temperature rising and variation with time in the tunnel is predicted and the result can serve as a useful reference for design and ventilation of such kind of tunnel .%由于通风不畅,深埋长隧道中高速列车能耗与空调及隧道中各种电力设备所散发产生的大量热量不能及时排出,会造成隧道内环境温度的持续上升.本文应用三维可压缩流体流动理论,针对列车横截面积与隧道横截面积比值阻塞比的不同,对长隧道内运行的高速列车进行了数值模拟研究,计算了车头车尾的压差阻力,车身表面的摩擦阻力及列车克服全部阻力高速运行所需能耗产生的热量,结合列车辅助设备发热,并考虑隧道与围岩之间的热传递,合理预测了不同阻塞比下高速列车

  12. Dependency of tunneling magneto-resistance on Fe insertion-layer thickness in Co{sub 2}Fe{sub 6}B{sub 2}/MgO-based magnetic tunneling junctions

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Kyo-Suk [MRAM Center, Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701 (Korea, Republic of); Park, Jea-Gun, E-mail: parkjgL@hanyang.ac.kr [MRAM Center, Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

    2015-04-21

    For Co{sub 2}Fe{sub 6}B{sub 2}/MgO-based perpendicular magnetic tunneling junctions spin valves with [Co/Pd]{sub n}-synthetic-antiferromagnetic (SyAF) layers, the tunneling-magneto-resistance (TMR) ratio strongly depends on the nanoscale Fe insertion-layer thickness (t{sub Fe}) between the Co{sub 2}Fe{sub 6}B{sub 2} pinned layer and MgO tunneling barrier. The TMR ratio rapidly increased as t{sub Fe} increased up to 0.4 nm by improving the crystalline linearity of a MgO tunneling barrier and by suppressing the diffusion of Pd atoms from a [Co/Pd]{sub n}-SyAF. However, it abruptly decreased by further increasing t{sub Fe} in transferring interfacial-perpendicular magnetic anisotropy into the IMA characteristic of the Co{sub 2}Fe{sub 6}B{sub 2} pinned layer. Thus, the TMR ratio peaked at t{sub Fe} = 0.4 nm: i.e., 120% at 29 Ωμm{sup 2}.

  13. Theoretical calculation of performance enhancement in lattice-matched SiGeSn/GeSn p-channel tunneling field-effect transistor with type-II staggered tunneling junction

    Science.gov (United States)

    Wang, Hongjuan; Han, Genquan; Wang, Yibo; Peng, Yue; Liu, Yan; Zhang, Chunfu; Zhang, Jincheng; Hu, Shengdong; Hao, Yue

    2016-04-01

    In this work, a lattice-matched SiGeSn/GeSn heterostructure p-channel tunneling field-effect transistor (hetero-PTFET) with a type-II staggered tunneling junction (TJ) is investigated theoretically. Lattice matching and type-II band alignment at the Γ-point is obtained at the SiGeSn/GeSn interface by tuning Sn and Si compositions. A steeper subthreshold swing (SS) and a higher on state current (I ON) are demonstrated in SiGeSn/GeSn hetero-PTFET than in GeSn homo-PTFET. Si0.31Ge0.49Sn0.20/Ge0.88Sn0.12 hetero-PTFET achieves a 2.3-fold higher I ON than Ge0.88Sn0.12 homo-PTFET at V DD of 0.3 V. Hetero-PTFET achieves a more abrupt hole profile and a higher carrier density near TJ than the homo-PTFET, which contributes to the significantly enhanced band-to-band tunneling (BTBT) rate and tunneling current in hetero-PTFET.

  14. 大尺度现浇暗埋段隧道裂缝控制关键技术%Key technology of crack control for large- scale cast- in- situ buried tunnel

    Institute of Scientific and Technical Information of China (English)

    谷坤鹏; 于铜; 陈克伟; 王成启; 赵辉; 孙洪春

    2015-01-01

    The maximum height of 11.4 m, the maximum width of 72.2 m of cast-in-situ buried tunnel main structure of east artificial island of Hongkong-Zhuhai-Macao Bridge, which is the largest structure section size of pipe gallery box of mass concrete structure for the domestic and foreign similar engineering, and restricted by sea island operation, to section and pouring step by step. According to the project research, theoretical calculation analysis and finite element simulation analysis, we researched on the crack control technology of cast-in-situ buried tunnel, put forward some key technologies for crack control, such as moving the construction joint to the top of the side wall, making the floor and side wall as a whole for one-time pouring, and controlling the section length, shortening the step-by-step pouring time interval, and temperature control of mass concrete, which can solved the key parts' cracking problems of side wall and floor in the cast-in-situ buried tunnel.%港珠澳大桥东人工岛现浇暗埋段隧道主体结构最大高度为11.4 m,最大宽度为72.2 m,为国内外同类工程中结构断面尺寸最大的管廊箱型大体积混凝土结构,受外海孤岛作业限制,需分段分步浇筑。通过工程调研、理论计算分析和有限元仿真计算分析对现浇暗埋段隧道的裂缝控制展开研究,提出将施工缝移至侧墙上部,底板和侧墙作为整体一次性浇筑,以及控制分段长度、缩短分步浇筑间隔时间及大体积混凝土温控等裂缝控制关键技术,解决了现浇暗埋段隧道关键部位侧墙和底板的裂缝问题。

  15. Large-Scale Experimental and Numerical Study of Blast Acceleration Created by Close-In Buried Explosion on Underground Tunnel Lining

    Directory of Open Access Journals (Sweden)

    Mohamad Reza Soheyli

    2016-01-01

    Full Text Available Despite growing demands for structures in water transportation tunnels, underground installations, subsurface dams, and subterranean channels, there is limited field knowledge about the dynamic behavior of these structures in the face of near-fault earthquakes or impulse excitations. This study conducted a large-scale test on underground tunnel excited by two close-in subsurface explosions. The horizontal and vertical acceleration were recorded on the vertical wall of the tunnel and the free field data including the acceleration on the ground surface at 11-meter distance from the tunnel. The frequency domain analysis of recorded results determined the frequency 961 Hz and 968 Hz for 1.69 kg and 2.76 kg equivalent T.N.T., respectively. Then, finite element analysis results were compared with the test data. The comparisons demonstrated a good correlation and satisfied the field data. Finally, based on numerical modeling, a parametric study was applied to determine the effects of shear wave velocity distance of the crater with respect to the tunnel on impulse response of the tunnel.

  16. Progress Towards High-Sensitivity Arrays of Detectors of Sub-mm Radiation using Superconducting Tunnel Junctions with Radio-Frequency Single-Electron Transistors

    Science.gov (United States)

    Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Stahle, C. M.; Wollack, E. J.; Schoelkopf, R. J.; Krebs, Carolyn (Technical Monitor)

    2002-01-01

    The science drivers for the SPIRIT/SPECS missions demand sensitive, fast, compact, low-power, large-format detector arrays for high resolution imaging and spectroscopy in the far infrared and submillimeter. Detector arrays with 10,000 pixels and sensitivity less than 10(exp 20)-20 W/Hz(exp 20)0.5 are needed. Antenna-coupled superconducting tunnel junction detectors with integrated rf single-electron transistor readout amplifiers have the potential for achieving this high level of sensitivity, and can take advantage of an rf multiplexing technique when forming arrays. The device consists of an antenna structure to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure currents through tunnel junction contacts to the absorber volume. We will describe optimization of device parameters, and recent results on fabrication techniques for producing devices with high yield for detector arrays. We will also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

  17. Nb/A1- AlOx/Nb隧道结的制备研究%Fabrication on Nb/A1 - AlOx/Nb tunnel junction

    Institute of Scientific and Technical Information of China (English)

    肖伟; 曹春海; 李梦月; 许钦印; 卢亚鹏; 康琳; 许伟伟; 陈健; 吴培亨

    2012-01-01

    By improving etching process and insulating layer growth process, we fabricated superconducting tunnel junctions with good performance. In order to decrease the etching of oxide layer and substrate during RIE, CF4 was used as etching gas. SiO2 is grown by using PECVD, to improve the performance of SiO2 insulation layer. Greatly improve the performance of the tunnel junction.%通过改进RIE的刻蚀工艺和绝缘层的生长工艺,在SiO2/Si衬底上制备出了性能良好的超导Nb/A1 AlOx/Nb隧道结.采用CF4作为刻蚀气体,降低了RIE对结势垒层和衬底SiO2层的刻蚀.使用PECVD生长绝缘层SiO2,改善了绝缘性能,从而降低了隧道结的漏电流.

