E-Paper Technology
E-paper is a revolutionary material that can be used to make
next generation I, electronic displays. It is portable reusable storage and
display medium that look like paper but can be repeatedly written one thousands
of times. These displays make the beginning of a new area for battery power
information applications such as cell phones, pagers, watches and hand-held
computers etc. Two companies are carrying our pioneering works in the field of
development of electronic ink and both have developed ingenious methods to
produce electronic ink. One is E-ink, a company based at Cambridge, in U.S.A.
The other company is Xerox doing research work at the Xerox's Palo Alto
Research Centre. Both technologies being developed commercially for
electronically configurable paper like displays rely on microscopic beads that
change color in response to the charges on nearby electrodes. Like traditional
paper, E-paper must be lightweight, flexible, glare free and low cost. Research
found that in just few years this technology could replace paper in many
situations and leading us ink a truly paperless world.
Gyricon
Electronic paper was first developed in the 1970s by Nick
Sheridon at Xerox's Palo Alto Research Center. The first electronic paper,
called Gyricon, consisted of polyethylene spheres between 75 and 106
micrometers across. Each sphere is a Janus particle composed of negatively
charged black plastic on one side and positively charged white plastic on the
other(each bead is thus a dipole). The spheres are embedded in a transparent
silicone sheet, with each sphere suspended in a bubble of oil so that they can
rotate freely. The polarity of the voltage applied to each pair of electrodes
then determines whether the white or black side is face-up, thus giving the
pixel a white or black appearance. At the FPD 2008 exhibition, Japanese company
Soken has demonstrated a wall with electronic wall-paper using this technology
An electrophoretic display forms visible images by rearranging
charged pigment particles using an applied electric field.
In the simplest implementation of an electrophoretic display,
titanium dioxide particles approximately one micrometer in diameter are
dispersed in a hydrocarbon oil. A dark-colored dye is also added to the oil,
along with surfactants and charging agents that cause the particles to take on
an electric charge. This mixture is placed between two parallel, conductive
plates separated by a gap of 10 to 100 micrometers. When a voltage is applied
across the two plates, the particles will migrate electrophoretically to the
plate bearing the opposite charge from that on the particles. When the
particles are located at the front (viewing) side of the display, it appears
white, because light is scattered back to the viewer by the high- index
titanium particles.
When the particles are located at the rear side of the
display, it appears dark, because the incident light is absorbed by the colored
dye. If the rear electrode is divided into a number of small picture elements
(pixels), then an image can be formed by applying the appropriate voltage to
each region of the display to create a pattern of reflecting and absorbing
regions. Electrophoretic displays are considered prime examples of the
electronic paper category, because of their paper- like appearance and low
power consumption. Electrophoretic displays can be manufactured using the
Electronics on Plastic by Laser Release (EPLaR) process developed by Philips
Research to enable existing AM-LCD (Active matrix liquid crystal display)
manufacturing plants to create flexible plastic displays.
Electronics on Plastic by Laser Release (EPLaR)
Electronics on Plastic by Laser Release (EPLaR) is a method for
manufacturing flexible electrophoretic display using conventional AM-LCD
manufacturing equipment avoiding the need to build new factories. The
technology can also be used to manufacture flexible OLED (Organic LED) displays
using standard OLED fabrication facilities. The technology was developed by
Philips Research and uses standard display glass as used in TFT-LCD processing
plants. It is coated with a layer of polyimide using a standard spin-coating
procedure used in the production of AM-LCD displays. This polymide coating can
now have a regular TFT matrix formed on top of it in a standard TFT processing
plant to form the plastic display, which can then be removed using a laser to
finish the display and the glass reused thus lowering the total cost of
manufacture.
