Al 0.78 Sc 0.22 N Lamb Wave Contour Mode Resonators.

This article presents the lamb wave contour mode resonators (CMRs) based on 22% aluminum scandium nitride (AlScN) thin film with $\lambda $ of 12–24 $\mu \text{m}$ , and operating in $\text{S}_{{0}}$ mode. We report the design, fabrication, and characterization of 500 nm-thick AlScN CMRs, which take advantage of optimized stress control of co-sputtered AlScN thin films and vertical inductively coupled plasma (ICP) etching profile. The experimental results are compared to theoretical predictions by finite element analysis (FEA). All Al $_{{0.78}}$ Sc $_{{0.22}}\text{N}$ devices show excellent agreement with simulations in piezoelectric coupling using modified AlScN film parameters. The best Al $_{{0.78}}$ Sc $_{{0.22}}\text{N}$ CMR has achieved an electromechanical coupling coefficient (${k}_{t}^{{2}}{)}$ of 5.24% and loaded quality factor (${Q}$) of 1219 with an operating frequency at approximately 300 MHz, which exhibits a high Figure-of-Merit (FoM) of 63.88 in piezoelectric microelectromechanical system (MEMS) lamb wave CMR. This article also presents the co-sputtering characteristics of the AlScN thin films under $\text{N}_{{2}}$ gas to achieve low-stress and high-quality piezoelectric materials, and the etching optimization of high concentration Sc doping aluminum nitride (AlN) thin films under Cl2/BCl3/Ar chemistry to obtain record profile angle of 77°, high selectivity of 1:1 with SiO2 hard mask. [ABSTRACT FROM AUTHOR]