  18. 86% TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers

    Institute of Scientific and Technical Information of China (English)

    Feifei LI; Xiufeng HAN; Lixian JIANG; Jing ZHAO; Lei WANG; Rehana Sharif

    2005-01-01

    Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21 (5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20, 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity HC of ≤4Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MT Js.

  19. Electron tunnel sensor technology

    Science.gov (United States)

    Waltman, S. B.; Kaiser, W. J.

    1989-01-01

    The recent development of Scanning Tunneling Microscopy technology allows the application of electron tunneling to position detectors for the first time. The vacuum tunnel junction is one of the most sensitive position detection mechanisms available. It is also compact, simple, and requires little power. A prototype accelerometer based on electron tunneling, and other sensor applications of this promising new technology are described.

  20. Effect of coupling ability between a synthetic antiferromagnetic layer and pinned layer on a bridging layer of Ta, Ti, and Pt in perpendicular-magnetic tunnel junctions.

    Science.gov (United States)

    Lee, Du-Yeong; Shim, Tae-Hun; Park, Jea-Gun

    2016-07-22

    By fabricating CoFeB/MgO/CoFeB-based perpendicular-magnetic tunnel junction (p-MTJ) spin-valves stacked with a [Co/Pd] n -SyAF layer based on a TiN bottom electrode on a 12 inch Si wafer (001) substrate, we investigated how the bridging layers of Ta, Ti, and Pt and their thickness variation affected the tunneling magneto-resistance (TMR) ratio of Co2Fe6B2 pinned-layer behavior in magnetic-tunnel-junctions. TMR ratios for Ta, Ti, and Pt bridging layers were observed to be 64.1, 70.2, and 29.5%, respectively. It was confirmed by high resolution transmission electron microscopy (HR-TEM) that this difference resulted from CoFeB/MgO/CoFeB MTJ layers with Ta and Ti bridging layers being textured well with a bcc (100) structure, indicating that Ta and Ti bridging layers bridged SyAF fcc (111) and MTJ bcc (100). On the other hand, the MTJ layer with Pt bridging layer was incorrectly textured, indicating that a Pt bridging layer is unsuitable to bridge SyAF fcc (111) and MTJ bcc (100) due to Pt being diffused into the CoFeB pinned-layer. In addition, perpendicular magnetic anisotropy (PMA) behavior of the CoFeB pinned-layer was found to depend strongly on a bridging layer thickness; higher TMRs of Ta and Ti were observed at the optimal bridging layers' thickness, which enable the realization of PMAs of the pinned-layer and ferro-coupling of the pinned-layer with the lower-SyAF layer. Among the three bridging materials (Ta, Ti, and Pt), we observed that Ti showed the highest TMR ratio and widest thickness range for a high TMR ratio, indicating that a higher TMR ratio is needed to obtain the best deposition process margin.

  1. A CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction coupled to an in-plane exchange-biased magnetic layer

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, M., E-mail: mzhu@sunycnse.com; Chong, H.; Vu, Q. B.; Vo, T.; Brooks, R.; Stamper, H.; Bennett, S.; Piccirillo, J. [Colleges of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, New York 12203 (United States)

    2015-05-25

    We report a stack structure which utilizes an in-plane exchange-biased magnetic layer to influence the coercivity of the bottom CoFeB layer in a CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction. By employing a thickness wedge deposition technique, we were able to study various aspects of this stack using vibrating sample magnetometer including: (1) the coupling between two CoFeB layers as a function of MgO thickness; and (2) the coupling between the bottom CoFeB and the in-plane magnetic layer as a function of Ta spacer thickness. Furthermore, modification of the bottom CoFeB coercivity allows one to measure tunneling magnetoresistance and resistance-area product (RA) of CoFeB/MgO/CoFeB in this pseudo-spin-valve format using current-in-plane-tunneling technique, without resorting to (Co/Pt){sub n} or (Co/Pd){sub n} multilayer pinning.

  2. Study of CoFeB thickness and composition dependence in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction

    Science.gov (United States)

    Zhu, M.; Chong, H.; Vu, Q. B.; Brooks, R.; Stamper, H.; Bennett, S.

    2016-02-01

    We studied the CoFeB thickness and composition dependence of tunneling magnetoresistance (TMR) and resistance-area product (RA) in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction (MTJ), in which the bottom CoFeB is coupled to an in-plane exchange biased magnetic layer. This stack structure allows us to measure TMR and RA of the MTJs in sheet film format without patterning them, using current-in-plane-tunneling (CIPT) technique. The thickness ranges for both top and bottom CoFeB to exhibit perpendicular magnetic anisotropy are similar to what are seen in each single magnetic film stack. However, CIPT measurement revealed that there exists an optimal thickness for both top and bottom CoFeB to achieve the highest TMR value. Magnetic hysteresis loops also suggest the thickness-dependent coupling between the top and bottom CoFeB layers. We studied MTJs with two CoFeB compositions (Co40Fe40B20 and Co20Fe60B20) and found that Co20Fe60B20 MTJs give higher TMR and also wider perpendicular thickness range when used at the top layer.

  3. Construction Technology of Hadapu Tunnel Soft PlasticⅥGrade Shallow Buried Adj oining Rock%哈达铺隧道软塑状Ⅵ级围岩浅埋段施工技术

    Institute of Scientific and Technical Information of China (English)

    朱洪莹; 武建广; 刘兴平; 王会军

    2014-01-01

    Crushing loose soft surrounding rock section,the ground settlement and level conver-gence value difficult to control,bench excavation difficult,is the difficulty of construction work. Lan yu railway Hadapu Tunnel exit is cross blacksmith ditch bottom shallow-buried section,geo-logical conditions complex.Through strata of geological studies revealed piecewise process of con-struction,comparative analysis the actual results and applicability of the horouchi horizontal rota-ry j et grouting piles,advanced tune shed,curtain grouting,surface chemical churning pile and oth-er programs.Finally,use surface vertical chemical churning pile scheme,accompanied by tunnel face advance strengthening and closed,to achieve effective control of soft plastic mucky Ⅵ grade shallow buried adjoining rock tunnel initial support deformation and surface settlement.%破碎松散的软弱围岩地段,地表沉降及水平收敛值难以控制,台阶开挖难度大、是施工作业的难点。兰渝铁路哈达铺隧道出口端穿越铁匠沟底浅埋段,地质条件复杂。通过对施工过程中逐段揭示的地层地质研究,对比分析了洞内水平旋喷桩、超前管棚+帷幕注浆、地表旋喷桩等施工工艺的实际效果及适用性,最终选择地表竖直旋喷桩方案并伴以掌子面超前加固及封闭,实现了对软塑淤泥质Ⅵ级围岩浅埋隧道的初期支护变形及地表沉降的有效控制。

