Third on our list of display tech to watch this year is e-paper, the technology behind most of today's popular ebook readers. Apple's April 2010 launch of the iPad media tablet and its runaway success gave e-reader manufacturers a scare. But while the market has bifurcated, the pie has gotten bigger and both markets continue to grow.
E-reader vendors are rolling out ever-more-sophisticated e-paper-based devices, including some with colour screens. And before long we'll even see e-paper displays fast enough to support video.
E-paper's killer app
Unlike LCDs and most other digital screens, e-paper displays are designed to look like ink on paper, with no backlighting required. The most popular type of e-paper in use today is E Ink's electrophoretic technology, which creates images by moving around charged white and black particles floating in a clear fluid. The current generation, called E Ink Pearl, offers faster refresh rates and better contrast than earlier displays and is found in such popular ebook readers as Amazon's Kindle 3.
In fact, the e-reader has become the quintessential application for e-paper display technology. The reflective, low-power, high-contrast display media is perfect for reading page after page of black-and-white text with minimal strain on the eyes.
Many people who spend a lot of time reading appreciate e-paper displays, which are thin and light enough to hold in one hand, easier on the eyes than backlit LCD screens and viewable in bright sunlight. "LCD technology is better suited [to] gaming and video than long-form reading," says E Ink vice-president Sriram Peruvemba.
E-paper-based e-readers can also last for weeks on a charge rather than hours. E-paper's power savings derive from the fact that the display media is bistable, which means it can maintain an image when power is turned off, and the reflective screen requires no backlight. (As with a paper book, you need an external light to read an e-paper screen in low-light conditions.)
After a few false starts for commercial e-paper-based e-readers in the mid-2000s, Amazon's original Kindle, launched in 2007, became an instant hit and gave the technology a major push. Competitors quickly launched their own models, and the market grew rapidly over the next two years, with about 3.6 million e-readers sold in 2009, according to Gartner.
"Then the iPad happened," says Vinita Jakhanwal, an analyst at market research firm iSuppli. Apple's wildly popular tablet, with its high-resolution, high-performance colour active-matrix LCD, split users into two camps: those who want a device optimised for ebook reading and those who read ebooks occasionally but also want a high-performance colour display that can support video and web surfing.
Following Apple's lead, other tablet vendors began incorporating ebook reading functionality into their own devices. And e-reader vendor Barnes & Noble has opted for LCD over e-paper in one of its offerings. The company's NookColor is an LCD-based device that runs on Android and blurs the line between e-readers and tablets.
However, despite the threat from the iPad and other media tablets the market for dedicated e-readers hasn't died. Quite the contrary: DisplaySearch predicts rapid growth for both types of devices. The market research firm expects more than 20 million e-reader units to ship this year, up from 14 million in 2010. Sales of touch-screen tablets and netbooks are expected to top 19 million units in 2010 before exploding to more than 50 million this year.
For its part, iSuppli is forecasting slower growth for the e-reader market in the wake of the iPad's disruption, but Jakhanwal says the trend is still upward.
Of course, e-paper isn't all about e-readers. E Ink says it has shipped 30 million displays for use in everything from wristwatches to smartphones and smart cards. E-paper also holds promise for applications such as electronic signage and shelf labeling.
But the e-reader, with its high-volume sales, is driving the market. It is the only application of e-paper currently in mass production - and E Ink controls 90 percent of that market segment, says Jennifer Colegrove, an analyst at DisplaySearch.
Overcoming e-paper's limitations
E-reader screens today suffer from two main drawbacks: screen-response times of about 200 ms (a page-turn time of about 1 second), make viewing video impractical; and the fact that today's e-paper-based e-readers offer only black-and-white displays. E Ink is working to solve both problems.
The performance of E Ink's e-paper displays has been doubling with each successive generation - about every 18 months - and "dynamic range reflectivity" (what we think of as contrast in an emissive display such as an LCD) has been doubling as well. "We see this trend continuing in the near term," says E Ink's Peruvemba. Page-turn times are poised to drop to about half a second - better, but still not sufficiently fast to support full-motion video.
Last November, E Ink introduced its first colour display, the Triton, and Hanvon Technology in China announced that it will begin selling the first colour ebook reader to use the Triton technology in the Chinese market in the second quarter of 2011, and in the US later in the year.
