This PDF file contains the front matter associated with SPIE Proceedings Volume 9070, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

In this paper we present first results from a backside illuminated CMOS image sensor that we fabricated on high resistivity silicon. Compared to conventional CMOS imagers, a thicker photosensitive membrane can be depleted when using silicon with low background doping concentration while maintaining low dark current and good MTF performance. The benefits of such a fully depleted silicon sensor are high quantum efficiency over a wide spectral range and a fast photo detector response. Combining these characteristics with the circuit complexity and manufacturing maturity available from a modern, mixed signal CMOS technology leads to a new type of sensor, with an unprecedented performance spectrum in a monolithic device. Our fully depleted, backside illuminated CMOS sensor was designed to operate at integration times down to 100nsec and frame rates up to 1000Hz. Noise in Integrate While Read (IWR) snapshot shutter operation for these conditions was simulated to be below 10e^- at room temperature. 2×2 binning with a 4× increase in sensitivity and a maximum frame rate of 4000 Hz is supported. For application in hyperspectral imaging systems the full well capacity in each row can individually be programmed between 10ke^-, 60ke^- and 500ke^-. On test structures we measured a room temperature dark current of 360pA/cm² at a reverse bias of 3.3V. A peak quantum efficiency of 80% was measured with a single layer AR coating on the backside. Test images captured with the 50μm thick VGA imager between 30Hz and 90Hz frame rate show a strong response at NIR wavelengths.

Low light level imaging applications requiring high detectivity demand photon shot noise limited performance at temperatures near 300K. Analytical models, however, have provided limited insight on underlying mechanisms limiting performance in conventional planar double heterointerface In_0.53Ga_0.47As on InP P⁺n photodiodes for imaging the visible and short wave infrared. Quantitative modeling provides tools to investigate performance sensitivities and their underlying mechanisms. In this work we use three-dimensional numerical simulation to investigate intrinsically limited diffusion and Shockley-Read-Hall generation recombination dark currents for a planar P⁺n photodiode situated in a 3×3 mini array. We assess the influence of geometry by varying pitch, junction location, and photodiode size. Modeling shows that SRH generation currents, not including surface effects, vary with both junction perimeter and area, and that the perimeter component dominates small radius junctions. By varying the axial junction placement we show that widegap junctions result in bias-dependent quantum efficiencies that require higher reverse bias, and result in higher dark currents, than shallow homojunctions at comparable efficiencies. Finally, numerical simulation explains lateral diffusion current suppression in dense arrays in terms of suppressed minority carrier density gradients. The analysis demonstrates that the boundary condition applicable to dense arrays requires no lateral diffusion current at symmetry planes bisecting segments connecting uniformly reverse biased nearest neighbor diodes. Following Grimbergen, this leads to radial geometry curves describing dark intrinsic diffusion reductions with pitch. The quantitative modeling provides insight explaining the observation that the ideal diode equation correctly estimates dense array dark diffusion currents.

Processing improvements have facilitated manufacturing reduced pixel dimensions for lattice-matched InGaAs on InP short-wave infrared detectors. Due to its technological maturity, this material system continues to garner attention for low-light level imaging applications. With pixel dimensions smaller than minority carrier diffusion lengths, optimizing array performance by reducing crosstalk from lateral carrier diffusion remains an important design issue. Analytical models, however, have provided limited insight on underlying mechanisms limiting device performance in the conventional planar double heterointerface device. Quantitative modeling provides tools to investigate performance sensitivities and their underlying mechanisms. In this work we develop a three-dimensional numerical simulation for dense P⁺n In_0.53Ga_0.47As on InP photo detector focal plane arrays using a conventional planar, back-illuminated structure. We evaluate optical generation with finite-difference time-domain analysis, and model carrier transport in a drift diffusion analysis simultaneously solving the carrier continuity and Poisson equations. Using this model we investigate modulation transfer function variations with pixel pitch and diffused junction geometries for small dimension arrays. By accounting for carrier diffusion effects, these results should provide a benchmark against which to evaluate modulation transfer function contributions from other effects, such as crosstalk attributable to photon recycling.

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. The recent transfer of imagery activities from III-VLab to Sofradir provides a framework for the production activity with the manufacturing of high performances products: CACTUS320 SW and CACTUS640 SW. The developments, begun at III-Vlab towards VGA format with 15μm pixel pitch, lead today to the industrialization of a new product: SNAKE SW. On one side, the InGaAs detection array presents high performances in terms of dark current and quantum efficiency. On the other side, the low noise ROIC has different additional functionalities. Then this 640×512 @ 15μm module appears as well suited to answer the needs of a wide range of applications. In this paper, we will present the Sofradir InGaAs technology, some performances optimization and the last developments leading to SNAKE SW.

High Sensitivity Megapixel and VGA shortwave IR imagers are presented. The imagers have 1280×1024 and 640×512 resolution FPAs with 12.5 μm pitch. The associated camera electronics are designed to optimize small SWaP and performance for a variety of applications including man-portable and airborne systems. Performance characterization of both these imagers is presented showing low-noise, high dynamic range capability suitable for challenging operational environments including light-starved and urban environments as well as a variety of industrial applications.

Photon counting imaging applications requires low noise from both detector and readout integrated circuit (ROIC) arrays. In order to retain the photon-counting-level sensitivity, a long integration time has to be employed and the dark current has to be minimized. It is well known that the PIN dark current is sensitive to temperature and a dark current density of 0.5 nA/cm² was demonstrated at 7 °C previously. In order to restrain the size, weight, and power consumption (SWaP) of cameras for persistent large-area surveillance on small platforms, it is critical to develop large format PIN arrays with small pitch and low dark current density at higher operation temperatures. Recently Spectrolab has grown, fabricated and tested 1024x1280 InGaAs PIN arrays with 12.5 μm pitch and achieved 0.7 nA/cm² dark current density at 15 °C. Based on our previous low-dark-current PIN designs, the improvements were focused on 1) the epitaxial material design and growth control; and 2) PIN device structure to minimize the perimeter leakage current and junction diffusion current. We will present characterization data and analyses that illustrate the contribution of various dark current mechanisms.

Detectors for the short-wave infrared (SWIR) spectral range are particularly suitable for observation under hazy weather conditions as well as under twilight or moon light conditions. In addition, SWIR detectors allow using the airglow for observation under moonless sky. SWIR detectors are commonly based on InGaAs or HgCdTe (MCT) and demand extremely low dark currents to ensure a high signal-to-noise ratio under low background light conditions. AIM has developed a read-out integrated circuit (ROIC) with 640×512 pixels and a 15 μm pixel pitch for low light level applications. The ROIC supports analog or digital correlated double sampling (CDS) for the reduction of reset-noise (also known as kTC-noise). Along with CDS, a rolling shutter (RS) mode has been implemented. The input stage of the ROIC is based on a capacitive transimpedance amplifier (CTIA) with two selectable gain settings. The dark current of our SWIR MCT detectors has recently been significantly reduced to allow for high operating temperatures. In contrast to InGaAs, the MCT material offers the unique possibility to adjust the cut-off wavelength according to the application while maintaining the matching of the lattice constant to the one of the CdZnTe substrate. The key electro-optical performance parameters of lately developed MCT based SWIR Focal Plane Arrays (FPA) with a 1.75 μm cut-off wavelength will be presented. In addition, AIMs SWIR detectors covering the spectral range from 0.9 μm to 2.5 μm and available in formats of 384×288 pixels - 24 μm pitch and 1024×256 pixels - 24×32 μm², will be introduced.

We report the development of high performance low cost SWIR infrared detectors from MBEgrown HgCdTe on 3-inch CdTe-buffered silicon substrates. The experimental findings demonstrate that despite the large lattice mismatch between HgCdTe and Si substrate, the materials and detector performances are sufficiently better than those reported for III-V mixed crystals. High minority carrier lifetime of the order 3 μs at room temperature was measured on the as grown material. Photodetectors fabricated from this material produced low dark current densities on the order of 10^-6 A/cm² and 10^-3 A/cm² at 200K and 300K. Quantum efficiency exceeding 70% at 2.0 μm, without antireflective coating, was measured on single element detectors. Further, 320 X 256, 30 μm pitch FPA’s have been fabricated with this HgCdTe on Si material and dark current operability of ~ 99.5% (mean dark current of 30 pA/Pixel) at 200K has been demonstrated.

This paper reports the development of a new miniature VGA SWIR camera called NanoCAM-6415, which is developed to demonstrate the key features of the MT6415CA ROIC such as high integration level, low-noise, and low-power in a small volume. The NanoCAM-6415 uses an InGaAs Focal Plane Array (FPA) with a format of 640 × 512 and pixel pitch of 15 μm built using MT6415CA ROIC. MT6415CA is a low-noise CTIA ROIC, which has a system-on-chip architecture, allows generation of all the required timing and biases on-chip in the ROIC without requiring any external components or inputs, thus enabling the development of compact and low-noise SWIR cameras, with reduced size, weight, and power (SWaP). NanoCAM-6415 camera supports snapshot operation using Integrate-Then-Read (ITR) and Integrate-While-Read (IWR) modes. The camera has three gain settings enabled by the ROIC through programmable Full-Well-Capacity (FWC) values of 10.000 e-, 20.000 e-, and 350.000 e- in the very high gain (VHG), high-gain (HG), and low-gain (LG) modes, respectively. The camera has an input referred noise level of 10 e- rms in the VHG mode at 1 ms integration time, suitable for low-noise SWIR imaging applications. In order to reduce the size and power of the camera, only 2 outputs out of 8 of the ROIC are connected to the external Analog-to-Digital Converters (ADCs) in the camera electronics, providing a maximum frame rate of 50 fps through a 26-pin SDR type Camera Link connector. NanoCAM-6415 SWIR camera without the optics measures 32 mm × 32 mm × 35 mm, weighs 45gr, and dissipates less than 1.8 W using a 5 V supply. These results show that MT6415CA ROIC can successfully be used to develop cameras for SWIR imaging applications where SWaP is a concern. Mikro-Tasarim has also developed new imaging software to demonstrate the functionality of this miniature VGA camera. Mikro-Tasarim provides tested ROIC wafers and also offers compact and easy-to-use test electronics, demo cameras, and hardware/software development kits for its ROIC customers to shorten their FPA and camera development cycles.

A SWIR FPA was designed and manufactured with 640*512 pixels, 20 μm pitch and InGaAs detectors for electroluminescence characterization and astronomical applications in the [0.9 – 1.55 μm] range. The FPA is mounted in a liquid nitrogen dewar and is operated by a low noise frontend electronics. One of the biggest problem in designing sensors and cameras for electro-luminescence measurements is the autoillumination of the detectors by the readout circuit. Besides of proper shielding of the detectors, the ROIC shall be optimized for minimal electrical activity during the integration time of the very-weak signals coming from the circuit under test. For this reason a SFD (or Source Follower per Detector) architecture (like in the Hawaii sensor) was selected, resulting in a background limited performance of the detector. The pixel has a (somewhat arbitrary) full well capacity of 400 000 e^- and a sensitivity of 2.17 μV/e^-. The dark signal is app. 1 e-/pixel/sec and with the appropriate Fowler sampling the dark noise lowers below 5 e^-_rms. The power consumption of the circuit is limited 2 mW, allowing more than 24 hours of operation on less than 1 l of liquid nitrogen. The FPA is equipped with 4 outputs (optional readout on one single channel) and is capable of achieving 3 frames per second. Due to the non-destructive readout it is possible to determine in a dynamic way the optimal integration time for each observation. The Cougar camera is equipped with ultra-low noise power supply and bias lines; the electronics contain also a 24 bit AD converter to fully exploit the sensitivity of the FPA and the camera.

Extended wavelength InGaAs infrared detector arrays in 1.0~2.5μm spectral rang based on three types of material structures grown by MBE were studied. The first type InGaAs detectors, marked by sample 1#, were fabricated using Pi- N epitaxial materials, mesa etching technique, side-wall and surface passivating film. The second type InGaAs detectors, marked by sample 2#, were fabricated using N-i-P epitaxial materials, mesa etching technique, side-wall and surface passivating film. The third type InGaAs detectors, marked by sample 3#, were fabricated using n-i-n epitaxial materials, planar diffusion process and surface passivating coating. I-V curves, low frequency noise and response spectra of these detectors were measured at the different temperature. The response spectra of these detectors cover 1.0~2.5μm wavelength range. The dark current density of three types InGaAs detectors are 28nA/cm², 2μA/cm², 9μA/cm² at 200K and -10mV bias voltage, respectively. Compared to Sample 2# and Sample 3#, sample 1# presents the lower dark current at the same temperature and the same bias voltage, which mainly results in the improvement of surface passivation film and the depth of mesa etching. The frequency spectrum of the noise of sample 1# has an inflection point at about 10Hz frequency, 1/f noise play an obviously role in the detectors below the 10Hz frequency.

This paper presents novel unit cell architecture for short wave infrared (SWIR) imaging applications. It has two input stages which are CTIA and SFD covering for both respectively low and high light, levels and automatic input stage selection circuitry that chooses best input stage. User can select 2 modes for FPA manual and automatic mode. In manual mode, user can set CTIA or SFD for all pixels according to user needs. In automatic mode, each pixel selects input stage itself according to light level. Light level threshold can be adjusted with reference voltage. Automatic input stage selection for each pixel brings high SNR level and low noise along with highest possible dynamic range for SWIR imaging applications. CMOS 0.18μm technology is used to realize unit cell. In the architecture of unit cell, circuit level techniques are used to optimize layout size.

