Patent Document

The present invention claims the benefit of Korean Patent Application No. P2002-083198 filed in Korea on Dec. 24, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, to a method of fabricating a color filter substrate for a liquid crystal display device. 
     2. Discussion of the Related Art 
     Due to rapid development in information technology, display devices have evolved to process and display increasingly large amounts of information. Flat panel display technologies have been recently conceived and developed for display devices having small thickness, light weight, and low power consumption. Among these technologies, the liquid crystal display (LCD) device is already widely used for notebook computers, desktop monitors, and other application because of its superior resolution, color image display, and image quality. 
     In general, an LCD device includes an upper substrate, a lower substrate, and a liquid crystal layer disposed between the upper and lower substrates. The LCD device uses an optical anisotropy of a liquid crystal material and produces an image by varying the transmittance of light according to the arrangement of liquid crystal molecules by an electric field. 
     The lower substrate, which is usually referred to as an array substrate, includes thin film transistors and pixel electrodes. The lower substrate is fabricated through repeated photolithography processes to pattern a previously formed thin film. The upper substrate, which is usually referred to as a color filter substrate, includes a color filter layer for displaying color images. The color filter layer commonly includes sub-color filters of red (R), green (G), and blue (B). The color filter layer is formed by various methods including, for example, a dyeing method, an electro-deposition method, a pigment dispersion method, and a printing method. In general, the pigment dispersion method is more commonly used because it forms a fine pattern with good reproducibility. 
     FIGS. 1A to  1 D are cross-sectional views showing a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art. Here, the pigment dispersion method is used. 
     In FIG. 1A, a black matrix  15  is formed on an insulating substrate  10  by depositing a metal material or coating a resin and patterning the metal material or the resin through a photolithography process. The black matrix  15  blocks light leakage, which is caused by irregular operation of liquid crystal molecules, in regions except pixel electrodes of an array substrate (not shown). The black matrix  15  also prevents light from going into a channel of a thin film transistor of the array substrate. 
     As shown in FIG. 1B, a color resist  17 , which may be one of red, green and blue resists, for example a red one, is coated on the substrate  10  including the black matrix thereon by spin coating. A mask  20  having a light transmitting portion and a light blocking portion is disposed over the red resist  17 , and the red resist  17  is exposed to light using the mask  20 . Here, the red resist  17  is shown to have a negative property. That is, a portion of the red resist  17  that is not exposed to light is removed. 
     As shown in FIG. 1C, the red resist  17  of FIG. 1B is developed, and a red color filter pattern  17   a  is formed. Then, the red color filter pattern  17   a  is cured and hardened. 
     As shown in FIG. 1D, green and blue color filter patterns  17   b  and  17   c  are formed on the black matrix  15  through similar processes as shown in FIGS. 1B and 1C. Next, an overcoat layer  23  and a common electrode  25  are subsequently formed on the substrate  10  including the color filter patterns  17   a ,  17   b  and  17   c . The overcoat layer  23  protects the color filter patterns  17   a ,  17   b  and  17   c , and flattens the surface of the substrate  10  having the color filter patterns  17   a ,  17   b  and  17   c . The common electrode  25  is made of a transparent conductive material, such as indium-tin-oxide and indium-zinc-oxide. The overcoat layer  23  may be omitted. 
     In the fabrication method of the color filter substrate using the pigment dispersion, since the color filter substrate is fabricated by repeated processes of coating, exposing, developing, and curing of a color resist, the fabrication method is complicated, thereby requiring much time and equipment. To solve the above problem, a fabrication method of a color filter substrate using thermal imaging has been proposed, as disclosed for example in U.S. Pat. No. 6,242,140. 
     FIGS. 2A to  2 D show a method of fabricating a color filter substrate using thermal imaging according to the related art. 
     As shown in FIG. 2A, a black matrix  35  is formed on an insulating substrate  30  by depositing a metal material or coating a resin, and patterning the metal material or the resin by photolithography. 
     Then, as shown in FIG. 2B, a first color transcription film  40  is disposed over the substrate  30  including the black matrix  35 . The first color transcription film  40  includes a supporting film  40   a , a light-to-heat conversion (LTHC) layer  40   b , and a color filter layer  40   c.    
