Tuesday, December 19, 2006

Making Nanoelectronics for Displays

A new way to print devices made of diverse materials could prove to be an invaluable tool in making nanoscale electronics and optics.

By Kevin Bullis

A new method of printing layers of high-performance transistors on a sheet of plastic could lead to flexible electronics. Credit: John Rogers, University of Illinois, Urbana-Champagne

A new, inexpensive way to make nanoscale electronics could lead to, among other things, better displays, more-compact and higher-performance cell phones, and small wide-angle night-vision systems that mimic the structure of the human eye.

John Rogers, professor of chemistry and materials science and engineering at the University of Illinois, Urbana-Champaign, and his coworkers have developed a printing technique that allows them to combine a wide variety of inorganic structures, such as single-walled carbon nanotubes, assorted nanoscale wires, and ribbons made of gallium arsenide or silicon, to create multilayered, high-performance optical and electronic devices. They can also print on flexible or curved surfaces.

"This is a lovely and remarkably complete piece of work, and [it] provides probably the best method to date" for integrating dissimilar materials onto one platform, says James Heath, professor of chemistry at Caltech. It has been a challenge to do this in part because the manufacturing processes, including high-temperature deposition, that are needed for some materials can damage others. Rogers's method makes it possible to process incompatible materials separately but then combine them using a low-temperature process onto a variety of surfaces, including flexible plastic ones.

Rogers's method, which is described in the current issue of Science, begins with the fabrication of nano- and microstructures, such as an array of semiconducting silicon nanowires, using conventional techniques. The researchers then press a soft stamp onto these structures, and when the stamp is peeled away, the structures stick to it, much as dust will cling to a strip of tape. The nanostructure-bearing stamp is then pressed onto another surface that is covered with a glue-like polymer. Once this polymer cures, it adheres to the nanostructures more strongly than to the stamp: when the stamp is lifted off, it leaves the nanostructures behind, still ordered in the same configuration in which they were originally patterned. This is then repeated for the other structures.

Once the nanostructures are in place, the researchers use conventional techniques to deposit electrodes and other structures to make working devices, such as transistors. Different nanostructured materials, such as carbon nanotubes, can be printed next to the first ones on the same surface.

The method can also be used to make multilayered systems. After the first layer of devices is printed, the researchers coat it with a thin layer of the polymer glue. This serves to anchor the next layer of devices, as well as insulate between the layers. Because the polymer is thin, small holes can easily be etched into it to allow connections between selected devices in different layers.