Transversally Extended Laser Plasmonic Welding for Oxidation-Free Copper Fabrication toward High-Fidelity Optoelectronics

Laser direct processing is a promising approach for future flexible electronics because it enables easy, rapid, scalable, and low-temperature fabrication without using expensive equipment and toxic material. However, its application for nanomaterials with high chemical susceptibility, such as representatively Cu, is limited because severe oxidation occurs under ambient conditions. Here, we report the methodology of a transversally extended laser plasmonic welding process, which outstandingly improves the electrical performance of a Cu conductor (4.6 μΩ·cm) by involving the spatially concurrent laser absorption to the surface oxide-free Cu nanoparticles (NPs). Physical/chemical properties of fabricated Cu conductors are fully analyzed in perspectives of the mechanism based on the thermo-physical-chemical interactions between photon energy and pure Cu NPs. The resultant Cu conductors showed an excellent durability in terms of bending and adhesion. Furthermore, we successfully demonstrated a single layer Cu-mesh-based touch screen panel (TSP) on thermally sensitive polymer film as a breakthrough of typical metal oxide-based transparent touch sensors. The Cu metal mesh exhibited high transmittance (95%) and low sheet resistance (30 Ω/square). This self-capacitance type and multitouchable TSP operated with a fast response, high sensitivity, and durability.