E-paper closes in on video
Technology Research News
Books, newspapers and posters with moving
pictures -- mainstays of the Harry Potter novels -- could become part
of the real world before long.
Several electronic paper technologies are poised to deliver thin,
flexible screens whose pictures rival the crispness of printed paper.
Making pixels change fast enough to display video has been difficult,
Scientists from Philips Research in the Netherlands have come
up with an electronic paper scheme that works fast enough to be used for
video, draws little power, and paints a bright picture. It could also
be used to control fluids in other technologies like labs-on-a-chip.
The key to electronic paper is electronic ink -- tiny amounts
of substances that can be manipulated electrically like the pixels of
a display screen.
The Philips electronic ink changes color when electricity alters
the interface between water and a dyed oil, said Robert Hayes, a principal
scientist at Philips Research. Other types of electronic ink use tiny
colored particles suspended in fluid.
Each pixel of the Philips electronic ink is a thin sandwich of
a white insulator that is hydrophobic, a film of colored oil, and water,
said Hayes. "Because the insulator is hydrophobic the water does not want
to contact it and the colored oil film lies in between."
The position of the colored oil can be changed by sending electric
current to the insulator. In the presence of electricity "the surface
properties of the insulator are changed to hydrophilic," said Hayes. "Water
wants to contact the insulator and the colored oil film is moved aside
like a curtain," he said.
The oil is pushed into a corner of the pixel, exposing about 70
percent of the background through the water. The change makes that portion
of the pixel switch from the color of the oil to the white of the insulator
The pixels can be switched fast enough to show video, according
to Hayes. It takes 13 milliseconds to turn a pixel 90 percent of the way
on or off, which works out to switching more than 70 times per second.
Full motion video images change 24 to 30 times per second. The oil and
water scheme avoids the principal drawback to current particle-based electronic
paper -- a slow switching time of about four times per second.
The Philips method can also be used to switch among two different
layers of colored oil and the background, making each pixel able to reflect
two colors. The researchers used cyan, magenta and yellow oils and combined
three two-oil pixels with colored filters to make a single, full-color
pixel. Cyan, magenta and yellow are used in the subtractive color mixing
scheme of printing. Electronic displays use combinations of red, green
The three-in-one pixels make the screen brighter, according to
Hayes. The researchers' single-color-and-white prototype has a reflectivity
of 35 percent, and a three color display would have a reflectivity of
67 percent, versus 40 percent for particle-based electronic paper and
17 percent for liquid crystal displays, according to Hayes.
The oil films can be as close as 100 microns apart, which provides
a wide viewing angle, according to Hayes. One hundred microns is one tenth
of one millimeter, or about the thickness of a human hair.
The method is "a clever approach," said John Rogers, a professor
of materials science and engineering at the University of Illinois. "It's
interesting stuff, and has the potential to be an important technology,"
The approach is one of several technologies in the race to bring
electronic paper to market. The Philips system offers some advantages,
most notably speed, over other approaches, said Rogers. Ultimately the
winning technology will be determined by a large number of considerations,
including manufacturability, cost and reliability, he said. "It will be
a good horserace."
The researchers are working on finding cost-effective manufacturing
processes for the method, according to Hayes. The method could be ready
for practical use in three to four years, he said.
The ultimate goal is to make colored electronic paper that has
the ability to display moving pictures and that is bright enough to be
easily viewed both indoors and outdoors, according to Hayes.
The same method could be used to control layers of fluid in other
emerging technologies, including adaptive lenses, labs-on-a-chip, and
pixelated optical filters, said Hayes.
Hayes's research colleague was B. J. Feenstra. The work appeared
in the September 25 issue of Nature. The research was funded by
Timeline: 3-4 years
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Video-Speed Electronic
Paper Based on Electrowetting," Nature, September 25, 2003
October 8/15, 2003
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