Electrical Noise in a TES as a Resistively Shunted Conducting Junction

We present results of the analysis of electrical noise in a transition edge sensor (TES) as a resistively shunted conducting junction (the RSJ model). We derive an expression for the spectral density of voltage fluctuations taking into account weak superconductivity of a TES. We analyse and discuss differences in voltage noise in a TES compared to the familiar situation for the Josephson junction. The spectral density of voltage noise in the RSJ model has a unique analytical structure and cannot be reduced to the expression for the nonlinear Johnson noise near equilibrium.     

Resonant Tunnel Magnetoresistance in a Double Magnetic Tunnel Junction

We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FM^L/I/FM^W/I/FM^R, where the magnetization of the middle ferromagnetic metal layer FM^W can be aligned parallel or antiparallel with respect to the fixed magnetizations of the left FM^L and right FM^R 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 FM^W.     

Inherent Thermometry in a Hybrid Superconducting Tunnel Junction

We discuss inherent thermometry in a Superconductor-Normal metal-Superconductor tunnel junction. In this configuration, the energy selectivity of single-particle tunneling can provide a significant electron cooling, depending on the bias voltage. The usual approach for measuring the electron temperature consists in using an additional pair of superconducting tunnel junctions as probes. In this paper, we discuss our experiment performed on a different design with no such thermometer. The quasi-equilibrium in the central metallic island is discussed in terms of a kinetic equation including injection and relaxation terms. We determine the electron temperature by comparing the micro-cooler experimental current-voltage characteristic with isothermal theoretical predictions. The limits of validity of this approach, due to the junctions asymmetry, the Andreev reflection or the presence of sub-gap states are discussed.     

Cross-Whisker Intrinsic Josephson Junction as a Probe of Symmetry of the Superconducting Order Parameter

As a test of the superconducting order parameter, we have developed an intrinsic Josephson junction by the name of cross-whisker junction. This junction was made using two Bi₂Sr₂CaCu₂O_8+d single crystal whiskers. Two whiskers were connected at their c planes with various cross-angles. Angular dependence of the critical current densities shows d-wave-like fourfold-symmetry. However, the angular dependence is much stronger than that of the conventional d_x ^{2-y 2} wave. The Jc shows its smallest value around 45 deg, which suggests that the Josephson penetration depth becomes longer. We have successfully observed a Fraunhofer pattern in the cross-whisker junction with cross-angle 45 deg.     

新型磁性隧道结材料及其隧穿磁电阻效应

典型的磁性隧道结是“三明治”结构,即由上下两个铁磁电极以及中间厚度为1 nm量级的绝缘势垒层构成.当外加磁场使两铁磁电极的磁矩由平行态向反平行态翻转时,隧穿电阻会发生低电阻态向高电阻态的转变.自从1995年发现室温隧穿磁电阻(TMR)以来,非晶势垒的AlOx磁性隧道结在磁性随机存储器(MRAM)和磁硬盘磁读头(Read Head)中得到了广泛的应用,2007年室温下其磁电阻比值可达到80％.下一代高速、低功耗、高性能的自旋电子学器件的发展,迫切需要更高的室温TMR比值和新型的调制结构.2001年通过第一性原理计算发现:由于MgO(001)势垒对不同对称性的自旋极化电子具有自旋过滤(Spin Filter)效应,单晶外延的Fe(001)/MgO(001)/Fe(001)磁性隧道结的TMR比值可超过1000％,随后2004年在单晶或多晶的MgO磁性隧道结中获得室温约200％的TMR比值,2008年更是在赝自旋阀结构CoFeB/MgO/CoFeB磁性隧道结中获得高达604％的室温TMR比值.伴随着新势垒材料的不断发现和各种磁性隧道结结构的优化,共振隧穿和自旋依赖的库仑阻塞磁电阻等新效应以及磁性传感器、磁性随机存储器和自旋纳米振荡器及微波检测器等新器件逐渐成为科学和工业界所关注的研究与应用热点.对磁性隧道结(MTJ)材料及其器件应用研究和进展进行了简要介绍.     

