Investigations of the properties of a thermoelectric IR-detector for low working temperature

Abstract

Thermoelectric IR-detectors have been developed and built to work at a temperature of 170 K in the CIRS experiment as part of the CASSINI mission to Saturn. Thermoelectric legs of p and n-type are soldered to a metallized ceramic substrate, isolated one from another. Pyramidal legs are formed by electric discharge machining (EDM). A thin gold foil is welded to the pyramides and blackened for high absorption of radiation. Characterization measurements were carried out to correlate detector properties to the preparation process. Thermoelectric behavior is described by measuring the current-voltage characteristics from liquid nitrogen up to room temperature. Materials of the composition (Bi/sub 0.4/Sb/sub 0.6/)/sub 2/Te/sub 3/ (for p type) and Bi/sub 2/(Te/sub 0.95/Se/sub 0.95/)/sub 3/ (for n-type) have been used for detector preparation. The material was doped to have maximum figure of merit at temperatures below room temperature. It has been found that the EDM process changes the properties of the thermoelectric material and that electro etching can remove degraded layers. Electro etched detectors exhibit properties which are closer to the values expected from the original material.