Thin film loading effects on SAW velocity dispersion curves

Surface acoustic waves propagating on several thin film materials (Cr, Cu, Mo, SiO2, V, ZnO and Zr) of various thicknesses, deposited on different substrates (silicon, quartz, and sapphire), have been investigated. From the initial slope of the velocity dispersion curves it is shown that, for small thicknesses, the loading effect is responsible for the decrease in phase velocities; a simple universal relation between relative velocity changes and materials densities is proposed.