Thin film bulk acoustic wave filters with ring-dot electrodes

We propose a new structure of ZnO or AlN thin film bulk acoustic wave filters using a ring-dot driving electrode operating with thickness-extensional modes. A theoretical analysis is performed to show the operating frequencies and modes of the proposed filter. The scalar differential equation by Tiersten and Stevens (1983) is used. An analytical solution is obtained. Numerical calculations based on the solution show that the vibration tends to be trapped in the electroded central and annular areas and decays away from the electrode edges. It is also shown that by properly designing the electrode dimensions and mass density, the nodal line of one of the two operating modes can be adjusted to lie in the gap between the ring and the dot driving electrodes which is ideal for a filter.