KR20120078127A - In-plane switching mode liquid crystal display device - Google Patents

Abstract

PURPOSE: An in-plane switching mode liquid crystal display device is provided to lower a driving voltage and increase transmittance. CONSTITUTION: A gate line is formed on an inner surface of a first substrate(110). A data line crosses the gate line. A thin film transistor is connected to the gate line and the data line. Pixel electrodes(134a,134c) are formed on a pixel area. A common electrode(118) crosses the pixel electrode on the pixel area. A chiral dopant(174) is added to a liquid crystal layer(170). The pixel electrode and the common electrode form a rubbing direction with the liquid crystal layer.

Description

Horizontal field drive mode liquid crystal display device

The present invention relates to a liquid crystal display device, and more particularly, to a horizontal electric field drive type liquid crystal display device in which first and second electrodes for driving a liquid crystal are formed on the same substrate.

In general, a liquid crystal display device is formed by arranging two substrates on which electric field generating electrodes are formed so that the surfaces on which the two electrodes are formed face each other, injecting a liquid crystal material between the two substrates, and then applying a voltage to the two electrodes. By moving the liquid crystal molecules by an electric field, the device expresses an image by the transmittance of light that varies accordingly. The liquid crystal display device is applied to a variety of applications ranging from portable devices such as mobile phones and multimedia devices to computer monitors and large televisions.

A liquid crystal display can be formed in various forms. Currently, an active matrix liquid crystal display (AM-LCD) having a thin film transistor and pixel electrodes connected to the thin film transistor in a matrix manner has excellent resolution and video performance. It is the most noticeable.

The liquid crystal display device has a structure in which a pixel electrode is formed on a lower substrate and a common electrode is formed on an upper substrate, and the liquid crystal molecules are driven by an electric field in a direction perpendicular to the substrate between the two electrodes. The liquid crystal display device by a vertical electric field is excellent in characteristics, such as transmittance | permeability and aperture ratio.

However, the liquid crystal display device due to the vertical electric field has a narrow viewing angle. Accordingly, various methods have been proposed to overcome these disadvantages, and one example thereof is a horizontal electric field driving method, that is, an LCD in an in-plane switching (IPS) mode.

Hereinafter, a liquid crystal display of the conventional IPS mode will be described with reference to the accompanying drawings.

1 is a schematic cross-sectional view of a general IPS mode liquid crystal display.

As shown in FIG. 1, the upper substrate 1 and the lower substrate 2 are disposed at a predetermined distance, and the liquid crystal molecules 3 are positioned between the two substrates 1 and 2. The pixel electrode 4 and the common electrode 5 for driving the liquid crystal molecules 3 are formed on the lower substrate 2. Therefore, when a voltage is applied to the two electrodes 4, 5, a horizontal electric field 6 parallel to the substrate is generated between the two electrodes 4, 5, and the liquid crystal molecules 3 of the liquid crystal layer generate this horizontal electric field. It is operated by (6).

As described above, in the IPS mode liquid crystal display, a liquid crystal display is formed by forming a pixel electrode and a common electrode on the same substrate, and generating a horizontal electric field parallel to the substrate between the two electrodes, so that the liquid crystal molecules are aligned with the horizontal electric field. The viewing angle of can be widened.

In particular, the viewing angle is further widened by forming a plurality of domains in each pixel region to change the arrangement direction of the liquid crystal molecules in each domain.

However, in the case of a portable terminal or the like, since the demand for viewing angle is relatively small, a high transmittance pixel structure in which one pixel region has one domain has been applied.

At this time, the pixel electrode and the common electrode of the IPS mode liquid crystal display are formed obliquely with respect to the gate wiring or the data wiring, and the arrangement direction of the liquid crystal molecules, that is, the rubbing direction is parallel to the gate wiring or the data wiring, thereby making the internal foreground line ( disclination) area is minimized, thereby preventing additional domain defects that may occur during operation.

For example, as shown in FIG. 2, the rubbing direction for the liquid crystal molecules is made parallel to the data line (not shown), and the pixel electrode PXL and the common electrode COM are about 15 degrees to about the rubbing direction. Make an angle θ of 20 degrees.

