Noise parameters of SIS mixers

It has been shown that low-noise receivers can be constructed at millimeter wavelengths by using mixers containing superconducting tunnel junctions as the nonlinear elements. This is possible because of both the low intrinsic noise of these devices and their potential for high conversion gain. Here, the quantum theory of mixing is used to derive the full-noise parameters and small-signal parameters of sinusoidally pumped SIS (superconductor-insulator-superconductor) junctions. These are then put into a form that allows the theory of two-port linear networks to be brought to bear, allowing calculation of such useful parameters as minimum noise temperature, optimum source impedance, available (or exchangeable) gain at minimum noise, and stability factor. These quantities are properties of the pumped junction that do not depend on the source or load impedance, but do depend on the terminations at the image and harmonic sideband frequencies. The harmonic sidebands are taken to be shorted, and the image termination dependence is studied. Numerical results are presented for both ideal (BSC theory) and practical (measured current-voltage characteristic) junctions. The noise parameters of the cascade connection of an SIS mixer and a (noisy) IF amplifier are considered, leading to a specification of the optimum coupling network between the two. It is noted that the SIS mixer is usually not unconditionally stable, but that oscillation can be avoided by careful design of the IF coupling network     

超导隧道结亚谐波混频器的研究

本文探讨了新型的超导隧道结亚谐波混频器。其混频作用是通过由超导体—隔离体—超导体(SIS)构成的隧道结完成。在性能上可同通常的Schottky二极管亚谐波混频器媲美,基于Tucker量子混频理论,对这种新型混频器进行了噪声和变频效率的分析研究。     

High-speed photodetectors

This paper is intended as a status report on high-speed detectors for the visible and near-infrared portion of the optical spectrum. Both vacuum and solid-state detectors are discussed, with the emphasis on those devices which can be used as direct (noncoherent) detectors of weak optical signals modulated at microwave frequencies. The best detectors for this application have internal current gain and in this regard the relevant properties and limitations of high-frequency secondary emission multiplication in vacuum tube devices and avalanche multiplication in p-n junctions are summarized.     

HgCdTe Photon Trapping Structure for Broadband Mid-Wavelength Infrared Absorption

This work investigates the use of photon trapping structures in HgCdTe detectors for use in mid-wavelength infrared (MWIR) detectors. Model results based on finite-difference time-domain electromagnetic simulation and a finite-element model of electronic performance are compared with Fourier-transfer infrared (FTIR) spectroscopy and measured device performance results. Reduced fill factor devices with lowered dark current and no appreciable decrease in quantum efficiency are demonstrated. This is compared against devices with reduced fill factor but no photon trapping capability, which exhibit reduced dark current but also reduced quantum efficiency.     

Quantitative Comparison of Solid-State Microwave Detectors

A method for quantitative comparison of solid-state microwave square-law detectors is presented. The threshold response of the square-law detectors are compared for unit video bandwidth using the concept of noise equivalent power (NEP). NEP is the microwave input power required for unity signal-to-noise ratio in a 1 Hz bandwidth at the output of the detector. Contours of constant NEP in the microwave (RF) and video frequency plane clearly describe the dependence of threshold sensitivity on both video and radio frequencies, and thereby provide comparison of the threshold sensitivities of devices over the entire video and RF frequency spectrum. A criterion for the upper RF power lid of square-law operation for detectors is also presented. Dynamic range for a device can be found using this criterion and the threshold sensitivity of the device. Six solid-state detection devices are described briefly, then compared on the basis of the foregoing concepts. Four of these devices are familiar: the point-contact and planar Schottky-barrier ("hot carrier") diodes, and the tunnel and back diodes. Two relatively new devices are also discussed: the so-called "hot carrier" thermoelectric detector, and the space-charge-limited (SCL) dielectric diode.     

Dual-band infrared detectors

IntroductionMulticolor capabilities are highly desirable foradvance infrared(IR) systems.Systems that gatherdata in separate IR spectral bands can discriminateboth absolute temperature and unique signatures ofobjects in the scene.By providing this new dimensionof contrast,multiband detection also enables ad-vanced color processing algorithms to further im-prove sensitivity above that of single- color devices.This is extremely important for the process of identi-fying temperature difference b…     

新型电子器件和光学器件的共振隧穿结构

描述了一种新型共振隧穿结构器件，这种器件包含了通过可变间隙超晶格能量滤波器（ＶＳＳＥＦ）中的耦合量子附态的隧穿过程．论证了通过ＡｌＡｓ／ＧａＡｓＶＳＳＥＦ器件高能态和ＡｌＧａＡｓ／ＧａＡｓ超晶格受激态的共振隧穿，描述了这种器件作为较高功率微波源和共振隧穿晶体管的应用，并讨论了共振隧穿结构作为雪崩探测器和红外发射器等光学器件的潜在应用．     

