A monolithic thermopile detector fabricated using integrated circuit technology

A thermopile infrared detector fabricated using silicon integrated-circuit technology has been investigated. The device uses a series-connected array of thermocouples whose hot junctions are supported on a thin silicon membrane formed using anisotropic chemical etching and a diffused boron etch-stop. The membrane size and thickness control the speed and responsivity of the structure, which can be designed for a given application. For a membrane measuring 400 cu microns and containing sixty bismuth-antimony couples, the structure produces a responsivity of 6 volts/watt and a time constant of about 15 msec. This responsivity is comparable to that of commercial thermopile detectors of similar die size, while the speed is faster by a factor of about four. Using sixty polysilicon-gold thermocouples on the same size diaphragm, the responsivity is increased to 7 volts/watt for p-polysilicon and to about volts/watt for n-polysilicon without any appreciable change in the time constant of the detector.