SiGe based focal plane arrays offer a low cost alternative for developing visible- near-infrared focal plane arrays that
will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based foal plane arrays take
advantage of silicon based technology that promises small feature size, low dark current and compatibility with the
low power silicon CMOS circuits for signal processing. This paper will discuss performance characteristics for the
SiGe based VIS-NIR Sensors for a variety of defense and commercial applications using small unit cell size and
compare performance with InGaAs, InSb, and HgCdTe IRFPA's. We will present results on the approach and
device design for reducing the dark current in SiGe detector arrays. We will discuss electrical and optical properties
of SiGe arrays at room temperature and as a function of temperature. We will also discuss future integration path for
SiGe devices with Si-MEMS Bolometers.
High resolution imaging in UV band has a lot of applications in Defense and Commercial systems. The
shortest wavelength is desired for spatial resolution which allows for small pixels and large formats.
UVAPD's have been demonstrated as discrete devices demonstrating gain. The next frontier is to develop UV
APD arrays with high gain to demonstrate high resolution imaging.
We will discuss an analytical model that can predict sensor performance in the UV band using p-i-n or APD
detectors with and without gain and other detector and sensor parameters for a desired UV band of interest.
SNR's can be modeled from illuminated targets at various distances with high resolution under standard
MODTRAN atmospheres in the UV band and the solar blind region using detector arrays with unity gain
and with high gain APD along with continuous or pulsed UV lasers.
The performance can be determined by the signal level which results from the UV laser return energy (laser
power, beam divergence, target reflectance and atmospheric transmittance), the optics f/number, the response
of the detector (collection area, quantum efficiency, fill factor and gain), and the total noise which will be the
sum of the dark current noise, the scene noise, and the amplifier noise. We also discuss trades as a function
of detector response, dark current noise and the 1/f noise. We also present various approaches and device
designs that are being evaluated for developing APD's in wide band gap semiconductors. The paper also
discusses current state of the art in UV APD and the future directions for small unit cell size and gain in the
SiGe based Focal Plane Arrays offer a low cost alternative for developing visible- NIR focal plane arrays
that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based IRFPA's
will take advantage of Silicon based technology, that promises small feature size, low dark current and
compatibility with the low power silicon CMOS circuits for signal processing. This paper discusses
performance comparison for the SiGe based VIS-NIR Sensor with performance characteristics of InGaAs,
InSb, and HgCdTe based IRFPA's.
Various approaches including device designs are discussed for reducing the dark current in SiGe detector
arrays; these include Superlattice, Quantum dot and Buried junction designs that have the potential of
reducing the dark current by several orders of magnitude. The paper also discusses approaches to reduce
the leakage current for small detector size and fabrication techniques. In addition several innovative
approaches that have the potential of increasing the spectral response to 1.8 microns and beyond.
Proc. SPIE. 7055, Infrared Systems and Photoelectronic Technology III
KEYWORDS: Bolometers, Signal to noise ratio, Sensors, 3D modeling, Image sensors, Modulation transfer functions, Minimum resolvable temperature difference, Performance modeling, Thermal modeling, Atmospheric modeling
Presented is a comprehensive, physics-based model for microbolometer detector and sensor performance prediction. The
model combines equations found in the literature and various standard models that generate NETD, MRTD, 3-D noise
statistics and atmosphere characteristics (MODTRAN-based), with a comprehensive microbolometer model and HgCdTe
model developed by the author to provide an end-to-end detector/FPA/sensor analysis and design tool, as well as a
realistic image sequence generation tool. The model characterizes the individual pixel element based on the structure
used, the various layer thicknesses, the electrical and thermal characteristics of the bolometer material and the biasing
and readout circuit, and uses these results to calculate response and noise, NEP and NETD. The NETD, MTF and
MRTD are predicted from the optics, detector and readout. Predicted NETD has been compared and verified with values
found in literature, results from other models, and to uncooled camera measurements. The MRTD prediction has been
verified with camera measurements and with standard industry MRTD model outputs. The model also calculates
atmospheric path radiance and transmittance for horizontal paths based on MODTRAN outputs for the LWIR band at
altitudes from 0 to 10km and ranges from 1 to 50km for assessments of air-to-air engagement SNR's. The model in
matlab utililizes a 3-D noise model to provide accurate realistic imagery used to present realistic sensor images and to
further validate the NETD and MRTD routines.(1) Images at 30Hz and 60Hz have been generated for visual assessment
by the user and have mirrored industry model results and real-time camera images for MRTD's for the temporal noise
case. The model's 3-D noise generation feature allows the prediction of MRTD vs. frequency under any 3-D noise
combination. This model provides an end-to-end performance prediction tool useful in bolometer element design,
readout design and for system level trade studies.
