Uncooled infrared detectors based on MEMS technologies

Abstract

Uncooled infrared (IR) detectors are gaining importance over the HgCdTe based IR photon detectors because of their room temperature operation, low power consumption and smaller in size. Silicon micromachining has made it possible to make micro bolometer base IR detector. In a focal plane array (FPA), there is a two dimensional assembly of bolometers and each bolometer acts as a thermally sensitive pixel. The detector element consists of thermal sensitive material suspended above the readout electronics having an air gap of 2 micron and supported by thermally isolated hinges. The most important task is to design the structure of the sensor having the lowest possible thermal conductance. The characterization gives that thermal conductance and thermal mass are the deciding factors for the higher responsivity and detectivity. This paper presents a modified design based on thermal characterization of the membranes of micro bolometer. Based on our theoretical analysis, the required thermal conductance can be achieved even with short hinges. This can be done by reducing the thermal conductivity of the material of hinges. Our experimental investigations are in good agreement with this concept. This will also enhance the fill factor of the two dimensional IR array.