Bistable MEMS Micro Switch Design

MEMS Acceleration switch is an inertial device which integrates functions of sensing, judging and actuating. It not only senses acceleration but also performs on-off functions under the effects of the threshold forces. The domestic and abroad research show that there are still some difficulties and problems to be solved in its basic design theory,research methods and fabrication technologies. In particular, an effective switch-based design theory and research method is the extreme lack of. The present design mainly relies on the trial and error method, which results high costs and lacks high performance micro-acceleration switch in our domestic markets.According to threshold characteristics of bistable structures and working principle of acceleration switch, this paper established adhesion bistable micro-acceleration switch models. Application of Coulomb's law, the electric force calculation formula which considers the edge effect has been derived from the theory of electrostatic structure capacitance. This paper analyses the electric field force and elastic force with the changes of contact distance. Based on quantum mechanics theory, Casimir force calculation formula has been obtained, which analyses the Casimir force changes with contact distance. Based on micro-continuum theory, Van der Waals force has been obtained, which analyses the Van der Waals force changes with contact distance. Based on Reynolds equation, the analytical formula of gas-film damping inside two parallel plates has been obtained, which analyses gas-film damping coefficient changes with contact distance. This paper respectively makes static and dynamic analysis about micro-switches of silicon-based and copper-based. By the static analyzing, silicon-based micro-switches acceleration threshold value is 6.8g and copper-based micro-switch acceleration threshold is 24.6g. Dynamic analysis obtains two results, one is silicon-based micro-switches with acceleration threshold 6.84g, response time 0.014s, and another is copper-based micro-switch with acceleration threshold 24.74g, response time 0.036s. According to Fowler-Nordheim formula analyses changes of tunnel current in the switch contact. This paper establishes the three-dimensional models and two-dimensional engineering drawings by PRO/E and AUTO/CAD, and micro-switch sample have been obtained.