Analysis of pseudo-surface acoustic waves (PSAW) in quartz periodic structures with electrode fingers

A finite element study of the piezoelectric Lagrangian equations for frequency-temperature behavior was performed for a two-dimensional periodic PSAW structure of quartz. Plane strain assumptions were used to enable a two-dimensional analysis of straight crested pseudo surface acoustic waves in the structure. Two PSAW modes can exist on a partially metallized substrate surface; one has an anti symmetric electric potential field about the electrode center and the other has a symmetric field. The anti symmetric mode has a higher phase velocity and is less affected by the electrode mass. These two modes degenerate into one mode on a fully metallized surface or a free surface. The attenuation of the PSAW mode is strongly affected by both the electrode height and crystal cut angles. Strong PSAW modes with good frequency-temperature behavior can be obtained by a proper combination of electrode material, electrode height and the substrate cut angle.