Controlled selectivity of polysiloxane coatings - their use in capacitance sensors

Capacitance sensors were prepared by spin-on coating interdigital thin-film structures with chemically modified polymers. The sensors were characterized electrically by their frequency response behaviour and spectroscopically by Fourier transform infrared spectroscopy (FTIR). The electrical response of the structures was monitored by impedance spectroscopy at different frequencies, temperatures and partial pressures of organic aliphatic and aromatic compounds in air. At an optimum frequency and temperautre, the capacitance part in the sensor response was then used for systematic sensor tests. The results are explained by a solution of organic gases in the polymer. Implications are discussed to tailor the polymer coatings for specific selectivities.