Indigo Operations, a division of FLIR Systems, Inc., has teamed with the Air Force Research Laboratory (AFRL) to develop an ultra high-speed, sixteen channel focal plane array camera that operates in the near-infrared (NIR) region of the electromagnetic spectrum. This science-grade camera can generate over 2,300 frames per second operating with a full-frame spatial resolution of 320 horizontal by 256 vertical pixels and over 22,000 frames per second when windowed to a spatial resolution of 64 by 64 pixels. The camera features FLIR's ISC0207 read-out integrated circuit that provides unique functional modes for the research community such as pixel binning, wavefront sensing, zero dead-time, and external synchronization. The camera employs a standard Camera Link^® compatible interface for system control and image acquisition with FLIR's ThermaCAM^® RTools^TM software suite. A pre-production version of the high-speed camera will be integrated into the AFRL Directed Energy Directorate's Starfire Optical Range at Kirtland AFB, New Mexico, to be used for adaptive optics research.

We report on our 640x512 pixel InGaAs/InP focal plane array camera for visible and short-wavelength infrared imaging. For this camera, we have fabricated a 640x512 element substrate-removed backside-illuminated InGaAs/InP photodiode array (PDA) with a 25 mm pixel pitch. The PDA is indium bump bonded to a silicon read out integrated circuit. Removing the InP substrate from the focal plane array allows visible wavelengths, which would otherwise be absorbed by the InP substrate due to its 920 nm wavelength cut-off, to reach the pixels' active region. The quantum efficiency is approximately 15% at 500 nm, 70% at 850 nm, 85% at 1310 nm, and 80% at 1550 nm. Features incorporated into this video-rate, 14-bit output camera include external triggering, windowing, individual pixel correction, 8 operational settings of gain and exposure time, and gamma correction. The readout circuit uses a gate-modulated pixel for high sensitivity imaging over a wide illumination range. This camera is useable for visible imaging as well as imaging eye-safe lasers and is of particular interest seeing laser designators and night vision as well as hyperspectral imaging.

We report on a 320 x 256 pixel InGaAs focal plane array based camera with the ability to perform range gated imaging with sub-200 ns gates, while also allowing integration times longer than 16 ms for imaging in a staring mode at video rates. The combination of gated and video imaging is achieved through a high bandwidth pixel with a capacitive transimpedance amplifier (CTIA) design. The low dark current and high bandwidth of the InGaAs photodetectors enables both high sensitivity imaging at long exposure times and high bandwidth at short exposure times. The pixels are fabricated on a 25 μm pitch allowing for a compact device, and all pixels are gated simultaneously for "snapshot" exposure. The all solid-state gated camera improves reliability, while also allowing the system to be small and lightweight. The spectral sensitivity of InGaAs extends from 0.9 μm to 1.7 μm, allowing the use of eye-safe commercially available pulsed lasers with 1.5 μm wavelength, several millijoule pulse energies, and nanosecond scale pulse durations. In these experiments a 4 mJ and 2 ns pulse has allowed gated imaging to be achieved with a target at a range greater than 350 m away.

Large focal planes with InGaAs detector arrays have been developed that meet the demanding requirements of astronomy and other low background systems. With high quantum efficiency between 0.9 and 1.7 μm, the InGaAs detectors are ideally suited for many SWIR applications. This paper describes two types of arrays with more than one million detector elements-one with 1280 × 1024 elements and the other with 1024 × 1024 elements-developed by Raytheon Vision Systems with detectors provided by Sensors Unlimited. The detector elements of both formats are on a 20 μm pitch. The 1024 × 1024 array utilizes a standard Virgo astronomy multiplexer (readout) that reads out the array at a maximum frame rate of 8 Hz. An innovative readout was designed for the 1280 × 1024 array with the support of DARPA's MANTIS program. This readout features a high gain front-end amplifier that can operate up to a 60 Hz frame rate and is designed to operate at room temperature. Summary performance data of each of these array types are presented.

Superlattices composed of InAs and GaSb layers were first proposed for infrared detection in 1978. Later work by Smith and Mailhoit extended this premise to model InAs and InGaSb ternary layers for infrared detection in the long wavelength infrared range. What makes this material system so interesting is that these superlattice materials are essentially the III-V equivalent of HgCdTe materials. They have comparable absorption coefficients, the cut-off wavelengths can be continuously adjusted from short wavelength infrared to very long wavelength infrared (VLWIR), and photovoltaic operation is possible. One difference between these two materials is that with the superlattices the energy band structure, as well as the band gap, can be tailored to enhance detector performance. The band structure tailoring provides the superlattices with some advantages over HgCdTe alloys, particularly for very narrow band gaps. These superlattice advantages are a higher electron effective mass and large separation of the heavy and light-hole bands to suppress Auger recombination. These inherent properties of the InAs/GaInSb superlattices have made them an attractive material for VLWIR applications. As the type-II superlattice materials and devices mature, they will play a significant role as an alternative material for photovoltaic focal plane arrays in the LWIR and MWIR regimes as well. This paper provides an overview of the type-II superlattice development, accomplishments and issues.

Surfaces of GaSb substrates currently available from various commercial vendors are nowhere close to device grade GaAs, Si or InP wafer surfaces. Hence epitaxial growth and device fabrication on as-received commercial substrates poses significant difficulties amongst antimonide based researchers. Antimonide based materials are known to have poor surface oxide quality and not so well understood chemical reactions with various chemicals used to remove the oxides prior to growth. There are no existing reports on the detailed recipe for the preparation of "atomically flat and clean" surfaces that works on wafers obtained from various commercial vendors. This paper presents a detailed recipe for obtaining atomically flat and clean GaSb surfaces, irrespective of the initial polishing source. The same recipe (with slight modification) has been found to be successful with other III-V and II-VI compounds. The novel surface preparation process developed in our laboratory includes, chemical-mechanical polishing using an agglomerate-free sub-micron alumina slurry on a soft pad such as velvet, surface cleaning using dilute ammonium or potassium hydroxide-H2O solution and surfactant or glycerol, surface degreasing using organic solvents, oxide desorption using HCl-H₂O and HF-H₂O mixtures, mild chemical etching using ammonium sulfide and a final rinse in high purity deionized (DI) water and methanol. Using this recipe, we have been able to achieve surfaces with atomic flatness (RMS surface roughness close to 0.5 nm over a 10 x 10 mm²) and extremely clean surfaces, irrespective of the initial contamination or the sources of the wafers. Results of wafer surfaces before and after polishing using our recipe will be presented.

We present our most recent results and review our progress over the past few years regarding InAs/GaSb Type II superlattices for photovoltaic detectors and focal plane arrays. Empirical tight binding methods have been proven to be very effective and accurate in designing superlattices for various cutoff wavelengths from 3.7 μm up to 32 μm. Excellent agreement between theoretical calculations and experimental results has been obtained. High quality material growths were performed using an Intevac modular Gen II molecular beam epitaxy system. The material quality was characterized using x-ray, atomic force microscopy, transmission electron microscope and photoluminescence, etc. Detector performance confirmed high material electrical quality. Details of the demonstration of 256×256 long wavelength infrared focal plane arrays will be presented.

III-V antimonide based devices suffer from leakage currents. Surface passivation and subsequent capping of the surfaces are absolutely essential for any practical applicability of antimonide based devices. The quest for a suitable surface passivation technology is still on. In this paper, we will present some of the promising recent developments in this area based on dry etching of GaSb based homojunction photodiodes structures followed by various passivation and capping schemes. We have developed a damage-free, universal dry etching recipe based on unique ratios of Cl₂/BCl₃/CH₄/Ar/H₂ in ECR plasma. This novel dry plasma process etches all III-V compounds at different rates with minimal damage to the side walls. In GaSb based photodiodes, an order of magnitude lower leakage current, improved ideality factor and higher responsivity has been demonstrated using this recipe compared to widely used Cl₂/Ar and wet chemical etch recipes. The dynamic zero bias resistance-area product of the Cl₂/BCl₃/CH₄/Ar/H₂ etched diodes (830 Ω cm²) is higher than the Cl₂/Ar (300 Ω cm²) and wet etched (330 Ω cm²) diodes. Ammonium sulfide has been known to passivate surfaces of III-V compounds. In GaSb photodiodes, the leakage current density reduces by a factor of 3 upon sulfur passivation using ammonium sulfide. However, device performance degrades over a period of time in the absence of any capping or protective layer. Silicon Nitride has been used as a cap layer by various researchers. We have found that by using silicon nitride caps, the devices exhibit higher leakage than unpassivated devices probably due to plasma damage during SiN_x deposition. We have experimented with various polymers for capping material. It has been observed that ammonium sulfide passivation when combined with parylene capping layer (150 Å), devices retain their improved performance for over 4 months.

We have performed wet chemical passivation tests on GaInSb/InAs superlattice photodiode structures grown by molecular beam epitaxy. The details of the devices growth and characterization as well as the results of chemical passivation involving RuCl₃ and H₂SO₄ with SiO₂ dielectric depositions are presented.

Multiband detection capability is a critical attribute of practical infrared (IR) sensing systems for use in missile defense detect-and-track applications. This capability, already demonstrated in mercury-cadmium telluride (MCT) photodiodes and quantum well infrared photodetectors (QWIPs), has not previously been explored in type II-superlattices (T2SLs), a newer system which is under consideration to meet next-generation sensor needs. Like QWIPs, T2SLs are composed of layers of III-V compound semiconductors grown by molecular beam epitaxy (MBE), and have an infrared gap that is determined primarily by the layer thicknesses. With the exceptional control of MBE over layer thicknesses and the ability to grow multiple bandgap structures under compatible growth conditions, T2SL-based multiband IR focal plane arrays (FPAs) are expected to have advantages in spectral control and pixel-to-pixel uniformity over MCT. Additionally, T2SLs have intrinsically higher quantum efficiency than QWIPs, in which the optical selection rules for intersubband transitions forbid the absorption of normally incident light. Here we describe the first results for a T2SL dual band detector with independent long-wave and very-long-wave infrared responsivity bands, with cutoffs of 11.4 and 17 μm respectively. The p-n-p device contains "W"-structured T2SL (WSL) active regions for enhanced band selectivity, owing to the quasi-two-dimensional density of states for WSLs. Photodetector results are demonstrated using a maskset designed to fabricate single-band diodes, 3-terminal dual band devices, and 2-terminal band selectable devices to comply with different dual band FPA read-out architectures.

An infrared camera based on a 256x256 focal plane array for the Mid-IR spectral range (3-5 μm) has been realized for the first time with InAs/GaSb short-period superlattices. The detector shows a cut-off wavelength of 5.4 μm and reveals a quantum efficiency of 30%. The noise equivalent temperature difference (NETD) reaches 9.4 mK at 73 K with F/2 optics and 6.5 ms integration time. Excellent thermal images with low NETD values and a very good modulation transfer function are presented. Furthermore, a new method to passivate InAs/GaInSb superlattice photodiodes for the 8-10 μm regime is demonstrated. The approach is based on the epitaxial overgrowth of wet-etched mesa diodes using lattice matched AlGaAsSb. A complete suppression of surface leakage currents in small sized test diodes with 70 μm diameter is observed.

InAs-GaSb strained layer superlattices (SLSs) form a narrow band gap material whose cut-off wavelength can be tuned from 3 um to beyond 30 um. Theory predicts that in the LWIR and VLWIR, the SLS narrow bandgap layer structures can be engineered to reduce Auger recombination, relative to other narrow bandgap materials, such as HgCdTe. This should result in the SLS diodes having better performance than currently available detectors. A key to achieving this improved performance is knowing the detailed layer structure of the superlattice, and being able to accurately model this layer structure. Having an accurate model to guide the improved performance is essential to optimizing this material system. Cross-sectional scanning tunneling microscopy data will be presented which shows that the actual layer structure differs significantly from the intended layer structure, due to the detailed dynamics of MBE growth and the very thin layers in the superlattice. Specifically, cross-sectional scanning tunneling microscopy demonstrates that the InAs contains excess antimony, and the GaSb excess indium, due to segregation from the underlying arsenide-on-antimonide, or antimonide-on-arsenide, heterojunctions respectively. These deviations from the intended structure have a significant impact on the predicted properties of the superlattice. The predicted behavior of the intended and actual superlattice structures will be compared to measured performance.

