Stretchability of PMMA-supported CVD graphene and of its electrical contacts

Abstract

The remarkable mechanical robustness and excellent electrical/thermal properties make graphene a promising candidate for future flexible, stretchable and bio-integrated electronics. In practice, many soft electronics such as the graphene electronic tattoos (GETs) demand the chemical vapor deposited (CVD) graphene to be supported by a deformable substrate. Moreover, various conductive overlayers need to directly laminate on graphene to make electrical contacts. To investigate the mechanical reliability of CVD graphene in these situations, we fabricated CVD monolayer graphene supported by ultrathin poly(methyl methacrylate) (PMMA) substrate and also placed gold/polyethylene terephthalate (Au/PET) and graphene/PMMA (Gr/PMMA) overlayers on graphene. The stretchability of the Gr/PMMA and the overlayer-Gr/PMMA interface was characterized by electrical resistance change during uniaxial tensile tests. Combined with in situ microstructure and Raman investigation, we identified four deformation/fracture stages of Gr/PMMA—pre-cracking elastic deformation, limited micro-cracking in graphene, extensive cracking in graphene, and macro-cracking in PMMA. While micro-cracks emerged in graphene at very small strain (~0.9%), the electrical conductivity of the Gr/PMMA specimen remained up to tensile strains of ~14.5%. In contrast, 100 nm-thick Au film supported by the same PMMA substrate fully ruptured after tensile strains of ~1%. When laminating Au/PET and Gr/PMMA over Gr/PMMA, we found that the Au/PET- Gr/PMMA interface is very vulnerable but the Gr/PMMA- Gr/PMMA interface behaves very similar to intact Gr/PMMA electromechanically. The cyclic behaviour of Gr/PMMA, the effects of PMMA thickness and adhesion are also briefly discussed. The present experimental study provides fundamental insight into the failure of ultrathin polymer-supported graphene and its electrical contacts, which is critical for designing future graphene-based soft electronics.