Liquid crystal display device and method for fabricating the same

A liquid crystal display device includes a gate line and a data line crossing each other to define a pixel region on a substrate; common electrode parts arranged at both sides of the data line to shield the data line; a black matrix over a region including the data line and a portion of the common electrode parts; and a color filter arranged at the pixel region.

This application claims the benefit of Korean Patent Application Nos. 2004-118478 and 2005-46945 filed in Korea on Dec. 31, 2004, and Jun. 1, 2005, respectively, both of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a color filter on thin film transistor structure and a method for fabricating the same.

2. Description of the Related Art

In general, a liquid crystal display device (LCD) displays images using the optical anisotropy and double refraction properties of liquid crystal molecules. The arrangement of the liquid crystal molecules is changed by an applied electric field. The light transmittance of the liquid crystal molecules also changes in accordance with the alignment direction of the liquid crystal molecules.

The LCD device includes two substrates facing each other. Electrodes are provided on the facing surfaces of the respective substrates for generating an electric field. A liquid crystal material is injected between the two substrates. The alignment direction of liquid crystal molecules is changed by the electric field generated by a voltage applied to the two electrodes. Thus, the LCD device displays an image by varying the light transmittance of the liquid crystal molecules in accordance with the alignment direction of the liquid crystal molecules.

FIG. 1is a schematic plane view of the related art LCD device. Referring toFIG. 1, the related art LCD device11includes an upper substrate (not shown) including a color filter (not shown) and a common electrode (not shown) deposited on the color filter (not shown). The color filter (not shown) includes sub-color filters (not shown) and a black matrix (not shown) formed between the sub-color filters (not shown). A liquid crystal material (not shown) is filled between the upper substrate (not shown) and the lower substrate (not shown). The lower substrate is also called an array substrate.

Pixel regions P are defined on a lower substrate (not shown) of the LCD device. A pixel electrode (not shown) and a switching device T are formed at each pixel region. Gate lines13and data lines15lines crossing each other form an array. Crossings of the gate lines and data lines define the pixel regions P. The switching devices T, for example thin film transistors (TFT), are arranged in a matrix on the lower substrate. Each of the switching devices is electrically connected to one of the gate lines13and one of the data lines15.

A transparent pixel electrode17is formed at each of the pixel regions P. The pixel electrode17is formed of transparent conductive metal having a relatively high light transmittance, such as indium-tin-oxide (ITO). Storage capacitors C are formed on the gate line13. The storage capacitors C are electrically connected to the pixel electrodes17in parallel. A part of the gate line13is used as a first electrode of the storage capacitor C, and a source/drain metal layer30having an island shape and formed of the same material as source/drain electrodes of the switching device T is used as a second electrode of the storage capacitor C. The source/drain metal layer30contacts the pixel electrode17to receive signals from the pixel electrode17.

As described above, when the liquid crystal panel is formed by attaching the upper color filter substrate (not shown) and the lower array substrate (not shown), light leakage or other problems may occur because of misalignment between the color filter substrate (not shown) and the array substrate (not shown).

FIG. 2is a cross-sectional view taken along line II-II ofFIG. 1illustrating a method of fabricating the related art LCD device. Referring toFIG. 2, the method for fabricating the related art LCD device includes disposing an array substrate as a lower substrate22, and a color substrate as an upper substrate5, with a specific gap therebetween; and injecting liquid crystals14between the lower and upper substrates22and5. Also, switching devices T (shown inFIG. 1), for example thin film transistors, and a passivation layer40are formed on the lower substrate22. Each of the thin film transistors includes a gate electrode32, an active layer34, a source electrode36and a drain electrode38. The passivation layer40protects the thin film transistors formed on the lower substrate22.

A transparent pixel electrode17is formed at each pixel region P. The transparent pixel electrode17contacts the drain electrode38of the switching device T. Storage capacitors C (shown inFIG. 1) are formed on a gate line13to be electrically connected to the pixel electrodes17in parallel. In the related art array substrate, the data line15and the pixel electrode17are separated from each other by a specific interval A to prevent vertical cross talk. The gate line13and the pixel electrode17are also separated from each other by a specific interval B.

