This PDF file contains the front matter associated with SPIE Proceedings Volume 11002, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

FLIR Systems has recently developed and begun manufacturing a miniature linear Stirling cryocooler, the FL-100, which has been designed to meet the needs of compact systems using High Operating Temperature (HOT) detectors. These include low cost, long life, high efficiency, and a very compact packaging size. A compact and efficient drive electronics board, the Cryogenic Cooler Controller (CCC), has also been developed to pair with the FL-100. This paper presents the design specifications of the FL-100 cryocooler and summarizes the results of the testing which has been completed thus far on prototype and early production units.

Cryogenically cooled infrared detectors are known to have better temperature resolution and shorter integration time as compared to the uncooled “competitors”. These advantages allow for longer detection distances, better spatial resolution and the ability to detect fast moving objects. However, high ownership cost of the mechanical cryogenic refrigerator, along with tough export regulations, prevent the widespread deployment of cryogenically cooled infrared imagers in the commercial marketplace. CRYOTECH LTD reports on the development of cost-effective, low size, weight, and power cryogenic solutions for commercial high operational temperature infrared imagers. The authors present the outcomes of the feasibility study, predictions of theoretical performance along with size and weight assessments.

The Northrop Grumman Aerospace Systems (NGAS)`s MicroCooler is a split configuration pulse tube cooler incorporating a coaxial cold head connected via a transfer line to a vibrationally balanced back to back linear flexure bearing compressor. Designed for > 10 year operation with no degradation in performance, this 900 gram cryocooler incorporates a very efficient pulse tube cold head for operation over a range of temperatures above 40K. This paper presents the results of a series of tests designed to qualify the NGAS MicroCooler to the Technology Readiness Level (TRL) 6. The MicroCooler was subjected to launch vibration and thermal cycling conditions appropriate to space applications. The measured load lines and unchanged refrigeration performance of the cooler throughout the qualification program demonstrated the robustness of the design. The performance of the MicroCooler was also characterized over a range of rejection temperatures and input powers to demonstrate its suitability for a wide range of missions and applications. The successful completion of series of tests has demonstrated that this very small, low vibration, high frequency cooler is qualified to be integrated into space payloads or an integrated detector cooler assembly (IDCA) for tactical applications, similar to those used with shorter lived tactical coolers.

Designing custom hardware for space payloads often imposes many constraints in terms of non-recurring design effort and material lead times. Transitioning the use of Commercial-Off-The-Shelf (COTS) hardware for increased-severity environmental service can prove a desirable alternative when mission requirements have some flexibility in terms of weight and envelope. Surviving the extreme vibration conditions present during a rocket launch is one of the most difficult challenges for the use of COTS-based solutions. IRCameras has provided a pathway means of ruggedizing common weak links within Integrated Dewar Cooler Assembly (IDCA) to support CubeSat space launch missions.

With miniature high operating temperature cryocoolers becoming commonplace, there is an increasing importance of accurate determination of the thermal properties of infrared dewars such as heat load and thermal mass, as well as an increasing challenge to obtaining these properties. Especially in the case where operating temperature in the application is far from liquid nitrogen temperature, such as with HOT detectors, the use of the various known methods should be carefully evaluated. Inconsistencies in results between the various available methods, such as nitrogen boil-off, multi-slope warm-up calorimetry, and theoretical thermal modelling will be discussed, and the work being done at Thales Cryogenics to resolve these inconsistencies is presented.

Over the past decade, AIM has developed a family of compact, highly reliable cryocoolers to meet the demands of various customers and its products. These developments mainly focused on the improvement and optimization of size, weight, power consumption and cost (SWaP,C). In particular, efforts have been made to meet the requirements for ultra-compact camera cores using high operating temperature (HOT)-IR sensors as well as for high performance IR-modules using the latest digital ROIC technology. Design features and performance data of the most recent cryocooler and cooler electronics developments will be presented. Technical details introduced to meet demanding customer requirements will be discussed.

The RMs1 is the new SWaP rotary cooler qualified by Thales in 2018. The architecture and the building blocks used to design that cooler have led to significant improved efficiency. The paper will describe the performances of the product, especially its thermal efficiency. An updated presentation of the reliability figures will also be done. The current available cryogenics power and the thermal efficiency allow RMs1 to be used for a wide range of applications. Either large detector arrays could be cooled by an RMs1 at High Operating Temperature, either smaller dies could be cooled down to lower temperature. The presentation will focus on the associated tuning of some parameters like the filling pressure to find the best trade-off adapted to the application. For instance, 24/7 applications will focus on reliability while HHTI may be more concerned by the power consumption. Also a first reflection will be presented on the potential definition and performance of a splitted RMs1 cooler where the cold fingers is detached from the compressor enabling a more flexible integration with a significantly reduced length in the axis of the cold finger. As a result, a mapping of cryogenics performances will be presented.

To suppress the surface leakage current of InAs/GaSb Type-II superlattice (T2SL) infrared photodetectors, atomic layer deposited (ALD)-Al₂O₃ passivation effects have been investigated. By using the ALD-Al₂O₃ passivation layers, surface leakage current was more effectively suppressed than by using chemical vapor deposited-SiO₂ passivation layers. The deposition temperature of ALD Al₂O₃ played an important role in minimizing the surface leakage current of T2SL infrared photodetectors. We found that the dark current density of mid-wavelength (MW) p-i-n structures was limited by their bulk components with Al₂O₃ passivation layers deposited at or below 200 °C, while the dark current density increased with the surface leakage when the layers were deposited at 260 °C. From the capacitance–voltage analysis, it was found that the deposition at 260 °C led to a large interface trap density at the Al₂O₃/GaSb interface. The results of X-ray photoelectron (XPS) spectroscopy show that the spectra of Sb₂O₃ decreases while that of Ga₂O₃ increases when the deposition temperature increases from 200 to 260 °C. This indicates that the reaction of Sb₂O₃ with GaSb is thermally enhanced. Based on these results, we conclude that Ga₂O₃ and/or elemental Sb may lead to an additional leakage path. Hence, suppression of the thermal decomposition of Sb-related oxides during Al₂O₃ deposition is required to obtain good passivation effects.

Type-II superlattices (T2SLs) are considered the III/V alternative to HgCdTe for infrared (IR) detectors and have already reached market maturity. Fraunhofer IAF has demonstrated mono- and bi-spectral T2SL focal plane arrays up to 640×512 pixels for mid- and long-wavelength IR. In order to develop an industry-compatible T2SL technology, we have established the complete chain for detector array fabrication including design and modelling, epitaxial growth, as well as front- and backside processing. The epitaxial growth of T2SLs is performed by molecular beam epitaxy (MBE) in multi-wafer reactors. In this paper, we report on the control of growth rates during epitaxy, uniformity and reproducibility of the growth process, as well as characterization techniques to monitor the quality of the epitaxial layers. For the superlattice period, an average thickness variation far below a single atomic monolayer is required and achieved routinely. The standard deviation of the photoluminescence peak for both colors of bi-spectral IR detectors is around 0.04 μm for consecutive growth runs. With this very stable and reproducible epitaxial growth process in conjunction with our mature front- and backside processing we have been able to set up a pilot line production for bi-spectral T2SL IR detector arrays.

We report resonant-cavity infrared detectors with absorbers that consist of only five quantum wells, but exhibiting 34% external quantum efficiency at room temperature at the resonant wavelength of 4.0 μm. The FWHM linewidth is 46 nm, and the peak absorption is enhanced by nearly a factor of 30 over that for a single pass through the absorber. Although the Shockley-Read lifetime in the current material is much shorter than the state of the art, the dark current density is at the level of HgCdTe detectors as quantified by “Rule 07”. The Johnson-noise limited detectivity (D*) at 21°C is 7 × 10⁹ cm Hz^½/W. We expect that future improvements in the device design and material quality will lead to higher quantum efficiency, as well as a significant reduction of the dark current density consistent with the very thin absorber.

Stability over time has recently become a figure of merit of major importance to compare the performances of infrared focal plane arrays (FPA) of different technologies. Indeed, this parameter dictates how often the calibration of operational electro-optical systems has to be done, and thus reflects the availability of the system during an operational mission. The stability over time is generally estimated through fixed pattern noise (FPN) and residual fixed pattern noise (RFPN) measurements after a two-point correction. However, each laboratory or industrial has its own protocols and criteria, such that published results cannot be easily compared. Recent studies also showed that random telegraph signal (RTS) noise, which leads to flickering pixels, can strongly affect the image quality, so the question arises as to wether these RTS pixels have an effect on RFPN. In this paper, we describe our experimental protocol to evaluate the stability over time of an FPA and to count up/classify flickering pixels. We then present the results obtained on a T2SL MWIR Integrated Detector Dewar Cooler Assembly (IDDCA) provided by IRnova. Our measurements show that the stability over time of the T2SL MWIR IDDCA are excellent: first, in terms of FPN/RFPN; then, in terms of RTS noise with only a few blinking pixels. We also show that the RTS pixels having an effect on the RFPN are fully detected by the algorithm used to rule out defective pixels before calculating RFPN.

