Mechanical integrity and behavior of thin films and their applications in MEMS

This dissertation, consisting of three papers, presents the mechanical integrity and behavior of thin films and their applications in Micro-electromechanical Systems (MEMS). In the first paper, a solid-mechanics model is derived for the electromechanical deformation of a thin film in a capacitive MEMS-RF-switch and the associated "pull-in" phenomenon for both a 1-D rectangular bridge and a 2-D axisymmetric plate. The ratio of film-pad gap to film thickness (g/h) is found to play a significant role in the device behavior. The proposed analytical solution has some advantages over the existing models in formulating the design criteria.; In the second paper, an elastic model is constructed to account for "pull-in" in terms of the applied voltage, the residual stress, and the film-pad gap for a 2-D axisymmetric film. The new model determines the validity range of the classical solution and accounts for the deviation for large elastic strain and high membrane stress. Both tensile and compressive residual stresses are allowed. New design criteria are derived for MEMS devices.; In the third paper, an elastic model is constructed to account for the phenomena for ranges of film-pad gap, residual stress and fringing field effects for a 1-D rectangular bridge. The results compare favorably with finite element analysis (FEA) in the literature, and possess much advantage over other available closed-form solutions.; In Appendix A, a rigorous theoretical model is constructed for the contact mechanics of the transition from pre- to post-"pull-in" and the elastic recovery of the film at the removal of external electrostatic potential. The contact mechanics theory is extended for the design criteria of microstructure presented in Appendix B.