IR FPA Research Articles

Method for Evaluation of the Shape and Dimensions of a Photosensitive Element of an IR FPA

Method for Evaluation of the Shape and Dimensions of a Photosensitive Element of an IR FPA

Photoelectric Characteristics of Multielement Photodiode-Based IR FPAs by the Monte Carlo Method on Epitaxial HgCdTe Films

The calculations of photocharacteristics, such as spatial resolution, threshold sensitivity with photosensitive elements sized from 5 µm × 5 µm to 20 µm × 20 µm under uniform illumination, for multielement IR FPAs and also for point objects are presented. The obtained results are based on the simulation of a three-dimensional diffusion process of photo-excited minority charge carriers in the photosensitive layer of photodiode elements by the Monte Carlo method. Numeric estimates are presented for IR FPAs based on photodiodes for epitaxial HgCdTe films, but the model is applicable for the calculations of photoelectric characteristics for photodiodes on other substrates. The requirements for the main photoelectric and design parameters of photosensitive elements and optical system (spot diameter from a point source), which provide reaching IR FPA maximal sensitivity and spatial resolution values, are formulated.

A Self-Test Method of Structural Failures of Uncooled Infrared Focal Plane Array

Defective pixels always exist in an uncooled infrared focal plane array (IR FPA), and have a significant impact on image quality. To fundamentally reduce defective pixels and improve IR FPA's reliability, failure analysis (FA) is critically needed. In this work, a self-test (ST) method is proposed to detect the structural failures of uncooled IR FPA. Based on the lumped thermal parameters of a pixel, a structural failures model is presented, and an electrical circuit is designed. The insufficient released, normal released, over released and contaminated IR FPAs are measured. The measured results show that their lumped thermal parameters have a clear differentiation, which not only experimentally verifies the validity of this method, but also shows that it is an effective method for nondestructive analysis of structural failures.

Photodiodes based on p-on-n junctions formed in MBE-grown n-type MCT absorber layers for the spectral region 8 to 11 μm

Results of measurement of the dark currents and photocurrents of p-on-n photodiodes (PD) formed in In-doped MBE-grown n-type mercury cadmium telluride (MCT) films are reported. We used 3 in. in diameter (0 1 3) GaAs and (0 1 3) Si substrates. The p-on-n junctions were fabricated using the implantation of As+ ions followed by the thermal annealing activation. It was shown that the regime of background-limited performance (BLIP) of the p-on-n PD with experimentally measured long-wave cutoff wavelength (LW) cutoff (λc) of 11.1 and 10.3 μm at 77 K is observed up to elevated temperatures of 105 K and 117 K, respectively. The temperature dependence of the noise equivalent temperature difference (NETD) for p-on-n PD sized 30 × 30 μm was calculated taking into account only PD shot noise. It was shown that such LW p-on-n photodiodes allows to increase the operating temperature of IR FPA detectors up to 100–105 K with the NETD less than 30 mK.

Extension of the Dynamic Range of Short-Wavelength IR FPAs

Necessity of extension of the dynamic range of short-wavelength IR FPAs is substantiated. Conventional methods exhibit low efficiency, especially, in large-scale arrays with a pitch of no greater 15 μm. Integrating cells with individually tunable transfer function depending on the fragment brightness have the maximum efficiency with respect to the extension of the dynamic range (up to 100 dB). A simple (in topological implementation) and efficient method is proposed for extension of the dynamic range. The method is based on the individual self-tuning of integration time in each cell of the readout integrated circuit. Relatively high steepness and conversion linearity are maintained in integrating cells under moderate irradiation (up to 50–70% of the maximum signal) but the sensitivity is decreased in the cells that are close to saturation. The resulting linear–logarithmic transfer function provides extension of the dynamic range. Examples of images obtained with the extended dynamic range in the short-wavelength IR spectrum are presented.

