Piezoelectrically excited surface acoustic waves in diamond-based components

Polycrystalline diamond film layers are considered as attractive substrates for surface acoustic wave (SAW) devices operating at GHz frequencies because the diamond produces the highest acoustical wave velocities among all other materials. To enable SAW excitation by interdigital transducers, non-piezoelectric diamond layers are covered with thin piezoelectric coatings. In addition to SAW modes, such structures support pseudo-surface acoustic waves (PSAWs). Their velocities are even greater than that of any SAW one, however, high attenuation caused by leakage losses (LL) obstructs their effective application. Nevertheless, at certain film-thickness-to-wavelength ratios h/λ the LL might become so small that the PSAW, in fact, degenerates into a high-velocity SAW propagating with practically negligible attenuation. Earlier such optimal ratios were discovered and experimentally verified for the first pseudo-surface (Sezawa) mode excited in a two-layer structure. The present work is focused on the revealing and studying such effects for higher modes as well as for three-layer structures with different diamond-to-piezocoating thickness ratios H/h.