The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) is an adjustable band gap, broad-band III-V infrared detector material that has emerged in recent years as an alternative to the more established InAs/GaSb type-II superlattice. We have reported results on a mid-wavelength focal plane array (FPA) based on the InAs/InAsSb T2SLS unipolar barrier infrared detector architecture. Significantly, the FPA exhibits very good operating characteristics at 160 K, demonstrating a considerably operating temperature advantage over the MWIR market-leading InSb FPAs, while maintaining III-V semiconductor manufacturing robustness. In this article we summarize the development at the NASA Jet Propulsion Laboratory leading to the mid-wavelength InAs/InAsSb T2SLS infrared detectors, provide a brief look at the history of the development of the InAs/InAsSb T2SLS absorber, and survey the current status of InAs/InAsSb T2SLS detectors.

Third generation of infrared imagers demand performances for higher detectivity, higher operating temperature, higher resolution, and multi-color detection all accomplished with better yield and lower manufacturing costs. Antimonide-based gap-engineered Type-II superlattices (T2SLs) material system is considered as a potential alternative for Mercury- Cadmium-Telluride (HgCdTe) technology in all different infrared detection regimes from short to very long wavelengths for the third generation of infrared imagers. This is due to the incredible growth in the understanding of its material properties and improvement of device processing which leads to design and fabrication of better devices. We will present the most recent research results on Antimonide-based gap-engineered Type-II superlattices, such as high-performance dual-band SWIR/MWIR photo-detectors and focal plane arrays for different infrared regimes, toward the third generation of infrared imaging systems at the Center for Quantum Devices. Comparing metal-organic chemical vapor deposition (MOCVD), vs molecular beam epitaxy (MBE).

There has been significant advancement in 6.1 Å InAs/GaSb/AlSb type II superlattices in the past decade due to significant investments by the department of defense for applications in infrared detectors and focal plane arrays. One of the advantages of the antimonide system is the large variety of materials options (bulk/Ga-bearing, Ga-free, binary/ternary superlattices) and the various device architectures enabled by designer offsets. However these degrees of freedom require careful trade-off balancing performance and complexity. In this talk, I will describe some of the physics of the superlattices including the various techniques to engineer the band structure using quantum confinement. I will then discuss some of the approaches to engineer band-diagrams in this system to achieve high performance detectors. Finally, I will describe our efforts to break the conventional trade-off between signal, noise and speed using architectures involving dielectric resonators coupled with deep sub-wavelength detectors and novel integration schemes with read-out integrated circuits.

Have we finally accomplished full maturity infrared focal planes? Are the pitches small enough, array sizes large enough, well capacity (and digital ROIC) deep enough, and quantum efficiency high enough? Have we exploited every photon that is available? Have we achieved full optical performance to include diffraction, aberrations, and processing? If not, what is left? Have we exploited spectral characteristics, polarization, and time to the limits? At what point, do these systems become adaptive imaging systems that can respond to multiple missions? At what point do these systems become known as computational imaging systems? In fact, one important question might be: are we still specifying the performance requirements of advanced infrared imagers the right way? The author does not know the answer to most of these questions, but will discuss future possibilities.

The need for greater flexibility, tunability, and performance has led to the more recent development of IR detector materials and technologies based on an array of Sb-based III-V compounds and structures. While these approaches have proved successful for some applications, practical limitations related to accessible materials properties and integrable combinations still exist. To provide a larger materials palette from which long-wave (8-14 μm) IR photodetectors may be produced, the use of high-quality metamorphic (i.e. strain-relaxed lattice-mismatched) virtual substrates that provide access to lattice constants between GaSb and InSb is of substantial interest. To this end, we are engaged in the investigation of multiple metamorphic pathways via MBE and MOCVD based compositional grading to support the development of high-performance InAsSb long-wave IR photodetectors. These efforts are focused on two main avenues: (1) a novel digital alloy approach for MBE-grown AlInSb metamorphic buffers; and (2) MOCVD-based growth of more traditional InAsSb compositionally-graded buffers. In both cases, preliminary work has resulted in threading dislocation densities at target lattice constants on the order of 1-3×10^6 cm^-2, with room for significant further reduction. Initial prototype InAsSb nBn test devices (8 μm cutoff), grown via MBE on AlInSb virtual substrates, have yielded dark currents as low as 3×10^-6 A/cm^2 (at 0.3 V), an order of magnitude below the equivalent “Rule 07” HgCdTe value, indicating strong promise for the development of high-performance devices. At the conference, we will present up-to-date results on the metamorphic buffer development and integrated devices for these two promising pathways.

GaSb-based infrared (IR) photodetector technology progression is toward larger-format focal plane arrays (FPAs). This requires a performance-based and cost-based manufacturing process on larger diameter substrates for improved throughput, volume, and yield. IQE has demonstrated molecular beam epitaxy (MBE) growth processes for barrier-design detectors (nBn) in multi-wafer configurations on 4-inch and 5-inch diameter GaSb substrates, and via a metamorphic process on 4-inch and 6-inch GaAs substrates. Recently we took the next step in this progression, growing nBn detectors on 6-inch Si substrates coated with CVD-grown Ge, opening the door for potential integration with Si-based electronic circuitry. Here, we compare the epiwafer characteristics (morphology, x-ray, PL) and diode performance (turn-on, QE, cutoff wavelength) of this M-nBn on Ge-Si with the same M-nBn on GaAs and the corresponding nBn structure grown on native GaSb substrate. Similar performance was obtained on all three types of substrates. We also present FPA data based on a 640×512 pixel, 15 μm pitch process without substrate removal, where QE ~ 80%, NE▵T < 20 mK, and operability <99% was demonstrated. The results represent an important technological path toward next-generation large-format IR detector array applications.

We recently evaluated the optical and electric characteristics of mid-wave photodetector (PD) diodes grown on high-index substrates. Preliminary results indicate that substrate orientation and surface polarity can modify PD parameters such as photoluminescence (PL), dark current (J_d), quantum efficiency, and spectral characteristics. In this work, we focused on growth parameter optimization for long-wave type-II strained layer superlattice (T2SL) PD structures grown on (211)B and (311)A GaSb substrates. Material and PD diode characteristics were compared with reference data obtained on (100)-oriented substrates. Material quality was evaluated by HRXRD, AFM, Nomarski microscopy, 77 K PL, and PD J-V and spectral testing. Photoluminescence and cutoff wavelength measurements for diode structures fabricated on (211)B and (311)A substrates demonstrate a significant redshift due to a reduction of the optical bandgap in the SL. The extent of redshift increases with superlattice period and Sb mole fraction in the InAsSb layers in the absorber. All wafers demonstrated reasonable surface morphology without surface corrugation, with minor variability in roughness. Redshift in 77 K PL and cutoff wavelength, in combination with high QE and low J_d, obtained from growths on these high-index substrates offer a potential path to achieve enhanced PD characteristics with reduced SL period for a given wavelength by comparison to (100) substrates.

In this paper we report our success in increasing length of n-type region and decreasing EPD in doped GaSb crystals grown with new oriented seed method. The importance and challenges of growing high quality (low and high doped) GaSb crystals suitable for the routine production of large area focal plane arrays is discussed. Also comparisons and advantages of using oriented seed growth method suitable for wafer production is elucidated. The purity and the stoichiometric ratio of the starting charge has been designed in such a way, the grown crystals have an improved yield of n-type single crystal. This is attributed to the stoichiometric optimization mechanism with respect to the grown-in acceptors, which additionally, has also favoured by decreasing the EPD levels in the grown crystals. Also, we report our recent developments in the bulk growth of large size (up to 25 kg) higher doped crystals grown with oriented seed method, these being required for a new applications of GaSb where very low resistivity substrates are required. The results of quantitative measurements (EDX) as well as structural (dislocation density by EPD assessments and X-Ray analyses) and electrical (carrier concentration by Hall measurements) are presented. High quality crystals (both low and high doped) using the oriented seed method were grown. This work constitutes an important milestone in the development of higher throughput production processes for GaSb substrates which are based upon the volume production of single crystal GaSb boules which meet not only meet well established quality requirements for infrared focal plane array applications but also an emerging set of new GaSb based device technologies which place additional demands on the quality of bulk crystals grown.

High quality substrates are a critical requirement for the epitaxial growth of high performance Group III-V (GaSb, InP, GaAs) or II-VI (MCT) based IR detector structures. Techniques such as MBE, LPE or MOCVD used to grow complex multilayer structures where the bulk and surface characteristics of the underlying substrate strongly influences the quality of the deposited device layers and thus the performance of the detector fabricated too. And whilst for Group III-V substrates, ‘epitaxy ready’ surfaces are very much the norm with no surface pre-treatment required prior to growth, much debate exists over whether it is possible to prepare Cadmium Zinc Telluride (CZT) substrates in the same way with commercially available substrates often etched or pre-polished prior to epitaxial growth. In this work we discuss the key factors which determine the ‘epi-readiness’ of a compound semiconductor substrate and identify the challenges which are associated with polishing ternary materials when compared with binary compounds. We also discuss the role which bulk CZT crystal quality plays on chemo-mechanical polish surface quality and the importance of substrate selection and screening steps to ensure that high quality substrates are obtained. We also compare the maturity level of infrared substrate materials such as GaSb with CZT and propose how CZT substrates can be chemo-mechanically polished in a production setting with the same tool sets as used to produce volume quantities of III-V compound semiconductor substrates in epitaxy ready form, as opposed to smaller scale, bespoke finishing processes. A forward looking view is given on the potential to align II-VI and III-V substrate manufacturing technologies in a way that supports product standardization and conformity at a time when demands for IR specification substrates is forecast to increase. Not only in quantity but also size where more stringent bulk and surface quality is required if state of the art, very large format detectors are to be delivered.

