Complex peripheral Lamb modes in FBARs

In this paper we give experimental observations of the complex valued Lamb mode in a FBAR resonator, using the AIM [1] and standard S-parameter measurements. Furthermore, a theoretical explanation of the observed behavior, based on the Berlincourt formula for the effective coupling coefficient, is offered. This explanation proposes a laterally “self-confined” mode that arises through the mechanical boundary conditions present at the periphery of the resonator structure.