In a scene from Steven Spielberg’s 2002 film Minority Report, a future cop on the run ducks into the Washington Metro to evade his pursuers. Within seconds, a passenger’s paper-thin digital newspaper, displaying USA Today, updates to show the fugitive’s face.
We’ve reached the stage where people are reading on instantly updatable digital devices, but our devices don’t resemble newspapers so much as, well, tablets. Now, a breakthrough in computer displays that are both flexible and potentially inexpensive is poised to make this moment of movie sci-fi gadgetry a reality with a tablet that is rollable, researchers say.
The key is improvements in electronic paper, or e-Paper, which is designed to mimic the look of ink on a sheet. E-Paper enjoys multiple advantages over the displays currently used in tablets. First, it does not emit light like a TV but instead shares paper’s reflective qualities, meaning that it does not require constant power to be read—leading to significant energy savings. Second, since less energy is required, the battery is lighter. Third, e-Paper has minimal glare so not only does it tire eyes less but it also can be read in sunlight.
But e-Paper can look somewhat dim, often reflecting only about 40 percent of all incoming white light because it fails to completely hide its ink. Furthermore, it often switches between images relatively sluggishly, too slow for anything but crude video.
Now, scientists have devised a new kind of e-Paper that demonstrates more than 90 percent reflectivity, exceeding the 76 percent of magazine-quality paper. In addition, the device can switch the images it displays every 15 milliseconds, compatible with video rates of speed. It combines the best elements of tablets and e-Paper.
“Other people have demonstrated rollable paper-thin displays before,” said researcher Jason Heikenfeld, a display scientist at the University of Cincinnati and director of the Ohio Center for Microfluidic Innovation. “But those were too dark to give color, and too slow to give video. We’re getting closer to giving both.”
Moreover, unlike most tablets, which are manufactured with rigid glass, this new e-Paper is made of plastic. This makes it flexible and thin enough to be rollable.
In conventional e-Paper, the pixels comprising the images making up text, photos and video are each typically separated by borders that keep pixels from bleeding into one another. Although these borders are invisible to the eyes of consumers, they are basically dead, inactive space that dull any display.
This new e-Paper is a first in that its pixels have no borders. At its heart is a white porous film that ink can move through to show in front of or hide behind. Below it is a layer that holds all the ink. Sandwiching these are transparent plastic sheets that also hold the e-Paper’s electronics, which apply the electric fields on the ink that make it move back and forth.
The ink is allowed to pool underneath the white film, and when it is needed, it is electronically summoned up through pores in the film. This ink spreads out over the surface of the white film in droplets just large enough to fill the desired pixels. The design of the ink and the film allows these droplets to cling on the surface, just as raindrops can grip onto the surface of a car even when wind is blowing. Structures jutting out from the film help make sure the ink does not run together when the paper is squeezed.
“We spent about 12 to 18 months at the whiteboard just working through this theoretically before we had our ‘aha’ moment,” Heikenfeld said.
The new e-Paper’s lack of pixel borders also significantly simplifies the manufacturing process, he added.
Higher resolution needed
So far the e-Paper has a resolution of 150 pixels per inch, which is useful enough for billboards and other signs. “Much higher resolution is fairly straightforward to fabricate, and will be developed,” Heikenfeld said.
Thus far, this new e-Paper is black and white. Researchers plan on developing a color version that works much like LCD screens do. The white sheet would have color filters put over it, effectively splitting each pixel into four sub-pixels that are side by side — red, green, blue and white. Color e-Paper cuts the brightness by about half, Heikenfeld said, but the breakthrough means the brightness would still be commercially acceptable.
“If this technology turns out to be robust and if it can be manufactured at a low cost, there is a high probability of commercialization,” said display scientist Jurgen Daniel at technology consulting firm Booz Allen Hamilton, who did not participate in this work.
The scientists are currently working with Cincinnati-based startup company Gamma Dynamics to develop their e-Paper. Their plan is to make signs with the e-Paper in two years and e-readers in three years, Heikenfeld said.
Charles Q. Choi has written for Scientific American, The New York Times, Wired, Science and Nature, among others. In his spare time, he has traveled to all seven continents, including scaling the side of an iceberg in Antarctica, investigating mummies from Siberia, snorkeling in the Galapagos, climbing Mt. Kilimanjaro, camping in the Outback, avoiding thieves near Shaolin Temple and hunting for mammoth DNA in Yukon.