Analysis Of Diffusion, Stress And Deformation Of Microstruetures Applied By Loading Of Mechanical And Electro-mechanical Coupling

The structure damage caused by the interaction of chemical and mechanical effects is in-timately associated with the diffusion of atoms or ions. Diffusion of atoms in structure can lead to the evolution of local stresses. On the other hand, the stresses produced during prac-tical manufacture and application can also influence the diffusion process. Therefore, under-standing of mass diffusion and migration is significant for analyzing and controlling the age-ing and reliability deterioration of long life structure. Studies on the diffusion behavior, stress and deformation under stress and electro-mechanical coupling effects have been systemically investigated in this contribution. The main contents and conclusions are as follows:A self-consistent diffusion model including the coupling effects of diffusion and stress is developed under the frame of the thermodynamic theory and Fick's law. With the help of fi-nite difference method, the evolutions of concentration and diffusion-induced stress during diffusion process and the interaction between diffusion and stress concentration are analyzed. Results show that the external stress field will accelerate the diffusion process, and thus pro-mote the value of concentration while reduce the magnitude of stress induced by diffusion when the direction of diffusion is identical to that of external stress gradient with the coupling effects. The stress concentration around geometrical discontinuities and defects could be re-lieved by diffusion of solute.According to the equilibrium conditions of force and moment, the exact closed-form so-lutions of curvature and diffusion-induced stress in the film/substrate structure are derived. And then, the self-consistent diffusion model involving the coupling effects of thermal misfit stress and diffusion-induced stress are developed. The theoretical model is available for ana-lyzing the diffusion behavior, diffusion-induced bending and stress with the coupling effects of diffusion and stress. Results indicate that thermal misfit stress can extend or shorten the time for achieving the saturated state, but won't change the magnitude of curvature at saturated state. The diffusivity and other structure parameters have great influence on the diffu-sion-induced curvature and stress distribution, which are meaningful for structural optimiza-tion of film/substrate cantilever-based device.Based on energy minimization principle, the analytic solutions of diffusion-induced bending curvature and stress in film/substrate system are derived with coupling effects of rough surface and surface energy. The effects of surface roughness and residual surface stress have been analyzed quantitatively. Results show that the diffusion-induced stress and bending of film/substrate structure will dramatically changes with the variation of surface roughness and residual surface stress of the top and bottom surface.Aiming at the failure of electronic packing and interconnection structure under the coupling effects of stress and electric field, tensile creep experiments on creep behavior of copper have been carried out. The creep behavior is analyzed under different stress and elec-tric current. Based on the grain boundary diffusion theory, a simple expression has been de-rived for the prediction of the steady state creep rate. According to the comparison of experi-ment results and theoretical predictions, the steady creep strain rate and creep strain of copper increase with increasing stress and electric current. The creep deformation is controlled by grain boundary diffusion at lower stress level, while it's controlled by dislocation glide or climb at higher stress level. The theoretical predictions of steady creep strain rate agree with the experiment results under low stress and electric field.