Spray-deposited metal-chalcogenide photodiodes for low cost infrared imagers
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.324
Spray-deposited metal-chalcogenide photodiodes for low cost infrared imagers Tommy O. Boykin II,1,2 Nagendra Dhakal,1,2 Javaneh Boroumand,1 F. Javier Gonzalez,1,2 Isaiah O. Oladeji,2 Pedro Figueiredo,2 Stephen Neushul,3 and Robert E. Peale1,2 1
Physics, University of Central Florida, Orlando, FL 32816 USA
2
Truventic LLC, 1209 W. Gore St. Orlando, FL 32805 USA
3
iCRco, Goleta, CA
Abstract
Low-cost, light-weight, low-power, large-format, room-temperature, mid-wave infrared (MWIR) detectors are needed for reduced-scale aircraft. An opportunity, suggested by direct-read X-radiography systems, is the use of thin film transistor (TFT) array as readout integrated circuit (ROIC) for low-cost sensors deposited directly and unpatterned onto this ROIC. TFTs have already been thoroughly optimized for power, weight, largeformat, and cost by the flat-panel-display industry. We present experimental investigation of aqueous-spray-deposited, mid-wave-IR, metal-chalcogenide heterojunction CdS/PbS photodiodes for this application. Measured responsivity, detectivity D*, and photoresponse spectra are reported.
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INTRODUCTION Low cost infrared detector technology is needed in the 1-to-2.7 and 3-to-5 m wavelength bands. These correspond to spectral windows of high atmospheric transmission, usually referred to as short-wave (SWIR) and mid-wave (MWIR) infrared. This need was articulated by the US Air Force in a recent Small Business Innovative Research (SBIR) solicitation [1]. We describe preliminary research performed to support a proposal for that solicitation. Current SWIR and MWIR imaging systems are expensive, power hungry, bulky, and require cryogenic operating temperatures. These factors make them poorly suited for deployment in (e.g.) unmanned aerial vehicles. An inexpensive, compact, ambient-temperature imager would enable new infrared applications. Costs can be reduced and manufacturing throughput increased by depositing a photosensitive film directly and unpatterned on a read-out integrated circuit (ROIC). ROIC pitch should be 10-30 µm to compete with current technology. The ROIC itself should be inexpensive. We consider the conventional thin film transistor (TFT) array as a potential ROIC. TFTs have achieved extraordinary economies of scale and optimization in the flat-panel-display industry. An inspiration for considering TFTs as an IR-detector ROIC is their established use in commercial direct-read X-ray imagers, e.g. [2]. UCF has developed a detailed fabrication process for a suitable TFT under contract from iCRco [3]. This process, comprising just 7 contact photo-masks, was designed for execution in a university wafer fab for the purpose of developing experimental X-ray imager prototypes based on an entirel
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