An Uncooled Infrared Microbolometer Array for Low-Cost Applications

Abstract

This letter describes the implementation of a low-cost 32 × 32 uncooled infrared microbolometer array using a standard 0.5-μm CMOS process and a surface sacrificial layer technique, in which the CMOS metal interconnection layers are used as the infrared sensitive material. The sacrificial layer embedded during the CMOS fabrication can be etched using a simple wet etching process following the CMOS processes, without the need for any lithography or material deposition steps. The CMOS metal interconnect layers are aluminum, with a temperature coefficient of resistance of 0.398%/K. The 32 × 32 focal plane array (FPA) has a pixel size of 65 μm × 65 μm and a fill factor of 29%. The thermal conductance of the FPA was measured to be 3.47 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> W/K, with a thermal time of 3.85 ms, and a dc responsivity of 1050 V/W at a 10-Hz chopper frequency. The total measured rms noise of the microbolometer is 0.706 μV for a 10-kHz bandwidth, resulting in a detectivity of 5.2 × 108 cmHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W.