Electronic paper, also sometimes called e-paper or electronic ink, is a display technology designed to mimic the appearance of regular ink on paper. Basically, light is reflected on the display, and no power is used to display a page since the electronic ink is bi-stable.
 The Technology
There are five competing technolgies for e-paper devices:
|EPD||Electrophoretic displays, also wrongly referred to as Electronic paper displays|
|ChLCD||Cholesteric LCD displays, also known as BCD = bi-stable cholesteric displays|
|IPE||in-plane electrophoretics can achieve color.|
|gyricon||bichromal by XEROX|
EPD (used by E Ink and SiPix) is a technology that, in the case of E Ink, uses tiny liquid filled bubbles that contain both white and black "ink". Each bubble represents a pixel on the screen display. Electronic charges are applied to the bubble to bring either the white ink or the black ink to the surface. Once the charge is removed the ink will stay at the surface so it can been seen without any power applied. The bubbles are the same size as a pixel on the screen and the connection of all these bubbles can form text characters and images on the surface of the screen. A positive charge will cause white ink to appear while a negative charge will cause black to appear. A charge can be applied to affect a small portion of the bubble instead of the whole bubble. This can be used to cause a mix of white and black (gray) to appear.
SiPix also has developed EPD but in their case, white particles are suspended in black ink that is contained in small microcups. When the white particles are at the viewing surface, the display is white and when they are at the back surface, the display is black. Like E Ink, the particles can be partially switched to achieve gray scale and the display is bistable.
Brigestone's QR-LPD technology is similar to E Ink in that it uses black and white particles but differs in that they are suspended in air, not liquid. This allows for faster movement resulting in quicker display changes.
ChLCD (used by Nemoptics, ZBD, and Kent Displays) uses a special spiral arrangement of LCDs to produce the needed bi-stable effect. Nemoptics promotes this technology under the name "BiNem". Like EPD, ChLCD only needs power to update a page. The LCDs remain in either the "white" or "black" state even when no power is applied. This is the reason why they are called Zero-power LCD. These displays were used on early Jinke eBook Readers which they called BCD (bi-stable cholesteric displays).
Xerox's e-paper solution, called gyricon, uses mini-balls (beads) that are bichromal -- black-and-white. (Other contrasting colors may be used.) These beads are charged and then placed between transparent layers of plastic and the beads, each contained in an oil-filled cavity, are free to rotate within those cavities. As a charge passes over select portions of the e-paper, the beads spin to black or white as necessary. See technical description comparison to E Ink. Note that this technology is unique in that an electronically charged 'pencil' can be used to write on the e-paper.
 Color capable
All of the E-paper devices can offer 2 color systems. But some can lend themselves to true color displays although grayscale versions can use the same technologies.
IMOD (Qualcomm calls it "mirasol") is a rather new technology (2008) based on MEMS (micro-electro-mechanical systems). It has a much faster response time than EPD and ChLCD but needs a very small amount of power to display the page. It's not a zero-power technology but very low-power. It is easier to produce colored e-paper with this technology. See Mirasol Display.
Initial e-books were able to show 4 levels of gray (black to white) but the latest technology has been able to achieve 16 levels of gray. Additional apparent gray levels can be done using dithering to achieve more levels than what can be done with the controller. Supporting Gray scale can improve the looks of images in the eBooks and may (depending on the implementation) even be used to smooth font edges that use diagonal lines or curves (this technique is called anti-aliasing). Note that the performance (speed) of the display is better if only 2 colors are used (monochrome).
IPE - Philips technology achieves a color display. It is similar to the E-Ink EPD but relies on two particle-filled capsules for each pixel, one containing yellow and cyan, the other magenta and black. By controlling voltages, the colored particles either spread across the pixel or move out of sight altogether, making it possible to render different colors by controlling the number of colored particles shown. To create white, the particles simply shift to reveal the white substrate beneath the capsules. In-plane electrophoretics research has been maturing and a product is likely soon.
E Ink Triton - This is the latest E Ink display with increased contrast. It uses color filters which would otherwise reduce contrast to achieve color contrast that rivals the E Ink Pearl screens. It can achieve 4096 colors as is aimed at eBooks, eNewspapers and eTextbooks.
Fujitsu has an ePaper device called the Fujitsu FLEPia. It uses the technology first introduced in 2006. See Fujitsu 4096 Color E-Paper. They call it a mobile terminal and has a variable refresh rate depending on how many colors. It can achieve 260,000 colors in high definition mode.
E-paper has sufficient contrast to be read quite well in direct sunlight. E-paper is not transparent so it cannot be backlit, thus it requires external lighting to be read in the dark. A new technology called Flex Lighting can provide a front light that is built-in.
