Stop Press! Electronic paper is here
Published: 15 Jul 2005 12:10 BST
What is e-paper technology?
The reason it has taken so long to create a commercially practical electronic paper is that two entirely new technologies are required. The first is the electronic ink that will create the actual 'print' display on the e-paper page, and the second is the flexible electronics required to generate the pattern of text and images on the page of electronic ink.
The development of both technologies has proved to be a lot more complex than was initially conceived. Most flat panel displays, such as LCDs, consist of two main elements: a backplane that controls which pixels on the display turn on and off, and a frontplane that either emits light, or acts as a shutter controlling the light coming from another source at the pixel locations determined by the backplane.
On most modern flat panel displays the backplane has an electronic 'switch' under each pixel, so that the pixel can be turned on and off without affecting its neighbours; this is referred to as an active matrix display. Older displays did not have this 'switch', just a matrix of connections, and are known as passive matrix displays. TThey have the disadvantage that the length of the conductor that links the driving circuit and the pixel delays and distorts the precise signal needed to generate a sharp, rapidly refreshed picture and are thus too slow and smeary for modern applications.
The usual way of fabricating the transistors used to construct the backplane switches is to deposit a thin layer of silicon onto a glass substrate and then use conventional semiconductor manufacturing techniques to create the transistors and associated circuitry. The trouble is that these manufacturing processes require very high temperatures and this makes such backplanes not only expensive to manufacture but also precludes the use of a substrate made of a material such as plastic, since this would melt during processing.
The solution is to use a semiconductor other than silicon to fabricate the transistors, one that can be formed into the appropriate circuitry at room temperature. The newly developed technology of organic semiconductors fits the bill perfectly, and is the solution that has been adopted by Philips Polymer Vision and Plastic Logic.
Both these companies have developed organic electronic materials that are soluble, and can thus be used at room temperature allowing the circuitry to be mounted upon a flexible plastic substrate. Another advantage of organic semiconductors is that the circuitry can be created using conventional screen printing and ink jet technologies, this makes manufacturing such displays a lot cheaper since they do not require such an enormous investment in capital equipment.
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