  4. The influence of the Dresselhaus spin-orbit coupling on the tunnelling magnetoresistance in ferromagnet/insulator /semiconductor/ insulator /ferromagnet tunnel junctions

    Institute of Scientific and Technical Information of China (English)

    Wang Xiao-Hua; An Xing-Tao; Liu Jian-Jun

    2009-01-01

    This paper investigates the effect of Dresselhaus spin-orbit coupling on the spin-transport properties of ferro-magnet/insulator/semiconductor/iusulator/ferromagnet double-barrier structures. The influence of the thickness of the insulator between the ferromagnct and the semiconductor on the polarization is also considered. The obtained results indicate that (I) the polarization can be enhanced by reducing the insulator layers at zero temperature, and (ii) the tunnelling magnctoresistance inversion can be illustrated by the influence of the Dresselhaus spin-orbit coupling effect in the double-barrier structure. Due to the Dresselhaus spin-orbit coupling effect, the tunnelling magnetoresistance inversion occurs when the energy of a localized state in the barrier matches the Fermi energy EF of the ferromagnetic electrodes.

  5. Free- and reference-layer magnetization modes versus in-plane magnetic field in a magnetic tunnel junction with perpendicular magnetic easy axis

    Science.gov (United States)

    Mazraati, Hamid; Le, Tuan Q.; Awad, Ahmad A.; Chung, Sunjae; Hirayama, Eriko; Ikeda, Shoji; Matsukura, Fumihiro; Ohno, Hideo; Åkerman, Johan

    2016-09-01

    We study the magnetodynamic modes of a magnetic tunnel junction with perpendicular magnetic easy axis (p-MTJ) in in-plane magnetic fields using device-level ferromagnetic resonance spectroscopy. We compare our experimental results to those of micromagnetic simulations of the entire p-MTJ. Using an iterative approach to determine the material parameters that best fit our experiment, we find excellent agreement between experiments and simulations in both the static magnetoresistance and magnetodynamics in the free and reference layers. From the micromagnetic simulations, we determine the spatial mode profiles, the localization of the modes and, as a consequence, their distribution in the frequency domain due to the inhomogeneous internal field distribution inside the p-MTJ under different applied field regimes. We also conclude that the excitation mechanism is a combination of the microwave voltage modulated perpendicular magnetic anisotropy, the microwave Oersted field, and the spin-transfer torque generated by the microwave current.

  6. Temperature increase due to Joule heating in a nanostructured MgO-based magnetic tunnel junction over a wide current-pulse range.

    Science.gov (United States)

    Jeong, Boram; Lim, Sang Ho

    2011-07-01

    The temperature increase due to Joule heating in a nanopillar of a magnetic tunnel junction sandwiched by top and bottom electrodes was calculated by the finite element method. The results for the critical condition for the current-induced magnetization switching measured over a wide current-pulse range were taken from the literature. At long pulse widths, the temperature increase was solely dependent on the magnitude of the critical current density. However, no saturation in the temperature increase occurred for short pulse widths. In this case, the temperature increase additionally depended on the pulse width, so that a broad maximum occurred in the pulse width (or the critical current density) dependence of the temperature increase. The original results for the critical condition were corrected by accounting for the temperature increase and these corrected results, together with the Slonczewski equation, were used to extract an accurate value for the thermal stability factor.

  7. Design and fabrication of a perpendicular magnetic tunnel junction based nonvolatile programmable switch achieving 40% less area using shared-control transistor structure.

    Science.gov (United States)

    Suzuki, D; Natsui, M; Mochizuki, A; Miura, S; Honjo, H; Kinoshita, K; Fukami, S; Sato, H; Ikeda, S; Endoh, T; Ohno, H; Hanyu, T

    2014-05-07

    A compact nonvolatile programmable switch (NVPS) using 90 nm CMOS technology together with perpendicular magnetic tunnel junction (p-MTJ) devices is fabricated for zero-standby-power field-programmable gate array. Because routing information does not change once it is programmed into an NVPS, high-speed read and write accesses are not required and a write-control transistor can be shared among all the NVPSs, which greatly simplifies structure of the NVPS. In fact, the effective area of the proposed NVPS is reduced by 40% compared to that of a conventional MTJ-based NVPS. The instant on/off behavior without external nonvolatile memory access is also demonstrated using the fabricated test chip.

  8. Magnetic stability under magnetic cycling of MgO-based magnetic tunneling junctions with an exchange-biased synthetic antiferromagnetic pinned layer

    Directory of Open Access Journals (Sweden)

    Qiang Hao

    2016-02-01

    Full Text Available We investigate the magnetic stability and endurance of MgO-based magnetic tunnel junctions (MTJs with an exchange-biased synthetic antiferromagnetic (SAF pinned layer. When a uniaxially cycling switching field is applied along the easy axis of the free magnetic layer, the magnetoresistance varies only by 1.7% logarithmically with the number of cycles, while no such change appears in the case of a rotating field. This observation is consistent with the effect of the formation and motion of domain walls in the free layer, which create significant stray fields within the pinned hard layer. Unlike in previous studies, the decay we observed only occurs during the first few starting cycles (<20, at which point there is no further variance in all performance parameters up to 107 cycles. Exchange-biased SAF structure is ideally suited for solid-state magnetic sensors and magnetic memory devices.

  9. Improvement of soft x-ray detection performance in superconducting-tunnel-junction array detectors with close-packed arrangement by three-dimensional structure

    Science.gov (United States)

    Fujii, G.; Ukibe, M.; Ohkubo, M.

    2015-10-01

    Superconducting-tunnel-junction (STJ) array detectors have exhibited excellent characteristics for fluorescence-yield x-ray absorption fine structure (XAFS) for trace light elements in structural and functional materials. For XAFS, we have developed new fabrication processes for close-packed STJ pixels by using a three-dimensional structure (3D-STJ), in which the layers of STJ pixels are formed after caldera planarization of the base SiO2 layer deposited on the patterned wiring leads. The 3D-STJ has an operation yield of 88% and a mean energy resolution of 23.8 +/-1.9 eV for the C-Kα x-ray.

  10. Integrated ZnO Nano-Electron-Emitter with Self-Modulated Parasitic Tunneling Field Effect Transistor at the Surface of the p-Si/ZnO Junction.

    Science.gov (United States)

    Cao, Tao; Luo, Laitang; Huang, Yifeng; Ye, Bing; She, Juncong; Deng, Shaozhi; Chen, Jun; Xu, Ningsheng

    2016-09-22

    The development of high performance nano-electron-emitter arrays with well reliability still proves challenging. Here, we report a featured integrated nano-electron-emitter. The vertically aligned nano-emitter consists of two segments. The top segment is an intrinsically lightly n-type doped ZnO nano-tip, while the bottom segment is a heavily p-type doped Si nano-pillar (denoted as p-Si/ZnO nano-emitter). The anode voltage not only extracted the electron emission from the emitter apex but also induced the inter-band electron tunneling at the surface of the p-Si/ZnO nano-junction. The designed p-Si/ZnO emitter is equivalent to a ZnO nano-tip individually ballasted by a p-Si/ZnO diode and a parasitic tunneling field effect transistor (TFET) at the surface of the p-Si/ZnO junction. The parasitic TFET provides a channel for the supply of emitting electron, while the p-Si/ZnO diode is benefit for impeding the current overloading and prevent the emitters from a catastrophic breakdown. Well repeatable and stable field emission current were obtained from the p-Si/ZnO nano-emitters. High performance nano-emitters was developed using diamond-like-carbon coated p-Si/ZnO tip array (500 × 500), i.e., 178 μA (4.48 mA/cm(2)) at 75.7 MV/m.

