A layered surface acoustic wave ZnO/LiTaO3 structure with a WO3 selective layer for hydrogen gas sensing

A layered surface acoustic wave (SAW) gas sensor is investigated for hydrogen concentrations of 0.5% and 1% in air at different operational temperatures. The device structure is based on a layered SAW device fabricated on a 36° X-cut, Y-propagating LiTaO3 substrate. A ZnO guiding layer is employed to increase sensor sensitivity, and a thin film of WO3 provides the selectivity toward hydrogen gas. Such a structure has the advantage of confining the acoustic wave energy at the surface of the device, which increases the sensitivity of the device. In this paper, the fabrication of the ZnO/36° YXLiTaO3 sensor is described, and the sensor's response features are analyzed in terms of response time, recovery time, and response magnitude as a function of operational temperature. Furthermore, the hydrogen interaction with the WO3 selective layer is briefly described.