Signatures of differential Log R–V characteristics for non-uniformity analysis of HgCdTe infrared photodiode arrays

In continuation to our research on the non-uniformity in infrared focal plane arrays of HgCdTe photodiodes, we have examined and found a few important signature parameters in the forward bias region of the electrical characteristics of the photodiodes. These signatures are the peaks of the first and second order derivatives of dynamic resistance–voltage characteristics. They show good correlation with the material and devices parameters and have been investigated to be good signatures for statistical performance variation analysis. In this note, by using theoretical model and statistical analysis of these signatures, we show that the variations in the proposed signatures represent underlying non-uniformity in important material/device parameters. Such signatures may be used along with the other conventional signatures of reverse biased photodiode characteristics to identify the root cause of response non-uniformity in the array with high confidence level.     

Electrical characteristic signatures for non-uniformity analysis in HgCdTe photodiode arrays

In this paper we present a method of analyzing the performance non-uniformity of HgCdTe photodiode arrays for infrared imaging applications. For quantifying the characteristic behavior of various photodiodes, we have parametrized the dynamic resistance verses voltage signatures in such a way that the obtained signature parameters have some relevance with different physical parameters. We also estimated the sensitivity of the proposed signatures on physical parameters using statistical technique. These characteristics signatures may be used to quantify the non-uniformity of the HgCdTe photodiodes in IR imaging arrays and its analysis. The method presented here is based on theoretical calculation of MWIR HgCdTe photodiodes. However, the method is generic and may be implemented on any other type of diode arrays for theoretical or experimental analysis of their non-uniformity.     

Principal component analysis of non-uniformity in electrical characteristics of HgCdTe photodiode arrays

We present a method of analyzing the non-uniformity in electrical characteristics of HgCdTe photodiode arrays for infrared imaging applications. We have selected dynamic resistance–voltage (R–V) characteristics for analyzing electrical behavior of HgCdTe photodiodes because the dynamic resistance at a given operating voltage directly governs the imager performance and being derivative of current–voltage (I–V) characteristics, it has little impact of the constant shifts due to stray illumination during dark measurements, relaxing the stringent requirement of perfect dark conditions to some extent for performance analysis. We have demonstrated that by using statistical analysis such as correlation of the selected signatures and their principal component analysis, we can identify the root cause of the high non-uniformity among sensor pixels in the array. The method has been implemented using theoretical I–V model of MWIR HgCdTe photodiodes, but it is generic and may be implemented on any other types of diode arrays for theoretical or experimental analysis of their non-uniformity.     

A New CMOS Read-out IC for Uncooled Microbolometer Infrared Image Sensor

An uncooled microbolometer image sensor, used in an IR image sensor, is made by a micro electro mechanical systems (MEMS) process, so the value of the microbolometer resistor has a process variation. Also, the reference resistor, which is used to connect to the microbolometer, is fabricated by a standard CMOS process, and the difference between the values of the microbolometer resistor and the reference resistor generates an unwanted output signal for the same input from the sensor array. In order to minimize this problem, a new CMOS read-out integrated circuit (ROIC) was designed. Instead of a single input mode, a differential input mode scheme and a simple method to compensate the resistor value are proposed. Using results from a computer simulation, it is observed that the output characteristic of the ROIC was improved and the effect of the process variation was decreased without using complex compensation circuits. Based on the simulation results, a prototype device including an ROIC that was fabricated by a standard 0.25um CMOS process and a microbolometer with a 16 x 16 sensor array was fabricated and characterized.     

A Nonlinear Electric Model of the Transient Photoelectric Current in an Organic Photodiode

One of the possible causes of the degradation of organic photodiodes is explained in terms of a nonlinear resistance–capacitance model. Electronic switches for switching photodiode parameters when light is turned on and off are used as nonlinear elements in the equivalent circuit. The model treats the photodiode as a spatially localized photovoltage generator loaded on a passive four-terminal device connected with the electrodes through passive interface layers. The presence of passive layers that have areas with oppositely directed built-in pulling electric fields is the main cause of the degradation of photodiode characteristics. The proposed equivalent circuit well reproduces the experimental transient and steady-state processes in organic photodiodes and can be useful both for measuring the electrical parameters of photodiodes and for studying the processes leading to their degradation.     

Simulation of laser beam induced current for HgCdTe photodiodes with leakage current

We report on 2D numerical simulations of laser beam induced current (LBIC) for HgCdTe photovoltaic detector. The effect of junction leakage current on LBIC signal is investigated, and different leakage paths caused by different reasons in HgCdTe photodiode arrays are taken into account in the simulation. The simulation results are in good agreement with the experiment data. Simulation results suggest that LBIC can be used to determine the existence of junction leakage current and investigate the origin of junction leakage current.     

Characterization and optimization of high-power InGaAs/InP photodiodes

The performance of 34-μm-diameter InGaAs/InP charge compensated modified uni-traveling carrier photodiodes (CC MUTCs) is studied using a commercial device simulator based on a drift-diffusion model. Excellent agreement has been achieved between simulations and experiments. The origin of the degradation of responsivity at high optical injection level is investigated. Parameters of the photodiode are further optimized to maximize the saturation current without sacrificing bandwidth and responsivity.     

