Previously, we have reported on advances made with our CTIA based TEC-less SWIR cameras [1, 2, 3, 4]. Here, we present our next generation TEC-less small SWaP SWIR cameras which are built upon a current mirror type pixel. The standard packaged FPAs are modified by replacing the TECs with copper shims. These FPAs are incorporated into cameras with similar electronics to our COTS cameras (CSX and JSX series), and then fully characterized from -30 °C to 60 °C. From these data, we developed algorithms that provide temperature-based corrections resulting in nonuniformity of approximately 0.5 % over the entire operating temperature. Additionally, over this range, the 640 x 512 resolution camera exhibited power consumption in the 1.2-1.3 W range, whereas the 1280 x 1024 camera exhibited power consumption in the 1.3-1.4 W range.

In recent years SCD has developed InGaAs/InP technology for Short-Wave Infrared (SWIR) imaging. The first product, Cardinal 640, has a 640x512 (VGA) format at 15μm pitch, and more than a thousand units have already been delivered. We now present Cardinal 1280, having the smallest pitch available today (10μm), with a 1280x1024 (SXGA) format. Cardinal 1280 addresses both long-range daylight imaging, and passive or active imaging in Low Light Level (LLL) conditions. The Readout Integrated Circuit supports snapshot imaging at 13 bit resolution with a frame rate of 160Hz at full format, or a frame rate of 640Hz with 2x2 binning. It also has a Low Noise Imaging (LNIM) mode with 35ereadout noise with internal Correlated Double Sampling (CDS). An asynchronous Laser Pulse Detection (ALPD) mode is implemented with 2x2 binning in parallel to SWIR imaging (with 10 μm resolution). The new 10 μm pixel is sensitive down to the visible (VIS) spectrum, with a typical dark current of ~ 0.5fA at 280K, and a quantum efficiency >80% at 1550nm. The Focal Plane Array is integrated into a ruggedized, high vacuum integrity, metallic package, with a Thermo- Electric Cooler (TEC) for optimized performance, and a high grade Sapphire window. In this paper we will present the architecture and preliminary measurement results.

SiOnyx has extended the spectral sensitivity of a high performance low cost CMOS image sensor to cover the spectral band from 400nm to 1200nm. The enhanced quantum efficiency is combined with a CMOS sensor design that demonstrates state of the art read noise characteristics and low fixed pattern noise. The resultant sensor exhibits high signal to noise ratio throughout all lighting conditions from noon day sun to moonless clear starlight. In outdoor nighttime conditions, the extended quantum efficiency at wavelengths beyond 1000nm enables the silicon sensor to image “nightglow” illumination. This spectral range has historically only been accessible using non-silicon based SWIR sensors. This enables a true digital nightvision sensor with demonstrated imaging performance at 60 FPS at light levels below 1 mLux. The quantum efficiency enhancement is achieved by utilizing SiOnyx’s proprietary ultrafast laser semiconductor processing technology that enhances the absorption of light within a thin pixel layer. Recent progress in device architecture has enabled a further step change in near infrared quantum efficiency performance leading to improved nightglow imaging. SiOnyx has integrated this sensor into various camera systems for surveillance, nightvision and 1064nm laser see-spot.

Current designs of combined VIS-color/SWIR camera optics use constant F-number over the full field of view (FOV) range. Especially in the SWIR, limited space for the camera integration in existing system volumes and relatively high pitch dimensions of 15μm or even 20μm force the use of relatively high F- numbers to accomplish narrow fields of view less than 2.0° with reasonable resolution for long range observation and targeting applications. Constant F-number designs are already reported and considered [1] for submarine applications. The comparison of electro-optical performance was based on the given detector noise performance and sensitivity data by the detector manufacturer [1] and further modelling of the imaging chain within linear MTF system theory. The visible channel provides limited twilight capability at F/2.6 but in the SWIR the twilight capability is degraded due to the relatively high F-number of F/7 or F/5.25 for 20 μm and 15 μm pitch, respectively. Differences between prediction and experimental verification of sensitivity in terms of noise equivalent irradiance (NEI) and scenery based limiting illumination levels are shown for the visible and the SWIR spectral range. Within this context, currently developed improvements using optical zoom designs for the multispectral SWIR/VIS camera optics with continuously variable Fnumber are discussed, offering increased low light level capabilities at wide and medium fields of view while still enabling a NFOV < 2° with superior long range targeting capabilities under limited atmospherical sight conditions at daytime.

Indium gallium arsenide (In_1−xGa_xAs) is an ideal material choice for short wave infrared (SWIR) imaging due to its low dark current and excellent collection efficiency. By increasing the indium composition from 53% to 83%, it is possible to decrease the energy gap from 0.74 eV to 0.47 eV and consequently increase the cutoff wavelength from 1.7 μm to 2.63 μm for extended short wavelength (ESWIR) sensing. In this work, we apply our well-established numerical modeling methodology to the ESWIR InGaAs system to determine the intrinsic performance of pixel detectors. Furthermore, we investigate the effects of different buffer/cap materials. To accomplish this, we have developed composition-dependent models for In_1−xGa_xAs, In_1−xAl_xAs, and InAs_1−y P_y. Using a Green’s function formalism, we calculate the intrinsic recombination coefficients (Auger, radiative) to model the diffusion-limited behavior of the absorbing layer under ideal conditions. Our simulations indicate that, for a given total thickness of the buffer and absorbing layer, structures utilizing a linearly graded small-gap InGaAs buffer will produce two orders of magnitude more dark current than those with a wide gap, such as InAlAs or InAsP. Furthermore, when compared with experimental results for ESWIR photodiodes and arrays, we estimate that there is still a 1.5x magnitude of reduction in dark current before reaching diffusion-limited behavior.

Xenics has developed a family of stitched SWIR long linear arrays that operate up to 400 KHz of line rate. These arrays serve medical and industrial applications that require high line rates as well as space applications that require long linear arrays. The arrays are based on a modular ROIC design concept: modules of 512 pixels are stitched during fabrication to achieve 512, 1024 and 2048 pixel arrays. Each 512-pixel module has its own on-chip digital sequencer, analog readout chain and 4 output buffers. This modular concept enables a long array to run at a high line rates irrespective of the array length, which limits the line rate in a traditional linear array. The ROIC is flip-chipped with InGaAs detector arrays. The FPA has a pixel pitch of 12.5μm and has two pixel flavors: square (12.5μm) and rectangular (250μm). The frontend circuit is based on Capacitive Trans-impedance Amplifier (CTIA) to attain stable detector bias, and good linearity and signal integrity, especially at high speeds. The CTIA has an input auto-zero mechanism that allows to have low detector bias (<20mV). An on-chip Correlated Double Sample (CDS) facilitates removal of CTIA KTC and 1/f noise, and other offsets, achieving low noise performance. There are five gain modes in the FPA giving the full well range from 85Ke- to 40Me-. The measured input referred noise is 35e-rms in the highest gain mode. The FPA operates in Integrate While Read mode and, at a master clock rate of 60MHz and a minimum integration time of 1.4μs, achieves the highest line rate of 400 KHz. In this paper, design details and measurements results are presented in order to demonstrate the array performance.

Based on AIM’s state-of-the-art MCT IR technology, detector modules for the SWIR spectral range have been developed, fabricated and characterized. While LPE grown MCT FPAs with extended 2.5μm cut-off have been fabricated and integrated also MBE grown MCT on GaAs is considered for future production. Two imaging applications have been in focus operating either in passive mode by making use of e.g. the night glow, or in active mode by laser illumination for gated viewing. Dedicated readout integrated circuits (ROIC), realized in 0.18μm Si-CMOS technology providing the required functionality for passive imaging and gated imaging, have been designed and implemented. For both designs a 640x512 15μm pitch format was chosen. The FPAs are integrated in compact dewar cooler configurations using AIM’s split linear coolers. A command and control electronics (CCE) provides supply voltages, biasing, clocks, control and video digitization for easy system interfacing. For imaging under low-light conditions a low-noise 640x512 15μm pitch ROIC with CTIA input stages and correlated double sampling was designed. The ROIC provides rolling shutter and snapshot integration. To reduce size, weight, power and cost (SWaP-C) a 640x512 format detector in a 10μm pitch is under development. The module makes use of the extended SWIR spectral cut-off up to 2.5μm. To be used for active gated-viewing operation SWIR MCT avalanche photodiodes have been implemented and characterized on FPA level in a 640x512 15μm pitch format. The specific ROIC provides also the necessary functions for range gate control and triggering by the laser illumination. First lab and field tests of a gated viewing demonstrator have been carried out. The paper will present the development status and performance results of AIM’s MCT based SWIR Modules for imaging applications.

We report InAs/InAs_1-xSb_x type-II superlattice base photodetector as high performance long-wavelength infrared nBn device grown on GaSb substrate. The device has 6 μm-thick absorption region, and shows optical performance with a peak responsivity of 4.47 A/W at 7.9 μm, which is corresponding to the quantum efficiency of 54% at a bias voltage of negative 90 mV, where no anti-reflection coating was used for front-side illumination. At 77K, the photodetector’s 50% cut-off wavelength was ~10 μm. The device shows the detectivity of 2.8x10¹¹ cm.√Hz/W at 77 K, where RxA and dark current density were 119 Ω•cm² and 4.4x10^-4 A/cm² , respectively, under -90 mV applied bias voltage.

We present a high-performance short-wavelength infrared n-i-p photodiode, whose structure is based on type-II superlattices with InAs/InAs_1-xSb_x/AlAs_1-xSb_x on GaSb substrate. At room temperature (300K) with front-side illumination, the device shows the peak responsivity of 0.47 A/W at 1.6mm, corresponding to 37% quantum efficiency at zero bias. At 300K, the device has a 50% cut-off wavelength of ~1.8mm. For −50mV applied bias at 300 K the photodetector has dark current density of 9.6x10^-5 A/cm² and RxA of 285 Ω•cm², and it revealed a detectivity of 6.45x10¹⁰ cm•Hz^1/2/W. Dark current density reached to 1.3x10^-8 A/cm² at 200 K, with 36% quantum efficiency which leads to the detectivity value of 5.66x10¹² cm•Hz^1/2/W.