Barkhausen Noise Measurement System Using a Three-Pole Probe

In the present study, a three-pole probe is proposed for measurement of Barkhausen noise (BN). A system was constructed for forming a magnetic field using the three-pole probe and succeeded in forming rotating magnetic fields of the same amplitude in all directions and arbitrary orientated stationary alternating magnetic fields. Furthermore, a BN measurement system was constructed and used to measure the BN of a grain-oriented electrical steel sheet. The results show that the BN exhibits a large output in the direction of the easy magnetization axis of the specimen, and it is demonstrated that the BN measurement result using the rotating magnetic field formed by the three-pole probe is reliable.     

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

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 detector is related to an asymmetry of the switching rates.      

Heating of Superconducting Tunnel Junction Detector by X-Ray Flux

Superconducting tunnel junction (STJ) detectors are in common use for high-resolution soft X-ray spectroscopy at high count rates. Each quasiparticle in superconductor should be treated as quantum superposition of electron-like and hole-like excitations. This duality nature of quasiparticle leads to multitunneling in STJ. Because of the multitunneling process, one quasiparticle can transfers into heat the energy that equals to the difference in quasiparticle energy between two electrodes more than once. As a result, the energy transferred into heat in STJ detector is several times grater the energy of X-ray quantum. In this work, the theory of branching cascade processes is applied to the process of energy transfer caused by quasiparticle multitunneling. The mean and the variance of STJ temperature shift from the substrate temperature caused by heating of STJ by X-rays flux were derived.     

Effects of Charging Energy on SINIS Tunnel Junction Thermometry

We have investigated theoretically the effects of the charging energy to the normal metal–insulator–superconductor (NIS) tunnel junction used as a thermometer. We demonstrate by numerical calculations how the charging effects modify NIS thermometry, and how the voltage-to-temperature response and the responsivity |dV/dT| of a current biased thermometer are affected. In addition, we show that the responsivity of the thermometer can be modulated with an additional gate electrode. The maximum responsivity is achieved when the Coulomb blockade is maximal, i.e. with a closed gate.     

Charge Transport in 2D DNA Tunnel Junction Diodes

Recently, deoxyribonucleic acid (DNA) is studied for electronics due to its intrinsic benefits such as its natural plenitude, biodegradability, biofunctionality, and low‐cost. However, its applications are limited to passive components because of inherent insulating properties. In this report, a metal–insulator–metal tunnel diode with Au/DNA/NiO_x junctions is presented. Through the self‐aligning process of DNA molecules, a 2D DNA nanosheet is synthesized and used as a tunneling barrier, and semitransparent conducting oxide (NiO_x) is applied as a top electrode for resolving metal penetration issues. This molecular device successfully operates as a nonresonant tunneling diode, and temperature‐variable current–voltage analysis proves that Fowler–Nordheim tunneling is a dominant conduction mechanism at the junctions. DNA‐based tunneling devices appear to be promising prototypes for nanoelectronics using biomolecules.     

On the Modeling of New Tunnel Junction Magnetoresistive Biosensors

A fully integrated biochip based on a 16 $times$ 16 scalable matrix structure of aluminum oxide magnetic tunnel junctions (MTJs) and thin-film diodes (TFDs of hydrogenated amorphous silicon) was fabricated and included as the biosensor of a portable handheld microsystem developed for biomolecular recognition detection using magnetic labels [deoxyribonucleic acid (DNA) hybridization, antibody antigen interaction, etc.]. The system uses magnetic field arraying of magnetically tagged biomolecules and can potentially be used to detect single or few biomolecules. Each biosensor matrix node is the series between a TFD (p-i-n or Schottky-barrier type) and an MTJ. In this paper, this matrix basic cell biosensor element is completely characterized and modeled. Experimental measured data are provided and compared with the proposed theoretical models results. It is shown that the diode may be used both as the matrix switching device and as an in-site temperature sensor and that the MTJ may act as the magnetoresistive sensor for detecting the fringe field of immobilized magnetic markers. Therefore, the fabricated fully integrated biochip included in the developed handheld microsystem may be used for biomolecular recognition.      