  11. Integrated ZnO Nano-Electron-Emitter with Self-Modulated Parasitic Tunneling Field Effect Transistor at the Surface of the p-Si/ZnO Junction

    Science.gov (United States)

    Cao, Tao; Luo, Laitang; Huang, Yifeng; Ye, Bing; She, Juncong; Deng, Shaozhi; Chen, Jun; Xu, Ningsheng

    2016-01-01

    The development of high performance nano-electron-emitter arrays with well reliability still proves challenging. Here, we report a featured integrated nano-electron-emitter. The vertically aligned nano-emitter consists of two segments. The top segment is an intrinsically lightly n-type doped ZnO nano-tip, while the bottom segment is a heavily p-type doped Si nano-pillar (denoted as p-Si/ZnO nano-emitter). The anode voltage not only extracted the electron emission from the emitter apex but also induced the inter-band electron tunneling at the surface of the p-Si/ZnO nano-junction. The designed p-Si/ZnO emitter is equivalent to a ZnO nano-tip individually ballasted by a p-Si/ZnO diode and a parasitic tunneling field effect transistor (TFET) at the surface of the p-Si/ZnO junction. The parasitic TFET provides a channel for the supply of emitting electron, while the p-Si/ZnO diode is benefit for impeding the current overloading and prevent the emitters from a catastrophic breakdown. Well repeatable and stable field emission current were obtained from the p-Si/ZnO nano-emitters. High performance nano-emitters was developed using diamond-like-carbon coated p-Si/ZnO tip array (500 × 500), i.e., 178 μA (4.48 mA/cm2) at 75.7 MV/m. PMID:27654068

  12. Integrated ZnO Nano-Electron-Emitter with Self-Modulated Parasitic Tunneling Field Effect Transistor at the Surface of the p-Si/ZnO Junction

    Science.gov (United States)

    Cao, Tao; Luo, Laitang; Huang, Yifeng; Ye, Bing; She, Juncong; Deng, Shaozhi; Chen, Jun; Xu, Ningsheng

    2016-09-01

    The development of high performance nano-electron-emitter arrays with well reliability still proves challenging. Here, we report a featured integrated nano-electron-emitter. The vertically aligned nano-emitter consists of two segments. The top segment is an intrinsically lightly n-type doped ZnO nano-tip, while the bottom segment is a heavily p-type doped Si nano-pillar (denoted as p-Si/ZnO nano-emitter). The anode voltage not only extracted the electron emission from the emitter apex but also induced the inter-band electron tunneling at the surface of the p-Si/ZnO nano-junction. The designed p-Si/ZnO emitter is equivalent to a ZnO nano-tip individually ballasted by a p-Si/ZnO diode and a parasitic tunneling field effect transistor (TFET) at the surface of the p-Si/ZnO junction. The parasitic TFET provides a channel for the supply of emitting electron, while the p-Si/ZnO diode is benefit for impeding the current overloading and prevent the emitters from a catastrophic breakdown. Well repeatable and stable field emission current were obtained from the p-Si/ZnO nano-emitters. High performance nano-emitters was developed using diamond-like-carbon coated p-Si/ZnO tip array (500 × 500), i.e., 178 μA (4.48 mA/cm2) at 75.7 MV/m.

  13. Co2MnSi Heusler alloy as an enhancing layer of perpendicular magnetic anisotropy for MgO-based magnetic tunnel junctions with L10 ordered FePd

    Science.gov (United States)

    Bae, Taejin; Ko, Jungho; Lee, Sangho; Cha, Jongin; Hong, Jongill

    2016-01-01

    Ultra-thin Co2MnSi Heusler alloy improves perpendicular magnetic anisotropy of FePd in an MgO-based magnetic tunnel junction after annealing it just once at a temperature of as low as 400 °C. Co2MnSi as thin as 1.0 nm inserted between MgO and FePd facilitated phase-transformation of 3-nm-thick FePd to ordered L10 and led a change in magnetic anisotropy to perpendicular-to-the-plane. To make it even better, FePd also helped the phase-transformation of Co2MnSi to ordered B2 known to have high spin polarization, which makes the L10 FePd/B2 Co2MnSi bilayer promising for perpendicular-magnetic tunnel junction and improving both thermal stability and tunnel magnetoresistance.

  14. Tunnel oxide passivated rear contact for large area n-type front junction silicon solar cells providing excellent carrier selectivity

    Directory of Open Access Journals (Sweden)

    Yuguo Tao

    2016-01-01

    Full Text Available Carrier-selective contact with low minority carrier recombination and efficient majority carrier transport is mandatory to eliminate metal-induced recombination for higher energy conversion efficiency for silicon (Si solar cells. In the present study, the carrier-selective contact consists of an ultra-thin tunnel oxide and a phosphorus-doped polycrystalline Si (poly-Si thin film formed by plasma enhanced chemical vapor deposition (PECVD and subsequent thermal crystallization. It is shown that the poly-Si film properties (doping level, crystallization and dopant activation anneal temperature are crucial for achieving excellent contact passivation quality. It is also demonstrated quantitatively that the tunnel oxide plays a critical role in this tunnel oxide passivated contact (TOPCON scheme to realize desired carrier selectivity. Presence of tunnel oxide increases the implied Voc (iVoc by ~ 125 mV. The iVoc value as high as 728 mV is achieved on symmetric structure with TOPCON on both sides. Large area (239 cm2 n-type Czochralski (Cz Si solar cells are fabricated with homogeneous implanted boron emitter and screen-printed contact on the front and TOPCON on the back, achieving 21.2% cell efficiency. Detailed analysis shows that the performance of these cells is mainly limited by boron emitter recombination on the front side.

  15. Spin dependent transport properties of Mn-Ga/MgO/Mn-Ga magnetic tunnel junctions with metal(Mg, Co, Cr) insertion layer

    Energy Technology Data Exchange (ETDEWEB)

    Liang, S. H.; Tao, L. L.; Liu, D. P., E-mail: dpliu@iphy.ac.cn; Han, X. F., E-mail: xfhan@iphy.ac.cn [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Lu, Y. [Institut Jean Lamour, UMR 7198, CNRS-Nancy Université, BP 239, 54506 Vandoeuvre (France)

    2014-04-07

    We report a first principles theoretical investigation of spin polarized quantum transport in Mn{sub 2}Ga/MgO/Mn{sub 2}Ga and Mn{sub 3}Ga/MgO/Mn{sub 3}Ga magnetic tunneling junctions (MTJs) with the consideration of metal(Mg, Co, Cr) insertion layer effect. By changing the concentration of Mn, our calculation shows a considerable disparity in transport properties: A tunneling magnetoresistance (TMR) ratio of 852% was obtained for Mn{sub 2}Ga-based MTJs, however, only a 5% TMR ratio for Mn{sub 3}Ga-based MTJs. In addition, the influence of insertion layer has been considered in our calculation. We found the Co insertion layer can increase the TMR of Mn{sub 2}Ga-based MTJ to 904%; however, the Cr insertion layer can decrease the TMR by 668%; A negative TMR ratio can be obtained with Mg insertion layer. Our work gives a comprehensive understanding of the influence of different insertion layer in Mn-Ga based MTJs. It is proved that, due to the transmission can be modulated by the interfacial electronic structure of insertion, the magnetoresistance ratio of Mn{sub 2}Ga/MgO/Mn{sub 2}Ga MTJ can be improved by inserting Co layer.

