Effects of Thin-Film Thickness on Sensing Properties of SnO2-Based Gas Sensors for the Detection of H2S Gas at ppm Levels

SnO 2 thin-film gas sensors were easily created using the ion sputtering technique. The as-deposited SnO 2 thin films consist of a tetragonal SnO 2 phase and densely packed nanosized grains with diameters of approximately 20−80 nm, which are separated by microcracks. The as-deposited SnO 2 thin film is well crystallized, with a dense columnar nanostructure grown directly onto the alumina material and the Pt electrodes. The grain size and thickness of SnO 2 thin films are easily controlled by varying the sputtering time of the ion coater. The responses of the SnO 2 thin-film sensors decrease as the SnO 2 film thickness is increased, indicating that a negative association exists between the sensor response and the SnO 2 film thickness due to gas diffusion from the surface. The SnO 2 thin-film sensor, which was created by ion sputtering for 10 min, shows an excellent sensor response (R a /R g where Ra is the electric resistance under air and R g is the electric resistance under the test gas) for detecting 1 ppm H 2 S at 350°C.