Patent Document

[0001]    This application claims the benefit of Korean patent application Nos. 2000-64739 and 2000-64740, both filed on Nov. 1, 2000 in Korea, which is hereby incorporated by reference as if fully set forth herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display (LCD) device implementing selectable reflective and transmissive modes.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Generally, a transflective LCD device has advantages of both a transmissive LCD device and a reflective LCD device. Because the transflective LCD device uses a back light as well as an ambient light source, it is not dependent upon exterior light source conditions, and consumes relatively low power.  
           [0006]    [0006]FIG. 1 is an exploded perspective view illustrating a typical transflective LCD device. The transflective LCD device  11  includes an upper substrate  15  and a lower substrate  21  that are opposed to each other, and a liquid crystal layer  23  interposed therebetween. The upper substrate  15  and the lower substrate  21  are called a color filter substrate and an array substrate, respectively. On the upper substrate  15 , a black matrix  16  and a color filter layer  17  including a plurality of red (R), green (G), and blue (B) color filters are formed. The black matrix  16  surrounds each color filter such that an array matrix feature is formed. Further on the upper substrate  15 , a common electrode  13  is formed to cover the color filter layer  17  and the black matrix  16 .  
           [0007]    On the lower substrate  21  opposing the upper substrate  15 , thin film transistors (TFTs) “T”, as switching elements, are formed in shape of an array matrix corresponding to the color filter layer  17 . In addition, a plurality of crossing gate and data lines  25  and  27  are positioned such that each TFT “T” is located near each crossing portion of the gate and data lines  25  and  27 . The crossing gate and data lines define a pixel region “P”. On the pixel region “P”, a pixel electrode  19  is formed. The pixel electrode  19  includes a transmissive portion “A” and a reflective portion “C”.  
           [0008]    [0008]FIG. 2 is a schematic cross-sectional view illustrating operation modes of the typical transflective LCD device  11 . As shown, the transflective LCD device  11  includes the upper substrate  15  having the common electrode  13 , the lower substrate  21  having the pixel electrode  19 , the liquid crystal layer  23  interposed therebetween, and a back light  41  disposed below the lower substrate  21 . The pixel electrode  19  includes a reflective electrode  19   b  having a through-hole “A” and a transparent electrode  19   a  positioned below the reflective electrode  19   b.  The transparent electrode  19   a  is separated from the reflective electrode  19   b  by a passivation layer  20  interposed therebetween.  
           [0009]    For a reflective mode, the transflective LCD device  11  uses a first ray “B” of ambient light, which may radiate from an exterior natural light source or from an exterior artificial light source. The first ray “B” passes through the upper substrate  15  and is reflected by the reflective electrode  19   b  back through the liquid crystal layer  23 , which is aligned by the application of an electric field between the reflective electrode  19   b  and the common electrode  13 . Accordingly, the aligned liquid crystal layer  23  controls the first ray “B” so as to display an image.  
           [0010]    For a transmissive mode, the transflective LCD device  11  uses a second ray “F” of light, which radiates from the back light  41 . The second ray “F” sequentially passes through the transparent electrode  19   a,  the through-hole “A” of reflective electrodes  19   b  and the liquid crystal layer  23  which is aligned by the application of an electric field between the transparent electrode  19   a  and the common electrode  13 . Accordingly, the aligned liquid crystal layer  23  controls the second ray “F” so as to display an image.  
           [0011]    [0011]FIG. 3 is an expanded plan view illustrating a portion of an array substrate for a conventional transflective LCD device. As shown in FIG. 3, gate lines  25  are arranged in a transverse direction, and data lines  27  are arranged perpendicular to the gate lines  25 . Both the gate lines  25  and the data lines  27  are formed upon an array substrate  21  (in FIG. 1), and a pair of gate lines  25  and data lines  27  define a pixel region “P”. Each of thin film transistors (TFTs) “T” is arranged at a position where both the gate line  25  and the data line  27  cross one another. A pixel electrode  19  comprising both a transparent electrode  19   a  and a reflective electrode  19   b  is disposed on the pixel region “P” defined by the gate line  25  and data line  27 .  
           [0012]    Each TFT “T” includes a gate electrode  32  to which a scanning signal is applied, a source electrode  33  to which a video signal is applied, and a drain electrode  35  which inputs the video signal to the pixel electrode  19 . Further, each TFT “T” includes an active layer  34  between the source electrode  33  and the drain electrode  35 . A portion of the gate line  25  defines a storage capacitor “S” with a portion of the pixel electrode  19 . Furthermore, gate pads  29  and data pads  31  are respectively disposed at end portions of gate lines  25  and data lines  27 . The gate pads  29  and the data pads  31  are to be electrically connected with a drive IC (not shown).  
           [0013]    Still referring to FIG. 3, the pixel electrode  19  is a transflective electrode having both the transparent electrode  19   a  and the reflective electrode  19   b.  Specifically, the transparent electrode  19   a  is first formed on the pixel region “P”, and is electrically connected with the drain electrode  35 . Then, the reflective electrode  19   b  is formed over the transparent electrode  19   a,  and is also electrically connected with the drain electrode  35  via the transparent electrode  19   a.  Thus, the reflective electrode  19   b  has a through hole “A” corresponding to a transmissive portion of the LCD device  11  such that rays of back light  41  (in FIG. 2) can pass through the through hole “A” for function in the transmissive mode. Portion “C” of the reflective electrode  19   b  serves as a reflective portion of the LCD device  11  such that rays of the ambient light are thereby reflected.  
