A facility was developed at the Arnold Engineering Development Center (AEDC) to provide complete radiometric characterization offocal plane arrays (FPAs). The highly versatile facility provides the capability to test single detectors, detector arrays, and hybrid FPAs. The primary component of the AEDC test facility is the Focal Plane Characterization Chamber (FPCC). The FPCC provides a cryogenic, low-background environment for the test focal plane. Focal plane testing in the FPCC includes flood source testing, during which the array is uniformly irradiated with JR radiation, and spot source testing, during which the target radiation is focused onto a single pixel or group of pixels. For flood source testing, no optical elements are required between the source output aperture and the array. During flood source testing, performance parameters such as power consumption, responsivity, noise equivalent input, dynamic range, radiometric stability, recovery time, and array uniformity can be assessed. Sufficient data are acquired to permit complete parametric characterization of the array. Crosstalk is evaluated during spot source testing. Spectral response testing is performed in a spectral response test station using a three-grating monochromator. Because the chamber can accommodate several types oftesting in a single test installation, a high throughput rate and good economy ofoperation are possible. Data from the focal plane characterization tests can be presented in a wide variety of formats.

The reliable knowledge of a detector is very important in astrophysical research The aim of IAC (Instituto de Asirofisica de Canarias Spain) is to dispose of a versatile system to test evaluate and calibrate a big vanety of imaging detectors which viill be opc ned in the future to the scientific community The main features of this detector test bench are as follows (a) Wide spectral range (JR and visible) and (b) Wide radiation response range For this purpose a compact and c omplete arrangement has been designed Optical, mechanic ,cryogenic and electronic devices are flexible enough to allow the acquisition of data necessary to characterize the detector in a direct way (linearity, dark noise, spectral and time response,...). The high speed of the readout, the data acquisition system and other parameters are designed in such a way, that will make the facility virtually independent of the detector itself. This will allow reliable comparison between different detectors, and also with approved standards. Several procedures and practical examples are extensively discussed in the paper

The production of low co t IR focal plane array cameras at Cincinnati Electronics has generated a need for an equally low cost data collection system A data capture board is described that has been developed to allow easy interfacing to CE s ( amera products and to provide control and status signals required for detector characterizations The board may be used in any ISA bus compatible computer and provides a simple 16 bit parallel data interface that O( rates up to 4 megawords/sec Up to 8 megawords is stored on-board and multiple boards may be operated concurrently for systems that have multiple OUtpUt5. In addition to the ISA bus, the board has been successfully interfaced to an HP 425S UNIX workstation.

A program to upgrade the test capability for JR focal plane arrays and readouts is in progress at Aerojet. The objective of the development is to reduce the number and complexity of the steps in the test process, reduce in socket test time and provide a simplified set up procedure for production testing. There are two areas of study in the program. One is concerned with examining multiple fabrication sources for readout circuits. Cooperative studies are being performed with Orbit Semiconductor, Harris Semiconductor, TRW, UTMC, and Matra (France). Temperature profiles of noise performance, threshold variation, gain and subthreshold operation are being developed for several different manufacturers. The objective is to determine the feasibility of eliminating all cryogenic testing for sorting of readouts before final hybrid assembly thus reducing test steps. The second area of development, which will be discussed in this paper, is the application of a commercially available automated test system for production testing and engineering characterization ofreadouts and focal plane arrays. The Sentry Series 80 mixed signal tester is being fixtured for low noise measurements and interfacing to dewars for cryogenic testing. The multiuser foregroundlbackground operating system software has the advantage of allowing noise and other statistical calculations to be performed in the background without impeding test measurements. It also has the advantage in production of requiring no manual instrumentation set up or interconnect. The improvements in test throughput and analysis capability will be shown in adapting this class of tester as opposed to assembling test instruments in a custom made computer controlled test approach

This paper describes an automated calibration system that we developed to calibrate JR flight cameras for a series of sub-orbital experiments. Short schedules as well as concern over cryo-cooler lifetimes dictated a totally automated calibration system that obtained as much data as possible over a short period of time. The data must be as complete as possible since the cameras are not recovered. For this reason the system calibrates each pixel individually. The output of the calibration is a set of calibration coefficients which convert the gray level output of the camera into physical units of radiance (Watts/cm2-str-.tm). We have calibrated Hughes 256x256 pixels PtSi cameras and 128x128 pixels HgCd cameras and Amber 128x128 pixels JnSb cameras. These cameras put out 8 bit digital data and sync signal at a given camera setting. This paper describes the calibration acquisition system and shows the results for the Hughes 256x256 PtSi camera.

