DC SQUID RF amplifiers

The noise and signal parameters of several types of RF amplifiers based on different SQUIDs with integrated and hybrid input coils were studied. A new type of multiloop DC SQUID with an integrated input coil and extremely low stray capacitances was designed. The inductance of a four-loop SQUID was 100 pH, the input coil inductance 1.3 nH, and mutual inductance 300 pH. The tuned integrated four-loop amplifier at 420 MHz had a noise temperature lower 0.5 K and a power gain of nearly 20 dB in a 60-MHz bandwidth. For the noise calibration of such amplifiers, SIS junctions were used as a shot noise source, or a cooled attenuator and a room temperature semiconductor noise source were used     

Broadband nuclear magnetic resonance using DC SQUID amplifiers

We have constructed two pulsed NMR spectrometers in which the signal is coupled to the input coil of a low T_c DC SQUID using a superconducting flux transformer, yielding broadband response, with bandwidth determined by the SQUID electronics. A 50 kHz bandwidth commercial system has been used to observe free induction decay signals from platinum powder, bulk platinum, ³He gas and surface monolayers of ³He in the temperature range from 1.4 to 4.2 K and at frequencies from 5 to 40 kHz. The observed signal-to-noise ratio is as calculated with the noise dominated by flux noise in the SQUID in all samples but the bulk metal. A second system, which operates in flux-locked loop mode with bandwidth of 3.4 MHz using a SQUID with additional positive feedback, has been used to observe NMR signals from platinum powder at frequencies from 38 to 513 kHz and at a temperature of 4.2 K. The advantage of this technique in the study of systems with short T₂ at frequencies below 1 MHz is discussed. In addition we discuss the benefits of both broadband and tuned input circuits for NMR detection and we describe the performance of a spectrometer with a tuned input circuit which has been used to obtain signals at 1 MHz from platinum powder at 4.2 K and from ∼2 layers of ³He absorbed on a surface area of 0.11 m² at 1.7 K. The amplifier noise temperature is predicted to be 60 mK in the ³He experiment. This demonstrates the potential of the tuned set-up for measurements at low millikelvin temperatures on systems with low spin density and with T₂ greater than several hundred microseconds.     

Temperature dependence performances of fully integrated DC SQUID magnetometers

Temperature dependence of the main characteristics of integrated dc superconducting quantum interference device magnetometers based on niobium technology including an additional positive feedback circuit is reported. Temperatures above 4.2 K have been considered. A nonlinear temperature dependence of the spectral density of the field noise has been observed. The reported measurements show a slow increasing of the field noise up to temperatures of about 5 K, giving a considerable tolerance of the working temperature of niobium magnetometers in some innovative multichannel systems for magnetoencephalography.     

Modelling of the coupling structure of a HTS DC SQUID amplifier

In order to estimate self- and mutual inductances of the input coil and the pick-up loop of a YBCO SQUID amplifier operating at 77 K, a simple method based on the determination of the current and flux distributions into the superconductors is presented. The cases of inductors (single loop and spiral) and induced circuits (closed and open loop) are considered. The authors stress the difference between a SQUID pick-up loop and a directly coupled magnetometer depending upon their action on the input inductance. Finally, the coupling efficiency and the ground plane effect are calculated and measured for various patterns     

Quantum flux parametron (QFP) shift registers clocked by aninductive power distribution network and errorless operation of the QFP

The authors present 4- and 12-b shift registers capable of operating from DC up to 8.56 and 4.24 GHz, respectively. These circuits' total on-chip power dissipation is estimated to be roughly 10 nW. A novel clock current distribution network permits such high clock frequency and such low on-chip power dissipation. The clock is applied as a standing wave and is distributed by inductive division. With this clock current distribution scheme, no power is dissipated along the clock lines. In spite of the circuits' low output amplitude (tens of microvolts) and of the large crosstalk with the clock frequency, the output waveforms are captured in time domain at microwave frequencies. Also, for the 12-b device, 10¹⁵ error free operations per quantum flux parametron (QFP) are demonstrated. Finally, the 12-b shift register is the largest QFP circuit reported to date; it is composed of 48 QFPs and one DC SQUID     

