Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-11
2003-11-18
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S141000, C349S143000
Reexamination Certificate
active
06650388
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device which is called In-Plane Switching Mode.
Liquid crystal display device which is called In-Plane Switching Mode has a construction in which a pixel electrode and a counter electrode which causes an electric field (an in-plane electric field) having a component parallel to transparent substrates to be generated between the counter electrode and the pixel electrode are formed in each liquid crystal-side pixel area of one of the transparent substrates disposed in opposition to each other with a liquid crystal interposed therebetween.
This type of liquid crystal display device is constructed so that the amount of light to be transmitted through the area between the pixel electrode and the counter electrode is controlled by the driving of the liquid crystal to which the electric field is applied.
Such a liquid crystal display device is known as a type which is superior in so-called viewing angle characteristics and enables a displayed image to be unchanged even when its display surface is observed from an oblique direction.
The pixel electrode and the counter electrode have so far been formed of a metal layer which does not transmit light therethrough.
In recent years, a liquid crystal display device constructed in the following manner has been known: a counter electrode made of a transparent electrode is formed over the entire area of a pixel area except the periphery thereof, and strip-shaped pixel electrodes are formed on the counter electrode with an insulating film interposed therebetween, in such a manner as to be extended in one direction and to be juxtaposed in a direction traverse to the one direction.
The liquid crystal display device having this construction causes an in-plane electric field to be generated between each of the pixel electrodes and the counter electrode, and is still superior in viewing angle characteristics and is greatly improved in aperture ratio.
Incidentally, this art is described, for example, in SID (Society for Information Display) 99 DIGEST: pp. 202-205 and Japanese Patent Laid-Open No. 202356/1999, which is incorporated herein by reference.
However, in the liquid crystal display device having this construction, the occurrence of so-called horizontal smear is visually observed on its display portion, and the occurrence of image retention is also visually observed.
It has been found out that the cause of the occurrence of horizontal smear is that the capacitance between the counter electrode formed over the entire area of the pixel area except the periphery thereof and the plural strip-shaped pixel electrodes formed in juxtaposition on the counter electrode with the insulating film interposed therebetween becomes larger than in previous type and the charge of the pixel electrodes with signal voltages becomes insufficient, and also the voltage of the counter electrode is distorted and the time required for the distorted voltage to be restored to its original state becomes long.
It has also been found out that the cause of the occurrence of image retention is that an electric field other than an electric field which has a component parallel to the substrate between the pixel electrode and the counter electrode and contributes to the control of the optical transmissivity of the liquid crystal, i.e., an electric field having a component perpendicular to the substrate between the counter electrode and the pixel electrode, is excessively strong.
SUMMARY OF THE INVENTION
The present invention has been made on the basis of the above-described situations, and provides a liquid crystal display device which can restrain the occurrence of horizontal smear.
The present invention also provides a liquid crystal display device which can restrain the occurrence of image retention.
A representative aspect of the invention disclosed in the present application will be described below in brief.
In one embodiment, a liquid crystal display device includes a first substrate. A second substrate is facing the first substrate. A liquid crystal layer is interposed between the first and second substrates. At least one pixel area is defined by a plurality of gate lines and a plurality of drain lines arranged in a matrix over the first substrate, wherein the plurality of gate lines are extending in a first direction, and the plurality of drain lines are extending in a second direction. A first electrode is assigned to the pixel area, wherein the first electrode is provided over the first substrate. A second electrode is assigned to the pixel area and is facing the first electrode, wherein the second electrode is provided over the first substrate and is transparent. The second electrode has a solid portion and a hollow portion. The hollow portion is superposed to at least a portion of the first electrode. An insulating layer is provided between the first and second electrodes.
In another embodiment, a liquid crystal display device according to the present invention includes a pair of substrates, a liquid crystal layer interposed between the pair of substrates, a plurality of pixel parts being constructed with a plurality of gate lines and a plurality of drain lines arranged in a matrix on one of the pair of substrates, at least one pair of the first electrodes and the second electrodes provided for each pixel part between one of the pair of substrates and the liquid crystal layer, wherein the first electrode and the second electrode being disposed with an insulating film interposed therebetween, and the second electrode is transparent electrode formed in a rectangular shape and having a slit formed in a portion which is superposed on the first electrodes.
In the liquid crystal display device constructed in this manner, the selected ones of the plural electrodes of the other electrode (for example, pixel electrodes) are formed not to be superposed on the one of the pair of electrodes (for example, a counter electrode).
Accordingly, it is possible to decrease the capacitance occurring between the pixel electrode and the counter electrode, whereby it is possible to restrain the occurrence of horizontal smear.
In addition, it is possible to weaken an electric field other than an electric field which contributes to the control of the optical transmissivity of the liquid crystal, i.e., an electric field having a component perpendicular to the substrate between the counter electrode and the pixel electrode, from among electric fields occurring between the pixel electrode and the counter electrode, whereby it is possible to restrain the occurrence of image retention.
Moreover, since the holes formed in the other-side electrode are disposed with respect to one-side electrodes that are not adjacent to one another, the holes are formed with a comparatively large space, whereby the holes have the advantage of being easily worked.
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Lee, S.H., et a., “16.4L: Late-News Paper: A Novel Wide-Viewing-Angle Technology:Ultra-Trans View,”SID 99 Digest(1999) pp:202-205.
Hikiba Masayuki
Konishi Nobutake
Ohta Masuyuki
Ohwada Jun-ichi
Hitachi , Ltd.
Kim Robert H.
Qi Mike
Townsend and Townsend / and Crew LLP
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