Layered SAW hydrogen sensor with modified tungsten trioxide selective layer

Layered surface acoustic wave (SAW) devices are investigated for sensing hydrogen (H2) concentrations less than 1% in air. Platinum (Pt) and gold (Au) catalyst activated tungsten trioxide (WO3) selective layers are investigated. The SAW sensors consist of two thin film metal interdigital transducers (IDTs) on a 36° Y-cut, X-propagating LiTaO3 substrate. A ZnO guiding layer is used to confine the acoustic energy at the active surface of the device for increased sensitivity. In this paper, the fabrication of an Au-WO3 and a Pt-WO3 based layered SAW device are described. The sensor response have been analysed in terms of frequency shift as a function of different hydrogen concentrations and operating temperatures. The responses of the catalyst activated WO3 sensors show much higher sensitivity when compared against a layered SAW sensor employing only a bare WO3 selective layer. Frequency shifts of 705 and 118 kHz towards 1% H2 in air were observed for the Au-WO3 and Pt-WO3 sensors, respectively. Characterization by scanning electron microscope (SEM) of the Au catalyst activated tungsten trioxide sensor is also presented.