In this paper, our recent study on InGaAs/GaAsSb Type II photodetector for extended short wavelength infrared detection is reported. The high quality InGaAs/GaAsSb superlattices (SLs) was grown successfully by molecular beam epitaxy. The full width of half maximum of the SLs peak is 39”. Its optical properties were characterized by photoluminescence (PL) at different temperature. The dependences of peak energy on temperature were measured and analyzed. The photodetector with InGaAs/GaAsSb absorption regions has a Quantum Efficiency (QE) product of 12.51% at 2.1um and the 100% cutoff wavelength is at 2.5um, at 300K under zero bias. The dominant mechanism of the dark current is discussed.

HgCdTe (MCT) is predominantly used for infrared imaging applications even in SWIR region. However, MCT is expensive and contains environmentally hazardous substances. Therefore, its application has been restricted mainly military and scientific use and was not spread to commercial use. InGaAs/GaAsSb type-II quantum well structures are considered as an attractive material for realizing low dark current PDs owing to lattice-matching to InP substrate. Moreover, III-V compound material systems are suitable for commercial use. In this report, we describe successful operation of focal plane array (FPA) with InGaAs/GaAsSb quantum wells and mention improvement of optical characteristics. Planar type pin-PDs with 250-pairs InGaAs(5nm)/GaAsSb(5nm) quantum well absorption layer were fabricated. The p-n junction was formed in the absorption layer by the selective diffusion of zinc. Electrical and optical characteristics of FPA or pin-PDs were investigated. Dark current of 1μA/cm² at 210K, which showed good uniformity and led to good S/N ratio in SWIR region, was obtained. Further, we could successfully reduce of stray light in the cavity of FPA with epoxy resin. As a result, the clear image was taken with 320x256 format and 7% contrast improvement was achieved. Reliability test of 10,000 heat cycles was carried out. No degradations were found in FPA characteristics of the epoxy coated sample. This result means FPA using InGaAs/GaAsSb type-II quantum wells is a promising candidate for commercial applications.

Two-dimensional photo detector arrays with a cutoff wavelength of 2.5 μm were fabricated on InP/InGaAs epitaxial wafers with graded buffer layers in a 320x256 geometry on a 12.5μm pitch. Novel growth and fabrication techniques were employed to fabricate these arrays and optimize the performance. The dark current of the detector was investigated for a wide range of temperatures. The fabricated detector array was mated with a ROIC and packaged with a multi-stage TEC and investigated further at the FPA level. The effect of the graded buffer layers on the sensor performance was investigated and the results were compared to other methods used to develop and fabricate 2D image sensors on extended wavelength materials.

The thin nanolayer film of ZnO was synthesized through Langmuir-Blodgett (LB) organic precursor film. The zinc stearate monolayer was formed at air-water interface using zinc acetate as a subphase. The zinc stearate monolayers were deposited on silicon (Si), glass, and gold (Au)/chromium (Cr) plated Silicon (Si) substrates using LB technique. Later, the zinc stearate multilayers LB films on various substrates were annealed at two different temperatures (300oC and 550oC) for the fabrication of zinc oxide (ZnO) nanolayer film. The zinc stearate monolayers as well zinc oxide (ZnO) nanolayer films were characterized using atomic force microscopy (AFM) and X-ray diffraction techniques. The X-ray diffraction measurement has shown the hexagonal wurtzite structure of the ZnO nanolayer on the substrate. The average surface roughness was estimated to be 1.076 nm using AFM technique. The metal-insulator-metal (MIM) diode structure was realized by sandwiching ZnO nanolayer film between thin layer of Gold (Au)/Chromium (Cr) and Nickel (Ni) on silicon substrates. The electron tunneling conduction mechanism is understood through the current-voltage (I-V) characteristics of MIM diode. The highest measured sensitivity magnitude of 20 in inverse of voltage (V-1) with rectification ratio of nearly 10 at ±400 mV in MIM diode is an indicative of its potential application in infrared sensing applications. However, the thin film of ZnO synthesized using LB film as an insulating layer in metal-insulator-metal diode structure was studied for the first time.

The metal-insulator-metal (MIM) diodes are considered to be very attractive candidate for infrared energy harvesting and detection applications. The high speed and compatibility with integrated circuits (IC’s) makes MIM diodes good choice for infrared (IR) regime of the electromagnetic spectrum. Moreover, it is possible to obtain large volume of devices in same unit area due to smaller active area required for MIM diodes. The aim of this work is to design and develop MIM diodes for energy harvesting and IR detection. For this work three different sets of materials; Au-Al₂O₃-Al, Au-Cr₂O₃-Cr, Au-TiO2-Ti Al₂O₃, are used for fabricating MIM diodes. Furthermore, the effect of the insulator thickness and diode active areas are investigated for Au-Al₂O₃-Al MIM diode to study diode characteristics further. The optimization of fabrication processes in physical vapor deposition (PVD) systems for the MIM diodes resulted in the devices having high non-linearity and responsivity. The non-linearity of 80 μA/V² and a responsivity of 15 A/W are achieved for Al-Al₂O₃-Au MIM diodes under low applied bias of 50 mV. The responsivity of Au-Cr₂O₃-Cr and Au-TiO₂-Ti diodes with insulating layers of Cr₂O₃ and TiO₂ are found to be 8 A/W and 2 A/W respectively.

InGaAs based long-wavelength near infrared detector arrays are very important for high dynamic range imaging operations seamlessly from daylight environments to dark environments. These detector devices are usually made by open-hole diffusion technique which has the advantage of lower leakage current and higher reliability. The diffusion process is usually done in a sealed quartz ampoule with dopant compounds like ZnP₂, ZnAs₃, CdP₂ etc. side by side with semiconductor samples. The ampoule needs to be prepared and sealing process needs to be done in very clean environment and each time can have variations. In this work we demonstrated using MOCVD growth chamber to perform the diffusion process. The advantages of such a process are that the tool is constantly kept in ultra clean environment and can reproducibly provide clean processes without introducing unexpected defects. We can independently control the temperature and flow rate of the dopant - they are not linked as in the ampoule diffusion case. The process can be done on full wafers with good uniformity through substrate rotation, which is good for large detector array fabrications. We have fabricated different types of InGaAs/InP detector arrays using dimethyl zinc as the dopant source and PH3 or AsH3 for surface protection. Pre-studies of Zn-diffusion profiles in InGaAs and InP at different temperatures, flow rates, diffusion times and followed annealing times were conducted to obtain good control of the process. Grown samples were measured by C-V profilometer to evaluate the diffusion depth and doping concentration. The dependence of the diffusion profile with temperature, dopant partial pressures, and annealing temperature and time and some of the fabricated device characteristics are reported.

The mid and thermal infrared (MTIR) for the Earth surface is defined between 3 and 14µm. In the outer solar system, objects are colder and their Planck response shifts towards longer wavelengths. Hence for these objects (e.g. icy moons, polar caps, comets, Europa), the thermal IR definition usually stretches out to 50µm and beyond. Spectroscopy has been a key part of this scientific exploration because of its ability to remotely determine elemental and mineralogical composition. Many key gas species such as methane, ammonia, sulfur, etc. also have vibrational bands which show up in the thermal infrared spectrum above the background response. Over the past few decades, the Jet Propulsion Laboratory has been building up a portfolio of technology to capture the MTIR for various scientific applications. Three recent sensors are briefly reviewed: The airborne Hyperspectral thermal emission spectrometer (HyTES), the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) and Mars Climate Sounder (MCS)/DIVINER. Each of these sensors utilize a different technology to provide a remote sensing product based on MTIR science. For example, HyTES is a push-brooming hyperspectral imager which utilizes a large format quantum well infrared photodetector (QWIP). The goal is to transition this to a new complementary barrier infrared photodetector (CBIRD) with a similar long wave cut-off and increased sensitivity. ECOSTRESS is a push-whisk Mercury Cadmium Telluride (MCT) based high speed, multi-band, imager which will eventually observe and characterize plant/vegetation functionality and stress index from the International Space Station (ISS) across the contiguous United States (CONUS). MCS/DIVINER utilizes thermopile technology to capture the thermal emission from the polar caps and shadow regions of the moon. Each sensor utilizes specific JPL technology to capture unique science.

SOFRADIR was selected in the late 90’s for the production of 320×256 MW detectors for major European missile programs. This experience has established our company as a key player in the field of missile programs. SOFRADIR has since developed a vast portfolio of lightweight, compact and high performance JT-based solutions for missiles. ALTAN is a 384x288 Mid Wave infrared detector with 15μm pixel pitch, and is offered in a miniature ultra-fast Joule- Thomson cooled Dewar. Since Sofradir offers both Indium Antimonide (InSb) and Mercury Cadmium Telluride technologies (MCT), we are able to deliver the detectors best suited to customers’ needs. In this paper we are discussing different figures of merit for very compact and innovative JT-cooled detectors and are highlighting the challenges for infrared detection technologies.

The mid-wave infrared is an especially informative wavelength range, permitting detection and characterization of a diverse range of materials and processes. The development of a new way to measure in this region, using a Sagnac interferometer spectrometer, has lead us to design the Miniaturized Infrared detector of Atmospheric Species (MIDAS). Instruments like MIDAS are attractive for space applications due to their low-mass and low-power consumption. An uncooled microbolometer and a cooled InSb photon detector version of MIDAS are currently set up for bench top characterization and preliminary science data collection.

