This PDF file contains the front matter associated with SPIE Proceedings Volume 8353, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Advances in imaging technology have huge impact on our daily lives. Innovations in optics, focal plane arrays (FPA), microelectronics and computation have revolutionized camera design. As a result, new approaches to camera design and low cost manufacturing is now possible. These advances are clearly evident in visible wavelength band due to pixel scaling, improvements in silicon material and CMOS technology. CMOS cameras are available in cell phones and many other consumer products. Advances in infrared imaging technology have been slow due to market volume and many technological barriers in detector materials, optics and fundamental limits imposed by the scaling laws of optics. There is of course much room for improvements in both, visible and infrared imaging technology. This paper highlights various technology development projects at DARPA to advance the imaging technology for both, visible and infrared. Challenges and potentials solutions are highlighted in areas related to wide field-of-view camera design, small pitch pixel, broadband and multiband detectors and focal plane arrays.

Images from a novel shortwave infrared (SWIR, 900 nm to 1.7 μm) camera system are presented. Custom electronics and software are combined with a digital micromirror device (DMD) and a single-element sensor; the latter are commercial off-the-shelf devices, which together create a lower-cost imaging system than is otherwise available in this wavelength regime. A compressive sensing (CS) encoding schema is applied to the DMD to modulate the light that has entered the camera. This modulated light is directed to a single-element sensor and an ensemble of measurements is collected. With the data ensemble and knowledge of the CS encoding, images are computationally reconstructed. The hardware and software combination makes it possible to create images with the resolution of the DMD while employing a substantially lower-cost sensor subsystem than would otherwise be required by the use of traditional focal plane arrays (FPAs). In addition to the basic camera architecture, we also discuss a technique that uses the adaptive functionality of the DMD to search and identify regions of interest. We demonstrate adaptive CS in solar exclusion experiments where bright pixels, which would otherwise reduce dynamic range in the images, are automatically removed.

The shortwave infrared spectral range (SWIR) has certain advantages for the observation during day under fog and haze weather conditions. Due to the longer wavelength compared to the visible spectrum the range performances in the SWIR is here considerably extended. In addition cooled SWIR focal plane arrays reach in the meantime sensitivities to be useable for night viewing under twilight or moon light conditions. The presented SWIR camera system combines the color imaging in the visible spectrum with the imaging in the SWIR spectrum. The 20x zoom optics is fully corrected between 440 nm and 1700 nm. A dichroic beam splitter projects the visible spectrum on a color chip with HDTV resolution and the SWIR spectrum on a 640x512 InGaAs focal plane array. The open architecture of the camera system allows the use of different SWIR sensors and CMOS sensors. A universal designed interface electronic operates the used cameras and provides standard video outputs and compressed video streams on an ethernet interface. The camera system is designed to be integrated in various stabilized platforms. The camera concept is described and the comparison with pure SWIR or combined SWIR / MWIR dual band cameras are discussed from an application and system point of view.

Short wavelength Infra Red (SWIR) imaging has gained considerable interest in recent years. The main applications among others are: active imaging and LADAR, enhanced vision systems, low light level imaging and security surveillance systems. In this paper we will describe SCD's considerable efforts in this spectral region, addressing several platforms: 1. Extension of the mature InSb MWIR product line operating at 80K (cut-off wavelength of 5.4μm). 2. Extension of our new XB_nn InAsSb "bariode" technology operating at 150K (cut-off of 4.1μm). 3. Development of InGaAs detectors for room temperature operation (cut-off of 1.7μm) 4. Development of a SNIR ROIC with a low noise imaging mode and unique laser-pulse detection modes. In the first section we will present our latest achievements for the cooled detectors where the SWIR region is combined with MWIR response. Preliminary results for the NIR-VIS region are presented where advanced substrate removal techniques are implemented on flip-chip hybridized focal plane arrays. In the second part we will demonstrate our VGA, 15μm pitch, InGaAs arrays with dark current density below 1.5nA/cm² at 280K. The InGaAs array is hybridized to the SNIR ROIC, thus offering the capability of low SWaP systems with laser-pulse detection modes.

We present in this paper a flexible Wide Dynamic Range VGA ROIC for InGaAs SWIR imaging application. The pixel design of this ROIC incorporates both the unique solar cell mode from NIT and also a source-follower (SF) based direct injection linear mode. The solarcell mode operation can cover an instantaneous dynamic range of more than 120dB in a single frame without off-chip digital NUC, while the SF mode can operation sensor in a conventional SF linear mode but with a on-chip offset compensation. The off-chip digital KTC noise cancellation is also possible in the SF mode. This ROIC has been designed and fabricated with a standard 0.18um 1P3M process, destinated to 640x512-pixel PDA of 15um pitch. The horizontal scanning speed is maximum 100MHz and 80MHz guaranteed, giving more than 150 frames per second. The overall performance of this ROIC coupled to III-VLab extended visible InGaAs PDA will be presented at the conference.

Through collaboration between III-V Lab and CEA-Leti, a 640 x 512 InGaAs image sensor with 15 μm pixel pitch has been developed. Based on a thinned substrate, the photodiode array detects the light from the visible to the near infrared wavelength (0.4 to 1.7 μm) with a dark current lower than 18 fA per pixel at room temperature. The readout IC (ROIC) design in a standard CMOS 0.18 μm technology is presented. The pixel circuit is based on a capacitive transimpedance amplifier (CTIA) stage with two selectable charge-to-voltage conversion gains. The input stage has been optimized for low noise performance in the high gain mode. In this mode, the charge-to-voltage conversion factor is 17.6 μV/electron and the full well capacity is above 105 x 10³ electrons. The integration time can be set up to the frame period thanks to a rolling shutter approach. The frame rate can be up to 120 fps or 60 fps if the Correlated Double Sampling (CDS) capability of the circuit is enabled. The readout noise measured in CDS with short exposure time is around 30 electrons for a dynamic range of 71 dB in high-gain mode and 108 electrons and 79 dB in low-gain mode.

SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. For few years, III-VLab has been studying InGaAs imagery, gathering expertise in InGaAs material growth and imaging technology respectively from Alcatel-Lucent and Thales, its two mother companies. This work has lead to put quickly on the market a 320x256 InGaAs module, exhibiting high performances in terms of dark current, uniformity and quantum efficiency. In this paper, we present the last developments achieved in our laboratory, mainly focused on increasing the pixels number to VGA format associated to pixel pitch decrease (15μm) and broadening detection spectrum toward visible wavelengths. Depending on targeted applications, different Read Out Integrated Circuits (ROIC) have been used. Low noise ROIC have been developed by CEA LETI to fit the requirements of low light level imaging whereas logarithmic ROIC designed by NIT allows high dynamic imaging adapted for automotive safety.

Teledyne Judson Technologies (TJT) has been developing technology for small pixel, large format, low dark current, and low capacitance NIR/SWIR InGaAs detector arrays, aiming to produce <10μm pixels and >2Kx2K format arrays that can be operated at or near room temperature. Furthermore, TJT is now developing technology for sub-10μm pixel arrays in response to requirements for a variety of low light level (LLL) imaging applications. In this paper, we will review test data that demonstrates lower dark current density for 10-20μm pixel arrays. We will present preliminary results on the successful fabrication of test arrays with pixels as small as 5μm. In addition, a lot of effort has been made to control and reduce the detector pixel capacitance which can become another source of detector noise. TJT is also developing 4" InGaAs wafer process and now offers four different types of InGaAs 2D arrays/FPAs that are tailored to different customer requirements for dark current, capacitance, spectral response, and bias range.

FLIR Electro Optical Components will present our latest developments in large InGaAs focal plane arrays, which are used for low light level imaging in the short wavelength infrared (SWIR) regime. FLIR will present imaging from their latest small pitch (15 μm) focal plane arrays in VGA and High Definition (HD) formats. FLIR will present characterization of the FPA including dark current measurements as well as the use of correlated double sampling to reduce read noise. FLIR will show imagery as well as FPA-level characterization data.

Significant research and development efforts are currently underway to produce robust Short Wave Infrared (SWIR) camera systems with low power consumption. Substantial improvements in power can be achieved through the elimination of the thermoelectric cooler (TEC) on the FPA. Removing the TEC from the system introduces temperature as a significant parameter effecting FPA spatial uniformity, effectively requiring more complex temperature dependent non-uniformity image correction algorithms. We present here our latest work in developing a parameterized non-uniformity correction algorithm for a low-power no-TEC camera. The camera used in these experiments is the Goodrich GA1280J-15 high resolution, high sensitivity, InGaAs SWIR camera operating at 30 Hz, and modified to operate without a TEC. The FPA size is 1280 x 1024 pixels, with a 15 μm pitch. Typical power when operating with parameterized non-uniformity corrections consumption is 3 W or less. The camera under test was mounted inside of an environmental chamber and images at varying illumination levels were acquired from -50 to 70 °C with a 10 °C step. Analysis of these images yielded the optimal orders and coefficients for a parameterized non-uniformity corrections model consisting of a sum of polynomials in raw counts, and FPA temperature. The optimized model was determined to be 1^st order in counts and 5^th order in FPA temperature, with an average R² between the target counts and corrected counts of 0.999 ± 0.001, and average reduction of spatial noise of 83 ± 7 % across all camera operational modes.

We report here first results carried out at CEA and Sofradir to build ultra low dark current focal plane arrays (FPA) in the short wave infrared range (SWIR) for space applications. Those FPAs are dedicated to very low flux detection in the 2μm wavelength range. In this purpose, Sofradir has designed a source follower per detector readout circuit (ROIC), 384x288, 15μm pitch. This ROIC has been hybridized on different HgCdTe diode configurations processed at CEA-LETI and low flux characterisations have been carried out at CEA-SAp at low temperature (from 60 to 160K). Both ion implanted p/n and n/p diodes have been evaluated. The metallurgical nature of the absorbing layer is also examined and both molecular beam epitaxy (MBE) and liquid phase epitaxy (LPE) have been processed. Dark current measurements are discussed in comparison with previous results from the literature. State of the art dark currents are recorded for temperatures higher than 120K. At temperatures lower than 100K, the decrease in dark current saturates for both technologies. In this regime, currents between 0.4 and 0.06 e/s/pixel are reported.

This paper reports the development of a new CTIA ROIC (MT6425CA) suitable for SWIR InGaAs detector arrays. MT6425CA has a format of 640 × 512 with a pixel pitch of 25 μm and has a system-on-chip architecture, where all the critical timing and biasing for this ROIC are generated by programmable blocks on-chip. MT6425CA is a highly configurable and flexible ROIC, where many of its features can be programmed through a 3-wire serial interface allowing on-the-fly configuration of many ROIC features. The ROIC runs on 3.3V supply voltage at nominal clock speed of 10 MHz clock. It performs snapshot operation both using Integrate-Then-Read (ITR) and Integrate-While- Read (IWR) modes. The CTIA type pixel input circuitry has a full-well-capacity (FWC) of about 320,000e-, with an input referred read noise of less than 110e- at 300K. MT6425CA has programmable number of outputs, where 4, 2, or 1 output can be selected along with an analog reference for pseudo-differential operation. The integration time can be programmed up to 1s in steps of 0.1μs. The gain and offset in the ROIC can be programmed to adjust the output offset and voltage swing. ROIC dissipates less than 130mW from a 3.3V supply at full speed and full frame size with 4 outputs, providing both low-power and low-noise operation. MT6425CA is fabricated using a modern mixed-signal CMOS process on 200mm CMOS wafers with a high yield above 75%, yielding more than 50 working parts per wafer. It has been silicon verified, and tested parts are available either in wafer and die levels with a complete documentation including test reports and wafer maps. A USB based camera electronics and camera development platform with software are available to help customers to evaluate the imaging performance of MT6425CA in a fast and efficient way.

Infrared (IR) focal plane arrays (FPAs) with multispectral detector elements promise significant advantages for airborne threat warning, surveillance, and targeting applications. At present, the use of type II superlattice (T2SL) structures based on the 6.1Å-family materials (InAs, GaSb, and AlSb) has become an area of interest for developing IR detectors and their FPAs. The ability to vary the bandgap in the IR range, suppression of Auger processes, prospective reduction of Shockley-Read-Hall centers by improved material growth capabilities, and the material stability are a few reasons for the predicted dominance of the T2SL technology over presently leading HgCdTe and quantum well technologies. The focus of the work reported here is on the development of T2SL based dual-band IR detectors and their applicability for multispectral imaging. A new NpBPN detector designed for the detection of IR in the 3-5 and 8-12 μm atmospheric windows is presented; comparing its advantages over other T2SL based approaches. One of the key challenges of the T2SL dual-band detectors is the spectral crosstalk associated with the LWIR band. The properties of the state-of-the-art T2SLs (i.e., absorption coefficient, minority carrier lifetime and mobility, etc.) and the present growth limitations that impact spectral crosstalk are discussed.

Infrared (IR) detectors operated in the space environment are required to have high performance while being subjected to a variety of radiation effects. Sources of radiation in space include the trapped particles in the Van Allen belts and transient events such as solar events and galactic cosmic rays. Mercury cadmium telluride (MCT)-based IR detectors are often used in space applications because they have high performance and are generally relatively tolerant of the space environment when passivated with CdTe; often, the readout-integrated circuit is far more susceptible to radiation effects than the detector materials themselves. However, inherent manufacturing issues with the growth of MCT have led to interest in alternative detector technologies including type-II strained-layer superlattice (T2SLS) infrared detectors with unipolar barriers. Much less is known about the radiation tolerance properties of these SLS-based detectors compared to MCT. Here, the effects of 63 MeV protons on variable area, single element, dual-band InAs/GaSb SLS detectors in the pBp architecture are considered. When semiconductors devices are irradiated with protons with energies of 63 MeV the protons are capable of displacing atoms within their crystalline lattice. The SLS detectors tested here utilize a pBp architecture, which takes advantage of the higher mobility electrons as the minority photocarrier. These detectors are also dual-band, implying two absorbing regions are present and separated by the unipolar barrier. The absorbers have cutoff wavelengths of roughly 5 and 9 μm allowing for mid-wave (MWIR) and long-wave (LWIR) infrared detection, respectively. The radiation effects on these detectors are characterized by dark current and quantum efficiency as a function of total ionizing dose (TID) or, equivalently, the incident proton fluence.

