Stacked Temperature and Humidity SOC with Enhanced Sensitivity and low Hysteresis via CMOS-MEMS Integration

This paper presents a stacked temperature and humidity sensing System-on-Chip (SoC) fabricated using a CMOS-MEMS monolithic integration process. The humidity sensor adopts interdigitated electrodes with a plasma-treated polyimide (PI) coating to significantly enhance the hygroscopicity and sensitivity. Integrated with an on-chip differential switched-capacitor readout circuit, the humidity sensor achieves a high sensitivity of 82.8 m V /%RH above 80 %RH and an average sensitivity of 39.2 mV/%RH across the 5–95 %RH range, with low hysteresis (max. 2.85 %RH). Additionally, the temperature sensor exhibits a linear sensitivity of 42.7 m V /oC over 0-60°C. These results position the proposed SoC as a compact, high-performance sensing node for environmental monitoring, with the potential for improved response time following MEMS release.