Infrared Search and Track systems are an essential element of the modern and future combat aircrafts. Passive automatic search, detection and tracking functions, are key points for silent operations or jammed tactical scenarios. SKYWARD represents the latest evolution of IRST technology in which high quality electro-optical components, advanced algorithms, efficient hardware and software solutions are harmonically integrated to provide high-end affordable performances. Additionally, the reduction of critical opto-mechanical elements optimises weight and volume and increases the overall reliability. Multiple operative modes dedicated to different situations are available; many options can be selected among multiple or single target tracking, for surveillance or engagement, and imaging, for landing or navigation aid, assuring the maximum system flexibility. The high quality 2D-IR sensor is exploited by multiple parallel processing chains, based on linear and non-linear techniques, to extract the possible targets from background, in different conditions, with false alarm rate control. A widely tested track processor manages a large amount of candidate targets simultaneously and allows discriminating real targets from noise whilst operating with low target to background contrasts. The capability of providing reliable passive range estimation is an additional qualifying element of the system. Particular care has been dedicated to the detector non-uniformities, a possible limiting factor for distant targets detection, as well as to the design of the electro-optics for a harsh airborne environment. The system can be configured for LWIR or MWIR waveband according to the customer operational requirements. An embedded data recorder saves all the necessary images and data for mission debriefing, particularly useful during inflight system integration and tuning.

Short Wave InfraRed(SWIR) spectral imager is good at detecting difference between materials and penetrating fog and mist. High spectral resolution SWIR hyperspectral imager plays a key role in developing earth observing technology. Hyperspectral data cube can help band selections that is very important for multispectral imager design. Up to now, the spectral resolution of many SWIR hyperspectral imagers is about 10nm. A high sensitivity airborne SWIR hyperspectral imager with narrower spectral band will be presented. The system consists of TMA telescope, slit, spectrometer with planar blazed grating and high sensitivity MCT FPA. The spectral sampling interval is about 3nm. The IFOV is 0.5mrad. To eliminate the influence of the thermal background, a cold shield is designed in the dewar. The pixel number of spatial dimension is 640. Performance measurement in laboratory and image analysis for flight test will also be presented.

The instrumentation for measuring infrared polarization signatures has seen significant advancement over the last decade. Previous work has shown the value of polarimetric imagery for a variety of target detection scenarios including detection of manmade targets in clutter and detection of ground and maritime targets while recent work has shown improvements in contrast for aircraft detection and biometric markers. These data collection activities have generally used laboratory or prototype systems with limitations on the allowable amount of target motion or the sensor platform and usually require an attached computer for data acquisition and processing. Still, performance and sensitivity have been steadily getting better while size, weight, and power requirements have been getting smaller enabling polarimetric imaging for a greater or real world applications. In this paper, we describe Pyxis®, a microbolometer based imaging polarimeter that produces live polarimetric video of conventional, polarimetric, and fused image products. A polarization microgrid array integrated in the optical system captures all polarization states simultaneously and makes the system immune to motion artifacts of either the sensor or the scene. The system is battery operated, rugged, and weighs about a quarter pound, and can be helmet mounted or handheld. On board processing of polarization and fused image products enable the operator to see polarimetric signatures in real time. Both analog and digital outputs are possible with sensor control available through a tablet interface. A top level description of Pyxis® is given followed by performance characteristics and representative data.

Geolocation is the process of calculating a target position based on bearing and range relative to the known location of the observer. A high performance thermal imager with integrated geolocation functions is a powerful long range targeting device. Firefly is a software defined camera core incorporating a system-on-a-chip processor running the Android^TM operating system. The processor has a range of industry standard serial interfaces which were used to interface to peripheral devices including a laser rangefinder and a digital magnetic compass. The core has built in Global Positioning System (GPS) which provides the third variable required for geolocation. The graphical capability of Firefly allowed flexibility in the design of the man-machine interface (MMI), so the finished system can give access to extensive functionality without appearing cumbersome or over-complicated to the user. This paper covers both the hardware and software design of the system, including how the camera core influenced the selection of peripheral hardware, and the MMI design process which incorporated user feedback at various stages.

We report the upgraded performance of the National Institute of Standards and Technology (NIST) facility for spectral responsivity calibrations of infrared (IR) detectors in both radiant power and irradiance measurement modes. The extension of the wavelength range of the previous scale, below 0.8 μm and above 19 μm in radiant power mode as well as above 5.3 μm in irradiance mode, became available as a result of multiple improvements. The calibration facility was optimized for low-level radiant flux. A significantly reduced noise-equivalent-power and a relatively constant spectral response were achieved recently on newly developed pyroelectric detectors. Also, an efficient optical geometry was developed for calibration of the spectral irradiance responsivity without using an integrating sphere. Simultaneously, the upgrade and maintenance of the NIST transfer standards, with an extended spectral range, were supported by spectral reflectance measurements of a transfer standard pyroelectric detector using a custom integrating sphere and a Fourier transform spectrometer. The sphere reflectance measurements performed in a relative mode were compared to a bare gold-coated mirror reference, separately calibrated at the Fourier transform Infrared Spectrophotometry facility to 18 μm. Currently, the reflectance data for the pyroelectric standard, available in the range up to 30 μm, are supporting the absolute power responsivity scale by the propagation of the reflectance curve to the absolute tie-spectrum in the overlapping range. Typical examples of working standard pyroelectric-, Si-, MCT-, InSb- and InGaAs- detectors are presented and their optimal use for scale dissemination is analyzed.

We investigate high-temperature and high-frequency operation of interband cascade infrared photodetectors (ICIPs)-two critical properties. Short-wavelength ICIPs with a cutoff wavelength of 2.9 μm had Johnson-noise limited detectivity of 5.8×10⁹ cmHz^1/2/W at 300 K, comparable to the commercial Hg_1-xCd_xTe photodetectors of similar wavelengths. A simple but effective method to estimate the minority carrier diffusion length in short-wavelength ICIPs is introduced. Using this approach, the diffusion length was estimated to be significantly shorter than 1 μm at high temperatures, indicating the importance of a multiple-stage photodetector (e.g., ICIPs) at high temperatures. Recent investigations on the high-frequency operation of mid-wavelength ICIPs (λc=4.3 μm) are discussed. These photodetectors had 3-dB bandwidths up to 1.3 GHz with detectivities exceeding 1x10⁹ cmHz^1/2/W at room temperature. These results validate the ability of ICIPs to achieve high bandwidths with large sensitivity and demonstrate the great potential for applications such as: heterodyne detection, and free-space optical communication.

Reduction of surface leakage is a major challenge in most photodetectors that requires the elimination of surface oxides on etched mesas during passivation. Engineering the passivation requires close attention to chemical reactions that take place at the interface during the process. In particular, removal of surface oxides may be controlled via Gibbs reactivity. We have compared electrical performance of type-II superlattice photodetectors, designed for MWIR operation, passivated by different passivation techniques. We have used ALD deposited Al₂O₃, HfO₂, TiO₂, ZnO, PECVD deposited SiO₂, Si₃N₄ and sulphur containing octadecanethiol (ODT) selfassembled monolayers (SAM) passivation layers on InAs/GaSb p-i-n superlattice photodetectors with cutoff wavelength at 5.1 μm. In this work, we have compared the result of different passivation techniques which are done under same conditions, same epitaxial structure and same fabrication processes. We have found that ALD deposited passivation is directly related to the Gibbs free energy of the passivation material. Gibbs free energies of the passivation layer can directly be compared with native surface oxides to check the effectiveness of the passivation layer before the experimental study.

In the development of InAs/GaSb Type-II superlattice (T2SL) infrared photodetectors, the surface leakage current at the mesa sidewall must be suppressed. To achieve this requirement, both the surface treatment and the passivation layer are key technologies. As a starting point to design these processes, we investigated the GaSb oxide in terms of its growth and thermal stability. We found that the formation of GaSb oxide was very different from those of GaAs. Both Ga and Sb are oxidized at the surface of GaSb. In contrast, only Ga is oxidized and As is barely oxidized in the case of GaAs. Interestingly, the GaSb oxide can be formed even in DI water, which results in a very thick oxide film over 40 nm after 120 minutes. To examine the thermal stability, the GaSb native oxide was annealed in a vacuum and analyzed by XPS and Raman spectroscopy. These analyses suggest that SbO_x in the GaSb native oxide will be reduced to metallic Sb above 300°C. To directly evaluate the effect of oxide instability on the device performance, a T2SL p-i-n photodetector was fabricated that has a cutoff wavelength of about 4 μm at 80 K. As a result, the surface leakage component was increased by the post annealing at 325°C. On the basis of these results, it is possible to speculate that a part of GaSb oxide on the sidewall surface will be reduced to metallic Sb, which acts as an origin of additional leakage current path.

SCD has developed a range of advanced infrared detectors based on III-V semiconductor heterostructures grown on GaSb. The XBn/XBp family of barrier detectors enables diffusion limited dark currents, comparable with MCT Rule-07, and high quantum efficiencies. This work describes some of the technical challenges that were overcome, and the ultimate performance that was finally achieved, for SCD’s new 15 μm pitch “Pelican-D LW” type II superlattice (T2SL) XBp array detector. This detector is the first of SCD's line of high performance two dimensional arrays working in the LWIR spectral range, and was designed with a ~9.3 micron cut-off wavelength and a format of 640 x 512 pixels. It contains InAs/GaSb and InAs/AlSb T2SLs, engineered using k • p modeling of the energy bands and photo-response. The wafers are grown by molecular beam epitaxy and are fabricated into Focal Plane Array (FPA) detectors using standard FPA processes, including wet and dry etching, indium bump hybridization, under-fill, and back-side polishing. The FPA has a quantum efficiency of nearly 50%, and operates at 77 K and F/2.7 with background limited performance. The pixel operability of the FPA is above 99% and it exhibits a stable residual non uniformity (RNU) of better than 0.04% of the dynamic range. The FPA uses a new digital read-out integrated circuit (ROIC), and the complete detector closely follows the interfaces of SCD’s MWIR Pelican-D detector. The Pelican- D LW detector is now in the final stages of qualification and transfer to production, with first prototypes already integrated into new electro-optical systems.

