Diamond has the highest known 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 had much larger propagation loss than single-crystal materials such as LiNbO3. Hence, in this study, we fabricated and characterized one-port SAW resonators on single-crystal diamond substrates synthesized using a high-pressure and high-temperature method to identify and minimize sources of propagation loss. A series of one-port resonators were fabricated with the interdigital transducer/ AlN/diamond structure and their characteristics were measured. The device with the best performance exhibited a resonance frequency f of 5.3 GHz, and the equivalent circuit model gave a quality factor Q of 5509. Thus, a large fQ product of approximately 2.9 × 10(13) was obtained, and the propagation loss was found to be only 0.006 dB/wavelength. These excellent properties are attributed mainly to the reduction of scattering loss in a substrate using a single-crystal diamond, which originated from the grain boundary of diamond and the surface roughness of the AlN thin film and the diamond substrate. These results show that single-crystal diamond SAW resonators have great potential for use in low-noise super-high-frequency oscillators.

Indium tin oxide (ITO) thin films were epitaxially grown on sapphire substrates by solid-source electron cyclotron resonance (ECR) plasma deposition. Compared with the other methods such as sputtering and evaporation methods, the ECR plasma method resulted in a flat surface and a low resistivity with a relatively low substrate temperature. The surface roughness was strongly dependent on the ratio of oxygen gas flow during deposition. With optimal deposition conditions, the ITO thin film epitaxially grew on a c-plane sapphire substrate with twelvefold symmetry. The surface roughness and resistivity were estimated to be 0.4 nm and 1.4×10-4 Ω·cm, respectively. The X-ray rocking curve revealed 0.025° of full width at half maximum (FWHM) on the epitaxial ITO thin film. The ITO film deposited on an epitaxial GaN(001) layer on a c-plane sapphire substrate showed sixfold in-plane symmetry, indicating the epitaxial growth of ITO(111) on the GaN(001)/c-plane sapphire substrate.

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A high dose impurity doping process for 4H-SiC crystals has been developed using electron cyclotron resonance (ECR) sputtered carbon cap film and ECR plasma ashing. ECR-sputtered carbon films are newly found crystalline carbon films of which the hardness is comparable to that of diamonds. Since this carbon film showed such a high thermal tolerance that the hardness did not change after 1900oC annealing, this carbon cap film worked well for suppressing roughening during annealing for aluminum-ion implanted 4H-SiC. Cap carbon film can be removed successfully by using high density ECR plasma ashing.

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