Red, green and blue color filters8a,8band8care formed on the upper substrate5to correspond to the pixel regions P of the lower substrate22. A black matrix6is also formed on the upper substrate5to correspond to the gate lines13, the data lines15and the switching devices T. The black matrix6formed at the upper substrate5covers the gaps A and B between the data line15and the pixel electrode17, and between the pixel electrode17and the gate line13, to block light leaking through the gaps A and B. Also, the black matrix6overlies the thin film transistor T to block irradiated external light from passing through the passivation layer40and affecting the active layer34.

The upper substrate5and the lower substrate22may be misaligned during the attachment process. In consideration of such misalignment, a specific margin is included when the black matrix6is designed. The margin causes a corresponding decrease in an aperture ratio. If the misalignment error exceeds the margin, light leakage regions A and B may not be completely covered by the black matrix6. Thus, light leakage occurs in these regions. Accordingly, image quality deteriorates.

As described above, the related art LCD device employs a method of fabricating a color filter substrate and a thin film transistor array substrate through different processes and attaching them together. Recently, a new design concept for a thin film transistor array, called a Color Filter on TFT (COT) method in which a color filter is formed on a thin film transistor array substrate, has been introduced. The LCD device employing the COT method is fabricated in such a manner that the switching devices, for example TFTs, are formed, and then, red, green and blue color resins are formed on the TFTs.

FIG. 3is a schematic plane view of an LCD device having a COT structure in accordance with the related art. Referring toFIG. 3, gate lines102and data lines116cross each other. A switching device T, including a gate electrode104, an active layer108and source/drain electrodes112and114, is formed at each crossing of these gate and data lines102and116. Also, transparent electrodes (not shown) contacting the drain electrodes114and colors filter124a,124band124care formed at regions defined by crossings of the gate and data lines102and116. The transparent electrodes (not shown) are formed on the color filters124a,124band124c. The color filters indirectly contact the drain electrodes114through the transparent electrodes (not shown). Also, each of the transparent electrodes (not shown) is electrically connected to the storage capacitor C formed on the gate line102. The storage capacitor C uses a part of the gate line102as a first electrode, and uses a capacitor upper electrode118as a second electrode. The capacitor upper electrode118is electrically connected to the transparent electrode (not shown) and is concurrently formed on the same layer as the source/drain electrodes112and114.

In accordance with the COT structure, a black matrix120and the red, green and blue color filters124a,124band124care formed on the switching device T of the array part. The black matrix120covers regions where light might leak. The black matrix120is formed by applying an opaque material, blocks light, and protects the switching device T.

FIGS. 4A to 4Eare cross-sectional views taken along line IV-IV ofFIG. 3illustrating a method for fabricating an LCD device having a COT structure in accordance with the related art. Referring toFIG. 4A, a conductive material is deposited on a substrate100. The deposited conductive material is patterned to form a gate line102and a gate electrode104. Then, a gate insulation film106, which is a first insulating film, is formed by depositing an inorganic insulating material, for example silicon nitride (SiNx) or silicon oxide (SiO2), over the entire surface of the substrate100, including the gate line102and the gate electrode104formed thereon. Then, an active layer108and an ohmic contact layer110are formed on the gate insulation film106by depositing, then patterning, an intrinsic amorphous silicon (a-Si:H) and an impurity-doped amorphous silicon (n+a-Si:H) on the gate insulation film106.

Then, a conductive metal, such as chrome (Cr), molybdenum (Mo), copper (Cu), tungsten (W), tantalum (Ta) and the like, is deposited over the entire surface of the substrate100, including the active layer108and the ohmic contact layer110thereon. The deposited conductive metal is patterned to form a source electrode112and a drain electrode114, a data line116, and a capacitor upper electrode118. The source electrode112and the drain electrode114contact, respectively, the ohmic contact layer110. The data line116contacts the source electrode112. The capacitor upper electrode118is a storage node formed on the gate line102and has an island shape.

Then, a second insulating film119is formed by depositing an inorganic insulating material, such as silicon nitride and silicon oxide, over the entire surface of the substrate100, including the source and drain electrodes112and114thereon. The second insulating film119prevents a potential defective contact between the active layer108and an organic film (not shown) to be formed hereafter. The second insulating layer119is not formed if the contact is not defective.

