Optimization and characterization of RF sputtered piezoelectric zinc oxide thin film for transducer applications

This paper demonstrates the substrate dependency of the c-axis zinc oxide growth In radio-frequency sputtering system. Different deposition conditions were designed to study the influences Of Si, SiO2/Si, Au/Ti/Si, and Au/Ti/SiO2/Si substrates on the piezoelectric and crystalline qualities of the ZnO thin films. Experimental results showed that the multilayer of Au/Ti/SiO2/Si-coated silicon substrate provided a surface that facilitated the growth of ZnO thin film with the most preferred crystalline orientation. The thermally grown amorphous silicon dioxide layer effectively masked the crystalline surface of the silicon substrate, thus allowing the depositions of high-quality titanium adhesion layer followed by gold thin film. The gold-coated surface allowed deposition of highly columnar ZnO polycrystalline structures. it was also demonstrated that by lowering the deposition rate at the start of sputtering, a fine ZnO seed layer could be created for subsequent higher-rate deposition. This two-step deposition method resulted in substantially enhanced ZnO film quality compared to single-step approach.