A CMOS uncooled heat-balancing infrared imager

Abstract

In this paper, we report the fabrication, design, and testing of an uncooled 8/spl times/8 infrared imager based on an active pixel heat balancing technique. The imager is fabricated using a commercial CMOS process plus a simple electrochemical etch stop releasing step. The basic active pixel detector structure consists of a simple cascode CMOS amplifier in which the PMOS devices are built inside a thermally isolated floating n-well. The intrinsic coupling of the cascode currents with the self-heating of the well forms an electrothermal feedback loop that tends to maintain the well temperature constant, By employing the heat balance between incoming infrared radiation and the PMOS device power dissipation, the responsivity of the detector is controlled by the cascode biasing current. Measurements show responsivities between 0.3-1.2/spl times/10/sup 6/ V/W when the infrared source is chopped at 20 Hz and a detectivity D*=3/spl times/10/sup 7/ cm/spl radic/(Hz)W/sup -1/ at 30 Hz. Noise measurements suggest that a D* of 10/sup 8/ cm/spl radic/(Hz)W/sup -1/ is achievable in this design.