Piezoelectric Properties of Transparent Zinc Oxide Thin Plate with C-Axis Orientation

Large transparent specimens of polycrystalline zinc oxide with c-axis orientation have been prepared by the modified vapor transport method. The cut and mirror-finished specimen is transparent enough to allow a view of distant objects. Based on the X-ray diffraction measurement on the plane vertical to the growing direction, the reflection peak is not observed except for those from (001) plane. The obtained specimens arc n-type semiconductors with resistivity below 50 Omega cm at room temperature, which increases remarkably to be > 10 G Omega cm by doping with Li2O. Such a doped material shows piezoelectric characteristics. The electro-mechanical coupling constant (k) depends strongly on the crystal axis orientation, and the specimen under the optimum condition in the Li2O doping and the crystal axis orientation shows the comparable piezoelectric performance to the reported data for the single crystal. All specimens of various thicknesses (1000-27.5 mum) show resonance-induced impedance changes on both radial and thickness extensional vibration modes. The thinnest specimen (27.5 mum in thickness) shows the resonance of the longitudinal vibration mode at 110 MHz.