Then, a black matrix120is formed over the switching device T, the data line116and the gate line102by depositing an opaque organic material on the second insulating film119to form an organic layer, and patterning the organic layer. In an embodiment of the present invention, a transparent organic insulating material or an inorganic insulating material having a low permittivity may be used as a passivation film for protecting the switching device T, instead of the black matrix120. In this case, a special black matrix may be used at an upper substrate of the LCD device.

Referring toFIG. 4B, the black matrix120is selectively patterned. Portions of the black matrix120are removed at a region corresponding to a contact hole to be formed for contacting a drain electrode, at a region where the capacitor upper electrode118electrically contacts a common electrode. The remaining portions of the black matrix120overlap the thin film transistor T region and the storage capacitor C region. Then, a color resin is applied to an upper surface of the entire structure including the selectively-patterned black matrix120to form red, green and blue color filters124a,124band124cin a plurality of pixel regions.

Referring toFIG. 4C, an acryl resin is applied to an upper surface of the entire structure including the color filters124a,124band124cto form an overcoat layer126.

Referring toFIG. 4D, the overcoat layer126and the black matrix120are selectively patterned to form a drain contact hole128and a capacitor contact hole130exposing parts of the drain electrode114and the capacitor upper electrode118.

Referring toFIG. 4E, a transparent electrode material is deposited on the overcoat layer126including the drain contact hole128and the capacitor contact hole130. The transparent electrode material is patterned to form a common electrode132.

In the related art array substrate of the LCD device, the overcoat layer, such as an acryl resin, is used on the TFT lower substrate for the COT structure to prevent a decrease in a aperture ratio caused by a corresponding increase in an attachment margin when manufacturing a large glass substrate. The acryl film flattens an uneven surface generated by the organic film of the lower substrate and prevents a flow of impurity ions from the color filters to a liquid crystal layer. However, the use of the acryl material increases cost. Furthermore, although temporarily improved through a post exposure process, the transmittance of the acryl keeps decreasing during subsequent processes, thereby reducing the transmittance of the LCD panel. Therefore, to avoid such defects of the COT structure, research is actively ongoing on a COT structure that does not include acryl.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystal display device having a color filter on thin film transistor structure and a method for fabricating the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an LCD device and a fabrication method thereof so as to be capable of preventing leakage of light caused by a disclination in a COT structure.

Another object of the present invention is to provide an LCD device and a fabrication method thereof so as to be capable of reducing a fabrication cost.

Another object of the present invention is to provide an LCD device and a fabrication method thereof so as to be capable of preventing a decrease in transmittance.

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 array substrate of a liquid crystal display device, comprising: a gate line and a data line crossing each other and defining a pixel regions on a substrate; data line shielding common electrodes arranged at both sides of the data line; a thin film transistor formed at an crossing of the gate line and the data line; a black matrix arranged over the data line and a portion of the data line shielding common electrodes; a color filter arranged at a pixel region defined by the gate line and the data line crossing each other; and a common electrode and a pixel electrode arranged at the pixel region defined by the gate line and the data line crossing each other.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a liquid crystal display device includes a gate line and a data line crossing each other to define a pixel region on a substrate; common electrode parts arranged at both sides of the data line to shield the data line; a black matrix over a region including the data line and a portion of the common electrode parts; and a color filter arranged at the pixel region.

In another aspect, a method for fabricating an array substrate of a liquid crystal display device includes crossing a gate line and a data line on a substrate, thereby defining a pixel region; forming common electrode parts at both sides of the data line to shield the data line, the common electrode parts being separated from the data line; forming a thin film transistor at a region defined by the gate line and the data line crossing each other, wherein the thin film transistor includes a gate electrode, an active layer and a source electrode and a drain electrode; arranging a black matrix over the data line and a portion of the common electrode parts; forming a color filter on a pixel region defined by the gate line and the data line crossing each other; and forming a common electrode and a pixel electrode at the pixel region.

In another aspect, a liquid crystal display device includes a plurality of gate lines and a plurality of data lines crossing each other to define a pixel region on a substrate; a plurality of common electrode lines, each of the common electrode lines spaced apart from and parallel to a corresponding one of the gate lines; a pair of common electrode parts corresponding to each one of the data lines, the common electrode parts extending from the common electrode line, and arranged at both sides of the one of the data lines to shield the data lines; a black matrix over a region including the data lines and a portion of the common electrode parts; and a color filter arranged at the pixel region.

