500GHz超导SIS混频器的设计

超导SIS(Superconductor-Insulator-Superconductor)混频技术是新兴的低噪声检测技术,其卓越的低噪声性能使其成为太赫兹波段理想的接收技术之一.如何提高太赫兹波和SIS超导结之间的信号耦合是设计超导SIS混频器的一个关键问题.本文依据准光耦合技术,研究了两种改善两者间信号的耦合方法:一是设计工作于500GHz波段的对数周期天线,二是设计微带阻抗变换器以实现对数周期天线和SIS超导结之间的阻抗匹配.     

超导SIS结偏置源电路的设计

针对超导SIS隧道结器件的传输特性,设计和制备了为超导SIS器件提供直流偏置的电路,该偏置源电路采用恒压源与恒流源合二为一的技术,恒压源采用了电压深度负反馈设计,恒流源采用了电流反馈法。并用MULTISIM10对电路进行仿真和参数验证。利用该偏置源对SIS结进行供电实测,取得了良好效果。实现了高稳定度、高精度、低噪声的电路设计。     

量子态统计测量电路探讨

本文讨论了超导隧道结(SIS)从零电压态跃迁到正常态过程的量子特征.对SIS结的临界电流的统计分布测量的可行性作了探讨.由于SIS结的临界电流是温度敏感的量,并且,其量子跃迁的电流变化很小, 因此,对温度的稳定性和测量的精度均要求很高.我们提出了一种改进的以测量时间间隔的方法取代直接测量临界电流的方法的测量方案,去测量SIS结从零电压态跃迁到正常态过程临界电流变化的统计分布.电路的计算机模拟表明,这种方法较直接法有更好的精度. 实验上的测量在准备中.     

电子器件散粒噪声测试方法研究

本文分析了超导量子干涉器(SQUID)和超导-绝缘-超导(SIS)约瑟夫森结散粒噪声测试方法的应用局限性,提出了常规器件的散粒噪声测试方案.针对常规电子器件散粒噪声特性,研究了噪声测试基本条件,并建立了低温测试系统.通过采用双层屏蔽结构和超低噪声前置放大器,实现了较好的电磁干扰屏蔽和极低的背景噪声.在10 K温度下对常规二极管散粒噪声进行了测试,通过理论和测试结果对比分析,验证了测试系统的准确和可信性. 关键词： 散粒噪声 电子器件 噪声测试     

利用倾斜角度蒸发法制备Al/Al_2O_3/Al超导隧道结

利用电子束曝光法对双层光刻胶进行曝光来制备悬空掩模结构,在此基础上利用电子束蒸发系统采用倾斜角度蒸发法制备铝超导薄膜,采用热氧化法在底层铝膜表面形成氧化铝作为势垒层,制备出铝SIS超导隧道结,并在360mK的情况下对铝结进行了Ⅰ～Ⅴ特性的初步测量.铝隧道结的成功制备为下一步构建超导量子比特器件,研究其量子特性奠定了良好的基础.     

高灵敏度高温超导接收机前端

概述了高温超导接收机前端在地面移动通信、为卫星有效载荷星上通信机和其它电子系统方面的应用.介绍了超导接收机中决定灵敏度最关键的器件高温超导带通滤波器和低噪声放大器的近年发展情况,进而介绍了高温超导接收机前端的技术发展开发.电子科技大学应用高温超导薄膜研制了X波段低插损(L=0.3dB)窄带通滤波器(BPF)和中频带通滤波器(IFBPF),同时研制了X波段工作于77K液氮温区的NF为0.36dB的低噪声放大器(LNA).引进了工作于77K液氮温区的插损为6dB的混频器(MIX)和中频放大器(IFA).从而研制成功国内第一台高温超导高灵敏度接受机前端系统.为尽可能提高接收机灵敏度,采用低插损、低导热的薄壁不锈钢电缆为输入端电路,组建了用液氮制冷的BPF-LNA-MIX-IFBPF-IFA电路型式的接收机前端电路.获得的主要指标为:工作频率:f=9500MHz;中频带宽:BIF=5MHz;工作温度:T=77K;灵敏度:S=-106.18dBm(24.1μμW);噪声温度:Te=58K.     

