Engineers at Princeton University have developed a simple mechanical technique for creating periodic lines on microchips with separations of as little as 60 nm. Gratings of this size are useful in a number of optical, electronic and microfluidic devices.
Traditional methods for creating micro- and nanoscale grooves include electron beam etching and interference lithography, but they are all relatively complex, slow and/or expensive. The technique developed by researchers led by Stephen Chou and William Russel can self-generate gratings from a featureless polymer thin film sandwiched between two rigid flat plates, and does not require the use of masks or complex equipment.
In fracture-induced structuring, the polymer film is first painted onto a silicon plate or similar. A second plate is then placed on top, forming a sandwich with the polymer as filling. Heat is applied to bond the layers together.
When the plates are prised apart the film fractures, breaking into two complementary sets of gratings, one on each plate. The grating period, or distance between the lines, is four times the film thickness.
“Currently, the method can easily create gratings over several square centimetres,” says Chou. “We believe that with proper scaling it can in principle be much larger. That is one of the areas for future study.” Chou adds that the method is quite reliable, and the researchers are currently attempting to quantify this. He also points out that the polymer gratings can be used to make moulds for nanoimprint lithography.
“The result reported by Russel, Chou and their co-workers has a wonderful combination of characteristics,” says Brown University mechanical engineer Ben Freund. “What is observed is quite unexpected scientifically, and the result has the potential for immediate application in nanofabrication.”
A patent has been filed on the technique, which Chou and his colleagues say is viable for use on an industrial scale.
Further reading: Self-formation of sub-60-nm half-pitch gratings with large areas through fracturing, Pease et al., Nature Nanotech. 2, 545 (2007).
Figure: Schematic of the fracture-induced structuring process. A thin glassy film (yellow) is sandwiched between two rigid plates (blue). When prised apart from an edge the film fractures, leaving complementary sets of nanoscale gratings on each plate (© 2007 Nature Publishing Group).
Article first published in Nanomaterials News.