Nikkei Electronics Asia has a cover story on the growing market for electronic ink applications.
Apparently E Ink has solved the ‘after-image’ or ‘ghosting’ problem seen in early applications, such as the Sony Librie. Two of the products available (in Japan) since January 2006 are the Seiko E Ink Watch and the Ishida shelf price tag system using SiPix. Electronic ink is ideally suited for such applications with very low refresh rates (e.g. 1 update per second), but in the longer run, we can expect to see it used in more demanding applications such as notebook screens:
In March 2005, Intel Corp of the US disclosed that Intel Capital Corp of the US had invested into E Ink. A source at Intel explained: “About a third to a half of power used in today’s notebook PCs is used by the display. If notebooks could use E-paper it would mean a significant reduction in power consumption, and at the same time provide a big improvement in readability outdoors.”
Regarding the different technologies,
the E-papers expected to reach the practical level in 2006 to 2007 can be broadly divided into the particle-based type from firms like E Ink, SiPix Imaging and Bridgestone Corp of Japan, and the cholesteric liquid crystal type from companies including Asahi Glass, Fuji Xerox Co Ltd of Japan and Fujitsu. Even under a single type category, though, the implementation technology may be widely different, with each manufacturer stressing the unique advantages of its own approach (Table 1).
Particle-based E-paper uses an electric field to move black and white particles up and down to change the image. The E Ink method of handling black and white particles is probably the best-known of the microcapsule liquid approaches, but the Bridgestone approach, for example, moves the particles up and down in air for an extremely fast response speed of only 0.2ms. Unlike E Ink’s device, which is designed for dot display with active drive, the Bridgestone design offers high-definition dot displays even with a passive drive. Dr Hiroaki Wada, general manager, Dept of High Performance Product Development, Research & Development Div, Bridgestone, pointed out: “We have already prototyped a high-definition E-paper using the cheap and simple passive-drive design, achieving XGA resolution (1,024 x 768 pixels) on a 7.5-inch screen.”
Cholesteric liquid crystal E-paper is stable in both transparent and reflective states, making use of the unique properties of liquid crystal. Fujitsu stacked three cholesteric liquid crystal layers, each selectively reflecting a different wavelength, to prototype a 4,096-color design. The firm’s Hashimoto commented, “We will also develop a 260,000-color model before the end of fiscal 2005.” Asahi Glass’s Satoshi Niiyama, unit leader, Research Center, said, “We have built in a technology to eliminate the ‘burning in’ that can occur with cholesteric liquid crystal.”
The article discusses optically rewritable e-paper, where
new data can be projected onto the paper from the rear to rewrite the displayed image. This is possible because of a unique structure, with a photosensitive layer positioned under the cholesteric liquid crystal film. When irradiated by light from the side opposite the liquid crystal, the resistance of the photosensitive layer changes in proportion to optical intensity. The liquid crystal film, connected in series to the photosensitive layer, changes the displayed image because the voltage input changes in relation to that resistance.
This principle of operation makes it possible to eliminate electrode patterning, for pixels. In fact, the only drive electrode is the single one covering the entire plane. Because of this, explained Fuji Xerox’s Mita, “Our approach is not limited by the drive electrodes, making it a lot easier to drop costs and fabricate larger screen sizes.”
In the future, the firm hopes to make it possible to just press this E-paper against a computer monitor in the office to automatically write the screen image to the E-paper. At present, however, a dedicated writer is required to provide the high optical intensity and directional light beams required.
Color and flexibility of the display are also addressed:
The most aggressive player in this field is E Ink, which displayed a prototype E-paper full of original technology at FPD International 2005, in October 2005. The prototypes included a 4,096-color model made using color filters developed by Toppan Printing Co, Ltd of Japan; a model with improved display performance, such as reflectivity, made with an improved ink which retains brightness even when used with color filters; and a flexible model using thin-film transistors (TFT) on a stainless steel substrate, developed jointly with LG Philips LCD Co, Ltd of Korea and others. At present these characteristics are implemented in independent products, but the firm plans to bring all of the constituent technologies together into one E-paper product in about 2007.
Regarding available technologies for the TFT backplane on a flexible substrate the article states:
Organic TFT and other materials are not expected to be ready for commercial use by around 2007, though, meaning that the firm [E Ink] could lose the business window of opportunity. It identified TFT on stainless steel substrate as a strong candidate; it can be manufactured on the same equipment used to make amorphous Si TFT, leading Kuwada to believe that it “…is the technology for TFT on a flexible substrate likely to be brought to the practical level first.” […]
[There] are a number of competitors for TFT on flexible substrate. Seiko Epson has a proprietary technology to transfer TFT from a glass substrate to a plastic one, using Surface Free Technology by Laser Ablation/Annealing (SUFTLA). The firm is applying SUFTLA in the development of peripheral technologies such as microprocessors and memory, in addition to E-paper (Fig 4).