  16. First-principles study of spin transport in BN doped CrO{sub 2}–graphene–CrO{sub 2} magnetic tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Choudhary, Sudhanshu, E-mail: sudhanshu@nitkkr.ac.in; Mishra, Pradeep, E-mail: pradeepmshr26@gmail.com; Goyal, Rohit, E-mail: rohit91.goyal@gmail.com

    2016-03-06

    We investigate the spin-dependent electronic transport properties of Magnetic tunnel junction (MTJ) consisting of Boron (B) and Nitrogen (N) doped graphene nanosheet sandwiched between two CrO{sub 2} half-metallic–ferromagnet (HMF) electrodes. A large value of tunnel magnetoresistance (TMR) and perfect spin filtration was obtained as compared to un-doped graphene MTJ structures reported in past. The use of HMF electrodes further raises the TMR and improves the spin filtration in comparison to MTJs with metallic and ferromagnetic (FM) electrodes, which suggest HMF electrodes as a suitable candidate over metallic and FM electrodes for implementing graphene sheet based MTJs. A high value of TMR ∼100% is obtained at zero bias voltage, which remains constantly high at higher bias voltages in the range of 0 V to 1 V. The higher value of TMR and better (near perfect) spin filtration abilities suggest its usefulness in spin-valves and other spintronics based applications. The spin-dependent non-equilibrium transport is also investigated by analyzing the bias dependent transmission coefficients. - Highlights: • Higher TMR was observed in BN doped graphene based MTJ in comparison with undoped structure. • Perfect Spin Filtration Effect was observed in doped structure in comparison with undoped structure. • Use of HMF electrodes further raises TMR and Spin Filtration Effect.

  17. Giant voltage manipulation of MgO-based magnetic tunnel junctions via localized anisotropic strain: A potential pathway to ultra-energy-efficient memory technology

    Science.gov (United States)

    Zhao, Zhengyang; Jamali, Mahdi; D'Souza, Noel; Zhang, Delin; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha; Wang, Jian-Ping

    2016-08-01

    Voltage control of magnetization via strain in piezoelectric/magnetostrictive systems is a promising mechanism to implement energy-efficient straintronic memory devices. Here, we demonstrate giant voltage manipulation of MgO magnetic tunnel junctions (MTJ) on a Pb(Mg1/3Nb2/3)0.7Ti0.3O3 piezoelectric substrate with (001) orientation. It is found that the magnetic easy axis, switching field, and the tunnel magnetoresistance (TMR) of the MTJ can be efficiently controlled by strain from the underlying piezoelectric layer upon the application of a gate voltage. Repeatable voltage controlled MTJ toggling between high/low-resistance states is demonstrated. More importantly, instead of relying on the intrinsic anisotropy of the piezoelectric substrate to generate the required strain, we utilize anisotropic strain produced using a local gating scheme, which is scalable and amenable to practical memory applications. Additionally, the adoption of crystalline MgO-based MTJ on piezoelectric layer lends itself to high TMR in the strain-mediated MRAM devices.

  18. Change of Electronic Structure and Magnetic Properties with MgO and Fe Thicknesses in Fe/MgO/Fe Magnetic Tunnel Junction

    Institute of Scientific and Technical Information of China (English)

    YANG Fan; BI Xiao-fang

    2006-01-01

    The effects of the thickness of MgO and Fe on the electronic structure and magnetic properties of Fe/MgO/Fe magnetic tunnel junction was studied using the first principle method. Two series of models with MgO of different thicknesses: Fe(3)MgO(t)Fe(3) (t=1,3,5,7) and with Fe of varied thicknesses: Fe(t)MgO(3)Fe(t) (t=3,4,5,6,7) were established. Calculated results show that in all the models the magnetic moment of Fe increases at the Fe/MgO interface and surface as compared with that of the inner layers. The magnetic moment of each Fe layer was found to be independent of MgO thicknesses, while the spin-polarization of Fe layer at the interface shows a slight change in function of the MgO thicknesses. The tunneling magnetoresistance (TMR) ratio estimated by the Julliere model has the same change tendency as the spin-polarization has, and the largest value is obtained at the MgO thickness of 5 atomic layers. When the Fe thickness increases, the spin-polarization of interface Fe layer follows up an increase with a decrease. The highest TMR value is achieved when the Fe thickness is of 4 atomic layers.

  19. Charge transport in molecular electronic junctions: Compression of the molecular tunnel barrier in the strong coupling regime

    OpenAIRE

    Sayed, Sayed Y.; Fereiro, Jerry A.; Yan, Haijun; Richard L. McCreery; Bergren, Adam Johan

    2012-01-01

    Molecular junctions are essentially modified electrodes familiar to electrochemists where the electrolyte is replaced by a conducting “contact.” It is generally hypothesized that changing molecular structure will alter system energy levels leading to a change in the transport barrier. Here, we show the conductance of seven different aromatic molecules covalently bonded to carbon implies a modest range ( 2 eV range). These results are explained by considering the effect of bonding the molecule...

  20. Enhancement of the spin accumulation at the interface between a spin-polarized tunnel junction and a semiconductor.

    Science.gov (United States)

    Tran, M; Jaffrès, H; Deranlot, C; George, J-M; Fert, A; Miard, A; Lemaître, A

    2009-01-23

    We report on spin injection experiments at a Co/Al2O3/GaAs interface with electrical detection. The application of a transverse magnetic field induces a large voltage drop DeltaV at the interface as high as 1.2 mV for a current density of 0.34 nA.microm(-2). This represents a dramatic increase of the spin accumulation signal, well above the theoretical predictions for spin injection through a ferromagnet/semiconductor interface. Such an enhancement is consistent with a sequential tunneling process via localized states located in the vicinity of the Al2O3/GaAs interface. For spin-polarized carriers these states act as an accumulation layer where the spin lifetime is large. A model taking into account the spin lifetime and the escape tunneling time for carriers traveling back into the ferromagnetic contact reproduces accurately the experimental results.

  1. Transport properties of La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/LaAlO{sub 3}/Pt tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Galceran, R.; Balcells, Ll.; Pomar, A.; Konstantinović, Z.; Sandiumenge, F.; Martínez, B. [Instituto de Ciencia de Materiales de Barcelona - CSIC, Campus UAB, Bellaterra 08193 (Spain)

    2015-03-14

    Magnetotransport properties of La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/LaAlO{sub 3}/Pt tunnel junctions have been thoroughly analyzed, as a function of temperature and magnetic field, to test the suitability of LaAlO{sub 3} for insulating barriers and spin injection processes. The insulating behavior of LaAlO{sub 3} maintained down to 1–2 nm (corresponding to 4–5 unit cells) renders this material useful as tunnel barrier. The temperature dependence of the junction resistance, R(T), down to 200 K confirms direct tunneling as the dominant conduction channel. The barrier parameters of the junctions, φ{sub 0} and s, are estimated using Simmons' model in the intermediate voltage range. The energy of the barrier was estimated to be φ{sub 0} ∼ 0.4 eV at room temperature. The dependence of R(T) and φ{sub 0} on the magnetic field shows an anisotropic tunneling magnetoresistance of ∼4% at low T when changing the direction of the magnetization with respect to the current flow.

