Jan 19, 2010
Magnetic field assembles lithography mask
Nanofabrication techniques are typically characterized into two categories – a "top-down" approach, where a lithographic process patterns the structure based on a mask; or a "bottom-up" approach, where elementary components self assemble to form functional geometries. Both approaches have their advantages – lithographic techniques allow better pattern control and assembly processes are more cost-efficient. Now, a new hybrid process hopes to combine the benefits of both approaches.
In a recent study published in the journal Nanotechnology, researchers in the US and Singapore have developed a tunable nanostructured lithography mask composed of self-assembled nanoparticles. The group was able to use magnetic fields to control the nanoparticle assembly, and therefore the shape of the "lithography mask," to pattern different geometries. This new technique could pave the way for more versatile, scalable and cost-effective nanomanufacturing tools.
In this new approach, called self-assembled ferrofluid lithography (SAFLi), the team used iron oxide nanoparticles (diameter ~10 nm) in a liquid solution, referred to as a "ferrofluid," as a dynamic lithography mask. The particles, typically randomly dispersed in the solution, assemble to form ordered structures when external magnetic fields are applied.
In the system proposed by the team, microfluidic channels confine the ferrofluid over photosensitive film, which is then exposed by ultraviolet light. The assembled nanoparticles have higher optical absorption than the liquid and function as a lithography mask by replicating the assembly pattern in the polymer film. The assembly pattern can be actively controlled by tuning the external field, which allows various geometries to be patterned.
Using this technique the team has demonstrated a microdot array with controllable dot spacing and microring pattern with 250 nm feature sizes. Going forward, the group will try to use this technique to pattern more complex patterns with smaller feature sizes.
About the author
Dr Chih-Hao Chang is a postdoctoral associate at the Singapore-MIT Alliance for Research and Technology (SMART) Centre in Singapore, and a visiting scholar at MIT. His research involves the design and fabrication of nanostructured optical materials. Chee-Wee Tan is a research engineer at the SMART Centre, where he focuses on the development of piezoelectric MEMS sensors. Dr Jianmin Miao is an associate professor of mechanical and aerospace engineering and director of the Micromachines Centre at Nayang Technological University, focusing on MEMS and carbon nanotube devices. Dr George Barbastathis is an associate professor of mechanical engineering at MIT, where he leads the 3D Optical Systems (3DOS) Group and conducts research in 3D imaging systems, subwavelength optics and 3D nano/microsystems.