Gas-sensing properties and sensitivity promoting mechanism of Cu-added SnO2 thin films deposited by ultrasonic spray pyrolysis

Abstract

Tin oxide-based thin films for gas sensors were deposited by the ultrasonic spray pyrolysis technology. The thin films were porous and comprised nano-sized crystallites with fast responses to the H2S gas. The sensor performance was observed to be enhanced by the Cu additive, which was incorporated at the Cu/Sn ratio of 0–1. The influences of Cu-doping amount on the gas-sensing properties were discussed. The values of power law exponent n for each thin film sensor were calculated to discuss the sensitivity of the sensors, which was promoted by the Cu additive. Two mechanisms were found to be responsible for determining the sensitivity of Cu-doped SnO2 thin films. One is the known receptor function of the SnO2 grain, and the other is the promoting mechanism caused by the transformation between CuO and CuS in the H2S detection. The former one produces a temperature-dependent sensitivity, which is ascribed to the various types of adsorbed oxygen on grain surface at different operating temperatures. The latter one results in a promoted sensitivity according to the present evaluation. The contribution of each mechanism to the thin film sensors with various Cu/Sn ratios was discussed.