However, in such a conventional IPS mode liquid crystal display device, since the angle formed between the electrode and the liquid crystal molecules, that is, the electrode angle is large, the liquid crystal efficiency in the same opening area is inferior, and thus the transmittance is low.

In order to improve this, when the electrode angle is made small, the foreground line is generated and the transmittance is lowered. In addition, the driving voltage is also increased, which is a major disadvantage in application to portable devices requiring low voltage and low power consumption.

3A and 3B are diagrams showing whether a foreground line is generated according to an electrode angle in a conventional IPS mode liquid crystal display, and FIG. 4 is a graph showing transmittance versus driving voltage according to an electrode angle in a conventional IPS mode liquid crystal display. to be. Here, the case where the pixel and the common electrode have an angle of 20 degrees and 0 degrees with respect to the rubbing direction is shown.

As shown, when the pixel and the common electrode and the liquid crystal molecules are 20 degrees, the foreground line does not occur, but when the pixel and the common electrode and the liquid crystal molecules are 0 degrees, that is, when the parallel lines, the foreground line is generated. Able to know. In addition, when the pixel, the common electrode, and the liquid crystal molecules reach 0 degrees, the transmittance is also lowered, and a higher voltage is required to obtain the same transmittance.

An object of the present invention is to provide a horizontal field type liquid crystal display device having a high transmittance and an improved driving voltage.

In order to achieve the above object, the present invention, the first and second substrates spaced apart from each other, the gate wiring formed on the inner surface of the first substrate, and the data wiring defining the pixel region crossing the gate wiring, A thin film transistor connected to a gate wiring and a data wiring, a pixel electrode formed in the pixel region, and connected to the thin film transistor, a common electrode intersecting with the pixel electrode in the pixel region, and positioned between the first and second substrates. A liquid crystal layer including a chiral dopant is added, and the pixel electrode and the common electrode provide a horizontal electric field driving method liquid crystal display having an angle of 15 degrees or less with an arrangement direction of the liquid crystal layer, that is, a rubbing direction.

An arrangement direction of the liquid crystal layer is parallel to the data line or parallel to the gate line.

The chiral dopant content is about 0.09% to about 0.3% compared to the liquid crystal layer.

The pitch of the liquid crystal layer is ± 10㎛ to ± 100㎛.

The pitch of the liquid crystal layer is ± 10 μm, and the pixel electrode and the common electrode form 0 degrees with the alignment direction of the liquid crystal layer.

In the horizontal electric field driving type liquid crystal display device according to the present invention, the common electrode, the pixel electrode and the liquid crystal molecules are arranged in an angle of 15 degrees or less, so as to increase the transmittance while preventing a problem occurring accordingly. A chiral dopant is added to the liquid crystal layer in order to. Therefore, the generation of the foreground line can be prevented and the driving voltage can be lowered.

1 is a schematic cross-sectional view of a general IPS mode liquid crystal display.
2 is a view schematically showing an electrode direction and a rubbing direction in a conventional IPS mode liquid crystal display.
3A and 3B are diagrams illustrating whether a foreground line is generated according to an electrode angle in a conventional IPS mode LCD.
4 is a graph showing transmittance versus driving voltage according to an electrode angle in a conventional IPS mode liquid crystal display.
5 is a plan view of an IPS mode liquid crystal display according to an exemplary embodiment of the present invention.
FIG. 6 is a cross-sectional view corresponding to line VI-VI of FIG. 5.
7 is a view schematically showing an electrode direction and a rubbing direction in an IPS mode liquid crystal display according to the present invention.
8 is a diagram illustrating whether foreground lines are generated in an IPS mode LCD according to the present invention.
9 is a graph showing transmittance versus driving voltage in the IPS mode LCD according to the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 5 is a plan view of an IPS mode liquid crystal display according to an exemplary embodiment of the present invention, and is illustrated with the center of the array substrate. FIG. 6 is a cross-sectional view corresponding to the VI-VI line of FIG. 5.

