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| Electronic paper |
Electronic paper, e-paper and electronic ink are a range of display technologies which are designed to mimic the appearance of ordinary ink on paper. Unlike conventional backlit flat panel displays, electronic paper displays reflect light like ordinary paper. Many of the technologies can hold text and images indefinitely without using electricity, while allowing images to be changed later. Flexible electronic paper uses plastic substrates and plastic electronics for the display backplane.
Electronic paper is often considered to be more comfortable to read than conventional displays. This is due to the stable image, which has no need to be refreshed constantly, a wider viewing angle, and that it reflects ambient light rather than emitting its own light. An ideal e-paper display can be read in direct sunlight without the image appearing to fade. The contrast ratio in available displays as of 2008 might be described as similar to that of newspaper, though newly-developed displays are slightly better. There is ongoing competition among manufacturers to provide full-color ability.
Applications include electronic pricing labels in retail shops, and general signage, time tables at bus stations, electronic billboards, mobile phone displays, and e-readers able to display digital versions of books and e-paper magazines. Electronic paper should not be confused with digital paper, which is a pad to create handwritten digital documents with a digital pen.
Electronic paper was first developed in the 1970s by Nick Sheridon at Xerox's Palo Alto Research Center. The first electronic paper, called Gyricon, consisted of polyethylene spheres between 75 and 106 micrometres across. Each sphere is a janus particle composed of negatively charged black plastic on one side and positively charged white plastic on the other (each bead is thus a dipole). The spheres are embedded in a transparent silicone sheet, with each sphere suspended in a bubble of oil so that they can rotate freely. The polarity of the voltage applied to each pair of electrodes then determines whether the white or black side is face-up, thus giving the pixel a white or black appearance. At the FPD 2008 exhibition, Japanese company Soken has demonstrated a wall with electronic wall-paper using this technology.
In the simplest implementation of an electrophoretic display, titanium dioxide (titania) particles approximately one micrometer in diameter are dispersed in a hydrocarbon oil. A dark-colored dye is also added to the oil, along with surfactants and charging agents that cause the particles to take on an electric charge. This mixture is placed between two parallel, conductive plates separated by a gap of 10 to 100 micrometres. When a voltage is applied across the two plates, the particles will migrate electrophoretically to the plate bearing the opposite charge from that on the particles. When the particles are located at the front (viewing) side of the display, it appears white, because light is scattered back to the viewer by the high-index titania particles. When the particles are located at the rear side of the display, it appears dark, because the incident light is absorbed by the colored dye. If the rear electrode is divided into a number of small picture elements (pixels), then an image can be formed by applying the appropriate voltage to each region of the display to create a pattern of reflecting and absorbing regions.
Electrophoretic displays are considered prime examples of the electronic paper category, because of their paper-like appearance and low power consumption.
Examples of commercial electrophoretic displays include the high-resolution active matrix displays used in the Amazon Kindle, Barnes & Noble Nook, Sony Librie, Sony Reader, and iRex iLiad e-readers. These displays are constructed from an electrophoretic imaging film manufactured by E Ink Corporation.
The EPD technology has been developed also by Sipix and Bridgestone/Delta. SiPix Imaging Inc. is now part of AU Optronics Corp, one of the three largest LCD-panel manufacturers in the world. Other than E-Ink's 0.04mm-diameter micro-capsule structure, Sipix's is 0.15mm-diameter microcup. On the other side, Bridgestone Corp.'s Advanced Materials Division has been cooperating with Delta Optoelectronics Inc. in developing the Quick Response Liquid Powder Display (QR-LPD) technology. The Motorola MOTOFONE F3 was the first mobile phone to use the technology, in an effort to help eliminate glare from direct sunlight during outdoor use.
Electrophoretic displays can be manufactured using the Electronics on Plastic by Laser Release (EPLaR) process developed by Philips Research to enable existing AM-LCD manufacturing plants to create flexible plastic displays.
