Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-11-08
2003-10-28
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S105000, C359S296000, C359S297000
Reexamination Certificate
active
06639580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophoretic display device for displaying migrated charged particles, and a method for addressing the display device.
2. Related Background Art
Various methods are used for output of a line of information since data volume of various information is being expanded in recent years as a result of development of information instruments. In general, output of information is roughly categorized into two groups of display on a cathode ray picture tube or a liquid crystal panel, and hard copy display on a sheet of paper using a printer. Needs of a thin type display device with low power consumption has been increasingly required, and the display device that can correspond to these needs has been aggressively developed and put into the market. However, images such as letters on the screen become hardly distinguishable depending on the view angle of the screen or by the reflection light, or the problem of burden on the vision caused by flickering or low brightness of the light source has not been sufficiently solved. Although the display device using the cathode ray picture tube has more sufficient contrast and brightness as compared with the liquid crystal display device, the display quality of the former is not so sufficient yet in the appearance of flickering as compared with the hard copy display to be described hereinafter. The display device using the cathode ray picture tube has also another problem that it has such a large size that it is not suitable as a portable device.
While the hard copy display has been considered to be of no use by utilizing electronic information, a vast amount of hard copy outputs are actually used. This is because, in addition to the problem of the image quality of information on the screen, resolution of the screen is substantially as low as about 120 dpi as compared with resolution of print-out on a sheet of paper (usually 300 dpi or more). Accordingly, display image on a panel gives a larger burden on the vision as compared with the hard copy display. As a result, a line of information is often output as a hard copy, even when the image is distinguishable on the display. It is also the reason why the hard copy display is used together even when the panel display is possible, that a number of the hard copy information can be arranged with no restriction of the display area depending on the display size contrary to the panel display, the information lines can be rearranged without any complicated hard ware operation, or the information lines can be sequentially confirmed. In addition, the hard copy display requires no energy, and is so excellent in handiness that the lines of information can be reconfirmed anytime and anywhere, so long as the information size is not extremely large.
While the hard copy display has many advantages over the panel display except moving images or provided that hazardous rewriting is not required, the hard copy display has a drawback that a lot of paper is consumed. Accordingly, development of recording media capable of rewriting (recording media capable of many recording and erase cycles of the images that are high recognizable by the vision, and requires no energy for holding of display images) has been actively carried out. The third display method capable of rewriting that succeeds the characteristics of the hard-copy is called herein as a paper-like display.
The essential conditions of the paper-like display are being capable of rewriting, requiring no or small energy for retaining display images (memory characteristics), and being excellent in handiness and display image quality. Display methods that are currently considered to be the paper-like display include reversible display media using matrix systems of low molecular weight organic molecule and polymer resins (disclosed in, for example, Japanese Patent Laid-Open Nos. 55-154198 and 57-82086) in which images are recorded and erased with a thermal printer head. While this system is partly utilized as display portions of a prepaid card, it involves some problems that contrast is not so high and the repeating number of recording and erasing is relatively as small as about 150 to 500 times.
Another display method that can be utilized as the paper-like display include an electrophoretic display device (U.S. Pat. No. 3,612,758). The electrophoretic display device is also disclosed in Japanese Patent Laid-Open No. 9-185087.
This display device comprises a dispersion system composed of colored and charged particles dispersed in an insulation liquid and a pair of electrodes opposed across this dispersion system. When a voltage is applied to the dispersion system through the electrodes, a Coulomb force allows the colored and charged particles to be absorbed to the electrode at the side having an opposite electric charge to the charge of the colored and charged particles themselves, by taking advantage of the electrophoretic property of the colored and charged particles. Images are displayed by taking advantage of the color difference between the colored and charged particles and dyed insulation liquid. In other words, the color of the colored and charged particles is observed when the colored and charged particles are absorbed on the surface of the first light-permeable electrodes proximal to an observer. When the particles are absorbed on the surface of the second electrode distal to the observer, on the contrary, the color of the insulation liquid, which has been colored to have optical characteristics different from the colored and charged particles, is observed.
However, no dyes or ions should be mixed with the insulation liquid in such an electrophoretic display device. Presence of these chromatic substances tends to act as instability factors in electrophoretic operations due to exchange of additional charges, to cause deterioration of the performance, service life and stability as the display device.
For solving these problems, Japanese Patent Laid-Open No. 49-5598 and Japanese Patent Publication No. 10-005727 have disclosed a display device in which a pair of electrodes comprising first and second display electrodes are arranged on the same substrate, and the colored and charged migration particles are made to transfer toward the horizontal direction as viewed by an observer. A voltage is applied through a transparent insulation liquid, and the images are displayed by allowing the colored and charged particles to horizontally transfer toward the direction parallel to the surface of the substrate between the first and second display electrodes by taking advantage of the electrophoretic property of the particles.
The insulation liquid is transparent in this in-plane (transfer) type electrophoretic display device, and the first display electrode has a color different from the color of the second display electrodes when viewed from the observer's side. The color of one of the electrodes is made to coincide with the color of the charged particles. For example, when the first electrode, the second electrode and the charged particles are colored black, white and black, respectively, the second electrode is exposed with white color when the charged particles are distributed on the first electrode, and the second electrode is colored black when the charged particles are distributed on the second electrode.
The methods for electrically addressing the display device on which pixels are arranged in a matrix are roughly classified into an active matrix method and a passive matrix method.
In the active matrix method, switching elements such as thin film transistors are formed for every pixel, and the voltage applied for each pixel is independently controlled to one another. This method enables the in-plane (transfer) type electrophoretic display element to be addressed with high display contrast. However, this active matrix method involves the problems that the process cost is high in this method, and forming the thin film transistors on the polymer substrate is difficult due to h
Kishi Etsuro
Matsuda Yojiro
Uno Yoshinori
Chang Kent
Sheng Tom
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