基于共振隧穿结构的压阻系数

以共振隧穿结构为压阻器件可以得到较高的灵敏度,但是当实验选择不同的工作偏压时,这种压阻效应表现得极其不同.由于高灵敏度是依靠较高的I-V曲线斜率获得的,因此最初人们希望选择具有较高峰谷比结构作为器件.但是有些区域的斜率过大,以至于压阻效应失去线性及稳定性而变得没有实用价值.另外,在某些工作区域由于共振隧穿结构本身具有的双稳态特性,而使其完全失去压阻特性.本文对这些问题进行了系统分析,并对一个具体的结构,分析其工作区域及特性,给出最高灵敏度可达700左右.     

Phonon structure in the tunneling characteristics of thin proximity effect sandwiches

The tunneling spectra of Al-oxide-N-S proximity effect junctions show phonon structure not only from the superconducting layerS, but also from the normal metal layerN. We report experimental results for junctios with Ag, Cu, and Al normal metal layers (100–400 Å thick) and Pb or Sn superconducting layers (3000 Å thick). We compare these experimental results with the McMillan geometrical resonance model of the proximity effect and with an extended McMillan tunneling model. The extension includes the effect of the frequency-dependent electron-phonon interaction in the normal metal. Finally, we estimate the electron-phonon coupling constant for the normal metals from the size of their phonon structure in the tunneling spectra.Research supported by National Science Foundation under Grant #NSF DMR 73-7518 A01.Research supported by National Science Foundation under Grant #NSF DMR 75-19544.Research supported by National Science Foundation under Grant #GH 37239.     

New type of oscillations in bistable resonant tunneling diodes

It is shown that that the coupling of resonant tunneling diodes with an external electrical circuit containing an oscillatory loop can lead to the excitation of spatiotemporal oscillations. Pis’ma Zh. Tekh. Fiz. 25, 64–68 (May 26, 1999)     

自对准栅型谐振隧穿晶体管试制

针对谐振隧穿二极管(RTD)在通用电路应用中的局限性,提出并设计了自对准栅型谐振隧穿晶体管结构,进行了材料的分子束外延,采用传统湿法腐蚀、金属剥离、台面隔离和空气桥互连工艺,初步研制出具有较明显栅控能力的谐振隧穿晶体管(RTT)单管,其峰值电流密度高达80.8 kA/cm2,峰谷电流比为3.6,负阻阻值在20Ω左右.研究还发现,器件的峰值电流随栅压增大而减小,谷值电流随栅压增大而增大,而且出现零点分离.这些现象与栅的纵向位置控制不当有关,可以通过减小栅间发射极宽度,缩短栅与势垒层距离,和减小发射层掺杂浓度得到改善.     

Magnetic field enhanced resonant tunneling in a silicon nanowire single-electron-transistor

We report fabrication, measurement and simulation of silicon single-electron-transistors made on silicon-on-insulator wafers. At T-2 K, these devices showed clear Coulomb blockade structures. An external perpendicular magnetic field was found to enhance the resonant tunneling peak and was used to predict the presence of two laterally coupled quantum dots in the narrow constriction between the source-drain electrodes. The proposed model and measured experimental data were consistently explained using numerical simulations.     

肖特基栅型共振隧穿三极管器件模型的研究

基于共振隧穿二极管(RTD)的电流-电压方程,结合对肖特基栅型共振隧穿三极管(SGRTT)物理机制的分析和计算,推导出了SGRTT器件的器件模型。根据实际器件的材料结构、版图参数等指标计算得到的SGRTT器件模型,能很好地与实际器件的特性相吻合。利用PSPICE软件,该模型可准确快捷地实现电路功能验证和仿真,此项研究的结果为共振隧穿器件的电路集成和研制奠定了基础。     

SQUIDs on the Base of Strained YBCO Films

Strained films of YBCO in which stresses caused by mismatching of film and substrate lattices and thermal expansion coefficients are frozen by quenching are grown on substrates LAO (1 0 0) by laser ablation method. Critical current in these films is suppressed about 2–3 orders of magnitude. The strained films have unusual temperature dependences with the minimum at the temperature range of 55–57~K. In spite of granular films with the same critical current the strained films are stable to thermocycles. DC-SQUIDs are manufactured on the base of the strained films with the sensitivity by flux up to 4.5 mk ₀/ Hz.     

