Microstructure and properties of Cu-doped ZnO films prepared by dc reactive magnetron sputtering

ZnO film is promising for high frequency surface acoustic wave device application when coupled with diamond. In order to get good performance and reduce insertion loss of the device, which demand a piezoelectric material possessing high electrical resistivity and piezoelectric constant d(33), Cu-doped ZnO films have been prepared by direct current reactive magnetron sputtering using a zinc target with various Cu-chips attached. The influences of a Cu-doping condition on the microstructure and properties of ZnO films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, a four-point probe resistivity test system and the periodic compressional force method. The experimental results indicate that high resistivity (9 x 10(8) Omega cm) and piezoelectric constant (d(33) = 13.5 pC N-1) ZnO films with perfect e-axis orientation and fine grain polycrystalline can be achieved by 2.0 at% Cu-doping. The contribution of the Cu-doping to the electrical resistivity and piezoelectric constant d(33) is discussed.