Over the past decade, we have witnessed a growing demand for electro-optical systems that can provide continuous 360⁰ coverage. Applications such as perimeter security, autonomous vehicles, and military warning systems are a few of the most common applications for panoramic imaging. There are several different technological approaches for achieving panoramic imaging. Solutions based on rotating elements do not provide continuous coverage as there is a time lag between updates. Continuous panoramic solutions either use "stitched" images from multiple adjacent sensors, or sophisticated optical designs which warp a panoramic view onto a single sensor. When dealing with panoramic imaging in the visible spectrum, high volume production and advancement of semiconductor technology has enabled the use of CMOS/CCD image sensors with a huge number of pixels, small pixel dimensions, and low cost devices. However, in the infrared spectrum, the growth of detector pixel counts, pixel size reduction, and cost reduction is taking place at a slower rate due to the complexity of the technology and limitations caused by the laws of physics. In this work, we will explore the challenges involved in achieving 360⁰ panoramic thermal imaging, and will analyze aspects such as spatial resolution, FOV, data complexity, FPA utilization, system complexity, coverage and cost of the different solutions. We will provide illustrations, calculations, and tradeoffs between three solutions evaluated by Opgal: A unique 360⁰ lens design using an LWIR XGA detector, stitching of three adjacent LWIR sensors equipped with a low distortion 1200 lens, and a fisheye lens with a HFOV of 180º and an XGA sensor.

In the continuity of its current strategy, HGH maintains a deep effort in developing its most recent product family: the infrared (IR) panoramic 360-degree surveillance sensors. During the last two years, HGH optimized its prototype Middle Wave IR (MWIR) panoramic sensor IR Revolution 360 HD that gave birth to Spynel-S product. Various test campaigns proved its excellent image quality. Cyclope, the software associated with Spynel, benefitted from recent image processing improvements and new functionalities such as target geolocalization, long range sensor slue to cue and facilitated forensics analysis. In the frame of the PANORAMIR project sustained by the DGA (Délégation Générale de l’Armement), HGH designed a new extra large resolution sensor including a MWIR megapixel Focal Plane Array (FPA) detector (1280×1024 pixels). This new sensor is called Spynel-X. It provides outstanding resolution 360-degree images (with more than 100 Mpixels). The mechanical frame of Spynel (-S and -X) was designed with the collaboration of an industrial design agency. Spynel got the “Observeur du Design 2013” label.

The development of a new thermal imaging camera, for long range surveillance applications, is described together with the enabling technology. Previous publications have described the development of large arrays of 12μm pixels using Metal Organic Vapour Phase Epitaxy (MOVPE) grown Mercury Cadmium Telluride (MCT) for wide area surveillance applications. This technology has been leveraged to produce the low cost 1280×720 pixel Medium Wave IR focal plane array at the core of the new camera. Also described is the newly developed, high performance, ×12 continuous zoom lens which, together with the detector, achieves an Instantaneous Field of View (IFOV) of 12.5μrad/pixel enabling long detection, recognition and identification ranges. Novel image processing features, including the turbulence mitigation algorithms deployed in the camera processing electronics, are also addressed. Resultant imagery and performance will be presented.

The tomographic scanner (TOSCA) detects signals using line detectors scanning a scene at regularly distributed angles. These line scan signals are then processed to reconstruct 2-dimensional images. In the simplest form, a 1-axis rotating conical scan optics scans across a simple patterned reticle, the signal collection being done with a single pixel detector. Experimental mono- and multispectral cameras using this approach are demonstrated under varying illumination conditions. Of particular interest is the TOSCA system’s ability to handle and compensate for light sources modulated with a frequency higher than that of the frame rate. We also demonstrate for the first time a TOSCA imager operating in the infrared region. The device is put together using 3D-printed key parts and low cost optical components, leading to a very economical infrared camera.

Operating in a degraded visual environment due to darkness can pose a threat to navigation safety. Systems have been developed to navigate in darkness that depend upon differences between objects such as temperature or reflectivity at various wavelengths. However, adding sensors for these systems increases the complexity by adding multiple components that may create problems with alignment and calibration. An approach is needed that is passive and simple for widespread acceptance. Our approach uses a type of augmented display to show fused images from visible and thermal sensors that are continuously updated. Because the raw fused image gave an unnatural color appearance, we used a color transfer process based on a look-up table to replace the false colors with a colormap derived from a daytime reference image obtained from a public database using the GPS coordinates of the vehicle. Although the database image was not perfectly registered, we were able to produce imagery acquired at night that appeared with daylight colors. Such an approach could improve the safety of nighttime navigation.

For years, scientists have been using broadband cameras to perform measurements in the infrared spectral bands. In order to improve the outcomes of these studies, Telops has developed a fast multispectral imaging system in the LWIR and MWIR band. This paper presents the improvement that a fast infrared multispectral imager adds to the traditional infrared investigations and how this system can be applied in defence innovation research. An overview over the technology is presented and discussed along the results obtained during a combustion experiment.

The conventional photographs only record the sum total of light rays of each point on image plane so that they tell little about the amount of light traveling along individual rays. The focus and lens aberration problems have challenged photographers since the very beginning therefore light field photography was proposed to solve these problems. Lens array and multiple camera systems are used to capture 4D light rays, by reordering the different views of scene from multiple directions. The coded aperture is another method to encode the angular information in frequency domain. However, infrared light field sensing is still widely opening to research. In the paper, we will propose micro plane mirror optics together with compressive sensing algorithm to record light field in infrared spectrum. The micro mirror reflects objects irradiation and forms a virtual image behind the plane in which the mirror lies. The Digital Micromirror (DMD) consists of millions microscale mirrors which work as CCD array in the camera and it is controlled separately so as to project linear combination of object image onto lens. Coded aperture could be utilized to control angular resolution of infrared light rays. The carbon nanotube based infrared detector, which has ultra high signal to noise ratio and ultra fast responsibility, will sum up all image information on it without image distortion. Based on a number of measurements, compressive sensing algorithm was used to recover images from distinct angles, which could compute different views of scene to reconstruct infrared light field scence. Two innovative applications of full image recovery using nano scale photodetector and DMD based synthetic aperture photography will also be discussed in this paper.

HySpex ODIN-1024 is a next generation state-of the-art airborne hyperspectral imaging system developed by Norsk Elektro Optikk AS. Near perfect coregistration between VNIR and SWIR is achieved by employing a novel common fore-optics design and a thermally stabilized housing. Its unique design and the use of state-of-the-art MCT and sCMOS sensors provide the combination of high sensitivity and low noise, low spatial and spectral misregistration (smile and keystone) and a very high resolution (1024 pixels in the merged data products). In addition to its supreme data quality, HySpex ODIN-1024 includes real-time data processing functionalities such as real-time georeferencing of acquired images. It also features a built-in onboard calibration system to monitor the stability of the instrument. The paper presents data and results from laboratory tests and characterizations, as well as results from airborne measurements.

Today's world is going mobile. Smartphone devices have become an important part of everyday life for billions of people around the globe. Thermal imaging cameras have been around for half a century and are now making their way into our daily lives. Originally built for military applications, thermal cameras are starting to be considered for personal use, enabling enhanced vision and temperature mapping for different groups of professional individuals. Through a revolutionary concept that turns smartphones into fully functional thermal cameras, we have explored how these two worlds can converge by utilizing the best of each technology. We will present the thought process, design considerations and outcome of our development process, resulting in a low-power, high resolution, lightweight USB thermal imaging device that turns Android smartphones into thermal cameras. We will discuss the technological challenges that we faced during the development of the product, and what are the system design decisions taken during the implementation. We will provide some insights we came across during this development process. Finally, we will discuss the opportunities that this innovative technology brings to the market.

Infrared technology and imaging systems are already used extensively by the law enforcement (LE) community, typically to gain a tactical advantage or obtain immediate situational awareness. As the use of infrared technology becomes more affordable and widespread, LE is finding new ways to use it and leverage the results in the courtroom as evidence. A case study will be presented where infrared imagery was used to support the Portland Police Bureau (PPB) in prosecuting an individual for a crime where a conviction might not have been assured without said imagery. Tests conducted at FLIR Systems, combined with expert witness testimony by a FLIR employee, helped a jury understand the significance of a key piece of infrared evidence, resulting in a conviction of the criminal. This case was the first Federal case of its kind where infrared imagery was used forensically as evidence and, as such, established precedence. Prior to this, infrared imagery has been offered and debated in court only as to whether it constitutes a legal search. Courtroom observations and lessons learned from this trial have shown that both industry and LE can do a better job of making the prosecution’s cases stronger utilizing infrared technology and thus taking criminals off the street.

This paper shows the current status of cooled IR detector technologies at i3system, South Korea. Mass production technology of i3system has successfully supplied lots of QVGA cooled IR detectors to camera customers. i3system has also developed small pitch cooled IR detectors with 320×256 and 640×512 formats for several different applications such as thermal sights and 24-hour operation observation units. In 2013, i3system’s cooled IR detector has been launched in STSAT(Science and Technology SATellite)-2C through Naro-1 program which was South Korea’s first successful launch vehicle for satellite. Owing to i3system’s robust, intensive design and test programs, IR detector technologies have been space qualified without any further efforts by the space program. Currently, development programs for SXGA(1280×1024) with small pitch cooled detector are being progressed and its status is addressed.

Electro-optical missile seekers pose exceptional requirements for infrared (IR) detectors. These requirements include: very short mission readiness (time-to-image), one-time and relatively short mission duration, extreme ambient conditions, high sensitivity, fast frame rate, and in some cases small size and cost. SCD is engaged in the development and production of IR detectors for missile seeker applications for many years. 0D, 1D and 2D InSb focal plane arrays (FPAs) are packaged in specially designed fast cool-down Dewars and integrated with Joule-Thomson (JT) coolers. These cooled MWIR detectors were integrated in numerous seekers of various missile types, for short and long range applications, and are combat proven. New technologies for the MWIR, such as epi-InSb and XBn-InAsSb, enable faster cool-down time and higher sensitivity for the next generation seekers. The uncooled micro-bolometer technology for IR detectors has advanced significantly over the last decade, and high resolution - high sensitivity FPAs are now available for different applications. Their much smaller size and cost with regard to the cooled detectors makes these uncooled LWIR detectors natural candidates for short and mid-range missile seekers. In this work we will present SCD's cooled and uncooled solutions for advanced electro-optical missile seekers.

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). SOFRADIR and ONERA have launched a new research and innovation partnership, called OSMOSIS, to develop disruptive technologies for DDCA to improve the performance and compactness of optronic systems. With this collaboration, we will break down the technological barriers of DDCA, a sealed and cooled environment dedicated to the infrared detectors, to explore Dewar-level integration of optics. This technological breakthrough will bring more compact multipurpose thermal imaging products, as well as new thermal capabilities such as 3D imagery or multispectral imagery. Previous developments will be recalled (SOIE and FISBI cameras) and new developments will be presented. In particular, we will focus on a dual-band MWIR-LWIR camera and a multichannel camera.

New development of imaging systems implies the use of multi band wavelength, VIS and IR, for imaging enhancement and more data presenting. Some of those systems, such as <see spot<, are designed for applications requiring in plus, the ability to see the aiming point of a laser designator. The use of a designating laser to assist in target identification and tracking can unintentionally result in a laser beam reflected back into the sensor, leading to transient dazzling or permanent damage of the sensor. We propose a novel passive Wideband Protection Filter (WPF) that blocks the transmission only if the power exceeds a certain threshold. We present a special design of WPF suitable for dual- and multi- band wavelength range, including transmission and functionality performances. We demonstrate a new design transferring our WPF filter from VIS/NIR into the MW/LWIR.

To enable higher operating temperatures in InAs/GaSb superlattice detectors for the long-wavelength infrared atmospheric window at 8-12 μm, a reduction of the bulk dark current density is indispensable. To reduce the dark current of conventional homojunction pin-diode device designs, bandstructure-engineering of the active region is considered most promising. So far, several successful device concepts have been demonstrated, yet they all rely on the inclusion of Aluminum within the active layers. Driven by manufacturing aspects we propose an Al-free heterojunction device concept that is based on a p⁺-doped InAs/GaSb superlattice absorber layer combined with an adjacent N^--doped high gap region, which again is realized with an InAs/GaSb superlattice. To calculate the superlattice band gap and the position of the conduction band edge at the heterojunction we employ the Superlattice Empirical Pseudopotential Method. With a series of three heterojunction p⁺N^- InAs/GaSb superlattice devices with an absorber band gap of 124 meV (10.0 μm) we give a first proof of the advocated device concept.

InAs/GaSb Type II superlattices (T2SLs) are a promising III-V alternative to HgCdTe (MCT) for infrared Focal Plane Array (FPA) detectors. Over the past few years SCD has developed the modeling, growth, processing and characterization of high performance InAs/GaSb T2SL detector structures suitable for FPA fabrication. Our LWIR structures are based on an XB_pp design, analogous to the XB_nn design that lead to the recent launch of SCD’s InAsSb HOT MWIR detector (T_OP= 150 K). The T2SL XB_pp structures have a cut-off wavelength between 9.0 and 10.0 μm and are diffusion limited with a dark current at 78K that is within one order of magnitude of the MCT Rule 07 value. We demonstrate 30 μm pitch 5 × 5 test arrays with 100% operability and with a dark current activation energy that closely matches the bandgap energy measured by photoluminescence at 10 K. From the dependence of the dark current and photocurrent on mesa size we are able to determine the lateral diffusion length and quantum efficiency (QE). The QE agrees very well with the value predicted by our recently developed k · p model [Livneh et al, Phys. Rev. B86, 235311 (2012)]. The model includes a number of innovations that provide a faithful match between measured and predicted InAs/GaSb T2SL bandgaps from MWIR to LWIR, and which also allow us to treat other potential candidate systems such as the gallium free InAs/InAsSb T2SL. We will present a critical comparison of InAs/InAsSb vs. InAs/GaSb T2SLs for LWIR FPA applications.

InAs/GaSb superlattices are characterized by a broken-gap type II band alignment. Their effective band gap can be engineered to match mid to long wavelength infrared (IR) photon energies. Fraunhofer IAF has developed image detectors for threat warning systems based on this material system that are capable of spatially and temporally coincident detection in two mid-IR wavelength ranges. We review the present status of the processing technology, report continuous improvements achieved in key areas of detector performance, including defect density and noise behavior, and present initial results for statistical characterization of ensembles of detector elements with respect to diode characteristics and noise.

