Over the last decade, SCD has developed and manufactured high quality InSb Focal Plane Arrays (FPAs), which are
currently used in many applications worldwide. SCD's production line includes many different types of InSb FPA with
formats of 320x256, 480x384 and 640x512 elements and with pitch sizes in the range of 15 to 30 μm. All these FPAs
are available in various packaging configurations, including fully integrated Detector-Dewar-Cooler Assemblies
(DDCA) with either closed-cycle Sterling or open-loop Joule-Thomson coolers.
With an increasing need for higher resolution, SCD has recently developed a new large format 2-D InSb detector with
1280x1024 elements and a pixel size of 15μm. The InSb 15μm pixel technology has already been proven at SCD with
the "Pelican" detector (640x512 elements), which was introduced at the Orlando conference in 2006.
A new signal processor was developed at SCD for use in this mega-pixel detector. This Readout Integrated Circuit
(ROIC) is designed for, and manufactured with, 0.18 μm CMOS technology. The migration from 0.5 to 0.18 μm CMOS
technology supports SCD's roadmap for the reduction of pixel size and power consumption and is in line with the
increasing demand for improved performance and on-chip functionality. Consequently, the new ROIC maintains the
same level of performance and functionality with a 15 μm pitch, as exists in our 20 μm-pitch ROICs based on 0.5μm
CMOS technology. Similar to Sebastian (SCD ROIC with A/D on chip), this signal processor also includes A/D
converters on the chip and demonstrates the same level of performance, but with reduced power consumption. The pixel
readout rate has been increased up to 160 MHz in order to support a high frame rate, resulting in 120 Hz operation with
a window of 1024×1024 elements at ~130 mW. These A/D converters on chip save the need for using 16 A/D channels
on board (in the case of an analog ROIC) which would operate at 10 MHz and consume about 8Watts
A Dewar has been designed with a stiffened detector support to withstand harsh environmental conditions with a
minimal contribution to the heat load of the detector. The combination of the 0.18μm-based low power CMOS
technology for the ROIC and the stiffening of the detector support within the Dewar has enabled the use of the Ricor
K508 cryo-cooler (0.5 W). This has created a high-resolution detector in a very compact package.
In this paper we present the basic concept of the new detector. We will describe its construction and will present
electrical and radiometric characterization results.
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. InAs<sub>1-x</sub>Sb<sub>x</sub> 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.
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.
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 3<sup>rd</sup> 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.
Antimonide Based Compound Semiconductors (ABCS) and a new family of advanced analogue and digital silicon read-out integrated circuits form the basis of the SCD 3rd generation detector program, which builds on the firm platform of SCDs existing InSb-FPA technology. We have devised a staged roadmap at SCD which begins with epitaxial InSb mesa diodes and gradually increases in technological sophistication. In the initial stages we have focused in particular on In<sub>1-z</sub>Al<sub>z</sub>Sb alloys grown on InSb by Molecular Beam Epitaxy (MBE). Some of our achievements with these materials are presented in this paper. For epitaxial InSb (z = 0), we demonstrate the performance of Focal Plane Arrays (FPAs) with a format of 320x256 pixels, at focal plane temperatures between 77K and 110K. An operability has been achieved which is in excess of 99.5%, with a Residual Non-Uniformity (RNU) at 95K of less than 0.03% (standard deviation/dynamic range) between 15 and 80% well fill. Moreover, after a two point Non-Uniformity Correction (NUC) has been applied at 95K, the RNU remains below ~0.1% at all focal plane temperatures down to 85K and up to 100K without the need to apply any further correction. This is a major improvement in both the temperature of operation and the temperature stability compared with implanted diodes made from bulk material. We also demonstrate rapid progress in the development of epitaxial InAlSb FPAs with comparable operability and RNU to the InSb FPAs but which exhibit lower dark current and offer a range of cut-off wavelengths shorter than in InSb. These FPAs are intended for temperatures of operation in excess of 100K.
