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.
This article describes new imaging capabilities and technologies developed for infrared focal plane arrays (FPAs) at SCD. One of the new technologies is the patterning of the back surface of the FPA, whose front surface is bonded to a silicon readout integrated circuit (ROIC). Another is the hybridization of a spectral filter to the same back surface.
Increased image resolution has been achieved by using an opaque mask on the backside of the FPA with small central apertures. The reduced fill factor of the sensor leads to lower crosstalk between neighboring pixels and a higher Nyquist frequency. A highly detailed multi-mega pixel image is obtained when the sensor is micro-scanned relative to the imaging optics.
Spectral filtering was achieved by hybridization of a designated filter to the backside of the FPA. The filter was glued to the FPA with high accuracy achieving single pixel resolution. System implementation of these SWIR sensor cameras has been demonstrated at imec and is reported in this paper.
First results are reported for a continuously varying monolithic filter deposited onto the FPA, which has a high spectral dispersion. We report electro-optical measurements on several different sensors and describe some of their key parameters.
Night Vision Imaging in the Short-Wave Infra-Red (SWIR) has some unique advantages over Visible, Near Infra-Red (NIR) or thermal imaging. It benefits from relatively high irradiance levels and intuitive reflective imaging. InGaAs/InP is the leading technology for two-dimensional (2D) SWIR detector arrays, utilizing low dark current, high efficiency and excellent uniformity. SCD's SWIR Imager is a low Size, Weight and Power (SWaP) video engine based on a low noise 640x512/15μm InGaAs Focal Plane Array (FPA) embedded in a low cost plastic package which includes a Thermo-Electric Cooler (TEC). The SWIR Imager dimensions are 31x31x32 mm3, it weighs 50 gram and has less than 1.4W Power consumption (excluding TEC). It supports conventional video formats, such as Camera Link and BT.656. The video engine image processing algorithms include Non-Uniformity Correction (NUC), Auto Exposure Control (AEC), Auto Gain Control (AGC), Dynamic Range Compression (DRC) and de-noising algorithms. The algorithms are specifically optimized for Low Light Level (LLL) conditions enabling imaging from sub mlux to 100 Klux light levels. In this work we will review the optimized video engine LLL architecture, electro-optical performance and the applicability to night vision systems.
There has been a growing demand over the past few years for infrared detectors with a smaller pixel dimension. On the one hand, this trend of pixel shrinkage enables the overall size of a given Focal Plan Array (FPA) to be reduced, allowing the production of more compact, lower power, and lower cost electro-optical (EO) systems. On the other hand, it enables a higher image resolution for a given FPA area, which is especially suitable in infrared systems with a large format that are used with a wide Field of View (FOV). In response to these market trends SCD has developed the Blackbird family of 10 μm pitch MWIR digital infrared detectors. The Blackbird family is based on three different Read- Out Integrated Circuit (ROIC) formats: 1920×1536, 1280×1024 and 640×512, which exploit advanced and mature 0.18 μm CMOS technology and exhibit high functionality with relatively low power consumption. Two types of 10 μm pixel sensing arrays are supported. The first is an InSb photodiode array based on SCD's mature planar implanted p-n junction technology, which covers the full MWIR band, and is designed to operate at 77K. The second type of sensing array covers the blue part of the MWIR band and uses the patented XBn-InAsSb barrier detector technology that provides electro-optical performance equivalent to planar InSb but at operating temperatures as high as 150 K. The XBn detector is therefore ideal for low Size, Weight and Power (SWaP) applications. Both sensing arrays, InSb and XBn, are Flip-chip bonded to the ROICs and assembled into custom designed Dewars that can withstand harsh environmental conditions while minimizing the detector heat load. A dedicated proximity electronics board provides power supplies and timing to the ROIC and enables communication and video output to the system. Together with a wide range of cryogenic coolers, a high flexibility of housing designs and various modes of operation, the Blackbird family of detectors presents solutions for EO systems which cover both the very high-end and the low SWaP types of application. In this work we present in detail the EO performance of the Blackbird detector family.
