Carbon nanotube displays that outperform today's flat-panel televisions are ready to move out of the lab and into factories, say researchers at Motorola. The carbon nanotubes make possible high-definition TVs with the color, contrast, and fast response characteristic of bulky screens based on cathode-ray tubes (CRTs), but in a flat-screen format.

The new TV screens are a nano version of the field emission displays (FEDs) developed by Motorola and others during the 1990s. Although that technology produced dazzling prototype displays, it cost too much to compete with liquid crystal displays (LCDs). "It didn't make sense to build a factory [for conventional FEDs]. The cost [of LCDs] was halving each year," says Kenneth Dean, who leads development for carbon nanotube displays at Motorola. However, he says, carbon nanotubes have given field emission technology a second wind by yielding cheaper components that can be manufactured more easily.

Motorola does not intend to build its own factories to manufacture the displays, so the company is now in licensing talks with several manufacturing companies. James Jaskie, chief scientist at Motorola, says two companies in Asia are now building factories to produce carbon-nanotube-based displays that may use some aspects of the Motorola technology.

Field emission displays, like CRTs, work by directing electrons at red, green, and blue phosphors arrayed on the screen. But rather than using one electron gun positioned a foot and a half behind the screen, as in CRTs, field emission displays use millions of tiny electron emitters placed within millimeters of the screen. Early field emission displays used sharp metal points for the emitters, but these were difficult to make over large areas, and they required such high voltages that expensive electronics were needed to control where and when pixels lit up.

Carbon nanotubes, however, are so thin that they make it possible to lower the voltage and use cheaper electronics. "We're using an electric field to pull electrons out, and the taller and sharper it is, the lower the voltage you need," says Dean. Because the nanotubes perform so well as electron emitters, they can also be placed farther from the control electronics, which Dean says should make large displays easier to produce.

But working with nanotubes brings challenges of its own. Researchers needed a low-temperature method for making them that would not melt the glass in the display; they also had to find a way to distribute the nanotubes uniformly, since the eye can detect subtle differences in brightness between neighboring pixels. Finally, the nanotubes must be spaced at a specific distance from each other, since they work best when they are not too close to neighboring nanotubes. Dean says the Motorola solution involves materials that self-assemble to form tiny particles just three nanometers in diameter. Exposed to a hydrocarbon gas such as methane, these particles catalyze the formation of nanotubes three nanometers in diameter, much smaller than the 20-nanometer tips used before.