As shown in FIGS. 5 and 6, the gate wiring 112, the gate electrode 114, the common wiring 116, and the common electrode 118 are formed of a conductive material such as metal on the transparent first substrate 110. Is formed. The gate wiring 112 extends along the first direction, and the gate electrode 114 protrudes from the gate wiring 112. The common wiring 116 is parallel to the gate wiring 112, and a common electrode 118 extending from the common wiring 116 is formed along the second direction toward the gate wiring 112.

A gate insulating film 120 is formed on the gate wiring 112, the gate electrode 114, the common wiring 116, and the common electrode 118, and an active layer is formed on the gate insulating film 120 above the gate electrode 114. The 122 and the ohmic contact layer 124 are sequentially formed. The gate insulating layer 120 may be made of silicon nitride (SiNx) or silicon oxide (SiO 2). In addition, the active layer 122 may be made of pure amorphous silicon, the ohmic contact layer 124 may be made of impurity amorphous silicon, and the active layer 122 and the ohmic contact layer 124 constitute a semiconductor layer.

Source and drain electrodes 126 and 128 are formed on the ohmic contact layer 124 with a conductive material such as metal, and the source and drain electrodes 126 and 128 are spaced apart from the gate electrode 114.

Here, the gate electrode 114, the active layer 122, and the source and drain electrodes 126 and 128 form a thin film transistor T.

The data line 130 connected to the source electrode 126 extends along the second direction, and the data line 130 crosses the gate line 112 to define a pixel area.

The passivation layer 132 is formed on the data line 130, the source electrode 126, and the drain electrode 128, and the passivation layer 132 has a contact hole 132a exposing the drain electrode 128.

A pixel electrode is formed on the passivation layer 132, and the pixel electrode includes first and second horizontal portions 134a and 134b and a plurality of vertical portions 134c. The first horizontal portion 134a and the second horizontal portion 134b connect both ends of the vertical portion 134c, respectively, and the vertical portion 134c is alternately disposed with the common electrode 118. The first horizontal portion 134a is connected to the drain electrode 128 through the contact hole 132a, and the second horizontal portion 134a overlaps the common wiring 116 to form a storage capacitor. Here, the pixel electrodes 134a, 134b, and 134c are made of a transparent conductive material such as indium tin oxide or indium zinc oxide. Alternatively, the pixel electrodes 134a, 134b, and 134c may be formed on the same layer of the same material as the drain electrode 128. In addition, although the first horizontal portion 134a of the pixel electrode is connected to the drain electrode 128, any one of the vertical portions 134b may be connected to the drain electrode 128 without the first horizontal portion 134a. .

The first alignment layer 136 is formed on the pixel electrodes 134a, 134b, and 134c.

Meanwhile, the transparent second substrate 150 is spaced apart from the upper portion of the first substrate 110, and a black matrix 152 is formed below the second substrate 150 to correspond to the thin film transistor T. Although not shown, the black matrix 150 is also formed at a position corresponding to the gate wiring 112 and the data wiring 130 and has an opening corresponding to the pixel region.

The color filter layer 154 is formed under the black matrix 152 and under the second substrate 150 corresponding to the opening of the black matrix 152. The color filter layer 154 includes red, green, and blue color filter patterns each corresponding to a pixel area.

An overcoat layer 156 is formed under the color filter layer 154 to protect the color filter layer 154.

A second alignment layer 158 is formed under the overcoat layer 156.

The liquid crystal layer 170 is positioned between the first and second alignment layers 136 and 158, and a chiral dopant 174 is added to the liquid crystal layer 170. The first and second alignment layers 136 and 158 determine the initial arrangement of the liquid crystal molecules of the liquid crystal layer 170, and are aligned by rubbing or the like along a second direction parallel to the data line 130.

In the present invention, one pixel region is in the form of a mono-domain in which the alignment direction of the liquid crystal molecules is one, and the common electrode 118 and the pixel electrode, more specifically, the vertical portion 134c of the pixel electrode are connected to the data line. Make an angle of less than 15 degrees with 130. For example, in FIG. 5, the common electrode 118 and the vertical portion 134c of the pixel electrode are formed to be parallel to the data line 130. At this time, the common electrode 118 and the vertical portion 134c of the pixel electrode form 0 degrees with the rubbing direction.

