Corrosion-Resistant Ultrathin Cu Film Deposited on N-Doped Amorphous Carbon Film Substrate and Its Use for Crumpleable Circuit Board.

Copper (Cu) is widely used as an industrial electrode due to its high electrical conductivity, mechanical properties, and cost-effectiveness. However, Cu is susceptible to corrosion, which degrades device performance over time. Although various methods (alloying, physical passivation, surface treatment, etc.) are introduced to address the corrosion issue, they can cause decreased conductivity or vertical insulation. Here, using the nitrogen-doped amorphous carbon (a-C:N) thin film is proposed as a substrate on which Cu is directly deposited. This simple method significantly inhibits corrosion of ultrathin Cu (<20 nm) films in humid conditions, enabling the fabrication of ultrathin electronic circuit boards without corrosion under ambient conditions. This study investigates the origin of corrosion resistance through comprehensive microscopic/spectroscopic characterizations and density-functional theory (DFT) calculations: i) diffusion of Cu atoms into the a-C:N driven by stable C-Cu-N bond formation, ii) diffusion of N atoms from the a-C:N to the Cu layer heading the top surface, which is the thermodynamically preferred location for N, and iii) the doped N atoms in Cu layer suppress the inclusion of O into the Cu lattice. By leveraging the ultrathinness and deformability of the circuit board, a transparent electrode and a crumpleable LED lighting device are demonstrated.