Never a Dull Moment

Plasma and LCD monitors may face fierce competition fromOLEDs.

Philips’ 1.4in. passive-matrix monochrome polymer OLED. Photocourtesy of Philips Components.

If you had a chance to peruse Video Systems' first annualPlasma and LCD Buyer's Guide (see August issue), the number of modelsor the range of screen sizes might have surprised you. You might evenhave thought that this is what the future of monitors and televisionsis going to look like.

There is no doubt that direct-view monitors will employ flat screenswith a fixed-pixel structure. What isn't so certain, however, is thespecific technology used for those flat screens. It is possible thatthe technology may change several times over the next couple ofdecades.

When you think of plasma panels, do the words dinosaur andextinction ever cross your mind? Probably not, given theever-increasing numbers of plasma monitors and integrated televisionsflowing from factories in Asia to our shores. Currently, plain CRTsstill account for more than 90% of all consumer-television salesworldwide, while the majority of big-screen TV sets still use 7in. and8in. projection tubes. Plasma monitors have some catching up to do,which probably won't happen until 2006 or 2007, according toiSuppli/Stanford Resources.

Even so, plasma display panels will find stiff competition fromlarger, improved active matrix liquid-crystal display panels, such asthose now emerging from Samsung, LG-Philips, and Sharp factories in30in. and even 40in. sizes. But that's not where the long-term threatto plasma lies.

Way off on the horizon, where most people aren't even looking, isthe unexpected challenger for the title King of Flat Screens. It'ssolid-state, uses lower voltages than plasma, and can be manufacturedin profiles thinner than AM LCDs. The new kid on the block is theorganic light emitting diode, or OLED. We're all familiar with LEDs— they've been around for decades and are used in everything fromcar dashboards to portable electronics as indicator lamps. But theseare the more common forms of LEDs, using conventional semiconductor PMjunctions.

Organic LEDs are quite different. For one thing, they aremanufactured in thin films, which means they can literally be ink-jetprinted. For another, some versions can sustain a certain amount offlexing — ideal for cellular phones and portable electronics.Best of all, OLEDs operate at fairly low voltages, typically in therange of 0-20 VDC, depending on the technology.

If you think a television that you can hang on the wall is cool,what would you say about a television with a peel-off adhesive backinglayer that you could simply stick on a wall? It's definitely possiblewith OLED technology. The only question that remains is, when willOLEDs become a serious competitor to AM LCD and plasma imaging?

The first OLEDs were developed by Eastman Kodak in the late 1980s,using the small-molecule method. In a simple OLED, the cathodeelectrodes and anode electrodes are separated by a conductive organiclayer. The number of “holes” must equal the number ofelectrons because when an electron collides with a “hole,”a photon is emitted.

Think of a solid-state replacement for a CRT, and OLEDs comeimmediately to mind. As emissive displays, they are inherently brightand have wide viewing angles. Their resolution can be every bit as highas LCD or plasma, and given their low-power consumption, OLEDs,according to some in the industry, will eventually replace plasma— and perhaps LCDs — if manufacturing costs and technicalhurdles for OLEDs can be overcome.

Most important, the switching speeds for LEDs are fast enough tohandle the high refresh rates needed for full-motion video. They dothis in one of two ways: they can respond in an analog fashion,producing varying levels of brightness depending on the drivingvoltage, or rapidly switch on and off in a pulse-width modulation (PWM)system as used by large LED tiled displays.

There are many believers in OLEDs. Kodak has licensed itssmall-molecule OLED technology to Sanyo and is producing small displayssuitable 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 — apolymer OLED developed by CDT — is being fabricated by such heavyhitters as Dow Chemical, DuPont, Three-Five Systems, Osram, andPhilips.

Other manufacturers are being added to the list each month. At therecent Society for Information Display (SID) show in Boston,Toshiba/Matsushita showed a 17in., 1280×768-pixel AM OLED displaythat had beautiful color and nice video. Sony attracted a crowd to its13in., 800×600 AM OLED screen that was showing only still images.This particular display measured less than 3/8in. thick (try that withplasma), as did some 2in. and 3in. AM OLEDs shown by Samsung andKodak.

Kodak’s AM550L 2.16in. LTPS active-matrix, full-color OLEDfeatures crisp images and rich, saturated colors. Photo Courtesy ofEastman Kodak.

The Kodak exhibit was particularly intriguing. They had examples ofOLEDs installed in cellular phones, PDAs, and even game controllers,such as those made by Nintendo. For OLEDs to really take off, there hasto be a big demand for them at the outset, and small, active-matrixcolor displays used in personal electronics comprise the biggest marketanyone can define for displays. Mass production and mass demand meansthat manufacturing economies of scale and price will be achieved morequickly.

As usual, there are a few technical obstacles in the way. OLEDscurrently require twice as many driving devices to operate, mainly toassure uniform brightness and color saturation across the image.Consider that basic high-temperature polysilicon (HTPS) panels inportable and installation projectors use one and often two switchingtransistors per pixel, with the second transistor being redundant incase of device failure.

In contrast, OLEDs require as many as four switching transistors perpixel, which adds to the cost of silicon drivers. And being diodes,they use a fair amount of current, so there's the chance thatindividual LED junctions can and will burn out — just as plasmapixels can burn in, or TFT switches in AM LCDs can fail.

Still, OLEDs have the advantage of emissive direct-view imaging withlow operating voltages, something plasma may never be able to do.Consider that a typical plasma pixel cell must fire at 160V- 200V andsustain at 80V-100V to overcome the high impedance and low conductivityof the argon-neon gas mixture. OLEDs don't have this problem since theyare low-impedance current-switching devices — and there's no gasto seal in.

How do OLEDs stack up to AM LCDs? Quite nicely. Remember that AMLCDs are transmissive light shutters and merely regulate the light froma constantly ignited cold-cathode lamp. But in an OLED, individualpixels don't use any power unless they are turned on. Black levels andcontrast may even be improved over what LCDs can possibly achieve, andgrayscales with 256 levels of R, G, and B are now being demonstrated attrade shows.

There are some analysts who feel the real competition in the futurewill be between OLEDs and variations of AM LCD technology. Part of thereason is that AM LCD fabrication, unlike plasma, is a mature processin terms of manufacturing and costs. For proof, take a look at theSamsung, Zenith, ViewSonic, and LG-Zenith booths at any trade show.

According to display industry analyst David Mentley ofiSuppli/Stanford Resources, AM OLEDs should achieve parity with smallAM LCD screens by 2007. How fast OLEDs will catch up to plasma isanother matter, although at least one industry analyst, Ken Werner ofNutmeg Consultants and editor of SID's Information Display, sayswe could see a 40in., HD-resolution, 16×9 OLED display as early as2008.

By all accounts, OLEDs are capable of equaling, and in some caseslowering, many current plasma and AM LCD screens in price, resolution,and form factor benchmarks. It's only a matter of time and the millionsof dollars companies are willing to invest in OLED research. For now,successful production and use of OLED screens in handheld electronicdevices — cell phones, PDAs, TVs, and game controllers — isthe first step.

To comment on this article, email the Video Systems editorialstaff at vsfeedback@primediabusiness.com.