The Standard Advanced Dewar Assembly (SADA) is the critical module in the Department of Defense (DoD) standardization of scanning second-generation thermal imaging systems. The DoD has established a family of SADAs to fulfill a range of performance requirements for various platforms. The SADA consists of the Infrared Focal Plane Array (IRFPA), Dewar, Command & Control Electronics (C&CE), and the cryogenic cooler, and is used in platforms such as the Apache helicopter, the M1A2 Abrams main battle tank, the M2 Bradley Infantry Fighting Vehicle, and the Javelin Command Launch Unit (CLU). In support of the family of SADAs, the DoD defined a complementary family of tactical linear drive cryocoolers. The Stirling cycle linear drive cryocoolers are utilized to cool the Infrared Focal Plane Arrays (IRFPAs) in the SADAs. These coolers are required to have low input power, a quick cool-down time, low vibration output, low audible noise, and a higher reliability than currently fielded rotary coolers. These coolers must also operate in a military environment with its inherent high vibration level and temperature extremes. This paper will (1) outline the characteristics of each cryocooler, (2) present the status and results of qualification tests, (3) present the status of production efforts, and (4) present the status of efforts to increase linear drive cooler reliability.

The trade-offs that must be considered when selecting a cryocooler for infrared detector cooling are complex. When split- Stirling cryocoolers are used, the designer can select the expander separately from the compressor. However, there will be performance implications. Larger systems provide benefits in terms of performance margin and operating lifetime, but may not meet size and mass goals. Larger cryocoolers tend to generate more heat, albeit over a larger surface area, and generate higher vibration forces. The expander coldfinger must be stiff enough to achieve image plane motion requirements. The transfer tube should be as short and with as few bends as possible, while the path available for the transfer tube may be affected by the geometry of the expander and compressor. Several characteristics of tactical cryocoolers are considered in this paper in such a way that trends can be identified and design choices can be clarified. A step-by-step approach is recommended that will lead to a design solution in the most direct manner. This is accomplished by starting with "show-stopper" choices, then progressing to choices where concessions can be more easily made. The implications of the interfaces to the cryocooler will also be briefly discussed. Cryocooler developments at RVS that will expand the available design space are described. This enabling technology provides more options in terms of cryocooler size and performance, and continues the trend toward longer operating lifetime and higher reliability.

Overstroking in a linearly driven piston compressor of a cryogenic cooler may occur as a result of numerous factors, among which are: uncontrollable leaking of the working fluid from the compression into the bounce space, magnitude and asymmetry of the driving voltage, action of the gravity and g-forces, etc. The known solutions to a passive and active overstroking control are rather expensive, bulky and not always reliable. The authors report on the development of the novel approach to an overstroking protection, where instead of the piston position, the piston acceleration is evaluated using the analytical model of the linear actuator and a real-time measurement of the motor voltage and current, thus enabling for a convenient sensorless estimation of a direction and magnitude of the internal collisions. This eliminates the need in the dedicated position sensor and allows obtaining an observer which is insensitive to the environmental conditions (shock, vibration and temperature) and to the inaccuracies inherent in the regular sensorless observers. Based on this approach a full-scale controller was developed using the National Instrument real-time engine PCI 7030/6040E operating under the LabView software. From experimentation, the overstroking was practically eliminated in the wide range of the operational conditions without affecting the overall power consumption and cooling performance.

Pulse tube cryocoolers (PTC) can be regarded as the next step in the development of the Stirling cooler. The major advantage vs. the Stirling cooler is the omission of any moving part in the cold head, resulting in significantly increased MTTF. Further advantages are higher mechanical robustness and stability and the potential for cost reduction. AIM developed PTC's for several years in close cooperation with the University of Giessen. As a recent result at AIM, Coaxial PTC cold head are available within the outline dimension of typical IR Stirling cold head of 13mm diameter. The achieved performance data are comparable to the serial data of the Stirling cold head. This PTC cold head is designed to be operated in the orifice mode without a double inlet which is known to cause instabilities. Technical details and performance data represent the current technical status at AIM.

Raytheon has manufactured closed-cycle cryocoolers for both tactical military and space applications for over thirty years. Tactical and space cryocooler technologies have historically been treated as distinct both at Raytheon and throughout the industry. Differing technical requirements, operating lifetimes, and order quantities have driven these types of coolers to dramatically different design approaches and cost levels. For example, a typical space cryocooler system today costs approximately $2M as compared to roughly $10,000 for a tactical cryocooler. However, stimuli from both the tactical and space cooler user communities are driving the markets together. Tactical cryocooler requirements are starting to push towards operating lifetime requirements more characteristic of the space coolers (e.g., 20,000+ hours). Space cryocooler users, in particular Missile Defense Agency, are pushing for substantial cost reduction. In response, Raytheon is developing a low cost space cryocooler with an intended dual-use capability to also serve the tactical marketplace. This cooler leverages proven flexure-suspension technology to achieve long life, and a low cost concentric pulse tube cold head design has been developed that can be packaged into the existing Standard Advanced Dewar Assembly, Type One (SADA-I). The cooler meets or exceeds the SADA-I operational requirements (capacity, efficiency, etc.) as well. For the space-version of the cooler, the electronics cost has been reduced by an estimated 80% versus current designs, largely by approaching the vibration cancellation requirement from a dramatically different perspective. Fabrication of the brassboard expander is nearly complete, and the prototype design is well underway. The design approach, development progress, and proposed applications are presented.

Thales Cryogenics has been working on high reliability cryocoolers since 1997. During this period two cooler series have been developed, the LSF91xx series for cooling powers up to 3W at 80K and the LSF93xx series for cooling powers up to 8W at 80K. As a result of several design improvements, it was possible to decrease the length and mass of our flexure-bearing coolers. These improvements have been applied in the new LSF95xx series. With the length and mass reduction, the LSF95xx complies with the SADA II specification with respect to envelope and mass. Based on this, Thales Cryogenics is the first manufacturer offering a full flexure-bearing supported cooler that fits within the SADA II envelope. By using a moving magnet configuration in all our flexure-bearing coolers, the risk with respect to contamination problems due to out-gassing has been diminished because the coils are not part of the helium circuit. Furthermore, all connections in the LSF95xx are laser-welded, which means that there is no additional locking required inside the cooler. By using a different magnet design, no magnet segments have to be glued together, which decreases the risk of out-gassing and increases the reliability even more. This paper describes the trade-offs that have been considered in the design phase, and gives a detailed overview of the test results, the status of the qualification program and the resulting specification of the LSF95xx cooler series.

IR applications are more and more demanding regarding reliability. It is the case of handheld and lightweight UAV applications. To answer these needs, Sofradir and Thales Cryogenics developed a new product family in order to minimize system weight, cost and to increase detector and cooler reliability. Thales Cryogenics has been working on RM integral Stirling cryocoolers since 1995. Then, as a result of several design improvements, it has been possible to increase significantly the efficiency and the reliability of the RM2-Xi cooler over the last 2 years. The RM2-Xi reliability is measured through life time tests which are run continuously on samples taken out from the mass production. Several new tests profiles have been implemented with different climatic and cooler operation conditions. The results gathered enable an accurate evaluation of the cryocooler reliability in the various mission profiles of the customer's applications. Another important performance of an integral cryocooler is efficiency. New mechanical and thermal designs have been implemented. The resulting improvements will be presented and compared with the characteristics of the cryocooler previous version. Based on this new design, Sofradir offers new IR detector products well adapted to handheld and high reliability systems. These new product designs are discussed as well as reliability analysis results.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS), is overseen by the Integrated Program Office (IPO), a joint effort of the Department of Defense, Department of Commerce and NASA. One of the instruments on the NPOESS satellite is the Cross-track Infrared Sounder (CrIS) instrument. CrIS is a Fourier Transform interferometric infrared (FTIR) sensor used to measure earth radiance at high spectral resolution to derive pressure, temperature, and moisture profiles of the atmosphere from the ground on up. Each CrIS instrument contains three different cutoff wavelength (λ_c)focal plane modules (FPMs): an SWIR FPM [λ_c(98 K) ~ 5 mm], MWIR FPM [λ_c(98 K) ~ 9 mm] and a LWIR FPM [λ_c(81 K) ~ 15.5 mm]. There are nine large (850 mm diameter) photodiodes per FPM, the nine detectors being arranged in a 3 x 3 array. The nine detectors are placed under tight tolerances in the X, Y, and Z dimensions. The steps involved in the transfer of photodiodes as part of a newly fabricated wafer to the mounting of the photodiodes on the FPM involves many processing steps including a significant amount of dicing, cleaning, wire bonding and baking at elevated temperatures. Quantum efficiency and 1/f noise in Hg_1-xCd_xTe photodiodes are critical parameters that limit the sensitivity of infrared sounders. The ratio α, defined as the noise current in unit bandwidth i_n(f = 1 Hz, V_d, Δf = 1 Hz) to the dark current I_d(V_d), that is, α = i_n/I_d is one of the parameters used to select photodiodes for placement in FPMs. α is equivalent to √α_H/N that appears in the well-known Hooge expression. For the sixty-one, λ_c ~ 9 μm photodiodes measured at 60 mV reverse bias and at 98 K, the average value of α_dark = 1.3 x 10^-4 in the dark and α_PHOTO = i_n/I_PHOTO is ~ 2 x 10^-6 under illuminated conditions. These values of α are a factor of two lower than that reported previously. The λ_c ~ 15.5 μm photodiodes have average α_dark = 1.3 x 10^-5 with the highest performance, diffusion current limited photodiodes having values of α_dark in the mid 10^-6 range. All of the 850 μm diameter, λ_c ~ 15.5 μm photodiodes measured have excess low frequency noise, with the best performers having i_n(f = 100 Hz, V_d =-60 mV , Δf = 1 Hz) ~ 2 x 10^-11 A/Hz^1/2 and the best photodiode α_dark = 3.92 x 10^-6. I-V measurements, noise, and visual inspections are performed at several steps in the photodiodes manufacturing process. It was observed, following FPM fabrication, photodiode dark current and noise had increased from the initial pre-mounting leadless chip carrier (LCC) measurements for some of the nine photodiodes. The performance degradation observed led to an investigation into the cause (baking at elevated temperatures, mechanical handling, electrical stress etc.) of photodiode degradation that occurred between LCC and FPM testing. Correlations between I-V, noise and surface visual defects have been performed on some λ_c ~ 15.5 mm photodiodes. This paper outlines the results of the study, correlating the electrical performance observed to visual defects on the surface and to defects seen following cross sectioning of degraded photodiodes. In addition, other lessons learned and the corrective actions implemented that led to the successful manufacture of SWIR, MWIR and LWIR large photodiodes from the material growth to insertion into and successful demonstration of flight FPMs for the CrIS program are described.

This paper reviews and assesses progress in back-illuminated P-on-n photovoltaic HgCdTe detector technology, grown by two-layer Liquid Phase Epitaxy on CdZnTe substrates, for applications at wavelengths beyond 15 μm in a new generation of spaceborne multispectral instruments for remote sensing. We review data that demonstrate the feasibility of useful cutoff wavelengths as long as 17.5 μm. We recommend that LPE photovoltaic HgCdTe technology be extended to the 20-25 μm wavelength region for single elements and arrays for NASA remote-sensing applications.