E Ink's Triton display has colour filter overlays, which can have a negative effect on screen brightness, but the company says it compensates for that by using a brighter reflective background. The display supports a wide viewing angle, and the addition of colour will be a big step up for e-paper-based e-readers.
Still, "the colour reproduction [on the Triton display] is not even close to what you get on an LCD or OLED," says iSuppli's Jakhanwal. (Organic light-emitting diode is a competing low-power display technology that's steadily gaining traction in the smartphone market.)
One other Chinese company, Jinke Hanlin, showed a prototype Triton device at the 2011 Consumer Electronics Show, but there have been no additional product announcements yet.
Steve Secrist, an analyst at market research firm Insight Media, says the washed-out "comic book colours" of the Triton screen may have a hard time finding a market in the wake of the iPad. "It's kind of too little too late," he says. Instead, he sees a bifurcation of the market in which monochrome ebook readers hold one niche, while those who want a colour experience opt for a colour LCD tablet such as the iPad, which can offer brighter, more saturated colours.
And LCD technology may finally be ready to compete with another key advantage of e-paper displays. Pixel Qi has developed a transflective LCD technology that can be read in reflective mode in sunlight while supporting a transmissive backlight for indoor viewing. Beijing-based ZTE has introduced the ZTE Light 2 - it is the first tablet PC to use the technology in European and Asian markets but is not in the US yet.
Pixel Qi's reflective mode doesn't compare to E Ink's e-paper technology for contrast and readability for black-and-white ebook reading, says Norbert Hildebrand, an analyst at Insight Media. "But when you want to read at night, there's no comparison."
However, E-paper isn't standing still. Going forward, e-paper displays will continue to incrementally improve screen response times while increasing screen resolution and contrast ratios. "We are improving the electro-optic features to get closer to printed paper," E Ink's Peruvemba says. The company's current generation of e-paper displays already beat low-quality newspapers and paperback novels for readability, he claims.
Generally speaking, that's true, says Insight Media's Hildebrand, because a cheap paperback often has yellowed or grayish paper that offers lower contrast. E Ink-based displays are "in that range," he says. "But for every paperback? I would debate that."
New technologies on the horizon
Of course, E Ink isn't the only e-paper game in town, nor is electrophoretic technology the only option for creating e-paper displays. Many other companies are working on competing technologies.
Qualcomm is working on an alternative display technology that could further shake up the e-reader market by offering better colour and faster performance. Qualcomm's Mirasol display uses microelectromechanical system (MEMS) technology, which adjusts two conductive plates to either reflect light or absorb it for a series of screen subpixels.
By varying the gap between the plates and the voltage applied to them, Qualcomm can vary the wavelength of light emitted to create different visible colours. It then assembles red, green and blue subpixels into a single pixel capable of supporting an even wider range of colours. Think of MEMS as an array of very tiny, very fast shutters - fast enough to support full-motion video.
Mirasol is nearly bistable, using a tiny amount of voltage to maintain the display. Overall it consumes between one-tenth and one-hundredth the power of an LCD, depending on the application and its reflective screen doesn't require a backlight. The technology supports colour natively, without the need for colour filter or polariser layers, so colours are brighter. "We're positioned in the centre" for converged e-reader/tablet devices, says Qualcomm MEMS Technologies vice-president Jim Cathey.
Among E Ink's competitors, says analyst Hildebrand, "Mirasol is the closest to manufacturing volume". Qualcomm has been sampling a 5.7-inch display and says the first commercial e-reader/tablet to include it will arrive early in 2011. A smaller version for a much bigger market - smartphones - will debut sometime in 2013.
Cathey says Mirasol technology is not only more energy efficient than LCDs for tiny smartphone screens, but also more energy efficient "in general" than OLED displays.
Ken Werner, an analyst at Insight Media, agrees that because it's a reflective display, Mirasol probably would consume less power than emissive OLED technology for many applications. But for video, where refreshes occur 30 to 60 times per second, OLED might do better in some cases, he says.
