The current state and expected future performance of platinum silicide staring infrared focal plane array technology is discussed. The current performance limitations are identified and the improvement in performance that one would expect given the practical limitations of the technology are presented.
A 320 x 244-element IR-CCD imager was developed with 40μm x 40-μm pixels, 43% fill factor, and a saturation signal of 1.4 x 106 electrons/pixel. Charge-transfer inefficiency of less than 10-4 per transfer was achieved for operation of the imager at 77K with horizontal clock frequency of 6.2 MHz using a 12-μm-wide horizontal output register with a 3-μm-wide trench. The device was operated at temperatures as low as 50K with sufficiently low transfer losses to produce good quality video images. Excellent quality thermal imaging was demonstrated for operation of the 320 x 244 imager at 30 frames/s with 100 mm f/1.4 lens, an f/1.3 cold shield, and 3.4-μm long-pass filter at 77K.
This paper will show that large format PtSi Schottky diode infrared arrays are competitive alternatives to the smaller format photovoltaic arrays for ground-based astronomy. The modest quantum efficiency of the PtSi compared to the photo-voltaic devices is more than compensated for by the larger format. The particular array discussed here is the Hughes 256 X 256 hybrid Schottky array. The use of hybrid technology yields effective fill factors of nearly 100%, which further offset the modest quantum efficiency limitations. The very low dark current, low noise, imaging characteristics, cost, and solid nitrogen operating temperature add to the effectiveness of this array for ground-based imaging. In addition to discussing the characteristics of this array, we will present laboratory test data and astronomical results achieved at Kitt Peak.
Test exposures of cooled photovoltaic diode arrays to short (25 nanosecond) bursts of 1-2 mev gamma radiation have produced characteristic signal decay functions dependent on diode material and geometry. A diode transient response model was desired which: (1) would correlate pv diode measured transient decay behavior with diode design parameters, and; (2) would form a basis for design of pv diode arrays which exhibit desired decay behavior. It appeared at the outset of this study that experimentally measured diode decay functions were probably associated with charge carrier transient production and subsequent diffusion into the p-n junctions. Use of a charge carrier thermal diffusion model therefore appeared appropriate, and later was found to produce voltage decay results which agreed well with test data.
An infrared camera system has been developed to be used with a ground-based telescope. The camera system includes reimaging optics with a cold Lyot stop, provision for spectral filtering, and a detector/mux chip mounting assembly. The purpose of the camera is to provide a breadboard facility for the demonstration of advanced focal plane array (FPA) detector technologies in an actual field test environment. The initial demonstration described in this paper is with an impurity band conduction (IBC) extrinsic silicon FPA. The optical system is designed to couple to an f/4.2, 100-inch focal length Newtonian telescope in the 9.5 to 11.5 micron wavelength band. Versatility is offered by adapting to a variety of FPAs packaged in leadless chip carriers, interchangeable optics, and cryogenic dewar configurations. A LN2, LHe dewar was used because of its simplicity and freedom from vibration and EMI. Image generation is accomplished using an oscillating mirror in the optical path external to the dewar. Digitized FPA output is recorded for image reconstruction and analysis. The first application for the camera will be observations of missile plumes of launches from the Eastern Test Range at KSC and Cape Canaveral.
The current METEOSAT Operational Program will continue its service until 1995, possibly till 1997. Subsequently, the METEOSAT Second Generation (MSG) is planned to replace the current system (similar to the " compatible" US "GOES-Next" and the Japanese GMS follow-on generation as major elements of the global geostationary meteorological satellite systems). The payload of MSG is supposed to comprise a Microwave Vertical Sounder and two optical instruments which are described in this paper, i.e.: - a Visible/Infrared Imaging Radiometer (VIRI) - an IR Vertical Sounder (IRS).
The Hole-Accumulation Diode-Sensor (HAD-Sensor) structure, which allows to implement the variable speed electronic shutter in the Interline Transfer (IT) CCD imaging sensor, has been developed. Based on this technology, a 2/3 inch imaging sensor with 420,000 picture elements for consumer, industrial, and professional use was manufactured. The theoretical lower limit of variable shutter speed is about 1/1,000,000 sec. in the case of exposure within the vertical blanking interval (i.e. below 1/787 sec.). This HAD-Sensor achieves the following five major results, which are essential to yield the variable speed electronic shutter in an IT CCD: ( 1 ) complete draining of unwanted stored charges into n-type substrate, ( 2 ) negligibly small lag, ( 3 ) dark current reduced to 1/10 of the conventional level, ( 4 ) smear reduced to 1/5 of the conventional level, and ( 5 ) increased blue sensitivity.