     Next, as shown in FIG. 2C, the first color transcription film  40  is adhered to the substrate  30  without bubbles. A laser head  50 , from which a laser beam is generated, is disposed over the first color transcription film  40 . The laser beam is applied to the first color transcription film  40  in a portion where a first color filter pattern will be formed later while the laser head  50  is reciprocated in a straight line. In the first color transcription film  40  exposed to the laser beam, the LTHC layer  40   b  transforms light absorbed from the laser beam into thermal energy, thereby emitting thermal energy. Then, the color filter layer  40   c  is transferred on the substrate  30  due to the emitted thermal energy. Here, the color filter substrate may be a stripe type where color filter patterns in a line have the same color. In that case, a first line is exposed to the laser beam by moving the laser head in a straight line, but second and third lines are skipped. Similarly, a fourth line is exposed to the laser beam. In this manner, all the lines of the first color filter pattern are exposed by the above method, and the first color transcription film  40  is removed. 
     As shown in FIG. 2D, the first color filter pattern  45   a  is formed between the adjacent black matrixes  35  on the substrate  30 . The first color filter pattern  45   a  may be a red color filter. A second color filter pattern  45   b  and a third color filter pattern  45   c  are formed through the same process shown in FIGS. 2B and 2C. The second and third color filer patterns  45   b  and  45   c  may be green and blue color filters, respectively. The substrate  30  having the color filter patterns  45   a ,  45   b  and  45   c  is placed in a hardening furnace, and the color filter patterns  45   a ,  45   b  and  45   c  are hardened. An overcoat layer  47  is formed on the color filter patterns  45   a ,  45   b  and  45   c . The overcoat layer  47  protects the color filter patterns  45   a ,  45   b  and  45   c  and flattens the surface of the substrate  30  otherwise having steps. A common electrode  49  is formed on the overcoat layer  47  by depositing a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide. 
     In the thermal imaging method, manufacturing throughput of the color filter substrate is influenced by an application direction of the laser beam, wherein the laser beam is applied to the transcription film in a direction parallel to a pixel length of the LCD device. For example, in a color filter substrate of a video graphic array (VGA) LCD device, which has a resolution of 640 by 480, the VGA LCD device has sub-pixels of 640 by 3 lines (i.e., 1920 lines). Thus, the laser head  50  must scan 640 times for each color filter pattern. Therefore, total number of scans is 1920. Additionally, a size of the pixel depends on the resolution being used (e.g., VGA, SVGA (super video graphic array), XGA (extended graphic array), and so on), thereby causing difficulty to have a laser beam fit for each pixel size. 
     The scanning of the laser head  50  may be accomplished in a direction parallel to a pixel width of the LCD device, thereby reducing the scanning times. This may be referred to as a horizontal laser scan. The manufacturing throughput of the color filter substrate is improved due to reduction of the scanning times. However, in this case, there is a problem that scanning traces may be formed at pixel regions, thereby reducing image quality. 
     FIGS. 3A and 3B show a color filter substrate fabricated by a thermal imaging method using the horizontal laser scan according to the related art. FIG. 3B is an enlarged view of region A in FIG.  3 A. 
     In FIGS. 3A and 3B, a substrate  30  includes a black matrix  35  and a color filter pattern  45  thereon. The black matrix  35  has an opening in which the color filter pattern  45  is placed. The color filter pattern  45  is formed by the thermal imaging method using a horizontal laser scan. A laser head  50  having a plurality of laser pixels  52  first scans the substrate  30  in a direction parallel to a length of a pixel P turning the laser pixel  52  repeatedly on and off. After the first scan, the laser head  50  is moved in the vertical direction of the substrate  30  in the context of the Figure by a width of the first scan, and a second scan is accomplished. Here, a scanning trace  55  is formed in a border between first and second scanning regions. The scanning trace  55  is situated on the color filter pattern  45 . The scanning trace  55  on the color filter pattern  45  lowers image qualities. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method of fabricating a color filter substrate for a liquid crystal display device that substantially obviates one or more of problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method of fabricating a color filter substrate for a liquid crystal display device that reduces a total number of manufacturing processes and reduces manufacturing costs. 
     Another object of the present invention is to provide a method of fabricating a color filter substrate for a liquid crystal display device that improves image qualities. 
     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, a method of fabricating a color filter substrate for a liquid crystal display device comprises steps of forming a black matrix on a substrate; adhering a color transcription film to the substrate; disposing a laser head over the color transcription film; repeatedly scanning the color transcription film so that end lines defined by each one of the repeated scans are located on the black matrix; and removing the color transcription film so that a color filter pattern remains in color filter pattern regions defined inside the black matrix. 
