OLED: An Insider's Reality Check
OLEDs are like the old saw: They're always a bridesmaid, never a bride. Of all the display technologies developed during the latter part of the 20th century, none have captured the public's imagination like OLEDs.
Organic light-emitting diodes (OLEDs) are like the old saw—always a bridesmaid, never a bride. Of all the display technologies developed during the latter part of the 20th century, none have captured the public's imagination like OLEDs. They promise bright, super-thin displays that could be slapped on a wall like a refrigerator magnet, worn on your wrist a la Dick Tracy, or molded to a dashboard. But so far OLED hasn't made it to the mass adoption altar.
OLEDs don't require much power, and they're emissive displays by nature, making them excellent candidates for use under high ambient lighting. Best of all, OLEDs exhibit wide color gamuts and viewing angles. Sounds like the next big thing, right?
Unfortunately, OLEDs have been “the next big thing” for so long that announcements of breakthroughs in life cycle, manufacturing, and materials science are usually met with the same skepticism given the boy who cried “wolf.” AV pros find themselves wondering if they'll ever see mainstream OLED products make it to market in their lifetime.
Still, that hasn't stopped numerous companies from burning through millions of dollars developing and advancing OLED displays. Miraculously, these companies always seem to come up with a cool-looking OLED product (usually a hand-built big-screen TV or other display) in time for important trade shows, such as the Consumer Electronics Show or the Society for Information Display's DisplayWeek, kindling a new wave of industry buzz.
It's time for a fresh reality check of OLED.SERENDIPITY
What's the big deal anyway? To best answer that, let's step back in time a quarter century to the research labs at Eastman Kodak, where a pair of scientists inadvertently discovered organic compounds with light-emitting properties while trying to develop a new type of photocells. A patent was issued in 1987 for these compounds, known as small molecule organic light-emitting diodes (SM-OLEDs), and the race was on.
Two years later, researchers at the Cavendish Laboratory of Cambridge University found that OLEDs could also be made using conjugated polymers—specifically, a compound known as polyphenylene vinylene. That discovery led to a class of P-LEDS, or polymer OLEDs and the founding of Cambridge Display Technology, now a division of Sumitomo Chemical Co. What made the CDT discovery unique was that the phosphor compounds used in P-LEDs could literally be printed onto a display matrix.
Perhaps the most important discovery was that either approach (Eastman Kodak or CDT) could be adapted to a flexible display, one that could actually bend to a limited degree without breaking. And the display itself would be super-thin—less than a quarter-inch thick with protective glass and a substrate. In essence, you could build an OLED display into a cell phone, PDA, or a small TV and have it survive a moderate jolt (that's assuming the housing and associated electronics survive the fall).
The flexibility of OLEDs also led to developments in curved displays, such as virtual dashboards for automobiles. And it looked as though we'd finally be able to have a wristwatch TV, just like the one Dick Tracy used in the funnies back in the 1930s.IF AT FIRST YOU DON'T SUCCEED …
On paper, OLEDs sounded unbeatable. Unfortunately, a few problems stood in the way. The first was the relatively short lifespan of the organic compounds, which at the start was all of 1,000 hours for colors like yellow and green. Blue compounds weren't nearly bright enough and pooped out even faster, and red was also a challenge.
A Novaled technician examines red and green polymer OLEDs (P-OLEDs).
Another problem was uniformity. Early prototypes had severe problems with color shifts and changes in brightness across pixels, a big no-no for eventual use in televisions. And what about driving the pixels? Active matrix displays using thin-film transistors (TFTs) were a must for fast motion and switching speeds. Yet, it appeared that OLEDs might need twice as much silicon drivers as liquid-crystal displays (LCDs).
As the 1990s wore on and we crossed into a new century, nearly 40 companies were furiously at work trying to make OLEDs graduate from the lab bench to the production line. Some of the names you'd recognize, like DuPont, Toshiba, LG, Hitachi, Samsung, and Sony. Others you wouldn't, like Optrex, eMagin, Chi Mei, and Sumitomo.
Kodak stayed in the thick of things by creating a joint venture with Sanyo to build displays using white OLEDs with color filters that resembled LCD monitors. CDT made further advancements in its organic polymers and started work on a prototype P-OLED ink-jet printer that would microdeposit the red, green, and blue compounds automatically into an OLED substrate.
Over time, the market has seen several joint ventures come apart (most notably Kodak and Sanyo), a new business unit start up with a bang, then fade into the background (Dupont's Olight division), and several companies throwing in the towel altogether on OLEDs, such as Pioneer.
But there's also been good news. Both Samsung and Epson have shown 40-inch OLED TV prototypes in recent years. CDT continues to develop its proprietary inkjet P-OLED printing system. Ciba recently announced a new red phosphorescent material, developed for Dresden, Germany–based Novaled that is claimed to last 50,000 hours. And blue-channel OLED materials are now expected to exceed 20,000 hours before half-brightness.
Trenton, N.J.–based Universal Display Corp. has done considerable work in advancing SM-OLED technology. At last May's DisplayWeek show, UDC and partner LG Display showed a 4-inch QVGA full-color active matrix (AM) OLED display prototype that combines an amorphous-silicon backplane with UDC's proprietary PHOLED (phosphorescent) and TOLED (transparent compound-cathode) technologies. The display is built on thin metallic foil and was developed with support from the United State Department of Defense.
Sony created buzz last fall by finally getting its XEL-1 to market, making it the first commercially available OLED TV. The XEL-1 is an 11-inch display with 1024x600 pixel resolution, measuring 3 millimeters thick and using SM-OLED technology. Its peak power consumption is specified at about 45 watts.
The price? Ah, there's the rub. A whopping $2,500, which could also buy you either a 50-inch plasma or 52-inch LCD HDTV. The high cost of the XEL-1 may be a small price for early adopters to pay, but it reflects the low yields of current OLED manufacturing processes. (For some perspective, the XEL-1's retail cost per inch—about $227—works out to $9,545 for a 42-inch screen, which is what plasma displays were selling for a decade ago.)
Sony has also shown a 27-inch SM-OLED, but it's not ready for prime time. It measures 9 millimeters thick and has a 1920x1080 pixel matrix. Both it and the XEL-1 are rated at 200 nits average brightness and over 600 nits peak brightness. (Because OLEDs are emissive, their brightness varies dynamically with content, just like CRT and plasma displays.)
At the last CES, Samsung also showed a range of OLED TV products, including 14-inch and 31-inch prototypes, although neither is ready for market just yet. The company's SDI division, which also manufactures plasma displays, is fully engaged in active matrix OLED manufacturing and had previously set a target of Q4 2008 to start bringing OLED displays to market, but that target doesn't look certain now.