Tunneling spectroscopy of high-Tc superconductors

We have performed tunneling spectroscopy experiments on different kinds of high-temperature superconductors (HTS) and different types of junctions. Firstly, spectra were taken on surfaces of YBa₂Cu₃O_7-δ (YBCO) thin films and Nd_1.85Ce_0.15CuO_4-y (NCCO) single crystals by low-temperature scanning tunneling microscopy/spectroscopy (LTSTM/S) in a superconductor-insulator-normal metal (SIN) configuration. Second, the tunneling spectra of grain-boundary junctions (GBJs) fabricated on bicrystal substrates were measured for the materials YBCO, La_1.85Sr_0.15CuO_4-δ (LSCO), Bi₂Sr₂CaCu₂O_8+δ (BSCCO) and NCCO in a SIS configuration. The characteristics of the spectra in both systems could be related to the symmetry of the order parameter in the superconducting electrode(s). In particular, a zero bias conductance peak (ZBCP) was observed only in systems with a d-wave symmetry, but was completely absent in the s-wave system NCCO.     

Thermoelectric power sensor for microwave applications bycommercial CMOS fabrication

This work describes an implementation of a thermoelectric microwave power sensor fabricated through commercial CMOS process with additional maskless etching. The sensor combines micromachined coplanar waveguide and contact pads, a microwave termination which dissipates heat proportionally to input microwave power, and many aluminum-polysilicon thermocouples. The device was designed and fabricated in standard CMOS technology, including the appropriate superimposed dielectric openings for post-fabrication micromachining. By removing the bulk silicon located beneath the device through micromachining, thermal and electromagnetic losses are minimized. The sensor measures signal true RMS power in the frequency range up to 20 GHz with input power in the -30 dBm to +10 dBm range. Over this 40 dB dynamic range, output voltage versus input power is linear within less than ±0.16%. Automatic network analyzer data show an acceptable input return loss of less than -30 dB over the entire frequency range     

A new approach for the growth of high-Tc superconductors

In this paper we describe a modified liquid phase separation (double crucible) method for growth of superconducting Bi-Sr-Ca-Cu-O single crystals. We used alumina crucibles. The morphology and composition of as-grown crystals were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The stacking thin-plate single crystals of maximum 5 × 6 × 0.1 mm³ were obtained.     

On the use of high-Tc superconductors for Perot-Fabry mirrors coatings

In a very rough experiment using two MgO plates, coated with a 200 Å thick YBaCuO film to increase their reflectivity, and facing each other their YBaCuO films to make a Perot-Fabry (PF) interferometer, we have observed a 43% maximum transmission and a finesse around 33 at v=29 cm^?1, in good accordance with a new phenomenological model for YBaCuO. Much higher performances can be expected by optimizing the YBaCuO film thickness.     

Simple method for investigating electromagnetic properties of high-Tc superconductors at two-millimeter wavelengths

A method for investigating the electromagnetic properties of high-T_c superconductors (HTS) in a 2-mm wavelength band has been proposed. The method is based on the use of a cylindrical tube open dielectric resonator (ODR) loaded with a HTS sample. The Josephson harmonic generation at microwave frequencies can be investigated by means of the method. A small cross section of the ODR makes it possible to investigate surface variations of HTS sample electromagnetic properties and their temperature dependencies.     

On the far IR transmission spectra of high-Tc superconductors

After several years, the Far IR (FIR) results from several laboratories seem to converge. The very FIR transmission data at different temperatures in the normal phase, combined with dc resistivity measurements, lead to a constant plasma frequency in that phase, and a linear variation of collision frequency v_c versus temperature T. Approximately the same plasma frequency can be used to explain the FIR transmission spectra at 7 K from 20 to 200 cm^?1. These remarks obtained from purely FIR data are in good accordance with the recent conclusions of Fiory et al obtained by a quite different method, i.e. electrostatic measurements.     

Shorted two-dimensional high-Tc Josephson arrays for oscillator applications

We present results of our experimental investigations of the dynamic properties of two types of shorted two-dimensional (2D) arrays. The first type consisted of 4×4 YBCO step edge junctions integrated into a circuit, which allowed the simultaneous detection of all single row voltages. Thus, using only dc-measurements, the interaction and synchronization between the rows could be observed. In the second investigated array type the edge junctions of the rows were closed into superconducting loops in the form of coplanar resonators. Resonant steps were observed on the current–voltage characteristic due to interaction of the junctions with the resonators. The circuits were integrated into a stripline geometry and coupled to another (detector) Josephson junction. A clear detector response, i.e. Shapiro steps, was measured up to 460 GHz. Steps up to 4th harmonic were observed in the frequency range 150–200 GHz.     