The paper details some of the history of Clinical Virtual Reality (VR) as it has evolved over the last 25 years and provides a brief overview of the key scientific findings for making a judgment regarding its value in the areas of mental health and rehabilitation. This write-up is designed be a companion piece to my SPIE keynote on the topic of, “Is Clinical Virtual Reality Ready for Primetime?” As such, the paper is packed with citations to key scientific research in this area that should provide readers who are interested in this topic with a roadmap for further exploration of the literature. After presenting a brief history of the area, a discussion follows as to the theory, research, and pragmatic issues that support the view that this VR use case is theoretically informed, has a large and convincing scientific literature to support its clinical application, and that recent technology advances and concomitant cost reductions have made clinical implementation feasible and pragmatically supported. The paper concludes with the perspective that Clinical VR applications will soon become indispensable tools in the toolbox of psychological researchers and practitioners and will only grow in relevance and popularity in the future.

The performance of mid- and long-wavelength infrared (IR) detectors is still restricted with the dark current characteristics and associated noise behavior. In this work, we propose reducing the dark current and related noise of the IR detectors to elevate high operating temperature and improve the detector quantum efficiency (QE), by using a thin absorption layer of IR absorbing materials like lead selenide (PbSe) and mercury cadmium telluride (HgCdTe). A photon bending and trapping mechanism based on integrated micro/nanoscale holes was employed to ensure high quantum efficiency despite using a thin absorbing layer. Using finite-difference time-domain (FDTD) method, the effect of embedded hole arrays on the optical absorption enhancement of ultra-thin PbSe and HgCdTe has been investigated. The calculated optical absorptions in ultra-thin IR structures without holes were compared with that of similar structures embedded with hole arrays. The optical absorption in 2 μm thick PbSe film without holes is less than 5% for 3-5 μm mid-IR wavelengths. Although applying conventional anti-reflecting (AR) coatings leads to a slightly higher absorption, it can cause higher dark current due to increased surface traps. Integration of hole arrays in 2 μm thick PbSe film has shown a significant optical absorption enhancement, up to 20% at 4.5 μm wavelength. This is equivalent to more than 2- and 4-folds' enhancement compared to a 2 μm thick flat-surface structure with AR and without AR, respectively. In addition, embedding the hole arrays in 1.2 μm thick HgCdTe IR films enhances the optical absorption up to 75% at 4.5 μm, which is more than 4 times higher than that in HgCdTe structure without holes. Additionally, the optical absorption in 1.2 μm thick HgCdTe film with periodic array of photon-trapping micro-holes enhances to 27% at 10 μm, long-IR wavelength. This is more that 3 times higher than that in HgCdTe films without holes. Our work revealed that the embedding hole arrays not only enhances the optical absorption in IR ultra-thin structures but also can reduce that material filling ratio to ~50%, which leads to a lower dark current, ensuring higher temperature operation of the IR detectors.

In this paper, the performance of high operating temperature (HOT) type-II superlattice FPAs (640 × 512 pixels @ 15 μm pitch), are demonstrated. The type-II superlattice design used for these FPAs has a cut-off wavelength of 5.3 μm and the quantum efficiency is extracted to 80% at FPA level. The HOT FPAs are integrated in IDDCAs with small size, weight and power (SWaP) with F#4 configuration. Excellent imaging performance is demonstrated at 110 K with temporal NETD of 21 mK, spatial NETD of 7 mK, 10 ms integration time and typical operability > 99.8 %. From modelling and studies of the temperature dependence of the FPA performance, further increase of the operating temperature up 130 K is predicted for the 5.3μm design.

An analysis of the use of infrared technology in asymmetric warfare

There is great interest in MWIR Ga-free type II strained layer superlattice (T2SLS) nBn detectors for background limited photodetectors (BLIP) operating at temperatures higher than InSb (T ≥ 150K compared to T≈ 80-90K). Recently, Ting et al. [Proc. SPIE, Vol. 10624, 1062410-1 (2018)] reported on measurements of the dark current and quantum efficiency (QE) for e-SWIR (λ>1.7 μm), MWIR, and LWIR Ga-free nBn T2SLS detectors. Of particular interest is the reported MWIR nBn T2SLS data, since the measured dark current and QE provide the opportunity to analyze the measured detector optoelectronic characteristics using optical properties obtained separately from the hole minority carrier lifetime and optical absorption coefficient data, hence no adjustable parameters. The goal is to develop and utilize robust modeling techniques to explain real, measured nBn detector data to understand the technology limitations and the improvements needed to optimize performance and device designs. A notable result is the observation that the dark current data under reverse bias (-100 mV < bias ≤ 0 mV) obeys the ideal diode equation, where the saturation dark current is in agreement with the radiative recombination rate obtained from the measured absorption coefficient and a 9 μs Shockley-Read-Hall (SRH) lifetime obtained from the measured hole lifetime data. Most important is that the expected generation-recombination (G-R) space charge current based on the 9 μs SRH lifetime is not observed as expected for an ideal nBn heterojunction detector and that increasing excess dark currents are observed with decreasing temperature. The in-band external QE measured at 100K is in the range of 30% and is observed to increase with increasing operating temperature which indicates effects influenced by hole mobility anomalies. In contrast to the above listed observations, the Type II Ga-free nBn detector data reported by D. Ting et al. [Appl. Phys. Lett., 113, 021101, 2018] exhibits a hole energy barrier, G-R dark current like characteristics, and both temperature/voltage dependent QE.

GaSb has a high numerical index (approximately 3.90 at a wavelength of 2 μm), leading to reflection of about 35% of incoming photons, depending on wavelength. This results in a significant loss of quantum efficiency for GaSb-based infrared detectors when backside-illuminated, since GaSb is the first material encountered. Here we demonstrate a way of etching broadband antireflective GaSb grass using an inductively coupled Cl₂ plasma etch with O₂ micromasking, and we examine the possibility for using this material as an antireflective surface for infrared detectors (a patent is pending concerning integration with GaSb-based infrared detectors). We demonstrate sub-10% reflectivity for wavelengths ranging from 200 nm to 12.2 μm and at angles of incidence up to 58°.

Lattice matched InGaAs arrays grown on 100 mm InP substrates have been manufactured commercially into 1280x1024 arrays on 12 and 10 µm pixel pitches for several years. This effort demonstrates the ability to hybridize the same format arrays on smaller 8 µm pitch. The smaller pitch array has high operability and substrate removal enables response from 400 to 1700 nm. The array has 100% fill factor and is capable of room temperature operation. The read out architecture utilized a source follower per detector structure with two full wells of 120 ke- and 2 Me- with an onboard 12 bit digital ADC. The digital imager is capable of fast frame rates exceeding 150 frames/s at full resolution at sub 65e- of readnoise. This fast frame rate combined with the two full well capacities which have a large variation allow electronics in a future iteration for a high dynamic range camera system. The low magnitude and high uniformity of the dark current enables the use of a simple single point Non-Uniformity Correction (NUC) to produce a clear image. This imager is suitable for use in uncooled applications because of the low dark current and simple read out architecture. The smaller pixel pitch enables smaller optical trains and form factors at a significantly reduced cost. The cost savings are further enhanced as the technology transitions to wafer scale hybridization.

Reconnaissance tasks and the detection of camouflaged targets can be improved if the different surface reflection conditions of natural and artificial surfaces can be discriminated in multispectral images. Analogue to the visible, colorimetry in the shortwave infrared spectral range has been presented in praxis and theory in [1]. In this presentation we will discuss the influence of a four filter set onto the capability of the system to discriminate different spectral characteristics of two objects. An optimal choice of filters is presented in the sense of a homogenous discrimination characteristics across the SWIR band, taking into account the SWIR solar spectrum. Based on this choice two development issues were investigated: the accuracy of the color values with respect to measurement noise and the display of SWIR color images. As a figure of merit for color value accuracy the Noise Equivalent Wavelength Difference is introduced describing the minimum color difference that can be resolved/discriminated from the noise floor. Due to the lack of a physiologic counterpart as known from the visual colorimetry where the eye is used as reference for the three color channels, we will showcase a model for transforming and displaying SWIR colors in the R-G-B color space.

