Rigorous analysis of finite SAW devices with arbitrary electrode geometries

This paper proposes a rigorous numerical model allowing the analysis of finite SAW filters with only the 2D approximation: all the acoustical and electrical interactions are taken into account as well as mass loading effects. Areas outside the interdigital transducers can be either free surface or fully metallized: in the first case, a charge distribution formulation is used while, in the second one, a transverse E-field formulation is the most convenient representation. This method combines a BEM formulation using a semi-infinite dyadic Green´s function and a FEM computation of the mechanical behavior of each metallic electrode. In order to limit the CPU time needed to perform such an analysis it has been necessary to develop a new powerful method to integrate the Green´s functions. It has been possible to reduce this integration from a double integral of rapidly varying functions to a single integral of a slowly varying function, leading to easy numerical integration and allowing the use of this new numerical tool to rigorously analyze SAW filters with a total number of electrodes up to 200. It has been successfully used to analyze SAW filters based on short transducers for the 36° Y rotated cut of LiTaO₃. Comparisons between simulations and experiments will be presented, which show very good agreement