Comprehensive temperature modeling of strained epitaxial silicon-germanium alloy thermistors

Thermistor materials utilizing single-crystalline silicon-germanium alloys, embedded in lowly doped silicon are very suitable for bolometer applications since the inherent noise level is low and exhibits a normal 1/f spectrum. A thermal coefficient of resistance (TCR) value of at least 2%/K can be obtained at room temperature and the performance is directly comparable with nonsemiconductor materials such as vanadium-oxide, in wide use today. Bolometers, fabricated in silicon IC processes typically feature about 0.5 % TCR. Since SiGe layers can be integrated in standard process flows that approach becomes very attractive. There is a straightforward trade-off between the maximum feasible germanium concentration in the epitaxial layers and degradation of the noise properties [1]. The noise level can vary orders of magnitude for similar layer structures and some caution is recommended in the case of high germanium concentrations.