24 June 2004
24 June 2004
Philips shows functional, large-scale demonstrator of its
electrowetting-based electronic-paper technology
Eindhoven, The Netherlands - Philips generated considerable interest at this year's Society
for
Information Displays in Seattle, USA with a demonstration of its electrowetting-based
electronic-paper technology in a 1-inch square, monochrome direct-driven display demo. The
demonstrator represents a 50-fold increase in area over earlier prototypes and clearly shows
the scalability of this novel, low-power display technology to larger areas.
The advances presented at SID 2004 come primarily from improvements in the large-area
reliability of the insulation material, the development of an automated pixel-filling process
and improved sealing techniques. In addition, the pixel dimension has been scaled down to
a
resolution of 160 ppi, resulting in a significant increase in pixel count, which exceeds
11,000
pixels in the current 1-inch display.
Announced last year and also the subject of the cover article in the September 25, 2003
issue
of Nature, Philips' electrowetting-based electronic paper technology offers important
advantages over other electronic-paper technologies currently under development. Not only
does it provide sufficient speed to display moving video (with a response time less that
10
ms), it also offers a unique path towards full-color displays with a color brightness of
twice
that of any other emerging reflective display technology and at least four times that of
current
reflective liquid-crystal displays.
The technology is based on the micro control of fluid motion by an applied voltage. Oil
containing a dye is confined between a layer of water and a hydrophobic (water-repellent)
coating on an electrode. With no voltage applied, the oil naturally forms a barrier layer
between the water and the hydrophobic coating to create a colored pixel. When a (low)
voltage is applied between the electrode and the water, the interfacial tension between the
water and the coating changes. As a result, the stacked state is no longer the lowest energy
state, causing the water to move the oil aside. This results in a partly transparent pixel
or,
where a reflective white surface is used under the switchable element, a white pixel. Because
of the small size of the pixel, the eye sees only the average reflection. The result is a
highbrightness,
high-contrast switchable element which forms the basis of the reflective display.
In contrast to other reflective display technologies which use R, G and B filters or alternating
segments of the three primary colors, effectively resulting in only one third of the display
reflecting light in the desired color, electrowetting allows for a system in which one sub-pixel
is able to switch two different colors independently. This allows two thirds of the display
area
to be available to reflect light in any desired color, effectively doubling the color brightness
compared with other reflective displays. This is achieved by building up a pixel with a stack
of two independently-controllable colored oil films plus a color filter. The colors used
are
cyan, magenta and yellow, creating a so-called subtractive color-mixing system comparable
to that used in the printing industry. Moreover, in contrast to LCD, no polarizers are needed
resulting in a further factor of two gain in brightness.
Electrowetting has proven to be one of the most effective technologies for fast, micron-level
control of fluid motion and is rapidly finding application in a host of areas including the
biomedical field, micro pumps and variable-focus lenses. Philips' electronic paper is one
further example of this novel technology that is expected to find application in digital
camcorders, portable outdoor equipment and other applications requiring low-power
reflective displays capable of reproducing bright contrast-rich images with full color and
high-speed video.