Short-wave infrared (SWIR) detection systems are increasingly demanded for surveillance, reconnaissance, and remote sensing applications. Passive SWIR cameras can benefit from an extended spectral range, compared to standard nightvision goggles, and the exploitation of the faint night-glow emission from the night sky. Furthermore, eye-safe SWIR lasers can improve the contrast and range of night-vision systems. High-performance SWIR photodetectors can be realized in the InGaAs material system, providing a typical cutoff wavelength of 1.7 μm, which covers a wide part of the night-glow spectrum as well the emission lines of available laser sources at typical telecom wavelengths around 1.55 μm. However, the low photon flux in night-vision applications demand for high responsivities and very low dark-current characteristics of the InGaAs photodetectors. We report on the current development activities of InGaAs SWIR photodetectors at Fraunhofer IAF. We have implemented a planar process technology of InGaAs/InP pin photodiodes for the fabrication of low-light-level SWIR cameras with 640× 512 pixels with 15 μm pixel pitch. Electro-optical characterization results of early-stage process runs exhibit darkcurrent densities below 10^-7 A/cm² at room temperature for 15-μm pitch detector elements. The current activities focus on further reducing the dark current to reach the international state of the art. Moreover, InGaAs-based avalanche photodiode (APD) have been developed for active SWIR imaging. Gain values of M ≈ 10 on camera level at a reverse bias voltage around 20 V have been achieved by a sophisticated vertical detector design. FPAs of such InGaAs-APD material have been successfully integrated into SWIR cameras with 640 × 512 pixels at 15 μm pixel pitch and operated in SWIR laser gated viewing mode.

For improved long-range reconnaissance applications, a SWIR module for active imaging was developed at AIM. Using laser illumination together with gated viewing (GV) capability reduces noise, amount of background clutter and path radiance and helps e.g. to see through smoke obscuration. Based on AIM’s MCT technology a 2D SWIR electron avalanche photodiode (eAPD) array was developed. A 640×512 15μm pitch format was chosen to allow imaging with the desired resolution. The APD arrays have been designed and fabricated by liquid phase epitaxy (LPE) growth of MCT layers for a 2.5μm cut-off on lattice-matched CdZnTe substrates. Also, a specific ROIC was designed to enable the GV capability of the module. In GV operating mode, the gate can be controlled by an external trigger signal or by internal timing parameters. The gate-delay and integration can be programmed precisely. Focal Plane Arrays (FPAs) have been fabricated and integrated into a dewar/cooler assembly. A dedicated command and control electronics has been designed providing the system interface including power supply, triggering and digital video data. To demonstrate long-range reconnaissance capability of SWIR GV a field camera demonstrator was developed. The demonstrator incorporates the SWIR GV camera, a thermal camera with a wide field of view (WFOV) for detection and the laser illuminator. A user interface was implemented to operate the demonstrator in the field, having easy access to the gating capability. The paper will present the latest performance results of the SWIR GV module including results of field trials with the demonstrator.

Sensors Unlimited Inc. (SUI), a Collins Aerospace company, has developed a short wave infrared (SWIR) photodetector device structure using isolated mesa pixels to improve the detector modulation transfer function (MTF), an important parameter in determining the overall image quality of a camera system. A combination of device fabrication and simulation has been used to evaluate the design and manufacturability of various mesa morphologies. Because mesa formation entails both the removal of some portion of the active region of the photodetector and the introduction of non- planar surfaces, any MTF improvement must be balanced against a loss of quantum efficiency (QE) and potentially higher dark current. Focal plane arrays (FPAs) based on the optimal mesa morphology have been fabricated and compared for MTF and QE performance at the camera level to FPAs built using SUI’s standard pixel structure. The mesa structure described herein is implemented on the front side of the photodetector and could also be implemented across all of SUI’s backside-illuminated (i.e., VIS/SWIR, NIR/SWIR, SWIR) structures for applications where a premium is placed on MTF performance.

Attollo has developed large area low capacitance InGaAs detectors to meet the needs of LiDAR systems following the roadmap of technology development at the near Infrared (NIR) wavelengths of 850/905/940 nm with the eventual transition to eye-safe wavelengths near 1550 nm. Attollo InGaAs offers large photodetector areas while still meeting the bandwidth limitations of the amplified detection system. Large area photodetectors enable a large system Field of View (FOV) with a simpler and larger diameter lens and also provide lower input-referred noise from optimized transimpedance amplifier systems. Attollo will present results on InGaAs detectors achieving capacitance densities 3x lower than state-of-the-art with 16 pF/mm². Attollo will present LiDAR receiver modeling data utilizing these detectors and will quantify the advantages of low capacitance in LIDAR applications as it relates to system bandwidth and amplifier input referred noise performance of the system.

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 technologies including Indium Gallium Arsenide (InGaAs). As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and operability. Recent years have evidenced significant progress with InGaAs process maturity enabling low noise detectors operable at room temperature, with no cooling requirement. This new generation of so called Tecless devices meets a surging interest for affordable Short-Wave Infrared (SWIR) detectors for use in volume applications such as industrial machine vision, science imaging or surveillance applications. For these systems, the latest uncooled InGaAs sensors allow major cost savings without sacrificing performance. In this talk we will review and analyze the impact of temperature on InGaAs detectors. We will also discuss implementation and optimization tradeoffs which should be considered when using uncooled InGaAs SWIR detectors.

In recent years enormous development progress on key subcomponents of IR-modules was achieved: the operating temperature of MWIR FPAs has successfully been increased to high operating temperature (HOT) while preserving a 5μm cutoff-wavelength and small pixel pitch and miniature cryocoolers with low power consumption were introduced at AIM. This leads to new ultra-compact IR-solutions and improvements of existing IR-modules best suited to respond to the wide range of system needs in military and civilian applications. Key enabler for the realization of a low SWaP MWIR engine in a XGA, 10μm pitch format is AIM’s HOT MCT p-on-n detector technology, able to provide high electro-optical (e/o) performance at 160K. This technology has now been optimized and transferred to various detector formats and pitch sizes in the range from 10μm to 30μm. At moderate operating temperatures around 100K it can be used to provide highest e/o-performance including a very low defective pixel level. To improve thermal resolution of 640×512, 15μm pitch LWIR modules the charge handling capacity (CHC) of the associated ROIC has now been increased to nearly 20Me- . Typical integration times remain below 1ms ensuring high frame rates of 120Hz. In addition, an interlaced mode allows for an even higher CHC value of ~40Me^- , a 2×2 binning mode for 450Hz operation in a smaller format. Furthermore, an optimized ROIC design in a 1024×768 format, offering a high CHC of ~7.5Me^- in a small pixel pitch of 10μm, has been completed to improve existing MWIR modules and to provide a good basis for a XGA 10μm pitch LWIR version currently under development at AIM. In this paper latest performance results of improved MCT MWIR and LWIR detector arrays will be presented, together with optimization of associated cooled IR-modules.

Bispectral infrared-sensors that provide detection in two different spectral regions, e.g. short-wavelength infrared and mid-wavelength infrared (SWIR/MWIR) or MWIR/MWIR, offer compared to single-color sensors improved performance in a wide variety of space and ground-based applications. Possible applications are target identification, signature recognition and clutter rejection. In particular the combination of the SWIR/MWIR or MWIR/MWIR spectral regions promote an enhanced target discrimination and identification by increasing the identification range, by enabling the target acquisition in front of strongly structured backgrounds or of targets with low thermal signature. We have extended our MBE growth technology, primarily developed for the cost-effective production of standard IR-detectors in the MWIR spectral range, to the growth of mercury-cadmium-telluride (MCT) multi-layers with different cutoffwavelengths. The design of the bispectral pixel with two indium bumps per cell allows for temporal and spatial coincidence. To demonstrate the capabilities of the bispectral IR sensors, FPAs with a format of e.g. 320x256 pixels and a 30 μm pitch have been fabricated. In this paper we present the key performance parameters of recently optimized SWIR/MWIR and MWIR/MWIR bispectral MCT detectors along with images taken with the bispectral detectors by using SWIR or MWIR optics. The detectors demonstrate improved quantum efficiency, very low color cross-talk, and an excellent NETD in conjunction with low defect densities. Processing of the bispectral images with algorithms for combining the information from both spectral ranges provide striking evidence for the potential of these bispectral detectors in various applications.

Mercury Cadmium Telluride (MCT) grown by Metal Organic Vapour Phase Epitaxy (MOVPE) on GaAs substrates is a mature technology at Leonardo MW used for the production of high-performance infrared detectors in the short, mid and long wavebands. Recently reported developments of single waveband devices have seen pixel densities increase by almost an order of magnitude, driven by system requirements for increased resolution together with reduced size, weight and power. High resolution MWIR detectors with 8μm pixels are now in volume production. The mesa structure of MOVPE grown MCT pixels controls most sources of inter-pixel crosstalk with optical scattering, carrier diffusion and other blurring mechanisms reduced to negligible levels, resulting in characteristically sharp infrared images from systems which use these devices. More than a decade ago, Leonardo MW pioneered the development of Dual Waveband Infra-Red (DWIR) technology with devices using 30μm, 24μm and 20μm mesa pixels. Both MWIR-LWIR and MWIR-MWIR devices have been successfully fabricated. These devices use a “back-to-back” diode arrangement in which the waveband is selected by changing the bias polarity across the diode stack. This ensures the spatial correlation between the two wavebands, which is essential for many applications. Such DWIR structures are significantly thicker than single waveband devices, posing challenges to increasing pixel density whilst retaining the highly desirable benefits of mesa isolation. This paper discusses the evolution of the DWIR technology to high density, 12μm MWIR-LWIR pixels, enabling the manufacture of higher resolution, lower cost DWIR devices.