Various approaches now exist for obtaining spectral imagery over a broad range of infrared wavelengths. One involves use of a single grating element in two grating orders with dualband focal plane array (FPA) technology -- an approach offering high efficiency over both the MWIR & LWIR, and obviating the need for separate focal plane arrays, dispersing elements, and optical beamsplitters. Another approach achieves similar results by exploiting an FPA having broad wavelength response with an innovative grating having useable efficiency extending beyond the single octave limits of traditional gratings. Significant advantages result in either case for space-based hyperspectral imagers, for which a reduction in cryo-cooled mass translates into prodigious savings in overall payload mass, cryo-cooling requirements, and waste heat removal. By contrast, longer term approaches might realize infrared "hyperspectral pixels" in 2-D imaging focal plane arrays. In this case, each pixel would detect different wavelengths of radiation at different depths, and the resulting "spectral photocurrents" would be transported to read-out circuitry through a vertical grid of electrical contacts. Although not yet realized in practice, the conceptual basis for accomplishing this with the widely-available HgCdTe detector material has been described. With regard to employment, space-based thermal hyperspectral imaging (HSI) is characterized by coarser ground resolution as a result of aperture diameter limitations and diffraction considerations at the longer infrared wavelengths. The resulting sub-pixel detections based on spectral signature are often complementary with higher resolution, shorter wavelength, panchromatic imagery. Overlapping fields-of-view between the two sensor types on the dayside of the earth enable simultaneous correlation of infrared spectral signatures with spatially-resolved scene features; data collects on the night-side are limited to the thermal hyperspectral images and would await correlations with high resolution visible imagery at the next daytime opportunity.

Dual-color imaging in the Mid-Wave Infrared (MWIR) is required in some airborne Missile Warning Systems (MWS) due to its ability to reduce the number of false alarms in this application by comparing the signal in the two spectral bands. Furthermore, such systems demand high frame rate, spatial resolution, and spectral resolution, while at the same time call for simultaneous collection and readout of the two color images. Monolithic dual-color Focal Plane Arrays (FPAs) lack at least some of these requirements. In this work we introduce a new hybrid dual-color detector based on two 480×384/20μm digital InSb FPAs, assembled in a single Dewar, where the high degree of spatial registration between the two color channels enables a solution that achieves the above requirements. Each FPA has its own cold shield and spectral filter, and the signal is snapshot integrated and read out in parallel to obtain complete dual-color simultaneity. The sensor imaging optics is integrated inside the Dewar for both channels in order to reduce the overall system size and weight, and improve its performance at the extreme environmental conditions imposed by this application. In this case the hybrid dual-color Integrated Dewar-Cooler Assembly (IDCA) is designed for a very wide field of view (>100°), suited for the specific airborne Missile Warning System (MWS). We present the independent electro-optical results of both the red and the blue channels, together with the measured negligible spectral cross-talk and high spatial registration between them.

The EDA project "Detection in Urban scenario using Combined Airborne imaging Sensors" (DUCAS) is in progress. The aim of the project is to investigate the potential benefit of combined high spatial and spectral resolution airborne imagery for several defense applications in the urban area. The project is taking advantage of the combined resources from 7 contributing nations within the EDA framework. An extensive field trial has been carried out in the city of Zeebrugge at the Belgian coast in June 2011. The Belgian armed forces contributed with platforms, weapons, personnel (soldiers) and logistics for the trial. Ground truth measurements with respect to geometrical characteristics, optical material properties and weather conditions were obtained in addition to hyperspectral, multispectral and high resolution spatial imagery. High spectral/spatial resolution sensor data are used for detection, classification, identification and tracking.

The Osprey-E sensor module consists of an integrated detector-cooler assembly (IDCA) and custom proximity electronics mounted in a lightweight, ruggedized housing. Based on the half-TV format Osprey FPA, it implements recent improvement in SELEX Galileo's array hybridization technique. Ongoing tests have shown that performance is not significantly degraded after more than 5000 cooldown cycles. The FPA exploits SELEX Galileo's High Operating Temperature (HOT) HgCdTe (MCT) and is optimized for operation at 110K. Very low levels of defective pixels (<0.003%) have been achieved at this temperature. The proximity electronics are a new design that originates from SELEX Galileo's Centre of Excellence in Infrared Detectors. The electronics provide all the necessary supplies and signals for detector operation and digitize the detector output into 14-bit digital video. The sensor has been developed to offer a very lightweight, rugged camera core particularly suited to airborne applications.

In order to orient aerial vehicles such as unmanned aerial vehicles and guided munitions toward intended target points, it often becomes vital to acquire the correct information about the states of the targets during the flight of the vehicles. One of the most widely-used ways to achieve this task is the utilization of seekers. Physically, the measurement capability of seekers is restricted due to some physical, optical, and electronic limitations such as limited field-of-view (FOV), atmospheric transmittance, and noise effects. Regarding these characteristics, basically two types of seekers are employed in the relevant applications: strapdown or body-fixed seekers and gimbaled seekers. The strapdown seekers are directly mounted on the considered vehicle body. Therefore, their measurements become relative to the body fixed reference frame of the missile. For relieving the FOV limitations of the strapdown seekers, the gimbaled seekers are preferred in some of the implementations. In this scheme, the seeker is mounted on a platform supported by two orthogonal gimbals and stabilized by means of rate gyro feedbacks. This way, the FOV range of the seeker is increased considerably. Also, the line of sight (LOS) angle and the LOS angular rate can be measured directly independently of the missile motion. This study deals with the comparison of these two kinds of seekers according to certain criteria involving mounting properties, FOV, angle and rate measurements, guidance method utilization, measurement methods, major sources of measurement errors, and cost. A general evaluation is submitted at the end of the work.

Under certain conditions, laser directed at aircraft can be a hazard. The most likely scenario is when a bright visible laser causes distraction or temporary flash blindness to a pilot, during a critical phase of flight such as landing or takeoff. It is also possible, that a visible or invisible beam could cause permanent harm to a pilot's eyes. We present a non-linear, solid-state dynamic filter solutions protecting from dazzling and damage in a passive way. Our filters limit the transmission, only if the power exceeds a certain threshold as opposed to spectral filters that block a certain wavelength permanently.

Thermal cameras are widely used in driver vision enhancement systems. However, in pathless terrain, driving becomes challenging without having a stereoscopic perception. Stereoscopic imaging is a well-known technique already for a long time with understood physical and physiological parameters. Recently, a commercial hype has been observed, especially in display techniques. The commercial market is already flooded with systems based on goggle-aided 3D-viewing techniques. However, their use is limited for military applications since goggles are not accepted by military users for several reasons. The proposed uncooled thermal imaging stereoscopic camera with a geometrical resolution of 640x480 pixel perfectly fits to the autostereoscopic display with a 1280x768 pixels. An eye tracker detects the position of the observer's eyes and computes the pixel positions for the left and the right eye. The pixels of the flat panel are located directly behind a slanted lenticular screen and the computed thermal images are projected into the left and the right eye of the observer. This allows a stereoscopic perception of the thermal image without any viewing aids. The complete system including camera and display is ruggedized. The paper discusses the interface and performance requirements for the thermal imager as well as for the display.

Improved situational awareness results not only from improved performance of imaging hardware, but also when the operator and human factors are considered. Situational awareness for IR imaging systems frequently depends on the contrast available. A significant improvement in effective contrast for the operator can result when depth perception is added to the display of IR scenes. Depth perception through flat panel 3D displays are now possible due to the number of 3D displays entering the consumer market. Such displays require appropriate and human friendly stereo IR video input in order to be effective in the dynamic military environment. We report on a stereo IR camera that has been developed for integration on to an unmanned ground vehicle (UGV). The camera has auto-convergence capability that significantly reduces ill effects due to image doubling, minimizes focus-convergence mismatch, and eliminates the need for the operator to manually adjust camera properties. Discussion of the size, weight, and power requirements as well as integration onto the robot platform will be given along with description of the stand alone operation.

The development, integration and testing of a compact system for wide-area persistence surveillance in dedicated maritime environments is presented. The system is based around a large-format, 2560 x 512 pixel focal plane array, high dynamic range (16 bit), mid-wave infrared (MWIR) imager operating at 30 Hz that is equipped with a 90° horizontal field-of-view (HFOV) lens. The digitized image data is fed to a standard commercial-off-the-shelf (COTS) workstation equipped with a graphical processing unit (GPU) that is used to perform image de-warping, non-uniformity corrections, and algorithms for real-time object detection and tracking (NRL Harbor Tracking Software-NRLHaTS). Data is presented from several field experiments that illustrate the capabilities of the integrated system.

One of the main challenges in remote Fourier transform infrared (FT-IR) spectroscopy is the collection of a reliable background spectrum. Although suggested as a method to address the problem in prior literature, super clip apodization (SCA) has had little reported success for wide spectral features. SCA is a technique that involves the manipulation of different parts of the interferogram to calculate an absorbance spectrum from a single interferogram. A new method called complementary super clip apodization (CSCA) is developed here and is successfully used in conjunction with SCA in an iterative optimization algorithm. The umbrella term of super clip mathematics is also defined to encompass spectral calculation using SCA, CSCA or both in combination. The validity of super clip mathematics is demonstrated in an experimental study of gas-phase nitromethane. In an effort to mimic errors present in standoff detection, uniformly distributed noise and/or wavenumber shifting is added to the interferometric sample data to test the robustness of the algorithm. It will be shown that the implementation of SCA and CSCA in combination is more successful for concentration assessment than using SCA or CSCA alone.

In harsh environmental conditions characterized by unfavorable lighting and pronounced shadows, human recognition based on Short-Wave Infrared (0.9-1.7 microns) images may be advantageous. SWIR imagery (i) is more tolerant to low levels of obscurants like fog and smoke; (ii) the active illumination source can be eye-safe and (iii) the active illumination source is invisible to the human eye making it suitable for surveillance applications. The key drawback of current SWIR-based acquisition systems is that they lack the capability of real-time simultaneous acquisition of multiple SWIR wavelengths. The contributions of our work are four-fold. First, we constructed a SWIR multi-wavelength acquisition system (MWAS) that can capture face images at 5 different wavelengths (1150, 1250, 1350, 1450, 1550 nm) in rapid succession using a 5-filter rotating filter wheel. Each filter has a band pass of 100 nm and all 5 images are acquired within 260 milliseconds. The acquisition system utilizes a reflective optical sensor to generate a timing signal corresponding to the filter wheel position that is used to trigger each camera image acquisition when the appropriate filter is in front of the camera. The timing signal from the reflective sensor transmits to a display panel to confirm the synchronization of the camera with the wheel. Second, we performed an empirical optimization on the adjustment of the exposure time of the camera and speed of the wheel when different light sources (fluorescent, tungsten, both) were used. This improved the quality of the images acquired. Third, a SWIR spectrometer was used to measure the response from the different light sources and was used to evaluate which one provides better images as a function of wavelength. Finally, the selection of the band pass filter, to focus the camera to acquire the good quality SWIR images was done by using a number of image quality and distortion metrics (e.g. universal quality index and Structural index method).

The use of short wave infrared (SWIR) imaging and illumination technology is at the forefront of system development for military and law enforcement in both night and daytime operational scenarios^{1 2 3 4} . Along with enabling nighttime operations, a secondary benefit of SWIR imaging is that it offers the possibility to capture images through tinted materials, such as tinted architectural or automotive glass and sunglass lenses⁵. The use of SWIR technology introduces challenges to facial recognition when comparing cross-spectrally from a visible gallery to images captured in the SWIR⁶. The challenges of SWIR facial recognition are further compounded by the presence of tinted materials in the imaging path due to varying material types, lighting conditions, and viewing angle. The paper discusses material and optical characterization efforts undertaken to understand the effects of temperature, interior and exterior light sources, and viewing angle on the quality of facial images captured through tinted materials. Temperature vs. spectrum curves are shown for tinted architectural, automotive, and sunglass materials over the range of -10 to 55C. The results of imaging under various permutations of interior and exterior lighting, along with viewing angle, are used to evaluate the efficacy of eye detection for cross-spectral facial recognition under these conditions.

A mid wave infrared type-II superlattice focal plane array with 320x256 pixels, 30 μm pitch and 90 % fill factor was fabricated in house, using a conventional homojunction p-i-n photodiode design and the ISC9705 readout circuit. High-quality imaging up to 110 K is demonstrated with the substrate fully removed. The absorber is 2 μm thick, and no anti-reflection coating was used, so there is still room for significant improvement of the quantum efficiency, which is in the 40 % range. Studies of the dark current vs. temperature behavior indicate that the device is limited by Shockley-Read-Hall generation from the depletion region. The activation energy of this dark current component is 0.13 eV, suggesting an unidentified recombination center positioned halfway into the 0.24 eV bandgap. Furthermore, we report on detectors with 100 % cut-off at 13 μm. The dark current density at 60 K and -50 mV bias is 2x10^-4 A/cm². Quantum efficiency, NETD and BLIP temperature are also calculated. Position-sensitive photocurrent measurements on mesa-etched superlattice material were made at low temperatures using a focused laser spot. The lateral diffusion length for holes was extracted and is reported.

We report our recent efforts on advancing of antimonide superlattice based infrared photodetectors and demonstration of Focal Plane Arrays (FPA) based on a complementary barrier infrared detector (CBIRD) design. By optimizing design and growth condition we succeeded to reduce the operational bias of CBIRD single pixel detector without increase of dark current or degradation of quantum efficiency. We demonstrated a 1024×1024 pixel long-wavelength infrared focal plane array utilizing CBIRD design. An 11.5 μm cutoff FPA without anti-reflection coating has yielded noise equivalent differential temperature of 53 mK at operating temperature of 80 K, with 300 K background and cold-stop. In addition, we demonstrated 320×256 format FPA based on the n-CBIRD design. The resulting FPAs yielded noise equivalent differential temperature of 26 mK at operating temperature of 80 K, with 300 K background and cold-stop. These results advance state-of-the art of superlattice detectors and demonstrated advantages of CBIRD architecture for realization of FPA.

The performance of space-borne infrared detectors is required higher sensitivity, higher resolution, or larger format in comparison with that of ground-based infrared detectors. In order to realize higher mission requirements, JAXA decided to position the infrared detector technology as one of the strategic technologies of JAXA and to promote the development of the infrared detectors. InAs/GaSb Type II superlattice (T2SL) is the only known infrared material that has a theoretically predicted higher performance than HgCdTe. If the T2SL detector is realized, it can be applied for high sensitivity infrared sensors, which are required for many advanced instruments such as an imaging Fourier Transform Spectrometer. The final goal of the T2SL detector development is to realize an array detector having a cutoff wavelength of λc=15μm. We have started a basic research on the T2SL detector. In this paper, we report on the first results of the development of T2SL detectors of mid-wave infrared regime. The detector structure is a pin photodiode with SL of 9 InAs monolayers (MLs) and 7 GaSb MLs. We present results of optical evaluation of the detector. The cutoff wavelength is 5.5μm at 30K. The responsivity is 0.33±0.05A/W at 4.5 μm.