Meanwhile, the common electrode 118 and the vertical portion 134c of the pixel electrode may be formed in parallel with the gate wiring 130. In this case, the rubbing direction with respect to the liquid crystal layer is in a first direction parallel to the gate wiring 130. Becomes Therefore, the common electrode 118 and the vertical portion 134c of the pixel electrode form 0 degrees with the rubbing direction.

As described above, in the present invention, a chiral dopant for controlling the twist angle of the liquid crystal molecules while the electrode angle is 15 degrees or less can be added to prevent the foreground line generation, increase the transmittance, and reduce the driving voltage.

Here, the pitch of the liquid crystal is changed according to the electrode angle. That is, the smaller the electrode angle is, the smaller the pitch of the liquid crystal is. For example, when the electrode angle is 0 degrees, the pitch of the liquid crystal is about ± 10 μm, and when the electrode angle is 15 degrees, the pitch of the liquid crystal is about ± 10 μm to ± 100 μm.

On the other hand, the pitch of the liquid crystal can be adjusted according to the amount of chiral dopant added, the pitch of the liquid crystal becomes smaller as the content of the chiral dopant increases. As mentioned above, when the electrode angle is 15 degrees or less, the chiral dopant is included in the ratio of about 0.09 to 0.3% in the liquid crystal layer in order to obtain the pitch of the desired liquid crystal.

FIG. 7 is a view schematically showing an electrode direction and a rubbing direction in an IPS mode liquid crystal display according to the present invention, and FIG. 8 is a view showing whether foreground lines are generated in the IPS mode liquid crystal display according to the present invention, and FIG. 9. Is a graph showing transmittance vs. driving voltage in the IPS mode LCD according to the present invention. In FIG. 9, the transmittance versus the driving voltage according to a conventional electrode angle is also shown for comparison.

As shown in FIG. 7, the alignment direction of the liquid crystal molecules, that is, the rubbing direction is parallel to the data line 130 (see FIG. 5), and the pixel electrode PXL and the common electrode COM are set to the rubbing direction and 0 degrees. To achieve. Here, a chiral dopant for controlling the twist angle of the liquid crystal molecules is added to the liquid crystal layer.

As shown in the figure, it can be seen that the foreground line does not occur even when the pixel, the common electrode, and the liquid crystal molecules form 0 degrees. In addition, it can be seen that the driving voltage is lowered and the transmittance characteristic is improved as compared with the case where the chiral dopant is not added.

The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit of the present invention.

110: first substrate 114: gate electrode
118: common electrode 120: gate insulating film
122: active layer 124: ohmic contact layer
126: source electrode 128: drain electrode
132: protective layer 132a: contact hole
134a, 134b, and 134c: pixel electrode 136: first alignment film
150: second substrate 152: black matrix
154: color filter layer 156: overcoat layer
158: second alignment layer 170: liquid crystal layer
174: chiral dopant

Claims (6)

First and second substrates spaced apart from each other;
A gate wiring formed on an inner surface of the first substrate;
A data line crossing the gate line to define a pixel area;
A thin film transistor connected to the gate line and the data line;
A pixel electrode formed in the pixel region and connected to the thin film transistor;
A common electrode interposed with the pixel electrode in the pixel area;
A liquid crystal layer disposed between the first and second substrates and to which a chiral dopant is added.
Wherein the pixel electrode and the common electrode form an angle of 15 degrees or less with a rubbing direction of the liquid crystal layer.
The method according to claim 1,
And a rubbing direction of the liquid crystal layer is parallel to the data line.
The method according to claim 1,
And a rubbing direction of the liquid crystal layer is parallel to the gate line.
The method according to claim 1,
And the chiral dopant is about 0.09% to about 0.3% of the liquid crystal layer.
The method of claim 4,
The pitch of the liquid crystal layer is a horizontal electric field driving method liquid crystal display device of ± 10㎛ to ± 100㎛.
The method according to claim 5,
A pitch of the liquid crystal layer is ± 10㎛, the pixel electrode and the common electrode is a horizontal electric field drive type liquid crystal display device to form a 0 degree with the rubbing direction of the liquid crystal layer.

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