Surface Acoustic Wave Properties of Atomically Flat-Surface Aluminum Nitride Epitaxial Film on Sapphire

We have investigated the surface acoustic wave (SAW) properties of atomically flat-surface (0001)aluminum nitride on a (0001)sapphire (AlN/α-Al2O3) combination. SAW propagated along [1210]AlN/[1100]α-Al2O3 and [1010]AlN/[1120]α-Al2O3. SAW velocity was measured to be approximately 1.0% higher than that of a conventionally calculated curve. The dispersion of SAW velocity as a function of normalized thickness (kH) was as low as 1.3%. The measured temperature coefficient of delay was 9 ppm/°C at kH values of 5.9 and 9.9. The propagation loss in the case of using an atomically flat-surface AlN film was lower by one order of magnitude than that using a conventional AlN film. The propagation loss at 5.172 GHz was measured to be 0.0053 dB/λ.