Detection of ethanol and methanol vapors using polymer-coated piezoresistive Si bridge

A novel alcohol vapor sensor based on the swelling effect of polymer film is proposed for detection of alcohol such as methanol and ethanol vapor, which is composed of a Si bridge embedded with piezoresistive Wheatstone bridge and an epoxy acrylate thin polymer layer-coated Si bridge. When the polymer layer absorbs alcohol vapor molecules from ambient air, the swelling of the thin polymer layer leads to bending of the Si bridge which causes the piezoresistive Wheatstone bridge to produce an output voltage. A theoretical model of the interaction between Si bridge and polymer layer is presented based on elastic mechanics theory. An equivalent transverse gas load is presented. The output expression of sensor is obtained. The model of the sensor is verified by the experimental results. The experimental results show that the alcohol vapor sensor has good linearity, selectivity and reproducibility. The proposed alcohol vapor sensor has simply principle, mature technology, low cost, and can be integrated with signal processing circuit using the MEMS processes.