ZnO and AlN/diamond layered structure for SAW devices with subsurface damage

Diamond has the highest SAW velocity of around 11000 m/s among all materials. Therefore, diamond is of particular interest for use in the design of gigahertz-band SAW devices recently. To induce high-velocity SAW, diamond has to be combined with the piezoelectric film, such as aluminum nitride (AlN) or zinc oxide (ZnO) which has been deposited on diamond. Diamond surface acoustic wave (SAW) has been used to boost the frequency of thin film filters made of piezoelectric materials. An analytical study is carried out on the propagation of Rayleigh surface waves in a piezoelectric wafer with subsurface damage. The region of subsurface damage is considered to be a functionally graded piezoelectric thin film. Contrary to the analytical approach, the adopted numerical methods, including the ordinary differential equation (ODE) and the stiffness matrix method (SMM), treat the electrical and mechanical gradients. Results show that the first mode exhibits the largest coupling coefficient (5.74%) for the structure ZnO/diamond. For the mode 3 the K² curve shows the optimal value (11.81%) for the structure AlN/diamond. Realizations of additional devices with optimum normalized thicknesses determined by calculation are in progress in order to confirm the high potential of the new ZnO/AlN/diamond structure for high performance and high frequency saw filters.