This paper presents some recent research results in cryogenic bipolar technology which potentially can reduce 1/f noise and threshold variation at least an order of magnitude from the current CMOS technology. Silicon junction field effect transistors (JFETs) have been operated down to liquid-helium temperature. This is explained by a phenomenon newly observed in small-geometry JFETs. Silicon bipolar devices have been operated down to 40 K with current gain higher than 500. These device technologies have three application areas: (1) low-noise input circuits; (2) input circuits for low-impedance detectors such as mercury cadmim telluride (HgCdTe) photoconductors; and (3) interface circuits for superconducting devices which normally have low-input impedances. The results presented in this paper show the potential for very low-noise, high-density cryogenic bipolar circuits for on-focal-plane (on-FPA) signal processing.
Architectures for focal-plane image processing using CCD circuits are discussed. The choice of architecture depends on imager density and required throughput. High-density imagers require the reconstruction of local neighborhoods prior to image processing. Lower density imagers can utilize spatial parallelism to improve throughput. The use of three-dimensional structures can provide additional real-estate for processing circuitry.
A perspective plot is an important tool used for the interpretation of raw or processed image data. Unfortunately, most developers must give up resolution of their plotted images in order to obtain results in a timely fashion. Conventional plotting methods are computationally intensive, and as a result often limit the 'size of plotted images to 128 pixels on a side, or less. The technique presented in this paper has been used with favorable results on images as large as 1024 pixels on a side, with processing times of under one second.
The Airborne Stereo Multispectral Scanner (ASMSS) mission and design scenario are described. The obstacles to successful development of the scanner system are detailed. Results of simulation trials to determine errors relevant to system design considerations are provided. Finally, a relatively simple competing design scenario is presented.
Silicon linear image sensor arrays have been designed and fabricated which address a growing need for very high pixel data rates. A dual output 512 element linear array produced by DALSA INC. is described, with test results made by Quad/Tech illustrating operation at a pixel rate up to 60 megapixels per second (MPS) with excellent Modulation Transfer Function (MTF). This pixel data rate (DR) is an effective overall rate which results from two outputs with an output rate (OR) of 30 MHz each. Drive circuitry design for the device is also addressed, given the unusually high drive speed requirements.
This paper discusses the problems of the realistic evaluation of high speed, high performance infrared focal plane arrays. A measurement system has been developed based upon a previously reported flexible, electronic control and correction system. This approach allows focal plane arrays to be tested under operating conditions which are very close to those used in real systems. A number of test modes are available, allowing the operator to focus on particular aspects of the array performance. In addition, particular attention has been given to ensuring that tests can be carried out at realistic operating speeds. Both static and dynamic characteristics may be measured and compared directly with imaging performance. This is especially valuable for some focal plane architectures in which the photovoltaic elements are not directly accessible via external terminals, eg CCD readout. Relatively large numbers of data samples can be acquired from each array and a range of statistical techniques are available to assist in their interpretation. Both spatial and temporal analysis may be applied.
GaAs is a very attractive material for use at the 10.6-μm wavelength of the CO2 laser, and very little work has been done at this wavelength. This paper discusses recent investigations with n/n+-GaAs rib waveguides fabricated by molecular beam epitaxy and reactive ion etching. A simple effective index method of analysis was performed to predict the propagation constants of the bound modes. Comparison with other methods of analysis has shown this method to be fairly accurate for the geometries used. The prism-coupling technique was modified for rib waveguides. Experimental intensity curves as a function of incident angle (Θ) correlated well with the theoretical lower order modes.
