I. Introduction
The use of electronic ink is quite extensive. The first-generation products are used to replace conventional display devices. The second-generation products include display screens for handheld devices such as mobile communications and PDAs. The next-generation products planned for development are positioned on ultra-thin displays, forming and printing industries. Related application fields, such as portable e-books, e-newspapers, and IC cards, can provide similar reading functions and usage attributes as traditional books.
For a long time, paper has been used as the main medium for information exchange. However, graphic content cannot be changed once it is printed on paper. It has become the biggest drawback of the ink/paper replication process and cannot meet the requirements of modern society for the rapid update of information on the reproduction process. Therefore, the development of high-resolution display technologies that can change dynamically has become the goal pursued by people. The display materials are required to be thin, bendable, and the surface structure is similar to that of paper, thus making it possible to become a new generation of paper.
As long as there is an electric field and the mode of action of the electric field changes, the electronic ink can change the displayed image, which means that the information displayed on the surface of the electronic ink material can be continuously updated. Although the physical basis of the information presentation is different, there is no significant difference in the use of the electronic ink display from the paper. In addition, the power consumption of electronic ink is extremely low, and the weight is not different from paper.
Second, the working principle
Electronic ink is a special material that is processed into a film and used in combination with electronic display devices. It is a comprehensive application of chemistry, physics, and electronics. Electronic inks consist of millions of tiny microcapsules with diameters that are comparable to hair strands. Each microcapsule contains white and black particles with positive and negative charges, respectively, 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 used as the electrode end; the bottom is the other electrode of the electronic ink, and the microcapsules are sandwiched between these two electrodes. When the microcapsules are subjected to a negative electric field, the white particles are positively charged and move to the top of the microcapsules, and the corresponding positions appear white; the black particles, due to the negative charge, reach the bottom of the microcapsules due to the electric field force, and the user cannot see the black color. If the direction of action of the electric field is reversed, the display effect is reversed, 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 portion corresponds to the uninked portion of the paper, and the black portion corresponds to the printed image portion on the paper.
Third, the main performance advantages of electronic ink
The explosive development of broadband and wireless communication technologies allows people to access a large amount of information easily and quickly, but display size and readability are the main obstacles to limit the rapid transmission of information. At this time, electronic inks with high-resolution display capabilities have become The most ideal solution, the main performance advantages can be summarized as follows.
Readability
The existing display technologies are classified into two types: an emission type and a reflection type. Examples of the former include a cathode ray tube display, a plasma display, and a light emitting diode. The liquid crystal display and the rotating ball display belong to the latter, and the background light uses a reflective type. The premise of the monitor.
The readability of electronic display products is mostly measured by the two major technical indicators of brightness and contrast. The brightness of the reflective display is determined by the reflectance of the ambient lighting and the display in the white state; the contrast is defined as the ratio of the white state reflectance of the display to the black state reflectance, and the ability of the eye to distinguish the display results from light and shade is measured.
Emission-based displays can generate light by themselves. With the enhancement of ambient lighting, the display content gradually becomes blurred, and the readability is drastically reduced. In contrast, reflective displays use ambient light to produce images that vary in brightness as the eye adapts to changes in lighting conditions. In addition, since the ambient light has the same influence on the bright state and the dark state of the reflective display, the contrast is insensitive to changes in the ambient light and is suitable for use in different lighting conditions.
The benchmark for measuring display technology is the ink/paper reproduction process because paper is the easiest to read information recording material for different lighting conditions and viewing angles. The measurement results show that the reflectivity of the electronic ink display is 3 to 6 times that of the liquid crystal display, and the contrast ratio is 2 times that of the liquid crystal display. Although the reflectance is lower than that of the newspaper, the contrast is significantly higher than that of the newspaper. Therefore, the electronic ink display is much more readable than a liquid crystal display device and is comparable to a newspaper.
2. Power consumption
Compared with the liquid crystal display, the power consumption of the electronic ink display is greatly reduced, which means that the battery life is extended under the same other conditions, or a smaller battery can be used to reduce the display weight and the use cost.
The reason why the electronic ink display can reduce the power consumption is as follows: First, it is completely reflective, no background light is needed, and it can meet the lighting conditions of reading books; secondly, the memory effect of the electronic ink display, after the image is displayed on the screen That is, it does not need to be continued unless the user requests a new round of display. Therefore, the power consumption depends on the frequency of the image display state change, not the length of time the same image is displayed.
