Fabrication of chemical sensors based on Si/polymer bimorphs

Abstract

The fabrication and first results of a capacitive type chemical sensor based on a silicon/polymer bimorph structure are described. Upon exposure to analytes the polymer covering the thin silicon membrane swells inducing a deflection on the membrane which is measured as a capacitance change between membrane and substrate. Five different polymer layers [poly-hydroxy-ethyl-methacrylate (PHEMA), poly-methyl-methacrylate (PMMA), poly-vinyl-acetate (PVAc), epoxy-novolac (EPN) and poly-dimethylsiloxane (PDMS)] are examined. Exposure to water, methanol and ethanol vapors is used to evaluate performance. Sensitivities ranging from 4.5fF/%RH for PDMS up to 29fF/%RH for PHEMA covered devices are reported. Devices covered with PHEMA, PVAc and PMMA also exhibit strong response upon exposure to methanol and ethanol atmospheres. Differences in sensitivities between these layers may be exploited in constructing an effective chemical discriminating array.