Electronic paper

iLiad e-book reader equipped with e-paper display

Electronic paper, e-paper or electronic ink display is a display technology designed to mimic the appearance of ordinary ink on paper. Unlike a conventional flat panel display, which uses a backlight to illuminate its pixels, electronic paper reflects light like ordinary paper and is capable of holding text and images indefinitely without drawing electricity, while allowing the image to be changed later.

To build e-paper, several different technologies exist, some using plastic substrate and electronics so that the display is flexible. E-paper is considered more comfortable to read than conventional displays. This is due to the stable image, which does not need to be refreshed constantly, the wider viewing angle, and the fact that it reflects ambient light rather than emitting its own light. An e-paper display can be read in direct sunlight without the image fading. Lightweight and durable, e-paper can currently provide color display. The contrast ratio in available displays as of 2008 might be described as similar to that of newspaper, though newly-developed implementations are slightly better. There is ongoing competition among manufacturers to provide full-color capability.

Applications include electronic pricing labels in retail shops, and general signage, time tables at bus stations, electronic billboards, the mobile phone Motorola FONE F3, and e-Readers capable of displaying 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.

Technology

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 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.

Electrophoretic

Scheme of an electrophoretic display.

Scheme of an electrophoretic display using color filters.

An electrophoretic display forms visible images by rearranging charged pigment particles using an applied electric field.

In the simplest implementation of an electrophoretic display, titanium dioxide particles approximately one micrometre 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 titanium 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. Also the technology has been developed by Sipix Microcup and Bridgestone Quick Response Liquid Powder Display (QR-LDP). 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.

Development

In the 1990s another type of electronic paper was invented by Joseph Jacobson, who later co-founded the E Ink Corporation which 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. 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 (so it looked white to the viewer) or at the bottom of the capsule (so the viewer saw the color of the oil). This was essentially a reintroduction of the well-known electrophoretic display technology, but the use of microcapsules allowed the display to be used on flexible plastic sheets instead of glass.

One early version of electronic paper consists of a sheet of very small transparent capsules, each about 40 micrometres across. Each capsule contains an oily solution containing black dye (the electronic ink), with numerous white titanium dioxide particles suspended within. The particles are slightly negatively charged, and each one is naturally white.

The microcapsules are held in a layer of liquid polymer, sandwiched between two arrays of electrodes, the upper of which is made transparent. The two arrays are aligned so that the sheet is divided into pixels, which each pixel corresponding to a pair of electrodes situated either side of the sheet. The sheet is laminated with transparent plastic for protection, resulting in an overall thickness of 80 micrometres, or twice that of ordinary paper.

File:E-ink.png

Appearance of pixels

The network of electrodes is connected to display circuitry, which turns the electronic ink 'on' and 'off' at specific pixels by applying a voltage to specific pairs of electrodes. Applying a negative charge to the surface electrode repels the particles to the bottom of local capsules, forcing the black dye to the surface and giving the pixel a black appearance. Reversing the voltage has the opposite effect - the particles are forced from the surface, giving the pixel a white appearance. A more recent incarnation of this concept requires only one layer of electrodes beneath the microcapsules.

Electrowetting

Main article: Electrowetting

Electro-wetting display (EWD) is based on controlling the shape of a confined water/oil interface by an applied voltage. With no voltage applied, the (coloured) oil forms a flat film between the water and a hydrophobic (water-repellent), insulating coating of an electrode, resulting in a coloured 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 results in a partly transparent pixel, or, in case a reflective white surface is used under the switchable element, a white pixel. Because of the small size of the pixel, the user only experiences the average reflection, which means that a high-brightness, high-contrast switchable element is obtained, which forms the basis of the reflective display.

Displays based on electro-wetting have several attractive features. The switching between white and coloured reflection is fast enough to display video content.

It is a low-power and low-voltage technology, and displays based on the effect can be made flat and thin. The reflectivity and contrast are better or equal to those of other reflective display types and are approaching those of paper.

In addition, the technology offers a unique path toward high-brightness full-colour 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 (RGB) filters or alternating segments of the three primary colours, which effectively result in only one third of the display reflecting light in the desired colour, electro-wetting allows for a system in which one sub-pixel is able to switch two different colours independently.

This results in the availability of two thirds of the display area to reflect light in any desired colour. This is achieved by building up a pixel with a stack of two independently controllable coloured oil films plus a colour filter.

The colours used are cyan, magenta and yellow, which is a so-called subtractive system, comparable to the principle used in inkjet printing for example. Compared to LCD another factor two in brightness is gained because no polarisers are required.

Examples of commercial electrophoretic displays include Liquavista, ITRI, PVI and ADT.

