KR20070020868A - Thin film transistor array panel - Google Patents

Abstract

In an exemplary embodiment of the present invention, a thin film transistor array panel includes a substrate, a plurality of gate lines formed on the substrate, a plurality of common electrodes formed on the substrate, and made of a transparent conductor, data lines crossing the gate lines, gate lines, and data lines. A plurality of pixel electrodes connected to the thin film transistor and the thin film transistor, the pixel electrodes including a connection part overlapping the common electrode and connecting the plurality of branch electrodes and the branch electrode, wherein the branch electrodes of the neighboring pixel electrodes are in different directions. Are arranged. This can improve the visibility and viewing angle.

LCD, PLS, IPS, pixel electrode, common electrode, visibility, viewing angle, short circuit

Description

Thin Film Transistor Display Panels {THIN FILM TRANSISTOR ARRAY PANEL}

1 is a layout view illustrating a structure of a thin film transistor array panel for a liquid crystal display according to an exemplary embodiment of the present invention.

2 to 3 are cross-sectional views of the thin film transistor array panel of FIG. 1 taken along lines II-II and III-III, respectively.

4 is a layout view illustrating a structure of a pixel electrode and a common electrode in a thin film transistor array panel according to an exemplary embodiment of the present invention.

FIG. 5 is a cross-sectional view of the liquid crystal display device taken along the line V-V of FIG. 4, illustrating the electric force lines formed on the upper panel and the lower panel.

FIG. 6 is a layout view illustrating a change in twist angles of liquid crystal molecules in a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 7 is a graph illustrating a relationship between twist angles of liquid crystal molecules with respect to a line horizontal to a substrate and perpendicular to a pixel electrode in the liquid crystal display according to the exemplary embodiment of the present invention.

8 is a graph illustrating a change in the twist angle of liquid crystal molecules with respect to a line perpendicular to the substrate in the liquid crystal display according to the exemplary embodiment of the present invention.

9 is a graph illustrating a change in the inclination angle of liquid crystal molecules in the liquid crystal display according to the exemplary embodiment of the present invention.

FIG. 10 is a graph illustrating a change in inclination angle of liquid crystal molecules with respect to a line perpendicular to a substrate in the liquid crystal display according to the exemplary embodiment of the present invention.

FIG. 11 is a graph illustrating tilt angle changes of liquid crystal molecules with respect to a line horizontal to a substrate and perpendicular to a pixel electrode in an embodiment of the present invention;

12 to 14 are layout views illustrating the structure of a thin film transistor array panel for a liquid crystal display according to another exemplary embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

110: substrate 121, 129: gate line

124: gate electrode 131: common electrode

140: gate insulating film 151, 154: semiconductor

161 and 165: ohmic contact members 171 and 179: data line

173: source electrode 175: drain electrode

180: protective film 181, 182, 185: contact hole

191: pixel electrode 81, 82: contact auxiliary member

The present invention relates to a thin film transistor array panel, and more particularly, to a thin film transistor array panel used as a substrate of a liquid crystal display device.

The liquid crystal display is one of the most widely used flat panel display devices. The liquid crystal display includes two display panels on which field generating electrodes, such as a pixel electrode and a common electrode, are formed, and a liquid crystal layer interposed therebetween. Is applied to generate an electric field in the liquid crystal layer, thereby determining the orientation of liquid crystal molecules in the liquid crystal layer and controlling the polarization of incident light to display an image.

Among them, the vertical alignment (VA) mode liquid crystal display in which the long axis of the liquid crystal molecules are arranged perpendicular to the upper and lower display panels without an electric field applied to the display panel has a high contrast ratio.

However, there is a problem in the wide viewing angle, so that the liquid crystal display in the patterned vertically aligned (PVA) mode, the liquid crystal display in the in-plane switching (IPS) mode, and the fringe field switching (FFS) in which the incision is applied to the liquid crystal display in the vertical alignment mode. A liquid crystal display device in mode has been developed.

However, the liquid crystal display of the IPS mode and the FFS mode has a problem in that the side visibility is inferior to the front visibility, and since the common electrode and the pixel electrode are formed on one display panel, the common electrode and the pixel electrode are shorted to each other so that the pixels are darkly displayed. The off pixel defects are frequently generated, resulting in a decrease in process yield.

An object of the present invention is to provide a thin film transistor array panel which can improve side visibility and prevent off pixel defects.

According to an exemplary embodiment of the present invention, a thin film transistor array panel includes a substrate, a plurality of gate lines formed on the substrate, a plurality of common electrodes formed on the substrate, and made of a transparent conductor, data lines crossing the gate lines, and the gate lines. And a plurality of pixel electrodes connected to the data line and connected to the thin film transistor, the pixel electrodes including a plurality of branch electrodes overlapping the common electrode and connecting a plurality of branch electrodes and the branch electrodes. The branch electrodes of the pixel electrodes are arranged in different directions.