极化效应对AlN/GaN共振隧穿二极管电流特性的影响

本文采用半经验紧束缚能带理论,通过自洽计算薛定谔方程和泊松方程研究了AlN/GaN共振隧穿二极管中极化效应对电流的影响.结果发现,极化效应导致电流曲线发生不对称性,并影响电流的共振电压位置,这与实验报道的结果相一致.并且随着极化电荷的增加,在一定的偏压条件下,只能观测到一个子能级隧穿或者根本没有负微分电阻现象发生.     

The influence of the combination of coherent and sequential tunneling on the tunneling magnetoresistance in a ferromagnet-metal-insulator-ferromagnet tunneling junction

We apply the spin-polarized free-electron model to theoretically study the tunneling magnetoresistance (TMR) in a ferromagnet-metal-insulator-ferromagnet tunneling junction. In the presence of the metallic layer, the tunneling of electrons for current flow through the junction can be divided into two components: the coherent tunneling and the sequential tunneling components. Our calculations show that the attenuated TMR oscillation is well fitted by a damped oscillation function with an exponential decay if only the coherent tunneling is considered. But, if the sequential tunneling is included in the calculations, the behavior of the attenuated TMR oscillation slightly deviates from the damped oscillation function.     

Superconducting tunneling without the tunneling Hamiltonian. II. Subgap harmonic structure

The theory of superconducting tunneling without the tunneling Hamiltonian is extended to treat superconductor/insulator/superconductor junctions in which the transmission coefficient of the insulating barrier approaches unity. The solution for the current in such junctions is obtained by solving the problem of a particle hopping in a one-dimensional lattice of sites, with forward and reverse transfer integrals that depend on the site. The results are applied to the problem of subgap harmonic structure in superconducting tunneling. The time-dependent current at finite voltage through a junction exhibiting subgap structure is found to have terms that oscillate at all integer multiples of the Josephson frequency,n(2eV/). The amplitudes of these new, and as yet unmeasured, ac current contributions as a function of voltage are predicted.     

The effect of photon flux on the properties of a Ni-Cu foil

Experimental data on the irradiation-induced long-range effects in rolled Ni-Cu foils are presented. Dose-dependent variations in the microhardness and composition of the surface layers were observed on both exposed and unexposed sides of the samples. Based on the observed microhardness and composition variations in depth of the samples and the results of X-ray diffraction measurements, a hypothesis concerning the role of the initial nonequilibrium state of a material in the photoinduced long-range effect is put forward.     

量子隧道效应压敏复合材料

为探讨镍粉-水泥基复合材料的压敏性及其产生机理,首先验证了采用埋入式环状四电极进行镍粉-水泥基复合材料电阻测试的可行性,然后探讨了镍粉-水泥基复合材料的伏安特性,最后研究了一次加载至破坏时和弹性加载阶段镍粉-水泥基复合材料的电阻率变化规律.研究结果表明:基于埋入式环状电极的四电极法适用于镍粉-水泥基复合材料压敏性的测试;在测试电流＜10mA时,镍粉-水泥基复合材料的伏-安特性为线性,隧道导电具有欧姆特性;镍粉-水泥基复合材料一次加载至破坏,电阻率变化率最大达70%,弹性阶段电阻率变化率可达60%以上,量子隧道效应是致使其具有优异压敏性能的原因.     

Temperature dependence of the characteristics of the resonant magnetoelectric effect in a lead magnesium niobate-lead titanate/nickel structure

We have studied the temperature dependence of the characteristics of the resonant magnetoelectric (ME) interaction in the planar composite structure comprising a ferroelectric layer of lead magnesium niobate-lead titanate and a layer of nickel. It is established that an increase in the temperature in a 220?C340 K interval is accompanied by a decrease in the resonance frequency and in the efficiency of the interaction. The results can be used in developing methods for thermal stabilization of ME devices.     

