Determining effective crack lengths from electrical measurements in polymer-supported thin films

Although it is evident that the formation of multiple through-thickness cracks in polymer-supported thin films leads to an increase of the electrical resistance, the attempts to quantify the dependence of resistance growth only based on the induced crack density have not yet been successful. In this paper a recently developed relationship, representing the resistance growth as a two-variable polynomial function of crack density and crack length, is utilized to analyze the crack patterns induced by monotonic and cyclic tensile loading of 250 nm thick Cu films with a 10 nm Cr adhesion layer on polyimide. It is demonstrated that by knowing the in-situ resistance during deformation and post-mortem linear density of induced cracks, it is possible to extract the effective crack lengths, a parameter which is often ignored during experimental characterization of the damage induced through mechanical loading. The described algorithm is not only much more cost-effective in comparison to time-consuming in-situ microscopy methods, it also reflects the reliability of the whole sample rather than of only selected surface areas.