Low propagation loss in a one-port resonator fabricated on single-crystal diamond

Diamond has the highest known surface acoustic wave (SAW) phase velocity, sufficient for applications in the gigahertz range. However, although numerous studies have demonstrated SAW devices on polycrystalline diamond thin films, all have large propagation loss in comparison to single-crystal materials such as LiNbO₃. In this study, we successfully fabricated low-propagation-loss one-port SAW resonators on single-crystal diamond synthesized using a high-pressure and high-temperature method. The devices had an interdigital transducer (IDT)/AlN/diamond structure. The best performing device exhibited a resonance frequency of 5.3 GHz and a Q-value of 2440. After correcting for ohmic losses, the propagation loss was found to be 0.012dB/wavelength. Furthermore, a large fQ product value of 10¹³ was also obtained. These results show that single-crystal diamond SAW resonators have great potential for use in 5-GHz-band oscillators.