Low cost IR Sensors are needed for a variety of Military and Commercial Applications. SiGe based IR Focal Plane Arrays offer a low cost alternative for developing near IR sensors that will not require cooling and can operate in the visible and NIR bands. The attractive features of SiGe based IRFPA's will take advantage of Silicon based technology, that promises small feature size and compatibility with the low power silicon CMOS circuits for signal processing.
A feasibility study of an infrared sensor based on SiGe material system and its performance characteristics are presented. Simulations comparing the sensitivity of the SiGe detector with spectral cutoff wavelength of 1.6 micron to other IR Focal Plane arrays are discussed. Measured electrical and optical characteristics of Ge-on-Si photodetectors are also presented.
We present a CCD / CMOS hybrid focal plane array (FPA) for low light level imaging applications. The hybrid approach combines the best of CCD imaging characteristics (e.g. high quantum efficiency, low dark current, excellent uniformity, and low pixel cross talk) with the high speed, low power and ultra-low read noise of CMOS readout technology. The FPA is comprised of two CMOS readout integrated circuits (ROIC) that are bump bonded to a CCD imaging substrate. Each ROIC is an array of Capacitive Transimpedence Amplifiers (CTIA) that connect to the CCD columns via indium bumps. The proposed column parallel readout architecture eliminates the slow speed, high noise, and high power limitations of a conventional CCD. This results in a compact, low power, ultra-sensitive solid-state FPA that can be used in low light level applications such as live-cell microscopy and security cameras at room temperature operation. The prototype FPA has a 1280×1024 format with 12-um square pixels. Measured dark current is less than 5.8 pA/cm2 at room temperature and the overall read noise is as low as 2.9e at 30 frames/sec.
Great incentive exists for the development of infrared detectors that can operate without cooling near the limit of photon or thermal fluctuations. Great progress has been made in past 30 years developing uncooled thermal detectors that now provide enough sensitivity for many routine infrared imaging needs, albeit with relatively slow response times. Even now, however, the sensitivity of uncooled thermal detectors is 3-15× less sensitive than the ideal characteristics predict. In this paper we first examine the current status of uncooled thermal detectors to understand the limiting mechanisms which appear to be 1/f noise and system noise. Approaches for developing uncooled or minimally-cooled photon detectors are then reviewed. A modification of one current approach, bias extraction of minority carriers, is suggested involving photo-JFETs rather than photodiodes. It appears that the most promising prospect for uncooled or minimally-cooled photon detectors is in the MWIR spectral region.
The demand continues to grow for small, compact imaging sensors, which include new capabilities, such as response in multiple spectral bands, increased sensitivity, wide high dynamic range, and operating at room temperature. These goals are dependant upon novel concepts in sensor technology, especially advanced electronic processing integrated with the sensor. On-focal plane processing is especially important to realize the full potential of the sensor. Since the area available for focal plane processing is extremely limited, a new paradigm in sensor electronic read-out technology is necessary to bridge the gap between multi-functional, high performance detector arrays and the off-focal plane processing. The Vertically Integrated Sensor Array (VISA) Program addresses this need through development of pixel-to-pixel interconnected silicon processors at the detector, thus expanding the area available for signal and image processing. The VISA Program addresses not only the array interconnection technology, but also investigates circuit development adapted to this new three-dimensional focal plane architecture. This paper reviews progress in the first phase of the program and outlines direction for demonstrations of vertically integrated sensor arrays.
The VISA program has been sponsored by DARPA to enable a significant enhancement in signal conditioning, processing, and digitalization on the focal plane of visible and infrared sensors. The approach being developed builds on the traditional “hybrid” structure of a detector with a 2D array of indium-bump interconnects to a silicon readout. VISA will allow additional layers of silicon processing chips to be connected below the readout to provide more complex functionality. Connections will be fully arrayed two-dimensionally with one or more vias per pixel possible. The structural overview will be presented along with several application candidates that appear to be most promising to exploit this technology. These include active/passive sensors, expanded charge storage capacity for full flux utilization in the LWIR, cameras on a chip, high speed sub-frame collection to defeat pulsed laser interference, together with digital output with greater bit depth than currently possible from analog outputs. An A/D candidate circuit to achieve this performance within each pixel will be described.
Third-Generation, two-color infrared cooled sensors are being developed in order to allow the Army to detect and identify enemy forces at ranges beyond that at which the enemy can detect them. This will ensure that the Army continues to "own" night operations. Developing the technology needed to field these high-performance third-generation cooled imagers poses many challenges to the infrared community. These devices, which are expected to provide high spatial and temporal resolution simultaneously in two-to-three infrared bands, will dramatically increase the ability to find targets in defilade, and will be a major technological breakthrough. Performance has to be close to the theoretical limit, dominated by the limits of photon noise. Cost is also a major factor if sufficient numbers of such sensors are to be fielded. The benefits of this technology are now described, followed by a summary of the challenges faced in meeting the cost and performance objectives.