SPOT 4 will be an improved version of the SPOT 1,2 and 3 earth remonte sensing satellites ; a SWIR channel is added for agriculture monitoring, and the lifetime is entended to 4 years. The SWIR sensor was designed to be fully compatible with the visible and near IR silicon CCD : - the 3000 30 μm x 30 μm pixels can be registred to the visible detectors with an accuracy better than =/= 2 μm ; - the radiometric performance (uniformity of response, dynamic range, linearity,...) is imilar to that of the visible-channel CCD ; - the operating temperature is + 5°C. The 3000-pixel sensor consists of an ultra-precise assembly of ten elementary modules comprising 300 InGaAs photodiodes and two associated CCD multiplexers on both side. One single pixel is destroyed at the splice between two adjacent modules; The ten modules are read out in sequence. The reading sequence last 3 ms. Quantum efficiency of the photodiodes is typically 65%. Noise equivalent power is 10-13 W. A dynamic range of better than 4000 is obtained at the output of the multiplexer. The histogram of output noise voltages will be presented. A map of the relative sensitivity along the array will be displayed. The cut--off wave-length depends on the In/Ga ratio in the active layer, and the operating temperature. It is 1.690 0.005 μm at +5°C. Several detectors are presently undergoing re liability tests ; no significant alteration in performance has been noticed after aging at 125°C (operating).
An infrared photoconductor, designated as the Periodic Extrinsic InfraRed (PEIR) photoconductor, is proposed. The PEIR photoconductor will be useful for detecting wavelengths from 7 μm (1400 cm-1) to longer than 100 μm (100 cm-1). A PEIR photoconductor is made up of heavily doped layers separated by lightly doped layers. The heavily doped layers are doped such that an impurity band forms but are not doped high enough to cause the impurity band to merge with the conduction or valence band. The lightly doped layers are used to confine the carriers in the impurity bands and consequently, conduction can only occur due to carriers excited to the conduction (n-type device) or valence (p-type device) band. Radiation excites the carriers from the impurity band to the conduction or valence band. The impurity band layers are thin enough that even if the electric field in the impurity band layers is small, there is a high probability the excited carrier will scatter into the lightly doped layer and be swept away by the electric field in the lightly doped layer. In many ways, the PEIR photoconductor is similar to the Blocked Impurity Band (BIB) detector which has one impurity band layer and one blocking layer. The difference is that the Poole-Frenkel effect and tunneling out of the impurity band which limit the operation of a BIB detector appear to be much less serious problems in a PEIR photoconductor. The importance of this result is that a PEIR photoconductor should 1) have higher absorption rates (due to higher impurity band dopant concentrations) compared to a BIB detector designed to detect the same wavelength and 2) have the capability of detecting longer wavelengths with increasingly better quantum efficiencies than a BIB detector.
A novel infrared detection system is presented. A responsivity of 35 fringes per Watt and a time constant of approximately 220 milliseconds were measured at room temperature for a fiber optic interferometric thermal detector (ITD). These mea-surements compare well with predictions based on a thermal model of the sensor. Except for microphonics, the device was noiseless to the limit of measurement; a room temperature D* of about 7X108 centimeter - root Hertz per Watt is predicted by the model. Finally, the performance of alternate ITD designs is discussed.
The AuCriSiO2/InSb Metal-Oxide-Semiconductor capacitor was fabricated using photo-enhanced chemical vapor deposition. The electrical and structural properties were analyzed by capacitance-voltage and Auger electron spectroscopy , respectively. The high frequency (1 MHz) capacitance-voltage measurements were usually performed after positive or negative bias-temperature stressing. Both the flat-band voltage shift and the change of hysteresis of capacitance-voltage curve indicate the existence of enormous negative mobile charges in the bulk SiO2. Auger depth profile reveals that these negative mobile charges are metallic indium and antimony ions.
Linear arrays of 256 element indium gallium arsenide (InGaAs) detectors with 100 X 30 um pixels were mounted in multiplexer packages and tested in an optical multichannel analyser (OMA). Typical performance characteristics include dark current (-5V) of 400 picoamps and responsivities of 0.75 A/W (1.3 um) and 0.14 A/W (0.85 um). The 256 element exhibited a mean room-temperature dark current of under 400 picoamps when mounted in the OMA and a dynamic range over 11 bits (2000:1). Future applications, including room-temperature detector arrays for 2.5 um and avalanche photodiode arrays for 1.0-1.7 um, are discussed.
