Theoretical Study On The Propagating Characteristics Of Surface Acoustic Waves In Layered Structures

Recently, the rapid development of modern communication systems has stimulated a great demand for high frequency and high performance Surface Acoustic Wave (SAW) device. Diamond has the highest acoustic wave velocity among all materials, and when combined with a like ZnO or AlN piezoelectric thin film, they can provide great advantages in the manufacture of high frequency SAW devices in that interdigital tansducers (IDTs) can be made wider in line and spaces compared with those in conventional SAW materials such as LiNbO3 and quartz. Therefore, multilayered structure based on diamond in combinatiom with a piezoelectric thin film becomes the most promising substrate for fabricating gigahertz range SAW devices.However, diamond can not provide piezoelectricity. As the SAW is excited in the diamond layer by electromechanical conversion, a piezoelectric layer such as ZnO or AlN is required and metallic IDTs are therefore deposited on top of the diamond surface. But surface acoustic waves propagating in the multilayerd media are dispersive and sensitive to the thickness of the piezoelectric layer. So, it is necessary to take the frequency dispersion into account when simulate and design the high frequency SAW devices.Be aimed at the design requirements of SAW devices in multilayered structure, this paper, based on the basic theories of SAW, discussed the matrix method in detail, which is widely used to study the propagating characteristics of SAW in mutilayered structures in the last decade. The formulation based on the recursive stiffness matrix method (RSM) for calculating the generalized Green's function and the effective surface permittitivity of the piezoelectric thin film/diamond layered system with four types of electrode arrangements is deduced, and the corresponding calculation program was written with the help of Matlab software. In order to verify the derivation, the effective surface permittitivitys for ZnO/Diamond layered system with four different electrical boundary conditions were calculated, and by utilizing the effective surface permittitivity approach, phase velocity dispersions of surface acoustic waves in layered systems were given at last. The calculation results show that the aforementioned formulation has good accuracy, and will be usefull to simulate and design high frequency SAW devices base on piezoelectric thin film/diamond layered system in the future.