High performance bulk acoustic resonator based on ZnO:Li piezofilms with high crystallinity and uniformity

This work describes a bulk acoustic resonator (BAR) based on Pt/L_0.06Z_0.94O/Pt/Ti/Si structure. The L_0.06Z_0.94O piezofilms are grown by radio frequency magnetron sputtering system and post-treated with ultraviolet (UV)-ozone illumination. The structural and chemical evolutions through various illumination times of the predominantly c-axis orientation LZO films are investigated. The largest piezoelectric coefficient (14.87 pC/N) of the LZO film is obtained after 120 min UV-ozone illumination, which can be ascribed to better crystallization and fewer oxygen-related defects. Furthermore, we adopt the wet chemical etching method and the lift-off process to pattern the piezofilms and electrodes of the BAR device, respectively. The fabricated resonator exhibits high quality factor (Q = 1112) at ~500 MHz. The experimental results verify the crystallinity and the uniformity of the piezofilms play crucial roles of the BAR devices.