We first present an electro-optical characterization of the radiometric performances of a type-II InAs/GaSb superlattice (T2SL) pin photodiode operating in the mid-wavelength infrared domain. This photodiode was grown with an InAs-rich structure. We focused our attention on quantum efficiency and responsivity: quantum efficiency of mono-pixel device reaches 23% at λ = 2.1 μm for 1 μm thick SL structure and 77K operating temperature. Then we measured the angular response of this photodiode: the response of the photodiode doesn’t depend on the angle of incidence of the flux. We also report the QE of 2μm-thick InAs-rich T2SL pin 320×256 pixels focal plane array, which reaches 61% at λ = 2.6 μm.

Detectivity of mid-wave infrared (MWIR) detectors based on InAs/GaSb type II strained layer superlattices (T2SLs) can be significantly enhanced at select wavelengths by integrating the detector with a back-side illuminated plasmonic coupler. The application of a simple metal-T2SL structure directly on the GaSb substrate can result in radiation losses into the substrate due to the low refractive index of T2SL layer. However, insertion of a higher refractive index material, such as germanium (Ge), into the metal-SLS structure can confine the surface plasmon waveguide (SPW) modes to the surface. In this work, metal (Au)-Ge-T2SL structures are designed with an approximately 100 nm thick Ge layer. The T2SL layer utilized a p-i-n detector design with 8 monolayers (MLs) InAs/8 MLs GaSb. A plasmonic coupler was then realized inside the 300 μm circular apertures of these single element detectors by the formation of a corrugated metal (Au) surface. The T2SL single element detector integrated with an optimized plasmonic coupler design increased the quantum efficiency (QE) by a factor of three at an operating temperature of 77 K and 3 to 5 μm illumination wavelength, compared to a reference detector structure, and each structure exhibited the same level of dark current.

Focal plane array based on InAs/GaSb type-II superlattice (T2SL) is expected as an alternative to HgCdTe. To get more competitive performance of T2SL detector, we need building up more reliable fabrication process. Especially, mesa formation and passivation with understanding of surface leakage mechanism is critical issue. Generally, the existence of dangling bonds at crystal surface or damaged layer and native oxides on etched mesa sidewall leads to surface leakage currents, which mostly degrade the detector performance. Many researchers adopted SiO2 film as an effective passivation layer, which was deposited by plasma enhanced chemical vapor deposition at low temperature. However, good passivation requires not only stable film, but also an effective surface treatment before passivation. There are few reports, which discuss the relation between treatment before passivation and device characteristics in T2SL photodetectors. In this work, we present dry etching mesa formation and the effect of pretreatment of passivation on T2SL p-i-n photodetector fabrication. We investigate R0A-Perimeter/Area relation and R0A temperature dependence with in-situ plasma treatment prior to the passivation. From results of electrical characterization and interface analysis using STEM, it is recognized that in-situ N2 plasma treatment was effective to surface leakage reduction.

In past decade, T2SL detectors with promising performance have been reported by various institutions thanks to the extensive modeling efforts, improvement of T2SL material quality, and development of advanced low-dark-current architectures with unipolar barriers (Xbn, CBIRD, pBiBn, M-structure, etc). One of the most demanding challenges of present day T2SL technology is the suppression of surface leakage currents associated with the exposed mesa sidewalls, which appear during the definition of device optical area. Typical FPA pixels have large surface/volume ratio and their performance is strongly dependent on surface effects. In order to overcome the limitation imposed by surface leakage currents, a stable surface passivation layer is needed. In this paper we report on InAs/GaSb T2SL detectors operating in the LWIR spectral region (100% cut-off wavelength of ~10 μm at 77K) passivated with epitaxially grown ZnTe. In order to compensate for the high conductivity of ZnTe passivation it was doped with chlorine to 1 × 10¹⁸cm⁻³ concentration. Dark current measurements reveal the significant reduction of noise current after ZnTe passivation.

The effect of defects on the dark current characteristics of MWIR, III-V nBn detectors has been studied. Two different types of defects are compared, those produced by lattice mismatch and by proton irradiation. It is shown that the introduction of defects always elevates dark currents; however the effect on dark current is different for nBn detectors and conventional photodiodes. The dark currents of nBn detectors are found to be more tolerant of defects compared to pn-junction based devices. Defects more weakly increase dark currents, and cooling reduces the defect-produced dark currents more rapidly in nBn detectors than in conventional photodiodes.

Commercially available read out integrated circuits (ROICs) require the FPA to have high dynamic resistance area product at zero bias (R0A) which is directly related to dark current of the detector. Dark current arises from bulk and surface contributions. Recent band structure engineering studies significantly suppressed the bulk contribution of the type-II superlattice infrared photodetectors (N structure, M structure, W structure). In this letter, we will present improved dark current results for unipolar barrier complex supercell superlattice system which is called as “N structure”. The unique electronic band structure of the N structure increases electron-hole overlap under bias, significantly. N structure aims to improve absorption by manipulating electron and hole wavefunctions that are spatially separated in T2SLs, increasing the absorption while decreasing the dark current. In order to engineer the wavefunctions, we introduce a thin AlSb layer between InAs and GaSb layers in the growth direction which also acts as a unipolar electron barrier. Despite the difficulty of perfect lattice matching of InAs and AlSb, such a design is expected to reduce dark current. Experiments were carried out on Single pixel with mesa sizes of 100 × 100 – 700 × 700 μm photodiodes. Temperature dependent dark current with corresponding R0A resistance values are reported.

This paper presents one-dimensional numerical simulations and analytical modeling of InAs nBn detectors having n-type barrier layers with donor concentrations ranging from 1.8×10¹⁵ to 2.5×10¹⁶ cm^-3. We consider only “ideal” defect-free nBn detectors, in which dark current is due only to the fundamental mechanisms of Auger-1 and radiative recombination. We employ a simplified nBn geometry, with the absorber layer (AL) and contact layer (CL) having the same donor concentration and comparable thicknesses, to reveal more clearly the underlying device physics and operation of this novel infrared detector. Our simulations lead to a new model for the ideal nBn with an n-type barrier layer (BL) that consists of two ideal backto- back photodiodes connected by a voltage-dependent series resistance representing hole conduction within the BL. Increasing the BL donor concentration lowers exponentially the hole concentration in the BL, thereby exponentially increasing the BL series resistance. Reductions in dark current and photocurrent due to the valence band barrier in the n-type BL only become appreciable when the BL series resistance becomes comparable to or exceeds the sum of the diffusion current resistances of the AL and CL. This new model elucidates the overwhelming importance of the electrical type and doping concentration of the BL to the operation of the nBn detector.

Recently, a new strategy used to achieve high operation temperature (HOT) infrared photodetectors including III-V compound materials (bulk materials and type-II superlattices) and cascade devices has been observed. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. The barrier detectors are designed to reduce dark current associated with Shockley-Read (SR) processes and to decrease influence of surface leakage current without impeding photocurrent (signal). In consequence, absence of a depletion region in barrier detectors offers a way to overcome the disadvantage of large depletion dark currents. So, they are typically implemented in materials with relatively poor SR lifetimes, such as all III-V compounds. From considerations presented in the paper results that despite numerous advantages of III-V barrier detectors over present-day detection technologies, including reduced tunneling and surface leakage currents, normal-incidence absorption, and suppressed Auger recombination, the promise of a superior performance of these detectors in comparison to HgCdTe photodiodes, has not been yet realized. The dark current density is higher than that of bulk HgCdTe photodiodes, especially in MWIR range. To attain their full potential, the following essential technological limitations such as short carrier lifetime, passivation, and heterostructure engineering, need to be overcome.

We report the result of a dark current measurement of a Type-II superlattice (T2SL) infrared focal plane array (FPA), which consists of a 6 μm cutoff T2SL detector array and the readout integration circuit (ROIC) ISC0903 of FLIR Systems. In order to measure the dark current of the FPA, we obtained images with different exposure times in a fully closed cold shield of 77 K. Using the temporal change rate of the output and considering the charge conversion efficiency of the ROIC, we obtained a dark current density with an average value of 4 × 10^-5 A/cm² at a bias of -100 mV. We also compare the result of the FPA dark current measurement with that of a test element group (TEG), which was a single pixel detector, fabricated by the same process as the FPA. The dark current density of the TEG was 3 × 10^-6 A/cm² at a bias of -100 mV, lower than that of the FPA. We discuss the discrepancy between the dark current densities of the FPA and the TEG.

In this paper we report on an industry first; the growth and characterization of 6" diameter indium antimonide (InSb) substrates that are suitable for use in the fabrication of MWIR focal plane infrared detectors. Results will be presented on the production of single crystal 6" InSb ingots grown by the Czochralski (Cz) technique. We will also assess the electrical quality of new 6" InSb crystals and present uniformity information on Hall mobility, resistivity and carrier level from which we will infer comparisons on the relative dark current performance of the material grown. High quality, epitaxy-ready type surfaces have been prepared and we will demonstrate how the key surface quality characteristics of roughness (<0.5nm rms), oxide thickness (<100Å) and flatness (<7 μm TTV) have been maintained across production processes that scale 4" to 6" wafer formats. We conclude by presenting our road map for the development of large area InSb substrates and describe how developments in Czochralski crystal growth and surface finishing technology will support industry's requirements to deliver higher performance, large format IR focal place array type devices.

Photodiodes based on the GaInAs/InP material system responding in the 1.3-1.7 μm wavelength range are of interest in a wide range of applications, from optical power and channel monitors in telecommunication systems through to advanced night vision imaging using large format focal plane type detectors for defense and security applications. Here we report on our results of GaInAs PIN photo detector structures grown on 2”, 3” and 4” InP substrates by low pressure Metalorganic Chemical Vapor Deposition (MOCVD) in both standard and new larger volume format reactor configurations. High quality, lattice matched InP/GaInAs epitaxial layers were grown and we demonstrate that when moving to larger platen configurations, high degree of thickness uniformity (<3%, FTIR), lattice mismatch (<0.1%, XRD) and compositional uniformity (<2 nm, PL) can be maintained. The surface quality of epitaxial wafers will be assessed by various surface analytical techniques. We also make comparisons with the performance of 2”, 3” and 4” photodetector structures grown, this demonstrating that MOCVD production processes have been successfully scaled. We conclude by discussing the material requirements for large area infrared focal plane array photodetectors and describe how MOCVD growth technology will address industry’s requirements for increasing device sizes with improved performance.

Reactive ion beam etching (RIBE) with CH₄/H₂/Ar or Cl₂/Ar and ion beam etching (IBE) with Ar has been widely used for indium-contained compound semiconductors such as InAs, InP and InSb. To improve the performance of InSb FPAs, reduction of the ion-induced defects and the surface roughness is one of the key issues. To find the optimized plasma etching method for the fabrication of InSb devices, conventional plasma etching processes were comparatively investigated. RIBE of InSb was observed to generate residual by-products such as carbide and chloride causing the degradation of devices. On the other hand, very smooth surface was obtained by etching with N₂. However, the etch rate of the N₂ etching was too slow for the application to the device fabrication. As an alternative way to solve these problems, a multi-step plasma etching process, a combination of the Ar etching and the N₂ etching, for InSb was developed. As gradually increasing the amount of N₂ gas flow during the etching process, the plasma damage causing the surface roughen decreased and consequently smoother surface close to that of N₂ RIE could be obtained. Furthermore, Raman analysis of the InSb surface after the plasma etching indicated clearly that the multi-step etching process was an effective approach in reducing the ion-induced damages on the surface.

The growing demand for short wave infrared (SWIR) sensors and cameras has focused attention on the need for lower cost optics in this infrared region. Traditional low Tg moldable glasses typically stop transmitting in the SWIR region. New low dispersion, moldable glasses have been found that transmit through 3 microns and in combination with Precision Glass Molding (PGM) can bring this enabling technology to SWIR optics. This investigation reviews the material performance for a potential moldable solution in the SWIR range. Specific attention is given toward glasses that achieve high yields during precision glass molding and are candidates for commercial success.

Next-generation infrared (IR) optical components based on chalcogenide glasses (ChGs) may include structures which benefit from the enhanced optical function offered by spatially modifying regions with a nanocrystalline phase. Such modification may be envisioned if the means by which such spatial control of crystallization can be determined using the advantages offered through three-dimensional direct laser write (DLW) processes. While ChGs are well known to have good transparency in the IR, they typically possess lower thresholds for photo- and thermally- induced property changes as compared to other glasses such as silicates. Such low thresholds can result in material responses that include photoexpansion, large thermo-optic increases, mechanical property changes, photo-induced crystallization, and ablation. The present study examines changes in ChG material response realized by exposing the material to different laser irradiation conditions in order to understand the effects of these conditions on such material property changes. Thresholds for photoexpansion and ablation were studied by varying the exposure time and power with sub-bandgap illumination and evidence of laser induced phase change were examined. Simulations were carried out to estimate the temperature increase from the irradiation and the tolerances and stability of the calculations were examined. The models suggest that the processes may have components that are non-thermal in nature.

Laser durable multiband high reflective optics can be realized by depositing densified HfO₂/SiO₂ multilayers on aluminum alloy substrates. To further understand the impact of surface finishing and cleaning on laser-induced damage of multiband high reflective optics, 1” diameter witness samples were characterized by means of spectrophotometry, atomic force microscopy, confocal laser scanning microscopy, white light interferometry, scanning electron microscopy, and laser-induced damage threshold tests performed at 1064 nm, 20 ns, 20 Hz, and near normal angle of incidence. Laser-induced damage thresholds of 12.5 J/cm² and 47 J/cm² were obtained on a stained witness and unstained witness, respectively. A two-step laser damage process was proposed based on the post-damage analysis. The results suggest that nodule defects are the limiting factor for laser-induced damage thresholds. There exists the potential in aluminum-based dielectric coated multiband reflective optics for extremely high power laser applications.

