Patent Abstract:
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method of fabricating a color filter for an LCD device. 
     A method of fabricating a color filter uses a mold (PDMS mold) having a plurality of grooves. 
     Particularly, the mold (PDMS mold) is attached to a substrate such that the plurality of grooves face into the substrate. When a color resin is dropped into a side opening of each groove, the color resin is injected into each groove of the mold (PDMS mold) by a capillary force. 
     After the mold (PDMS mold) having the injected color resin is cured, the mold (PDMS mold) is detached from the substrate and a color filter pattern is formed at a desired position. 
     As compared with a method of fabricating a color filter according to the related art, since an exposure step and an etching step are not required in a method of fabricating a color filter of the present invention, a method of fabricating a liquid crystal panel of high resolution does not have a limitation due to an exposure apparatus, and material cost and production time are reduced.

Full Description:
The present invention claims the benefit of Korean Patent Application No. 2003-31316 filed in Korea on May 16, 2003, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of fabricating a liquid crystal display device, and more particularly, to a method of forming a color filter layer for a liquid crystal display device. 
     2. Discussion of the Related Art 
     In general, a liquid crystal display device uses optical anisotropy and polarization properties of liquid crystal molecules to produce an image. For instance, the orientation of the liquid crystal molecules can be aligned in a specific direction controlled by an applied electric field. As the applied electric field changes, so does the alignment of the liquid crystal molecules. Due to the optical anisotropy of the liquid crystal, the refraction of incident light on the liquid crystal molecules also changes depending on the alignment direction of the liquid crystal molecules. Thus, by properly controlling an electric field applied to a group of liquid crystal molecules in respective pixels of a liquid crystal display device, a desired image can be produced by diffracting light. 
     There are many types liquid crystal displays (LCDs) and one of such types is an active matrix liquid crystal display (AM-LCD) having a matrix of pixels. AM-LCDs are the subject of significant research and development because of their high resolution and superiority in displaying moving images. In general, each of the pixels in an AM-LCD has a thin film transistor (TFT) and pixel electrode. 
       FIG. 1  is a schematic exploded perspective view of a twisted nematic (TN) mode liquid crystal display device according to the related art. In  FIG. 1 , a liquid crystal display device  10  includes a first substrate  20 , a second substrate  50  spaced apart from the first substrate  20 , and a liquid crystal layer  80  interposed between the first and second substrates  20  and  50 . The first substrate  20  includes gate lines  22  and data lines  24 . The crossing of the gate lines  22  and data lines  24  defines pixel regions “P” and each of the pixel regions “P” includes a thin film transistor “T.” In addition, the TFT “T” includes a gate electrode  26  connected to the gate line  22 , an active layer  28 , a source electrode  30  connected to the data line  24 , a drain electrode  32  spaced apart from the source electrode  30 . A transparent pixel electrode  34  connected to the drain electrode  32  is formed in the pixel region “P.” 
     The second substrate  50  includes a black matrix  52 , a color filter layer  54  and a common electrode  56 . The black matrix  52  is formed on the second substrate  50  corresponding to the gate lines  22 , the data lines  24  and the TFT “T” on the first substrate  20 . The black matrix  52  shields light from exterior and is formed of one of an opaque metal and an opaque resin. The color filter layer  54  includes red, green and blue sub-color filters  54   a ,  54   b  and  54   c  alternately disposed. Each sub-color filter corresponds one of the pixel regions “P” and is formed by coating, exposing and developing photosensitive resin. 
     A first linear polarizing plate  85  having a first polarization axis “C1” is formed outside the first substrate  20  and a second linear polarizing plate  90  having a second polarization axis “C2” perpendicular to the first polarization axis “C1” is formed outside the second substrate  50 . 
     A longitudinal electric field is induced perpendicularly between the pixel electrode  34  and the common electrode  56  by voltages applied to the pixel electrode  34  and the common electrode  56 . Such an electric field changes the alignment of the liquid crystal layer  80 , thereby changing light transmittance of the liquid crystal layer  80 . Thus, as light passes through the liquid crystal layer  80  and the color filter layer  54 , desired color images are obtained. 
