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Chullhee Cho1 Pilgyu Kang1 SungWoo Nam1

1, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States

In flexible electronics, metal electrodes or metal contacts are essential components, but they are most susceptible to external mechanical loading. Metals such as copper or gold intrinsically suffer from poor mechanical flexibility where they can withstand low tensile strains (<2%). Furthermore, metals are often prone to fatigue failure resulting in a significant degradation of device performance during numbers of operation cycles in practical applications. Crucial key aspects of flexible electronic devices, thus, would be strain-tolerance to large deformation and mechanical robustness under the cyclic loading. To achieve advanced strain tolerance and mechanical robustness, many recent works on incorporating the outstanding mechanical properties of atomically-thin materials, especially graphene, as a composite material were reported. However, severe filler agglomeration hinders a realization of comparable electrical conductivity to the conventional metal electrodes. In contrast, several other approaches focused on structuring the conventional metal electrodes. Despite their enhanced flexibility, the resistance of flexible electrodes often sharply increased with even relatively small strains after a few thousands of cycles. In this presentation, we discuss a simple approach of inserting multilayer graphene under the metal electrode, which can be readily applied to versatile flexible electronics. We investigated the underlying mechanism of the mechanical reinforcement via in-situ bending test with environmental scanning electron microscope. The axial bending test results revealed thickness dependency of multilayer graphene on strain tolerance enhancement. Metal electrodes integrated with multilayer graphene sustained larger bending strains (>300%) compared with metal electrodes with single layer graphene. Furthermore, in contrast to a sharp increase measured in bare metal electrode device, the resistance gradually increased in the multilayer graphene integrated electrodes as bending strain increased. This new approach enables flexible electronics to operate without an abrupt performance failure at large strains.

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