SAW hydrogen gas sensor based on WO3 and Pd nanostructures

Bi-layer nanostructures of WO(3) (similar to 100 nm and 150 nm) with a very thin film of palladium (Pd similar to 10 nm) on the top, have been studied for hydrogen gas-sensing application at similar to 70 degrees C and medium hydrogen concentrations (1 - 4%) in air. The structures were obtained by vacuum deposition (first the WO(3) and then the Pd film) onto a LiNbO(3) 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 WO(3) film thickness and hydrogen gas concentration and is greater for the nanostructure with a thicker WO(3) film.