An infrared sensor technology that has made quick progress in recent years is the photodiode based on Type-II InAs/(In)GaSb strained layer superlattices (SLS). We have developed Focal Plane Arrays (FPAs) with up to a million pixels, quantum efficiency exceeding 50%, and cutoff wavelength ~ 10 microns. SLS offers the promise of the high quantum efficiency and operating temperature of longwave infrared mercury cadmium telluride (MCT) at the price point of midwave infrared indium antimonide (InSb). That promise is rapidly being fulfilled. This paper presents the current state-of-the-art of this sensor technology at this critical stage of its evolution.

We present an investigation of the quantum confined energy levels in a mid-wave infrared and long-wave infrared InAs/GaSb type II strained-layer superlattice (SLS) photodetector by computing the first derivative of the absorption spectra from 80K to 250K , with respect to the wavelength. Energy levels of both the fundamental transition and two other higher orders are identified for the SLS. The temperature evolution of each of these bands was also characterized by fitting the energy transitions to the Varshni equation, which showed that in general, the higher-energy transitions have a greater change in bandgap with temperature than the lower-energy ones. The transition energies appeared linearly dependent on the InAs layer thickness, and had a weaker dependence on the GaSb layer thickness. A feature that vanished at higher temperatures was also observed, which is due to a GaSb characteristic, rather than the superlattice.

Electronic transport parameters in a nominally P+/π/P+ InAs/GaSb type-II superlattice vertical photoconductor structure for long-wavelength infrared detectors have been characterized employing magnetic field dependent resistivity and Hall-effect measurements, and high-resolution mobility spectrum analysis. Carrier transport parameters from both the P+ and nominally π regions were obtained over the 80 to 300K temperature range. At 300 K, the minority carrier electrons in the nominally π region was found to be characterized by a mobility and concentration of 11,000 cm²/Vs and 1.1×10¹⁷ cm^-3, respectively. Taking into account our previously reported room-temperature vertical electron transport parameters,¹ the vertical to lateral mobility and carrier concentration ratios have been determined to be 0.19 and 5.5×10^-4 , respectively. A miniband energy gap of 192±8 meV was estimated from the thermal activation of the minority carrier electrons in the lightly doped InAs/GaSb superlattice region.

We have achieved significant improvement in the electrical performance of the InAs/GaSb midwave infrared photodetector (MWIR) by using atomic layer deposited (ALD) aluminium oxide (Al₂O₃) as a passivation layer. Plasma free and low operation temperature with uniform coating of ALD technique leads to a conformal and defect free coverage on the side walls. This conformal coverage of rough surfaces also satisfies dangling bonds more efficiently while eliminating metal oxides in a self cleaning process of the Al₂O₃ layer. Al₂O₃ passivated and unpassivated diodes were compared for their electrical and optical performances. For passivated diodes the dark current density was improved by an order of magnitude at 77 K. The zero bias responsivity and detectivity was 1.33 A/W and 1.9 x 10¹³ Jones, respectively at 4 μm and 77 K. Quantum efficiency (QE) was determined as %41 for these detectors.

Recent efforts to improve the performance of Type II InAs/GaSb superlattice photodiodes and focal plane arrays (FPA) have been reviewed. The theoretical bandstructure models have been discussed first. A review of recent developments in growth and characterization techniques is given. The efforts to improve the performance of LWIR photodiodes and the latest result have been reported. The results of both small and large format LWIR FPAs, the latest results to elevate the operating temperature of MWIR photodiodes and FPAs, the latest results of two color FPAs, the results of novel minority unipolar devices (pMp) and finally the results of photodiode and FPA fabrication on GaAs substrates are reviewed.

Narrow bandgap semiconductors GaSb, InAs, and InSb are important building blocks for infrared photodetectors based on type-II InSb quantum dots or an InAs/GaSb strained layer superlattice. Understanding the surface chemical composition of these materials can provide valuable information that enables optimization of device surface passivation techniques leading towards surface leakage free IR photodetectors. We report on an investigation into Ga-, In-, Sb-, and As-oxides and other chemical species on the surface of untreated, dry etched and thermally treated GaSb, InAs and InSb samples by x-ray photoelectron spectroscopy. The experimental results reveal the presence of Sb- and Ga-oxides on the surfaces of the untreated and treated GaSb samples. Both Sb- and In-oxides were observed on the surface of all InSb samples, and especially the dry etched sample had thicker oxide layers. In the case of the InAs samples, not only In- and As-oxides XPS signals were obtained, but also AsCl species were found on the ICP dry etched sample. These results helped to analyze the dark current of our fabricated IR detectors.

The optical properties of bulk unrelaxed InAsSb layers having a low temperature photoluminescence (PL) peak up to 10 μm are presented. The materials were grown on GaSb substrates by molecular beam epitaxy. The lattice mismatch between the epilayers and GaSb substrates was accommodated with linearly graded GaAlInSb buffers. An 11-meV width of PL at full-width half-maximum was measured for InAsSb with Sb compositions of 20 and 44% . The best fit for the dependence of the energy gap on Sb composition was obtained with a 0.9-eV bowing parameter. Temperature dependences of the energy gap for InAsSb alloys with 20 % and 44% Sb were determined from PL spectra in the temperature range from 12 to 300 K. A T=77 K minority carrier lifetime up to 350 ns in undoped InAsSb layers with 20% Sb was determined from PL kinetics.

Mega-pixel FPAs in both MWIR and LWIR spectral bands based on Sb strained layer superlattices and nBn epitaxial structures grown on GaSb substrates have recently demonstrated impressive performances at high operating temperatures. An essential component of SLS epitaxial growth initiation is the starting wafer flatness, smoothness and haze. Large diameter GaSb wafers must be manufactured meeting these stringent demands and current state-of-the-art GaSb substrate manufacturing is focused on 100mm wafer diameters. Using a newly developed polishing process, 100mm GaSb substrate manufacturing has resulted in consistent starting wafer peak-to-valley flatness well below 5μm and surface roughness below Rms of 0.2nm. Final substrate and epitaxial wafer Surfscan mapping (<1000/cm² surface defects) and surface roughness (Rms~0.2nm) are presented and compared with measurements of the starting substrates. This paper evaluates the manufacturing and epitaxial growth on 100mm GaSb substrates that have been processed to achieve an MBE grown InAsSb-based nBn MWIR photodetector structure.

In this paper we describe the crystal growth and surface characterisation of 'ultra-flat' 4" GaSb substrates suitable for the epitaxial deposition of advanced infrared detectors. Results will be presented on the production of single crystal 4" GaSb ingots grown by a modified version of the liquid encapsulated Czochralski (LEC) technique, supported by the analysis of bulk material quality by dislocation etch pit density assessments. This study will also describe how various techniques were used to characterize the quality of the bare substrate. Surface properties of the GaSb substrates will be characterized by spectroscopic ellipsometry, white light interferometry and haze/particle defect mapping. Bow, Warp and Total Thickness Variation (TTV) data will be presented for batches of 4" wafers processed on a volume multiwafer-type polishing platform. This study will conclude with a 'blueprint' for the manufacture of large diameter GaSb substrates, this defining the requirements for the production use of GaSb within a commercial epitaxial wafer foundry.

Recent efforts have been paid to elevate the operating temperature of Type II superlattice Mid Infrared photon detectors. Using M-structure superlattice, novel device architectures have been developed, resulting in significant improvement of the device performances. In this paper, we will compare different photodetector architectures and discuss the optimization scheme which leads to almost one order of magnitude of improvement to the electrical performance. At 150K, single element detectors exhibit a quantum efficiency above 50%, and a specific detectivity of 1.05x10¹² cm.Hz^1/2/W. BLIP operation with a 300K background and 2π FOV can be reached with an operating temperature up to 130K. High quality focal plane arrays were demonstrated with a noise equivalent temperature difference (NEDT) of 11mK up to 130K. Human body imaging is achieved at 165K with NEDT of 150mK.

We report on temperature dependence characteristics of medium wavelength InAs/GaSb type-II superlattice p-i-n and nBn photodetectors in a temperature range from 77 K to 300 K. A bulk based model with an effective band gap of superlattice material has been used in modeling of the experimental data. Temperature dependence and bias dependent dark current and dynamic resistance of the devices have been analyzed in detail to investigate contributing mechanisms that limit the electrical performance of the detectors. The I-V and RA(V) characteristics of both types of detectors (p-i-n and nBn structures) are dominated by diffusion and generation-recombination currents in the zero-bias and the low-bias regions. At medium values of reverse bias, the dark current is mostly due to trap-assisted tunneling. At high values of reverse bias, the bulk band-to-band tunneling dominates. A good fitting of theoretical predictions with experimental data in a wide range of bias voltages and temperatures has been possible assuming that the position of trap-assisted tunneling level depends on temperature. The temperature dependence of trap level position can be explained by its less sensitivity on temperature changes in comparison with superlattice miniband edges. Between room temperature and 200 K the generation-recombination component and the diffusion component of carrier lifetimes are similar and have shown values about 2-10 ns. At a lower temperature the diffusion lifetime is longer and increases to about 100 ns for p-i-n structures.

This paper presents a detailed characterization of silicon germanium oxide (Si_xGe_yO_1-x-y) thin films with an Oxygen concentration below 10%. The results demonstrated that a high TCR and a low corresponding resistivity can be achieved using various compositions, for example, Si_0.054Ge_0.877O_0.069 film has achieved a TCR and a resistivity of -3.516/K, and 629 Ω-cm, respectively. The lowest measured resistivity and the corresponding TCR were 119.6 Ω-cm and -2.202 %/K respectively, using Si_0.136Ge_0.838O_0.026 for film deposited at room temperature, whereas the highest achieved TCR and the corresponding resistivity at room temperature were -5.017 %/K, and 39.1×103 Ω-cm, respectively, using Si_0.167Ge_0.762O_0.071 for films deposited at room temperature. The calculated activation energy (E_a) from the slope of Arrhenius plots were varied between 0.1232 eV to 0.3788 eV. The X-ray diffraction study demonstrated that the films are amorphous but did not show any dependence on varying silicon at fixed oxygen concentration. The noise study demonstrated that these films exhibit relatively high 1/f.

In this report, we describe thin 200nm thick GaN film formation technology on Si which allows microbolometer application. GaN layer with AlN buffer layer obtained by the MOCVD has TCR of about -0.64 %/°C and sheet resistance of ~2800 ohm/sq. Acquired GaN films were analyzed by XRD, SEM, Hall measurement, and etc. The successful growth of thin single crystalline or polycrystalline GaN film on Si can be a good semiconductor bolometric material. And the multi wavelength detecting systems with GaN based devices including UV detector, power devices, amplifier with GaN and AlGaN MOSFET, HEMT, and etc can be realized. We obtained thin(~200nm) crystalline GaN layer on Si(111) with AlN buffer layers with FWHM(full width at half maximum) of ~1800 arcsec. And its bolometric characteristic was analyzed.

This work presents measured results demonstrating an uncooled infrared (IR) detector based on gallium nitride (GaN) micromechanical resonators. GaN-based photonic detectors are typically designed to operate in the ultraviolet (UV) regime as the absorption spectrum of wide-band gap GaN peaks at a wavelength of ~360 nm. In contrast, the transduction mechanism of the device presented in this work is the pyroelectric perturbation of a GaN micromechanical resonator, allowing the detection of radiation in the IR regime. IR radiation within the absorption spectrum of the resonating stack material (mainly the IR absorber) is converted into heat causing pyroelectric charge release, which in turn shifts the resonant frequency via changes in the acoustic velocity of GaN. A thin-film IR absorber based on carbon-nanotube nanocomposite is proposed, which offers IR absorptivity of more than 95%. As a proof of concept, we demonstrate a GaN resonant detector operated at 119 MHz, which exhibits an IR sensitivity of ~4 Hz/10nW.

By utilizing the band-selective nature of optically resonant nanoparticles, Tanner Research is developing a room temperature multi-spectral IR detection technology termed Nanobolometer. Because the device physics is not based on photodiode/photoconductive (cooled IR detectors) operation, it does not require cooling. It is also not a heat sensing (Microbolometers) scheme and is capable of multi-spectral detection from NIR to LWIR. A nanobolometer is built on a Si substrate for the entire detection bands (NIR-LWIR), which enables low material and fabrication costs, with an added advantage of being able to integrate UV/Vis detector pixels in the same platform. We present the theory and working principle of Tanner's Nanobolomter technology and report a proof-of-concept demonstration that achieved IR detection at 1.5 μm. Tanner's on-going R&D effort aims to extend the detection bands to MWIR/LWIR.

For the development of small microbolometer for mobile applications, new pixel design to enhance fill factor by sharedanchor structures is suggested and it can be possible to make a one anchor per unit pixel. Fill factor increases 10% more than that of normal unshared-anchor design. Amorphous-silicon based microbolometer has been fabricated with 64x64 arrays of 25um pixel size to verify proposed design. Mechanical flatness of shared-anchor structure is enhanced. Responsivity is enhanced from 1.08e+5 V/W to 1.23e+5 V/W due to the increase of fill-factor compared to unsharedanchor. There are no mechanical, electrical and thermal crosstalk problems with adjacent pixels.

This paper presents the first fabricated dual-band uncooled resistive infrared thermal microbolometer implemented with a resistive microbolometer and a tunable micro-mirror structure. Tunable reflective micro-mirrors are suspended underneath the suspended resistive microbolometers having a 35 μm pixel pitch, and they are switched between two positions by the application of an electrostatic force for obtaining different responses in two wavelength infrared atmospheric windows, namely the 3-5 and 8-14 μm, by tuning the optical tunable resonant cavity. This approach allows assessing the actual temperature of the viewed scene by comparing the responses of the detector in these two wavelength infrared atmospheric windows. The absorption coefficients of the detector are simulated by using the Cascaded Transmission Line (CTL) model, and the sacrificial layer thicknesses are optimized to obtain maximum absorption from these two wavelength regions. The absorption coefficients obtained from the measurements are in correspondence with the simulations. The responsivity measurements results shows that the absorption is decreased in an amount of 17.9 % in the 3-5 μm spectral band, while the absorption is increased in an amount of 8.5 % in the 8-14 μm spectral band, depending on the micro-mirror position. These initial results are promising for the dual-band detection using uncooled infrared microbolometer detectors.

