Influence of Cs doping in spray deposited SnO2 thin films for LPG sensors

Detection of low concentrations of petroleum gas was achieved using transparent conducting SnO₂ thin films doped with 0–4 wt.% caesium (Cs), deposited by spray pyrolysis technique. The electrical resistance change of the films was evaluated in the presence of LPG upon doping with different concentrations of Cs at different working temperatures in the range 250–400 °C. The investigations showed that the tin oxide thin film doped with 2% Cs with a mean grain size of 18 nm at a deposition temperature of 325 °C showed the maximum sensor response (93.4%). At a deposition temperature of 285 °C, the film doped with 3% Cs with a mean grain size of 20 nm showed a high response of 90.0% consistently. The structural properties of Cs-doped SnO₂ were studied by means of X-ray diffraction (XRD); the preferential orientation of the thin films was found to be along the (3 0 1) directions. The crystallite sizes of the films determined from XRD are found to vary between 15 and 60 nm. The electrical investigations revealed that Cs-doped SnO₂ thin film conductivity in a petroleum gas ambience and subsequently the sensor response depended on the dopant concentration and the deposition temperature of the film. The sensors showed a rapid response at an operating temperature of 345 °C. The long-term stability of the sensors is also reported.