On-line computer applications in the electric power industry

In two areas of major importance to the electric power industry-interconnected system operation and steam-electric energy conversion--on-line computer use has expanded during the past five years to applications of increasing complexity and importance. In systems operation, direct digital control is now in successful operation, and many aspects of system security are now monitored by centralized computers. In generating plants on-line computer use has progressed beyond simple data logging; it currently includes some closed-loop control applications, and will be applied to complete boiler control with assemblies now being installed. Simulation and analysis have played an important role in these advances in the application of on-line digital computers.     

Class E switching-mode power amplifier for high-frequency electric process heating applications

The letter is concerned with the application of a class E convertor to electric process heating. A simple efficient convertor is described which is suitable for high-frequency electric process heating loads.     

Application of chemical effects in X-ray spectra for characterization of the high-Tc superconductors

Chemical effects in X-ray spectra (energy shifts, emission probability changes, satellite formation and peak profile changes) may be used for characterization of the chemical circumstances and chemical bonding of the monitored element in the sample. For that purpose, an investigation of the chemical effects in ion induced X-ray spectra of the high-T_c superconductor materials Sr₂Ln_yCe_0.5TaCu₂O_10+δ (Ln=Eu,Sm) was carried out using a high resolution crystal X-ray spectrometer. The applicability of the chemical effects for the mapping of the crystal phases in the superconductor sample using an ion microbeam is discussed.     

Antenna applications of superconductors

The applicability of superconductors to antennas is examined. Potential implementations that are examined are superdirective arrays; electrically small antennas; tuning and matching of these two; high-gain millimeter-wavelength arrays; and kinetic inductance slow wave structures for array phasers and travelling wave array feeds. It is thought that superdirective arrays and small antennas will not benefit directly, but their tuning/matching networks will undergo major improvements. Miniaturization of antennas will not be aided, but much higher gain millimeter-wave arrays will be realizable. Kinetic inductance slow-wave lines appear advantageous for improved array phasers and time delay, as well as for traveling-wave array feeds     

Role of silver addition on mechanical and superconducting properties of high-Tc superconductors

The effect of silver additions on the mechanical and superconducting properties of sintered bulk YBa₂Cu₃O_δ (YBCO), Bi₂Sr_1.7CaCu₂O_δ (BSCCO-2212), and Bi_1.8Pb_0.4Sr_2.2Ca₂Cu₃O_δ (BSCCO-2223) has been evaluated. Strength and fracture toughness of YBCO and BSCCO bars increased with increasing Ag content up to 30 vol.% Ag. Addition of 30 vol. % Ag to YBCO increased strength from 87 to 136 MPa and fracture toughness from 1.82 to 3.9 MPa√m. Addition of 30 vol.% Ag to 2212 and 2223 increased strength from 58 to 107 and 41 to 90 MPa, respectively. Corresponding increases in fracture toughness were from 1.89 to 2.79 and 1.09 to 1.94 MPa√m, respectively. These improvements in strength and fracture toughness are believed to be due to the presence of Ag particles that may induce compressive stresses in the superconducting matrix and resist crack propagation by pinning the propagating cracks. The values of strength and fracture toughness of BSCCO-30 vol.% Ag specimens are comparable to those of monolithic BSCCO obtained by sinter forging, hot pressing, and hot isostatic pressing. On the other hand, the hardness of YBCO and BSCCO decreased with increasing Ag contents because of the lower hardness of Ag. Addition of Ag showed no adverse effects on superconducting properties (J_c and T_c) of YBCO or BSCCO superconductors.     

Dependence of critical current density on microstructure and processing of high-Tc superconductors

Microstructural origins for reduced weak-link behavior in high-J_c melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT) wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest J_c, polycrystalline, high-T_c superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223 thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of “colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223 films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization of high-J_c PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the four types of superconductors studied, reduced weak-link behavior can be ascribed to some degree of biaxial alignment between grains, either on a “local” or a “global” scale.     

