Gold metallization of hybrid organic-inorganic polymer microstructures 3D printed by two-photon polymerization

Two-photon polymerization is a femtosecond laser-based technique enabling printing of three-dimensional structures down to submicron resolution within photocurable polymers. Rendering the dielectric 3D printed structures conductive can be of great benefit for various applications in domains such as energy, photonics, or multifunctional devices. In this work, the microstructures of interest are made of a silicon-zirconium hybrid organic-inorganic polymer exhibiting low shrinkage during development. A simple and efficient metallization method by electroless plating is investigated to deposit a gold layer on the surface of the printed microstructures. The influence of the method parameters on the quality and properties of the deposited layer is studied. Among these parameters, the surface modification agent concentration and step duration, as well as the seeding solution concentration, must be adapted to the specific case of the considered hybrid microstructures. The concentration of metal ions in the plating bath is the most influential parameter on the morphology of the deposited gold layers. In particular, higher concentrations lead to smooth and continuous layers with electrical conductivities higher than half that of bulk gold. Finally, the deposited layers are shown to coat 3D printed microstructures of arbitrary shapes, thus confirming the conformality of the method at the micrometric scale.