The Focal Plane Characterization Chamber (FPCC) at the Arnold Engineering Development Center (AEDC) is used to provide complete radiometric characterization of infrared focal plane arrays (FPAs). The facility has been used to characterize arrays from a number ofprograms. The FPCC was recently used to provide independent evaluation of a significant number of arrays. The versatility of the FPCC and associated data system was demonstrated in that all of the radiometric performance specifications were readily evaluated with relatively minor hardware and software modifications.

Santa Barbara Research Center (SBRC) and Hughes Technology Center (HTC) have developed nuclear radiation testing methodology to measure performance of infrared (IR) focal plane arrays (FPAs) in simulated total ionizing dose, transient dose rate (and flux), and neutron fluence environments. Test methodology for FPAs requires that temperature, background, bias, and vacuum conditions be maintained and controlled during in-situ measurements of performance parameters, which are accomplished with specially fabricated dewars, configurable test sets, and a new FPA portable test set. Radiation sources, dewars and test-set configurations allow measurements of functionality, responsivity, noise, pulse-height distributions, and response/recovery time under operational conditions for the selected radiation environment. This paper summarizes test methodology for EPA testing that can be used for benign (clear) and radiation environments, and describes the use of custom dewars and integrated test equipment in an example environment. The test methodology, consistent with American Society for Testing Materials (ASTM) standards, is presented for the total accumulated gamma dose, transient dose rate, gamma flux, and neutron fluence environments. The merits and limitations of using Cobalt 60 for gamma environment simulations and of using various fast-neutron reactors and neutron sources for neutron simulations are presented. Test result examples are presented to demonstrate test data acquisition and FPA parameter performance under different measurement conditions and environmental simulations.

For many years personnel of NRaD, formerly NOSC, have been characterizing infrared focal plane filters and components at cryogenic temperatures. We have recently begun investigating the effects of ionizing radiation on these item

Co60 sources and test equipment have successfully been integrated to provide total, accumulated gamma dose and debris (delayed) gamma flux testing on a routine basis. Three Co60 sources provide a wide range of testing capabilities and dose rates: (1) one-curie source mated to a custom dewar and blackbody specifically designed for debris gamma testing, (2) a 2200-curie internal irradiator primarily used for discrete component testing, and (3) an 8000-curie Shepherd Cell internal irradiator with custom dewars utilizing graybody IR sources which is capable of complete radiometric characterizations of IR FPAs while being exposed to a wide range of position-selectable gamma fluxes and accommodates both total dose and debris gamma testing. Any of these sources and dewars can be interfaced with customer-specific test equipment, allowing the same test set to be used for clear environment and in-situ radiation testing. This paper describes the radiation sources and their associated dewars, the uses, and the test methodology utilized for testing IR focal plane arrays (FPAs) in the total gamma dose and the debris gamma environments. Examples of test data acquisition and reduction are presented.

Infrared sensors are being incorporated in more systems and are often placed close to radar systems. The IR sensor is thus subjected to various microwave levels from the sidelobes or reflections of the radar pulses. In this paper we address the effect of microwaves on the performance of mercury-cadmium-telluride longwave photodiodes. We examine the effects of microwaves entering directly through the optical window (front-door mechanism) and entering along wires connected to the dewar (back-door mechanism). The diode noise voltage was measured before, during, and after the microwaves pulses by transimpedance amplification. The diode noise characteristics were shown to respond very rapidly to the microwave pulse. A linear relationship between detector noise and microwave power was observed. A strong dependence of noise on microwave frequency was observed and attributed to the resonances of the dewar design.

InSb photodiodes were examined for performance degradation after pulsed laser illumination at 0.532 micron and 1.064 micron. Incident laser powers ranged from 6 x 10 exp-18 micron-watts to 16 micron-watts in a 50 pm diameter spot. Dark current and spectral response were both measured before and after illumination. Dark current measurements were taken with the diode blanked off and viewing only 77 K surfaces. Long term stability tests demonstrated that the blackbody did not exhibit long term drifts. Other tests showed that room temperature variations did not affect the diode signal chain or the digitization electronics used in data acquisition. Results of the experiment show that the diodes did not exhibit changes in dark current or spectral response performance as a result of the laser illumination. A typical change in diode spectral response (before/after laser exposure) was about 0.2 percent +/- 0.2 percent.