This paper introduces an analysis on the absorption enhancement in uncooled infrared pixels using resonant plasmon modes in metal structures, and it reports, for the first time in literature, broad-band absorption enhancement using integrated plasmonic structures in microbolometers for unpolarized long-wave IR detection. Different plasmonic structures are designed and simulated on a stack of layers, namely gold, polyimide, and silicon nitride in order to enhance absorption at the long-wave infrared. The simulated structures are fabricated, and the reflectance measurements are conducted using an FTIR Ellipsometer in the 8-12 μm wavelength range. Finite difference time domain (FDTD) simulations are compared to experimental measurement results. Computational and experimental results show similar spectral reflection trends, verifying broad-band absorption enhancement in the spectral range of interest. Moreover, this paper computationally investigates pixel-wise absorption enhancement by plasmonic structures integrated with microbolometer pixels using the FDTD method. Special attention is given during the design to be able to implement the integrated plasmonic structures with the microbolometers without a need to modify the pre-determined microbolometer process flow. The optimized structure with plasmonic layer absorbs 84 % of the unpolarized radiation in the 8-12 μm spectral range on the average, which is a 22 % increase compared to a reference structure with no plasmonic design. Further improvement may be possible by designing multiply coupled resonant structures.

This paper presents the performance evaluation of a unique method called heating based resistance nonuniformity compensation (HB-RNUC). The HB-RNUC method utilizes a configurable bias heating duration for each pixel in order to minimize the readout integrated circuit (ROIC) output voltage distribution range. The outputs of each individual pixel in a resistive type microbolometer differ from each other by a certain amount due to the resistance non-uniformity throughout the focal plane array (FPA), which is an inevitable result of the microfabrication process. This output distribution consumes a considerable portion of the available voltage headroom of the ROIC unless compensated properly. The conventional compensation method is using on-chip DACs to apply specific bias voltages to each pixel such that the output distribution is confined around a certain point. However, on-chip DACs typically occupy large silicon area, increase the output noise, and consume high power. The HB-RNUC method proposes modifying the resistances of the pixels instead of the bias voltages, and this task can be accomplished by very simple circuit blocks. The simplicity of the required blocks allows utilizing a low power, low noise, and high resolution resistance nonuniformity compensation operation. A 9-bit HB-RNUC structure has been designed, fabricated, and tested on a 384x288 microbolometer FPA ROIC on which 35μm pixel size detectors are monolithically implemented, in order to evaluate its performance. The compensation operation reduces the standard deviation of the ROIC output distribution from 470 mV to 9 mV under the same readout gain and bias settings. The analog heating channels of the HB-RNUC block dissipate around 4.1 mW electrical power in this condition, and the increase in the output noise due to these blocks is lower than 10%.

The high level of accumulated expertise by ULIS and CEA/LETI on uncooled microbolometers made from amorphous silicon enables ULIS to develop ¼ VGA IRFPA formats with 17μm pixel-pitch to enable the development of small power, small weight (SWAP) and high performance IR systems. ROIC architecture will be described where innovations are widely on-chip implemented to enable an easier operation by the user. The detector configuration (integration time, windowing, gain, scanning direction...), is driven by a standard I²C link. Like most of the visible arrays, the detector adopts the HSYNC/VSYNC free-run mode of operation driven with only one master clock (MC) supplied to the ROIC which feeds back pixel, line and frame synchronizations. On-chip PROM memory for customer operational condition storage is available for detector characteristics. Low power consumption has been taken into account and less than 60 mW is possible in analog mode at 60 Hz and < 175 mW in digital mode (14 bits). A wide electrical dynamic range (2.4V) is maintained despite the use of advanced CMOS node. The specific appeal of this unit lies in the high uniformity and easy operation it provides. The reduction of the pixel-pitch turns this TEC-less ¼ VGA array into a product well adapted for high resolution and compact systems. NETD of 35 mK and thermal time constant of 10 ms have been measured leading to 350 mK.ms figure of merit. We insist on NETD trade-off with wide thermal dynamic range, as well as the high characteristics uniformity and pixel operability, achieved thanks to the mastering of the amorphous silicon technology coupled with the ROIC design. This technology node associated with advanced packaging technique, paves the way to compact low power system.

We report the development of a 2-million-pixel, that is, a 2000 x 1000 array format, SOI diode uncooled IRFPA with 15 μm pixel pitch. The combination of the shrinkable 2-in-1 SOI diode pixel technology, which we proposed last year [1], and the uncooled IRFPA stitching technology has successfully achieved a 2-million-pixel array format. The chip size is 40.30 mm x 24.75 mm. Ten-series diodes are arranged in a 15 μm pixel. In spite of the increase to 2-million-pixels, a frame rate of 30 Hz, which is the same frame rate as our former generation (25 μm pixel pitch) VGA IRFPA, can be supported by the adoption of readout circuits with four outputs. NETDs are designed to be 60 mK (f/1.0, 15 Hz) and 84 mK (f/1.0, 30 Hz), respectively and a τ_th is designed to be 12 msec. We performed the fabrication of the 2-million-pixel SOI diode uncooled IRFPAs with 15 μm pixel pitch, and confirmed favorable diode pixel characteristics and IRFPA operation where the evaluated NETD and τ_th were 65 mK (f/1.0, 15 Hz) and 12 msec, respectively.

A new generation of high-performance uncooled detector arrays, with 17 and 25 μm pitch, improved sensitivity, and extended spectral response were developed recently by SCD. This development brings the uncooled infrared technology very close to the performance of traditional second generation cooled LWIR detectors, and enables a new range of applications. We demonstrate the use of our Very High Sensitivity (VHS) 25 μm pitch detector with F/2.4, for long range observation systems. We also present the new Wide-Band (WB) detector, where the detector absorption is tuned to both the MWIR and LWIR bands, which is optimal for use in some applications such as situation awareness. Furthermore, in this work we present our 17 μm pitch new family of detectors with different array formats (QVGA, VGA and XGA). These detectors are targeting a wide range of applications, from medium-performance with low Size, Weight and Power (SWaP) applications, up to high-performance imaging applications.

Vacuum packaging is definitely a major cost driver for uncooled IRFPA and a technological breakthrough is still expected to comply with the very low cost infrared camera market. To address this key issue, CEA-LETI is developing a Pixel Level Packaging (PLP) technology which basically consists in capping each pixel under vacuum in the direct continuation of the wafer level bolometer process. Previous CEA-LETI works have yet shown the feasibility of PLP based microbolometers that exhibit the required thermal insulation and vacuum achievement. CEA-LETI is still pushing the technology which has been now applied for the first time on a CMOS readout circuit. The paper will report on the recent progress obtained on PLP technology with particular emphasis on the optical efficiency of the PLP arrangement compared to the traditional microbolometer packaging. Results including optical performances, aging studies and compatibility with CMOS readout circuit are extensively presented.

We present a thermal property estimation method required for a bolometer design and demonstrate the utilization of a presented method to the scaled μ-bolometers. The estimated thermal properties of 25μm pitch VOx bolometers with our presented method shows K=1.33x10^-8 W/K, H=1.36x10^-10 J/K, τ_th=10.2 ms for an active bolometer and K=1.64x10^-6 W/K, H=1.82x10^-10 J/K, τ_th=111 μs for a reference bolometer. These estimated thermal properties have a good agreement with the previous reports and with results from the FEM analyses carried on the same bolometer designs. The presented method is useful to estimate thermal properties of a scaled bolometer and to estimate thermal properties of a specific design.

Presented is a novel design for an uncooled surface-micromachined thermoelectric (TE) infrared (IR) detector. The detector features a P-doped polysilicon/Nichrome (Cr20-Ni80) thermocouple, which is embedded into a thin layer of Parylene-N to provide structural support. The low thermal conductivity (~0.1W/m.K), chemical resistance, and ease of deposition/patterning of Parylene-N make it an excellent choice of material for use in MEMS thermal detectors. This detector also features an umbrella-like IR absorber composed of a three layer stack of NiCr/SiN/NiCr to optimize IR absorption. The total device area is 20 um * 20 um per pixel with an absorber area of ~19 um * 19 um resulting in a fill factor of 90%. At room temperature, a DC responsivity of ~170V/W with a rise time of less than 8 ms is measured from the fabricated devices in vacuum when viewing a 500K blackbody without any concentrating optics. The dominant source of noise in thermoelectric IR detectors is typically Johnson noise when the detectors are operating in an open circuit condition. The fabricated detectors have resistances about 85KOhm which results in Johnson noise of about 38nV/Hz^0.5. The D* is calculated to be 9 * 10⁶ cm*Hz^0.5/ W. Preliminary finite element analysis indicates that the thermal conduction from the hot junction to the substrate through the TE wires is dominant ( G_TE >> G_parylene) considering the fabricated dimensions of the parylene film and the TE wires. Thus, by further reducing the size of the TE wires, G_TE can be decreased and hence, responsivity can be improved while the parylene film sustains the structural integrity of the cell.

A newly designed highly detective intra-slit thermoelectric room-temperature linear array is presented. The thermoelectric sensor array ZS-64-2 with 64 individually readable channels was designed and developed for IR spectroscopy. It is suitable for analytical measurement technology, for example, in determining the age of technical oils in real time. For this, the selected absorption bands of the oil are analyzed and evaluated. This allows conclusions be drawn about the condition of lubricants and coolants, so that they can be replaced when it is needed. This method helps to save valuable resources and it helps to avoid costly damages. In order to achieve the high detectivity of D* = 1.8 x 10⁹ Jones the sensor was designed and optimized to be operated under vacuum conditions. For minimizing the thermal cross talk between the individual pixels, they are separated from each other by a 50 micron slit in the self-supporting silicon nitride membrane, which has a thickness of nearly 1 micron.

a-Si (amorphous Silicon) microbolometer FPAs (Focal Place Arrays) with TEC-less (without Thermo-Electric Cooler) and shutterless capabilities have become the technology of choice for low cost, high resolution and low SWaP (Size, Weight and Power) uncooled LWIR (Long Wave Infrared) cameras used in mobile applications. Over the past 10 years, a-Si microbolometric FPAs have seen a steady reduction in pixel pitch from 45μm to 17μm as well as an increase in pixel count from 160x120 to 1024x768. Next-generation arrays are projected to feature 12μm pixel pitch and resolution up to 1440x1080. However, microbolometer technology scaling has detrimental effects on pixel performance and the imaging system's optical complexity, which does not always yield a better infrared image quality. In this paper, we describe, from an information-theoretic perspective, the benefits of using computational imaging technologies and more specifically pupil function engineering to compensate for the optical resolution and noise sensitivity problems caused by shrinking pixel geometry in microbolometer FPAs. Computational imaging is a developing field in which the image acquisition process is shared between the optics and post-capture digital processing (cf. encoding-decoding scheme).

We present a bio-inspired system-on-chip focal plane readout architecture which at the system level, relies on an event based sampling scheme where only pixels within a programmable range of photon flux rates are output. At the pixel level, a one bit oversampled analog-to-digital converter together with a decimator allows for the quantization of signals up to 26 bits. Furthermore, digital non-uniformity correction of both gain and offset errors is applied at the pixel level prior to readout. We report test results for a prototype array fabricated in a standard 90nm CMOS process. Tests performed at room and cryogenic temperatures demonstrate the capability to operate at a temporal noise ratio as low as 1.5, an electron well capacity over 100Ge-, and an ADC LSB down to 1e-.

We propose a new way to correct for the non-uniformity (NU) and the noise in uncooled infrared-type images. This method works on static images, needs no registration, no camera motion and no model for the non uniformity. The proposed method uses an hybrid scheme including an automatic locally-adaptive contrast adjustment and a state-of-the-art image denoising method. It permits to correct for a fully non-linear NU and the noise efficiently using only one image. We compared it with total variation on real raw and simulated NU infrared images. The strength of this approach lies in its simplicity, low computational cost. It needs no test-pattern or calibration and produces no "ghost-artefact".

Increasingly complex specifications for next-generation focal plane arrays (FPAs) require smaller pixels, larger array sizes, reduced power consumption and lower cost. We have previously reported on the favorable features available in the commercially available TowerJazz CA18 0.18μm mixed-signal CMOS technology platform for advanced read-out integrated circuit (ROIC) applications. In his paper, new devices in development for commercial purposes and which may have applications in advanced ROICs are reported. First, results of buried-channel 3.3V field effect transistors (FETs) are detailed. The buried-channel pFETs show flicker (1/f) noise reductions of ~5X in comparison to surface-channel pFETs along with a significant reduction of the body constant parameter. The buried-channel nFETs show ~2X reduction of 1/f noise versus surface-channel nFETs. Additional reduced threshold voltage nFETs and pFETs are also described. Second, a high-density capacitor solution with a four-stacked linear (metal-insulator-metal) MIM capacitor having capacitance density of 8fF/μm² is reported. Additional stacking with MOS capacitor in a 5V tolerant process results in >50fC/μm² charge density. Finally, one-time programmable (OTP) and multi-time programmable (MTP) non-volatile memory options in the CA18 technology platform are outlined.

Design and realization of a 144x7 silicon readout integrated circuit (ROIC) based on switched capacitor TDI for MCT LWIR scanning type focal plane arrays (FPAs) and its corresponding hybrid integrated test circuits are presented. TDI operation with 7 detectors improves the SNR of the system by a factor of √7, while oversampling rate of 3 improves the spatial resolution of the system. ROIC supports bidirectional scan, 5 adjustable gain settings, bypass operation, automatic gain adjustment in case of mulfunctioning pixels and pixel select/deselect properties. Integration time of the system can be determined by the help of an external clock. Programming of ROIC can be done in parallel or serial mode according to the needs of the system. All properties except pixel select/deselect property can be performed in parallel mode, while pixel select/deselect property can be performed only in serial mode. ROIC can handle up to 3.75V dynamic range with a load of 25pF and output settling time of 80ns. Input referred noise of the ROIC is less than 750 rms electrons, while the power consumption is less than 100mW. To test ROIC in absence of detector array, a process and temperature compensated current reference array, which supplies uniform input current in range of 1-50nA to ROIC, is designed and measured both in room and cryogenic (77ºK) temperatures. Standard deviations of current reference arrays are measured 3.26% for 1nA and 0.99% for 50nA. ROIC and current reference array are fabricated seperately, and then flip-chip bonded for the test of the system. Flip-chip bonded system including ROIC and current reference test array is successfully measured both in room and cryogenic temperatures, and measurement results are presented. The manufacturing technology is 0.35μm, double poly-Si, four metal, 5V CMOS process.