The cutoff wavelength of 6μm is preferable for the full usage of the atmospheric window in the mid-wavelength region. An InAs/GaSb type-II superlattice (T2SL) is the only known infrared material that has a theoretically predicted high performance and also the cutoff wavelength can be easily controlled by changing the thickness of InAs and GaSb. In this study, we used a p-i-n structure with InAs/GaSb T2SL absorber and also barrier layers which was grown on a Tedoped GaSb substrate by molecular beam epitaxy. A mesa-type focal plane array (FPA) with 320×256 pixels and 30μm pixel pitch was fabricated. Mesa structures were formed by inductively coupled plasma reactive ion etching with halogen gas mixture. Prior to the deposition of the SiO₂ passivation film, N₂ plasma treatment was applied for reducing the dark currents. Measured dark current of the sensor was 4x10^-7A/cm² at temperature of 77K and reverse bias of -20mV. The quantum efficiency was 0.35 and the detectivity was 4.1x10¹²cm/Hz^1/2W. The sensor array was hybridized with the commercially available readout integrated circuit using indium bumps. The noise equivalent differential temperature measured with F/2.3 optics was 31mK at 77K. The operability was over 99%. This FPA is suitable for full usage of the atmospheric window in the mid-wavelength region.

We present an approach to realize antimonide based superlattices on silicon substrates without using conventional Indium-bump hybridization. In this approach, PIN based superlattice detectors are grown on top of a 60 nm Al0.6Ga0.4Sb sacrificial layer on a GaSb host substrate. Following the growth, the individual pixels are transferred using our epitaxiallift off technique, which consists of a wet-etch to undercut the pixels followed by a dry-stamp process to transfer the pixels to a silicon substrate prepared with a gold layer. Structural and optical characterization of the transferred pixels was done using an optical microscope, scanning electron microscopy and photoluminescence. The interface between the transferred pixels and the new substrate was abrupt and no significant degradation in the optical quality was observed. An Indium-bump-free membrane detector was then fabricated using this approach. Spectral response measurements provided a 100% cut-off wavelength of 4.3 μm at 77 K. The performance of the membrane detector was compared to a control detector on the as-grown substrate. The membrane detector was limited by surface leakage current. The proposed approach could pave the way for wafer-level integration of photonic detectors on silicon substrates, which could dramatically reduce the cost of these detectors.

For more than two decades, Antimony-based type-II superlattice photodetectors for the infrared spectral range between 3-15 μm are under development at the Fraunhofer Institute for Applied Solid State Physics (IAF). Today, Fraunhofer IAF is Germany’s only national foundry for InAs/GaSb type-II superlattice detectors and we cover a wide range of aspects from basic materials research to small series production in this field. We develop single-element photodetectors for sensing systems as well as two-dimensional detector arrays for high-performance imaging and threat warning systems in the mid-wavelength and long-wavelength region of the thermal infrared. We continuously enhance our production capabilities by extending our in-line process control facilities. As a recent example, we present a semiautomatic wafer probe station that has developed into an important tool for electrooptical characterization. A large amount of the basic materials research focuses on the reduction of the dark current by the development of bandgap engineered device designs on the basis of heterojunction concepts. Recently, we have successfully demonstrated Europe’s first LWIR InAs/GaSb type-II superlattice imager with 640x512 pixels with 15 μm pitch. The demonstrator camera already delivers a good image quality and achieves a thermal resolution better than 30 mK.

High-temperature characteristics of a mid-wavelength infrared detector based on the Maimon-Wicks InAsSb/AlAsSb nBn design indicates that the quantum efficiency does not degrade when the operating temperature increases to above room temperature. However, it was also found that the turn-on bias becomes larger at higher temperatures. This counter-intuitive behavior was originally attributed to the change in the band alignment between the absorber and top contact layers due to Fermi level temperature dependence. Recent analysis shows that this is more likely due to temperature-dependent band bending effects. Dark current mechanism is analyzed based on minority carrier lifetime measurements. The difference between the responsivity and absorption quantum efficiencies is clarified.

IRnova has been manufacturing mid wave infrared (MWIR) detectors based on InAs/GaSb type-II superlattices (T2SL) since 2014. Results from the first years of production of MWIR focal plane arrays (FPAs) with 320 x 256 pixels on 30 μm pitch using the ISC9705 readout integrated circuit (ROIC) is presented in terms of operability, temporal and spatial noise equivalent temperature difference (NETD) and other key production parameters. Results on image stability of T2SL detectors show that no deterioration of image quality over time can be observed. Furthermore it is shown that the non-uniformity correction remains stable even after repeated detector temperature cycles. Spatial and temporal NETD for fabricated mid wave arrays show a temporal NETD of 12 mK and a spatial NETD of 4 mK with f/2 optics and 8 ms integration time. When studied over a large scene temperature, the spatial noise is still less than 60 % of the temporal noise. Furthermore, 640 x 512 mid wave FPAs with 15 μm pitch using the ISC0403 ROIC are entering an industrialization phase. Temporal and spatial NETD values of 25 mK and 10 mK, respectively, are obtained with f/4 optics and 22 ms integration time and the operability is 99.85 %. A status update on the development of T2SL detectors for short wave, mid wave and long wave infrared wavelength regions for existing and new applications is given and recent development towards higher operating temperature, smaller pitch and larger FPA formats is presented.

We report on the development of dual-band InAs/GaSb type-II strained layer superlattices (T2SL) detectors with barrier designs at SK Infrared. Over the past five years, we demonstrated mid-wave/long-wave (MW/LWIR, cut-off wavelengths are 5 μm and 10.0 μm), and LW/LWIR (cut-off wavelengths are 9 μm and 11.0 μm) detectors with nBn and pBp designs. Recent results include a high performance bias-selectable long/long-wavelength infrared photodetector based on T2SL with a pBp barrier architecture. The two channels 50% cut-off wavelengths were ~ 9.2 μm and ~ 12 μm at 77 K. The “blue” and “red” LWIR absorbers demonstrated saturated QE values of 34 % and 28 %, respectively, measured in a backside illuminated configuration with a ~ 35 μm thick layer of residual GaSb substrate. Bulk-limited dark current levels were ~ 2.6 x 10^-7 A/cm² at + 100 mV and ~ 8.3 x 10^-4 A/cm² at - 200 mV for the “blue” and “red” channels, respectively.

Cadmium Zinc Telluride (CZT) is an important compound semiconductor material upon which Mercury Cadmium Telluride (MCT) layers are deposited epitaxially to form structures that are used in high performance detectors covering a wide infrared (IR) spectral band. The epitaxial growth of high quality MCT layers presents many technical challenges and a critical determinant of material performance is the quality of the underlying bulk CZT substrate. CZT itself is a difficult material to manufacture where traditional methods of bulk growth are complex and low yielding, which constrains the supply of commercially available substrates. In this work we report on the epitaxy-ready finishing of Travelling Heather Method (THM) grown Cd0.96Zn0.04Te substrates. The THM method is well established for the growth of high quality CZT crystals used in nuclear, X-ray and spectroscopic imaging applications and in this work we demonstrate the application of this technique to the growth of IR specification CZT substrates with areas of up to 5 cm x 5 cm square. We will discuss the advantages of the THM method over alternative methods of bulk CZT growth where the high yield and material uniformity advantages of this technique will be demonstrated. Chemo-mechanical polishing (CMP) of 4 cm x 4 cm CZT substrates reveals that III-V (InSb/GaSb) like levels of epitaxy-ready surface finishing may be obtained with modified process chemistries. Surface quality assessments will be made by various surface analytical and microscopy techniques from which the suitability of the material for subsequent assessment of quality by epitaxial growth will be ascertained.

We present a new method to produce low-cost, high quality gallium antimonide (GaSb) substrates for IR imaging applications. These methods apply high-volume wafer manufacturing standards from the silicon industry to increase performance and value of our wafers. Encapsulant-free GaSb single crystals were grown using the modified Czochralski method, yielding more than seventy 150mm wafers per crystal or several hundred 75mm or 100mm wafers per crystal. These were processed into epi-ready substrates on which superlattice structures were grown. Wafer and epitaxy structure characterization is also presented, including transmission X-ray topography, dopant level and uniformity.

InSb focal plane array (FPA) detectors are key components in IR imaging systems that significantly impact both cost and performance. Detector performance is affected by the electronic and crystallographic quality and uniformity of the semiconductor substrate. High-volume, high-yield production of InSb wafers to the standards required for FPA device manufacture requires growth of on-axis {111} crystals. An inherent source of variation hindering on-axis Czochralski crystal growth is anisotropic dopant incorporation. We report on newly developed growth methods that eliminate the negative effects of anisotropic dopant incorporation enabling high volume manufacturing of {111}-oriented substrates and discuss the consequential manufacturing benefits. We also report on a characterization technique to characterize microscale dopant variation across the wafer.

Gallium Antimonide (GaSb) is an important Group III-V compound semiconductor which is suitable for use in the manufacture of a wide variety of optoelectronic devices such as infra-red (IR) focal plane detectors. A significant issue for the commercialisation of these products is the production of epitaxy ready GaSb, which remains a challenge for the substrate manufacturer, as the stringent demands of the MBE process, requires a high quality starting wafer. In this work large diameter GaSb crystals were grown by the Czochralski (Cz) method and wafers prepared for chemo-mechanical polishing (CMP). Innovative epi-ready treatments and novel post polish cleaning methodologies were applied. The effect of these modified finishing chemistries on substrate surface quality and the performance of epitaxially grown MBE GaSb IR detector structures were investigated. Improvements in the lowering of surface defectivity, maintaining of the surface roughness and optimisation of all flatness parameters is confirmed both pre and post MBE growth. In this paper we also discuss the influence of bulk GaSb quality on substrate surface performance through the characterisation of epitaxial structures grown on near zero etch pit density (EPD) crystals. In summary progression and development of current substrate polishing techniques has been demonstrated to deliver a consistent improved surface on GaSb wafers with a readily desorbed oxide for epitaxial growth.

We are developing resonator-QWIPs for long wavelength applications. Detector pixels with 25 μm pitch were hybridized to fanout circuits for radiometric measurements. With a moderate doping of 0.5 x 1018 cm^-3, we achieved a quantum efficiency of 37% and conversion efficiency of 15% in a 1.3 μm-thick active material and 35% QE and 21% CE in a 0.6 μm-thick active material. Both detectors are cutoff at 10.5 μm with a 2 μm bandwidth. The temperature at which photocurrent equals dark current is about 65 K under F/2 optics. The thicker detector shows a large QE polarity asymmetry due to nonlinear potential drop in the QWIP material layers.

