van der Waals Contact Engineering of Graphene Field-Effect Transistors for Large-Area Flexible Electronics.

Graphene has great potential for high-performance flexible electronics. Although studied for more than a decade, contacting graphene efficiently, especially for large-area, flexible electronics, is still a challenge. Here, by engineering the graphene-metal van der Waals (vdW) contact, we demonstrate that ultralow contact resistance is achievable via a bottom-contact strategy incorporating a simple transfer process without any harsh thermal treatment (>150 °C). The majority of the fabricated devices show contact resistances below 200 Ω·μm with values as low as 65 Ω·μm achievable. This is on par with the state-of-the-art top- and edge-contacted graphene field-effect transistors. Further, our study reveals that these contacts, despite the presumed weak nature of the vdW interaction, are stable under various bending conditions, thus guaranteeing compatibility with flexible electronics with improved performance. This work illustrates the potential of the previously underestimated vdW contact approach for large-area flexible electronics.