Effect of device processing on 1/f noise in uncooled, auger-suppressed CdHgTe diodes

Auger suppression reduces the leakage current in uncooled CdHgTe diodes to the point where the shot noise limited D* is significantly higher than for other uncooled detectors. However, Auger-suppressed diodes exhibit high levels of 1/f noise and so applications have initially been in devices operating at high frequency such as CO₂ laser heterodyne detectors. In order to use Auger suppression in imaging devices, we need to reduce the 1/f noise and this paper describes a study of the effects of device processing on noise. We find that although some of the noise is associated with perimeter leakage currents, variations in the surface passivation treatment have little effect on the total noise. However, a post-passivation anneal can reduce the noise in some cases. We also find that CdTe passivated devices are more stable when baked than those passivated with ZnS.     

Stacked multijunction photodetectors of long-wavelength radiation

Uncooled, long-wavelength photovoltaic detectors suffer from poor quantum efficiency and low differential resistance. The problem can be solved by the use of stacked, multiple heterojunction-photovoltaic cells with thin absorber regions. We report here numerical simulation and optimization of the stacked, multiple Hg_1−xCd_xTe heterojunction cells used for detection of 10.6-μm infrared (IR) radiation, operating as zero-bias photovoltaic devices or Auger-suppressed photodiodes. It is shown that the devices can be used as high-performance and fast-response detectors of long-wavelength radiation operating at ambient temperature with detectivities larger by more than one order of magnitude than that of the present practical devices.     

The design of low jitter hard limiters

Hard limiters, which are nearly identical to level crossing detectors or zero crossing detectors, are an integral part of many communications systems, of devices for characterizing precision oscillators, and of analog-to-digital converters. The purpose of a hard limiter is to divide the continuous range of an analog input signal into two regions and to provide a digital output indicating the region in which the signal is. This digital output must, by definition, have an extremely short transition time. A hard limiter is thus a slope amplifier, since a slowly varying input must produce a very rapidly varying output. Noise in the amplifiers causes the output transition to be jarred from its correct position producing jitter in the output. This paper presents the analysis and details the design of very low jitter hard limiters. Their immediate application is to the measurement of high stability signal sources and to deep space communication and ranging; the results, however, are easily adapted to many other purposes such as waveform digitization. One of the devices described has been built. Its performance agrees closely with theory and is vastly superior to that of conventional instrumentation     

Current status of negative electron affinity devices

The introduction of electron emitters utilizing negative electron affinity has greatly improved the performance of many conventional light-sensing devices. The unique properties of such emitters have also made possible devices which were heretofore not feasible. Since their arrival as laboratory curiosities about five years ago, these emitters have had a large impact in the area of low-light-level detection, particularly scintillation counting. Recent advances in materials technology and surface activation processes have brought negative electron affinity photocathodes to the market place for use as detectors for both the Nd and GaAs lasers. In both cases, the detectors are more than an order of magntiude more sensitive to the laser light than previous photocathodes, and the dark currents (thermionic emission from the cathodes which can be limiting in low-light-level use) are several orders of magnitude less. Several other applications of negative electron affinity are presently under development which may further affect photocathodes, photomultipliers, imaging devices, and even the time-honored thermionic cathode. The operating principles of this type of electron emitter, the present state of the art and its effect on device performance, and the possible developments in the near future are discussed.     

Terahertz Imaging System for Medical Applications and Related High Efficiency Terahertz Devices

A terahertz (THz) imaging system and high efficient terahertz sources and detectors for medical applications were developed. A fiber laser based compact time domain terahertz tomography system was developed with a high depth resolution of less than 20 μm. Three-dimensional images of porcine skin were obtained including some physical properties such as applied skin creams. The discrimination between healthy human tissue and tumor tissue has been achieved using reflection spectra. To improve the THz imaging system, a ridge waveguide LiNbO₃ based nonlinear terahertz generator was studied to achieve high output power. A ridge waveguide with 5-7 μm width was designed for high efficiency emission from the LiNbO₃ crystal by the electro-optic Cherenkov effect. Terahertz electronic sources and detectors were also realized for future imaging systems. As electronic source devices, resonant tunneling diode (RTD) oscillators with a patch antenna were fabricated using an InGaAs/InAlAs/AlAs triple barrier structure. On the other side, Schottky barrier diode (SBD) detectors with a log-periodic antenna were fabricated by thin-film technology on a Si substrate. Both devices operate above 1 THz at room temperature. This electronic THz device set could provide a future high performance imaging system.     