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.
Shrinking the pixel size in advanced infrared Focal Plane Array (FPA) detectors allows either a reduction in the system size for the same number of pixels, or an increase in the pixel count for the same focal plane area. Smaller pitch and increased pixel count enables new applications such as long range surveillance, advanced Search and Track, missile warning, persistent surveillance, and infrared spectroscopy. In the last two decades SCD has followed this path of reducing the pixel size in InSb detectors for Mid-Wave Infrared (MWIR) applications, developing and manufacturing FPAs from 30μm down to 10μm pitch. The Blackbird InSb detector with 1920×1536/10μm format was introduced in 2013. Modern electro-optical systems are also designed towards a more compact, low power, and lower cost solution compared with traditional systems. In order to meet these requirements, detectors are being developed to work at Higher Operating Temperatures (HOT). In the last few years SCD has introduced 15μm pitch MWIR detectors based on the novel XBn-InAsSb technology, which enables outstanding electro-optical performance at temperatures as high as 150K. Two XBn FPA formats were developed and are now in production: 640×512/15μm and 1280×1024/15μm. Following the above trends, SCD is currently developing a 10μm XBn pixel, designed to operate at 150K with performance similar to the mature 15μm pixel. In this paper we present results from XBn FPA test devices, where the XBn array is flip-chip bonded to a Readout Integrated Circuit (ROIC) with a 10μm pitch. Test measurements in a laboratory Dewar at 150K demonstrate dark currents of 250fA, quantum efficiency greater than 70%, pixel operability of higher than 99.5%, and excellent array uniformity.
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.
Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD, which operates in the blue part of the MWIR atmospheric window (3.4 - 4.2 μm). This window is generally more transparent than the red part of the MWIR window (4.4 - 4.9 μm), and thus is especially useful for mid and long range applications. The detector has an InAsSb active layer and is based on the new "XBn" device concept, which eliminates Generation-Recombination dark current and enables operation at temperatures of 150K or higher, while maintaining excellent image quality. Such high operating temperatures reduce the cooling requirements of Focal Plane Array (FPA) detectors dramatically, and allow the use of a smaller closed-cycle Stirling cooler. As a result, the complete Integrated Detector Cooler Assembly (IDCA) has about 60% lower power consumption and a much longer lifetime compared with IDCAs based on standard InSb detectors and coolers operating at 77K. In this work we present a new large format IDCA designed for 150K operation. The 15 μm pitch 1280×1024 FPA is based on SCD's XBn technology and digital Hercules ROIC. The FPA is housed in a robust Dewar and is integrated with Ricor's K508N Stirling cryo-cooler. The IDCA has a weight of ~750 gram and its power consumption is ~ 5.5 W at a frame rate of 100Hz. The Mean Time to Failure (MTTF) of the IDCA is more than 20,000 hours, greatly facilitating 24/7 operation.
Electro-optical missile seekers pose exceptional requirements for infrared (IR) detectors. These requirements include: very short mission readiness (time-to-image), one-time and relatively short mission duration, extreme ambient conditions, high sensitivity, fast frame rate, and in some cases small size and cost. SCD is engaged in the development and production of IR detectors for missile seeker applications for many years. 0D, 1D and 2D InSb focal plane arrays (FPAs) are packaged in specially designed fast cool-down Dewars and integrated with Joule-Thomson (JT) coolers. These cooled MWIR detectors were integrated in numerous seekers of various missile types, for short and long range applications, and are combat proven. New technologies for the MWIR, such as epi-InSb and XBn-InAsSb, enable faster cool-down time and higher sensitivity for the next generation seekers. The uncooled micro-bolometer technology for IR detectors has advanced significantly over the last decade, and high resolution - high sensitivity FPAs are now available for different applications. Their much smaller size and cost with regard to the cooled detectors makes these uncooled LWIR detectors natural candidates for short and mid-range missile seekers. In this work we will present SCD's cooled and uncooled solutions for advanced electro-optical missile seekers.
