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September 01, 2009

A Step Towards High Throughput Continuous Nanoimprinting



ACS Nano reports that a step toward high throughput continuous nanoimprinting has been made. Nanoimprinting could eventually achieve 2 nanometer features. Currently this higher volume method is at about 50-300 nanometer features. The research team has performed some 50 nm large area nanoimprinting but this roll to roll process (higher speed) is at 300 nanometer features. Achieving the higher resolution and the high speed could enable nanoimprinting to displace conventional lithography. There is a significant step and research required to move from nanopatterning to more complete manufacturing capabilities.


UPDATE: MIT Technology Review has information on this.

Guo developed a stamp that can be used for roll-to-roll nanoimprinting over large areas. His setup uses a polymer mold wrapped around a rolling cylinder to press a pattern into a material called a resist that sits on top of either a rigid glass backing or a polymer one. To make the finished component, the pattern is then fixed by a flash of ultraviolet light. The process, described in the journal ACS Nano,can be done continuously at a rate of a meter per minute, and Guo says he's used it to print features as small as 50 nanometers over an area six inches wide. That resolution isn't good enough to make integrated circuits, but it is adequate for printing optical devices such as light concentrators and gratings.

This isn't the first time that roll-to-roll printing has been explored for nanoimprint lithography. But Yong Chen, professor of materials science and engineering at the University of California, Los Angeles, says the Michigan group "has made this process more reliable with lower defect density.

At first glance the new roll-to-roll printer resembles a newspaper printing press, but it's much more complex. The quality of the final nano product depends on achieving the right balance of properties in the printing materials. Silicon and other rigid materials used to make normal nanoimprint lithography stamps can't be wrapped around a cylinder. So Guo selected a polymer that's stiff enough to work as a reliable stamp, but also pliable enough to wrap around the printer's rolls. The finished resist also should stick to the substrate without being too viscous, and it must cure rapidly without shrinking.

"This work is an important industrial advance, which should [enable] a wider application of nanoimprinting," says Stephen Chou, professor of electrical engineering at Princeton University and a pioneer of nanoimprint lithography since the late 1990s.

The process developed by Guo's group could be used to make nanophotonic devices on a large scale and high-performance printed electronics, adds Ali Javey, assistant professor of electrical engineering and computer sciences at the University of California, Berkeley. However, Javey, who is developing roller-printing methods for electronic materials such as silicon nanowires, cautions that the longevity of the molds must be resolved before the technique is likely to be widely adopted by the industry.

The Michigan researchers will work on shrinking the resolution achieved by the technique and developing it for manufacturing. Guo says his group is working with companies that are interested in using the printing process for their products. "This is a baseline technique that can be used to make many things," he says.



Nano press: This 10-by-30-centimeter plastic sheet (top) has been patterned with a series of nanoscale polymer lines using roll-to-roll nanoimprint lithography (bottom). The film is iridescent because of the way its nanoscale features scatter light. Credit: ACS Nano


Se Hyun Ahn and L. Jay Guo,Department of Mechanical Engineering, University of Michigan, ACS Nano, 2009, 3 (8), pp 2304–2310 DOI: 10.1021/nn9003633

Article: Large-Area Roll-to-Roll and Roll-to-Plate Nanoimprint Lithography: A Step toward High-Throughput Application of Continuous Nanoimprinting

A continuous roll-to-roll nanoimprint lithography (R2RNIL) technique can provide a solution for high-speed large-area nanoscale patterning with greatly improved throughput; furthermore, it can overcome the challenges faced by conventional NIL in maintaining pressure uniformity and successful demolding in large-area imprinting. In this work, we demonstrate large-area (4 in. wide) continuous imprinting of nanogratings by using a newly developed apparatus capable of roll-to-roll imprinting (R2RNIL) on flexible web and roll-to-plate imprinting (R2PNIL) on rigid substrate. The 300 nm line width grating patterns are continuously transferred on either glass substrate (roll-to-plate mode) or flexible plastic substrate (roll-to-roll mode) with greatly enhanced throughput. In addition, the film thickness after the imprinting process, which is critical in optical applications, as a function of several imprinting parameters such as roller pressure and speed, is thoroughly investigated, and an analytical model has been developed to predict the residual layer thickness in dynamic R2RNIL process.




Se Hyun Ahn page at the University of Michigan.

Research Project: High-Speed, Roll-to-Roll Nanoimprint Lithography (R2RNIL) on Flexible Plastic Substrate Nanoimprint lithography (NIL) is considered as one of the most promising and competitive technologies for high-throughput and low-cost nanopatterning. However, the throughput in NIL is still far from meeting the demands of many practical applications, such as in organic electronics and biotechnologies. A faster and more economical fabrication method based on continuous Roll-to-Roll NanoImprint Lithography (R2RNIL) provides a practical solution for large-area nanoscale patterning. R2RNIL offers greatly improved throughput by overcoming the challenges faced by conventional NIL in maintaining pressure uniformity and successful large-area imprinting and demolding. We demonstrated a prototype printer capable of continuous imprinting of nanoscale structures on a flexible plastic substrate. Our new process used a flexible and non-sticking fluoropolymer mold, and fast thermal and UV curable liquid resist materials developed previously in our lab. Large-area, nano-grating patterns with linewidth down to 70nm have been successfully replicated continuously. As one of its many applications, high efficiency (extinction ratio~103) flexible polarizers are demonstrated. This research is supported by AFOSR (Grant No. F064-006-0084), NSF (Grant No. CMII 0700718), and the University of Michigan Technology Transfer Office (GAP Fund).



Lingjie Jay Guo page at the University of Michigan.

Guo Research group page.

Guo research groups nanoimprint page.



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