1. Field of the Invention
The present invention relates to a thin film transistor substrate and a method for fabricating the same, and more particularly, to a thin film transistor substrate and a method for fabricating the same in which an aperture ratio can be improved.
2. Discussion of the Related Art
Demands for various display devices have increased with development of an information society. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Some of flat display devices have already been applied to displays or equipment.
Among the various flat display devices, liquid crystal display (LCD) devices have been most widely used due to advantageous characteristics of thin profile, lightness in weight, and low power consumption, whereby the LCD devices provide a substitute for a Cathode Ray Tube (CRT). In addition to mobile type LCD devices such as a display for a notebook computer or mobile terminal, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
The LCD device includes a color filter substrate provided with a color filter array, a thin film transistor substrate provided with a thin film transistor array, and a liquid crystal layer formed between the color filter substrate and the thin film transistor substrate.
The color filter substrate is provided with a color filter for displaying colors and a black matrix for preventing light leakage from occurring. The thin film transistor substrate is provided with a plurality of pixel electrodes formed in a matrix arrangement, wherein a data signal is separately supplied to the plurality of pixel electrodes. Also, the thin film transistor substrate is provided with a plurality of thin film transistors (TFTs), each thin film transistor for separately driving the pixel electrodes. The thin film transistor substrate further includes gate lines controlling the thin film transistors, and data lines supplying data signals to the thin film transistors.
The aforementioned thin film transistor substrate includes gate drive ICs for driving the gate lines and data drive ICs for driving the data lines. As the thin film transistor substrate increases in size and requires a high resolution, the number of required drive ICs increases.
However, since the data drive IC is more expensive than the other devices, a double rate driving (DRD) type thin film transistor substrate has been suggested to reduce its fabricating cost. In the DRD type thin film transistor substrate, adjacent pixel regions use one data line in common. Also, in the DRD type thin film transistor substrate, the number of gate lines needed is increased to two times, whereas the number of data lines needed is reduced to ½ times and the number of data drive ICs needed is also reduced to ½ times. In this case, even though the number of data lines is reduced, the same resolution as that of the related art thin film transistor substrate can be obtained.
FIG. 1 is a plane view illustrating a DRD type thin film transistor substrate of a liquid crystal display device according to the related art.
As shown in FIG. 1, in the DRD type thin film transistor substrate, since two adjacent sub pixels use one data line DL1, DL2, or DL3 in common, the number of data lines can be reduced to half of that of the data lines needed in the non-DRD type thin film transistor. However, since gate lines GL1, GL2, GL3 and GL4 are additionally provided in the DRD type thin film transistor substrate, an aperture ratio is reduced within the range of 8% to 12%.
As a variation, a fringe electric field mode thin film transistor substrate is provided, which operates liquid crystal molecules through a fringe electric field formed between a pixel electrode and a common electrode, which are overlapped with each other by interposing an insulating film therebetween. In the fringe electric field mode thin film transistor substrate, a ‘’ shaped common line is formed in the pixel region to connect common electrodes of pixel regions that use the data line DL in common. The ‘’ shaped common line is rotated at ±90° and parallel with the gate line GL and the data line DL.
The common line is overlapped with the pixel electrode to form a storage capacitor. When the pixel electrode is formed on the insulating film, if a distortion with respect to the substrate occurs, the capacitance of the storage capacitor of the pixel regions at both sides of the data line DL is varied, whereby a spot caused by a luminance difference may occur, which is undesirable.