Direct and inverse energy trapping in the thin film resonators and optimization of their designs

In this communication we consider the application of the Tiersten theory of the energy trapping of the "essentially" thickness modes to thin film resonators using the thickness extensional modes of ZnO and AlN textured films. Considering mainly the applications to filtering, we discuss the conditions allowing obtaining a single mode response, the influence of the shape of the electrodes and of the boundary conditions. It is observed that circular geometries are more favorable, that particular geometries allow to obtains resonators and monolithic filters with lower inductance values and that particular filter topologies allows much better performance than those presently most often used.