Staring infrared focal plane arrays with epitaxial HgCdTe photovoltaic detectors coupled to surface channel CCD multiplexers have been fabricated and characterized. A source-coupled input circuit with background suppression is utilized. The HgCdTe backside-illuminated detector arrays have bandgaps suitable for operation in either the 3 - 5 or 8 - 12 μm region. Performance characterization of the multiplexer will be given at cryogenic temperatures. Charge transfer efficiency, subthreshold transconductance, threshold voltage temperature dependence, and 1/f noise measurements will be presented. These measurements will be compared with ideal models. Characteristics of the hybrid focal plane have been measured in a wide variety of backgrounds. Data will be presented on the noise characteristics, detectivity and noise equivalent temperature difference in backgrounds and temperatures suitable for passive thermal imaging.
Epitaxial HgCdTe/CdTe, combined with ion implantation technology, has proven ideally suited for proposed photodiode focal plane array applications. State-of-the-art performance planar photodiodes have been fabricated in epitaxial materials of all wavelengths. Important applications of these arrays are in tactical defense missions employing MWIR arrays operated at 77K and near 195K. A critical issue for these devices is stability through the bakeout required for the sealing off of dewar packaging. We report measurements of ion-implanted HgCdTe/CdTe devices and arrays which have broadband spectral response (when illuminated through the CdTe) and high RoA values (~ 11 Ω-cm2 at 195K for λc (50%) = 4.35 μmm, > 106 Ω-cm2 at 77K for λc (50%) = 4.7 μm). Stability of both planar and mesa devices and arrays through various bake conditions has been demonstrated.
Hybrid silicon focal plane arrays for infrared detection have progressed rapidly over the past year from the point of proof of concept to pilot production. Packaging schemes have been developed which will allow the integration of thousands of pixels into a large area, two-dimensional focal plane. The performance of silicon focal planes has been optimized and producibility aspects addressed. This paper discusses operating characteristics and packaging concepts of hybrid silicon focal planes and investigates their future applications.
Because of their simple structure, modest interconnect requirement, and read-out flexibility, charge-injection devices are attractive candidates for the realization of staring infrared focal-plane arrays. We have developed a CID technology in indium antimonide and have fabricated and tested a 32 x 32 imaging array. The CIDs are fabricated on bulk InSb wafers using a process which requires only five photomask steps and no p-n junctions. Read-out is performed without the requirement to operate in the charge-sharing mode. Point overloads do not result in column blooming. Data have been collected on array spatial uniformity, noise performance, and real-time imaging operation. This paper discusses the device fabrication and presents some of the results of the imager evaluation.
We describe the physics, construction, operational properties, and performance of Schottky mosaic sensors utilizing platinum silicide as the sensing layer. These devices are monolithic and are fabricated with standard integrated circuit grade silicon. Data are presented on quantum yield, transfer characteristic, uniformity, and integration element size. The construction and performance of a second generation, 32x64 element, area array is discussed. Several examples of thermal imaging are shown.
A system which provides complete offset and gain correction to the output of a hybrid (HCT/CCD) staring focal plane has been developed. This system provides high speed, real time compensation using custom processing electronics at the CCD output. A microprocessor controls the operation of the electronics and allows the user to implement any of several operating modes. The compensated output can be displayed on a high speed CRT or on a standard black & white TV monitor to enhance visual resolution. The compensation electronics described here is correcting a 64 x 64 array at pixel rates to 5 MHz. The system can be configured to operate on array sizes up to 256 x 256 at frequencies to 10 MHz as larger arrays and faster analog to digital converters become available.
Staring infrared (IR) detector arrays will have many applications in both imaging and nonimaging systems if the required signal conditioning can be performed in a simple low cost manner. Due to the large numbers of detectors and the high data rates inherent in staring IR arrays, the normal digital signal processing approach to the data handling problem is not desirable. One potential alternative to the all-digital approach is an electro-optical technique that uses both parallel optical processing as well as analog and digital processing. This hybrid technique offers both simplification and lower cost advantages over present techniques, as well as potential improvements in performance. This paper discusses these electro-optical techniques and their system advantages.
The integration of a commercially available microprocessor system (Commodore PET 2001) to control test equipment used in CCD array testing is described. The system can be used to determine charge transfer efficiency and noise of a CCD array for preliminary evaluation. The system is interactively controlled by an operator who runs a BASIC program from the keyboard of the microprocessor. Data collection is done by the computer/interface to minimize operator errors. The system is implemented primarily for quick-look quantitative evaluation of arrays being mass produced by industry.
The integration of successive frames from a 128 x 128 infrared detector array is complicated by (1) the large number (i.e. 16,384) of detector elements in the array, (2) the necessity of achieving computational precisions better than 0.01%, and (3) the space and power limitations that are implied by a 77°K focal plane location for the processing circuitry. The design of an analog frame integrator to meet the above requirements is discussed. In addition, a correlated triple sampling circuit, which is incorporated in the frame integrator and which can be adapted to a variety of read-out techniques, is described.
A laboratory version of an infrared staring imaging sensor, based on a 32 x 32 indium antimonide CID detector array, has been developed. That sensor serves both as a test bed for array evaluation and as a tool for investigating concepts such as non-uniformity compensation. The system is microprocessor based to provide for flexible array operation as well as for the collection and logging of array operating conditions and data. Design features of the sensor, including the focal plane and the supporting electronics, are described. Operation of the sensor is discussed and some of the imaging data collected with this system is presented.
Two dimensional solid-state pyroelectric (PE) arrays permit infrared detection and imaging in the 8 to 12 micron region without cryogenic cooling. Studies predict that a TV compatible PE camera should have a performance that is comparable to that specified for a military, man-portable IR Common Module system. A camera with a 32 x 32 element solid state array is being built to confirm these predictions. The detector array and camera are described and the results to date presented.
Target recognition performance for an RCA Shottky barrier staring FLIR with and without target motion is presented together with various minimum resolvable temperature (MRT) measurements obtained using both a 4-bar and a modulation perception requirement, i.e. using the strict requirement to see the 4-bars in the MRT bar pattern and the less restrictive requirement to see some modulation in the displayed image. In addition, both recognition and MRT results for a hand-held thermal viewer having approximately the same limiting spatial frequency as the staring system are presented. The various results are compared and examined to determine if the two dimensional aliasing in staring systems significantly degrades recognition performance relative to conventional scanning systems with similar size detectors and to establish which MRT, vertical 4-bar or modulation, or horizontal 4-bar or modulation is the best predictor of recognition performance when used in conjunction with the Night Vision & Electro-Optics Laboratory (NV&EOL) static recognition model.
Second generation infrared imaging systems require high density focal plane arrays for staring applications. To meet this need, a focal plane structure using HgCdTe photodiodes for detectors and Si CCDs for signal processing has been developed. Although conventional ion-implanted hybrid arrays have successfully been interfaced to CCD multiplexers, hybrid arrays fabricated on liquid phase epitaxial (LPE) layers offer some inherent advantages with respect to performance, processing and yields. It has been determined that heterostructure diodes fabricated by a Hg infinite melt LPE technique give superior performance relative to conventional ion-implanted devices. The devices exhibit high RoA products and good compositional uni formity. Data is presented on devices fabricated for both 8 to 12 μm and 3 to 5 μm applications.