Highly oriented c-axis 23° tilted ZnO films with high quasi-shear mode electromechanical coupling coefficients

摘要

A quasi-shear mode piezoelectric film with high electromechanical coupling coefficient k'{sub}15 is attractive for shear wave transducers, shear mode FBAR and SH-SAW devices. The single crystalline ideal ZnO film with c-axis-tilt angle of 28° from the surface normal of the film has high k'{sub}15 value of 0.38. In this study, we have investigated c-axis-tilted ZnO films to obtain sufficient tilt angle and good crystalline alignment using RF magnetron sputtering technique. We focused on the angle between the substrate surface and target surface during the sputtering deposition. In case that the film was deposited on the substrate set at 90° to the target surface, relatively large c-axis tilted angles of 22.6°-26.2° were obtained. Moreover, small ψ-scan FWHM values from 6.7° to 7.8° of the film indicated good crystalline alignment. Finally, k'{sub}15 value of this film was estimated as 0.26, which was the highest value ever reported for c-axis-tilted ZnO or AlN films.