This PDF file contains the front matter associated with SPIE Proceedings Volume 7660, including the Title Page, Copyright information, Table of Contents, the Conference Committee listing and introduction.

This paper presents a soft-real time simulator for IRST (InfraRed Search and Track) systems with ATR (Automatic Target Recognition) embedded functions to test airborne applications performance. The IR camera model includes detector, optics, available Field-of-Regard, etc., and it is integrated with the motion platform local stabilization system to consider all factors impacting IR images. The atmosphere contributions are taken into account by means of a link to ModTran computer program. Sensor simulation allows derivation and assessment of IR Figures of Merit (NEI, NETD, SNR...). IR signatures of targets derive both from data collected in specific trial campaigns and from laboratory built models. The simulation of the scan procedure takes into account different policies (ground points paths or defined angular volume) and different platform motion strategies (continuous or step steering scan). The scan process includes Kalman technique to face unexpected variations of aircraft motion. Track and ATR processors are simulated and run consistently on the output of the sensor model. The simulator functions are developed in MatLab and SIMULINK and then exported in C code to be integrated in soft real-time environment. The use of this simulator supports the definition and design of the IRST systems especially for the evaluation of the most demanding operative requirements. An application of this simulator is for the NEURON UCAV (Unmanned Combat Air Vehicle) technological demonstrator, which accommodates on board both IRST and ATR tasks.

Modern warships ranging from Air Warfare Destroyers to Offshore Patrol Vessels (OPV) and Fast Patrol Boats have to deal with an ever increasing variety of threats, both symmetric and asymmetric, for self-protection. This last category has introduced new requirements for combat systems sensors and effectors: situation awareness in proximity of the own ship has become a priority, as well as the need for new, lethal or non-lethal effectors for timely and proportional response. Naval Combat Systems (CS) architects are then faced with an alternative: they can either use existing CS sensors, C2 and weapons, or else rely on new, specialized equipments. Both approaches have their pros and cons, with the cost issue not necessarily trivial to assess. In this paper, we present a multifunction system that is both a passive IRST (InfraRed Search and Track) sensor, designed to automatically detect and track air and surface threats, and an Electro Optical Director (EOD), capable of providing identification of objects as well as accurate 3D tracks. Following an introduction reviewing the design goals for the equipment, the EOMS NG processing architecture is described (Image & Tracking Processes). Then, system performances are presented for different scenarios provided from Field Tests.

A high-resolution mid-wave infrared panoramic periscope sensor system has been developed. The sensor includes a catadioptric optical system that provides a 360° horizontal azimuth by -10° to +30° elevation field of view without requiring moving components (e.g. rotating mirrors). The focal plane is a 2048 x 2048, 15μm pitch InSb detector operating at 80K. An on-board thermo-electric reference source allows for real-time nonuniformity correction using the two-point correction method. The entire system (detector-dewar assembly, cooler, electronics and optics) is packaged to fit in an 8" high, 6.5" diameter volume. This work describes both the system optics and electronics and presents sample imagery. We also discuss the sensor's radiometric performance, quantified by the NEDT, as a function of key system parameters. The ability of the system to resolve targets as a function of imaged spatial frequency is also presented.

Dealing with military and asymmetric threats represents a key issue for any military vessel in various environment. In order to support ship's self protection, Thales has designed a new generation of naval InfraRed Search and Track (IRST) called ARTEMIS. It has been selected to equip Future European Multi Roles Frigates (FREMM). ARTEMIS is a fully new passive staring IRST system capable of automatically detecting and tracking both air and surface targets simultaneously. It is able to detect and track maneuvering and stealthy new threats as well as surface asymmetric threats. The paper describes the novelties of the ARTEMIS staring architecture and some of its technologies. It describes also the advantages offered by this new concept of electro-optical surveillance with full static sensor heads compared to existing and future solutions, and its capabilities to comply with future integrated masts standards. The paper concludes by a presentation of the product for the French Navy.

Modern naval warfare asks for alerting system able to detect classical & asymmetric threats in support to radar in environment in which radar has reduced performance (on or near the sea surface). More, capability to offer high resolution images helps in ship identification, coastal & harbor surveillance as well as night navigation and rescue. All these tasks can be performed by an infrared search and track (IRST) system. This paper describes the IRST named Silent Acquisition and Surveillance System (SASS), developed for the Italian Navy and the tests jointly carried out by SELEX GALILEO and Italian Navy to characterize the system.

We present image data and discuss naval sensing applications of SWIR and Hyperspectral SWIR imaging in littoral and marine environments under various light conditions. These environments prove to be challenging for persistent surveillance applications as light levels may vary over several orders of magnitude within and from scene to scene. Additional difficulties include imaging over long water paths where marine haze and turbulence tend to degrade radiation transmission, and discrimination of low contrast objects under low-light and night imaging. Image data obtained from two separate passive sensor systems, both of which are built around an RVS large format (1280 x 1024) InGaAs FPA with high dynamic range and low noise electronics, are presented. The SWIR camera imager is equipped with a custom 300 mm focal length f/2 narrow field-of-view (6° diagonal) refractive telescope. The Hyperspectral imager has a custom selectable 900/1800 mm focal length telescope with corresponding 1.55°/0.79° field-of-view and fnumbers of 3/6 respectively. The sensor uses 1280 pixels in the spatial direction and a window of 192 are used for the spectral and operates at a nominal frame rate of 120 Hz. To assess field performance of the SWIR/Hyperspectral imagers, comparison is made to output from a scientific grade VNIR camera and two state-of-the-art low-light sensors.

In the maritime environment, It is necessary for ship's self protection to search ad track approaching targets. We developed high performance search and tracking system with Infrared sensors. Our system can obtain high performance with several FPGAs and COTS processing boards. Dual band IR sensor (MWIR and LWIR) also gives two types of target detection and tracing abilities. Our system designed to automatically detect and track both air and surface targets such as sea skimming missiles, small ships, and aircrafts at a long range. In this paper, we describe technologies in our search and tracking system architecture. We describe software architecture for signal processing and target detection and tracking algorithms as well.

The new PUMA tank is equipped with a fully stabilized 360° periscope. The thermal imager in the periscope is identical to the imager in the gunner sight. All optronic images of the cameras can be fed on every electronic display within the tank. The thermal imagers operate with a long wave 384x288 MCT starring focal plane array. The high quantum efficiency of MCT provides low NETD values at short integration times. The thermal imager has an image resolution of 768x576 pixels by means of a micro scanner. The MCT detector operates at high temperatures above 75K with high stability in noise and correctibility and offers high reliability (MTTF) values for the complete camera in a very compact design. The paper discusses the principle and functionality of the optronic combination of direct view optical channel, thermal imager and visible camera and discusses in detail the performances of the subcomponents with respect to demands for new tank applications.

The paper describes a Mid-wave Infrared (MWIR) Panoramic Sensor using existing focal plane array (FPA) technologies and commercially available IR optics, and packaged in a relatively simple and rugged manner to provide a 360° azimuth and 60° elevation field-of-view (FOV) coverage, without any scanning mirror. This sensor can be deployed for initial target tracking, situational awareness, perimeter security, and other applications. The basic performance and parameters of the Sensor, such as mechanical, electrical interfaces, optical parameters, etc. are also included. Some basic sensor performance analysis (such as target signal-to-noise ratio verses range and background level), and field testing results are also presented and compared for some simple levels of processing.

The advent of uncooled infrared, XGA (1024×768) focal plane arrays (FPAs) enables new applications for ground vehicles and soldier equipment. A low-power digital imaging module, based on a 17μm-pitch FPA, has been developed and packaged in a rugged housing for demonstration in a distributed aperture system. Cameras and the embedded thermal imaging modules have been delivered during 2009 and the module will be commercially available in 2010. This new capability can extend the performance of existing uncooled ground-based systems. Some background is presented. The product is described and several applications are introduced.

The night sight clip on module based on uncooled infrared detector technology was designed around an infrared camera module. This camera module uses an uncooled 640 x 480 detector and has a highly integrated electronic. The night sight clip on module has a magnification of exactly one and a precisely pre-aligned line of sight with respect input to output. The module is designed to be used in front of a standard day sight telescopic aiming optic on an assault rifle. The sophisticated optical design of the clip on module eliminates the need of a realignment of the day sight optic when the module is placed in front of it. Also there is no need for a precise placement or angular alignment of the module in front of the day sight aiming telescope. The signal of the IR camera is displayed on a small monitor. This picture is then collimated to infinity and used as the input for the daysight telescope. The rifleman sees in the eyepiece of his telescopic daysight an infrared image of the scene. The magnification is done by the setting of his telescope. The aiming reticle is still the one from the day scope. The optical design of the night sight clip on module and the electronic block diagram will be presented.

The Trijicon ATWS is a high performance, lightweight, compact clip on thermal sight for use with the TA31RCO ACOG® weapon sight. FLIR Systems partnered with Trijicon to develop this sight using the Photon 640 imaging core. This paper will discuss the features and performance of the ATWS and describe some of the design challenges associated with this type of device.

Infrared Search and Track (IRST), Missile Warning Systems (MWS) and other optical target detection systems have established solutions in the MWIR, UV and LWIR bands. Imaging technology in the SWIR optical band which has small Size, Weight and Power (SWAP) has been recently added as detection means. We bring an update on recent field trials and demonstrations of Optigo's gun shot detection modules. We then provide some more insight into the advantages of using the SWIR band, and specifically InGaAs detectors for the typical HFI missions. We conclude by demonstrating that detection systems operating in the SWIR band can significantly improve their performance when the cutoff wavelength approaches longer edge of SWIR.

Oceanit Laboratories Inc. is collaborating with Raytheon Vision Systems (RVS) to develop a novel HgCdTe-based position sensitive detector (PSD) that can ultimately be implemented in target detection and tracking or target interception applications in the infrared spectral region.

The US Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC) is developing a micro-uncooled infrared (IR) capability for small unmanned aerial systems (SUAS). In 2007, AMRDEC procured several uncooled microbolometers for lab and field test evaluations, and static tower tests involving specific target sets confirmed initial modeling and simulation predictions. With these promising results, AMRDEC procured two captive flight test (CFT) vehicles and, in 2008, completed numerous captive flights to capture imagery with the micro-uncooled infrared sensors. Several test configurations were used to build a comprehensive data set. These configurations included variations in look-down angles, fields of view (FOV), environments, altitudes, and target scenarios. Data collected during these field tests is also being used to develop human tracking algorithms and image stabilization software by other AMRDEC personnel. Details of these ongoing efforts will be presented in this paper and will include: 1) onboard digital data recording capabilities; 2) analog data links for visual verification of imagery; 3) sensor packaging and design; which include both infrared and visible cameras; 4) field test and data collection results; 5) future plans; 6) potential applications. Finally, AMRDEC has recently acquired a 17 μm pitch detector array. The paper will include plans to test both 17 μm and 25 μm microbolometer technologies simultaneously in a side-by-side captive flight comparison.

Military applications for conventional InGaAs SWIR sensing have been limited by the requirement of thermoelectric cooler (TEC) temperature stabilization for nonuniformity correction (NUC). TEC operation restricts the operating temperature range and size, weight, and power (SWAP) of these systems. For battery-powered man portable and micro UAV applications elimination of the TEC is critical. This paper discusses the advantages of our non-TEC temperature parameterized NUC corrections algorithms versus TEC stabilized architectures. The corrections algorithms enable performance-tuned polynomial order correction of both pixel uniformity and temperature parameterization for each SWIR sensor. These advances enable SWIR InGaAs sensing to meet the SWAP requirements of next generation military applications.

Short wavelength IR imaging using InGaAs-based FPAs is shown. Aerius demonstrates low dark current in InGaAs detector arrays with 15 μm pixel pitch. The same material is mated with a 640x 512 CTIA-based readout integrated circuit. The resulting FPA is capable of imaging photon fluxes with wavelengths between 1 and 1.6 microns at low light levels. The mean dark current density on the FPAs is extremely low at 0.64 nA/cm² at 10°C. Noise due to the readout can be reduced from 95 to 57 electrons by using off-chip correlated double sampling (CDS). In addition, Aerius has developed laser arrays that provide flat illumination in scenes that are normally light-starved. The illuminators have 40% wall-plug efficiency and provide speckle-free illumination, provide artifact-free imagery versus conventional laser illuminators.

SiGe based focal plane arrays offer a low cost alternative for developing visible- near-infrared focal plane arrays that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based foal plane arrays take advantage of silicon based technology that promises small feature size, low dark current and compatibility with the low power silicon CMOS circuits for signal processing. This paper will discuss performance characteristics for the SiGe based VIS-NIR Sensors for a variety of defense and commercial applications using small unit cell size and compare performance with InGaAs, InSb, and HgCdTe IRFPA's. We will present results on the approach and device design for reducing the dark current in SiGe detector arrays. We will discuss electrical and optical properties of SiGe arrays at room temperature and as a function of temperature. We will also discuss future integration path for SiGe devices with Si-MEMS Bolometers.

Visible-band cameras using silicon imagers provide excellent video under daylight conditions, but become blind at night. The night sky provides illumination from 1-2 μm which cannot be detected with a silicon sensor. Adding short-wave infrared detectors to a CMOS imager would enable a camera which can be used day or night. A germanium-enhanced CMOS imager (TriWave®) has been developed with broadband sensitivity from 0.4 μm to 1.6 μm. A 744 x 576 format imager with 10 μm pixel pitch provides a large field of view without incurring a size and weight penalty in the optics. The small pixel size is achieved by integrating a germanium photodetector into a mainstream CMOS process. A sensitive analog signal chain provides a noise floor of 5 electrons. The imagers are hermetically packaged with a thermo-electric cooler in a windowed metal package 5 cm³ in volume. A compact (<650 cm³) camera core has been designed around the imager. Camera functions implemented include correlated double sampling, dark frame subtraction and non-uniformity corrections. In field tests, videos recorded with different filters in daylight show useful fog and haze penetration over long distances. Under clear moonless conditions, short-wave infrared (SWIR) images recorded with TriWave make visible individuals that cannot be seen in videos recorded simultaneously using an EMCCD. Band-filtered videos confirm that the night-sky illumination is dominated by wavelengths above 1200 nm.

SiOnyx has developed a novel silicon processing technology for CMOS sensors that will extend spectral sensitivity into the near/shortwave infrared (NIR/SWIR) and enable a full performance digital night vision capability comparable to that of current image-intensifier based night vision goggles. The process is compatible with established CMOS manufacturing infrastructure and has the promise of much lower cost than competing approaches. The measured thin layer quantum efficiency is as much as 10x that of incumbent imaging sensors with spectral sensitivity from 400 to 1200 nm.

