THE DAY you can download 快猫短视频 and read it on 鈥渆lectronic
paper鈥� just got a step closer. E Ink of Boston announced this week 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鈥檚 Dan Button, who
demonstrated the new colour display this week at the Society for Information
Display conference in San Jose, California.
Advertisement
The new display is based on E Ink鈥檚 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
(快猫短视频, 15 May 1999, p 36).
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鈥攖he same trick that lends colour to LCDs.
The firm admits it鈥檚 not an elegant approach. 鈥淭his route gets us on the market
quickly, since it uses technology that already exists,鈥� 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. 鈥淲e are either exposing a highly reflective
coloured surface or a black surface,鈥� says Button.
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
(快猫短视频, 21 October 2000, p 48).
The firm鈥檚 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鈥檛 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.