Modelization of thickness shear integrated filters

In order to optimize the design of bulk acoustic wave filters, a model based on the equations governing the thickness modes is established. Structures in which two electroded regions are separated by a "coupling" region are considered. The electroded and the coupling regions are surrounded by an external unelectroded region have a higher cutoff frequency to ensure that the energy can be trapped in the device. Depending on the distance between the electrodes and some other parameters, the resonators can be from strongly (monolithic filters) to negligibly acoustically coupled. A semi-algebraical method of solution is used, making use of series of exact solutions of the equations and of a discretization of the continuity conditions between the different regions. This makes it possible to obtain the eigenfrequencies and the eigenmodes. The forced modes of the structures are then computed as linear combinations of the eigenmodes. Using the forced modes, the terms of the admittance matrix of the four-port structure are calculated in order to obtain the elements of the lattice equivalent circuit