In-plane switching mode liquid crystal display device including a black matrix with slit around the pixels and method of fabricating the same

An In-Plane Switching mode liquid crystal display device includes a first substrate and a second substrate, a plurality of gate lines and data lines defining a plurality of pixels on the first substrate, a driving device disposed in each of the plurality of pixels, at least one pair of a first electrode and a second electrode arranged in each of the plurality of pixels to generate a horizontal electric field, a black matrix formed on the second substrate and having a slot around the plurality of pixels, and a liquid crystal layer formed between the first substrate and the second substrate.

This application claims the benefit of Korean Patent Application No. 2003-043979, filed on Jun. 30, 2003, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) device and a method of fabricating an LCD device, and particularly, to an In-Plane Switching mode LCD device and a method of fabricating the same.

2. Discussion of the Related Art

Recently, with the development of various portable electronic devices, such as mobile phones, PDAs, notebook computers, etc., a light, thin, small flat panel display device has been in great demand. Research and development are actively conducted for the flat panel display devices, such as an LCD, a PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display), etc. Among these devices, the LCD attracts much more attention because of its simple mass-production technique, easy driving system, and implementation of a high picture quality.

There are various display modes for the LCD device according to arrangement of liquid crystal molecules. Currently, a TN (twisted nematic) mode LCD device is being generally utilized because of its easy black and white display, short response time, and low driving voltage. When a voltage is applied to the TN mode LCD device, liquid crystal molecules aligned to be horizontal to a substrate are aligned to be nearly perpendicular to a surface of the substrate. Accordingly, there is a problem in that a viewing angle is narrowed by refractive anisotropy of the liquid crystal molecules in applying of the voltage.

In order to solve this problem, LCD devices of various modes having wide viewing angle characteristics have been proposed. Among those, an In-Plane Switch (IPS) mode LCD device is applied to actual mass-production, and thus is being fabricated. This IPS mode LCD device forms a horizontal electric field that is substantially parallel to a surface of a substrate by forming at least one pair of electrodes arranged parallel in a pixel, so that liquid crystal molecules are aligned along the plane.

FIG. 1is a schematic view of a structure of the above-mentioned IPS mode LCD device according to the related art. As shown inFIG. 1, a liquid crystal panel1has a pixel defined by a gate line3and a data line4that are disposed along lengthwise and widthwise directions. Although only the (n, m)thpixel is shown inFIG. 1, N (>n) gate lines3and M (>m) data lines are disposed in an actual liquid crystal panel, thereby forming N×M pixels over the entire liquid crystal panel1. A thin film transistor10is formed at an intersection of the gate line3and the data line4in the pixel. The thin film transistor10includes a gate electrode11to which a scan signal is applied from the gate line3, a semiconductor layer12formed on the gate electrode11and activated to form a channel layer when the scan signal is applied thereto, and a source electrode13and a drain electrode14formed on the semiconductor layer12, to which an image signal is applied through the data line4, thereby applying an image signal input from the outside to a liquid crystal layer.

A plurality of common electrodes5and a plurality pixel electrodes7are arranged substantially parallel to the data line4in the pixel. In addition, a common line16connected with the common electrode5is disposed in the middle of the pixel, and a pixel electrode line18connected with the pixel electrode7is disposed on the common line16and is thus overlapped with the common line16.

As discussed above, in the related art IPS mode LCD device, the liquid crystal molecules are aligned substantially parallel to the common electrode5and the pixel electrode7. When the thin film transistor10is operated and thus a signal is applied to the pixel electrode7, an horizontal electric field that is substantially parallel to the liquid crystal panel1is generated between the common electrode5and the pixel electrode7. The liquid crystal molecules are rotated along the same plane by the horizontal electric field, thereby preventing a gradation inversion due to refractive anisotropy. Here, a black matrix32serves to prevent light from being transmitted to an unwanted area, namely, an image non-displayed area.

The related art IPS mode LCD device having such a structure will now be described in more detail with reference toFIGS. 2A and 2B. Here,FIG. 2Ais a cross-sectional view taken along I–I′ ofFIG. 1to show a structure of the thin film transistor10according to the related art.FIG. 2Bis a cross-sectional view taken along11–11′ ofFIG. 1to show a structure of a pixel according to the related art. InFIG. 2A, the thin film transistor10(inFIG. 1) includes the gate electrode11formed on a first substrate20, a gate insulating layer22laminated over the entire surface of a first substrate20, the semiconductor layer12formed on the gate insulating layer22, the source electrode13and the drain electrode14formed on the semiconductor layer12. In addition, a passivation layer24is formed over the entire surface of the first substrate20. InFIG. 2B, the plurality of common electrodes5are formed on the first substrate20in a pixel, and the pixel electrode7and the data line4are formed on the gate insulating layer22, so that a horizontal electric field is generated between the common electrode5and the pixel electrode7.

