Electrophoretic display device

Abstract

An electrophoretic display device comprises a first substrate and a second substrate positioned to face each other. A first electrode is so mounted to the first substrate as to face second and third electrodes. The second and third electrodes have an area smaller than that of the first electrode. Also, the distance between the second and third electrodes is set shorter than the distance between the second and first electrodes and the distance between the third and electrodes. A suspension dispersing charged fine particles in an insulating liquid medium is interposed between the first electrode and the second and third electrodes. An AC voltage is applied between the second and third electrodes, and a DC voltage is applied between the first electrode and the second and third electrodes. Thus, the migration of charged fine particles are controlled in accordance with the dielectrophoretic and electrophoretic forces.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-202123, filed Jul. 25, 2003, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates an electrophoretic display device, particularly, to an electrophoretic display device that can be driven with low power consumption. [0004] 2. Description of the Related Art [0005] A reflective display device is low in its power consumption and permits lessening the burden given to the eye of the observer and, thus, is expected to be widely propagated in future. An electrophoretic display device is known to the art as one of the reflective display devices. The electrophoretic display device comprises a pair of electrodes and a suspension loaded in the space between the paired electrodes. The suspension is prepared by dispersing electr...

AI Technical Summary

Benefits of technology

The present invention provides an electrophoretic display device that can easily generate a threshold value for allowing charged fine particles to migrate and can be driven with a small power consumption. The device includes a suspension layer containing charged fine particles and a power source section for applying an AC voltage and a DC voltage to the electrodes. The driving method involves applying an AC voltage to restrict the charged fine particles to the second and third electrodes and then applying a DC voltage to allow the charged fine particles to migrate towards the first electrode. This results in a display with low power consumption and good image quality.

Problems solved by technology

However, the electrophoretic display device gives rise to a serious problem that it is essentially impossible to achieve both a high reflectance, i.e., a high brightness, and a high contrast simultaneously because, for example, the die dissolved in the medium may be attached to the particles to color the particles or the colored medium may be entered in the space between the surface of the electrode and the electrophoretic particles attached on the electrode.

Such being the situation, it is said to be substantially difficult for the simple matrix driving or the memory characteristics to be developed.

However, it is difficult to control the adsorption force so as to give rise to the problem that the threshold value is rendered widely non-uniform or fails to be stabilized over a long period of time.

On the other hand, the display device utilizing the dielectrophoresis is defective in that the response speed is low because of the lack in the restoring force for bringing the fine particles attracted toward the side remoter from the observing surface by the application of an AC electric field back to the side of the observing surface.

In addition, since there is no threshold value in the dielectric migrating force under a certain set frequency, it is difficult to cause the fine particles of a specified color to be allowed to migrate selectively with a high accuracy so as to make it difficult to achieve a color display device.

It should also be noted that it is necessary to control simultaneously the voltage level and the frequency of the AC voltage applied to a pair of electrodes mounted to each pixel, with the result that a difficulty is also generated in respect of the driving of the display device.

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