Abstract: A low-g (1 g~30 g) micro inertial switch based on planar rectangular helical spring was developed. Single crystal silicon with perfect mechanical property was used as the structure material. The onstate threshold fomula of the inertial switch was derived with the Castigliano’s theorem and the linear elasticity theory of material mechanics. The relative error is less than 3% between the theoretic and the ANSYS simulation results. Designs of double contact points and low natural frequency of the mass-spring structure were proposed to improve the environment adaptability of the micro inertial switch. The fabrication process utilizing SOI wafer with double buried layers was carried out to improve the precision of structure parameters. The micro inertial switch was fabricated using crucial technology including KOH etching, ICP etching and spray coating. The bulk of chip is about 7 mm×7 mm×1.3 mm in size. The laboratory centrifuge tests were performed on the fabricated inertial switch to measure the on-state threshold. The test results show that the threshold value is about 6.45 g with a closed precision of 0.5 g. Amount of on-state threshold transfer caused by environment tests including random vibration test and high temperature test is less than 0.5 g, which shows that the developed inertial switch has better environment adaptability and mechanical property.  

Key words: low-g micro inertial switch, planar rectangular helical spring, Castigliano’s theorem, SOI wafer with double buried layers, microelectromechanical system（MEMS）