Extended FEM/SDA software for characterising surface acoustic wave propagation in multi-layered structures

This paper describes the development of the extended version of the FEM/SDA software for the characterisation of SAW propagation in layered substrate and overlayered structures. First, the newly developed software was applied to the characterisation of SAW propagation under an infinitely-long Al interdigital transducer (IDT) on rotated Y-cut LiTaO3/sapphire substrate structure. Because of the finite LiTaO3 thickness, a series of spurious resonances appears. It is shown that the excitation strength of the spurious resonances changes with frequency as well as the rotation angle, which reflects the frequency and rotation angle dependence of the energy leakage. Next, the analysis was carried out for SAWs propagating in an SiO2 layer/Al IDT/42 degrees YX-LiTaO3 structure. It is shown that the influence of the SiO2 layer is significantly dependent on the location where the SiO2 layer is deposited. That is, the SiO2 layer on the IDT electrodes tends to increase the SAW reflectivity, whereas the SiO2 layer sandwiching the grating electrodes in reduces the SAW reflectivity.