The Promise of Flexible Displays New Screen Materials Could Lead to Portable Devices That Are Anything but Rectangular, Flat, and Unbendable

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Technology | doi:10.1145/1953122.1953130 Tom Geller The Promise of Flexible Displays New screen materials could lead to portable devices that are anything but rectangular, flat, and unbendable.

ver since scientists first hacked oscilloscopes in the 1950s, computer displays have been heavy, fragile things. Even in a super-thin Elaptop, the quarter-kilogram screen is one of its heaviest parts—and the case required to protect it adds further bulk and weight. The screen also defines the form factor of most electronic devices as it’s a single component that’s rectangular, flat, and unbendable. Now several developments portend an industrywide change to displays that are lighter, tougher, and more flexible than the sheet glass of a traditional liquid-crystal display (LCD). These displays are just beginning to appear on the market, and are produced with methods that may also improve energy efficiency, lower production costs, and allow for display shapes and sizes currently impossible to achieve. Already these displays have started to appear in a variety of applications. The 75th anniversary issue of Esquire magazine gave them wide exposure by featuring e-paper that blinked “The future is now” on its front cover. Other A flexible electronic display is rolled out at ArizonaS tate University’s (ASU’s) Flexible Display uses already in the market include key- Center. The unbreakable displays were developed by ASU and Hewlett-Packard Labs. boards with auto-changing layouts, Front Plane, Back Plane

low-power shelf tags and point-of-sale devices currently pair the flexible dis- lay Center p s ads, and display windows on credit- These new display technologies com- play layer with an inflexible glass back i

card-size smart cards. But designers are prise two parts: a front plane that con- plane. E-paper is a reflective display; its ble D also rethinking product design around tains the imaging component, and a brightness comes from ambient light xi these new screens’ possibilities. Carl back plane that controls which pixels hitting the display’s face, as on a sheet ’s) Fle Taussig, director of Advanced Display are on. For a display to be fully flexible, of paper. Pixels in E Ink’s e-paper are ASU ty’s ( Research at Hewlett-Packard, notes the both parts must have that character- electrically dipolar units colored white i vers Dutch company Polymer Vision has istic. While dozens of companies are i

on one side and black on the other, n demonstrated a cell phone with a roll- competing to provide back planes, two floating in thick oil. Their refresh rate U tate out display, and suggests other possible front plane technologies have taken is currently quite low, at about four S ona

form factors. “You might have a display the lead. frames per second. E-paper is bistable, iz r A

that you keep folded up like a piece of One is electronic paper, or e-paper, retaining its image until it receives the f paper,” Taussig says. “You might open like that used in the Amazon Kindle, next signal. As a result it consumes en-

it halfway and use it that way, or you Barnes & Noble Nook, and Sony Reader ergy only when transitioning from one ourtesy o c h might open it all the way. You might Digital Book. The producer of the e-pa- image to the next. p have it partitioned with a keyboard on per in all three devices is the Massachu- The other front plane technology is

one part and a screen on the other.” setts-based E Ink Corporation. Those organic light-emitting diodes (OLEDs), Photogra