Simulation of the Spatial Distribution of the Local Quantum Efficiency and Photoelectric Characteristics of Photodiode-Based Infrared Focal Plane Arrays

The results of calculation of the spatial distribution of the local quantum efficiency over the area of photodiode-based IR focal plane arrays (IR FPA) are presented. The diffusion of photogenerated charge carriers in the absorber layer of the array was calculated by Monte-Carlo simulation. Methods of reducing the amount of necessary calculations based on using the symmetry properties of the array are discussed. Requirements for the photoelectric and design parameters (absorber-layer thickness, chargecarrier diffusion length and optical absorption length in this layer, the ratio of the size of n–p junctions to the geometrical dimensions of the detector pixels) are formulated that ensure the threshold sensitivity and spatial resolution of IR FPAs.

Advanced Design of Scanning Infrared Focal Plane Arrays

Modern designs of time delay and integration (TDI) IR linear scanning focal plane arrays (IR FPAs) are analyzed. Advanced designs of linear IR FPAs with increased sensitivity and spatial resolution are proposed. The analysis is based on Monte-Carlo simulation of the diffusion of photogenerated charge carriers in photodiode arrays based on mercury–cadmium–telluride epitaxial layers taking into account the main photoelectric and design parameters of the detectors and optical system.

Solid-immersion metalenses for infrared focal plane arrays

Optical components based on metasurfaces (metalenses) offer an alternative methodology for microlens arrays. In particular, metalens arrays have the potential of being monolithically integrated with infrared focal plane arrays (IR FPAs) to increase the operating temperature and sensitivity of the latter. In this work, we demonstrate a type of transmissive metalens that focuses the incident light (λ = 3–5 μm) on the detector plane after propagating through the substrate, i.e., solid-immersion type of focusing. The metalens is fabricated by etching the backside of the detector substrate material (GaSb here), making this approach compatible with the architecture of back-illuminated FPAs. In addition, our designs work for all incident polarizations. We fabricate a 10 × 10 metalens array that proves the scalability of this approach for FPAs. In the future, these solid-immersion metalenses arrays will be monolithically integrated with IR FPAs.

MTF measurements of a type-II superlattice infrared focal plane array sealed in a cryocooler

In operational electro-optical systems, infrared focal plane arrays (IR FPA) are integrated in cryocoolers which induce vibrations that may strongly affect their modulation transfer function (MTF). In this paper, we present the MTF measurement of an IR FPA sealed in its cryocooler. The method we use to measure the MTF decorrelates operational constraints and the technological limitations of the IR FPA. The bench is based on the diffraction properties of a continuously self imaging grating (CSIG). The 26 µm pixel size extracted from the MTF measurement is in good agreement with the expected value.

Monte Carlo Simulation of Photoelectric Characteristics of Mercury-Cadmium-Tellurium- Based Infrared Focal-Plane-Array Detectors

A mathematical model was developed to enable the Monte Carlo analysis of the charge-carrier diffusion process in the absorber layer of mercury–cadmium–tellurium (MCT) photovoltaic infrared focal-plane-array (IR FPA) detectors. Using this model, the distribution of local internal quantum efficiency $\eta $ of FPA elements over the FPA area was calculated. Afterward, the integral quantum efficiency of arbitrarily illuminated FPAs was determined via convolution of the obtained distribution of $\eta $ with illumination intensity. Following such calculations, some requirements to photoelectric properties of MCT material, and some suggestions on design optimization of FPA elements, allowing one to improve the sensitivity and spatial resolution of IR FPA detectors, were formulated.

