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.
In recent years SCD has developed InGaAs/InP technology for Short-Wave Infrared (SWIR) imaging. The first product, Cardinal 640, has a 640×512 (VGA) format at 15μm pitch, and more than two thousand units have already been delivered to customers. Recently we have also introduced Cardinal 1280 which is an SXGA array with 10μm pitch aimed for long-range high end platforms . One of the big challenges facing the SWIR technology is its proliferation to widespread low cost and low SWaP applications, specifically Low Light Level (LLL) and Image Intensifier (II) replacements. In order to achieve this goal we have invested and combined efforts in several design and development directions: 1. Optimization of the InGaAs pixel array, reducing the dark current below 2fA at 20° C in order to save TEC cooling power under harsh light and environmental conditions. 2. Design of a new "Low Noise" ROIC targeting 15e noise floor and improved active imaging capabilities 3. Design of compact, low SWaP and low cost packages. In this context we have developed 2 types of packages: a non-hermetic package with thermo-electric cooler (TEC) and a hermetic TEC-Less ceramic package. 4. Development of efficient TEC-Less algorithms for optimal imaging at both day-light and low light level conditions. The result of these combined efforts is a compact low SWaP detector that provides equivalent performance to Gen III image intensifier under starlight conditions. In this paper we will present results from lab and field experiments that will support this claim.
In recent years SCD has developed InGaAs/InP technology for Short-Wave Infrared (SWIR) imaging. The first
product, Cardinal 640, has a 640x512 (VGA) format at 15μm pitch, and more than a thousand units have already
We now present Cardinal 1280, having the smallest pitch available today (10μm), with a 1280x1024 (SXGA)
format. Cardinal 1280 addresses both long-range daylight imaging, and passive or active imaging in Low Light
Level (LLL) conditions.
The Readout Integrated Circuit supports snapshot imaging at 13 bit resolution with a frame rate of 160Hz at full
format, or a frame rate of 640Hz with 2x2 binning. It also has a Low Noise Imaging (LNIM) mode with 35ereadout
noise with internal Correlated Double Sampling (CDS). An asynchronous Laser Pulse Detection (ALPD)
mode is implemented with 2x2 binning in parallel to SWIR imaging (with 10 μm resolution). The new 10 μm
pixel is sensitive down to the visible (VIS) spectrum, with a typical dark current of ~ 0.5fA at 280K, and a
quantum efficiency >80% at 1550nm.
The Focal Plane Array is integrated into a ruggedized, high vacuum integrity, metallic package, with a Thermo-
Electric Cooler (TEC) for optimized performance, and a high grade Sapphire window. In this paper we will
present the architecture and preliminary measurement results.
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.
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.
Advanced electro-optical systems are designed towards a more compact, low power, and low cost solution with respect to traditional systems. Integration of several components or functionalities, such as infrared imager, laser designator, laser range finder (LRF), into one multi-function detector serves this trend. SNIR Read-Out Integrated Circuit (ROIC) incorporates this high level of signal processing and with relatively low power consumption. In this paper we present measurement results from a Focal Plane Array (FPA) where the SNIR ROIC is Flip-Chip bonded to a 15µm pitch VGA InGaAs detector array. The FPA is integrated into a metallic vacuum sealed package. We present InGaAs arrays with dark current density below 1.5 nA/cm2 at 280K (typically 1fA), Quantum Efficiency higher than 80% at 1550 nm and operability better than 99.5%. The metallic package is integrated with a low power proximity electronics which delivers Camera Link output. The overall power dissipation is less than 1W, not including Thermal-Electric Cooling (TEC), which is required in some applications. The various active and passive operation modes of this detector will be reviewed. Specifically, we concentrate on the "high gain" mode with low readout noise for Low Light Level imaging application. Another promising feature is the Asynchronous Laser Pulse Detection (ALPD) with remarkably low detection thresholds.
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.
