Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-05-21
2003-09-23
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S139000, C349S143000, C349S038000, C349S039000
Reexamination Certificate
active
06624866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an in-plane switching type of an active matrix type of a liquid crystal display apparatus for executing a display by rotating a liquid crystal molecule through an electric field generated parallel to a surface of a substrate.
2. Description of the Related Art
In a display panel of an in-plane switching (IPS) type of a liquid crystal display apparatus, its feature lies in a mechanism that can attain a wide field angle by putting liquid crystals at a predetermined interval between a pair of transparent substrates, and applying an effectively parallel electric field to the substrates and then rotating molecules of the liquid crystals in a direction horizontal to the inner surface of the substrate. The electric field parallel to the substrate is generated by placing a pixel electrode and a common electrode on one of the pair of transparent substrates for putting the liquid crystals between them, at a predetermined interval in a form of comb. On the other hand, in the comb electrode, the liquid crystals are raised in a direction vertical to the surface of the substrate. Thus, if the comb electrode is constituted by a transparent electrode such as ITO and the like, this constitution results in a problem of a drop in contrast and the like. So, it is necessary that the comb electrode is constituted by using an opaque electrode.
In the IPS type liquid crystal display apparatus, the technique for protecting the drop in brightness and the deterioration in contrast and field angle property is disclosed in, for example, Japanese Laid Open Patent Application (JP-A-Heisei, 9-269508).
Here, the configuration of the display cell in the conventional IPS liquid crystal display apparatus is described with reference to the drawings.
FIG. 1
shows a first plan view (a side of a TFT substrate) according to the conventional display cell. A display cell
201
shown in
FIG. 1
has an amorphous silicon
1
, a pixel electrode
2
, a gate electrode
3
, a common electrode
4
, a data line
5
, a source electrode
6
and a drain electrode
7
. Orientation films
11
are printed on the thus-created TFT substrate and respective color filters, each containing a color layer for coloration of equi-process, by using a method such as offset-print and the like. In the thus-created orientation film of the TFT substrate and the color filter substrate, the molecules of the orientation films are aligned in a predetermined direction by using a rubbing method (rubbing direction
19
). Then, the cell gap material is put between the two substrates so that a predetermined interval is established between them, and they are combined in this way. Then, the liquid crystal is filled in the gap.
On the liquid crystal panel created as mentioned above, the full color display from a black display to a white display can be carried out by laminating the polarization plates, in which transmission axes are orthogonal to each other in a liquid crystal orientation direction defined by using the rubbing method, and freely applying a potential difference between the pixel electrode
2
and the common electrode
4
.
The configuration of the display cell
201
will be described below.
FIG. 2
is a section view taken on the line A-A′ of the cell
201
. In
FIG. 2
, the upper structure located on an upper portion of a liquid crystal layer in which a liquid crystal
20
is placed is provided with a polarization plate
17
, a conductive layer
16
, a second transparent substrate
14
, a black matrix
12
, a color layer (color filter)
13
, a smoothing film
15
and an orientation film
11
. An edge (not shown) of the black matrix
12
is placed on the common electrode
4
.
In
FIG. 2
, the lower structure located on the lower portion of the liquid crystal layer is provided with an orientation film
11
, a passivation film
22
, a data line
5
, a pixel electrode
2
, a layer-to-layer insulation film (gate insulation film)
10
, a common electrode
4
, a first transparent substrate
9
and a polarization plate
18
.
Also, a mutual interval between the common electrode
4
and the pixel electrode
2
to generate an electric field in an effectively lateral direction to the substrate is set at about 10 &mgr;m.
The polarization plates
17
,
18
are set at a thickness of about 0.2 mm. The conductive layer
16
is set at a thickness of about 500 Å. The first and second transparent substrates
9
,
14
are set at a thickness of about 0.7 mm. The black matrix
12
is set at a thickness of about 1 &mgr;m. The color layer
13
is set at a thickness of about 1 &mgr;m. The smoothing layer
15
is set at a thickness of about 1 &mgr;m. The orientation film
11
is set at a thickness of about 500 Å. The data line
5
and the pixel electrode
2
are set at a thickness of about 2000 Å. The layer-to-layer insulation film (gate insulation film)
10
is set at a thickness of about 5000 Å. The passivation film
22
is set at a thickness of about 3000 Å. The common electrode
4
is set at a thickness of about 5000 Å.
FIG. 3
shows a second plan view according to the conventional display cell. A display cell
202
shown in
FIG. 2
is provided with an amorphous silicon
1
, a pixel electrode
2
, a gate electrode
3
, a common electrode
4
, a data line
5
, a source electrode
6
and a drain electrode
7
.
FIG. 4
shows a section of the cell
202
.
FIG. 4
shows a second section according to the conventional display cell. In
FIG. 4
, the upper structure located on an upper portion of a liquid crystal layer in which a liquid crystal
20
is placed is provided with a polarization plate
17
, a conductive layer
16
, a second transparent substrate
14
, a black matrix
12
, a color layer
13
, a smoothing film
15
and an orientation film
11
.
In
FIG. 4
, the lower structure located on the lower portion of the liquid crystal layer is provided with an orientation film
11
, a passivation film
22
, a data line
5
, a pixel electrode
2
, a layer-to-layer insulation film (gate insulation film)
10
, a common electrode
4
, a first transparent substrate
9
and a polarization plate
18
.
The display cell
202
shown in
FIGS. 3
,
4
differ from the cell
201
shown in
FIGS. 1
,
2
in the shapes of the edges of the pixel electrode
2
and the common electrode
4
. The other configurations are same. Due to the difference between the shapes, there is no region where the liquid crystal is inversely rotated in the vicinity of the edge in the display cell
202
. Thus, it is possible to improve the display performance and the reliability.
FIG. 5
is a view showing a first drive performance of the IPS liquid crystal display apparatus. As shown in
FIG. 5
, the IPS liquid crystal display apparatus is designed such that when an interval between the comb electrodes (an interval between the pixel electrode
2
and the common electrode
4
) is made narrow, the liquid crystal can be driven at a low voltage. However, on the other hand, the narrower interval between the electrodes increases the areas of the common electrode and the pixel electrode which are opaque. Thus, this results in a problem that a brightness is reduced because of a drop in an aperture ratio.
FIG. 6
is a view showing a second drive performance of the IPS liquid crystal display apparatus. As shown in
FIG. 6
, a responsive speed is made shorter if a cell gap is made narrower (the interval between the color filter substrate and the substrate with TFT: the thickness of the liquid crystal layer). However, on the other hand, there is a problem that if the cell gap is made narrower, a predetermined brightness can not be obtained unless a voltage to drive the liquid crystal is made higher.
FIG. 7
is a view showing the drive concept in the vicinity of the comb electrode in the IPS liquid crystal display apparatus. As shown in
FIG. 7
, the liquid crystals
20
are oriented along the electric field generated by the actions of the pixel electrode
2
and the common electrode
4
(in a di
Chung David
Dudek James
NEC LCD Technologies Ltd.
Young & Thompson
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