Raytheon Vision Systems has achieved significant improvements in VLWIR (very long wavelength infrared) detector materials. These small bandgap detector materials are susceptible to tunneling of carriers across the bandgap via either band-to-band or trap-assisted tunneling phenomena. RVS' new procedures reduce exposure of the highly sensitive p-n junction to possible contamination sources during growth and processing. This reduction in impurities reduces the tunneling component of the detector current and yields high quality detectors out to the VLWIR range. Evidence of a highly uniform detector fabrication process is detailed within spanning the LWIR to VLWIR wavelength range.

Today, end users require Long Wave (LW) staring arrays to develop new compact IR cameras, and Very Long Wave (VLW) staring arrays to develop high performance applications with broadband detection up to more than 13μm. HgCdTe is the only available material to answer these needs with the same production line. Based on its HgCdTe Liquid Phase Epitaxy (LPE) process that has proven its maturity and reproducibility over the last thirteen years, with for example more than 14,000 288×4 IRFPAs already delivered worldwide, SOFRADIR has been offering for several years 320×256 LW detectors with a cut-off wavelength tuned between 9μm and 12μm depending on the required application. Based on that experience, two new LW HgCdTe products have been developed and are offered since beginning of 2005. For compact LW FLIRs, SOFRADIR offers the VENUS-LW: a higher resolution 25μm pitch 384×288 IDDCA with 0.5W micro cooler, with a cut-off between 9μm and 10μm for a spectral band pass fully satisfying the imagery requirements and for an operational temperature between 77K and 85K (thus enabling the use of a compact low power micro cooler). The manufacturing of this detector relies on the standard HgCdTe production process with the latest uniformity improvements. Following a similar approach and for VLW applications such as spectroscopy or broadband low flux applications, an improved HgCdTe material with optimized LPE and PhotoVoltaic (PV) detector processes, has been developed by SOFRADIR and LETI LIR for cut-off wavelengths above 12μm below 60K, enabling to have very low dark currents compatible with very low flux applications. These high performance low dark current detectors are offered with a standard 30μm pitch 320×256 readout circuit, integrated with a 1 Watt split Stirling cycle cooler enabling to reach the 50K range with very short cool down times. The performances of these new LW and VLW IR detectors are presented in this paper as well as the development trends for LW detectors at SOFRADIR.

High performance LWIR and VLWIR focal plane arrays have been produced on advanced HgCdTe/ZnCdTe materials. The ZnCdTe substrates typically are n-type with an infrared transmission over 65%. Mesa and planar ion-implantation-isolated heterojunction processes have been used to produce the arrays. The operability of 128x128, 10.6mm arrays reached 99.27% based on the criteria that the signal output is within +/-30% of the mean. Several 320x256 arrays with wavelength from 12mm to 13.75mm at 77-85K have also been produced. Excellent imaging pictures have been obtained at these temperatures.

A 128(H) x 64(V) x RGB CMOS imager is integrated with region-of-interest selection, RGB-to-HSI transformation, HSI-based pixel segmentation, 36-bins x 12bits HSI histogramming and sum-of-absolute-difference (SAD) template matching. 32 learned color templates are stored and compared to each image. The chip captures the R, G and B images using in-pixel storage before passing the pixel content to a multiplying digital-to-analog converter (DAC) for white balancing. The DAC can also be used to pipe in images for a PC. The color processing uses a biologically inspired color opponent representation and an analog look-up table to determine the Hue (H) of each pixel. Saturation (S) is computed using a loser-take-all circuit. Intensity (I) is given by the sum color components. A histogram of the segments of the image, constructed by counting the number of pixels falling into 36 Hue intervals of 10 degrees, is stored on chip and compared against the histograms of new segments using SAD comparisons. We demonstrate color-based image segmentation and object recognition with this chip. Running at 30fps, it uses 1mW. To our knowledge, this is the first chip that integrates imaging, color segmentation and color-based object recognition at the focal plane.

We present a detailed comparison between the operational performance of "conventional" and "foveating" large format infrared focal plane arrays (FPAs). Foveating FPAs provide its users with a substantial advantage when compared with imaging sensors currently in use. This paper details the differences between foveating and traditional FPAs and provides objective comparisons to aid systems designers select the appropriate imaging device for their applications. A variety of on-FPA operations are performed with foveating sensors; some of these operations require the use of a companion processor to spatially reprogram the foveal sensor. We will compare several critical sensor performance parameters including: frame rate, data bandwidth, spatial and temporal noise. In addition, operational comparisons will be made to contrast the various applications that may be best suited for the two respective imaging sensor types.

Cyan Systems has developed algorithms and architectures capable of performing temporal and spatial filtering near or on the FPA. Cyan is performing research into more advanced techniques to allow functional target detection near/on the FPA. The goals of this work is to perform image processing near or on the FPA to improve the size and power requirements for existing IR sensor systems which require larger board sets and hardware enclosures. We use representations of the biological vision system as models for the algorithm development. We report measured data on the near/on FPA target detection performance.

Extracting relevant visual information about the operating environment of a roving robot at the focal plane is a challenging problem. We present two image processing architectures for motion computation at the focal plane. The first imaging architecture, composed of 250 x 250 active pixel sensors, has spatiotemporal difference computation capabilities at the focal plane. This spatiotemporal difference imager, fabricated in a 0.35μ process, contains in-pixel storage elements for previous and current frames and difference computational units outside the imaging array. A novel scan out technique allows for parallel computation of spatial and temporal 1-D derivatives on the read out. The final motion estimation based on the image brightness constancy equation, which is approximated as the ratio of the temporal and spatial derivates, is computed off chip, but it can be easily implemented on-chip. This approach can only determine the motion component normal to the spatial gradient. In order to address this ill-posed problem, known as the aperture problem, we propose a second imaging architecture, which is an extension of the first imaging architecture. The latter imaging architecture contains in-pixel memory for storing partial computational results. Hence, the motion vectors are stored back into the pixel memories after an initial scan; iterative algorithms can be applied to the stored computational results to solve the aperture problem. Experimental data from both imaging architectures are presented to validate the accuracy of the magnitude and angle of the computed target velocities.

The visual pathway that leads from the retina to the tangential cells in the third optical ganglion of the fly is a sophisticated system for the detection of visual motion. The tangential cells, whose responses are thought to characterize the state of egomotion of the animal, show a remarkable ability to encode velocity information about optic flow patterns to which they are sensitive, independent of the structure and contrast of viewed scenery. We describe a simulation study based on a model that accounts for key physiological features observed in the biological system, which contains nonlinear features that we expect to contribute to this capability. One of these features is motion adaptation, a phenomenon on which recent research has shed new light. We conclude that our models significantly reduce dependence of response on variable natural scenery, although they still do not perform as well in this respect as the biological neurons. This biological system has inspired an implementation of visual motion processing in analog VLSI technology. The neuromorphic circuits are intended for eventual on- or near-focal plane integration with photosensing. We describe the design approach and present results from preliminary versions of these circuits.

Nova Sensors produces miniature electronics for a variety of real-time digital video camera systems, including foveal sensors based on Nova's Variable Acuity Superpixel Imager (VASI^TM) technology. An advanced image-processing package has been designed at Nova Sensors to re-configure the FPGA-based co-processor board for numerous applications including motion detection, optical, background velocimetry and target tracking. Currently, the processing package consists of 14 processing operations that cover a broad range of point- and area-applied algorithms. Flexible FPGA designs of these operations and re-programmability of the processing board allows for easy updates of the VASI^TM sensors, and for low-cost customization of VASI^TM sensors taking into account specific customer requirements. This paper describes the image processing algorithms implemented and verified in Xilinx FPGAs and provides the major technical performances with figures illustrating practical applications of the processing package.

Dual-waveband, Focal Plane Arrays (FPAs) based on Hg_1-xCd_xTe multi-layer structures have previously been produced by the Molecular Beam Epitaxy (MBE) growth technique. It is shown that the multi-layer structures required for dual-waveband devices can also be grown by Metal Organic Vapor Phase Epitaxy (MOVPE). The MOVPE growth process allows excellent control of both the composition and doping profiles and has the advantage of allowing growth on a range of substrates including silicon. Previous research on back-to-back diodes for dual-waveband has concentrated on npn structures. The design of the alternative pnp structures is discussed and a model is developed which gives a good fit to the measured spectra. We report on the design and characterization of dual-waveband detectors including current-voltage and spectral cross talk for the case of two close sub-bands within the 3-5 μm mid-wave infrared (MWIR) spectral range. The mechanisms for spectral cross talk are discussed including incomplete absorption, transistor action and radiative coupling. A custom readout circuit (ROIC) has been designed. This allows the capture of data from the two bands which is spatially aligned but sequential in time.

An overview of DRS' development of a very unique two-color infrared photodiode architecture for two-color infrared focal-plane arrays based on Hg_1-xCd_xTe is given. One unique feature of this architecture is that it requires only a mono-color based on Hg_1-xCd_xTe material growth technique for its implementation. Some data from this development are presented.

Raytheon Vision Systems (RVS) is developing two-color, large-format infrared FPAs to support the US Army's Third Generation FLIR systems. RVS has produced 640 x 480 two-color FPAs with a 20 micron pixel pitch. Work is also underway to demonstrate a 1280 x 720 two-color FPA in 2005. The FPA architecture has been designed to achieve nearly simultaneous temporal detection of the spectral bands while being producible for pixel dimensions as small as 20 microns. Raytheon's approach employs a readout integrated circuit (ROIC) with Time Division Multiplexed Integration (TDMI). This ROIC is coupled to bias-selectable two-color detector array with a single contact per pixel. The two-color detector arrays are fabricated from MBE-grown HgCdTe triple layer heterojunction (TLHJ) wafers. The single indium bump design is producible for 20 μm unit cells and exploits mature fabrication processes that are in production at RVS for Second Generation FPAs. This combination allows for the high temporal and spatial color registration while providing a low-cost, highly producible and robust manufacturing process. High-quality MWIR/LWIR (M/L) 640 x 480 TDMI FPAs with have been produced and imaged from multiple fabrication lots. These FPAs have LWIR cutoffs ranging to 11 micron at 78K. These 20 micron pixel FPAs have demonstrated excellent sensitivity and pixel operabilities exceeding 99%. NETDs less than 25 mK at f/5 have been demonstrated for both bands operating simultaneously.

The 3rd generation of infrared (IR) detection modules is expected to provide advanced features like higher resolution 1024x1024 or 1280x720 pixels and/or new functions like multicolor or multi band capability, higher frame rates and better thermal resolution. This paper is intended to present the current status at AIM on quantum well (QWIP) and antimonide superlattices (SL) detection modules for ground and airborne applications in the high performance range. For spectral selective detection, a QWIP detector combining 3-5μm (MWIR) and 8-10μm (LWIR) detection in each pixel with coincident integration has been developed in a 384x288x2 format with 40 μm pitch. Excellent thermal resolution with NETD < 30mK @ F/2, 6.8 ms for both peak wavelengths (4.8 μm and 8.0 μm) has been achieved. Thanks to the well established QWIP technology, the pixel outage rates even in these complex structures are below 0.5% in both bands. QWIP dual band or dual color detectors provide good resolution as long as integration times in the order of 5-10ms can be tolerated. This is acceptable for all applications where no fast motions of the platform or the targets are to be expected. For rapidly changing scenes-like e.g. in case of missile warning applications for airborne platforms-a material system with higher quantum efficiency is required to limit integration times to typically 1ms. AIM and IAF selected antimonide based type II superlattices (SL) for such kind of applications. The SL technology provides-similar to QWIP's-an accurate engineering of sensitive layers by MBE with very good homogeneity and yield. While promising results on single SL pixels have been reported since many years, so far no SL based detection module could be realized. IAF and AIM last year managed to realize first most promising SL based detectors. Fully integrated IDCA's with a MWIR SL device with 256x256 pixels in 40µm pitch have been integrated and tested. The modules exhibit excellent thermal resolution of NETD<10mk @ F/2 and 5ms. Product improvement meanwhile allowed to reduce pixel outage rates below 1% i.e. down to a level as required for the military use of such detectors. Presently under development is therefore a dual color MWIR device based on SL technology and the existing 384x288 read out circuit (ROIC) used in the dual band QWIP device. This detector is primarily intended for the use in missile approach warning systems where the dual color capability significantly improves suppression of false alarms. Details of the modules and results of the electrooptical performance will be presented for the different items mentioned above.