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
A new generation of high-performance uncooled detector arrays, with 17 and 25 μm pitch, improved sensitivity, and
extended spectral response were developed recently by SCD. This development brings the uncooled infrared technology
very close to the performance of traditional second generation cooled LWIR detectors, and enables a new range of
applications. We demonstrate the use of our Very High Sensitivity (VHS) 25 μm pitch detector with F/2.4, for long
range observation systems. We also present the new Wide-Band (WB) detector, where the detector absorption is tuned to
both the MWIR and LWIR bands, which is optimal for use in some applications such as situation awareness.
Furthermore, in this work we present our 17 μm pitch new family of detectors with different array formats (QVGA,
VGA and XGA). These detectors are targeting a wide range of applications, from medium-performance with low Size,
Weight and Power (SWaP) applications, up to high-performance imaging 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
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.
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
Over the last decade SCD has established a state of the art VOx μ-Bolometer product line. Due to its overall advantages
this technology is penetrating a large range of systems. In addition to a large variety of detectors, SCD has also recently
introduced modular video engines with an open architecture.
In this paper we will describe the versatile applications supported by the products based on 17μm pitch: Low SWaP
short range systems, mid range systems based on VGA arrays and high-end systems that will utilize the XGA format.
These latter systems have the potential to compete with cooled 2nd Gen scanning LWIR arrays, as will be demonstrated
by TRM3 system level calculations.
Proc. SPIE. 7834, Electro-Optical and Infrared Systems: Technology and Applications VII
KEYWORDS: Nonuniformity corrections, Infrared imaging, Digital signal processing, Detection and tracking algorithms, Sensors, Image processing, Video, Video processing, Analog electronics, Single crystal X-ray diffraction
SCD's new 17μm pitch VGA VOx μ-Bolometer detector was introduced in April 2010. Due to their overall size, weight
and power advantages, 17μm pitch uncooled detectors are currently being considered for next generation systems such
as thermal weapon sights (TWS), driver vision enhancers (DVE) and digitally fused goggles (DENVG). In this paper we
describe a new video engine developed at SCD to support the new 17μm pitch VGA detector. First, the modular design
concept of the hardware for the new video engine is described. This is followed by a description of the software design
concept, including features that emphasize the open architecture and the provision for a customer to add on his own
algorithms and software. The detector and the engine are on low rate production these days. Full production is planned
Last year we have introduced the development program of SCD's 17μm pitch VGA VOx μ-Bolometer detector (1). Due
to the overall size, weight and power advantages the 17μm pitch is currently being considered for the next generation
systems such as thermal weapon sights (TWS), driver vision enhancers (DVE) and digitally fused goggles (DENVG).
In the first part of this paper we will discuss in detail the performance of this detector. Specifically, we will elaborate on
the radiometric results, ROIC performance and operability. Detailed measurements for a wide temperature range will be
presented as well.
In the second part, we will describe some new capabilities and features that are enabled by the advanced 0.18um VLSI
technology. These features will be embedded in new products that are currently under development.
In this paper SCD's 17μm pitch large format VOx μ-Bolometer detector is introduced. In the first part the radiometric
performance and the challenges involved in achieving the desired pixel sensitivity are discussed. We elaborate on the
progress towards the performance design goal (< 50mK@F/1, 60Hz) utilizing various test structures and technology
demonstration platforms. The combination of reduced pixel size and high-end thermal sensitivity can provide smaller
light weight systems.
In the second part the ROIC architecture options will be presented in depth. New capabilities and features are enabled
by the advanced 0.18um VLSI technology. Explicitly, we address the contribution in terms of system flexibility,
simplification and reduced power dissipation. Some vital tasks, such as coarse non-uniformity correction, are done
internally thus facilitating the user interface.
In this paper we report on new developments associated with SCD VOx μ-Bolometer product line. Lately, we have
introduced the BIRD6401,2, which is a high-sensitivity (< 50 mK @ F/1, 60Hz) VGA format detector with 25 μm pitch.
