Event-based imagers are an emerging class of sensors with demonstrated advantages relative to traditional imagers. Event-based vision sensors have a limited number of output bits that are only responsive to image variations, thus overcoming the speed and power constraints of the conventional imagers based on image integration. The SWIFT EI the first event-based InGaAs sensor that is sensitive in the Visible to SWIR band (600–1700nm). The main novelty of this sensor is that the event channel outputs in parallel to a conventional fast imaging channel. Moreover, we can reconfigure the event channel to provide a fast laser pulse detection mode (3rd generation ALPD), which also outputs in parallel to the integrated image. In that context we described in detail the architecture, key features, and preliminary simulations of the ROIC. The SWIFT EI is a low SWaP product optimized for tactical wide distribution applications that incorporates the event based FPA. We will present measurement results of the high frame rate (HFR) imaging channel; the event channel that can reach up to 25 kHz of negative, null, or positive signal, and the laser detection channel providing a single bit detection frame up to 50 kHz. This feature is ideal for multi spot tracking and pulse repetition frequency (PRF).
Event-based imagers are an emerging class of sensors with demonstrated advantages relative to traditional imagers. Eventbased vision sensors have a limited number of output bits that are only responsive to image variations, thus overcoming the speed and power constraints of the conventional imagers based on image integration. So far, event-based vision has been implemented in visible CMOS sensors. SCD has developed a new event-based VGA/10µm InGaAs sensor that is sensitive in the Visible to SWIR band (600–1700nm) thus extending the standard imaging capabilities such as day light, low-light level, see-through fog and dust. Another novelty of this sensor is that the event channel outputs in parallel to a conventional integrating fast imaging channel. Moreover, the event channel can be reconfigured to provide a fast laser pulse detection mode, which also outputs in parallel to the integrated image. The new ROIC outputs standard video at 13 bit resolution with a high frame rate of 800 frames per second and can double this rate by lowering the resolution to 11 bit. The Event channel can reach up to 25 kHz of negative, null, or positive signal and the laser channel can double this output providing a single bit detection frame up to 50 kHz. In this work, we will elaborate on the architecture, key features, and preliminary simulations of the ROIC and sensor
SCD is a leading manufacturer of MWIR InSb Focal Plane Arrays (FPA) with formats up to 3 megapixels. Using photodiode layers grown by Molecular Beam Epitaxy (MBE), the operating temperature is raised to ∼ 100 K, compared with 80 K for our legacy implanted junction technology. Due to the excellent manufacturability of III-V MBE materials, we have extended this approach in the development of our newer High Operating Temperature (HOT) MWIR technologies, all of which are based on XBn and XBp barrier devices which suppress the dark current generated by traps in the depletion layer. As a result we now produce a family of InAsSb XBn FPAs operating at 150 K with a cut-off wavelength of λC = 4.2 μm. Formats range between 0.33 megapixels and 5.24 megapixels and our latest "Crane" FPA has a pitch of just 5 μm. These detectors are ideal for 24/7 surveillance and long-range applications, due to large formats, increased HOT cooler reliability and very high atmospheric transmission. For applications requiring HOT full MWIR (HFMW) performance (λC = ∼ 4.9 μm), we have explored three approaches, all of which have produced operating temperatures in the range 115 - 125 K with high FPA operability and uniformity. Using a suitable design of buffer layer, we have extended the InAsSb XBn cut-off wavelength while maintaining a high quantum efficiency above 70%. Comparable performance has also been obtained in two lattice matched type II superlattice (T2SL) architectures: XBn InAs/InAsSb and XBp InAs/GaSb. The three technologies give great flexibility in design optimization, and initial production of HFMW detectors is scheduled for mid 2022.
