Relationship between film stress and dislocation microstructure evolution in thin films

Abstract

AbstractMetals with one or more dimensions in the submicron regime are widely used in MEMS devices. Device stresses often exceed the strength of the corresponding bulk material by an order of magnitude and can lead to a variety of mechanical failures. At moderate temperatures, high stresses occur because dislocations are unable to move to relax the stress. This is partly because of an elastic dimensional constraint, but complex dislocation behavior, such as junction formation, annihilation, and nucleation, are also observed. In this report, we present results from analytical models, cellular automata simulations, and large-scale dislocation dynamics simulations of submicron films to examine the relationship between dislocation interactions and material strength. Our results reveal a complex relationship between dislocation interactions and stress inhomogeneity that arises from the stress fields of the dislocations. We show that the stress inhomogeneity increases both the likelihood of interactions and acts to increase the strain hardening rate.