We present the performance of a CMOS image sensor optimized for next generation fused day/night vision systems. The device features 5T pixels with pinned photodiodes on a 6.5μm pitch with integrated micro-lens. The 5T pixel architecture enables both correlated double sampling (CDS) to reduce noise for night time operation, and a lateral antiblooming drain for day time operation. The measured peak quantum efficiency of the sensor is above 55% at 600nm, and the median read noise is less than 1e- RMS at room temperature. The sensor features dual gain 11-bit data output ports and supports 30 fps and 60 fps. The full well capacity is greater than 30ke-, the dark current is less than 3.8pA/cm² at 20ºC, and the MTF at 77 lp/mm is 0.4 at 550nm. The sensor also achieves an intra-scene linear dynamic range of greater than 90dB (30000:1) for night time operation, and an inter-scene linear dynamic range of greater than 150dB for complete day/night operability.

This paper presents our research and development efforts in realizing and perfecting organic/inorganic photon upconversion devices for wavelengths from near infrared (1.5 μm) region to visible light (green). The basic idea is to integrate an InGaAs/InP photodetector with an organic light emitting diode (OLED), connected in series. The detected photocurrent drives the OLED to emit visible light, thereby achieving the wavelength conversion. We have adopted new strategies to improve the external device efficiency, including insertion of an embedded mirror and integration of a heterojunction phototransistor (HPT) and an OLED. As a result, infrared optical upconversion is demonstrated at room temperature with a built-in electrical gain of 15 from the HPT and an external upconversion efficiency that is improved by one order of magnitude.

The photocurrent of High Density Vertically Integrated Photodiodes (HDVIP) manufactured in LPE grown SWIR (λc ~ 2.5 μm) HgCdTe material is modeled as a function of incident spot location using a Monte Carlo diffusion calculation in the p-type bulk. The Monte Carlo calculation assumes a 3 x 3 mini-array of detectors surrounded by guard detectors. Carriers generated in the n-regions are always collected. The result is a responsivity map that yields the individual detector "spot scan" profile that is then used to calculate the detector modulation transfer function (MTF). Fourier transforms of detector "spot scan" response profile provided experimental confirmation of MTF that corresponded to the Monte Carlo modeled MTF.

Recent developments in low-noise, high temperature coefficient of resistance (TCR) amorphous silicon and amorphous silicon germanium material have led to the development of uncooled focal plane arrays, with TCR in the range 3.2%/K to 3.9%/K, which has been leveraged in the small pixel FPA development at L-3 EOS. In the 17μm pixel technology node at present, 1024x768, 640×480, and 320x240 FPAs have thus far been developed. All three formats employ waferlevel vacuum packaging, with the 1024x768 representing the largest format uncooled FPA wafer-level packaged to date. FPA results from all three formats will be discussed and images will be presented.

This paper presents an advanced 640 x 480 (VGA) IRFPA based on uncooled microbolometers with a pixel-pitch of 25μm developed by Fraunhofer-IMS. The IRFPA is designed for thermal imaging applications in the LWIR (8 .. 14μm) range with a full-frame frequency of 30 Hz and a high sensitivity with NETD < 100 mK @ f/1. A novel readout architecture which utilizes massively parallel on-chip Sigma-Delta-ADCs located under the microbolometer array results in a high performance digital readout. Sigma-Delta-ADCs are inherently linear. A high resolution of 16 bit for a secondorder Sigma-Delta-modulator followed by a third-order digital sinc-filter can be obtained. In addition to several thousand Sigma-Delta-ADCs the readout circuit consists of a configurable sequencer for controlling the readout clocking signals and a temperature sensor for measuring the temperature of the IRFPA. Since packaging is a significant part of IRFPA's price Fraunhofer-IMS uses a chip-scaled package consisting of an IR-transparent window with antireflection coating and a soldering frame for maintaining the vacuum. The IRFPAs are completely fabricated at Fraunhofer-IMS on 8" CMOS wafers with an additional surface micromachining process. In this paper the architecture of the readout electronics, the packaging, and the electro-optical performance characterization are presented.

The high level of accumulated expertise by ULIS and CEA/LETI on uncooled microbolometers made from amorphous silicon enables ULIS to develop VGA IRFPA formats with 17μm pixel-pitch to build up the currently available product catalog. This detector keeps all the innovations developed on the 25 μm pixel-pitch ROIC (detector configuration by serial link, low power consumption and wide electrical dynamic range). The specific appeal of this unit lies in the high spatial resolution it provides. The reduction of the pixel-pitch turns this TEC-less VGA array into a product well adapted for high resolution and compact systems. In the last part of the paper, we will look more closely at the high electro-optical performances of this IRFPA and the rapid performance enhancement. We will insist on NETD trade-off with wide thermal dynamic range, as well as the high characteristics uniformity, achieved thanks to the mastering of the amorphous silicon technology coupled with the ROIC design. This technology node paves the way to high end products as well as low end compact smaller formats like 160 x 120 or smaller.

In the outlook of the next 12μm pixel node uncooled IR FPA, the Laboratoire InfraRouge (LIR) of the Electronics and Information Technology Laboratory (LETI) is still pushing forward the amorphous silicon (a-Si) based microbolometer technology. A promising approach is the development of a lower resistance a-Si pixel, giving such a microbolometer IR sensor an edge for enhanced bias current capability, resulting in higher sensitivity. With this goal in sight, the paper reports on a preliminary study that aims at incorporating a germanium ratio in the standard amorphous silicon film. This approach successfully resulted in a significantly reduced thin film resistance. Both physical and electrical characteristics of these low resistance a-SiGe thin films are presented. From these basic parameter measurements, the paper further elaborates on the expected IR performance when such an a-SiGe film is applied to an uncooled FPA. Finally, we describe how this new generation of low resistance pixel fits perfectly with the maximum voltage requirement of advanced CMOS processes, which are needed for future smart ROIC and intelligent IR pixel.

Significant progress has been made over the past decade on uncooled focal plane array (UFPA) technology development and production capacity at DRS as well as other domestic and overseas suppliers. This resulted in the proliferation of uncooled IR detectors in commercial and military markets. The uncooled detectors are widely used in firefighting, surveillance, industrial process monitoring, machine vision, and medical applications. In the military arena, uncooled detectors are fielded among diverse systems such as weapon sights, driver enhancement viewers, helmet-mounted sights, airborne and ground surveillance sensors including UAVs and robot vehicles. Pixel dimensions have continually decreased with an increase in pixel performance. This paper presents an overview of the DRS 25- and 17-micron pixel pitch uncooled VOx detector technology development and production status. The DRS uncooled FPA products include 320x240 and 640x480 arrays while the larger 1024x768 17-micron pitch array is at engineering prototype quantities. Current production of the 25-micron pitch 320x240 and 640x480 arrays exceeds 5,000 units per month, supporting U.S. military systems such as Army thermal weapon sights (TWS) and driver vision enhancers (DVE). Next generation systems are moving towards the 17-micron pixel pitch detectors. Advancement in small pixel technology has enabled the 17-micron pitch detectors performance to surpass their 25-micron pitch counterparts. To meet future production demand of the 17-micron pitch UFPAs, DRS has made significant investment in production infrastructure to upgrade its tools. These investments include a new DUV stepper, coater, and plasma etcher plus improvements in its manufacturing techniques to enhance yield. These advanced tools reduce the minimum line width in production below 0.35μm and are now being used to manufacture the 17-micron 320x240 and 640x480 arrays. To further technology development, DRS continues to engage in R&D activities focusing on VOx microbolometer detector design, packaging, test capability, materials and fabrication processes to further improve the detector performance, reliability, producibility and yield. Some of the results are summarized in this paper.

Last year we have introduced the development program of SCD's 17μm pitch VGA VO_x μ-Bolometer detector ⁽¹⁾. Due to the overall size, weight and power advantages the 17μm pitch is currently being considered for the next generation systems such as thermal weapon sights (TWS), driver vision enhancers (DVE) and digitally fused goggles (DENVG). In the first part of this paper we will discuss in detail the performance of this detector. Specifically, we will elaborate on the radiometric results, ROIC performance and operability. Detailed measurements for a wide temperature range will be presented as well. In the second part, we will describe some new capabilities and features that are enabled by the advanced 0.18um VLSI technology. These features will be embedded in new products that are currently under development.

Over the past two years Raytheon has made a major investment aimed at establishing a high volume uncooled manufacturing capability. This effort has addressed three elements of the uncooled value stream, namely bolometer fabrication, packaging and calibration/test. To facilitate a low cost / high volume source of bolometers Raytheon has formed a partnership with a high volume 200mm commercial silicon wafer fabrication. Over a 12 month period Raytheon has installed 200mm VOx deposition equipment, matched the metrology used on the Raytheon 150mm line, transferred the process flow used to fabricate Raytheon's double layer bolometer process and qualified the product. In this paper we will review the process transfer methodology and bolometer performance. To reduce bolometer packaging cost and increase production rates, Raytheon has implemented an automated packaging line. This line utilizes automated adhesive dispense, component pick and place, wire bonding and solder seal. In this paper we will review the process flow, qualification process and line capacity Calibration and test has traditionally been performed using a number of temperature chambers, with increased throughput being obtained by adding more chambers. This comes at the expense of increased test labor required to feed the chambers and an increased energy and floor space foot print. To avoid these collateral costs, Raytheon has implemented an automated robotic calibration cell capable of performing in excess of 5,000 calibrations a month. In this paper we will provide an overview of the calibration cell along with takt time and throughput data.

BAE Systems continues to make dramatic progress in uncooled microbolometer sensors and applications. This paper will review the latest advancements in microbolometer technology at BAE Systems, including the development status of 17 micrometer pixel pitch detectors and imaging modules which are entering production and will be finding their way into BAE Systems products and applications. Benefits include increased die per wafer and potential benefits to SWAP for many applications. Applications include thermal weapons sights, thermal imaging modules for remote weapon stations, vehicle situational awareness sensors and mast/pole mounted sensors.

We have developed a 22um pitch and 320 × 240 pixel uncooled infrared radiation focal plane array on the silicon-oninsulator (SOI) substrate by means of 0.35um CMOS technology and bulk-micromachining. For IR detection, we use silicon single-crystal series p-n junctions that can realize high uniformity of sensitivity and low voltage drift. The supporting beam shrinkage enabled the pixel pitch shrinkage from 32um to 22um and 320 × 240 pixel number without deteriorating NETD. We also developed a SOI low-noise CMOS readout circuit that can calibrate chip temperature and introduced a noise canceling digital algorithm to cancel the reset noise generated in the readout circuit. The dominant noise source, SOI MOSFET noise, was decreased by optimizing the gate design. Finally the FPA has realized noise equivalent temperature difference (NETD) of 0.12K and requires no thermo-electric cooler (TEC) and is mounted on a low-cost standard ceramic package.

Previous reports to this SPIE forum have described a new generation of passive infrared (PIR) security sensors based on silicon microbolometer MOEMS technology. The technology is now patented and under development for commercial exploitation. This paper extends the PIR sensor analysis to smaller microbolometer size. This has been motivated by the availability of MEMS foundries offering high resolution lithography, hence smaller feature size. The performance of sensors with 10 and 25μm microbolometer size is given and compared with previous results. The flexibility of the technology to meet different applications is discussed.

The blackbody radiation limit has traditionally been set forth as the ultimate performance limit of thermal detectors. However, this fundamental limit assumes that the detector absorbs uniformly throughout the thermal spectrum. In much the same way as photon detectors can achieve very high D* because they do not absorb photon energies below their bandgap, so too can thermal detectors except that thermal detectors are not limited to cryogenic operation. In both cases, the enhanced theoretical D* is achieved because the radiation noise is reduced in a device that does not absorb at a uniform high level throughout the thermal emission band. There are multiple ways to achieve high D* in thermal detectors. One is to use materials that absorb only in a certain spectral range, just as in photon detectors. For example a detector made from PbSe, with proper optical coupling, absorbs only photons with wavelengths shorter than 4.9μm. The radiation limited detectivity of such a device can theoretically exceed 9 x 1010cmHz^1/2/W in the MWIR. Even with Johnson and 1/f noise estimates included, it can still exceed 2.5x1010cmHz^1/2/W in the MWIR. Another technique, applicable for narrowband thermal detectors, is probably even more powerful. Consider a thermal detector that is almost completely transparent. Here, the radiation noise has been reduced but the signal has been reduced even more. However, if the device is now placed inside an optical cavity, then at one wavelength and in one direction, the nearly transparent detector couples to the cavity resonance to absorb at 100%. Radiation from all other wavelengths and directions are rejected by the cavity or are absorbed only weakly by the detector. It is shown that theoretically, the D* of these devices are roughly proportional to the inverse square root of the spectral resonant width under certain conditions. It is also shown that even including Johnson noise and 1/f noise, the practically achievable D* approaches or exceeds 10¹¹ cmHz^1/2/W.

An important application of thin-film hydrogenated amorphous silicon (α-Si:H) is infrared detection and imaging with microbolometer focal plane arrays. Key α-Si:H electrical transport properties that influence detector design and performance are resistivity and temperature coefficient of resistance (TCR). These properties have been measured over a wide temperature range for p- and n-type doped α-Si:H thin-films deposited by plasma enhanced chemical vapor deposition using silane as a precursor gas. Resistivity near and above room temperature follows an Arrhenius thermally activated dependence. At low temperatures, resistivity transitions from Arrhenius behavior to a variable range hopping mechanism described by the Mott relation and TCR changes at a slower rate than predicted by thermally activated transport alone. Resistivity and TCR are affected by doping and film growth parameters such as dilution of the silane precursor with hydrogen. Resistivity decreases with dopant concentration for both p-type and n-type dopants. Resistivity and TCR increase with hydrogen dilution of silane. TCR and resistivity are interrelated and optimization of thin-film preparation and processing is necessary to obtain high TCR with resistivity values compatible with readout integrated circuit designs. Such optimization of transport properties of α-Si:H films has been applied to the development of high performance ambient operating temperature (uncooled) microbolometer arrays.

In this paper, the performance enhancing method by increasing optical fill factor of a μ-bolometer is proposed. The main idea of increasing optical fill factor of a μ-bolometer is the reducing the leg area without deteriorating the thermal and electrical properties of its legs. We propose 'the self align leg' structure in order to reduce the leg area without deteriorating electrical and thermal properties. From the analysis, this method can give some benefits, the improvement of responsivity up to 9% and noise equivalent temperature difference 13% through fill factor increasing by 5 to 7%. A new plausible method of increasing fill factor can easily be incorporated with a conventional process without considerable change of process.

In this work we report our results on the study of a-Ge_xSi_1-x intrinsic films used as thermo-sensing element in microbolometers. These intrinsic films are attractive because of their relatively high activation energy (Ea ≈ 0.37 eV) and consequently high temperature coefficient of resistance (TCR≈ -0.047 K^-1), and as well their higher room temperature conductivity (σRT ≈ 6x10-5 (Ωcm)-1), which is of around 3 - 4 orders of magnitude larger than that of the intrinsic a-Si:H films. Here we present a study of fabrication and performance characteristics of two different structures of microbolometers with a-Ge_xSi_1-x thermo-sensing films, labeled as planar and sandwich configurations. Metal electrodes were either planar providing current flow along the thermo-sensing layer or sandwich with current perpendicular to the thermosensing film surface. Current-voltage characteristics with and without IR illumination were performed and the responsivity of the devices was calculated. The noise spectra of the devices was studied, that allowed to determine the detectivity of the devices. The thermal response time was measured in the different microbolometer structures. These data are analyzed for the different micro-bolometer configurations and are compared with published data.