Thales Cryogenics has an extensive background in delivering reliable linear and rotary coolers for military, civil and space programs. Recent work carried out at detector level enable to consider a higher operation temperature for the cooled detectors. This has a direct impact on the cooling power required to the cryocooler. In continuation of the work presented last year, Thales cryogenics has studied the operation and optimization of the rotary cryocoolers at high cold regulation temperature. In this paper, the performances of the Thales Cryogenics rotary cryocoolers at elevated cold regulation temperature will be presented. From these results, some trade-offs can be made to combine correct operation of the cryocooler on all the ambient operational range and maximum efficiency of the cryocooler. These trade-offs and the impact on MTTF of elevated cold regulation temperature will be presented and discussed. In correlation with the increase of the cold operation temperature, the cryocooler input power is significantly decreased. As a consequence, the cooler drive electronics own consumption becomes relatively important and must be reduced in order to minimize global input power to the cooling function (cryocooler and cooler drive electronics). Thales Cryogenics has developed a new drive electronics optimized for low input power requirements. In parallel, improvements on RM1 and RM2 cryocoolers have been defined and implemented. The main impacts on performances of these new designs will be presented. Thales cryogenics is now able to propose an efficient cooling function for application requiring a high cold regulation temperature including a range of tuned rotary coolers.

Thales Cryogenics has an extensive background in delivering linear and rotary coolers for military, civil and space programs. During the last years several technical improvements have increased the lifetime of all Thales coolers resulting in significantly higher Mean Time To Failure (MTTF) figures. In this paper not only updated MTTF values for most of the products in our portfolio will be presented but also the methodology used to come to these reliability figures will be explained. The differences between rotary and linear coolers will be highlighted including the different failure modes influencing the lifetime under operational conditions. These updated reliability figures are based on extensive test results for both rotary and linear coolers as well as Weibull analysis, failure mode identifications, various types of lifetime testing and field results of operational coolers. The impact of the cooler selection for typical applications will be outlined. This updated reliability approach will enable an improved tradeoff for cooler selection in applications where MTTF and a correct reliability assessment is key. Improbing on cooler selection and an increased insight in cooler reliability will result in a higher uptime and operability of equipment, less risk on unexpected failures and lower costs of ownership.

State of the art Mid Wave IR-technology has the potential to rise the FPA temperature from 77K to 130-150K (High Operation Temperature, HOT). Using a HOT FPA will significantly lower SWaP and keep those parameters finally dominated by the employed cryocooler. Therefore, compact high performance cryocoolers are mandatory. AIM has developed the SX040 cooler, optimized for FPA temperatures of about 95K (presented at SPIE 2010). The SX040 cooler incorporates a high efficient dual piston driving mechanism resulting in a very compact compressor of less than 100mm length. Higher compactness - especially shorter compressors - can be achieved by change from dual to single piston design. The new SX030 compressor has such a single piston Moving Magnet driving mechanism resulting in a compressor length of about 60mm. Common for SX040 and SX030 family is a Moving Magnet driving mechanism with coils placed outside the helium vessel. In combination with high performance plastics for the piston surfaces this design enables lifetimes in excess of 20,000h MTTF. Because of the higher FPA temperature and a higher operating frequency also a new displacer needs to be developed. Based on the existing 1/4" coldfinger interface AIM developed a new displacer optimized for an FPA temperature of 140K and above. This paper gives an overview on the development of this new compact single piston cryocooler. Technical details and performance data will be shown.

The world growth in research and development of High Operating Temperature IR detectors impels the development process and the optimization of rotary crycoolers at RICOR. The design aspects of size weight and power and the tradeoffs between them, were taken into consideration during the development process in order to optimize IDDCA for future hand held thermal sights. This paper will present optimization tests results performed for rotary crycoolers at the temperature range of 110 - 200K FPA and also will review the development activities that will be implemented in order to minimize "Idle electronic and mechanical losses," hence minimizing the regulated power consumption. As a result of the new approach to Rotary crycoolers for HOT detectors, the improvement in the reliability is analyzed and will be reported in the paper.

In spite of a wide spreading the uncooled night vision technologies, the cooled systems are still known to be superior in terms of working ranges, resolution and ability to recognize/track fast moving objects in dynamic infrared scenes. Recent technological advances allowed development and fielding of high temperature infrared detectors working up to 200K while showing performances typical for their 77K predecessors. The direct benefits of using such detectors are the lowering of the optical, cooling and packaging constraints resulting in smaller and cost effective optics, electronics and mechanical cryocooler. The authors are formulating requirements and general vision of prospective ultra-compact, long life, lightweight, power efficient, acoustically and dynamically quiet linear cryogenic cooler towards forthcoming infrared imagers. In particular, the authors are revealing the outcomes of the feasibility study and discuss downscaling options.

This paper describes a series of experiments during which a particular cryocooler control electronics (CCE) was shown to successfully drive several very different cryocoolers and simulated cryocooler loads, including a space pulse tube cryocooler, long life tactical Stirling coolers, and even a simulated reverse turbo Brayton (RTB) cryocooler compressor. This CCE is an early brassboard version of a low cost, radiation hard cryocooler electronics module being developed primarily for cost-constrained, but nevertheless mission critical military and civilian spaceborne applications. This design is also applicable for tactical applications which seek to support multiple cryocooler types and/or vendors with a given CCE. The CCE provides high efficiency DC-to-AC conversion, automated cool down, and precision temperature control. The results demonstrate convincingly that this CCE design is broadly supportive of a wide range of thermodynamic-mechanical cryocooler units (TMUs) for a subsequently broad range of payloads and missions.

With the recent developments in multi-spectral detector technology the interest in common aperture, common focal plane multi-spectral imaging systems is increasing. Such systems are particularly desirable for military applications where increased levels of target discrimination and identification are required in cost-effective, rugged, lightweight systems. During the optical design of dual waveband or multi-spectral systems, the options for material selection are limited. This selection becomes even more restrictive for military applications as material resilience and thermal properties must be considered in addition to colour correction. In this paper we discuss the design challenges that lightweight multi-spectral common aperture systems present along with some potential design solutions. Consideration will be given to material selection for optimum colour correction as well as material resilience and thermal correction. This discussion is supported using design examples that are currently in development at Qioptiq.

The increasing availability of sensors that can image in the 1-5 micron region has allowed for systems to be developed that utilize the full spectrum. Past MWIR systems have typically only imaged in the 3-5 micron region, but the new detectors allow imaging in the SWIR and MWIR bands with the same system. The use of a single FPA reduces SWAP and allows the user to see laser rangefinder and laser designator wavelengths. NVESD and Axsys have designed and built a SWIR/MWIR optical system that images in the 1-5 micron band. The optical system utilizes a cooled infrared detector that images in the 3-5 micron band as well as 1.04 - 1.08 and 1.54 microns without having to refocus the system to see the SWIR wavelengths. This provided an optical challenge to design a system that would image from 1-5 microns on the same detector. A combination reflective/refractive design was chosen in order to minimize packaging and meet the different FOV requirements. This paper discusses the design and development of a multi-FOV optical system with the capability to image across the 1-5 micron spectral band utilizing a combination of reflective and refractive components.

We explore the spectral and angular selectivity of near surface normal transmission of grating modified metallic surfaces and their ultimate potential for application as narrow-band spectro-polarimetric planar filter components in the development of advanced infrared focal plane arrays. The developed photonic microstructures exhibit tailored spectral transmission characteristics in the long wavelength infrared, and can be fabricated to preferentially transmit a given linear polarization within the design band. Modification of the material and structural properties of the diffractive optical element enables sub-pixel tuning of the spectro-polarimetric response of the device allowing for intelligent engineering of planar filter components for development of advanced focal plane arrays in the long wavelength infrared. The planar nature of the developed components leaves them immune to fabrication issues that typically plague thin film interference filters used for similar applications in the infrared, namely, deposition of multiple low-stress quarter-wavelength films and modification of the film thicknesses for each pixel. The solution developed here presents the opportunity for subpixel modification of the spectral response leading to an efficient, versatile filter component suitable for direct integration with commercially available focal plane array technologies via standard fabrication techniques. We will discuss the theoretical development and analysis of the described components and compare the results to the current state-of-the-art.

Diamond Like Carbon (DLC) or Hard Carbon (HC) single layer coatings on optical substrates are commonly used. As a single layer, the resulting average reflectance in different spectral ranges (about 2.5% in the 3-5 μm region) needs improvements. We propose multilayer coatings having a DLC upper layer applied on Si, Ge and other materials. These coatings result in an average reflection of less than 0.5% in either the 3.4-5 μm or the 8-11.5 μm regions. The average transmittance in these regions is more than 97%. The durability is comparable to single layer DLC coatings. These coatings are suitable to front surface FLIR lens assemblies. The effect on the performance of a zoom lens assembly and the reduction of the Narcissus effect is shown.

The convergence of silicon photonics and infrared plasmonics allows compact, chip-scale spectral sensors. We report on the development of a compact mid-IR spectrometer based on a broad-band IR source, dielectric waveguides, a transformer to convert between waveguide modes and surface plasmon polaritons (SPP), an interaction region where analyte molecules are interrogated by SPPs, an array of ring resonators to disperse the light into spectral components, and photodetectors. The mid-IR light source emits into a dielectric waveguide, leading to a region that allows coupling of the incident photons into SPPs. The SPPs propagate along a functionalized metal surface within an interaction region. Interactions between the propagating SPP and any analytes bound to the surface increase loss at those wavelengths that correspond to the analyte vibrational modes. After a suitable propagation length the SPP will be coupled back into a dielectric waveguide, where specific wavelength components will be out-coupled to detectors by an array of ring resonators. We have selected a 3.4 micron LED as the IR source, based on both cost and performance. Initial experiments with circular waveguides formed from GLSO glass include measurement of the loss per mm. Electrodynamic simulations have been performed to inform the eventual Si taper design of the proposed photonic/plasmonic transformer. The SPP propagation length necessary for a discernible change in the signal due to absorption in the interaction region has been estimated to be on the order of 1 mm, well within the bounds of calculated propagation lengths for SPPs on Au.

Today, both military and civilian applications require miniaturized optical systems in order to give an imagery function to vehicles with small payload capacity. After the development of megapixel focal plane arrays (FPA) with micro-sized pixels, this miniaturization will become feasible with the integration of optical functions in the detector area. In the field of cooled infrared imaging systems, the detector area is the Detector-Dewar-Cooler Assembly (DDCA). A dewar is a sealed environment where the detector is cooled on a cold plate. We show in this paper that wide field of view imagery functions can be simply added to the dewar. We investigate two ways of integration and make two demonstrators. The first one called FISBI consists in replacing the window by a fish-eye lens and in integrating a lens in the cold shield. This optical system has a field of view of 180°. The second one, called IR-Cam-on-Chip, consists in integrating the optics directly on the focal plane array. This optical system has a field of view of 120°. The additional mass of the optics is sufficiently small to be compatible with the cryogenic environment of the DDCA. The performance of these cameras will be discussed and several evolutions of these cameras will be introduced too.

A concept of Fourier-transform infrared spectrometer integrated on a focal plane array (FTIR-FPA) has been developed for very fast acquisition of spectral signatures. The basic idea is to use the upper surface of the focal plane array as the first mirror of a two-wave interferometer, which creates interference fringes directly inside the active layer. Two technologies have been developed. In a "monolithic" version of our FTIR-FPA concept, the cavity is made by grinding the substrate to the shape of a wedge. In a "hybrid" version, the cavity is made by hybridizing a Silicon plate just above the focal plane array.

In some cases the FLIR has an open window in the 1.06 micrometer wavelength range; this capability is called 'see spot' and allows seeing a laser designator spot using the FLIR. A problem arises when the returned laser energy is too high for the camera sensitivity, and therefore can cause damage to the sensor. We propose a non-linear, solid-state dynamic filter solution protecting from damage in a passive way. Our filter blocks the transmission, only if the power exceeds a certain threshold as opposed to spectral filters that block a certain wavelength permanently. In this paper we introduce the Wideband Laser Protection Filter (WPF) solution for thermal imaging systems possessing the ability to see the laser spot.

Passive athermalization has become a key-technology for automotive and other outdoor applications using modern uncooled 25 and 17 micron bolometer arrays. For high volume applications, passive athermalized optical designs with only two lenses reduce costs. A two lens solution requires a careful choice of lens and housing materials. A first order approach to thermal drift uses the RAYLEIGH criteria for depth of focus. It can be seen that narrow field of view lenses are the most sensitive to defocus with temperature. The different methods used to achieve stable performance over the required Temperature Range can be compared, namely passive optical athermalization and passive mechanical athermalization. GASIR® possesses inherent properties enabling optical passive athermalization. High resolution, two element designs for different field angles are presented. Each lens category is present: Super Wide Angle, Wide Angle, Standard, Tele and Super Tele. All examples are designed for 17micron VGA-detectors. These designs use aspheres and diffractive structures. The impact of temperature on all these parameters can only be determined by ray tracing. The proposed metric is the average of the tangential and sagittal MTF versus image height at Nyquist frequency. A very nonlinear impact of temperature on MTFA at different image heights is clearly visible. Examples are shown. An MTF based criteria for judging athermalization is proposed. It contains two values: the admissible MTF-drop ▵MTF in % and the resulting Temperature Range ▵T in Kelvin. The procedure to get these values is demonstrated. Values of 9 lens assemblies are listed. A comparison with results of first order approach shows limitations of this approach. A general quantification of athermalization is proposed. The pair of values (▵MTF, ▵T) is independent of other lens indexes. The limitations of this method are discussed.

Long wave infrared (LWIR) optical systems are prone to defocus with changes in temperature. IR refractive materials are more thermally sensitive compared to conventional visible glass due to their larger therm-optic coefficients. LWIR systems can be designed to be passively athermal (little or no change to focus with varying temperatures). Chalcogenide glasses provide additional material choices for IR lens designers. In particular, AMTIR5 has been engineered so its therm-optic coefficient matches the coefficient of thermal expansion (CTE) of aluminum, allowing for an athermal singlet. This paper explores the benefits of using engineered chalcogenide glass for color corrected, passively athermal systems. Initially, we present color corrected and passively athermal doublets that are designed with different materials and / or diffractive surfaces. Their thermal and color performance are cataloged for axial beams only. These are intended to be starting components, which readers may then insert into common design forms, such as Petzval, Double Gauss, Telephoto, and Inverse Telephoto. A F/1.3, 20° full field of view, aspheric Petzval lens design form is explored and the MTF is evaluated for -50°C to 85°C in an aluminum housing. From this design, we explore the tradeoffs between using chalcogenide versus crystalline materials, diffractive versus pure refractive surfaces, and engineered chalcogenide (AMTIR5) versus "catalog" materials.

The recent trend in infrared optics has been toward higher resolution with wider fields of view, lower weight and size, and broader temperature ranges. This places much more stringent requirements on the measurement and control of the properties of the optical materials within these systems. In response to these demands, SCHOTT North America recently announced domestic production of the IG glass series (IG2-IG6) of chalcogenide glasses within the US which has spurred renewed focus the characterization to bring these glasses to a similar level as standard optical glasses. This paper will present and discuss the novel inspection systems and the process used to qualify refractive index of these materials, with a focus on data presentation, in order to demonstrate the methodology and utility of the methods and data produced.