In the first part we present new data extracted from extensive measurements. These measurements were conducted
under various environmental and power constraints, exhibiting superior temporal sensitivity, long-term stability and
In the second part we describe the system implications of special features that were embedded within the FPA.
Explicitly, we will address the benefits of some special features aimed at lowering the system power dissipation while
maintaining low temporal and spatial NETD.
Finally, in the last part we outline SCD's future roadmap and development directions. We will elaborate on our latest
progress towards improved pixel sensitivity (25mK@F/1), advanced 0.18um ROIC technology, and the combination of
the two towards smaller pitch (17 μm) arrays.
In this paper we report preliminary data of BIRD640, which is a high-sensitivity (50 mK @ F/1, 60Hz) VGA format
detector with 25 μm pitch. This high performance is achieved by utilizing an improved pixel design. The product is
architecturally compatible to BIRD384 and contains SCD's proprietary unique features (e.g. "Power-Save", Ambient drift
The ROIC architecture follows the framework of the previous designs. It consists of an internal timing machine with a
single clock that facilitates the system interface. Extensive effort was invested in reducing the detector and system power
dissipation. The ROIC supports special "low power" modes, where considerable power is saved with only minor
With its superior temporal sensitivity, long-term stability and operational flexibility BIRD640 serves as an ideal
candidate for high end and high resolution uncooled VGA systems, particularly hand-held applications.
SCD has established an uncooled detector product line based on the high-end VOx μ-bolometer technology. The first
PFA launched was BIRD384, a 384x288 (or 320x240) configurable format with 25μm pitch. Typical NETD values for
these FPAs are below 50mK with an F/1 aperture and 60 Hz frame rate.
The product exhibits superior image uniformity, stability and reduced power consumption, making it most suitable for a
broad range of "high-end" military and commercial applications.
In this paper we report on our progress in development of new products in accordance with SCD's uncooled products
1. A "sensitive" version of BIRD384 with an improved NETD of ~ 30mK @ F/1, 60Hz frame rate. This
performance is achieved by optimizing concurrently the membrane structure, pixel architecture and ROIC
2. An improved version of BIRD384 ROIC that supports 100/120Hz frame rate and high dynamic range ("Fire Man" option).
3. First data of the BIRD640 - a 640x480 array with 25μm pitch and NETD ≤ 50mK @ F/1, 60Hz frame rate.
Last year SCD presented an un-cooled detector product line based on the high-end VOx microbolometer technology. The first PFA (BIRD384) launched was a 384x288 software configurable (to 320x240 or other) format with 25μm pitch1. NETD values for these FPAs are better then 50mK with an F/1 aperture and 60 Hz frame rate.
Since then SCD has concentrated in improving both spatial and temporal performance. In order to reduce the Residual
Non-Uniformity (RNU) and increase the time span between shutter operations, SCD has incorporated various features within the FPA and supporting algorithms2.
Improved temporal performance was achieved by optimizing concurrently the membrane structure and ROIC electronics. SCD has demonstrated temporal NETD of ~ 20mK @ F/1 at 30Hz on a 160x120 BIRD compatible array.
This figure of merit, accompanied by the superior stability and reduced power consumption, makes SCD's VOx based detectors suitable candidates for a broad range of "high-end" military and commercial applications.
SCD has recently presented an uncooled detector product line based on the high-end VOx bolometer technology. The first FPA launched, named BIRD - short for Bolometer Infra Red Detector, is a 384x288 (or 320x240) configurable format with 25μm pitch. Typical NETD values for these FPAs range at 50mK with an F/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast thermal time constant of approximately 10 msec, as reported previously.
In this paper, the special features of BIRD optimized for unattended sensor applications are presented and discussed.
Unattended surveillance using sensors on unattended aerial vehicles (UAV's) or micro air vehicles (MAV's) , unattended ground vehicles (UGV's) or unattended ground sensor (UGS) are growing applications for uncooled detectors. This is due to their low power consumption, low weight, negligible acoustic noise and reduced price. On the other hand, uncooled detectors are vulnerable to ambient drift. Even minor temperature fluctuations are manifested as fixed pattern noise (FPN). As a result, frequent, shutter operation must be applied, with the risk of blocking the scenery in critical time frames and loosing information for various scenarios.
