If the screen on that sleek smartphone you just bought looks unusually bright and colorful, you might not be looking at an LCD at all. The displays in models such as the Samsung Galaxy S, the Google Nexus S and the HTC Droid Incredible rely on active-matrix organic light-emitting diodes (OLEDs), an alternative display technology that’s faster, thinner and lighter, offers more vivid colors at higher contrast, and uses as little as one quarter of the power consumed by your typical backlit, active-matrix LCD.
OLEDs have been around for more than a decade but have taken off only within last few years, and only for very small screens. Over 40 million active-matrix OLED phones shipped in 2010, and volumes will continue to increase this year, according to market research firm DisplaySearch.
Now the technology is getting ready to bust out of the mobile phone market and make its way into tablets, TVs and more — provided manufacturers can reduce production costs for OLED displays, which are now significantly higher than for LCDs.
And OLEDs have another cool attribute: The display media can be constructed on a flexible substrate, such as plastic or bendable foil, rather than the breakable, rigid glass backing used in LCDs. That sets the stage for a new generation of even lighter and more rugged displays in the next few years — and for curved, flexible, and even rollable displays down the road.
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Note: For greater readability, we’ve shortened AMOLED (active-matrix OLED) to OLED throughout this story. Passive-matrix OLED (PMOLED) displays are not used in smart computing devices or high-performance screens.
Fast, bright and energy efficient
Today’s commercially available active-matrix OLED displays are built on a version of the same electrical foundation as LCDs — an active-matrix thin film transistor (TFT) array fabricated on glass, which drives the display media above it (see “The display sandwich”).
But the layers of organic material that make up the OLED display media emit red, green and blue light, so no backlight is required, and the light doesn’t have to pass through color filters, as it does with LCDs. That’s what gives an OLED display its brilliance and energy-efficiency edge.
The display sandwich
A flat display is a complicated sandwich of materials, says Nicholas Colaneri, director of the Flexible Display Center at Arizona State University. Take an LCD, for example. At the bottom is a substrate, usually glass, upon which manufacturers fabricate a layer of thin film transistors out of silicon. The transistors in the TFT layer power the liquid crystal display media layer above it.
The TFT layer activates the liquid crystal layer, “which acts like a venetian blind,” Colaneri says. A backlight mounted behind the display sends light up through the liquid crystal and then through a color filter layer to produce the red, green and blue pixels that create the final image.
With an active-matrix OLED, manufacturers replace the liquid crystal and color filters with a series of four to seven layers of organic films sandwiched between two metal contacts. The films, mere thousandths of an angstrom thick, are a fraction of the size of the liquid crystals in an LCD.
The TFT layer applies the voltage to power the OLED layers. “When you push current through that stack, light comes out of it,” says Colaneri. So while the OLED stack still needs a TFT layer to make it work, the display sandwich can dispense with the backlight and color filter layers.
Samsung has been an early leader in OLED-based smartphones, notably with its Super AMOLED technology, found in the Galaxy S and other smartphones. By integrating touch sensors into the OLED panel “sandwich,” Samsung eliminated a layer of glass (or plastic) that the touch-panel overlay would usually include, which makes the display as a whole thinner.
The company’s next-generation display, dubbed Super AMOLED Plus, increases the sub-pixel count for a crisper, sharper image that’s more viewable in direct sunlight, according to Samsung. Super AMOLED Plus displays will be included in soon-to-be-released phones such as the Samsung 4G LTE, Galaxy S II and Infuse 4G.
So far, manufacturing challenges have limited volume production of OLED screens to just a few inches in size. But if manufacturers can scale up, an enormous market awaits: OLEDs promise faster response times, wider viewing angles and better color and contrast than LCD and plasma TV screens currently deliver.
OLEDs work on the basis of super-fast electron-hole interactions, in which negative and positive charges combine in the OLED’s emissive layer to produce light. In contrast, LCDs depend on electric-field-induced distortions of the complex molecules that make up liquid crystals, which respond much more slowly, says Ken Werner, analyst at Insight Media.
“OLEDs respond in microseconds — hundreds, if not a thousand times faster than LCDs,” says Janice Mahon, vice president and general manager at OLED technology provider Universal Display Corp. (UDC). “It switches like a semiconductor.”
While LCD response times fall into the 2 to 30 millisecond range, says Insight Media analyst Steve Sechrist, OLEDs respond in 2 microseconds. “It’s an order of magnitude in speed. It’s not just fast — it’s blazingly fast,” he adds.
Growing the market — and the displays
Manufacturers such as Samsung, LG Display and AUO are racing to build next-generation fabrication facilities in an effort to gradually scale up screens to the point where they can support the sizes demanded by the TV market.
Attempts to build larger screens have moved in fits and starts. Sony, for example, launched the XEL-1, an 11-in. OLED TV, back in 2008. But the $2,499 price tag put off many buyers, and Sony abruptly withdrew it from the market in 2010.
“We don’t have a timetable for commercialization at present,” a spokesperson says, although the company launched the PVM-740, a 7.4-in. OLED monitor aimed at professional video producers, last April. At $3,549, however, it is more a niche product than the XEL-1, which was targeted at the higher-volume commercial TV market.
But other manufacturers are pushing ahead — Samsung, for instance, has shown a prototype TV with a 31-in. OLED display at trade shows.