     The color filter layer  54  may be formed by various methods including, for example, an electro-deposition method, a dyeing method and a pigment dispersion method. In the electro-deposition method, a color filter layer is formed on an electrode using an electrochemical reaction. The electro-deposition method has superiority in large-sized LCD devices and a low consumption of materials. However, the color filter layer formed through the electro-deposition method has a great deviation in property according to process condition. In the dyeing method, a color filter layer is formed by dyeing a dyeable resin. The color filter layer formed through the dyeing method has low reliability for ultraviolet (UV) light and chemicals. Accordingly, the pigment dispersion method is more commonly used. In the pigment dispersion method, a color filter layer is formed by coating and exposing a material where polyimidic pigments are dispersed. The pigments are insoluble in the solvent. 
       FIGS. 2A to 2D  are schematic perspective views showing a process of forming a color filter substrate for a liquid crystal display device according to the related art. 
     In  FIG. 2A , a black matrix  52  is formed on a substrate  50  having red, green and blue pixel regions “P R ,” “P G ” and “P B ” corresponding to pixel regions on a thin film transistor substrate (not shown) facing the substrate  50 . The black matrix  52  is formed of one of chromium (Cr) and opaque resin. A double layer of chromium/chromium oxide (Cr/CrOx) also can be used for forming the black matrix  52 . 
     In  FIG. 2B , a red resist layer  53  is formed on the entire surface of the substrate  50  having the black matrix  52  by coating a photosensitive color resist including red pigment. The photosensitive color resist is a negative type photoresist where a portion exposed to light remains after development. Even though not shown in  FIG. 2B , a mask having a transmissive portion and a shielding portion is disposed over the red resist layer  53 , such that the transmissive portion corresponds to the red pixel region “P R .” Light is then irradiated onto the red resist layer  53  through the transmissive portion of the mask and then the red resist layer  53  is developed. 
     In  FIG. 2C , a red sub-color filter  54   a  corresponding to the red pixel region “P R ” is formed on the black matrix  52  after the red resist layer  53  shown in  FIG. 2B  is developed. The red sub-color filter  54   a  then is cured with heat in a subsequent process. 
     In  FIG. 2D , green and blue sub-color filters  54   b  and  54   c  are formed to correspond to the green and blue pixel regions “P G ” and “P B ” by repeating a process similar to the process shown in  FIGS. 2A to 2C  with a photosensitive color resist including respective color pigment. Thus, a color filter layer  54  including the red, green and blue sub-color filters  54   a ,  54   b  and  54   c  is formed. 
     The above-described steps of exposing and developing are generally referred to as a photolithographic process. For instance, the process may include providing a mask on a resist layer and exposing the resist layer through a mask using an exposing apparatus. The exposing apparatus can be a lens projection exposing device where a resist layer is exposed by sequentially moving a substrate and a mask in a stepping manner to obtain multiple sub-color filters on the substrate. In other words, the mask and a platform having the substrate thereon are moved sequentially with respect to the exposing device to expose the resist layer and to form a plurality of patterns on the substrate with only one mask. However, since one large pattern is formed using several masks having a pattern corresponding to a portion of the large pattern, each mask for the stepping method has a margin for misalignment. This margin reduces an effective area of the mask. Moreover, as patterns become more miniature, the exposing apparatus including lenses and photo becomes more expensive. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a liquid crystal display device and a method of fabricating a liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method of forming a color filter layer for a large-sized high-resolution liquid crystal display device. 
     Another object of the present invention is to provide a method of forming a color filter layer through a soft lithographic method without an exposing apparatus. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method of forming a color filter layer includes forming a first sub-color filter on a substrate by placing a first mold having at least a first groove on the substrate and injecting a first color resin into the first groove, the substrate including first, second and third regions and the first groove corresponding to the first region; forming a second sub-color filter on the substrate by placing a second mold having at least a second groove on the substrate and injecting a second color resin into the second groove, the second groove corresponding to the first and second regions; and forming a third sub-color filter on the substrate by placing a third mold having at least a third groove on the substrate and injecting a third color resin into the third groove, the third groove corresponding to the first, second and third regions. 
