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Printed Electronics World
Posted on December 21, 2009 by  & 

Race for color video e-readers

The e-reader is a killer application involving printed electronics. Despite costing more than an i-Pod, the Amazon Kindle achieved 500,000 unit sales in its first year of trading last year and now we are talking of millions. The i-Pod, an iconic success, only achieved 300,000 unit sales in its first year of trading.
It is easy to predict that the next major advances in e-readers will be color and video - preferably together. After all, we now have gorgeous color and video on our mobile phones thanks to Active Matrix Organic Light Emitting Diode AMOLED displays.
What is more difficult to predict is the e-reader technologies that will achieve such things because e-readers are perused for a very long time as people access books and business reports. Power is best conserved by using a bistable display such as the e-Ink displays currently favoured for almost all of them.
These are superb in bright sunshine unlike the displays on most mobile phones and laptops. To get color, companies such as Fujitsu have experimented with filters over such electrophoretic displays but they give a washed out appearance. E-Ink is also working on white electrophoretic pixels colored by filters. By contrast, electrophoretic competitor SiPix may be working on color electrophoretic microcapsules. Electrophoretics are not light emitting either. Reading in dim or dark surroundings calls for some form of lighting.
Edwin Thomas has developed promising tunable photonic crystals at Massachusetts Institute of Technology and the University of Toronto has spun off a photonics company Opalux. Opalux P-Ink gives rapidly tunable crystals of high color intensity. However, that tuning is not yet fast enough for video. No need for traditional red, green and blue pixels -here each pixel tunes to the required color giving a much more coherent and appealing image compared to color LCDs. It is called "field sequential" color display. Man-made photonic crystals are biomimetic in imitating the periodic structures of opals and butterfly wings. To be more precise, if the particles are about 200 nanometers in diameter, they provide Bragg interference at visible wavelengths, the precise wavelength i.e. color being controlled by the spacing between particles.
Opalux achieves this by embedding silica beads in an electroactive polymer substrate so this is yet another use of electroactive polymers in printed and partly printed electronics beyond the electronic shutters, reprogrammable Braille and electronic texture changing we have mentioned elsewhere in Printed Electronics World. Basically, when an electronic field is applied, the polymer swells or contracts, changing the color.
An alternative way of creating a photonic display is to use self-assembling copolymers that swell in response to chemicals. Yet another approach is based on dielectrophoresis, where Kodak, for example, electrically manipulated particles suspended in a fluid. Of course here the spacing is manipulated whereas in electrophoretic displays the field moves particles to the surface.
At Kodak, David Snoswell developed faster photonic crystal systems in this manner with "sub millisecond switching rates" before the work was terminated and he is now at the University of Cambridge in the UK. He says, "You induce an electric dipole in the particles with an electric field. Like little bar magnets, they all line up." Sadly most devices relying on movement in a fluid such as glycerine tend to be slow, and, at low temperatures, have sticky images and even freeze.
Switching at sub-microsecond times is achieved with fast photonics and that is more than adequate for video with fast photonics, however. With photonic crystals, the problem is far less severe because much smaller distances are involved. In the case of electrophoretic displays, Bridgestone, the Japanese car tire manufacturer has now demonstrated a version with particles that work in air giving video speed. Brightness and other challenges are being tackled before commercialisation.
Although Professor Chigrinov at Hong Kong University of Science and Technology and others are starting to print LCDs on flexible substrates that may be very low in cost and tightly rollable, the Canadians and others claim the better images and faster switching of their approach is superior. By contrast, E-Ink, now a subsidiary of e-reader manufacturer Prime View International in Taiwan, has only announced 50 millisecond switching, the equivalent of 20 frames per second and inadequate for video. But what do they have in the laboratory?
In yet another very different approach, electrowetting enthusiasts Liquavasta, now under new ownership and management, has changed course to prioritise e-reader displays with a target of marketing something in three years. ADT in Germany also makes electrowetting displays. The argument for electrowetting is that it already gives brilliant colors and video speeds and Liquavista appears to be three years from having a color video display for e-readers. It will take more current than today's E-Ink monochrome e-readers. Perhaps it will be bistable: ADT claims to use the technology in a bistable version though it is not prioritising e-readers and its displays are very basic so far.
Certainly there is everything to play for and no clear winner anywhere in sight. The situation is complicated by the many candidates for the color, video e-reader display and the uncertainty about whether such aspects as bistability, transparency and ability to be rolled tightly will be important in the marketplace.
For now, IDTechEx will only hazard that more power will probably be needed for color and video, adding weight in the form of bigger batteries and probably energy harvesting. The next ten years will see color video e-readers creating a higher cost up-market and not displacing today's monochrome bistable e-readers for some time.

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Posted on: December 21, 2009

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