The black matrix32and a color filter layer34are formed at a second substrate30. The black matrix32serves to prevent light from leaking to an area where the liquid crystal molecules are not operated (namely, undesired area where an image is not displayed), and is usually formed at the thin film transistor10area (inFIG. 1) and between pixels (i.e., gate line and data line areas). The color filter layer34includes R (Red), B(Blue) and G(Green) colors to implement an actual color. A liquid crystal layer40is formed between the first substrate20and the second substrate30, and then the liquid crystal panel1is thus completed. In addition, a black resin is usually utilized for the black matrix32, and the reason thereof will now be described next.

The black matrix32made of metal, such as Cr or CrOx, that is usually utilized for the TN mode LCD or the like may form an electric field between the data line4and itself by its characteristic low resistance. Such an electric field is a vertical electric field that is formed between the first substrate20and the second substrate30. Meanwhile, another electric field is formed between the pixel electrode7on the first substrate20and the common electrode5on the second substrate30. As a result, the vertical electric field may not greatly affect the electric field between the pixel electrode7and the common electrode5.

On the contrary, in the IPS mode LCD device, an electric field applied to the liquid crystal layer40is a horizontal electric field that is substantially parallel to a surface of the substrate20or30. Accordingly, when the horizontal electric field is formed by the black matrix32, the vertical electric field affects the horizontal electric field, thereby distorting the horizontal electric field. Such distortion may cause a vertical cross talk on a screen as a main factor of image quality deterioration. Accordingly, in the IPS mode LCD device, a black resin with high resistance is usually utilized as the black matrix32to prevent distortion of the horizontal electric field. However, there exist several problems because of disadvantages of the black resin itself.

First, since the resin has a bad anisotropy etching characteristic compared to metal in a photolithography, it is difficult to form the black matrix32with a fine pattern to make good resolution. Accordingly, it is difficult to fabricate an IPS mode LCD of high resolution.

Second, since the black matrix32has a low light blocking rate compared to Cr or CrOx (because transmittance of light is high), its thickness has to be thick compared to Cr or CrOx in order to completely block light transmitted to the image non-displayed area. Accordingly, a step is generated at the color filter layer34and makes it difficult to be flat.

Finally, since the black resin has a bad dispensability compared to the metal, such as Cr or CrOx, a protrusion is easily formed at a surface of the black matrix32compared to Cr or CrOx. Thus, defection occurs at the black matrix32, thereby degrading a yield of the LCD.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an In-Plane Switching mode LCD device and a method of fabricating the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an In-Plane Switching mode LCD device and a method of fabricating the same capable of forming a fine pattern and improving a yield by forming a black matrix as a metal layer.

Another object of the present invention is to provide an In-Plane Switching mode LCD device and a method of fabricating the same capable of preventing a vertical cross talk from occurring by electrically isolating a black matrix formed at each pixel from a neighboring pixel and thus minimizing distortion of a horizontal electric field.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an In-Plane Switching mode LCD device including a first substrate and a second substrate, a plurality of gate lines and a data lines formed on the first substrate and defining a plurality of pixels, a driving device disposed in each pixel of the first substrate, at least one pair of a first electrode and a second electrode arranged in each pixel of the first substrate and forming a horizontal electric field, a black matrix formed at the second substrate and having a slit around the pixel, and a liquid crystal layer formed between the first substrate and the second substrate.

In another aspect, an In-Plane Switching mode LCD device includes a first substrate and a second substrate, a plurality of gate lines and data lines defining a plurality of pixels on the first substrate, a driving device disposed in each of the plurality of pixels, at least one pair of first electrode and second electrode arranged in each of the plurality of pixels to generate a horizontal electric field, a black matrix formed on the second substrate and electrically isolated from a neighboring pixel, and a liquid crystal layer formed between the first substrate and the second substrate.

