Jun 4, 2009
Rigiflex mould turns out metallic nanopatterns
Metallic nanopatterns for thin-film transistors (TFTs), photonic crystals and optical devices such as wire grid polarizers can be easily fabricated by reversal rigiflex printing.
Researchers from Seoul National University and Kyungwon University in Korea report that the printing technique can fabricate sub-100 nm scale metallic patterns with high fidelity and high aspect ratios. Produced on a transparent template, the metal wires can be used as a reflective wire-grid polarizer. Encouraged by the result, the team believes that reversal rigiflex printing can open the door to the development of facile metallic nanofabrications such as NEMS, MEMS and micro- (nano-) fluidic channels.
The technique is based on a rigiflex mould (see image), which is flexible enough to transfer nanopatterns over a large area by roll-to-roll or screen printing and hard enough to endure high pressures of around 50 bar.
A silicon line and space pattern with features measuring 70 nm wide and 120 nm deep was used as a master mould. A PUA replica mould was then obtained from the silicon master and coated with a self-assembled monolayer of the organosilane – FOTCS. In the stack of PUA/FOTCS/Al layers, the SAM of FOTCS applied on the PUA mould reduces the work of adhesion at the FOTCS/Al interface. It helps to release the metal film from the PUA mould and also enables transfer of the metal film to the polymer-coated substrate during transfer printing.
To enable better metal filling, the aluminium film was slowly deposited onto a rotating-surface-treated PUA mould by thermal evaporation. Next aluminium films with gratings were fabricated on a transparent polymer-coated glass substrate by transfer printing with the metal-coated mould. The transferred metal gratings were then etched slightly by anisotropic RIE to remove any residual metal layer in the recessive parts of the pattern.
The researchers presented their work in Nanotechnology.
About the author
Tae-il Kim is currently a research associate in Khap Y Suh's group at the school of Mechanical and Aerospace Engineering, Seoul National University, Seoul, Korea. He is studying the unconventional patterning of nanostructures, together with the mimicking of bio-inspired structures such as Lotus and Gecko and their use as superhydrophobic (oleophobic) surfaces and dry-adhesives. Prof. Soon-min Seo is affiliated to Kyungwon University, Korea. His current research areas include unconventional lithography and its application to organic devices.