Characterization of polymer layers for silicon micromachined bilayer chemical sensors using white light interferometry

The swelling behavior of polymer layers used in silicon micromachined bilayer structures is studied using white light interferometry. The study focuses on poly-hydroxy-ethyl-methacrylate (PHEMA) films and their behavior in terms of film expansion, response time and sensitivity upon exposure to methanol and ethanol vapors. Thin films of PHEMA exhibit higher relative swelling than thicker films, in the presence of methanol, as well as lower diffusion coefficients corresponding to higher response times.