The overall market is set to take off like a rocket, according to DisplaySearch. The research firm expects sales for all types and sizes of OLEDs to jump from $1 billion in 2010 — which itself represents a 20% increase over the previous year — to $80 billion by 2017.
Right now Samsung owns the lion’s share of the total market for OLEDs, most of which are used in small-screen devices such as smartphones. Samsung supplied nearly 90% of the 46 million displays that shipped in 2010, according to market researcher iSuppli. While other manufacturers have plants in the works, “Samsung is the only one in mass production,” says analyst Vinita Jakhanwal.
With a new, $2 billion plant scheduled to come online later this year, the company will double its capacity, Jakhanwal adds. A spokesperson from Samsung’s Mobile Display unit in South Korea says the company projects that it will grow shipments by a factor of 35, to 700 million units by 2015.
The next generation of displays certainly won’t be big enough for television use, but the 5- to 7-in. screens likely to roll off Samsung’s production lines later this year will be perfect for small tablet PCs such as Samsung’s 7-in. Galaxy Tab, which currently uses an LCD screen.
Trouble spots
But can manufacturers overcome the obstacles to mass production of larger screens — and more demanding applications? Even in smartphone-sized screens, OLED-based displays cost 20-50% more to produce than comparable LCDs, a cost that’s usually passed on to the consumer, says Jennifer Colegrove, vice president of emerging display technologies at DisplaySearch. And at sizes larger than 10 inches, OLED displays can cost 500% more, she adds.
But Colegrove says that the technology has the potential to be cost competitive in the long term because the structure of an OLED display is simpler to build than an LCD.
OLEDs have another weakness: The lifespans of the organic materials that produce the red, green and blue colors vary — a problem known as differential aging. The blue OLEDs are the problem.
For example, UDC’s phosphorescent OLEDs, used in many manufacturers’ OLED display designs, can produce green and red colors that last for “hundreds of thousands of hours,” Mahon says. But the company doesn’t have a viable blue product yet. So for blue, display manufacturers use a fluorescent OLED technology that lasts only about 50,000 hours.
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Applications that use intense colors shorten color life faster, and those that use a blue background exacerbate the differential aging problem. Applications with a white background also cut down on display life and consume more power, since generating white light requires that the red, green and blue OLEDs all be on at the same time.
UDC’s Mahon says that the current generation of OLED displays exceeds the requirements for mobile applications and is “sufficient” for TVs. But Samsung and other display manufacturers are pushing UDC and others to produce longer lasting blue OLEDs for TVs and other demanding applications. UDC is working on it, Mahon says, but so far the company has been unable to create a blue OLED that can pass the 50,000-hour mark.
Rigidly flexible
Assuming those obstacles can be overcome and larger-sized OLED displays can be produced in volume, manufacturers will look next at moving off of glass substrates for the TFT backplane and onto either flexible plastic or metal foil, both of which are thinner, lighter and more durable than glass.
Some researchers say flexible OLEDs could potentially cost less to manufacture than LCDs because they can use print-based “roll-to-roll” processes to embed the transistor arrays onto the substrate, rather than the traditional, discrete process, called mask alignment. (For details, see “Flexible displays: What’s the holdup?“)
Samsung, Sony and others have demonstrated flexible OLED display products, and UDC has been working with LG Display to supply prototypes to the U.S. Army and Air Force, which value the flexible backplane’s durability.
The military prototypes are slightly thinner than normal OLEDs and slightly curved, but still mounted within a rigid case, UDC’s Mahon says. “But as the technology gets more robust we’ll conform it to a smaller radius, and then to something that you can roll in and out of a pen 100,000 times.”
But volume manufacturing of products with truly flexible or more dramatically curved displays is still a few years off. “It will take three to four years to be commercialized,” says DisplaySearch’s Colegrove. The first products won’t hit the market before 2013, and as with UDC’s prototypes, those displays will likely be housed in a rigid frame, integrated for the valued attributes of durability, thinness and light weight, rather than flexibility, she says.
In the short term, the ability to create curved displays will foster sleek new designs in OLED smartphones. For instance, Google’s recently released Nexus S features a subtly curved glass screen.
Technology hurdles aside, manufacturers need to see a sizable market demand before they begin mass-producing any new type of display. For flat OLED displays, that market is mobile phones and televisions. For flexible OLEDs, the jury is still out.
And even if there were a compelling market today, OLED manufacturers aren’t quite ready for production. Through 2011, Samsung and other OLED makers will have their hands full ramping up the new “Gen 5.5” fabrication facilities coming online that use glass substrates, says Insight Media’s Werner. “I don’t think we’ll see flexible active-matrix OLEDs in any volume before the second half of 2012, and maybe not then.”
A bright outlook
If flexible displays are still a year or two off, OLEDs are here to stay. Up until now the market has been supply-constrained, limiting the number of phones sporting the technology. “Samsung can’t supply enough OLEDs to its customers yet,” says Insight Media’s Sechrist.
But with Samsung and LG Display committed to bringing online new fabrication plants that can support small-tablet-sized displays later this year, not to mention investments by Taiwanese companies such as AUO, the technology is likely to start proliferating in cameras and smartphones later this year. And DisplaySearch predicts that the first OLED tablet devices will enter the market before year’s end.
“Even Apple might move in this direction,” Sechrist says. “OLED is the future of these smaller displays, and we’ve seen prototypes in laptops already.”