For preparing future military and industrial needs, SOFRADIR is working with CEA-LETI/LIR in the frame of DEFIR (Design of Excellence for the Future of InfraRed), on the third generation R&D mainly based on HgCdTe (MCT) material growth by Molecular Beam Epitaxy (MBE). Based on MCT grown by MBE, large wafers (4 inches and more) are available on Germanium in France and on Silicon in the USA. MBE process on alternative materials like Germanium, are in position to replace CZT homo-substrates and to compete with other material candidates. This enables very larger wafer size (4" and more) with a well-mastered thickness of the sensitive thin film deposition leading to very low cost 2D MCT arrays. In addition multi spectral arrays including advanced photodiode technologies are developed thanks to the MBE process. Therefore third generation IR detector studies in progress at DEFIR concern very large format sizes including small pixel pitch and high performance and mainly multi spectral and multi-color FPAs. New development results are presented and future trends are discussed.

The effectiveness of infrared imaging sensors for target detection and identification can be greatly enhanced by adding spectral analysis capability. Unfortunately, this usually comes with the penalties of increased size, weight, and significantly increased computational requirements, which limit the rate at which information can be made available to the user. By integrating MEMS, photonics and electronics technologies, a new type of staring spectral imager can be realized. An Adaptive Focal Plane Array (AFPA) device is being developed under DARPA sponsorship that consists of an array of MEMS tunable Fabry-Perot filters, hybridized with a dual band IR focal plane array. The MEMS filters will provide narrowband tuning in the LWIR (8.0-10.7 mm) and simultaneous broadband imaging in the MWIR (3-5 mm). Individual filter elements will be on the size scale of a small number of detector pixels. Each filter will be independently electrically addressable, enabling tailored spectral analysis of different regions in the scene. Rather than collecting the complete hyperspectral cube, work is focusing on methods that will enable selection of spatially optimized spectral band sets for a variety of targets and materials that are selected "on-the-fly" to maximize the contrast between the local background and the target or material to be identified. This paper discusses the structure and status of the AFPA device and highlights some unique challenges inherent in the integration of MEMS, photonics and electronics technologies.

The demand continues to grow for small, compact imaging sensors, which include new capabilities, such as response in multiple spectral bands, increased sensitivity, wide high dynamic range, and operating at room temperature. These goals are dependant upon novel concepts in sensor technology, especially advanced electronic processing integrated with the sensor. On-focal plane processing is especially important to realize the full potential of the sensor. Since the area available for focal plane processing is extremely limited, a new paradigm in sensor electronic read-out technology is necessary to bridge the gap between multi-functional, high performance detector arrays and the off-focal plane processing. The Vertically Integrated Sensor Array (VISA) Program addresses this need through development of pixel-to-pixel interconnected silicon processors at the detector, thus expanding the area available for signal and image processing. The VISA Program addresses not only the array interconnection technology, but also investigates circuit development adapted to this new three-dimensional focal plane architecture. This paper reviews progress in the first phase of the program and outlines direction for demonstrations of vertically integrated sensor arrays.

Conventional high performance infrared (IR) sensors need to be cooled to around 80K in order to achieve a high level of thermal sensitivity. Cooling to this temperature requires the use of Joule-Thomson coolers (with bottled gas supply) or Stirling cycle cooling engines, both of which are bulky, expensive and can have low reliability. In contrast to this, higher operating temperature (HOT) detectors are designed to give high thermal performance at an operating temperature in the range 200K to 240K. These detectors are fabricated from multi-layer mercury cadmium telluride (MCT) structures that have been designed for this application. At higher temperatures, lower cost, smaller, lighter and more reliable thermoelectric (or Peltier) devices can be used to cool the detectors. The HOTEYE thermal imaging camera, which is based on a 320x256 pixel HOT focal plane array, is described in this paper and performance measurements reported.

Great incentive exists for the development of infrared detectors that can operate without cooling near the limit of photon or thermal fluctuations. Great progress has been made in past 30 years developing uncooled thermal detectors that now provide enough sensitivity for many routine infrared imaging needs, albeit with relatively slow response times. Even now, however, the sensitivity of uncooled thermal detectors is 3-15× less sensitive than the ideal characteristics predict. In this paper we first examine the current status of uncooled thermal detectors to understand the limiting mechanisms which appear to be 1/f noise and system noise. Approaches for developing uncooled or minimally-cooled photon detectors are then reviewed. A modification of one current approach, bias extraction of minority carriers, is suggested involving photo-JFETs rather than photodiodes. It appears that the most promising prospect for uncooled or minimally-cooled photon detectors is in the MWIR spectral region.

Infrared avalanche diodes are key components in diverse applications such as eye-safe burst illumination imaging systems and quantum cryptography systems operating at telecommunications fiber wavelengths. HgCdTe is a mature infrared detector material tunable over all infrared wavelengths longer than ~850nm. HgCdTe has fundamental properties conducive to producing excellent detectors with low noise gain. The huge asymmetry between the conduction and valence bands in HgCdTe is a necessary starting point for producing impact ionization with low excess noise factor. Other factors in the band structure are also favorable. The low bandgap necessitates at least multi-stage thermoelectric cooling. Mesa diode structures with electron initiated multiplication have been designed for gains of up to around 100 at temperatures at or above 80K. Backside illuminated, flip-chip, test diode arrays have been fabricated by MOVPE using a process identical to that required for producing large imaging arrays. Test diode results have been obtained with the following parameters characterized, dark current vs. voltage and temperature, gain vs. voltage, and spectral response as a function of wavelength and bias. The effect of changing active region cadmium composition and active region doping is presented along with an assessment of some of the trade-offs between dark leakage current, gain, operating voltage and temperature of operation.

Three years ago, Indigo Systems launched its Omega camera line, which to this day remains one of the world's smallest, lightest, lowest powered infrared cameras. The concept of a miniature thermal imager has proven very successful, and thousands of cores have been employed in a number of portable applications, including firefighting, unmanned vehicles, and handheld imagers. A common thread to these high-volume markets is their elasticity-lowering cost substantially enhances demand. Hence the motivation behind Indigo’s newest miniature camera, Photon. Photon is a product family of small and mid-format sensor engines (160x128, 320x128, 320x256) specifically optimized for low cost and high volume. While it shares many of Omega's positive benefits, including remarkably small size, weight, and power, several aspects of the design contribute to it being more affordable than its fore-runner even with four times as many pixels. This paper compares the Photon design to the Omega with particular focus on those aspects affecting manufacturability and cost.

The Laboratoire Infrarouge (LIR) of the Electronics and Information Technology Laboratory (LETI) has been involved since 1993 in the development of subsequent bolometer technological process that aims at reducing the pitch of the amorphous silicon based uncooled microbolometer FPAs. These developments are primarily driven by cost reduction and system miniaturisation concerns. In this outlook, the LIR has recently developed a specific amorphous silicon technology for a 25 μm pitch IRFPA achievement. This new structure still relies on a single level microbridge arrangement and special cares have been taken in order to ensure noise reduction, thermal insulation increase with a special attention to low thermal time constant achievement. This paper presents a complete characterization of an advanced dedicated 320 x 240 IRCMOS circuit that takes advantage of this new 25 μm pitch bolometer process. Apart from NEDT (< 70 mK) histogram, the paper also puts emphasis on parameters that appear more and more as key points in IR system, like the thermal time constant and the residual fixed pattern noise.

Although IR detectors are old and well known devices, at present they have not reached the status of a mass-market product. The main reason is directly related to their lack of affordability. Fifteen years ago the latest generation of thermal infrared (IR) detectors, as large format focal plane arrays (FPA), appeared with very promising expectation. They have been called low cost detectors because they do not need cooling and, as a consequence, prices are sensitively lower. However, they are currently still not affordable. Issues related to packaging and processing are limiting the potential affordability of these type of devices. Meanwhile, the technology of uncooled photonic detectors such as polycrystalline lead salt detectors are evolving fast and now they are a real alternative in the field of cheap detectors. CIDA owns an innovative technology for processing low density polycrystalline PbSe FPAs. This technology presents some advantages compared to the standard technology, mainly for processing more complex devices, such as 2D arrays or multicolor detectors. Mass production and prices decrease depend strongly on the monolithic integration between detectors and read out electronics. The method developed makes possible to process monolithic devices without any fundamental limitation. This work presents the latest results obtained during a study of monolithic integration viability carried out in our laboratories. A complementary metal oxide semiconductor (CMOS) test circuitry was designed, processed and submitted to all PbSe processing with promising results. The next phase will consist of designing a proper CMOS circuitry and process sensors on top.

RVS is producing high-quality microbolometer FPAs with 25 μm pixels. We have developed formats in both 320 x 240 and 640 x 480 array formats. These FPAs have demonstrated sensitivities that are comparable to microbolometer FPAs with 50 μm pixels with the best measured NETD value for these FPAs now <25mK with an f/1 aperture and operating at 30 Hz frame rates. Pixel operability is greater than 99.9% on most FPAs, and uncorrected responsivity nonuniformity is less than 3% (sigma/mean). These 25 μm microbolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. These arrays have produced excellent image quality, and are currently fielded in a variety of systems. We will report on our latest performance data and IR captive flight test imagery. We will also show data on 25μm arrays that have been designed for faster time constants (5 msec), while maintaining high performance. RVS is also developing a 320 x 240 50μm mid-wave responding FPA. We will review the MWIR sensitivity improvements with this array and provide IR imagery. RVS is developing a 640 x 480 25μm uncooled FPA for a countermine detection application using a two-band assembly designed to be sensitive in both the Restrahlen and Thermal spectral bands. We will provide IR image data on these arrays. RVS has made a significant breakthrough in the development of a 640 x 512 array with a unit cell size of 20 μm x 20 μm, and performance approaching that of the 25μm arrays. The successful development of this array is the first step in achieving mega-pixel formats. This FPA is designed to ultimately achieve performance near the temperature fluxuation limited NETD (<20mK, f/1, 30 Hz). We will show updated performance and imagery on these arrays, which is currently being measured at <45mK, f/1, 30 Hz.

There have been recent innovations to reduce the cost of packaging for MEMS devices, without deteriorating their performance. One such novel design for device-level encapsulation (self-packaged) of uncooled infrared (IR) microbolometers is documented here. Device-level vacuum encapsulation has the potential to eliminate some major problems associated with the bolometer performance such as high thermal conductance of the ambient atmosphere, the high cost associated with conventional vacuum packaging, and the degradation of optical transmission at different wavelengths through a conventional package window. The device-level encapsulated bolometers can also be fabricated with flexible substrates, which have the advantage of conforming to non-planar surfaces compared to Si or other rigid substrates. In addition, a flexible superstrate with low shear stress has applications in robotics, aerospace, defense and biomedicine as a "Smart skin", a name given to multisensory arrays on conformal substrates to emulate human skin functions on inanimate objects. Self-packaged uncooled microbolometer arrays of 40x40 μm² and 60x60 μm² are fabricated on top of Si wafer with a sacrificial layer using semiconducting Yttrium Barium Copper Oxide (YBCO) as the infrared sensing material. A two-layer surface micromachining technique in conjunction with a resonant cavity and a reflecting mirror are used for the sensor structure. The devices have demonstrated voltage responsivities of 7.9x10³ V/W with a temperature coefficient of resistance of -2.5% K^-1, and thermal conductivity of 2.95x10^-6 W/K. The device performance was similar in air and vacuum, demonstrating vacuum integrity and a good device-level encapsulation.