Electrofluidic

Electrofluidic displays are a variation of an electrowetting display. Electrofluidic displays place an aqueous pigment dispersion inside a tiny reservoir. The reservoir comprises <5-10% of the viewable pixel area and therefore the pigment is substantially hidden from view. Voltage is used to electromechanically pull the pigment out of the reservoir and spread it as a film directly behind the viewing substrate. As a result, the display takes on color and brightness similar to that of conventional pigments printed on paper. When voltage is removed liquid surface tension causes the pigment dispersion to rapidly recoil into the reservoir. As reported in the May 2009 Issue of Nature Photonics, the technology can potentially provide >85% white state reflectance for electronic paper.

The core technology was invented at the Novel Devices Laboratory at the University of Cincinnati. The technology is currently being commercialized by Gamma Dynamics.

Other bistable displays

See also: Bistable

• Kent Displays, manufacturer of cholesteric liquid crystal display (ChLCD).
• Nemoptic, Nematic materials
• TRED

Other technologies

Other research efforts into e-paper have involved using organic transistors embedded into flexible substrates, including attempts to build them into conventional paper. Simple color e-paper consists of a thin colored optical filter added to the monochrome technology described above. The array of pixels is divided into triads, typically consisting of the standard cyan, magenta and yellow, in the same way as CRT monitors (although using subtractive primary colors as opposed to additive primary colors). The display is then controlled like any other electronic color display.

Examples of electrochromic displays include Acreo, Ajjer, Aveso and Ntera.

Disadvantages

Electronic paper technologies have a very low refresh rate comparing with other low-power display technologies, such as LCD. This prevents producers from implementing sophisticated interactive applications (using fast moving menus, mouse pointers or scrolling) like those which are possible on handheld computers. An example of this limitation is that a document cannot be smoothly zoomed without either extreme blurring during the transition or a very slow zoom.

An e-ink screen showing the "ghost" of a previous image

Another limitation is that an imprint of an image may be visible after refreshing parts of the screen. Those imprints are known as "ghost images", and the effect is known as "ghosting". This effect is reminiscent of screen burn-in but, unlike it, is solved after the screen is refreshed several times. Turning every pixel white, then black, then white, helps normalize the contrast of the pixels. This is why several devices with this technology "flash" the entire screen white and black when loading a new image, in order to prevent ghosting from happening.

Applications

Several companies are simultaneously developing electronic paper and ink. While the technologies used by each company provide many of the same features, each has its own distinct technological advantages. All electronic paper technologies face the following general challenges:

• A method for encapsulation
• An ink or active material to fill the encapsulation
• Electronics to activate the ink

Electronic ink can be applied to both flexible and rigid materials. In the case of flexible displays, the base requires a thin, flexible material tough enough to withstand considerable wear, such as extremely thin plastic. The method of how the inks are encapsulated and then applied to the substrate is what distinguishes each company from each other. These processes are complex and are carefully guarded industry secrets. The manufacture of electronic paper promises to be less complicated and less costly than traditional LCD manufacture.

There are many approaches to electronic paper, with many companies developing technology in this area. Other technologies being applied to electronic paper include modifications of liquid crystal displays, electrochromic displays, and the electronic equivalent of an Etch A Sketch at Kyushu University. Advantages of electronic paper includes low power usage (power is only drawn when the display is updated), flexibility and better readability than most displays. Electronic ink can be printed on any surface, including walls, billboards, product labels and T-shirts. The ink's flexibility would also make it possible to develop rollable displays for electronic devices. The ideal electronic paper product is a digital book that can typeset itself and could be read as if it were made of regular paper, yet programmed to download and display the text from any book. Another possible use is in the distribution of an electronic version of a daily paper.

Commercial applications

The Motorola F3 uses an e-paper display instead of an LCD.

Education: digital schoolbooks

• In January 2007, the Dutch specialist in e-Paper edupaper.nl started a pilot project in a secondary school in Maastricht, using e-Paper as digital schoolbooks to reduce costs and students' daily burden of books.

wristwatches

• In December 2005 Seiko released their Spectrum SVRD001 wristwatch, which has a flexible electrophoretic display.

• Phosphor of Hong Kong have launched 3 series of watches using flexible electrophoretic display using eink technology.

e-Books

Main article: List of e-book readers

• In September 2006 Sony released the PRS-500 Sony Reader e-book reader. On October 2, 2007, Sony announced the PRS-505, an updated version of the Reader. In November 2008, Sony released the PRS-700BC which incorporated a backlight and a touchscreen.

