Sputtering ZnO films on Langasite and its SAW properties

C-axis-oriented and fine structural ZnO films were successfully prepared on Langasite substrate (LGS, La₃Ga₅SiO₁₄) by r.f. magnetron sputtering. The crystalline structure of the films was determined by grazing incident angle X-ray diffraction (XRD), the surface microstructure of films was investigated by Scanning electron microscope (SEM), the atom composition ratio O /Zn of films was determined by Energy Dispersive X-ray Spectroscopy (EDS), and the resistivity of films was determined by the four point probe instrument. The dependence between the sputtering conditions and the physical structure of the films (crystalline structure and micromorphology) was investigated in order to get the optimal conditions. Surface acoustic wave (SAW) measurement was used to evaluate the acoustic properties of this new composite substrate (ZnO/LGS). The results showed the films prepared in the research were all polycrystalline hexagonal ZnO films. The optimal ZnO films prepared at the oxygen flow rate (O₂ / O₂ + Ar) of 20 %, the RF power of 200 W and the substrate temperature of 200degC. This films had the highly c-axis-oriented microstructures, dense surface morphology, the atom composition ratio (1.02) and the film thickness was 1.76 mum. The electromechanical coupling coefficient of this new composite substrate (ZnO/LGS) was 1.18%. The velocity of this composite substrate was 2756 m/s. This ZnO films can effectively tripled the electromechanical coupling coefficient of the LGS substrate.