SOFRADIR is a worldwide leader on the cooled infrared (IR) detector market for high-performance space, military and security applications thanks to a high maturity Mercury Cadmium Telluride (MCT) technology, and III-V technology: InGaAs, and QWIP quantum detectors. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. The current trend in quantum IR detector development is the design of very small pixel, operating at higher temperatures. In this context, keeping high image quality is a key challenge. This paper discusses the relevant criteria to quantify image quality: the Modulation Transfer Function (MTF) and the Residual Fixed Pattern Noise (RFPN). State of the art relevant performances for IR detection and imaging will be presented for Daphnis MW product, 10μm pitch XGA/HD720 extended MW matrix (cut-off wavelength 5.3μm) operating at 110K: range improvement, digital ROIC optimization, NUC (Non Uniformity Correction) table stability. Projections and results for smaller pixel pitch are also detailed.

ASELSAN A.S., the largest defense company in Turkey, develops high performance electro-optical systems for land, air and naval applications. Research activities on developing Mercury Cadmium Telluride (MCT) detectors are on-going for MW and LW infrared bands. In this paper, recent results on Cadmium Zinc Telluride substrate growth, long wavelength (LW) Mercury Cadmium Telluride (MCT) detector fabrication and readout integrated circuit design are summarized. LW MCT focal plane arrays with a format of 320×256/30 μm are fabricated. Noise Equivalent Temperature Difference (NETD) of these focal plane arrays (FPA) are 45.7 mK and 59.9 mK (f/1.5, 77K) while the operabilites are 98.14% and 99.28%, respectively.

HgCdTe has been called the ideal infrared detector material for good reason: high absorption coefficients and very long Shockley-Read-Hall (SRH) recombination lifetimes lead to the highest performance infrared detectors today for space applications. III-V materials, such as InAsSb, are currently limited by short SRH recombination lifetimes due to defects, and their performance is still relatively lacking for space applications where sensitivity requirements are extremely high. However, the performance of III-V superlattice infrared detectors has improved such that it is sufficient for tactical applications, which can now take advantage of the manufacturing benefits of III-V (greater uniformity and yield). With the growing NewSpace movement, there is a need for higher-volume, lower-cost infrared detectors capable of operating in space for applications such as environmental monitoring, space-based weather, and planetary science. One way to increase volume and lower cost is to grow the detectors on large-format substrates, such as 6-inch silicon or GaAs, but lattice-matched large substrates are not available for HgCdTe or InAsSb. Here a comparison between mid-wavelength infrared HgCdTe and InAsSb infrared detectors grown on non-lattice-mismatched substrates and designed for increased proton radiation tolerance, as compared to previous designs on mismatched substrates, is given. The comparison of these recent HgCdTe photodiode and InAsSb bariode designs for space applications shows that the InAsSb bariode has an order of magnitude better dark current density proton radiation tolerance while the HgCdTe photodiode has an order of magnitude better quantum efficiency proton radiation tolerance operating at 130 K. Therefore, the choice of detector material and architecture is not clear and will depend on the required performance for a specific space application.

We present CEA-LETI’s recent work on very small pitch HgCdTe focal-plane-arrays (FPA): materials, diode processing, readout circuit (ROIC) optimization and hybridization, done in the context of the common laboratory with SOFRADIR called DEFIR. We report on a 7.5μm pitch 640×512 FPA and a smaller 5μm pitch 64×152 FPA operating in middle wave infrared range (MWIR). The diode technology is n-on-p processed onto LPE grown HgCdTe. We will describe the two readout integrated circuits (ROIC) developed for 7.5μm and 5μm pitches and present the characterization of the IRFPAs hybridized to those ROICs. For these very small pitch detectors, we designed classic snapshot Direct-Injection (DI) Integrate-While-Read (IWR) ROICs that maximize the charge handling capacity by significantly increasing the dynamic range. For the 7.5μm ROIC, dedicated electronics has been embedded to measure the ROIC cross-talk. The 7.5μm pitch IRFPA operating at 110K displays nonlinearity under 0.5% across the maximum dynamic range, a full-well of 3.1 Me- with a 3.8V dynamic range, a ROIC noise of 210μV and SNR of 62 dB and NETD (Noise-Equivalent Temperature Difference) of 25 mK for an average current of 30 pA, and a responsivity of 1.3 pA/K.

Far- Infrared Rays (FIR) cameras can image FIR radiated from objects, so that far-distance shooting and image recognition at night can be performed without being influenced by light sources. Since it has other important performance as a sensing device in Autonomous car, it is attracting attention as a future of Autonomous car sensing technology. In this report, we introduce development history and advantage of in-vehicle FIR camera and image recognition system developed by our company.

Veoneer is the world’s largest pure-play company focused on Advanced Driving Assistance Systems and Automated Driving. Veoneer designs, compiles and sells state-of-the-art software, hardware and systems that make driving safer, and provides the key technologies like night vision, that drive the reliability, adoption, and success of self-driving mobility solutions. Veoneer is the single largest supplier of thermal night vision systems in the automotive marketplace. Veoneer develops and supplies both the hardware and software for a complete night vision system. As the leader, Veoneer continues to innovate smaller cameras with increased resolution, while adding critical safety features such as pedestrian detection, animal detection and automatic emergency braking. Far infrared cameras are rapidly expanding into the autonomous vehicle space by providing an essential added modality for sensing objects in complex driving situations. In this keynote, Mr. Stuart Klapper will discuss where automotive infrared systems are headed in the future. Next generation night vision cameras are anticipated to be at least 50 percent smaller with VGA resolution. Some concepts include wider field of view cameras and implementation of multiple cameras for 360-degree coverage surrounding the vehicle. The electronic control units used to process the signal from the camera may be shared with other sensors on the vehicle to enable lower cost applications. Night vision technology is viewed as unique for handling complex situations where other technologies like LiDAR, radar and vision cameras may have limitations.

Autonomous vehicle sensor suites must perform in a variety of weather conditions to achieve acceptable levels of safety and reliability. Fog is one of the most challenging driving conditions. This paper presents qualitative performance data of thermal infrared (both longwave and midwave), shortwave infrared, and visible-light imaging sensors under different testchamber fogs. We find that the performance of LWIR imaging is impacted significantly less by light-to-moderate fog than the other two IR sensors, the visible imager, and a low-resolution Velodyne LiDAR. The paper recommends additional fog chamber testing to generate data that will be useful for the development of imaging simulation capability that accurately models fog across these wavebands for improved reliability and coverage in the development of ADAS and autonomous vehicle (AV) vision systems.

An angle-resolved, true 3D laser sensor system for autonomous vehicles and driverless cars has been developed. This paper will describe the principle and architecture of autonomous vehicle laser sensors with the potential for nanowatt, single digit angular resolution at low false alarm rates, and wide angular coverage demonstrated so far for lasers in the 450-1550 nm spectral band, but with the capability for near-mid, mid-IR and longwave IR, as well as active/passive operation. The true 3D sensor determines in real-time, the range, angle and intensity of every resolved feature in the 3D point-cloud unlike conventional lidar sensor systems that can determine only the range of objects accurately. The underlying technology is based on ultra high gain, low excess noise, linear-mode APD detectors, angle resolving optics and open architecture software and interfaces all in a small form-factor. It is also based on a breakthrough tactical laser sensing technology, which have successfully undergone lab and outdoor testing and has demonstrated broadband, widefield- of-view operation with high sensitivity and low false alarm rates. The sensor architecture, design concepts, measured performance and projections will be presented, as well as trade-off characteristics among performance specifications, such as sensitivity, false alarm rates and detection probability.

The following paper serves as an Introduction to SPIE’s series of sessions on Driverless Vehicles. It will outline ways that thermal imaging can be a valuable complement to the suite of autonomous vehicle sensors to enhance safety and facilitate regulatory approvals.

The advantages of using far-infrared technology in guiding systems, warning systems or surveillance systems have been demonstrated in defense applications through a large span of imaging functions such as detection, target recognition and positive identification in complex environments. Used as a complementary tool in a set of camera sensing technologies, the far-Infrared thermal camera provides the key sense to improve system performance and increase human classification robustness. This enhanced capability relies on the detection of the unique thermal signature of a pedestrian in any weather and light conditions, day or night, without being glared by the sun or any light source. Implementing vision system based on shutterless far-infrared solution into an autonomous detection system can reduce the rate of false positive detection. Being an imaging technology, far-infrared camera using ULIS technology can be easily integrated into standard platform while minimizing computation resources required by detection algorithms thanks to the thermal signature detection.

Wavelength-selective uncooled infrared (IR) sensors have significant advantages for applications such as fire detection, gas analysis, hazardous material recognition, and biological analysis. We have demonstrated a wavelength-selective uncooled IR sensor with a plasmonic metamaterial absorber (PMA). However, unwanted modes are a serious issue for wavelength-selective detection and are attributed to the absorption by the materials used in the sensors that do not consist of PMAs. Elimination of unwanted modes in a wavelength-selective uncooled IR sensor with a PMA is demonstrated using a subtraction operation with a reference pixel. The reference pixel has the same sensor structure, except for the absorber area; a flat mirror was instead formed on the absorber surface. Wavelength-selective uncooled IR sensors were fabricated with PMAs and the reference pixels. Single-mode detection was achieved by the subtraction operation with the reference pixel.