     In another aspect, a method of fabricating a color filter substrate for a liquid crystal display device, comprises steps of forming a black matrix on a substrate, the black matrix defining a plurality of openings as color filter pattern regions; adhering a color transcription film to the substrate having the black matrix formed thereon; disposing a laser head over the color transcription film, the laser head including a plurality of laser pixels; repeatedly scanning the color transcription film by controlling ON/OFF states of the laser pixels to define an exposure pattern, wherein end lines of each one of the repeated scans is located on the black matrix; and removing the color transcription film so that a color filter pattern remains in desired ones of the color filter pattern regions. 
     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: 
     FIGS. 1A to  1 D are cross-sectional views showing a method of fabricating a color filter substrate for a liquid crystal display (LCD) device according to the related art; 
     FIGS. 2A to  2 D are cross-sectional views showing a method of fabricating a color filter substrate using thermal imaging according to the related art; 
     FIGS. 3A and 3B are plan views showing a color filter substrate fabricated by a thermal imaging method using the horizontal laser scan according to the related art; 
     FIGS. 4A and 4B are views of a laser head used in accordance with the present invention; 
     FIG. 5 is a view showing a laser pixel of the laser head in FIGS. 4A and 4B; 
     FIG. 6 is a plan view of a color filter substrate according to the present invention; 
     FIG. 7 is a cross-sectional schematic view showing a color transcription film; 
     FIGS. 8A to  8 D are cross-sectional views showing a method of fabricating a color filter substrate in accordance with the present invention; 
     FIGS. 9A and 9B and FIGS. 10A and 10B plan are views showing a color filter substrate fabricated by a thermal imaging method according to an embodiment of the present invention; and 
     FIG. 11 is a plan view showing a color filter substrate fabricated by a thermal imaging method according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIGS. 4A and 4B show a laser head used in the present invention. FIG. 4A is a perspective view of the laser head used in the present invention, and FIG. 4B is a view showing a base side of the laser head. FIG. 5 shows a laser pixel of the laser head. 
     In FIGS. 4A,  4 B, and  5 , the laser head  160  has  224  laser pixels  162  arranged in a line. The laser pixel  162  may have a length L of about 5 μm to about 20 μm and a width W of about 3 μm. Of course, the laser pixel  162  may have a different size, such as a larger size, than that described above. In this example, the entire size of the laser pixels  162  in the laser head  160  is about 4480 μm by 3 μm, and the scan width of the laser head  160  is about 4480 μm. The laser pixel  162  of the laser head  160  is automatically operated by a computer system such that the laser pixel  162  turns on and off according to color filter patterns of red, green and blue. 
     FIG. 6 is a plan view of a color filter substrate according to the present invention. In FIG. 6, A 1  indicates a width of a pixel P, A 2  designates a length of the pixel P, B 1  expresses a width of a color filter pattern CP, and B 2  represents a length of the color filter pattern CP. A first distance between the color filter patterns CP horizontally adjacent in the context of the Figure (that is, a horizontal width of a black matrix BM) is represented by C 1 . A second distance between the color filter patterns CP vertically adjacent in the context of the Figure (that is, a vertical width of the black matrix BM) is marked by C 2 . The size of the pixel P depends on the resolution and the display size of the LCD device. Here, the pixel width A 1  is generally within a range of about 70 μm to about 100 μm, the pixel length A 2  is generally within a range of about 200 μm to about 350 μm, and the first and second distances C 1  and C 2  are generally within a range of about 5 μm to about 40 μm. 
     For example, in a XGA LCD device of 14.1 inch, the pixel P has a width A 1  of about 93 μm and a length A 2  of about 280 μm. The vertical width C 2  of the black matrix BM is about 24 μm. Thus, the length B 2  and width B 1  of the color filter pattern CP are about 256 μm and 69 μm, respectively. 
     FIG. 7 schematically shows a color transcription film. As shown in FIG. 7, the color transcription film  110  includes three layers: a supporting film  110   a ; a light-to-heat conversion (LTHC) layer  110   b ; and a color filter layer  110   c . The lowest supporting film  110   a , which supports the LTHC layer  110   b  and the color filter layer  110   c , includes a high molecular substance, such as polyester and polyethylene, having transparent and high transmittance characteristics in order to transmit the laser beam to the LTHC layer  110   b  therethrough. The LTHC layer  110   b  is formed on the supporting film  110   a  of a material that can efficiently convert light into heat. Accordingly, the LTHC layer  110   b  converts light energy from the laser head  160  into heat energy. The LTHC layer  110   b  may include an organic material, such as carbon black and IR (infrared) pigments, or an inorganic material such as a metal material (e.g., aluminum (Al), a metallic oxide, or an alloy of the above materials). The color filter layer  110   c , which is the layer to be transferred, is formed on the LTHC layer  110   b  and includes one of red, green and blue colors. 
