A low-noise silicon-based 20μm*20μm uncooled thermoelectric infrared detector

Presented is an uncooled surface-micromachined thermoelectric (TE) infrared detector that features P-doped and N-doped polysilicon wires as the thermocouple pair and an umbrella like optical cavity as the absorber to achieve a high fill factor. A responsivity as high as1800V/W @5Hz and a response time of smaller than ~10ms are measured in vacuum when viewing a 500K blackbody with no concentrating optics at room temperature. The reported responsivity is more than 10 times higher than the value reported earlier [1] from similar structures due to the improvement in the thermoelectric coefficient and the thermal isolation of the cell. Finite Element Analysis is used to predict the detector’s performance and the results are in a good agreement with the measurements. The dominant source of noise is also investigated in these thermoelectric IR detectors and it is believed to be Johnson noise when they are operated under an open circuit condition. The fabricated detectors have resistances in the range of 20 to 70KOhm resulting in a Johnson noise of about 20 to 36 nV/Hz^0.5. The specific detectivity (D*) is calculated to be higher than 10^8cmHz^0.5/W. To the best of our knowledge, this is the highest reported D* for such small thermoelectric IR sensors. The measured NETD is 120mK with an f/1.5 lens.