1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device and a method of fabricating the LCD device.
2. Description of the Related Art
Presently, LCD devices are being developed as the next generation of display devices because of their light weight, thin profile, and low power consumption. In general, an LCD device is a non-emissive display device that displays images using a refractive index difference utilizing optical anisotropy properties of a liquid crystal material that is interposed between an array (TFT) substrate and a color filter substrate. Among the various type of LCD devices commonly used, active matrix LCD (AM-LCD) devices have been developed because of their high resolution and superiority in displaying moving images. The AM-LCD device includes a thin film transistor (TFT) in each pixel region as a switching device, a pixel electrode in each pixel region, and a second electrode used for a common electrode.
FIG. 1 is a perspective view of an LCD device according to the related art. In FIG. 1, first and second substrates 10 and 30 are arranged to face each other with a liquid crystal material 50 interposed therebetween. On an inner surface of the first substrate 10, a color filter layer 12 and a common electrode 16, which functions as an electrode for applying an electric field to the liquid crystal layer 50, are subsequently formed. The color filter layer 12 includes a color filter for passing only a specific wavelength of light, and a black matrix (not shown) that is disposed at the boundary of the color filter and shields light from a region in which alignment of the liquid crystal material is uncontrollable. On an inner surface of the second substrate 30, a plurality of gate lines 32 and a plurality of data lines 34 are formed in a matrix array defining individual pixel regions P. A TFT T, which functions as a switching device, is disposed in each pixel region P where a gate line 32 and a data line 34 cross. A pixel electrode 46 is connected to the TFT T. Although not shown, the thin film transistor T includes a gate electrode to where a gate voltage is applied, source and drain electrodes for applying a data voltage to the pixel electrode.
First and second polarizing plates 52 and 54, which transmit only light parallel to a polarizing axis, are disposed on outer surfaces of the first and second substrates 10 and 30, respectively. An additional light source, such as a backlight, is disposed under the polarizing plate 54. Although not shown, first and second alignment layers contacting the liquid crystal layer 50 are formed on inner surfaces of the first and second substrates. The surfaces of the first and second alignment layers are aligned along predetermined rubbing directions, respectively.
FIGS. 2A and 2B are schematic views showing a liquid crystal display device according to the related art. FIG. 2A is a plan view and FIG. 2B is a cross-sectional view taken along a line II—II of FIG. 2A.
As shown in FIG. 2A, a plurality of pixel regions P are defined on a substrate 60. A black matrix 64 is formed on the substrate 60 and has a plurality of open portions 62. Each of the open portions 62 corresponds to each of the pixel regions P.
A color filter layer 66 is formed over the substrate 60 having the black matrix 64 and includes red, green and blue sub-color filters 66a, 66b and 66c. The red, green and blue sub-color filters 66a, 66b and 66c are located in the open portions 62. In addition, a common electrode 68 and an alignment layer 70 are sequentially formed over the black matrix 64 and the color filter layer 66 on the substrate 60.
The black matrix 64 is made of one of chromium (Cr)-based materials and resin materials. Typically, the black matrix material is made of resin materials. A black matrix formed by coating a resin material is formed thicker than a black matrix formed by depositing a Cr-based material. Therefore, a large step difference is created by a portion of the color filter layer 66 that overlaps edges of the black matrix 64, as shown in FIG. 2B. When a rubbing direction rl of the substrate 60 is from a right upper portion to a left lower portion in 45 degrees as shown in FIG. 2A (similarly, the rubbing direction is from right to left in the cross sectional view of FIG. 2B), a rubbing defect occurs at a first sloped side SR, as shown in FIG. 2B, that causes light leakage. This light leakage severely degrades a black picture state.
To improve an aperture ratio by reducing an align margin, a structure in which both the thin film transistors and color filters are formed on the same substrate has been suggested. In such a structure, the black matrix has a thicker thickness than the black matrix shown in FIG. 2B in order to effectively block light due to an increased step difference caused by forming a the thin film transistor. Thus, a rubbing defect caused by an even larger step difference becomes more severe. Hereinafter, color filter layer on thin film transistor (COT) type LCD device in which the color filter device is formed on the substrate having the thin film transistor will be explained.
FIGS. 3A and 3B are schematic views showing a COT type LCD device according to the related art. FIG. 3A is a plan view and FIG. 3B is a cross sectional view taken along a line III—III of FIG. 3A.
As shown in FIGS. 3A and 3B, a gate line 72 is formed on a substrate 70 along a first direction, a data line 80 is formed along a second direction orthogonal to the first direction. A thin film transistor T is located adjacent to a crossing of the gate line 72 and the data line 80.
A color filter layer 86 that includes red, green and blue sub-color filters 86a, 86b and 86c is formed over the thin film transistor T, the gate line 72 and the data line 80 on the substrate 70. Each of the red, green and blue sub-color filters 86a, 86b and 86c is located in a pixel region P defined by the gate line 72 and the data line 80. Specifically, each of the red, green and blue sub-color filters 86a, 86b and 86c overlaps portions of the gate and data lines 72 and 80. A black matrix 88 is formed over the thin film transistor T as an island pattern. An insulating layer (not shown) is formed over the entire surface of the color filter layer 86 and the black matrix 88. A pixel electrode 92 is formed on the insulating layer and is connected to the thin film transistor T.
As shown in FIG. 3B, the black matrix 88 is thickly formed to minimize parasitic capacitance in the COT structure. Therefore, when the rubbing direction rl is from a right upper portion to a left lower portion at a 45 degree angle from one corner of the pixel electrode, as shown in FIG. 3A, and from right to left, as shown in FIG. 3B, light leakage caused by a rubbing defect in region RD can occur.