Freestanding a-Si Thin Film Transistor for Room-Temperature Infrared Detection

We present the fabrication and characterization of a novel uncooled infrared sensor for room-temperature infrared imaging. The sensitive element of the sensor is a freestanding amorphous silicon thin film transistor (a-Si TFT) with the temperature coefficient of the drain current (TCC) of 0.015-0.08/K. The TCC value is sensitive to the ambient temperature and can be controlled by the gate voltage of the a-Si TFT. The complete procedures based on the porous silicon micromachining technique for fabricating thermally isolated air bridges are described. The isolation structures have a thermal conductance of 5 x 10^-6W/K and a thermal capacitance of 4.9 x 10^-8J/K. The effects of the gate voltage on the performance figures such as responsivity, noise voltage and detectivity are described and analysed in details. The maximum detectivity reaches 4.33 x 10^-8cmHz^1/2W^-1 at a chopping frequency of 27 Hz and a gate voltage of -15 V.