Barbara Putz

Electro-Mechanical testing of conductive materials used in flexible electronics

The use of flexible electronics has increased in recent years. In order to have robust and long lasting flexible displays and sensors, the combined electro-mechanical behavior needs to be assessed. The most common method to determine electrical and mechanical behavior of conductive thin films used in flexible electronics is the fragmentation test, or uniaxial tensile straining of the film and substrate. When performed in situ fracture and deformation behavior can be determined. The use of in situ electrical resistance measurements can be informative about the crack onset strain of brittle layers, such as transparent conductors, or the stretchability of metal interconnects. The combination of in situ electrical measurements with in situ X-ray or confocal laser scanning microscopy can provide even more information about the failure mechanisms of the material systems. Lattice strains and stresses can be measured with X-rays, while cracking and buckle delaminations can be studied with confocal laser scanning microscopy. These new combinations of in situ methods will be discussed as well as methods to quantify interfacial properties of conductive thin films on polymer substrates. The combined techniques provide valuable correlated electrical and mechanical data needed to understand failure mechanisms in flexible devices.

Electromigration in Gold Films on Flexible Polyimide Substrates as a Self-healing Mechanism

The study of electromigration (EM) in metallisations for flexible thin film systems has not been a major concern due to low applied current densities in todays flexible electronic devices. However, the trend towards smaller and more powerful devices demands increasing current densities for future applications, making EM a reliability matter. This work investigates EM in 50 nm Au thin films with a 10 nm Cr adhesion layer on a flexible polyimide substrate at high current densities. Results indicate that EM does occur and could be used as a self-healing mechanism for flexible electronics. GRAPHICAL ABSTRACT