Development in Electrophoretic Display:
In the 1990s another type of electronic paper was invented by Joseph
Jacobson, who later co- founded the E Ink Corporation which formed a
partnership with Philips Components two years later to develop and market the
technology. In 2005, Philips sold the electronic paper business as well as its
related patents to Prime View International. This used tiny microcapsules
filled with electrically charged white particles suspended in colored oil. In
early versions, the underlying circuitry controlled whether the white particles
were at the top of the capsule (so it looked white to the viewer) or at the
bottom of the capsule (so the viewer saw the color of the oil). This was
essentially a reintroduction of the wellknown electrophoretic display technology,
but the use of microcapsules allowed the display to be used on flexible plastic
sheets instead of glass.
Electrowetting
Electro-wetting display (EWD) is based on controlling the shape of a
confined water/oil interface by an applied voltage. With no voltage applied,
the (coloured) oil forms a flat film between the water and a hydrophobic
(water-repellent), insulating coating of an electrode, resulting in a coloured
pixel. When a 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 stable, causing the water to move the oil aside.
This results in a partly transparent pixel, or, in case a reflective white
surface is used under the switchable element, a white pixel. Because of the
small size of the p ixel, the user only experiences the average reflection,
which means that a high-brightness, high-contrast switchable element is
obtained, which forms the basis of the reflective display. Displays based on
electro-wetting have several attractive features. The switching between white and coloured reflection is fast enough to display video content. It is a low-power and low-voltage technology, and displays based on the effect can be made flat and thin. The reflectivity and contrast are better or equal to those of other reflective display types and are approaching those of paper. In addition, the technology offers a unique path toward high-brightness full-colour displays, leading to displays that are four times brighter than reflective LCDs and twice as bright as other emerging technologies. Instead of using red, green and blue (RGB) filters or alternating segments of the three primary colours, which effectively result in only one third of the display reflecting light in the desired colour, electro-wetting allows for a system in which one sub-pixel is able to switch two different colours independently. This results in the availability of two thirds of the display area to reflect light in any desired colour. This is achieved by building up a pixel with a stack of two independently controllable coloured oil films plus a colour filter.
Electrofluidic
Electrofluidic displays are a variation of an electrowetting display.
Electrofluidic displays place an aqueous pigment dispersion inside a tiny
reservoir. The reservoir comprises <5-10% of the viewable pixel area and
therefore the pigment is substantially hidden from view. Voltage is used to
electromechanically pull the pigment out of the reservoir and spread it as a
film directly behind the viewing substrate. As a result, the display takes on
color and brightness similar to that of conventional pigments printed on paper.
When voltage is removed liquid surface tension causes the pigment dispersion to
rapidly recoil into the reservoir. As reported in the May 2009 Issue of Nature
Photonics, the technology can potentially provide >85% white state
reflectance for electronic paper.
Conclusion
The Holy Grail of electronic ink technology is a digital book that can
typeset itself and that readers could leaf through just as if it were made of
regular paper. Such a book could be programmed to display the text from a
literary work and once you've finished that tale, you could automatically
replace it by wirelessly downloading the latest book from a computer database.
Xerox had introduced plants to insert a memory device into the spine of the
book, which would allow users to alternate between up to 10 books stored on the
device. Just as electronic ink could radically change the way we read books, it
could change the way you receive your daily newspaper. It could very well bring
an end to newspaper delivery, as we know it. Instead of delivery people tossing
the paper from their bike or out their car window, a new high- tech breed of
paper deliverers who simply press a button on their computer that would
simultaneously update thousands of electronic newspapers each morning. Sure, it
would look and feel like your old paper, but you wouldn't have to worry about
the newsprint getting smudged on your fingers, and it would also eliminate the
piles of old newspapers that need recycling. Prior to developing digital books
and newspapers E-Ink will be developing a marketable electronic display screen
for cell phones, PDA's, pagers and digital watches.Electronic ink is not intended to diminish or do away with traditional displays. Instead electronic ink will initially co-exist with traditional paper and other display technologies. In the long run, electronic ink may have a multibillion-dollar impact on the publishing industry. Ultimately electronic ink will permit almost any surface to become a display, bringing information out of the confines of traditional devices and into the world around us.
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