MoO3 and WO3 based thin film conductimetric sensors for automotive applications

Un-doped semiconducting oxides suitable for automotive gas sensor applications have been studied in this work. Thin films of MoO3 and WO3 were fabricated by ion beam deposition on alumina substrates with gold interdigitated electrodes. The process pressure inside the deposition chamber was 1.6 × 10−4 Torr. The oxygen to argon ratio in the secondary plasma was maintained at 5:5 sccm. A stabilization heat treatment of 500°C for 8 h was performed for each set of films that produced nanocrystalline structures. Gas sensing tests were carried out at 450°C with nitrogen dioxide/ammonia with synthetic air background similar to those realized in diesel automotive exhausts. XRD and electron microscopy studies were performed to understand the microstructure of the thin films following the sensing tests. The MoO3 films were selective to ammonia whereas the WO3 films showed high senstitivity towards NO2 with respect to NH3. An attempt is made to correlate the structural characteristics to the sensing behavior of the materials.