Abstract:
A substrate for a liquid crystal display includes: a line-shaped fine groove formed on the substrate; and a metal line at least formed within the fine groove. The substrate enables a decrease in the height difference between the metal line and the surface of the substrate, thereby enhancing reliability in manufacturing the liquid crystal display. In addition, the aperture ratio of the pixel is enhanced, brightness is enhanced, and high resolution is realized.

Description:
This nonprovisional application claims priority under 35 U.S.C. §119(a) on patent application Ser. No. 20939/2002 filed in Korea on Apr. 17, 2002, which is herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate for a liquid crystal display, and more particularly, to a substrate for a liquid crystal display in which metal lines including a gate line and a data line are formed to be suitable for realizing a high resolution in a large-sized screen. 
     2. Discussion of the Background Art 
     Generally, a liquid crystal display (LCD) includes a TFT (thin film transistor) array substrate on which thin film transistors (TFTs) and pixel electrodes are arranged and a color filter substrate facing the TFT array substrate on which color filters and a common electrode are formed, and a liquid crystal injected into a space between the TFT array substrate and the color filter substrate. These LCDs display images by using an optical switching property of the liquid crystal interposed between the two substrates. In recent times, LCDs are increasing in popularity as a next generation display device to replace the cathode ray tube (CRT) because of their light weight and slim characteristics. 
       FIG. 1  is a plan view schematically showing a configuration of metal lines formed on a substrate for an LCD. 
     As shown in  FIG. 1 , a plurality of metal lines are formed on a substrate for an LCD. For instance, the metal lines include a plurality of gate lines  110   a  to  110   n  ( 110 ) formed in a length direction and a plurality of data lines  120   a  to  120   n  ( 120 ) formed in a width direction and perpendicularly crossed with the gate lines. A plurality of gate line pads  111   a  to  111   n  ( 111 ) into which gate driving signals for respective pixels are inputted, are formed at one end of the gate lines  110 . A plurality of data line pads  121   a  to  121   n  ( 121 ) into which data driving signals for respective pixels are inputted are formed at one end of the data lines  120 . 
     Here, unit pixel  130  is defined as a region in which a pair of gate lines are crossed with a pair of data lines. 
     In detail, the data lines  110  and the gate lines  120  are made of a conductive material and applies a driving current to the TFT element corresponding to the pixel  130 . The data lines  110  and the gate lines  120  are formed by a method including the steps of depositing a metal film and a photoresist film on a substrate on which TFTs are arranged, and selectively removing the photoresist film and the metal film through a photolithography process. 
     As time progresses, the metal line including these gate lines and data lines is becoming increasingly lengthened according to a trend of increasing the size of LCDs. 
       FIG. 2  is a perspective view of a metal line to depict the resistance characteristic of the metal line. 
     When the length of the metal line is l, the sectional area is A, and the conductivity is 6, a total resistance of the metal line R equals to l/6A. Accordingly, if the flowing current is I, a voltage drop ΔV in the metal line is expressed by the following equation: ΔV=iR=il/6A. This relation means that when the sectional area A (including elements of the thickness and the line width) of the gate line  110  and the data line  120  is constant, the voltage drop ΔV depends on the respective lengths of the gate line  110  and the data line  120 . 
     As a result, although an equal driving voltage is applied to the gate line pad  111   a  and the data line pad  121   a from the drive IC (not shown) of the LCD, the voltages applied to the gate line  110  or the data line  120  varies at a specific location depending on the resistance. For example, according to the lengths of the gate lines  110  and the data lines  120 , a lower voltage is applied to a pixel (Pn of  FIG. 1 ) further away from the pads  111   a ,  121   a  than a pixel (Pa of  FIG. 1 ) placed nearer to the pads  111   a ,  121   a . Accordingly, the pixel (Pn of  FIG. 1 ) needs a longer charging time than the pixel (Pa of  FIG. 1 ) when the pixels (Pn and Pa) are charged up to a specific electric charge. In other words, if the resistance increases, the current flowing through under the same voltage decreases, so that the charging time is lengthened. 
     The extended charging time causes a signal delay phenomenon in which the frequency for driving the LCD panel is lowered. 
     In order to solve this problem, it is necessary to decrease an overall resistance of the metal line by decreasing the length of the metal line, or increasing the sectional area of the metal line. 
     However, upon considering the trend in increasing a size of the LCDs, it is substantially difficult to shorten the length of the metal line. 
     A background art method for increasing the sectional area of the metal line, includes increasing the line width or increasing the thickness of the metal line. 
     However, if the line width of the metal line increases and the thickness decreases, little improvement in the height difference corresponding to the decrease in the thickness is obtained, but the lowering in the aperture ratio of the pixel due to the increase in the line width results. The lowering phenomenon in the aperture ratio is described with reference to  FIG. 3 . 
       FIG. 3   a  and  FIG. 3   b  are sectional views of substrates for LCDs illustrating the variation in the aperture ratio depending on the increase in the line width of the metal line. Specifically,  FIG. 3   a  shows a status prior to increasing the line width of the metal line, and  FIG. 3   b  shows a status after the line width of the metal line increases. 
