Investigation On The Bifurcation Problem Of Micro-nano Scale Metallic Film Under Tension

Micro-nano scale metallic film has been widely used in the electronic information,energy, biological, medical and other fields. Thin film in the process of work oftensubject tensile load. When the load reaches a certain value, membrane structurebifurcates instability under a small increment. Then the film will appear micro-crackand rupture. Due to the bifurcation on the membrane will directly affect the reliabilityand service life of the components, so it is very important to determine the bifurcationpoint of micro-nano scale metallic film and do research on this problem. The mainpurpose of this paper is to study on the bifurcation problem of micro-nano scalemetallic film under tension by using electrical resistance property.A theoretical analysis of resistance is given based on the transformation of thinfilm under tension. We established the relation of changing resistance among thestrain in an elastic deformation stage, even plastic deformation stage, and localizationstage.The resistance change measurement system and a tensile loading device aiming atthe film/substrate structure are independently designed and developed, which couldstretch the film/substrate structure in situ at high precision and get the real-timeobservation of the morphology and changing process of metallic film’s surface withhigh magnification optical microscope. The experimental investigation focuses on thecopper film deposited on polyimide substrate. The deformation and failure process ofthe copper film was analyzed and discussed. We find that the bifurcation point is notsingle, and it may be existing in various positions. The appearance of micro-cracks infilm’s surface is periodic. The micro-cracks keep parallel and perpendicular to thedirection of stretching.The relationship between the change of resistance and strain was obtained bymeasuring the change of resistance of the copper film under uniaxial tensile loading.The relation curve obtained was compared with the result of the theory deduction todetermine the bifurcation point of the copper film under tension. The results show thatpolyimide-supported copper film ruptures when the overall strain just exceeds thebifurcate initiation strain, which is not far beyond its elastic limit. In the process, thereare little plastic deformation and localization. There are a very small increasing rate of resistance in the elastic stage and a slightly larger increasing rate of resistance in theplastic stage, while a rapidly increasing rate of resistance after micro-cracks appearedon the film surface.Through altering the loading rate, its influence on the bifurcation is studied. Theresults show that the initial resistance plays a significant role on the bifurcation ofmetallic film under tension. The increase of stretching rate within a certain range has apromoting effect on the bifurcation.