1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and the method of fabricating the same, and more particularly to a method of fabricating the LCD device to prevent a malfunction due to the continuous inflow of direct current voltage into the outermost area of the LCD device.
2. Discussion of the Related Art
Typical liquid crystal display (LCD) devices use an optical anisotropic property and polarization properties of liquid crystal molecules to display images. The liquid crystal molecules have directional orientation characteristics resulting from their thin and long shape. An arrangement direction of the liquid crystal molecules can be controlled by applying an electrical field. Accordingly, when the electric field is applied, the polarization properties of light are changed according to the arrangement of the liquid crystal molecules such that the LCD devices display images.
The LCD device includes a first substrate, a second substrate and a liquid crystal layer interposed therebetween. A common electrode and a pixel electrode are respectively formed on the first and second substrates. The first and second substrates may be referred to as a color filter substrate and an array substrate, respectively. The liquid crystal layer is driven by a vertical electric field induced between the common and pixel electrodes. The LCD device usually has excellent transmittance and aperture ratio.
Among the known types of LCD devices, active matrix LCD (AM-LCD) devices, which have thin film transistors (TFTs) arranged in a matrix form, are the subject of significant research and development because of their high resolution and superior ability to display moving images.
FIG. 1 is a plan view of a pixel region of the array substrate according to the related art. As shown in FIG. 1, a plurality of gate lines 120 and a plurality of data lines 130 are formed on the substrate 110. The gate and data lines 120 and 130 cross each other to define a pixel region P on the substrate 110. A common line 150 spaced apart from each of the gate lines 120 is formed in the middle of the pixel region P.
A TFT “T” including a gate electrode 125, a semiconductor layer (not shown), a source electrode 132 and a drain electrode 134 is disposed at a crossing portion of the gate and data lines 120 and 130. The gate electrode 125 and the source electrode 134 are connected to the gate lines 120 and the data lines 130, respectively. The source and drain electrodes 132 and 134 are spaced apart from each other on the semiconductor layer. A pixel electrode 170 is formed in the pixel region “P” and contacts the drain electrode 134 through a drain contact hole CH1.
Accordingly, the common line 150 functions as a first electrode of a storage capacitor Cst. The pixel electrode 170 overlapped with a part of the common line 150 functions as a second electrode of the storage capacitor Cst. Therefore, the first and second electrodes and a gate insulating layer (not shown) made of a dielectric material and between the first and second electrodes constitute the storage capacitor Cst.
FIG. 2 is a plan view showing an outermost area of an array substrate for the LCD device according to the related art. As shown in FIG. 2, an array substrate 110 includes an active area AA and a non-active area NAA. The active area AA is a region in which images are displayed and the non-active area NAA is a region in which images are not displayed. The signal for the active area AA is transmitted through the signal line 165 and the common bridge line 175. Although not shown in FIG. 2, the signal line 165 may include diverse signal lines such as a gate bridge line, a data bridge line and a multi pattern search line. The diverse signal lines may be spaced apart from one another.
Since the common bridge line 175 is connected to the common line 150 (of FIG. 1), a common signal can be transmitted from a common voltage generator (not shown) on the array substrate 110 to the common electrode (not shown) on a color filter substrate (not shown) via the common bridge line 175. When the LCD device is driven, the voltage of the signal line 165 is not equal to the voltage of the common electrode at the non-active area NAA. Since the non-equality causes the potential difference between the common electrode and the signal line 165, direct current voltage DCV is continuously generated. The direct current voltage DCV continuously generated influences an array element (not shown) formed at the active area AA of the array substrate 110 via a liquid crystal layer (not shown). As a result, malfunctions such as flicker, cross talk and image sticking can occur in the LCD device.
FIG. 3 is a cross-sectional view taken along lines III-III of FIG. 2. As shown in FIG. 3, the LCD device includes a first substrate 105, a second substrate 110 and a liquid crystal layer 115 interposed therebetween. The first and the second substrates 105 and 110 face and are spaced apart from each other. The first and second substrates 105 and 110 include an active area AA and a non-active area NAA. The active area AA is a region in which images are displayed and the non-active area NAA is a region in which images are not displayed.
Moreover, a seal pattern 195 is formed at the edge portion of the first and second substrates 105 and 110. The seal pattern 195 may be made of thermosetting resin including a conductive material such as Ag paste and Au ball. Therefore, the seal pattern 195 can have electrical conductivity. A black matrix 192, a color filter layer 190 including R, G, B sub-color filters (not shown) and a common electrode 180 are sequentially formed on an inner surface of the first substrate 105. The common electrode 180 includes a transparent material such as an indium-tin-oxide (ITO) and an indium-zinc-oxide (IZO).
An array element, such as gate lines 120 (of FIG. 1), data lines 130 (of FIG. 1), a TFT T (of FIG. 1) and a pixel electrode 170 (of FIG. 1), is formed on an inner surface of the second substrate 110 corresponding to the active area AA. The signal line 165 and the common bridge line 175 spaced apart from each other are formed in the non-active area NAA. The common bridge line 175 transmits a common signal from a common voltage generator (not shown) on the second substrate 110 to the common electrode 180 on the first substrate 105 via a transparent pattern 185 and a seal pattern 195.
Even though the potentials of the common bridge line 175 and the common electrode 180 facing each other are substantially equal, the potentials of the signal line 165 and the common electrode 180 are different from each other. The potential difference between the signal line 165 and the common electrode 180 causes a continuous generation of direct current voltage DCV.
Accordingly, the liquid crystal molecules interposed in the liquid crystal layer 115 corresponding to the common electrode 180 and the signal line 165 may be degraded by the continuously generated direct current voltage DCV.
The liquid crystal molecules degraded by the direct current voltage DCV may move to the active area AA to cause a malfunction such as flicker, cross talk and image sticking, in the LCD device. As a result, the display quality of the LCD device is deteriorated.
USPTO Backgrounds
USPTO Backgrounds