Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-06-13
2002-06-25
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S155000, C349S110000
Reexamination Certificate
active
06411360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device comprising a spacer with a novel structure for keeping a distance between a pair of substrates thereof between which liquid crystal compounds are scaled, uniformly.
2. Description of the Related Art
Liquid crystal display devices are coming into wide use as display devices for notebook type computers or monitors of computers which can display color images with high definition image qualities.
The liquid crystal display device of this sort has basically so-called liquid crystal display panel being constructed by at least one pair of substrates at least one of which is formed of a transparent glass or plastic substrate, or the like, and interposing liquid crystal compounds in a gap (simply called, liquid crystals, or a liquid crystal layer, also hereinafter) between the one pair of substrates which are arranged so as to confront one another with the gap. Moreover, these liquid crystal display devices of are classified roughly into either a simple matrix type liquid crystal display device which lights a predetermined pixel thereof up/out by applying a voltage selectively to various electrodes of the pixel provided in the liquid crystal display panel, or an active matrix type liquid crystal display device which lights a predetermined pixel thereof up/out by selecting an active clement for selecting the pixel, the active element being provided together with the various electrodes in the liquid crystal display panel.
The active matrix type liquid crystal display devices are represented by a type thereof using a thin film transistor (TFT) as the active matrix element constituting the liquid crystal display panel thereof. As the liquid crystal display devices comprising the liquid crystal display panels using the thin film transistors are thinly-made and lightweight, and provide high image qualities equal to those of cathode-ray tubes (Braun tubes), the liquid crystal display devices become widespread as monitors for displaying terminals of office automation apparatuses, or the like.
Displaying schemes for the liquid crystal display devices are classified broadly in accordance with driving methods of the liquid crystal display panels thereof, into following two sorts. One of them is an image-displaying scheme by interposing liquid crystal compounds between a pair of substrates each of which has a transparent electrode formed on, by driving liquid crystal compounds in accordance with voltages applied to the transparent electrodes, and by modulating incident light into the layer of liquid crystal compounds through the transparent electrodes, and this scheme is employed in most of a currently popular products.
Another of the displaying schemes displays an image by generating electric fields between a pair of electrodes provided on the same substrate of the liquid crystal display panel substantially in parallel to a surface of the substrate so as to drive the liquid crystal compounds between the electrodes thereby, and by modulating incident light into a layer of the liquid crystal compounds through a gap between the pair of the electrodes. The liquid crystal display panel of this displaying scheme is characterized by an image having remarkably wide viewing angle displayed thereby, and thus an image of an extremely high quality can be obtained by an active matrix type liquid crystal display device using this liquid crystal display panel. Characteristics of this displaying scheme are described in such documents as e.g. Japanese Patent Application Laid-Open No. 05-505247 (JP-A-505247/1993), Japanese Patent Publication No. 63-021907 (JP-A-021907/1988), Japanese Patent Application Laid-Open No. 06-160878 (JP-A-160878/1994). The liquid crystal display device of this displaying scheme will be called a liquid crystal display device of a lateral electric field scheme, hereinafter. The liquid crystal display device of the lateral electric field scheme is also called an IPS (In Plane Switching) type liquid crystal display device.
FIG. 17
is a cross sectional view for explaining an electric field generated in a liquid crystal display panel constituting the liquid crystal display device of the lateral electric field type. The liquid crystal display panel has a video signal line DL, a counter electrode CT, and a pixel electrode PX each of which is formed on one of substrates thereof SUB
1
, a protective film PSV being deposited on these layers, and an alignment control layer (also called, an alignment layer, or alignment film) ORI
1
being formed at an interface with the liquid crystal layer LC. The liquid crystal display panel also has color filters FIL partitioned by a black matrix BM formed on another of the substrates thereof SUB
2
, an overcoat layer OC being deposited over these layers in order to prevent composing materials of the color filters and the black matrix from affect the liquid crystal compounds (called, liquid crystals, also hereinafter), and an alignment control layer ORI
2
being formed-at an interface with the liquid crystal layer LC.
Insulating films GI, AOF are also formed on the one of the substrates SUB
1
. Moreover, the video signal line DL is formed of two conductive films d
1
and d
2
stacked on one another, the counter electrode is formed of a conductive film g
1
, and the pixel electrode PX is formed of a conductive film g
2
, wherein each of these is provided on the one of the substrates SUB
1
.
Furthermore, a distance between a pair of the substrates SUB
1
and SUB
2
(i.e. a thickness of the liquid crystal layer: a cell gap) is generally set at a predetermined value by dispersing inorganic-base or plastic-base spherical spacers (i.e. beads, but not shown in
FIG. 17
) between both of the substrates. On each outer surface of the substrates SUB
1
and SUB
2
, a polarizer (a polarizer plate) POL
1
or a polarizer (a polarizer plate) POL
2
is stacked respectively.
On the other hand, Japanese Patent Application Laid-Open No. 09-073088 (JP-A-073088/1997) discloses conical spacers formed on the protective film on the color filter substrate (like a substrate SUB
2
, in
FIG. 17
) and columnar spacers formed by stacking color filter layers both of which are fixed to the color filter substrate, instead of such spherical spacers mentioned above regardless of the lateral electric field type liquid crystal display device.
The invention disclosed in Japanese Patent Application Laid-Open No. 09-073088 (JP-A-073088/1997) is to form conical spacers stably on the substrate so as to prevent deterioration of image contrast by light leaking through peripheries of the spherical spacers and displaying defects caused by spacers irregularly arranged during a step for spraying the spacers onto the substrate.
SUMMARY OF THE INVENTION
There are two problems to be solved by the present invention. First problem of the two problems is related to a design of pixels in the liquid crystal display panel of the lateral electric field scheme. For clarifying the problem, noise fields appearing in a area hidden by the black matrix will be mentioned.
In the liquid crystal display panel shown in
FIG. 17
, while an image is displayed by controlling orientation directions of liquid crystal molecules constituting the liquid crystal layer LC by applying an electric field E
L
generated substantially in parallel with the substrate between the pixel electrode PX and the counter electrode thereto, another electric field not contributing to displaying operation of the liquid crystal display panel (i.e. a noise field E
N
) is also generated between the video signal line DL and the counter electrode CT. If a space between these electrode is too narrow, an intensity of the noise field E
N
appearing in an area between the video signal line DL and the counter electrode CT becomes so large that the liquid crystals LC in the area are driven by the noise field and consequently permit undesirable light to penetrate in the area therethrough.
Unle
Asuma Hiroaki
Matsuyama Shigeru
Yanagawa Kazuhiko
Chowdhury Tarifur R.
Hitachi , Ltd.
Sikes William L.
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