A study is reported of the benefits of introducing antenna coupling to enhance the performance of IR detectors based on vanadium oxide. The spectral characteristics of devices containing arrays of inductively-coupled antennas have been measured and compared with the results of theoretical predictions. Response characteristics have been measured using focussed CO2 laser beams using an optical read-out technique. Performance enhancements of an order of magnitude can be achieved which can potentially overcome current limitations in achieving useful signal responses in detector elements with reduced absorber areas.

A novel microbolometer with peak responsivity in the longwave infrared region of the electromagnetic radiation is under development at Sensonor Technologies. It is a focal plane array of pixels with a 25μm pitch, based on monocrystalline Si/SiGe quantum wells as IR sensitive material. The novelty of the proposed 3D process integration comes from the choice of several of the materials and key processes involved, which allow a high fill factor and provide improved transmission/absorption properties. Together with the high TCR and low 1/f noise provided by the thermistor material, they will lead to bolometer performances beyond those of existing devices. The thermistor material is transferred from the handle wafer to the read-out integrated circuit (ROIC) by wafer bonding. The low thermal conductance legs that connect the thermistor to the ROIC are fabricated prior to the transfer bonding and are situated under the pixel. Depending on the type of the transfer bonding used, the plugs connecting the legs to the thermistor are made before or after this bonding, resulting in two different configurations of the final structure. Using a low temperature oxide bonding and subsequent plugs formation result in through-pixel plugs. Pre-bonding plugs formation followed by thermo-compression bonding result in under-pixel plugs. The pixels are subsequently released by anhydrous vapor HF of the sacrificial oxide layer. The ROIC wafer containing the released FPAs is bonded in vacuum with a silicon cap wafer, providing hermetic encapsulation at low cost. Antireflection coatings and a thin layer getter are deposited on the cap wafer prior to bonding, ensuring high performance of the bolometer.

Employing an optical readout architecture expands the capabilities offered by uncooled thermal imagers, such as extremely fast frame rates, dual-band imaging, and multi-megapixel resolution. It also affords the ability to incorporate multiple pixel designs on the same infrared sensor chip, which we have taken advantage of to fabricate an optical readout photomechanical imager with 12 distinct pixel designs in the sensor chip layout. Using this methodology, we were able to quickly sort the designs in terms of performance and suitability for manufacturing, and thus, in an expedient and highly cost-effective manner, determine which pixel designs have merited future consideration for full-scale prototyping. A fast frame rate MWIR photomechanical imager based on one of the best pixel designs was built and tested for high-speed imaging of small arms fire.

Past work has discussed infrared absorption using a patterned thin resistive sheet as the frequency-selective absorber for use in wavelength-selective long wave infrared (LWIR) microbolometer focal planes arrays. These patterned resistive sheets are essentially slot antennas formed in a lossy resistive ground plane layer placed a quarter-wavelength in front of a mirror. Design studies have shown that for efficient IR absorption cross-shaped slots require a lossy sheet with the optimized sheet resistance. For realistic metal layers, however, the skin effect produces a complex surface impedance that can be quite large in the LWIR band. In this paper we consider metal layers of thickness between one and three skin depths as the absorber layer instead of a thin resistive sheet layer, and show that the thick metal layers can still produce excellent absorption in the LWIR.

The pyroelectric effect has been characterized for single-pixel elements consisting of strontium bismuth tantalate (SBT) ferroelectric material as the sensing elements. These pixels have been integrated into second-generation focal plane arrays. The constituent second-generation pixels include thermal insulating layers and an infrared absorber layer. The MEMS-less arrays are operated in active mode, a technique that eliminates radiation choppers found in other passive pyroelectric IR imagers. This paper addresses the results of precursor 2x2 to 14x14 second-generation arrays of SBT elements, the active detection mechanism, and the unique read-out, interrogation signal, and the synchronization electronics. The second-generation 14x14 pixels array was implemented to demonstrate the performance of an active pyroelectric array as a precursor to larger size arrays using different pixel dimensions. The active mode detection eliminates the use of a chopper, enables the dynamic partition of the array into pixel domains in which pixel sensitivity in the domains can be adjusted independently. This unique feature in IR detection can be applied to the simultaneous tracking of diverse contrast objects. In addition, by controlling the thickness of the absorber material the arrays can be optimized for maximum response at specified wavelengths by means of quarter-wavelength interferometry.

This study investigates the feasibility of a reactively sputtered thin nickel oxide film for application to a microbolometer. The properties of the developed thin nickel oxide film depend on the sputter process parameters. The measured resistivity of the nickel oxide films ranges from 0.3 Ωcm to approximately 50 Ωcm. Negative Temperature Coefficient of Resistance (TCR) values as high as -3.3%/ °C were acquired. The feasible 1/f noise characteristic was also measured. The magnification of the TCR value and 1/f noise of the nickel oxide films was proportional to the resistivity of the nickel oxide films. Specifically, nickel oxide film with a high resistivity showed a higher TCR value and more 1/f noise. From the measured TCR and 1/f noise values, the theoretically calculated NETD showed a value suitable for use with a microbolometer. Additionally, an analysis of sputtered thin nickel oxide films was conducted through X-ray diffraction.

This paper describes the microfabrication process and characterization of wavelength selective germanium dielectric supported microbolometers, which should be compatible with standard microbolometer fabrication processes. Here we have demonstrated a micro fabricated robust germanium dielectric structure layer that replaces the usual silicon nitride structural layer in microbolometers. The fabricated microbolometers consist of a chromium resistive sheet as an absorber layer above an air-gap/germanium dielectric structure.

The current state-of-the-art infrared detection technology requires either exotic materials or cryogenic conditions to perform its duty. Implementing infrared detection by coupling infrared tuned antenna with a micro-bolometer offers a promising technological platform for mass production of un-cooled infrared detectors and imaging arrays. The design, fabrication, and characterization of a planar slotted antenna have been demonstrated on a thin silicon dioxide (SiO2) membrane for infrared detection. The planar slotted antenna was chosen due to its ease of fabrication and greater fabrication tolerance, higher gain and greater bandwidth coveted for the infrared applications. The employment of the SiO2 membrane technology mitigates the losses due to surface waves generated as the radiation coupling into the substrates. In addition, by retaining the membrane thickness to be less than a wavelength, the amount of interference is greatly reduced. A strategically designed planar slotted dipole antenna is implemented along with an integrated direct current (DC) block enabled by co-fabricated on-chip capacitors between the two DC patches to separate DC and high frequency signals without the need for sub-micron DC separation line. As a result of this revision, standard UV photolithography instead of e-beam lithography can be used to fabricate the infrared detectors for mass production. This research is considered as an important step toward our main goal, which is developing ultrafast infrared detector by coupling a planar slotted antenna with a metal insulator metal (MIM) tunneling diode.

The antimonide superlattice infrared detector technology program was established to explore new infrared detector materials and technology. The ultimate goal is to enhance the infrared sensor system capability and meet challenging requirements for many applications. Certain applications require large-format focal plane arrays (FPAs) for a wide field of view. These FPAs must be able to detect infrared signatures at long wavelengths, at low infrared background radiation, and with minimal spatial cross talk. Other applications require medium-format pixel, co-registered, dual-band capability with minimal spectral cross talk. Under the technology program, three leading research groups have focused on device architecture design, high-quality material growth and characterization, detector and detector array processing, hybridization, testing, and modeling. Tremendous progress has been made in the past few years. This is reflected in orders-of-magnitude reduction in detector dark-current density and substantial increase in quantum efficiency, as well as the demonstration of good-quality long-wavelength infrared FPAs. Many technical challenges must be overcome to realize the theoretical promise of superlattice infrared materials. These include further reduction in dark current density, growth of optically thick materials for high quantum efficiency, and elimination of FPA processing-related performance degradation. In addition, challenges in long-term research and development cost, superlattice material availability, FPA chip assembly availability, and industry sustainability are also to be met. A new program was established in 2009 with a scope that is different from the existing technology program. Called Fabrication of Superlattice Infrared FPA (FastFPA), this 4-year program sets its goal to establish U.S. industry capability of producing high-quality superlattice wafers and fabricating advanced FPAs. It uses horizontal integration strategy by leveraging existing III-V industry resources and taking advantage of years of valuable experiences amassed by the HgCdTe FPA industry. By end of the program span, three sets of FPAs will be demonstrated-a small-format long-wave FPA, a large-format long-wave FPA, and a medium-format dual-band FPA at long-wave and mid-wave infrared.

In recent years, the type-II superlattice (T2SL) material platform has seen incredible growth in the understanding of its material properties which has lead to unprecedented development in the arena of device design. Its versatility in band-structure engineering is perhaps one of the greatest hallmarks of the T2SL that other material platforms are lacking. In this paper, we discuss advantages of the T2SL, specifically the M-structure T2SL, which incorporates AlSb in the traditional InAs/GaSb superlattice. Using the M-structure, we present a new unipolar minority electron detector coined as the P-M-P, the letters which describe the composition of the device. Demonstration of this device structure with a 14μm cutoff attained a detectivity of 4x10¹⁰ Jones (-50mV) at 77K. As device performance improves year after year with novel design contributions from the many researchers in this field, the natural progression in further enabling the ubiquitous use of this technology is to reduce cost and support the fabrication of large infrared imagers. In this paper, we also discuss the use of GaAs substrates as an enabling technology for third generation imaging on T2SLs. Despite the 7.8% lattice mismatch between the native GaSb and alternative GaAs substrates, T2SL photodiodes grown on GaAs at the MWIR and LWIR have been demonstrated at an operating temperature of 77K.

In the past years, the development of the type-II InAs/GaSb superlattice technology at the Fraunhofer-Institute for Applied Solid State Physics (IAF) has been focused on achieving series-production readiness for third generation dualcolor superlattice detector arrays for the mid-wavelength infrared spectral range. The technology is ideally suited for airborne missile threat warning systems, due to its ability of low false alarm remote imaging of hot carbon dioxide signatures on a millisecond time scale. In a multi-wafer molecular beam epitaxy based process eleven 288×384 dualcolor detector arrays are fabricated on 3" GaSb substrates. Very homogeneous detector arrays with an excellent noise equivalent temperature difference have been realized. The current article presents the type-II superlattice dual-color technology developed at IAF and delivers insights into a range of test methodologies employed at various stages during the fabrication process, which ensure that the basic requirements for achieving high detector performance are met.

Type-II superlattice (SL) materials research in the Materials & Manufacturing Directorate of the Air Force Research Laboratory began in 1988. This materials system holds great promise as the III-V equivalent to HgCdTe alloys for infrared detection. Great progress has been made on the epitaxial growth of InAs/Ga_1-xIn_xSb superlattices in the past twenty years by a number of research groups. However, not all of the materials issues have been solved. To continue to resolve these limiting materials issues, basic superlattice materials, without photodiode fabrication, are used to characterize the impact of growth processes and SL design on the structural, electrical and optical properties. An integrated approach of theoretical modeling, in-house molecular beam epitaxy, and a host of materials measurement techniques is employed to study the optimization of the superlattices for infrared detection. In the past few years the majority of the samples grown in-house have been designed for the middle wavelength infrared (MWIR) band. However, there are challenges in applying MWIR SL growth optimization to longer wavelength SLs. Recent progress on understanding the complex interplay between InAs/GaSb superlattice composition and fundamental electrical and optical properties will be covered.

Ga(In)Sb/InAs-based strained-layer superlattices (SLS) have received considerable attention recently for their potential in infrared (IR) applications. These heterostructures create a type-II band alignment such that the conduction band of InAs layer is lower than the valence band of Ga(In)Sb layer. By varying the thickness and composition of the constituent materials, the bandgap of these SLS structures can be tailored to cover a wide range of the mid-wave and long-wave infrared (MWIR and LWIR) absorption bands. Suppression of Auger recombination and reduction of tunneling current can also be realized through careful design of the Type-II band structure. The growth of high-quality Ga(In)Sb/InAs-based SLS epiwafers is challenging due to the complexity of growing a large number of alternating thin layers with mixed group V elements. In this paper, the development of a manufacturable growth process by molecular beam epitaxy (MBE) using a multi-wafer production reactor will be discussed. Various techniques were used to analyze the quality of the epitaxial material. Structural properties were evaluated by high-resolution x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Optical properties were assessed by low-temperature photoluminescence measurements (PL). Surface morphology and roughness data as measured by Nomarski optical microscope and atomic force microscope (AFM) will be presented. Device characteristics such as dynamic impedance, responsivity, quantum efficiency, and J-V characteristics of photodiodes fabricated using our SLS epiwafers will be discussed.

In this work newly developed 4" GaSb substrates are investigated for their suitability in the epitaxial growth of type II InAs/GaInSb superlattice detectors. The Czochralski technique was used to grow 4" GaSb crystals with etch pit densities in the range of 1.5-2.5E3 cm^-2. Bulk crystal structure was investigated by X-ray topography and revealed large central areas of zero or low dislocation density. Epitaxy-ready substrate surfaces were characterized by low levels of surface roughness and uniform oxide coverage. The material quality of superlattice detector structures grown on 2" and 4" GaSb substrates has been compared. Surface morphology evaluations of a 4" GaSb epiwafer reveal very low haze surface and defect density level that is similar to a 2" epiwafer. An rms surface roughness of 4.4 A was measured by AFM which is only 1-2 A larger than seen on 2" diameter SLS epiwafers. High resolution X-Ray measurements of the epitaxial layer structure indicate high structural quality and reproducible SL periodicity. Good layer thickness uniformity with a center-to-edge variation just over 2% has been achieved.

Type II superlattices (SLs) offer a broad range of design degrees of freedom to help optimize their properties for infrared detection. Under the AFRL STEPS contract, we focus on mid-wavelength infrared (MWIR; 2-5 μm bandpass) Type II structures with two-layer InAs/GaInSb and four-layer "W-structure" InAs/GaInSb/InAs/AlInGaAsSb SL periods. We consider details of the electronic band structures that reduce Auger recombination rates in p-type SLs specifically by affecting the density of final states available to one of the involved carriers. This work assesses the potential impact of final state optimizations on 5 μm band gap SLs in the 200-225 K operating temperature range.

Type-II strained layer superlattices (SLS) are a rapidly maturing technology for infrared imaging applications, with performance approaching that of HgCdTe1,2,3,4. Teledyne Imaging Sensors (TIS), in partnership with the Naval Research Laboratory (NRL), has recently demonstrated state-of-the-art, LWIR, SLS 256 × 256 focal plane arrays (FPAs) with cutoff wavelengths ranging from 9.4 to 11.5 μm. The dark current performance of these arrays is within a factor of 10-20 of (state-of-the-art) HgCdTe. Dark current characteristics of unpassivated and passivated devices exhibit bulk-limited behavior, essential for FPA applications. TIS has also demonstrated rapid substrate thinning processes for increased infrared transmission through the GaSb substrate. In addition to this work, this presentation will discuss the recent developments of 1K x 1K LWIR SLS FPAs.

