The effect of depth-dependent residual stresses on the propagation of surface acoustic waves in thin Ag films on Si

We give detailed calculations of the acoustoelastic effect (AE) in highly textured thin silver films on silicon substrates. The AE relates the phase velocity of the surface waves to the stresses within the films. Therefore, we have investigated several stress states that were produced by annealing and measured by X-ray grazing incidence diffraction. The selected temperatures range from 25 to 700 °C. The stress profiles are modelled by a stratification of the films into different layers. Subsequently, by application of the stiffness-matrix method (SMM) for acoustic wave propagation, the corresponding AE is calculated. No measurements of the AE itself will be reported here. Our calculations show that the AE is fairly weak and becomes maximal when the wavelength is on the order of some few film thicknesses.