SiGe/Si quantum structures as a thermistor material for low cost IR microbolometer focal plane arrays

Abstract

Uncooled microbolometer thermal infrared detector technology is presently revolutionizing the infrared technology field. Essential improvement of the cost/performance ratio would be achieved by microbolometer arrays with higher sensitivity, since this allows the use of simpler and less costly camera optics, which implies a lower cost of the complete IR camera. The sensitivity of the microbolometers depends critically on the signal-to-noise ratio of the integrated thermistor material, which is set by its temperature coefficient of resistance (TCR) and noise characteristics. In this work we have investigated the use of epitaxial silicon–germanium/silicon (SiGe/Si) quantum well (QW) structures as a thermistor material. Si 0.68Ge 0.32/Si QW structures typically give a TCR of 3.0%/K and low noise values. A calculation of the noise equivalent temperature NETD of a bolometer gives 25 mK using the following assumptions: f-number = 1, 30 Hz video frame rate for a 640 × 480 array, with a pixel size 25 × 25 μm. Higher TCR values are foreseen for SiGe/Si quantum dot structures, and the noise is expected to be similar to the QW based structures.