Mechanical Shock, Electrostatic Force And Damping Research On Microbeam

The application of MEMS products becomes more and more widely in recent years,understanding the behavior and modes of failure of micro-electro-mechanical systems(MEMS) under different conditions is crucial to enhance their reliability and optimize theirdesign. Mechanical shock is key problem to MEMS microstructure, a MEMS device can beexposed to shock loads during fabrication, transporting and in service. Short circuits, fracture,and stiction are common failure modes caused by mechanical shock. Electrostatic actuation isthe most common method of actuation in MEMS devices. For MEMS devices actuated byelectrostatic force, the coupling effect between shock and electrostatic force may lead topull-in instability for a stable system. While damping is very important in MEMS devices,which strongly affects their performance, design and control.In this work, the response of microstructure under shock is firstly analyzed based onlumped-parameter model and distributed-parameter model. The effect of the motion of aprinted circuit board (PCB) on the response of a MEMS device to shock load is investigatedbased on2-DOF systems and a distributed parameter-1-DOF model, The effect of electrostaticforce, and the combined effect of the electrostatic force and mechanical shock are investigated,a numerical method is also presented to solve the electrostatic nonlinear differential equation.The microstructure is assumed to be placed under vacuum condition, thus the air damping isneglected, the squeeze film damping is investigated through analytic method and finiteelement method in this work.It is concluded that the micro cantilever can experience the shock force as a quasi-staticload or a dynamic load, which depends on the ratio between the shock duration and naturalperiod of the micro cantilever. The effect of PCB is related to the frequency of PCB, shock load and micro cantilever. In the presence of electrostatic forces, a stable system, whichoperates far from the instability threshold, can go unstable under the effect of shock load. Thevibration of microstructure is damped by squeeze film damping, when the elastic dampingcan’t be neglected, squeeze film damping can lead to natural frequency shift for MEMSdevice under different pressures.