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.     

Exploration of Terahertz Imaging with Silicon MOSFETs

We summarize three lines of development and investigation of foundry-processed patch-antenna-coupled Si MOSFETs as detectors of THz radiation: (i) Exploiting the pinciple of plasma-waved-based mixing in the two-dimensional electron gas of the transistors’ channels, we demonstrate efficient detection at frequencies as high as 9 THz, much above the transit-time-limited cut-off frequencies of the devices (tens of GHz). Real-time imaging at 600 GHz with a 12 × 12 detector array is explored. (ii) Given the limited THz power usually available for applications, we explore imaging with enhanced sensitivity in heterodyne mode. We show that real-time operation of a 100 × 100-pixel heterodyne camera should be possible at 600 GHz with a better dynamic range (30 dB) than for direct power detection (20 dB), even if only a quarter-milliwatt of local-oscillator power, distributed radiatively over all detector pixels, is available. (iii) Finally, we present an all-electronic raster-scan imaging system for 220 GHz entirely based on CMOS devices, combining the CMOS detectors with an emitter circuit implemented in a 90-nm CMOS process and delivering radiation with a power on the 100- μW scale. Considering progress in the field, we anticipate that the emitter concept of oscillator-based power generation with on-chip frequency multiplication will carry well into the sub-millimeter-wave regime.     

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.     

SIMS characterization of HgCdTe and related II-VI compounds

The production of consistent high purity materials is critical for improvement in performance and sensitivity of II-VI photovoltaic and photoconductive devices. Information regarding the energy band structure and impurity or defect levels present in the material is essential to understand and enhance the performance of current detectors along with the development of future novel devices. Secondary ion mass spectrometry (SIMS) is capable of providing information of purity, junction depths, dopant distribution, and stoichiometry in the material. SIMS techniques can achieve high detection sensitivities in very small analytical volumes and for a wide range of elements (almost the entire periodic table). SIMS analysis also provides unique capabilities for localizing atomic distribution in two and three dimensions. Ion images can be obtained by registering the positions of mass selected ions formed in the sputtering process. The combination of excellent detection sensitivity, high mass resolution, depth profiling capability, and high resolution image acquisition on a wide spectrum of elements by a SIMS instrument is not matched by any other instrumentation technique.     

4路长积分时间CCD成像电路的设计与实现

基于CCD47-20和CCD55-30探测器设计了一种4路探测器成像电路。由于积分时间长,该系统可以在弱光条件下实现高灵敏度成像。建立了探测器的驱动电路模型,分析了CCD探测器对驱动的要求,以选择合适的驱动芯片;在分析探测器噪声特性的基础上,通过相关双采样法和合理的滤波器设置抑制了电路噪声。针对4路探测器信号处理电路之间的串扰问题进行了分析和对比,为合理的PCB布局布线提供了参考。该成像电路与商用镜头搭配使用后已成功获取了微光条件下的低噪声外景图像。     

Low-Pressure Chemical Vapor Deposition of CdS and Atomic Layer Deposition of CdTe Films for HgCdTe Surface Passivation

HgCdTe narrow-bandgap materials are used in the fabrication of infrared detectors and focal-plane arrays. Many of these advanced devices require complex structures to be processed into them. Passivation of planar detectors is typically done with vacuum-evaporated CdTe or related II–VI materials. New advanced detector topology necessitates the use of low-pressure chemical vapor deposition (LPCVD) and atomic layer deposition (ALD) for improved conformal coverage. Preliminary studies on LPCVD of CdS and ALD of CdTe were carried out and characterized for conformal coverage. The effects of CdS and CdTe films on HgCdTe minority-carrier lifetime are also studied at 300 K and 77 K.     

