Characteristics of SAW hydrogen sensors based on InOx/128°YX-LiNbO3 structures at room temperature

A new kind of SAW hydrogen sensors based on 128°YX-LiNbO3 SAW delay lines covered by InOx sensing layers is presented, in which the InOx layers are prepared by RF diode sputtering method and Pt films are deposited on the surfaces of the sensing layers as catalysts. The experimental results indicate that an apparent frequency shift of 11.83 kHz of the sensor towards 400 ppm hydrogen mixed in natural air is observed at room temperature, which displays very high sensing characteristics. By using XRD, AFM and XPS analyses, it is found that the InOx sensing layers deposited by RF diode sputtering method have small and uniform nano-grains (∼16 nm in diameter), high oxygen vacancies and high ratios of the chemisorbed oxygen to that in the lattice, which make the response properties of the sensors greatly improved.