     In another aspect, the method of forming a color filter layer includes attaching a first mold having at least a first groove on a substrate and forming a first channel between the first groove and the substrate; filling the first channel with a first color resin to form a first sub-color filter; attaching a second mold having at least a second groove on the substrate and forming a second channel between the second groove and the substrate; filling the second channel with a second color resin to form a second sub-color filter; attaching a third mold having at least a third groove on the substrate and forming a third channel between the third groove and the substrate; and filling the third channel with a third color resin to form a third sub-color filter. 
     In a further aspect, the method of fabricating a color filter substrate for a liquid crystal display device includes forming a black matrix on a substrate having first, second and third regions; attaching a first mold having a first groove on the substrate, the first groove corresponding to the first region, the first groove and the substrate constituting a first channel; filling the first channel with a first color resin to form a first sub-color filter; curing the first sub-color filter; detaching the first mold from the substrate; attaching a second mold having a second groove on the substrate, the second groove corresponding to the first and second regions, the second groove, the first sub-color filter and the substrate constituting a second channel; filling the second channel with a second color resin to form a second sub-color filter; curing the second sub-color filter; detaching the second mold from the substrate; attaching a third mold having a third groove on the substrate, the first groove corresponding to the first region, the third groove, the first sub-color filter, the second sub-color filter and the substrate constituting a third channel; filling the third channel with a third color resin to form a third sub-color filter; curing the third sub-color filter; detaching the third mold from the substrate; and forming a common electrode on a color filter layer including the first, second and third sub-color filters. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a schematic exploded perspective view of a twisted nematic (TN) mode liquid crystal display device according to the related art; 
         FIGS. 2A to 2D  are schematic perspective views showing a process of forming a color filter substrate for a liquid crystal display device according to the related art; 
         FIGS. 3A to 3D  are schematic perspective views showing a process of forming a red sub-color filter for a color filter layer according to an embodiment; 
         FIG. 4A to 4D  are schematic perspective views showing a process of forming a green sub-color filter for a color filter layer according to an embodiment; 
         FIG. 5A to 5C  are schematic perspective views showing a process of forming a blue sub-color filter for a color filter layer according to an embodiment; and 
         FIG. 6  is a schematic cross-sectional view of a liquid crystal display device having a color filter layer formed through a method according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings. 
       FIGS. 3A to 3D  are schematic perspective views showing a process of forming a red sub-color filter for a color filter layer according to an embodiment. 
     In  FIG. 3A , a first mold  200  may be disposed to contact a substrate  100  having red, green and blue pixel regions “P R ,” “P G ” and “P B .” The first mold  200  may be transparent and may be formed of elastomeric polymer such as polydimethylsiloxane (PDMS). The first mold  200  may include a plurality of first grooves “A” facing the substrate  100  and corresponding to the red pixel regions “P R .” As a result, the first grooves “A” may constitute a plurality of first channels “CH1” corresponding to the red pixel regions “P R .” 
     In  FIG. 3B , a red color resin  102  may be then disposed to contact one end of the first mold  200 , such that the red color resin  102  may be at an opening of the first grooves “A.” 
     In  FIG. 3C , the red color resin  102  may be injected into the first channels “CH1” between the first grooves “A” and the substrate  100  by a capillary force. Accordingly, the first channels “CH1” between the first grooves “A” and the substrate  100  may be gradually filled with the red color resin  102 . Time for filling up the first channels “CH1” with the red color resin  102  may be determined by a property of the color resin and a structure of the first channels “CH1” based on the following equation.
 
 t =(2η z   2 )/( R γ cos θ),
 
where t is a time for filling up the first channel with the color resin, η is a viscosity of the color resin, z is a length of the first channel, R is a hydraulic radius of the color resin, γ is an interface free energy (surface tension) between the color resin and air, and θ is a contact angle between the color resin and the mold.
