High frequency thermal-piezoresistive MEMS resonators for detection of organic gases

This paper reports on high frequency micromechanical resonant silicon microbalances capable of detection and concentration measurement of volatile organic compounds in gas phase. In this work, regular gasoline has been used as the source of organic compounds in gas phase and 1813 photoresist has been used as the absorbent coating on the resonator surfaces. A new technique for formation of thicker polymer coatings on resonator surfaces has been utilized allowing frequency shifts as high as 2200ppm to be achieved for the resonators upon exposure to gasoline vapor. This is equivalent to an effective thickness of ~40nm for the absorbed organic compounds. Measured response time constants are around 40 seconds. Faster and more sensitive responses are expected to be achievable by maximization of the absorbing surface area using porous resonator structure coatings.