Design and fabrication of state of the art uncooled thermopile infrared detectors with cavity coupled absorption

Abstract

We present the design, fabrication, and characterization of uncooled thermopile infrared detectors with cavity coupled absorption in the long wave infrared with performance exceeding all published works. These detectors consist of a two die optical cavity which enhances absorption in the desired spectral range while rejecting unwanted noise off resonance. The electrical transduction mechanism is a thermopile consisting of four thermoelectric junctions of co-sputtered Bi₂Te₃ and Sb<sub>2<\sub>Te<sub>3<\sub> having a room temperature unitless thermoelectric figure of merit of .43. Processing steps are described in detail for the fabrication of extremely thermally isolated structures necessary for highly sensitive detectors. Optical characterization of the devices reveals a responsivity of 4700 V/W, thermal time constant of 58 ms, and specific detectivity of at least 3.0x10<super>9<\super> cmHz<super>1/2</super>/W. Also presented are a theoretical proposal for a midwave infrared detector using semiconductor selective absorption to enhance detectivity beyond the blackbody radiation limit and a new method for the analysis of radiation thermal conduction in highly thermally isolated structures.