Form‐Factor Free 3D Copper Circuits by Surface‐Conformal Direct Printing and Laser Writing

Abstract Recently, the fabrication of 3D circuits has attracted significant attention in the context of the realization of a new‐generation of printed electronics. In particular, form‐factor free Cu conductors have been recognized as the key to a constituent layer that can interconnect on demand a variety of active/passive components on arbitrarily designable platforms. However, even with their characteristic advantages of cost‐effectiveness and high electrical conductivity, 3D printed Cu circuits have been not suggested, owing to the difficulty of suppressing undesirable oxidation reactions and the absence of appropriate strategies for transforming the 3D particulate layers into device‐quality conductive ones. In this study, multidimensional particles are proposed that allow for deep penetration of incident photons in the surface‐conformal laser writing process, mechanisms of which are fully clarified based on an optical simulation‐based physical interpretation. The critical factors determining the electrical properties are elucidated through a spectroscopy‐based investigation for 3D structured Cu conductors. It is demonstrated that 16.5 µm thick Cu features (with values of resistivity and resistance of 15 µΩ cm and 0.91 Ω cm −1 , respectively) can be created simply by successive 3D printing and laser writing processes, facilitating a user‐friendly design of low‐cost, high performance, form‐factor free electrical circuits.