Ti–W–O sputtered thin film as n- or p-type gas sensors

We present some recent trends about research on gas sensors based on semiconducting thin films together with a discussion on the development of novel nanostructured materials such as TiO, TiO2, and WO3 in single phase or as mixed oxides. The films, deposited by RF reactive sputtering from a composite target of W and Ti at two different abundances, are investigated through scanning and transmission electron microscopy (SEM and TEM) techniques for structural characterisation and by volt-amperometric technique for electrical and gas-sensing properties. All of the layers were capable to sense NO2, no effect of poisoning of the surface was recorded, and recovery of the resistance was complete. A concentration as low as 0.5 ppm was detected with a relative change in the resistance ΔR/R about 1400% and as short a response time as 2 min. A detection limit lower than 100 ppb of NO2 is expected.