  2. TMR- and TAMR-effects of (Ga,Mn)As and GaAs tunnel junctions; TMR- und TAMR-Effekt an (Ga,Mn)As und GaAs Tunnelstrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Brinkmeier, Eva

    2009-07-30

    This thesis is concerned with the experimental investigation of the tunnel magnetoresistance (TMR) and tunnel anistropic magnetoresistance (TAMR) in GaAs and (Ga,Mn)As tunnel junction. A special emphasis was put on the study of the newly discovered TAMR effect, which consists in the variation of the TMR with the magnetization's angle. The tunnel junctions were fabricated by means of optical lithography and wet chemical etching. The dependence of the TAMR effect on the layer system, the barrier thickness, the bias voltage, the temperature and the applied magnetic field magnitude was subsequently examined. The conducted measurements on (Ga,Mn)As junctions showed a TMR effect as well as various anisotropic effects which are in good agreement with the experimental reports published so far. The observed dependences of the TAMR effect on the aforementioned parameters were discussed within the framework of two distinct preexisting theoretical models and the experimental data could be explained by the superimposition of two effects stemming in one case from the spin orbit coupling in the (Ga,Mn)As layer and in the other from the concurrent action of the Rashba and Dresselhaus spin orbit interaction within the barrier. (orig.)

  3. APPLICATION OF DIGITAL ELECTRON DETONATOR IN THE BLASTING SHOCK ABSORPTION TECHNOLOGY TO SHALLOW-BURIED TUNNEL AT TOWN%数码电子雷管在城镇浅埋隧道减振爆破中的应用

    Institute of Scientific and Technical Information of China (English)

    孟小伟; 黄明利; 谭忠盛; 阮清林

    2012-01-01

    在建筑物密集且部分建筑物抗震性能差的城镇地区地下,进行浅埋隧道爆破开挖施工,只有采用减振控制爆破技术才能使地表建(构)筑物免受爆破振动的危害.以重庆在建的渝利铁路长洪岭隧道下穿江池镇区间为工程背景,针对地表民房密集、房屋抗振等级低,爆破控制标准要求严格,通过数码电子雷管和非电毫秒雷管爆破对比试验,形成数码电子雷管减振爆破技术,保证隧道安全快速通过江池镇.试验表明:数码电子雷管引起的爆破振动降低50%~60%,炮孔利用率达到98%.全断面爆破进尺控制在3m左右,不仅降低了振速,而且改善了爆破块度,还保证了施工进度.%Blasting shock absorption technology is only adopted to make surface buildings avoiding dam-age caused by blasting vibration, when blasting excavation of shallow-buried tunnel is constructed in the town with crowded buildings. In the blasting excavation of Changhongling tunnel under-traversing Jiangchi town at Chongqing city, according to the dense residences, the building with low resistance seismic level, and the strict blasting control standard, the blasting shock absorption technology of the digital electron detonator was form by the comparative tests between ordinary detonator and digital electron detonator, which guaranteed Chang-Hongling tunnel to pass through Jiangchi town safely. The test indicated that blasting vibration could be reduced 50%~60%, utilization ratio of the bore-hole reached 98%, and full-face blasting footage was about 3m by using the digital electron detonator. So the blasting shock absorp-tion technology not only reduced vibration velocity but also improve blasting fragment and guaranteed the speed of construction.

  4. Exploring the Tilt-Angle Dependence of electron tunneling across Molecular junction of Self-Assembled Alkanethiols

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Munuera, C.; Ocal, C.;

    2009-01-01

    by contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger...... for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect....

  5. A new approach for design and investigation of junction-less tunnel FET using electrically doped mechanism

    Science.gov (United States)

    Nigam, Kaushal; Kondekar, Pravin; Sharma, Dheeraj; Raad, Bhagwan Ram

    2016-10-01

    For the first time, a distinctive approach based on electrically doped concept is used for the formation of novel double gate tunnel field effect transistor (TFET). For this, the initially heavily doped n+ substrate is converted into n+-i-n+-i (Drain-Channel-Source) by the selection of appropriate work functions of control gate (CG) and polarity gate (PG) as 4.7 eV. Further, the formation of p+ region for source is performed by applying -1.2 V at PG. Hence, the structure behave like a n+-i-n+-p+ gated TFET, whereas, the control gate is used to modulate the effective tunneling barrier width. The physical realization of delta doped n+ layer near to source region is a challenging task for improving the device performance in terms of ON current and subthreshold slope. So, the proposed work will provide a better platform for fabrication of n+-i-n+-p+ TFET with low cost and suppressed random dopant fluctuation (RDF) effects. ATLAS TCAD device simulator is used to carry out the simulation work.

  6. Tunnelling spectroscopy of BaFe{sub 2}As{sub 2}/Au/PbIn thin film junctions

    Energy Technology Data Exchange (ETDEWEB)

    Doering, Sebastian; Schmidt, Stefan; Schmidl, Frank; Tympel, Volker; Grosse, Veit; Seidel, Paul [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena (Germany); Haindl, Silvia; Iida, Kazumasa; Kurth, Fritz; Holzapfel, Bernhard [IFW Dresden, Institut fuer Metallische Werkstoffe, Dresden (Germany)

    2011-07-01

    Tunnelling spectroscopy is an important tool to investigate the properties of iron-based superconductors. In contrast to commonly used point contact Andreev reflection (PCAR) technique, we fabricated hybrid superconductor / normal metal / superconductor (SNS) thin film structures, with tunable barrier thickness and area. For the base electrode we use Ba(Fe{sub 0.9}Co{sub 0.1}){sub 2}As{sub 2} thin films, produced via pulsed laser deposition (PLD). A gold layer was sputtered to form the barrier, while the counter electrode material is the conventional superconductor PbIn with a T{sub c} of 7.2 K. For temperatures below 7.2 K the spectrum shows a subharmonic gap structure (SGS), described by an extended model of Octavio, Tinkham, Blonder and Klapwijk (OTBK), while at higher temperatures the SGS vanishes and an SN-like behaviour can be observed.

  7. ALD grown bilayer junction of ZnO:Al and tunnel oxide barrier for SIS solar cell☆

    Science.gov (United States)

    Bethge, O.; Nobile, M.; Abermann, S.; Glaser, M.; Bertagnolli, E.

    2013-01-01

    Various metal oxides are probed as extrinsic thin tunnel barriers in Semiconductor Insulator Semiconductor solar cells. Namely Al2O3, ZrO2, Y2O3, and La2O3 thin films are in between n-type ZnO:Al (AZO) and p-type Si substrates by means of Atomic Layer Deposition. Low reverse dark current–density as low as 3×10−7 A/cm2, a fill factor up to 71.3%, and open-circuit voltage as high as 527 mV are obtained, achieving conversion efficiency of 8% for the rare earth oxide La2O3. ZrO2 and notably Al2O3 show drawbacks in performance suggesting an adverse reactivity with AZO as also indicated by X-ray Photoelectron Spectroscopy. PMID:26877596

  8. Interface properties of magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3 superlattices studied by standing-wave excited photoemission spectroscopy

    NARCIS (Netherlands)

    Gray, A.X.; Papp, C.; Balke, B.; Yang, S.-H.; Huijben, M.; Rotenberg, E.; Bostwick, A.; Ueda, S.; Yamashita, Y.; Kobayashi, K.; Gullikson, E.M.; Kortright, J.B.; Groot, de F.M.F.; Rijnders, G.; Blank, D.H.A.; Ramesh, R.; Fadley, C.S.