This paper presents a study of metasurface integrated microbolometers. The semiconductor absorber is sandwiched between a metal Frequency-Selective Surface (FSS) and ground plane. When the semiconductor absorber is electrically isolated from the ground plane by a thin dielectric it can be used to measure the temperature of the pixel. The integration with the FSS removes the need for a Fabry-Perot cavity. The FSS allows control the attributes of radiation absorbed by the microbolometer on a pixel-by-pixel basis which provides the potential for spectral or polarimetric imaging. The FSS also affects he electrical performance of the semiconductor absorber and the thermal performance of the microbolometer. In addition, the complex permittivity of the semiconductor affects the optimal design of the FSS. The Si/Ge/O system is selected because it allows the properties of the absorber to be engineered (e.g., less oxygen gives lower absorptance and higher resistivity). This paper explores the absorber/FSS parameter space with an emphasis on the electrical and noise properties of the integrated system. Models are developed to explain results. Preliminary results show that the addition of the FSS improves TCR of the microbolometer by 10% while dramatically lowering its resistivity (factor of 5×). The resistivity reduction leads to a dramatic reduction of the noise power spectral density with the addition of FSS improving the measured 1/f noise by two orders of magnitude over an identical sample without the FSS. In addition, this paper will present the microbolometer figures of merits including voltage responsivity, detectivity, and thermal response time.

This paper reports the design, fabrication, characterization, and noise reduction of metasurface based uncooled infrared microbolometers with focus on device architecture. Two designs are investigated. In the first design, the devices are fabricated with the legs positioned underneath the microbolometer pixel. This is facilitated by the use of the metasurface which removes the need for a Fabry-Perot 1/4 cavity. Placing the legs underneath the pixel permits longer legs without sacrificing fill factor and raises the thermal resistance between the microbolometer and the substrate. The metasurface potentially allows spectrally dependent IR absorption. The second design extends this architecture to include a second microbolometer suspended above the first microbolometer to form a single pixel. Metasurfaces on each microbolometer can be designed to capture a portion of the spectrum with the combined structure maximizing the total absorptance across the Long Wave Infrared (LWIR) band. The TCR and resistivity are measured on the fabricated devices with and without the addition of the metasurface for both designs. The metasurface produces a slight increase in the TCR 5% to 12% and a dramatic reduction in the resistivity (>5×) which leads to a two order of magnitude reduction in the microbolometer noise voltage Power Spectral Density (PSD) after annealing in vacuum. The measured single cavity microbolometer has a voltage responsivity of 4.1×10⁴ V/W and detectivity of 3.57×10⁸ cm·Hz^1/2/W.

Pyroelectric imagers lost the competition against bolometers for two reasons: 1) the need for a chopper, and 2) the inability to effectively reduce pixel size. The advantage it had in the competition was extremely low spatial noise, which resulted from its inherent AC coupling, which is what necessitated the chopper. The need for a chopped signal was also at least partly responsible for the difficulty in reducing pixel size, because chopping reduces the time the detector is exposed to the scene. Past concepts for chopper-less pyroelectric detectors have introduced spatial noise at least as problematic as that of bolometers, and they also eliminated the 1/f noise suppression afforded by AC coupling. A patent⁵ issued in 1996 addressed these problems by using electrostatically-driven micromechanical movement to touch an active pyroelectric pixel to the substrate, thereby resetting the pixel temperature to that of the substrate. While this promised significant improvement, and while it was demonstrated in mechanical test pixels, it was never attempted in any kind of operational device. That concept has now been further developed in theory, and it has been dramatically improved in terms of potential performance. By increasing the reset rate and recursively averaging the resulting signals, the signal is substantially increased because the temperature rise never experiences the thermal roll-off of longer exposures. Noise, which is dominated by far by 1/f noise, is also suppressed by the increased rate of correlated double sampling.

Thermal Image Sensor performances for high end applications can be compared using a Factor of Merit (FoM) based on NETD and thermal time constant (τ_th). This FoM is defined as FoM = NETD × τ_th and is expressed in mK.ms. Best bolometers FoM range from 500 to 720 mK.ms. When fast response is required from the detector due to short events or fast moving objects in the scene, bolometers can be limited by their τ_th , today around 12 ms for ULIS 17 μm components, leading to blurred images or poorer signal to noise ratio. Adjusting the bolometer τ_th can be achieved simply by lowering the pixel responsivity, keeping FoM globally unchanged and leading to unacceptable NETD performance. This paper discusses the bolometer key parameters and tradeoffs that can lead to improved FoM associated with drastically decreased thermal time constant. Thanks to a multi-parameter design optimization, ULIS has developed an improved 17μm pixel with an exceptional FoM of 125 mK.ms and thermal time constant below 3 ms, which is 4 times better than the state of the art. Prototypes characterization will be presented and the image quality will be compared with the one of a standard camera.

This paper introduces a 160×120 CMOS-based microbolometer array with a 35 μm pixel pitch operating in the 8-12 μm wavelength range, where the detector is fabricated with the LWIR-band CMOS infrared technology, shortly named as CIR, which is a patented novel approach that allows implementing microbolometers with standard CMOS and simple post-CMOS MEMS processes. Post-CMOS processes require only one mask lithography process and simple subtractive etching steps to obtain suspended microbolometer pixels, as opposed to the 8-15 mask deposition and etching processes in the widely used conventional surface micromachined microbolometer approaches that require the use of special high TCR materials like VOx or a-Si. Needing simple subtractive post-CMOS fabrication steps allows the CIR technology to be carried out in any CMOS and MEMS foundry in a truly fabless fashion, where industrially mature and Au-free wafer level vacuum packaging technologies can also be carried out, leading to cost advantage, simplicity, scalability, and flexibility. The implementation of an 80x80 FPA with 35 μm pixel pitch, namely MS0835, using the CIR technology was previously demonstrated, where wafer level vacuum packaged sensors with one side AR coating demonstrated to provide an NETD (Noise Equivalent Temperature Difference) values of 112 mK at 4 fps with f/1.1 optics. As a further study, this paper reports the implementation of the 160×120 FPA with a 35 μm pixel pitch, namely MS1635A using the CIR technology, where a 0.18 μm CMOS process is used. The sensor has a die size of 9.3 mm× 9.1 mm including the area for wafer level vacuum packaging and dissipates less than 50 mW at 30 fps while operating with 3.3V supply. The fabricated sensor is measured to provide a peak NETD of 161 mK, 117 mK, and 89 mK at 17 fps, 11 fps, and 4 fps, respectively, in a dewar environment with f/1.0 optics, i.e., it demonstrates a good performance for high volume low-cost consumer market applications like advanced presence detection and human counting. The CIR approach of MikroSens is scalable with the used CMOS processes, allowing to reduce the pixel pitch even further while increasing the array size and/or improving the sensor performance if necessary for IoT and various other low-cost, high volume markets.

Molecular dynamics (MD) simulations of nerve agent-sorbent binding are presented for interpretation of infrared molecular binding spectroscopy, which is for nerve agent detection. Potential-energy-function parameters for the MD simulations are adjusted according to attenuated total reflection (ATR) measurements of surface interaction between a custom sorbent material and nerve agent simulant. The physical assumptions underlying these MD simulations and sensitivity of potential-function parameters are examined with respect to viability for quantitative prediction and interpretation of ATR spectra associated with nerve agent detection.

Inserting an infrared detector architecture into an optical cavity between two high-reflectivity mirrors allows incident light to reflect and pass through the detector multiple times, thereby enhancing absorption within the active region. This allows for a 40-100x thinner optical absorbing region compared to conventional infrared detector structures which reduces the detector dark current and noise and enhances SNR. We report the design, growth, fabrication and characterization of resonant cavity enhanced MWIR photodiodes on GaSb substrates. Devices on GaSb use AlAsSb/GaSb mirrors, AlAsSb spacer layers, and a narrow 96 nm InAsSb absorber. Dark current and detectivity behavior better than equivalent broadband nBn detectors in the literature have been observed. 34nm linewidth detector response is observed. Resonant cavity-enhanced photodiodes with resonant wavelengths of 3.6μm and 3.72μm are demonstrated with dark currents equal to or lower than Rule 07 over the operating temperature range of the device. D* in excess of 1×10¹⁰ cm Hz^1/2W^-1 at 300K and 8×10¹⁰ cm Hz^1/2W^-1 at 250K have been achieved. Amethyst Research has produced packaged resonant-cavity detectors. The 3.6 μm resonant-cavity enhanced photodiode was packaged within an Amethyst Research designed pre-amplifier package with an integrated TEC for detector cooling.

Sparrow, a low Size, Weight and Power (SWaP), high-end thermal imaging video core is presented, based on XBn- InAsSb Focal Plane Array (FPA) with 640×512 format and 10μm pitch, which is operated at 150K. The Sparrow video core offloads a range of functions from the host system, such as detector power supply, clocking and image processing, resulting in a very compact and low power module equipped with a miniature Split-Linear Stirling cooler. The Sparrow Module is optimized for a wide range of low SWaP applications, with a volume of 58×62×42 mm³, a weight of 300g, and typical power consumption of 5W at room temperature. It provides sub-frame video latency and supports a variety of output video formats and user-configurable advanced image processing algorithms.

