MIT TEchnology Review reports A new approach developed by Philips now offers fresh hope for color e-paper displays that are so bright and clear that even traditional liquid crystal displays (LCDs) will pale in comparison.
The new approach has the potential to create color images that are three times brighter than displays that use color filters, including LCDs. Another aspect that could make in-plane electrophoretics more attractive: the fact that it relies on cheaper and simpler electronics to address the pixels. Electrophorectics promise the possibility of cheaper, flexible displays with brighter colors.
One of the most common e-paper technologies was created by E-Ink and is used for the monochrome screens in a wide range of devices, from Sony’s Reader and Amazon’s Kindle to Polymer Vision’s forthcoming foldable Readius. The technology employs electrophoresis: colored particles dispersed in a liquid that are controlled using an electric field. Each pixel is made of a microcapsule filled with a black oily liquid within which very small white particles are suspended. Because these particles are charged, they can be made to migrate to the top of the microcapsule–the surface of the page–by applying an electric field across them. The presence or absence of these particles at the surface of the screen acts like ink, changing the way that light reflects and giving it a lighter or darker appearance.
Philips’s technique, which is called in-plane electrophoretics, differs in that it involves suspending colored particles in a clear liquid and moving them horizontally instead of vertically. Each pixel is made up of two microcapsule chambers: one containing yellow and cyan particles, the other, below, containing magenta and black particles. Within each microcapsule, one set of colored particles is charged positively while the other is charged negatively.
By carefully controlling the voltages at electrodes positioned on the edges of the pixels, it is possible to spread the colored particles across the pixel or remove them from view altogether by hiding them behind the electrodes, says Lenssen. This means that different shades of color can be achieved by controlling how many of each group of colored particles are visible. To create white, all of the particles are simply shifted to the side to reveal the white substrate beneath the two microcapsules.
“It seems like a good approach,” says Polymer Vision’s van Lieshout. But he notes that the technology is still very much in its infancy compared with more traditional approaches, such as using color filters. Because of this, he believes that the first full-color e-paper displays will use filters.
Electrofluidic Display Technology: Alternative for Color E-Book Displays
This new entry into the race for full-color, from the University of Cincinnati, electronic paper can potentially provide better than 85 percent “white-state reflectance,” a performance level required for consumers to accept reflective display applications such as e-books, cell-phones and signage.
“If you compare this technology to what’s been developed previously, there’s no comparison,” says developer Jason Heikenfeld, assistant professor of electrical engineering in UC’s College of Engineering. “We’re ahead by a wide margin in critical categories such as brightness, color saturation and video speed.”
An electrofluidic display is built from two sheets of plastic. Onto one sheet, mesa-like polymer structures are printed to form pixels. For each pixel, a hole taking up 5 to 10 percent of the pixel area (about 50 micrometers) is formed in the polymer and filled with a droplet of pigmented fluid. Surrounding the pixel is a trench cut into the polymer that contains air or oil. The pixels are topped by another sheet of plastic—this one containing a transparent electrode—leaving a 3-µm gap between it and the polymer pixel.
When there is no voltage between the plastic sheets, the pigment will stay inside the hole, essentially invisible to the naked eye. But when a voltage is applied, the pigment is pulled out of the hole and spread out along the glass, revealing its rich color to the viewer. The air or oil surrounding the pixel prevents the pigment in one pixel from spilling into another. Switching off the power lets the pigment recoil back into the hole.
If they meet their potential, electrofluidic displays “would be the best technology there is,” says Russell J. Schwartz, vice president of color technology at Sun Chemical. “It’s got durability, it has brightness of color, it has video speed, it has very low power consumption. So what am I missing?”
Michael Sinclair, a principal researcher working on displays at Microsoft who was not involved in the research, says electrofluidic displays are a novel idea. “The fact that it is a reflective display is a big plus,” says Sinclair. “Competing against the less than 10 percent efficiency of today’s LCD and their backlights, this technique ought to be a tremendous power-efficiency improvement.”
But Sinclair points out that researchers still need to work on a gray scale. And, he notes, if this new technology is to compete with the likes of the E Ink display in the Kindle, the Ohio engineers will have to find a way for the display to hold an image even when the power is off—a property called bistability.
Response time is another challenge. The current prototype has an average response time of just over 30 milliseconds, barely fast enough to display video. But the researchers say they have identified ways to improve the design that would theoretically decrease the response time to less than 1 ms.
Bigger E-book Screens
Fujitsu Flepia Here Already
The FLEPia is a color eBook reader that has an 8 inch XGA screen that can display 260000 colors. Other features include Bluetooth and WiFi for connectivity. The device can be expanded up to 4GB in storage capacity by way of an SD card. It measures less then half an inch thick. Battery life will see this color eBook reader last for up to 40 continuous hours which is quite good. The screen is touchscreen allowing you to flick through various eBooks and pages of books.