New Electromagnetic Compatibility Instrumentation and Measurement Requirements and Techniques

This paper illustrates some fundamental instrumentation and measurment terms and the vague or midlesding manner in which they are frequently used. For example, the subject of accuracy is shown in four different common uses and interpretations. Misuse of the accuracy term is also illustrated in describing the performance of receiver linearity and dynamic range, the synthesis of recorder requirements and specifications, and the development of uncertainties in instrumentation and measurement. The damage results in either incorrect or poor decisions based on erroneous data, or wanton waste of dollars and effort by developing the wrong data, or both. Several examples are set forth on how a better technological communication can be effected. Some new instrumentation and measurement techniques recommended for use by the Electromagnetic Compatibility Community are presented. Regarding new instruments or updating of existing instruments, some examples described include statistical signal level detectors, peak-signal vs frequency plotting units, antenna pattern intercept platforms and equipments, and multi-channel crystal-video receivers with RF preamplification, peak detection and hold, and output sampling for X-Y plotting over 9 decades. Many of the EMC instrumentation techniques are borrowed from the EMW and ELINT Communities. Regarding measurement techniques, shielded enclosure attenuation, antenna pattern measurements using the sun as a signal generator and the conduct of electromagnetic site surveys are reviewed. Clearly, this paper covers only a few of a number of new opportunities awaiting EMC Community action.     

A fieldbus prototype for educational purposes

One of the problems with instrumentation systems is the interconnection between the multiple devices with different communication protocols. Exacerbating this problem are two typical requirements of interconnection: minimize cabling cost and avoid degradation of the signal during transmission. Cabling cost can be reduced through several multidrop communication systems: industrial local area networks or wireless communication. Reduction of signal to noise can restrict system performance and the quality of manufactured products, even if high-accuracy devices are used. Another problem in the field of manufacturing instrumentation networks is that industry uses multiple solutions to interconnect instrumentation with different communication protocols. This article presents the development of a prototype for an instrumentation network with the goal to study and analyze the characteristics of the different communication solutions. The overall system contains a large number of instrumentation devices, which is a great advantage for educational purposes and laboratory experiments. The students can configure, calibrate, and operate a large number of instruments connected to different segments of the DCS. We also connected some current-loop devices to the FF system to evaluate their performance when connected to a fully digital network. Results from the prototype DCS show that networking between different instrumentation devices and protocols can be successful and that a hybrid solution using conventional 4-20 mA current loop and fully digital instrumentation can work to leverage existing analogue systems. Future work will include the development of a fieldbus network analyzer to trace messages in the network and study the quality of FF service parameters, such as packet loss and delay measurement, as a function of network load.     

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.     

TDI型红外探测器空间校正方法的设计与实现

时间延迟积分(TDI)型红外探测器作为第二代红外探测器,具有更高的温度灵敏度和更大的扫描成像视场.和面阵成像探测器相比,TDI型红外探测器必须在装置中加入扫描机构进行扫描成像,由于TDI型红外探测器光敏元在空间的位置交错排列,为了保证奇偶像元对同一目标成像,这就涉及到扫描方向与探测器奇偶像元空间匹配的问题.以480×6红外探测器为例,详细介绍了TDI型红外探测器光敏元的排列结构、工作方式以及空间校正的原理,给出了空间校正的算法和FPGA实现方法,并通过仿真和实验验证了方法的正确性.     

板壳状微电子器件的数字层析成像检测方法

 传统工业CT(industrial computed tomography, ICT)成像方法受扫描原理和探测器、射线源等硬件条件的限制,难以对芯片、印刷电路板等板、壳状微电子器件实施有效的数字层析成像检测. 为此,讨论了一种基于锥束射线倾斜扫描和代数重建技术（Algebraic Reconstruction Technique, ART）的薄板层析成像（Computed Laminography, CL）方法,研究了其基于投影凸集理论的投影预处理方法及基于不同区域相似性的重建图像非局部平均降噪后处理方法,建立了基于非晶硅面阵探测器的实验系统,并完成了CPU芯片和印刷电路板的CL成像. 实验结果证明了该方法的正确性.     

