Abstract:
The invention provides a color filter substrate and a method for manufacturing the same, including a substrate, a plurality of color filters, and a plurality of banks. The banks separate the color filters, and the angle between the sidewall and the substrate is about 60° to 90°. The banks of the invention efficiently prevent cross-contamination of color materials, thereby improving the resolution of an LCD panel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a color filter substrate, and in particular to banks thereon preventing cross-contamination of color materials. 
         [0003]    2. Description of the Related Art 
         [0004]    In general, an LCD comprises a liquid crystal layer disposed between a TFT array substrate and a color filter substrate. Manufacture of the color filter substrate comprises forming R, G, B organic materials in each pixel of the substrate, respectively. The color filter substrate is highest cost of the critical components of the LCD. In a 14.1-inch panel, the color filter substrate occupies 28% of total material cost, with backlight module and driving integrated circuits (IC) occupying 18% and 17%, respectively. 
         [0005]    Coloration of the color filter substrate can utilize dye, pigment dispersal, printing, electro-deposition, or inkjet printing methods, with pigment dispersal the most popular. First, fine particles of dyes (R, G, B) are averagely dispersed in a transparent photosensitive resin. The color resins are spun, exposed, and developed to form R, G, B patterns. Typically, black matrix (BM) is formed between the R, G, B patterns to prevent light leakage. Black matrix is conventionally formed by sputtering single layer chromium film. Composite film of chromium and chromium oxide, or carbon mixed resin can be selected as a black matrix. In addition, a passivation film and ITO electrode layer are formed on the black matrix. Because the liquid crystal box comprises the color filter substrate and the TFT array substrate, pixels of these substrates are aligned with each other, a procedure requiring expensive color photoresist, with corresponding lithography consuming considerable time and labor. Accordingly, the pigment dispersal method increases costs. 
         [0006]    U.S. Pat. No. 5,340,619 discloses a method of manufacturing a color filter substrate. First, a black matrix is formed on a substrate, and part of the black matrix is ablated by laser. The ablation regions are filled with color material by spin coating. After curing, only desired color material (such as R region) remains, and the color material in other ablation regions (such as G or B region) is removed by plasma or laser. Repeated laser ablation, spin coating, curing, and removing redundant material results in the completed color filter substrate. The process consumes considerable color material. Moreover, spin coating requires subsequent additional polishing to avoid cross-contamination of color materials. 
         [0007]      FIGS. 1A-1F  show an inkjet method reducing high cost of the pigment dispersal method. As shown in  FIG. 1A , a photosensitive bank layer  12  serving as a black matrix layer is formed on a substrate  10 .  FIGS. 1B-1C  show sequential steps in which the bank layer  12  is exposed by photomask  11  and developed to define a plurality of banks  14 . Angle θ between the banks  14  sidewalls and the substrate  10  is less than 60°.  FIG. 1D  shows a surface treatment resulting in banks  14  having a color material-phobic top surface and color material-philic sidewalls. As shown in  FIGS. 1E-1F , ablation regions are filled by ink  16  by color material nozzle  17 . After hard baking, the color filters  19  are formed, thereby completing a color filter substrate  18 . As shown in  FIG. 1G , mixed color materials  16  degrade quality of the color filter substrate  18 . 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The invention provides a method for manufacturing a color filter substrate, comprising providing a substrate, forming a bank layer on the substrate, ablating part of the bank layer to define a plurality of ablation regions and a plurality of banks, wherein the ablation regions are separated by the banks, processing a surface treatment, such that the banks have color material-phobic top surface, filling at least one color material into the ablation regions, respectively; and hard baking the color material. 
         [0009]    The invention further provides a color filter substrate, comprising a substrate, a plurality of color filters, and a plurality of banks, wherein the color filters are separated by the banks, and the sidewalls of the banks and the substrate form an angle of about 60′ to about 90°. 