Fabrication process of arsenic-sulfide (As-S) and arsenic-selenide (As-Se) optical fibers has been improved to enhance the transmission in the mid-IR region. Typical attenuation spectrum of As-S or As-Se optical fibers shows impurities bands, such as S-H, Se-H, O-H, which limit their operation and cause the increase of the attenuation loss in the mid-IR. Precursors purification methods and glass processing were improved to minimise those impurities bands. Regarding As- S fibers, the attenuation around 2.7 μm is 0.12 dB/m and S-H concentration is lower than 0.3 ppm. In the case of As-Se fibers, the minimum of attenuation located at 6 μm is 0.2 dB/m and Se-H concentration is lower than 0.5 ppm. Efforts have been also made to improve the mechanical properties which are usually affected by several parameters such as drawing conditions or heterogeneous inclusions contained in the glass. The double-crucible method gives high quality core/clad interface and consequently increases the strength of the fiber. Inclusions consist mainly of carbon and silica particles. Those impurities enter the glass from initial precursors and are also formed by interaction with the apparatus material. Thanks to the process improvement, impurities particles are minimized and tensile strengths up to 0.32 GPa and 0.41 GPa are reached for As-Se and As-S fibers respectively.

High operating temperature (HOT) IR-detectors are a key factor to size, weight and power (SWaP) reduced IR-systems. Such systems are essential to provide infantrymen with low-weight handheld systems with increased battery lifetimes or most compact clip-on weapon sights in combination with high electro-optical performance offered by cooled IR-technology. AIM’s MCT standard n-on-p technology with vacancy doping has been optimized over many years resulting in MWIR-detectors with excellent electro-optical performance up to operating temperatures of ~120K. In the last years the effort has been intensified to improve this standard technology by introducing extrinsic doping with Gold as an acceptor. As a consequence the dark current could considerably be suppressed and allows for operation at ~140K with good e/o performance. More detailed investigations showed that limitation for HOT > 140K is explained by consequences from rising dark current rather than from defective pixel level. Recently, several crucial parameters were identified showing great promise for further optimization of HOT-performance. Among those, p-type concentration could successfully be reduced from the mid 10¹⁶ / cm³ to the lower 10¹⁵/ cm³ range. Since AIM is one of the leading manufacturers of split linear cryocoolers, an increase in operating temperature will directly lead to IR-modules with improved SWaP characteristics by making use of the miniature members of its SX cooler family with single piston and balancer technology. The paper will present recent progress in the development of HOT MWIR-detector arrays at AIM and show electro-optical performance data in comparison to focal plane arrays produced in the standard technology.

In 2012 Selex ES demonstrated High Operating Temperature (HOT) MCT detectors with 5μm cut-off wavelength and f/4 aperture operating at temperatures above 200K. These detectors are grown by Metal Organic Vapour Phase Epitaxy (MOVPE) which enables fine control over the photo-diode structure. Since 2012 Selex has created two further generations of MOVPE HOT MCT, progressively improving operability and yield. This paper presents performance data for Selex’s third generation of HOT MCT technology and describes the improvements to the diode design and materials processing that have enabled these advances. A parallel program has developed miniature Dewars with lower heatload and reduced manufacturing costs. When integrated with the latest generation of miniature linear cryo-engines the required cooler power is reduced to the region of 1W at temperatures of 200K. This paper will present example imagery from a detector operating with <1 Watt cooler input power. The combination of third generation HOT MCT, high efficiency Dewars and miniature linear coolers will allow a drastic reduction in SWAP-C for long range hand-held thermal imagers.

Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD, which operates in the blue part of the MWIR atmospheric window (3.4 - 4.2 μm). This window is generally more transparent than the red part of the MWIR window (4.4 - 4.9 μm), and thus is especially useful for mid and long range applications. The detector has an InAsSb active layer and is based on the new "XBn" device concept, which eliminates Generation-Recombination dark current and enables operation at temperatures of 150K or higher, while maintaining excellent image quality. Such high operating temperatures reduce the cooling requirements of Focal Plane Array (FPA) detectors dramatically, and allow the use of a smaller closed-cycle Stirling cooler. As a result, the complete Integrated Detector Cooler Assembly (IDCA) has about 60% lower power consumption and a much longer lifetime compared with IDCAs based on standard InSb detectors and coolers operating at 77K. In this work we present a new large format IDCA designed for 150K operation. The 15 μm pitch 1280×1024 FPA is based on SCD's XBn technology and digital Hercules ROIC. The FPA is housed in a robust Dewar and is integrated with Ricor's K508N Stirling cryo-cooler. The IDCA has a weight of ~750 gram and its power consumption is ~ 5.5 W at a frame rate of 100Hz. The Mean Time to Failure (MTTF) of the IDCA is more than 20,000 hours, greatly facilitating 24/7 operation.

Progress on development of lead-salt thermoelectrically-cooled (TE-cooled) imaging sensors will be presented. The imaging sensor architecture has been integrated into field-ruggedized hardware, and supports the use of lead-salt based detector material, including lead selenide and lead sulfide. Images and video are from a lead selenide focal plane array on silicon ROIC at temperatures approaching room temperature, and at high frame rates. Lead-salt imagers uniquely possess three traits: (1) Sensitive operation at high temperatures above the typical ‘cooled’ sensor maximum (2) Photonic response which enables high frame rates faster than the bolometric, thermal response time (3) Capability to reliably fabricate 2D arrays from solution-deposition directly, i. e. monolithically, on silicon. These lead-salt imagers are less expensive to produce and operate compared to other IR imagers based on II-VI HgCdTe and III-V InGaAsSb, because they do not require UHV epitaxial growth nor hybrid assembly, and no cryo-engine is needed to maintain low thermal noise. Historically, there have been challenges with lead-salt detector-to-detector non-uniformities and detector noise. Staring arrays of lead-salt imagers are promising today because of advances in ROIC technology and fabrication improvements. Non-uniformities have been addressed by on-FPA non-uniformity correction and 1/f noise has been mitigated with adjustable noise filtering without mechanical chopping. Finally, improved deposition process and measurement controls have enabled reliable fabrication of high-performance, lead-salt, large format staring arrays on the surface of large silicon ROIC wafers. The imaging array performance has achieved a Noise Equivalent Temperature Difference (NETD) of 30 mK at 2.5 millisecond integration time with an f/1 lens in the 3-5 μm wavelength band using a two-stage TE cooler to operate the FPA at 230 K. Operability of 99.6% is reproducible on 240 × 320 format arrays.

Low-frequency noise has been studied in a mid-wavelength infrared InAs/GaSb type-II superlattice-based focal plane array. Low-frequency noise is observed under reverse bias but not at zero bias, even in the presence of photo-current. The magnitude of low-frequency noise was separately measured as a function of operating temperature and operation bias. The low-frequency noise is linearly correlated with the generation-recombination component of the dark current. No correlation of low-frequency noise with photo-current or diffusion dark current was found.

Recently, a new strategy used to achieve high operation temperature (HOT) infrared photodetectors including III-V compound materials (bulk materials and type-II superlattices) and cascade devices has been observed. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. The barrier detectors are designed to reduce dark current associated with Shockley-Read (SR) processes and to decrease influence of surface leakage current without impeding photocurrent (signal). In consequence, absence of a depletion region in barrier detectors offers a way to overcome the disadvantage of large depletion dark currents. So, they are typically implemented in materials with relatively poor SR lifetimes, such as all III-V compounds. From considerations presented in the paper results that despite numerous advantages of III-V barrier detectors over present-day detection technologies, including reduced tunneling and surface leakage currents, normal-incidence absorption, and suppressed Auger recombination, the promise of a superior performance of these detectors in comparison to HgCdTe photodiodes, has not been yet realized. The dark current density is higher than that of bulk HgCdTe photodiodes, especially in MWIR range. To attain their full potential, the following essential technological limitations such as short carrier lifetime, passivation, and heterostructure engineering, need to be overcome.

The Interband Cascade (IC) detector with InAs/Ga(In)Sb type-II superlattice (T2-SL) absorbers is a new type of high-performance infrared photodetector that has many unique features. In this IC detector design, the T2-SL absorber is sliced into multiple thinner segments that are sandwiched between electron and hole barriers, forming one stage. Multiple stages are electrically connected in series. The asymmetric energy-band alignment and ultra-fast carrier transport channel have enabled IC detectors to operate under/near zero-bias. The large lifetime contrast and the great design flexibility make IC detectors very suitable for high temperature operations. Our effort has led to the demonstration of mid-IR single pixel devices operating up to 450 K under zero-bias. These devices achieved superior electrical performance compared to HgCdTe technology at higher operation temperatures. In this presentation, we will discuss the new developments of low-noise mid-IR IC photodetectors and their focal plane arrays. Device studies on the influence of design on their optical and electrical performance will be discussed, and the most recent technical progress is also reported.

The nBn structure with an electron barrier sandwiched by n-type cap and absorber layers was predicted to suppress the Shockley-Read-Hall (SRH) generation-recombination processes and surface leakage. The MCT nBn structure has been studied by several groups to implement high operating temperature (HOT) device. In this report, the numerical analysis of the Hg_1-xCd_xTe nBn device in LWIR region (x=0.225) is performed utilizing Crosslight APSYS. The detector performance characterized by dark current, photo-current and detectivity is optimized by adjusting structural parameters such as Cd component and doping of each layer under various biases. Among the parameters, the trade-off between ΔEc and ΔEv is most intensively affected by Cd component of the barrier which was modified carefully and accomplished firstly. Furthermore, the effect of the trap density and trap energy level on the device performance is also investigated especially according to the processing techniques. At 110K, the optimized detectivity of the LWIR MCT nBn device reaches 7.5×10¹⁰ cmHz^1/2/W in this report, comparable with that of the DLPH device (7.6×10¹⁰ cmHz^1/2/W). The novel nBn HgCdTe structure is potentially valuable in LWIR region since the controllable p-doping issue is circumvented and passivation process is simplified.

This paper presents the results of an advanced digital IRFPA-family developed by Fraunhofer IMS. The IRFPA-family compromises the two different optical resolutions VGA (640 ×480 pixel) and QVGA (320 × 240 pixel) by using a pin-compatible detector board. The uncooled IRFPAs are designed for thermal imaging applications in the LWIR (8 .. 14μm) range with a full-frame frequency of 30 Hz and a high thermal sensitivity. The microbolometer with a pixel-pitch of 17μm consists of amorphous silicon as the sensing layer. By scaling and optimizing our previous microbolometer technology with a pixel-pitch of 25μm we enhance the thermal sensitivity of the microbolometer. The microbolometers are read out by a novel readout architecture which utilizes massively parallel on-chip Sigma-Delta-ADCs. This results in a direct digital conversion of the resistance change of the microbolometer induced by incident infrared radiation. To reduce production costs a chip-scale-package is used as vacuum package. This vacuum package consists of an IR-transparent window with an antireflection coating and a soldering frame which is fixed by a wafer-to-chip process directly on top of the CMOS-substrate. The chip-scale-package is placed onto a detector board by a chip-on-board technique. The IRFPAs are completely fabricated at Fraunhofer IMS on 8” CMOS wafers with an additional surface micromachining process. In this paper the architecture of the readout electronics, the packaging, and the electro-optical performance characterization are presented.

Silicon-based vacuum packaging is a key enabling technology for achieving affordable uncooled Infrared Focal Plane Arrays (IRFPA) required by a promising mass market that shows momentum for some extensive consumer applications, such as automotive driving assistance, smart presence localization and building management. Among the various approaches studied worldwide, CEA, LETI in partnership with ULIS is committed to the development of a unique technology referred to as PLP (Pixel Level Packaging). In this PLP technology, each bolometer pixel is sealed under vacuum using a transparent thin film deposition on wafer. PLP operates as an array of hermetic micro caps above the focal plane, each enclosing a single microbolometer. In continuation of our on-going studies on PLP for regular QVGA IRFPAs, this paper emphasizes on the innate scalability of the technology which was successfully demonstrated through the development of an 80 × 80 pixel IRFPA. The relevance of the technology with regard to the two formats is discussed, considering both performance and cost issues. We show that the suboptimal fill factor inherent to the PLP arrangement is not so critical when considering smaller arrays preferably fitted for consumer applications. The discussion is supported with the electro-optical performance measurements of the PLP-based 80×80 demonstrator.

This paper presents the development of a miniature LWIR thermal camera, MSE070D, which targets value performance infrared imaging applications, where a 160x120 CMOS-based microbolometer FPA is utilized. MSE070D features a universal USB interface that can communicate with computers and some particular mobile devices in the market. In addition, it offers high flexibility and mobility with the help of its USB powered nature, eliminating the need for any external power source, thanks to its low-power requirement option. MSE070D provides thermal imaging with its 1.65 inch³ volume with the use of a vacuum packaged CMOS-based microbolometer type thermal sensor MS1670A-VP, achieving moderate performance with a very low production cost. MSE070D allows 30 fps thermal video imaging with the 160x120 FPA size while resulting in an NETD lower than 350 mK with f/1 optics. It is possible to obtain test electronics and software, miniature camera cores, complete Application Programming Interfaces (APIs) and relevant documentation with MSE070D, as MikroSens want to help its customers to evaluate its products and to ensure quick time-to-market for systems manufacturers.

Vanadium oxide (VO_x) and hydrogenated silicon germanium (Si_xGe_1-x) are the two predominant thin film material systems used as the active layer in resistive infrared imaging. Thin films of VOx used in microbolometers have a resistivity typically between 0.1 and 1 Ω-cm with a temperature coefficient of resistance, |TCR| between 1.4%/K to 2.4%/K, while Si_xGe_1-x:H thin films have a resistivity between 200-4,000 Ω-cm with a |TCR| between 2.9%/K to 3.9%/K. Future devices may require higher TCR materials, however, higher TCR is loosely associated with higher resistivity and therefore also with high noise. This work compares 1/f noise of high resistivity VO_x and Ge:H thin films having |TCR| < 3.6%/K. The high TCR thin films of VO_x were found to be amorphous while, depending on the deposition conditions, the Ge:H thin films were either amorphous or mixed phase of amorphous + nanocrystalline. Evaluation of these VO_x and Ge:H thin films indicates a prospects for a superior process-property relation of 1/f noise in Ge:H thin films in comparison with thin films of VO_x.