Over the past few years, a new type of High Operating Temperature (HOT) photon detector has been developed at SCD,
which operates in the blue part of the MWIR window of the atmosphere (3.4-4.2 μm). This window is generally more
transparent than the red part of the MWIR window (4.4-4.9 μm), especially for mid and long range applications. The
detector has an InAsSb active layer, and is based on the new "XBn" device concept. We have analyzed various electrooptical
systems at different atmospheric temperatures, based on XBn-InAsSb operating at 150K and epi-InSb at 95K,
respectively, and find that the typical recognition ranges of both detector technologies are similar. Therefore, for very
many applications there is no disadvantage to using XBn-InAsSb instead of InSb. On the other hand XBn technology
confers many advantages, particularly in low Size, Weight and Power (SWaP) and in the high reliability of the cooler
and Integrated Detector Cooler Assembly (IDCA). In this work we present a new IDCA, designed for 150K operation.
The 15 μm pitch 640×512 digital FPA is housed in a robust, light-weight, miniaturised Dewar, attached to Ricor's
K562S Stirling cycle cooler. The complete IDCA has a diameter of 28 mm, length of 80 mm and weight of < 300 gm.
The total IDCA power consumption is ~ 3W at a 60Hz frame rate, including an external miniature proximity card
attached to the outside of the Dewar. We describe some of the key performance parameters of the new detector,
including its NETD, RNU and operability, pixel cross-talk, and early stage yield results from our production line.
Long range sights and targeting systems require a combination of high spatial resolution, low temporal NETD, and wide
field of view. For practical electro-optical systems it is hard to support these constraints simultaneously. Moreover,
achieving these needs with the relatively low-cost Uncooled μ-Bolometer technology is a major challenge in the design
and implementation of both the bolometer pixel and the Readout Integrated Circuit (ROIC).
In this work we present measured results from a new, large format (1024×768) detector array, with 17μm pitch. This
detector meets the demands of a typical armored vehicle sight with its high resolution and large format, together with
low NETD of better than 35mK (at F/1, 30Hz). We estimate a Recognition Range for a NATO target of better than 4 km
at all relevant atmospheric conditions, which is better than standard 2nd generation scanning array cooled detector. A
new design of the detector package enables improved stability of the Non-Uniformity Correction (NUC) to
environmental temperature drifts.
In MWIR photodiodes made from InSb, InAs or their alloy InAs1-xSbx, the dark current is generally limited by
Generation-Recombination (G-R) processes. In order to reach a background limited operating temperature higher than
~80 K, steps must be taken to suppress this G-R current. At SCD we have adopted two main strategies. The first is to
reduce the concentration of G-R centres, by changing from an implanted InSb diode junction to a higher quality one
grown by Molecular Beam Epitaxy (MBE). Our epi-InSb diodes have a background limited performance (BLIP)
temperature of ~105 K at F/4, in 15 to 30 μm pitch Focal Plane Arrays (FPAs). This operation temperature increase
delivers a typical saving in cooling power of ~20%. In order to achieve even higher operating temperatures, we have
developed a new XBnn bariode technology, in which the bulk G-R current is totally suppressed. This technology
includes nBnn and pBnn devices, as well as more complex structures. In all cases, the basic unit is an n-type AlSb1-yAsy /
InAs1-xSbx barrier layer / photon-absorbing layer structure. These FPAs, with 15 to 30 μm pitch and a cut-off
wavelength of ~ 4.1 μm, exhibit a BLIP temperature of ~ 175K at F/3. The cooling power requirement is reduced by
~60% compared with conventional 77K operation. The operation of both our diode and bariode detectors at high
temperatures results in an improved range of solutions for various applications, especially where Size, Weight, and
Power (SWaP) are critical. Advantages include faster cool-down time and mission readiness, longer mission times, and
higher cooler reliability, as well as very low dark current and an enhanced Signal to Noise Ratio (SNR) at lower
operating temperatures. This paper discusses the system level performance for cut-off wavelengths appropriate to the
sensing materials in each detector type. Details of the radiometric parameters of each detector type are then presented in
Dual-color imaging in the Mid-Wave Infrared (MWIR) is required in some airborne Missile Warning Systems (MWS)
due to its ability to reduce the number of false alarms in this application by comparing the signal in the two spectral
bands. Furthermore, such systems demand high frame rate, spatial resolution, and spectral resolution, while at the same
