Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-28
2004-04-20
Ngo, Julie-Huyen L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S110000
Reexamination Certificate
active
06724454
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-61934 filed on Oct. 20, 2000 which is hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an Liquid Crystal Display (LCD) Device, and more particularly, to an in-plane switching mode LCD and a method of manufacturing the same.
2. Discussion of the Related Art
Twisted Nematic (TN) mode LCDs are generally used in current LCD devices. In the TN technique, electrodes are installed on each of two substrates and a liquid crystal (LC) director is arranged as a twisted 90°, then voltage is applied to the electrodes to drive the LC director.
However, TN mode LCDs have the disadvantage that the phase of light passing through the liquid crystal cell varies according to the direction of the light, causing a narrow viewing angle.
Recently, techniques have been actively developed for solving such a problem of the narrow viewing angle. Techniques for widening the viewing angle include a film-compensated mode for compensating the viewing angle with a compensating film, a multi-domain mode for dividing one pixel into several domains to vary the main viewing angle direction of each domain so that the pixel characteristic becomes the mean value of the several domain characteristics; an in-plane switching mode for applying a parallel electric field to twist the LC director in a plane parallel to an orientation film; a Vertical Alignment (VA) mode for using a negative liquid crystal and a vertically oriented film to vertically arrange the long axis of liquid crystal molecules about the oriented film; an Optically Compensated Birefringence (OCB) mode, and the like.
In the in-plane switching mode LCD, two electrodes are formed on one substrate for rotating the liquid crystal molecules in a plane parallel to the substrate. Voltage is applied between the two electrodes to induce an electric field parallel to the substrate, thereby reducing variation in birefringence of the liquid crystal.
Therefore, the in-plane switching mode LCD has excellent viewing angle characteristics compared to the TN mode LCD of the related art.
Hereinafter the in-plane switching mode LCD of the related art will be described with reference to the appended drawings as follows:
FIG. 1A
is a plan view showing an in-plane switching mode LCD of the related art.
FIG. 1B
shows a cross section along line I-I′ in
FIG. 1A
, and
FIG. 1C
shows a cross section along line II-II′ in FIG.
1
A.
FIG. 2A
is a plan view for showing a general structure of an ITO—ITO electrode of the in-plane switching LCD.
FIG. 2B
shows transmitting and shielding areas of the ITO—ITO electrode of the in-plane switching LCD when positive DC voltage is applied to a data electrode.
FIG. 2C
shows the transmitting and shielding areas of the ITO—ITO electrode of the in-plane switching LCD when negative DC voltage is applied to the data electrode.
The general in-plane switching mode LCD as shown in
FIG. 1A
comprises data lines
10
and gate lines
11
arranged on a first substrate for defining a pixel area, a common line
12
arranged in the pixel area parallel to the gate lines
11
, a thin film transistor placed in intersecting regions of the gate lines
11
and the data lines
10
, data electrodes
14
arranged parallel to the data lines
10
in the pixels, common electrodes
13
extended from the common lines
12
and arranged between the data electrodes
14
, and storage electrodes
55
extended from the data electrodes
14
and formed in the upper parts of the gate lines
11
.
Referring also to
FIG. 11B
, the in-plane switching mode LCD is formed by joining the first substrate
18
and the second substrate
19
together in opposition to each other and injecting a liquid crystal layer
30
between the two substrates. The gate lines
11
are formed parallel to the common lines
12
on the first substrate
18
. The common electrodes
13
, which extend from the common lines
12
, are commonly formed with the common lines
12
. Here, a portion of the gate lines
11
functions as gate electrodes of the thin film transistor.
Then, a silicon nitride (SiNx) or a silicon oxide (SiOx) film is applied to the surface, including the gate lines
11
and the common electrodes
13
, to form a gate insulation film
20
, and a semiconductor layer
15
is formed on a portion of the gate insulation film as an active layer.
Next, the data lines
10
are formed on top of the gate insulation film
20
to form a matrix shape with the gate lines
11
, and source/drain electrodes
16
and
17
are simultaneously formed to extend from the data lines
10
and be placed on a semiconductor layer
15
. Here, the data electrodes
14
parallel to the common electrodes
13
and the storage electrodes
55
are formed at the same time, which connect the data electrodes
14
.
The gate electrodes, the gate insulation film
20
, the semiconductor layer
15
, the source/drain electrodes
16
and
17
form the thin film transistor.
Then, a silicon oxide film, a silicon nitride film or an organic insulation film such as a BCB (Benzocyclobutene) film is applied on the surface, including the data lines
10
, to form a protective film
25
.
In the in-plane switching LCD, the common electrodes and the data electrodes can be formed on different planes, with the insulation film sandwiched as above or can be formed on one plane.
Also, the common electrodes and the data electrodes can be formed simultaneously with the lines made of metals including Cu, Al, Cr, Mo, Ti, Al alloy and the like for shielding a light, or a transparent conductive material such as ITO (Indium Tin Oxide) can be used in forming the same by further using a mask. When forming the electrodes using a mask, however, care should be used to avoid a short between the lines or electrodes.
When the data electrodes
14
and the common electrodes
13
are formed of ITO, which is a transparent conductive film that is excellent in transmitting light, the LCD is called an ITO—ITO in-plane switching LCD. A general structure of an ITO—ITO electrode is shown in FIG.
2
.
A black matrix
21
is formed on the second substrate
19
to prevent light leakage, and an R, G, B color filter layer
22
is formed between the black matrix
21
.
An overcoat layer
23
is formed on top of the color filter layer
22
to protect and planarize the color filter layer
22
.
The ITO—ITO in-plane switching LCD formed as above has a horizontal or parallel electric field rather than a vertical electric field between the data and common electrodes, a vertical electric field in a middle portion of the electrodes, and horizontal or parallel and vertical electric fields commonly formed at corners of the electrodes.
Initially, the liquid crystal molecules between the electrodes are rotated parallel to the substrate due to a side electric field. After a certain time period, the liquid crystal molecules on the electrodes are rotated due to the vertical and side electric fields and an elastic force of the liquid crystal at the electrodes.
In an ITO—ITO in-plane switching LCD, the liquid crystal molecules on the electrodes have an orientation according to positive or negative voltage applied to the electrodes, thereby causing light transmissivity to be different at the data electrodes and the common electrodes.
In other words, when a positive DC voltage is applied to the data electrodes and a negative DC voltage is applied to the common electrodes, light is transmitted in a larger amount at the common electrodes than at the data electrodes, as shown in FIG.
2
B. Also, when a negative DC voltage is applied to the data electrodes and a positive DC voltage is applied to the common electrodes, light is transmitted in a larger amount at the data electrodes
14
, as shown in FIG.
2
C.
In other words, a luminance difference is created at each electrode depending on whether a positive or negative voltage is applied.
As shown herein before, the foregoing in-plane switching LCD of the related art has
Kim Gi Hong
Lee Yun Bok
LG.Philips LCD Co. Ltd
McKenna Long & Aldridge LLP
Ngo Julie-Huyen L.
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