     FIGS. 8A to  8 D show a method of fabricating a color filter substrate according to the present invention. 
     As shown in FIG. 8A, a black matrix  135  is formed on an insulating substrate  130  by depositing a metal material, such as chromium (Cr), or coating a resin, such as an epoxy. Then, the metal material or resin is patterned through photolithography. 
     Next, as shown in FIG. 8B, a first color transcription film  110 —which includes a supporting film  110   a , a light-to-heat conversion (LTHC) layer  110   b , and a color filter layer  110   c —is disposed over the substrate  130  including the black matrix  135  with the color filter layer  110   c  facing the substrate  130 . The first color transcription film  110  is adhered to the substrate  130  without bubbles, and a laser head  160  is disposed at a distance over the first color transcription film  110 . A laser beam of the laser head  160  is applied to the first color transcription film  110  as the laser head  160  scans the substrate  130 . 
     As shown in FIG. 8C, the first color transcription film  110  is removed after the whole substrate  130  is scanned. Accordingly, a first color filter pattern  145   a  is formed between the adjacent black matrixes  135  on the substrate  130 . In the example shown, the first color filter pattern  145   a  may be a red color filter. 
     The scanning of the laser head  160  in a thermal imaging method according to the present invention will be described hereinafter with reference to FIGS. 9A and 9B, and FIGS. 10A and 10B. FIGS. 9B and 10B show a color filter substrate fabricated by the thermal imaging method according to the first embodiment of the present invention while FIGS. 9A and 10A are provided for comparison. 
     Here, the scanning of the laser head  160  is accomplished with the laser head  160  parallel to a pixel width direction. In this example, a pixel has a length within a range of about 200 μm to 350 μm. The laser head  160  includes a plurality of laser pixels (not shown), and the laser head  160  has a length of about 4480 μm. The laser head length, which is a scanning width, corresponds to 14 to 20 pixels arranged in a vertical line in the context of the Figures. In the illustrated example, the scanning width corresponds to almost 15 pixels. A first scanning is accomplished in a horizontal direction in the context of the Figures, and a second scanning is carried out after the laser head  160  moves in a vertical direction by the scanning width. A border between the first and second scanning may be formed on the black matrix BM or on a color filter pattern to be formed later depending on the pixel length, which is determined from the resolution of a LCD device. 
     In a first exemplary embodiment, the pixel has a size of about 100 μm by about 300 μm, and the black matrix has the vertical width of about 26 μm for a 15.1 inch XGA LCD device. 
     FIG. 9A shows a typical first scan in a manner similar to that of FIG.  3 A. As shown in FIG. 9A, the laser head  160  horizontally scan the substrate with a width of about 4480 μm. In a first scanning, pixels from a first line to fifteenth line would be scanned, and a lower line LL 1  of a first scanning region would be undesirably placed on a color filter pattern CP 15  in the fifteenth line (fifteenth color filter pattern CP 15 ). More particularly, the lower line LL 1  of the first scanning region would be about 7 μm from the bottom of the fifteenth color filter pattern CP 15 . The lower line LL 1  of the first scanning region, which would also be a border line between the first scanning region and a second scanning region, would cause a horizontal line during driving of the related art LCD device. In contrast, in this exemplary embodiment of the present invention, the laser head moves by various distances in order to locate the border line LL 1  between the first and second scanning regions on the black matrix BM. That is, the laser head  160  does not move by regular widths, and therefore, the scanning regions may overlap or may be spaced apart (i.e., defining a gap) from each other. 
     Instead as shown in FIG. 9B, an upper line of the first scanning region is about 10 μm from the top PU 1  of the first pixel P 1 . Since the scan width is about 4480 μm, the lower line LL 1  of the first scanning region is situated on the place being 4490 μm from the top PU 1  of the first pixel P 1  (that is, on the black matrix BM). The lower line LL 1  of the first scanning region is 3 μm from the bottom of the fifteenth color filter pattern CP 15 . 
     Next, as shown in FIG. 10A, the laser head  160  would move by about 4480 μm from the lower line LL 1  of the first scanning region to a position of 4490 μm, and a second scanning would be performed. Thus, the lower line LL 2  of the second scanning region would be located on a place being about 8970 μm from the top PU 1  of the first pixel P 1  of FIG. 9B, and would also be situated on a color filter pattern CP 30  in the thirtieth line (thirtieth color filter pattern CP 30 ). That is, the lower line LL 2  of the second scanning region would be about 17 μm from the bottom of the thirtieth color filter pattern CP 30 . As a result, another horizontal line would be formed due to the lower line LL 2  of the second scanning region. 
