A surface acoustic wave H2S gas sensor employing nanocrystalline SnO2 thin film

A surface acoustic wave (SAW) H2S gas sensor with high sensitivity and good recovery characteristics was presented. SnO2 films with an average grain size of 25 nm were deposited as the sensitive film at the surface of the SAW devices using an aqueous sol–gel technique. The sensitivity toward H2S gas was increased by optimizing parameters including film thickness and operating temperature. The maximal response (center frequency change) toward 68.5 ppm of H2S was 112.232 kHz when the sensor was operated at 120 °C with SnO2 film thickness of 275 nm. The frequency response of the SAW sensor showed good selectivity and a linear relation to H2S gas with different concentrations. We demonstrated that the dominant sensing mechanism of this SAW sensor is the acoustoelectric effect arising from the electrical conductivity change of the SnO2 film. Further analysis of the optimum parameters and the good recovery characteristics were conducted based on the acoustoelectric effect.