Surface acoustic wave methods to determine the anisotropic elastic properties of thin films

We have developed experimental and analytical methods to measure the anisotropic elastic properties of thin supported films. In this approach, SAWs were generated using a line-focused laser. Waves with frequency components up to 400 MHz were detected by a Michelson interferometer. Dispersion relations for the SAW phase velocity were calculated from displacement waveforms acquired with source-detector separations of 5-15 mm. To determine film properties from the dispersion relations, we developed a new inversion algorithm based on the delta-function representation of the fully anisotropic, elastodynamic Green function for wave propagation. Our methods were first applied to an elastically isotropic aluminum film on an isotropic fused silica substrate. The results show the validity of our methods and were in good agreement with literature values. The results also illustrate various aspects of measurement uncertainty. The same SAW methods were used to examine a series of titanium nitride films on single-crystalline silicon wafers. (Author)