POTP在电力通信网中的应用和演进

随着十二五国家智能电网的发展,未来电力通信业务将全面向IP化和高带宽转型,加上电力通信系统现有各种传统业务,对光通信网络统一承载所有业务提出了新要求。针对当前电力系统通信业务的现状和存在的问题,提出了在电力系统中采用POTP综合传送平台组网的可行性和必要性,并介绍了POTP技术在电力通信网的应用方案建议。     

Recent issues in fabrication of Ag-clad BSCCO superconductors

Long lengths of mono-and multifilament Ag-clad BSCCO superconductors were fabricated by the powder-in-tube technique. Critical current density (J_c) up to 12,000 A/cm² has been achieved in an 850 m long multicore conductor. Long length conductors were formed into pancake-shaped coils by the wind-and-react approach. Test magnets were then fabricated by stacking the pancake coils and connecting them in series. The magnets were characterized as a function of applied magnetic field at various temperatures. A test magnet, fabricated with ≈770 m of BSCCO tape, generated fields of ≈1 T at 4.2K and ≈ 0.6 T at 27K, both in an applied background field of 20 T. Additionally, the strain tolerance of both mono-and multifilament conductors at 77K in 0.5 T applied field has been studied. We observed that multifilament conductors have better strain tolerance than monofilament tapes, retaining more than 90% of the initial critical current (at 0.5 T) with strain ≥1%.     

功率VDMOS器件设计及研制

分析了VDMOS器件击穿电压、导通电阻、阈值电压和开关特性等主要性能指标的影响因素,并借助半导体模拟仿真软件Sentaurus对VDMOS器件进行建模,调整器件各个结构参数,提出采用P体区间厚氧化层方法提高器件的动态特性,获得满足设计目标要求的器件电性能参数,最终形成器件设计版图,并依此在现有生产线上进行工艺流片,根据流片结果进一步优化调整设计参数,最终获得一款击穿电压400 V、导通电阻0.45?、阈值电压2.5 V、开关特性较好的功率VDMOS器件。     

CMOS工艺兼容多晶硅压力敏感膜的设计与加工

在MEMS表面加工工艺中，多晶硅薄膜是微结构的重要组成部分。本文考虑加工工艺中残余应力的影响和多晶硅材料的强度范围，建立多晶硅膜的大变形模型，设计可用于压力传感器应用的多晶硅薄膜几何尺寸。采用有限元方法对多晶硅薄膜进行力学分析和设计验证，提出了CMOS工艺兼容的多晶硅压力敏感膜的加工方法，并且根据所设计的工艺进行了电容式压力传感器微结构的加工，加工结果说明了多晶硅薄膜设计的合理性和CMOS兼容工艺的可行性。     

Simulation and fabrication of submicron channel length DMOStransistors for analog applications

The use of an asymmetric MOS structure for superior analog circuit performance is considered. Results from the fabrication of 1-μm-gate length DMOS transistors show increases of up to 1.9 in transconductance, 10 in output resistance, and 8 in intrinsic gain when compared to NMOS structures of similar gate length and threshold voltage. Substrate current is also reduced by up to a factor of 10. This represents the first reported results of submicron channel length DMOS transistors. The standard 7° implantation angle has significant impact on DMOS fabrication and is shown to produce a usable asymmetric DMOS from an otherwise symmetric DMOS. An optimal implant energy and diffusion time are shown to exist for DMOS enhancement region formation. Two-dimensional process and device simulators have proved necessary to develop the DMOS process, as well as to qualitatively explain body effect reduction and threshold voltage determination. The DMOS process has successfully yielded experimental circuits including a single ended operational amplifier of folded cascode technology and a 101-state ring oscillator     

CMOS工艺兼容多晶硅压力敏感膜的设计与加工

在MEMS表面加工工艺中 ,多晶硅薄膜是微结构的重要组成部分。本文考虑加工工艺中残余应力的影响和多晶硅材料的强度范围 ,建立多晶硅膜的大变形模型 ,设计可用于压力传感器应用的多晶硅薄膜几何尺寸。采用有限元方法对多晶硅薄膜进行力学分析和设计验证 ,提出了CMOS工艺兼容的多晶硅压力敏感膜的加工方法 ,并且根据所设计的工艺进行了电容式压力传感器微结构的加工 ,加工结果说明了多晶硅薄膜设计的合理性和CMOS兼容工艺的可行性