The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) currently has efforts internally and externally to develop advanced readout integrated circuits (ROICs) with on- chip processing capabilities. We have funded Raytheon Infrared Operations through a Dual Use Science and Technology program to develo and fabricate an advance ROIC with processing features including non-uniformity correction, extended charge handling, motion detection and edge enhancement. This advanced ROIC has been demonstrated through the successful development of the 'Adaptive Infrared Sensors' camera. Discussions of the circuit concepts and architecture of the 'AIRS' ROIC/FPA, as well as simulation results and test results of the camera is presented. Our internal investigations has resulted in an advanced readout design capable of real-time spatial and temporal filtering, to perform edge detection, edge enhancement, motion detection, and motion enhancement. The details of the circuit design, simulation results, as well as test data is presented.
Uncooled infrared cameras have made dramatic strides recently. Very low cost, lightweight, low power cameras have been built. Also low cost high performance uncooled cameras have been built. A discussion of this technology to make this happen and the resulting new applications will follow.
Fusion of reflected/emitted radiation light sensors can provide significant advantages for target identification and detection. The two bands -- 0.6 - 0.9 or 1 - 2 micrometer reflected light and 8 - 12 micrometer emitted radiation -- offer the greatest contrast since those bands have the lowest correlation, hence the greatest amount of combined information for infrared imaging. Data from fused imaging systems is presented for optical overlay as well as digital pixel fusion. Advantages of the digital fusion process are discussed as well as the advantages of having both bands present for military operations. Finally perception tests results are presented that show how color can significantly enhance target detection. A factor of two reduction in minimum resolvable temperature difference is postulated from perception tests in the chromaticity plane. Although initial results do not yet validate this finding, it is expected with the right fusion algorithms and displays that this important result will be proven shortly.
Small, low cost, low poer infrared imaging sensors are relatively recent innovation, employing the most advanced MEMS processing techniques, integrated circuit design, optical materials, and focal plane array packaging. We will review the rationale behind the development of low cost, small IR cameras, discuss several of the medium performance applications for these sensors via a modeling analysis, discuss the goals and status of our applied research uncooled focal plane array technology programs, and discuss the future of uncooled focal plane arrays.
Raytheon's Infrared Operations (RIO) has invented and developed a new class of focal plane arrays; the Adaptive IR Sensor (AIRS) and Thinfilm Analog Image Processor (TAIP). The AIRS FPA is based upon biologically inspired on-focal- plane circuitry, which adaptively removes detector and optic temperature drift and l/f induced fixed pattern noise. This third-generation multimode IRFPA, also called a Smart FPA, is a 256x256-array format capable of operation in four modes: 1) Direct Injection (DI), 2) Adaptive Non-uniformity Correction (NUC), 3) Motion/Edge Detection, and 4) Subframe Averaging. Also the 320x240 TAIP results have shown excellent image processing in the form of Spatial and Temporal processing.
Third generation focal plane arrays are being actively developed for the U.S. Army and other branches of the Department of Defense. The objective is to ensure that future soldiers will have superior night-fighting equipment. The requirements defined by this objective and the technology under development to support a demonstration of this capability is described. Issues associated with the development and exploitation of the high-performance cooled component of a family of third generation imager systems are discussed. Also discussed are two classes of uncooled imagers; one having high resolution and medium-high performance, and the second being very low cost.
The Army after Next will be lighter, faster, and more lethal than today's force. Survival of the force will be highly dependant on accurate and timely information about enemy forces and movements. CECOM NVESD has a number of ongoing efforts that directly support the vision of networked, low cost, low power, multifunction microsensor to enhance the lethality and survivability of the force. The three key technical areas of investigation: microsensor, signal processing, and communications.
Second generation forward looking infrared sensors, based on either parallel scanning, long wave (8 - 12 um) time delay and integration HgCdTe detectors or mid wave (3 - 5 um), medium format staring (640 X 480 pixels) InSb detectors, are being fielded. The science and technology community is now turning its attention toward the definition of a future third generation of FLIR sensors, based on emerging research and development efforts. Modeled third generation sensor performance demonstrates a significant improvement in performance over second generation, resulting in enhanced lethality and survivability on the future battlefield. In this paper we present the current thinking on what third generation sensors systems will be and the resulting requirements for third generation focal plane array detectors. Three classes of sensors have been identified. The high performance sensor will contain a megapixel or larger array with at least two colors. Higher operating temperatures will also be the goal here so that power and weight can be reduced. A high performance uncooled sensor is also envisioned that will perform somewhere between first and second generation cooled detectors, but at significantly lower cost, weight, and power. The final third generation sensor is a very low cost micro sensor. This sensor can open up a whole new IR market because of its small size, weight, and cost. Future unattended throwaway sensors, micro UAVs, and helmet mounted IR cameras will be the result of this new class.