1. Field of the Invention
The present invention relates to an alignment material for a liquid crystal display (LCD) device, and more particularly, to an LCD device with a simplified manufacturing process using the same.
2. Discussion of the Related Art
Liquid crystal display (hereinafter, referred to as “LCD”) devices are becoming more important as a visual information transmitting medium. In order to compete, other various types of display devices are being developed. Therefore, superior operating conditions, such as low power consumption, thin size, light weight, high quality, and the like, are required to occupy a leading position among the various types of display devices.
Currently, LCD devices are used as a main component of flat panel display (FPD) devices because LCD devices satisfy both performance and mass productivity conditions described above. Accordingly, the LCD device is widely utilized in various types of applications, such as in televisions (TVs), navigation systems, and the like. Moreover, the LCD device is regarded as a key display device capable of replacing the existing cathode ray tube (CRT) dominated market.
Generally, LCD devices include a lower substrate referred to as a thin film transistor (TFT) array substrate, an upper substrate referred to as a color filter substrate, and a liquid crystal layer formed of a liquid crystal material filled in a space between the upper substrate and the lower substrate. In this instance, N×M pixels are arranged on the lower substrate in horizontal and vertical directions. Each unit pixel includes a thin film transistor for transmitting an image signal and a pixel electrode for forming an electric field. The upper substrate includes a color filter pattern, a black matrix, and the like. A vertical electric field is generated between a common electrode and a corresponding pixel electrode. The liquid crystal layer, which is filled in the space between the upper substrate and the lower substrate, is made of a material having an optically anisotropic property. In this instance, the liquid crystal is arranged differently depending upon the electric field to be generated between the pixel electrode and the common electrode, thereby generating a transmittance change according to a polarization property of light.
An alignment film is formed on the surfaces of the upper substrate and the lower substrate, respectively, that is to come in contact with the liquid crystal layer. The alignment film functions to control the direction of the electric field that is generated between the pixel electrode and the common electrode in a state where liquid crystal molecules have uniform alignment.
In general, polyimide corresponding to a polymeric material is generally utilized for the alignment film, and the alignment film is aligned in a certain direction to align the liquid crystal in a predetermined direction. In this case, various types of alignment methods may be utilized. An alignment method by rubbing is currently most widely used.
The alignment method by rubbing includes the steps of initially forming an alignment film on a substrate and rubbing the alignment film by using a rubbing membrane, thereby forming uniform microgrooves on the alignment film. Specifically, in the above-described method, liquid crystal molecules interact with the alignment film formed with the microgrooves formed by rubbing to control the alignment of the liquid crystal molecules. Therefore, the liquid crystal molecules may be uniformly aligned into a desired direction over the whole surface of the alignment film.
Hereinafter, a section structure of a TFT array substrate and a color filter substrate according to a related art will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the related art TFT array substrate 117 includes a gate electrode 103 formed of a metal layer on a substrate 101. A gate insulating layer 105 consisting of SiO2 or SiNx is provided on the substrate 101 including the gate electrode 103. An active layer pattern 107 patterned into a shape of an island is formed on the gate insulating layer 105. Source and drain electrodes 109a and 109b are formed on the active layer pattern 107 to overlap the active layer pattern 107 in a predetermined shape. In this instance, an inter-layer insulating layer 111 is formed on the substrate 101 including the source and the drain electrodes 109a and 109b. A pixel electrode 113 is formed on the inter-layer insulating layer 111 to be electrically connected with the drain electrode 109b via a contact hole (not shown) formed in the inter-layer insulating layer 111. Finally, an alignment film 115 is formed on the whole surface of the substrate including the pixel electrode 113.
As shown in FIG. 2, the color filter substrate 213 includes black matrices 203 made of a metal material or a black resin on a substrate 201. In this instance, the black matrixes 203 are formed around a pixel area. Color filter patterns 205a, 205b, and 205c, which are red, green, and blue, respectively, are formed between the black matrixes 203. An overcoat layer 207 is formed on the color filter patterns 205a, 205b, and 205c, and a common electrode 209 is formed on the overcoat layer 207. An alignment film 211 is formed on the whole surface of the substrate including the common electrode 209.
As shown in FIG. 3, a liquid crystal panel 300 is formed by bonding the TFT array substrate 117 and the color filter substrate 213 to each other and filling a space between the TFT array substrate 117 and the color filter substrate 213 with a liquid crystal layer 301. The liquid crystal layer 301 contacts with the alignment films 115 and 211. Because the liquid crystal layer 301 is formed between the TFT array substrate 117 and the color filter substrate 213, a light dielectric ratio changes due to an electric field.
As described above, the related art LCD device requires separate alignment films on the pixel electrode and the common electrode respectively. This is because the material used to form the pixel electrode and the common electrode consists of a metal oxide film, such as indium tin oxide (ITO) or indium zinc oxide (IZO). The metal oxide films cannot be used as alignment films. Therefore, in the LCD device of the related art, additional alignment films are required on the pixel electrode and the common electrode, thereby increasing the number of process steps and reducing productivity.