Effects of diamond-like carbon and other dielectric layers on EPCOS SAW devices and structured wafers

Abstract

Diamond-like carbon (DLC) films were deposited on Y-X quartz, Y-Z LiNbO3 and 42orot.Y-X LiTaO3 substrates through incorporation of a few nanometers’ thick SiC interlayer using plasma enhanced CVD (PECVD) technique. The “D” and “G” peaks of Raman scattering spectra were located at 1360-1376 and 1578-1588 cm-1, respectively. The “D” to “G” peak intensity ratio was 2.28, 1.96 and 1.63 for DLC/LiNbO3, DLC/LiTaO3 and DLC/quartz samples, respectively, indicating that the DLC films had a high carbon sp3/sp2 ratio and reasonably high hardness. Young’s modulus, hardness and adhesion of the DLC films on LiNbO3 substrates were about 150 GPa, 19 GPa and 15 N, respectively. Fractional changes in the velocity of surface acoustic waves (SAW) due to the DLC coatings were found to be +2.4% (at 198 MHz), +2.5% (at 430 MHz) and – 1.3% (at 512 MHz) for DLC/quartz, DLC/LiNbO3 and DLC/LiTaO3 samples, respectively.