Fujitsu--the originator of plasma display technology--is developing a new type of plasma display suitable for indoor commercial spaces and far larger than any current display type. The new design promises greatly improved energy efficiencies to boot.
The Tokyo-based company has developed long, narrow plasma tubes that it lines up together horizontally to make a display. Fujitsu describes its work as a breakthrough in creating displays wider than 250 centimeters.
So far, the company has built a prototype color display, with 128 glass plasma tubes, each measuring 1 millimeter in diameter, which provides a screen size of 128 mm by 1 meter. The tubes, which operate in the same manner as standard plasma displays, are filled with xenon and neon gas. Their inside walls are partly coated with either red, green, or blue phosphor, which together produce the full color spectrum [see diagram, " Modular Plasma Display"]. The tubes are packed together vertically and are sandwiched between two thin and lightweight glass or plastic retaining plates. In contrast, a standard plasma display is built with thick, heavy, glass plates.
The display electrodes in the tubular display run across its front, perpendicular to the tubes, while the address electrodes are on the back, parallel to the tubes. When current runs through any pair of intersecting display and control electrodes, an electric charge prompts gas in the tube to discharge and emit ultraviolet light at the intersection point, which in turn causes the phosphor coating to emit visible light. The combination of three tubes at any corresponding intersection point defines a pixel, and by varying the pulses of applied voltage in the underlying control electrodes, the intensity of each subpixel's color can be regulated to produce myriad combinations of red, blue, and green.
The photons interact with the phosphor coating, causing the emission of red, blue, or green visible light. The three colors in each pixel combine according to the number of electric pulses fed to each subpixel, which varies according to the signals sent to the electrodes by the display's electronics.
Because the plasma-tube display is essentially a modular assembly of tubes, displays of considerable length and height can be constructed simply by adding more tubes. In contrast, a standard plasma or liquid-crystal display is fabricated directly on a flat glass substrate. The same kind of processes and tools used in making semiconductors are employed to construct the various display elements layer by layer. The new plasma tubes can be produced relatively easily, without a clean room or photomasks.
Fujitsu believes the maximum size a standard glass substrate can be practically manufactured is about 1200 mm by 1800 mm, for a diagonal display size of just over 200 cm. With larger glass substrates, maintaining the uniform surface flatness essential to fabrication would be difficult, while the additional weight of the glass would increase the likelihood of breakage.
A standard display that is as large as the tube displays Fujitsu is developing would weigh hundreds of kilograms; the huge photomasks required to make such displays would tend to bend; and they'd be too costly, as would other equipment big enough to fabricate these giant displays.
Using modular tubes to build such large displays sidesteps all these obstacles. "The basic idea is to be able to show real-sized images," says Manabu Ishimoto, a member of the research group that conceived the technology at Fujitsu's lab in Kawasaki, Japan. He says the group is now developing two sizes of plasma tube displays: 3 by 2 meters and 6 by 3 meters, with resolutions of 1000 by 700 pixels and 2000 by 1000 pixels, respectively.
Given that the pixels are larger than standard plasma pixels, Ishimoto says that "the luminous efficacy of the plasma tube is almost 4 lumens per watt, about four times higher per unit area. It means that a power consumption of one-fourth can be achieved with the same screen size." On the other hand, the larger pixels mean the technology cannot easily be scaled down to meet the higher resolution required for displays in the home.
Fujitsu Fellow Tsutae Shinoda, an inventor of the new display and head of the plasma-tube development group, notes that a major advantage of the tubes lies in their low production cost. The technology is currently being tested for reliability and luminance lifetime, Shinoda says. Meanwhile, the research group is developing production and assembly techniques. Shinoda expects technical issues to be resolved by the end of 2005, paving the way for commercialization.