Design,Fabrication And Characterization Of A Low-g Passive Inertial Switch With Low-stiffness Fixed Electrode

MEMS inertial switch has the advantages of small size,low cost,high reliability and easy integration.So it has an exciting prospect in the fields of aerospace,electronic communication,automobile industry and safe transportation.In this paper,a low-g MEMS inertial switch with unidirectional sensitivity is designed for the acceleration switch applied to the airbag restraint system.The designed switch has the advantages of fast response,well contact effect and anti-overload performance.The inertial switch was fabricated based on UV-LIGA technology.Finally,the performance parameters of the switch prototype are tested by the dropping hammer and the centrifuge device,including the acceleration threshold,response time and contact time.Based on the switch basic model,the influence factors of the acceleration threshold,response time and contact time are analyzed.The relative motion between the proof mass and fixed electrode under the acceleration is studied.And then the influence of the switch structural parameters and environment load characteristics on the switch performance is analyzed.It is also revealed that the main influence factor of contact time is the stiffness of fixed electrode.Based on the research contents of the switch performance and the application environment of the airbag restraint system,the switch design approach is determined.The most appropriate natural frequency of the switch under the acceleration pulse width is determined,and then the structure and size are designed.To achieve the purpose of low-g value,four Archimedes spiral beams are used as the support springs.The external support is adopted in the mass-spring system so that the switch can identify the impact signal steadily.Compared with the one-piece structure-ring electrode,the designed cantilever type arc electrode has lower stiffness,which extents contact time.The limited post is set at the center of the proof mass to prevent the springs from yield failure.Ultimately,the simulation software ANSYS is employed to carry out the dynamic simulation of the designed switch model.Under the acceleration signal with 20 g amplitude and 4ms pulse width,the simulated response time and contact are 1.5ms,155?s,respectively.Under the 500 g overload acceleration,the simulated structural stress is less than yield limit of nickel,which shows that the switch has anti-load performance.The designed switch is fabricated by the technology of the terrace photoresist,micro electroforming,sputtering and sacrificial layer technology.In the fabrication process,the method of line width compensation is introduced to reduce the fabrication errors.The overall dimension of the fabricated switch is 3850?m×3850?m×240?m and it was packaged using ceramic package carrier.Finally,the dynamic and static performances are carried out by the dropping hammer and the centrifuge device,respectively.The test results indicate that the acceleration thresholds of the switch are between 20 g and 30 g,and the corresponding response time and contact time are 2ms,240 s respectively.There is no skip phenomenon in the contact process,which shows that the switch has better contact effect.