 
     After filling up the first channel “CH1” with the red color resin  102 , the red color resin  102  may be cured with heat or light. For example, when the red color resin  102  is a photosensitive resin, light such as ultra violet (UV) is irradiated onto the red color resin  102  through the first mold  200 . Since the first mold  200  may be formed of transparent elastomeric polymer such as PDMS having a refractive index of about 1.4, light may be irradiated onto the red color resin  102  through the first mold  200 . When the red color resin  102  is a heat-curable resin, the red color resin  102  is cured through a heat treatment. After curing the red color resin  102  in the first channel “CH1,” the first mold  200  may be detached from the substrate  100 . 
     In  FIG. 3D , a plurality of red sub-color filters  104  corresponding to the red pixel regions “P R ” may be obtained after the first mold  200  shown in  FIG. 3C  is detached from the substrate  100 . Since the red sub-color filters  104  may be formed by filling the first channels “CH1” shown in  FIG. 3C  with the red color resin  102  shown in  FIG. 3C , a volume of the red sub-color filter  104 . may be substantially the same as the volume of the first channels “CH1” shown in  FIG. 3C  or the first grooves “A” shown in  FIG. 3C . 
       FIG. 4A to 4D  are schematic perspective views showing a process of forming a green sub-color filter for a color filter layer according to an embodiment. 
     In  FIG. 4A , a second mold  202  may be disposed to contact the substrate  100  having the red sub-color filters  104 . The second mold  202  may be transparent and may be formed of elastomeric polymer such as polydimethylsiloxane (PDMS). The second mold  202  may include a plurality of second grooves “A2” facing the substrate  100  and corresponding to the red and green pixel regions “P R ” and “P G .” As a result, the second grooves “A2” may constitute a second channel “CH2” corresponding to the green pixel regions “P G .” In other words, the second grooves “A2” may include the red sub-color filters  104  and the second channels “CH2.” 
     In  FIG. 4B , a green color resin  106  may be then disposed to contact one end of the second mold  202 , such that the green color resin  106  may be at an opening of the second grooves “A2.” 
     In  FIG. 4C , the green color resin  106  may be injected into the second channels “CH2” between the second grooves “A2,” the red sub-color filters  104  and the substrate  100  by a capillary force. Accordingly, the second channels “CH2” may be gradually filled up with the green color resin  106 . Time for filling up the second channels “CH2” with the green color resin  106  may be determined by a property of the color resin and a structure of the channel based on the above-mentioned equation. After filling up the second channels “CH2” with the green color resin  106 , the green color resin  106  may be cured with heat or light. 
     In  FIG. 4D , a plurality of green sub-color filters  108  corresponding to the green pixel regions “P G ” may be obtained after the second mold  202  shown in  FIG. 4C  is detached from the substrate  100 . A sum of volumes of the red and green sub-color filters  104  and  108  may be substantially the same as a volume of the second grooves “A2” shown in  FIG. 4C   
       FIG. 5A to 5C  are schematic perspective views showing a process of forming a blue sub-color filter for a color filter layer according to an embodiment. 
     In  FIG. 5A , a third mold  204  may be disposed to contact the substrate  100  having the red and green sub-color filters  104  and  108 . The third mold  204  may be transparent and may be formed of elastomeric polymer such as polydimethylsiloxane (PDMS). The third mold  204  may include a plurality of third grooves “A3” facing the substrate  100  and corresponding to the red, green and blue pixel regions “P R ,” “P G ,” and “P B .” As a result, the third grooves “A3” may constitute a plurality of third channels “CH3” corresponding to the blue pixel region “P B .” In other words, the third grooves “A3” may include the red sub-color filters  104 , the green sub-color filters  108  and the third channels “CH3.” 
     In  FIG. 5B , a blue color resin  110  may be disposed to contact one end of the third mold  204 , such that the blue color resin  110  may be at an opening of the third grooves “A3.” Even though not shown, the blue color resin  110  may be injected into the third channels “CH3” between the third grooves “A3,” the red sub-color filters  104 , the green sub-color filters  108  and the substrate  100  by a capillary force. Accordingly, the third channels “CH3” may be gradually filled up with the blue color resin  110 . Time for filling up the third channels “CH3” with the blue color resin  110  may be determined by a property of the color resin and a structure of the channel. After filling up the third channels “CH3” with the blue color resin  110 , the blue color resin  110  may be cured with heat or light. 
