A Laterally Driven MEMS Inertial Switch With Double-Layer Suspended Springs for Improving Single-Axis Sensitivity

Abstract

A novel laterally driven inertial switch with double-layer springs has been proposed and fabricated by surface micromachining technology for improving single-axial sensitivity. The symmetrical distribution of double-layer suspended springs and the constraint structures limits the displacement of the proof mass in the off-axis sensitive direction under an acceleration disturbance. The ANSYS simulation results reveal that compared with the inertial switch with one layer springs, the symmetrical distribution of double-layer serpentine springs effectively reduces the displacement of the proof mass in the off-axis direction. The design of symmetrical distribution of double-layer serpentine springs plays an important role in resisting small acceleration disturbance from the off-axis sensitive $z$ -direction, and the constraint structures can resist the large acceleration disturbance. The modal analysis, contact time, and the collision response in the inertial switch have also been simulated and discussed. Finally, the proposed inertial switch has been fabricated successfully, and the prototype is tested by a dropping hammer system. The test results show that the threshold level of the fabricated inertial switch is 272 g with 20- $\mu \text{s}$ contact time. The combined efforts of double-layer suspended springs and constraint structures effectively lower off-axis sensitivity and improve the single-axis sensitivity of the microelectromechanical system inertial switch.