     The metal line for the gate line and the data line are generally made of an opaque metal. To this end, the increase in the line width allows the light transmission area of a substrate  320  to be decreased from L1 to L2. The decrease in the light transmission area causes more of the light irradiated from a backlight to be lost while light is transmitted from the substrate resulting in the aperture ratio of the pixel being lowered. 
     The occurrence of the aforementioned phenomenon is not restricted only to the transmission type LCD substrate but is applied to the reflection type LCD substrate likewise. 
     Of course, the problem of lowering in the aperture ratio can be resolved by increasing the thickness of the metal line instead of increasing the line width of the metal line. 
       FIG. 4  is a schematic view for illustrating that a crack is generated in the inorganic insulating film formed on the metal line. 
     As shown in  FIG. 4 , when the thickness of the metal line is increased, a serious height difference is generated between the metal line portion and the non-metal line portion. So, if the inorganic insulating film  330  is further deposited on the metal line  120 , a problem occurs in that a crack is generated in the inorganic insulating film  330 , so that many defective devices are mass-produced. Hence, the thickness of the metal line cannot be increased above a certain limit. 
     Because of the above problems, the background art method for forming the metal line has prevented process failures by decreasing the aperture ratio of the pixel so as to solve the signal delay problem. 
     However, in the manufacturing process of a large-sized, high brightness and high resolution LCD sought after at the present time, there is a problem in applying the aforementioned methods due to a limitation on the application. Especially, in order to realize a large-sized LCD, it is essentially required to decrease the resistance of the metal line. 
     SUMMARY OF THE INVENTION 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a substrate for a liquid crystal display. The substrate includes: a line-shaped fine groove formed on the substrate; and a metal line at least formed within the fine groove. 
     In an aspect of the present invention, there is provided a substrate for a liquid crystal display. The substrate includes: a plurality of first line-shaped fine grooves formed parallel to one another in a length direction on the substrate; a plurality of second line-shaped fine grooves formed parallel to one another in a width direction on the substrate; a first metal line at least formed within the first line-shaped fine grooves; and a second metal line at least formed within the second line-shaped fine grooves. 
     In another aspect of the present invention, there is provided a liquid crystal display. The liquid crystal display includes: a TFT array substrate including thin film transistors, pixel electrodes, a line for supplying current to the thin film transistors, and a fine groove formed on the TFT array substrate and in which the line is received to reduce a height difference between the line and the surface of the TFT array substrate; a color filter substrate facing the TFT array substrate, and on which a color filter and a common electrode are formed; and a liquid crystal layer interposed between the TFT array substrate and the color filter substrate. 
     According to the above liquid crystal display, it is possible to decrease the resistance of the metal line formed on the substrate. 
     In addition, the sectional area of the metal line can be increased and the resistance can be decreased, thereby achieving an objective of easily realizing a large-sized LCD. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the present invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the present invention and together with the description serve to explain principles of the present invention. In the drawings: 
         FIG. 1  is a plan view schematically showing a configuration of metal lines formed on a substrate for an LCD; 
         FIG. 2  is a perspective view of a metal line to depict the resistance characteristic of the metal line; 
         FIG. 3   a  and  FIG. 3   b  are sectional views of substrates for LCDs illustrating the variation in the aperture ratio depending on the increase in the line width of the metal line; 
         FIG. 4  is a schematic view for illustrating that a crack is generated in the inorganic insulating film formed on the metal line; 
         FIG. 5  is a schematic view of metal lines formed on a substrate for a liquid crystal display according to an embodiment of the present invention; 
         FIG. 6  is a schematic sectional view of the first metal line shown in  FIG. 5 ; and 
         FIG. 7  is a schematic sectional view of the second metal line shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to a preferred embodiment of the present invention with reference to the attached drawings. 
       FIG. 5  is a schematic view of metal lines formed on a substrate for a liquid crystal display according to an embodiment of the present invention. 
     As shown in  FIG. 5 , a substrate  530  for a liquid crystal display according to the present invention includes a plurality of first fine grooves  511  formed parallel to each other in a length direction on the substrate, and a plurality of second fine grooves  521  formed parallel to each other in a width direction perpendicular to the length direction on the substrate. A first metal line  510  including a gate line is formed at least within the first fine groove and a second metal line  520  including a data line is formed at least within the second fine groove  521 . 
     Width and thickness of the first and second fine grooves  511  and  521  can be concretely determined by the line width and thickness of the first and second metal lines  510  and  520  formed on the first and second fine grooves  511  and  521 . For instance, in an LCD of the background art, the first and second metal lines  510  and  520  have a line width ranging from 7 μm to 20 μm and a thickness ranging from 1,000 Å to 4,000 Å. Accordingly, the first and second fine grooves  511  and  521  are also formed to have a line width ranging from 7 μm to 20 μm and a thickness ranging from 1,000 Å to 4,000 Å. 