Improved LWIR sensors are needed for defense applications. We report an advance in sensor technology based on diodes in type-II strained layer superlattice structures built in the InAs/GaSb/AlSb materials system. A key feature of the devices is a pair of complementary barriers, namely, an electron barrier and a hole barrier formed at different depths in the growth sequence. The structure is known as CBIRD. This work is a collaborative effort between Raytheon Vision Systems and Jet Propulsion Laboratory, with design and growth being performed at JPL, and processing and testing at RVS. We have analyzed the current-voltage characteristics as functions of temperature and junction area, and have measured the spectral response and quantum efficiency as functions of bias voltage. From the temperature dependence of the dark current in a typical case, we infer that the effective barrier height is 0.175 eV. This indicates that dark current is limited by the barriers rather than diffusion or GR mechanisms occurring within the absorber region where the bandgap is 0.13 eV. The barriers prove to be very effective in suppressing the dark current. In the case of a detector having a cutoff wavelength of 9.24 μm, we find R0A > 10⁵ ohm cm² at 78 K, as compared with about 100 ohm cm2 for an InAs/GaSb homojunction of the same cutoff. For good photo response, the device must be biased to typically -200 or -250 mV. In this condition we find the internal quantum efficiency to be greater than 50%, while the RA remains above 10⁴ ohm cm². Thus, the device shows both high RA and good quantum efficiency at the same operating bias. We have also measured the capacitance of the CBIRD device as functions of bias and frequency to help characterize the behavior of the barriers. A 256×256 focal plane array was fabricated with this structure which showed at 78K a responsivity operability of more than 99%.

InAs/GaSb-based type II superlattices (T2SL) offer a manufacturable FPA technology with FPA size, scalability and cost advantages over HgCdTe. Work at Jet Propulsion Laboratory (JPL), Naval Research Laboratory (NRL), and Northwestern University (NWU) has shown that the performance gap between HgCdTe and T2SL FPAs has narrowed to within 5-10x over the last two years^1,2,3. Due to the potential of T2SL technology for fabrication of large format (> 1k x1k) and dual-band arrays, HRL has recently resurrected efforts in this area⁴. We describe the progress on the FastFPA program funded by the Army Night Vision Labs towards the development of detectors and focal plane arrays (FPAs). Progress made in the areas of MBE growth, mesa diode fabrication, dry etch processing, and FPA fabrication over the last one year is presented.

We present the performance of longwave infrared focal plane arrays (FPAs) made from Type-II InAs/GaSb strained layer superlattice (SLS) photodiodes. In 320x256 FPAs operating at 77K, we measure cutoff wavelength ~ 8.5 μm, dark current density ~ 10^-5 A/cm², quantum efficiency > 5% (with 2 μm -thick absorber photodiode), and pixel operability ~ 96%. Device physics and FPA performance are graphed. Current challenges are discussed.

Much has been accomplished in the last few years in advancing the performance of type-II superlattice (T2SL) based infrared photodiodes, largely by focusing on device and heterostructure design. Quantum efficiency (QE) has increased to 50% and higher by using thicker absorbing layers and making use of internal reflections, and dark currents have been reduced by over a factor of ten by using bandstructure engineering to suppress tunneling and generation-recombination (G-R) currents associated with the junction. With performance levels of LWIR T2SL photodiodes now within an order of magnitude of that of HgCdTe (MCT) based technology, however, there is renewed interest in understanding fundamental materials issues. This is needed both to move performance toward the theoretical Auger limit, and to facilitate the task of transitioning T2SL growth from laboratories to commercial institutions. Here we discuss recent continuing efforts at NRL to develop new device structures for enhanced detector performance, and to further our understanding of this material system using advanced structural and electronic probes. Results from electron beam induced current (EBIC) imaging and analysis of point defects in T2SL photodiodes will be presented, showing differentiated behavior of bulk defect structures. We will also describe a study comparing intended vs. as-grown T2SL photodiode structures by crosssectional scanning microscopy (XSTM). Using parameters extracted from the XSTM images, we obtain detailed knowledge of the composition and layer structures through simulation of the x-ray diffraction spectra.

The nearly lattice-matched InAs/GaSb/AlSb (antimonide) material system offers tremendous flexibility in realizing high-performance infrared detectors. Antimonide-based alloy and superlattice infrared absorbers can be customized to have cutoff wavelengths ranging from the short wave infrared (SWIR) to the very long wave infrared (VLWIR). They can be used in constructing sophisticated heterostructures to enable advanced infrared photodetector designs. In particular, they facilitate the construction of unipolar barriers, which can block one carrier type but allow the unimpeded flow of the other. Unipolar barriers are used to implement the barrier infra-red detector (BIRD) design for increasing the collection efficiency of photo-generated carriers, and reducing dark current generation without impeding photocurrent flow. We report our recent efforts in achieving state-of-the-art performance in antimonide alloy and superlattice based infrared photodetectors using the BIRD architecture. Specifically, we report a 10 μm cutoff superlattice device based on a complementary barrier infrared detector (CBIRD) design. The detector, without antireflection coating or passivation, exhibits a responsivity of 1.5 A/W and a dark current density of 1×10^-5 A/cm² at 77K under 0.2 V bias. It reaches 300 K background limited infrared photodetection (BLIP) operation at 87 K, with a blackbody BLIP D* value of 1.1×10¹¹ cm-Hz^1/2/W for f/2 optics under 0.2 V bias.

We have demonstrated the use of bulk antimonide based materials and type-II antimonide based superlattices in the development large area long wavelength infrared (LWIR) focal plane arrays (FPAs). Barrier infrared photodetectors (BIRDS) and superlattice-based infrared photodetectors are expected to outperform traditional III-V MWIR and LWIR imaging technologies and are expected to offer significant advantages over II-VI material based FPAs. Our group has developed a novel complementary barrier infrared detector (CBIRD) which utilizes properties unique to the antimonide material system to incorporate unipolar barriers on either side of a superlattice absorber region. We have used molecular beam epitaxy (MBE) technology to grow InAs/GaSb CBIRD structures on large area 100mm GaSb substrates with excellent results. Furthermore, we have fabricated initial 1024x1024 pixels superlattice imaging FPAs based on the CBIRD concept.

We report heterojunction bandgap engineered long wave infrared (LWIR) photodetectors based on type-II InAs/GaSb strained layer superlattices (SLS) which show significant improvement in performance over conventional PIN devices. For this study, a device with unipolar barriers but same absorber region as PIN has been studied and compared. Unipolar barriers reduce the tunneling currents and SRH recombination current in the active region due to reduced electric field drop across the active region, while maintaining the photocurrent level. Moreover, they also reduce the diffusion current by blocking the minority carriers from the two sides of the junction. We report three orders of magnitude reduction in the dark current with the use of unipolar barriers. The reduction in the dark current results in significant improvement in signal to noise ratio, resulting in measured specific detectivity of 2×10¹⁰ (cm-√Hz)/W and dark current density of 8.7 mA/cm² at -0.5 V applied bias, for the 50% cutoff wavelength of 10.8μm.

We report on surface passivation studies for type-II InAs/GaSb superlattice (SL) PIN detectors designed to operate in the mid-wave infrared (MWIR) region and the long wavelength infrared (LWIR) spectrum. The two SL structures were grown by molecular beam epitaxy and processed into mesa diodes using standard lithography. A simple spin on photoresist, SU-8, was used to passivate the sample after a wet etch. Optical and electrical measurements were then undertaken on the two devices. The dark current density of a single pixel device with SU-8 passivation is reduced by four orders of magnitude and by a factor of eight compared to devices without any passivation for the MWIR and LWIR pin detectors, respectively, at 77K.

Minority carrier lifetime, photoluminescence (PL), and interband absorption in midinfrared range of spectra were measured in InAs/GaSb strained-layer superlattices (SLS) grown by molecular beam epitaxy (MBE) on GaSb substrates. The carrier lifetime was determined by time-resolved PL (TRPL) and from analysis of PL response to sine-wavemodulated excitation. Studies of the PL kinetics in the frequency domain allowed for direct lifetime measurements in SLS structures with an excess carrier concentration level of 3.5×10¹⁵ cm^-3. The minority carrier lifetime at T = 77 K was obtained from the dependence of the carrier lifetime on excitation power. SLS structures with similar absorption wavelengths but with different InAs and GaSb layer thicknesses and with different amounts of strain were investigated and compared with mercury cadmium telluride (MCT) samples. No apparent trend was seen in structures with different number of interfaces per unit length. All SLS lifetime values measured so far are more than an order of magnitude lower than those of MCT.

A novel heterostructured dual carrier multiplication extremely high gain MWIR InAs/InGaSb Type II strained layer superlattice (T2SLS) impact ionization engineered (I2E) APD was designed and simulated. Spatially separated T2SLS electron and hole multiplication regions are designed using 14 band k.p bandstructure modeling. In the novel dual carrier device, the I2E T2SLS electron and hole multiplication regions are placed right next to each other. This allows for a carrier feedback between the electron and hole multiplication regions. This feedback between the electron and hole multiplication regions allows for extremely high gain values for the overall device. While the individual gain of the electron and hole multiplication regions can be kept extremely low, the overall gain can be >10³. This can be achieved at a reverse bias of 3.5V. The effective k is designed to be approximately .07. Such low bias operation of the MWIR APD allows for active operation and passive mode operation on the same pixel using standard ROIC and this opens up possibility of large format dual mode imaging arrays.

Multiple fields of view are achieved by two methods. The system can have optical groups that flip in and out to change the field of view, and/or optical groups that move axially to change the field of view. For flip in systems, the fields of view are discreet and they may have greatly different fields of view. A zoom system can have a continuous change in the field of view, but is often limited in the field of view range that can be achieved. Corning Incorporated has developed a thermal imaging zoom system with greater than 30X zoom range. With a solid fundamental design and appropriate selection of moving group focal lengths, the zoom system provides continuous changes in the field of view from the narrow field of view to the wide field of view. Corning accomplished this result in a short package with just two moving groups. The system is for the MWIR band.

The MONTAGE program sponsored by the Microsystems Technology Office of the Defense Advanced Research Projects Agency (DARPA) resulted in the demonstration of a novel approach to designing compact imaging systems. This approach was enabled by an unusual four-fold annular lens originally designed and demonstrated for operation exclusively in the visible spectral band. To accomplish DARPA's goal of an ultra-thin imaging system, the folded optic was fabricated by diamond-turning concentric aspheric annular zones on both sides of a CaF₂ core. The optical properties of the core material ultimately limit the operating bandwidth of such a design. We present the latest results of an effort to re-engineer and demonstrate the MONTAGE folded optics for imaging across a broad spectral band. The broadband capability is achieved by taking advantage of a new design that substitutes a hollow core configuration for the solid core. Along with enabling additional applications for the folded optics, the hollow-core design offers the potential of reducing weight and cost in comparison to an alternative solid-core design. We present new results characterizing the performance of a lens based on the new design and applied to long-wave infrared imaging.

Cryogenically cooled IR detectors, which are used in applications such as situational awareness, search & track, missile launch and approach warning, typically use wide angle, single field of view optical systems. We describe a complete IR imaging optical assembly for such applications, which is mounted inside a cold shield and is maintained at a stabilized cryogenic temperature inside the dewar. A typical system houses two to four lenses and a cold filter, and weighs 5 grams or less. Despite this integration and added complexity, the resulting Detector-Dewar-Cooler Assembly (DDCA) has overall dimensions similar to those of equivalent-performing DDCAs without integrated optics. Moreover, Compact designs integrating wide-angle optics and a warm, high-magnification, telescope module for narrow FOV applications are seen as a straightforward extension of our system. We conclude with an in-depth, technical overview describing the design considerations for a typical wide-field imaging system.

As lens design using aspheric diffractive lenses has become more popular in designing faster, low F/# infrared (IR) optical systems; the increased quantities manufactured of these glass lenses is following suit. Historically, Single Point Diamond Turning (SPDT) has been the method of choice in producing high quality glass aspheric and diffractive lenses, but with the volume of lenses produced and technological advances in Precision Molded Optics (PMO), it is now becoming highly cost efficient to use molding as a means of producing these glass optic lenses. This paper will discuss lens shapes, tolerances, present and future optic lens sizes that are being done using PMO as well as present an experiment conducted comparing the surface quality of a chalcogenide lens manufactured with SPDT and PMO.

The needs of surveillance/detection operations in the infrared range, for industrial, spatial and military applications continuously tend toward larger field of view and resolution while maintaining the system as compact as possible. To answer this need, INO has developed a 1280x960 pixel thermal imager, said HRXCAM, with 22.6° field of view. This system consists in the assembly of a catadioptric optics with microscan mechanism and a detection electronic module based on a 640x480 25μm pitch pixel bolometric detector. The detection module, said IRXCAM, is a flexible platform developed for fast prototyping of varied systems thanks to its ability to support a large range of infrared detectors. With its multiple hardware and software functionalities, IRXCAM can also be used as the complete electronic module of a finalized system. HRXCAM is an example of fast prototyping with IRXCAM and an optical lens that fully demonstrates the imaging performance of the final system. HRXCAM provides 1280x960 pixel images at a nominal 5-15 Hz frequency with 60 mK NETD. It can also be used in the 640x480 mode at 58 Hz with the same sensitivity. In this paper, the catadioptric optics with integrated microscan and IRXCAM architecture and specifications are reviewed. Some typical examples of image obtained with HRXCAM in outdoor conditions are presented.

Over the past decade, several technological breakthroughs have been achieved in the field of optical detection, in terms of spatial and thermal resolutions. The actual trend leads to the integration of new functions at the vicinity of the detector. This paper presents two types of integrated optics in the cryo-cooler, close to the MCT (CdHgTe) infrared detector array. The first one, for spectro-imaging applications, is a Fourier-transform microspectrometer on chip (MICROSPOC), developed for very fast acquisition of spectral signatures. Experimental results will be presented. The second one, for large field of view applications, illustrates the high potentiality of the integration of advanced optical functions in the Dewar of MCT detectors.

Most of optoelectronic semiconductor devices, especially quantum well based ones, make use of a grating to couple the active layer to free space. To go beyond the simplistic coupling role of the grating we propose a specifically designed metal-dielectric corrugated interface that squeezes normal incidence light in subwalength scale, taking advantage of the very active work achieved over the last few years in near field electromagnetism. This structure coherently combines three surface plasmon engineering tools: Bragg reflection, microcavity, and grating coupling. These electromagnetic properties are demonstrated experimentally in the gigahertz regime, as a function of design parameters. Light squeezing is observed down to a quarter of a wavelength.