Missile Defense Agency/Advanced Systems, in partnership with both EUTECUS/University of Notre Dame (UND) and ITN Energy Systems/University of Central Florida (UCF) has embarked on developing a multispectral imaging IR sensor. This technology, when matured, could revolutionize IR sensor technology by reducing the need for cooling, eliminating lattice matching and avoiding epitaxial fabrication processes. This paper describes the approaches employed by both EUTECUS/UND and ITN/UCF teams to integrate nano-antenna technology with the existing cellular neural network (CNN) processor to produce multispectral IR sensors. This effort is a leap into the performance realm where biological systems operate.

We present a new technology for uncooled focal plane arrays, which is based on optical readout. An electrooptic crystal, operated in the paraelectric phase, is used as the temperature sensitive element. A lateral readout configuration is utilized, and an entire row of pixels is read simultaneously through electrical triggering. The optical readout diminishes the electronic noise mechanisms resulting in a predicted NETD of 5-7mk. This low NETD of the device is determined by the temperature fluctuations noise, thus approaching the theoretical limit for uncooled FPAs.

A novel uncooled long-wave infrared imaging technology with optical readout is proposed and developed targeted for low cost thermal imaging applications. This technology uses the thermo-optic effect in a semiconductor to detect infrared signals rather than the thermal-resistance effect used in traditional microbolometers. The key component of the imager, the focal plane array, is made up of thermally tunable thin film filter membrane pixels. Each thermal pixel acts as a wavelength translator, converting far infrared radiation signals into near infrared signals which are then detectable by off-the-shelf CCD or CMOS cameras. This approach utilizes optical filter and MEMS technologies, to build a low-cost passive long wavelength infrared focal plane array without electrical leads or active cooling. Within one year since the commencement, NETD values of 0.28K in a 160x120 array operating at 22Hz video frame rate have been achieved without temperature control.

The value of infrared imaging in defense, security and public safety applications has been well established. A number of camera technologies have been developed and are commercially available. Yet the cost, size and power consumption of the typically cryogenically cooled cameras remain a significant impediment to more widespread deployment for these missions and extended exploitation in other fields. Agiltron has been developing a MEMS microcantilever technology offering high sensitivity and expanded operating temperature range in order to address the fundamental shortcomings of currently available technology. Here we report results achieved to date with our imagers and present an analysis of the performance potential of the architecture. We derive the fundamental mechanical limit to NEDT of this photomechanical imager architecture.

InfraredVision Technology Corporation ("ITC") has improved the performance of the 320x240 microbolometer Uncooled Focal Plane Array ("UFPA") by increasing the pixel fill-factor. This allows state-of-the-art performance for applications requiring high sensitivity. Measurements taken on microbolometer test structures and detector arrays show a factor of two improvements in the responsivity over that previously reported for our standard 37.5-um pixel UFPA. Performance results for microbolometer pixels ranging in size from 50um down to 15um are presented. Our ITC-1000 series detector product addresses both imaging and radiometric commercial-camera applications. With the development of a high fill-factor pixel design, ITC will soon provide a high-performance VOx microbolometer-based sensor to camera manufacturers requiring state-of-the-art detector performance. FPA performance is presented to demonstrate the sensor improvements accomplished. The use of our on-chip NonUniformity Correction (NUC) feature, available on the ITC-1000 detector, is characterized to demonstrate the performance limitations.

Having delivered over 30,000 uncooled microbolometer based thermal imaging engines, BAE Systems is the world's leading producer. Advancements in technology include the demonstration of broadband microbolometers on a 46 μm pixel pitch which have excellent sensitivity in the MWIR (NETD ≈180 mK, 3-5 μm) and LWIR (NETD ≈ 15 mK, 8-12 μm) wavebands. Application advancements include the development of a family of thermal weapons sights for the military which will replace current cooled systems with lighter, lower power systems and the introduction of a new generation of handheld and pole mounted thermal imagers for commercial markets.

Uncooled infrared focal plane arrays are being developed for a wide range of thermal imaging applications. ULIS now offers a new type of detector for middle and long wave applications. This detector has been designed from the standard product using the same focal plane array and the same package, only the window is different in terms of spectral transmission. This device is well adapted to high temperature measurements, special industrial processes and gas detection. After some brief microbolometer technological background, we will present the interest for such detectors by comparing LWIR/MWIR detector signal to noise ratio, we will then determine the advantages for different applications. Finally, we will describe and give the main EO characteristics and performances of this Ulis product.

The cost of high sensitivity, high resolution, (640x480) Uncooled IR (UCIR) sensors is too high for the sensors to widely proliferate. To achieve cost reduction and production capacity goals, improvements are required in the following areas: the Read-out Integrated Circuit (ROIC), the pixel design, the Integrated Circuit Processing of MEMS structures, vacuum package design, batch assembly package processing and automated testing. The improvements result in increased yield at the wafer level, increased yield through packaging, lower labor assembly and testing costs and improved performance. A cost model will be presented to show the interrelationship of the various costs and how the reduction in cost may be achieved.

A novel concept for low-cost, wafer-level packaging of MEMS is proposed and applied to vacuum packaging of INO's 160x120 pixel uncooled bolometric focal plane arrays, FPAs, based on vanadium oxide as thermistor material. The wafer-scale fabrication of both metallic and ceramic micropackages is described. In the former case, a nickel tray composed of several tens of micropackages is electroplated by using a thick negative resist as micromold. In the latter case, micropackages are fabricated from up to 1 mm-thick, polished, laser machined alumina wafers equipped with solderable layers and solder seals. FPA dies and infrared windows are then soldered to the main tray by thermo-compression bonding. Contrary to the conventional wafer-to-wafer bonding approach, assembly and vacuum sealing steps are dissociated. For that purpose, each micropackage is equipped with a pump-out hole for outgassing prior to vacuum sealing. To monitor in-situ pressure changes within the sealed microcavity, micromachined pressure sensors were specifically designed for thermal conductance measurements. The initial characterization of dies after assembly in the metallic micropackage is presented.

SCD is unveiling the first member of its new uncooled product line based on the high-end VOx technology. The detector is software configurable to various format standards including 384x288, 320x240 and others with 25μm pitch. The NETD values for these FPAs are better then 50mK with F#/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast thermal time constant of approximately 10msec. In order to improve the system level "cost-performance" in terms of power consumption and weight, SCD has introduced special features within the FPA & package. Among them is a proprietary "Power Save" architecture, in which the die temperature can be stabilized to the ambient temperature or a close enough discrete value, covering the range between -40c and 70c. Thus, the TEC power consumption is considerably reduced with minimal performance degradation. An additional benefit is improved "mission readiness" which is of vital importance for various system applications. A major limitation of systems based on uncooled detectors is the poor resilience to the ambient temperature drift. This drift degrades the spatial non-uniformity. As a result, frequent corrections using an optical shutter are required, specifically during the camera stabilization period. In order to increase the time span between shutter operations, SCD has incorporated various real-time monitoring features within the FPA and supporting algorithms. These features reduce the spatial noise by an order of magnitude.

DRS Technologies has designed and delivered Thermal Weapon Site (TWS) and Driver's Viewer Enhancer (DVE) system using its U3500 (320x240) and U6000 (640x480) 1-mil detector arrays. The detectors are modified to enhance its manufacturability, thermal time constant, package life time, and its reliability under shock and vibration to meet TWS and DVE requirements. The U6000 array operates at 30 Hz frame rate with NETD less than 50 mK normalized to F/1.0 optics. At a saving to the system weight and power, these arrays operate from -40°C to +65°C without the aid of a TE cooler. This is accomplished through a combination of sensor calibration and smart ROIC architecture.

This paper describes the structure and performance of a 25-micron pitch 640 x 480 pixel uncooled infrared focal plane array (IR FPA) with silicon-on-insulator (SOI) diode detectors. The uncooled IR FPA is a thermal type FPA that has a temperature sensor of single crystal PN junction diodes formed in an SOI layer. In the conventional pixel structure, the temperature sensor and two support legs for thermal isolation are made in the lower level of the pixel, and an IR absorbing structure is made in the upper pixel level to cover almost the entire pixel area. The IR absorption utilizes IR reflections from the lower level. Since the reflection from the support leg portions is not perfect due to the slits in the metal reflector, the reflection becomes smaller as the support leg section increases in reduced pixel pitches. In order to achieve high thermal isolation and high IR absorption simultaneously, we have developed a new pixel structure that has an independent IR reflector between the lower and upper levels. The structure assures perfect IR reflection and thus improves IR absorption. The FPA shows a noise equivalent temperature difference (NETD) of 40 mK (f/1.0) and a responsivity non-uniformity of less than 0.9%. The good uniformity is due to the high uniformity of the electrical characteristics of SOI diodes made of single crystal silicon (Si). We have confirmed that the SOI diodes architecture is suitable for large format uncooled IR FPAs.

This paper reviews ULIS’progress, on 35 μm pitch, in amorphous silicon uncooled microbolometer focal plane (UFPA) technology and product development over the last year. The ULIS FPA products have been described in great detail, including product capabilities and complete EO performances. At 60 Hz frame rate, focal planes with 40 mK (f/1) NETD are now achieved in production with a spatial fixed pattern noise lower than 25 mK after gain and offset compensation. Key improvements, compared to 45 μm pitch technology, have been the achievement of microbolometer resistance uniformity better than 0.5 % (standard deviation) on the IRFPA die for the different formats. Thanks to a new pixel design, high fill factor along with low thermal time constant (7 ms), 35 μm pitch amorphous silicon UFPAs are prime candidates for FLIR applications.

At the time of the 2004 SPIE Defense and Security Symposium the optical, electrical and mechanical components of the fire control system for the PDRR program phase of the XM29 combat rifle were being delivered and the build of the systems was about to begin. In the following four months the hardware was integrated and extensively tested in both laboratory and field environments. Fully tested fire control units were delivered to Alliant Techsystems (ATK) in August '04. The XM25 rifles, the weapons for delivering the 25 mm High Explosive Air Burst (HEAB) rounds of the XM29 system, were delivered to Alliant a few weeks later. After only twenty days the weapon, fire control, system battery and ammunition system components were successfully integrated and the first demonstration of air burst fuzing of the 25 mm high explosive rounds was conducted successfully. This paper presents test results for the 2&1/2 lb fire control system with its 25-μm uncooled thermal imager, direct view optics, laser rangefinder and low power fuzing electronics. The paper also discusses the HEAB testing and provides an update on the XM29 program and the progress towards a Milestone B decision.

RF sputtered thin films of Si_1-xGe_x and Si_1-xGe_xO_y were investigated by measuring their composition, electrical, and optical properties. As Si concentration was increased to the Ge to form Si_1-xGe_x films, the resistivity was increased while the activation energy and TCR both were decreased. For Si_1-xGe_xO_y films, the addition of O₂ to the Si_1-xGe_x, increased the resistivity, activation energy and TCR. The TCR was measured to vary from -2.27%/K to -8.69%/K, while the resistivity varied from 4.22×10² Ω-cm to 3.47×10⁹ Ω-cm. A good atomic composition of Si1-xGexOy to be used in microbolometers as the sensitive layer was found to have a TCR of -5.10%/K with a moderate resistivity of ~10⁴ Ω-cm. Microbolometers using doped Si_0.15Ge_0.85 and Si_0.15Ge_0.85O_y thermometers have been fabricated using a polyimide sacrificial layer. The 1/f-noise is observed to be relatively high in the Si_1-xGe_x thin films and microbolometers.