微波超导接收机

微波超导接收机是低温超导技术和无线电电子学相结合的产物.近年来,国际上对这种高灵敏度、低噪声的接收机颇为重视.我们在3厘米和8毫米波段研制的宽带视频检测器即属其中的一种.它主要用于观祭射电天体发出的宽带连续信号或用作热辐射的测量系统.目前,3厘米波段的检测器配以直径为70厘米的小型实验性抛物面天线后,可以清楚地收到太阳辐射的电磁信号;在8毫米波段,检测器可以很好地测量和分辨处于300K、78K等一系列温度下的黑体所辐射的热噪声,灵敏度优于0.8K. 这些应用的主要依据是弱耦超导体的约瑟夫逊效 应.例如,用两根铌棒分别磨成 平…     

MgO衬底NbN/AlN/NbN多层膜的制备

本文主要讨论磁控溅射设备制备的NbN/AlN/NbN三层结构的技术工艺,为制备All-NbN的 NbN/AlN/NbN SIS 隧道结作准备.我们在室温下利用直流磁控溅射工艺制备了单晶NbN薄膜,并对其超导电性做了初步的研究;又利用射频磁控溅射工艺制备了取向较好的AlN薄膜.我们利用磁控溅射方法制作NbN/AlN/NbN多层薄膜,然后对制备SIS隧道结进行了一些探索.     

超导隧道结的唯象理论

对SIS系统,在超导部分使用TDGL方程,在势垒两侧使用唯象边界条件,在V→0时,SIS系统的解完全可以基于微扰方法来求得.这样获得的cosθ项前面的系数,其符号和大小与实验结果相一致,但是应伴随条件:电流源必须是与时间有关的.PFL实验正是在上述条件下进行的.在恒流源情形下,我们的计算表明,与随时间变化的电流源情况相比,cosθ项前面的系数不但符号相反而且其大小和电容成正比.因此,如果忽略隧道结的电容,在恒流源情形下,cosθ项是不出现的.     

超导接收机静态真空保持设计及分析

超导接收机的真空寿命决定着整个系统的性能指标和可靠性,杜瓦的长寿命高真空保持至关重要,超导接收机的杜瓦相对于红外杜瓦及大型的低温接收机杜瓦有许多新的不同和难点。本文介绍了在小型超导接收机杜瓦真空设计以及工艺过程方面的一些经验做法,包括杜瓦内部材料选型、材料清洗及预排气处理、焊接及排气过程控制等方面的设计要求,通过实验数据分析估算了杜瓦真空寿命时间,能够满足工程使用要求。     

A Multibeam SIS Mixer Module for a Focal Plane Array Receiver

The integration of many receiver units into a receiver array is a common method of improvement of imaging systems. This approach, well known in the mm band for Schottky mixer arrays, has not so far been developed for Superconductor - Insulator - Superconductor (SIS) junction mixers, which give the best sensitivity in the short mm wave range and in the submm range.We demonstrate for the first time a practical low noise multibeam receiver module using SIS mixer technology. The basis for the integration of several SIS mixers with a common local oscillator source is given by the saturation of the SIS receiver noise dependence upon local oscillator power. The module comprises three identical SIS mixers integrated with a common local oscillator, coupled through a three branch waveguide directional coupler. The multibeam module has been developed for a focal plane array receiver of the 30 meter radio telescope of the Institut de Radioastronomie Millimétrique (IRAM).     

A Low Noise NbTiN-Based 850 GHz SIS Receiver for the Caltech Submillimeter Observatory

We have developed a niobium titanium nitride (NbTiN) based superconductor-insulator-superconductor (SIS) receiver to cover the 350 micron atmospheric window. This frequency band lies entirely above the energy gap of niobium (700 GHz), a commonly used SIS superconductor. The instrument uses an open structure twin-slot SIS mixer that consists of two Nb/AlN/NbTiN tunnel junctions, NbTiN thin-film microstrip tuning elements, and a NbTiN ground plane. The optical configuration is very similar to the 850 GHz waveguide receiver that was installed at the Caltech Submillimeter Observatory (CSO) in 1997. To minimize front-end loss, we employed reflecting optics and a cooled beamsplitter at 4 K. The instrument has an uncorrected receiver noise temperature of 205K DSB at 800 GHz and 410K DSB at 900 GHz. The degradation in receiver sensitivity with frequency is primarily due to an increase in the mixer conversion loss, which is attributed to the mismatch between the SIS junction and the twin-slot antenna impedance. The overall system performance has been confirmed through its use at the telescope to detect a wealth of new spectroscopic lines.     

A 110 GHz SIS receiver for radio astronomy

A 110 GHz superconductor insulator superconductor (SIS) tunnel junction receiver has been developed and used in regular astronomical observations on the 4m radio telescope at the Department of Astrophysics, Nagoya University. The SIS junction consists of a sandwich structure of Nb/AlOx/Nb, and is cooled to 4.2K with a closed cycle He-gas refrigerator. The receiver exhibits a best double side band noise temperature of 23±2 K at 110GHz. Additional measurements at 98–115 GHz indicate that the receiver has a good response over this input frequency range.     

A low noise receiver for millimeter and submillimeter wavelengths

A broadband, low noise heterodyne receiver, suitable for astronomical use, has been built using a Pb alloy superconducting tunnel junction (SIS). The RF coupling is quasioptical via a bowtie antenna on a quartz lens and is accomplished without any tuning elements. In this preliminary version the double sideband receiver noise temperature rises from 205 K at 116 GHz to 375 K at 349 Ghz, and to 815 K at 466 GHz. This is the most versatile and sensitive receiver yet reported for sub-mm wavelengths.     

