Effect of Alumina Film on the Surface Acoustic Wave Properties of Crystalline Quartz and Lithium Niobate

摘要

Alumina films have been successfully deposited on ST-cut quartz and 128° Y-X UNbO_3 substrates by electron beam evaporation without any interlayer between them to ensure good adhesion of the alumina films to quartz and LiNbO_3 substrates. The alumina films markedly increase the surface acoustic wave (SAW) velocity and coupling coefficient, and they can be used to improve the performance of SAW devices. The increase in SAW velocity with increasing thickness of the alumina film results from the the high stiffness of the alumina layer. The temperature coefficient of frequency (TCF) value of the alumina film is positive, and it can be used to compensate the negative TCF value of the LiNbO_3 substrate. More temperature-stable SAW devices on UNbO_3 substrates with a higher phase velocity and coupling coefficient could be obtained by depositing the alumina overlayer.