Unmanned aerial vehicles (UAVs) and smart munitions require low-cost IR sensors that fit within very small volumes, yet offer acceptable performance and landing/launch survivability. The LWIR band provides unique contrast for specific applications in both UAVs and smart munitions, with smart munitions presenting an additional challenge of high g-loads during launch. These high g-loads are not typically a design target of low-cost, un-cooled commercial off the shelf (COTS) LWIR sensors. This work addresses the challenges of adapting a COTS un-cooled LWIR imager for launch survivability. The sensor was modeled for mechanical stability and weaknesses identified. Modifications were made to improve launch survivability and multiple units were tested. Data is presented on the optical performance as measured through the modulation transfer function (MTF) both before and after launches for multiple locations across the lens.

This paper reports on the deposition of vanadium oxide thin films with sheet resistance uniformity better than 2.5% over a 150 mm wafer. The resistance uniformity within the array is estimated to be less than 1%, which is comparable with the value reported for amorphous silicon-based microbolometer arrays. In addition, this paper also shows that the resistivity of vanadium oxide, like amorphous silicon, can be modeled by Arrhenius' equation. This result is expected to significantly ease the computation of the correction table required for TEC-less operation of VO_x-based microbolometer arrays.

Vanadium oxide (VO_x) thin films have been intensively used as sensing materials for microbolometers. VO_x thin films have good bolometric properties such as low resistivity, high negative temperature coefficient of resistivity (TCR) and low 1/f noise. However, the processing controllability of VO_x fabrication is difficult due to the multiple valence states of vanadium. In this study, metal oxides such as nickel oxide (NiO_x) and molybdenum oxide (MoO_x) thin films have been investigated as possible new microbolometer sensing materials with improved process controllability. Nickel oxide and molybdenum oxide thin films were prepared by reactive sputtering of nickel and molybdenum metal targets in a biased target ion beam deposition tool. In this deposition system, the Ar⁺ ion energy (typically lower than 25 eV) and the target bias voltage can be independently controlled since ions are remotely generated. A residual gas analyzer (RGA) is used to precisely control the oxygen partial pressure. A real-time spectroscopic ellipsometry is used to monitor the evolution of microstructure and properties of deposited oxides during growth and post-deposition. The properties of deposited oxide thin films depend on processing parameters. The resistivity of the NiO_x thin films is in the range of 0.5 to approximately 100 ohm-cm with a TCR from -2%/K to -3.3%/K, where the resistivity of MoO_x is between 3 and 2000 ohm-cm with TCR from -2.1%/K to -3.2%/K. We also report on the thermal stability of these deposited oxide thin films.

A polarization-selective uncooled infrared (IR) sensor has been developed based on an asymmetric two-dimensional plasmonic absorber (2-D PLA). The 2-D PLA has a Au-based 2-D periodic dimple structure, where photons can be manipulated by spoof surface plasmon polaritons. Asymmetry was introduced into the 2-D PLA to realize a polarization selective function. Numerical investigations demonstrate that a 2-D PLA with ellipsoidal dimples (2-D PLA-E) gives rise to polarization-dependent absorption properties due to the asymmetric dimple shape. A microelectromechanical systems-based uncooled IR sensor was fabricated using a 2-D PLA-E through a complementary metal oxide semiconductor (CMOS) and micromachining techniques. The 2-D PLA-E was formed by a Au layer sputtered on a SiO2 layer with ellipsoidal holes. An Al layer was then introduced on the backside of the 2-D PLA-E to reflect scattered light and prevent absorption at the SiO2 substrate. Measurement of the responsivity dependence on the polarization shows that the responsivity is selectively enhanced depending on the polarization and the asymmetry of the ellipse. The results provide direct evidence that a polarization-selective uncooled IR sensor can be realized simply by introducing asymmetry to the surface structure of a 2-D PLA without any polarizer or optical resonant structures. In addition, a pixel array where each pixel has a different detection polarization could be developed for polarimetric imaging using standard CMOS and micromachining techniques.

A MEMS cantilever IR detector that repetitively lifts from the surface under the influence of a saw-tooth electrostatic force, where the contact duty cycle is a measure of the absorbed IR radiation, is analyzed. The design is comprised of three parallel conducting plates. Fixed buried and surface plates are held at opposite potential. A moveable cantilever is biased the same as the surface plate. Calculations based on energy methods with position-dependent capacity and electrostatic induction coefficients demonstrate the upward sign of the force on the cantilever and determine the force magnitude. 2D finite element method calculations of the local fields confirm the sign of the force and determine its distribution across the cantilever. The upward force is maximized when the surface plate is slightly larger than the other two. The electrostatic repulsion is compared with Casimir sticking force to determine the maximum useful contact area. MEMS devices were fabricated and the vertical displacement of the cantilever was observed in a number of experiments. The approach may be applied also to MEMS actuators and micromirrors.

Pyroelectric detector is a class of thermal detector in which the change in temperature causes the change in the spontaneous polarization in the sensing material. In this work, we report the design of uncooled pyroelectric detectors which utilized a nanometer sized truss to support the suspended detector. The design and performance of pyroelectric detectors have been conducted by simulating the structure with Intellisuite™ utilizing Finite Element Method (FEM). The simulated detectors had a spider web-like structure with each of the strut of spider web had a width of 100 nm. Ca modified lead titanate (PCT) was employed as the thermometer because of its high pyroelectric figure of merit. The pyroelectric detectors utilized Ni_0.8Cr_0.2 absorber, PCT sensing layer, Ti electrodes, Al₂O₃ structural layer to obtain low thermal conductance between the detector and Si substrate. Three different types of pyroelectric detectors were designed and analyzed. The first design had linear electrode and simple spider web support. The value of the thermal conductance of this detector was found to be 3.98×10^-8 W/K. The second design had a longer thermal path than the first one and had a thermal conductivity of 2.41×10^-8 W/K. The design was optimized for the best result by modifying the shape, dimension and thickness of various layers namely absorber, electrodes, sensing layer and struts. The thermal conductance of the third design was found to be as low as 4.57×10^-9 W/K which is significantly lower than previously reported values. The highest calculated detectivity and reponsivity values were 1.15 × 10¹⁰ cm Hz^1/2/W and 4.9 × 10⁷ V/W respectively.

The beetle Melanophila acuminata detects forest fires from distances as far as 80 miles away. To accomplish this, the beetle uses highly specific IR receptors with a diameter of approximately 15 μm. These receptors are mechanoreceptors that detect deformations induced by the absorption of radiation. Although the detection mechanism is understood in principle, it is still unclear how the beetle reaches such high sensitivity. In this work, we present the biomimetic approach of an uncooled IR sensor based on the beetle’s receptors. This sensor is based on a fluid-filled pressure cell and operates at room temperature. Upon absorbing IR radiation, the fluid heats up and expands. The expanding fluid deflects one electrode of a plate capacitor. By measuring the change in capacitance, the volume increase and the absorbed energy can be inferred. To prevent the risk of damage at high energy absorption, a compensation mechanism is presented in this work. The mechanism prevents large but slow volume changes inside the pressure cell by a microfluidic connection of the pressure cell with a compensation chamber. The channel and the compensation chamber act as a microfluidic low-pass filter and do not affect the overall sensitivity above an appropriate cut-off frequency. Using MEMS technology, we are able to incorporate the complete system into a silicon chip with an area of a few mm². Here, we show a proof-of-concept and first measurements of the sensor.

In this work, a novel fabrication method for VOx-ZnO multilayers with mixed phase of the VO₂ and V₂O₃ through the diffusion of oxygen by annealing at low temperature is presented. A stable sandwich structure of a VOx/ZnO/VOx multilayer was deposited at room temperature, through the oxygen gas flow rate, by RF sputtering system, and the mixed phase was formed through oxygen diffusion by annealing at O₂ atmosphere. The results show that the single phase like multilayer formed by this process has a high TCR of more than -2.5%/K and low resistance of about 100 kohm at room temperature. XRD results for the as-deposited VOx/ZnO/VOx multilayer.

A three-dimensional plasmonic metamaterial absorber (3-D PMA) was theoretically investigated and designed for the performance enhancement of wavelength selective uncooled infrared (IR) sensors. All components of the 3-D PMA are based on thin layers of plasmonic metals such as Au. The post produces a narrow gap, such as a few hundred nanometers, between the micropatch and the metal plate. The absorption properties of the 3-D PMA were investigated by rigorous coupled-wave analysis. A strong wavelength selective absorption is realized by the plasmonic resonant mode of the micropatch and the narrow-gap resonant mode between the micropatch and the plate. The disturbance of the post for both resonance modes is negligible. The absorption wavelength is defined mainly by the size of the micropatch, regardless of the micropatch array period and is longer than the micropatch array period. The absorption mode can also be controlled by the shape of the micropatch. Through-holes can be formed on the plate area, where there is no gap resonance to the micropatch. The thickness of each component can be reduced considering the skin depth effect and there is no added absorption of materials such as SiO₂. A small pixel size with reduced thermal mass can be realized using a 3-D PMA structure. The results obtained here will contribute to the development of high-performance uncooled IR sensors for multicolor imaging.

We present a design for a low-noise bolometer linear array based on the temperature-dependent conductivity of a VO_x- Au film. Typical thin film bolometers must compromise between low resistivity to limit Johnson noise and high temperature coefficient of resistivity (TCR) to maximize responsivity. Our vanadium oxide is alloyed with a small concentration of gold by co-sputtering, which gives very low resistivity and very high TCR simultaneously. The film is fabricated on an air bridge device having high thermal conductivity and small thermal time constant optimized for 30 to 60 Hz frame rates. The linear array functions as a low-power profile sensor with a modulated bias. For 1 V bias, we predict responsivity exceeding 1200 V/W. Johnson noise dominates with predicted NEP values as low as 1.0 × 10^-11 W/Hz^1/2. Preliminary device testing shows film resistivity below 2.5 Ω-cm with TCR exceeding -2.0%. Preliminary measurements of NEP and D* are reported.

Thermomechanical noise for a MEMs-based infrared detector using null switching (US patent 7977635) depends on vibrational amplitude, since IR radiation is transduced to a change in the duty cycle of a repetitively closing switch. Equipartition theorem gives a maximum rms vibrational amplitude of 45 pm for the fabricated cantilever switch at its natural frequency. This gives a worst case timing uncertainty of 700 ns and an NEP of 2 pW/Sqrt[Hz].

This paper introduces a method for a broadband absorption enhancement in the LWIR range (8-12 μm), in single layer microbolometer pixels with 35 μm pitch. For the first time in the literature, this study introduces a very simple and low cost approach to enhance the absorption by embedding plasmonic structures at the same level as the already existing metallic layer of a microbolometer pixel. The metal layer comprises the electrode and the arm structures on the body. Even though the periodicity of the plasmonic structures is slightly disturbed by the placement of the electrodes and the connecting metal, the metal arms and the electrodes compensate for the lack of the periodicity contributing to the resonance by their coupling with the individual plasmonic resonators. Various plasmonic structures are designed with FDTD simulations. Individual, plasmonically modified microbolometer pixels are fabricated, and an increase in the average absorption due to surface plasmon excitation at Au/Si₃N₄ interfaces is observed. Plasmonic structures increase the average absorption from 78% to 82% and result in an overall enhancement of 5.1%. A good agreement between the simulation and the FTIR measurement results are obtained within the LWIR range. This work paves the way for integration of the plasmonic structures within conventional microbolometer devices for performance enhancement without introducing additional costs.

This paper presents a digital ROIC for staring type arrays with extending counting method to realize very low quantization noise while achieving a very high charge handling capacity. Current state of the art has shown that digital readouts with pulse frequency method can achieve charge handling capacities higher than 3Ge^- with quantization noise higher than 1000e^-. Even if the integration capacitance is reduced, it cannot be lower than 1-3 fF due to the parasitic capacitance of the comparator. For achieving a very low quantization noise of 161 electrons in a power efficient way, a new method based on measuring the time to measure the remaining charge on the integration capacitor is proposed. With this approach SNR of low flux pixels are significantly increased while large flux pixels can store electrons as high as 2.33Ge^-. A prototype array of 32×32 pixels with 30μm pitch is implemented in 90nm CMOS process technology for verification. Measurement results are given for complete readout.

In many high dynamic range applications, Sigma-Delta modulator (SDM) architectures have displaced most other architectures for analog to digital conversion (ADC). SDMs have not typically been applied to ROIC applications due to the interaction of spatial discontinuities and the temporal bandwidth limitation of the SDM. By using a novel serpentine readout sequence, we have reduced the temporal bandwidth and enabled application of SDM technology for high dynamic range Focal Plane Arrays (FPA). In addition, it is reconfigurable on-the-fly for a power vs. Signal to Noise plus Distortion Ratio (SNDR) tradeoff without “binning” or reducing the pixel pitch. This technique has been applied to enable low power foveal imaging. This reconfigurable ADC has been coupled with a low noise extended dynamic range photodiode input stages.

