Full Wafer Scale Manufacturing of Directly Printed TiO₂ Metalenses at Visible Wavelengths with Outstanding Focusing Efficiencies

Highly efficient metalens arrays designed for 550 nm are directly printed using UV-assisted nanoimprint lithography (UV-NIL) and a TiO₂ nanoparticle (NP)-based ink on 8″ optical wafers with imprint times less than 5 min. Approximately one-thousand 4-mm metalenses are fabricated per wafer with uniform optical performance using a reusable PDMS-based elastomeric stamp. The absolute and relative focusing efficiencies are as high as 81.2% and 90.4%, respectively, matching closely with the simulated maximum efficiencies of 83% and 91% achievable with the given master design, indicating that future improvements are possible, and efficiencies are not limited by materials or process. The imprinted metalenses are free from organics due to a post-imprint calcination step and exhibit outstanding dimensional and optical stabilities. The highest efficiencies are attained using imprint formulations comprised of mixtures of 10 and 20 nm TiO₂ NPs, whose denser packing not only increases the refractive index (RI) of the calcined lenses up to 2.0 but also reduces the feature shrinkage relative to the master. 25 cycles of atomic layer deposition of TiO₂ following imprinting increase the RI up to 2.3 without changing dimensions by uniform gap filling between NPs. This work opens a path for true, full-scale additive manufacturing of metaoptics.