Hydrogen gas-sensing with bilayer structures of WO3 and Pd in SAW and electric systems

A bi-layer sensor structure of WO3 (similar to 100 nm) with a very thin film of palladium (Pd similar to 18 nm) on the top, has been studied for hydrogen gas-sensing application at similar to 80 degrees C and similar to 120 degrees C and low hydrogen concentrations (0.025-1%). The structures were obtained by vacuum deposition (first the WO3 and then the Pd film) onto a LiNbO3 Y-cut Z-propagating substrate making use of the Surface Acoustic Wave method and additionally (in this same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of planar resistance of the structure. A very good correlation has been observed between these two methods - frequency changes in SAW method correlate very well with decreases in the bi-layer structure resistance. The SAW method is faster at the lower interaction temperature such as 80 degrees C, whereas at an elevated temperature of 120 degrees C, the electrical planar method is also fast and has a lower limit of detection. (C) 2009 Elsevier B.V. All rights reserved.