Micro-3D sculptured metastructures with deep trenches for sub-10 μm resolution.

Three-dimensional (3D) printing allows for the construction of complex structures. However, 3D-printing vertical structures with a high aspect ratio remains a pending challenge, especially when a high lateral resolution is required. Here, to address this challenge, we propose and demonstrate micro-3D sculptured metastructures with deep trenches of 1:4 (width:height) aspect ratio for sub-10 µm resolution. Our construction relies on two-photon polymerization for a 3D-pattern with its trenches, followed by electroplating of a thick metal film and its dry etching to remove the seed layer. To test the proposed fabrication process, we built up three-dimensional RF metastructures showcasing the depth effect as the third dimension. Using the numerical solutions, we custom-tailored these metastructure resonators to fall within a specific resonance frequency range of 4-6 GHz while undertaking comparative analyses regarding overall footprint, quality factor, and resonance frequency shift as a function of their cross-sectional aspect ratio. The proposed process flow is shown to miniaturize metal footprint and tune the resonance frequency of these thick 3D-metastructures while increasing their quality factor. These experimental findings indicate that this method of producing trenches via 3D-printing provides rich opportunities to implement high-aspect-ratio, complex structures.