Trade parameters and relative advantages of beryllium, silicon carbide and Visible Quality (VQ) aluminum in terms of the currently available optical finishing characteristics, as well as their physical and thermal characteristics are presented. Combinations of constraints, environments, mount options and required performance may affect the choice between these materials. Guidelines are provided which may help a designer evaluate choices based on the current state of the art.

We will discuss mid-spatial frequency (MSF) optical surface errors, and how they affect optical performance of an optical system, including contrast, ensquared energy and pixel cross-talk. MSF errors will be represented in terms of Power Spectral Density (PSD), and examples will be discussed where PSD is well controlled and poorly controlled. We will show recent examples of PSDs of aspheric mirrors, sometimes with very challenging aspheric departure or other attributes, as routinely finished Tinsley, and suggest ways the designer can effectively specify an optic for smoothness.

With an emphasis on highest reliability, infrared (IR) imagers have traditionally used simplest-possible shutters and field-proven technology. Most commonly, single-step rotary or linear magnetic actuators have been used with good success. However, several newer shutter drive technologies offer benefits in size and power reduction, enabling man-portable imagers that are more compact, lighter, and more durable. This paper will discuss improvements in shutter and shutter drive technology, which enable smaller and more power-efficient imagers. Topics will transition from single-step magnetic actuators to multi-stepping magnetic drives, latching vs. balanced systems for blade position shock-resistance, motor and geared motor drives, and associated stepper driver electronics. It will highlight performance tradeoffs pertinent to man-portable military systems.

Silicon is a promising material as an IR(Infrared Ray) transparent window platform for packaging MEMS( microelectro mechanical systems), especially, IR sensors with WLP(wafer level package), because silicon has advantages in price and CMOS process compatibility compared to Ge, although Ge exhibits higher IR transmittance than Si. This paper reports on optimizing the thickness of Si window in the range of 8 ~ 12 um, LW-IR(Long wave IR). Two of important things which have to be considered in window material of IR sensor are minimizing absorption of IR(maximizing transmittance) and minimizing deformation due to the pressure differences between outside and inside of the package. Because of trade-off between minimizing IR absorption and minimizing mechanical deformation, optimization of thickness is important. Infrared absorbance of silicon was measured as varying thickness from 100 um to 700 um of the Si window. Decreasing the thickness of silicon made the absorption smaller. Under 300 um, the difference of absorbance with decreasing thickness becomes negligible. Degree of deformation according to the thickness of the Si window was calculated by simulation varying pressure differences, and package area. Based on this analysis, we suggest the optimized thickness of silicon window for WLP of LW-IR sensor.

Recent advancement has been made in producing difficult aspheric mirrors in bare aluminum to visible imaging quality. Polished bare aluminum mirrors offer significant producability and cost advantages for defense and surveillance systems, and can satisfy the environmental and performance needs of many systems. We describe the finish of both bare VQ Al mirrors in terms of power spectral density levels that can now be routinely achieved. Parameters are provided to guide the designer in specifying VQ mirrors, and in considering trades with other materials.

At the DSS conference in 2011, Tinsley introduced to the optics industry a unique bare Aluminum polishing capability that produced truly visible quality optical surfaces. This process, which can produce an optical surface with roughness as low as 15Å, achieves these results without the need for claddings or coatings. This makes Tinsley's bare Aluminum mirrors ideal for telescopes which must function over a wide range of temperatures and cannot tolerate the bi-metallic effects associated with conventional Aluminum mirror approaches. The single point diamond turning (SPDT) manufacturing process has inherent advantages in regards to both the mechanical position of the asphere surface relative to mounting datums, and manufacturing leadtime. This manufacturing process, when followed by Tinsley's bare Aluminum polishing process, can very quickly yield high-precision aspheric mirrors. The technologies outlined above can now be leveraged to quickly produce a high-precision telescope assembly which is athermal, and can be "snapped" together.

Future NASA light detection and ranging (LIDAR) mapping systems require multi-channel receivers with high sensitivity and bandwidth operating at 1-1.5 μm wavelengths. One of the ways to improve the system performance is to improve the sensitivity of photoreceiver. InGaAs avalanche photodiode (APD) sensor technology is considered for this wavelength region because of high reliability. However, commercially available InGaAs APDs have low sensitivity due to the high excess-noise of InP material. Spectrolab has been developing low excess noise InGaAs avalanche photodiodes (APDs) with impact ionization engineering (I²E) structures and recently, APDs with excess noise factor of 0.15 have been demonstrated using an I²E design. Single channel photoreceivers built using low noise I²E APDs show a noise equivalent power (NEP) of 150 fW/rt(Hz) over a bandwidth of 1 GHz, a record for InGaAs based APDs. A 16 channel GHz SWIR photoreceiver was designed and built at Spectrolab. The photoreceiver was designed to work with a custom fiber bundle which couples the light from telescope to detectors. The photoreceiver shows a system level NEP less than 300 fW/rt(Hz) with 1 GHz bandwidth.

Raytheon is developing NIR sensor chip assemblies (SCAs) for scanning and staring 3D LADAR systems. High sensitivity is obtained by integrating high performance detectors with gain, i.e., APDs with very low noise Readout Integrated Circuits (ROICs). Unique aspects of these designs include: independent acquisition (non-gated) of pulse returns, multiple pulse returns with both time and intensity reported to enable full 3D reconstruction of the image. Recent breakthrough in device design has resulted in HgCdTe APDs operating at 300K with essentially no excess noise to gains in excess of 100, low NEP <1nW and GHz bandwidths and have demonstrated linear mode photon counting. SCAs utilizing these high performance APDs have been integrated and demonstrated excellent spatial and range resolution enabling detailed 3D imagery both at short range and long ranges. In the following we will review progress in real-time 3D LADAR imaging receiver products in three areas: (1) scanning 256 × 4 configuration for the Multi-Mode Sensor Seeker (MMSS) program and (2) staring 256 × 256 configuration for the Autonomous Landing and Hazard Avoidance Technology (ALHAT) lunar landing mission and (3) Photon-Counting SCAs which have demonstrated a dramatic reduction in dark count rate due to improved design, operation and processing.

There is a growing interest at reducing the size, weight, power and cost of military systems which often have to contain a large number of thermal and visible electro-optic functions in one camera. In the meantime, Active systems, using a near-infrared pulse laser and a fast, gated detector, are now commonly regarded as potential candidates for application requiring performances beyond ranges usually achieved with thermal imaging. This paper describes three recent developments using DEFIR (Sofradir and CEA-LETI's joint laboratory) MCT e-APD technology that addresses these needs. The first is a 15μm pixel pitch detector that can be switched to operate as a passive thermal imager, a laser-gated imager or a solar flux imager. A second development concerns an ultra-sensitive dual 2D/3D detector providing range information in a dynamic environment. Finally, an ultra high speed solution with a very low floor noise has been set up for applications with fast moving targets or Astronomy instrumentation. MCT e-APD solutions with small pixel pitch open a wide range of potential applications and contribute to bringing new generation EO sensor capability in a compact and lightweight payload configuration with extended performances. Perspectives and ongoing developments are discussed.

There is a strong interest in developing sensitive Short Wavelength Infrared (SWIR) avalanche photodiodes (APDs) for applications like eye safe laser ranging and robotic vision. The excess noise associated with the avalanche process is critical in dictating the sensitivity of APDs. InGaAs APDs that are commonly used in the SWIR region have either InP or InAlAs as an avalanche layer and these materials have excess noise factor of 0.5 and 0.22, respectively. Earlier, Spectrolab had developed APDs with impact ionization engineering (I²E) structures based on InAlAs and InGaAlAs heterostructures as avalanche layers. These I²E APDs showed an excess noise factor of 0.15. A photoreceiver based on the I²E APD exhibited an noise equivalent power (NEP) of 150 fW/rt(Hz) over 1 GHz bandwidth at 1.06 μm. In this paper, a new multiplier structure based on multiple stages of I²E is studied. The APDs show optical gains over 100 before device breakdown. The increased gain and low excess noise will improve the sensitivity of InGaAs APDs based photoreceivers.

HgCdTe passivation process must be performed at low temperature in order to reduce Hg depletion. Low temperature plasma enhanced atomic layer deposition (PE-ALD) is an emerging deposition technology for thin highly conformal films to meet the demand. Room temperature PE-ALD Al₂O₃ film's passivation on HgCdTe has been studied. Conformal film was investigated through SEM images of the Al₂O₃ film deposited onto high aspect ratio features dry etched into HgCdTe. Minority carrier lifetime was measured and compared by photoconductive decay transients of HgCdTe before and after deposition. Room temperature ALD Al₂O₃ film increased the minority carrier lifetime of HgCdTe.

SELEX Galileo are developing 12μm arrays focal plane arrays fabricated from Metal Organic Vapour Phase Epitaxy (MOVPE) MCT grown on GaAs substrate arrays for use with megapixel array programmes. We report on a 256 x 256 format 12μm pixel pitch test array and provide an update on our HD1920 x 1080p format 12μm pixel pitch MW program. An overview of some of the technical challenges is given along with a summary of the low power device showing the 3-side buttable design approach, ROIC floor plan, preliminary results and the formation of larger mosaic arrays.

This paper describes the recent developments of Mercury Cadmium Telluride (MCT) infrared technologies in France at Sofradir and CEA-LETI made in the frame of the common laboratory named DEFIR. Among these developments, one can find the crystal growth of high quality and large Cadmium Zinc Telluride (CZT) substrates which is one of the fundamental keys for high quality and affordable detectors. These last years, a great effort was done on this topic and also on MCT epitaxy layer process from Short Waves (SW) to Very Long Waves (VLW). These developments about the quality of the material are needed for the challenge of the High Operating Temperature (HOT). Over these lasts years, the operating temperature of n-on-p MCT detectors was increase of several tens of Kelvin. In addition the development of the p-on-n MCT technology that reduces dark current by a factor ~100 saves about twenty Kelvin more. The next step for the increase in operating temperature will be the complex photodiodes architectures using molecular beam epitaxy layer. The reduction of the pixel pitches is another challenge for infrared technologies for Small Weight and Power (SWAP) detectors. Moreover, this reduction allows the increase in the resolution and consequently in the detection range of the systems. In addition, last results on 3rd generation detectors such as multicolor focal plan arrays, 2D, 3D, low noise and high images rate focal plane array using Avalanche Photodiode (APD) are described.

Current trends on the enhancement of MCT FPA IR-modules are reduction of size, weight and power (SWaP), increase of resolution with large detector arrays, provision of staring LWIR or dual-band capability. This is achieved by reduction of pixel size, higher operating temperatures (HOT) or complex pixel structures together with the optimization of dewars, adapted cooling engines and proximity electronics. To meet these demands AIM is working on MCT single-band MWIR or LWIR modules with formats 640x512 or 1280x1024 in 15μm pitch and a dual-band MWIR/LWIR module 640x512 in 20μm pitch. As a first step high operating temperatures for MWIR 120K and LWIR 80K were demonstrated, development for MWIR >= 150K and LWIR >= 90K is ongoing. The modules are realized as integrated detector cooler assemblies (IDCA) with proximity electronics. The 640x512/15μm pitch modules are already available in application specific configurations e.g. having integral rotary or split linear cooling engines. Besides implementation of the above mentioned capabilities also improvement in long term and cycle stability of IRmodules has been achieved which is important to fully benefit from increased mission times and longer maintenance periods by HOT. Especially staring MCT LWIR modules so far required sophisticated non-uniformity correction (NUC) processing to provide acceptable long term image quality while former scanning systems usually used implemented temperature references for NUC update. For a thermal imager setup with the LWIR 640x512/15μm module two-point correction with factory calibrated gain coefficients together with a new offset calibration after every cool down cycle is used. The paper will present the results of AIM's current staring single-band MCT IR-modules in MWIR or LWIR configuration especially regarding to their long term and cycle stability.

SELEX Galileo in collaboration with the Astronomy Technology Centre (ATC) undertook an activity to develop near infrared (NIR) and short wave (SWIR) sensor arrays as a precursor to a large format array in future phases of work. In this study, SELEX grew wafers of mercury cadmium telluride (MCT) material (cut off wavelengths ranging from 1.9μm to 2.7μm) using metal organic vapour phase epitaxy (MOVPE) on GaAs substrates. With substrate sizes up to 150mm available, this technology is ideal for very large arrays. Mesa structure arrays were processed and hybridised to multiplexers with a floating gate input. MOVPE requires the growth of buffer layers which would absorb the shortest wavelengths. Results will be presented showing how the cut-on wavelength can be controlled by thinning these buffer layers and the subsequent achievement of a response to radiation shorter than 0.8 μm. Data will be presented showing sub 0.1 e/s/pix dark current at 80K, quantum efficiencies of 75% in H-band, and less than 3 minutes persistence after spot illumination into "double saturation".

Developments made last years at CEA-LETI on p-on-n planar HgCdTe (MCT) photodiodes technology on long-, midand short-wavelength led to the manufacture of focal plane arrays (FPA) demonstrators with high performances. This technology has been successfully transferred to SOFRADIR for industrial production. Improvements have been done on both technology and process to index very long-wavelength spectral band. MCT base layer has been grown by liquid phase epitaxy (LPE) on lattice matched CdZnTe. The n-type doping is achieved during epitaxy by Indium incorporation, as In is naturally active as a donor in MCT. Planar p-on-n photodiodes were manufactured by Arsenic doping. As incorporation is achieved by ion-implantation and activation is done by post-implantation annealing under Hg overpressure. Multiples process settings were tested to find optimized conditions in order to obtain the best detector performances. Cutoff wavelength increase from LWIR at 9.2 μm at 77K was done in two steps, by adjusting technology process to get firstly 12.3 μm cutoff and then 15 μm at 77K. The second step was funded by french National Space Studies Center (CNES) to evaluate p-on-n IRFPAs performances for very long-wavelength detection for space applications such as IASI-NG. Electro-optical characterizations were performed both on test arrays and FPAs. Results show excellent operabilities (over 99.9% with ±0.5×mean value criterion) in responsivity and NETD, and current shot noise limited photodetectors. R₀A figure of merit is very high and at the state of the art.