A focal-plane-array chip designed for real-time, general-purpose, image preprocessing is reported. A 48 X 48 pixel detector array and a 24 X 24 processing element processor array are monolithically integrated on the chip. The analog, charge-coupled device-based VLSI chip operates in the charge domain and has sensing, storing, and computing capabilities. It captures the image data and performs local neighborhood operations. It is digitally programmable and uses a single instruction, multiple data parallel architecture. Various image preprocessing tasks such as level shifting, gain adjustment, thresholding, smoothing, sharpening, and edge detection can be implemented. Frame-to-frame operations such as motion detection and tracking can be implemented as well. It can be programmed to perform A/D conversion prior to output. The chip was fabricated with a double-poly, double-metal process in a commercial CCD foundry. The prediction of the performance is based on numerical analysis and experimental results of testing a prototype charge-coupled computer. Operating at a modest clock frequency of 25 MHz, the chip is projected to achieve an internal throughput as high as 576 Mops with a 54 dB dynamic range (9-bit equivalent accuracy). The total power dissipation is estimated to be 20 mW. The total size of the 59-pad chip is 9.4 X 9.4 mm2.
This paper is concerned with testing and characterizing superconducting thin films as infrared detectors. A laboratory test facility has been designed, assembled, and checked out at the Infrared Laboratory of the Optical Sciences Center, University of Arizona. Several superconducting thin films have been installed in the test facility and subjected to preliminary testing. None of these films were specifically designed to be infrared detectors and there was no reason to expect high performance from them. The tests, however, served to confirm the ability of the test setup to obtain accurate, repeatable, reliable detector-performance data.
The finite difference method has been used to solve the one dimensional carrier transport equation in order to study the surface recombination velocity s in (Hg,Cd)Te. This numerical approach was applied to the analysis of typical (Hg,Cd)Te configurations and was implemented in the reduction of photoconductive lifetime data to experimentally determine s in (Hg,Cd)Te. Contour maps of effective minority carrier lifetime and surface recombination velocity were used to study the spatial distribution and relationship between bulk and surface recombination. Experimentally, the PC lifetime and surface recombination velocity have been mapped on bromine-methanol polished surfaces and on anodic oxide passivated surfaces for (Hg,Cd)Te produced both by the solid state recrystallization (SSR) and the traveling heater methods (THM). The anodic oxide passivation has been observed to alter the magnitude and distribution of the PC lifetime measured, and it reduced the surface recombination velocity.
In this paper, we've studied the distribution of excess carrier in SPRITE device by solving the ambipolar continuity equation. Therefore, we've analysed boundary recombination effect and sweep-out effect on the lifetime of excess carrier in a device and the effect of applied field on the distribution, lifetime and Dλ* value.The results show the effect of boundary recombination on lifetime has to be less than body lifetime of material. The sanning velocity, body lifetime and applied field relate to each other. Only after synthesizing all kinds of specific needs, we can chose their values.
In this paper, we've studied the effects of exciton absorption and the Burstain-Moss shift on the absorption above the energy gap of n-type direct semiconductors and derived a more common expression of absorption. In addition, we've discussed the reasons why the absorption peaks of exciton in HgCdTe haven't been observed in experiments. We also have calculated the absorption coefficient of the free carrier in n-type HgCdTe samples by assuming the four processes of electron transition in the conduction band are independent to each other.
The electronic mobility is an important parameter to express HgCdTe characters. The performance of photoconductive detectors, photovoltaic detectors and sprite detectors are all concerned with it. In our work, besides ionized impurity scattering, polar-optical scattering, acoustic deformation potential scattering and piezoelectric scattering, we also consider the dislocation scattering and give the result in accord with experiment. It shows that dislocation scattering is one of the important factors to influence HgCdTe electronic mobility. In our work, we also give a kind of amendment formula of ionized density. In addition, we also discuss the relationships between mobility and temperature and dislocation density. The result shows that, in the region 40K and 100K, the influence of dislocation is important and can not be neglected.
In application, the HgCdTe photovoltaic arrays exist crosstalk. There are many factors to cause it, and the surface channel is one of them. Because there are electric charges on the surface of HgCdTe photovoltaic device, they can form the surface channel between arrays. We calculate the crosstalk caused by diffusion of carrier through the surface channel under applied voltage. Using the LMC crosstalk instrument, we have measured the crosstalk. The calculative values conform to the result of experiment well. It shows that the surface channel is one of the important factors to effect the crosstalk of HgCdTe photovoltaic arrays. The thicker channel of the surface, the greater crosstalk of the arrays. The crosstalk decreases following with increasing of majority concentration.