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Single-crystal films of ZnO have been epitaxially grown on the (0001) and (011̄2) planes of sapphire by rf sputtering. Crystalline structures and electrical properties of the films were investigated. Surface acoustic wave (SAW) properties, including a phase velocity, a coupling coefficient, a propagation loss, and a temperature coefficient of delay, were measured for SAW propagating along the c-axis of the ZnO films, on the (011̄2) planes of sapphire. Availability of this structure for high-frequency SAW devices has been demonstrated by a filter with a 1050-MHz center frequency.

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Crystallographic structure of as-grown epitaxial Pb͑Zr,Ti͒O 3 ͑PZT͒ films was investigated with regard to the Zr/Ti ratio and crystalline orientation. PZT films with ͑001͒ and ͑111͒ orientation were epitaxially grown on ͑100͒ and ͑111͒SrTiO 3 substrates respectively using radio-frequency ͑rf͒ sputtering. Four circle x-ray diffraction measurements revealed that the crystallographic dependence on Zr/Ti composition in PZT films was much different from bulk PZT. In particular, ͑001͒-oriented PZT films showed tetragonal structure even in the Zr/Ti composition of 70/30 where the bulk PZT ceramics are rhombohedral phase. In addition, although ͑001͒-oriented PZT films with Zr/Ti ratio of 53/47 and 70/30 showed tetragonal structure, ͑111͒-oriented PZT films with the same Zr/Ti ratio were identified as the rhombohedral structure. The cell volume of the PZT films with both orientations increased, suggesting the excess Pb atoms in the films due to the impinging energetic sputtered particles induces the anomalous crystalline structure of the PZT films. Dielectric properties of the PZT films exhibited stable value independent of Zr/Ti ratio and characteristic increase of dielectric constant near Zr/Tiϭ53/47 could not be observed. These results suggest that the internal stress due to the sputter deposition plays an important roll in the unique characteristics of crystallographic and electrical properties of the epitaxial PZT films.

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