Mechanical properties, stretchability and fatigue behavior of metal thin films

Abstract

Thin metal films with thickness well below 1μm are widely used as functional and structural elements in microelectronic devices and large-scale integrated circuits including thin-film solar cells, electrical sensors and electronic textiles. Decreasing dimensions of micro-electronic and micro-mechanical devices have motivated research on the micro- and nano-scale mechanical behavior of materials. Much work has gone into characterizing the mechanical behavior of thin metal films and observed that the mechanical properties of thin-films are very different from those of bulk counterparts. Conventional mechanical testing methods used for bulk materials have difficulty in obtaining precise stress-strain curves for thin films and capturing size-dependence. Thus, much attention has been directed to experimentally measure the mechanical properties of thin films by a variety of techniques and to model their behavior using phenomenological continuum plasticity constitutive relations and discrete dislocation descriptions of plastic flow. In this thesis, we introduce a novel experimental technique based on the membrane deflection experiment (MDE) for resistively heated specimens to investigate the stress-strain behavior of thin films at elevated temperatures. Specimens were designed to have homogeneous strain at the gage section when a line load is applied at the middle of the span and to have uniform temperature distribution at the gage section. Finite element method (FEM) simulation were performed to ensure the assumptions made for mechanical modeling and to estimate the temperature profile of the gage section. Through this method, we were available to obtain repeatable stress-strain curves of 0.5um and 1um thick Cu thin films at elevated temperatures. Motivated by the research of metal thin film on elevated temperature, we````ve also built a new tester which enables in-situ SEM tensile testing of metal thin films while observing the microstructure change. For in-situ...