非制冷红外探测器研究进展（特邀）

非制冷红外探测器由于无需制冷装置,能够工作在室温状态下,具有成本低、体积小、功耗低等特点,在红外领域得到了广泛的应用。在军事应用方面,非制冷型探测器的应用逐渐进入了之前制冷型探测器的应用范围,大量应用在一些低成本的武器系统,甚至在一些应用领域取代了原来的非制冷型探测器。在民用领域方面,更表现出了其价格和使用方便的优势,在民用车载夜视、安防监控等应用领域引起了广泛的兴趣和关注。文中介绍了Bolometer、热释电、热电堆等几种典型非制冷红外探测器的工作原理,列举了目前已实现商业化应用的主要产品在国内外的情况,着重介绍了目前应用最广泛的Bolometer器件主流产品的像元间距、阵列规格、性能及其封装发展的情况。除了已实现商业化应用的Bolometer、热释电、SOI二极管等探测器等产品,还详细介绍了一些非制冷探测新技术或新型器件:比如超表面在增强某些波段吸收方面的应用,新材料的Bolometer探测器、双材料新型非制冷器件、石墨烯、量子点、纳米线等光电探测技术的研究进展。最后文章还对今后非制冷红外探测器的发展趋势作了预测。     

Analysis of SIS heterojunctions for use as mm-wave mixers exhibiting coversion gain

We apply the quantum formulation of heterodyne mixer theory to SIS heterojunctions (junctions between dissimilar superconductors). Conversion gain is predicted over a wide range of mm-wave frequencies in the 3-port Y-mixer model by exploiting the naturally occurring region of negative conductance in the DC I-V characteristic. In the signal frequency range 50–250 GHz this region persists in the pumpedjunction I–V characteristic for local oscillator power <1 nW and leads to a negative conductance at the mixer's IF port.     

Production of high quality Nb/Al-oxide/Nb SIS trilayers for submillimeter wave mixers

Owing to a very sharp nonlinearity in the quasiparticle currentvoltage characteristic, which fortuitously occurs on the scale of a few millivolts rather than a few volts as with semiconductor devices, superconductor/insulator/superconductor (SIS) tunnel junctions are the most sensitive detectors for heterodyne mixing at millimeter and submillimeter wavelengths. They can also provide sources of coherent local oscillator power at very high frequencies; more broadly, they have a number of interesting applications as fast, low-power logic elements and as detectors at optical wavelengths. For submillimeterwave mixers, in many ways the most demanding of these applications, the Nb/Al-oxide/Nb material system has emerged as the system of choice to frequencies of ～ 700 GHz and beyond. Production of SIS devices requires careful attention to a number of critical microfabrication issues, and I describe here some of the insights gained from developing a process for high-quality niobium trilayers that successfully yielded small-area junctions with unusually low sub-gap leakage current.     

红外光电探测器的前沿热点与变革趋势

红外光电探测技术通常工作在无源被动的传感模式,具有作用距离远、抗干扰性好、穿透烟尘雾霾能力强、全天时工作等优点,在航天遥感、军事装备、天文探测等方面都有广泛应用。至今,二代、三代红外光电探测器已大规模进入装备,高端三代也在逐步推进实用化,并出现了前沿前瞻性的新概念、新技术、新器件。本文聚焦国内外的红外技术研究现状,重点介绍红外光电探测器当前的研究热点与未来的发展趋势。首先,介绍针对战术泛在化、战略高性能的SWaP³概念。其次,综述以超高空间分辨率、超高能量分辨率、超高时间分辨率、超高光谱分辨率为特征的高端三代红外光电探测器,分析挑战光强探测能力极限的红外探测器的技术特征与实现方法。然后,论述基于人工微结构的四代红外光电探测器,重点介绍偏振、光谱、相位等多维信息融合的实现途径与技术挑战。最后,从片上数字化升级为片上智能化的角度,探讨未来极具变革性趋势的红外探测器。     

Detector material and sensitivity analysis for space-based infrared sensors

The ultimate detection performance of HgCdTe, quantum well (QW) and extrinsic Si detectors under low temperatures is analyzed. The theoretical limits of the internal photon response for the three detectors are compared. The materials of space-based detectors in space tracking and surveillance system (STSS) are discussed. The results show that among three detectors, the best performance can be obtained from HgCdTe detectors under 40 K in the mid-long wave infrared (MLWIR) and long wave infrared (LWIR) spectr...     

Quantum noise in heterodyne detection

A fully quantum mechanical theory of diode mixers which includes quantization of the external circuit is presented. We find that Tucker's theory for SIS mixer conversion efficiencies is correct, but that his expression for the measurement noise must be augmented by an amount corresponding to half a photon at every frequency to which the mixer responds. Noise in high quality SIS mixers is shown to be accurately described by the conceptually simpler photodiode mixer noise theory. The radiation coupling efficiency term, η, which appears in photodiode theory turns out to be the coupling efficiency between the signal source admittance and the admittance which the SIS presents to the LO. Our theory reduces to Caves' quantum linear amplifier formalism, and therefore predicts measurement noises bounded by the quantum lower limit ofhv/k_{B}. Predictions of performance versus frequency for SIS's are made. We predict that NbN SIS's will behave as nearly ideal photodiodes for frequencies as high as 3000 GHz.     