It is preferable that the branch electrode is inclined at an arbitrary angle with respect to the gate line or the data line, and the branch electrode has a symmetrical structure with respect to the data line.

The branch electrodes may be inclined in different directions with respect to the horizontal and vertical directions.

The pixel electrode may be formed of a first subpixel electrode and a second subpixel electrode separated from each other. Preferably, the first and second subpixel electrodes are disposed at both sides of the data line, and the drain electrode of the thin film transistor includes first and second drain electrodes connected to the first and second subpixel electrodes, respectively. It is preferable to include.

The branch electrodes arranged in the vertical direction may be parallel to each other, and the gate line may be folded by being formed in parallel with the branch electrodes.

The branch electrodes arranged in the vertical direction may be inclined in different directions.

Then, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

A thin film transistor array panel used as a substrate of a liquid crystal display according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, a thin film transistor array panel according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.

1 is a layout view of a thin film transistor array panel for a liquid crystal display according to an exemplary embodiment of the present invention, and FIGS. 2 and 3 are cut along the lines II-II and III-III'-III "of FIG. 1. It is sectional drawing.

A plurality of gate lines 121, a plurality of common electrode lines 125, and a plurality of common electrodes 131 are formed on an insulating substrate 110 made of transparent glass or plastic.

The gate line 121 transmits a gate signal and mainly extends in a horizontal direction. Each gate line 121 includes an end portion 129 having a large area for connecting a plurality of gate electrodes 124 to another layer or an external driving circuit. A gate driving circuit (not shown) for generating a gate signal is mounted on a flexible printed circuit film (not shown) attached to the substrate 110 in the form of an integrated circuit chip, or the substrate 110. May be mounted directly on the substrate, or integrated into the substrate 110. When the gate driving circuit is integrated on the substrate 110, the gate line 121 may extend to be directly connected to the gate driving circuit.

The common electrode line 125 transmits a common voltage and extends in the horizontal direction substantially in parallel with the gate line 121. The common electrode line 125 is formed of the same layer as the gate line 121, and is positioned at the center between two neighboring gate lines 121 and may have an extension part projecting up and down to block leakage light.

The plurality of common electrodes 131 are commonly connected to the common electrode line 121 to receive a common voltage from the common electrode line 131. The common electrode 131 has a rectangular shape and is arranged in a matrix to almost fill the space between the gate lines 121. The common electrode 131 may be made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO), and the common electrode line 125 may be made of the same layer as the common electrode 131.

The gate line 121 and the common electrode line 125 may be formed of aluminum-based metal such as aluminum (Al) or aluminum alloy, silver-based metal such as silver (Ag) or silver alloy, copper-based metal such as copper (Cu) or copper alloy, or molybdenum ( It may be made of molybdenum-based metals such as Mo) or molybdenum alloy, chromium (Cr), tantalum (Ta) and titanium (Ti). However, they may have a multilayer structure including two conductive films (not shown) having different physical properties. One of the conductive films is made of a metal having low resistivity, such as aluminum-based metal, silver-based metal, or copper-based metal, so as to reduce signal delay or voltage drop. In contrast, other conductive films are made of other materials, particularly materials having excellent physical, chemical, and electrical contact properties with indium tin oxide (ITO) and indium zinc oxide (IZO), such as molybdenum-based metals, chromium, tantalum, and titanium. Good examples of such a combination include a chromium bottom film, an aluminum (alloy) top film, and an aluminum (alloy) bottom film and a molybdenum (alloy) top film. However, the gate line 121 may be made of various other metals or conductors.

Side surfaces of the gate line 121 and the common electrode line 125 are inclined with respect to the surface of the substrate 110, and the inclination angle is preferably about 30 degrees to about 80 degrees.

A gate insulating layer 140 made of silicon nitride (SiNx) or silicon oxide (SiOx) is formed on the gate line 121, the common electrode line 125, and the common electrode 131. The gate insulating layer 140 prevents the gate line 121 and the common electrode 131 from being short-circuited with each other, and insulates the other conductive thin film formed thereon.

On the gate insulating layer 140, a plurality of island semiconductors 154 made of hydrogenated amorphous silicon (amorphous silicon is abbreviated as a-Si), polycrystalline silicon, or the like are formed. The island type semiconductor 154 is positioned on the gate electrode 124 and includes an extension covering the boundary of the gate line 121.

