Fully quantitative characterization of CMOS–MEMS polysilicon/titanium thermopile infrared sensors

Abstract

This study demonstrates a fully quantitative characterization of a highly sensitive CMOS–MEMS polysilicon/titanium thermopile infrared sensor by using the simulations of non-sequential ray tracing and solid conduction, and the measurements of voltage response and frequency response in atmosphere and in vacuum. The thermal time constants of 17.0 ms in air and 37.0 ms in vacuum for the polysilicon/titanium thermopile with a gold-black absorber were estimated by the measurements of frequency response. The solid conductance, gas conductance, radiation loss, and heat capacitance of the thermopile were characterized as 112 μW/K, 141 μW/K, 5.88 μW/K, and 4.40 μJ/K in atmosphere by the simulation of solid conduction using ANSYS and the measurements of frequency response. The voltage responsivity, sensor noise, noise equivalent power, and specific detectivity of the gold-black coated thermopile in air were estimated as 63.1 V/W, 27.0 nV/Hz 1/2, 0.43 nW/Hz 1/2, and 1.87 × 10 8 cm Hz 1/2/W by the simulation of received optical power using LightTools ray tracing software and the measurements of voltage response. It shows that the sensor has the highest specific detectivity compared to the published CMOS–MEMS thermopiles in atmosphere due to the design of low solid conductance and high emissivity. Eventually, the Seebeck coefficient of the polysilicon/titanium pair was first evaluated and has a magnitude of 170.2 μV/K.