Capacitive-type chemical sensors using thin silicon/polymer bimorph membranes

Capacitive-type chemical sensing devices based on a silicon/polymer bimorph structure have been fabricated and evaluated. 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), epoxydized novolac (EPN) and poly-dimethylsiloxane (PDMS)] were used. Exposure to water, methanol and ethanol vapors was used for evaluating performance. Sensitivities ranging from 4.5 fF/%RH for PDMS to 29 fF/%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. (C) 2004 Elsevier B.V. All rights reserved.