An ultrasensitive uncooled heat-balancing infrared detector

In this paper we report the fabrication and initial testing of a highly sensitive uncooled infrared detector based on an active heat balancing technique. The detector is fabricated using a commercial CMOS process plus an electrochemical etch releasing step. The basic active 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. Initial 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*=10/sup 7/ cm /spl radic/(Hz)W/sup -1/ at 30 Hz. The observed device responsivity is one order of magnitude higher than that reported for passive uncooled VO/sub 2/ microbolometers.