A composite structure comprises a copper layer and first and second graphene layers sandwiching the copper layer, wherein the composite structure provides electron-path tunnels between the copper layer and the first and second graphene layers. The electron-path tunnels may enhance the electrical conductivity. A multilayer composite structure comprises a first copper layer, a first graphene layer on the first copper layer, a second graphene layer on the first graphene layer, and a second copper layer on the second graphene layer.