Solidly Mounted Scandium Aluminum Nitride on Acoustic Bragg Reflector Platforms at 14-20 GHz.

Abstract

This paper reports the first groups of low-loss acoustic solidly mounted resonators (SMR) and acoustic delay lines (ADL) at 14-20 GHz. Bulk acoustic waves (BAW) are confined in thin-film scandium aluminum nitride (ScAlN) on top of dielectric acoustic Bragg reflectors, consisting of alternating silicon dioxide with tantalum pentoxide (Ta₂O₅/SiO₂) or niobium pentoxide (Nb₂O₅/SiO₂) on Si carrier wafers. Stack material parameters are extracted via high-resolution X-ray diffraction (HRXRD) and X-ray reflectivity (XRR). The simulation and experiment show confinement for longitudinal BAW from 14-20 GHz. ADLs show high propagation Q above 478 and 171 for Ta₂O₅/SiO₂ and Nb₂O₅/SiO₂, respectively. SMRs in both stacks perform similarly, showing coupling coefficient (k²) of 2.0%, series Q (Q_s) of 156, and parallel Q (Qp) values of 140 for Ta₂O₅/SiO₂, while k² of 2.4%, Q_s of 140, and Qp of 109 for Nb₂O₅/SiO₂, both at 18.6 GHz. Upon development, ScAlN solidly mounted platforms will enable signal processing elements with better power handling.