    2010-01-01

    The chemical and electronic-structure profiles of magnetic tunnel junction (MTJ) La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) superlattices have been quantitatively determined via soft and hard x-ray standing-wave excited photoemission, x-ray absorption and x-ray reflectivity, in conjunction with x-ray optical

  9. Magneto-transport properties of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction

    Indian Academy of Sciences (India)

    P Raychaudhuri; C Mitra; K Dorr; K H Muller; G Kobernik; R Pinto

    2002-05-01

    Hole-doped rare-earth manganite La0.7Ca0.3MnO3 and the electron-doped manganite La0.7Ce0.3MnO3 both show a metal–insulator transition around 250 K associated with a ferromagnetic transition and colossal magnetoresistance. In an earlier publication we have reported the rectifying characteristic of La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3 tunnel junction at room temperature, showing that it is possible to fabricate a diode out of the polaronic insulator regime of doped manganites. Here we report the magneto-transport properties of such a tunnel junction above and below the metal–insulator transition. We show, from the large positive magnetoresistance of the tunnel junction at low temperature, that La0.7Ce0.3MnO3 could be a minority spin carrier ferromagnet. The implication of this observation is discussed.

  10. Mechanical Monitoring and Analysis of Umbrella Arch Structure in Shallow-buried Bias Loess Tunnel Entrance%黄土隧道浅埋偏压洞口段套拱结构受力监测与分析

    Institute of Scientific and Technical Information of China (English)

    陈建勋; 乔雄

    2011-01-01

    为了解黄土隧道浅埋偏压洞口段套拱结构的受力状况,对刘家坪2号隧道洞口段套拱基底应力、钢架应力、混凝土应力及拱顶下沉进行施工监测,并对监测结果进行分析.结果表明:浅埋偏压情况下,套拱两侧基底应力分布不均匀,拱顶填土引起基底应力急剧增长,仰拱施作后基底应力趋于稳定;套拱钢架受力复杂,有拉有压,且值很大,仰拱开挖引起钢架应力急剧增长,钢架在套拱支护结构中发挥了强大的支护作用;冬、夏季温差引起套拱混凝土应力随时间(季节)的变化呈现拉、压交替变化,夏季出现最大压应力,冬季出现最大拉应力,且压应力较小,拉应力较大,多处测点都超过了C25模筑混凝土设计轴心抗拉强度;套拱拱顶下沉主要由洞顶填土施工和仰拱开挖引起.%In order to understand the structural mechanical properties of umbrella arch in shallowburied bias loess tunnel entrance, stress of umbrella arch base, stress of steel frame, concrete stress and vault crown settlement were monitored and analyzed in tunnel entrance of Liujiaping 2# Tunnel. The results show that in shallow-buried bias tunnel, the stress distribution in the umbrella arch base is not uniform, and filling soil in the vault crown makes the stress of umbrella arch base increase rapidly, the stress of umbrella arch base tends to be steady after the contruction of inverted arch. Stress of steel frame of umbrella arch increases rapidly after the excavation of inverted arch, which is very complex, including tension and compression, and the value is large, support action of steel frame in the umbrella arch is significant. The umbrella arch is statically indeterminate structure, temperature difference in winter and summer makes concrete stress of umbrella arch alternatively change with the variation of time (season), compressive stress is maximum in summer and tensile stress is maximum in winter, and the compressive stress

  11. Testing epitaxial Co{sub 1.5}Fe{sub 1.5}Ge(001) electrodes in MgO-based magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Neggache, A. [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre lès Nancy (France); Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin BP48, 91192 Gif-sur-Yvette (France); Hauet, T.; Petit-Watelot, S.; Boulet, P.; Andrieu, S., E-mail: stephane.andrieu@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre lès Nancy (France); Bertran, F.; Le Fèvre, P.; Ohresser, P. [Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin BP48, 91192 Gif-sur-Yvette (France); Devolder, T. [Institut d' Electronique Fondamentale, CNRS, UMR 8622, 91405 Orsay (France); Mewes, C. [Department of Physics and Astronomy/Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Maat, S.; Childress, J. R. [San Jose Research Center, HGST, a Western Digital company, San Jose, California 95135 (United States)

    2014-06-23

    The ability of the full Heusler alloy Co{sub 1.5}Fe{sub 1.5}Ge(001) (CFG) to be a Half-Metallic Magnetic (HMM) material is investigated. Epitaxial CFG(001) layers were grown by molecular beam epitaxy. The results obtained using electron diffraction, X-ray diffraction, and X-ray magnetic circular dichroism are consistent with the full Heusler structure. The pseudo-gap in the minority spin density of state typical in HMM is examined using spin-resolved photoemission. Interestingly, the spin polarization found to be negative at E{sub F} in equimolar CoFe(001) is observed to shift to positive values when inserting Ge in CoFe. However, no pseudo-gap is found at the Fermi level, even if moderate magnetization and low Gilbert damping are observed as expected in HMM materials. Magneto-transport properties in MgO-based magnetic tunnel junctions using CFG electrodes are investigated via spin and symmetry resolved photoemission.

  12. Tandem Solar Cells from Solution-Processed CdTe and PbS Quantum Dots Using a ZnTe–ZnO Tunnel Junction

    Energy Technology Data Exchange (ETDEWEB)

    Crisp, Ryan W.; Pach, Gregory F.; Kurley, J. Matthew; France, Ryan M.; Reese, Matthew O.; Nanayakkara, Sanjini U.; MacLeod, Bradley A.; Talapin, Dmitri V.; Beard, Matthew C.; Luther, Joseph M.

    2017-01-10

    We developed a monolithic CdTe-PbS tandem solar cell architecture in which both the CdTe and PbS absorber layers are solution-processed from nanocrystal inks. Due to their tunable nature, PbS quantum dots (QDs), with a controllable band gap between 0.4 and ~1.6 eV, are a promising candidate for a bottom absorber layer in tandem photovoltaics. In the detailed balance limit, the ideal configuration of a CdTe (Eg = 1.5 eV)-PbS tandem structure assumes infinite thickness of the absorber layers and requires the PbS band gap to be 0.75 eV to theoretically achieve a power conversion efficiency (PCE) of 45%. However, modeling shows that by allowing the thickness of the CdTe layer to vary, a tandem with efficiency over 40% is achievable using bottom cell band gaps ranging from 0.68 and 1.16 eV. In a first step toward developing this technology, we explore CdTe-PbS tandem devices by developing a ZnTe-ZnO tunnel junction, which appropriately combines the two subcells in series. We examine the basic characteristics of the solar cells as a function of layer thickness and bottom-cell band gap and demonstrate open-circuit voltages in excess of 1.1 V with matched short circuit current density of 10 mA/cm2 in prototype devices.

  13. Nanosecond-Timescale Low Energy Switching of In-Plane Magnetic Tunnel Junctions through Dynamic Oersted-Field-Assisted Spin Hall Effect.

    Science.gov (United States)

    Aradhya, S V; Rowlands, G E; Oh, J; Ralph, D C; Buhrman, R A

    2016-10-12

    We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel junctions (MTJs) within 3-terminal devices in which spin-transfer torque is applied to the MTJ by the giant spin Hall effect. We measure reliable switching, with write error rates down to 10(-5), using current pulses as short as just 2 ns in duration. This represents the fastest reliable switching reported to date for any spin-torque-driven magnetic memory geometry and corresponds to a characteristic time scale that is significantly shorter than predicted possible within a macrospin model for in-plane MTJs subject to thermal fluctuations at room temperature. Using micromagnetic simulations, we show that in the three-terminal spin-Hall devices the Oersted magnetic field generated by the pulse current strongly modifies the magnetic dynamics excited by the spin-Hall torque, enabling this unanticipated performance improvement. Our results suggest that in-plane MTJs controlled by Oersted-field-assisted spin-Hall torque are a promising candidate for both cache memory applications requiring high speed and for cryogenic memories requiring low write energies.