IRnova has a long history of producing QWIPs for the LWIR band. In this paper we give an overview of the current products (FPAs with 640x480 and 384x288 pixels respectively, and 25 μm pitch) and their performance. Their superior stability and uniformity inherent to detectors based on III/V material system will be demonstrated. Furthermore, an IDCA specifically designed for hand-held systems used for the detection of SF6 gas using a 0.5 W cooler will be presented. The detector format is 320x256 pixels with 30 μm pitch using the ISC9705 read out circuit. The peak wavelength is at 10.55 μm and the NETD is 22 mK.

Monodisperse suspensions of HgTe colloidal quantum dots (CQD) are readily synthesized with infrared energy gaps between 3 and 12 microns. Infrared photodetection using dried films of these CQDs has been demonstrated up to a wavelength of 12 microns, and HgTe CQD single-elemnet devices with 3.6 micron cutoff have bee nreported nad show ogod absorption <(10^4 cm^-1), response time and detectivity (2*10^10 Jones) at at emperature of 175 K; with the potential fo uncooled imaging. The synthesis of CQDs and fabrication of detector devices employ bench-top chemistry techniques, leading to the potential for rapid, wafer-scale manufacture of MWIR imaging devices with low production costs and overhead. The photoconductive, photovoltaic and optical properties of HgTe CQD films will be discussed relative to infrared imaging, along with recent achievements in integrating CQD films with readout integrated circuits to produce CQD-based MWIR focal plane arrays.

Reflow soldering is the primary method for Flip-chip bonding without high bonding pressure. Reflow process during flip-chip technology in short wavelength infrared (SWIR) InGaAs/InP Focal Plane array (FPA) with indium solder was studied in this paper. In order to analyze the formation of Indium oxide and its effects on Indium bump reflow process. Indium bumps were investigated by X-ray Photoelectron Spectroscopy (XPS). The profiles of Indium bumps after reflow were observed by scanning electron microscopy (SEM). The interaction between Indium and the metal in under bump metallization (UBM) during reflow process was discussed. The current–voltage (I–V) curves of InGaAs/InP photodiodes were measured before and after the reflow process. The dark current density at 0.1 V reverse bias of InGaAs/InP photodiodes were studied. It was confirmed that the characteristics of InGaAs photodetectors haven’t degenerated after reflow in this paper.

We report on InAs SML QD infrared photodetector performance for long wavelength infrared detection. The device structure consists of InAs SML QDs embedded in InxGa1-xAs quantum well (QW) surrounded by GaAs and AlxGa1- xAs barrier. In order to investigate the structural properties of SML QDs, we took cross-sectional STEM images. We have measured the polarization dependent spectral response of SML-QD based photodetector using various angular inplane and out-plane polarizations. We also report a systematic approach for controlling the intersubband transition energy level in SML QD infrared photodetectors, in order to control the peak wavelength of the device.

In this paper AIM presents its latest results on both n-on-p and p-on-n low dark current planar MCT photodiode technology LWIR and VLWIR two-dimensional focal plane detector arrays with a cut-off wavelength >11μm at 80K and a 640x512 pixel format at a 20μm pitch. Thermal dark currents significantly reduced as compared to ‘Tennant’s Rule 07’ at a yet good detection efficiency >60% as well as results from NETD and photo response performance characterization are presented. The demonstrated detector performance paces the way for a new generation of higher operating temperature LWIR MCT FPAs with a <30mK NETD up to a 110K detector operating temperature and with good operability.

Shrinking the pixel size in advanced infrared Focal Plane Array (FPA) detectors allows either a reduction in the system size for the same number of pixels, or an increase in the pixel count for the same focal plane area. Smaller pitch and increased pixel count enables new applications such as long range surveillance, advanced Search and Track, missile warning, persistent surveillance, and infrared spectroscopy. In the last two decades SCD has followed this path of reducing the pixel size in InSb detectors for Mid-Wave Infrared (MWIR) applications, developing and manufacturing FPAs from 30μm down to 10μm pitch. The Blackbird InSb detector with 1920×1536/10μm format was introduced in 2013. Modern electro-optical systems are also designed towards a more compact, low power, and lower cost solution compared with traditional systems. In order to meet these requirements, detectors are being developed to work at Higher Operating Temperatures (HOT). In the last few years SCD has introduced 15μm pitch MWIR detectors based on the novel XBn-InAsSb technology, which enables outstanding electro-optical performance at temperatures as high as 150K. Two XBn FPA formats were developed and are now in production: 640×512/15μm and 1280×1024/15μm. Following the above trends, SCD is currently developing a 10μm XBn pixel, designed to operate at 150K with performance similar to the mature 15μm pixel. In this paper we present results from XBn FPA test devices, where the XBn array is flip-chip bonded to a Readout Integrated Circuit (ROIC) with a 10μm pitch. Test measurements in a laboratory Dewar at 150K demonstrate dark currents of 250fA, quantum efficiency greater than 70%, pixel operability of higher than 99.5%, and excellent array uniformity.

In this paper we present progress in MOCVD growth of (100) HgCdTe epilayers achieved recently at the Institute of Applied Physics, Military University of Technology and Vigo System S.A. It is shown that MOCVD technology is an excellent tool in fabrication of different HgCdTe detector structures with a wide range of composition, donor/acceptor doping and without post grown annealing. Particular progress has been achieved in the growth of (100) HgCdTe epilayers for long wavelength infrared photoconductors operated in HOT conditions. The (100) HgCdTe photoconductor optimized for 13-μm attain detectivity equal to 6.5x10⁹ Jones and therefore outperform its (111) counterpart. The paper also presents technological progress in fabrication of MOCVD-grown (111) HgCdTe barrier detectors. The barrier device performance is comparable with state-of-the-art of HgCdTe photodiodes. The detectivity of HgCdTe detectors is close to the value marked HgCdTe photodiodes. Dark current densities are close to the values given by “Rule 07”.

Infrared (IR) photon detectors must be cryogenically cooled to provide the highest possible performance, usually to temperatures at or below ~ 150K. Such low operating temperatures (T_op) impose very stringent requirements on cryogenic coolers. As such, there is a constant push in the industry to engineer new detector architectures that operate at higher temperatures, so called higher operating temperature (HOT) detectors. The ultimate goal for HOT detectors is room temperature operation. While this is not currently possibly for photon detectors, significant increases in T_op are nonetheless beneficial in terms of reduced size, weight, power and cost (SWAP-C). The most common HgCdTe IR detector architecture is the P⁺n heterostructure photodiode (where a capital letter indicates a wide band gap relative to the active layer or “AL”). A variant of this architecture, the P⁺N−n−N−N heterostructure photodiode, should have a near identical photo-response to the P+n heterostructure, but with significantly lower dark diffusion current. The P⁺N−n−N−N heterostructure utilizes a very low doped AL, surrounded on both sides by wide-gap layers. The low doping in the AL, allows the AL to be fully depleted, which drastically reduces the Auger recombination rate in that layer. Minimizing the Auger recombination rate reduces the intrinsic dark diffusion current, thereby increasing Top. Note when we use the term “recombination rate” for photodiodes, we are actually referring to the net generation and recombination of minority carriers (and corresponding dark currents) by the Auger process. For these benefits to be realized, these devices must be intrinsically limited and well passivated. The focus of this proceeding is on studying the fundamental physics of the intrinsic dark currents in ideal P⁺N−n−N−N heterostructures, namely Auger recombination. Due to the complexity of these devices, specifically the presence of multiple heterojunctions, numerical device modeling techniques must be utilized to predict and understand the device operation, as analytical models do not exist for heterojunction devices.

SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. Strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, low excess noise and high operability. The actual trend in quantum IR detector development is the design of very small pixel, with high operating temperature. To maintain the detector performances and operability at high temperature, the number of pixels exhibiting extra noise like 1/f and RTS noise must be limited. This paper presents the recent developments achieved in Sofradir in terms of HOT MCT extrinsic p on n technology, blue MW band (cut-off wavelength of 4.2μm at 150K) and extended MW band (cut-off wavelength of 5.3μm at 130K). Comparison between optimized and non-optimized technology will be presented in terms of NETD temperature dependency, MTF, 1/f noise and the corresponding impact on RFPN (Residual Fixe Pattern Noise) and its stability up to 170K will be shown.

In recent years, interband cascade detectors (ICIP) based on typer-II superlattice have shown great performance potential at high operation temperature. In this paper, we report our studies on mid-infrared interband cascade photodetectors first grown on InAs substrate. We examined the photo-generated carriers’ transport in ICIP structures by comparing three detectors grown on InAs substrate. The 2-stages ICIP device has demonstrated a high quantum efficiency around 20% at room temperature. The dark current density of the 2-stages ICIP device at -0.05V is as low as 1 nA at 80K, 1 mA at 150K, which is comparable to the state of art PIN superlattice photodetectors with similar cutoff wavelength. The Johnson-noise limited D* reaches 1.64×10¹⁴cm.Hz^1/2/W at 3.65 μm and 80K, and 4.1×10¹⁰cm.Hz^1/2/W at 3.8 μm and 200K. The 300 K background limited infrared performance (BLIP) operation temperature is estimated to be over 140 K.

A high temperature operation mid-wavelength 128×128 infrared focal plane arrays (FPA) based on low Al component In_1-xAl_xSb was presented in this work. InAlSb materials were grown on InSb (100) substrates using MBE technology, which was confirmed by XRD and AFM analyses. We have designed and grown two structures with and without barrier. The pixel of the detector had a conventional PIN structure with a size of 50μmx50μm. The device fabrication process consisted of mesa etching, passivation, metallization and flip-chip hybridization with readout integrated circuit (ROIC), epoxy backfill, lap and polish. Diode resistance, imaging, NETD and operability results are presented for a progression of structures that reduce the diode leakage current as the temperature is raised above 80K. These include addition of a thin region of InAlSb to reduce p-contact leakage current, and construction of the whole device from InAlSb to reduce thermal generation in the active region of the detector. An increase in temperature to 110K, whilst maintaining full 80K performance, is achieved. The I-V curves were measured at different temperature. Quantum efficiency, pixel operability, non-uniformity, and the mean NETD values of the FPAs were measured at 110K. This gives the prospect of significant benefits for the cooling systems, including, for example, use of argon in Joule-Thomson coolers or an increase in the life and/or decrease in the cost, power consumption and cool-down time of Stirling engines by several tens of percent.

