Enhancement of high-frequency bulk acoustic wave resonator performance via rapid thermal annealing

Abstract

The Mo electrode thickness in AlScN-based bulk acoustic wave (BAW) resonators is constrained to sub-100 nm to satisfy high-frequency operational requirements, leading to degraded electrical conductivity and increased electrical losses. In this work, the electrical properties of the Mo electrode were enhanced through rapid thermal annealing (RTA). The Mo films showed a 102.5% enhancement in electrical conductivity, attributed to improved crystalline quality and suppressed surface scattering. Furthermore, thermal annealing reduced the residual stress in the film and promoted in-plane atomic rearrangement, thereby enhancing the effective electromechanical coupling coefficient (keff2) and reducing acoustic losses in the resonators. As a result, the figure of merit of the device increased by approximately 46.5%, reaching 152 after the annealing process. Moreover, the influence of electrode conductivity on resonator performance was analyzed using finite-element analysis. This work presented a promising strategy—the RTA process—for enhancing the electrical properties of the Mo electrode and improving the performance of BAW filters at high operating frequencies.