H2S gas sensing characteristics of WO3 thick-films

The WO 3 thick films fabricated as gas sensor exhibit good sensitivity for H 2 S over a wide range of operation temperatures. The sensor characteristics are influenced with the microstructure and the thickness of the WO 3 films. The sensitivity of the sensor decreases with increase in thickness of the films. Relative variation of the fabricated sensor's resistance at varying temperatures between 240° and 420°C with heater power and with varying concentrations of the H 2 S gas under analysis have been derived. The best results for sensing H 2 S gas in the concentration range between 0.05 and 25 ppm have been obtained when the film thickness is kept between 20-22μm. The response of WO 3 films for sensing H 2 S gas is not influenced by the presence of several testing reference gases like SO 2 up to 12 ppm, NH 3 up to 10.8 ppm, CO up to 19 ppm and CH 4 up to 187 ppm. However, presence of NO x interferes when present in ambient air. Addition of small amounts of SnO 2 (3-10%), however, corrects the result and H 2 S can be determined in the presence of NO x up to 11 ppm.