Preparation of AZO/ZnO/AZO/SiO2/Si thin film for FBAR

In this research, zinc oxide (ZnO) piezoelectric thin films for film bulk acoustic resonator (FBAR) applications for a high frequency range were studied by use of FTS (facing target sputtering) system, which enables to provide high density plasma, a high deposition rate at a low working gas pressure, and high quality thin films. In order to improve the crystallographic property of ZnO thin films, an AZO (ZnO:Al thin film) bottom electrode which has an equal crystalline structure to a ZnO thin film was deposited on a SiO₂/Si substrate. ZnO thin films were deposited at a different oxygen gas flow ratio, and various SiO₂/Si substrate temperatures were tried at a 2mTorr discharge gas pressure and a 0.8A sputtering current. The film thickness and c-axis preferred orientation of ZnO thin films were measured by α-step and an x-ray diffraction (XRD) instrument. In the results, we could prepare the ZnO thin film with c-axis preferred orientation of 5° on substrate temperature 200°C at O₂ gas flow rate 0.7.