Graphene - from Synthesis to the Application as a Virtually Massless Electrode Material for Bulk Acoustic Wave Resonators

Mechanical and electrical losses strongly determine the performance characteristic of Bulk Acoustic Wave (BAW) resonators. The focus of this work lies in the deeper investigation of extrinsic electrode-induced losses. Here, mainly viscous and ohmic losses play a role due to an electrode's specific mass and limited conductivity. A conflict of objectives lies here in the requirement of ideally massless and highly conductive materials, which commonly used metal electrodes suffer from due to their comparably high mass density. The chance to overcome this problem lies in the use of graphene as a 2D virtually massless carbonic layer with remarkable electronic properties. This work investigates the first time graphene as an active top electrode material for solidly mounted Bulk Acoustic Wave resonators. Here, a process development from the graphene synthesis, a specifically elaborated graphene transfer technique and a subsequent successful fabrication of working BAW resonators with an optimized graphene-based electrode design are reported. In a nutshell, the findings of this work strongly highlight the advantages of graphene and possibly other 2D materials as an alternative electrode material in electroacoustic resonators for radio frequency devices.