Electronic paper

Electronic paper or intelligent paper, is a display device that reflects ambient light, mimicking the appearance of ordinary ink on paper – unlike conventional flat-panel displays which need additional energy to emit their own light. This may make them more comfortable to read, and provide a wider viewing angle than most light-emitting displays. The contrast ratio in electronic displays available as of 2008 approaches newspaper, and newly developed displays are slightly better. An ideal e-paper display can be read in direct sunlight without the image appearing to fade.
Technologies include Gyricon, electrowetting, interferometry, and plasmonics.
Many electronic paper technologies hold static text and images indefinitely without electricity. Flexible electronic paper uses plastic substrates and plastic electronics for the display backplane. Applications of e-paper include electronic shelf labels and digital signage, bus station time tables, electronic billboards, smartphone displays, and e-readers able to display digital versions of books and magazines.

Technologies

Gyricon

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 micrometers across. Each sphere is a Janus particle composed of negatively charged black plastic on one side and positively charged white plastic on the other. The spheres are embedded in a transparent silicone sheet, with each sphere suspended in a bubble of oil so that it 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.
A benefit of this type of e-paper is that the contents are retained even after the voltage have been stopped. At the FPD 2008 exhibition, Japanese company Soken demonstrated a wall with electronic wall-paper using this technology. In 2007, the Estonian company Visitret Displays was developing this kind of display using polyvinylidene fluoride as the material for the spheres, dramatically improving the video speed and decreasing the control voltage needed.

Electrophoretic

An electrophoretic display forms images by rearranging charged pigment particles with an applied electric field.
In the simplest implementation of an EPD, titanium dioxide 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 migrate electrophoretically to the plate that bears the opposite charge from that on the particles. When the particles are located at the front side of the display, it appears white, because the 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 light is absorbed by the colored dye. If the rear electrode is divided into a number of small picture elements, 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.
EPDs are typically addressed using MOSFET-based thin-film transistor technology. TFTs are often used to form a high-density image in an EPD.
A common application for TFT-based EPDs are e-readers. 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 Reader, Kobo eReader, and iRex iLiad e-readers. These displays are constructed from an electrophoretic imaging film manufactured by E Ink Corporation. A mobile phone that used the technology is the Motorola Fone.
Electrophoretic Display technology has also been developed by SiPix and Bridgestone/Delta. SiPix is now part of E Ink Corporation. The SiPix design uses a flexible 0.15 mm Microcup architecture, instead of E Ink's 0.04 mm diameter microcapsules. Bridgestone Corp.'s Advanced Materials Division cooperated with Delta Optoelectronics Inc. in developing Quick Response Liquid Powder Display technology.
Electrophoretic displays can be manufactured using the Electronics on Plastic by Laser Release process, developed by Philips Research, to enable existing AM-LCD manufacturing plants to create flexible plastic displays.

Microencapsulated electrophoretic display

In the 1990s another type of electronic ink based on a microencapsulated electrophoretic display was conceived and prototyped by a team of undergraduates at MIT as described in their Nature paper. J.D. Albert, Barrett Comiskey, Joseph Jacobson, Jeremy Rubin and Russ Wilcox co-founded E Ink Corporation in 1997 to commercialize the technology. E Ink subsequently formed a partnership with Philips Components two years later to develop and market the technology. In 2005, Philips sold the electronic paper business as well as its related patents to Prime View International.

"It has for many years been an ambition of researchers in display media to create a flexible low-cost system that is the electronic analog of paper. In this context, microparticle-based displays have long intrigued researchers. Switchable contrast in such displays is achieved by the electromigration of highly scattering or absorbing microparticles, quite distinct from the molecular-scale properties that govern the behavior of the more familiar liquid-crystal displays. Micro-particle-based displays possess intrinsic bistability, exhibit extremely low power d.c. field addressing and have demonstrated high contrast and reflectivity. These features, combined with a near-lambertian viewing characteristic, result in an 'ink on paper' look. But such displays have to date suffered from short lifetimes and difficulty in manufacture. Here we report the synthesis of an electrophoretic ink based on the microencapsulation of an electrophoretic dispersion. The use of a microencapsulated electrophoretic medium solves the lifetime issues and permits the fabrication of a bistable electronic display solely by means of printing. This system may satisfy the practical requirements of electronic paper."

This used tiny microcapsules filled with electrically charged white particles suspended in a colored oil. In early versions, the underlying circuitry controlled whether the white particles were at the top of the capsule or at the bottom of the capsule. This was essentially a reintroduction of the well-known electrophoretic display technology, but microcapsules meant the display could be made on flexible plastic sheets instead of glass.
One early version of the electronic paper consists of a sheet of very small transparent capsules, each about 40 micrometers across. Each capsule contains an oily solution containing black dye, with numerous white titanium dioxide particles suspended within. The particles are slightly negatively charged, and each one is naturally white.
The screen holds microcapsules in a layer of liquid polymer, sandwiched between two arrays of electrodes, the upper of which is transparent. The two arrays are aligned to divide the sheet into pixels, and each pixel corresponds to a pair of electrodes situated on either side of the sheet. The sheet is laminated with transparent plastic for protection, resulting in an overall thickness of 80 micrometers, or twice that of ordinary paper.
The network of electrodes connects to display circuitry, which turns the electronic ink 'on' and 'off' at specific pixels by applying a voltage to specific electrode pairs. A negative charge to the surface electrode repels the particles to the bottom of local capsules, forcing the black dye to the surface and turning the pixel black. Reversing the voltage has the opposite effect. It forces the particles to the surface, turning the pixel white. A more recent implementation of this concept requires only one layer of electrodes beneath the microcapsules. These are commercially referred to as Active Matrix Electrophoretic Displays.

Reflective LCD

This technology is similar to common LCD while the backlight panel is substituted by a reflective surface.
A comparable technology is also obtainable in backlight LCDs by software or hardware deactivating the backlight control.

Electrowetting

Electrowetting display is based on controlling the shape of a confined water/oil interface by an applied voltage. With no voltage applied, the oil forms a flat film between the water and a hydrophobic insulating coating of an electrode, resulting in a colored pixel. When a voltage is applied between the electrode and the water, the interfacial tension between the water and the coating changes. As a result, the stacked state is no longer stable, causing the water to move the oil aside. This makes a partly transparent pixel, or, if a reflective white surface is under the switchable element, a white pixel. Because of the small pixel size, the user only experiences the average reflection, which provides a high-brightness, high-contrast switchable element.
Displays based on electrowetting provide several attractive features. The switching between white and colored reflection is fast enough to display video content. It is a low-power, low-voltage technology, and displays based on the effect can be made flat and thin. The reflectivity and contrast are better than or equal to other reflective display types and approach the visual qualities of paper. In addition, the technology offers a unique path toward high-brightness full-color displays, leading to displays that are four times brighter than reflective LCDs and twice as bright as other emerging technologies. Instead of using red, green, and blue filters or alternating segments of the three primary colors, which effectively result in only one-third of the display reflecting light in the desired color, electrowetting allows for a system in which one sub-pixel can switch two different colors independently.
This results in the availability of two-thirds of the display area to reflect light in any desired color. This is achieved by building up a pixel with a stack of two independently controllable colored oil films plus a color filter.
The colors are cyan, magenta, and yellow, which is a subtractive system, comparable to the principle used in inkjet printing. Compared to LCD, brightness is gained because no polarisers are required.