Моделирование фотоэлектрических характеристик матричных ИК фотоприемников методом Монте-Карло

Моделирование фотоэлектрических характеристик матричных ИК фотоприемников методом Монте-Карло

Relative performance analysis of IR FPA technologies from the perspective of system level performance

The majority of high performance infrared systems today utilize FPAs composed of intrinsic direct bandgap semiconductor photon detectors such as MCT or InSb. Quantum well detector technologies such as QWIPs, QDIPs, and SLS photodetectors are potentially lower cost alternatives to MCT and InSb, but the relative performance of these technologies has not been sufficiently high to allow widespread adoption outside of a handful of applications. While detectors are often evaluated using figures of merit such as NETD or D∗, these metrics, which include many underlying aspects such as spectral quantum efficiency, dark current, well size, MTF, and array response uniformity, may be far removed from the performance metrics used to judge performance of a system in an operationally relevant scenario. True comparisons of performance for various detector technologies from the perspective of end-to-end system performance have rarely been conducted, especially considering the rapid progress of the newer quantum well technologies.System level models such as the US Army’s Night Vision Integrated Performance Model (NV-IPM) can calculate image contrast and spatial frequency content using data from the target/background, intervening atmosphere, and system components. This paper includes results from a performance parameter sensitivity analysis using NV-IPM to determine the relative importance of various FPA performance parameters to the overall performance of a long range imaging system. Parameters included are: QE, dark current density, quantum well capacity, downstream readout noise, well fill, image frame rate, frame averaging, and residual fixed pattern noise. The state-of-the art for XBn, QWIP, and SLS detector technologies operating in the MWIR and LWIR bands will be surveyed to assess performance of quantum structures compared to MCT and InSb. The intent is to provide a comprehensive assessment of quantum detector performance and to identify areas where increased research could provide the most benefit to overall system level performance.

Development of analog-digital readout integrated circuits for infrared focal plane arrays

This paper describes the design of readout integrated circuits (ROICs) for hybrid infrared focal plane arrays (IR FPAs). This work contains the estimation of the noise equivalent temperature difference (NETD) of IR FPAs based on frame and row integration of pixel signals in the spectral ranges of 8 to 14 and 3 to 5 μm. This paper also describes the development of ROICs for IR FPAs created with the use of mercury—cadmium—telluride (MCT) photodiodes and quantum well infrared photodetectors (QWIPs). The designed ROICs ensure the use of matrix and linear photodetector chips, including those with increased dark currents, in order to produce IR FPAs with temperature resolution corresponding to the world level of array analogs.

集成式光读出FPA红外成像系统设计

集成式光读出FPA红外成像系统设计

Analysis of charge-carrier diffusion in the photosensing films of HgCdTe infrared focal plane array photodetectors

The lateral diffusion of minority charge carriers in the photosensitive films of photovoltaic HgCdTe infrared focal plane array (IR FPA) detectors with a continuous (without mesa insulation of the diodes) absorber layer was experimentally studied and analyzed. The experimental study was performed using the spot-scan technique, implemented by scanning a narrow strip-shaped illumination spot with a selected FPA diode at various levels of diode photocurrents in the detector. The local diffusion lengths of the charge carriers in the film regions beneath and outside the FPA diodes were estimated. The values obtained for the bulk diffusion length of minority carriers in the HgCdTe material of the examined middle-wave and long-wave IR FPA detectors were found to be in good agreement with previously reported data. Moreover, the estimated local diffusion length of minority carriers in the film region beneath the back-biased photodiodes proved to be consistent with a theoretical estimate of this length.

New frontiers for infrared

ÀbstractInfrared (IR) science and technology has been mainly dedicated to surveillance and security: since the 70’s specialized techniques have been emerging in thermal imaging for medical and cultural heritage diagnostics, building and aeronautics structures control, energy savings and remote sensing. Most of these applications were developed thanks to IR FPAs sensors with high numbers of pixels and, actually, working at room temperatures. Besides these technological achievements in sensors/ receivers, advanced developments of IR laser sources up to far IR bands have been achieved in the form QCL (quantum cascade laser), allowing wide band TLC and high sensitivity systems for security. recently new sensors and sources with improved performances are emerging in the very far IR region up to submillimeter wavelengths, the so called terahertz (THz) region.A survey of the historical growth and a forecast of the future developments in Devices and Systems for the new frontier of IR will be discussed, in particular for the key questions: “From where and when is IR coming?”, “Where is it now?” and “Where will it go and when?”. These questions will be treated for key systems (Military/Civil), key devices (Sensors/ Sources), and new strategic technologies (Nanotech/TeraHertz).

