© Max-Planck-Institut für Eisenforschung GmbH

Temperature effects on the mechanical behavior of single and multilayer thin films on flexible substrates

The production of reliable flexible electronic devices are believed to be a future key-technology. The material systems thereby suffer from various loading conditions (e.g. temperature variation, monotone and cyclic strains,…). The pronounced differences in mechanical behavior between metal and polymer makes film/substrate systems prone to failure.

In this study, various different as-deposited and annealed metal films on polymer substrates were investigated with different characterization techniques during straining. Thereby, films with various thicknesses awere strained in situ under the atomic force microscope (AFM) or in the scanning electron microscope (SEM) to determine the cracking and deformation behavior of the thin films.

Additionally, tensile tests were performed in a synchrotron to measure the lattice strains and stresses in the film under tensile load using synchrotron diffraction (sin²ψ method). With the simultaneous measurement of the resistance, we were able to analyze the stresses and strains that were necessary for the crack initiation visible by the electrical failure of the film.

The combination of these techniques with the characterization of the microstructure and interfaces allowed us to sustain a complete impression of the material system under an applied load and at different temperatures.

Figure: AFM image of a 200 nm thick Cu film with a 10 nm Cr interlayer on 50 µm polyimide strained to 15 % strain. Cracks and necks (localized thinning) are visible on the Cu surface.
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