Tetrahedral amorphous carbon films as a frequency-increasing interlayer of surface acoustic wave devices with a ZnO/Si configuration

Tetrahedral amorphous carbon (ta-C) films deposited using filtered cathodic vacuum arc technology have been applied to the interlayer of surface acoustic wave devices with a ZnO/Si configuration. The phase velocity in the multilayered structure was analyzed in the first instance by theoretical calculations and was then measured by means of a network analyzer. It has been shown that the ta-C interlayer between piezoelectric film and Si substrate can strikingly increase the phase velocity of the surface acoustic wave. The greater the interlayer thickness is and the higher the content of the sp³ hybridization is, the faster surface acoustic wave propagates. However, the increment of phase velocity gradually decreases with increasing interlayer thickness. It was confirmed in this paper that the measured values of the phase velocity as a function of the interlayer thickness agree with the theoretical calculations.