Fully integrated System-On Chip gas sensor in CMOS technology

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 A_μHP=100×100μm² and the switched capacitor temperature controller, low power consumption P_el=24mW at high temperatures T=400°C and short rise time of i_nîe=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 A_chip=3.4×2.4mm², a power consumption P_chip=180mW and is well suited for various low power gas sensing applications.