The InAs/InSb/GaSb/AlSb family of III-V alloys and superlattice materials offer unique possibilities for band structure engineering, because they can be grown on GaSb or InSb substrates with high quality and satisfactory control of strain, doping and composition. The band profiles and oscillator strengths are also quite predictable, enabling full simulation of detector performance from a basic knowledge of layer and stack thicknesses. In conventional III-V p-n devices, Shockley-Read-Hall (SRH) traps generate a significant flow of thermal carriers in the device depletion region. At SCD, we have overcome this problem by developing XBn and XBp barrier device architectures that suppress these depletion currents, leading to higher operating temperatures or lower dark currents. Our first barrier detector product was launched in 2013 and operates at 150K. It uses a mid-wave infrared (MWIR) XBn device with an InAsSb absorber well matched to the most transparent of the atmospheric windows, at wavelengths between 3 and 4.2μm. However to span the full MWIR and to sense the long-wave infrared (LWIR) spectrum, we have investigated InAs/GaSb type II superlattices (T2SLs), because they offer full tunability. In this work we show that minority carriers in n-type T2SLs are localized and diffuse by variable range hopping, even when the period is short and the valence miniband has a width of 30-40 meV. Unfortunately, this leads to sub-micron diffusion lengths and a low quantum efficiency (QE) of ~20% in a full MWIR XBn device. On the other hand, p-type layers exhibit “metallic” minority carrier transport with much longer diffusion lengths, typically ~7 μm in our LWIR device layers. The successful development of p-type devices has led to our second barrier detector product, which uses an XBp LWIR T2SL and operates at 77K with a cut-off wavelength of 9.5 μm, a focal plane array (FPA) QE of ~50% and background limited performance up to ~90K at F/3. Moreover, the FPA operability is typically above 99.5%, based on stringent production-line criteria. Together with high spatial uniformity and good temporal stability, these barrier detectors are already a realistic alternative to MCT photodiode arrays, and further products operating at other wavelengths will be launched in due course.
In recent years, a worldwide growing demand for Short-Wave Infrared (SWIR) imaging has increased dramatically. The requirement for such imagers span military, space and commercial applications. The ideal SWIR detector realizes low power, small size, and low noise, capable of imaging under a wide range of illuminations from daylight to starlight, with on-die advanced imaging capabilities, such as high dynamic range (HDR) and active imaging. In this paper we present a new 640x512/15μm InGaAs focal plane array (FPA) specifically developed for low noise (LN) applications. The detector temperature is stabilized by a thermoelectrical cooler (TEC) typically at 20 C demonstrating extremely low dark current with excellent imaging under low light level (LLL) conditions. The detector's read out noise was measured to be lower than 15e- with correlated double sampling. We demonstrate the ROICs active imaging applications at sub μs gates and elaborate on the overall electro-optical performance.
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.
When incorporated into the active layer of a "XBp" detector structure, Type II InAs/GaSb superlattices (T2SLs) offer a high quantum efficiency (QE) and a low diffusion limited dark current, close to MCT Rule 07. Using a simulation tool that was developed to predict the QE as a function of the T2SL period dimensions and active layer stack thickness, we have designed and fabricated a new focal plane array (FPA) T2SL XBp detector. The detector goes by the name of "Pelican-D LW", and has a format of 640 ×512 pixels with a pitch of 15 μm. The FPA has a QE of 50% (one pass), a cut-off of ~9.5 μm, and operates at 77K with a high operability, background limited performance and good stability. It uses a new digital read-out integrated circuit, and the integrated detector cooler assembly (IDCA) closely follows the configuration of SCD’s Pelican-D MWIR detector.
InAs/GaSb Type II superlattices (T2SLs) are a promising III-V alternative to HgCdTe (MCT) for infrared Focal Plane Array (FPA) detectors. Over the past few years SCD has developed the modeling, growth, processing and characterization of high performance InAs/GaSb T2SL detector structures suitable for FPA fabrication. Our LWIR structures are based on an XBpp design, analogous to the XBnn design that lead to the recent launch of SCD’s InAsSb HOT MWIR detector (TOP= 150 K). The T2SL XBpp structures have a cut-off wavelength between 9.0 and 10.0 μm and are diffusion limited with a dark current at 78K that is within one order of magnitude of the MCT Rule 07 value. We demonstrate 30 μm pitch 5 × 5 test arrays with 100% operability and with a dark current activation energy that closely matches the bandgap energy measured by photoluminescence at 10 K. From the dependence of the dark current and photocurrent on mesa size we are able to determine the lateral diffusion length and quantum efficiency (QE). The QE agrees very well with the value predicted by our recently developed k · p model [Livneh et al, Phys. Rev. B86, 235311 (2012)]. The model includes a number of innovations that provide a faithful match between measured and predicted InAs/GaSb T2SL bandgaps from MWIR to LWIR, and which also allow us to treat other potential candidate systems such as the gallium free InAs/InAsSb T2SL. We will present a critical comparison of InAs/InAsSb vs. InAs/GaSb T2SLs for LWIR FPA applications.