E-paper displays are expected to find applications in signage, on shelving for the display of information, and on packaging for the display of pricing and instructions. These displays are also already used in portable eBook reading devices, in clocks and watches, and in USB sticks.
See also: Paper Display for a near-zero power bistable technology.
 E-paper Technology Providers
|E Ink||Cambridge, MA|
|Fujitsu Frontech Limited||Tokyo, Japan|
|Kent Displays||Kent, OH|
|Eastman Kodak||Rochester, NY|
|Nemoptic||Magny les Hameaux, France|
|Ntera||West Conshohocken, PA|
|PVI||PVI, Taiwan ROC|
- Current displays are only in greyscale, not color.
- The refresh rate of the screen is very low compared to standard LCD screens : about 1 to 2 seconds, compared to about 30 ms for LCD. Mixing pure text content with Flash or video content is not currently possible. Web browsing using scrolling is not really suitable on E-ink displays
- The refresh of an eInk page creates a black flash and can create temporary "ghosting" effect which can be annoying to some people.
 For more information
- Xerox Electronic Reusable Paper
- The future of electronic paper
- E-book Reader Matrix for a comparison of devices that use e-paper.
 E Ink display
The following data is included from the article E Ink display.
 E Ink Display Specifications
|White State Reflectivity:||40% (typical)||70% (minimum)||74%|
|Dark State Reflectivity||24% (maximum)||19%|
|Contrast Ratio:||7:1 (typical)||10:1 (minimum)||15:1|
|Viewing Angle:||180°||near 180°||near 180°|
|Grayscale Capability:||4-bit (16 gray levels)||4-bit, 16 gray levels||4-bit|
|Image Update Time:||740 ms (grayscale mode)
260 ms (1-bit mode)
|600 ms (grayscale)
120 ms (1 bit)
|120 ms (1 bit)|
|Resolution||200 ppi max||200 ppi plus||300 ppi plus|
In actual practice the grayscale capability is up to the controller hardware and can range from 4 levels to 16 levels in currently shipped devices.
 Mechanical / Dimensional for 6" Display
|Pixel Count:||800 x 600 (SVGA) 167 ppi|
|Pixel Size:||rectangular, 151 x 153 micron|
|Active Area:||122.4 x 90.6 mm (4.8" x 3.6")|
152.3 mm (6 inches) diagonal
|Display Thickness:||1.25 mm|
|Display Weight:||35 g|
There are other display sizes available.
- 13.3" (271 x 203 mm, 10.67" x 8.0") 1600 x 1200 pixels, 150 ppi
- 10.2" (207 x 155 mm, 8.15" x 6.1") 1280 x 1024 pixels, 158 ppi
- 9.7" (203 x 139.5 mm, 8.0" x 5.5") 1200 x 825 pixels, 150 ppi and 1600 x 1200, 200 ppi (pearl)
- 8.0" (162.6 x 121.9 mm, 6.4" x 4.8") 1024 x 768, 160 ppi
- 6.0" (122.4 x 90.6 mm, 4.8" x 3.6") 800 x 600, 167 ppi and 1024 x 768, 213 ppi (pearl)
- 5.0" (101.5 x 76.1 mm, 4.0" x 3.0") 800 x 600, 200 ppi
Available sizes range from 2" to 13.3" diagonal.
|Operating Temperature Range:||0 — 50 C (32 — 122 F)|
|Storage Temperature Range:||-27 — 70 C (-17 — 158 F)|
|Supply Voltage:||2.7—3.3 V DC|
|Power Consumption:||Active update peak: 1800 mW|
Active update typical: 750 mW
Standby typical: 1 mW
 E Ink controllers
The current controllers
- Apollo is the original controller and is still popular and used on many readers.
- IRex builds their own custom controller offering 16 levels of Grayscale.
- Epson controller available in late 2008 with improved features. Used on Sony PRS700, Amazon Kindle 2, Kindle DX, Hanlin V5, and others. Newer controllers are also available that can be used for grayscale or color screens.
Here is a discussion of interfacing to these controllers for Linux applications.
 Notes on earlier E Ink devices.
The older display technology has 4 level gray scale and slower update times of 1000 ms for gray scale and 500 ms for 1-bit mode. These were primarily 6" devices. They also had less reflectivity. This causes these devices to appear less white (light grey background) and have less contrast.
The iRex iLiad, on the other hand, uses a custom display controller that achieves 16 levels of gray scale. They are also using an 8.1" display featuring a 1024 x 768 pixel display.
See also E-paper and E Ink