It is to be understood that both foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 5A to 5Dare plane views sequentially showing the layout of a liquid crystal display having a COT structure in accordance with an embodiment of the present invention. Referring toFIG. 5A, a gate line202is arranged horizontally on an array substrate. A common electrode line206is horizontally arranged at a specific interval from the gate line202. The common electrode line206includes a data line shielding common electrode part206avertically arranged to minimize the cross-talk level, and a storage capacitor part206bhorizontally arranged to form a storage capacitor. In one embodiment of the present invention, at least two data line shielding common electrode parts206aare arranged to face each other at a certain interval therebetween. Also, the gate line202and the common electrode line206are simultaneously patterned in gate patterning.

Referring toFIG. 5B, a data line214crossing the gate line202perpendicularly and source/drain electrodes216and218are arranged on the array substrate200(not shown). In an embodiment of the present invention, the data line214is arranged between a pair of adjacent data line shielding common electrode parts206a. The data line214is spaced apart from the adjacent data line shielding common electrode parts206a. The data line214and the adjacent data line shielding common electrode parts206afor a zigzag pattern. Also, the drain electrode218overlaps the storage capacitor part206b. Here, the drain electrode218and the storage capacitor part206bof the common electrode line206form a capacitor.

An insulation film220(not shown) is deposited over the entire surface of the substrate, and a black matrix222(not shown) is formed thereon, overlapping the data line214and the data line shielding common electrode part206aincluding a portion between the data line214and the data line shielding common electrode part206a. Here, the black matrix222(not shown) overlaps the entire gate line214and a specific portion of the data line shielding common electrode part206a. Also, the black matrix222(not shown) is arranged so as not to overlap a flattening organic film228(not shown) where a drain contact hole229is to be later formed for exposing the drain electrode218.

A color filter layer224(not shown) is formed on a second insulation film220including a part of an upper surface of the black matrix222(not shown). Here, the color filter layer224(not shown) is formed on a pixel region formed by a crossing of the gate line202and the data line214, and is arranged so as to overlap one portion of the upper surface of the black matrix222.

Referring toFIG. 5C, a flattening organic film228(not shown) is formed over the entire surface of the substrate including the black matrix222(not shown) and the color filter layer224(not shown). The flattening organic film228(not shown) and the second insulation film220(not shown) are sequentially patterned to form a drain contact hole229exposing the drain electrode218. The drain contact hole229can be formed because a thick black matrix222(not shown) or a color filter layer224(not shown) is not placed on the flattening organic film228(not shown).

Referring toFIG. 5D, a pixel electrode230and a common electrode232are formed. The pixel electrode230and the common electrode232are electrically connected to the drain electrode218through the drain contact hole229. The pixel electrode230overlaps the drain electrode218. A vertical portion230aextends from the pixel electrode230in a vertical direction. The common electrode232overlaps the gate line202, the data line212and the data line shielding common electrode part206a. A vertical portion232aextending from the common electrode232is disposed between the vertical portions230aof the pixel electrode. The common electrode232contacts the common electrode line206at an outer edge region of the pixel region. Thereby, the common electrode232and the common electrode line206are in an equipotential state. The data line shielding common electrode parts206areduces a vertical cross-talk level, thereby preventing a data signal from affecting an electric field between the common electrode and the pixel electrode. Thus, a reduction in an aperture ratio is prevented.

FIGS. 6A to 6Fare cross-sectional views taken along lines VIa-VIa and VIb-VIb ofFIG. 5Dillustrating a method for fabricating an LCD device having a COT structure in accordance with an embodiment of the present invention. Referring toFIG. 6A, a conductive metal is deposited on a substrate200. The deposited conductive metal is patterned to form a gate line202(shown inFIG. 5A) and a gate electrode204. Concurrently, pairs of data line shielding common electrode parts206aare formed. Then, a gate insulation film208if formed as a first insulating film by depositing an inorganic insulating material, such as silicon nitride (SiNx) and silicon oxide (SiO2), over the entire surface of the substrate200, including the data line shielding common electrode parts206a, the gate line202(shown inFIG. 5A) and the gate electrode204. Then, an active layer210and an ohmic contact layer212are formed on the gate insulation film208by depositing thereon, and patterning, an intrinsic amorphous silicon (a-Si:H) and an impurity-doped amorphous silicon (n+a-Si:H).

