Electronic Paper Technology Overview

Electronic Paper Technology Overview

Electronic paper technology was born in the 1970s, but it is now 35 years later that it has truly prospered. Electronic paper was originally invented to replace the large consumption of traditional paper. Today, the impact of the emergence of electronic paper on the traditional paper publishing industry is gradually being reflected. Currently, more than 20 electronic paper carriers have appeared in the world. In 2007 alone, 8 new electronic paper carriers were born. It is expected that this number will be close to 40 in 2008. Table 1 is a statistical analysis of the development of the electronic paper market in recent years. However, don't forget that the essence of electronic paper is first a flexible display. Behind its thin and soft characteristics, it has a more thorough impact on the traditional flat panel display industry.

Table 1 Electronic paper market size from 2004 to 2010 (Source: Fuji Chimera Research Institute)

Introduction to e-paper

The carrier of electronic paper is a special thin film. Through a layer of charged material (electronic ink) "coated" on the film, the background control is carried out according to the different contents, and the purpose of content display is achieved through the corresponding display combination. The core of electronic paper is an IC in a broad sense, and the entire reader can be regarded as a thin embedded remote control display board. Electronic ink is a lot of black and white particles with positive and negative charges, which are sealed in microcapsules. Due to the different applied electric fields, different aggregations are produced on the surface of the monitor, showing black or white effects. The most commercialized non-liquid crystal electronic paper technology is E-Ink's electronic ink technology (electrophoretic electronic paper). It has many advantages, the most important of which is that the content can be rewritten, and the text or image can be updated at will, so as to realize the unified platform browsing of a large amount of content. At the same time, it is very suitable for naked eye reading. Due to the high contrast, the text and image are clear, and there is no change from which direction to read, which makes reading comfortable and easy. Power saving is also a major feature of electronic paper. After the text is refreshed, it will stay on the screen for a long time, and the battery can be removed when reading. In other words, it does not consume power when reading, but only consumes power when turning pages to refresh, so the battery life will be very long. Because the film is light, the electronic paper can also be folded and curled appropriately, which is light and easy to carry.

Another form of electronic paper is a portable thin-film display panel, namely a "paper-type" flexible liquid crystal display. This method uses the properties of liquid crystals whose molecular arrangement is changed after applying voltage to express contrast by adjusting the transmittance and changing the direction of light. The idea of ​​making electronic paper liquid crystal displays is to separate the liquid crystal panel from the device part for writing images to achieve thinness and lightness, and to be able to curl up and make it like paper. Writing can be achieved by applying light, heat, surface charge and other methods. Compared with other electronic papers realized by non-liquid crystal technology, this type of product is slightly disadvantageous in cost. Its main feature is that the visual reading condition is relatively good, and even if you stare for a long time, it will not make your eyes feel tired, and the light perception can be adjusted and processed on the surface. It is equipped with a CPU and semiconductor memory, and the device is easy to carry and easy to use. You can read electronic documents or electronic books with just a button. It is also expected to be linked to the network for free access. The electronic notebook made of electronic paper bundles can provide access to digital data and can store information with the help of records. Because electronic paper has the above-mentioned functions and utilization value, it is easily accepted by users.

How electronic paper works

At present, there are five mainstream electronic ink technologies in the world, namely microcapsule electrophoresis, bichromal, cholesteric liquid crystal (ChLCD), electrowetting technology and electrochromic technology. Among them, E-Ink's electrophoresis technology is relatively mature and widely used.

E-Ink's electronic paper consists of electronic ink and two substrates: the first part is the electronic ink, sometimes called the "front plane"; the second is the combination of electronic devices required to generate text and images in the electronic ink, including the control part and the display part, which is called the "backplane". The backplane is coated with electronic ink composed of countless tiny transparent particles, the diameter of which is only half the size of a human hair. Electronic ink is a special material processed into a film and used in combination with electronic display devices. It is a comprehensive application of chemistry, physics and electronic technology. Electronic ink is composed of millions of extremely small microcapsules with a diameter comparable to that of a hair. Each microcapsule contains positively charged white particles and negatively charged black particles, which are suspended in a clean liquid. As shown in Figure 1, the top of the electronic ink film is a layer of transparent material, which is used as the electrode end; the bottom is the other electrode of the electronic ink, and the microcapsule is sandwiched between these two electrodes. When the microcapsule is subjected to a negative electric field, the white particles carry a positive charge and move to the top of the microcapsule, and the corresponding position is displayed as white; the black particles carry a negative charge and move to the bottom of the microcapsule under the action of the electric field, and the user cannot see the black. If the direction of the electric field is opposite, the display effect is also opposite, that is, black is displayed and white is hidden. It can be seen that as long as the direction of the electric field is changed, the display can be switched between black and white. The white part corresponds to the uninked part of the paper, and the black corresponds to the printed image on the paper.