In-situ electrical characterisation of a photodiode during nano-structuring with a focussed ion beam

We study the fabrication and power conversion efficiency of GaAs photodiodes, which have been nano-structured and covered with colloidal quantum dots. A focussed ion beam is used to etch vertical channels into the photodiodes and the detrimental effects of this treatment are characterised in-situ during the fabrication process. A novel experimental configuration allows the electrical characterization of the photodiodes under laser illumination during the nano-fabrication process and reveals the gradual decrease of the photodiodes’ shunt resistance with increasing laterally revealed surface along the etched channels. This is interpreted as evidence for leakage currents through redeposited material and surface states on the lateral channel surface. After the fabrication step the channels are filled with colloidal quantum dots, which upon absorption of light transfer electronic excitations to the photodiode via resonance energy transfer. It is found that after the addition of quantum dots the nano-structured photodiodes show larger enhancements of the energy conversion efficiency under simulated solar irradiance than the pristine photodiodes. Nevertheless, the device degradation induced by the ion beam treatment itself cannot be compensated for.     

An equivalent circuit model of a novel photodetector

An equivalent circuit model of a novel photodetector (PD) is proposed in this article. We use this model to describe the relation between the bias voltage and current (I–V), also the bias voltage and capacitance(C–V) of this kind of novel PD. The circuit model could optimize the structure of the circuit and could be linked with the readout circuit. According to the comparison between the simulation result and the experimental result by circuit testing, we could find they are in good agreement, which proving the correctness of the equivalent circuit model. The signification of this equivalent circuit model is to design an optimal readout circuit (ROIC) for the novel PD.     

用激光微细加工制作平面型InGaAs/InP PIN 光探测器

 采用激光微细加工技术来制作单片集成光接收机的探测器,在制作过程中,用固态杂质源10.6 μm激光诱导Zn扩散工艺来进行探测器的p-区掺杂。制作出平面型顶部入射的InGaAs/InP PIN 光探测器,响应度为0.21 A/W。分析了激光诱导扩散中影响探测器性能的因素,因此提出了扩散温度自动控制、扩散区温度分布均匀化及激光焦斑与扩散区精确对准等相应的改进方法。     

Study on the structural characteristics of HgCdTe photodiodes using laser beam-induced current

The structural characteristics of typical n⁺-on-p HgCdTe photodiodes have been studied by laser beam-induced current (LBIC). The dependence of LBIC on laser wavelength, junction depth and localized leakage has been presented. The diffusion length of minority carrier of p-type region is extracted by the exponential decay fitting of the curve of LBIC. It is found that the peak magnitude of LBIC and junction depth approximate to a linear relationship for practical values of device fabrication. The diffusion length monotonously increases with the junction depth. A notable shift of LBIC profile is observed when localized leakage exists. This provides a useful explain for LBIC applying to characterize the structure and process uniformity of HgCdTe infrared detectors.     

Ultralow-noise near-infrared detection system with a Si p-i-n photodiode

Noises associated with materials and devices in the readout circuits for a Si p-i-n photodiode have been measured. The dielectric polarization noise of the materials and devices near the gate circuit of the junction field-effect transistor used for the preamplifier determined the photodetection limits of photodiodes with a diameter smaller than several millimeters. We fabricated an ultralow-noise photodetection system, minimizing the polarization noise as much as possible. The readout noises of the system were 10 and 18 electrons in a correlated double sample for 0.1- and 1-mm-diameter Si p-i-n photodiodes at 77 K, respectively.     

Simplified model of dislocations as a SRH recombination channel in the HgCdTe heterostructures

A simple model of dislocation band formed by the dangling bonds of atoms of a dislocation core has been presented and discussed. The parameters of this model, which could be verified experimentally, are the average energy of the dislocation band states and the average length of the dislocation as well as electron and hole emission coefficients. The formulas for statistical functions of distribution of electrons in these bands have been derived. Next, we have developed a model of the SRH recombination channel connected with dislocation band states and we have adopted it to determine an effective lifetime of electron-hole pairs including effect of dislocations. In addition, influence of the tunnelling current from and into dislocation band has been considered, which seems to be a serious issue in reverse biased heterostructue HgCdTe photodiodes. Exemplary results of calculations for HgCdTe structures show that the number of the ionized atoms of the dislocation cores is of the order of a few percent. Moreover, the electric potential distributions in the area of the dislocation core has been calculated. Some experimental I-V characteristics of near room temperature HgCdTe devices are presented and compared with numerical simulations, what indicate on contribution of dislocations as a SRH recombination channel.     

