Investigation of surface acoustic waves propagating in ZnO–SiO2–Si multilayer structure

The investigations of the propagation of the SAW in the multilayered structures have been of great interest since the combination of the surface acoustic wave (SAW) technology with the microelectromechanical system (MEMS) technology comes true. In this paper, the recursive asymptotic method (RAM) is applied to analysis the propagation of the SAW in the ZnO–SiO2–Si multilayered structure. The influences of the ZnO layer thickness and the SiO2 layer thickness to the phase velocity and the electro-mechanical coupling coefficient for the Rayleigh wave and Love wave are discussed. The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate. In order to prove the theoretical results, a series of Love mode SAW devices based on the ZnO–SiO2–Si multilayered structure is fabricated by micromachining, and their frequency responses are detected. The experimental results are found to be mainly consistent with the theoretical ones except the little larger velocities induced by the residual stresses produced in the fabrication process of the films. The deviation of the experimental results from the theoretical ones is reduced by thermal annealing.

► The propagation of the SAW in the ZnO–SiO2–Si structure is calculated.
► Love waves are found to can be predominantly generated in ZnO–SiO2–Si structure.
► Some SAW devices are fabricated to prove the calculated results.
► The residual stress is found to cause the increase of SAW velocity and frequency.