A plurality of island type ohmic contacts 163 and 165 are formed on the island type semiconductor 154. The ohmic contacts 163 and 165 may be made of a material such as n + hydrogenated amorphous silicon in which n-type impurities such as phosphorus are heavily doped, or may be made of silicide. The island-like ohmic contacts 163 and 165 are paired and disposed on the island-like semiconductor 154.

Side surfaces of the island-like semiconductor 154 and the ohmic contacts 163 and 165 are also inclined with respect to the surface of the substrate 110, and the inclination angle is about 30 degrees to about 80 degrees.

A plurality of data lines 171 and a plurality of drain electrodes 175 are formed on the ohmic contacts 163 and 165 and the gate insulating layer 140.

The data line 171 transmits a data signal and mainly extends in the vertical direction to cross the gate line 121. Each data line 171 includes a plurality of source electrodes 173 extending toward the gate electrode 124 and an end portion 179 having a large area for connection with another layer or an external driving circuit. A data driving circuit (not shown) for generating a data signal is mounted on a flexible printed circuit film (not shown) attached to the substrate 110, directly mounted on the substrate 110, or integrated in the substrate 110. Can be. When the data driving circuit is integrated on the substrate 110, the data line 171 may be extended to be directly connected to the data driving circuit.

The drain electrode 175 is separated from the data line 171 and faces the source electrode 173 with respect to the gate electrode 124.

One gate electrode 124, one source electrode 173, and one drain electrode 175 together with the island-like semiconductor 154 form one thin film transistor (TFT), and a channel of the thin film transistor ( A channel is formed in the semiconductor 154 between the source electrode 173 and the drain electrode 175.

The data line 171 and the drain electrode 175 are preferably made of a refractory metal such as molybdenum, chromium, tantalum, and titanium, or an alloy thereof, and include a refractory metal film (not shown) and a low resistance conductive film. It may have a multilayer structure including (not shown). Examples of the multilayer structure include a double layer of chromium or molybdenum (alloy) lower layer and an aluminum (alloy) upper layer, and a triple layer of molybdenum (alloy) lower layer and aluminum (alloy) interlayer and molybdenum (alloy) upper layer. However, the data line 171 and the drain electrode 175 may be made of various metals or conductors.

The ohmic contacts 163 and 165 exist only between the semiconductor 154 thereunder and the data line 171 and the drain electrode 175 thereon to lower the contact resistance therebetween. An extension of the semiconductor 154 positioned on the gate line 121 may soften the profile of the surface to prevent the data line 171 from being disconnected. The semiconductor 154 includes portions exposed between the source electrode 173 and the drain electrode 175 and not covered by the data line 171 and the drain electrode 175.

A passivation layer 180 is formed on the data line 171, the drain electrode 175, and the exposed semiconductor 151. The passivation layer 180 is made of an inorganic insulator, and examples of the inorganic insulator include silicon nitride and silicon oxide. However, the passivation layer 180 may have a double layer structure of the lower inorganic layer and the upper organic layer so as not to damage the exposed portion of the semiconductor 151 while maintaining excellent insulating properties of the organic layer.

In the passivation layer 180, a plurality of contact holes 182 and 185 exposing the end portion 179 and the drain electrode 175 of the data line 171 are formed, respectively, and the passivation layer 180 and the gate insulating layer are formed. A plurality of contact holes 181 exposing the end portion 129 of the gate line 121 are formed at 140.

A plurality of pixel electrode lines 191 and a plurality of contact assistants 81 and 82 are formed on the passivation layer 180. They may be made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

The pixel electrode 191 mainly extends in the vertical direction and overlaps the common electrode 131.

The pixel electrode 191 includes a plurality of branch electrodes 192 arranged in parallel with each other and a connection unit 193 for connecting the plurality of branch electrodes 192 in common.

The branch electrode 192 is inclined at a predetermined angle (Фs) with respect to the gate line 121 or the horizontal direction, and the connection part 193 includes a vertical connection part and a branch electrode 192 connecting both ends of the plurality of branch electrodes 192. It includes a horizontal connection located at the top and bottom of the). The outer boundary of the connection unit 193 defining the boundary of the pixel electrode 191 is a rectangular shape.

The pixel electrode 191 to which the data voltage is applied generates an electric field together with the common electrode 131 to which the common voltage is applied to determine the direction of the liquid crystal molecules of the liquid crystal layer 3 positioned on the two electrodes 191 and 131. . The polarization of light passing through the liquid crystal layer varies according to the direction of the liquid crystal molecules determined as described above.

The pixel electrode 191 and the common electrode 131 form a liquid crystal capacitor using the liquid crystal layer 3 as a dielectric to maintain an applied voltage even after the thin film transistor is turned off, and these 191 and 131 also have a gate insulating layer 140. ) And the passivation layer 180 as a dielectric to enhance the voltage holding capability of the liquid crystal capacitor.