• In November 2006, the iRex iLiad was ready for the consumer market. Consumers could initially read e-Books in PDF and HTML formats, and in July 2007 support for the popular Mobipocket PRC format was added, but price was still a problem. With the introduction of the competing Cybook, prices have decreased almost 50%.

• In late 2007, Amazon began producing and marketing the Amazon Kindle, an e-book with an e-paper display. In February 2009, Amazon released the Kindle 2 and in May 2009 the larger Kindle DX was announced.

Newspapers

• In February 2006, the Flemish daily De Tijd distributed an electronic version of the paper to select subscribers in a limited marketing study, using a pre-release version of the iRex iLiad. This was the first recorded application of electronic ink to newspaper publishing.

• In September 2007, the French daily Les Échos announced the official launch of an electronic version of the paper on a subscription basis. Two offers are available, combining a one year subscription and a reading device. One interesting point of the offer is the choice of a light (176g) reading device (adapted for Les Echos by Ganaxa) or the iRex iLiad. Two different processing platforms are used to deliver readable information of the daily, one based on the newly developed GPP electronic ink platform from Ganaxa, and the other one developed internally by Les Echos.

• Since January 2008, the Dutch daily NRC Handelsblad is distributed for the iRex iLiad reader.

Digital Photo Frame

• In the future as electronic paper displays improve and full high quality color is possible, the technology may become incorporated in digital photo frame products. Existing digital photo frames require a constant power supply and have a limited viewing angle and physical thickness that is inferior to a conventional photograph. A digital photo frame using e-paper technology would address all of these shortcomings. A well-designed digital photo frame using an electronic ink display could, in theory, run for months or years from batteries, because such a device would require electricity only to briefly boot up to connect to a USB memory stick (or other storage device) and change the display before powering off all components.

Information Board

• An extension of the Digital Photo Frame concept is to display other media such as webpages or other documents. Examples include web pages such as news sites or status pages such as stocks or other information. The current days weather forecast would be a good example for installation in a domestic location such as near the front door in a hall way. Such a device could also be connected wirelessly allowing remote or automatic updates without human intervention. Such a product will have a low physical and energy footprint compared to older technology. At present (Q4 2009) no such product is available on the market despite the technology already existing to manufacture it. Unlike digital photo frames, digital information boards could run acceptably with greyscale epaper.

Displays embedded in smart cards

• Flexible display cards enable financial payment cardholders to generate a one-time password to reduce online banking and transaction fraud. Electronic paper could offer a flat and thin alternative to existing key fob tokens for data security. The world’s first ISO compliant smart card with an embedded display was developed by Smartdisplayer using SiPix Imaging’s electronic paper.

Cell phones

• Motorola's low-cost mobile phone, the Motorola F3, also uses an alphanumeric black/white electrophoretic display.
• The Samsung Alias 2 mobile phone incorporates electronic ink from E Ink into the keypad, which allows the keypad to change character sets and orientation while in different display modes.

Display makers

• Delta Electronics
• LG
• NEC
• Plastic Logic
• Prime View Internstional, flexible EPLaR
• i-Rex
• Samsung
• Seiko Epson

See also

• E-book
• E_Ink
• Electrofluidic
• Flexible electronics
• List of e-book readers
• Display examples

Further reading

• New Scientist - Electric paper (2003)
• New Scientist - E-paper may offer video images (2003)
• New Scientist - Paper comes alive (2003)
• New Scientist - Most flexible electronic paper yet revealed (2004)
• New Scientist - Roll-up digital displays move closer to market (2005)
• Electronista - Seiko Epson develops ultra-dense e-paper display (11-2007)
• Unidym Press Room - Unidym and Samsung Electronics demonstrate the world's first colour carbon-nanotube-based electrophoretic display (10-2008)

External links

• Epaper Central - Electronic Paper News, Information, and Analysis
• E-paper display market reaches $1.17 billion in 2014
• Electronic Paper:Merging between Traditional Publishing & e-Publishing
• Wired article on E Ink-Philips partnership, and background
• Bosner, Kevin. How Electronic Ink Will Work at HowStuffWorks. Retrieved on 2007-08-26.
• MIT ePaper Project
• Xerox PARC epaper project
• Gamma Dynamics - Commercializing a New Pigment-Based Electrowetting Display
• Office of Tomorrow
• Tanaka, Naoki (2007-12-06). "Fuji Xerox Exhibits Color Electronic Paper w/ Optical Writing System". Japan: Tech-On!. Retrieved 2007-12-10.
• The Future of Electronic Paper - Past, present and future of e-paper including an interview with Nick Sheridon, Father of E-paper at Xerox
• Fujitsu Develops World's First Film Substrate-based Bendable Color Electronic Paper featuring Image Memory Function.