Sep 1, 2002 12:00 PM,
PETER H. PUTMAN, CTS
The dealer selling the 50-inch plasma display, the commercial or home theater installer who sets it up, and the customer who drools in anticipation probably never look at a plasma panel and consider the wordsdinosaurandextinction. That probably stems from the ever-increasing numbers of plasma monitors and integrated TVs flowing from factories in Asia to dealer showrooms and boardrooms and media rooms.
More likely, those words are associated with CRT rear-projection monitors and integrated TVs, as well as direct-view monitors and TVs.
However, the lowly direct-view picture tube still accounts for more than 90 percent of all consumer TV sales worldwide. Most big-screen TV sets still have 7- and 8-inch projection tubes tracing away inside them. Plasma monitors have a ways to go to catch up, which they probably won’t do until 2006 or 2007, according to one major display research firm.
Even so, plasma display panels are challenged with larger, improved active matrix LCD panels, such as those emerging from Samsung, LG-Philips, and Sharp factories in 30- and even 40-inch sizes. Yet the long-term threat to plasma lies elsewhere.
Way off on the horizon is another challenger for the title King of Flat Screens. It is solid-state, uses lower voltages than plasma, and can be manufactured in even thinner profiles than AM-LCDs.
The new kid on the block is the organic light-emitting diode (OLED). Everyone is familiar with LEDs — they’ve been around for decades and are used in everything from car dashboards to portable electronics as indicator lamps. But those are the more common forms of LEDs, using conventional semiconductor PM junctions.
OLEDs are different. Manufactured in thin films, they can literally be ink-jet printed. They can sustain a certain amount of flexing, which makes them ideal for cellular phones and portable electronics. Best of all, OLEDs operate at fairly low voltages, typically in the range of 0 to 20 VDC, depending on the technology being used.
Eastman Kodak developed the first OLEDs in the late 1980s, using the small-molecule method. In a simple OLED, a conductive organic layer separates the cathode electrodes and anode electrodes. The number of “holes” must equal the number of electrons, for as each electron collides with a hole, a photon is emitted.
Think of a solid-state replacement for a CRT, and OLEDs come immediately to mind. As emissive displays, OLEDs are inherently bright and have wide viewing angles. Their resolution can be every bit as high as LCD or plasma, and they exhibit low power consumption. Many in the industry think OLEDs will eventually replace plasma — and perhaps LCDs, if the manufacturing costs and technical hurdles can be overcome.
Most importantly, LED switching speeds are fast enough to handle the high refresh rates needed for full motion video. They can do so in one of two ways: either by responding in an analog fashion, producing varying levels of brightness depending on the driving voltage, or by switching on and off rapidly in a pulse-width modulation system as used by large LED tiled displays.
There are more than a few believers in OLEDs. Kodak has licensed its small-molecule OLED technology to Sanyo and is producing small displays suitable for handheld electronics in a Kodak-Sanyo factory in Japan. Other small-molecule OLED research is being conducted by Pioneer, Sharp, Sony, Samsung, and eMagin while a competing method — polymer OLED, developed by CDT — is being fabricated by heavy hitters such as Dow Chemical, DuPont, Three-Five Systems, Osram, and Philips.
Other major players are being added to the list each month. At the recent Society for Information Display show in Boston, Toshiba/Matsushita showed a 17-inch, 1,280-by-768-pixel AM-OLED display that had beautiful color and nice video. Sony attracted a crowd to its 13-inch, 800-by-600-pixel AM-OLED screen, which showed only still images. That display measured less than ⅜-inches thick (try that with plasma), as did some 2- and 3-inch AM-OLEDs shown by Samsung and Kodak.
The Kodak exhibit was particularly intriguing, because it had examples of OLEDs in cellular phones, PDAs, and even game controllers such as Nintendo. For OLEDs to really take off, there has to be a big demand for them at the outset, and small, active-matrix color displays used in personal electronics constitute the biggest market you can define for displays. Mass production and mass demand mean that manufacturing economies of scale and price will be achieved that much faster.
That is a good thing, too, because a few technical obstacles stand in the way. OLEDs require twice as many driving devices to operate, mainly to assure uniform brightness and color saturation across the image. Consider that basic high-temperature polysilicon panels used in portable and installation projectors employ one and often two switching transistors per pixel, with the second transistor being redundant in case of device failure.
In contrast, OLEDs require as many as four switching transistors per pixel, which adds to the cost of silicon drivers considerably. Being diodes, they use a fair amount of current, so there’s the chance that individual LED junctions can burn out, just as plasma pixels can burn-in or TFT switches in AM-LCDs can fail.
Still, OLEDs bring the advantage of emissive direct-view imaging to the table with low operating voltages, something plasma may never be able to do. Consider that a typical plasma pixel cell must fire at 150V to 200V and sustain at 75V to 100V to overcome the high impedance and low conductivity of the argon-neon gas mixture. OLEDs have no such difficulty, as they are low-impedance devices, and there’s no gas to seal in.
How do OLEDs stack up against AM-LCDs? Nicely. Remember that AM-LCDs are transmissive light shutters and merely regulate the light from a constantly ignited cold-cathode lamp. But in an OLED, individual pixels don’t use any power unless they are turned on. Black levels and contrast may even be improved over what LCDs can possibly achieve, and gray scales with 256 levels of RGB are being demonstrated at trade shows.
THE RACE IS ON
Some analysts feel the real race in the future will be between OLEDs and variations of AM-LCD technology. Part of the reason is that AM-LCD fabrication (unlike plasma) is a mature process in terms of manufacturing and costs. Look at the Samsung, Zenith, ViewSonic, and Zenith booths at trade shows if you need proof.
Want a 15-inch, DTV-ready, 1,024-by-768 AM-LCD TV that weighs less than eight pounds? That will set you back only $800. How about a 30-inch, 1,280-by-768 wide-screen DTV-ready monitor with speakers? You’ll need to fork over $6,000. (You can get a 32-inch plasma for about the same amount, but it won’t have true HD resolution.)
By all accounts, OLEDs are capable of equaling several of those benchmarks (price, resolution, and form factor) and, in some cases, lowering them (weight). It is only a matter of time and how many millions of dollars companies are willing to invest in OLED research. Successful production and use of OLED screens in handheld electronic devices will be the key.
How long will it be before the storm hits? Probably not for another five years, according to display industry analyst David Mentley of iSuppli/Stanford Resources. His forecasts show AM-OLEDs first becoming competitive with small AM-LCD screens in 2007. How fast OLEDs will achieve parity with plasma is another guess, though at least one industry analyst (Ken Werner of Nutmeg Consultants and the editor of SID’s Information Display magazine) says a 40-inch, HD-resolution, 16:9 OLED display could be seen as early as 2008.
If you think a TV that you can hang on the wall is cool, what would you say about a TV with a peel-off, adhesive-backing layer that you could simply stick on a wall? It’s definitely possible with OLED technology. The only question is, when?
Peter H. Putman owns PHP Communications, in Doylestown, Pennsylvania. The author of The Toastmasters Guide to Audio/Visual Presentations, Putman is also a regular columnist in S&VC.