開發間苯二酚─甲醛氣凝膠之CMOS-MEMS電容式溼度感測器

Abstract

Currently, state-of-the art humidity sensors that have been used in mobile applications are mostly capacitive-based sensors integrated with electronics monolithically and fabricated with the industrial standard CMOS process to achieve a cost-effective solution for accuracy, performance and reliability. As for the moisture sensitive films, polymer-based and especially polyimide-based sensors have been used predominantly inasmuch as the superior properties over wide humidity range and the compatibility with CMOS platforms. However, based on a great deal of on-going researches, polyimide features slow diffusion constant and have long-term stability problems. As a result, RF-Aerogel, shown great potential in humidity sensing and capability to integrate with CMOS platforms, was adopted herein. This study presents the design, implementation and characterization of a high-sensitivity capacitive humidity sensor. TSMC 0.18 m 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 sensitive material, 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 12s and maximum hysteresis of 1.1%RH have been obtained. In addition, a resistive type temperature sensor had been integrated with humidity sensor on the same chip. Furthermore, this study proposed a method to calibrate the temperature-dependent readout of a humidity sensor by means of an on-chip temperature sensor. For further investigation, a new kind of sensor topology – VPP array is proposed. In the design, VPP ensures sensors’ sensitivity; meanwhile, RF-aerogels are patterned by plasma etching in column shapes so as to shorten the diffusion path of water vapors and thus reduced response time of the sensor. The aim of this study is to design a high-sensitivity and high-speed humidity sensor.