3. Use function
The electronic ink display has excellent use functions, not only is thinner than the liquid crystal display, but also has the advantages of light weight, firmness, durability, flexibility, and extremely low power consumption, and can produce an ultra-thin lightweight handheld display device. This brings about the portability of the electronic ink display, which is necessary for simulating the combination of the conventional ink/paper reproduction technology, so that the electronic book prepared by the electronic ink technology has a function similar to that of a paper book.
Fourth, structure and application examples
E-Ink has developed RadioPaper technology, meaning that it can be used without wires, and it can conveniently exchange information and display with the support of various communication technologies at any time and any place. Currently, there are two types of electronic ink display structures. The first type is called a composite structure, and the total thickness is about 0.9 mm. Partially borrows the structure of liquid crystal display units, which is used for the first generation of electronic ink display screens; The structure is the basis for the formation of a flexible display or electronic paper, giving up the use of glass as the back panel, with a thickness of less than 0.5 mm.
Figure 2 compares the structural differences of TFT (thin-film transistor) liquid crystal display cells, first-generation electronic ink displays, and flexible electronic ink displays. It can be seen that the liquid crystal display unit is developed with the liquid crystal thin layer as the center toward the top surface and the bottom surface. The upper and the lower two layers of the liquid crystal thin layer are called the front panel and the rear panel respectively, and the thickness is about 0.7 mm. In addition, two layers of polarizing films are also required, arranged on the front and back panel surfaces, with a thickness of about 0.25 mm. In this way, the total thickness of the liquid crystal display unit is at least 2 mm. In general, in order to enhance the optical performance of the display, the liquid crystal display unit also needs an additional thin film, which is thicker and heavier.
The display products based on electronic ink imaging technology are divided into two major platforms, of which high-resolution, active matrix displays are suitable for applications such as e-books, and have high requirements for display quality; group display technologies are used for low- and medium-resolution products. The initial electronic ink display product only provided two gray display capabilities, followed by a 4-bit grayscale display device. Currently, E-Ink and its partners are working to develop the next generation of electronic ink display products. The target application area is electronic paper products, with the dominant direction of flexible color displays and IC cards, and plans to develop faster display video displays. .
The use of electronic ink is quite extensive. The first-generation products are used to replace conventional display devices. The second-generation products include display screens for handheld devices such as mobile communications and PDAs. The next-generation products planned for development are positioned on ultra-thin displays, forming and printing industries. Related application fields, such as portable e-books, e-newspapers, and IC cards, can provide similar reading functions and usage attributes as traditional books.
For a long time, paper has been used as the main medium for information exchange. However, graphic content cannot be changed once it is printed on paper. It has become the biggest drawback of the ink/paper replication process and cannot meet the requirements of modern society for the rapid update of information on the reproduction process. Therefore, the development of high-resolution display technologies that can change dynamically has become the goal pursued by people. The display materials are required to be thin, bendable, and the surface structure is similar to that of paper, thus making it possible to become a new generation of paper.
As long as there is an electric field and the mode of action of the electric field changes, the electronic ink can change the displayed image, which means that the information displayed on the surface of the electronic ink material can be continuously updated. Although the physical basis of the information presentation is different, there is no significant difference in the use of the electronic ink display from the paper. In addition, the power consumption of electronic ink is extremely low, and the weight is not different from paper.
Second, the working principle
Electronic ink is a special material that is processed into a film and used in combination with electronic display devices. It is a comprehensive application of chemistry, physics, and electronics. Electronic inks consist of millions of tiny microcapsules with diameters that are comparable to hair strands. Each microcapsule contains white and black particles with positive and negative charges, respectively, 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 used as the electrode end; the bottom is the other electrode of the electronic ink, and the microcapsules are sandwiched between these two electrodes. When the microcapsules are subjected to a negative electric field, the white particles are positively charged and move to the top of the microcapsules, and the corresponding positions appear white; the black particles, due to the negative charge, reach the bottom of the microcapsules due to the electric field force, and the user cannot see the black color. If the direction of action of the electric field is reversed, the display effect is reversed, 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 portion corresponds to the uninked portion of the paper, and the black portion corresponds to the printed image portion on the paper.
Third, the main performance advantages of electronic ink
The explosive development of broadband and wireless communication technologies allows people to access a large amount of information easily and quickly, but display size and readability are the main obstacles to limit the rapid transmission of information. At this time, electronic inks with high-resolution display capabilities have become The most ideal solution, the main performance advantages can be summarized as follows.
