Characteristics of Highly Area‐Mismatched Graphene‐to‐Substrate Transfers and the Predictability of Wrinkle Formation in Graphene for Stretchable Electronics

Abstract The indirect‐transfer process is the primary technique used to fabricate graphene electrodes on an arbitrary substrate. The area mismatch between the initial graphene‐Cu substrate and the transfer substrate causes irregularities in the transferred graphene film; wrinkles are one of the primary results. In this paper, it is found that nanoscale surface roughness (wavelength below 500 nm) in the graphene‐Cu 3D substrate (with up to a 4 µm cavity) results in amplified wrinkles (amplitude over 24.4 nm) or newly generated wrinkles (low‐amplitude corrugations) that depend on the corrugation amplitude. Further, a deep‐cavity graphene‐Cu structure (≈20 µm) causes predictable formation of wrinkles in terms of direction and position. The direction of the wrinkle is decided by the true area difference, which creates a strain difference in two perpendicular directions. For unidirectional wrinkles, the position is decided by the strain‐gradient difference. The understanding of highly area‐mismatched transfers facilitates the fabrication of predictable well‐defined wrinkles on an arbitrary substrate. Wrinkled graphene shows better electrical properties (≈1 kΩ between contacts) under strained conditions than regular graphene film.