Display Week 2009 Review: Flexible Displays
The technology moves closer to "product" status.
by Robert Zehner
DISPLAY WEEK 2009 marked a turning point in the development of flexible displays. While there were still a number of technical presentations and posters detailing new scientific findings on ways to manufacture flexible electronics, this year a handful of firms appear to be on the verge of launching non-glass active-matrix display products in high-volume consumer products.
This move from the lab toward the factory was made clear in the opening-day keynote address from Martin Jackson, CTO of Plastic Logic. Jackson spent very little time reviewing the organic-transistor technology behind Plastic Logic's E Ink electrophoretic-display technology that won its originators a Nobel Prize and would have been viewed as just short of magic a decade ago. Instead, he focused primarily on the challenges of building a business around it. "One of the difficulties with a new technology," Jackson said, "is convincing people to use it." In response to this difficulty, Plastic Logic is building not just a first-of-its-kind plastic display, but also an ultra-thin wirelessly connected reader device to bring those displays to the market. According to Jackson, the Plastic Logic reader will officially be launched at CES 2010 in January, although details of price and availability have not yet been announced.
Edzer Huitema from Dutch start-up Polymer Vision told a similar story in his invited symposium talk on Tuesday. Much like its competitors at Plastic Logic, Polymer Vision has tooled up an organic-transistor-backplane production line to mate with E Ink's electrophoretic display film. How-ever, Polymer Vision's display is not just bendable, but also rollable. Prototypes of its Readius handheld wireless reader have the display wrapping around the exterior of the unit when not in use, then unfurling for reading or Web surfing. Huitema's data show that the display performance remains rock-solid, even after 15,000 roll–unroll cycles. Unfortunately, recently published interviews with Polymer Vision CEO Karl McGoldrick sug-gest that the market launch of the Readius has been sidelined by the economic slowdown, which has dried up sources of capital. Actual product is still yet to come from this company. (For earlier references to Polymer Vision in Information Display, see "The Past, Present, and Future of Electronic Paper" in the January 2008 issue.)
Fig. 1: An example of numerous other flexible displays shown at Display Week was this curved e-paper display that Taiwanese panel-maker Wintek created by heating and bending a thin glass substrate.
Two other flexible e-paper displays caught my eye: LG Display's in-panel touch demonstrator and Wintek's curved glass display. Although LG Display has previously showed monochrome and color electrophoretic displays on ultra-thin stainless steel, this year they upped the ante by adding in-panel touch sensing. Visitors were able to use finger touch to interact with an 11.5-in. UXGA pro-totype constructed with E Ink's Vizplex electro-phoretic film, navigating forward and backwards in an electronic document. Using in-panel touch allows LG Display to preserve the brightness and contrast of the reflective display, while also supporting flex and curvature. Wintek was also showing a curved electro-phoretic display, built using a glass backplane (Fig. 1). The trick, according to Wintek, is to use relatively thin glass (0.3 mm) and to apply heat while bending to form the backplane into its final shape. While the resulting display is not truly flexible, there may be applications where a non-flat panel with a fixed curvature may fit the bill.
OLED makers are also making progress toward commercializing flexible emissive displays. I spent some time chatting with Rui-Quing Ma of Universal Display Corp. about the 4-in. QVGA flexible OLED display (co-developed with LG Display), integrated into a curved wrist-mounted unit that served as the centerpiece of UDC's booth (Fig. 2). "What makes this display special is how close it is to mass production," he answered. "One of the samples that we're showing has been around for over a year, and it still looks great."
Looking back 2 or 3 years, I have to imagine that many of the flexible demonstrators shown at SID were lucky to last through the week; i.e., if they were not changed out every night for a fresh sample. They seem to be more substantial now. On the other hand, the flexible OLEDs in Samsung's booth tended to the more conceptual. Consider, for example, the "flapping display," a 4-in. flex OLED suspended by one edge and fluttering in the breeze from a nearby fan. Nearby was a prototype of an electronic identity card with an embedded OLED display, apparently powered by an RF field projected from a coil placed a few inches behind the card. The display stepped through photos of a woman's face from a variety of angles, reminiscent of scenes from science fiction movies such as Minority Report or Total Recall.
In the trade-show world, there were very little true surprises; most of the above demonstrations and talks were well-publicized in advance of Display Week, to ensure that customers and press were on-hand. Hewlett-Packard, however, managed to deliver some excitement with a Monday morning press release announcing the launch of its new eSkins display technology. H-P did not officially exhibit at Display Week; the only way to see the first samples of eSkins was by private appointment. And so, Tuesday afternoon, I strolled a few blocks from the convention center to meet up with Ken Abbott, H-P's director of emerging technology, at an area hotel. After a brief introduction to the eSkins concept, Abbott revealed a series of prototypes, including both basic black films and an eye-popping trio of cyan, yellow, and magenta displays. The eSkins displays are thin, flexible plastic composites that can switch from highly colored to nearly invisible (H-P quotes 50–65% transparency) in about half a second.Abbott was tight-lipped about the underlying display technology, calling it "electrokinetic" – my unconfirmed best guess is that it is based on collecting or spreading colored fluid droplets, similar to an electrowetting display. Currently, eSkins are monochrome, with relatively coarse pre-defined segments and icons. That said, after attending H-P's symposium presentation by Tim Koch, it seems this might just be a first step in creating a full-color active-matrix reflective display by combining the eSkins imaging layers with H-P's inorganic flexible TFTs built using a similar process.
Fig. 2: Universal Display Corp. exhibited a 4-in. QVGA OLED panel integrated into a wrist-worn information device. Built using stainless flex TFTs supplied by LG Display, the display is only 0.3 mm thick and is held to a constant curvature within the device housing.