A low-noise SIS receiver measured from 480 GHz to 650 GHz using Nb junctions with integrated RF tuning circuits

A heterodyne receiver using an SIS waveguide mixer with two mechanical tuners has been characterized from 480 GHz to 650 GHz. The mixer uses either a single 0.5 × 0.5 µm² Nb/AlO_x/Nb SIS tunnel junction or a series array of two 1 µm² Nb tunnel junctions. These junctions have a high current density, in the range 8 – 13 kA/cm². Superconductive RF circuits are employed to tune the junction capacitance. DSB receiver noise temperatures as low as 200 ± 17 K at 540 GHz, 271 K ± 22 K at 572 GHz and 362 ± 33 K at 626 GHz have been obtained with the single SIS junctions. The series arrays gave DSB receiver noise temperatures as low as 328 ± 26 K at 490 GHz and 336 ± 25 K at 545 GHz. A comparison of the performances of series arrays and single junctions is presented. In addition, negative differential resistance has been observed in the DC I–V curve near 490, 545 and 570 GHz. Correlations between the frequencies for minimum noise temperature, negative differential resistance, and tuning circuit resonances are found. A detailed model to calculate the properties of the tuning circuits is discussed, and the junction capacitance as well as the London penetration depth of niobium are determined by fitting the model to the measured circuit resonances.     

A 100-GHz-band heterodyne sis receiver for the trao telescope

A 100-GHz-band Superconductor-Insulator-Superconductor (SIS) receiver has been developed for radio astronomy. The mixer used in this receiver has no mechanical tuning elements, such as a backshort or an E-plane tuner. The SIS junction consists of an array of four Nb/Al-AIOx/Nb junctions in series. The quasi-optic system for this receiver has been designed by frequency-independent matching method. The average DSB receiver noise temperature measured in the frequency range from 85 to 115 GHz is 40 K. The receiver is being successfully operated at the Taeduk Radio Astronomy Observatory in Korea.     

Low noise submillimeter SIS receiver with niobium nitride quasiparticle tunnel junctions

We have developed and tested a submillimeter waveguide SIS mixer with NbN-MgO-NbN quasiparticle tunnel junctions. The two junction array is integrated in a full NbN printed circuit. The NbN film critical temperature is 15 K and the junction gap voltage is 5 mV. The size of the junctions is 1.4 × 1.4 µm and Josephson critical current density is about 1.5 KA/cm² resulting in junction R_NC product about 40. The inductive tuning circuit in NbN is integrated with each junction in two junction array. A single non contacting backshort was tuned at each frequency in the mixer block.At 306 GHz the minimum DSB receiver noise temperature is as low as 230 K. The sources of the receiver noise and of the limits of the NbN SIS submillimeter mixer improvement are discussed.     

100 GHz mixer vertically integrated (stacked) SIS junction array

A Vertically Integrated Array (stacked array) of single windowSIS junctions (VIA SIS), based on a stacked five layer structure of Nb-AlO_x-Nb-AlO_x-Nb, has been fabricated and tested in a quasi optical mixer configuration at 106 GHz. This particular VIA SIS design has two stacked junctions fabricated by standard tri-layer process employing photolithography, reactive ion and wet etching processes. A simple expression for calculating the specific capacitance of single and arrayed SIS junctions is suggested. Due to the absence of interconnection leads between the individual junctions and reduced overall capacitance, compared to a single SIS junction, has the VIA SIS good future prospects for use in submillimeter wave SIS mixers The VIA SIS may be regarded as a lumped rather than a distributed structure at least up to the gap frequency at 730 GHz for Nb. DC-IV measurements show high quality of the Individual SIS junctions and good reproducibility of the array parameters over the substrate area. The first VIA SIS mixer experiments yielded a receiver noise temperature of 95 K (DSB) at a LO frequency of 106 GHz.     

A Novel LO Power Injection Method for SIS Mixers

We propose a novel LO power injection method developed for SIS mixers in this paper. Based on the feature of extremely small LO power requirements of SIS quantum mixing, the new method fulfills SIS pumping through a DC/IF route based built-in LO path, which is composed of an additional LO waveguide and the existing microstrip choke filter on the junction substrate. With the new method, traditional external LO diplexers(e.g., crossguide-couplers or beamsplitters) become unnecessary, resulting in a lower loss, compact, and stable receiver system. Experiments at 110- and 230 GHz bands have shown that the present method is efficient in coupling sufficient pumping power to SIS junctions from general LO sources, and the receiver sensitivities have a further improvement of about 10 K. We expect this method is also able to be applied into submillimeter wave band for SIS mixers.