ePaper
More and more you see people reading a book on their eReader. The two most popular eReaders in the USA are the Kindle, from Amazon, and the Nook, from Barnes & Noble. Of course you can read a book on an iPad or Notebook, but their displays are based on LCD technology and that is considered not very relaxing on the eyes. An eReader’s display is based on electronic paper and that has major advantages. The main player in the ePaper display business is EInk, which developed and marketed together with Philips the electrophoretic display.
ePaper, or e-ink, as it was known at the start, was developed to mimic the appearance of real paper. A major drive in the development was the ability to display an image/text without needing additional energy input, after the page was loaded.
LCD display
Although it is not obvious, LCD displays refresh (even static images) many times a second and this can become a nuisance for the observer. This also means that power is continuously needed to run the display, with low battery life as a consequence. Â Because of the back-light, achieving good contrast of an LCD display is a constant struggle for developers all over the world.
Electrophoretic display
The basis of an ePaper is based on a simple implementation of an electrophoretic display. This display consists out of little capsules, 10 to 100 micrometer thick and about 40 micrometer across, representing the pixels. The capsules are filled with a hydrocarbon oil, a dark coloured dye and a charging agent. Floating in the oil are tiny 1 micrometer titanium dioxide particles, which have a slightly positive charge due to the charging agent. The particles are designed to have a high refractive index and will reflect light back when exposed to sunlight. The capsules are placed between two parallel conductive plates, with the rear plate divided into pixels corresponding with the position of the capsules and the front plate being transparent.
When a voltage is applied across the plates, the titanium dioxide particles will migrate through the oil to the negative plate. When this is the viewing side of the display, the pixel appears to be white, because of the reflection of sunlight from the particles back to the viewer. When the particles are arranging themselves against the backside plate, all the light is absorbed by the coloured dye in the capsule and the pixel appears black. In this way a display is created with reflecting and absorbing regions of sunlight and with a very high contrast.
At the moment a new page is loaded, no extra energy is needed to keep the image on the display. A good feature when using ePaper as the display in an eReader.
Colour ePaper
Colour ePaper is the next step. Qualcomm with their Mirasol display based on Interferometric Modulator (IMOD) (a technology developed by Iridigm), and Samsung with their Electrowetting display (developed by Liquavista) are making it happen as we speak.