Antimonide Based Compound Semiconductors (ABCS) and a new family of advanced analogue and digital silicon read-out integrated circuits form the basis of the SCD 3<sup>rd</sup> generation detector program, which builds on the firm platform of SCDs existing InSb-FPA technology. In order to cover the MWIR atmospheric window, we recently proposed the epitaxial alloys: InAs<sub>1-y</sub> Sb<sub>y</sub> on GaSb with 0.07 < <i>y</i> < 0.11 and In<sub>1-z</sub>Al<sub>z</sub> Sb on InSb with 0 < <i>z</i> < 0.03. In this paper we focus on the results of some of our recent work on epitaxial In<sub>1-z</sub>Al<sub>z</sub> Sb grown on InSb by Molecular Beam Epitxay (MBE). In epitaxial InSb (<sub>z</sub> = 0), we demonstrate the performance of Focal Plane Arrays (FPAs) with a format of 320x256 pixels, at focal plane temperatures between 77K and 100K. An operability has been achieved which is in excess of 99.5%, with a Residual Non-Uniformity (RNU) <i>at 95K</i> of less than 0.03% (standard deviation/dynamic range). Moreover, after a two point Non-Uniformity Correction (NUC) has been applied at 95K, the RNU remains below ~0.1% at all focal plane temperatures down to 85K and up to 100K without the need to apply any further correction. This is a major improvement in both the temperature of operation and the temperature stability compared with implanted diodes made from bulk material. We also demonstrate rapid progress in the development of low current epitaxial InAlSb photodiodes with high uniformity and low dark current that offer a range of cut-off wavelengths shorter than in InSb. Preliminary results are presented on FPAs with a cut-off wavelength in the range λ<sub>C</sub>~5μ.
Proc. SPIE. 5074, Infrared Technology and Applications XXIX
KEYWORDS: Staring arrays, Infrared sensors, Digital signal processing, Sensors, Interference (communication), Field programmable gate arrays, Signal processing, Analog electronics, Signal detection, Single crystal X-ray diffraction
A Focal Plane Array (FPA) with a digital output for cooled IR detectors has recently attracted a lot of attention due to its advantages over detectors with analog outputs. Of special importance is the potential to have a better long term stability of the Residual Non Uniformity (RNU). Last summer SCD introduced a new high performance digital signal processor for 640x512 InSb infrared detectors, which includes analog to digital conversion performed inside the signal processor itself (at the focal plane). This signal processor has been bonded to InSb detector arrays and tested both electrically and radiometrically within a dewar. Special proximity electronics was developed for the operation of the FPA, including a Field Programmable Gate Array (FPGA) device. The complete device functions as a multi-chip system, enabling high degree of flexibility and easy integration at the system level. The total power dissipation of the FPA is less than 100mW at a frame rate of 100Hz, which is even less than that obtained with comparable/conventional analog FPAs. The NETD of the detector is less than 10.5mK at 50% of the full range 13Me-. The RNU is less than 0.02%STD/DR from 2% up to 90% of the full range. It is important to note that in the case of a digital detector the readout noise the NETD and the RNU of the detector are the total system values. This stand alone Digital Detector Dewar Cooler (D<sup>3</sup>C) presents a new industrial standard for cooled IR detectors.
SCD Focal Plane Arrays (FPAs) are based on 320×256 InSb elements, or 640×512 InSb elements. In this paper we introduce the outstanding FPA based on the signal processor 'blue fairy' (BF) that has been designed at SCD, and is now in standard production for the 320×256 InSb FPAs. The BF Focal Plane Processor (FPP) enables integration capacity of more than 15Me- at Integrate While Read (IWR) mode, and more than 30 Me- at Integrate Than Read (ITR) mode. A combined mode for large dynamic range with high sensitivity is possible. An excellent linearity and residual non-uniformity is achieved, starting from extremely low electron capacity up to 13Me- at IWR mode and 24Me- at ITR mode. Many other modes can be selected via a communication channel such as: ITR/IWR, one of seven different gains, one of seven different biases for the detector, windows size and window location. A Correlated Double Sampling (CDS) between frames and rows can be used for low frequency noise reduction, and/or any external electronic gain and offset drift corrections. All these features enable the integration of the BF FPA in large variety application, with high performance at each application.
Proc. SPIE. 4028, Infrared Detectors and Focal Plane Arrays VI
KEYWORDS: Staring arrays, Nonuniformity corrections, Digital signal processing, Detection and tracking algorithms, Sensors, Calibration, Black bodies, Signal detection, Temperature metrology, Single crystal X-ray diffraction
Performance of InSb focal plane array (FPA) detectors depends to a great extent on both the absolute temperature and the temperature fluctuations of the detector. The residual spatial noise, which can be achieved and maintained after a two-point non-uniformity correction (NUC), increases with the FPA temperature changes relative to that at which the NUC procedure was performed. A model is described, which allows prediction of the InSb FPA residual non-uniformity (RNU) as a function of the FPA temperature fluctuations for a given set of the FPA, cold shield and background radiation parameters. The calculated values are confirmed by experimental data. It is demonstrated that, as predicted, RNU degradation is primarily caused by signal offset changes corresponding to the InSb dark current variations, which are induced by the FPA temperature instability. The influence of the FPA temperature variation on NUC can be effectively compensated by a one-point offset correction. When this procedure is impractical, the dark current compensation method is proposed, which allows for a real-time, continuous compensation of the FPA temperature variations, resulting in a low residual non-uniformity.