time call for simultaneous collection and readout of the two color images. Monolithic dual-color Focal Plane Arrays
(FPAs) lack at least some of these requirements. In this work we introduce a new hybrid dual-color detector based on
two 480×384/20μm digital InSb FPAs, assembled in a single Dewar, where the high degree of spatial registration
between the two color channels enables a solution that achieves the above requirements. Each FPA has its own cold
shield and spectral filter, and the signal is snapshot integrated and read out in parallel to obtain complete dual-color
simultaneity. The sensor imaging optics is integrated inside the Dewar for both channels in order to reduce the overall
system size and weight, and improve its performance at the extreme environmental conditions imposed by this
application. In this case the hybrid dual-color Integrated Dewar-Cooler Assembly (IDCA) is designed for a very wide
field of view (>100°), suited for the specific airborne Missile Warning System (MWS). We present the independent
electro-optical results of both the red and the blue channels, together with the measured negligible spectral cross-talk and
high spatial registration between them.
A bariode is a new type of "diode-like" semiconductor photonic device, in which the transport of majority carriers is
blocked by a barrier in the depletion layer, while minority carriers, created thermally or by the absorption of light, are
allowed to pass freely across the device. In an n-type bariode, also known as an XBnn structure, both the active photon
absorbing layer and the barrier layer are doped with electron donors, while in a p-type bariode, or XBpp structure, they
are both doped with electron acceptors. An important advantage of bariode devices is that their dark current is
essentially diffusion limited, so that high detector operating temperatures can be achieved. In this paper we report on
MWIR n-type bariode detectors with an InAsSb active layer and an AlSbAs barrier layer, grown on either GaSb or
GaAs substrates. For both substrate types, the bariodes exhibit a bandgap wavelength of ~ 4.1 μm and operate with
Background Limited Performance (BLIP) up to at least 160K at F/3. Different members of the XBnn device family are
investigated, in which the contact layer material, "X", is changed between n-InAsSb and p-GaSb. In all cases, the
electro-optical properties of the devices are similar, showing clearly the generic nature of the bariode device
architecture. Focal Plane Array detectors have been made with a pitch of 15 or 30μm. We present radiometric
performance data and images from our Blue Fairy (320×256) and Pelican (640×512) detectors, operating at
temperatures up to 180K. We demonstrate for both GaSb and GaAs substrates that detector performance can be
achieved which is close to "Rule 07", the benchmark for high quality, diffusion limited, Mercury Cadmium Telluride
Since the late 1990s Semiconductor devices (SCDs) has developed and manufactured a variety of InSb two-dimensional (2D) focal plane arrays (FPAs) that were implemented in many infrared (IR) systems and applications. SCD routinely manufactures both analog and digital InSb FPAs with array formats of 320×256, 480×384, and 640×512 elements, and pitch size in the range 15 to 30 μm. These FPAs are available in many packaging configurations, including fully integrated detector-Dewarcooler-assembly, with either closed-cycle Stirling or open-loop Joule-Thomson coolers. In response to a need for very high resolution midwave IR (MWIR) detectors and systems, SCD has developed a large format 2D InSb detector with 1280×1024 elements and pixel size of 15 μm. The ROIC is fabricated in CMOS 0.18-μm technology, that enables the small pixel circuitry and relatively low power generation at the focal plane. The digital ROIC has an analog to digital (A/D) converter per-channel and allows for full frame readout at a rate of 100 Hz. Such on-chip A/D conversion eliminates the need for several A/D converters with fairly high power consumption at the system level. The digital readout, together with the InSb detector technology, lead to a wide linear dynamic range and low residual nonuniformity, which is stable over a long period of time following a nonuniformity correction procedure. A special Dewar was designed to withstand harsh environmental conditions while minimizing the contribution to the heat load of the detector. The Dewar together with the low power ROIC, enable a megapixel detector with overall low size, weight, and power with respect to comparable large format detectors. A variety of applications with this detector make use of different cold shields with different f-number and spectral filters. In this paper we present actual performance characteristics of the megapixel InSb detector and demonstrate its high manufacturability.
