Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-06-11
2003-02-04
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S039000, C349S043000, C349S138000, C349S139000, C349S187000, C349S129000
Reexamination Certificate
active
06515719
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and a manufacturing method for the same, and more particularly to a multi-domain liquid crystal display apparatus, in which a liquid crystal layer is divided into a plurality of domains by control electrodes and a manufacturing method for the same.
2. Description of the Related Art
An active matrix drive type liquid crystal display apparatus using an active device such as a thin film transistor has characteristics such as a small size, a thin type and a low power consumption. Therefore, such a liquid crystal display apparatus has come to practical use in the fields of office automation (OA) equipment and audio and video (AV) equipment. Various driving system are known for the liquid crystal display apparatus. A liquid crystal display apparatus of a vertical electric field, i.e., a twisted nematic (TN) type is mainly used and is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 10-68971). In the TN type, a liquid crystal layer is interposed between two substrates and the liquid crystal layer is driven in response to the voltage applied between the substrates.
In the typical active matrix drive type TN liquid crystal display apparatus, one of the above substrates is composed of a drain wiring line and a gate wiring line extending in orthogonal directions to each other, a the pixel electrode formed in the region surrounded by these wiring lines, and a thin film transistor (TFT) formed in the neighborhood of an intersection of the gate wiring line and the drain wiring line. Also, an orientation film is formed on the TFT and the pixel electrode of the substrate. The orientation film is used to drive liquid crystal molecules to turn to predetermined direction. A color filter, a common electrode, an orientation film are formed by a counter substrate as the other substrate. To form a liquid crystal display apparatus, a liquid crystal layer is interposed between the above substrate and the counter substrate.
A manufacturing method of such a conventional TN-type liquid crystal display apparatus will be described.
FIG. 1A
to
FIG. 5D
are diagrams schematically showing the conventional manufacturing method of a substrate of the active matrix drive type TN type liquid crystal display apparatus.
FIGS. 1A
,
2
A,
3
A,
4
A and
5
A are plan views of one pixel, respectively.
FIGS. 1B
,
2
B,
3
B,
4
B and
5
B are cross sectional views of a TFT section along the A-A′ lines of the plan views, respectively.
FIGS. 1C
,
2
C,
3
C,
4
C and
5
C are cross sectional views of a gate terminal section along the B-B′ lines of the plan views, respectively.
FIGS. 1D
,
2
D,
3
D,
4
D and
5
D are cross sectional views of a drain terminal section along the C-C′ lines of the respective plan views, respectively.
As shown in
FIG. 1A
to
FIG. 1D
, a Cr layer as a gate electrode metal layer is deposited on a transparent insulative substrate (a TFT substrate)
1
by a sputtering method, and a resist pattern is formed using a first photomask. A Cr layer exposed by a lithography process using the resist pattern is etched and a gate bus line
2
, a common capacitance line
10
and a gate terminal
2
a
are formed.
Next, as shown in
FIGS. 2A
to
2
D, the first insulating film
3
composed of silicon nitride (SiNx) film, an amorphous silicon (a-Si) film
4
a,
an n
+
-type amorphous silicon film
4
b
as an ohmic contact film are continuously formed by a CVD (Chemical Vapor Deposition) method. After that, a resist pattern is formed using a second photomask, and the n
+
-type amorphous silicon film
4
b
exposed by a lithography process using the resist pattern and the amorphous silicon film
4
a
are removed by a dry etching using the resist pattern, to form an island
4
.
Subsequently, as shown in
FIGS. 3A
to
3
D, a Cr layer as a source/drain metal layer is formed by a sputtering method. After that, a resist pattern is formed using a third photomask and the Cr layer exposed by a lithography process using the resist pattern is removed by a wet etching using the resist pattern. Thus, source/drain electrodes
5
b
and
5
c
of a pixel transistor (TFT: thin film transistor), a drain bus line
5
and a drain terminal
5
a
are formed. After that, using the Cr layer of the source/drain electrodes as an etching mask, the n
+
-type amorphous silicon film
4
b
in the channel region is etched to form the pixel transistor.
Next, as shown in
FIGS. 4A
to
4
D, a second insulating film
7
of silicon nitride SiNx is deposited on the transparent insulative TFT substrate
1
, and the second insulating film
7
and the first insulating film
3
are exposed using a fourth photomask and is etched. In this way, openings
8
a
and
8
b
of the source/drain terminal are formed. After that, as shown in
FIG. 5A
to
FIG. 5D
, an ITO film is deposited on the transparent insulative TFT substrate
1
. After that, the ITO film exposed using a fifth photomask is removed, and the pixel electrode
9
and gate/drain terminal electrodes are formed to connect with the source electrode
5
c.
Subsequently, an orientation film is formed on the pixel transistor on this TFT substrate and on the pixel electrode
9
to make liquid crystal to direct to a predetermined direction. After that, a liquid crystal layer is interposed between this TFT substrate and a counter substrate, so that a liquid crystal display apparatus is completed. Other components such as a color filter, a common electrode, and an orientation film are formed on the counter substrate.
In such a conventional TN-type liquid crystal display apparatus, in the display state of “white” in no voltage application, a liquid crystal molecule has the orientation which is parallel to the TFT substrate. The orientation of the liquid crystal molecule changes from the display state of “white” to the direction of an electric field in accordance with the application voltage. As a result, the display state changes from the display state of “white” to the display state of “black” gradually. The TN-type liquid crystal display apparatus has a small view angle because of the peculiar behavior of the liquid crystal molecules in this voltage application. Also, there is a case where an electric field in the lateral direction is generated due to the unevenness of the TFT substrate and the potential difference between the electrodes in the liquid crystal cell. The existence of the electric field in the lateral direction causes a region where the orientations of liquid crystal molecules are different from each other. As a result, discrimination occurs in the boundary of this region.
For the purpose of the improvement of the above mentioned narrow view angle and discrimination in the conventional TN-type liquid crystal display apparatus, it is proposed to use the liquid crystal having negative permittivity anisotropy. The proposal is given in Japanese Laid Open Patent applications (JP-A-Heisei 6-43461, JP-A-Heisei 7-199190, JP-A-Heisei 7-230097 and JP-A-Heisei 10-20323). In a multi-domain liquid crystal display apparatus in these proposals, a liquid crystal cell is formed such that the liquid crystal has homeotropic orientation in a perpendicular direction. Also, an opening is provided for a common electrode or the pixel electrode, and an oblique electric field is generated in each pixel to form a plurality of domains in the pixel.
Especially, in Japanese Patent Application Nos. (Heisei 11-180615 and Heisei 11-359411) which have been filed by the assignee of the present invention, a control electrode is provided to control the orientation state of liquid crystal. However, these applications were not laid opened until two Japanese Patent Applications corresponding to the present application were filed. The pixel electrode in an electrically floating state is connected through a capacity with the control electrode which is connected in turn with the source electrode. This structure is called a floating pixel electrode structure.
Hirai Yoshihiko
Ishii Toshiya
Kido Syuusaku
Matsuyama Hiroaki
Suzuki Masayoshi
Chowdhury Tarifur R.
McGinn & Gibb PLLC
Sikes William L.
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