Effects of deposition conditions on the structural and acoustic characteristics of (1120) ZnO thin films on R-sapphire substrates

(1120) ZnO films with the c-axis lying in the plane deposited on R-sapphire substrates by RF magnetron sputtering are studied. The focusing investigation is the effect of substrate positions in the sputtering on structural and acoustic characteristics of the ZnO films. The crystallographic characteristics of the films are characterized by X-ray diffraction analysis. It is found that the crystalline orientation of ZnO films varies with the variation of substrate position deviated from the normal direction of the anode center and there is an optimized deviation position. To investigate the variations of acoustic characteristics of these piezoelectric ZnO films, multilayered structures are prepared to fabricate shear-mode highovertone bulk acoustic resonators (HBARs). The results show that the electromechanical coupling coefficient k₁₅ of the (1120) ZnO films obtained at the optimized position approaches a maximum.