Abstract
This work investigates the effects of spurious mode suppression in tethered thin-film bulk acoustic resonators (FBAR). In such a design, the quasi-free lateral boundary reduces the amplitude of the spurious modes as compared with conventional FBARs clamped on all sides. In order to quantify the degree of spurious mode suppression through the number of tethers at the periphery, FBAR resonators with various supporting structures were designed and characterized at 2.25 GHz. We experimentally confirmed that the quasi-free edge design not only shows a significant spurious mode reduction but also achieves a 1.06X enhancement in the electromechanical coupling coefficient (kt2), but at the cost of quality factor (Q) degradation caused by the increased electrical resistance.