Fully integrated System-On Chip gas sensor in CMOS technology

Abstract

Within this work the development of an integrated gas sensor as System-On Chip (SOC) in a 0.35μm standard CMOS process plus CMOS compatible SnO2-deposition and Si-release steps is presented. The SnO2 layer provides high gas sensitivity to 10ppm for CO in humid air. An optimized Micro-Hotplate (μHP) consisting of a fully released membrane with a poly-Si heater in the oxide stack is designed. Due to the small area of AμHP=100×100μm2 and the switched capacitor temperature controller, low power consumption Pel=24mW at high temperatures T=400°C and short rise time of inie=11.8ms are achieved. The differential setup contains sense and dummy sensors in order to compensate drift and tolerances. The readout stage consists of a gain adjustable amplifier with digital offset compensation and shows a relative error e<;±1%. The complete multichannel chip carries six sensors at a size Achip=3.4×2.4mm2, a power consumption Pchip=180mW and is well suited for various low power gas sensing applications.