Figure 1 Working principle of electrophoretic electronic ink

When this electronic ink is applied to paper, cloth or other flat objects, people can change the color of hundreds of millions of particles by giving it an appropriate electric shock, thereby constantly changing the displayed pattern and text according to people's settings. As long as the color of the dye and microparticles in the particles is adjusted, the electronic ink can display colors and patterns. This method uses microcapsules that can change black and white states under voltage to achieve image display. The charged white titanium oxide particles and black carbon powder particles in the microcapsules move up and down under voltage to draw a black and white image. Its characteristics are ideal in terms of contrast, brightness vision, etc., low power consumption, light weight and easy to make it thin, free shape, etc. In addition, some products use the electrophoresis phenomenon of charged toner to increase the density of toner to increase the black and white contrast.

Electrophoretic-based electronic ink outperforms two-color twist-ball-based electronic ink in terms of brightness and resolution, but both technologies are monochromatic. To create color electronic ink, E-Ink teamed up with Toppan Printing to produce color filters. Another drawback of electrophoretic electronic ink is its low refresh rate, which makes it unsuitable for displaying animations or videos. Because it takes a certain amount of time to move particles from one microcapsule to the other when drawing a new text or image, this creates a flickering picture that affects the continuous display effect. A complete solution to these problems is called cholesteric liquid crystal (ChLCD), or "paper-like" flexible liquid crystal display. The technology is based on liquid crystal display (LCD) technology, and when working, the current can quickly change from vertical to horizontal position in the form of spiral liquid crystal molecules, thereby achieving fast display. Currently, several companies, including IBM, Philips, HP and Fujitsu, are working together to develop devices based on this technology. Although other potential technologies are also developing advanced color electronic paper, such as photonic crystals (P-ink), many analysts believe that ChLCD technology may become the dominant electronic paper technology in the next decade. On the one hand, there is a fairly mature LCD industry as a technical support, and on the other hand, ChLCD technology meets the most ideal functional requirements of e-paper, such as flexibility and even foldability, ultra-thin thickness of about 0.8mm, excellent display brightness and contrast, bi-stability, no power required to maintain the image, only very little energy is needed to change the display content, and vivid colors and decent refresh rates can display animations and even videos, as shown in Figure 2.

Broad application space

E-Ink has developed RadioPaper technology, which means that it can be used without wires, and can easily exchange and display information at any time and any place with the support of various communication technologies. It currently has two electronic ink display structures. The first is called a composite structure with a total thickness of about 0.9mm. It partially borrows the structural form of the liquid crystal display unit and is adopted by the first generation of electronic ink display screens; the second structure is the basis for forming a flexible display or electronic paper, abandoning the use of glass as the back panel, and the thickness is less than 0.5mm. Display products based on electronic ink imaging technology are divided into two main platforms, among which high-resolution, active matrix displays are suitable for application fields such as e-books, and have high requirements for display quality; low and medium resolution products use grouping display technology. Initial electronic ink display products only provide 2-bit gray display capabilities, followed by 4-bit grayscale display devices. At present, E-Ink and its partners are committed to developing the next generation of electronic ink display products, with the target application field being electronic paper products, the leading direction being flexible color displays and IC cards, and plans to develop video displays with faster display speeds.

In 2007, more than 20 electronic newspapers, e-books and electronic players were launched. Moreover, as an emerging display technology, electronic paper has also been applied in unexpected fields. Seiko Watch of Japan launched the watch "Seiko SPECTRUM" with electronic paper on the dial. The electronic paper with a size of 25.6mm×78.5mm is bent along the curve of the bracelet. Motorola has realized the use of electronic paper instead of the display screen on its latest Razer series of mobile phones, thus bringing the ultra-thin characteristics of mobile phones to the extreme. In airports and other public places, electronic paper will most likely replace traditional display devices and become a new platform for public information and outdoor advertising.

From the commercialization development of electronic paper displays in recent years, it can be found that it has expanded from personal application products (such as e-books) to commercial application products (such as electronic paper advertising billboards). In addition, manufacturers related to electronic paper displays are also actively developing technology in the direction of colorization, large-scale, flexible substrates, etc., and have also achieved breakthrough progress. With the maturity of electronic paper display technology and the promotion of manufacturers to develop more diversified application products, electronic paper displays are expected to move from the introduction stage of the product life cycle to the growth stage.

It is expected that by 2012, there will be a color dynamic "newspaper" with instant messaging function, high storage capacity and the ability to be updated at any time. Its cost will be controlled at around US$100, and it is very likely that the player will be given away with the purchase of content. By then, electronic paper will not only bring a revolutionary impact to the traditional publishing industry, but also fundamentally change the traditional news content service!