Synthesis of disc-shaped copper flakes by mechanical milling: Green laser-sintered, highly conductive printed Cu features

Abstract

Recently, a digital fabrication technique has been recognized as one of requisite processing methods that can realize large-area, low-cost, form-factor free optoelectronics applications. Digitally printed conductive layers are implemented in practical device layouts for electrically interconnecting active/passive components. In terms of high conductivity, printing processability, and cost-effectiveness, printable Cu fluids are most appropriate to generate highly conductive printed features. To resolve critical issues in printed Cu conductors, we propose a selective green-laser-sintering process with a usage of a mixture of Cu nanoparticles and flakes. Surface oxide-free Cu nanoparticles and sub-micron Cu particles are synthesized through highly concentrated solvothermal synthetic methods. Sub-micron spherical Cu particles are transformed into disc-shaped Cu flakes by a subsequent mechanical milling process. The printable Cu fluids including the mixed particles and a photo-reactive polymer, enable the formation of printed particle assemblies that can be sintered by highly energetic green-wavelength photons. It is demonstrated that highly conductive printed layers are generated with values in resistivity and resistance as low as 16μΩcm and 1.9 Ω/cm, respectively, by the combined approach of mask-free printing and selective green-laser sintering processes.