Short wavelength Infra Red (SWIR) imaging has gained considerable interest in recent years. The main applications
among others are: active imaging and LADAR, enhanced vision systems, low light level imaging and security
surveillance systems.
In this paper we will describe SCD's considerable efforts in this spectral region, addressing several platforms:
1. Extension of the mature InSb MWIR product line operating at 80K (cut-off wavelength of 5.4μm).
2. Extension of our new XBnn InAsSb "bariode" technology operating at 150K (cut-off of 4.1μm).
3. Development of InGaAs detectors for room temperature operation (cut-off of 1.7μm)
4. Development of a SNIR ROIC with a low noise imaging mode and unique laser-pulse detection modes.
In the first section we will present our latest achievements for the cooled detectors where the SWIR region is combined
with MWIR response. Preliminary results for the NIR-VIS region are presented where advanced substrate removal
techniques are implemented on flip-chip hybridized focal plane arrays.
In the second part we will demonstrate our VGA, 15μm pitch, InGaAs arrays with dark current density below 1.5nA/cm2
at 280K. The InGaAs array is hybridized to the SNIR ROIC, thus offering the capability of low SWaP systems with
laser-pulse detection modes.
Modern electro-optical systems contain several components such as thermal imager, laser designator, laser range finder,
etc. The demand for compact systems with low power consumption and low cost can be addressed by incorporating
some of the traditional system abilities into the IR detector. We present SNIR, a new type of detector, which consists of a
Read Out Integrated Circuit (ROIC) with advanced on-chip signal processing. The ROIC is flip chip-bonded to a
640x512 InSb detector array of 15μm pitch. SNIR digital ROIC can be operated in either one of the following four
different modes of operation. The first operation mode is standard thermal imaging, which has typical functionalities and
performance of MWIR detector. The second operation mode is a dual-function mode that includes both standard thermal
imaging and information on Asynchronous Laser Pulse Detection (ALPD) for each pixel. The detection probability of a
laser pulse is significantly increased by integrating a dedicated in-pixel circuit for identifying a fast signal temporal
profile. Since each pixel has internal processing to identify laser pulses, it is possible also to measure the elapsed time
between a trigger and the detection of a laser pulse. This yields a third mode of operation in which the detector is
synchronized to a laser and becomes a Two-dimensional Laser Range Finder (TLRF). The forth operation mode is
dedicated to Low Noise Imaging (LNIM) for the SWIR band, where the IR radiation signal is low. It can be used in both
passive or active imaging. We review some of the predicted and measured results for the different modes of operation,
both at the detector level and at the system level.
The aim of this research is to measure the electromagnetic radiation scattering properties of the atmosphere and to compare the experimental results with a Monte Carlo type model. The radiation scattered by suspended particles, known as aerosols, is the topic of interest. The presence of aerosols between a point source and an observation system causes the formation of a corona around the point source. The intensity of this corona is the Point Spread Function (PSF). A comparison is presented between the measured atmospheric PSF (caused by scattering) and the PSF which is calculated using a Monte Carlo calculation. While in previous studies the maximum path length was 600 meters, in the present research the path length was increased to 2000 meters. The spectral range was extended from the visible to 3.6 micrometers in the infrared. The authors used a collimated black body source for illumination and an IR radiometer as an observation system. The conclusion from the experimental results is that an increase of the beam divergence causes an increase in the scattered light received, as predicted by the model.
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