STABILITY, SENSITIVITY AND SELECTIVITY OF TUNGSTEN TRIOXIDE FILMS FORSENSING APPLICATIONS

The stability, sensitivity and selectivity of r.f. sputtered gold-dope d tungsten trioxide (WO3) films for gas-sensing applications have been examined. The WO3 film sensing properties, such as electrical conduct ivity and carrier type, concentration and mobility, have been measured . It is found that in order to improve the WO3 film stability, sensiti vity and response time, it is necessary to subject the as-deposited fi lms to a heat treatment or 'activation' process. This process enables concentrations of less than 1 part per billion (ppb) of hydrogen sulfi de (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 H2 S-sensing applications. The present work clearly shows that properly t reated gold-doped WO3 films are extremely stable, sensitive and select ive to H2S gas in the ppb range.