In order to increase the time span between shutter operations, SCD has incorporated various features within the FPA and supporting algorithms. This paper will discuss these features and present some illustrative examples.
Minimum power consumption is another critical issue for unattended applications. SCD has addressed this topic by introducing the "Power Save" concept. For very low power applications or for TEC-less (Thermo-Electric-Cooler) applications, the flexible dilution architecture enables the system to operate the detector at a number of formats. This, together with a smooth frame rate and format transition capability turns SCD's uncooled detector to be well suited for unattended applications. These issues will be described in detail as well.
SCD has recently presented an un-cooled detector product line based on the high-end VOx bolometer technology1. The
first PFA launched, BIRD, is a 384x288 (or 320x240) configurable format with 25μm pitch. Typical NETD values for
these FPAs range at 50mK with an F/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast
thermal time constant of approximately 10 msec.
In this paper we elaborate on the special advanced features that were incorporated within the ROIC and supporting
algorithms. In this framework we have addressed two important issues: the power consumption and the time span
between shutter activations. Minimum power consumption is a critical issue for many un-cooled applications. SCD has
addressed this by introducing the "Power-Save" concept accompanied with flexible dilution architecture. The paper will
present recent results exhibiting the various advantages.
One of the limiting factors on the performance of un-cooled detectors is their vulnerability to ambient drift. Usually,
even minor temperature fluctuations are manifested as high residual non-uniformity (RNU) or fixed pattern noise (FPN).
As a result frequent shutter operations must be applied, with the risk of blocking the scenery in critical time frames. The
challenge is thus twofold: increase the time span between shutter corrections and achieve better control of its activation.
For this purpose BIRD provides two complementing mechanisms: A real-time (frame-by-frame) ambient drift compensation accompanied by an RNU prediction mechanism. The paper will discuss these features in detail and present illustrative system implementations.
SCD is unveiling the first member of its new uncooled product line based on the high-end VOx technology. The detector is software configurable to various format standards including 384x288, 320x240 and others with 25μm pitch. The NETD values for these FPAs are better then 50mK with F#/1 aperture and 60 Hz frame rate. These detectors also exhibit a relatively fast thermal time constant of approximately 10msec. In order to improve the system level "cost-performance" in terms of power consumption and weight, SCD has introduced special features within the FPA & package. Among them is a proprietary "Power Save" architecture, in which the die temperature can be stabilized to the ambient temperature or a close enough discrete value, covering the range between -40c and 70c. Thus, the TEC power consumption is considerably reduced with minimal performance degradation. An additional benefit is improved "mission readiness" which is of vital importance for various system applications. A major limitation of systems based on uncooled detectors is the poor resilience to the ambient temperature drift. This drift degrades the spatial non-uniformity. As a result, frequent corrections using an optical shutter are required, specifically during the camera stabilization period. In order to increase the time span between shutter operations, SCD has incorporated various real-time monitoring features within the FPA and supporting algorithms. These features reduce the spatial noise by an order of magnitude.
In this paper we present a long Infrared Detector (LIRD) with Time Delayed Integration (TDI) mechanism in the 3mm - 5mm spectral band. The detector consists of four segments that are 'butted' on a single substrate in a staggered format. A novel butting technique ensures high accuracy and extremely uniform temperature distribution along the array. Each detector segment (DS) consists of an advanced CMOS readout integrated circuit (ROIC) attached to a back-illuminated diode array. The diode array is implemented with SCD's proprietary high performance InSb process. The ROIC is designed and optimized to be used with high F#, 'slow scan rate' systems. Very low power dissipation is emphasized. In order to achieve high flexibility, the signal processor is externally programmable, enabling TDI operation with or without over-sampling on any combination of elements. Some other features include: Bi-directional operation, defective pixel de-selection, variable line rates and integration times, externally controlled gain and background subtraction capability. The paper presents electrical and radiometric predictions. Measured results that were performed on the first prototype are also presented.
