A Nonlinear MEMS Inertial Switch Fabricated by Induction-Electrode Through-Mask Electrochemical Micromachining

To improve the threshold accuracy of inertial switches, this study proposes a monolithic metal MEMS inertial switch with nonlinear springs. The switch uses two sets of inclined beams with asymmetric initial angles as suspension springs. Geometric nonlinearity produces low displacement sensitivity away from the design threshold and high sensitivity near the threshold. This response improves threshold discrimination and reduces the deviation between the actual and design thresholds. A nonlinear switch and a linear reference switch are designed with the same static threshold of 27.5 g. Their responses are compared using Abaqus static and explicit dynamic simulations. Both switches are monolithically fabricated from 50 μm thick 304 stainless steel by induction-electrode through-mask electrochemical micromachining (IETMEMM). Key dimensional deviations are below 2.5%. Drop-weight tests show measured nonlinear-switch thresholds of 27.8, 27.8, 26.9, and 25.4 g under half-sine shocks with pulse widths of 4, 6, 8, and 10 ms, respectively. The maximum threshold deviation is 2.1 g. The overall threshold accuracy is 92.4%, substantially higher than the 56.0% of the linear reference switch. This work combines a nonlinear threshold-regulation mechanism with monolithic IETMEMM fabrication and provides a new strategy for metal MEMS inertial switches with high threshold accuracy.