16 communications of the acm | june 2011 | vol. 54 | no. 6 news which emit rather than reflect light. In Memoriam OLED displays consume more power Flexible displays than e-paper, but are brighter and have Philippe faster refresh rates. They have a higher will have fast lumen-per-watt rating—that is, they use less power for comparable bright- growth during Flajolet ness—than comparable LCDs because the next several the latter cause liquid crystals to block Dies at 62 photons coming from a backlight. On years, but won’t the other hand, OLEDs actually emit Soon after Philippe Flajolet become mainstream passed away from a serious light themselves. illness on March 22, tributes Nick Colaneri, director of the Flex- before 2018, says started appearing in an online ible Display Center at Arizona State Jennifer Colegrove. book of tribute at INRIA from University, believes OLED displays colleagues, former students, and the legions of computer may eventually consume as little as scientists who were influenced 1/10th the power of LCDs, even as they by his contributions to the study deliver “a kind of intangibly superior of algorithms. Those who knew Flajolet, image quality. Put side-by-side, OLED an INRIA research director, displays are often seen as strikingly cost competitive with traditional glass- best remember him as more better looking.” That makes them a based displays. than just an important theorist, likely challenger in the $100 billion however; he was a proudly independent researcher, as well LCD industry, although OLED dis- Beyond Rectangular Thinking as a gifted raconteur and free plays are extra difficult to ruggedize Commercial products are available spirit who loved to play practical because they’re far more sensitive to for both e-paper and OLED displays, jokes on friends using complex oxygen and moisture. (E-paper is more including e-readers and advertising mathematical formulae. While working at INRIA, likely to be used in applications where displays. Today, e-paper claims far Flajolet earned the nickname pow-er and reliability trump bright- greater market pull than OLED, largely “Algorithmyx,” a nod to the ness and contrast.) because of e-readers. But Sriram Pe- popular Asterix books. As Richard J. Lipton noted in Some manufacturers have proposed ruvemba, E Ink’s chief marketing of- a blog post after Flajolet’s trying to capture both markets with ficer, points to other uses for e-paper death, the nickname could hybrid transflective versions based on that weren’t possible with previous hardly have fit more perfectly: e-paper, similar to the Pixel Qi LCD display technologies. “Most requests I “More than his development of particular algorithms, one can screen on One Laptop Per Child’s XO get from design engineers are for rect- credit him much toward the computer. That screen includes both a angular displays, because that’s all development of algorithmics as backlight for low-light situations and they were able to get before,” says Peru- a professional discipline.” From his perch at INRIA, a reflective layer for easy reading when vemba. “I tell them, ‘Think outside the Flajolet devoted most of the sun is out. Transflective displays rectangle.’ With our flexible display, his career to studying the with e-paper or OLED front planes are you can cut it in any shape, so it’s only computational complexity not currently available, but they’re limited by imagination. Right now the of algorithms, the theory of average-case complexity, his possible because the back plane could device has to accommodate the dis- transform-based asymptotic be made from reflective or transpar- play, but in the future the display will analysis, and the symbolic ent materials. accommodate the device.” method, a novel approach to deriving the properties of With their similarity to LCDs, the Shape isn’t the only feature avail- combinatorial objects. potential rewards for OLED displays able to this new breed of displays but “The contribution of Philippe are enormous. At the same time, e- unavailable to LCDs. Because an LCD’s to the research on algorithms paper is defining new market seg- transparent electrodes must remain was essentially analytical,” says Micha Hofri, a computer ments, notably in portable electronics a set distance apart, they can’t be flex- science professor at Worcester and large-scale signage. According to ible, and are therefore made of thick, Polytechnic Institute, “and even Jennifer Colegrove, vice president of rigid glass. Transporting large sheets his algorithmic innovations, emerging display technology at Dis- of glass is difficult and expensive, so such as approximate counting of elements in multisets, came playSearch, flexible plastic displays LCDs are generally limited to a few as the result of a mathematical will grow at an annual rate of nearly square feet in size. But flexible displays insight.” 60%, surpassing $8 billion in sales in can be made on material that’s stored Hofri recalls meeting Flajolet at INRIA in the 1980s, 2018 from its current level of about and shipped in a roll, much like a web- when Flajolet wagered a bottle $300 million. Colegrove believes that fed paper press, enabling display sizes of champagne over whether one although flexible displays will have of a few meters wide by hundreds of of Hofri’s analyses had already fast growth in the next several years, meters long. been completed by another researcher. Hofri lost the bet, they won’t become truly mainstream But with that flexibility are some but made a lifelong friend. “It before 2018, both because of technical practical problems. “How do you han- was a good bottle,” he recalls. problems and the task of making them dle flexible substrates for TFT [thin- —Alex Wright