This paper reports the development of a new microbolometer Readout Integrated Circuit (ROIC) called MT3825BA. It has a format of 384 × 288 and a pixel pitch of 25μm. MT3825BA is Mikro-Tasarim’s second microbolometer ROIC product, which is developed specifically for resistive surface micro-machined microbolometer detector arrays using high-TCR pixel materials, such as VO_x and a-Si. MT3825BA has a system-on-chip architecture, where all the timing, biasing, and pixel non-uniformity correction (NUC) operations in the ROIC are applied using on-chip circuitry simplifying the use and system integration of this ROIC. The ROIC is designed to support pixel resistance values ranging from 30 KΩ to 100 KΩ. MT3825BA is operated using conventional row based readout method, where pixels in the array are read out in a row-by-row basis, where the applied bias for each pixel in a given row is updated at the beginning of each line period according to the applied line based NUC data. The NUC data is applied continuously in a row-by-row basis using the serial programming interface, which is also used to program user configurable features of the ROIC, such as readout gain, integration time, and number of analog video outputs. MT3825BA has a total of 4 analog video outputs and 2 analog reference outputs, placed at the top and bottom of the ROIC, which can be programmed to operate in the 1, 2, and 4-output modes, supporting frames rates well above 60 fps at a 3 MHz pixel output rate. The pixels in the array are read out with respect to reference pixels implemented above and below actual array pixels. The bias voltage of the pixels can be programmed over a 1.0 V range to compensate for the changes in the detector resistance values due to the variations coming from the manufacturing process or changes in the operating temperature. The ROIC has an on-chip integrated temperature sensor with a sensitivity of better than 5 mV / K, and the output of the temperature sensor can be read out the output as part of the analog video stream. MT3825BA can be used to build a microbolometer FPAs with an NETD value below 100 mK using a microbolometer detector array fabrication technology with a detector resistance value up to 100 KΩ, a high TCR value (< 2 % / K), and a sufficiently low pixel thermal conductance (G_th ≤ 20 nW / K). MT3825BA measures 13.0 mm × 13.5 mm and is fabricated on 200 mm CMOS wafers. The microbolometer ROIC wafers are engineered to have flat surface finish to simplify the wafer level detector fabrication and wafer level vacuum packaging (WLVP). The ROIC runs on 3.3 V analog and 1.8 V digital supplies, and dissipates less than 85 mW in the 2-output mode at 30 fps. Mikro-Tasarim provides tested ROIC wafers and offers compact test electronics and software for its ROIC customers to shorten their FPA and camera development cycles.

Implementation of a CMOS digital readout integrated circuit (DROIC) based on pixel level digital time delay integration (TDI) for scanning type LWIR focal plane arrays (FPAs) is presented. TDI is implemented on 8 pixels with over sampling rate of 3. Analog signal integrated on integration capacitor is converted to digital domain in pixel, and digital data is transferred to TDI summation counters, where contributions of 8 pixels are added. Output data is 16 bit, where 8 bits are allocated for most significant bits and 8 bits for least significant bits. Control block of the ROIC, which is responsible of generating timing diagram for switches controlling the pixels and summation counters, is realized with VerilogHDL. Summation counters and parallel-to-serial converter to convert 16 bit parallel output data to single bit output are also realized with Verilog HDL. Synthesized verilog netlists are placed&routed and combined with analog under-pixel part of the design. Quantization noise of analog-to-digital conversion is less than 500e-. Since analog signal is converted to digital domain in-pixel, inaccuracies due to analog signal routing over large chip area is eliminated. ROIC is fabricated with 0.18μm CMOS process and chip area is 10mm². Post-layout simulation results of the implemented design are presented. ROIC is programmable through serial or parallel interface. Input referred noise of ROIC is less than 750 rms electron, while power consumption is less than 30mW. ROIC is designed to perform in cryogenic temperatures.

With the growth of uncooled infrared imaging in the consumer market, the balance between cost implications and performance criteria in the objective lens must be examined carefully. The increased availability of consumer-grade, long-wave infrared cameras is related to a decrease in military usage but it is also due to the decreasing costs of the cameras themselves. This has also driven up demand for low-cost, long-wave objectives that can resolve smaller pixels while maintaining high performance. Smaller pixels are traditionally associated with high cost objectives because of higher resolution requirements but, with careful consideration of all the requirements and proper selection of materials, costs can be moderated. This paper examines the cost/performance trade-off implications associated with optical and mechanical requirements of long-wave infrared objectives. Optical performance, f-number, field of view, distortion, focus range and thermal range all affect the cost of the objective. Because raw lens material cost is often the most expensive item in the construction, selection of the material as well as the shape of the lens while maintaining acceptable performance and cost targets were explored. As a result of these considerations, a low-cost, lightweight, well-performing objective was successfully designed, manufactured and tested.

In an electro-optical sensor suite for long range surveillance tasks the optics for the visible (450nm – 700nm) and the SWIR spectral wavelength range (900nm – 1700 nm) are combined with the receiver optics of an integrated laser range finder (LRF) .The incoming signal from the observed scene and the returned laser pulse are collected within the common entrance aperture of the optics. The common front part of the optics is a broadband corrected lens design from 450 – 1700nm wavelength range. The visible spectrum is split up by a dichroic beam splitter and focused on a HDTV CMOS camera. The returned laser pulse is spatially separated from the scene signal by a special prism and focused on the laser receiver diode of the integrated LRF. The achromatic lens design has a zoom factor 14 and F#2.6 in the visible path. In the SWIR path the F-number is adapted to the corresponding chip dimensions . The alignment of the LRF with respect to the SWIR camera line of sight can be controlled by adjustable integrated wedges. The two images in the visible and the SWIR spectral range match in focus and field of view (FOV) over the full zoom range between 2° and 22° HFOV. The SWIR camera has a resolution of 640×512 pixels. The HDTV camera provides a resolution of 1920×1080. The design and the performance parameters of the multispectral sensor suite is discussed.

There are many applications for zoom systems which operate through a range of working distances while at the same time allowing multiple zoom levels or a smoothly varying magnification range. The problems involved in creating a system to support such applications are greater than either a fixed focal length system or a zoom system operating with an image at infinity. In this paper we will explore some of the optical and mechanical issues involved in such efforts, the tradeoffs between high optical performance and simple mechanical designs, and provide some of the solutions we’ve developed to address these issues.

Folded path reflection and catadioptric optics are of growing interest, especially in the long wave infrared (LWIR), due to continuing demands for reductions in imaging system size, weight and power (SWAP). We present the optical design and laboratory data for a 50 mm focal length low f/# folded-path compact LWIR imaging system. The optical design uses 4 concentric aspheric mirrors, each of which is described by annular aspheric functions well suited to the folded path design space. The 4 mirrors are diamond turned onto two thin air-spaced aluminum plates which can be manually focused onto the uncooled LWIR microbolometer array detector. Stray light analysis will be presented to show how specialized internal baffling can be used to reduce stray light propagation through the folded path optical train. The system achieves near diffraction limited performance across the FOV with a 15 mm long optical train and a 5 mm back focal distance. The completed system is small enough to reside within a 3 inch diameter ball gimbal.

Tunable, narrow-wavelength spectral filters with a ms response in the mid-wave/long-wave infrared (MW/LWIR) are an enabling technology for hyperspectral imaging systems. Few commercial off-the-shelf (COTS) components for this application exist, including filter wheels, movable gratings, and Fabry-Perot (FP) etalon-based devices. These devices can be bulky, fragile and often do not have the required response speed. Here, we present a fundamentally different approach for tunable reflective IR filters, based on coupling subwavelength plasmonic antenna arrays with liquid crystals (LCs). Our device operates in reflective mode and derives its narrow bandwidth from diffractive coupling of individual antenna elements. The wavelength tunability of the device arises from electrically-induced re-orientation of the LC material in intimate contact with antenna array. This re-orientation, in turn, induces a change in the local dielectric environment of the antenna array, leading to a wavelength shift. We will first present results of full-field optimization of micron-size antenna geometries to account for complex 3D LC anisotropy. We have fabricated these antenna arrays on IR-transparent CaF2 substrates utilizing electron beam lithography, and have demonstrated tunability using 5CB, a commercially available LC. However, the design can be extended to high-birefringence liquid crystals for an increased tuning range. Our initial results demonstrate <60% peak reflectance in the 4- 6 μm wavelength range with a tunability of 0.2 μm with re-orientation of the surface alignment layers. Preliminary electrical switching has been demonstrated and is being optimized.

Extreme light-weighting is important in many aerospace and defense applications but the cost associated with beryllium or other exotic materials can be prohibitive. The current standard for producing cost effective, high performance mirrors is to diamond machine mirror blanks from aluminum alloy stock. About 80% material removal is the limit for geometrical lightweighting while still retaining the structural integrity required for optical fabrication. To reduce weight further requires alternative materials. This paper summarizes the status of diamond machined finishing and coating of magnesium alloys to produce cost effective, lightweight mirrors with high, broadband reflectivity and low scatter finish.

ZERODUR^®, known as the “gold standard” material for systems which require dimensional stability in the presence of gradients and transients, is now available lightweighted to the 85% to 90% level for use in high performance spaceborne telescopes and sensor systems. This establishes a design option that may have cost, testability, performance and risk advantages for an entire sensor system payload. The technical approach to making these primary mirrors is the same, whether the aperture is <0.3m to <4.0m. Since each mirror blank is made from a single monolithic billet of near zero-expansion, isotropic and homogeneous ZERODUR^® material, the resulting mirror is very stable over a wide range of scenes and orbits, with minimal to no need for ancillary thermal stability and wavefront sensing and control systems. Telescopes using ZERODUR^® and low expansion metering structures can accommodate thermal design challenges of both non-thermal (UV, VIS, LLLTV, NIR, SWIR and mm) and thermal (MWIR, LWIR) imaging systems, and deliver optimal performance. This lightweight mirror technology is discussed, with actual examples by SCHOTT of 0.3m and 1.2m mirrors presented. Lightweight ZERODUR^® mirrors offer superior optical performance, attractive cost and aggressive lead times, and are available to present and future spaceborne sensor trades.

The growing demand for lower cost infrared sensors and cameras has focused attention on the need for low cost optics for the long wave and mid-wave infrared region. The thermal properties of chalcogenides provide benefits for optical and optomechanical designers for the athermalization of lens assemblies as compared to Germanium, Zinc Selenide and other more common infrared materials. This investigation reviews typical infrared materials’ thermal performance and the effects of temperature on the optical performance of lens systems manufactured from various optical materials.

The thermal imaging market has experienced a strong growth during the recent years due to continued cost reduction of night vision devices. The development of uncooled focal plane detector arrays is the major reason for the cost reduction. Another reason is the continuous improvement of the optical solution. In this paper, we present a new multispectral material which responds to the increasing demand for optics operating simultaneously in the visible/SWIR (Short Wave InfraRed) and the thermal infrared region. The most important properties of some glasses from the GeS2-Ga2S3- CsCl system are highlighted in this study. A stable composition 15Ga₂S₃-75GeS₂-10CsCl allowed the synthesis of a large glass without crystallization. The refractive index of this glass was precisely measured from 0.6 to 10.4μm by using the Littrow method. The chromatic dispersion was then calculated and compared with other multispectral materials.

We report new materials that transmit from 0.9 to > 14 μm in wavelength and fill up the glass map for multispectral optics having refractive index from 2.38 to 3.17. They show a large spread in dispersion (Abbe number) and offer some unique solutions for multispectral optics designs. The new IR glasses can be easily molded and also fused together to make bonded doublets. We present the benefits of these new materials through dual-band optics designs and compare to designs using currently available crystalline materials.

The development of organic polymers with low infrared absorption has been investigated as a possible alternative to inorganic metal oxide, semiconductor, or chalcogenide-based materials for a variety of optical devices and components, such as lenses, goggles, thermal imaging cameras and optical fibers. In principle, organic-based polymers are attractive for these applications because of their low weight, ease of processing, mechanical toughness, and facile chemical variation using commercially available precursors. Herein we report on the optical characterization of a new class of sulfur copolymers that are readily moldable, transparent above 500 nm, possess high refractive index (n > 1.8) and take advantage of the low infrared absorption of S-S bonds for potential use in the mid-infrared at 3-5 microns. These materials are largely made from elemental sulfur by an inverse vulcanization process; in the current study we focus on the properties of a chemically stable, branched copolymer of poly(sulfur-random-1,3-diisopropenylbenzene) (poly(S-r- DIB). Copolymers with elemental sulfur content ranging from 50% to 80% by weight were studied by UV-VIS spectroscopy, FTIR, and prism coupling for refractive index measurement. Clear correlation between material composition and the optical properties was established, confirming that the high polarizability of the sulfur atom leads to high refractive index while also maintaining low optical loss in the infrared.

A technique for fabricating novel infrared (IR) lenses can enable a reduction in the size and weight of IR imaging optics through the use of layered glass structures. These structures can range from having a few thick glass layers, mimicking cemented doublets and triplets, to having many thin glass layers approximating graded index (GRIN) lenses. The effectiveness of these structures relies on having materials with diversity in refractive index (large Δn) and dispersion and similar thermo-viscous behavior (common glass transition temperature, ΔTg = 10°C). A library of 13 chalcogenide glasses with broad IR transmission (NIR through LWIR bands) was developed to satisfy these criteria. The lens fabrication methodology, including glass design and synthesis, sheet fabrication, preform making, lens molding and surface finishing are presented.

Solid-state optical refrigeration is an emerging cooling technology that can provide vibration free and reliable refrigeration to cryogenic temperatures in a lightweight and compact device. The technology has matured over the past two decades and is currently being considered for applications where the mechanical vibrations, limited reliability, or insufficient portability of existing cooling technologies pose challenges. Possible applications include satellite-borne infrared imaging, laser metrology, and gamma-ray spectroscopy as well as high-reliability cooling of semiconductors and high-temperature superconductors. The best results achieved so far have been in cooling rare-earth-doped solids, especially materials doped with ytterbium. We discuss the fundamental physical principles of solid-state laser cooling, the resulting material and device design requirements, and the estimated payload heat lift of an optical cryocooler.

In a Stirling-type pulse-tube cooler with a dual-opposed piston compressor, the residual vibration exported by the cooler is primarily a result of residual imbalances between compressor motors. Using an electronic feedback loop ^[1] and driving compressor motors in a master-slave configuration, the exported force from the compressor can be regulated to negligible levels. This has been demonstrated in a multitude of commercial applications ^[2] as well as in space applications. In a novel application of the same electronic feedback technology, the residual exported forces resulting from the motion of the free moving displacer of a Stirling cold finger are compensated, by using the linear dual-opposed piston compressor as an active balancer. Theoretical analysis of this is provided, measurements are presented on different cooler types, and the effect of integration aspects - hard mount versus suspended – is discussed. The effect on exported vibration as well as power efficiency is discussed and compared between Stirling and pulse-tube type coolers. Currently available off-the-shelf hardware, the CDE7232, is presented and future developments are discussed.

