Response study of electron-beam evaporated thin-film tin oxide gas sensors

Abstract

Thin-film SnO 2 gas sensors are fabricated using an electron-beam evaporation method at pre-optimized substrate temperatures and post-deposition heat-treatment temperature. The response of these sensors is studied for various operating temperatures and reducing gas ambients. Reducing gases used for testing the response are hydrogen, carbon monoxide and methane, as they belong to three distinct chemical families. It is observed that the response of these sensors follows a power-law relationship, with the exponent value always remaining less than one at higher concentrations of reducing gas. Films deposited at 25 and 350 °C and heat treated at 650 °C in O 2 ambient for 2 h are found to be more suitable for sensor application compared to films deposited at intermediate temperatures and heat treated under identical conditions. Further, the response of the sensor is found to deteriorate with a decrease in operating temperature. It is also concluded from the results that a thin-film SnO 2 sensor can be used as a selective sensor for H 2 at either low operating temperature or under very low background concentrations of other reducing gases. Finally, the above-mentioned results are explained using existing physical models.