Frequency-Angle Decoupling Design for Grid-Etched Piezoelectric MEMS Cantilevers and its Application to Quasi-Static Micromirrors

Micro-electro-mechanical systems (MEMS) cantilever actuators are pivotal in applications ranging from micro-optics to precision manipulation. However, their performance is fundamentally constrained by a trade-off between dynamic response and static deformation. To address this limitation, this paper presents a segmented grid-etched technique for MEMS cantilever actuators that decouples the resonant frequency from the tilting angle and displacement. The proposed approach strategically modulates the stiffness and mass distribution along the cantilever by etching grid patterns on the segment near the free end, thereby creating a compliant zone for large deformation while preserving the stiffness of the segment near the fixed end to maintain a high resonant frequency. The proposed cantilevers were fabricated using a Cavity SOI-based Single Piezoelectric Layer Double Release (C-SSD) process, achieving a 100% increase in tip inclination angle and a 54% increase in tip displacement, while maintaining a resonant frequency equivalent to that of a conventional uniform cantilever. Additionally, the practical application of this approach is demonstrated through its application to a biaxial piezoelectric micromirror that integrates resonant motion for the fast horizontal axis and quasi-static motion for the slow vertical axis. Notably, the grid-etched structure on the slow axis enhances the optical scan angle by 257% and the frequency-angle product by 64%, achieving a field of view (FOV) of 25°. Furthermore, the successful implementation of this grid-etched cantilever structure in a micromirror validates its potential as a general-purpose design strategy for a wide range of MEMS cantilever actuators.