The world growth in research and development of High Operating Temperature IR detectors impels the development process and the optimization of HOT Cryocoolers at RICOR. The development emphasizes the “SWaP” configuration which is Small Size, Low Weight and Low Power consumption, in order to optimize IDDCA for future hand held thermal sights and other various applications. This paper will present optimization tests results performed on HOT Lab Demonstration Cryocoolers at the temperature range of 130 - 180K 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. The new Cryocoolers developed for HOT detectors aim for higher reliability which is analyzed and reported in the paper.

Cryogenically cooled infrared electro-optical payloads have to operate and survive frequent exposure to harsh vibrational and shock conditions typical of the modern battlefield. This necessitates the development of special approaches to ruggedizing their sensitive components. The ruggedization requirement holds true specifically for Integrated Dewar-Detector Assemblies (IDDA), where the infrared Focal Plane Array (FPA) is usually supported by a thin-walled cold finger enveloped by an evacuated tubular Dewar. Without sufficient ruggedization, harsh environmental vibration may give rise to structural resonance responses resulting in spoiled image quality and even mechanical fractures due to material fatigue. The authors present their approach for the ruggedization of the IDDA by attaching the FPA to a semi-rigid support extending from the dynamically damped Dewar envelope. A mathematical model relies on an experimentally evaluated set of frequency response functions for a reference system and a lumped model of a wideband dynamic absorber. By adding only 2% to the weight of the IDDA, the authors have managed to attenuate the relative deflection and absolute acceleration of the FPA by a factor of 3. The analytical predictions are in full agreement with experiment.

Significantly increased FPA temperatures for both Mid Wave and Long Wave IR detectors, i.e. HOT detectors, which have been developed in recent years are now leaving the development phase and are entering real application. HOT detectors allowing to push size weight and power (SWaP) of Integrated Detectors Cooler Assemblies (IDCA’s) to a new level. Key component mainly driving achievable weight, volume and power consumption is the cryocooler. AIM cryocooler developments are focused on compact, lightweight linear cryocoolers driven by compact and high efficient digital cooler drive electronics (DCE) to also achieve highest MTTF targets. This technology is using moving magnet driving mechanisms and dual or single piston compressors. Whereas SX030 which was presented at SPIE in 2012 consuming less 3 WDC to operate a typical IDCA at 140K, next smaller cooler SX020 is designed to provide sufficient cooling power at detector temperature above 160K. The cooler weight of less than 200g and a total compressor length of 60mm makes it an ideal solution for all applications with limited weight and power budget, like in handheld applications. For operating a typical 640x512, 15μm MW IR detector the power consumption will be less than 1.5WDC. MTTF for the cooler will be in excess of 30,000h and thus achieving low maintenance cost also in 24/7 applications. The SX020 compressor is based on a single piston design with integrated passive balancer in a new design achieves very low exported vibration in the order of 100mN in the compressor axis. AIM is using a modular approach, allowing the chose between 5 different compressor types for one common Stirling expander. The 6mm expander with a total length of 74mm is now available in a new design that fits into standard dewar bores originally designed for rotary coolers. Also available is a 9mm coldfinger in both versions. In development is an ultra-short expander with around 35mm total length to achieve highest compactness. Technical solutions and key performance data for AIM’s HOT cryocoolers will be presented.

Closed-cycle cryogenic refrigerators, or cryocoolers, are an enabling technology for a wide range of aerospace applications, mostly related to infrared (IR) sensors. While the industry focus has tended to be on the mechanical cryocooler thermo mechanical unit (TMU) alone, implementation on a platform necessarily consists of the combination of the TMU and a mating set of command and control electronics. For some applications the cryocooler electronics (CCE) are technologically simple and low cost relative to the TMU, but this is not always the case. The relative cost and complexity of the CCE for a space-borne application can easily exceed that of the TMU, primarily due to the technical constraints and cost impacts introduced by the typical space radiation hardness and reliability requirements. High end tactical IR sensor applications also challenge the state of the art in cryocooler electronics, such as those for which temperature setpoint and frequency must be adjustable, or those where an informative telemetry set must be supported, etc. Generally speaking for both space and tactical applications, it is often the CCE that limits the rated lifetime and reliability of the cryocooler system. A family of high end digital cryocooler electronics has been developed to address these needs. These electronics are readily scalable from 10W to 500W output capacity; experimental performance data for nominally 25W and 100W variants are presented. The combination of a FPGA-based controller and dual H-bridge motor drive architectures yields high efficiency (>92% typical) and precision temperature control (± 30 mK typical) for a wide range of Stirling-class mechanical cryocooler types and vendors. This paper focuses on recent testing with the AIM INFRAROT-MODULE GmbH (AIM) SX030 and AIM SF100 cryocoolers.

In response to continuing requirements for smaller, lighter, and lower power cryocoolers for tactical IR applications, DRS Technologies has developed its smallest linear drive cooler for the micro-Integrated Dewar Cooler Assembly (μIDCA). The entire cooler/Dewar assembly occupies slightly more than 4 cubic inches in a rectangular form that measures about 1-inch by 2-inch by 2-inches. The design goals and constraints are presented and the resulting design is discussed. Operating parameters and testing results are summarized. In addition to the review of the μDCA cryocooler, this paper presents a brief update of long-term reliability and life testing for a variety of DRS’ linear drive cryocoolers. This testing program was initiated in the 1990’s and has demonstrated cooler lifetimes in excess of 50,000 hours.

The growing demand for Electro Optic (EO) applications that work around the clock 24hr/7days a week, such as in border surveillance systems, emphasizes the need for a highly reliable Cryocooler having increased operational availability and decreased integrated system Life Cycle (ILS) cost. In order to meet this need, RICOR has developed Integral Rotary and Split Linear Cryocoolers technologies which meet this challenge. RICOR’s Cryocoolers reliability characteristics are assessed by analytical reliability models, demonstrated by normal and accelerated life tests and finally verified by field data. The paper will focus on the reliability evaluation models for different technologies, report and analyze life demonstration test data at different mission profiles and verify the results by fielded Cryocoolers operating as a feedback to approve the theoretical assumptions and calculation models. In addition, it will review the system's end user needs and expectations from advanced high reliable Cryocoolers.

InfraRed (IR) sensor systems like night vision goggles, missile approach warning systems and telescopes have an increasing interest in decreasing their size and weight. At the same time optical aberrations are always more difficult to optimize with larger Focal Plane Arrays (FPAs) and larger field of view. Both challenges can now take advantage of a new optical parameter thanks to flexible microelectronics technologies: the FPA spherical curvature. This bio-inspired approach can correct optical aberrations and reduce the number of lenses in camera conception. Firstly, a new process to curve thin monolithic devices has been applied to uncooled microbolometers FPAs. A functional 256×320 25μm pitch (roughly 1cm²) uncooled FPA has been thinned and curved. Its electrical response showed no degradation after our process (variation of less than 2.3% on the response). Then a two lenses camera with a curved FPA is designed and characterized in comparison with a two lenses camera with a flat FPA. Their Modulation Transfer Functions (MTFs) show clearly an improvement in terms of beams dispersion. Secondly, a new process to fabricate monolithic cooled flip-chip MCT-IRCMOS FPAs was developed leading to the first spherical cooled IR FPA: with a radius of 550 mm. Other radii are achieved. A standard opto-electrical characterization at 80 K of the imager shows no additional short circuit and no mean response alteration compared to a standard IRCMOS shown in reference. Noise is also studied with a black body between 20 and 30°C.

This paper reports on the status of advanced infrared detectors exploiting Metal-Organic Vapour Phase Epitaxy (MOVPE) grown HgCdTe on GaAs at Selex ES. MOVPE has the maturity and flexibility to enable 3^rd generation devices to be custom engineered to achieve small pixels, higher operating temperature, high sensitivity and tailored spectral response. The MOVPE technology has now been exploited in the latest development of avalanche photodiodes and single photon imaging is reported. In support of this the latest ROICs have been designed to be compatible with APD operation.

In today’s typical military operations situational awareness is a key element for mission success. In contrast to what is known from conventional warfare with typical targets such as tanks, asymmetric scenarios now dominate military operations. These scenarios require improved identification capabilities, for example the assessment of threat levels posed by personnel targets. Also, it is vital to identify and reliably distinguish between combatants, non-combatants and friendly forces. To satisfy these requirements, high-definition (HD) large format systems are well suited due to their high spatial and thermal resolution combined with high contrast. Typical applications are sights for long-range surveillance, targeting and reconnaissance platforms as well as rotorcraft pilotage sight systems. In 2012 AIM presented first prototypes of large format detectors with 1280 × 1024 elements in a 15μm pitch for both spectral bands MWIR and LWIR. The modular design allows integration of different cooler types, like AIM’s split linear coolers SX095 or SX040 or rotary integral types depending whatever fits best to the application. Large format FPAs have been fabricated using liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE) grown MCT. To offer high resolution in a more compact configuration AIM started the development of a 1024 × 768 10μm pitch IRmodule. Keeping electro/optical performance is achieved by a higher specific charge handling capacity of the readout integrated circuit (ROIC) in a 0.18μm Si CMOS technology. The FPA size fits to a dewar cooler configuration used for 640 × 512 15μm pitch modules.

Sofradir IR detectors are being deployed in a lengthening line of space applications (earth observation, atmospheric observation, scientific missions, etc…), and also in the whole range of tactical applications (portable cameras, missile seekers, land, airborne and naval systems, etc…). Sofradir is taking advantage of these two areas. Firstly, space applications are developing new advances and technologies that can later be introduced in the production of IR detectors for tactical applications, thereby increasing their quality and reliability. In addition, Sofradir can better satisfy space application requirements for failure rates, as these can only be demonstrated with the large number of detectors manufactured, which tactical applications provide. As a result, this approach offers a continuous cycle for reliability of IR detectors, accelerating reliability growth in production, and at the same time meeting requirements for space applications. This paper presents recent improvements introduced in production lines of HgCdTe detectors, that increase performances, image quality, and reliability.

We propose plasmonic metal-insulator-metal (MIM) metamaterial designs for the sensing of two infrared wavelength bands, the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) band by using a photon sorting technique. The proposed structures can capture light effectively on the metasurfaces based on coupling of free space energy to a subwavelength plasmonic mode. Photon sorting can be performed such that the incident light with a broad spectrum upon the metasurfaces can be "split" according to wavelength, channeling different spectral bands to different physical regions of the array on the surface where it is then absorbed by the insulator. Two different structures described in this work are (1) Square-type structure which consists of MIM resonators being periodically arranged to form a polarization independent sensor and (2) Meander-type structure which consists of MIM resonators being connected to form the meander shaped sensor. Mercury Cadmium Telluride (HgCdTe) posts are used as absorbing material within the MIM structure to generate free carriers and allow for collection of carrier charges. The proposed structures have compact designs and exhibit efficient light splitting and absorption for the IR spectral band. Structural and material properties, the electric field distribution and Poynting vector fields at the resonance frequencies are provided. Applications include thermal imaging, night vision systems, rifle sights, missile detection and discrimination, dual bandwidth optical filters, light trapping, and electromagnetically induced transparency.

Since 2005, in the scope of “DEFIR”, the joint laboratory between CEA-LETI and SOFRADIR, p-on-n photodiodes and FPAs (Focal Plane Arrays) have been developed and optimised. This p-on-n architecture, obtained by As implantation into an In doped base layer, offered a significant decrease of the dark current compared to our n-on-p standard architecture. Following these developments, this p-on-n technology has been successfully transferred to SOFRADIR for industrial production [1]. Results obtained on TV format, 15μm pitch, showed that this first architecture has reached its maturity with excellent results in LWIR and MWIR. In parallel, further developments and studies are still in progress at CEA-LETI in order to improve the photodiode performance and understanding of the physical mechanisms. In this way, new p-on-n architectures have been studied on LPE (Liquid Phase Epitaxy) in the VLWIR spectral band. Using this new architecture, the transition temperature, where the dark current shifts from diffusion limited regime to another one, has been lowered by more than 10K. Extremely low dark current has been obtained, down to 50 e-/s/pixel. The p-on-n technology also been studied at DEFIR in SWIR range specifically for space applications were 2Kx2K MCT arrays are required with dark current below 0.01e-/s at 18μm pitch in the 80-140 K. Finally in the MWIR and LWIR spectral bands, the reduction of production cost and the increase of resolution call for smaller pixel pitches with larger format. In this way, first results have been obtained on test diodes with pixel pitch as low as 5 μm. The I(V) and R(V) plots illustrate the very good characteristic of our p-on-n diodes. These photodiodes present large reverse breakdown voltage, witnessing the quality of our device fabrication procedure.

This paper reports on the disappearance of photosensitive area extension effect and the novel temperature dependence of junction performance for mid-wavelength HgCdTe detectors. The performances of junction under different temperatures are characterized by laser beam induced current (LBIC) microscope. The physical mechanism of temperature dependence on junction transformation is elaborated and demonstrated using numerical simulations. It is found that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation depended on temperature, and wider band gap compared with the long-wavelength HgCdTe photodiode may correlate with the disappearance of photosensitive area extension effect.

In this work, a novel junction profile measurement method is proposed. A serial of junctions were fabricated by B+ implantation. Then a beveled bar which was about 10mm long and several micrometers deep was formed by carefully controlled wet-etching. The remaining depth of n region changes from the full depth that is about 5.3mm after ion implantation to zero depending on its lateral position and the slope of the etching bar. Voltage-current and Laser Beam Induced Current (LBIC) measurements were applied to determine the HgCdTe junction edge. The LBIC signal orrectification characteristic indicates the existence of a PN junction. The junction depth is extracted from the position where the PN junction disappears and the slope of the etching bar. The junction depth of intrinsic doped HgCdTe was measured, which is about 2.4μm. A significant 0.4mm thick N-region was observed. Moreover, junction depths of samples annealed for different time were also investigated. By this method, it’s possible to measure the three dimensional profile of a planar PN junction.