Referring toFIG. 6B, a data line214, a source electrode216, and a drain electrode218extending from the data line214are formed by depositing and patterning a conductive metal, such as chrome (Cr), molybdenum (Mo), copper (Cu), tungsten (W), tantalum (Ta) and the like over the entire surface of the substrate200, including the active layer210and the ohmic contact layer212thereon. The source electrode216and the drain electrode218respectively contact the ohmic contact layer212. While patterning the data line214, a capacitor upper electrode (not shown) electrically contacting the source electrode216is also formed on the gate line202. The data line214is separated from the adjacent data line shielding common electrode parts206aby intervals of W1and W2, respectively.

Then, a second insulating film220is formed by depositing an inorganic insulating material, such as silicon nitride and silicon oxide, over the entire surface of the substrate200, including the source and drain electrodes216and218thereon. The second insulating film220prevents a potential defective contact between the active layer210and an organic film (not shown) to be later formed. The second insulating film220may not be formed if there is no defective contact between the active layer210and the organic film to be formed.

Referring toFIG. 6C, a black matrix222is formed by applying an opaque glass material on the entire surface of the substrate200including the second insulating film220thereon. Instead of a black matrix, a transparent organic insulating material or an inorganic insulating material having a low permittivity may be used as a passivation film for protecting the switching device T. In this case, a special black matrix is used at an upper substrate of the LCD device.

Referring toFIG. 6D, the black matrix222is selectively patterned to overlap the data line214and a portion of the data line shielding common electrode parts206aincluding a portion between the data214and the data line shielding common electrode part206a. Also, the patterned black matrix222has an edge overlapping the data line shielding common electrode parts206a. A portion of the black matrix222is removed to expose a portion of the second insulation film220corresponding to a contact hole region to be formed for contacting the drain electrode218.

Referring toFIG. 6E, a color resin is applied to an upper surface of the entire structure including the selectively-patterned black matrix222, thereby forming red, green and blue color filters224at a plurality of pixel regions. An uneven portion226is formed at a region where the color filter224overlaps the black matrix222, and a rubbing direction is twisted at the uneven inclined portion226, which causes a disclination. To avoid such problems, as shown inFIG. 6D, the black matrix222overlaps an interval W1between the data line214and the data line shielding common electrode part206aand an interval W2between the data line214and the data line shielding common electrode part206a, thereby blocking light from a backlight in the disclination regions. Also, to reduce the level of unevenness caused by the absence of an acryl overcoat layer, the black matrix222may be of the same height as the color filter224, or the height difference H2between the black matrix222and the color filter224may be smaller than 0.2*H1, where H1the thickness of the color filter224.

Referring toFIG. 6F, instead of an overcoat layer formed using an acryl resin, a third insulating film228is formed by depositing an inorganic insulating material, such as silicon nitride (SiNx) and silicon oxide (SiO2), over an upper surface of the array substrate including the color filter224. Then, the third insulating film228is selectively removed to form a drain contact hole229(shown inFIG. 5C) exposing the drain electrode218. A transparent electrode material, such as ITO, is deposited on the third insulating film228including the drain contact hole229. Then, the transparent electrode layer is selectively patterned to form a pixel electrode230and a common electrode232electrically connected to the drain electrode218. Then, a flattening film (not shown) is formed over the entire surface of the array substrate200and an alignment film (not shown) is formed thereon.

In an embodiment of the present invention, a height difference between the color filter and the black matrix is minimized, thereby minimizing unevenness due to the absence of an acryl overcoat layer. Also, manufacturing cost may be reduced. Furthermore, a decrease in transmittance may be prevented because an expensive acryl resin is not used. Also, because the black matrix is patterned with its edge overlying the data line shielding electrode parts, light leakage is completely blocked in disclination regions.

It will be apparent to those skilled in the art that various modifications and variation can be made in the liquid crystal display device having a color filter on thin film transistor structure and the method for fabricating the same of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.