A multiplexed silicon infrared thermal imager

The design, fabrication, and testing of a multiplexed infrared thermal imager based on silicon thermopiles is presented. The imager consists of 32 individual thermopile detectors arranged in two linear arrays of 16 elements each. The thermopiles are formed using n/sup +/ polysilicon-gold thermocouples and are supported on 1 mu m-thick dielectric diaphragms of LPCVD (low-pressure chemical vapor deposited) silicon dioxide and silicon nitride. They provide a responsivity of 64 V/W, a noise voltage of less than approximately 50 nV/ square root Hz at 20 Hz, and a specific detectivity of 7*10/sup 7/ cm square root Hz/W. The detector outputs are fed to off-chip amplifiers using on-chip ED-NMOS analog multiplexers. The entire imager is 5.5*11 mm/sup 2/ and requires seven masks for fabrication. The imager has been used for the thermal imaging of silicon wafers during processing and for the accurate measurement of dielectric thicknesses using infrared absorption techniques.<>