Deposition and structural properties of RF magnetron-sputtered ZnO thin films on Pt/Ti/SiNx/Si substrate for FBAR device

This work investigates high-quality bottom electrode and piezoelectric film used in a thin-film bulk acoustic resonator (TFBAR) device. The titanium (Ti) seeding layer and platinum (Pt) bottom electrode were deposited on silicon substrates by DC sputtering using a dual-gun system. Zinc oxide (ZnO) was then deposited onto the Pt bottom electrode by RF magnetron sputtering. Field-emission scanning electron microscopy (SEM), atom force microscopy (AFM) and the four-point probe method showed that the Pt bottom electrode deposited on the Ti seeding layer exhibited favorable characteristics, such as a crystallite size of less than 10 nm, a surface roughness of 0.69 nm and a sheet resistance of 2.27 Ω/□. The ZnO thin film with a highly c-axis-preferred orientation (FWHM = 0.28°) and a roughness of 6.22 nm was investigated by X-ray diffraction (XRD) and AFM analysis, respectively. The bottom electrode with a low resistance and the highly crystalline ZnO thin film will contribute significantly to the favorable characteristics of the FBAR devices.