EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Thin film architectures often incorporate easy to fracture brittle layers for functionality. In flexible electronic applications, these brittle layers (e.g. Mo or Cr) are needed as adhesion, diffusion barrier or protective layers, while more ductile layers (e.g. Al or Cu) are deployed as conductive layers. Using dc magnetron sputtering, three thin film architectures of Mo and Al layers were deposited on flexible polyimide (PI) substrates for in-situ biaxial tensile tests with X-ray diffraction analysis. The three architectures, Al/PI, Al/Mo/PI and Mo/Al/PI, were prepared to demonstrate the impact of the brittle layers on the fracture behavior under quasi equi-biaxial tensile loading. Variations of the layer order and the Al layer thickness in the three material systems enabled more insights into the underlying deformation and fracture mechanisms, and the significance of layer arrangement in simple multilayers. The in-situ quasi equi-biaxial tensile tests, performed at the Diffabs beamline (Synchrotron Soleil, France), allowed the extraction of film stress and full width at half-maximum data as a function of strain. These data were used to differentiate between elastic and plastic deformation domains of the individual layers, as well as necking and fracture. Post-mortem scanning electron microscopy analysis of the surface and cross sections revealed different fragmentation behavior not only dependent on the architecture, but on the thickness of the Al layer as well. It will be shown that, the layer order strongly impacts the observed mechanical behavior, particularly for the brittle Mo layers, and further changes regarding deformation and fracture mechanisms of the three thin film architectures (Al/PI, Al/Mo/PI and Mo/Al/PI) are observed as a function of ductile layer thickness.