FEM/BEM simulation of SAW components with electrode passivation by anodic oxidation

In order to reduce the sensibility of SAW components to surface contamination and avoid short cuts between electrodes, anodic oxidation is employed to passivate the electrode with a thin dielectric layer. This layer covers the electrodes, but not the regions between electrodes. Since for these structures, only part of the electrode/substrate interface carries charge, the efficient standard ab inito simulation method for SAW devices, based on the approximation of charge localization at the electrode/substrate interface, is not directly applicable. In this work this approach is generalized to devices passivated by anodic oxidation. As in the prior scheme, electrodes are treated as purely mechanical and introduction of an orthogonal Chebyshev basis set leads to an efficient Finite element/Boundary element (FEM/BEM) coupling scheme. For test resonators on 42°YX lithium tantalate the method is verified. Comparison with the Finite Element method shows that the underlying approximation of a purely mechanical electrode is justified. A good agreement with measurement is obtained.