Wavelength-selective uncooled infrared (IR) sensors have significant advantages with regard to applications such as fire detection, gas analysis, hazardous materials recognition, and biological analysis. We have previously demonstrated an uncooled IR sensor based on a two-dimensional plasmonic absorber (2D PLA) that exhibited wavelength-selective absorption over a wide range spanning the middle and long-wavelength IR regions. This device had a Au-based 2D periodic dimple-array structure, in which surface plasmon modes were induced, leading to wavelength-selective absorption, such that the absorption wavelength was determined by the period of the surface dimples. However, dual-band operation based on this concept has not yet been investigated, even though the ability to absorb in two different wavelength bands is extremely important for object recognition. In the present study, a dual-band uncooled IR sensor was developed using a 2D PLA with asymmetric dimple periods (2-D PLA-AP). To achieve multiband absorption, the Au-based dimples in this device were fabricated so as to have different periods in the orthogonal x and y directions. Theoretical calculations predicted asymmetric absorption spectra, attributed to Fano resonance in the 2-D PLA-AP. A sensor was subsequently fabricated using complementary metal oxide semiconductor and micromachining techniques. Measurement of the spectral responsivity demonstrated that selective absorption occurred in two different wavelength bands, determined by the dimple periods in the x and y directions. The results obtained in this study will be applicable to the development of advanced sensors capable of multiband detection in the IR region.

In this paper a novel concept for the fabrication of highly sensitive uncooled microbolometers is presented. The approach is based on the realization of thermal isolation and simultaneous electrical contacting of the microbolometers by means of sufficiently long and thin coated nanotubes, which can be fabricated by post processing on top of CMOS wafers comprising the ROIC. Thus, the effective area of the absorption layer is maximized at a given pixel size, as lateral legs, which have been the main component of the thermal isolation commonly, are completely omitted. The resulting thermal conductivity can be tuned independently from the pixel size by varying the geometry and structuring of the nanotubes. Based on test structures the nanotube microbolometers are characterized with respect to electro-optical and mechanical properties. The focus in this paper is on nanotube microbolometers with a pixel size of 12 μm.

The benefit of 10um pitch uncooled detectors is demonstrated through the use of image emulation. The image emulation uses the theoretical image of point sources for 10um wavelength radiation, then integrates the energy from multiple sources which fall into FPA pixel areas and produces representative images. Arrays of pixel pitches of 25um, 17um, 12um, 10um, 5um, and 4um are included. These images, and movies when presented live at the conference, make evident why array pitches smaller than the wavelength of radiation are useful and being considered. While the argument for sub-wavelength pixel pitches is already made by other authors, this representation might be clearer to a larger audience. Representative images, and movies when presented live at the conference, from a DRS 1280x1024 format, 10um pitch array are shown. Details of the DRS 10um pitch UFPA family are shown.

Metamaterial electromagnetic wave absorbers, which usually can be fabricated in a low weight thin film structure, have a near unity absorptivity in a special waveband, and therefore have been widely applied from microwave to optical waveband. To increase absorptance of CMOS MEMS devices in 2-5 μmm waveband, multi-color infrared metamaterial absorbers are designed with CSMC 0.5 μmm 2P3M and 0.18 μmm 1P6M CMOS technology in this work. Metal-insulator-metal (MIM) three-layer MMAs and Insulator-metal-insulator-metal (MIMI) four-layer MMAs are formed by CMOS metal interconnect layers and inter metal dielectrics layer. To broaden absorption waveband in 2-5μmm range, MMAs with a combination of different sizes cross bars are designed. The top metal layer is a periodic aluminum square array or cross bar array with width ranging from submicron to several microns. The absorption peak position and intensity of MMAs can be tuned by adjusting the top aluminum micro structure array. Post-CMOS process is adopted to fabricate MMAs. The infrared absorption spectra of MMAs are verified with finite element method simulation, and the effects of top metal structure sizes, patterns, and films thickness are also simulated and intensively discussed. The simulation results show that CMOS MEMS MMAs enhance infrared absorption in 2-20 μmm. The MIM broad MMA has an average absorptance of 0.22 in 2-5 μmm waveband, and 0.76 in 8-14 μm waveband. The CMOS metamaterial absorbers can be inherently integrated in many kinds of MEMS devices fabricated with CMOS technology, such as uncooled bolometers, infrared thermal emitters.

Subwavelength resonant structures designed for long-wave infrared (LWIR) absorption have been integrated with a standard vanadium-oxide microbolometer. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 μm LWIR wavelength band, a broader range than can be achieved using the usual quarter-wave resonant cavity engineered into the air-bridge structures. Experimental measurements show a 49% increase in responsivity for LWIR and a 71% increase across a full waveband as compared to a similar device designed for only LWIR absorption, using a 300°C blackbody at 35 Hz chopping rate. Increased thermal time constant due to additional mass is shown to lessen this enhancement at higher chopping rates.

Although standard uncooled infrared (IR) sensors can be used to record information such as the shape, position, and average radiant intensity of objects, these devices cannot capture color (that is, wavelength) data. Achieving wavelength selectivity would pave the way for the development of advanced uncooled IR sensors capable of providing color information as well as multi-color image sensors that would have significant advantages in applications such as fire detection, gas analysis, hazardous material recognition, and biological analysis. We have previously demonstrated an uncooled IR sensor incorporating a two-dimensional plasmonic absorber (2D PLA) that exhibits wavelength selectivity over a wide range in the mid- and long-IR regions. This PLA has a 2D Au-based periodic array of dimples, in which surface plasmon modes are induced and wavelength-selective absorption occurs. However, the dependence of the absorption bandwidth on certain structural parameters has yet to be clarified. The bandwidth of such devices is a vital factor when considering the practical application of these sensors to tasks such as gas detection. In the present study, control of the bandwidth was theoretically investigated using a rigorous coupled wave analysis approach. It is demonstrated that the dimple sidewall structure has a significant impact on the bandwidth and can be used to control both narrow- and broadband absorption. Increasing the sidewall slope was found to decrease the bandwidth due to suppression of cavity-mode resonance in the depth direction of the dimples. These results will contribute to the development of high-resolution, wavelength-selective uncooled IR sensors.

Graphene consists of a single layer of carbon atoms with a two-dimensional hexagonal lattice structure. Recently, it has been the subject of increasing interest due to its excellent optoelectronic properties and interesting physics. Graphene is considered to be a promising material for use in optoelectronic devices due to its fast response and broadband capabilities. However, graphene absorbs only 2.3% of incident white light, which limits the performance of photodetectors based on it. One promising approach to enhance the optical absorption of graphene is the use of plasmonic resonance. The field of plasmonics has been receiving considerable attention from the viewpoint of both fundamental physics and practical applications, and graphene plasmonics has become one of the most interesting topics in optoelectronics. In the present study, we investigated the optical properties of graphene on a plasmonic metamaterial absorber (PMA). The PMA was based on a metal-insulator-metal structure, in which surface plasmon resonance was induced. The graphene was synthesized by chemical vapor deposition and transferred onto the PMA, and the reflectance of the PMA in the infrared (IR) region, with and without graphene, was compared. The presence of the graphene layer was found to lead to significantly enhanced absorption only at the main plasmon resonance wavelength. The localized plasmonic resonance induced by the PMA enhanced the absorption of graphene, which was attributed to the enhancement of the total absorption of the PMA with graphene. The results obtained in the present study are expected to lead to improvements in the performance of graphene-based IR detectors.

This paper presents the design, modelling and simulation results of silicon/silicon-germanium (Si/SiGe) multi-quantum well based bolometer detector for uncooled infrared imaging system. The microbolometer is designed to detect light in the long wave length infrared (LWIR) range from 8 to 14 μm with pixel size of 25 x 25 μm. The design optimization strategy leads to achieve the temperature coefficient of resistance (TCR) 4.5%/K with maximum germanium (Ge) concentration of 50%. The design of microbolometer entirely relies on standard CMOS and MEMS processes which makes it suitable candidate for commercial infrared imaging systems.

This paper reports the NETD values of various uncooled bolometers fabricated at INO. They are measured using an external readout circuit that emulates the readout scheme of a commercial ROIC. The measured NETD values range between 6 and 75 mK, depending on the pixel pitch and response time. Pixel pitches of 12, 17 and 35 μm are considered. The figure of merit of the characterized detectors is below 350 mK*ms.

Frequency Selective Surfaces (FSS) are periodic array of sub-wavelength antenna elements. They allow the absorptance and reflectance of a surface to be engineered with respect to wavelength, polarization and angle-of-incidence. This paper applies this technique to microbolometers for uncooled infrared sensing applications. Both narrowband and broadband near perfect absorbing surfaces are synthesized and applied engineer the response of microbolometers. The paper focuses on simple FSS geometries (hexagonal close packed disk arrays) that can be fabricated using conventional lithographic tools for use at thermal infrared wavelengths (feature sizes > 1 μm). The affects of geometry and material selection for this geometry is described in detail. In the microbolometer application, the FSS controls the absorption rather than a conventional Fabry-Perot cavity and this permits an improved thermal design. A coupled full wave electromagnetic/transient thermal model of the entire microbolometer is presented and analyzed using the finite element method. The absence of the cavity also permits more flexibility in the design of the support arms/contacts. This combined modeling permits prediction of the overall device sensitivity, time-constant and the specific detectivity.