单晶热释电探测器混合集成制造方法研究

在比较几种探测器集成制造方法的基础上,提出采用各向异性导电膜作为电信号互联的手段,实现热释电探测器与信号处理电路的混合集成,从而演示了一种兼容性良好的集成化多传感器制造方法.对单晶钽酸锂热释电探测器采取机械研磨减薄获得其薄膜,利用3M的5552R各向异性导电膜,实现了探测器与信号读出电路的互联.对探测器的测试表明:机械研磨减薄获得的钽酸锂薄膜表现出与晶体接近的热释电特性,探测器表现出良好的绝热性质和动态响应特性.     

High-speed CMOS readout integrated circuit for large-scale and high-resolution microbolometer array

A new CMOS readout integrated circuit (ROIC) for microbolometric focal plane array (FPA) is proposed in this paper. By applying multiple-module parallel working technique, the pixel readout speed of the CMOS ROIC can reach 10 MHz, which is very suitable for large-scale microbolometer array. The CMOS ROIC of each parallel working module consists of three major parts: direct injection (DI) input circuits, column-shared integrating circuits, and common noise-suppressing circuits. The readout structure of the ROIC is simple because of the DI input, shared and common circuits, and this makes the ROIC satisfy the requirements of small-pixel microbolometric FPA. Furthermore, the voltage signals from different working modules can be output according to a certain order through a high-speed output circuit. An experimental readout chip based on the proposed ROIC has been designed and fabricated to verify its readout function and performance. The measurement results of the experimental readout chip have successfully proved that the proposed CMOS ROIC can be applied to high-speed, low-noise, large-scale and high-resolution microbolometric FPA.     

Modeling of dark characteristics for long-wavelength HgCdTe photodiode

A data-processing approach has been developed to obtain device parameters from resistance–voltage (R–V) characteristics measured on long-wavelength HgCdTe n-on-p photodiodes. A simple carrier density approximation is proposed to take account of carrier degeneracy and conduction band non-parabolicity into its physical model. Some basic parameters and their estimated errors can be extracted from the measured R–V curves. The method is applied to fit the R–V curves measured at different temperatures. We also analyze larger amount of long-wavelength HgCdTe n-on-p photodiodes, and obtain statistical device parameters.     

基于MOS电阻阵列的红外目标模拟器非均匀性校正技术研究

红外成像目标模拟器是红外成像半实物仿真系统中的关键组成部分,基于微机械技术发展起来的MOS电阻阵列是红外图像生成器的重要发展方向。其中红外图像生成的质量是设计和研制红外成像目标模拟系统需重点考虑的问题。多种原因导致电阻阵列具有一定的非均匀性,因此在使用之前必须对其进行非均匀性校正。结合实际应用,阐述了基于MOS电阻阵列的红外成像目标模拟器的非均匀性产生机理,建立红外目标模拟器的非均匀性修正数据库对红外目标模拟器的图像数据源进行校正和补偿,产生校正后的图像数据,完成对红外目标模拟器存在非均匀性的离线修正。     

绝缘栅型双极晶体管串联匀压并联匀流模拟分析

 绝缘栅型双极晶体管(IGBT)采用串联和并联方法构成大功率开关组件能够有效提高工作电压和电流,是实现开关重频高功率应用的主要技术途径,同时也存在着动、静态的匀压、匀流问题。从电路层面详细分析了IGBT串并联运行时导致电压、电流不均衡的主要原因及其表现,研究了动静态不均衡的发展过程及其影响因素,针对性地提出了电阻/电容/二极管（RCD）缓冲网络及电流平衡变压器等匀压、匀流措施,解析推导出了IGBT串、并联模块的设计判据,建立了相应的等效电路模型,对所提出的解决方案进行了仿真验证。仿真模拟结果表明,所提出的方法是可行可靠的。     

Hydrodynamic simulation of electron transport in n-type Hg<Subscript>0.8</Subscript>Cd<Subscript>0.2</Subscript>Te

A hydrodynamic approach based on concentration, velocity and energy conservation equations is developed and used for the simulation of the electron transport in bulk HgCdTe. Both transient and steady-state regimes are simulated using input parameters calculated with a Monte Carlo simulator. The model is validated through a comparison in excellent agreement with Monte Carlo results.     

离散电阻加载的大型垂直极化EMP辐射波模拟器的并行FDTD模拟

将电阻设置为跨网格有耗介质，进行离散电阻加载的大型垂直极化电磁脉冲（EMP）辐射波模拟器时域场的并行FDTD模拟.给出不同离散电阻加载方式下模拟器辐射场的时域波形，分析离散电阻加载对模拟器辐射场的影响，并给出离散电阻加载的模拟器有圆筒效应物时的时域波形.结果表明：电阻加载能有效减小模拟器顶端的电流反射，从而改善辐射场的时域波形，但电阻加载也可能会导致模拟器辐射性能的降低；当效应物开孔所在的侧面靠近模拟器且与模拟器极化方向平行时耦合进入圆筒内的电磁波能量较多.计算方法具有通用性，可用于进行离散电阻加载的其它大型垂直极化EMP辐射波模拟器时域场的模拟，包括导电地面存在且有效应物存在时的时域耦合场的模拟.