Study of a Voltage-Mode Readout Configuration for Micromachined CMOS Transistors for Uncooled IR Sensing

Micromachined CMOS transistors, dubbed as “TMOS”, have been developed in recent years as a novel type of uncooled thermal sensors. The TMOS consists of a thermally isolated suspended transistor, fabricated in a 130-nm process and released by dry etching, which absorbs thermal radiation, inducing an increase of the transistor temperature and, therefore, generating a signal by changing the transistor I-V characteristics. With respect to conventional thermal sensors, as the TMOS is an active sensing element, it features advantages in terms of internal gain, resulting in high temperature sensitivity, which makes the TMOS particularly appealing. The TMOS sensing performance depends on the transistor operating region and on its configuration. In this paper, different configurations are investigated by means of Cadence simulations, in order to identify the voltage-mode readout configuration which maximizes the sensor performance. Voltage-mode, and not current-mode, readout is considered in order to be able to directly compare the TMOS performance with the one of an integrated micromachined thermopile sensor, which, given its characteristics, only supports voltage-mode readout.