Performance Analysis of a Thermionic Thermal Detector at 400K, 300K, and 200K
AIR FORCE RESEARCH LAB HANSCOM AFB MA
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The Thermionic Thermal Detector TTD is a silicon Schottky diode LWIR infrared sensing element whose operation is not related to classic photoemissive Schottky diode photon detectors. The TTD operates with the individual elements thermally isolated as in a microbolometer, and uses a reverse bias Schottky diode as the thermal sensing element. The Schottky diode is thermally modulated and the reverse bias current is measured. For a fixed bias voltage and Schottky barrier height, the magnitude of the reverse bias current from the diode is a measure of the diode temperature. Experimental Schottky barrier heights were determined using Richardson activation energy plots. The reverse bias current in a Schottky diode is exponentially dependent on the temperature of the detector, it has a high temperature coefficient 6K, at room temperature. The operating temperature of the detector is designed into the device by selecting a metal with the appropriate Schottky barrier height. An array of silicon based Schottky diodes is highly uniform, has no 1f noise, provides a high impedance source to the multiplexer, and is 100 silicon processing compatible. This paper describes the theoretical performance of an LWIR sensor based on a state of the art microbolometer multiplexer, using the TTD as the sensing element. The analysis models the detector using the appropriate optical radiation, thermal diffusion, and electrical conduction equations for 400K, 300K, and 200K operation using three different metal silicides.
- Miscellaneous Detection and Detectors