Development Of Omnidirectional Metal Micro-inertial Switch With Load Direction Identify

With the development of MEMS technologies,a variety of MEMS products proliferate.As a passive device,MEMS inertia switch,with its advantages of small volume,low cost and strong anti-interference ability,is widely used in the fields of unattended remote monitoring,industrial transportation of special cargo,Internet of Things(IOT)and fuse technology.In this paper,considered the working characteristics of inertia switches in different sensitive directions,a low-g MEMS inertia switch with load direction identify was designed for the modern logistics transportation.The main contents are as follows:The application environment was firstly analyzed,and the design objectives such as low threshold value,omnidirectional sensitivity and identifiable direction of the MEMS inertia switch were set.Corresponding performance indexes were preset.Based on the simplified physical model of the MEMS inertia switch,the mathematical equation containing acceleration signal,switch structure parameters and natural frequency of induction units was established.Besides,the changing rules of the influence of each factor on the switch performance were revealed through the method of control variable and numerical calculation.According to these changing rules,the natural frequency of the switch,the structure and dimension of the "spring-mass",the structure of the electrode and its position were determined in turn.Finally,the design of the MEMS inertia switch was preliminarily completed with low stiffness C-type spring,octagonal mass and mutually insulated electrodes.Based on the design results of the MEMS inertia switch,the performances of the switch were simulated by ANSYS software.Modal simulation was used to obtain the vibration shape and the corresponding natural frequencies of the switch.Simulated results show the acceleration thresholds of the switch in XOY plane distribute in the range of 8-9g,which verifies the effectiveness of the spherical electrode on the switch threshold precision.Besides,the ANSYS dynamic simulation module was used to analyze the dynamic performance of the switch.Under the acceleration signal with 10 g amplitude and 5ms pulse width in different directions,the axial response time of the switch is 1.53 ms and the contact time is 290 s,the radial response time is 1.35 ms and the contact time is greater than 300 s.Finally,on account of the complexity of the application environment,the adaptability of the inertia switch was analyzed.The optimal environmental parameters and the anti-overload performance of the switch were simulated and solved in ANSYS.Based on terrace photoresist sacrificial layer technology and precise electrochemical deposition processes,the MEMS inertia switch was fabricated.The negative deviation caused by exposure diffraction,photoresist swelling and removing corrosion was compensated by the method of line-width compensation.The method of thickness compensation was used to adjust thickness deviation caused by flattening treatment.The overall dimension of the fabricated switch is 5300μm×5300μm×270μm and the minimum line width is 20μm.In order to verify the working performance of the switch,the package and test were carried out successively.The switch was conducted quasi-static and dynamic tests by the centrifuge device and the dropping hammer respectively.The results show that the dynamic threshold of the switch is between 7.9-11.3g,and the response time in each direction is less than 2ms.The axial contact time of the switch is 240μs,the radial contact time is 300-460μs,and the collision direction can be recognized in the XOY plane.Structures of the switch remain intact after the overload shock.