Top Metal Coverage Impact on the Performance of Thin-Film Piezoelectric-on-Substrate Resonators

In this paper, the effect of top electrode design on the electromechanical coupling coefficient (k
t
²
) and the quality factor (Q) of lateral bulk-acoustic thin-film piezoelectric-on-substrate (TPoS) MEMS resonators is studied. Several TPoS resonators with various top electrode coverage ranging from 40% to 86% fabricated at a center frequency of 25 MHz. The resonators with 60% top electrode coverage exhibit improved Figure of Merit (FOM), defined as the product of electromechanical coupling coefficient (k
t
²
) and quality factor (Q) compared to both higher and lower coverage. Our finding suggests that by careful optimization of the top electrodes we can significantly improve the performance of systems that utilize such resonators.