Large format high resolution FPAs are the key elements for medium to high performance applications including enhanced vision, thermal sights, and industrial applications. In this work, the characteristics of recently developed 10 μm pitch SXGA InSb detector are presented. To develop the 10 μm pitch SXGA InSb detector, three important technical issues were resolved. At first, physically isolating pixels to reduce the crosstalk was adopted to enhance the Modulation Transfer Function (MTF). It was found that the MTF of fabricated detector tested with slanted edge method was improved largely. The MTF of 10 μm pitch FPAs at the Nyquist frequency showed the same MTF of 15 μm pitch device at the Nyquist frequency. Therefore the zoomed image of 10 μm pitch device will have the same image quality as the 15 μm device. Another important issue is the indium bump fabrication process. To fabricate fine bump with uniform height, electrodeposition technology was developed. With this method, uniform indium bump over the 8' ROIC could be achieved. Finally, to achieve large capacitance, 0.18 μm CMOS technology was adopted. To use 0.18 μm CMOS technology, the ROIC should have to be designed all again. The designed and fabricated ROIC has 2.4 Me- with 3.3 V bias voltage and has 8 output channels with 20 MHz output rate. The developed 10 μm pitch InSb SXGA detector showed median NETD (Noise Equivalent Temperature Difference) of 22.6 mK. To measure the stability of developed 10 _m pitch InSb SXGA detector, system NETD(SNETD) was measured after thermal cycling. The SNETD of 30 mK was measured for more than 200 thermal cycling, which shows that the output of developed FPA is very stable.

In this paper we demonstrate how the QWIPs are keeping all their promises in terms of performance, versatility and cost, partly thanks to excellent uniformity, stability and manufacturability, as well as the flexibility of tailoring both the detection wavelength and the polarization sensitivity. Thanks to the intrinsic uniformity and stability of the III-V technology combined with the process maturity at IRnova, high resolution (VGA format, 15 µm pitch) QWIPs are now integrated in compact Integrated Detector Dewar Cooler Assemblies (IDDCAs). For regular high-end thermography applications, these IDDCAs operate with moderate 500 mW cryocoolers, which opens the field for handheld cameras. Thanks to the band gap engineering, the detector’s spectral response can be tailored and optimized for different wavelength ranges. In addition to the 8.5 µm QWIP, which is optimized for thermal imaging, a QWIP with 10.5 µm peak wavelength has been tailored for detection of harmful gases, such as SF6. The performance of high resolution QWIPs with peak detection at 10.5 µm integrated in IDDCAs is demonstrated showing the impact of high sensitivity and high resolution on the image quality. Thanks to the intrinsic sensitivity of QWIP to the polarization of the light it is possible to complement the thermal information with polarimetric information. This opens new possibilities for detection of certain features such as oil spill and de-camouflage. In this paper we demonstrate the high polarimetric contrast obtained with our 320×256 polarimetric IDDCA.

Antenna coupled detectors break the intrinsic tradeoff between signal and noise by “collecting over a large area” and “detecting over a small area”. Most antenna coupled detectors in the infrared rely on a metal resonator structure. However, there are losses associated with metallic structures. We have demonstrated a novel long-wave infrared (LWIR) detector that combines a dielectric resonator antenna with an antimonide-based absorber. The detector consists of a 3D, subwavelength InAsSb absorber embedded in a resonant, cylindrical dielectric resonator antenna made of amorphous silicon. This architecture enables the antimonide detection element to shrink to deep subwavelength dimensions, thereby reducing its thermal noise. It is important to note that this concept only applies when (a) the detector noise is limited by bulk noise mechanisms with negligible surface leakage currents and (b) the dominant source of current in the device is due to dark current (such as diffusion) that scales with the volume of the detector. The dielectric resonator enhances the collection of photons with its resonant structure that couples incident radiation to the detector. We will present results on the absorption in structures with and without the dielectric resonator antenna. The signal to noise enhancement in the LWIR photodiodes integrated with the dielectric resonator antenna using radiometric characterization will be discussed.

This LETI/Sofradir/Defir study aims at realizing sub-10 μm pitch HgCdTe infrared FPAs. To cope with the different diode process issues related to pitch reduction-morphologic realization, short-circuits, FTM optimization - a parametric study was carried out - contact size, passivation properties, doping levels, diode processing conditions-. A wafer-level test campaign was conducted to evaluate the process window. It revealed functional MWIR diodes from 15 μm to 3 μm pitch. 7.5 μm pitch 640×512 and 5 μm pitch 64×152 FPA were characterized and turned out to be functional.

Graphene has remarkable optoelectronic properties and thus would represent a means to improve infrared (IR) photodetectors. As a result of its Dirac-cone structure, graphene exhibits broadband light absorption and a rapid response. Unlike quantum photomaterials, graphene can also be synthesized inexpensively via a non-toxic process. Despite these advantages, graphene-based photodetectors suffer from low responsivity due to the low absorption of graphene of around 2.3%. Therefore, there is a strong demand to enhance the IR responsivity of graphene photodetectors and expand the range of IR applications. In this study, enhancement of the middle-wavelength IR (MWIR) photoresponsivity of graphene photodetectors using the photogating effect was investigated. The photo-gating effect is induced by photosensitizers, which are located around the graphene channel and couple incident light and generate a large electrical change. The graphenebased MWIR photodetectors consisted of a top graphene channel, source-drain electrodes, insulator layer, and photosensitizer. The photoresponse characteristics were investigated through current measurements using a device analyzer. The device was vacuum-cooled and the graphene channel was irradiated with light from a MWIR laser. The device exhibited a clear MWIR photoresponse observed as modulation of the output current during irradiation. The MWIR photoresponse with the photo-gating effect was 100 times higher than that of conventional graphene photodetectors without the photo-gating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The results obtained in this study will contribute to the development of high-performance graphene-based IR image sensors.

Advanced functional infrared (IR) photodetectors with wavelength selectivity are promising for a wide range of applications, such as multicolor imaging, gas analysis and biomedical analysis. Graphene is considered to be a promising material for novel IR detectors. However, the absorption of graphene is constant at approximately 2.3% and rather small. We have developed multispectral high-performance graphene IR photodetectors using metal-insulator-metal (MIM) or single-layer (SL) plasmonic metasurfaces (PMs). MIM- or SL-PMs induce localized surface plasmons on their surfaces and enhance absorption at the wavelength, which can be controlled by their surface patterns, such as the period or the gaps between micropatches. The absorption of graphene with PMs was theoretically investigated for various structural parameters. The absorption wavelength can be controlled based on plasmonic resonance by varying the surface geometry of the PMs. Graphene-based IR photodetectors with SL-PMs were fabricated by the chemical vapor deposition of graphene and then transferred onto the PMs. Wavelength-selective enhancement of the optical absorption and detection by graphene could be achieved due to the effect of the PMs. The results obtained here are expected to contribute to the realization of multispectral graphene infrared image sensors.

Strong motivation for low-cost infrared imaging devices over the past few years have given rise to advances in infrared detector technology, specifically in the mid-wave infrared (MWIR) region. With increasing demand for small pixel sizes and large format focal plane arrays (FPAs), the extreme complexity in realizing MWIR imagers is expected to increase in difficulty. In this work, a novel approach to provide improved infrared detection at high operating temperatures is proposed by integrating proven MWIR photovoltaic material and mature digital CMOS Image Sensor (CIS) technology in a resultant technology concept of an open circuit voltage photodetector (VocP). With this new approach to photon detection, the photosensitive material generates an open circuit voltage to control the drain current of a transistor. The drain current can then be considered the photocurrent in the proposed pixel design. The VocP design decouples the photocurrent from the pixel area, exploits the invariance of open circuit voltage to pixel dimensions, improves the detectors dark current, and results in higher sensitivity. The proposed approach also couples an infrared sensitive material to CIS technology that is well established and continues to be advanced for visible imagers. In this paper, initial research demonstrations and test results are presented to provide evidence of MWIR detection at high operating temperatures to prove the concept and modeling predictions for the sensitivity and dynamic range of VocP.

Infrared small target detection under intricate background and heavy noise is one of the crucial tasks in the field of infrared search and tracking (IRST) system. The images with small targets are usually of quite low signal-to-noise ratios, which makes the targets very difficult to be detected. To solve this problem, an effective infrared small target detection algorithm is presented in this paper. Firstly, a nested structure of the original pixel-wise image is constructed and the local structural discontinuity of each pixel is measured by a vector so-called local contrast vector (LCV). Each element of LCV describes the minimal difference between the central region and its neighboring regions, and the scale variety of regions results in the variety of elements. Then, a multi-dimensional image is generated with respect to LCV. After that, a confidence map for small target detection is reconstructed by signed normalization, that is, each pixel in the confidence map is generated by signed inner product of LCV. Finally, we segment the targets from the confidence map by utilizing an adaptive threshold. Extensive experimental evaluation results on a real test dataset demonstrate that our algorithm is superior to the state-of-the-art algorithms in detection performance.

