18 GHz Solidly Mounted Resonator in Scandium Aluminum Nitride on SiO₂/Ta₂O₅ Bragg Reflector

This work reports an acoustic solidly mounted resonator (SMR) at 18.64 GHz, among the highest operating frequencies reported. The device is built in scandium aluminum nitride (ScAlN) on top of silicon dioxide (SiO2) and tantalum pentoxide (Ta2O5) Bragg reflectors on silicon (Si) wafer. The stack is analyzed with X-ray reflectivity (XRR) and high-resolution X-ray diffraction (HRXRD). The resonator shows a coupling coefficient ( $k^{2}$ ) of 2.0%, high series quality factor ( $Q_{s}$ ) of 156, shunt quality factor ( $Q_{p}$ ) of 142, and maximum Bode quality factor ( $Q_{max}$ ) of 210. The third-order harmonics at 59.64 GHz is also observed with $k^{2}$ around 0.6% and Q around 40. Upon further development, the reported acoustic resonator platform can enable various front-end signal-processing functions, e.g., filters and oscillators, at future frequency range 3 (FR3) bands.[2024-0120]