SOFRADIR is one of the leading companies involved in the development and manufacturing of MCT (Mercury Cadmium Telluride) infrared detectors for space programs. The panel of space applications in which SOFRADIR is involved is wide and covers a large spectrum ranging from visible up to very long wavelength infrared (VLWIR). The last mission requirements for space applications, in particular for imagers and sounders, have brought new specifications for LWIR and VLWIR infrared detectors with cut-off wavelength of more than 15 μm. These requirements call for technology and design optimizations in order to find the best trade-off between detector performances and operational constraints such as operating temperature. In this paper, we present first a review of the different needs for current and future LWIR and VWLIR space applications in terms of detector architectures and requirements. Then, a presentation is made of the latest MCT technology optimizations for LWIR and VLWIR spectral bandwidths to meet these needs (n-onp and p-on-n technologies). Finally, different read-out circuit architectures are discussed to improve operability and performances in these bandwidths. Anyway, as mission requirements are always different depending on applications, a trade-off between the different solutions proposed in this paper is necessary in the early phases of the programs to find the best compromise to comply with customer needs.

Well recognized are the potential benefits in camera simplicity, power reduction and increased cooler life associated with the capability of operating infrared focal plane arrays at or near room ambient temperatures. Quality imagery in the 3 to 5 μm spectral band at scene temperature of 300K with focal plane array temperatures up to 175K was demonstrated recently. The array consisted of 640*512, 16 μm pitch N⁺p(As) detector elements grown by metal organic vapor phase epitaxy on a GaAs substrate. In this paper, a carrier recombination model is presented that explains the dark current density data as a function of inverse temperature. Basically the dominant carrier recombination occurs through ionized donor-like flaws centered in the upper half of the energy gap. For Hg_1-xCd _x Te, x=0.3 and 0.2867 materials, the flaw energy level, E_flaw(0K) respectively, is centered at 0.189 eV and 0.1181 eV above the valence band edge; The shortest possible lifetime τ_p0 for hole capture respectively is 3.5 and 550 μs. Band to band recombination is not observed to be dominant even in the temperature region T ≈ 300K, where the radiative and Auger lifetimes are significantly smaller than τ_p0. The asymmetry parameter γ = τ_n0/τ_p0 <<1.

As an alternative to the traditional liquid phase epitaxy (LPE) for HgCdTe (MCT) fabrication, molecular beam epitaxy (MBE) technology has generated a great amount of interest for well over two decades. MBE promises improved layer quality in terms of homogeneity, availability of large-area, inexpensive alternative substrates, and the possibility to fabricate 3^rd generation infrared detectors. The question about the most suitable alternative substrate has not been answered conclusively to date. AIM has focused its MCT growth efforts on the (211)B GaAs substrate which has received comparatively little attention in the last years. In this paper we present the state of MBE technology at AIM. We will describe the MBE growth and material quality of MCT on (211)B GaAs. Electro-optical characterization of focal plane arrays (FPAs) of detectors with cut-off wavelengths in both the mid- and long-wavelength (MW and LW) IR regions will be shown. The FPAs (640 x 512 pixels with 15 μm pitch) have been processed by AIMs standard planar n-on-p technology. For a MWIR detector, a low NETD of 18.3 ± 2.0 mK at 99.31% pixel operability has been achieved. The promising results in both wavelength regions illustrate the potential of (211)B GaAs as alternative substrate for MCT growth.

This paper investigates arrays of HgCdTe photon trapping detectors. Performance of volume reduced single mesas is compared to volume reduced photon trap detectors. Good agreement with model trends is observed. Photon trap detectors exhibit improved performance compared to single mesas, with measured noise equivalent temperature difference (NEDT) of 40 mK and 100 mK at temperatures of 180 K and 200 K, with good operability. Performance as a function of temperature has also been investigated.

The polarity inversion of laser beam induced current (LBIC) signal at low temperature and high laser power density in As-doped p-type HgCdTe is investigated in this paper. It is found that the polarity of LBIC signal reverses at 87 K compared to that at 300 K and the high laser power density is also an important factor in inducing the LBIC signal reverse. The results demonstrate that the shape of the LBIC signal profile is strongly dependent on the temperature of the device and the laser irradiation. To provide a reasonable analysis for this interesting fact, a photocarrier spreading mode is presented in this paper.

A novel mask technique, combining high selectivity silicon dioxide patterns over high aspect-ratio photoresist (PR) patterns has been exploited to perform mesa etching for device delineation and electrical isolation of HgCdTe third-generation infrared focal plane arrays (IRFPAs). High-density silicon dioxide film covering high aspect-ratio PR patterns was deposited at the temperature of 80°C and silicon dioxide film patterns over high aspect-ratio PR patterns of HgCdTe etching samples was developed by standard photolithography and wet chemical etch. Scanning electron microscopy (SEM) shows that the surfaces of inductively coupled plasma (ICP) etched samples are quite clean and smooth. The etching selectivity between the novel mask and HgCdTe of the samples is increased to above 32: 1 while the side-wall impact of etching plasma is suppressed by the high aspect ratio patterns. These results show that the combined patterning of silicon dioxide film and thick PR film is a readily available and promising masking technique for HgCdTe mesa etching.

The paper presents the new infrared detection module developed at the VIGO System Ltd. Its high sensitivity of was achieved by both matching the IR detector to the preamp and minimizing noises. High sensitivity of the detector was achieved by using photodiodes with immersion lens. Immersion lens enables optimization of the detector area, decreasing detector capacity and time constant. Detector noise was reduced as a result of photodiode cooling by means of a thermoelectric cooler and reverse biasing. Developed module is dedicated to NOx optoelectronic sensors operates basing on Cavity Enhanced Absorption Spectroscopy technique.

High sensitivity SWIR(ShortWave Infra-Red) hyperspectral imager is benefit of national resources sensing. Background radiation results in noise and fluctuation of system's dark level, which does much harm to instrument's radiometric performance. Basing on the analysis of background radiation and object reflectance signal, a SWIR hyperspectral system solution is given which utilize advanced infrared focal plane array technology. By system integration and testing, it's showed that ROIC's charge to voltage gain plays an important role in enhancing Signal to Noise Ratio(SNR). At lower light condition, high gain of ROIC and long integration time will lead to smaller dynamic range because of background radiation. A real-time background radiation monitoring method was validated which did a favor for eliminating background radiation in the image data.

Raising the operating temperature of infrared detectors has benefits in terms of reduced cooler power and increased life and enables an overall reduction in size and weight for handheld applications. With MCT the composition can be tuned to achieve the required wavelength range at a given temperature. Work on detectors operating in the 3-5μm atmospheric transmission window at operating temperatures up to 210K will be described. The influence of limiting factors such as excess noise, radiation shield emission, dark current and injection efficiency will be presented. Packaging aspects will be discussed emphasizing the importance of achieving low cost, weight and power for handheld applications. The impact of the detector design on overall system size and performance is considered with specific attention to time to image, passband and f-number. Finally images will be presented showing performance from a high operating temperature (HOT) camera.

Mid wave infrared (MWIR) imaging in the 3-5 um spectral band has traditionally been performed by InSb sensors. InSb technology is presently limited to a near 80K operating temperature and the hunt has been on for a higher operating temperature (HOT) technology that does as well at 150K as InSb at 80K, but with reduced power requirements. Amongst these alternative technologies are photovoltaic sensors consisting of heterostructures of HgCdTe (MCT). In previous work we assessed the device performance of several alternative MWIR HOT technologies (MCT on Si, MCT on GaAs) as a function of operating temperature. In this work we compare the NEDT histograms for these alternative technologies with InSb to better understand how their performance can be improved at higher temperatures. We also present analysis formalism for quantitatively assessing the number of FPA pixels which reside in the central versus the shoulder portions of the histogram.Begin the Introduction two lines below the Keywords. The manuscript should not have headers, footers, or page numbers. It should be in a onecolumn format. References are often noted in the text1 and cited at the end of the paper.

In MWIR photodiodes made from InSb, InAs or their alloy InAs1-xSbx, the dark current is generally limited by Generation-Recombination (G-R) processes. In order to reach a background limited operating temperature higher than ~80 K, steps must be taken to suppress this G-R current. At SCD we have adopted two main strategies. The first is to reduce the concentration of G-R centres, by changing from an implanted InSb diode junction to a higher quality one grown by Molecular Beam Epitaxy (MBE). Our epi-InSb diodes have a background limited performance (BLIP) temperature of ~105 K at F/4, in 15 to 30 μm pitch Focal Plane Arrays (FPAs). This operation temperature increase delivers a typical saving in cooling power of ~20%. In order to achieve even higher operating temperatures, we have developed a new XB_nn bariode technology, in which the bulk G-R current is totally suppressed. This technology includes nB_nn and pB_nn devices, as well as more complex structures. In all cases, the basic unit is an n-type AlSb_1-yAs_y / InAs_1-xSb_x barrier layer / photon-absorbing layer structure. These FPAs, with 15 to 30 μm pitch and a cut-off wavelength of ~ 4.1 μm, exhibit a BLIP temperature of ~ 175K at F/3. The cooling power requirement is reduced by ~60% compared with conventional 77K operation. The operation of both our diode and bariode detectors at high temperatures results in an improved range of solutions for various applications, especially where Size, Weight, and Power (SWaP) are critical. Advantages include faster cool-down time and mission readiness, longer mission times, and higher cooler reliability, as well as very low dark current and an enhanced Signal to Noise Ratio (SNR) at lower operating temperatures. This paper discusses the system level performance for cut-off wavelengths appropriate to the sensing materials in each detector type. Details of the radiometric parameters of each detector type are then presented in turn.

Infrared (IR) detector technologies with the ability to operate near room temperature are important for many applications including chemical identification, surveillance, defense and medical diagnostics. Reducing the need for cryogenics in a detector system can reduce cost, weight and power consumption; simplify the detection system design and allow for widespread usage. In recent years, infrared (IR) detectors based on uni-polar barrier designs have gained interest for their ability to lower dark current and increase a detector's operating temperature. Our group is currently investigating detectors based on the InAs/GaSb strain layer superlattice (SLS) material system that utilize barrier heterostructure engineering. Examples of such engineering designs include pBp, nBn, PbIbN, CBIRD, etc. For this paper I will focus on LW (long wave) pBp structures. Like the built-in barrier in a p-n junction, the heterojunction barrier blocks the majority carriers allowing free movement of photogenerated minority carriers. However, the barrier in a pBp detector, in contrast with a p-n junction depletion layer, does not significantly contribute to generation-recombination (G-R) current due to the lack of a depletion region across the narrow band gap absorber material. Thus such detectors potentially work like a regular photodiode but with significantly reduced dark current from G-R mechanisms. The mechanism of photoconductive (PC) gain has not been fully characterized in such device architectures and in many recent studies has been assumed to be unity. However, studies conducted with similar device structures have shown the presence of PC gain. In this report we will measure and analyze the impact of PC gain in detectors utilizing single unipolar barriers such as the case of pBp detectors.

This paper describes our recent results on three-dimensional (3D) numerical simulations of quantum efficiency and crosstalk in back-illuminated InAs nBn detector arrays. Our 3D simulations reveal that the p-type barrier layer, in the region between adjacent mesas where the n-type collector layer is removed, has a "built-in" potential well for holes, caused by the transfer of electrons from the absorber layer into the barrier layer. This well forms a channel in which holes are "trapped," and where the spatial separation of excess electron-hole pairs inhibits recombination, allowing holes trapped in the channel to diffuse long distances toward the nearest mesa where they are collected in the collector mesa. This mechanism may explain the anomalously long lateral collection lengths for photocarriers measured in nBn detectors with p-type barrier layers that have been reported by two groups. We used our 3D numerical model to confirm the lateral collection behavior of this hole channel in the barrier layer, and to calculate quantum efficiency and crosstalk in a 3×3 back-illuminated nBn array with 15×15 μm² pixels, with a variety of mesa sizes and diffusion lengths in the absorber layer, and for two mesa geometries, including one in which both the collector and the barrier layer are removed to form the mesa, thereby eliminating the hole channel.

A 320 x 256 Complementary Barrier Infrared (CBIRD) focal plane array for long-wavelength infrared (LWIR) imaging is reported. The arrays were grown by molecular beam expitaxy (MBE) with a 300 period 1.9 um thick absorber. The mean dark current density of 2.2 x 10^-4 A/cm² was measured at an operating bias of 128 mV with a long wavelength cutoff of 8.8 μm observed at 50% of the peak. The maximum quantum efficiency was 54% measured at 5.6 μm. Operating at T = 80K, the array yielded an 81% fill factor with 97% operability. Good imagery with a mean noise equivalent different temperature (NE▵T) of 18.6 mK and a mean detectivity of D* = 1.3 x 10¹¹ cm-Hz^1/2/W was achieved. The substrate was thinned using mechanical lapping and neither an AR coating nor a passivation layer was applied. This article provides the details of the fabrication process for achieving low-dark current LWIR CBIRD arrays. Discussion for an effective hard mask for excellent pattern transfer is given and appropriate mounting techniques for good thermal contact during the dry etching process is described. The challenges and differences between etching large 200 μm test diodes and small 28 μm FPA pixels are given.

The nBn or XBn barrier infrared detector has the advantage of reduced dark current resulting from suppressed Shockley-Read-Hall (SRH) recombination and surface leakage. High performance detectors and focal plane arrays (FPAs) based on InAsSb absorber lattice matched to GaSb substrate, with a matching AlAsSb unipolar electron barrier, have been demonstrated. The band gap of lattice-matched InAsSb yields a detector cutoff wavelength of approximately 4.2 μm when operating at ~150K. We report results on extending the cutoff wavelength of midwave barrier infrared detectors by incorporating self-assembled InSb quantum dots into the active area of the detector. Using this approach, we were able to extend the detector cutoff wavelength to ~6 μm, allowing the coverage of the full midwave infrared (MWIR) transmission window. The quantum dot barrier infrared detector (QD-BIRD) shows infrared response at temperatures up to 225 K.

In InAs_1-xSb_x material alloy composition was adjusted to achieve 200K cutoff wavelengths in the 5 μm range. Reflectance was minimized and absorption in the InAs_1-xSb_x material maximized by the use of pyramid shaped structures fabricated in the InAs_1-xSb_x material which function as an AR coating. Compound-barrier (CB) detectors were fabricated and tested for optical response and dark current density versus bias measurements were acquired as a function of temperature. For 5 μm cutoff detectors, QE is high, ~ 75 % between 4.0 μm and 4.6 μm and > 80 % between 2.0 μand 4.0 μm, demonstrating the efficacy of the pyramids as photon trap structures and as a replacement for multi-layer AR-coatings. J_dark in the low 10^-3 A/cm² range at 200 K and low 10^-5 A/cm² range at 150 K was measured at the bias at which the QE peaked.