"Network-centric Warfare" is a common slogan describing an overall concept of networked operation of sensors, information and weapons to gain command and control superiority. Referring to IR sensors, integration and fusion of different channels like day/night or SAR images or the ability to spread image data among various users are typical requirements. Looking for concrete implementations the German Army future infantryman IdZ is an example where a group of ten soldiers build a unit with every soldier equipped with a personal digital assistant (PDA) for information display, day photo camera and a high performance thermal imager for every unit. The challenge to allow networked operation among such a unit is bringing information together and distribution over a capable network. So also AIM's thermal reconnaissance and targeting sight HuntIR which was selected for the IdZ program provides this capabilities by an optional wireless interface. Besides the global approach of Network-centric Warfare network technology can also be an interesting solution for digital image data distribution and signal processing behind the FPA replacing analog video networks or specific point to point interfaces. The resulting architecture can provide capabilities of data fusion from e.g. IR dual-band or IR multicolor sensors. AIM has participated in a German/UK collaboration program to produce a demonstrator for day/IR video distribution via Gigabit Ethernet for vehicle applications. In this study Ethernet technology was chosen for network implementation and a set of electronics was developed for capturing video data of IR and day imagers and Gigabit Ethernet video distribution. The demonstrator setup follows the requirements of current and future vehicles having a set of day and night imager cameras and a crew station with several members. Replacing the analog video path by a digital video network also makes it easy to implement embedded training by simply feeding the network with simulation data. The paper addresses the special capabilities, requirements and design considerations of IR sensors and imagers in applications like thermal weapon sights and UAVs for networked operating infantry forces.

The Sea Star SAFIRE is a commercially developed, off the shelf, military qualified system (COTS-MQS) consisting of a 640 by 480 InSb infrared imager, laser rangefinder and visible imager in a gyro-stabilized platform designed for shipborne applications. These applications include search and rescue, surveillance, fire control, fisheries patrol, harbor security, and own-vessel perimeter security and self protection. Particularly challenging considerations unique to shipborne systems include the demanding environment conditions, man-machine interfaces, and effects of atmospheric conditions on sensor performance. Shipborne environmental conditions requiring special attention include electromagnetic fields, as well as resistance to rain, ice and snow, shock, vibration, and salt. Features have been implemented to withstand exposure to water and high humidity; anti-ice/de-ice capability for exposure to snow and ice; wash/wipe of external windows; corrosion resistance for exposure to water and salt spray. A variety of system controller configurations provide man-machine interfaces suitable for operation on ships. EO sensor developments that address areas of haze penetration, glint, and scintillation will be presented.

We have shown a method of target acquisition with a high Probability of Detection (Pd), extremely low False Alarm Rate (FAR), which can be implemented in real time hardware existing in most of ELOP's FLIRs. This target acquisition method is based on sensing the linear polarized radiation of the scene and is based on the phenomenon that facets found on most man made targets show a high degree of linear polarization while natural background elements do not. Using this phenomenon (after fixing all the engineering hurdles such as polarizer wobble, etc) can give us a powerful tool for acquiring targets in cluttered backgrounds, where "regular FLIRs", even the most sensitive ones, fail to acquire targets. This phenomenon is most successful where the limiting factor for detection is the clutter, so although lowering scenes SNR (Signal to Noise Ratio), by introducing the polarizer, we get higher SCR (Signal to Clutter Ratio) which is often the real limiting factor in real life. The phenomenon was found to be very robust over different targets and backgrounds in the LWIR and much weaker in the MWIR.

In recent years some major technological developments in the fields of electro-optics and computer H/W took place, which call for reconsideration of the development paths for missile warning systems (MWS). In this work, we provide a review of the technological developments, and then suggest a framework for the following issues: (a) Prioritization of requirements for MWS, (b) Selection of best candidate technologies for next-generation MWS, (c) Establishing a generic parameter sensitivity model for MWS performance, with which we could quantify the effects of different design choices on system-level performance. Our work shows that (a) Infrared optical H/W remains the leading technology for MWS applications, (b) 3rd generation infrared imaging H/W will make a significant impact on MWS performance, compared with 2nd generation based IR-MWS system's performance. (c) Dual band infrared sensor FPAs now under development will further improve performance, yet the improvement will be offset by the lack of some of the more important features of the 3rd generation imagers-very high resolution and frame rate (d) A combination of 3rd generation and dual band IR imaging, when it becomes available, will provide yet another significant improvement.

The Air Force Research Laboratory (AFRL) has embarked on a variety of research programs that embrace the insertion of new electro-optical and infrared technology as well as advanced operational concepts to significantly improve capabilities for the detection and discrimination of difficult targets. The AFRL vision employs a distributed, layered sensor system combining passive and active sensors to rapidly detect battlefield threats and support high confidence identification to take immediate action. This paper will provide an overview of this layered sensing vision as well as describe the technology development directions that AFRL is pursuing in support of this advanced concept. The paper will specifically focus on relevant passive infrared technology areas such as spatial, spectral, polarimetric, and temporal sensing (separate and combined). It will also discuss how this technology is envisioned to be applied to the range of operational platforms, from standoff surveillance from large aircraft to close-in sensing from small unmanned aerial vehicles.

The Sensors Directorate at the Air Force Research Laboratory (AFRL) along with Defense Research Associates, Inc. (DRA) conducted a flight demonstration of technology that could potentially satisfy the Federal Aviation Administration's (FAA) requirement for Unmanned Aerial Vehicles (UAVs) to sense and avoid local air traffic sufficient to provide an "...equivalent level of safety, comparable to see-and-avoid requirements for manned aircraft". This FAA requirement must be satisfied for autonomous UAV operation within the national airspace. The real-time on-board system passively detects approaching aircraft, both cooperative and non-cooperative, using imaging sensors operating in the visible/near infrared band and a passive moving target indicator algorithm. Detection range requirements for RQ-4 and MQ-9 UAVs were determined based on analysis of flight geometries, avoidance maneuver timelines, system latencies and human pilot performance. Flight data and UAV operating parameters were provided by the system program offices, prime contractors, and flight-test personnel. Flight demonstrations were conducted using a surrogate UAV (Aero Commander) and an intruder aircraft (Beech Bonanza). The system demonstrated target detection ranges out to 3 nautical miles in nose-to-nose scenarios and marginal visual meteorological conditions. (VMC) This paper will describe the sense and avoid requirements definition process and the system concept (sensors, algorithms, processor, and flight rest results) that has demonstrated the potential to satisfy the FAA sense and avoid requirements.

This paper reviews current IR security sensor technology and considers how new developments could impact on this increasingly important field, with relevance to military, industrial and domestic markets. We consider performance specifications for various applications, and investigate how trades can be made to meet market requirements. We address the definition of 'low cost', and suggest what might be acceptable for the various market segments. The paper discusses novel new patented technology, including the active microbolometer, where the IR detector functions as a transistor, and where arrays and readout are fabricated in the same technology on silicon wafer or other suitable substrates. Methods are discussed for achieving the desired performance for imaging and non-imaging 'smart' sensors in low cost packaging, including sealing at atmospheric pressure. We introduce the concept of mosaic pixel focal plane arrays (MP-FPA).

In the modern world of high value security systems a successful installation requires the sensors to produce more than just good IR images, preprocessed data from these images, imagery in multiple bands fused in intelligent ways with each other and with non imaging information such as Laser ranging is required. This paper describes a system where LW uncooled, color TV, low light level TV, and laser ranging information are fused in a integral Pan and Tilt system to provide a sensor suite with exceptional capabilities for seamlessly integration into an advanced security system. Advances integrated in this system includes the advances sensor suite, sensible symbology for situational awareness in case of operator intervention, parallax and focus tracking through zoom and sensor changes to enhance auto tracking and motion detection algorithms.

U.S. Army Research, Development, and Engineering Command (RDECOM) Communications Electronics Research, Development and Engineering Center (CERDEC) Night Vision and Electronic Sensors Directorate (NVESD) has performed early work to develop a Distributed Aperture System (DAS). The DAS aims at improving the situational awareness of armored fighting vehicle crews under closed-hatch conditions. The concept is based on a plurality of sensors configured to create a day and night dome of surveillance coupled with heads up displays slaved to the operator's head to give a "glass turret" feel. State-of-the-art image processing is used to produce multiple seamless hemispherical views simultaneously available to the vehicle commander, crew members and dismounting infantry. On-the-move automatic cueing of multiple moving/pop-up low silhouette threats is also done with the possibility to save/revisit/share past events. As a first step in this development program, a contract was awarded to United Defense to further develop the Eagle Vision^TM system. The second-generation prototype features two camera heads, each comprising four high-resolution (2048x1536) color sensors, and each covering a field of view of 270°hx150°v. High-bandwidth digital links interface the camera heads with a field programmable gate array (FPGA) based custom processor developed by Sarnoff Corporation. The processor computes the hemispherical stitch and warp functions required for real-time, low latency, immersive viewing (360°hx120°v, 30° down) and generates up to six simultaneous extended graphics array (XGA) video outputs for independent display either on a helmet-mounted display (with associated head tracking device) or a flat panel display (and joystick). The prototype is currently in its last stage of development and will be integrated on a vehicle for user evaluation and testing. Near-term improvements include the replacement of the color camera heads with a pixel-level fused combination of uncooled long wave infrared (LWIR) and low light level intensified imagery. It is believed that the DAS will significantly increase situational awareness by providing the users with a day and night, wide area coverage, immersive visualization capability.

Standard GaAs/AlGaAs Quantum Well Infrared Photodetectors (QWIPs) are from now seriously considered for the 3rd generation of IR imagers. Since 2002, the THALES Group has been manufacturing sensitive arrays using QWIP technology based on AsGa techniques through THALES Research and Technology Laboratory. This QWIP technology allows the realization of large staring arrays for Thermal Imagers (TI) working in the IR band III (8-12 μm). A review of the current QWIP products is presented. In the past researchers claimed many advantages of QWIPs. Uniformity was one of these and was the key parameter for the production start. By presenting our first results of a 640x512 LWIR FPA at a pitch of 20μm, we also demonstrate that very high performances can be achieved even with small pixels which opens the field for the realization of usable and affordable megapixel FPAs. Another advantage widely claimed in the past for QWIPs was the so-called band-gap engineering and versatility of the III-V processing. This allows the custom design of quantum structure to fulfill the requirements of specific applications like very long wavelength or multispectral detection. In this presentation, we present the performances of our first 256x256 MWIR / LWIR and LWIR/LWIR two color FPAs at a pitch of 25 μm.

A novel quantum-well infrared photodetector (QWIP) with peak responsivity in the mid-wavelength (MW) range was characterized, and the performance of a focal-plane array (FPA) based on the MW-QWIP was investigated. InGaAs/AlGaAs quantum wells were used for the QWIP, resulting in a peak absorption wavelength in the range of 4.5~5.0 μm. The doping concentration and In composition of the well layers were varied to improve the photocurrent of the QWIP. The relationship between the noise of the QWIP and the number of multi quantum well (MQW) layers was also investigated, and the optical gain g was estimated. The noise-equivalent temperature differences (NETDs) of QWIPs with various numbers of MQW layers were calculated, and the optimum number of MQW layers was evaluated. It was found that controlling the In composition of the wells was very effective for improving the photocurrent. As a result, a MW-QWIP FPA with a NETD of 21 mK at an operation temperature of 80 K, an integration time of 16 ms, and F2.0 optics was fabricated.

