This e-paper is currently under development by Ricoh.
It has a unique structure, with layers of a new electrochromic material that turn magenta, yellow, and cyan from their transparent state. In this way, Ricoh’s e-paper enables a bright, full-color display, like ordinary paper, which hasn’t been possible with e-paper until now.
This prototype is a 3.5-inch, QVGA display, with a pixel density of 113.6 ppi. Its reflectivity is 70%. Compared with current color-filter displays, this e-paper is 2.5 times brighter. It has a color reproduction range of 35%, higher than that of a newspaper, which is 31% in Japan.
“To produce colors, CMY subtractive mixing is ideal, and that’s the model used in printing. We’ve implemented this by coating the panel with layers of yellow, magenta, and cyan. Ordinarily, if you try to use layers like this, you need an electrode driver for each layer. But in this display we’re developing, the electrodes are active TFTs. So, we can achieve all colors with a single TFT, by switching the electrodes on the display side.”
The material used for the chromic layers is transparent in its oxidized state, but becomes colored when it’s reduced. To achieve a color display, rewriting is done three times in the order magenta, yellow, cyan. As the spaces between the electrochromic layers are narrow, at about 2 microns, the result is an ideal color-mixing display.
“The stage we’re at right now is, we’re checking that this model works with an actual active panel. Regarding the color drive, we haven’t refined this yet, so switching takes over a second for each color. But the reaction speed of the chromic material is, ideally, about 100 ms.”
“From now on, we’d like to increase the size to 6 inches, then 10 inches. We also want to work on achieving stable driving and faster response.”