This paper presents a system-on-chip solution that acts as a companion to infrared focal plane arrays (IR-FPAs), providing them with precision references, regulated power supplies, clocks and timing signals, as well as sampling analog or digital outputs for signal conditioning, correction and processing. To serve a wide variety of infrared imaging detectors, the chip is designed in a fully configurable manner that allows users to program specifications of signals going to an FPA and implement any custom signal correction, processing and application-specific algorithms.

Graphene is an atomically thin carbon sheet with a two-dimensional hexagonal lattice structure that has drawn significant attention in many fields due to its unique electronic and optical properties. In this study, graphene Salisbury screen metasurfaces (GSMs) were theoretically investigated as wavelength-selective plasmonic metamaterial absorbers. The GSMs consist of a top graphene sheet, a middle insulator layer and a bottom reflector. The absorption wavelengths of GSMs with a continuous graphene sheet are demonstrated to be controllable according to the insulator layer thickness, which is similar to the case for a conventional Salisbury screen. The insulator thickness can be used to control the optical impedance to incident light using the graphene as a resistive sheet. GSMs with a periodic micropatch array of graphene can be used to control the absorption wavelength, mainly based on the graphene micropatch size and symmetry in conjunction with the insulator thickness. This wavelength selectivity is mainly attributed to the plasmonic resonance in graphene. In both structures, the chemical potential of graphene can be used to tune the absorbance and the absorption wavelength. These results will contribute to the development of electrically tunable and high-performance graphenebased wavelength- or polarization-selective absorbers or emitters.

Recently, infrared detectors have become increasingly dense and miniaturized. The development of micro solder bumps with small diameter and high aspect ratio is necessary for high pixel density and miniaturized infrared detectors. Indium solder bump has been used for infrared detectors because of its stability at low temperature, electrical conductivity and ductility. In this work, the method and results of forming indium bumps with uniform and high aspect ratio by electroplating is presented. In particular, the electroplating method for forming a uniform micro bump and the method for manufacturing a bump having a uniform height will be presented in detail. Finally, the result of indium bump made of pixel pitch 5 μm and 7.5 μm is presented.

In this study, we develop a shutter-less algorithm for a silicon-on-insulator (SOI) diode uncooled infrared focal plane array (IRFPA). The optimal non-uniformity correction is calculated onboard. The effectiveness of the proposed algorithm was verified using a prototype uncooled IR camera. The performance of the shutter-less algorithm was studied by measuring a fixed pattern noise (FPN) at different correction points and verification of favorable camera operation. Even at two correction points, the FPN was at a practical level. The temperature behavior of the proposed SOI diode is highly uniform and predictable, which leads to simpler device modeling and therefore simpler shutter-less operation. A new pixel structure was also developed for pixel size reduction. This approach is based on the realization of a novel thermal isolation structure that can be fabricated by post processing on top of CMOS wafers. Ten series diodes can be arranged in a pixel by designing a 12 μm pixel pitch IRFPA with the new pixel structure. These developed technologies have significantly enhanced the performance of the SOI diode uncooled IRFPA, which inherently possesses excellent uniformity and low noise.

InAsSb ternary alloy is considered to be an alternative to HgCdTe (MCT) in long-wavelength infrared (LWIR) spectral region. The high operation temperature conditions are successfully reached with A^IIIB^V bariodes, where InAsSb/AlAsSb system is playing dominant role. Since theoretically there is no depletion region in the active layer, the generation-recombination and trap-assisted tunneling mechanisms are suppressed leading to lower dark currents in comparison with standard photodiodes. As a consequence, the bariodes operate at a higher temperature than standard photodiodes which could be used in wide range of system applications, especially where the size, weight, and power consumption are crucial, to include - Free Space Optics (FSO) system. In terms of FSO the LWIR provides limited scattering and atmosphere turbulence in comparison to the commonly used ~ 1550 nm range. Currently, as reported HgCdTe LWIR with peak wavelength ~ 10 μm exhibiting ~ 9×10⁹ cmHz^1/2/W (unbiased) and ~ 3×10¹⁰ cmHz^1/2/W (200 mV) and response time 0.3-4 ns are used. The paper presents detailed analysis of the bariode’s performances (such as dark current, detectivity and response time) versus applied voltage, operating wavelength, temperatures (4-, 2- stage thermoelectrical cooling) and structural parameters (active layer Sb composition, x_Sb). The optimal working conditions are simulated (non-equilibrium). Theoretical predictions of bariode’s performances are compared with experimental data published for commonly used FSO HgCdTe detectors.

For ultra-fine pixel pitch focal plane array (FPA) applications, flip-chip hybridization has advantages including high I/O density and short distance between the photodiode array (PDA) and the readout integrated circuit (ROIC). Indium has become the primary interconnect material because of its high ductility at low temperature. Successful mating of large format die becomes increasingly difficult, however, for finer pitch applications where bumps are shorter, as tolerance for bowing is low. Simultaneously, the epoxy filling process for large image format, hybridized focal planes becomes more challenging. These constraints call for tall indium bumps with high aspect ratio to accommodate die bowing and provide larger openings for the flow of fill epoxy. A process for the fabrication of highly uniform, high aspect ratio (height:diameter) indium bumps has been developed by Sensors Unlimited Inc. (SUI), a Collins Aerospace Company. The grain size of the deposited indium metal is minimized by optimizing process parameters as well as introducing intermediate metal layers underneath the indium bumps. Anisotropic deposition has been achieved by optimizing deposition rate and controlling substrate parameters. Indium bumps with aspect ratios over 2:1 and flat bump heads have been achieved. The developed bump process has been successfully applied to the fabrication of high resolution indium gallium arsenide (InGaAs) FPAs. Key control parameters for bump formation will be discussed in this paper.

We present detector characterization of a state-of-the-art near-infrared (950nm - 1650 nm) Discrete Avalanche Photodiode detector (NIRDAPD) 5×5 array. We designed an experimental setup to characterize the NIRDAPD dark count rate, photon detection efficiency (PDE), and non-linearity. The NIRDAPD array was illuminated using a 1050 nm light-emitting diode (LED) as well as 980 nm, 1310 nm, and 1550 nm laser diodes. We find a dark count rate of 3.3×10⁶ cps, saturation at 1.2x10⁸ photons per second, a photon detection efficiency of 14.8% at 1050 nm, and pulse detection at 1 GHz. We characterized this NIRDAPD array for a future astrophysical program that will search for technosignatures and other fast (> 1 Ghz) astrophysical transients as part of the Pulsed All-sky Near-infrared Optical Search for Extraterrestrial Intelligence (PANOSETI) project. The PANOSETI program will consist of an all-sky optical (350 - 800 nm) observatory capable of observing the entire northern hemisphere instantaneously and a wide-field NIR (950 - 1650 nm) component capable of drift scanning the entire sky in 230 clear nights. PANOSETI aims to be the first wide-field fast-time response near-infrared transient search.

The paper considers the question of stitching of infrared images obtained from different points and with the modified internal parameters of the camera. As test data, we use images taken by the thermal camera. To combine pairs of images, we use the several auxiliary algorithms are required, including: elimination of noise on images (denoising); restoration of sharpness on images (deblurring); search for basic elements on pairs IR images; separation of images into elements with given threshold values; search for correlations between base elements; elimination of false matches; search for the image conversion coefficient; search for the boundary of stitching and check the conditions for overlapping objects; if necessary, the perform the color correction operation and change the color balance; stitching pair of images and finding a common border. On the set of test images show the effectiveness of the proposed approach.

This article presents the InAs/GaSb type-II superlattice interband cascade photodetector low-frequency noise analysis. Presented noise measurements were conducted in temperature range 77-300 K and in frequency range 1-10 kHz. The spectral characteristics of the detector noise at various voltages are analyzed. The measured power spectral density is compared to the theoretical prediction. This comparison suggests that noise estimates based on the dark current may not always be valid and the noise source is difficult to be extract. We showed two samples, one of which was characterized by a large leakage currents contribution being directly translated into increased noise.

Recent developments of small SWAP² (Size, Weight, Power, and Price) cryocoolers designed for HOT IR electro-optical devices have already yielded a range of commercial products available from the leading companies in this area. To date, RICOR has contributed to this range the two cryocoolers – K580 rotary model, and K588 linear model. However, continuous demand of the market in further improvements did initiate further K588 model development, intended to meet even more challenging requirements of SWAP² than its predecessors. The improvements implemented in this new development do involve the whole range of the SWAP² parameters, still providing withstanding at challenging environmental conditions of shock, vibration and ambient temperature. This paper provides a report on the status of new K588 linear HOT cryocooler development, including specification, outline, prototype performance and pre-qualification test results under specified shock, vibration and ambient temperature. The current phase of the project resulted in meeting of the most specified parameters, while some of them still need further improvement at the next project phase.

The modern needs of the electro optical market for small low-power and light-weight IR systems are impelling development of High Operating Temperature (HOT) IR detectors, requiring development of dedicated cryocoolers. The development of cryocoolers focused on “SWAP-C” configuration means small size, low weight, low power consumption and attractive cost, in order to optimize IDDCA for modern compact thermal imagers. This paper will review the progress made with the new rotary K580 cryocooler for HOT detectors, update on qualification and life demonstration test results, present test results accumulated from production ramp-up and review the compliance with advanced HOT format arrays. The paper will also review planning for advanced Rotary version as further step of excellence with "SWAP-C" parameters.