Abstract
High-frequency and wideband surface acoustic wave (SAW) devices have become an important topic in 5G communication systems and beyond. For this purpose, piezoelectric ScAlN thin films deposited on high SAW velocity diamond are studied in SAW resonators on the polycrystalline diamond (PCD) and hetero-epitaxial diamond (HED) substrates. A very strong c-axis orientation of ScAlN on HED was confirmed. Interdigital transducers of 0.8 μm and 0.5 μm were fabricated to realize 2.2 to 3.5 GHz high-frequency resonators. High Q values were obtained for the 2.3–2.5 GHz device on both PCD and HED. Additionally, a high electro-mechanical coupling coefficient (K2) of 5.40–5.52% and high SAW velocities of 7400–7766 m/s were obtained in the 2.3–2.5 GHz devices. In comparison to the simulated coupling coefficient results of a previous report, ScAlN/diamond might have higher K2 for the Sezawa wave.
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