Characteristics of silicon-micromachined gas sensors based on Pt/TiOx thin films

Thin, discontinuous Pt/Ti films with different film thick:nesses on microfabricated conductometric sensors were exposed to ppm levels of hydrogen or propylene at elevated temperatures in the presence of excess oxygen. Exposure to hydrogen at temperatures between 100 and 400 degrees C resulted in a decrease in film resistance, with a trend towards higher response with increasing temperature. Thinner Pt/Ti films (35 Angstrom Pt on 65 Angstrom Ti) showed larger relative resistance changes than thicker Pt/Ti films (75 Angstrom Pt on 65 Angstrom Ti). Neither of the films were sensitive to propylene until the temperature exceeded 350 degrees C, coinciding with the onset of catalytic oxidation of propylene. Above 350 degrees C, the film resistance decreased with increasing propylene concentration. Thus, operating the films in different temperature regimes permits differentiation between hydrogen and propylene. Reversible sensor response can be accomplished in the presence of excess gas phase oxygen. (C) 1997 Elsevier Science S.A.