Solvent-free, transparent, high-refractive index ZrO₂ nanoparticle composite resin for scalable roll to roll UV-nanoimprint lithography

High-throughput fabrication of nanostructures for photonics still presents certain challenges, specifically with respect to obtaining a wide control over refractive index. We demonstrate the formulation of a UV-curable resin with a refractive index tunable from 1.58 to greater than 1.7. Refractive index tuning is achieved using small, well-dispersed ZrO₂ nanoparticles as well as the addition of N-vinylcarbazole as a co-monomer to commercial resin formulations. Composites containing the UV- curable resin and 30% nanoparticles (by volume) reached an uncured refractive index of 1.69, while the formulation containing a 2:1 wt ratio of UV resin to N-vinylcarbazole with an overall loading of 30 vol% of nanoparticles reached a cured index of 1.73. The formulation maintains good transparency in the visible region with greater that 80% transmittance for composition UV resin to N-vinylcarbazole 4:1 with 30 vol% nanoparticles. Additionally, we demonstrate defect-free imprinting of various nanostructures using the composite, high- index UV-curable resin with critical dimensions ranging from 400 nm to 20 ensuremathmum. Our formulations consist of commercially available materials and are solvent free, rendering them well-suited to scaling for roll-to-roll processing. The composite resins with up to 30 vol% ZrO₂ nanoparticles were processed in a custom designed roll to roll UV-assisted nanoimprint processing line and 30 in. per minute (76.2 cm per min) continuous speed was achieved.