Gunning for the Future
Field emission displays are an old idea that suddenly became more attractive in 1991, when Sumio Iijima, an electron-microscope specialist at NEC Research in Tsukuba, Japan, discovered that carbon molecules could link together into long, thin cylinders later dubbed nanotubes. (The “nano,” like the “nano” in “nanotechnology,” comes from “nanometer,” a billionth of a meter.) The tubes were like tiny sheets of carbon molecules that had been rolled up into cylinders one-ten-thousandth the width of a human hair. Scientists quickly learned that these unusual structures had a host of interesting properties, including great strength, and high electrical and thermal conductivity.
But what attracted Saito, the Nagoya researcher, to carbon nanotubes was the possibility that they could act as electron guns. Placed in a properly aligned electric field, theoretical physicists said, the little tubes should shoot out electrons like hoses emitting streams of water. Many materials emit electrons when sufficient voltage is applied; the difference, the physicists said, is that nanotubes should actually accelerate the particles along their lengths, which would allow them to emit electrons of sufficient energy to activate phosphors in very low-voltage fields. Saito, now a professor of quantum engineering, first publicly demonstrated this effect in 1998. Working with Noritake, a big Nagoya ceramics and electronics firm, he assembled a small array of nanotubes that shot electrons into a phosphor screen, creating a bright light.
Saito’s experiments had an obvious commercial target: the $61-billion-a-year world market in television sets. The cathode ray tubes inside traditional TVs have changed little since they were invented in the 1920s – in stark contrast to almost every other piece of consumer electronic equipment. They shoot electrons from the tips of wires onto phosphor screens, creating patterns of glowing dots that the human eye interprets as moving images. Cathode ray tubes are inherently bulky, because the electron gun must sit back far enough to hit the entire screen. As a result, the picture tube in a typical home-theater screen is a massive object that almost fills a room; manufacturers believe the devices would be more popular if they were more manageable.
To make thinner, lighter big-screen TVs, manufacturers have turned to plasma and liquid-crystal displays, but these have their own drawbacks, beginning with their high price (see “Screen Test,” p. 65). Plasma screens, for example, are vulnerable to “burn-in,” in which motionless images, if displayed for too long, become seared permanently into the glass. They also consume as much as 700 watts of power, enough to make some critics worry about the environmental consequences if the displays were widely adopted. In LCDs, meanwhile, pixels switch relatively slowly from one color to another, which causes fast-moving images to smear or leave ghosts as the cells fail to keep up with the action.
Field emission displays will, in theory, solve many of these problems. They aren’t vulnerable to burn-in, and they use much less power. At the same time, the pixels in a field emission display can turn on and off faster than those in a liquid-crystal display, meaning that fast-moving images don’t smear. And those images can be viewed from any angle, while liquid-crystal displays require viewers to be directly in front of the screen.
But getting carbon nanotubes to shoot electrons at a screen in an actual consumer TV will require scores of innovations in several fields – the kind of effort often best coordinated by very large companies. Indeed, about the time that Saito produced his first field emission display, he learned that he faced competition from an unlikely place: South Korea.
Cathode ray tubes have dominated TV display technology for nearly 70 years, but today theyre locked in a four-way race for the future of home entertainment.
CATHODE RAY TUBES
FIELD EMISSION DISPLAYS
HOW THEY WORK
An electron beam steered by magnetic fields strikes phosphors on a glass screen
Polarized light shines through liquid-crystal “gates” that control pixels’ color and intensity
An electric pulse sets off a burst of ionized gas in each pixel, as though it were a tiny neon sign
Carbon nanotubes glued to a substrate shoot electrons at phosphors on a glass screen
The electron gun must sit far behind the screen, making tubes bulky and heavy
The viewer must be positioned directly in front of the screen
High power consumption
Unsolved technical problems, such as maintaining a vacuum between substrate and glass