     Therefore, as shown in FIG. 10B, the second scanning region starts according to the first exemplary embodiment at the point being about 20 μm from the lower line LL 1  of the first scanning region. Then, the lower line LL 2  of the second scanning region is about 8990 μm from the top PU 1  of the first pixel P 1 , and is located on the black matrix BM. As stated above, if nth scanning is accomplished by controlling a shift width of the laser head after (n−1)th scanning, the border between the scanning regions is located on the black matrix BM. Accordingly, degradation of image quality is prevented. 
     The shift width of the laser head is the scanning width ± the black matrix width C 2 , 4480 μm±26 μm, for example. Since the scan width depends on the number of the laser pixels and on the size of the laser pixel, the border lines between the scanning regions can be placed on the black matrix, which has a width within a range of 5 μm to 40 μm, by controlling the overlapping width or spacing distance between the scanning regions. 
     Next, as shown in FIG. 8D, a second color filter pattern  145   b  and a third color filter pattern  145   c  are formed on the substrate  130  by using second and third color transcription films with the same method above. The color filter patterns  145   a ,  145   b  and  145   c  are hardened in a hardening furnace under temperatures of about 200-300 degrees centigrade. An overcoat layer  147  and a common electrode  150  are subsequently formed on the color filter patterns  145   a ,  145   b  and  145   c . The overcoat layer  147  protects the color filter patterns  145   a ,  145   b  and  145   c  and flattens the surface of the substrate  130  otherwise having steps. The common electrode  150  is made of a transparent conductive material, such as indium-tin-oxide and/or indium-zinc-oxide. 
     FIG. 11 shows a color filter substrate fabricated by a thermal imaging method according to another exemplary embodiment of the present invention. In this second exemplary embodiment of the present invention, a border between the scanning regions is located on a black matrix by controlling some laser pixels of a laser head to be in an inactive state. 
     As shown in FIG. 11, the laser head  260  including a plurality of laser pixels  262  is disposed over the first color transcription film (not shown). Then, for example, a first laser scanning is performed horizontally with respect to FIG.  11 . When a lower line LL 1  of a first scanning region is located on a color filter pattern CPc, laser pixels  262  overlapping the color filter pattern CPc turn off, and the laser head  260  scans the substrate with off laser pixels  262 . 
     Next, the laser head  260  moves in a vertical direction, and at this time, a first end of the laser head  260  should correspond to the lower line LL 1  of the first scanning region. If a lower line of a second scanning region is located on a color filter pattern CPd, laser pixels  262  overlapping the color filter pattern CPd turn off as well, and the second scanning is accomplished. The off laser pixels have a shorter length than the pixel region of the color filter substrate. That is, the effective length of the laser head is rounded down to the next integral number of pixel regions to keep the boundary lines of the scan regions on the black matrix. In this second exemplary embodiment, because the borders between scanning regions are located on the black matrix BM, degradation of image quality is prevented. 
     In yet another exemplary embodiment of the present invention, the thermal imaging methods of the first and second exemplary embodiments can be mixed. 
     In the second exemplary embodiment, when the lower line of the scanning region is located on a lower part of the color filter pattern in the context of the Figure, laser pixels overlapping the color filter pattern turn off. That is, when the lower line of the scanning region is situated on a place being about 270 μm from the top of a pixel, which has a size of about 100 μm by 300 μm, 13 laser pixels from the bottom, 212 th  to 224 th  laser pixels, turn off. This scanning is inefficient. Therefore, the laser scanning is carried out by controlling an upper line of a scanning region within the vertical width of the black matrix, about 20 μm. Then, the scanning region may cover the color filter pattern, and scanning efficiency is improved. 
     It should be recognized that the present invention can be embodied in a number of alternative configurations and variations. For example, the present invention has been explained with the laser head being moved. However, the color filter substrate may be moved or a combination of the color filter substrate and the laser head may be moved. The invention has been described with the orientation of the laser head along the direction of the pixel regions to generally achieve improved efficiency. However, other orientations may be used to achieve scanning of the color filter substrate. It should also be recognized that the present invention can be utilized with other types of liquid crystal display devices, including in-plane switching mode (IPS) devices. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the color filter substrate and method of fabricating a color filter substrate of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.

Technology Category: 3