Regulating optical power levels within various systems, such as cameras, requires today an electronic feedback control or offline data processing, which introduces complex and expensive systems. Sometimes the blooming is such that data is lost and cannot be recovered by any sophisticated software. We explore the unique capabilities and advantages of nanotechnology in developing next generation non-linear components and devices to control and regulate optical power in a passive way. We report on the Dynamic Sunlight Filter (DSF) enabling High Dynamic Range (HDR) for various types of camera. The DSF solution is completely passive and can be added to any camera as an external add-on.

Precision Photonics Corporation (PPC) has developed a method of applying Ion Beam Sputtered (IBS) MWIR antireflective coatings to the interior of a tangent ogive dome. Although IBS has traditionally not been used in this application, it is known that IBS provides the highest density coatings using very hard, durable materials. We achieve a variable coating thickness profile by means of shadow masking coupled with sophisticated 3 dimensional mathematical modeling, which optimizes the antireflection performance over a wide range of look angles for an infrared seeker inside the dome. The coating design for this project survives temperatures up to 1000ºC.

A method of antireflection coating the interior and exterior surfaces of a deep concave optic is under development and is described. The challenges of coating such an optic include obtaining uniform performance, good mechanical and optical performance across a temperature range of ambient to 1000oC, and the transition to cost effective production. The coating process utilizes a tuned cylindrical magnetron sputtering source which sits inside the nose cone to coat the inner surface and a complementary cylindrical sputtering source to coat the outside surface. The flux from the sputtering source is tuned along the length of the cylinder by stacking an inner core of magnets in such a way as to produce a spatially variant magnetic field which allows the source distribution to approximate a uniform deposition on the surface of the optic. A deposition occulting mask provides fine tuning of source uniformity.

Requirements for shutters used in Infrared Thermal Weapon Sight (TWS) systems, Driver Vision Enhancement (DVE) and other thermal imaging systems are becoming increasingly more demanding. These performance requirements have been achieved using a unique, modular, reconfigurable rotary drive actuator with bi-stability and direct connection to the blade. A "Smart Shutter" acts as a complete sub-system that can be tested as an integral module. A multi-blade variant has been developed that retains the reliability of the rotary drive system and decreases the physical size of largeraperture shutters. Predictions of next-generation application-specific shutter designs will be offered in the paper.

Chalcogenide glasses are compounded from chalcogen elements, such as sulphur, selenium, and tellurium. These glasses are applied to commercial applications, e.g., night vision, because they transmit infrared in the spectral range of 0.8-16μm. Chalcogenide glasses have greater advantages over germanium (Ge), i.e., their wide spectral range of high transmissivity and their small temperature dependence of the refractive index. We have developed the Compact Infrared Camera (CIRC) with an uncooled infrared array detector (microbolometer) for space applications. The CIRC has been scheduled to launch in 2013 to demonstrate the usability of a microbolometer as a space application. The optics of the CIRC adopts two different kinds of materials for athermal optics. One is germanium, and the other is GASIR1® which is a chalcogenide glass (Ge₂₂As₂₀Se₅₈) developed by Umicore. However, the radiation tolerance of GASIR® has not been investigated in the past. We carried out irradiation tests to investigate the radiation tolerance of GASIR1®. We irradiated GASIR1® with gamma-rays (Co60, 1.17 MeV and 1.33 MeV) up to 3Mrad. We measured the transmissivity and refractive index in the infrared range before and after irradiation. In this paper, we report the results of the irradiation tests of GASIR1®.

Optical design of an imager that works in two sub bands of the infrared spectrum which are called midwave and longwave (3-5 and 8-12 μm) is described in this work. The relevant design issue is not affected by the rate of change of temperature in terms of various season and atmosphere conditions in operation. In this study, the first attempt dealt with is to describe the broadband concept and to highlight that term. Then, basic information is presented about infrared subbands. After describing the details of optical design in an infrared band, the decisions on necessary design parameters are made. In this scene, environmental conditions regarded during the design process are chosen as challenging weather conditions in Turkey within the range from -35 to 50°C.

Passive athermalization of infrared (IR) imager objectives such as thermal goggles and binoculars which are exposed to variable atmospheric conditions is a critical issue. In this study, an athermal 50 mm f2 midwave objective design is compared with three similar commercially available objectives in terms of modulation transfer function (MTF) in Nyquist frequency under varying temperature conditions. The test setup constructed to enable the experimental comparison and the test process utilized are described. Finally, the results obtained are comparatively evaluated.

There are times when it would be helpful to share performance information about an optical system without disclosing proprietary information between multiple parties. A combination of Zernike phase surfaces and paraxial surfaces can be used to model an optical system and provide a method to safely transfer the required information without disclosing the specifics of the design such as details about the optical materials or the specific element geometry. This paper deals with some of the practical aspects of this approach such as aperture stop location, the affects of windows which may change thickness on the construction of the model, and the need for multiple field positions and wavelengths.

ABB Bomem is expanding its line of infrared remote sensing products with the addition of a new multipixel imaging spectroradiometer. This hyperspectral instrument is based on the proven MR spectroradiometers. The instrument is modular and support several configurations. One of its configurations is optimised for differential acquisition in the VLWIR (cut-off near 14 μm) to support research related to the stand-off detection and quantification of chemicals. In that configuration, the instrument is equipped with a dualinput telescope to perform optical background subtraction. The resulting signal is the differential between the spectral radiance entering each input port.

We report on low strain quantum dot infrared photodetectors (QDIP) with 80 dot in a well (DWELL) stacks. These QDIPs have been grown with lattice matched Al0.1Ga0.9As barriers and GaAs wells allowing a large number of stacks to be grown leading to an increased absorption volume. The QDIPs show a strong spectral response that varies significantly with applied bias, with four distinct peak wavelengths ranging from 5.5μm to 10.0μm. The highly tunable nature of the intrinsic responses makes these QDIPs very attractive as multispectral imagers in the MWIR and LWIR regions. The spectral diversity of these QDIPs has been exploited using an algorithm to produce a highly versatile algorithmic spectrometer. The algorithm assigns a specific weighting factor to each of the intrinsic responses and then sums these weighted responses to achieve any desired spectral shape. Triangular narrowband filters have been synthesised in this way with full width at half maximums (FWHM) as narrow as 0.2μm. The QDIPs can be used to image objects in the MWIR and LWIR regions by measuring the photocurrent generated at each specific bias and summing them using the calculated weighting factors for every wavelength of interest. This technique has been successfully used to capture the radiated power from a blackbody source through IR filters with different centre wavelengths and bandwidths as a function of wavelength in the LWIR and MWIR regions.

The current mainstay for short-wave infrared (SWIR) imaging is InGaAs-based focal plane arrays (FPAs). They provide excellent detectivity and low noise, but suffer from high costs, limited spectral response, and the same integration issues that limit array size for most inorganic FPA technologies. RTI has demonstrated a novel photodiode technology based on IR-absorbing, solution-processed colloidal quantum dots that can overcome the limitations of InGaAs FPAs. We have fabricated preliminary devices with quantum efficiencies exceeding 50%. These devices also show response times less than 10 μS, making them suitable for high speed imaging. The have demonstrated excellent linearity with over 40 dB of dynamic range. These devices are processed entirely at room temperature, and are compatible with monolithic integration onto readout ICs, thereby removing any limitation on device size. The process steps involve low-cost, high volume techniques that do not require sophisticated infrastructure, which should serve to dramatically reduce costs. This combination of high performance, dramatic cost reduction, and multispectral sensitivity is ideally suited to expand the use of SWIR imaging in current applications, as well as to address applications which require a multispectral sensitivity not met by existing technologies.

Interferometric hyperspectral imagers using infrared focal plane array (FPA) sensors have received increasing interest within the field of security and defence. Setups are commonly based upon either the Sagnac or the Michelson configuration, where the former is usually preferred due to its mechanical robustness. However, the Michelson configuration shows advantages in larger FOV due to better vignetting performance and improved signal-to-noise ratio and cost reduction due to relaxation of beamsplitter specifications. Recently, a laboratory prototype of a more robust and easy-to-align corner-cube Michelson hyperspectral imager has been demonstrated. The prototype is based upon an uncooled bolometric FPA in the LWIR (8-14 μm) spectral band and in this paper the noise properties of this hyperspectral imager are discussed.

We present a miniature snapshot multispectral imager that operates in the short wavelength infrared region (SWIR) and has a number of applications. The system is low-weight, portable with a miniature platform and requires low power. The imager uses a 4×4 Fabry-Perot filter array operating from 1487 to 1769 nm with a spectral bandpass ~ 10 nm. The design of the filters is based on using a MEMS shadow mask technique to fabricate a Fabry-Perot etalon with multilayer dielectric mirrors. The filter array subsystem is installed in a commercial handheld InGaAs camera and the imaging lens of the camera is replaced by a custom designed 4×4 microlens array with telecentric imaging performance in each of the 16 sub-imaging channels. The imager was used to image a number of different indoor and outdoor scenes. The microlens optics and filter design is quite flexible and can be tailored for any wavelength region from UV to LWIR and the spectral bandpass can also be customized to meet the requirements. In this paper we will discuss the design and characterization of the filter array, the microlens optical package, and the imager and present imaging results obtained.

Our group designed a thermal IR hyper-spectral imaging system in this paper mounted in a vacuum encapsulated cavity with temperature controlling equipments. The spectral resolution is 80 nm; the spatial resolution is 1.0 mrad; the spectral channels are 32. By comparing and verifying the theoretical simulated calculation and experimental results for this system, we obtained the precise relationship between the temperature and background irradiation of optical and mechanical structures, and found the most significant components in the optic path for improving imaging quality that should be traded especially, also we had a conclusion that it should cool the imaging optics and structures to about 100K if we need utilize the full dynamic range and capture high quality of imagery.

We present initial performance data from a cryogenic Fourier transform spectrometer (Cryo-FTS) designed for lowbackground spectral infrared calibrations. The Cryo-FTS operates at a temperature of approximately 15 K and has been integrated into an infrared transfer radiometer containing a calibrated Si:As blocked impurity band (BIB) detector. Because of its low operating temperature, the spectrometer exhibits negligible thermal background signal and low drift. Data from tests of basic spectrometer function, such as modulation efficiency, scan jitter, spectral range, spectral resolution and sweep speed will be presented. We will also discuss calibration techniques and results pertinent to operation of the Cryo-FTS as part of a calibration instrument, including background, signal offset and gain, and spectral noise equivalent power. The spectrometer is presently limited to wavelengths below 25 micrometers but can be in principle extended to longer wavelengths by replacing its KBr beamsplitter with another beamsplitter engineered for use beyond 25 micrometers.

Because acoustic power density is proportional to frequency, the size of pulse tube cryocoolers for a given refrigeration power can be reduced by operating them at higher frequencies. A frequency of about 60 Hz had been considered the maximum frequency that could be used while maintaining high efficiency. Recently, we have shown through modeling that by decreasing the volume and hydraulic diameter of the regenerator and increasing the average pressure, it is possible to maintain high efficiency even for frequencies of several hundred hertz. Subsequent experimental results have demonstrated high efficiencies for frequencies of 100 to 140 Hz. The very high power density achieved at higher pressures and higher frequencies leads to very short cooldown times and very compact devices. The use of even higher frequencies requires the development of special compressors designed for such conditions and the development of regenerator matrices with hydraulic diameters less than about 30 Μm. To demonstrate the advantages of higher frequency operation, we discuss here the development of a miniature pulse tube cryocooler designed to operate at 80 K with a frequency of 150 Hz and an average pressure of 5.0 MPa. The regenerator diameter and length are 4.4 mm and 27 mm, respectively. The lowest temperature achieved to date has been 97 K, but a net refrigeration power of 530 mW was achieved at 120 K. Acoustic mismatches with existing compressors significantly limit the efficiency, but necessary modifications to improve the acoustic impedance match between the compressor and the cold head are discussed briefly.

Split linear cryocoolers find use in a variety of infrared equipment installed in airborne, heliborne, marine and vehicular platforms along with hand held and ground fixed applications. An upcoming generation of portable, high-definition night vision imagers will rely on the high-temperature infrared detectors, operating at elevated temperatures, ranging from 95K to 200K, while being able to show the performance indices comparable with these of their traditional 77K competitors. Recent technological advances in industrial development of such high-temperature detectors initialized attempts for developing compact split Stirling linear cryogenic coolers. Their known advantages, as compared to the rotary integral coolers, are superior flexibility in the system packaging, constant and relatively high driving frequency, lower wideband vibration export, unsurpassed reliability and aural stealth. Unfortunately, such off-the-shelf available linear cryogenic coolers still cannot compete with rotary integral rivals in terms of size, weight and power consumption. Ricor developed the smallest in the range, 1W@95K, linear split Stirling cryogenic cooler for demanding infrared applications, where power consumption, compactness, vibration, aural noise and ownership costs are of concern.

The growth in world demand for infrared missile warning systems (MWS) has impelled the development of new technologies, in particular, special cryogenic coolers. Since the cryocooler is a core component in MWS RICOR has met the challenge by developing new models able to withstand high ambient temperatures above 110°C as well as harsh vibration levels, both derived from airborne fighter applications. The development focused on a cryocooler regenerator and cold finger optimization in order to achieve high cooling capacity and a thermodynamic efficiency of about 4.4% at 95°C ambient for one of the cooler models. In order to withstand harsh environmental vibration, the cold finger and outer Dewar structure have been significantly ruggedized; efficient heat sinking methods have been applied and also novel vibration isolation methods have been implemented. The electronic design concept is based on an analog controller, the PCB of which has been designed with internal heat sinking paths and special components being able to withstand ambients temperatures up to 125°C. As a final stage of development, such cryocoolers were successfully qualified by RICOR and system manufacture in harsh environmental conditions and life demonstration tests were performed.

The RM3 is the new development in RM series, thanks to its innovative onboard drive electronics it is now possible for users to extend easily their systems through new functionalities. During this presentation you will have an overview of advantages and benefits of this onboard digital driver electronics both for the Detectors'Module makers and the End-users. Furthermore you will appreciate the specific performances of the RM3. Sofradir and SCD, both leading manufacturers of Detectors'module, have contributed through their expertise to evaluate successfully the RM3, operated by the onboard driver electronics. The results of these new functionalities and cryogenic performances will be revealed throughout the presentation. We plan to adapt this onboard drive electronics to the other products of the RM-series. The next generation of small sized camera's requires increasingly reliable and yet compact Cryocoolers. The customers also need Easy to use & Easy to replace products. We will demonstrate how the RM3 can provide user-friendly solutions to meet these expectations.

Highest efficiency states a crucial requirement for modern tactical IR cryocooling systems. For enhancement of overall efficiency, AIM cryocooler designs where reassessed considering all relevant loss mechanisms and associated components. Performed investigation was based on state-of-the-art simulation software featuring magnet circuitry analysis as well as computational fluid dynamics (CFD) to realistically replicate thermodynamic interactions. As a result, an improved design for AIM linear coolers could be derived. This paper gives an overview on performance enhancement activities and major results. An additional key-requirement for cryocoolers is reliability. In recent time, AIM has introduced linear coolers with full Flexure Bearing suspension on both ends of the driving mechanism incorporating Moving Magnet piston drive. In conjunction with a Pulse-Tube coldfinger these coolers are capable of meeting MTTF's (Mean Time To Failure) in excess of 50,000 hours offering superior reliability for space applications. Ongoing development also focuses on reliability enhancement, deriving space technology into tactical solutions combining both, excelling specific performance with space like reliability. Concerned publication will summarize the progress of this reliability program and give further prospect.

