January 5, 2005 4:00 AM PST
Carbon TVs to edge out liquid crystal, plasma?
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energy of the electrons, and the light that emerges on the other side of the glass forms the picture.
An LCD panel, by contrast, is created by sandwiching layers of components, such as transistors, crystal silicon and various filters, between two pieces of glass. Images are displayed when an electrical charge is sent through the panel, shifting the positions of the crystals. A light source behind the panel brightens the image and the pixels, depending on their positions, and blocks light or permits it to pass through, creating an image.
The images produced by CRT tubes are crisper and aren't subject to the shifting and ghosting of LCD screens. However, the electron gun in CRTs requires a large vacuum: the tube in a 30-inch diagonal television is 23-inches deep, though slim CRTs coming next year will only need 16-inch deep tubes.
Like an LCD, an FED is made up of layers. A layer of glass is coated with a cathode and a layer of diamond dust coated with lithium or carbon nanotubes. The negatively charged cathode, organized in a grid, then emits electrons through the diamonds or nanotubes, which focus that energy like a tiny lightening rod.
But then, like a CRT, the electrons shoot through a vacuum at a layer of phosphorescent glass covered with pixels. The big difference is that the source of electrons, the carbon, is located only 1 millimeter to 2 millimeters rather than nearly 2 feet from the target glass, and instead of one electron source--the electron gun--there are thousands. The electrons are attracted to the pixilated glass because this layer contains a positively charged anode.
"This generates light the same way a CRT tube does," said Pitstick, leading to similar picture quality. At the same time, a FED is only slightly thicker than an LCD panel.
Advance Nanotech spokeswoman Liza Mullins described it in lunch terms. "There are two layers of glass (the bread in the sandwich), and some layers of thin material deposited in the inner side of each (butter on the bread), and a near-vacuum gap," she wrote in an e-mail.
FEDs will consume less electricity than plasmas or LCDs because, among other factors, they will contain fewer electronic parts, Pitstick said. Costs will also decline over time because fairly simple manufacturing processes are used, and FEDs contain fewer chips.
Size isn't an issue: A 2004 prototype of a nanotube FED measures 38 inches across, far larger than commercially available LCDs. FEDs, in fact, largely will be incorporated into televisions and large computer monitors, Pitstick said. Toshiba's SED televisions will start at 50 inches. Advance, however, said the technology could be used in screens ranging from 2 inches to 100 inches in diameter.The diamonds or nanotubes do not need to be precisely positioned. Instead, both are scattered randomly in the coating, like sugar crystals in coffee, but enough exist in the mix to ensure that each points in the right direction to transmit electrons.
The diamonds are deposited as evenly as possible over the lower layer. "Only those particles which have an emitter structure behind them actually participate in the display function," Mullins said.
But getting all of the parts to work well together could be a challenge. The companies have to devise coatings that will let the carbon adhere to the glass. More work needs to be accomplished on the electrodes as well.
"All of these technologies have to control a vacuum with a thin cell size over a large area," iSuppli's Semenza said. Nonetheless, "it is probably prudent for these guys (large manufacturers) to have people working on this."
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