The influence of a brittle Cr interlayer on the deformation behavior of thin Cu films on flexible substrates: Experiment and model.
Thin metal films deposited on polymer substrates are used in flexible electronic devices such as flexible displays or printed memories. They are often fabricated as complicated multilayer structures. Understanding the mechanical behavior of the interface between the metal film and the substrate as well as the process of crack formation under global tension is important for producing reliable devices. In the present work, the deformation behavior of copper films (50-200 nm thick), bonded to polyimide directly or via a 10 nm chromium interlayer, is investigated by experimental analysis and computational simulations. The influence of the various copper film thicknesses and the usage of a brittle interlayer on the crack density as well as on the stress magnitude in the copper after saturation of the cracking process are studied with in situ tensile tests in a synchrotron and under an atomic force microscope. From the computational point of view, the evolution of the crack pattern is modeled as a stochastic process via finite element based cohesive zone simulations. Both, experiments and simulations show that the chromium interlayer dominates the deformation behavior. The interlayer forms cracks that induce a stress concentration in the overlying copper film. This behavior is more pronounced in the 50 nm than in the 200 nm copper films.
Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, D-40237 Düsseldorf, Germany ; Department Material Physics, Montanuniversität Leoben, Jahnstr. 12, A-8700 Leoben, Austria.
Vera M
VM
Marx
Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gußhausstr. 27-29, A-1040 Vienna, Austria.
Florian
F
Toth
Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gußhausstr. 27-29, A-1040 Vienna, Austria.
Andreas
A
Wiesinger
Department Material Physics, Montanuniversität Leoben, Jahnstr. 12, A-8700 Leoben, Austria.
Julia
J
Berger
Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, D-40237 Düsseldorf, Germany ; Department Material Physics, Montanuniversität Leoben, Jahnstr. 12, A-8700 Leoben, Austria.
Christoph
C
Kirchlechner
Erich Schmid Institute for Materials Science, Austrian Academy of Science, Jahnstr. 12, A-8700 Leoben, Austria.
Megan J
MJ
Cordill
Institute of Mechanics, Montanuniversität Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria.
Franz D
FD
Fischer
Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gußhausstr. 27-29, A-1040 Vienna, Austria.
Franz G
FG
Rammerstorfer
Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, D-40237 Düsseldorf, Germany.
Gerhard
G
Dehm
Finite-element simulation; Synchrotron diffraction; Tensile test; Thin films