Margherita Zanini-Fisher

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

Thin, discontinuous Pt/Ti films with different film thicknesses 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°C resulted in a decrease in film resistance, with a trend towards higher response with increasing temperature. Thinner Pt/Ti films (35 A Pt on 65 A Ti) showed larger relative resistance changes than thicker Pt/Ti films (75 A Pt on 65 A Ti). Neither of the films were sensitive to propylene until the temperature exceeded 350°C, coinciding with the onset of catalytic oxidation of propylene. Above 350°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.