Fabrication of SAW resonators on single-crystal diamonds using Minimal-Fab process

Diamond has the highest sound velocity among all materials and has been applied in high frequency surface acoustic wave (SAW) devices in the gigahertz range. To date, numerous researches have reported that the SAW devices built on a diamond wafer can work in the frequency range from 2 GHz to 10 GHz. S. Fujii et al. reported that the one-port resonator with an interdigital transducer (IDT)/AlN/single crystal diamond structure has an excellent quality factor Q of 8346 at 5.2 GHz. Hashimoto et al. also reported that an SAW resonator based on the ScAlN/single crystal diamond structure exhibited resonance Q, anti-resonance Q, and K
²
values of 520, 130, and 6.1%, respectively, at 3.6 GHz. In both reports, a small size single type Ib crystal diamond with a 3 × 3 mm
²
area was employed as a substrate. However, these devices are far from becoming commercial devices because of the small substrate. Many researchers are still making an effort to realize a large diamond wafer. AIST has developed a large size single crystal diamond having a 10 × 10 mm
²
area using plasma CVD method for application in power transistors and acoustic devices.