Abstract
In this work, we demonstrate a 700 MHz one-port aluminum nitride (AlN) S0-mode residual stress-resilient Lamb wave resonator (LWR) with lithographically defined acoustic boundaries based on a CMOS-compatible 8-inch MEMS process, exhibiting a high-quality factor (Q) of 2,422 and an electromechanical coupling factor (k <sub>eff</sub> <sup>2</sup> ) of 1.05%. Although a well-defined shallow “etch sandbox” provides a higher quality factor and better mechanical robustness to the LWR over conventional isotropic silicon etching processes, the performance of the LWR becomes sensitive to the deformation caused by residual stress in the thin films. In this work, with the assistance of laser scanning confocal microscopy, the physical contact between deformed LWR and the bottom of the cavity is identified as a new failure mode. We investigate three LWRs with different aspect ratios and anchors, revealing that the width of the anchors is the key to suppressing out-of-plane deformations. The residual stress-resilient wide-anchor LWR shows a promising f-Q product of 1.69 × 10 <sup>12</sup> and k <sub>eff</sub> <sup>2</sup> > 1.05%, which is comparable with that of state-of-the-art AlN LWRs.