The contact auxiliary members 81 and 82 are connected to the end portion 129 of the gate line 121 and the end portion 179 of the data line 171 through the contact holes 181 and 182, respectively. The contact auxiliary members 81 and 82 compensate for and protect the adhesion between the end portion 129 of the gate line 121 and the end portion 179 of the data line 171 and the external device.

In the thin film transistor array panel according to the exemplary embodiment of the present invention, the branch electrodes 192 of the pixel electrodes 191 which are adjacent to each other up, down, left and right are inclined in different directions, and thus, liquid crystal molecules positioned in neighboring pixel regions when voltage is applied. Are rotated in different directions so that the liquid crystal molecules are divided into multiple regions. Therefore, a wide viewing angle can be obtained and side visibility can be improved, which will be described in more detail later with reference to the drawings.

Hereinafter, an operation of the liquid crystal display including the thin film transistor array panel according to the exemplary embodiment of the present invention will be described in detail with reference to FIGS. 4 to 11.

FIG. 4 is a layout view illustrating a common electrode and a pixel electrode in a thin film transistor array panel according to an exemplary embodiment of the present invention. FIG. 5 is a cross-sectional view of a liquid crystal display, taken along a line VV, of FIG. 4. Figure is a diagram showing the electric field of force. Here, the pixel electrode is illustrated by showing only the branch electrodes shown in FIGS. 1 to 3.

4 and 5, a planar common electrode 131 is formed on the lower substrate 110, a gate insulating layer 140 and a passivation layer 180 are covered on the common electrode 131, and a passivation layer. On the 180, a plurality of narrow pixel electrodes 191 extend in parallel to each other in the vertical direction. The width of the pixel electrode 191 is smaller than the gap between the pixel electrodes 191. An alignment layer 11 made of a material such as polyimide is coated on the pixel electrode 191, which may be a horizontal alignment layer. The polarizer 12 is attached to the outer surface of the lower substrate 110.

The color filter 230 is formed on the upper substrate 210, and an alignment layer 21 made of a material such as polyimide is coated on the color filter 230, and they may be horizontal alignment layers. The polarizer 22 is attached to the outer surface of the upper substrate 210.

The liquid crystal layer 3 having positive dielectric anisotropy is injected between the alignment layers 11 and 21 of the two substrates 110 and 210. Therefore, the liquid crystal molecules of the liquid crystal layer 3 are aligned with their major axes substantially parallel to the direction of the pixel electrode 191 (at the direction of the pixel electrode and at a predetermined angle (øs, see FIG. 1) in the absence of an electric field. When the voltage is applied, the long axis of the liquid crystal molecules is arranged perpendicular to the direction of the pixel electrode 191 due to the electric force formed between the pixel electrode 191 and the common electrode 131, thereby passing through the liquid crystal layer. The polarization of light is different.

The liquid crystal display may perform display operation by adjusting the transmittance of light generated from a backlight unit (not shown) positioned below the lower substrate 110. However, in the case of a reflective liquid crystal display, the lower polarizing plate may be used. 12 is not necessary. In the case of a reflective liquid crystal display, it is preferable to make both the pixel electrode 191 and the common electrode 131 made of a material such as aluminum (Al), which is opaque and has high reflectance.

As shown in FIG. 5, when a voltage is applied to the common electrode 131 and the pixel electrode 191 of the liquid crystal display to give a potential difference, an electric field is generated, and the electric field lines are indicated by dotted lines in FIG. 5.

The shape of the electric field is the longitudinal center line C (actually a plane) of the narrow region NR on the pixel electrode 191 and the longitudinal center line B of the wide region WR between the pixel electrode 191. It is symmetrical about (actually corresponding to face). In the region from the centerline C of the narrow region NR to the centerline B of the large region WR, the vertex is at the boundary line A (actually a plane) between the narrow region NR and the large region WR. An electric field having an electric field line shape having a half ellipse shape or parabolic shape (hereinafter, referred to as a half ellipse shape for convenience) having a shape is generated. The tangent of the electric line of force is almost parallel to the substrate 10 on the boundary line A between the narrow region NR and the large region WR, and the substrate 10 at the central position of the narrow region NR and the large region WR. It is almost perpendicular to. In addition, the center and longitudinal vertices of the ellipse are located on the boundary line A between the narrow region NR and the wide region WR, and the two vertices of the horizontal direction are positioned in the large region WR and the narrow region NR, respectively. do. At this time, the horizontal vertex located in the narrow area NR has a shorter distance from the center of the ellipse than the horizontal vertex located in the wide area WR. Thus, the ellipse does not have symmetry with respect to the boundary line A. FIG. In addition, the density of electric field lines varies with position, and the strength of the electric field varies proportionally thereto. Thus, the intensity of the electric field is greatest on the boundary line AA between the narrow region NR and the large region WR, and toward the centerline CC, BB of the narrow region NR and the large region WR, and the upper portion. It becomes smaller toward the substrate 210.