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film transistor] manufacturing?” Co- for a mechanic or technician who’s plastic, or some other material, flex- legrove of DisplaySearch has asked. assembling jet aircraft, and won’t ible display technologies represent the “Glass is easy: It’s a rigid sheet, and you have to go back to a table to see a sche- leading edge in changing the shape just put layers on it. But with flexible matic. Or a health-care technician or of computing devices. Consider the displays it can be hard to register for nurse could keep track of medication laptop computer, which in essence the very accurate positioning you need. and patients and such. It’s very hands comprises a screen, keyboard, and pro- Also, some plastics deform when you free. If it gets smashed into a door it’s cessor. Flexible rubber keyboards are heat them up, which can affect manu- not going to break. It’s very low power, already available at big-box stores, and facturing. Therefore, several new pro- and it’s light.” several manufacturers make “virtual cesses have been invented.” Hewlett-Packard’s devices will be keyboards” that project laser images To address registration problems, built with E Ink’s e-paper displays of the keys onto any flat surface. Flex- some manufacturers have champi- on a plastic substrate. But plastic ible plastic electronics are in active oned a roll-to-roll process that allows wouldn’t work for OLED displays as development, with the Russian corpo- them to print electronics with greater its permeability would doom the sen- ration Rusnano recently announcing precision than traditional photoli- sitive OLEDs to a short life. For those development of a $700 million factory thography allows. Photolithography applications, Corning Inc. is develop- to produce such electronics. The age is an “exposure” system: Light affects ing a kind of flexible glass by extend- of the Dick Tracy wrist computer is al- chemistry that etches electronics, ing its proprietary fusion process, ready upon us. With flexible displays similar to how an old-fashioned photo which it already uses to create thin leading the way, there’s no limit to the enlarger affects an image on paper. By glass substrates such as the Eagle XG shapes of computers to come. comparison, the roll-to-roll process line. While glass is necessarily heavier places electronics directly on a sub- and more sensitive to certain stresses, strate and is more similar to a modern Corning flexible glass commercial Further Reading inkjet printer. program manager Jill VanDewoestine Chung, I.-J. and Kang, I. Hewlett-Packard’s explorations believes the industry will respond well Flexible display technology—opportunity and challenges to new business application, with unusual form factors led it to close to this development because of glass’ Molecular Crystals and Liquid Crystals 507, a contract with the U.S. Army for wrist- distinctive qualities. Sept. 2009. mounted devices that would make crit- “Glass is really the standard,” FlexTech Alliance for Displays & Flexible ical information more easily available Van-Dewoestine says. “Its surface Printed Electronics to soldiers in the field. As designed, is very smooth; it’s stable; high pro- http://www.flextech.org/ the devices are only about 1.5mm thick cess temperatures are possible; it’s Forge, S., Blackman, C., and Lindmark, S. and feature a screen that curves half- transparent; and it’s an excellent bar- Plastic promises: the disruptive potential way around the wrist, the other half rier against oxygen and moisture. So of OLEDs and e-paper for the European being a set of flexible photovoltaic cells people really want to work with flex- display industry, Foresight 11, 3, 2009. to provide power. Taussig expects to ible glass—it gives them the handle- Jeong, J.K. deliver prototypes to the Army by this ability of roll-to-roll processes with The status and perspectives of metal autumn, and sees viability for such de- the characteristics of glass that make oxide thin-film transistors for active matrix flexible displays, Semiconductor Science vices well beyond its first customer. high-quality electronics possible.” The and Technology 26, 3, 2011. “We imagine a lot of use cases,” he company is currently developing flex- says. “[A flexible plastic screen] could ible glass that’s 1/10th of a millimeter Tom Geller is an Oberlin, OH-based science, technology, be built into the cuff of a delivery driv- thick and can be wrapped around a and business writer. er’s uniform and include mapping in- core that’s three inches in diameter. formation and the like. Or maybe it’s But whether incorporating glass, © 2011 ACM 0001-0782/11/06 $10.00

Milestones American Academy Announces the Class of 2011

The American Academy of and the arts. Members Michael I. Jordan, University and technologies. Arts and Sciences elected 212 contribute to studies of science of California, Berkeley; Shree “It is a privilege to honor new members in its Class of and technology policy, global K. Nayar, Columbia University; these men and women for 2011, including nine computer security, social policy and Patricia Griffiths Selinger, their extraordinary individual scientists. As members of one of American institutions, the IBM Almaden Research accomplishments,” said Leslie the most prestigious honorary humanities, and education. Center; Peter Williston Shor, Berlowitz, American Academy societies and a center for Newly elected members Massachusetts Institute of president. “The knowledge and independent policy research, the in the computer sciences are Technology; and Avi Wigderson, expertise of our members give Class of 2011 includes some of Edmund M. Clarke, Carnegie Institute for Advanced Study. the Academy a unique capacity— the world’s most accomplished Mellon University; Edward W. Leah H. Jamieson, Purdue and responsibility—to provide leaders in academia, business, Felten, Princeton University; University, was inducted in the practical policy solutions to the public affairs, the humanities, Eric Horvitz, Microsoft Research; section of engineering sciences pressing challenges of the day.”

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