Dr. Philippe Goudeau, Research Director at the French National Center for Scientific Research (CNRS), Physics and Mechanics of Materials Department, Pprime Institute, France

Title: Strain engineering in ITO thin films deposited on polymer: a synchrotron study

Abstract: Mechanical properties of composite materials are highly relevant for a wide variety of technological applications such as flexible perovskite light-emitting device, biosensors, and optical gratings. The mechanical behavior of thin films depends on the microstructure (grain texture, size defects ...). To get closer to the load conditions in actual use but also to simulate the phenomena of aging, controlled tests of biaxial strain on composites formed by thin films deposited on polyimide substrate (Kapton ®) are performed. Understanding strain effect on the microstructure and physical properties of functional oxide type materials is a major challenge in materials science and technological applications such as stretchable microelectronics. This is the case for transparent conductive oxides - TCO films such as Indium (tin) oxides - ITO. Most oxides significantly change their electronic structure upon the influence of elastic strain, with consequences, for instance, in transport improvement. The high elastic strains necessary (up to 1% and more) can only be achieved in absolutely perfect materials, which can more likely be found at small length scales such has ultra-thin films. By applying constraints on the thin film/ polymer composite, it is possible to modulate in a controlled way the physical properties of the thin film. Our objective is to characterize in-situ the physical properties (electrical conductivity) of ITO thin films during cyclic mechanical testing. The oxide phase is studied simultaneously in-situ under step by step and controlled biaxial loading/unloading extending our previous studies. The mechanical behavior is analyzed plotting the X-rays strains as a function of the applied digital image correlation - DIC strains as well as the physical properties thanks to the evolution of resistivity as a function of strain.

Keywords: XRD, DIC, mechanical behavior, 4 point probes, resistivity, TCO, functional oxide thin films