Abstract: A HACT device employing a thin-film overlay of a more strongly piezoelectric material can operate as a delay line and as a tapped delay line, or transversal filter, while requiring less total power for the SAW clock signal. The increased electrical potential per unit total SAW power thus realized facilitates coupling between the total SAW energy and the mobile charge carriers. Some materials systems, such as a GaAs substrate and a ZnO thin-film overlay, will require an intervening thin-film dielectric layer in between the HACT substrate and epitaxial layers and the thin-film piezoelectric overlay. This may be necessitated by chemical, semiconductor device processing, or adhesion incompatibilities between the substrate material and the thin-film overlay material.