In another aspect, a method of fabricating an In-Plane Switching mode LCD device includes forming a plurality of gate lines and data lines defining a plurality of pixels on a first substrate, deposing a driving device on each of the plurality of pixels, arranging at least one pair of a first electrode and a second electrode on each of the plurality of pixels to generate a horizontal electric field, forming a black matrix having a slit around the plurality of pixels on a second substrate, and forming a liquid crystal layer between the first substrate and the second substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3Ais a schematic plan views of an exemplary black matrix of an IPS mode LCD device according to the present invention. InFIG. 3A, a black matrix132formed on a second substrate130(ofFIG. 5) is integrally formed over the entire surface of the second substrate130. Thus, in a case where the black matrix132made of metal of low resistance is integrally formed over the entire pixel, the entire black matrix132operates as one metal layer, thereby forming relatively large parasitic capacitance. Accordingly, an intensity of a vertical electric field formed by the black matrix132and a data line104(ofFIG. 4) is increased, thereby distorting a horizontal electric field. Furthermore, during a vertical blanking period of an image signal input to the data line104, a time for an electric charge at the parasitic capacitance to be discharged is lengthened. Hence, the vertical electric field that distorts the horizontal electric field during a next image signal period becomes stronger.

In addition, if the metal black matrix132is integrally formed over the entire pixel, the pixels are mutually affected by each other. For example, when an image signal is applied along the data line104(inFIG. 5), a vertical electric field is formed even at a pixel to which a weak image signal is currently applied by a strong signal of another pixel, thereby distorting the vertical electric field.

According to the present invention, the above-mentioned problems can be solved by electrically isolating the black matrix132made of metal pixel by pixel. That is, by limiting the influence of the vertical electric field in each pixel to only a corresponding pixel, intensity of the vertical electric field is minimized. Accordingly, the distortion of the horizontal electric field due to the vertical electric field can be prevented. Thus, the vertical electric field is formed in the corresponding pixel by the black matrix132. However, the influence due to other pixels is excluded, so that the generated vertical electric field almost does not affect the horizontal electric field.

FIG. 3Bis a schematic plan views of an exemplary black matrix of an IPS mode LCD device according to the present invention. InFIG. 3B, the black matrix132formed at an edge of each pixel (i.e, an area where data and gate lines are formed) is electrically insulated from the black matrix132at a neighboring pixel. The black matrix132may be formed by removing a predetermined central portion of the black matrix132(inFIG. 3A). Since the black matrix132is formed by laminating a metal layer and then patterning it, the central portion is not substantially removed. Thus, the central portion where the black matrix has been removed may be referred to as a removal area or slit133formed at the black matrix132.

FIG. 3B, a width of the black matrix132(including width of slit133) is formed to be almost the same as that of the black matrix132(inFIG. 3A). Accordingly, in view of the slit133, the actual area of the black matrix132is decreased, thereby decreasing intensity of a vertical electric field formed between itself and the data line. Accordingly, the distortion of the horizontal electric field can be minimized.

FIG. 4is a schematic plan view of an exemplary IPS mode LCD device according to the present invention, andFIG. 5is a cross-sectional view taken along III–III′ ofFIG. 4. InFIG. 4, a gate line103and the data line104defining a pixel are arranged in a liquid crystal panel101. A thin film transistor110is formed at an intersection of the gate line103and the data line104in the pixel. At least one pair of a common electrode105and a pixel electrode107arranged substantially parallel to the data line104are disposed in the pixel, and form a horizontal electric field that is substantially parallel to a surface of the liquid crystal panel between the common electrode105and the pixel electrode107when a signal is applied to the pixel electrode107through the thin film transistor110. Also, a common line116connected with the common electrode105and a pixel electrode line118connected with the pixel electrode107are disposed in the pixel. The common line116and the pixel electrode line118are overlapped with each other, thereby forming storage capacitance.

The black matrix132made of metal, such as Cr, CrOx, Cr/CrOx or the like is formed at an edge of the pixel, where the gate and date lines103,104and the thin film transistor110are formed. The slit133(inFIG. 5) with a predetermined width is formed in the black matrix132, thereby separating the black matrix132of a corresponding pixel from the black matrix132of a neighboring pixel. InFIG. 4, the width of the slit133is not limited if the black matrix132of the corresponding pixel can be electrically isolated from that of the neighboring pixel. Since the black matrix132is made of metal having good etching anisotropy, a desired width of the slit133may be formed.

InFIG. 5, the common electrode105and the pixel electrode107are respectively formed on a first substrate120and a gate insulating layer122made of a transparent insulating material, such as glass or the like. Even though not shown inFIG. 5, a gate electrode111is formed on the first substrate120, a semiconductor layer112is formed on the gate insulating layer122, and a thin film transistor110is formed on the semiconductor layer122when a source electrode113and a drain electrode114are formed. A passivation layer124is formed on the source electrode113and the drain electrode114.