Implied Open-circuit Voltage Imaging via a Single Bandpass Filter Method—Its First Application in Perovskite Solar Cells

A novel, camera-based method for direct implied open-circuit voltage (iV_OC) imaging via the use of a single bandpass filter (s-BPF) is developed for large-area photovoltaic solar cells and precursors. The photoluminescence (PL) emission is imaged using a narrow BPF with centre energy inside the high-energy tail of the PL emission, utilising the close-to-unity and nearly constant absorptivity of typical photovoltaic devices in this energy range. As a result, the exact value of the sample's absorptivity within the BPF transmission band is not required. The use of an s-BPF enables a fully contactless approach to calibrate the absolute PL photon flux for spectrally integrated detectors, including cameras. The method eliminates the need for knowledge of the imaging system spectral response. Through an appropriate choice of the BPF centre energy, a range of absorber compositions or a single absorber with different surface morphologies, such as planar and textured, can be imaged, all without the need for additional detection optics. The feasibility of this s-BPF method is first validated. The relative error in iV_OC is determined to be ≤1.5%. The method is then demonstrated on device stacks with two different perovskite compositions commonly used in single-junction and monolithic tandem solar cells.     

Fabrication and Characterization of Small Unit-Cell Molecular Beam Epitaxy Grown HgCdTe-on-Si Mid-Wavelength Infrared Detectors

Small 15 μm unit-cell mid-wavelength infrared (MWIR) detectors have been fabricated and characterized at Raytheon Vision Systems (RVS) to enable the development of high resolution, large format, infrared imaging systems. The detectors are fabricated using molecular beam epitaxy (MBE) grown 4-in. HgCdTe-on-Si wafers with a p-on-n double layer heterojunction (DLHJ) device architecture. Advanced fabrication processes, such as inductively coupled plasma (ICP) etching, developed for large format MBE-on-Si wafers and 20 μm unit-cell two-color triple layer heterojunction (TLHJ) focal plane arrays (FPAs) have been successfully extended and applied to yield high performance 15 μm unit-cell single color detectors that compare favorably with state-of-the-art detectors with larger pitch. The measured 78 K MWIR cut-off wavelength for the fabricated detectors is near 5.5 μm, and the current–voltage characteristics of these devices exhibit strong reverse breakdown and RoA performance as a function of temperature with diffusion limited performance extending to temperatures down to 120 K.     

IEEE standard 488 and microprocessor synergism

The assembly and use of more new and versatile instrumentation systems is now enhanced dramatically with the widespread application of IEEE Standard 488-1975, "Digital Interface for Programmable Instrumentation." This Standard interface provides an easy-touse high performance concept that links instruments, calculators or computers, and peripheral devices to function as automated instrumentation systems. Microprocessor technology applied to both smart instrumentation and the implementation of IEEE Standard 488's interface functions provides still further benefits to system designers and users. This article describes both the interface function concepts important to instrumentation systems and the roles played by IEEE Standard 488 and microprocessor techniques in support of these functional concepts. Microprocessor and IEEE Standard 488 interface techniques combine to provide designers and users with significant new tools for improved product performance, something neither technology alone could provide. In the near future, special LSI chips optimized to integrate the two technologies should further enhance the benefits for all concerned.     

红外热成像在电气设备维护中的应用

红外热成像技术在工业检测中应用广泛，介绍了红外测温原理，讨论了电力设备的发热原理，过热损耗的危害，热像测温的影响因素等，利用AGEMA570非制冷，焦平面红外热像仪对供电厂炉前隧道的照明线路等进行了实测，获得一定工作温度，环境温度下的线路接头温度及其温升，最后针对企业电气设备维护中的红外热成像应用结果进行了讨论。