HgCdTe (MCT) is a very versatile material for IR detection. Indeed, the ability to tailor the cutoff frequency as close as possible to the detection needs makes it a perfect candidate for high performance detection in a wide range of applications and spectral ranges. Moreover, the high quality material available today, either by liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE) allows for very low dark currents at low temperatures and make it suitable for very low flux detection application such as science imaging. MCT has also demonstrated its robustness to aggressive space environment and faces therefore a large demand for space application such as staring at the outer space for science purposes in which case, the detected photon number is very low This induces very strong constrains onto the detector: low dark current, low noise, low persistence, (very) large focal plane arrays. The MCT diode structure adapted to fulfill those requirements is naturally the p/n photodiode. Following the developments of this technology made at DEFIR and transferred to Sofradir in MWIR and LWIR ranges for tactical applications, our laboratory has consequently investigated its adaptation for ultra-low flux in different spectral bands, in collaboration with the CEA Astrophysics lab. Another alternative for ultra low flux applications in SWIR range, has also been investigated with low excess noise MCT n/p avalanche photodiodes (APD). Those APDs may in some cases open the gate to sub electron noise IR detection.. This paper will review the latest achievements obtained on this matter at DEFIR (CEA-LETI and Sofradir common laboratory) from the short wave (SWIR) band detection for classical astronomical needs, to the long wave (LWIR) band for exoplanet transit spectroscopy, up to the very long waves (VLWIR) band.

Finmeccanica (formerly Selex ES) introduced high performance mercury cadmium telluride (MCT) infrared detectors on an 8μm pitch in 2015 with their SuperHawk device which builds on standard production processes already used for the manufacture of 24μm, 20μm, 16μm and 12μm pitch devices. The flexibility of the proprietary Finmeccanica designed diode structure, used in conjunction with the mature production Metal Organic Vapour Phase Epitaxy (MOVPE) MCT growth process at Finmeccanica, enables fine control of diode electrical and optical structure including free choice of cut-off wavelength. The mesa pixel design inherently provides major system performance benefits by reducing blurring mechanisms, including optical scattering, inter-pixel cross-talk and carrier diffusion, to negligible levels. The SuperHawk detector has demonstrated unrivalled MTF and NETD performance, even when operating at temperatures in excess of 120K. The SuperHawk Integrated Detector Cooler Assembly (IDCA) benefits from recent dewar developments at Finmeccanica, which have improved thermal efficiencies while maintaining mechanical integrity over a wide range of applications, enabling use of smaller cryo-coolers to reduce system SWAP-C. Performance and qualification results are presented together with example imagery. SuperHawk provides an easy high resolution upgrade for systems currently based on standard definition 16μm and 15μm infrared detector formats. The paper also addresses further work to increase the operating temperature of the established 8μm process, exploiting High Operating Temperature (HOT) MCT at Finmeccanica, as well as options for LWIR variants of the SuperHawk device.

It is only some years ago, since VGA format detectors in 15μm pitch, manufactured with AIM’s MCT n-on-p LPE standard technology, have been introduced to replace TV/4 format detector arrays as a system upgrade. In recent years a rapid increase in the demand for higher resolution, while preserving high thermal resolution, compactness and low power budget is observed. To satisfy these needs AIM has realized first prototypes of MWIR XGA format (1024x768) detector arrays in 10μm pitch. They fit in the same compact dewar as 640x512, 15μm pitch detector arrays. Therefore, they are best suited for system upgrade purposes to benefit from higher spatial resolution and keep cost on system level low. By combining pitch size reduction with recent development progress in the fields of miniature cryocoolers, short dewars and high operating temperatures the way ahead to ultra-compact high performance MWIR-modules is prepared. For cost reduction MBE grown MCT on commercially available GaAs substrates is introduced at AIM. Recently, 640x512, 15μm pitch FPAs, grown with MBE have successfully passed long-term high temperature storage tests as a crucial step towards serial production readiness level for use in future products. Pitch size reduction is not limited to arrays sensitive in the MWIR, but is of great interest for high performance LWIR or 3rd Gen solutions. Some applications such as rotorcraft pilotage require superior spatial resolution in a compact design to master severe weather conditions or degraded visual environment such as brown-out. For these applications AIM is developing both LWIR as well as dual band detector arrays in HD-format (1280x720) with 12μm pitch. This paper will present latest results in the development of detector arrays with small pitch sizes of 10μm and 12μm at AIM, together with their usage to realize compact cooled IR-modules.

HgCdTe has dominated the high performance end of the IR detector market for decades. At present, the fabrication costs of HgCdTe based advanced infrared devices is relatively high, due to the low yield associated with lattice matched CdZnTe substrates and a complicated cooling system. One approach to ease this problem is to use a cost effective alternative substrate, such as Si or GaAs. Recently, GaSb has emerged as a new alternative with better lattice matching. In addition, implementation of MBE-grown unipolar n-type/barrier/n-type detector structures in the HgCdTe material system has been recently proposed and studied intensively to enhance the detector operating temperature. The unipolar nBn photodetector structure can be used to substantially reduce dark current and noise without impeding photocurrent flow. In this paper, recent progress in MBE growth of HgCdTe infrared material at the University of Western Australia (UWA) is reported, including MBE growth of HgCdTe on GaSb alternative substrates and growth of HgCdTe nBn structures.

Sofradir recently presented Daphnis, its latest 10 μm pitch product family. Both Daphnis XGA and HD720 are 10μm pitch mid-wave infrared focal plane array. Development of small pixel pitch is opening the way to very compact products with a high spatial resolution. This new product is taking part in the HOT technology competition allowing reductions in size, weight and power of the overall package. This paper presents the recent developments achieved at Sofradir to make the 10μm pitch HgCdTe focal plane array based on the legacy technology. Electrical and electro-optical characterizations are presented to define the appropriate design of 10μm pitch diode array. The technological tradeoffs are explained to lower the dark current, to keep high quantum efficiency with a high operability above 110K, F/4. Also, Sofradir recently achieved outstanding Modulation Transfer Function (MTF) demonstration at this pixel pitch, which clearly demonstrates the benefit to users of adopting 10μm pixel pitch focal plane array based detectors. Furthermore, the HgCdTe technology has demonstrated an increase of the operating temperature, plus 40K, moving from the legacy to the P-on-n one at a 15μm pitch in mid-wave band. The first realizations using the extrinsic P-on-n technology and the characterizations of diodes with a 10μm pitch neighborhood will be presented in both mid-wave and long-wave bands.

Detection in the very long wave infrared range (LWIR, 12-15µm) using third-generation infrared focal plane array (FPAs) is essential for remote atmosphere sounding. Indeed, these wavelengths are particularly rich in information about humidity and CO2 levels and provide additional information about cloud structure and temperature profile across the atmosphere. However, the dark current characteristic and associated noise behavior of the HgCdTe photodiode in the wavelength range of 12-15µm, operating at ~77K, are very sensitive to surface passivation techniques as well as to surface material treatments. For current HgCdTe material and device technology, detection of LWIR and VLWIR energy is the subject of current research. Within this range of shrinking band-gaps in detector material, precise control of the quality of the surface passivation and treatment is of great importance. The underlying physics of dark current mechanism is theoretically investigated by using a previously developed simultaneous current extraction approach and numerical simulations. In addition, HgCdTe electron avalanche photodiodes (e-APD) have been widely used for low-flux and high-speed application. To better understand the dark current transport and electron-avalanche mechanism of the devices and optimize the structures, we perform accurate numerical simulations of the current-voltage characteristics and multiplication factor in planar and mesa homojunction (p-i-n) HgCdTe electron-avalanche photodiodes.

To fabricate various advanced structures with HgCdTe material, the Inductively Coupled Plasma enhanced Reactive Ion Etching system is indispensable. However, due to low damage threshold and complicated behaviors of mercury in HgCdTe, the lattice damage and induced electrical conversion is very common. According to the diffusion model during etching period, the mercury interstitials, however, may not diffuse deep into the material at cryogenic temperature. In this report, ICP etching of HgCdTe at cryogenic temperature was implemented. The etching system with cryogenic assembly is provided by Oxford Instrument. The sample table was cooled down to 123K with liquid nitrogen. The mask of SiO2 with a contact layer of ZnS functioned well at this temperature. The selectivity and etching velocity maintained the same as reported in the etching of room temperature. Smooth and clean surfaces and profiles were achieved with an optimized recipe.

The barrier cap layer (BCL) is considered to be able to absorb partially implant induced damages during ion implantation, thus its structure and property could impact the result of ion implantation. In this paper, for As ion implantation in HgCdTe, the different BCLs were deposited on the CdZnTe-based (LPE) and GaAs-based (MBE) HgCdTe epilayers, respectively. Then, the influences of thicknesses and structures of these BCLs on dopant profiles and implant damages were investigated. The as-grown BCLs include thermally evaporated (TE) ZnS, TE CdTe, electron beam evaporated (EBE) CdTe and in-situ CdTe/ZnTe grown by MBE. The SIMS profiles and TEM characterization indicate: For TE ZnS BCLs, there exists an optimized thickness to obtain the deepest As indiffusion after high temperature annealing, and the end-of-range (EOR) depth is linearly proportional to the thickness ratio of a-MCT layer/damage layer. For TE CdTe BCLs, the barrier layer induced channeling effect (BLICE) occurs to the thin BCL samples, while this effect is suppressed in the thick BCL samples. The phenomenon might be due to that the blocking effect of the layered structure inside each crystal column becomes dominate in the thick BCL samples. Additionally, the EBE CdTe BCL with layered structure can suppress effectively the BLICE effect; in the in-situ CdTe/ZnTe BCL, the short defect layer generated in the CdTe buffer layer and the amorphization of the ZnTe layer during ion implantation also play a significant role in suppressing the BLICE effect.