Large area HgCdTe focal plane arrays (FPAs) are now available with a 5um pitch, and excellent performance. This analysis examines the benefits associated with ultra-small pixels in enabling not only a reduction in system size, weight, and power, but also an improvement in system thermal performance. A comparison is made between today’s III-V and HgCdTe materials technologies, regarding both performance in today’s FPAs, and the ultimate achievement of background- and diffraction-limited photon detection at room temperature for all spectral bands.

Infrared detector pixel pitch has been decreasing, driven by interest in higher resolution, larger displays, and decreased cost. Previous generations of focal plane arrays (FPAs) were on 50, 40, 30, and 20μm pitch. 12μm pitch FPAs are now available. DRS Network and Imaging Systems has developed ultra-small 5μm pitch infrared detectors for the long-wave infrared (LWIR) and medium-wave infrared (MWIR) bands as part of the DARPA AWARE Lambda Scale effort. The smaller pitch was achieved using DRS’ high-density vertically integrated photodiode (HDVIP®) architecture. This technology is a major advance in the state of the art for infrared imaging sensors. The pixel density of 4 million pixels/cm² enables the production of lower cost FPAs from HDTV resolution up to many millions of pixels. Dark current, collection efficiency, cross-talk, and operability are similar to larger pitch HDVIP FPAs.

Recent advances in miniaturization of IR imaging technology have led to a burgeoning market for mini thermalimaging sensors. Seen in this context our development on smaller pixel pitch has opened the door to very compact products. When this competitive advantage is mixed with smaller coolers, thanks to HOT technology, we achieve valuable reductions in size, weight and power of the overall package. In the same time, we are moving towards a global offer based on digital interfaces that provides our customers lower power consumption and simplification on the IR system design process while freeing up more space. Additionally, we are also investigating new wafer level camera solution taking advantage of the progress in micro-optics. This paper discusses recent developments on hot and small pixel pitch technologies as well as efforts made on compact packaging solution developed by SOFRADIR in collaboration with CEA-LETI and ONERA.

Infrared Focal Plane Arrays have been developed with reductions in pixel size below the Nyquist limit imposed by the optical systems Point Spread Function (PSF). These smaller sub diffraction limited pixels allows spatial oversampling of the image. We show that oversampling the PSF allows improved fidelity in imaging, resulting in sensitivity improvements due to pixel correlation, reduced false alarm rates, improved detection ranges, and an improved ability to track closely spaced objects.

The actual trend in quantum IR detector development is the design of very small pixel pitch large arrays. From previously 30μm pitch, the standard pixel pitch is today 15μm and is expected to decrease to 12μm in the next few years. Furthermore, focal plane arrays (FPA) with pixel pitch as small as small as 10μm has been demonstrated. Such ultra-small pixel pitches are very small compared to the typical length ruling the electrical characteristics of the absorbing materials, namely the minority carrier diffusion length. As an example for low doped N type HgCdTe or InSb material, this diffusion length is of the order of 30 to 50μm, i.e. 3 to 5 times the targeted pixel pitches. This has strong consequences on the modulation transfer function (MTF) for planar structures, where the lateral extension of the photodiode is limited by diffusion. For such aspect ratios, the self-confinement of neighboring diodes may not be efficient enough to maintain optimal MTF. Therefore, this issue has to be addressed in order to take full benefits of the pixel pitch reduction in terms of image resolution. This paper aims at investigating the MTF evolution of HgCdTe and InSb FPAs decreasing the pixel pitch below 15μm. Both experimental measurements and finite element simulations are used to discuss this issue. Different scenarii will be compared, namely deep mesa etch between pixels, internal drift, surface recombination, thin absorbing layers.

The quantum efficiency of QWIPs is difficult to predict and optimize. Recently, we have established a quantitative 3- dimensional electromagnetic model for QE computation. In this work, we used this model to design and optimize new detector structures. In one approach, we adjusted the detector volume to resonate strongly with the scattered light from the diffractive elements (DEs). The resulting intensified field increases the detector QE correspondingly. We tested this resonator-QWIP concept on four detector materials and obtained satisfactory agreements between theory and experiment. The observed single detector QE ranges from 15 to 71%, depending on the realized pixel geometry and the matching detector material. We processed one of the materials into hybridized FPAs and observed a QE of 30% with a conversion efficiency of 11%, in agreement with theory. By using rings as DEs, the FPA spectral nonuniformity can also be minimized with an observed value of 4% in comparison with the 7% for gratings. With a proven EM model, we further designed different R-QWIPs for a wide range of applications, including high conversion efficiency detection, narrow band detection through a medium, narrow band detection at a gaseous medium, simultaneous two-color detection, sequential voltage tunable two-color detection, and broadband detection at Landsat wavelengths. Experimental efforts are underway.

The Surface Plasmonic Resonances (SPRs) excited by two complementary Plasmonic structures, 2 dimensional metallic disc array (2DMDA) and subwavlength hole array (2DSHA), are simulated and analyzed. The 2DMDA and 2DSHA enhancement on quantum dot infrared photodetectors (QDIPs) are also evaluated and compared. The 2DSHA give a large peak photocurrent enhancement about 40 times, whereas the 2DMDA provide 10 times with broad band enhancement. The cause of the difference in enhancement is analyzed. It’s indicated that the QDIP enhancement depends on the interaction of the plasmonic fields with the quantum dots (QDs). Based on the experimental and simulations results, suggestions are provided for future improving the device enhancement. The results reported in this paper consolidate our efforts in bringing the innovative view of plasmonic research through two complementary plasmonic structures.

RTI has developed a novel photodiode technology based on solution-processed PbS colloidal quantum dots (CQD) capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. The most significant advantages of the CQD technology are ease of fabrication, small pixel size, and extended wavelength range. The devices are fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. We will discuss recent advances in device architecture and processing that result in measured dark currents of 15 nA/cm² at room temperature and enhanced SWIR responsivity from the UV to ~1.7 μm, compare these results to InGaAs detectors, and present measurements of the CQD detectors temperature dependent dark current.

Human factors issues related to head mounted imaging systems have driven the requirements for system latency to nearly the bounds of sensor physics. Image processing must therefore be performed in an envelope that is ever decreasing in size. This paper presents a complete method for intelligent fusion of a long wave infrared and visible sensor, including contrast enhancement in both spectrums, with end to end processing latency of less than 1 millisecond. The use of image statistics and opponent color theory allows fusion with minimal computational resources and latency. This algorithm has demonstrated performance without inducing any noticeable human factors issues during user trials.

A digital pixel CMOS focal plane array has been developed to enable low latency implementations of image processing systems such as centroid trackers, Shack-Hartman wavefront sensors, and Fitts correlation trackers through the use of in-pixel digital signal processing (DSP) and generic parallel pipelined multiply accumulate (MAC) units. Light intensity digitization occurs at the pixel level, enabling in-pixel DSP and noiseless data transfer from the pixel array to the peripheral processing units. The pipelined processing of row and column image data prior to off chip readout reduces the required output bandwidth of the image sensor, thus reducing the latency of computations necessary to implement various image processing systems. Data volume reductions of over 80% lead to sub 10μs latency for completing various tracking and sensor algorithms. This paper details the architecture of the pixel-processing imager (PPI) and presents some initial results from a prototype device fabricated in a standard 65nm CMOS process hybridized to a commercial off-the-shelf short-wave infrared (SWIR) detector array.

“Lucky-region” fusion (LRF) is a synthetic imaging technique that has proven successful in enhancing the quality of images distorted by atmospheric turbulence. The LRF algorithm extracts sharp regions of an image obtained from a series of short exposure frames, and fuses the sharp regions into a final, improved image. In our previous research, the LRF algorithm had been implemented on a PC using the C programming language. However, the PC did not have sufficient processing power to handle real-time extraction, processing and reduction required when the LRF algorithm was applied to real-time video from fast, high-resolution image sensors rather than single picture images. This document describes a hardware implementation of the LRF algorithm on a VIRTEX-7 field programmable gate array (FPGA) to achieve real-time image processing. The novelty in our approach is the creation of a “black box” LRF video processing system with a general camera link input, a user controller interface, and a camera link or DVI video output. We also describe a custom hardware simulation environment we have built to test our LRF implementation.

Smart pixel imaging with computational-imaging arrays (SPICA) transfers image plane coding typically realized in the optical architecture to the digital domain of the focal plane array, thereby minimizing signal-to-noise losses associated with static filters or apertures and inherent diffraction concerns. MIT Lincoln Laboratory has been developing digitalpixel focal plane array (DFPA) devices for many years. In this work, we leverage legacy designs modified with new features to realize a computational imaging array (CIA) with advanced pixel-processing capabilities. We briefly review the use of DFPAs for on-chip background removal and image plane filtering. We focus on two digital readout integrated circuits (DROICS) as CIAs for two-dimensional (2D) transient target tracking and three-dimensional (3D) transient target estimation using per-pixel coded-apertures or flutter shutters. This paper describes two DROICs – a SWIR pixelprocessing imager (SWIR-PPI) and a Visible CIA (VISCIA). SWIR-PPI is a DROIC with a 1 kHz global frame rate with a maximum per-pixel shuttering rate of 100 MHz, such that each pixel can be modulated by a time-varying, pseudorandom, and duo-binary signal (+1,-1,0). Combining per-pixel time-domain coding and processing enables 3D (x,y,t) target estimation with limited loss of spatial resolution. We evaluate structured and pseudo-random encoding strategies and employ linear inversion and non-linear inversion using total-variation minimization to estimate a 3D data cube from a single 2D temporally-encoded measurement. The VISCIA DROIC, while low-resolution, has a 6 kHz global frame rate and simultaneously encodes eight periodic or aperiodic transient target signatures at a maximum rate of 50 MHz using eight 8-bit counters. By transferring pixel-based image plane coding to the DROIC and utilizing sophisticated processing, our CIAs enable on-chip temporal super-resolution.

This paper discusses a Biologically Inspired Shortwave Infrared (SWIR) imager that performs on chip object detection using temporal and spatial processing embedded in the imager’s readout integrated circuit (ROIC). The sensor circuit is designed to detect pixel level intensity changes and correlate the change with nearby intensity changes using multiple thresholding criteria to output object exceedances. The sensor is capable of automatically outputting both normal video and also a reduced data set of binarized exceedances. Therefore this SWIR sensor with onboard temporal spatial sensing should be well suited to both manned and unmanned sensing scenarios which could benefit from automated object detection and reduced data sets.

ARINC 818, titled Avionics Digital Video Bus (ADVB), is the standard for cockpit video that has gained wide acceptance in both the commercial and military cockpits including the Boeing 787, the A350XWB, the A400M, the KC- 46A and many others. Initially conceived of for cockpit displays, ARINC 818 is now propagating into high-speed sensors, such as infrared and optical cameras due to its high-bandwidth and high reliability. The ARINC 818 specification that was initially release in the 2006 and has recently undergone a major update that will enhance its applicability as a high speed sensor interface. The ARINC 818-2 specification was published in December 2013. The revisions to the specification include: video switching, stereo and 3-D provisions, color sequential implementations, regions of interest, data-only transmissions, multi-channel implementations, bi-directional communication, higher link rates to 32Gbps, synchronization signals, options for high-speed coax interfaces and optical interface details. The additions to the specification are especially appealing for high-bandwidth, multi sensor systems that have issues with throughput bottlenecks and SWaP concerns. ARINC 818 is implemented on either copper or fiber optic high speed physical layers, and allows for time multiplexing multiple sensors onto a single link. This paper discusses each of the new capabilities in the ARINC 818-2 specification and the benefits for ISR and countermeasures implementations, several examples are provided.

Some new filters inspired in quantum models are used as edge detectors in infrared images. In this case, Bessel, Hermite and Morse filters will be applied to detect edges and fibrillar structures in infrared images. The edge detectors will be built by the Laplacian of the mentioned quantum filters. Furthermore, using curvature operators, curvature detectors and amplifiers of contrast will be constructed to analyze infrared images. The quantum filter prototyping will be done using computer algebra software, specifically Maple and its package, ImageTools. The quantum filters will be applied to infrared images using the technique of convolutions and blurred derivatives. It is expected that designed quantum filters will be useful for analysis and processing of infrared images. As future investigations, we propose to design plugins with the quantum filters that can be incorporated into the program ImageJ, which will facilitate the use of the quantum filters for the infrared image processing.

Commercially available hardware, freely available algorithms, and authors’ developed software are synergized successfully to detect and recognize subjects in an environment without visible light. This project integrates three major components: an illumination device operating in near infrared (NIR) spectrum, a NIR capable camera and a software algorithm capable of performing image manipulation, facial detection and recognition. Focusing our efforts in the near infrared spectrum allows the low budget system to operate covertly while still allowing for accurate face recognition. In doing so a valuable function has been developed which presents potential benefits in future civilian and military security and surveillance operations.

Covert, long-range, night/day identification of stationary human subjects using face recognition has been previously demonstrated using the active-SWIR Tactical Imager for Night/Day Extended-Range Surveillance (TINDERS) system. TINDERS uses an invisible, eye-safe, SWIR laser illuminator to produce high-quality facial imagery under conditions ranging from bright sunlight to total darkness. The recent addition of automation software to TINDERS has enabled the autonomous identification of moving subjects at distances greater than 100 m. Unlike typical cooperative, short range face recognition scenarios, where positive identification requires only a single face image, the SWIR wavelength, long distance, and uncontrolled conditions mean that positive identification requires fusing the face matching results from multiple captured images of a single subject. Automation software is required to initially detect a person, lock on and track the person as they move, and select video frames containing high-quality frontal face images for processing. Fusion algorithms are required to combine the matching results from multiple frames to produce a high-confidence match. These automation functions will be described, and results showing automated identification of moving subjects, night and day, at multiple distances will be presented.