Research On Processing Technique Of MEMS Omnidirectional Inertial Switch

With the development of MEMS technology, micro sensors and micro actuators have been used in some industrial fields. MEMS inertial switches, also known as to shock sensors or threshold accelerometers, have great potential to be widely used in toys, accessories, automotive, military weapons and industrial applications. Therefore, the fabrication method of inertial switches has attracted more and more attention. In this paper, the process technique of MEMS inertial switch based on the UV-LIGA technology was studied, and a kind of MEMS omnidirectional inertial switch was fabricated by UV-LIGA technology. The MEMS omnidirectional inertial switch has six-layer structure. The research provides reference for the development of process technique of MEMS inertial switch.First, based on the existing process techniques, a fabrication method of MEMS omnidirectional inertial switch combined with UV-LIGA technology was presented in this paper. By introducing some basic technologies, such as micro electro forming, sacrificial layer technology, the choice of sacrificial layer material, terrace photoresist technology, the sacrificial layer material was determined, and a method was used in the terrace photoresist technology to improve the thickness uniformity of electro formed layer and photoresist layer.Then, based on UV-LIGA technology, a kind of MEMS omnidirectional inertial switch was fabricated by the terrace photoresist technology in this paper. And SU-8 photoresist was chosen as the sacrificial layer material in the fabrication process. The fabrication process consisted of substrate treatment, alignment marks etching process on the back of substrate and fabrication of six-layer structure. Meanwhile, some process problems were studied, such as poor adhesion property among electro forming deposit layers, low interlayer alignment accuracy and efficiency in multilayer microstructures fabrication, high stress in electro formed layer, difficulty of preparing the SU-8 mould with high aspect ratio and removal of SU-8 layer were solved effectively. By solving these problems, the rate of finished micro switches is increased.Finally, in the paper, MEMS omnidirectional inertial switch was packaged, and tests were done. Through test of structural parameters, manufacture error of three key structure dimensions was provided. The three structure dimensions were spring width, gap between limit column and proof mass and distance between radial flexible and proof mass, respectively. Then shock test was carried out, and the test results show that when half-sine accelerations are applied to the switch from a direction deviated 45°with the X-axis direction and Z-axis direction, the switch can obtain a long contact time, which means the switch can get more reliable and stable output signals. The results indicate that the flexible structures are beneficial for prolonging contact time.