Superconducting Tunnel Junction Photon Detectors: Theory and Applications

Superconducting tunnel junctions (STJs) are being developed for photon and particle detection because they combine the high energy resolution of low temperature detector technologies with the high count rate capabilities of athermal devices. This makes them attractive sensors for applications in optical astronomy, synchrotron-based material science and biophysics, and plasma diagnostics. This review provides an overview about STJ design, operation and performance, and discusses some of the scientific applications that are currently driving STJ development.      

Controlling Chaos in the RF-Biased Josephson Junction with Thermal Noise

In this paper the control of chaos in the rf-biased Josephson junction circuit is studied. Numerical simulation indicates that the unstable periodic orbits (UPO) embedded in the chaotic attractor can be stabilized with the delayed feedback technique. Upon controlling, operation state of the chaotic Josephson junction circuit switches back to its conventional state. Namely, phase locking is reestablished and typical I-V curve recovers. Furthermore, we investigate the influence of thermal noise on the control and estimate the range of the environmental temperature for an effective control through numerical simulation.     

Thermopower Properties of Ferromagnetic/Insulator/Ferromagnetic Tunnel Junction

The thermal conductance, thermopower, and figure of merit in the ferromagnetic/insulator/ferromagnetic tunnel junction are investigated by using the nonequilibrium Green’s function technique. The magnetic regions are treated as band ferromagnetic and are described by using the single-band Hubbard model; the insulator region and the hybridization between neighboring regions are also described, respectively, by using a quantum microscopic model. It was found that the strength of the thermal conductance, the thermopower, and the figure of merit increased with the increase of the level of the left ferromagnet $\varepsilon _{k_\mathrm{L}}$ ε k L and the temperature $T.$ T . Finally, the calculated results of thermal properties are explained theoretically.     

高速公路隧道内交通噪声预测和降噪措施

结合公路隧道工程,利用波动声学和房间声学理论,研究公路隧道内噪声预测方法和降噪措施,给出预测模式、参数确定的方法和算例以及降噪措施的几种方案比较。     

MgO-Based Tunnel Junction Material for High-Speed Toggle Magnetic Random Access Memory

We report the first demonstration of a magnetoresistive random access memory (MRAM) circuit incorporating MgO-based magnetic tunnel junction (MTJ) material for higher performance. We compare our results to those of AlOx-based devices, and we discuss the MTJ process optimization and material changes that made the demonstration possible. We present data on key MTJ material attributes for different oxidation processes and free-layer alloys, including resistance distributions, bias dependence, free-layer magnetic properties, interlayer coupling, breakdown voltage, and thermal endurance. A tunneling magnetoresistance (TMR) greater than 230% was achieved with CoFeB free layers and greater than 85% with NiFe free layers. Although the TMR with NiFe is at the low end of our MgO comparison, even this MTJ material enables faster access times, since its TMR is almost double that of a similar structure with an AlO$_ x$barrier. Bit-to-bit resistance distributions are somewhat wider for MgO barriers, with sigma about 1.5% compared to about 0.9% for AlO$_ x$. The read access time of our 4 Mb toggle MRAM circuit was reduced from 21 ns with AlO$_ x$to a circuit-limited 17 ns with MgO.     

Fast and High Dynamic Range Imaging with Superconducting Tunnel Junction Detectors

We have demonstrated a combined test of the submillimeter-wave SIS photon detectors and GaAs-JFET cryogenic integrated circuits. A relatively large background photo-current can be read out by fast-reset integrating amplifiers. An integration time of 1 ms enables fast frame rate readout and large dynamic range imaging, with an expected dynamic range of 8,000 in 1 ms. Ultimate fast and high dynamic range performance of superconducting tunnel junction detectors (STJ) will be obtained when photon counting capabilities are employed. In the terahertz frequencies, when input photon rate of 100 MHz is measured, the photon bunching gives us enough timing resolution to be used as phase information of intensity fluctuation. Application of photon statistics will be a new tool in the terahertz frequency region. The design parameters of STJ terahertz photon counting detectors are discussed.