Thales Cryogenics (TCBV) has an extensive background in delivering long life cryogenic coolers for military, civil and space programs. This cooler range is based on two main compressor concepts: close tolerance contact seals (UP) and flexure bearing (LSF/LPT) coolers. Main difference between these products is the Mean Time To Failure (MTTF). In this paper an overview of lifetime parameters will be listed versus the impact in the different cooler types. Also test results from both the installed base and the Thales Cryogenics test lab will be presented. New developments at Thales Cryogenics regarding compact long lifetime coolers will be outlined. In addition new developments for miniature linear cooler drive electronics with high temperature stability and power density will be described.

This paper presents the design, development, optimization experiment and performance of the SITP two-stage Stirling cryocooler. The geometry size of the cooler, especially the diameter and length of the regenerator were analyzed. Operating parameters by experiments were optimized to maximize the second stage cooling performance. In the test the cooler was operated at various drive frequency, phase shift between displacer and piston, fill pressure. The experimental results indicate that the cryocooler has a higher efficiency with a performance of 0.85W at 35K with a compressor input power of 56W at a phase shift of 65°, an operating frequency of 40Hz, 1MPa fill pressure.

A single-stage miniature coaxial pulse tube cryocooler prototype is developed to provide reliable low-noise cooling for an infrared detector system to be equipped in the future space mission. The challenging work is the exacting requirement on its dimensions due to the given miniature Dewar. The limited dimensions result in the insufficiency of the phaseshifting ability of the system when inertance tubes alone are employed. A larger filling pressure of 3.5 Mpa and higher operating frequency up to 70 Hz are adopted to increase the energy density, which compensates for the decrease in working gas volume due to the miniature structure, and realize a fast cool down process. A 1.5 kg dual opposed linear compressor based on flexure bearing and moving magnet technology is used to realize light weight, high efficiency and low contamination. The design and optimization are based on the theoretical CFD model developed by the analyses of thermodynamic behaviors of gas parcels in the oscillating flow. This paper describes the design approach and trade-offs. The cooler performance and characteristics are presented.

A robust U-type pulse tube cryocooler has been developed to replace the heavy and cumbersome passive radiator system for cooling the cold optics component of a sophisticated infrared sensors system used in a weather satellite. The U-type other than coaxial arrangement is chosen to obtain a robust and simple system, and also to avoid the potential loss introduced by the possible mismatch of the temperature profiles of pulse tube and regenerator as well. Besides the conventional integral "U"-shaped cold tip, a novel detachable two-half cold head is designed to enhance cooling performance. Some fine grooves are engraved in the cold head using electro discharge machining technology, which can not only increase the heat transfer area, but also serve as a straightener for the turbulence introduced by the flow reversal. The cooler is powered by a 7.5 cc dual opposed piston compressor and the overall weight is less than 11 kg. It can lift over 8.0W of heat at 150K with 87 W of electric input power and at 310 K of reject temperature. The design considers, experimental results, and performance analyses are presented.

A 2.0W@60K single-stage coaxial pulse tube cryocooler has been developed to provide reliable low-vibration cooling for the space-borne long wave infrared focal plane array. The coaxial configuration result in a compact system and the inertance tube together with a gas reservoir serves as the only phase-shifting to realize a highly reliable system. The inertance tube consists of two parts with different inner diameter and length to obtain the desirable phase relationship. Both cold tip and warm flange integrated with fine slit heat exchanges fabricated with electro discharge machining technology to enhance heat exchange performance. A split Oxford-type linear compressor with dual-opposed piston configuration is connected to the cold finger with a 30 cm flexible metallic tube. The overall weight without control electronics is below 8 kg. The preliminary experiments show that a no-load temperature of 46 K and a cooling power of 2 W at 60 K with 104 W of input power at 300K reject temperature have been achieved.

This paper briefly reviews the development of space Stirling and pulse tube cryocoolers in Shanghai Institute Technical Physics, Chinese Academy of Sciences (SITP/CAS). The status of both types of coolers is outlined, including those currently undergoing performance optimization, qualification investigation, or characterization and endurance evaluation. The approaches for vibration control and the efforts to increase reliability are also presented. The purpose is to present a brief overview of the data package of both types of coolers developed and under developing in SITP/CAS, and also demonstrates our efforts to enable space qualified cryogenic technologies in China.

Cooled IR technologies are challenged for answering new system needs like the reduction of energy. This reduction is requested in new IR system design in particular for cooled IR detection. The goal is to reduce system sizes, to increase system autonomies and reliabilities and globally to reduce system costs! One of the key drivers for cooled systems is the cooler and the operating temperature. As far as operating temperature is concerned, Sofradir put a lot of efforts for years for adapting its technologies to increase the operating temperatures of IR detectors. Main examples are dealing with long wave staring arrays based on QWIP technology and on MCT technology as well as medium wave staring arrays using MCT technologies.

The utilization of the non-equilibrium photodiode concept for high operating temperature (HOT) FPAs is discussed, both generically, and with regard to the specific example of MWIR HgCdTe. The issues of dark current, surface passivation, and 1/f noise are considered for three different architectures, namely N⁺/N^-/P⁺, N⁺/P^-/P⁺, and nBn. These architectures are examined with regard to possible FPA performance limitations, and potential difficulty in reduction to practice. Performance data obtained at DRS for the N⁺/N^-/P⁺ and N⁺/P^-/P⁺ HgCdTe architectures will be presented.

Raytheon Vision Systems (RVS) is producing large format, high definition HgCdTe-based MWIR and SWIR focal plane arrays (FPAs) with pitches of 15 μm and smaller for various applications. Infrared sensors fabricated from HgCdTe have several advantages when compared to those fabricated from other materials -- such as a highly tunable bandgap, high quantum efficiencies, and R0A approaching theoretical limits. It is desirable to operate infrared sensors at elevated operating temperatures in order to increase the cooler life and reduce the required system power. However, the sensitivity of many infrared sensors, including those made from HgCdTe, declines significantly above a certain temperature due to the noise resulting from increasing detector dark current. In this paper we provide performance data on a MWIR and a SWIR focal plane array operating at temperatures up to 160K and 170K, respectively. The FPAs used in the study were grown by molecular beam epitaxy (MBE) on silicon substrates, processed into a 1536x1024 format with a 15 μm pixel pitch, and hybridized to a silicon readout integrated circuit (ROIC) via indium bumps to form a sensor chip assembly (SCA). This data shows that the noise equivalent delta temperature (NEDT) is background limited at f/3.4 in the SWIR SCA (cutoff wavelength of 3.7 μm at 130K) up to 140K and in the MWIR SCA (cutoff wavelength of 4.8 μm at 115K) up to 115K.

One of the main advantages of increasing the operating temperature of infrared focal plane arrays (FPAs) is to take advantage of lower cost cooling options such as thermoelectric coolers. However the maximum reduction in temperature available from the current generation of coolers (e.g. 4-stage) is around 110 K. For a maximum operating temperature of 70 oC, this means that the FPA needs to operate above 233 K. In this region, the performance becomes a strong function of array temperature and designing a system becomes a trade-off between the performance of the fpa; the speed of the optics; the maximum temperature of operation; and the cooler power and complexity. In this paper, previous results will be extrapolated to estimate the FPA performance across this trade space by varying cut-off wavelength. Possible techniques to enhance the performance of the FPAs by reducing low frequency noise or adding optical concentrators will also be considered. These extrapolated results indicate that in an f/2 system at 210 K, an NETD of around 30 mK could be achievable. Potential applications for the technology are in systems where long lifetime; no moving parts; or reduced weight are an advantage. Ideally the maximum ambient temperature should be limited to maintain the best thermal sensitivity. Suitable applications could include sensors which operate from UAVs or in space.

An XBn photovoltaic device has a band profile similar to that of a standard homojunction p-n diode, except that the depletion region is made from a wide bandgap barrier material with a negligible valence band offset but a large conduction band offset. In this notation, "X" stands for the n- or p-type contact layer, "B", for the n-type, wide bandgap, barrier layer, and "n", for the n-type, narrow bandgap, active layer. In this work, we report on the fabrication of XBn devices, which were grown by Molecular Beam Epitaxy (MBE) on GaSb substrates. Each structure has an InAsSb active layer of thickness ~1.5μm and a 0.2-0.5μm thick AlSbAs barrier layer. Good growth uniformity was achieved with lattice matching of better than 500ppm. Selected layers have been processed into devices which operate with a high internal quantum efficiency at a bias of ~0.1-0.2V, and which exhibit a very low dark current due to the strong suppression of the current component due to bulk Generation-Recombination processes. From dark current measurements, a minority carrier lifetime of >670nS has been estimated in devices with an active layer doping of ~4×10¹⁵cm^-3. In optimized, lattice matched, devices with this doping and an active layer thickness of 4μm, a cut-off wavelength of ~ 4.0 - 4.1μm is expected at 160K, with a dark current density of ~10^-6 A cm^-2 and a quantum efficiency of >70% (λ<4μm). These figures correspond to BLIP operation at 160K with a photocurrent to dark current ratio of ~4 at f/3.

The development of InAsSb detectors based on the nBn design for the mid-wave infrared (MWIR) spectral region is discussed. Comparisons of optical and electrical properties of InAsSb photodetectors with two different barrier material, namely, AlAs _0.15Sb_0.75 (structure A) and AlAs_0.10Sb_0.9 (structure B) are reported. The dark current density in the AlAs0.15Sb0.85 is lower possibly due to the larger valence band offset. Clear room temperature spectral responses is observed and a specific detectivity (D*) of 1.4x10¹² and 1.01x10¹² cmHz^1/2/W at 0.2 V, and a responsivity of 0.87 and 1.66 A/W under 0.2 V biasing at 77 K and 3.5 μm, assuming unity gain, was obtained for structures A and B, respectively.

Overcoming the stringent cooling requirement for the operation of most of the infrared (IR) detectors is one of the major challenges towards capturing their full potential. Split-off (SO) transitions based detector exhibit encouraging results and gives hope to provide a novel alternative to the conventional IR detectors operating with cryogenic aid. Recently, a GaAs/AlGaAs SO detector operating up to 330 K in the 3-5 μm spectral region was developed. This paper presents various design modifications including graded barrier (in place of flat barrier), and double barrier resonant structure (in place of a single barrier) to improve the performance of these detectors. The graded barrier improves the detector performance by reducing the space charge buildup due to the trapping of charge carriers at the emitter-barrier interface; additionally, the model implementation on GaAs/AlGaAs based detectors also suggests that a barrier offset of 20 meV approximately doubles the responsivity. The implementation of a double barrier resonant structure increases the escape of holes from the SO to the light/heavy hole (LH/HH) bands by bringing the two bands into resonance and increases the response by a factor of ~ 85. The results from our ongoing efforts to extend the concept of SO mechanism based IR detection towards longer wavelength are also presented. This should be possible by exploiting SO absorption in alternative material systems such as phosphides and nitrides. The successful utilization of SO mechanism can result in the high operating temperature detectors operating in mid-IR and terahertz (THz) region.

The nominally sharp interfaces in layered HgCdTe heterostructures are affected by interdiffusion for growth at a temperature of above 300 K. Significant composition and doping grading always occur in layered HgCdTe heterostructures grown with MOCVD (360°C), LPE (480°C), and ISOVPE (500°C) epitaxial techniques. MBE (170°C) is the only technique that practically does not introduce significant diffusion grading, but it can be introduced by post growth processing, especially during dopants activation. The purpose of this paper was to explain how the grading affects performance of photodetectors operating at near room temperatures (190-300 K). Influence of the growth related and intentional grading on dark currents and response time was studied with numerical calculations and experiments. Practical infrared devices with controlled grading were grown with programmed MOCVD and characterized. The studies revealed interesting properties of the N⁺pP⁺ devices with graded interfaces. Controlled grading minimizes Auger, Shockley-Read and tunnel currents, increases responsivity and linearity range. The grading is also important for high frequency performance of the devices.

This paper presents the development of non-cryogenic-cooling spectrum infrared (IR) focal plane array (FPA) using a single carbon nanotube (CNT). The FPA consists of an array of CNT-based photodiodes. The CNT-based photodiodes can be made by our nanomanufacturing process and band gaps of CNTs can be tuned precisely by the electric breakdown system. As a result, the CNT-based photodiodes with high sensitivity at a special wavelength can be achieved. In this paper, design, fabrication and experimental results of the CNT-based IR photodiode are reported. The results indicate that CNTs are very sensitive of middle-wave IR (MWIR) signal at room temperature. Moreover, the performances of the photodiodes have been evaluated. These results suggest that CNTs can be used in high throughput sensing applications.

The theoretical performance of medium wavelength infrared (MWIR) InAsSb-based ternary alloy photodiodes is examined theoretically taking into account thermal generation governed by the Auger and radiative mechanisms. The contribution of spin-off band on carrier lifetime in p-type InAsSb ternary is re-examined due to new insight into composition dependence of spin-orbit-splitting band gap energy. The investigations are carried out for photodiodes operated at room temperature. The effects of doping profiles on the photodiode parameters (R₀A product and detectivity) are considered. The theoretical predictions of photodiode parameters are compared with experimental data published in the literature.

During the last 15 years, the Spanish MoD laboratories (CIDA) have developed the VPD PbSe technology (Vapor Phase Deposited). The excellent properties of the material (sensitivity in the MWIR band, high performance in uncooled operation, and photodetector), together with a new method of processing the material based on PbSe deposition by phase vapor, which is fully compatible with Si-CMOS technology, have opened tremendous perspectives with multiple applications for the detector where fast responses and low cost are main requirements. In 2008 the VPD manufacturing technology was transferred to New Infrared Technologies, S.L. (NIT) This paper shows the actual situation of the technology, describing the last advances reached with the new 32x32 uncooled imager, able to provide frame rates above 1,000 fps. The work also describes the industrial strategy adopted for bringing the technology towards the industrialization and the roadmap of the technology from the point of view of future devices and systems.

This paper describes progress in the development of dual-band (MW / LW) infrared detectors made from HgCdTe grown by Metal-Organic Vapor Phase Epitaxy. The technologies of LW and MW single band detectors, which feed into dualband capability, are discussed. The performance of single-band detectors is detailed to give an indication of the quality that can be achieved through MOVPE processes. For single-band detectors, pixel resolution has reached 1024 x 786, while pixel pitch has been reduced to 16μm. Operability for single-band detectors has exceeded 99.98% in both bands. Full-TV (640 x 512 pixels) dual-band arrays on 24μm and 20μm pitches have been developed. MW median NETD values achieved are 10mK and 14mK for the 24μm and 20μm pitch arrays respectively. The corresponding LW median NETD values are 23mK and 27mK respectively.

