62.6 GHz ScAlN Solidly Mounted Acoustic Resonators

We demonstrate a record-high 62.6 GHz solidly mounted acoustic resonator (SMR) that uses a 67.6 nm Sc0.3Al0.7N piezoelectric layer on a 40 nm buried platinum (Pt) bottom electrode, above an acoustic Bragg reflector composed of alternating SiO2 (28.2 nm) and Ta2O5 (24.3 nm) layers in 8.5 pairs. The Bragg reflector and piezoelectric stack are designed to confine a third-order thickness-extensional (TE) bulk acoustic wave (BAW) mode while enabling efficient thickness-field excitation. The fabricated SMR exhibits an extracted electromechanical coupling coefficient k2 of 0.8% and a maximum Bode quality factor Q of 51 at 63 GHz, representing the highest operating frequency reported for an SMR to date. These results establish a pathway toward millimeter-wave SMR devices for filters and resonators in next-generation RF front ends.