     In  FIG. 5C , a plurality of blue sub-color filters  112  corresponding to the blue pixel regions “P B ” may be obtained after the third mold shown in  FIG. 5B  is detached from the substrate  100 . A sum of volumes of the red, green and blue sub-color filters  104 ,  108  and  112  may be substantially the same as a volume of the third groove “A3” shown in  FIG. 5B . In addition, a color filter layer  120  including red, green and blue sub-color filters  104 ,  108  and  112  may be completed where the red, green and blue sub-color filters  104 ,  108  and  112  having a stripe shape may be alternately formed on an entire surface of the substrate  100 . 
     Further, color purity of the color filter layer of the present invention may be easily changed by changing types of color resin used therein. In addition, even though the above-illustrated method for forming a color filter layer  120  is for a liquid crystal display device, the method of forming the color filter layer according to the present invention may be applied to other devices including a color filter layer. Moreover, even though not shown in figures, the red, green and blue sub-color filters may be formed to have different shapes and thickness from each other by changing designs of the molds, for example, by differing heights of the grooves in the molds. 
       FIG. 6  is a schematic cross-sectional view of a liquid crystal display device having a color filter layer formed through a method according to an embodiment. In  FIG. 6 , a liquid crystal display (LCD) device  400  may include first and second substrates  100  and  300  facing and spaced apart from each other, and a liquid crystal layer “LC” interposed between the first and second substrates  100  and  300 . The first and second substrates  100  and  300  may include red, green and blue pixel regions “P R ,” “P G ” and “P B .” A gate line (not shown), a data line  314  and a thin film transistor (TFT) “T” connected to the gate line and the data line  314  may be formed on a top surface of the second substrate  300  in each pixel region “P R ,” “P G ” and “P B .” The TFT “T” may include a gate electrode  302  connected to the gate line, an active layer  306 , a source electrode  310  connected to the data line  314  and a drain electrode  312  spaced apart from the source electrode  310 . A transparent pixel electrode  316  may be formed to contact the drain electrode  312  in each pixel region “P R ,” “P G ” and “P B .” 
     A black matrix  101  may be formed on a bottom surface of the first substrate  100  to correspond to borders between the pixel regions “P R ,” “P G ” and “P B .” A color filter layer  120  including red, green and blue sub-color filters  104 ,  108  and  112  may be formed on the black matrix  101  through a method using molds of elastomeric polymer such as polydimethylsiloxane (PDMS). The red, green and blue sub-color filters  104 ,  108  and  112  may correspond to the red, green and blue pixel regions “P R ,” “P G ” and “P B ,” respectively. A common electrode  114  may be formed on the color filter layer  120 . 
     In an LCD device according to the present invention, since a color filter layer is formed through a soft lithographic process using a mold of an elastomeric polymer such as PDMS, a total process of forming the LCD device is simplified. The soft lithographic process using a mold of an elastomeric polymer may be used not only for an LCD device but also for other devices such as electroluminescent display device. In addition, a color filter layer including sub-color filters having thickness may be easily formed through a soft lithographic process using molds with grooves of different heights. In a plane view, a color filter layer formed through a soft lithographic process using a mold of an elastomeric polymer such as PDMS also may have one of a zigzag shape and a round shape by using molds with grooves of desired shapes. 
     Consequently, since a color filter layer is formed through a soft lithographic process using a mold of an elastomeric polymer such as PDMS without using an exposing apparatus, a production cost is reduced. In addition, since a process of forming a color filter layer is simplified, a process time is reduced and a production yield is improved. Moreover, since a color filter layer is formed to have a length up to about 2 meters using a capillary force, a soft lithographic process using a mold of an elastomeric polymer such as PDMS may be applied to a large-sized LCD device having high resolution. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the method of forming color filter layer and the method of fabricating liquid crystal display device using the same without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Classification (CPC): 6