Sensitivity and selectivity improvement of rf sputtered WO3 microhotplate gas sensors

Active layers consisting of rf sputtered WO3 were deposited on microhotplate substrates. The films were doped with seven different materials (Pt, Au, Ag, Ti, SnO2, ZnO and ITO (indium tin oxide)). The eight types of sensors (including pure tungsten oxide ones) were tested in the presence of ammonia, hydrogen sulphide, nitrogen dioxide, carbon monoxide and methane. It was found that gold improved the sensitivity to H2S. On the other hand, doping with Ag and Pt led to higher responses to NO2 and NH3, respectively. No response to CH4 was observed. The sensitivity to CO was very low. The influence of the working temperature on the sensor response was also studied. Our study proves that selective gas detection is possible combining a few tungsten oxide sensors with different dopants.