Flexible display slims down
Technology Research News
The long-running quest to build a computer
screen that you can fold up like paper and put in your pocket is a little
closer to reality.
Researchers from E Ink Corp. have produced a high-resolution electronic
display that is 0.3 millimeters thick -- about four times the thickness
of a typical piece of printer paper -- and can be rolled into 4-millimeter
The researchers' prototype is a little larger than a business
card and has a resolution of 96 dots per inch, which is comparable to
today's handheld computer screen resolutions. The screen has an ink-on-paper
appearance, a 180-degree viewing angle, and can be bent into a curve 3
centimeters in diameter without affecting the picture, said Yu Chen, a
senior engineer at E Ink.
The device could eventually be used in electronic books that are
more paper-like that today's tablets, and it paves the way for lightweight
screens for wearable computers, said Chen.
There are two major challenges to making electronic displays in
a paper-like form, said Chen. The first is developing an electronically
controllable ink that has the optical properties of regular ink and can
retain its image without any applied power, he said.
The electronic ink used by the researchers' prototype was first
demonstrated by Massachusetts Institute of Technology researchers in 1998.
It consists of many tiny capsules of charge-sensitive pigment.
The capsules are tens of microns in diameter, said Chen. A red blood cell,
in comparison, is 5 microns across. In the researchers' black-and-white
prototype, capsules contain both black and white particles of pigment.
A negative voltage causes the white particles to move to the surface,
and a positive voltage causes the black ones to move to the surface. When
the power is off, the pigment stays put.
The second challenge is to to produce a thin, flexible network
of electronic circuits that connect every pixel in the display so they
can be turned on and off.
The researchers' relatively thin display is a four-layer sandwich
of electronic ink capsules, thin-film transistors that switch each capsule
on and off, an insulating material and a 75-micron-thick steel-foil substrate,
or backing. The researchers used standard photolithography processes,
which employ light and chemicals to etch out tiny features, to form transistors
in the thin-film layer. They laminated the electronic ink layer on top
of the electronics.
The researchers increased the speed, contrast ratio and image
stability of the electronic ink by improving the materials and chemistry
involved, said Chen. The researchers' device switches pixels between black
and white within a quarter of a second, which is considerably slower than
a computer screen, but is sufficient for an electronic book page-turn.
The researchers' next steps are to improve the ink switching speed,
make the device thinner, and add color, said Chen.
The ink switching speed would have to improve from 250 to 15 milliseconds
to be able to support today's computer video applications, said Chen.
And to make the device thin enough to be folded like a piece of paper,
the thickness of the steel-foil substrate must be reduced to 25 microns,
The device is currently ready for black-and-white applications
like electronic readers and smart ID cards. It will probably take several
years to develop a full-color display that switches quickly enough to
support video and is thin enough to be folded into a pocket, said Chen.
Ultimately, "electronic paper and wearable computer screens...
might have a large impact on environmental protection... and how our society
distributes information," said Chen. "Just imagine the billions of trees
we can save each year."
Chen's research colleagues were Joanna Au, Peter Kazlas, Andrew
Ritenour, Holly Gates and Michael McCreary. At the early stages of the
prototype's development the researchers also worked with Sigurd Wagner
and James Sturm of Princeton University, said Chen.
The work appeared in the May 8, 2003 issue of Nature. The research was
funded by E Ink.
Timeline: Now, > 3 years
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Flexible Active-Matrix
Electronic Ink Display," Nature, May 8, 2003.
May 21/28, 2003
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