  14. Magnetic tunnel junctions for magnetic field sensor by using CoFeB sensing layer capped with MgO film

    Energy Technology Data Exchange (ETDEWEB)

    Takenaga, Takashi, E-mail: takenaga@leap.or.jp; Tsuzaki, Yosuke; Yoshida, Chikako; Yamazaki, Yuichi; Hatada, Akiyoshi; Nakabayashi, Masaaki; Iba, Yoshihisa; Takahashi, Atsushi; Noshiro, Hideyuki; Tsunoda, Koji; Aoki, Masaki; Furukawa, Taisuke; Fukumoto, Hiroshi; Sugii, Toshihiro [Low-power Electronics Association and Project (LEAP), Tsukuba 305-8569 (Japan)

    2014-05-07

    We evaluated MgO-based magnetic tunnel junctions (MTJs) for magnetic field sensors with spin-valve-type structures in the CoFeB sensing layer capped by an MgO film in order to obtain both top and bottom interfaces of MgO/CoFeB exhibiting interfacial perpendicular magnetic anisotropy (PMA). Hysteresis of the CoFeB sensing layer in these MTJs annealed at 275 °C was suppressed at a thickness of the sensing layer below 1.2 nm by interfacial PMA. We confirmed that the CoFeB sensing layers capped with MgO suppress the thickness dependences of both the magnetoresistance ratio and the magnetic behaviors of the CoFeB sensing layer more than that of the MTJ with a Ta capping layer. MgO-based MTJs with MgO capping layers can improve the controllability of the characteristics for magnetic field sensors.

  15. Tandem Solar Cells from Solution-Processed CdTe and PbS Quantum Dots Using a ZnTe-ZnO Tunnel Junction.

    Science.gov (United States)

    Crisp, Ryan W; Pach, Gregory F; Kurley, J Matthew; France, Ryan M; Reese, Matthew O; Nanayakkara, Sanjini U; MacLeod, Bradley A; Talapin, Dmitri V; Beard, Matthew C; Luther, Joseph M

    2017-02-08

    We developed a monolithic CdTe-PbS tandem solar cell architecture in which both the CdTe and PbS absorber layers are solution-processed from nanocrystal inks. Due to their tunable nature, PbS quantum dots (QDs), with a controllable band gap between 0.4 and ∼1.6 eV, are a promising candidate for a bottom absorber layer in tandem photovoltaics. In the detailed balance limit, the ideal configuration of a CdTe (Eg = 1.5 eV)-PbS tandem structure assumes infinite thickness of the absorber layers and requires the PbS band gap to be 0.75 eV to theoretically achieve a power conversion efficiency (PCE) of 45%. However, modeling shows that by allowing the thickness of the CdTe layer to vary, a tandem with efficiency over 40% is achievable using bottom cell band gaps ranging from 0.68 and 1.16 eV. In a first step toward developing this technology, we explore CdTe-PbS tandem devices by developing a ZnTe-ZnO tunnel junction, which appropriately combines the two subcells in series. We examine the basic characteristics of the solar cells as a function of layer thickness and bottom-cell band gap and demonstrate open-circuit voltages in excess of 1.1 V with matched short circuit current density of 10 mA/cm(2) in prototype devices.

  16. Time scales of bias voltage effects in FE/MgO-based magnetic tunnel junctions with voltage-dependent perpendicular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Lytvynenko, Ia.M. [Sumy State University, 2, Rimskogo-Korsakova Str., 40007 Sumy (Ukraine); Hauet, T., E-mail: thomas.hauet@univ-lorraine.fr [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre les Nancy (France); Montaigne, F. [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre les Nancy (France); Bibyk, V.V. [Sumy State University, 2, Rimskogo-Korsakova Str., 40007 Sumy (Ukraine); Andrieu, S. [Institut Jean Lamour, UMR CNRS 7198, Université de Lorraine, 54506 Vandoeuvre les Nancy (France)

    2015-12-15

    Interplay between voltage-induced magnetic anisotropy transition and voltage-induced atomic diffusion is studied in epitaxial V/Fe (0.7 nm)/ MgO/ Fe(5 nm)/Co/Au magnetic tunnel junction where thin Fe soft electrode has in-plane or out-of-plane anisotropy depending on the sign of the bias voltage. We investigate the origin of the slow resistance variation occurring when switching bias voltage in opposite polarity. We demonstrate that the time to reach resistance stability after voltage switching is reduced when increasing the voltage amplitude or the temperature. A single energy barrier of about 0.2 eV height is deduced from temperature dependence. Finally, we demonstrate that the resistance change is not correlated to a change in soft electrode anisotropy. This conclusion contrasts with observations recently reported on analogous systems. - Highlights: • Voltage-induced time dependence of resistance is studied in epitaxial Fe/MgO/Fe. • Resistance change is not related to the bottom Fe/MgO interface. • The effect is thermally activated with an energy barrier of the order of 0.2 eV height.

  17. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    Science.gov (United States)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-01-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses. PMID:27405788

  18. Demonstration of a III-nitride vertical-cavity surface-emitting laser with a III-nitride tunnel junction intracavity contact

    Energy Technology Data Exchange (ETDEWEB)

    Leonard, J. T., E-mail: jtleona01@gmail.com; Young, E. C.; Yonkee, B. P.; Cohen, D. A.; Margalith, T.; Speck, J. S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); DenBaars, S. P.; Nakamura, S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States)

    2015-08-31

    We report on a III-nitride vertical-cavity surface-emitting laser (VCSEL) with a III-nitride tunnel junction (TJ) intracavity contact. The violet nonpolar VCSEL employing the TJ is compared to an equivalent VCSEL with a tin-doped indium oxide (ITO) intracavity contact. The TJ VCSEL shows a threshold current density (J{sub th}) of ∼3.5 kA/cm{sup 2}, compared to the ITO VCSEL J{sub th} of 8 kA/cm{sup 2}. The differential efficiency of the TJ VCSEL is also observed to be significantly higher than that of the ITO VCSEL, reaching a peak power of ∼550 μW, compared to ∼80 μW for the ITO VCSEL. Both VCSELs display filamentary lasing in the current aperture, which we believe to be predominantly a result of local variations in contact resistance, which may induce local variations in refractive index and free carrier absorption. Beyond the analyses of the lasing characteristics, we discuss the molecular-beam epitaxy (MBE) regrowth of the TJ, as well as its unexpected performance based on band-diagram simulations. Furthermore, we investigate the intrinsic advantages of using a TJ intracavity contact in a VCSEL using a 1D mode profile analysis to approximate the threshold modal gain and general loss contributions in the TJ and ITO VCSEL.

  19. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    Science.gov (United States)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-07-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses.

  20. Sign change in the tunnel magnetoresistance of Fe3O4/MgO/Co-Fe-B magnetic tunnel junctions depending on the annealing temperature and the interface treatment

    Directory of Open Access Journals (Sweden)

    L. Marnitz

    2015-04-01

    Full Text Available Magnetite (Fe3O4 is an eligible candidate for magnetic tunnel junctions (MTJs since it shows a high spin polarization at the Fermi level as well as a high Curie temperature of 585°C. In this study, Fe3O4/MgO/Co-Fe-B MTJs were manufactured. A sign change in the TMR is observed after annealing the MTJs at temperatures between 200°C and 280°C. Our findings suggest an Mg interdiffusion from the MgO barrier into the Fe3O4 as the reason for the change of the TMR. Additionally, different treatments of the magnetite interface (argon bombardment, annealing at 200°C in oxygen atmosphere during the preparation of the MTJs have been studied regarding their effect on the performance of the MTJs. A maximum TMR of up to -12% could be observed using both argon bombardment and annealing in oxygen atmosphere, despite exposing the magnetite surface to atmospheric conditions before the deposition of the MgO barrier.