We demonstrate the suppression of the bulk generation-recombination current in nBn devices based on an InAsSb active layer (AL) and a AlSbAs barrier layer (BL). This leads to much lower dark currents than in conventional InAsSb photodiodes operating at the same temperature. When the BL is p-type, very high doping must be used in the AL (nBpn+). This results in a significant shortening of the device cutoff wavelength due to the Moss-Burstein effect. For an n-type BL, low AL doping can be used (nBnn), yielding a cutoff wavelength of ∼4.1 μm and a dark current close to ∼3 × 10−7 A/cm2 at 150 K. Such a device with a 4-μm-thick AL will exhibit a quantum efficiency (QE) of 70% and background-limited performance operation up to 160 K at f/3. We have made nBnn focal plane array detectors (FPAs) with a 320 × 256 format and a 1.3-μm-thick AL. These FPAs have a 35% QE and a noise equivalent temperature difference of 16 mK at 150 K and f/3. The high performance of our nBnn detectors is closely related to the high quality of the molecular beam epitaxy grown InAsSb AL material. On the basis of the temperature dependence of the diffusion limited dark current, we estimate a minority carrier lifetime of ∼670 ns.
The XBnn high operating temperature (HOT) detector project at SCD is aimed at developing a HOT (~150K) mid-wave
infrared (MWIR) detector array, based on InAsSb/AlSbAs barrier detector or "bariode" device elements. The essential
principle of the XBnn bariode architecture is to suppress the Generation-Recombination contribution to the dark current
by ensuring that the depletion region of the device is contained inside a large bandgap n-type barrier layer (BL) and
excluded from the narrow bandgap n-type active layer (AL). The band profile of the XBnn device leads to effective
blocking of electron transport across the BL while maintaining a free path for the holes, thus assuring a high internal
quantum efficiency (QE). Our devices exhibit a very large minority carrier lifetime (~700 ns), leading to a very low
dark current of <10-6 A cm-2 at 150K, which is essentially diffusion limited. We compare bariode devices with both a p-type
GaSb contact layer (CL) and an n-type InAsSb CL (termed CpBnn and nBnn, respectively). Apart from a ~0.3V
shift in the operating bias, the optical and electrical properties of both architectures are virtually identical,
demonstrating the generic nature of the XBnn barrier detector family. We have fabricated FPAs from nBnn bariode
arrays bonded both to a 320×256, 30 μm pitch Read-Out Integrated Circuit (ROIC) and a 640×512, 15 μm pitch ROIC.
For lattice matched FPAs the cut-off wavelength at >50% of maximum response is ~ 4.1 μm. We show an image
registered at 150K with a 640×512/15 μm Pelican FPA, using f/3.2 optics. The operability at 150K is >99.5% and the
measured NETD, limited only by shot and Read-Out noise, is 20 mK for a 22 ms integration time. At this f/number, the
detector has a background limited performance (BLIP) up to ~165K.
