“This is the first time someone has shown solution-deposited, purified semiconducting tubes for high-quality transistors,” says John Rogers, professor of materials science and engineering at the University of Illinois at Urbana-Champaign. “The accomplishment is in the integration of several promising approaches to demonstrate a full sequence for the fabrication of electronics.”
Now that his group has demonstrated the feasibility of these techniques, Zhou says, it’s working to build a truly integrated organic LED display that is flexible and transparent. Such a display might be rolled up to fit in a pocket, or mounted on a car windshield to display information to the driver. The first step is eliminating the rigid silicon. Because the nanotubes may be laid down at room temperature, the USC researchers can build them on electrically active plastic sheets that can’t tolerate high temperatures. They’re also working to replace the stiff metal electrodes with a coating of indium tin oxide, a commonly used, flexible, transparent electrode material. In their prototype, the organic LED pixels are connected to the transistor array by wires; to integrate them they’ll need to come up with methods for building the LEDs on top of the control circuit.
Zhou says he is talking with display companies about commercializing these methods. Korean display giant LG has demonstrated interest in carbon nanotube electronics, and IBM researchers have been publishing on the topic. However, the only company to come out with a nanotube electronic product so far is the Menlo Park, CA startup Unidym, which makes electrodes from the material.
Researchers in the field have been talking about nanotube displays for years, and the holdup, says Mark Hersam of Northwestern University, has been the lack of a big enough supply of semiconducting carbon nanotubes. In 2006, materials science professor Hersam developed a simple method for purifying nanotubes based on their properties by centrifuging them in a soapy solution. He then founded a company, called NanoIntegris, which has been supplying semiconducting nanotubes to groups including Zhou’s and the research team at IBM. A newly formed company in China and one in Japan are also supplying the semiconducting nanotubes needed for making transistor arrays to control displays.
With this supply in place, says Hersam, it’s only a matter of time before a company comes out with a product, whether it’s made using a method like Zhou’s or some other method. “I’m confident there will be a suite of products in the foreseeable future,” says Hersam. “It’s a matter of going from prototyping to market.”