Fast response H2S gas sensing characteristics with ultra-thin CuO islands on sputtered SnO2

Response characteristics of undoped SnO2 are compared with two different types of Cu–SnO2 thin film bilayer structures: (a) SnO2 surface covered by an ultra-thin (∼10 nm) Cu layer, and (b) SnO2 surface covered with thin Cu dots, and the bilayers were annealed in air/O2 to form CuO. Response speed for sensing H2S gas concentration in the range 20–1200 ppm was measured using platinum (Pt) inter-digital electrodes underneath the SnO2 film. SnO2 film with CuO dotted islands is found to exhibit a high sensitivity of 7.4×103 at 150 °C, and a fast response time of 15 s to 20 ppm of H2S, and the recovery time is approximately 118 s. The high sensitivity and the fast response are shown to be primarily due to a dominant role played by the spill-over mechanism.