Display Week 2009 Review: E-Paper and Reflective Displays

Momentum builds for electrophoretic and other reflective technologies.

by Paul Drzaic

MORE THAN AT ANY OTHER TIME in the past, this year's SID Symposium provided strong evidence that the value of paper-like displays is finally being recognized. Reflective LCDs have been around for about 40 years, and electrophoretic displays for about 30 years. Early uses of LCDs were in low power, relatively low-resolution applications such as watches and calculators. Despite this long history, there has rarely been a set of high-resolution applications that took advantage of the positive aspects of reflective displays, while also balancing their shortcomings as compared to conventional backlit LCDs. These days, though, increased interest in mobile devices that are low power and can be used in any viewing environment has finally resulted in greater demand for electronic-paper solutions. Now, major companies and startups alike are promoting their visions of e-paper.

E Ink, more than any other company, helped establish the modern view of what a reflective paper-like display should be. The SID Business Conference opened with the announcement that Taiwanese company PVI and E Ink had agreed to terms for PVI to acquire E Ink for the sum of $215 million. (For more on the acquisition, see "E Ink to Be Acquired by Prime View International" in the Industry News section of the July issue of ID.)

In its booth on the exhibit floor, E Ink showed its latest developments in reflective color displays, including several panels capable of rendering animations in small windows within the panel. E Ink Vice President of Marketing Sriram Peruvemba indicated that E Ink plans on launching color products next year (Fig. 1).

A number of major display companies were demonstrating electronic-paper panels that used the electrophoretic-display medium sourced from E Ink. NEC had an impressive example in its exhibit – a 13.8-in. panel with 43% reflectivity, 16 gray levels, and a resolution of nearly 150 ppi.

Another company showing a range of e-paper products in its booth was iRex Technologies, an early proponent of electronic-paper displays. The CTO of iRex, Alex Henzen, also presented a well-attended symposium paper on the prospects for full-color e-paper displays using subtractive-color schemes. Henzen noted that the electro-phoretic displays of today will provide increasing levels of performance (Fig. 2), but some challengers, such as cholesteric displays and electrowetting displays, may be better suited for bright, full-color displays.

Fig. 1: E Ink showed color prototypes at Display Week.

Fig. 2: With 16 gray levels, an integrated touch screen, WiFi connectivity, and more, this electronic reader from iRex Technologies embodies most of the desirable features of today's electronic readers.

Success breeds competition, and a number of companies made it very clear that E Ink's digital ink technology is not the only game in town. In the electrophoretic arena, SiPix Imaging has tightened its relationship with Taiwanese panel maker AU Optronics Corp. through substantial investments. The SiPix booth had an e-reader panel from the collaboration with AUO. Wintek was also showing at its booth a number of electronic-paper displays that had been built using SiPix films.

There were also multiple reminders that electrophoretic technology is not the only option for reflective displays. Qualcomm, for example, showed the latest advances in its Mirasol displays in its booth. The Mirasol display relies on micromechanical elements that produce color through the same mechanism of reflective interference that gives butterfly wings their iridescence. The displays are effectively bistable; one particularly striking demonstration showed that a 2.2-in. panel required less than 1 mW of power to hold an image. While current displays are still relatively small in area, the capability for video-rate performance, good color in a sunlight-viewable reflective display, and a low-power static mode makes this technology a serious candidate in the reflective race (as well as the race for advanced mobile displays) (Fig. 3).

At the Display Week Business Conference, Mary Lou Jepsen of Pixel Qi (a spin-off from the One Laptop per Child initiative) showed slides of the company's new display prototype. The panel works as a reflective display in bright ambient lighting conditions, including direct sunlight, and has an appearance somewhat similar to electrophoretic-based displays. Unlike electrophoretic displays, however, the display also has a backlight for low-ambient-light conditions, which produces a full-color image. Because it is based on conventional liquid-crystal technology, it should also possess response times suitable for motion video. Jepsen claims that the display entry into the marketplace will benefit by compatibility with the existing LCD manufacturing infrastructure. No other details regarding the actual construction or specific performance are available from the company at this time.

Sharp demonstrated an interesting set of polymer-network liquid-crystal displays, which rely on a liquid-crystal layer coupled to a reflective surface that switches from scattering to transparent. These displays were connectedto a memory element built into the display backplane, so the display is effectively bistable, possessing a low-power memory capability.

Liquavista also emerged as a contender on the electronic-paper front, demonstrating both reflective and transflective electrowetting displays. The reflectivity of these displays is quite respectable, with the capability of switching at video rates. The company has recently shifted focus away from simple displays for high-volume consumer items toward high-resolution, reflective display products.

Electronic skins were a hot topic in San Antonio. Kent Displays exhibited its Reflex line of products, featuring a thin polymer "skin" that can be thermoformed around various shapes, and then switched between multiple colors. Imagine a cell phone that instead of vibrating, turns red, blue, or green based on the identity of the caller! The skins, which draw power only when switching, hold potential for numerous applications (Fig. 4).

Hewlett-Packard also presented a paper on its vision of electronic skins, showing samples of plastic film that could switch between intensely colored and less-colored states. The film is fabricated on a roll/roll basis.

Overall, many of these displays were somewhat reminiscent of the magical newspapers that appeared in the popular Harry Potter movie series: paper-like displays, but with areas of color and animation, providing a mix of static and dynamic images. I believe that technology is catching up with vision in these cases. Much of that technology is still in the demonstration category, but the race is definitely on to roll out the best applications with these new capabilities and get them to market. •

Fig. 3: This Qualcomm Mirasol display holds an image using less than 1 mW of power.

Fig. 4: Electronic-skin technology from Kent Displays allows switching between multiple colors.