The optimization of a tungsten trioxide film for application in a surface acoustic wave gas sensor

Tungsten trioxide (WO3) thin films were r.f. magnetron sputtered onto quartz substrates in various argon/oxygen (Ar/O-2) atmospheres at various deposition rates and temperatures. The electrical conductivity of the WO3 films was monitored as they were subjected to annealing cycles of successively higher temperatures with gas testing performed after each cycle. This work demonstrates that the electrical conductivity of the WO3 films is a function of deposition parameters such as argon/oxygen ratio, deposition rate and substrate temperature and annealing conditions. Furthermore, it is shown that by a judicious choice of deposition parameters and annealing conditions, WO3 films whose electrical conductivity falls within the optimum range of operation for a surface acoustic wave (SAW) gas sensor may be produced.