Transverse reflector Lamb-wave resonators with spurious-free response and wafer-level transfer on 8-in. wafers

Abstract

This study reports AlSc0.095N Lamb-wave resonators (LWRs) using an interdigitated (IDT)–IDT transducer and integrated transverse reflectors that simultaneously suppress transverse spurious modes and mitigate anchor loss. The influence of the electrode metal ratio (η) on the resonators’ frequency, quality factor (Q) values, and effective electromechanical coupling coefficient (kt2) was explored through theoretical analysis, finite-element simulations, and measurements. To enable crack-free AlScN above patterned electrodes, we develop an 8-in. wafer-level transfer flow (Si–SiO2 bonding) that decouples AlScN deposition from bottom-IDT patterning and improves film crystallinity. Placing Mo reflectors around the bus and tether regions forms a low-acoustic-velocity frame that impedes lateral standing-wave build-up and reflects leakage at anchors, removing the parasitic responses between series and parallel resonance peaks. Prototypes operating near 412.8 MHz exhibit spurious-free spectra, Bode-Qmax up to 2387, and kt2 of 2.8%, yielding FoM = Bode-Qmax⋅kt2 = 66.83.