PULL-IN INSTABILITY OF CIRCULAR PLATE MEMS: A NEW MODEL BASED ON STRAIN GRADIENT ELASTICITY THEORY

Size-dependent characteristics have been widely observed in microscale devices. For the electrostatically actuated circular microplate-based MEMS, we propose a new model to predict the size-dependent pull-in instability based on the strain gradient elasticity theory. The model embeds three material length scale parameters (MLSPs), which can effectively predict the size-dependent pull-in voltage. The model can be reduced to the classical continuum model when MLSPs are ignored. The results show that the normalized pull-in voltage predicted by the present model increases nonlinearly with the decrease of the size scale of the plate, and the size effect becomes prominent if the characteristic dimension (plate thickness) is on the order of microns or smaller. The effects of the plate thickness and gap on the pull-in voltage are also investigated.The work is supported by Independent Innovation Fund of Shandong University (2011GN055). XC acknowledges support from National Science Foundation (CMMI-0643726), DARPA (W91CRB-11-C-0112), Changjiang Scholar Program from Ministry of Education of China, and National Natural Science Foundation of China (11172231 and 50928601)