In-situ CLSM characterization of deformation and fracture behavior of (Cu, Cr) metal thin films on flexible substrates

Magnetron sputter deposited Cu thin films on an insulating polymer substrate such as polyimide are frequently used as flexible printed circuits. Understanding the tensile behavior of films deposited on polymer substrates is critical to optimize them for applications requiring flexibility. In this study, single layer copper, chromium (Cu, Cr) films, and Cu/Cr bilayer films were deposited on flexible polyimide substrates by magnetron sputtering. The mechanical behavior of these systems was investigated under tensile loading using the advanced in situ confocal laser scanning microscope (CLSM) technique. The results demonstrate that the buckled shapes, crack density and crack spacing are closely related to the film material and film thickness. The Cr interlayer greatly influences the cracking behavior of the overlying ductile Cu film. Moreover, the in situ tensile experiments indicate that the crack density of the film is obviously related to the loading rate. The findings in this work provide a qualitative guidance for the material selection and structural optimization of metal-based single layer and bilayer flexible electronics.