QWIPs are nowadays considered as rather good candidates for multispectral imaging. Indeed, their narrow spectral bandwidth can be tailored by band gap engineering, and they rely on the use of the mature GaAs technology. However, a light coupling scheme, such as 2D-grating for example, is required to obtain normal incidence absorption. The geometrical parameters of this 2D-grating (grating period, etch depth of the grating) need to be optimized. This optimization is particularly difficult for dual-band pixels, since a compromise is required between the two wavelengths. This paper deals with the influence of the etch depth of the grating on the angular response of quantum well infrared photodetectors. We will first present the experimental setup which was specifically developed at ONERA to perform angular response measurements on infrared photodetectors from different technologies. The results obtained on "low-noise" QWIP samples provided by Fraunhofer-IAF will be presented and analyzed, with emphasis on the effect of the etch depth of the grating on the angular response.

In recent years quantum well infrared (IR) photodetector (QWIP) focal plane array (FPA) technology has developed to the point where it may be considered a candidate for insertion into 3rd generation FLIR systems. Large format 1024x1024 pixels FPAs have been produced using QWIP technology. We report on the application of a large format FPAs to the challenges facing today's military. These include the collection of signatures of military vehicles for long-range target detection/identification. The FPA used was a 1024x1024 pixel array which is available commercially. from QWIP Technologies, Inc. We show imagery of military targets at ranges from 500 m to 5 km acquired in the field. The results of the performance in the field are compared to that predicted by computer models and the performance of the large format QWIP FPA will be evaluated in terms of the capabilities of a notional 3rd generation FLIR system.

A photovoltaic intersubband detector based on electron transfer on a cascade of quantum levels is presented: a Quantum Cascade Detector (QCD). Optical and electrical performances of a QCD are presented: high responsivity at null bias voltage about 44mA/W, high resistivity. Because they work with no dark current, QCDs are very promising for small pixel and large focal plane array applications. A dark current modelling is explained.

Successful past experience of implementing long wave MCT 1st and 2nd Generation thermal imagers has demonstrated to THALES Optronics that MCT presents difficult challenges when correcting non-uniformity errors caused by rapidly changing detector element gain and offset drifts. These problems become even more demanding when the move is made from long linear arrays to focal plane arrays due to the significantly larger number of detector elements. Relaxation of these demands would make a significant impact on the price/performance trade which inevitably occurs in a camera development. In recognition of the need to offer UK MOD best value, THALES Optronics has initiated a programme to achieve a SXGA resolution camera and is working with UK MOD, over a two year period, to investigate whether an alternative technology can maintain the high resolution required whilst achieving a downward step change in price. The selected technology is 3rd Generation Gallium Arsenide long wave Quantum Well Infra-red Photodiode (QWIP) chosen because initial indications are that drift rates are orders of magnitude slower than MCT. The programme involves studies to determine effects of defect clusters, bimodalism, non-uniformity correction levels and higher than normal operating temperatures on achieving acceptable performance, including logistics, in user scenarios whilst maximising detector yield. Development of demonstrator IR camera hardware (technology readiness level 6/7) based on a THALES Research & Technology QWIP array is also part of the programme.

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024x1024 pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17 mK at a 95K operating temperature with f/2.5 optics at 300K background and the LWIR detector array has demonstrated a NEΔT of 13 mK at a 70K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90K and 70K operating temperatures respectively, with similar optical and background conditions. In addition, we are in the process of developing MWIR and LWIR pixel collocated simultaneously readable dualband QWIP focal plane arrays. In this paper, we will discuss the performance in terms of quantum efficiency, NEΔT, uniformity, operability, and modulation transfer functions of the 1024x1024 pixel arrays and the progress of dualband QWIP focal plane array development work.

CEA/LETI has been working for several years on the development of HgCdTe-based infrared dual band detectors [3]. Since 2001 CEA/LETI is also involved in a large program for the demonstration of dual band QWIP FPAs presenting large format and small pitch. This study is carried out with the QWIP team of THALES Research and Technology (TRT) in charge of QWIP design, MBE growth and GaAs processing for the detector side. As part of this program TRT investigated different quantum structures and pixel architectures for the realization of two-band FPAs for MWIR/LWIR and LWIR/LWIR applications. At the end of this study a choice of the most appropriate architecture was done. On its side, CEA/LETI designed readout circuits optimized for the selected dual-band QWIP. TRT delivered QWIP arrays and CEA/LETI proceeded to the assembly, integration and electro-optical characterization. The aim of this paper is to describe the architecture of these dual-band demonstrators and to present the first results concerning their electro-optical performances measured at 70K and 65K.

The objective of this project is to seamlessly integrate multiple spectral-band focal plane detector arrays into a single multi-band imaging sensor. The resulting product can be applied to a telescope or a microscope, as simply as changing a lens on a camera. The video stream output provides a set of co-registered digital images from a multiple of spectral bands spanning the Visible, NIR, MWIR and LWIR radiation regions (.4um to 14um). These images have a format that is suitable both for direct observation by a human operator and as a data feed for Automated Target Recognition (ATR) algorithms.

There is a growing need for dual band cameras in airborne reconnaissance systems having simultaneous operation in the 0.5-0.9 μm and 3-5 μm spectral bands. The dual band requirement stems from considerations of system performance and cost as well as installation on the platform. Airborne reconnaissance cameras require optical systems with long focal length and large apertures in the 3-5 mm wavelength IR region. A large optical system conflicts with the limitations of weight and volume often associated with long-range reconnaissance platforms. A dual-waveband airborne telescope and camera system has been developed by El-Op Ltd. This system provides high-resolution images in the thermal IR at night and simultaneous IR and visible images during day. It offers low weight, compact size and high dimensional stability over a wide range of environmental conditions. To enable the operation of the dual band, a unique dichroic beam splitter with special coating and broad band anti-reflection coating was developed for optimization of the transmittance in each band. The optical design of the telescope, the coating and its performance will be presented in the paper.

This work focuses on methods used in the mechanical design of infrared catadioptric lenses. Multiple lens designs are presented to allow elaboration on mirror design considerations, alignment, athermal principles, system focusing options and design ruggedization. Catadioptric lenses are commonly used in the infrared as a cost effective solution to their refractive design counterparts. Janos Technology Inc. has designed, fabricated, and tested many catadioptric systems and this paper draws from their history. A summary of the assembly and testing process is also included.

An infrared imaging lens that produces beams with long focal depth whilst preserving the entire aperture for full light capturing and high transverse resolution is presented. It is a diffractive optical element that generates a long range of pseudo-non-diffractive rays. The design technique is based on the conjugate-gradient algorithm. The surface relief pattern was generated on a thick film photoresist and then the pattern was transferred to germanium substrate. Preliminary experimental results demonstrated four times improvement in depth of focus at 10.6 μm wavelength.

Data from multiple spectral wavebands can significantly increase the information available to the observer. Of particular utility is combination of images into a single multi-spectral image. When such images are combined properly, the resulting image can be an extremely powerful tool, sometimes offering more information than the imagery from either waveband individually. Substantial care must be taken in the combination of these images, however, since mis-registration of the two images can cause significant confusion and image degradation when combined into a single image. Mis-registration from sources such as relative lateral or rotational shift, differences in image size, and differences in distortion can cause significant degradation in the combined image. Special care must be taken in both the optical and mechanical design to minimize these effects and to maximize the utility of multi-spectral image fusion.

Thales Optics Ltd. have been involved in a joint funded technology demonstrator program between UK MOD and Thales called Thermal Imager for Dismounted Infantry, run in conjunction with QinetiQ. The aim of this program was to evaluate and demonstrate a cost effective route to equipping the infantry soldier with a small, lightweight, rugged, short range, weapon mounted thermal imaging sight, intended for mass deployment. To address the requirements of this program, Thales Optics Ltd. performed a detailed trade-off analysis considering the effect of using alternative sensors, displays and optical configurations on the sight cost, mass, volume, power and performance. This effort was supported with equipment trials and user assessments. Based on this work, six technical demonstrator sights have been manufactured and delivered to UK MOD for evaluation on several programmes including the UK's FIST soldier modernisation program. Thales Optics has since progressed the TIDI concept further into two product streams, a family of weapon sights called VIPIR and a surveillance sight called VIPIR-S. This paper will summarise the work undertaken on the TIDI program and how this has been applied to the VIPIR and VIPIR-S family of products.

Dual f/number cooled IR optics allow future systems (i.e. 3rd Gen FLIR) to be optimized for each operational mode, while maintaining the same size packages. This permits improved signal-to-noise ratios for search applications while maintaining long ranges for targeting applications. In addition, it enables the optimization of dual band sensor optics (MWIR and LWIR) based on the change of the diffraction limit with wavelength and f/number. In essence, dual f/number optics allow for improvements in either sensitivity or resolution for a given operational mode of a sensor, depending on which is more critical. To make the transition from 2nd Generation systems to 3rd Generation dual f/number systems, both the optics and cold stop require changes. This paper details the concept of dual f/number optics, their design requirements, and the optics related issues that are inherent in their design.

In this paper the construction of both mechanically and optically compensated zoom lenses is discussed. Particular attention is paid to the Computer Optics Inc. Infrared Optically Compensated Zoom Lens.

Umicore IR Glass has developed an industrial process to manufacture low cost chalcogenide glasses with well controlled properties. These materials called GASIR® 1 and GASIR® 2 are transparent in the 3-5 and 8-12 μm atmospheric windows allowing a great range of applications in thermal imaging. In the past two years, several optics based on Germanium existing optics (60 mm and 100 mm) have been redesigned for GASIR® glass and are now produced as standards in medium volume series. This year Umicore is passing another step in the production of infrared moulded optics by opening the first high volume factory entirely dedicated to GASIR® optics for driving vision enhancement (DVE). This new facility will have a capacity of several tens of thousands of optics per year. In this article, the first results of performance of the corresponding optics will also be presented.

The evolution of InSb Focal Plane Arrays (FPAs) at L-3 Communications Cincinnati Electronics (L-3 CE) has resulted in large format, high reliability, and high yields for 256x256, 640x512, 1Kx1K and even 2Kx2K formats using our patented front-side illuminated, reticulated pixel design. Baseline processes matured at 30um pitch and gradually were made producible at 25um pitch. Recent progress in process technology, specifically dry etch plasma processes and photolithography tools, has created a new set of processes/design capabilities which enable 15um pixel pitch FPAs, thus allowing us to develop a 15um pitch FPA with 4 times as many pixels, in the same foot print as the previous 30um pitch designs. We have developed a new 15um pitch, reticulated pixel design, implemented on a 512x512 format, which can then be sized into larger arrays, similar to the evolution that occurred on 30um pitch FPAs. As unit cell dimensions shrink by a factor of two, both the feature size and the alignment tolerances begin to limit optical fill factor. Addition of a novel micro-optic design, which optimizes signal collection to near 100% efficiency while maintaining near theoretical pixel MTF, will be presented.

Progress of selected FPA (Focal Plane Array) technology development at Rockwell Scientific Company is reviewed: very large format monolithic visible CMOS, hybrid silicon pin visible CMOS, ultra high frame rate (360ns interframe time) burst mode camera, substrate removed HgCdTe infrared detectors for continuous visible through infrared spectral sensitivity, astronomical focal plane arrays, mosaic (16 megapixel) infrared FPAs, JWST, and the SIDECAR ASIC readout interface chip.

Negative luminescent devices, which absorb more light than they emit when reverse biased, have a large number of applications including, reference planes for thermal cameras, infrared (IR) sources and IR scene projection. This paper describes devices made from mercury cadmium telluride grown on silicon substrates, focusing on large area arrays with reduced operating powers. Novel growth structures and device designs have been investigated in order to reduce the series resistance. Results from the first dry etched, LW MCT on Si, 1 cm² device with optical concentrators are presented.