Infrared heterodyne detection

Heterodyne experiments have been performed in the middle infrared region of the electromagnetic spectrum using the CO2laser as a radiation source. Theoretically optimum operation has been achieved at kHz heterodyne frequencies using photoconductive Ge:Cu detectors operated at 4°K, and at kHz and MHz frequencies using Pb1-xSnxSe photovoltaic detectors at 77°K. In accordance with the theory, the minimum detectable power observed is a factor of 2/η greater than the theoretically perfect quantum counter, hvΔf. The coefficient 2/η varies from 5 to 25 for the detectors investigated in this study. A comparison is made between photoconductive and photodiode detectors for heterodyne use in the infrared, and it is concluded that both are useful. Heterodyne detection at 10.6 µm is expected to be useful for communications applications, infrared radar, and heterodyne spectroscopy. It has particular significance because of the high radiation power available from the CO2laser, and because of the 8 to 14 µm atmospheric window.     

A novel technology for fabrication of beam-leaded GaAs Schottky-barrier mixer diodes

The fabrication of mixer diodes for use at millimeter-wave frequencies requires the definition of extremely small area Schottky-barrier junctions. It is not a trivial matter to fabricate such devices at low cost which simultaneously are mechanically rugged, exhibit low parasitics, and present high figures of merit. This paper presents a novel technology for accomplishing these objectives. By incorporating "shadow masked" proton bombardment and metal evaporation, planar beam-leaded devices of low capacitance are realized in the absence of the critical processing steps which have traditionally resulted in low yields. GaAs devices having zero bias capacitance of 0.06 pF are obtained with a series resistance of less than 3 Ω giving a cutoff frequency in excess of 800 GHz. Initial RF tests have resulted in a noise figure and conversion loss of 5.8 and 3.8 dB, respectively, at 10.7 GHz. This technology should result in the availability of inexpensive GaAs mixer diodes suitable for use at millimeter-wave frequencies.     

Fourier transform spectrometer studies (300-1000 GHz) of Nb-basedquasi-optical SIS detectors

Three Nb/AlO_x/Nb SIS detectors, designed to operate in the 400-550, 550-700, and 600-750 GHz bands, have been studied in direct detection mode using a Fourier-transform spectrometer. All three detectors were of quasi-optical type and had on-chip-integrated-fixed tuned SIS junctions. The tuning ranges of the detectors were selected to cover the interesting region around the superconducting gap frequency of Nb (about 700 GHz). Measurements show detector responses at frequencies above the gap frequency, i.e., up to ≈920 GHz, and that cooling the detectors to 3.1 K improved the direct detection responses about 15% below 700 GHz and about 50% for frequencies up to 800 GHz, compared to the responses at 4.2 K. The 500 GHz SIS detector was also studied in a 440-520 GHz heterodyne receiver set up. Good agreement between modeled tuning circuit characteristics, tuning range of the mixer and the direct detection response bandwidths were found. However, it is essential that the dispersion of the field penetration depth into the superconductor is included in the modeling of the tuning circuits when the detector is operated at frequencies above the superconducting gap     

双曲型量子阱中非线性光学吸收率的计算

量子阱中的非线性光学效应因其潜在的实用价值而引起了人们的广泛的关注,而量子阱内带间的光学吸收问题对研究远红外光学探测器等光电子器件具有重要的理论指导意义.用量子力学中的密度矩阵算符理论导出了双曲型量子阱中的线性与三阶非线性光学吸收系数的表达式.因双曲型量子阱中有一个可调参数,随着参数的增加,阱宽将相应增加,因此势阱的形状以及阱内的非线性光学吸收率将随参数变化而发生规律性的变化,并且当入射光强增强到一定程度会出现较强的饱和吸收现象,通过对这些规律的研究从而为实验研究提供了必要的理论依据.     

Infrared detectors and applications

A large variety of methods for the detection of infrared radiation have been developed primarily over the last ten to twenty years. These include thermal detection using bolometers, thermocouples and pyroelectric detectors, photon detection by extrinsic and intrinsic semiconductor photoconductors, photodiodes and photoemitters, and infrared imaging using these devices. These methods also include the use of devices with internal gain such as avalanche photodiodes and infrared photomultipliers as well as various unconventional detector schemes. General considerations of infrared imaging and high speed detection are discussed and many of these methods are reviewed and compared, with particular attention given to their applications and limitations. This work was sponsored by the Department of the Air Force.