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Electronic paper

Electronic paper, e-paper and electronic ink are display technologies which are designed to mimic the appearance of ordinary ink on paper.[1] Unlike conventional backlit flat panel displays which emit light, electronic paper displays reflect light like ordinary paper, theoretically making it more comfortable to read, and giving the surface a wider viewing angle compared to conventional displays. 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.[2] An ideal e-paper display can be read in direct sunlight without the image appearing to fade.

Many electronic paper technologies can hold static text and images indefinitely without using electricity. Flexible electronic paper uses plastic substrates and plastic electronics for the display backplane. There is ongoing competition among manufacturers to provide full-color ability.

Applications of electronic visual displays include electronic pricing labels in retail shops, and digital signage,[3] time tables at bus stations,[4] electronic billboards,[5] mobile phone displays, and e-readers able to display digital versions of books and e-paper magazines.

Contents

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 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).[6] 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.[7] At the FPD 2008 exhibition, Japanese company Soken demonstrated a wall with electronic wall-paper using this technology.[8]

Electrophoretic

Appearance of pixels

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, Kobo eReader 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, a LCD-panel manufacturers. SiPix uses Microcup architecture with flexible PET material, instead of microcapsule. Other than E-Ink's 0.04mm-diameter microcapsule structure, Sipix's is 0.15mm-diameter Microcup.[9][10] 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.[11][12] The Motorola MOTOFONE

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.

Electrophoretic display

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.

Macro photograph of Kindle 3 screen; microcapsules are evident at full size

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.[13] 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.[7]

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.

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 to the surface, giving the pixel a white appearance. A more recent incarnation of this concept requires only one layer of electrodes beneath the microcapsules.[14][15]

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, if 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.[16]

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 than 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.[17]

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.[18]

Examples of commercial electrowetting displays include Liquavista,[19] ITRI,[20] PVI and ADT.[21][22]

Miortech’s 2nd generation electrowetting display technology solves a number of issues of 1st generation electrowetting display technology and large-area devices are easy to manufacture since the pixel walls act as spacers. Miortech develops rearview mirrors using its 2nd generation EWD technology.[23]

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.[24] 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[citation needed], 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.

Interferometric modulator

Main article: Interferometric modulator display

Other bistable displays

See also: Bistable

Other technologies

Other research efforts into e-paper have involved using organic transistors embedded into flexible substrates,[28][29] including attempts to build them into conventional paper.[30] Simple color e-paper[31] 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,[32] Ajjer,[33] Aveso[34] and Ntera.[35]

Disadvantages

Electronic paper technologies have a very low refresh rate compared to 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 mobile devices. An example of this limit 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 prior image

Another limit is that a shadow of an image may be visible after refreshing parts of the screen. Such shadows are termed "ghost images", and the effect is termed "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.[citation needed]

Electronic paper is still a topic in the R&D community and remains under development for manufacturability, marketability, and reliability considerations.[citation needed]

Applications

An e-paper display on a watch refreshes to remove ghosts.

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 flexible or rigid materials. For 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 others. These processes are complex and are carefully guarded industry secrets. Nevertheless, making electronic paper promises to be less complex and costly than making traditional LCDs.

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

Wristwatches

In December 2005 Seiko released the first electronic ink based watch called the Spectrum SVRD001 wristwatch, which has a flexible electrophoretic display[36] and in March 2010 Seiko released a second generation of this famous e-ink watch with an active matrix display.[37] In 2013, the pebble wristwatch will also use e-paper technology.

e-Books

Main article: Daftar/Tabel -- e-book readers

In 2004 Sony released Librié EBR-1000EP in Japan, the first e-book reader with an electronic paper display. In September 2006 Sony released the PRS-500 Sony Reader e-book reader in the USA. 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 late 2007, Amazon began producing and marketing the Amazon Kindle, an e-book reader with an e-paper display. In February 2009, Amazon released the Kindle 2 and in May 2009 the larger Kindle DX was announced. In July 2010 the third generation Kindle was announced, with notable design changes.[38] The fourth generation of Kindles were announced in September 2011. This generation was unique as it marked the Kindle's first departure from keyboards in favor of touchscreens. In September 2012, Amazon announced the fifth generation of the Kindle which incorporates a LED frontlight and a higher contrast display.[39]

In November 2009 Barnes and Noble launched the Barnes & Noble Nook, running an Android operating system. It differs from other big name readers in having a replaceable battery, and a separate touch-screen color LCD below the main electronic paper reading screen.

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.

The French daily Les Échos announced the official launch of an electronic version of the paper on a subscription basis, in September 2007. Two offers were available, combining a one year subscription and a reading device. The offer included either a light (176g) reading device (adapted for Les Echos by Ganaxa) or the iRex iLiad. Two different processing platforms were 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.

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 offers 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 Innovative Card Technologies and nCryptone in 2005. The cards were manufactured by Nagra ID.

Status displays

USB flash drive with E Ink-implemented capacity meter of available flash memory

Some devices, like USB flash drives, have used electronic paper to display status information, such as available storage space.[40] Once the image on the electronic paper has been set, it requires no power to maintain, so the readout can be seen even when the flash drive is not plugged in.

Mobile phones

Motorola's low-cost mobile phone, the Motorola F3, uses an alphanumeric black-and-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.

Electronic shelf labels

E-Paper based electronic shelf labels (ESL) are used to digitally display the prices at retail stores. Electronic paper based labels are updated via two-way infrared or radio technology.

Other

Other proposed applications include clothes, digital photo frames, information boards and keyboards. Keyboards with dynamically changeable keys are useful for less represented languages, or for special non-alphabetical applications such as video editing or games.

Display manufacturers

See also

References

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Further reading

External links

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