Self-align method for improving sensitivity and resolution of infrared focal plane array

In this Letter, it is discussed whether a non-self-align process based on microelectronics technology causes the alignment error (AE) between two material layers in a gold–silicon nitride (Au–SiN) bi-material uncooled optic readout infrared focal plane array (UOR IR FPA). That the AE reduces sensitivity of the FPA and causes extra noise to the FPA is analysed. A self-align method including both process and pattern design, related to an aluminium–silicon nitride (Al–SiN) bi-material UOR IR FPA, is proposed. The method effectively eliminates the AE. As a result, the measured value of thermomechanical response of an Al–SiN pixel is closer to the design value in comparison with the Au–SiN FPA fabricated by the non-self-align process. The measured value of the thermomechanical response of an Al–SiN pixel is 3.73 × 10−3 rad/°C and is 3.3 times as large as that of the Au–SiN FPA. Thus, the sensitivity of the FPA is improved. There is also no the extra noise. In addition, without the AE, a certain amount of alignment distance is not required while designing the FPA patterns. Therefore it is possible to improve the resolution of the FPA through increasing the quantity of pixels for a given FPA size.

Size, weight, and power reduction of mercury cadmium telluride infrared detection modules

Application requirements driving present IR technology development activities are improved capability to detect and identify a threat as well as the need to reduce size weight and power consumption (SWaP) of thermal sights. In addition to the development of 3rd Gen IR modules providing dual-band or dual-color capability, AIM is focused on IR FPAs with reduced pitch and high operating temperature for SWaP reduction. State-of-the-art MCT technology allows AIM the production of mid-wave infrared (MWIR) detectors operating at temperatures exceeding 120 K without any need to sacrifice the 5-μm cut-off wavelength. These FPAs allow manufacturing of low cost IR modules with minimum size, weight, and power for state-of-the-art high performance IR systems. AIM has realized full TV format MCT 640×512 mid-wave and long-wave IR detection modules with a 15-μm pitch to meet the requirements of critical military applications like thermal weapon sights or thermal imagers in unmanned aerial vehicles applications. In typical configurations like an F/4.6 cold shield for the 640×512 MWIR module an noise equivalent temperature difference (NETD) <25 mK @ 5 ms integration time is achieved, while the long-wavelength infrared (LWIR) modules achieve an NETD <38 mK @ F/2 and 180 μs integration time. For the LWIR modules, FPAs with a cut-off up to 10 μm have been realized. The modules are available either with different integral rotary cooler configurations for portable applications that require minimum cooling power or a new split linear cooler providing long lifetime with a mean time to failure (MTTF) > 20000, e.g., for warning sensors in 24/7 operation. The modules are available with optional image processing electronics providing nonuniformity correction and further image processing for a complete IR imaging solution. The latest results and performance of those modules and their applications are presented.

Infrared photodetectors based on the system “Hg1−xCdxTe photodiode — direct-injection readout circuit”

AbstractA mathematical model for multi-element IR FPAs based on Hg1−xCdxTe photodiodes with direct-injection readout circuits is developed. This model was used to identify the main factors that limit the performance characteristics of thermography systems based on such FPAs.

320×256 HgCdTe IR FPA with a built-in shortwave cut-off filter

A photovoltaic detector design based on the graded band gap HgCdTe MBE structure with high conductivity layer (HCL) at interface, which provides photodiodes series resistance and a shortwave cut.off filter is developed. The optimal HCL parameters giving high quantum efficiency and minimal noise equivalent temperature difference were determined by calculations and experimentally confirmed. The hybrid 320×256 IR FPA operating in 8–12 μm spectral range was fabricated. The threshold power responsivity and minimal noise equivalent temperature difference values at wavelength maximum were 1.02×10−7 W/cm2, 4.1×108 V/W and 27 mK, respectively.