We have previously presented results from our mercury cadmium telluride (MCT, Hg1-xCdxTe) growth on silicon substrate technology for different applications, including negative luminescence, long waveband and mid/long dual waveband infrared imaging. In this paper, we review recent developments in QinetiQ's combined molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE) MCT growth on silicon; including MCT defect density, uniformity and reproducibility. We also present a new small-format (128 x 128) focal plane array (FPA) for high frame-rate applications. A custom high-speed readout integrated circuit (ROIC) was developed with a large pitch and large charge storage aimed at producing a very high performance FPA (NETD ~10mK) operating at frame rates up to 2kHz for the full array. The array design allows random addressing and this allows the maximum frame rate to be increased as the window size is reduced. A broadband (2.5-10.5 μm) MCT heterostructure was designed and grown by the MBE/MOVPE technique onto silicon substrates. FPAs were fabricated using our standard techniques; wet-etched mesa diodes passivated with epitaxial CdTe and flip-chip bonded to the ROIC. The resulting focal plane arrays were characterized at the maximum frame rate and shown to have the high operabilities and low NETD values characteristic of our LWIR MCT on silicon technology.

In recent years AIM has expanded its portfolio of standard IR focal plane arrays (FPA) in the 3-5μm (MWIR) and 8- 10μm (LWIR) spectral range by 2-dimensional IR detectors, sensitive in the 0.9-2.5μm (SWIR) and especially in the 10- 15μm VLWIR. As far as dark current behavior, homogeneity, and operability are concerned, the VLWIR spectral range constitutes a major challenge for sensor material improvement and device development. This paper reports on the latest technological advancements at AIM. These advancements are not limited to the applications demonstrated in this paper, but a wide range of AIM products will benefit. A reduction of the pixel pitch from 24μm to 15μm is the result of increasing demands for compact detection modules with reduced weight, size, power consumption and improved costefficiency. Performance characterization for such a reduced pitch of 640x512 module in the LWIR (cut-off 9.2μm at 67 K) yields a mean NETD of ~37 mK and an operability of >99.8%. Extending the detection wavelength further into the VLWIR is of major interest for space applications such as Meteosat Third Generation (MTG), which poses challenging requirements for sensor material homogeneity and dark current density. To meet this requirement, an extrinsic doping approach is utilized on a 256x256 HgCdTe Focal Plane Array (FPA) with ~14μm cut-off wavelength at 55K operating temperature, a dark current density of about 1pA/μm² is demonstrated.

Additional to the development of 3rd Gen IR modules like dual-band and dual-color devices AIM is focused on IR FPAs with reduced pitch. These FPAs allow manufacturing of compact low cost IR modules with minimum power consumption for state-of-the-art high performance IR systems. AIM has realized full TV format MCT 640x512 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 UAV applications. In typical configurations like a F/4.6 cold shield for the 640x512 MWIR module an NETD < 25 mK @ 5 ms integration time is achieved, while the LWIR modules achieve an NETD < 38 mK @ F/2 and 180 μs integration time. For the LWIR modules FPAs with a cut-off of 9 and 10 μm have been realized. The modules are available either with different integral rotary cooler configurations for portable applications which require minimum cooling power or a new split linear cooler providing long lifetime with a MTTF > 20,000 h as required e.g. for warning sensors in 24/7 operation. The modules are available with an optional image processing electronics providing non-uniformity correction and further image processing for a complete IR imaging solution. A double field of view FLIR for an upgrade of the German Army UAV LUNA has been developed by AIM using the MCT 640x512 MWIR 15μm pitch engine. The latest results and performance of those modules and their applications are presented.

A numerical model of the current noise spectral density in elements of infrared focal plane array based on HgCdTe photodiodes has been developed. Model is based on Langevine method and applied to the photodiode with p⁺-n-junction and base of finite length d. Dominated dark current diffusion mechanism and random nature of thermal generationrecombination and scattering processes determined the diffusion current fluctuations has been taken into account. The model main peculiar properties are the stochastic boundary conditions on the interface between the depletion and quasineutral regions. Current noise spectral density of the diode with thin base d < L_p, where Lp is the hole diffusion length in n-region, has been calculated. In thin base diodes with blocking contact to substrate, in which recombination velocity S = 0, a noise suppression effect is revealed. At noticeable reverse junction biases |qV| > 3kT the diffusion current noise suppression is to be observed in whole frequency band ωtfl << 1, where tfl is the hole flight time through the depletion region. In this case the diffusion current noise spectral density is less than in diodes with thick base (d >> L_p) by a factor th(d/L_p). At slight biases |qV| < 3kT the diffusion current noise suppression occurs only in limited frequency band ωτ < 1, where τ is the minority carriers lifetime. At high frequencies ωτ >> 1 diffusion current noise comes out of fluctuations caused by scattering processes and is independent on the diode structure. Photocurrent noise spectral density has been calculated too. Model developed is useful for the photodiode elements and arrays optimization.

Low IR input flux conditions are answering different system applications as gas detection needs, active imagery, very long ranges detection and identification and some scientific applications. Then for other applications like ground applications, some system design trade-off could be made between thermal performance and identification and equipment size and cost.

SELEX Galileo has developed avalanche photodiode technology in HgCdTe to serve a whole range of applications in defence, security, commercial and space research. Burst-illumination LIDAR (BIL), using a near-infrared pulse laser and a fast, gated detector, is now adopted for most long range imaging applications. New results from range trials using prototype systems based on multifunctional and 3D detectors are reported. In the astronomy field, APD arrays at 2.5 μm cutoff can provide near-single photon sensitivity for future wavefront sensors and interferometric applications. Under a contract from European Southern Observatories arrays have been successfully demonstrated with gains up to 20× and negligible dark current at 77K. Under a European Space Agency contract, a large area, single element detector has been designed for the 2.015μm CO₂ absorption line. The sensor is specifically designed to be operated at 200K so that thermoelectric cooling is viable. The element is made up of many sub-pixel diodes each deselectable to ensure high breakdown in the macro-pixel. The latest results of the detector and its associated transimpedance amplifier (TIA) are presented.

CEA-Leti has developed a new 320x256 hybrid focal plane array (FPA) for flash LADAR imaging. The detector array consists of 30μm pixel pitch MWIR HgCdTe avalanche photodiodes operating at 80K and the readout integrated circuit (ROIC) is fabricated on a standard 0.18μm CMOS process. The custom ROIC can operate as a passive thermal imager or a flash LADAR imager. In this second mode, each pixel will provide the time of flight measurement (3D) and the returned intensity (2D) of one laser pulse. For the first laboratory trials the e-APD photodiode array performances were measured in passive mode and the same FPA was then tested in one shot LADAR mode. This paper describes the readout IC pixel architecture and reports the first electro-optical test results in both passive and active modes. This new prototype takes advantage of the latest developments of the partnership between Sofradir and CEA-Leti.

Single-photon imaging in infrared will add a new valuable tool to night imaging cameras. Despite years of development, high-sensitivity SWIR cameras are still expensive and not ready for large-volume production. Germanium (Ge) is a promising semiconductor to convert SWIR radiation and it has seen extensive development in conjunction with highspeed optical communications. We are demonstrating a new low-light level infrared array technology based on the single-photon sensitive Geiger avalanche PhotoDiode (Si-GPD) array technology developed at aPeak and low-dislocation Germanium processing developed at MIT. The core of the imaging camera is a Ge:Si photon-counting GPD pixel with CMOS readout. The primary technology objective is to demonstrate through prototyping and semiconductor process development the technical feasibility of single-photon detection cameras sensitive in the SWIR and set the performance specifications. We report on prototype Ge:Si structures compatible with the GPD operation and technology. We demonstrate >80% quantum efficiency at 1310nm and 45%-60% quantum efficiency at 1550nm. Dark current measurements indicate that single-photon sensitivity (2.6x10-18W/pixel) is achievable by cooling the detector at cryogenic temperatures down to 53K. A digital developed to provide adjustable dynamic range and frame rate is reported. Because the GPD detectors have intrinsic excellent gating and ranging capability, the pixel architecture is developed to enable the dual mode operation - passive illumination two-dimensional imaging (night vision) and active illumination three-dimensional imaging.

There is strong interest in developing Short Wavelength Infrared (SWIR) photo receivers for applications like laser ranging and robotic vision. Recently, Spectrolab has developed a first generation low noise receiver for NASA. The receiver shows a bandwidth of 180 MHz, presently limited by the transimpedance amplifier (TIA). The first generation photoreceiver has InP avalanche photodiode (APD). The overall photoreceiver noise equivalent power (NEP) is less than 300 fW/√Hz. Furthermore, Spectrolab is developing low excess noise APDs with Impact Ionization Engineering (I2E). The I²E low noise APDs were built from baseline InAlAs APDs with a keff value of 0.22. A thin layer of InGaAlAs alloy was incorporated into the InAlAs multiplication layer in these devices. All the I²E APDs show lower keff-value than InAlAs and very low dark currents. Values as low as k_eff<0.1 have been demonstrated. These I²E APDs will be used in Spectrolab's second generation photoreceiver. A Noise Equivalent Power (NEP) of 300 fW/√Hz is expected over a 1GHz response bandwidth.

In this paper we present a separate-absorption-charge-multiplication Ge/Si avalanche photodiode, which has a high gain-bandwidth product (e.g., >860GHz at a wavelength of 1310nm). Such a high gain-bandwidth product is attributed to the peak enhancement of the frequency response at the high frequency range. From a small signal analysis, we establish an equivalent circuit model which includes a capacitance parallel connected with an inductance due to the avalanche process. When the APD operates at high bias voltages, the LC circuit provides a resonance in the avalanche, which introduces a peak enhancement.

Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High sensitivity is obtained by integrating high performance detectors with gain i.e. APDs with very low noise Readout Integrated Circuits. Unique aspects of these designs include: independent acquisition (non-gated) of pulse returns, multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image. Recent breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise to gains in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting. SCAs utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range resolution enabling detailed 3D imagery both at short range and long ranges. In this presentation we will review progress in high resolution scanning, staring and ultra-high sensitivity photon counting LADAR sensors.

The Thermal Infrared Sensor (TIRS) is a QWIP based instrument intended to supplement the Operational Land Imager (OLI) for the Landsat Data Continuity Mission (LDCM) [1]. The TIRS instrument is a dual channel far infrared imager with the two bands centered at 10.8μm and 12.0μm. The focal plane assembly (FPA) consists of three 640x512 GaAs Quantum Well Infrared Photodetector (QWIP) arrays precisely mounted to a silicon carrier substrate that is mounted on an invar baseplate. The two spectral bands are defined by bandpass filters mounted in close proximity to the detector surfaces. The focal plane operating temperature is 43K. The QWIP arrays are hybridized to Indigo ISC9803 readout integrated circuits (ROICs). Two varieties of QWIP detector arrays are being developed for this project, a corrugated surface structure QWIP and a grating surface structure QWIP. This paper will describe the TIRS system noise equivalent temperature difference sensitivity as it affects the QWIP focal plane performance requirements: spectral response, dark current, conversion efficiency, read noise, temperature stability, pixel uniformity, optical crosstalk and pixel yield. Additional mechanical constraints as well as qualification through Technology Readiness Level 6 (TRL 6) will also be discussed.

We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (C-QWIP FPAs) into the far infrared regime. Specifically, we are developing the detectors for the Thermal Infrared Sensor (TIRS) used in the Landsat Data Continuity Mission. This mission requires infrared detection cutoff at 12.5 μm and FPAs operated at 43 K. To maintain a low dark current in these extended wavelengths, we adopted a low doping density of 0.6 × 10¹⁸ cm^-3 and a bound-to-bound state detector in one of the designs. The internal absorption QE is calculated to be 25.4% for a pixel pitch of 25 microns and 60 periods of QWs. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external QE is 14.4%. To yield the theoretical conversion efficiency CE, the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1 × 10^-6 A/cm² at 43 K. For regular infrared imaging above 8 μm, the FPA will have an NETD of 16 mK at 2 ms integration time in the presence of 260 read noise electrons, and it increases to 22 mK at 51 K. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30 μm cutoff.

QWIPs are well known for their stability, high pixel-pixel uniformity and high pixel operability which are quintessential parameters for large area imaging arrays. In this paper we report the first demonstration of the megapixel-simultaneously-readable and pixel-co-registered dual-band QWIP focal plane array (FPA). The dual-band QWIP device was developed by stacking two multi-quantum-well stacks tuned to absorb two different infrared wavelengths. The full width at half maximum (FWHM) of the mid-wave infrared (MWIR) band extends from 4.4 - 5.1 μm and FWHM of the long-wave infrared (LWIR) band extends from 7.8 - 8.8 μm. Dual-band QWIP detector arrays were hybridized with direct injection 30 μm pixel pitch megapixel dual-band simultaneously readable CMOS read out integrated circuits using the indium bump hybridization technique. The initial dual-band megapixel QWIP FPAs were cooled to 68K operating temperature. The preliminary data taken from the first megapixel QWIP FPA has shown system NE▵T of 27 and 40 mK for MWIR and LWIR bands respectively.

This paper presents a method to predict the responsivity of quantum well infrared photodetectors based in interband and intersubband transitions. The transfer matrix method (TMM) is used in a self consistent loop to calculate initial and final states as well as their respective wavefunctions, allowing the estimation of the absorption coefficient along the entire detection range. The transmission coefficient (tunneling factor) is also computed using the TMM. The spectral response is compared with measurements of AlGaAs/GaAs/InGaAs QWIPs sensitive to NIR, MWIR and LWIR, showing a good match for peak wavelength and a reasonable back-of-the-envelope result for the overall response. The results indicate that the technique has a great potential to be further improved and used in QWIP design.

Low dark current photodiodes (PDs) in the short wavelength infrared (SWIR) upto 2.5μm region, are expected for many applications. HgCdTe (MCT) is predominantly used for infrared imaging applications. However, because of high dark current, MCT device requires a refrigerator such as stirling cooler, which increases power consumption, size and cost of the sensing system. Recently, InGaAs/GaAsSb type II quantum well structures were considered as attractive material system for realizing low dark current PDs owing to lattice-matching to InP substrate. Planar type PIN-PDs were successfully fabricated. The absorption layer with 250 pair-InGaAs(5nm)/GaAsSb(5nm) quantum well structures was grown on S-doped (100) InP substrates by solid source molecular beam epitaxy method. InP and InGaAs were used for cap layer and buffer layer, respectively. The p-n junctions were formed in the absorption layer by the selective diffusion of zinc. Diameter of light-receiving region was 140μm. Low dark current was obtained by improving GaAsSb crystalline quality. Dark current density was 0.92mA/cm² which was smaller than that of a conventional MCT. Based on the same process as the discrete device, a 320x256 planar type focal plane array was also fabricated. Each PD has 15μm diameter and 30μm pitch and it was bonded to read-out IC by using indium bump flip chip process. Finally, we have successfully demonstrated the 320 x256 SWIR image at room temperature. This result means that planer type PD array with the type II InGaAs/GaAsSb quantum well structure is a promising candidate for uncooled applications.

