A full-wave analysis of surface acoustic waves propagating on a SiO2 overlay/metal grating/rotated YX-LiNbO3 substrate structure

This paper describes full-wave analysis of the SiO₂ overlay with finite thickness/metal grating/rotated YX-LN substrate structure. The influence of thickness and surface topology of the SiO₂ overlay, metal grating selection (copper or aluminum) upon excitation and propagation characteristics of acoustic guided modes are discussed in detail. It is shown that in the structure there propagate several types of acoustic guided modes. One type of mode concentrates the energy near the metal grating, and becomes the piezoelectric boundary acoustic waves with relatively large electromechanical coupling when SiO₂ thickness becomes semi-infinite. Another mode concentrates its energy near the top surface of the SiO₂ overlay and becomes the Rayleigh-type SAW on SiO₂ when thickness is semi-infinite. With an increase in SiO₂ thickness, it rapidly loses its piezoelectric coupling. The remaining mode is a series of guided modes bounded in the SiO₂ layer, in which the SiO₂ layer behaves as a waveguide because of its low acoustic wave velocities.