Then, the state in which the liquid crystal molecules are rearranged by the electric field is divided into components that are horizontal to the substrate and components that are perpendicular thereto. First, the initial state will be described.

The two alignment layers 11 and 21 are aligned by rubbing or ultraviolet irradiation, so that the liquid crystal molecules are all arranged in one direction but have a slight pretilt angle with respect to the substrates 110 and 210 but are substantially horizontal. When viewed on a plane parallel to 210, the pixels are oriented to form a predetermined angle øs (see FIG. 1) with respect to the direction of the pixel electrode 191 and a direction perpendicular thereto. The polarization axes of the polarizing plates 12 and 22 are arranged to be perpendicular to each other, and the polarization axes of the lower polarizing plate 12 substantially coincide with the rubbing direction.

Next, a voltage is applied to the pixel electrode 191 and the common electrode 131, respectively, and a high voltage is applied to the pixel electrode 191. At this time, the arrangement of the liquid crystal molecules is determined by equilibrium between the force due to the electric field (depending on the direction and intensity of the electric field) and the elastic restoring force generated by the alignment process.

The rearrangement state of the liquid crystal molecules is divided into components parallel to the substrate and perpendicular to the substrate. For convenience of description, a direction perpendicular to the substrate is z-axis, a direction parallel to the substrate and perpendicular to the direction of the pixel electrode 191 is determined as an x-axis, and a direction parallel to the direction of the pixel electrode 191 is defined as the y-axis. That is, the x-axis direction from left to right in FIG. 4, the y-axis direction from bottom to top along the pixel electrode 191, and the z-direction direction from the lower substrate 110 to the upper substrate 210 in FIG. 8. Determine the axis.

First, a change in the torsion angle of the liquid crystal molecules 310, that is, the angle formed by the long axis of the liquid crystal molecules on the plane (xy plane) parallel to the substrate with respect to the x axis or the initial alignment direction is illustrated in FIGS. It explains for reference.

FIG. 6 is a layout view illustrating a change in the twist angle of liquid crystal molecules in a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 7 is horizontal to a substrate and perpendicular to a pixel electrode in the liquid crystal display according to the exemplary embodiment of the present invention. 8 is a graph illustrating a change in twist angle of liquid crystal molecules with respect to a phosphorus line, and FIG. 8 is a graph illustrating a change in twist angle of liquid crystal molecules with respect to a line perpendicular to the substrate in the liquid crystal display according to the exemplary embodiment of the present invention.

로, 전기장의 x-y 평면 성분은 벡터

로, 아래 편광판(12)의 광축은 벡터

로 나타내었으며, 러빙 방향이 x축과 이루는 각은 ΦR로, 액정 분자의 장축이 x축과 이루는 각을 ΦLC로 나타내었다. 그런데 여기에서 아래 편광판(12)의 광축은 러빙 방향과 일치하므로 아래 편광판(12)의 광축이 x축과 이루는 각 ΦP=ΦR이다.As shown in Figure 6, the rubbing direction is a vector

Xy plane component of the electric field is a vector

The optical axis of the lower polarizer 12 is a vector

The angle formed by the rubbing direction with the x-axis is Φ R, and the angle formed by the long axis of the liquid crystal molecules with the x-axis is represented by Φ LC. By the way, since the optical axis of the lower polarizing plate 12 coincides with the rubbing direction, the angle Φ P = Φ R in which the optical axis of the lower polarizing plate 12 forms the x axis.

)의 방향은 경계선(A)으로부터 넓은 영역(WR)의 중앙선(B)에 이르기까지는 양의 x 방향이고, 넓은 영역(WR)의 중앙선(B)으로부터 다음 경계선(D)까지는 음의 x 방향이다. 전기장 성분의 세기는 경계선(A, D) 상에서 가장 크고 중앙선(B-B) 쪽으로 갈수록 작아져 중앙선(B-B) 상에서는 0이 된다.Xy plane component of the electric field (

) Is the positive x direction from the boundary line A to the center line B of the wide area WR, and is the negative x direction from the center line B of the wide area WR to the next boundary line D. . The intensity of the electric field component is largest on the boundaries A and D and becomes smaller toward the center line BB and becomes zero on the center line BB.