     A manufacturing process of the substrate for a liquid crystal display is described with reference to  FIG. 6 . 
       FIG. 6  is a schematic sectional view of the first metal line shown in  FIG. 5 . 
     First, referring to  FIG. 6   a , a substrate  530  for forming TFTs and pixel electrodes is prepared. The substrate  530  is made of glass or plastic. A first fine groove  511  for the formation of a first metal line  510  including a gate line is formed in a length direction on the substrate  530 . 
     In the meanwhile, if the substrate  530  is made of glass, the first fine groove  511  can be formed by an etch process. If the substrate  530  is made of plastic, the first fine groove  511  can be formed by a molding process using a die. 
     If the first fine groove  511  is formed on the substrate  530  by the etch process or the molding process, a first metal line  510  is formed on the first fine groove  511 . In more detail, a conductive material, for instance, aluminum or an aluminum alloy is deposited on the substrate  530 , a photoresist film is coated on the conductive material, the photoresist film is patterned by a photolithography process, the underlying conductive material is selectively removed by an etch process with the patterned photoresist film as a mask, and the patterned photoresist film is then removed. The finally remaining conductive material pattern forms the first metal line  510 . 
     The substrate formed as above does not cause a height difference problem between the uppermost surface of the first metal line  510  and the upper surface of the substrate  530  although it uses a thicker metal line than the metal line of the background art. Also, it is possible to further decrease the height difference by making the first fine groove  511  deeper. In other words, the height difference between the first metal line  510  and the substrate  530  decreases by the thickness of the substrate  530 . 
     Thus, as the height difference of the metal line  510  decreases, although an upper film such as an inorganic insulating film  610  is formed on the first metal line  510  as shown in  FIG. 6   b , the possibility of a crack occurring in the inorganic insulating film  610  decreases remarkably, such that yield in the manufacturing process of the LCDS is enhanced. In addition, as shown in  FIG. 6   b , since the sidewall of the metal line  510  is formed with a slope, the possibility of a crack occurring further decreases. 
     Also, since the metal line  510  decreases in line width but increases in thickness, it has an area that is equal to or greater than the area of the metal line in the background art. This means that resistance per unit length of the metal line decreases compared with the resistance of the background art. 
     In other words, the metal line according to the present invention achieves a low resistance characteristic and accordingly the signal delay and the signal distortion phenomenon due to the voltage drop in the metal line decrease remarkably. 
       FIG. 7  is a schematic sectional view of the second metal line shown in  FIG. 5 . 
     Referring to  FIG. 7   a , a substrate for a liquid crystal display includes a second fine groove  521  formed in a width direction on the substrate, an inorganic insulating film  710  formed on a predetermined portion of the substrate including the second fine groove  521 , and a second metal line  520  formed on the inorganic insulating film  710 . A passivation layer  720  is further formed on the second metal line  520  and the inorganic insulating film  710  as shown in  FIG. 7   b.    
     Particularly, the second metal line  520  is formed on the inorganic insulating film  710  as shown in  FIG. 7   a.    
     Here, the inorganic insulating film  710  is provided to insulate the first metal line  510  ( FIG. 5 ) and the second metal line  520  formed crosswise with the first metal line  510 . In more detail, the inorganic insulating film  710  is insertedly formed on a contact surface between the first metal line  510  and the second metal line  520  at the crossing portion of the first metal line  510  and the second metal line  520 , but is formed between the second fine groove  521  and the second metal line  520  as shown in  FIGS. 7   a  and  7   b  at a region other than the crossing portion. 
     Since the inorganic insulating film  710  is formed in a recessed shape like the shape of the second fine groove  521 , although the second metal line  520  having a thickness greater than that of the background art is formed, the height difference decreases remarkably compared with the height difference in the background art. As a result, although an upper film such as the passivation layer  720  is formed, the possibility of crack occurrence decreases. Also, as shown in  FIGS. 7   a  and  7   b , since the side portions of the second metal line  520  are formed with a slope, the possibility in crack occurrence decreases remarkably. 
     In the meanwhile, the forming processes of the second metal line  520 , the inorganic insulating film  710  and the passivation layer  720  can be formed by the same method as that of the first metal line  510 . 
     Thus, although the first and second metal lines  510  and  520  according to the present invention have a thickness greater than a thickness of the lines in the background art, they have a height difference less than a height difference in the background art, due to the existence of the fine grooves. As a result, the quality of the upper films formed on the metal lines  510  and  520 , i.e., the inorganic insulating film  610  and the passivation layer  720  is enhanced and the reliability in the manufacturing process is also improved. 
     In addition, the aperture ratio of the pixels and the luminance are enhanced, so that a high resolution can be obtained. 
     Further, it becomes possible to form the metal lines of the low resistance characteristic which is required in manufacturing a large-sized LCD without lowering of the aperture ratio or increase in the height difference. 
     In particular, in case the substrate of the present invention is used, a high quality large-sized LCD can be produced and a high resolution even in a small-sized LCD can be obtained. 
     The foregoing embodiment is merely exemplary and is not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.