In a particular application, a Si:As focal plane array may experience many thermal cycles from ambient down to its operating temperature (10 Kelvin) at a very rapid cooldown rate. Aerojet Electronic Systems Division's task, under company funds, was to consistently produce focal plane arrays that could reliably survive this kind of thermal cycling with no degradation in performance or mechanical damage. Of utmost importance in the verification of the focal plane array reliability is the assurance that the test configuration reflects flight configuration in material, interfaces, and process procedures. Using flight-like hardware, process procedures were developed to optimize hybridization parameters (the means of bonding the indium bumped readout electronics to the detector array) with bonding strength and electrical resistance selected as the figures of merit. When the materials, processes and assembly procedures were developed, a final verification was conducted which consisted of rapidly thermal cycling two flight-like hybrids. The hybrids successfully withstood more than 800 cycles from 60 Kelvin to 10 Kelvin and over 20 cycles from 300 Kelvin to 60 Kelvin with no degradation in performance or mechanical integrity.

The development of focal plane arrays with considerable on-chip processing, notably time-delayed integration, imposes new and severe requirements on the instrumentation to establish the modulation transfer function (MTF) of the integrated focal plane array. This paper describes an instrument to obtain the MTF for such arrays with a high level of accuracy. This instrument was built, and associated errors were obtained experimentally. The instrument uses sine-wave amplitude modulation across the spatial frequency spectrum to reach the Nyquist frequency of the focal plane array. Various algorithms to derive the MTF from the experimental data were investigated; the preferred approach is presented.

The present Focal Plane Characterization Chamber (FPCC), which is a cryogenic low-IR background chamber, has been the subject of a spectral band measurement capability's implementation in order to allow IR focal-plane array (FPA) output signal and noise values to be directly measured within spectral bands of interest. Attention is given to recent FPA radiometric characterization results. A comparison is conducted between measured and calculated noise-equivalent output.

The integration of various IR sensor subcomponents as early as possible in the development cycle furnishes an efficient feedback indicator for the compatibility of elements and units. Possible system defects are in this way identified and corrected sooner, thereby saving development process time and money. The procedure also reduces the risk in overall system design by verifying the sensor subsystem design's compliance with performance requirements.

Crosstalk between two neighboring elements in a focal plane array (FPA) occurs when signal incident on one element in the array is seen on another. This undesired effect can occur due to both the electrical and optical properties of the FPA. An effort is underway at the U.S. Army's Night Vision and Electro-Optics Directorate to develop a capability to measure crosstalk on both mid-wave infrared and long-wave infrared FPAs. A single detector in an array is illuminated using a laser source coupled with a beam expander, collimating lens, and focusing lens. The relative response of that detector to that of its neighboring detectors is measured to calculate crosstalk. The various components of the test station, the methodology for implementing the crosstalk measurement, and a model of the laser spot size are discussed.

This paper discusses a method for characterizing the combined effects of temporal and spatial noise in staring infrared focal plane arrays (IRFPA) and presents example measurements using a metric called D*(array). Two staring MWIR IRFPA's (HgCdTe and InSb) were calibrated and operated using an automated data acquisition system. Measurements were made under varying flux levels to determine the effects of nonlinearities on the nonuniformity correction process and the related ultimate performance of an IR sensor. The results show that the sensitivity of IRFPA's can be significantly degraded by very small nonlinearities. It was also found that the usable operating range of an array after two-point nonuniformity correction can be much less than that expected from simple dynamic range measurements of the IRFPA response function.

Testing infrared detectors at varying background flux densities can be very time consuming. Using existing in house cryogenic dewars, a way to reduce the down time when changing background flux was needed. The solution to this problem and problems encountered during design and fabrication are discussed.

