Effect of crystalline quality of diamond film to the propagation loss of surface acoustic wave devices

Diamond films with various crystal qualities were grown by chemical vapor deposition on silicon wafers. Their crystallinity was characterized by Raman scattering and electron backscattering diffraction. By fabricating a device structure for surface acoustic wave (SAW) using these diamond films, the propagation loss was measured at 1.8 GHz and compared with the crystallinity. It was found that the propagation loss was lowered in relatively degraded films having small crystallites, a narrow distribution in the diamond crystallite size, and preferential grain orientation. This experiment clarifies diamond film characteristics required for high-frequency applications in SAW filters.