  This work reports on the modeling, fabrication, and experimental
characterization of a 13 GHz 30% Scandium-doped Aluminum Nitride (ScAlN)
Overmoded Bulk Acoustic Resonator (OBAR) for high-frequency Radio Frequency
(RF) applications, notably in 5G technology and beyond. The Finite Element
Analysis (FEA) optimization process targets the top and bottom metal electrode
thicknesses, balancing the electromechanical coupling coefficient and acoustic
energy distribution to enhance device Figure of Merit (FOM). Experimental
results on fabricated devices employing platinum and aluminum as bottom and top
electrode, respectively, demonstrate a quality factor at resonance (Qs) of 210
and a coupling coefficient (kt2) of 5.2% at 13.3 GHz for the second bulk
thickness overtone, effectively validating the simulation framework and hinting
at the possible implementation of OBARs for advanced RF filters in 5G networks.
