December 2001

Plasma Displays

Plasma displays produce extraordinarily crisp TV images using hundreds of thousands of xenon-filled cells.

By Technology Review

Plasma displays are wide enough, thin enough and light enough to hang on the wall as art. And though consumers have historically been reluctant to dole out the $15,000 to $25,000 it takes to buy a 127- to 160-centimeter unit, prices are starting to fall. Fujitsu Hitachi Plasma Display (a joint venture between the two Japanese giants) recently announced it would begin selling 81- and 94-centimeter versions for $4,500-not cheap, but not far from the price of top-of-the-line projection TVs used for home theater systems.

The sources of such high-quality images are hundreds of thousands of tiny, xenon-gas-filled cells sandwiched between two layers of glass embedded with rows of electrodes. Transparent electrodes in the top layer of glass run perpendicular to address electrodes in the bottom layer. Each cell is lined with either a red, green or blue phosphor, a material that glows when exposed to radiation. Application of an alternating current to two electrodes (via a third auxiliary electrode) produces an electric field in the xenon cell between them. The field energizes the xenon atoms, knocking loose electrons. This creates a plasma, or cloud of electrons and positively charged xenon ions. Within microseconds, some of the electrons fall back into orbit around xenon atoms and relinquish their energy in the form of ultraviolet light. The ultraviolet light strikes the cell's phosphor lining, stimulating it to glow brightly in its characteristic color.

Three cells-one red, one blue and one green-combine to produce one pixel. Different intensities of the three primary colors blend to create more than 16 million different colors-a long way from the 1964 prototype designed by electrical engineers Donald Bitzer and H. Gene Slottow at the University of Illinois at Urbana-Champaign, which projected monochromatic points of orange light and shapes. Because each pixel is illuminated, the image is perfectly focused across the screen, offering viewers a 160-degree viewing angle-instead of the 120-degree angle afforded by projection televisions-and a chance to spread out across the living room for more comfy seats.

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