Shear bulk wave transducer made of (1120)-plane epitaxial ZnO film on R-sapphire

A (11 (2) over bar0) -plane epitaxial ZnO film is deposited on an R-plane ((01 (1) over bar2) -plane) sapphire substrate. In order to generate a shear bulk wave using the ZnO film, metal electrodes are required at both planes of the ZnO film; namely, the top plane on the top surface of the ZnO film and the bottom plane at the boundary between the ZnO film and the R-sapphire substrate. A c-plane ((0001)-plane) polycrystal ZnO film is conventionally deposited on the metal film on the R-sapphire substrate. Thus, the (11 (2) over bar0)-plane epitaxial ZnO film for the shear bulk transducer has not been realized until now. The authors realized a (11 (2) over bar0)-plane epitaxial ZnO film with low electrical resistivity (rho of the order of 10(-4) Omega(.)cm) on an R-sapphire substrate by doping with an impurity such as Al, Ga, or V as a substitute for the metal electrode, and a (11 (2) over bar0) -plane piezoelectric epitaxial ZnO film with high electrical resistivity (rho > 10(+10) Omega(.)cm) on this epitaxial ZnO film with low electrical resistivity for fabricating a shear wave transducer. An Al electrode was deposited on the piezoelectric ZnO film. By using the Al electrode as the top-plane electrode and a (11 (2) over bar0)-plane epitaxial ZnO film with low electrical resistivity as the bottom-plane electrode substituting for the metal film, strong shear bulk waves have been generated.