In this paper we review the intrinsic and extrinsic technological properties of the incumbent technology, InP/In_0.53Ga_0.47As/InP, for imaging in the visible- short wavelength spectral band, InSb and HgCdTe for imaging in the mid-wavelength spectral band and HgCdTe for imaging in the long wavelength spectral band. These material systems are in use for a wide range of applications addressing compelling needs in night vision imaging, low light level astronomical applications and defense strategic satellite sensing. These materials systems are direct band gap energy semiconductors hence the internal quantum efficiency η, is near unity over a wide spectral band pass. A key system figure of merit of a shot noise limited detector technology is given by the equation (1+J_dark. /J_photon), where J_dark is the dark current density and J_photon ~qηΦ is the photocurrent density; Φ is the photon flux incident on the detector and q is the electronic charge. The capability to maintain this factor for a specific spectral band close to unity for low illumination conditions and low temperature onset of non-ideal dark current components, basically intrinsic diffusion limited performance all the way, is a marker of quality and versatility of a semiconductor detector technology. It also enables the highest temperature of operation for tactical illumination conditions. A purpose of the work reported in this paper is to explore the focal plane array data sets of photodiode detector technologies widely used to bench mark their fundamental and technology properties and identify paths for improvements.

Rapid sensing of near infrared (IR) energy on a composite structure would provide information that could mitigate damage to composite structures. This paper describes a novel technique that implements photoconductive sensors in a radio frequency (RF) switching network designed to locate in real time the position and intensity of IR radiation incident on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches in a two layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous doped silicon photoconductive sensors are inserted in GHz range RF transmission lines. Photoconductive sensors use semiconductor materials that are optically sensitive at material dependent wavelengths. Incident radiation at the appropriate wavelength produces hole-electron pairs, so that the semiconductor becomes a conductor. By permitting signal propagation only when a sensor is illuminated, the RF signals are selectively routed from the lower layer transmission lines to the upper layer lines, thereby pinpointing the location and strength of incident radiation on a structure. Simulations based on a high frequency 3D planar electromagnetics model are presented and compared to experimental results. Experimental results are described for GHz range RF signal control for 300 mW and 180 mW incident energy from 975 nm and 1060 nm wavelength lasers respectively, where upon illumination, RF transmission line signal output power doubled when compared to non-illuminated results. Experimental results are reported for 100 W incident energy from a 1060 nm laser. Test results illustrate that real-time signal processing would permit a structure or vehicle to be controlled in response to incident radiation

A 15um pixel pitch digital pixel for LWIR time delay integration (TDI) applications is implemented which occupies one fourth of pixel area compared to previous digital TDI implementation. TDI is implemented on 8 pixels with oversampling rate of 2. ROIC provides 16 bits output with 8 bits of MSB and 8 bits of LSB. Pixel can store 75 M electrons with a quantization noise of 500 electrons. Digital pixel TDI implementation is advantageous over analog counterparts considering power consumption, chip area and signal-to-noise ratio. Digital pixel TDI ROIC is fabricated with 0.18um CMOS process. In digital pixel TDI implementation photocurrent is integrated on a capacitor in pixel and converted to digital data in pixel. This digital data triggers the summation counters which implements TDI addition. After all pixels in a row contribute, the summed data is divided to the number of TDI pixels(N) to have the actual output which is square root of N improved version of a single pixel output in terms of signal-to-noise-ratio (SNR).

This paper reports the development of a new dual-polarity Direct-Injection (DI) Readout Integrated Circuit (ROIC), called MT6420DDA, designed to support back-to-back connected photodiodes with a single contact per pixel using dual pixel input circuitries suitable for both p-on-n and n-on-p type detectors. The ROIC has a format of 640 × 512 (VGA) and a pixel pitch of 20μm, and can be used to build dual-color or dual-band FPAs working in the MWIR and/or LWIR bands. The ROIC supports snapshot operation with Integrate-then-Read (ITR) and Integrate-while-Read modes (IWR). MT6420DDA has a system-on-chip architecture, with programmable biasing, timing, and configuration. The ROIC supports 2, 4, and 8-output modes at pixel output rates up to 12.5 MHz per output. It runs on 3.3 V analog and 1.8 V digital supplies, and dissipates less than 135 mW in the 4-output mode at 10 MHz. The ROIC has separate programmable full well capacitance values of 1.5 Me-, 3.0 Me-, and 6.0 Me- for both polarities in the high-gain (HG), mid-gain (MG), and low-gain (LG) modes. The ROIC supports two type of polarity switching modes as PSBF (Polarity Switching between Frames) and PSWF (Polarity Switching within Frames). In the PSBF modes, an alternating input polarity is used for each detector type for each frame during each integration period, possibly with different full-well and integration time settings. In the PSWF mode, both type of pixels are exposed almost simultaneously, where detector current is integrated in a time multiplexed manner using the two separate integration capacitors of the pixel input circuitry. The PSBF mode is simple, but the time stamp for each image frame is different. The PSWF mode is complex, but results in a pseudo simultaneous registration of images for each color or spectral band. The ROIC has been developed for cryogenic operation down to 65K with an input referred noise level of less than 470 e- rms in the low-gain (LG) mode at 77K. The MT6420DDA ROIC has been fabricated on 200 mm wafers containing a total of 89 parts with typically 75 working parts. 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. MT6420DDA can also be used together with MTAS1410X8, an 8-channel ASIC from Mikro-Tasarim, that can be used to drive the FPA and digitize its analog outputs to build compact and low-noise Integrated-Detector-Dewar-Cooler-Assembly (IDDCA) units and camera cores.

Digital pixels based on pulse frequency modulation (PFM) employ counting techniques to achieve very high charge handling capability compared to their analog counterparts. Moreover, extended counting methods making use of leftover charge (residue) on the integration capacitor help improve the noise performance of these pixels. However, medium wave infrared (MWIR) focal plane arrays (FPAs) having smaller pixel pitch are constrained in terms of pixel area which makes it difficult to add extended counting circuitry to the pixel. Thus, this paper investigates the performance of digital pixels employing off-pixel residue measurement. A circuit prototype of such a pixel has been designed for 15μm pixel pitch and fabricated in 90nm CMOS. The prototype is composed of a pixel front-end based on a PFM loop. The frontend is a modified version of conventional design providing a means for buffering the signal that needs to be converted to a digital value by an off-pixel ADC. The pixel has an integration phase and a residue measurement phase. Measured integration performance of the pixel has been reported in this paper for various detector currents and integration times.

Crosstalk characteristics of high density FPA detectors attract widespread attention in the application of electro-optical systems. Crosstalk characteristics of near-infrared (NIR) InGaAs photodiodes and focal plane arrays (FPAs) were studied in this paper. The mesa type detector was investigated by using laser beam induced current technique (LBIC) to measure the absorption outside the designed photosensitive area, and the results show that the excess absorption enlarges the crosstalk of the adjacent pixels. The structure optimization using the effective absorption layer between the pixels can effectively reduce the crosstalk to 2.5%. The major crosstalk components of the optimization photodiode come from the electronic signal caused by carrier lateral diffusion. For the planar type detectors, test structures were used to compare the crosstalk of different structures, and the guard ring structure shows good suppression of the crosstalk. Then the back-illuminated 32x32 InGaAs photodiodes with 30μm pitch were designed, and LBIC was used to measure its lateral diffusion of the effective carriers and fill factor of photosensitive area. The results indicate that the fill factor of detectors can reach up to 98% when the diffusion region is optimized, and the minimum response exists between two neighborhood pixels. Based on these crosstalk measurement results and optimizing structure designs, the linear InGaAs photodiodes were designed and thus the InGaAs FPA assembly was fabricated. The assembly shows higher electro-optical performance and good improvement on crosstalk. The assembly was applied in infrared imaging system and modulation transfer function (MTF) of FPA assembly was calculated to be above 0.50. The clear image based on FPA assembly was obtained.

The electric simulation models of CMOS devices provided by the foundries are valid at the standard temperature range of -55 to 125°C. These models are not suitable to the design of circuits intended to operate at cryogenic temperatures as is the case of cooled infrared readout circuits. To generate a library of CMOS electric simulation models valid at cryogenic temperatures, the characterization of wide and long CMOS transistors are investigated. The EKV2.6 model, which is an industry-standard compact simulation model for CMOS transistors, is used in this characterization. Due to its relatively small number of parameters the EKV2.6 model is well suited to the parameter extraction procedures when not disposing of an expensive automated parameter extraction system. It is shown that to provide an appropriate IV-characteristic fit to cryogenic temperature range it is sufficient to extract only five parameters - threshold voltage VT0, body effect GAMMA, Fermi potential PHI, transconductance factor KP, and the vertical characteristic field for mobility reduction E0. The proposed approach is tested in a standard 0.35μm/3.3V CMOS technology, employing extraction procedures recommended in the literature. Simulations are made with a BSIM3V3 standard library provided by the foundry changing the temperature parameter and with the generated library. The results are compared with the measurements. As expected, the simulations made with the generated library show a best agreement with the performed measurements at 77K than the simulations with the BSIM3V3 model. The proposed methodology is shown to be particularly effective above strong freeze-out temperature.

This work is a continuation of our preliminary tests on NIRCA - the Near Infrared Readout and Controller ASIC [1]. The primary application for NIRCA is future astronomical science and Earth observation missions where NIRCA will be used with mercury cadmium telluride image sensors (HgCdTe, or MCT) [2], [3]. Recently we have completed the ASIC tests in the cryogenic environment down to 77 K. We have verified that NIRCA provides to the readout integrated circuit (ROIC) regulated power, bias voltages, and fully programmable digital sequences with sample control of the analogue to digital converters (ADC). Both analog and digital output from the ROIC can be acquired and image data is 8b/10bencoded and delivered via serial interface. The NIRCA also provides temperature measurement, and monitors several analog and digital input channels. The preliminary work confirms that NIRCA is latch-up immune and able to operate down to 77 K. We have tested the performance of the 12-bit ADC with pre-amplifier to have 10.8 equivalent number of bits (ENOB) at 1.4 Msps and maximum sampling speed at 2 Msps. The 1.8-V and 3.3-V output regulators and the 10-bit DACs show good linearity and work as expected. A programmable sequencer is implemented as a micro-controller with a custom instruction set. Here we describe the special operations of the sequencer with regards to the applications and a novel approach to parallel real-time hardware outputs. The test results of the working prototype ASIC show good functionality and performance from room temperature down to 77 K. The versatility of the chip makes the architecture a possible candidate for other research areas, defense or industrial applications that require analog and digital acquisition, voltage regulation, and digital signal generation.