Readability
The existing display technologies are classified into two types: an emission type and a reflection type. Examples of the former include a cathode ray tube display, a plasma display, and a light emitting diode. The liquid crystal display and the rotating ball display belong to the latter, and the background light uses a reflective type. The premise of the monitor.
The readability of electronic display products is mostly measured by the two major technical indicators of brightness and contrast. The brightness of the reflective display is determined by the reflectance of the ambient lighting and the display in the white state; the contrast is defined as the ratio of the white state reflectance of the display to the black state reflectance, and the ability of the eye to distinguish the display results from light and shade is measured.
Emission-based displays can generate light by themselves. With the enhancement of ambient lighting, the display content gradually becomes blurred, and the readability is drastically reduced. In contrast, reflective displays use ambient light to produce images that vary in brightness as the eye adapts to changes in lighting conditions. In addition, since the ambient light has the same influence on the bright state and the dark state of the reflective display, the contrast is insensitive to changes in the ambient light and is suitable for use in different lighting conditions.
The benchmark for measuring display technology is the ink/paper reproduction process because paper is the easiest to read information recording material for different lighting conditions and viewing angles. The measurement results show that the reflectivity of the electronic ink display is 3 to 6 times that of the liquid crystal display, and the contrast ratio is 2 times that of the liquid crystal display. Although the reflectance is lower than that of the newspaper, the contrast is significantly higher than that of the newspaper. Therefore, the electronic ink display is much more readable than a liquid crystal display device and is comparable to a newspaper.
2. Power consumption
Compared with the liquid crystal display, the power consumption of the electronic ink display is greatly reduced, which means that the battery life is extended under the same other conditions, or a smaller battery can be used to reduce the display weight and the use cost.
The reason why the electronic ink display can reduce the power consumption is as follows: First, it is completely reflective, no background light is needed, and it can meet the lighting conditions of reading books; secondly, the memory effect of the electronic ink display, after the image is displayed on the screen That is, it does not need to be continued unless the user requests a new round of display. Therefore, the power consumption depends on the frequency of the image display state change, not the length of time the same image is displayed.
3. Use function
The electronic ink display has excellent use functions, not only is thinner than the liquid crystal display, but also has the advantages of light weight, firmness, durability, flexibility, and extremely low power consumption, and can produce an ultra-thin lightweight handheld display device. This brings about the portability of the electronic ink display, which is necessary for simulating the combination of the conventional ink/paper reproduction technology, so that the electronic book prepared by the electronic ink technology has a function similar to that of a paper book.
Fourth, structure and application examples
E-Ink has developed RadioPaper technology, meaning that it can be used without wires, and it can conveniently exchange information and display with the support of various communication technologies at any time and any place. Currently, there are two types of electronic ink display structures. The first type is called a composite structure, and the total thickness is about 0.9 mm. Partially borrows the structure of liquid crystal display units, which is used for the first generation of electronic ink display screens; The structure is the basis for the formation of a flexible display or electronic paper, giving up the use of glass as the back panel, with a thickness of less than 0.5 mm.
Figure 2 compares the structural differences of TFT (thin-film transistor) liquid crystal display cells, first-generation electronic ink displays, and flexible electronic ink displays. It can be seen that the liquid crystal display unit is developed with the liquid crystal thin layer as the center toward the top surface and the bottom surface. The upper and the lower two layers of the liquid crystal thin layer are called the front panel and the rear panel respectively, and the thickness is about 0.7 mm. In addition, two layers of polarizing films are also required, arranged on the front and back panel surfaces, with a thickness of about 0.25 mm. In this way, the total thickness of the liquid crystal display unit is at least 2 mm. In general, in order to enhance the optical performance of the display, the liquid crystal display unit also needs an additional thin film, which is thicker and heavier.
The display products based on electronic ink imaging technology are divided into two major platforms, of which high-resolution, active matrix displays are suitable for applications such as e-books, and have high requirements for display quality; group display technologies are used for low- and medium-resolution products. The initial electronic ink display product only provided two gray display capabilities, followed by a 4-bit grayscale display device. Currently, E-Ink and its partners are working to develop the next generation of electronic ink display products. The target application area is electronic paper products, with the dominant direction of flexible color displays and IC cards, and plans to develop faster display video displays. .
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