LAUSR

As a fast prototyping technique, direct writing of flexible electronics is gaining popularity for its low-cost, simplicity, ultrahigh portability, and ease of use. However, the latest handwritten circuits reported either have relative low conductivity or require additional post-treatment, keeping this emerging technology away from end-users. Here, a one-step react-on-demand (RoD) method for fabricating flexible circuits with ultralow sheet resistance, enhanced safety, and durability is proposed. With the special functionalized substrate, a real-time 3D synthesis of silver plates in microscale is triggered on-demand right beneath the tip in the water-swelled polyvinyl alcohol (PVA) coating, forming a 3D metal–polymer hybrid structure of ≈7 µm with one single stroke. The as-fabricated silver traces show an enhanced durability and ultralow sheet resistance down to 4 mΩ sq−1 which is by far the lowest sheet resistance reported in literatures achieved by direct writing. Meanwhile, PVA seal small particles inside the film, adding additional safety to this technology. Since neither nanomaterials nor a harsh fabrication environment are required, the proposed method remains low cost, user friendly, and accessible to end users. With little effort, the RoD approach can be extended to various printing systems, offering a particle-free, sintering-free solution for high-resolution, high-speed production of flexible electronics.