A CMOS humidity sensor with on-chip calibration

Abstract

This paper describes a capacitive humidity sensor with on-chip calibration circuit fabricated by a standard CMOS process to achieve a cost-effective solution for accurate and reliable humidity measurement. The humidity sensing property on-chip is obtained by a post-processing step after the standard CMOS fabrication and whereby a commercial polyimide is deposited on the packaged chip. The sensing principle of the sensor is the dielectric constant change of deposited polyimide due to absorption/desorption of water. The on-chip calibration circuit is based on a switched-capacitor front-end, featuring high linearity, insensitivity to temperature, as well as low power consumption. The measured results show that the offset and the sensitivity of the sensor can be precisely calibrated by the integrated circuit which also provides a readable output. The sensor has a linear function with relative humidity in the range of 10–90% RH and a negligible hysteresis.