Dual-Mode Hybrid Quasi-SAW/BAW Resonators With High Effective Coupling Coefficient

This article reports on a design journey for Sc
_x
Al
₁
-N-based dual-mode hybrid quasi-surface and bulk acoustic wave (quasi-SAW/BAW) resonators. Four types of acoustic excitation configurations are proposed in these designs based on Sc
_x
Al
_1-x
N/6H-SiC stack architectures. The influence of Sc
_x
Al
_1-x
N materials, film thickness, and device configurations on the performance is investigated. After design optimization, the final dual-mode hybrid quasi-SAW/BAW resonators comprise of top electrode, partially etched Sc
_x
Al
_1-x
N pillars, and bottom electrode, which are stacked on a 6H-SiC substrate. The coupled quasiSAW and BAW excited in the hybrid resonators enhance the resonance for both quasi-Rayleigh and quasi-Sezawa modes which results in a high effective coupling coefficient (K
_eff
²
) and phase velocity (v). Simulation results show that the optimized hybrid quasi-SAW/BAW resonator based on Mo/Sc
_0.4
Al
_0.6
N/Mo/6H-SiC configuration with SiO
₂
filling the grooves has a remarkable K
_eff
²
value of 14.55% and a high v above 7500 m/s, which make this kind of dual-mode hybrid quasi-SAW/BAW resonators have great potential in wideband and high-frequency applications.