)에 대하여 거의 평행하고 러빙 방향에 대해서는 큰 각도를 가지지만, 영역(NR, WR)의 중심선(C, B)으로 갈수록 액정 분자의 장축이 러빙 방향에 대하여 이루는 각(│ΦR - ΦLC│)이 작아지고, 중심선(B, C)에서는 액정 분자의 장축과 러빙 방향이 동일해진다. 아래 편광판(20)의 광축은 러빙 방향과 평행하므로, 아래 편광판(20)의 광축과 액정 분자의 장축이 이루는 각도도 이와 동일한 분포를 가지며, 이 값은 빛의 투과율과 밀접한 관련이 있다.The magnitude of the elastic restoring force by the orientation treatment is constant regardless of the position on the xy plane. Since the liquid crystal molecules should be arranged such that these two forces are in equilibrium, as shown in FIG. 7, in the boundary lines A and D, the long axis direction of the liquid crystal molecules is determined by the electric field component (

Is substantially parallel to the rubbing direction and has a large angle with respect to the rubbing direction, but the angle (│ΦR-ΦLC│) formed by the long axis of the liquid crystal molecules with respect to the rubbing direction It becomes small and in the center line B and C, the long axis of a liquid crystal molecule and a rubbing direction become the same. Since the optical axis of the lower polarizing plate 20 is parallel to the rubbing direction, the angle formed between the optical axis of the lower polarizing plate 20 and the long axis of the liquid crystal molecules also has the same distribution, and this value is closely related to the transmittance of light.

By varying the ratio of the width of the narrow area NR to the wide area WR, various types of electric fields can be generated. When the pixel electrode 191 is made of a transparent material, the narrow area NR may also be used as the display area. However, when the pixel electrode 191 is used as the opaque electrode, the narrow area NR on the pixel electrode 191 may be used as the display area. none.

)은 아래 배향막(11)으로부터 위 배향막(21)에 이르기까지, 즉 z축을 따라가며 점점 작아지며, 배향에 의한 탄성적 복원력은 배향막(11, 21)의 표면에서 가장 크고, 두 배향막(11, 21) 사이 액정층의 중앙으로 갈수록 점점 작아진다.On the other hand, the xy plane component of the electric field (

) Becomes smaller from the lower alignment layer 11 to the upper alignment layer 21, i.e., along the z-axis, and the elastic restoring force due to the alignment is largest on the surfaces of the alignment layers 11 and 21, and the two alignment layers 11, 21) becomes smaller toward the center of the liquid crystal layer.

FIG. 8 is a diagram illustrating a torsion angle in which the long axis direction of the liquid crystal molecules is along the x axis along the z axis, in which a gap between two alignment layers, that is, a cell gap is d. Here, the horizontal axis represents the height from the lower alignment layer 11, and the vertical axis represents the twist angle.

As shown in FIG. 8, the torsion angle is large on the surfaces of the alignment layers 11 and 21 because of the strong force due to the alignment force, and it becomes smaller toward the center of the liquid crystal layer and becomes closer to the direction of the electric field. Immediately above (11, 21), the long axes of the liquid crystal molecules are arranged in the same direction as the rubbing direction. Here, when the difference in the twist angles of adjacent liquid crystal molecules is called twist, the twist in FIG. 11 corresponds to the slope of the curve, which is larger on the surfaces of the alignment layers 11 and 21 and smaller toward the center of the liquid crystal layer.

12, 13 and 14 will be described with reference to the inclination angle of the liquid crystal molecules, that is, the angle formed on the plane (zx plane) perpendicular to the substrate with respect to the x-axis or the initial alignment direction.

FIG. 9 is a view illustrating a change in the inclination angle of liquid crystal molecules in a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 10 is a view illustrating the liquid crystal molecules with respect to a line perpendicular to the substrate in the liquid crystal display according to the exemplary embodiment of the present invention. 11 is a graph showing a change in the inclination angle, and FIG. 11 is a graph showing the change in the inclination angle of liquid crystal molecules with respect to a line horizontal to the substrate and perpendicular to the pixel electrode in one embodiment of the present invention.

의 zx 평면에 대한 성분을 벡터

로, 전기장의 zx 평면 성분은 벡터

로 나타내었으며, 전기장의 zx 평면 성분

가 x축과 이루는 각은 ??E로, 액정 분자의 장축이 x축과 이루는 경사각을 ??LC로 나타내었다. 그런데, 여기에서 벡터

은 xy 평면상에 존재하므로(선경사각은 무시)

는 x 방향이 된다.In FIG. 9, only the substrates 110 and 210 are illustrated for convenience, and a vector representing the rubbing direction illustrated in FIG. 6.

Vector components for zx plane of

The zx plane component of the electric field is a vector

The zx plane component of the electric field

The angle formed by the x axis is ?? E, and the inclination angle formed by the long axis of the liquid crystal molecules with the x axis is represented by ?? LC. By the way, here the vector

Is on the xy plane (ignore pretilt)

Becomes the x direction.

