CMOS Uncooled Heat-Balancing Infrared Imager

In this paper we report the fabrication, design and testing of an uncooled 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 responsivites between 0.3-1.2 V/W when the infrared source is chopped at 20 Hz and a detectivity "! at 30 Hz. Noise measurements suggest that a of # $ % "! is achievable in this design.