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This program was directed at fabricating infrared focal planes consisting of Schottky-barrier detectors multiplexed by charge-coupled shift registers, and demonstrating their imaging capability against 300K background radiation. Three devices were designed and fabricated: a 64-bit, three-phase line-array with transfer gaps, a 62-bit line array, and a 25x50 area array, the latter two with four-phase, sealed-channel, overlapping-gate, double-polysilicon structure. The detectors were palladium silicide and platinum silicide on p- silicon. Fabrication involved only standard silicon-processing operations. Excellent agreement has been obtained between calculated infrared performance and experimental data. Detector uniformity better than 1%, already achieved with palladium silicide, is adequate for staring-mode thermal imagers. These sensors make possible imagers with thermal resolution on the order of tenths of a degree C, and production costs less than present scanned systems., Sponsored in part by DARPA.

A program is under way to fabricate infrared-sensitive, charge- coupled imagers with Schottky-barrier detectors. The previous work has been with three-phase, single metallization line arrays using palladium-silicide, Schottky-barrier detectors. The present effort is directed at fabrication of a 25 x 50 area array. The design of the 25 x 50 area array is nearly complete, and masks will soon be ordered. Arrays of this design will be made with both Pd2Si and PtSi Schottky barriers. There will be optional masks for guard rings and for buried-channel operation. Processing has begun on a batch of wafers with Pt. Optical absorption measurements revealed a possible problem in the processing procedure, and an appropriate change was made. Infrared calculations were made demonstrating that thermal imaging with PtSi is possible, but that excess dark current at the detectors must be avoided., See also report dated 14 Nov 1975, ADA025224.

The ultimate goal of this work is the fabrication of a two- dimensional infrared imager. The authors previous work with the 64 x 1 line array has proven the feasibility of the Schottky-barrier detector silicon/CCD system, and has, in the vidicon mode, demonstrated a uniformity approaching that needed for thermal imaging. In the present work, the two-dimensional imager is being designed and fabricated. The first arrays will again have palladium- silicide on p-silicon as the detector system, but subsequent arrays will be made with platinum-silicide for deeper IR response. A line array is also included on the chip to provide additional features. The considerations that have gone into the design are discussed below. Quantitative infrared measurements have already begun and have yielded good agreement with previous measurements on the absolute quantum efficiency of PdSi:p-Si detectors., See also report dated 15 May 1975, ADA018057.

A charge-coupled imager sensitive to infrared light up to 3 micrometers has been fabricated and operated. It consists of a linear array of 64 Pd:p-Si Schottky-barrier detectors adjacent to a three-phase charge-coupled shift register. The design has a single level of metallization with gaps. A single transmission gate, when pulsed on, coupled each detector to its associated shift register gate, thereby setting each barrier to a reverse bias determined by the potential applied to the transmission gate. Incident infrared light discharges the individual detectors during the detector exposure time. The charges transferred into the CCD shift register the next time the transmission gate is pulsed are transferred out sequentially by the charge- coupled shift register to produce the video signal. Visible images were sensed directly by illumination of the shift register through the gaps as well as through the unthinned substrate. Infrared images were sensed by the Schottky- barrier detectors illuminated through the (transparent) substrate., See also AD780546.

Cold cathode emission was obtained from forward biased silicon p-n junctions whose p-surfaces were activated to a state of negative electron affinity. In operation, electrons injected into the p-layer diffuse to the surface where they are emitted into vacuum. A Si:SiO2 structure has been developed to overcome the problems associated with current crowding, and, with this structure, efficiencies (ratio of emitted current to bias current) as high as 10% have been observed. Emitted current densities as large as 225 amps/sq cm and currents as large as 7 mA have been drawn under pulsed conditions while continuous current densities of 1 amp/sq cm and currents of tens of microamperes have been drawn for many hours. The electrical characteristics exhibited space-charge-limited and emission-limited regimes as well as Schottky effect. Calculations made of the current density profiles across the junctions indicate that practical levels of operation can be achieved with reasonably uniform emitted current profiles. The silicon cold cathode may have advantages in applications such as vidicons where some aspects of performance are presently limited by the thermionic cathode. (Author)

Silicon cold cathodes were successfully operated for the first time. Planar structures were operated at efficiencies as high as 0.0005 while Si:Si02 structures had efficiencies as high as 0.3%. Pulsed currents as large as 0.6 mA were drawn, corresponding to current densities in excess of 100 mA/sq cm. The silicon cold cathodes were also operated continuously, and it was found that tens of microamperes could be drawn for several hours, and encouraging result from the viewpoint of practical devices. The procedure for fabricating and testing Si:Si02 cold cathodes is discussed, and methods are proposed for achieving more efficient operation. (Author)