)의 크기는 아래 기판(110)에서 위 기판(210)으로 갈수록 작아지고, 각도 ??E 또한 아래 기판(110)에서 위 기판(210)으로 갈수록 작아진다.Zx plane component of the electric field (

) And the size of the lower substrate 110 from the lower substrate 110 toward the upper substrate 210 becomes smaller, and the angle ?? E also decreases from the lower substrate 110 to the upper substrate 210.

As described above, the magnitude of the elastic restoring force due to the alignment treatment is the largest on the surfaces of the two substrates 10 and 11 and decreases toward the center of the liquid crystal layer.

The liquid crystal molecules must be arranged such that these two forces are in equilibrium. As shown in FIG. 13, since the alignment force is strong on the surface of the lower substrate 110, the liquid crystal molecules are arranged in parallel with the x-axis, but as the upward force increases, the magnitude of the inclination angle ?? It continues to increase to a certain point and then decreases again, and is arranged parallel to the x-axis on the upper substrate 11 surface again. At this time, the peak of the curve appears at a position close to the lower substrate 10.

)이 x축에 대하여 이루는 각 ??E는 경계선(A, D) 상에서는 0에 가깝고 중앙선(B-B) 쪽으로 갈수록 커지며, 전기장의 zx 평면 성분(

)의 크기는 경계선(A, D) 상에서 가장 크고 중앙선(B-B) 쪽으로 갈수록 작아진다.Meanwhile, the zx plane component of the electric field (

) Is approximately 0 on the boundaries (A, D) and increases toward the centerline (BB) on the x-axis, and the zx plane component (

) Is the largest on boundaries A and D and decreases toward the center line BB.

The magnitude of the elastic restoring force by the orientation treatment is constant regardless of position on the x axis.

)이 x축과 이루는 각(??E)과 유사한 분포를 가진다. 그러나, ??E보다는 완만하게 변화한다.Therefore, as shown in FIG. 11, the inclination angle of the liquid crystal molecules is almost zero at the boundary lines A and D, but increases toward the center lines C and B, thereby increasing the zx plane component of the electric field (

) Has a distribution similar to the angle (?? E) with the x-axis. However, it changes more slowly than ?? E.

As such, when voltage is applied to the common electrode and the pixel electrodes 131 and 191, the liquid crystal molecules are rearranged at a torsion angle and an inclination angle, and the transmittance of light is changed due to a change in the torsion angle and the inclination angle. On the boundary lines A and D, there is little change in the inclination angle when viewed along the z axis, but the change in the torsion angle is large. On the other hand, on the center lines B and C, there is little change in the torsion angle when viewed along the z axis, but the inclination angle is slightly changed. Therefore, in the area between the boundary lines A and D and the center lines B and C, the torsion angle and the inclination angle are both changed. As a result, the transmittance curve according to the position becomes a shape similar to that of the electric field lines.

As illustrated in FIG. 1, the liquid crystal molecules 310 positioned in a region corresponding to the branch electrode 192 of the pixel electrode 191 are aligned to have an initial twist angle øs with respect to the branch electrode 192. have.

The initial torsion angle øs is defined as the angle formed by the rubbing direction P and the longitudinal direction S of the branch electrode 192, or the rubbing direction P and the branch electrode 192 as angles. In order to be greater than 0 degrees and less than or equal to 10 degrees, it is desirable.

In this case, the liquid crystal molecules 310 positioned in the region corresponding to the branch electrode 192 of the pixel electrode 191 rotate counterclockwise by an initial twist angle øs when a voltage is applied. The branch electrodes 192 of 191 are inclined in different directions to rotate clockwise when voltage is applied. Therefore, a plurality of domains are formed, and the visibility in the left and right directions is improved, and a wide viewing angle can be obtained.

Although the liquid crystal layer 3 having the positive dielectric anisotropy has been described in the embodiment of the present invention, the liquid crystal layer 3 may have a negative dielectric constant. In this case, since the liquid crystal molecules are arranged perpendicular to the electric field formed between the pixel electrode 191 and the common electrode 131, the alignment direction of the liquid crystal molecules is substantially perpendicular to the direction of the branch electrode 192 of the pixel electrode 191. Also in this case, it is preferable to have an initial twist angle? In order to determine the direction in which the liquid crystal molecules rotate when voltage is applied.

Next, a thin film transistor array panel for a liquid crystal display according to another exemplary embodiment of the present invention will be described with reference to FIGS. 12 to 14.

12 to 14 are layout views illustrating a structure of a thin film transistor array panel for a liquid crystal display according to another exemplary embodiment of the present invention.

Since the layer structure of the thin film transistor array panel 100 according to the present exemplary embodiments is substantially the same as that of FIGS. 3 to 6, cross-sectional views will be omitted.

