Resonant Confiners for Acoustic Loss Mitigation in Bulk Acoustic Wave Resonators

This paper presents a new method to mitigate the lateral acoustic energy leakage and improve the parallel Q factor (Q
p
) of thickness-extensional BAW resonators. The proposed technique consists in surrounding the top electrode with concentric λ/2 metal rings (a.k.a. resonant confiners) that vibrate at the A
0
-mode present in the substrate outskirts at the parallel resonance frequency (f
p
). Experimental results from dual-Bragg acoustic resonators (DBARs) of different electrode shapes (circle, square and pentagon) and normalized area ratios (100%, 75%, 50% and 25%) show double-digit percentage boosts, validating our technique to improve Q
p
and setting a precedent for its implementation in other types of BAW technologies.