Rigorous 3D Electrostatic Field Analysis of SAW Transducers with Closed-Form Formulae

Abstract

The extreme requirements of SAW filter design for stringent specifications demand the knowl- edge of the exact nonuniform charge distribution along the fingers, especially for narrow-aperture, curved-finger and for apodized transducers. To solve this problem we present a natural extension of our previously pub- lished work, developing a self-contained, comprehensive method for three dimensional (3D) electrostatic field anal- ysis of SAW transducers. The method is based on an analytically formulated Green's function and utilizes the advantages of the method of moments. No restrictions have to be imposed on the substrate anisotropy proper- ties, the 2D topology of the fingers and the potentials applied to specific finger groups. Much effort has been devoted to the solution of the problem with closed-form formulae making the method applicable to SAW filter design with a reasonable amount of computing time. Computational results of SAW structures on YZ-L.IbO3, rotated LiNbO3 and Quartz are presented, fully taking into account the influence of bus-bars. Considerable attention has been paid to the development of general guidelines for the design of SAW transducers. The de- pendence of the finger capacitances on the aperture width and on the anisotropic properties of the substrate are tabulated for commonly used materials.