Effective Approach for Fabricating Highly Precise High-Curvature Structural Patterns via Air-Bubble Induction.

Developing a new master mold-based patterning technology that can be used to accurately, precisely, and uniformly create large-area micropatterns while controlling the micropatterns of curved structures is essential for promoting innovative developments in various application fields. This study develops a new top-down lithographic process that can effectively produce structural patterns with high curvatures by growing isolated microbubbles in the master pattern holes. The isolated air-pocket lithography (IAL) we developed is based on the controlled behavior of micrometer-sized air pockets trapped between the grooves of the master pattern and the curable polymer. We successfully fabricated a concave array polydimethylsiloxane (PDMS) film and a convex array polymer film. In addition, the IAL mechanism was proven by confirming the expansion process of micrometer-sized air pockets trapped between the deep groove of the silicon master pattern and the PDMS coating film by using optical microscopy images. We successfully obtained complex three-dimensional structural patterns containing both 3D hollow spherical concave and ring-shaped two-dimensional convex patterns. This simple, fast, and effective high-curvature patterning technique is expected to provide innovative solutions for future applications such as nanoelectronics, optical devices, displays, and photovoltaics.