Abstract
A Lamb wave exists in high-density states when its wavelength is comparable to substrate thickness. It propagates through the boundaries of the upper and lower surfaces in many modes. In this paper, proposes a hydrogen gas sensor fabricated using the good characteristics of a Lamb wave. The film thickness of a sensitive membrane and Lamb wave mode dependence are defined by theoretical analysis and experiment. A Y-cut, Z-direction propagation LiNbO3 substrate (91-µm-thick, double-sided polishing) was used as a piezoelectric substrate of a device. An interdigital transducer with a wavelength of 100 µm was installed on the surface of the device; a sensitive membrane was attached on to the rear face using an RF sputtering process. A palladium silver alloy was used as the sensitive membrane. The maximum frequency shift is 9.21 ppm at hydrogen concentration 9.1%.