The black matrix132and a color filter layer134are formed on the second substrate130made of glass or the like. As mentioned above and shown inFIG. 5, the black matrix132(132a,132b) is formed by etching Cr, CrOx, Cr/CrOx or the like by photolithography, forming the slit133with a predetermined width, so that a corresponding pixel is electrically isolated from other pixels. By such electrical isolation, an actual black matrix-formed area is decreased, and the black matrix132aof the corresponding pixel is not affected by the black matrix132bof the neighboring pixel. Accordingly, a vertical electric field between the data line104and the black matrix132aof the corresponding pixel is decreased.

InFIG. 5, the slit133is formed around the pixel. Since the slit133is an area where no black matrix is formed, light is directly leaked. Therefore, preferably, the slit133is formed along the gate line103and the data line104that define a pixel, to thereby prevent leakage of light. InFIG. 5, the black matrix132is formed so as to block only the data line104(or the gate line103). But the black matrix132may be formed to block the data line104and the common electrode105disposed near the data line104. The common electrode105is disposed near the data line104in order to prevent distortion of the horizontal electric field due to the data line104and the pixel electrode107by shielding therebetween with the common electrode105. Accordingly, since a space between the data line104and the common electrode105becomes an image non-displayed area where the horizontal electric field is not applied, the black matrix132amay be enlarged to the common electrode105. Even though not shown, an overcoat layer may be formed on the color filter layer124in order to protect the color filter layer124and improve flatness. Finally, by forming a liquid crystal layer140between the first substrate120and the second substrate130, an IPS mode LCD device is thus completed.

In general, since Cr, CrOx or the like has a good light blocking property, light can be effectively blocked even with a film having a thin thickness. Accordingly, in the IPS mode LCD device in accordance with the present invention, the black matrix132can be formed to have a thin thickness, so that flatness of the second substrate130can be improved. In addition, a step between the slit133and the black matrix132(132a,132b) can be minimized.

The black matrix132in accordance with the present invention may be made of metal other than Cr, CrOx, Cr/CrOx or the like. That is, any kind of metal may be used for the black matrix in accordance with the present invention, if it has a good light blocking property and processability (etching anisotropy). In addition, while a specific structure of the IPS mode LCD device has been described, those descriptions are for explaining the present invention, not for limiting the present invention. For example, inFIG. 5, the common electrode105and the pixel electrode107are respectively formed on the first substrate120and the gate insulating layer122. However, the common electrode105and the pixel electrode107may be respectively formed on the gate insulating layer122and the first substrate120. In addition, both of the common electrode105and the pixel electrode107may be formed on the passivation layer124or on the first substrate120. Metal for forming the common electrode105and the pixel electrode107is not also limited to a specific metal. Also, the data line104, the common electrode105and the pixel electrode107may be shaped as a zigzag form.

As described above, in the IPS mode LCD device in accordance with the present invention, the black matrix132for preventing leakage of light is formed as a metal layer, so that the black matrix132can be formed with a fine pattern. Accordingly, the IPS mode LCD device having a high resolution can be fabricated.

In addition, since Cr, CrOx or the like used for the present invention has a good light blocking rate compared to a black resin, even though a metal layer made of Cr, CrOx or the like has a relatively thin thickness, light transmitting a liquid crystal layer can be effectively blocked. Accordingly, the black matrix132with a thin thickness can be realized, and a step can be prevented from being generated.

Furthermore, in the present invention, the distortion of the horizontal electric field applied to the liquid crystal layer140can be minimized by separating the black matrix132aformed in one pixel from the black matrix132bformed in a neighboring pixel. Hence, the vertical cross talk due to the distortion of the horizontal electric field can be prevented from occurring.

In the present invention, a fine pattern can be formed, a color filter layer can be flattened, no step is generated, and the quality of a black matrix is not degraded. Further, a black matrix which can prevent a vertical cross talk from being generated by a horizontal electric field distortion between a common electrode and a pixel electrode is provided. Furthermore, since such a black matrix is formed, an IPS mode LCD device having improved quality and an improved yield can be fabricated.

Therefore, in the present invention, a black matrix is formed as a metal layer of Cr, CrOx, Cr/CrOx or the like. Since the metal has good etching anisotropy, a fine line width may be formed and thus the black matrix having a fine pattern may be formed by being made of Cr, CrOx, Cr/Ox or the like. In addition, since the metal layer of Cr, CrOx, Cr/CrOx or the like has a good light blocking rate, light transmitting a liquid crystal layer may be effectively blocked even with the metal layer having thin thickness. Accordingly, the black matrix with a thin thickness can be formed. Meanwhile, in the present invention, by separating the black matrix formed in one pixel from another black matrix formed in a neighboring pixel, the black matrix in each pixel is electrically isolated from the outside.