DC SQUID series arrays with intracoil damping to reduce resonance distortions

We report on low-noise DC SQUID series arrays incorporating intracoil damping, which show smooth DC characteristics. The voltage-flux characteristics of these devices are reproducible upon repeated cooling and do not require multiple heating/cooling cycles to maximize peak-to-peak output voltage modulation depth. The devices consist of 100 DC SQUIDs with individual signal and feedback coils connected in series. The total input inductance is 600 nH, and the peak-to-peak output modulation is 4 mV with a transfer function of 350 V/A. The bandwidth is 5 MHz and the equivalent input current noise is approximately 2.5 pA/√$\text{Hz}$. With these characteristics, these devices are useful as preamplifiers for microcalorimeter X-ray detectors.     

DC SQUID series array amplifiers with 120 MHz bandwidth (corrected)

We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L_sq=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 Ω per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 pm center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA/√Hz equivalent input current noise at 4 K, and 120 MHz bandwidth     

Fundamental limit to the performance of fibre-optic metallic glass DC magnetometers

Thermal strains and eddy currents impose a fundamental limit to the minimum detectable field capability of metallic glass based fibre-optic DC magnetometers. A room-temperature magnetometer operating with a resonance Q of 100 exhibits a theoretical minimum detectable field of ~3×10?11 Oe in the DC to 1 Hz bandwidth.     

Optimization of input impedance and mechanism of noise suppressionin a DC SQUID RF amplifier

The optimal input impedance and noise of a DC SQUID RF amplifier at frequencies of the order of 1 GHz with a resonant input matching circuit have been studied analytically, numerically, and experimentally. A model for noise temperature and power gain has been developed for the practical resonant input tank circuit. A new effect of the output noise increasing or decreasing with changing the sign of voltage-to-flux transfer coefficient has been observed experimentally and explained analytically. The different values of noise temperature for the opposite dV/dΦ values have been interpreted using a model with partially correlated current and voltage noise sources. The equivalent layout for optimal input matching of a SQUID amplifier comprising series and parallel resonant circuits has been presented. Using such a matching circuit and SIS junction as a signal source the SQUID amplifier noise temperature about 1 K has been measured at 1.1 GHz     

QFP焊点可靠性研究

随着人们对健康和环境的要求越来越高,无铅焊料的研究倍受封装业的重视。塑性应变是影响电子封装焊点可靠性的主要因素,文章采用在多次温度循环条件下进行有限元数值模拟的方法,针对由不同元素(Sn,Pb,Ag,Cu)及配比构成的焊料,计算QFP焊点的塑性应变,定量评估其可靠性。给出焊料各参数对焊点可靠性的影响程度,仿真表明焊料激活能与气体常数的比值的变化对焊点可靠性影响最大,相应的焊点Y向塑性应变均值仅为优化前的11%。所得的结果可为今后QFP封装时的焊料选择提供新的理论依据。     

航天产品新型QFP器件高可靠性返修

QFP器件在电子产品中使用非常广泛,首先对QFP器件进行了简介。在分析QFP器件特点的基础上,针对底部有大面积接地的新型QFP器件和航天产品高可靠性要求的特点,提出了此类QFP器件的返修工艺难点;列举出了两种返修方案,并根据实际情况加以分析和比较从而选择其中更为合适的一种方案,然后通过实验确定返修过程中所需的温度曲线,提高了返修的可靠性,嚣后详细说明了利用3592返修工作站对底部大面积接地的QFP器件返修过程。     

Modelling DC characteristics of HEMTs

A simple empirical equation is presented to relate the drain current to drain-source and gate-source voltages of the high electron mobility transistors (HEMTs). This equation covers the entire ID/VDS characteristics. The accuracy of this equation is better than the theoretically developed separate equations.     

