Development of a CMOS-MEMS RF-aerogel-based capacitive humidity sensor

This study presents the design, implementation and characterization of a high-sensitivity capacitive humidity sensor. TSMC 0.18μm CMOS process was used followed by in-house maskless post-processing and pneumatic dispensing of precursors of aerogels to form a vertical parallel-plate (VPP) topology for capacitive sensing. A new kind of sensitive polymer, resorcinol-formaldehyde (RF) organic aerogel, was prepared by the sol-gel method and supercritical fluid (SCF) drying. The low-density RF-aerogels synthesized by this method exhibit high surface areas, high porosities, and mesoporosity, which are beneficial to moisture diffusion and sensing reaction. Despite the sensor response to moisture is non-linear, a minimum sensitivity up to 0.571% capacitance change per percent relative humidity (RH), is achieved. Further measurements show that a response time of 19s, maximum hysteresis of 1.1%RH and a 48-hr signal drift of 0.75%RH have been obtained.