Scalable Nanoimprint Lithography Process for Manufacturing Visible Metasurfaces Composed of High Aspect Ratio TiO₂ Meta-Atoms

We report a one-step additive manufacturing process to fabricate metalenses for visible wavelengths. Nanostructures with aspect ratios larger than eight and critical dimensions smaller than 60 nm were produced using nanoimprint lithography and a titanium dioxide nanocrystal-based imprint material, resulting in inorganic structures exhibiting a refractive index of n = 1.9. As a demonstration, we fabricate metalenses with numerical apertures (NAs) of 0.2 and focusing efficiencies over 50%. Manufacturability was assessed by performing 15 manual imprints in 30 min (2 min of process time per imprint) with a single stamp. All imprinted lenses exhibit comparable performance, paving the way for high-throughput and low-cost manufacturing of flat optical devices. Metalenses with a diameter of 4 mm were also fabricated to investigate the success of large area replication using this process, showing efficiencies of 43%, indicating good macroscopic imprinting.