SAW hydrogen gas sensor based on WO3 and Pd nanostructures

Bi-layer nanostructures of WO3 (∼100 nm and 150 nm) with a very thin film of palladium (Pd∼10 nm) on the top, have been studied for hydrogen gas-sensing application at ∼700C and medium hydrogen concentrations (1 – 4%) in air. The structures were obtained by vacuum deposition (first the WO3 and then the Pd film) onto a LiNbO3 Y- cut Z-propagating substrate and were tested by means of Surface Acoustic Wave method in a three channel delay line configuration. Very repeatable results have been observed for these two nanostructures with changes in frequency on the level of 500 to 1800 Hz for hydrogen concentration from 1 to 4 % in air. The absolute response value depends on the WO3 film thickness and hydrogen gas concentration and is greater for the nanostructure with a thicker WO3 film.