Santa Barbara Research Center (SBRC) is actively involved in the design, fabrication, and evaluation of infrared detector arrays, both linear and two-dimensional. The large scale production of 64x64 HgCdTe arrays requires that testing be accomplished quickly and with minimum operator interaction. The optical components of the test set described provide stimuli to measure over eight detector parameters, including 2-dimensional Modulation Transfer Function (MTF), with a test time of only a few minutes. The optical design stresses the fundamental radiometry for each test while accounting for, and minimizing, the contributions from unwanted, but mostly controlled, background sources.

The U.S. Army Strategic Defense Command facility for the characterization of advanced low- background mosaics (CALM) is operated by Rockwell International Corporation. The facility supports a cryogenic test chamber with controlled background (flood) and target sources. The test chamber allows the measurement of focal plane array response to a moving point image in the presence of a radiant background that may be controlled over a range from less than 10⁹ to over 10¹⁴ photons/second-square centimeter. An ancillary data acquisition system is capable of performing a 15-bit analog-to-digital conversion of focal plane array output data and storing processed digital data at 2 megabytes per second. This paper describes the facility and its use in the evaluation of a solid state photomultiplier (SSPM) focal plane array. The SSPM is a back illuminated, impurity band conduction device capable of detecting individual photons over infrared wavelengths extending from 1 to 28 micrometers. A description of the test configuration, test conduct, and data analysis are presented along with results of the SSPM evaluation.

The development of a long-wave infrared optical simulator facilitates evaluation of the end-to-end performance of long wavelength infrared (LWIR) focal plane arrays (FPAs) in a system-like environment. This simulator provides selectable structured scene inputs to a focal plane module or array. Background irradiances as low as 10 exp 10 photons/sq cm s are achievable when the simulator is cooled with liquid helium. The optical simulator can generate single or multiple targets of controllable intensities, and uniform or structured background irradiances. The infrared scenes can be viewed in a stationary mode or dynamically scanned across the focal plane.

When testing infrared readouts, detector-readout hybrid assemblies, or focal plane arrays (FPAs), performance optimization is usually limited to adjustment of biases or clock rails, or subtle changes in readout timing. These generally result in global changes to the characteristics of the entire array rather than affecting individual pixels and channels. Using a scanning system that incorporates per channel gain normalization and a redundant time delay and integrate (TDI) architecture in the readout, pixels can be enhanced or deselected using an on- chip static RAM according to user-defined criteria resulting in improved uniformity of performance. A series of tests can be run automatically that evaluate each pixel's behavior at the readout or the hybrid level. When compared to or compiled against array-wide averages or system specifications, a map of dead or degraded pixels is created, and the timing necessary to either normalize each channel from a gain standpoint or mask out individual pixels is applied to the device under test. This technique has been successfully applied to 480 X 6 (120 X 4 X 6 in TDI) scanning architectures in both InSb and HgCdTe systems as well as multiple-chip and dual-band configurations. This paper describes a methodology and details how readout devices were screened and selected for hybridization and FPA build. The chip architecture and control timing is discussed to show how normalization and deselection was accomplished with a minimum of clock lines involved. A software utility is presented that allowed easy graphical interface to the user for manipulating the functions of the device. Algorithms for optimizing performance are then discussed and evaluated. Trade-offs made in optimizing one parameter against another are analyzed. Finally, results are presented demonstrating improved performance, customized by pixel to suit application specifications.

The spectral content of radiation incident on a bulk photoconductor can significantly affect the measured photocurrent. We show that front-illuminated Si:As bulk photoconductors operated at low temperature (approximately 10 degree(s)K) are sensitive to the spectral characteristics of the background, as well as signal fluxes. Our analysis is applied to spectral response measurements on bulk photoconductors themselves, and to filter transmission measurements that have been made utilizing these devices as IR detectors.

A simple technique based on the measurement of gate induced drain leakage current (Idl) is developed to measure the radiation induced charge in the metal oxide semiconductor transistor. After irradiation Idl of n-channel MOS transistors decreases while that of p-channel devices increases. The change of leakage current at higher tunneling fields is proportional to the increase of hole trap density in the gate oxide region. The leakage current measurement technique is an useful tool for characterizing radiation effects in MOS transistors because at high biases Idl is dependent on the increase of oxide charge while independent of the interface states. It depends on gate and drain overlap geometry and independent of the channel length. Hence Idl measurement technique is advantageous over threshold voltage technique which depends on the channel length.