The estimation of residual stresses by the brittle thin film's initial cracks on a ductile substrate subjected to tensile stresses

Thin metal films in the nanometer range are extensively used for electronic and optoelectmnic devices. However, the residual stress has a profound impact on the durability of the devices during their lifetime. This paper developed a two-dimensional (2D) elastic model to study the residual stress and opening-mode fractures (OMFs) in a film/substrate assembly. The fracture strength expressed by crack length is derived by the strength criterion. This paper also studies fragmentation of 100-400 nm thin Cr films on 125 mu m polyimide substrates. The residual stress in the coating process is estimated based on the onset strains of fragmentation. For films with thicknesses of 100 nm, 200 nm, and 400 nm, the estimated residual stresses are -1.204 GPa, -0.889 GPa, and -0.305 GPa respectively. This method shows more convenient than some traditional methods (including the use of X-ray diffraction technique or other methods of determining curvature). The tensile fragmentation tests would provide data to verify the accuracy of the estimation during crack accumulation; a good agreement is found between the experimental results and those predicted using the estimated residual stresses.

Automated summary

This study focuses on the residual stress and opening-mode fractures in nanometer thin metal films, developing a two-dimensional elastic model and estimating residual stresses in film/substrate assemblies. Tensile fragmentation tests confirm a good agreement between experimental results and estimated residual stresses.