The effect of seawater on fracture mode transition in fatigue

The fracture mode transition for two steels fatigued in air and seawater was investigated by measuring the crack growth rates and by examining the fractured surfaces using scanning electron microscopy. It was found that the transition from normal to shear fracture mode did not always occur in seawater under the same fatigue conditions as in air. Three possible mechanisms, based on the effective stress intensity factor range, the threshold stress intensity factor range and environmentally assisted brittle fracture, are proposed to account for this behaviour and their validity is discussed.     

Discontinuous conduction mode analysis of phase-modulated series resonant converter

This paper proposes an analytical approach to derive voltage gain for phase-modulated dc–dc series resonant converter (SRC) operating in discontinuous conduction mode (DCM). The conventional fundamental harmonic approximation technique is extended for a non-ideal series resonant tank to clarify the limitations of SRC operating in continuous conduction mode (CCM). The DCM analysis is described in a normalized form defining appropriate base quantities. The converter is analysed both in time and frequency domain to derive a non-linear algebraic function of diode rectifier extinction angle. The root of this function is numerically determined using MATLAB and used to predict the dc bus voltage. Analytical derivation of critical load resistance is discussed, which indicates the CCM–DCM boundary condition. Experimental results are presented to validate the analysis.     

The effect of surfaces on the tunneling density of states of an anisotropically paired superconductor

We present calculations of the tunneling density of states in an anisotropically paired superconductor for two different sample geometries: a semi-infinite system with a single specular wall, and a slab of finite thickness and infinite lateral extent. In both cases we are interested in the effects of surface pair breaking on the tunneling spectrum. We take the stable bulk phase to be of d_x ²–y² symmetry. Our calculations are performed within two different band structure environments: an isotropic cylindrical Fermi surface with a bulk order parameter of the form k _x ² –k _y ² , and a nontrivial tight-binding Fermi surface with the order parameter structure coming from an antiferromagnetic spin-fluctuation model. In each case we find additional structures in the energy spectrum coming from the surface layer. These structures are sensitive to the orientation of the surface with respect to the crystal lattice, and have their origins in the detailed form of the momentum and spatial dependence of the order parameter. By means of tunneling spectroscopy, one can obtain information on both the anisotropy of the energy gap, ¦(p)¦, as well as on the phase of the order parameter, (p) = ¦(p)¦ e^i(p).     

Physics and applications of Si/SiGe/Si resonant interband tunneling diodes

Room temperature (RT) current–voltage characteristics of Si/Si_1−xGe_x/Si p⁺-i-n⁺ interband tunneling diodes are presented. The variation of the structural properties results in a more detailed picture of the tunneling process in these diodes, which allows further improvement of the relevant parameter. Special attention is paid to the peak current density (PCD) and the peak-to-valley current ratio (PVCR) of the devices. For an optimized structure with a 3-nm thick Si_0.54Ge_0.46 layer in the intrinsic zone a record PVCR of 6.0 at a PCD of approximately 1.5 kA/cm² was achieved. By reducing the layer thickness to 2.6 nm and simultaneously increasing the Ge content to 54%, the PCD increases to 30 kA/cm² at a high PVCR of 4.8.     

Sources and implications of resonant mode splitting in silicon nanowire devices

This work investigates the effects of asymmetric cross-sectional geometry on the resonant response of silicon nanowires. The work demonstrates that dimensional variances of less than 2% qualitatively alter a nanosystem's near-resonant response, yielding a non-Lorentzian frequency response structure, which is a direct consequence of resonant mode splitting. Experimental results show that this effect is independent of device boundary conditions, and can be easily modeled using continuous beam theory. Proper understanding of this phenomenon is believed to be essential in the characterization of the dynamic response of resonant nanowire systems, and thus the predictive design of such devices.