An XBn photovoltaic device has a band profile similar to that of a standard homojunction p-n diode, except that the
depletion region is made from a wide bandgap barrier material with a negligible valence band offset but a large
conduction band offset. In this notation, "X" stands for the n- or p-type contact layer, "B", for the n-type, wide bandgap,
barrier layer, and "n", for the n-type, narrow bandgap, active layer. In this work, we report on the fabrication of XBn
devices, which were grown by Molecular Beam Epitaxy (MBE) on GaSb substrates. Each structure has an InAsSb
active layer of thickness ~1.5μm and a 0.2-0.5μm thick AlSbAs barrier layer. Good growth uniformity was achieved
with lattice matching of better than 500ppm. Selected layers have been processed into devices which operate with a
high internal quantum efficiency at a bias of ~0.1-0.2V, and which exhibit a very low dark current due to the strong
suppression of the current component due to bulk Generation-Recombination processes. From dark current
measurements, a minority carrier lifetime of >670nS has been estimated in devices with an active layer doping of
~4×1015cm-3. In optimized, lattice matched, devices with this doping and an active layer thickness of 4μm, a cut-off
wavelength of ~ 4.0 - 4.1μm is expected at 160K, with a dark current density of ~10-6 A cm-2 and a quantum efficiency
of >70% (λ<4μm). These figures correspond to BLIP operation at 160K with a photocurrent to dark current ratio of ~4
Recently, a new "XBn" device architecture, based on heterostructures, has been proposed as an alternative to a
homojunction photodiode. The main difference is that no depletion layer exists in any narrow bandgap region of the
device. Instead, the depletion layer is confined to a wide bandgap barrier material. The Generation-Recombination (G-R)
contribution to the dark current is then almost totally suppressed and the dark current becomes diffusion limited.
This lowering of the dark current allows the device operating temperature to be raised relative to that of a standard
photodiode made from the same photon absorbing material, with essentially no loss of performance. At SCD we have
been developing XBn devices grown on GaSb substrates with an InAsSb photon absorbing layer and an AlSbAs barrier
layer. The results of optical and electrical measurements are presented on devices with a bandgap wavelength of about
4.1μm. Strong suppression of the G-R current is demonstrated over a range of almost two orders of magnitude in the
doping of the photon absorbing active layer (AL), while at the same time very high internal quantum efficiencies are
achieved. A model of the spectral response is developed which can reproduce the observed behaviour very well at 88K
and 150K over the whole AL doping range. In properly optimized devices, the BLIP temperature is shown to be in the
region of 160K at f/3.
Detectors composed of novel Antimonide Based Compound Semiconductor (ABCS) materials offer some unique
advantages. InAs/GaSb type II superlattices (T2SL) offer low dark currents and allow full bandgap tunability from the
MWIR to the VLWIR. InAs1-xSbx alloys (x~0.1) also offer low dark currents and can be used to make MWIR devices
with a cut-off wavelength close to 4.2μm. Both can be grown on commercially available GaSb substrates and both can
be combined with lattice matched GaAlSbAs barrier layers to make a new type of High Operating Temperature (HOT)
detector, known as an XBn detector. In an XBn detector the Generation-Recombination (G-R) contribution to the dark
current can be suppressed, giving a lower net dark current, or allowing the same dark current to be reached at a higher
temperature than in a conventional photodiode. The ABCS program at SCD began several years ago with the
development of an epi-InSb detector whose dark current is about 15 times lower than in standard implanted devices.
This detector is now entering production. More recently we have begun developing infrared detectors based both on
T2SL and InAsSb alloy materials. Our conventional photodiodes made from T2SL materials with a cut-off wavelength
in the region of 4.6μm exhibit dark currents consistent with a BLIP temperature of ~ 120-130K at f/3. Characterization
results of the T2SL materials and diodes are presented. We have also initiated a program to validate the XBn concept
and to develop high operating temperature InAsSb XBn detectors. The crystallographic, electrical and optical properties
of the XBn materials and devices are discussed. We demonstrate a BLIP temperature of ~ 150K at f/3.
Accurate and reliable numerical simulation tools are necessary for the development of advanced semiconductor devices.
SCD is using the Silvaco Atlas simulation tool to simultaneously solve the Poisson, Continuity and transport equations
for 3D detector structures.
In this work we describe a set of systematic experiments performed in order to calibrate the Atlas simulation to SCD's
backside illuminated InSb focal plane arrays (FPA) realized with planar technology. From these experiments we extract
physical parameters such as diffusion length, surface recombination velocity, and SRH lifetime. The actual and predicted
performance (e.g. dark-current and MTF) of present and future detectors is presented.
