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

This article reports the first groups of low-loss acoustic solidly mounted resonators (SMRs) and acoustic delay lines (ADLs) at 14-20 GHz. Bulk acoustic waves (BAWs) 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/SiO ${}_{{2}}\text {)}$ or niobium pentoxide (Nb2O5/SiO ${}_{{2}}$ ) 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 to 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 ( ${k}^{{2}}\text {)}$ of 2.0%, series Q ( ${Q}_{s}\text {)}$ of 156, and parallel Q ( ${Q}_{p}\text {)}$ values of 140 for Ta2O5/SiO2, while ${k}^{{2}}$ of 2.4%, ${Q}_{s}$ of 140, and ${Q}_{p}$ 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.