STABILITY, SENSITIVITY AND SELECTIVITY OF TUNGSTEN TRIOXIDE FILMS FOR SENSING APPLICATIONS

The stability, sensitivity and selectivity of r.f. sputtered gold-doped tungsten trioxide (WO3) films for gas-sensing applications have been examined. The WO3 film sensing properties, such as electrical conductivity and carrier type, concentration and mobility, have been measured. It is found that in order to improve the WO3 film stability, sensitivity and response time, it is necessary to subject the as-deposited films to a heat treatment or 'activation' process. This process enables concentrations of less than 1 part per billion (ppb) of hydrogen sulfide (H2S) in air to be measured reproducibly. The films are exposed to several interferent gases and are found to be weakly sensitive only to hydrogen (H-2); however, this is not expected to be problematic in H2S-sensing applications. The present work clearly shows that properly treated gold-doped WO3 films are extremely stable, sensitive and selective to H2S gas in the ppb range.