The transition to second generation backside-illuminated dense LWIR FPAs requires consideration of issues not previously relevant in first generation modules: unlike in front illuminated arrays, the MTF (or effective area) of a pixel is no longer close to the ideal sinc function. The cutoff wavelength, quantum efficiency and crosstalk depend on the thickness and composition grading of the epitaxial layer. The tradeoff between resolution and sensitivity demands extensive engineering and optimization of the array configuration. The transition was accomplished by comparisons of simulations with experimental results. Expectations of performance indicators, such as MTF, quantum efficiency and crosstalk were obtained by detailed Monte-Carlo simulations. The results were used to configure the focal plane array. This paper discuses the basic assumptions and simulation results and compares them with the performance of actual detectors and various test structures.
There are several responsivity and gain models adequate to MQW detectors. All are related to two fundamental properties: the escape efficiency of a photo-excited carrier out of the well boundary (Pout) and the capture (or crossing) probability (Pc or Pw equals 1-Pc). In this work we present a rigorous calculation of the escape and capture probabilities based on a Quantum Mechanical approach. In this vicinity of the well the electrons are treated as Gaussian Wave-Packets. The simulation calculates the quantum mechanical reflections encountered by the packets at the interfaces as a function of kinetic energy and applied electric field. The relaxation processes into the bound sub-level are taken into account by introducing an imaginary potential. The simulations are carried out on both stepped and rectangular structures. The step reduces the dwell time above the well and hence the capture probability. This result is in good qualitative agreement with responsivity measurements on such structures. The effects of interface charge and non-uniform charge distribution are also considered. We assume an accumulation of negative sheet charge on the `inverted' interface facing the substrate. This excess charge, introduced during the growth sequence, induces structural asymmetry. The modified well potential is calculated self-consistently and results in an increased barrier height for carriers propagating towards the substrate. Those results are consistent with the asymmetrical responsivity and noise characteristics measured by various groups.
The traveling heater method (THM) is usually characterized by crystal defects such as grain boundaries and dislocations. The need for low cost HgCdTe FPA systems requires high photodiode yield. This demands understanding the crystal defect-diode relationships and necessitates a sorting method that is able to sort the as grown THM wafers before process according to the probability of achieving large photodiode arrays. This paper discusses the influence of crystals defects on photodiode performance and presents a sorting method which is under development. Oriented  THM HgCdTe crystals were grown and long wave N+P photodiode arrays were fabricated on the A (metal) face. It is found that individual or clusters of high current diodes which deviate drastically from their neighbors -- in current magnitude and in their slope on a Weibull distribution -- could be explained by a correspondence of excessive leakage and low angle sub-grain boundaries which cross the diode location. The distribution of single and multiple defects is compared to models based on isolated point defects and line defects. Yield implications of these results as a function of array design are described.
A new type of asymmetric stepped GaAs/AlGaAs multi quantum well infrared detectors is reported. These asymmetric detectors utilize the usual bound to continuum transition. The current responsivity is remarkably asymmetric with regard to the voltage polarity. In contrast with rectangular wells, in which responsivity is saturated in both bias polarities, these wells exhibit saturation only for negative bias. The responsivity increases monotonously with positive electric field. The difference between polarities for the noise is much smaller at low temperatures. As a result, the highest D* in positive polarity is much higher than in the negative one. This is attributed to changes induced by the field on the transport properties of the excited electrons. In particular, the bias affects the dwell time spent by the carrier wave packet in the well region. Employing this model, we achieve a very good fit with experimental data. The transport asymmetry is further studied using identical asymmetric wells which were grown in opposite sequences. It is shown that the effect of the asymmetry in the interfaces is of the same order of magnitude as the structural asymmetry.