粘片工艺对QFP封装可靠性的影响

集成电路封装行业的快速发展对粘片后产品的质量与可靠性提出了更高的要求,粘片工艺对集成电路可靠性有着至关重要的影响。采用单一控制变量法,研究硅微粉含量对QFP(Quad Flat Package)封装可靠性的影响;利用正交试验工具,探究在粘片工艺中,不同的胶层厚度和胶层面积对QFP封装后可靠性的影响。研究发现,添加适量的硅微粉有助于提高环氧模塑料对QFP封装后的可靠性;粘片工艺中,当胶层厚度为30μm、胶层面积大于或等于芯片面积时,QFP封装后的可靠性最好。     

密脚间距QFP集成电路引线成形工艺研究

集成电路引线成形原本是集成电路封装的后道工序,成形质量将直接影响电子装联产品的可靠性,其关键工艺点在于成形的肩宽、站高、焊接长度和共面度等关键工艺参数的选择以及成形工艺装备的合理配置与优化.论述了目前表面贴装密脚间距QFP封装器件在应用中遇到的引线成形问题,介绍了该类器件成形中的相关技术要求及目前国内外器件成形的现状,提出了引线手工成形的解决方案.     

Fitting transducer characteristics to measured data

There are no rules to select the best curve-fitting method for a given set of data. This problem is of great importance in measurement applications. Optimizing analog and digital methods for a transducer's characteristic interpolation or linearization is a field where constant research is being done, particularly since auto-calibration and self-test of intelligent transducers is a topic of major interest. We present an overview of classical methods for data interpolation and least mean squares regression. We make a comparative evaluation of the relative performance of polynomial and artificial neural networks approximations to measurement data with particular attention paid to the reduction of the required calibration set dimension to obtain a given accuracy     

Paramagnetic-center detection by SQUID measurement of static magnetic susceptibility

A method is proposed for counting small numbers of impurity paramagnetic centers in semiconductor specimens. It involves SQUID measurement of static magnetic susceptibility under resonant microwave saturation of the magnetic sublevels. The ultimate sensitivity of the method is calculated and compared with those of other approaches.     

电波传播研究70年

对流层电波传播特性是影响无线电系统性能的重要因素,是电波传播研究的主要领域. 本文系统综述了近60年来中国电波传播研究所在无线电气象、地面无线电业务电波传播、空间无线电业务电波传播、电波传播效应对无线电系统影响评估等对流层电波传播不同方向开展的研究和取得的研究进展. 在此基础上,最后给出了对对流层电波传播研究的展望.     

遮光法测量铝薄板高压加载下的动态特征量

为了检测强脉冲激光冲击加载材料发生的动态变化,采用遮光原理设计了一种新的检测仪器,能较为准确地检测出在冲击过程中试样的动态特征量。结果表明,铝薄板（L2）在激光冲击成形过程中弹性变形和塑性变形同时存在,塑性变形的时间远远大于弹性变形。试样中心区域在弹性变形阶段的平均变形速率为3.2103m/s,试样的平均应变率为8.9 104s-1。该结果为相关激光冲击成形技术发展提供了实验依据。     

Calculation of transfer characteristics from measured harmonic levels

Much has been published on the evaluation of harmonics and intermodulation products generated in nonlinear devices. The inverse problem, i.e. the derivation of the nonlinear characteristic from measured harmonic levels, is sometimes of interest, although it has been only sketchily treated in the literature. The present note supplies the fundamental formulas required for this problem.     

锥形光子晶体光纤的基模特性分析

本文研究了锥形光子晶体光纤(TPCF)的基模演化特性,分析了包层空气填充率对其特性的影响.数值计算结果表明TPCF比常规锥形光纤更能束缚模场;在相同的拉锥条件下,包层空气填充率越大的TPCF,其模场能保持芯模的形式传输更长的距离并且其芯区能量密度也越大.而TPCF的有效面积沿锥体纵向先缓慢减小,后急剧增大,最后又减小,随着空气填充率的增大,有效面积的最大值逐渐向锥尾方向移动.同时,对色散研究表明,在整个锥体中,色散值先负向增大,后正向增大;在空气填充率较小时,其色散曲线沿锥体纵向变化平缓,而空气填充率较大时,色散曲线起伏明显;并且随着空气填充率的减小,色散曲线的最低点移向初始拉锥端.