Looking further out, a new e-paper display technology developed by Liquavista and now owned by Samsung also has the potential to support video. Liquavista's electrowetting technology is similar to electrophoretic technology in that it's liquid-based, but it combines an electrolyte of oil and water with a polymer layer that either attracts or repels the water droplets to create black, white or gray.
Applying one voltage pushes the oil into a corner; another pulls it back. Like E Ink's Triton, Liquavista's display adds colour by using a standard colour filter.
Liquavista's approach pushes oil across a liquid surface rather than through it, which makes it faster than E Ink's electrophoretic technology. "Moving the surface compression works faster than moving particles through liquid. It's really the physics," says Insight Media's Hildebrand.
Liquavista is targeting smartphones and converged tablet/e-readers and recently demonstrated an 8.5-inch prototype display that the company says is fast enough to support video at between 60 and 70 frames per second - well above the 30 frames per second required for full-motion video.
Former Liquavista CEO Guy Demuynck, who left the firm shortly after the Samsung acquisition, said Liquavista's technology is seven to eight times more energy efficient than a standard LCD "when images are changing or when playing video," and when the user is reading an -book, the display lowers the refresh rate frequencies to save power. But the technology is not bistable. For viewing static text and images, such as the pages of an ebook, electrophoretic displays will squeeze more hours out of the battery.
Electrowetting technology sandwiches the display media between a top and bottom layer of glass, while electrophoretic technology simply uses a polymer layer on top. That means that e-paper displays based on electrowetting designs will be thicker. But the technology also will allow manufacturers to build e-paper displays more cost-effectively by using existing LCD fabrication facilities with only relatively minor modifications.
As with electrophoretic technology, e-paper displays built using Liquavista's technology could be manufactured on a flexible plastic substrate, making them thinner and lighter. According to Demuynck, most returned e-reader products come back because the display glass gets broken. So the company is partnering with Plastic Logic, which is developing a display substrate that embeds the TFT array on an organic, plastic backplane. However, a commercial implementation is still three to four years away, according to Plastic Logic.
With its acquisition by Samsung, Liquavista has refocussed. Johan Feenstra, the founder and former CTO of Liquavista, has been named CEO and Liquavista now has the resources to produce, says Hildebrand. "If [Samsung] feels that it can be done within a year or two, there will be an enormous push for electrowetting. If they feel it can't be done, they will kill it. It will be a very good proving ground for the technology," he adds.
Flex it, curve it, fold it
The next innovation will be flexible e-paper displays. Unlike LCDs, which manufacturers build on a rigid glass substrate using a discrete, one-at-a-time manufacturing process, e-paper displays can be literally printed onto a range of surfaces - including glass, plastic, fabric, metal foil or even paper - using a potentially less expensive, but still unproven, "roll-to-roll" manufacturing technique. A substrate made from plastic or another nonrigid material allows manufacturers to create flexible displays.
While today's e-reader displays are built on plastic, they're housed in a rigid enclosure. The focus is on other benefits of plastic, such as its durability, thinner size and lighter weight compared with glass. Colegrove expects that to change. "Within 12 months, the consumer will be able to purchase flexible active-matrix e-paper displays," she predicts.
Eventually, the screens may lead to truly flexible product designs that can be rolled up, but early attempts are focussed on creating contoured display surfaces. LG Display, for instance, recently demonstrated a prototype 19-inch flexible e-paper display that can be gently flexed without a degradation of image quality.
E Ink already offers flexible displays in its small, low-resolution product lines, such as wristwatches. "Our imaging films are intrinsically flexible," says Peruvemba. The next step will be to create the same capabilities for use in the larger, higher-resolution screens used in ebook readers.
Peruvemba says E Ink has helped about a dozen manufacturers of e-readers and other devices create flexible backplanes for use with its flexible display. "In the next several months, we anticipate that our customers will commercialise high-resolution displays that are flexible," he says.
In the meantime
Rigid e-readers will continue to be the norm for the time being - the first with flexible displays won't appear before 2012 or 2013, says Hildebrand. This year, he says, "we will see some colour devices and we will see a lot of different products that try to cross the border between tablets and e-book readers".
And look for a slew of new, low-priced e-readers from Chinese manufacturers in time for the 2011 holiday season. "You'll see some very low-cost devices that Wal-Mart or someone will have for 60 bucks," he says.