We have studied arrays with pitch in the range of 15 to 30 μm. We find that the MTF width is inversely proportional to
the pitch. Thus, the spatial resolution of the detector improves with decreasing pixel size as expected. Using the Atlas
simulation we predict the performance of planar InSb arrays with smaller pixel dimensions, e.g., 12 and 10 μm.
Over the last decade, SCD has developed and manufactured high quality InSb Focal Plane Arrays (FPAs), that are currently used in different applications worldwide. SCD's production line includes InSb FPAs with mid format (320x256 elements), and large format (640x512 elements), all available in various packaging configurations, including fully integrated Detector-Dewar-Cooler Assemblies (DDCA). Many of SCD's products are fully customized for customers' needs, and are optimized for each application with respect to the weight, power, size, and performance.
In 2006, SCD has added to its broad InSb product portfolio the new "Pelican" detector family. All Pelican detectors include a large format 640×512 InSb FPA with 15&mgr;m pitch, which is based on the FLIR/Indigo ISC0403 Readout Integrated Circuit (ROIC). Due to its small size, the Pelican FPA fits in any mid format Dewar, enabling upgrading of mid format systems with higher spatial resolution due to its good MTF.
This work presents the high performance of Pelican products. As achieved in all SCD's InSb DDC's, the Pelican detectors demonstrate high uniformity and correctability (residual non uniformity less than 0.05% std/DR) and remarkable operability (typically better than 99.9%). The Pelican FPA can be integrated in various DDCA configurations as per application needs, such as light weight, low power and compact form for hand held imagers, or a rigid configuration for environmentally demanding operating and storage conditions.
The two-dimensional spatial response of a pixel in SCD's back-side illuminated InSb Focal Plane Array (FPA) is
measured directly for arrays with a small pitch, namely 30, 20 and 15&mgr;m. The characterization method uses a spot-scan
measurement and de-convolution algorithm to obtain the net spatial response of a pixel. Two independent methods are
used to measure the detector spatial response: a) direct spot-scan of a pixel with a focused beam; b) uniform illumination
upon back-side evaporated thin gold coating, in which sub-pixel apertures are distributed in precise positions across the
array. The experimental results are compared to a 3D numerical simulation with excellent agreement for all pitch
dimensions. The spatial response is used to calculate the crosstalk and the Modulation Transfer Function (MTF) of the
pixel. We find that for all three pixel dimensions, the net spatial response width (FWHM) is equal to the pitch, and the
MTF width is inversely proportional to the pitch. Thus, the spatial resolution of the detector improves with decreasing
pixel size as expected. Moreover, for a given optics and smaller array pitch, the overall system spatial resolution is
limited more by the optical diffraction than by the detector. We show actual improved spatial resolution in an imaging system with a detector of smaller array pitch.
Over the past few years SCD has developed a new InAlSb diode technology based on Antimonide Based Compound Semiconductors (ABCS). In addition SCD has lead in the development of a new standard of silicon readout circuits based on digital processing. These are known as the "Sebastian" family of focal plane processors and are available in 384 × 480 and 512 × 640 formats. The combination of ABCS diode technology with digital readout capability highlights an important cornerstone of SCDs 3rd generation detector program. ABCS diode technology offers lower dark currents or higher operating temperatures in the 100K region while digital readouts provide very low noise and high immunity to external interference, combined with very high functionality. In this paper we present the current status of our ABCS-digital product development, in which the detectors are designed to provide improved performance characteristics for applications such as hand-held thermal imagers, missile seekers, airborne missile warning systems, long-range target identification and reconnaissance, etc. The most important Detector-Dewar-Cooler Assembly (DDCA) parameters are reviewed, according to each specific application. Benefits of these products include lower power consumption, lighter weight, higher signal-to-noise ratio, improved cooler reliability, faster mission readiness, longer mission times and more compact solutions for volume-critical applications. All these advantages are being offered without sacrificing the standard qualities of SCDs InSb Focal Plane Arrays (FPAs), such as excellent radiometric performance, image uniformity, high operability and soft-defect cosmetics.