Zero SAW velocity dispersion for aluminum on rotated Y-cut quartz

The effect of a finite metal film thickness on the SAW propagation velocity for common material combinations, such as rotated Y-cuts of quartz with aluminum metallization, is important with regard to the increasing interest in SAW filters above 1 GHz. We have considered the solution for SAW of the vectorial wave equation for this simple layered structure. Both a local minimum and a local maximum in the velocity as a function of the film thickness were found. The local velocity minimum occurs for a film thickness realizable for SAW filters in the GHz range. It has practical implications with respect to obtainable performance and robustness towards manufacturing variations. Measured SAW velocities confirm a low sensitivity to metal film thickness variations near the predicted velocity minimum