Direct Photopatterning of Metals on Polymer Surfaces at Ambient Conditions

Metal interconnects on polymer substrates are an integral part of many stretchable and flexible electronic devices. However, metal deposition typically involves harsh conditions, such as high vacuum and temperature. These requirements limit compatibility with many substrates and impede rapid prototyping and increases and energy requirements. Solution-phase depositing such metal features is an attractive alternative to conventional processes, especially when combined with a rapid additive manufacturing technique.<br/>Here we present an aqueous gold ink, comprised of H[AuCl₄] as a metal source, a reducing agent and a benign, nontoxic dye as an initiator, that allowed us to deposit gold onto silicone surfaces upon UV illumination at ambient conditions. Altering the reaction time and ink composition, we could tune the morphology of the deposited metal, between isolated nanoparticles and a continuous film. Using this ink, we deposit stretchable gold interconnects on pre-strained silicone, using solely UV illumination, achieving conductivity of 40% of bulk gold. We additionally used a commercial sterelithographic printer without any modifications as a maskless lithography system, allowing us to pattern conductive features of 300 μm. Investigating different substrates suggests a preference for polymers with reducible species on the surface. Lastly, we have successfully performed the reaction with AgNO₃ as a metal source, depositing silver on silicone. We are working towards 2-photon illumination, in order to increase resolution and expand to 3D metal structures.