Direct-Write Transfer Printing of Low-Loss Copper Interconnects onto Arbitrary Substrates

<title>Abstract</title> <p>Conformal and wearable electronic systems, from smart textiles to bioelectronics, increasingly require metal interconnects capable of operating at gigahertz-to-millimeter-wave frequencies for wireless communication and power transfer. At these frequencies, the skin effect confines current to a nanometer-scale surface layer, so conductor loss is governed jointly by the resistivity and the surface roughness of the metal, both of which are set by the deposition process. However, existing metallization routes each sacrifice one of these properties: vapor-phase deposition yields smooth, near-bulk copper but requires vacuum, elevated temperature, and line-of-sight access that excludes porous and textured substrates, while particle-based inks pattern freely on arbitrary substrates but leave porous, rough films that recover one property only at the expense of the other. Here, we demonstrate a direct-write transfer printing process that decouples copper deposition from the target substrate: copper is written by meniscus-confined electrodeposition onto a stainless-steel cathode and then transferred intact onto the receiver substrate, without masks, vacuum, or a thermal budget. Deterministic control over nozzle position, velocity, and dwell time allows closed-path and geometrically complex patterns to be written without the seam defects and delamination that arise from slicer-generated paths designed for conventional extrusion. Copper patterns were transferred onto substrates spanning polymer films, adhesive tapes, and woven and nonwoven textiles, preserving feature geometry and linewidths down to 550 µm. The transferred films presented a smooth, substrate-templated working surface with 40–55 nm roughness and near-bulk resistivity of 2.3–2.6 µΩ·cm, yielding surface resistance within 1.2 times that of bulk copper and conductor loss 1.4 to 7.1 times lower than printed copper across 5–30 GHz, while withstanding handling and mounting as free-standing foils. By separating metal growth from the receiving surface, this approach provides a mask-free, vacuum-free route to gigahertz-compatible copper interconnects on arbitrary and textured substrates, opening a pathway toward high-frequency smart textiles and conformal bioelectronics.</p>