GaInAs/GaAsSb type-II multiple quantum wells (MQWs) grown on InP substrates by molecular beam epitaxy (MBE) were investigated for potential use in p-i-n photodiodes operating in the mid-infrared spectral region. In these quantum well structures, electrons and holes are spatially separated. The resulting spatially indirect type-II detection occurs at longer wavelength than the spatially direct intraband recombination in either GaInAs or GaAsSb. A 4-band k · p Hamiltonian model was employed to calculate the detection wavelengths and wavefunction overlaps. A p-i-n structure with 100 pairs of Ga_0.66In₀₃₄As (~7.0 nm)/GaAs_0.25Sb_0.75 (~5.0 nm) MQWs structure with operation wavelength of above 3.0 μm was designed and grown by MBE. The compressively strained GaAsSb layers are strain-compensated by tensile strained GaInAs. Photo response of above 3 μm was observed by room temperature responsivity measurements.

Next generation infrared photodetector technology will require focal plane array (FPA) systems that have multi-spectral imaging capabilities. One proposed approach to realizing these multicolor devices is to use plasmonic resonators. However, device development and characterization are commonly addressed with large front side illuminated single pixel detectors on a supporting epitaxial substrate. The focal plane arrays on the other hand are backside illuminated. Moreover, in a front side illuminated device, there is significant substrate scattering of the incident light. Here, we propose a method for the accurate measurement of device performance by using a hybridized chip design (hybrid chip) that is similar to the fabrication of an FPA system, with the substrate completely removed through a combination of mechanical polishing and subsequent wet etching techniques. The hybrid chip was also designed to precisely characterize the effects of varying mesa size by incorporating square mesa structures that range from 25 to 200 μm in width. This approach offers an advantage over conventional device characterization because it incorporates mesas that are on the same scale as those normally used in FPA systems, which should therefore provide a fast transition of new photodetector technology into camera based systems. The photodetector technology chosen for this work is a multi-stack quantum dots-in-a-well (DWELL) structure designed to absorb electromagnetic radiation in the mid-infrared spectral range.

The Quantum Cascade Detector (QCD) is a multiple quantum well photodetector working at low bias or zero bias. It has a zero dark current occurring at 0V, together with a high photovoltaic photoresponse, since the QCD does not need any applied field to improve the collection of electrons. QCDs have been tested at various wavelengths, from short wavelengths (1.5 microns) up to THz waves, through the entire infrared spectrum (middle and long wavelengths). Theory of transport in QCD is now well established, and leads to accurate calculations of current and noise in QCDs, with a very good agreement with experimental results. Latest results and state of the art of performances of QCDs are presented.

The infrared photon flux emitted by an object depends not only on its temperature but also on a proportionality factor referred to as its emissivity. Since the latter parameter is usually not known quantitatively a priori, any temperature determination based on single-band radiometric measurements suffers from an inherent uncertainty. Recording photon fluxes in two separate spectral bands can in principle circumvent this limitation. The technique amounts to solving a system of two equations in two unknowns, namely, temperature and emissivity. The temperature derived in this manner can be considered absolute in the sense that it is independent of the emissivity, as long as that emissivity is the same in both bands. QmagiQ has previously developed a 320x256 midwave/longwave staring focal plane array which has been packaged into a dual-band laboratory camera. The camera in question constitutes a natural tool to generate simultaneous and independent emissivity maps and temperature maps of entire two-dimensional scenes, rather than at a single point on an object of interest. We describe a series of measurements we have performed on a variety of targets of different emissivities and temperatures. We examine various factors that affect the accuracy of the technique. They include the influence of the ambient radiation reflected off the target, which must be properly accounted for and subtracted from the collected signal in order to lead to the true target temperature. We also quantify the consequences of spectrally varying emissivities.

Lockheed Martin's Advanced Technology Center in Palo Alto has developed a prototype 8x8 NIR focal plane capable of simultaneous Fourier processing per pixel. Experiments will be described in which 10 kHz Fourier processed frame rates are used to drive a closed loop tracking servo loop. The pointing direction of one laser with wavelength λ1, and amplitude modulation f1 is adjusted with a fast stirring mirror to track the motion of two targets illuminated by two other lasers with wavelengths λ2 and λ3, amplitude modulated at two other distinct frequencies. Closed loop tracking control at 1kHz is demonstrated using only the single 8x8 focal plane to sense position of the three lasers simultaneously at all pixels. Random noise generated by heat sources and a fan applied to the track laser beam path, and a white light source with 100x larger signal then the received laser signal shown directly on the focal plane, has no effect on the track loop. A final discussion will show the capability of the sensor to simultaneously measure range, as well as position.

CEA Leti has recently developed a new readout IC (ROIC) with pixel-level ADC for cooled infrared focal plane arrays (FPAs). It operates at 50Hz frame rate in a snapshot Integrate-While-Read (IWR) mode. It targets applications that provide a large amount of integrated charge thanks to a long integration time. The pixel-level analog-to-digital conversion is based on charge packets counting. This technique offers a large well capacity that paves the way for a breakthrough in NETD performances. The 15 bits ADC resolution preserves the excellent detector SNR at full well (3Ge-). These characteristics are essential for LWIR FPAs as broad intra-scene dynamic range imaging requires high sensitivity. The ROIC, featuring a 320x256 array with 25μm pixel pitch, has been designed in a standard 0.18μm CMOS technology. The main design challenges for this digital pixel array (SNR, power consumption and layout density) are discussed. The IC has been hybridized to a LWIR detector fabricated using our in-house HgCdTe process. The first electro-optical test results of the detector dewar assembly are presented. They validate both the pixel-level ADC concept and its circuit implementation. Finally, the benefit of this LWIR FPA in terms of NETD performance is demonstrated.

We have previously discussed the potential of using an Hg1-xCdxTe (MCT) source as a reference plane for the nonuniformity correction of thermal imagers. Due to the fast switching speed, the apparent temperature can be changed on a frame to frame basis. This allows multipoint correction data to be obtained without having to wait for temperatures to stabilize as with a Peltier reference source. Also, the operation of the device can be synchronized to the integration period of the camera to reduce the mean power requirements by the ratio of the frame to the integration time and hence thermal heating effects are also reduced. In this paper, we discuss a practical implementation of this concept in a thermal imaging camera, which is being developed as part of the UK MOD Albion program. This development has involved increasing the device size, increasing the effective temperature range and matching the drive requirements to typical camera power supplies. The factors determining the achievable effective temperatures are discussed, together with modifications to the device design that have been implemented to obtain a useful temperature range. The drive requirements have been improved by developing a series connected structure. This has reduced the peak current by a factor of 4 and allows the devices to be controlled with conventional Peltier reference electronics rather than a custom unit. The improved devices have now been incorporated into a state-of-the-art infrared camera and their performance in this system will be discussed.

Today's modular, mixed-signal CMOS process platforms are excellent choices for manufacturing of highly integrated, large-format read out integrated circuits (ROICs). Platform features, that can be used for both cooled and un-cooled ROIC applications, can include (1) quality passives such as 4fFμm² stacked MIM capacitors for linearity and higher density capacitance per pixel, 1kOhm high-value poly-silicon resistors, 2.8μm thick metals for efficient power distribution and reduced I-R drop; (2) analog active devices such as low noise single gate 3.3V, and 1.8V/3.3V or 1.8V/5V dual gate configurations, 40V LDMOS FETs, and NPN and PNP devices, deep n-well for substrate isolation for analog blocks and digital logic; (3) tools to assist the circuit designer such as models for cryogenic temperatures, CAD assistance for metal density uniformity determination, statistical, X-sigma and PCM-based models for corner validation and to simulate design sensitivity, and (4) sub-field stitching for large die. The TowerJazz platform of technology for 0.50μm, 0.25μm and 0.18μm CMOS nodes, with features as described above, is described in detail in this paper.

A radiation-resistant readout integrated circuit for focal plane arrays was studied to improve the reliability of infrared image systems operating in a radioactive environment, such as in space or in the surroundings of a nuclear reactor. First, as radiation-hardened NMOSFET structure, which includes a layout modification technique, was proposed. The readout integrated circuit for infrared focal plane arrays was then designed on basis of the proposed NMOSFET layout. Commercial 0.35 um process technology was used to fabricate the proposed unit NMOSFET and the designed readout integrated circuit which is based on the proposed NMOSFET. The measured electrical characteristics of the fabricated unit NMOSFET and readout integrated circuit are in good agreement with the simulated results. For verification of the radiation tolerance, the fabricated chip was exposed to 1 Mrad (Si) of gamma radiation, which is high enough to guarantee reliable usage in space or in a very harsh radiation environment. While exposed to gamma radiation, the fabricated chip was connected to a power supply (3.3 V) for testing under the worst conditions. After being exposed to 1 Mrad of gamma radiation, the unit NMOSFET showed only a slight increment of a few picoamperes in the leakage current, and the designed readout integrated circuit showed little change at an output voltage of less than 10% of a proper output voltage. The changes in the characteristics of the unit NMOSFET and the designed readout infrared integrated circuit are at an allowable level in relation to process variation.

Design of a silicon readout integrated circuit (ROIC) for LWIR HgCdTe Focal Plane is presented. ROIC incorporates time delay integration (TDI) functionality over seven elements with a supersampling rate of three, increasing SNR and the spatial resolution. Novelty of this topology is inside TDI stage; integration of charges in TDI stage implemented in current domain by using switched current structures that reduces required area for chip and improves linearity performance. ROIC, in terms of functionality, is capable of bidirectional scan, programmable integration time and 5 gain settings at the input. Programming can be done parallel or serially with digital interface. ROIC can handle up to 3.5V dynamic range with the input stage to be direct injection (DI) type. With the load being 10pF capacitive in parallel with 1MΩ resistance, output settling time is less than 250nsec enabling the clock frequency up to 4MHz. The manufacturing technology is 0.35μm, double poly-Si, four-metal (3 metals and 1 top metal) 5V CMOS process.

In areas like military systems, surveillance systems, or industrial process control, more and more often there is a need to operate in limited visibility conditions or even in complete darkness. In such conditions vision systems can benefit by using thermal vision cameras. In thermal imaging an infrared radiation detector arrays are used. Contemporary infrared detector arrays suffers from technological imprecision which causes that the response to uniform radiation results in nonuniform image with superimposed fixed pattern noise (FPN). In order to compensate this noise there is a need to evaluate detectors characteristics like responsivity and offset of every detector in array. Some of the detectors in cooled detector arrays can be also defective. Signal from defective pixels has to be in such system replaced. In order to replace defective pixels, there is a need to detect them. Identification of so-called blinking pixels needs long time measurement, which in designed calibration stand is also possible. The paper presents the design of infrared detector array measurement stand allowing measurement of mentioned parameters. Measurement stand was also used to evaluate temporal noise of infrared detection modules. In article there is a description of optical system design and parameters of used reference blackbodies. To capture images from camera modules a specially designed digital image interface was used. Measurement control and calculations were made in specially written IRDiag software. Stand was used to measure parameters for cameras based on cooled focal plane arrays from Sofradir. Results of two-point nonuniformity correction are also presented.

Rapid development of infrared detector arrays caused a need to develop robust signal processing chain able to perform operations on infrared image in real-time. Every infrared detector array suffers from so-called nonuniformity, which has to be digitally compensated by the internal circuits of the camera. Digital circuit also has to detect and replace signal from damaged detectors. At the end the image has to be prepared for display on external display unit. For the best comfort of viewing the delay between registering the infrared image and displaying it should be as short as possible. That is why the image processing has to be done with minimum latency. This demand enforces to use special processing techniques like pipelining and parallel processing. Designed infrared processing module is able to perform standard operations on infrared image with very low latency. Additionally modular design and defined data bus allows easy expansion of the signal processing chain. Presented image processing module was used in two camera designs based on uncooled microbolometric detector array form ULIS and cooled photon detector from Sofradir. The image processing module was implemented in FPGA structure and worked with external ARM processor for control and coprocessing. The paper describes the design of the processing unit, results of image processing, and parameters of module like power consumption and hardware utilization.

Methods of estimating range to an emissive target based on the depth of an atmospheric absorption band are presented. The present work uses measurements of the CO₂ absorption band centered at 2.0 μm where signal-to-background ratios are maximum for many applications. Observed spectra are compared to model spectra to estimate range. Spectral regions with minimal attenuation are used to estimate source parameters in order to isolate atmospheric transmission. The spectra of 21 high explosive events were used to test this technique. A simple technique treating the fireball as a blackbody consistently underestimated true range by approximately 13%. A more realistic source model using some order-of-magnitude assumptions of fireball composition reduces range error to 3%. The technique produces accurate results without requiring detailed knowledge of source parameters or atmospheric conditions.

Today Optronic Countermeasure (OCM) concerns imply an IR Focal-Plane Array (FPA) facing an in-band laser irradiation. In order to evaluate the efficiency of new countermeasure concepts or the robustness of FPAs, it is necessary to quantify the whole interaction effects. Even though some studies in the open literature show the vulnerability of imaging systems to laser dazzling, the diversity of analysis criteria employed does not allow the results of these studies to be correlated. Therefore, we focus our effort on the definition of common sensor figures of merit adapted to laser OCM studies. In this paper, two investigation levels are presented: the first one for analyzing the local nonlinear photocell response and the second one for quantifying the whole dazzling impact on image. The first study gives interesting results on InSb photocell behaviors when irradiated by a picosecond MWIR laser. With an increasing irradiance, four different successive responses appear: from linear, logarithmic, decreasing ones to permanent linear offset response. In the second study, our quantifying tools are described and their successful implementation through the picosecond laser-dazzling characterization of an InSb FPA is assessed.

Open-path quantum cascade laser (QCL) systems are being developed for remote environmental monitoring applications for detection of small levels of toxins or pollutant gases in ambient air. In monostatic systems that rely on topographic backscatter, the surface reflection of the target becomes important. To address the feasibility of natural targets in an open-path geometry, we present the backscattering measurements of common urban building materials (aluminum, natural stones, ceramic wall tiles and concrete block) using a distributed feedback (DFB) pulsed QCL. Real surface roughness in the materials was taken into account. In particular, oblique scattering cases which are often unavoidable in field measurements were also investigated. The QCL measurements were evaluated with a FTIR system in which wide frequency range (2.8μm - 25μm) measurements were possible. These results were applied to a total link model to define the potential and range of an open path QCL chemical sensor system.

Considering the aerial surveillance and reconnaissance applications the use of infrared detectors gains importance. In this scene, one of the primary issues that should be decided happens to be the operating range of the detectors. Namely, the midwave and longwave ranges which are usually defined in the ranges of 3-5 and 8-12 μm, respectively, come into the picture as viable alternatives. In this work, the basic properties of infrared detectors operating in midwave and longwave regions are presented and then they are compared in terms of certain performance criteria. The study is concluded by a general evaluation.