That is, the plurality of gate lines 121 including the gate electrode 124, the plurality of common electrodes 131, and the plurality of common electrode lines 125 connecting the common electrodes 131 are formed on the substrate 110. The gate insulating film 140, the plurality of island-like semiconductors 154, and the plurality of linear ohmic contacts 163 and 165 are sequentially formed thereon. A plurality of data lines 171 and a plurality of drain electrodes 175 including the source electrode 173 are formed on the ohmic contacts 163 and 165 and the gate insulating layer 140, and the passivation layer 180 is disposed thereon. A plurality of contact holes 181, 182, and 185 are formed in the passivation layer 180 and the gate insulating layer 140. A plurality of pixel electrodes 190 and a plurality of contact assistants 81 and 82 are formed on the passivation layer 180.

However, unlike FIGS. 1 to 3, as illustrated in FIGS. 12 to 14, in the thin film transistor array panel according to the present exemplary embodiment, the pixel electrodes 191 are separated from each other, and the first and second subpixel electrodes 191a and 191b are separated from each other. ). In this case, the first and second subpixel electrodes 191a and 191b are disposed at both sides of the data line 171, and include branch electrodes 192a and 192b and connection parts 193a and 193b. The branch electrodes 192a and 192b of the first and second subpixel electrodes 191a and 191b are inclined at an angle with respect to the gate line or the horizontal direction, and have a symmetrical structure with respect to the data line 171.

The drain electrode 175 and the source electrode 173 also have first and second drain electrodes 175a and 175b and first and second source electrodes 173a and 173b disposed on both sides of the data line 171. It includes.

In such a structure, even if shorted with one of the common electrode 131 and one of the first and second subpixel electrodes 191a and 191b, the data signal is normally transmitted to the other subpixel electrodes, so that a pixel having a short circuit has a half transmittance. Have. Thus, it is possible to prevent off pixel defects in which the pixels appear completely dark.

In addition, since one pixel electrode 191 has two electrodes 192a and 192b extending in different directions, one pixel has two domains in which liquid crystal molecules are arranged in different directions. Therefore, the structure of this embodiment can improve visibility and viewing angle as in the previous embodiment, and is suitable for large liquid crystal display devices.

12 and 13, the branch electrodes 192a and 192b of the pixel electrodes 191 neighboring each other in the vertical direction are arranged in parallel to each other. In the structure as shown in FIG. 12, the portion of reducing transmittance does not occur in the pixel row direction, but the distance between the branch electrodes 192a and 192b of the pixel electrodes 191 adjacent to each other in the pixel column direction decreases the transmittance. To make it happen. In order to solve this problem, the gate line 121 may be disposed in parallel with the branch electrodes 192a and 192b. That is, by bending the gate line 121 as described above, the number of branch electrodes 192a and 192b of the pixel electrode 191 may be maximized in the pixel column direction to improve the transmittance of the pixel. At this time, since the gate line 121 increases within the range of 2%, the delay with respect to the gate signal does not appear as a problem.

On the other hand, as shown in FIG. 14, the branch electrodes 192a and 192b may be disposed in different directions in the pixel column direction to maximize visibility.

The thin film transistor array panel according to the present invention can prevent off pixel defects in the liquid crystal display of the IPS mode and the FFS mode.

Although the preferred embodiments of the present invention have been described in detail above, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims (10)

Board, A plurality of gate lines formed on the substrate, A plurality of common electrodes formed on the substrate and made of a transparent conductor, A data line intersecting the gate line, A thin film transistor connected to the gate line and the data line, A plurality of pixel electrodes connected to the thin film transistor and including a plurality of branch electrodes overlapping the common electrode and connecting a plurality of branch electrodes and the branch electrodes; Including, The thin film transistor array panel of which the branch electrodes of the pixel electrodes adjacent to each other are arranged in different directions. In claim 1, And the branch electrode is inclined at an angle with respect to the gate line or the data line. In claim 2, The branch electrode has a symmetrical structure with respect to the data line. In claim 3, The branch electrode is inclined in different directions in both the horizontal and vertical directions. In claim 3, The pixel electrode includes a first subpixel electrode and a second subpixel electrode separated from each other. In claim 5, The first and second subpixel electrodes are disposed on both sides of the data line. In claim 6, The drain electrode of the thin film transistor includes first and second drain electrodes connected to the first and second subpixel electrodes, respectively. In claim 7, The thin film transistor array panel in which the branch electrodes arranged in the vertical direction are parallel to each other. In claim 8, And the gate line is bent in a portion parallel to the branch electrode. In claim 7, The thin film transistor array panel in which the branch electrodes arranged in a vertical direction are inclined in different directions.

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