Cooled IR technologies are challenged for answering new system needs like the compactness and the reduction of cryopower which is a key feature for the SWaP (Size, Weight and Power) requirements. Over the last years, SOFRADIR has improved its HgCdTe technology, with effect on dark current reduction, opening the way for High Operating Temperature (HOT) systems that can get rid of the 80K temperature constraint, and therefore releases the Stirling cooler engine power consumption. Performances of the 640×512 15μm pitch LW detector working above 100K will be presented. A compact 640×512 15μm pitch MW detector presenting high EO performance above 130K with cut-off wavelength above 5.0μm has been developed. Its different performances with respect to the market requirements for SWaP will be discussed. High performance compact systems will make no compromise on detector resolution. The pixel pitch reduction is the answer for resolution enhancement with size reduction. We will therefore also discuss the ongoing developments and market needs for SWaP systems.

In this paper, the physical mechanism of unipolar barrier structures is elaborated for dark current suppression. To better understand the performance characteristics of the devices and optimize the structures, we have performed numerical drift-diffusion simulations of both n-side and p-side InAs based unipolar barrier photodiodes with AlAs_0.18Sb_0.82 barriers, as well as conventional pn junction detectors. Numerical simulation was used to calculate the current-voltage (I-V) characteristic and R₀A values for InAs unipolar barrier photodiodes and traditional pn junction photodiodes. The performances of different device structures have been investigated for temperatures from 150 K to 350 K. Comparing to conventional devices, the unipolar barrier device has shown significant performance improvement.

We have investigated optical properties and figures of merit of sub-monolayer quantum dots (SML-QD) infrared photodetector and compared them with conventional Stranski-Krastanov quantum dots (SK-QD) with a similar design. The purpose of this study is to examine the effects of varying the number of stacks(2,3,4,5 and 6) in SML-QD detector on its device performance The peak of photoluminescence (PL) spectra of SK-QD and SML-QDs are observed at 1.07eV and 1.24~1.35eV at room temperature, respectively. The PL peak of 2 and 3 stacks SML QD are very close to the GaAs band edge peak (1.42eV) and the full width at half maximum (FWHM) of all the SML-QD are much narrower than SK-QD. Normal incidence photoresponse peak of 4 stacks SML QDIP are obtained at 7.5μm with responsivity of 0.5 A/W and detectivity of 1.2×10¹¹ cm.Hz^1/2/W (77K, 0.4V, f/2 optics), which is much narrower than spectral response of SK QDIP possibly due to bound-to-bound transition.

While InGaAs-based focal plane arrays (FPAs) provide excellent detectivity and low noise for SWIR imaging applications, wider scale adoption of systems capable of working in this spectral range is limited by high costs, limited spectral response, and costly integration with Si ROIC devices. RTI has demonstrated a novel photodiode technology based on IR-absorbing solution-processed PbS colloidal quantum dots (CQD) that can overcome these limitations of InGaAs FPAs. We have fabricated devices with quantum efficiencies exceeding 50%, and detectivities that are competitive with that of InGaAs. Dark currents of ~2 nA/cm² were measured at temperatures compatible with solid state coolers. Additionally, by processing these devices entirely at room temperature we find them to be compatible with monolithic integration onto readout ICs, thereby removing any limitation on device size. We will show early efforts towards demonstrating a direct integration of this sensor technology onto a Si ROIC IC and describe a path towards fabricating sensors sensitive from the visible to 2200 nm at a cost comparable to that of CMOS based devices. This combination of high performance, dramatic cost reduction, and multispectral sensitivity is ideally suited to expand the use of SWIR imaging in current applications, as well as to address applications which require a multispectral sensitivity not met by existing technologies.

The Self-assembled InGaAs/GaAs quantum dot infrared detectors (QDIPs) have emerged as a promising technology in many applications such as missile tracking, night vision, medical diagnosis, environmental monitoring etc. On account of the 3-D confinement of carriers in QDs, a number of advantages arise over the QW counterparts. Here we report a quaternary (InAlGaAs) capped In(Ga)As/GaAs QDIP. The samples were grown on a semi-insulating (001) GaAs substrate by solid source molecular beam epitaxy (MBE), and the dots were then capped with a combination of 30A quaternary (In_0.21Al_0.21Ga_0.58As) and 500Å of GaAs layer. Both the QD layer and the combination capping were repeated for 35 periods. The device was fabricated by conventional photolithography, ICP etching and metal evaporation technique. XTEM image of the sample depicted nice stacking of defect free quantum dot layers. The dark current is symmetric both for positive and negative bias with a low dark current density of 4.32x10^-6A/cm² at 77K and 1.6 x10 ^-3A/cm² at 200K at a bias of 2V. The high intense peak response observed at 10.2μm, with a very narrow spectral width (▵λ/λ) of 14% (▵λ is the FWHM), is probably due to bound-to-bound transition of carriers in the QDs. A very high responsivity of 2.16 A/W was measured at a bias of -0.40 Volt bias. The highest value of detectivity is measured to be ~10¹¹ cm.Hz^1/2/W at a bias of 0.3V.

Since 1997, Sofradir has been working with Thales Research & Technologies (TRT) to develop and produce Quantum Well Infrared Photodetectors (QWIP) as a complementary offer with Mercury Cadmium Telluride (MCT) Long Wave (LW) detectors, to provide large LW staring arrays. Thanks to the low dark current technology developed by TRT, the QWIP detectors can be operated at FPA temperature above 73K, enabling the production of compact Infrared (IR) cameras thanks to the use of compact microcoolers. The TV/2 VEGA-LW detector (25μm pitch 384×288 Integrated Detector Dewar Assembly (IDDCA)) is integrated in the Catherine-XP thermal imager from Thales Optronique SA (TOSA). To date, more than one thousand units have been manufactured. The TV SIRIUS-LW detector (20μm pitch 640×512 IDDCA) is integrated in the Catherine-MP thermal imager from Thales Optronics Ltd. (TOL). To date, several hundreds of units have been manufactured. We will discuss in this paper statistical results of these productions and our latest reliability study results, which highlight the stability of the TRT QWIP technology. Thanks to this mature technology, TRT and Sofradir have been able to increase the QWIP wafer size from 3 inches to 4 inches, without any impact on yields and FPA performances. A dual-band Mid Wave-Long Wave (MW-LW) QWIP detector (25μm pitch 384×288 IDDCA) is currently under development. We will present in this paper its latest results.

EO/IR Sensors and imagers using nanostructure based materials are being developed for a variety of Defense Applications. In this paper, we will discuss recent modeling effort and the experimental work under way for development of next generation carbon nanostructure based infrared detectors and arrays. We will discuss detector concepts that will provide next generation high performance, high frame rate, and uncooled nano-bolometer for MWIR and LWIR bands. The critical technologies being developed include carbon nanostructure growth, characterization, optical and electronic properties that show the feasibility for IR detection. Experimental results on CNT nanostructures will be presented. We will discuss the path forward to demonstrate enhanced IR sensitivity and larger arrays.

We demonstrate the effects of integrating a nanoantenna to a midwave infrared (MWIR) focal plane array (FPA). We model an antenna-coupled photodetector with a nanoantenna fabricated in close proximity to the active material of a photodetector. This proximity allows us to take advantage of the concentrated plasmonic fields of the nanoantenna. The role of the nanoantenna is to convert free-space plane waves into surface plasmons bound to a patterned metal surface. These plasmonic fields are concentrated in a small volume near the metal surface. Field concentration allows for a thinner layer of absorbing material to be used in the photodetector design and promises improvements in cutoff wavelength and dark current (higher operating temperature). While the nanoantenna concept may be applied to any active photodetector material, we chose to integrate the nanoantenna with an InAsSb photodiode. The geometry of the nanoantenna-coupled detector is optimized to give maximal carrier generation in the active region of the photodiode, and fabrication processes must be altered to accommodate the nanoantenna structure. The intensity profiles and the carrier generation rates in the photodetector active layers are determined by finite element method simulations, and iteration between optical nanoantenna simulation and detector modeling is used to optimize the device structure.

Thin-film getter integration is one of the key technologies enabling the development of a wide class of MEMS devices, such as IR microbolometers and inertial sensors, where stringent vacuum requirements must be satisfied to achieve the desired performances and preserve them for the entire lifetime. Despite its importance, the question about lifetime prediction is still very difficult to answer in a reliable way. Here we present an experimental approach to the evaluation of lifetime, based on an accelerated life test performed varying both the storage conditions and the getter area. A test vehicle based on a resonator device was used. The hermeticity was evaluated by means of specific leak testing, while MEMS behavior during the ageing test was studied monitoring device functional parameters and by residual gas analysis (RGA). Unexpected results were observed leading to the discovery that methane is pumped by the getter below 100°C. These results served as the inputs of a suitable model allowing extrapolating the device lifetime in operating? conditions, and pointed out that RGA is an essential tool to correctly interpret the aging tests.

We present 16-element and 32-element lattice-mismatched InGaAs photodiode arrays having a cut-off wavelength of ~2.2 um. Each 100 um × 200 um large pixel of the 32-element array has a capacitance of 2.5 pF at 5 V reverse bias, thereby allowing a RC-limited bandwidth of ~1.3 GHz. At room temperature, each pixel demonstrates a dark current of 25 uA at 5 V reverse bias. Corresponding results for the 16-element array having 200 um × 200 um pixels are also reported. Cooling the photodiode array to 150K is expected to reduce its dark current to < 50 nA per pixel at 5 V reverse bias. Additionally, measurement results of 2-micron single photodiodes having 16 GHz bandwidth and corresponding PIN-TIA photoreceiver having 6 GHz bandwidth are also reported.

A near infrared (NIR) and long-wavelength infrared (LWIR) dual-band infrared photodetector, which can switch detection bands with light bias, is demonstrated at 77 K. The demonstrated scheme consists of series connected photodetectors for different bands. The basic operating principle of the scheme is that without light bias, shorter wavelength detector limits the total current and thus the device operates in NIR mode. With light bias on the NIR detector, the LWIR detector becomes the current limiting device and the device then operates in LWIR mode. Proposed design allows single indium-bump per pixel focal plane arrays, and in principle allows covering all tactical bands such as UV, visible, NIR, SWIR, MWIR and LWIR bands with a single pixel.

Optical and structural properties of InAs/InAsSb type-II superlattices (T2SL) and their feasibility for mid- and longwavelength infrared (MWIR and LWIR) photodetector applications are investigated. The InAs/InAsSb T2SL structures with a broad bandgap range covering 4 μm to 12 μm are grown by molecular beam epitaxy and characterized by highresolution x-ray diffraction and photoluminescence (PL) spectroscopy. All of the samples have excellent structural properties and strong PL signal intensities of the same order of magnitude, indicating that non-radiative recombination is not dominant and the material system is promising for high performance MWIR and LWIR detectors and multiband FPAs.

We discuss the design, construction, and initial test results of a Si:As blocked-impurity-band (BIB) trap detector. The trap consists of two rectangular BIB devices configured in a v-shaped geometry. This trapping geometry is designed to ideally yield a minimum of 7 bounces before exit for incident light within an f/4 cone with 3 mm clear aperture. The individual BIB devices consist of 70 μm thick active layers with As doping near 1.7×10¹⁸ cm^-3, and have dark currents of approximately 100 nA at an operating temperature of 9 K. A simple ray-tracing model of the trap, along with data on the quantum yield of typical BIB detector elements, indicates that it is possible to achieve an external quantum efficiency of > 0.99 over the 4 μm to 28 μm spectral range and significant suppression of the etalon fringes present in the spectral responsivity of a single element. We have made initial responsivity measurements of the trap compared to a calibrated 5 mm diameter pyroelectric detector over the 3 μm to 17 μm spectral range using the fiber-coupled output of a Fourier-transform spectrometer. We also discuss the results of comparison measurements between the trap detector and an absolute cryogenic radiometer viewing the output of a calibrated blackbody source at discrete filter bands from 5 μm to 11 μ. In initial testing the performance of the trap is limited by the poor performance of the individual BIB detectors, but the advantages of boosted quantum efficiency and suppressed etalon are realized by the trap.

SiOnyx has developed a CMOS image sensor with enhanced infrared sensitivity. The technology deployed in this remarkable device is based on SiOnyx's proprietary ultrafast laser semiconductor process. We have established a high volume manufacturing process while maintaining complete compatibility with standard CMOS image sensor process flows. The enhanced performance proves the viability of a highly scalable low cost digital infrared sensor. The spectral sensitivity is from 400 to 1200 nm with measured quantum efficiency improvements of more than 3x at 940 nm.

Anti-sniper detection devices are the urgent requirement in modern warfare. The precision of the anti-sniper detection system is especially important. This paper discusses the location precision analysis of the anti-sniper detection system based on the dual-thermal imaging system. It mainly discusses the following two aspects which produce the error: the digital quantitative effects of the camera; effect of estimating the coordinate of bullet trajectory according to the infrared images in the process of image matching. The formula of the error analysis is deduced according to the method of stereovision model and digital quantitative effects of the camera. From this, we can get the relationship of the detecting accuracy corresponding to the system's parameters. The analysis in this paper provides the theory basis for the error compensation algorithms which are put forward to improve the accuracy of 3D reconstruction of the bullet trajectory in the anti-sniper detection devices.

We have developed Compact Infrared Camera (CIRC) with an uncooled infrared array detector (microbolometer) for space applications. The main mission of the CIRC is to demonstrate technology for wildfire detection. Wildfires are a major and chronic disaster that affects many countries, especially those in the Asia-Pacific region, and the situation may get worse with global warming and climate change. The CIRC detector has the largest format (640 × 480 pixels) ever used for observations of Earth from space. Microbolometers have the advantage of not requiring cooling systems such as a mechanical cooler and are suitable for resource-limited sensor systems or small satellites. In addition, the CIRC employs athermal optics and a shutter-less system, and hence, it is of a small size, is lightweight, and consumes low electrical power. The CIRC design was based on a commercial infrared camera and employs commercial-off-the-shelf (COTS) parts to reduce the cost and time for development. The CIRC will be carried as a technology demonstration payload of ALOS-2 and ISS/JEM, which will be launched in 2013 and 2014. We have developed the CIRC Proto Flight Model (PFM) and performed experiments for calibration in January 2012. In this paper, we present the verification results of the athermal characteristics and the calibration of the shutter-less system.

In this paper, we report the development of low flux short wavelength infrared radio-imaging systems to study the radiance due to nightglow emission. This radiation is mainly due to the desexcitation of hydroxyl molecules in the upper atmosphere. It is present in the visible range and reaches its maximum value (at ground level) in the short wavelength infrared band between 1.4 and 1.8μm. The nightglow may be an interesting additional light source for night vision systems in moonless or cloudy sky conditions. In this paper, we describe the experimental setup and present first results of the measurement campaigns that we performed at the Observatoire de Haute-Provence in France and at the European Southern Observatory site of La Silla in Chile.