full color electronic paper

["De Beer, Jennifer" <jad@maties.sun.ac.za>]

Colleagues,  Possibly of interest to you.

Regards,

---
Jennifer De Beer
IT - Universiteit Stellenbosch University
(W3) sun.ac.za

http://www.newscientist.com/dailynews/news.jsp?id=ns9999837

Electronic paper now works in full colour, thanks to a fine filter 
Exclusive from New Scientist magazine 

The day you can download print onto "electronic paper" and take it
anywhere to read just got a step closer. E Ink of Boston has announced
that it has succeeded in making electronic paper work in full colour. Like
ordinary paper, electronic paper works entirely by reflection. This means
that, unlike competing electronic displays like LCDs, it never needs a
backlight. In addition, it only needs power when the image changes. Once
an image has been produced it will remain visible even with the power
switched off.

Laptops, palmtops and cellphones with rigid electronic paper screens will
be on the market within the next two years, says E Ink's Dan Button, who
demonstrated the new colour display this week at the Society for
Information Display conference in San Jose, California.

The new display is based on E Ink's monochrome e-paper, which consists of
millions of transparent microcapsules sandwiched in a thin layer between
two arrays of electrodes. The array corresponding to the surface of the
paper is transparent (New Scientist, 15 May 1999, p 36).

Quick switch 

Each tiny capsule contains white granules suspended in a dark, oily
liquid. When an electrode in the upper surface is given a negative charge,
it attracts granules towards it, making the surface appear white. Reverse
the polarity and the granules are pulled to the bottom, revealing the dark
liquid and making the surface appear black. The spaces between electrodes
are small enough to give a resolution of 300 monochrome dots per inch
(dpi).

To create a full colour display they laid a fine coloured filter across
the top of the monochrome display - the same trick that lends colour to
LCDs. The firm admits it's not an elegant approach.

"This route gets us on the market quickly, since it uses technology that
already exists," explains Button. E Ink developed the colour technology
with Japanese printing company Toppan, which makes transparent colour
filters for LCD displays.

The filter makes each pixel appear either red, green or blue when the pixel
below it is white. When the pixel is black, the filter above reflects very
little light so no colour is seen. "We are either exposing a highly
reflective coloured surface or a black surface," says Button.

Flexible friend 

Eventually, they hope e-paper will be flexible enough to be a paper
substitute. Meanwhile, E Ink expects it to rival liquid crystal displays
and the emerging organic LED displays (New Scientist, 21 October 2000, p
48).

The firm's next challenge is to improve the resolution of the colour
display. A drawback of the filter approach to colour generation is that
the filters need a single pixel for each primary colour. This effectively
reduces the resolution by about a third, to 80 dpi.

This shouldn't be a major problem, says Button, since the resolution is
not so much determined by the size of the microcapsules as by the size of
the electrodes and filters.

Correspondence about this story should be directed to
letters@newscientist.com 

0930 GMT, 11 June 2001

Duncan Graham-Rowe 
New Scientist Online News