         [0010]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0012]      FIGS. 1A-1G  are serial cross sections of a conventional process for color filter substrate; and 
           [0013]      FIGS. 2A-2E  are serial cross sections of process in an embodiment of the invention for color filter substrate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0015]    As shown in  FIG. 2A , the invention provides a bank layer  22  on a substrate  20 . The substrate  20  includes flexible transparent material (such as plastic) or inflexible transparent material (such as glass or quartz). The bank layer  22  may serve as a black matrix layer. Because the bank layer  22  is ablated, it can be photosensitive or photo-insensitive. Photosensitive material includes a liquid photoresist dissolved in solvent, a liquid resin, a dry film photoresist, or transfer film photoresist. For example, the photosensitive material can be acrylic resin, epoxy resin, or polyimide resin, wherein the resins have photosensitive functional groups. The photosensitive material may be mixed with dye, pigment, or carbon black to reduce transparency of the photosensitive material. The photo-insensitive material may be acrylic resin, epoxy resin, or polyimide resin. Similar to the photosensitive material, the photo-insensitive material may be mixed with dye, pigment, or carbon black. Photo-insensitive material does not need functional groups, thereby reducing the material cost. Alternatively, photo-insensitive material can be metal material such as chromium or chromium oxide. If wet photosensitive material is adopted as bank layer  22 , it is preferable to process a pre-hard baking to remove solvent from photosensitive material before ablation. In an embodiment, the pre hard baking is preferably at about 150° C. to 250° C., and more preferably at about 220° C. 
         [0016]    As shown in  FIG. 2B , a photo mask  21  is used to apply a removing process, part of the bank layer  22  is defined to banks  24  and recesses (for example, ablation regions  25 ) separated by the banks  24 . If lithography serves as removing process, the previously formed bank layer  22  is photosensitive material. If laser process such as solid state laser or eximer laser serves as removing process, the bank layer  22  can be inexpensive photo-insensitive material. Optionally, the laser process can directly write or combine a photo mask to define the banks  24 . The banks  24  defined by the removing process have sidewalls, which and substrate  20  form an angle θ′ of about 60° to 90°. Because of diffraction, exposure value of the top surface exceeds bottom of conventional banks, such that banks formed by conventional lithography have sidewalls contacting substrate at less than 60°. The banks  24  of the present embodiment have a thickness of about 0.5 μm to about 5.0 μm. 
         [0017]    As shown in  FIG. 2C , a surface treatment such as plasma treatment is then processed, providing banks  24  with color material-phobic top surface and color material-philic sidewalls. If the color material is hydrophilic, a suitable surface treatment is adopted to provide banks  24  with hydrophilic sidewalls and hydrophobic top surface. If color material is hydrophobic, another type of surface treatment is adopted to make banks having hydrophobic sidewalls and hydrophilic top surface. 
         [0018]    As shown in  FIG. 2D , color materials  26  are then filled into ablation regions  25  in turns. Apply a filling process to fill at least one color material into the ablation regions  25 , respectively. Note that although only one color material nozzle  27  is shown in  FIG. 2D , it is possible to utilize a plurality of color material nozzles (not shown) to fill different color materials  26  into different ablation regions  25  simultaneously or non-simultaneously. The color material  26  can be red ink, blue ink, green ink, or cyan ink. Color material  26  is optionally hydrophilic or hydrophobic, corresponding to the properties of the bank sidewalls. Because angle θ′ between the banks  24  sidewalls and the substrate  20  is about 60° to about 90°, the top surface width of the banks  24  will not reduce or disappear even with reduced critical dimension, thereby preventing cross-contamination of color materials. 
         [0019]    Finally, as shown in  FIG. 2E , the color material  26  is hard baked to form color filters  29  and further complete color filter substrate  28 . The preferable temperature, which baking process provides, of the hard bake process is about 150° C. to about 250° C., and more preferably 220° C. The color of color filters  29  is determined by previously filled color material  26 , such as red, green, blue, white, or cyan. 
         [0020]    The banks  24  of the invention have a wider top surface in smaller size, thereby avoiding color mixing. Accordingly, the color filter substrate of the invention is suitable for use in high-resolution LCD panels. 
         [0021]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.