A new study has unveiled a ‘mould’ that dissolves in water, enhancing the efficiency of the fabrication process for metasurface manufacturing

When will the protruding rear camera on smartphones become obsolete?

The implementation of a metasurface, which completely disregards the properties of light, promises to reduce the thickness of a camera lens to 1/10,000 of a conventional lens.

However, despite this advancement, challenges still persist due to high production costs and intricate processes.

A collaborative team led by Professor Junsuk Rho from the Department of Mechanical Engineering and the Department of Chemical Engineering and Joohoon Kim from the Department of Mechanical Engineering at Pohang University of Science and Technology (POSTECH), and Professor Heon Lee from the Department of Materials Science and Engineering at Korea University accomplished a feat by developing a water-soluble mould.

Through its successful application, they managed to fabricate a flawless high-resolution and high aspect ratio metasurface.



Producing metasurfaces


There are two major technologies for producing metasurfaces.

Electron beam lithography involves using an electron beam to draw a pattern, but it comes at a considerable cost and slow fabrication.

In contrast, nanoimprint lithography employs an engraved mould to stamp the desired structure, making it a more affordable and faster method.

Nevertheless, this approach has its own challenges, particularly with the risk of damaging the structure during the separation from the mould.

The larger the structure, the higher the likelihood of damage, which poses difficulties in achieving the necessary high-resolution and high aspect ratio crucial for metasurfaces.

To address these constraints, the research team devised a water-soluble nanoimprint mould.

Instead of physically separating the structure from the mould, they adopted a technique of dissolving the mould in water, thereby eliminating the risk of damaging the structure.

The water-soluble mould was fabricated using polyvinyl alcohol (PVA), a flexible material that dissolves easily in water.

Furthermore, the research team conducted experiments using the water-soluble mould, achieving the successful fabrication of a metalens with a significant 1cm area.

This metalens exhibited a high-resolution and high aspect ratio of 10:1, allowing it to transcribe structures smaller than 100nm.

Notably, the mould retained its functionality within the visible regime.

This novel approach offers an affordable and rapid nanoimprint process capable of achieving high-resolution and high aspect ratio results.

Rho, who led the research, explained: “The research represents an achievement in attaining both high-resolution and high aspect ratio through nanoimprinting using a water-soluble mould.

“I hope this approach coupled with a large-area mould fabrication technology based on deep ultraviolet lithography will enable the mass production of not only lenses but various metasurfaces.

“Such progress would pave the way for affordable and fast manufacturing of metasurfaces.”

These research findings have been published in Photon X, the prestigious journal renowned in the field of photonics.

Image: Various high aspect ratio structures and metalenses with a large area transcribed by water-soluble nanoimprint. Credit: POSTECH.

Research Aether / Technology Uncovered