A monolithically integrated low temperature MEMS and HgCdTe infrared detector technology has been implemented and characterised. The MEMS-based optical filter, integrated with an infrared detector, selects narrow wavelength bands in the range from 1.6 to 2.5 μm within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The entire fabrication process is compatible with two-dimensional infrared focal plane array technology. The fabricated device consists of an HgCdTe SWIR photoconductor, two distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity, which is then removed to leave an air-gap, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors shows a wide tuning range and high percentage transmission is achieved with a tuning voltage of only 7.5 V. The FWHM ranged from 95-105 nm over a tuning range of 2.2 μm to 1.85 μm. Finite element modelling of various geometries for the silicon nitride membrane will also be presented. The modelling is used to determine the best geometry in terms of fill factor, voltage displacement prediction and membrane bowing.

A new second generation advanced thermal imager, which can be used for battle tank sight has been developed in Korea. The IR optics has dual field of views such as 2.67×2° in NFOV and 10×7.5° in WFOV. This system uses a 480×6 TDI HgCdTe detector, operating in the 8-12μm wavelength, made by Sofradir. In order to correct non-uniformity of detector array, the two point correction method has been developed by using the thermo electric cooler. Additionally, to enhance the image of low contrast and improve the detection capability, the new technique of histogram processing has been proposed. Through these image processing techniques, we obtained the high quality thermal image.

Resonant cavity enhanced photodetectors are promising candidates for applications in high-speed optical communications due to their high quantum efficiency and large bandwidth. This is a consequence of placing the thin absorber of the photodetector inside a Fabry-Perot microcavity so the absorption could be enhanced by recycling the photons with resonance wavelength. The performance of uncooled resonant cavity enhanced InGaAs/InAlAs photovoltaic devices operating near 1.55 μm has been studied both theoretically and experimentally. The analyses include two different types of structures with cavity end mirrors made of semiconducting and metallic reflectors as well as semiconducting and hybrid (dielectric Si₃N₄/SiO₂ + metal) Bragg reflectors. Optimization of the device design includes: absorption layer thickness, position of absorption layer within the cavity and number of layers in distributed Bragg reflectors. Dependence of absorption on wavelength and incidence angle are discussed. Various issues related to applications of resonance cavity enhanced photodiodes in optical systems are considered. Practical devices with metallic and hybrid mirrors were fabricated by molecular beam epitaxy and by microwave-compatible processing. A properly designed device of this type has potential for subpicosecond response time.

A method is described for the direct measurement of the thermal time constant of microbolometer arrays: The emitted radiation from an array due to time varying Joule heating is monitored by a fast photodetector. Applying a bias voltage pulse to the array the thermal time constant is measured from the time dependence of the emission decay at the end of the pulse. In particular, we have used HgCdTe photodetector and digital signal acquisition and analysis to measure the thermal time constant of uncooled a-Si:H microbolometer 120 x 160 arrays with 50 micron pixels. Measured typical thermal time constant values for such arrays are in the range of 8ms to 10ms.

Interest and growth of biometric recognition technologies surged after 9/11. Once a technology mainly used for identity verification in law enforcement, biometrics are now being considered as a secure means of providing identity assurance in security related applications. Biometric recognition in law enforcement must, by necessity, use attributes of human uniqueness that are both observable and vulnerable to compromise. Privacy and protection of an individual's identity is not assured during criminal activity. However, a security system must rely on identity assurance for access control to physical or logical spaces while not being vulnerable to compromise and protecting the privacy of an individual. The solution resides in the use of non-observable attributes of human uniqueness to perform the biometric recognition process. This discussion will begin by presenting some key perspectives about biometric recognition and the characteristic differences between observable and non-observable biometric attributes. An introduction to the design, development, and testing of the Thermo-ID system will follow. The Thermo-ID system is an emerging biometric recognition technology that uses non-observable patterns of infrared energy naturally emanating from within the human body. As with all biometric systems, the infrared patterns recorded and compared within the Thermo-ID system are unique and individually distinguishable permitting a link to be confirmed between an individual and a claimed or previously established identity. The non-observable characteristics of infrared patterns of human uniqueness insure both the privacy and protection of an individual using this type of biometric recognition system.

An Indium Gallium Arsenide linear photodiode array in the 1.1-2.5 μm spectral range was characterized. The array has 1024X1 pixels with a 25 μm pitch and was manufactured by Sensors Unlimited, Inc. Characterization and analysis of the electrical and optical properties of a camera system were carried out at room temperature to obtain detector performance parameters. The signal and noise were measured while the array was uniformly illuminated at varying exposure levels. A photon transfer curve was generated by plotting noise as a function of average signal to obtain the camera gain constant. The spectral responsivity was also measured, and the quantum efficiency, read noise and full-well capacity were determined. This paper describes the characterization procedure, analyzes the experimental results, and discusses the applications of the InGaAs linear array to future earth and planetary remote sensing mission.

A method of controlling the coordinate sensitivity in a high temperature superconducting microbolometer is described. A laser beam, precisely focused on the patterned superconducting structure, was used to nucleate a resistive area that is sensitive to external thermal effects. The electron beam lithography and wet chemical etching were applied as pattern transfer processes in epitaxial Y-Ba-Cu-O films. Two different sensor designs were tested: (i) 3 millimeters long and 40 micrometers wide stripe and (ii) 1.25 millimeters long, and 50 micron wide meander -like structure. It is shown experimentally that scanning the laser beam along the stripe leads to physical displacement of the sensitive area and, therefore may be used as a basis for imaging over a broad spectral range. Our approach, by which the coordinate sensitivity of a microfabricated superconducting stripe is controlled, is an alternative solution to Focal Plane Array (FPA) design. For example, patterning the superconducting film into a meander structure is equivalent to a two-dimensional detector array. In additional to the simplicity of the detector fabrication sequence (one step mask transfer), a clear advantage of this approach is the simplicity of the read-out process: an image is formed by registering the signal with only two electrical terminals. The proposed approach can be extended for imaging over a wide spectral range; the limiting factor is the wavelength-dependent efficiency of thermal conversion in the film/substrate system.

Light-weight, low-power consumption, low-cost IR sources are required for combat ID (IFF, identify friend or foe), trail markers, pallet markers, etc. They must be visible with conventional viewers at 200 meters in the 3-5 micron or 8-12 micron bands and emit no visible or near infrared radiation. Ion Optics has tested a prototype MEMS IR source that can meet all of these requirements. It uses a hermetically sealed filament with a photonic crystal-enhanced (PCE^TM) coating that efficiently generates narrowband IR light. The photonic crystal surface structure limits emission to (tunable) predetermined bands (3-5 and 8-12 microns specifically). These devices generate 10mW of IR light in the 3-5 micron band with "wall-plug" efficiency of 10%, 2 orders of magnitude more efficient than conventional IR LED's. This high efficiency enables overnight battery operation. Using traditional 3-5 micron MWIR cameras, we measured visibility ranges of 200 meters. Current research and development on wafer-level packaging of the MEMS device promises to increase device yield, improve reliability, reduce package size and reduce total cost.

The performance of uncooled photodetectors operating in the middle and long wavelength spectral range is limited by the noise originated from thermal generation and recombination processes in semiconductors. The noise level exponentially increases with decreasing band gap of the semiconductor. Therefore, the uncooled short wavelength devices are characterized by good performance while the long wavelength ones are much less sensitive. The consequence is very poor performance of long wavelength devices at short wavelength range. We report here two-lead multilayer photoconductors that operate over a wide spectral band with performance improved by a large factor at short wavelength ranges. The devices consist of several stacked active regions (absorbers) with their outputs connected in parallel so the resulting output signal current is the sum of the signals generated at all active regions. Due to a high photoelectric gain in the wider gap absorbers and low thermal generation and recombination, the devices offer significantly better performance at short wavelengths while the long wavelength response remains essentially unaffected. The practical devices have been obtained using complex Hg_1-xCd_xTe heterostructures grown on CdTe or GaAs substrates by ISOVPE, MOCVD or combination of the two epitaxial techniques. An example is an uncooled photoconductor operating up to 11μm, with response at 0.9-4μm increased by ≈3 orders of magnitude in comparison to the conventional 11 μm device.

The non-linearity of the responsivity of infrared (IR) focal plane arrays (FPA) is a major concern when IR images are evaluated. This will affect both the detection and classification ability of the IR sensor. The nonuniformity correction (NUC) method proposed here is based on polynomial fitting to pixel responsivities. It is applied to infrared data obtained from two cooled multi-band sensors in the MWIR region. The method is shown to give both suitable data restoration and a simple and efficient computer implementation. Bad pixels were identified by evaluating the coefficents obtained from the multi degree polynomial. Bad pixels were also replaced by using a nearest neighbour-hood algorithm. The NUC method, including the bad pixel identification and replacement, was implemented in a user friendly GUI (graphic user interface) for calibration of registered IR data.

We have investigated the use of forward looking infrared (FLIR) sensors to verify aircraft navigation information during approach and landing. Our research includes the development of an experimental primary flight display (PFD) integrated with a synthetic vision system (SVS). The effectiveness of a traditional SV display is limited by navigation equipment position and orientation errors, database limitations, and lack of knowledge of temporary obstacles. However, integrating information from the navigation system with an external FLIR sensor has the potential to increase information provided to the pilot, improving flight safety. In prior work, we developed software to correct aircraft orientation inaccuracies. Our algorithm locates the runway in a LWIR image and uses the extracted runway location to validate and correct the SV system's understanding of aircraft orientation. Evaluations demonstrated that this orientation correction worked well when there were no position errors. However, uncorrected position inaccuracies introduce errors into the pitch and heading correction estimates as the aircraft approaches the runway. To address this problem, we have developed a new algorithm to separate the image effects of orientation and position errors. This allows our system to correct for both orientation and position errors. We evaluated our system using LWIR video and navigation data recorded by test aircraft during runway approaches. Our results show significant improvements in correction accuracy using dual orientation and position estimation compared to orientation correction alone.

Silicon nitride microbridges (50x50 mm², 0.6 mm thick), suspended over a silicon substrate, were patterned and thinned. These patterns consist of 2 to 12 windows that were thinned to approximately 0.3 mm. Microbolometers were fabricated by sputtering a YBaCuO thin film over the bridges. The experimental results showed that the regionally thinned microbridges have a lower thermal time constants t (about 1.6 ms) than that of the standard pixel configuration (2.6 ms). On the other hand, the fact that the regionally thinned microbolometers having detectivity D* values comparable to or even six times superior than that of the standard pixel showed that the decrease in response time is not penalized by loss of detection performance. The simulation results also show that as the amount of material removed is increased, the thermal time constant drops significantly while the (τ/G)^1/2 ratio (where G is the thermal conductance of the pixel) only decreases slightly, suggesting that the reduced response time will not cause a significant drop in detectivity D*. The simulation results of mechanical integrity show that a specific regionally thinned microbridge design has 22 % higher stiffness than that of a standard pixel design with similar thermal properties. The fact that thick regions remained on the regionally thinned pixels (like the edges of the pixels) provide significant mechanical support to the microstructures. This confirms the validity of the regionally thinned microbridges approach.

Quantum-well infrared photodetector (QWIP) technology has shown remarkable success by realizing large-format focal plane arrays in both broadband and in multiband. The spectral response of these detectors based on the III-V material system is tailorable within the mid- and long-wavelength infrared bands (~3-50 μm). Recently, we have extended this wavelength limit by monolithically integrating a near-infrared (1-1.5 μm) p-i-n photodiode with a mid-infrared (3-5μm) QWIP. This multiband detector involves both intersubband and interband transitions in III-V semiconductor layer structures. Each detector stack absorbs photons within the specified wavelength band while allowing the transmission of photons in other spectral bands, thus efficiently permitting multiband detection. Monolithically grown material characterization data and individual detector test results ensure the high quality of material suitable for near-infrared/QWIP dual-band focal plane array.