Computers Today, December 1-15, 1998 Tech Trends

December 1-15, 1998 TECH TRENDS

FLAT PANEL DISPLAY
Cut for the Multimedia Age

Hang it from the wall, embed it in a desk, or take it with you as a portable screen in a flight case: the plasma display panels are the latest rage in colour screen technology.

By Atanu Roy

Flat panel displays have always been the key to wall-hanging TVs and space saving PCs. But for many years, it looked like there would always be severe limitations in size, making the technology peripheral rather than central to the AV/PC industries. With its mass-produced large sized plasma panels, however, Fujitsu, Sony and Sharp have opened up a whole new chapter in the history of this product. Now, wall-hanging TVs are tangible realities.

What is a Plasma Display?

A plasma display uses two parallel glass panels on which electrodes covered with a dielectric glass layer have been etched. The front panel first goes through the patterning of transparent electrodes, followed by sputtering a film of chromium/copper/chromium (CrCuCr). The BUS electrodes (CrCuCr) are then patterned, a dielectric layer screen-printed and a final protective layer of Magnesium Oxide evaporated on. The back panel is processed a little differently: Address electrodes (CrCuCr) are first constructed, followed by printing of a dielectric layer and a rib pattern. The ribs are then sand-blasted and a fluorescent layer is screen printed, with a the sealant construction as the final step.

The 0.1 mm wide gap between the two plates is then filled with a xenon/neon (XeNe) gas mixture. When voltage is applied between the electrodes, ionised gas collects at the surface layer according to the polarity. The collected charge is called the wall charge, and it produces an internal voltage difference (wall voltage). As a result of the surface discharge, ultraviolet ray radiation occurs. This activates phosphor dots and visible light is emitted. A colour display is achieved by controlling the luminance from individual phosphors in the three prime colours. To maintain the discharge, the polarity of the external voltage is reversed. The applied voltage is lower than the initial voltage because the wall voltage remains inside the panels, so once discharging occurs, it continues unless it is stopped.

The PDP technology is simpler than that of active matrix liquid crystal displays where the sheets of glass have thin films of connected transistors etched into their inner surfaces and these are operated as individual switches, turning on and off to polarise the liquid crystal between the sheets, and so make light. There are currently two manufacturing methods for plasma displays. One is the AC-power method favoured by Fujitsu which developed the colour technology, and the other is the DC-power method, used by Sony, Sharp and other PDP developers.

War on the Display

Until recently, most people associated flat panel displays with liquid crystal display (LCD) technology. As the quality of colour plasma displays has improved, they in turn have become major contenders in this field, but there is room in the market for both technologies since their strong points and eventual applications differ.

The LCD panel suffers from a number of limitations such as severe yield problems as the size of the panel grows bigger and a narrow viewing angle. The problems with yield are likely to keep a focus on mass production of smaller screens. As for the viewing angle, what may be viewed as problematic for certain applications such as TVs or monitors that are used by several people simultaneously, can in fact be an asset on a single-user device such as a notebook computer. For example, the narrow viewing angle is a guarantee of privacy in a public place such as an aeroplane. More significant is the contrast between the self-luminescent PDP and the requirement for back lighting for a truly bright LCD.

In terms of image quality and viewing angle, colour plasma displays offer the biggest challenge to the traditional CRT, and industry watchers believe that they will eventually replace the CRT for larger size applications, that is 20-25 inch and larger, up to about 100 inches. The largest size of PDP currently on the market, 42 inch panel, weighs only 18 kilograms, one sixth the weight of an equivalent CRT. It is only about 65 mm deep, one tenth the depth of a CRT.

Applications for Plasma Displays

Flat panel displays can be divided broadly into three categories: LCDs, Projection LCDs and PDPs. LCDs are best used in devices such as notebook or desktop computers and other relatively small screens that are used by one person at a time, with screens generally no larger than 20 inches. Projection type LCDs usually cover the other side of the display size spectrum with screens that are generally larger than 70 inches but with less quality picture. PDPs, which are expected to cover the middle and the widest market of flat panel displays with applications such as large screen TVs, home theatres and large public displays.

Within the framework of PDP technology for home use in applications using screens ranging from 20 to 100 inches, demand for larger displays in the home will be fuelled by factors such as high definition television and a better multimedia infrastructure with services such as video on demand. PDPs have viewing angles of more than 160-degree which makes them even more suitable for television purposes than CRT since the flat surface of the panel in fact gives a wider angle than the curved CRT.

Outside the home, PDPs will be the technology of choice for applications such as financial terminals, public transportation, in-store displays, medium-sized displays in places such as department stores, museums, libraries or government offices as well as leisure facilities of all types. They are already in use at locations such as the New York Stock Exchange, Tokyo Central Train Station, and at CBS Evening News for remote interviews.

The last market to go over to PDPs will be the desktop PC market where cost is a major consideration and consumers increasingly demand greater sophistication for an inexpensive price tag. In the long run, however, CRTs of all sizes are likely to be completely eliminated in favour of flat panel displays such as PDPs due to the considerable advantages of the latter.

The Issue of Pricing

One of the most crucial elements in the success of any new technology is to price it within the reach of eventual consumers. The initial sample price of the 42 inch PDP was 1.0 million Yen but prices have already dropped to 500,000 Yen (about Rs 1.5 lakh) with mass production under way. By the time production reaches the 100,000 units per month scale, around the year 2000, the price of a television set should have fallen to around 420,000 Yen for the 42 inch size. Although these prices may appear high, they do in fact compare favourably with those of the larger CRTs since the list price of 36 inch models currently on the market is close to 500,000 Yen. Over the next few years, the existing 21 and 42 inch displays will be joined by a new generation of larger displays ranging from 50 inch to 70 inch. Fujitsu officials say the firm is targeting prices for TV sets using these displays ranging from 500,000 Yen to 700,000 Yen at that time.

As far as comparative pricing with LCDs goes, there is hardly an issue here since the two are unlikely to compete head-on. The fact, however, that PDPs are considerably easier to manufacture than LCDs should give the former a clear price advantage once mass production is under way.

The Major Players

Fujitsu has been developing PDP technology for the last 25 years and, following its experiences with monochrome PDPs, it has already been mass producing 21 inch colour PDPs for three years. Until now, the smaller displays have generally been used for notebooks, a product which has a relatively short life span due to rapid technological changes. TVs, on the other hand, are used for much longer periods and therefore need a longer-lasting display. Other companies are pursuing other variants of the technology. For example, Sony and Sharp are working together on a process called PALC (Plasma Address Liquid Crystal) which uses liquid crystal technology for the display and plasma technology for the memory. Sample shipments have already begun.

Multimedia is gradually moving from a vague concept to a real product. The integration of computer technology, game technology and TVs into a single unit is becoming likelier as home-use computers look up. PDP is the perfect platform for this confluence and its versatility will open up new possibilities for home entertainment.

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