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.
Peruvemba agrees. E-Ink has explored the use of colored particles in the past, he says, but they are more difficult to manufacture. “Filters are probably the easiest way to get to the market–they are already used in LCDs, so it’s a lower cost solution compared to other approaches.” In light of this, he predicts that it will be at least three years before any nonfilter color e-paper technologies hit the market.
However, one aspect that could make in-plane electrophoretics more attractive: the fact that it relies on cheaper and simpler electronics to address the pixels. According to Lenssen, this not only offers distinct advantages in terms of ease of manufacturing: it also makes the screens more suitable for creating flexible displays.