           [0014]    In the above-mentioned structure, however, two patterning processes are respectively required when forming the transparent electrode  19   a  and the reflective electrode  19   b.  At this time of patterning, the transparent electrode  19   a  and the reflective electrode  19   b  are corroded by an etching solution due to Galvanic corrosion. Accordingly, to solve this problem, an insulator (e.g., the passivation layer  20  of FIG. 2) is interposed between the transparent electrode  19   a  and the reflective electrode  19   b.    
           [0015]    With reference to FIGS. 4A to  4 D,  5 A to  5 D and  6 A to  6 D, a fabrication process for the conventional array substrate is explained. FIGS. 4A to  4 D are sequential cross-sectional views taken along line IV-IV of FIG. 3, FIGS. 5A to  5 D are sequential cross-sectional views taken along line V-V of FIG. 3, and FIGS. 6A to  6 D are sequential cross-sectional views taken along line VI-VI of FIG. 3.  
           [0016]    At first, as shown in FIGS. 4A, 5A and  6 A, a first metal is deposited and patterned upon a transparent substrate  21  such that a gate pad  29 , a gate line  25 , and a gate electrode  32  are formed. For the first metal, aluminum (Al) or aluminum neodymium (AlNd) is conventionally employed. The gate line  25  extends from and is connected with the gate pad  29 , and the gate electrode  32  protrudes from the gate line  25  (in FIG. 3). Thereafter, a gate-insulting layer  43  is formed on the transparent substrate  21  to cover the metal layer previously formed. The gate-insulating layer  43  may be an inorganic substance, such as silicon nitride (SiN x ) or silicon oxide (SiO 2 ). Subsequently, amorphous silicon (a-Si) and impurity-doped amorphous silicon (n + /p + a-Si) are formed in series on the gate-insulating layer  43 . The amorphous silicon and impurity-doped amorphous silicon are simultaneously patterned to form an active layer  34  and an ohmic contact layer  47 , respectively. The active layer  34  is formed on the gate-insulating layer  43 , particularly over the gate electrode  32  and the ohmic contact layer  47  is formed on the active layer  34 . Also, a source electrode  33  and a drain electrode  35  are formed of a second metal on the ohmic contact layer  47 . By depositing and patterning this second metal, not only are the source electrode  33  and the drain electrode  35  formed, but the data line  27 , a capacitor electrode  49  and a data pad  31  are also formed on the gate-insulating layer  43  such that the source electrode  33  extends from the data line  27 . The source electrode  33  and the drain electrode  35  are spaced apart from each other and respectively overlap opposite ends of the gate electrode  32 . The capacitor electrode  49  overlaps a portion of the gate line  25  to define the storage capacitor “S” of FIG. 3. Moreover, a portion of the ohmic contact layer  47  between the source electrode  33  and drain electrode  35  is eliminated to form a channel region “CH.” 
           [0017]    Now referring to FIGS. 4B, 5B and  6 B, a first passivation layer  51  is formed on and over the above-mentioned intermediates by depositing an organic substance such as BCB (benzocyclobutene) or an acryl-based resin. By patterning the first passivation layer  51 , a first drain contact hole  53  that exposes a portion of the drain electrode  35  is formed. At this time, a first capacitor contact hole  57  and a first data pad contact hole  61  are also formed by patterning the first passivation layer  51 . Furthermore, by patterning both the first passivation layer  51  and the gate-insulating layer  43 , an etching hole  55  corresponding to the through-hole “A” and a first gate pad contact hole  59  are formed. The first capacitor contact hole  57  exposes a portion of the capacitor electrode  49 , the first gate pad contact hole  59  exposes a portion of the gate pad  29 , and the first data pad contact hole  61  exposes a portion of the data pad  31 . Thereafter, a transparent conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO), is deposited upon the first passivation layer  51  having the holes and subsequently patterned to form a transparent electrode  19   a,  a gate pad terminal  65  and a data pad terminal  67 . The transparent electrode  19   a  electrically contacts the drain electrode  35  through the first drain contact hole  53 , and the gate pad terminal  65  electrically contacts the gate pad  29  through the first gate pad contact hole  59 . Additionally, the data pad terminal  67  electrically contacts the data pad  31  through the first data pad contact hole  61 . At this point, the transparent electrode  19   a  preferably overlaps portions of the gate line  25  and contacts the capacitor electrode  49 , and thus the transparent electrode  19   a  and the capacitor electrode  49  acts as one capacitor electrode in the storage capacitor “S”. Further, a portion of the gate line  25  acts as the other capacitor electrode in the storage capacitor “S”.  
           [0018]    Next, as shown in FIGS. 4C, 5C and  6 C, an insulating material such as silicon oxide, for example, is deposited upon the transparent electrode  19   a  and subsequently patterned to form a second passivation layer  69 . The second passivation layer  69  comprises a second drain contact hole  53   a  positioned over the drain electrode  35  and a second capacitor contact hole  57   a  over the capacitor electrode  49 . Thereafter, a third metal is deposited upon the second passivation layer  69  and subsequently patterned to form a reflective electrode  19   b  having a through-hole “A”. The third metal is preferably aluminum (Al) or aluminum alloy (e.g., aluminum neodymium (AlNd)) which have low resistance and high reflectance properties. The reflective electrode  19   b  electrically contacts the transparent electrode  19   a  via the second drain contact hole  53   a  and second capacitor contact hole  57   a  such that the reflective electrode  19   b  and the drain electrode  65  are electrically interconnected. Namely, a first portion of the reflective electrode  19   b  is electrically connected with the drain electrode  35  through the second drain contact hole  53   a,  and a second portion of the reflective electrode  19   b  is electrically connected with the capacitor electrode  49  through the second capacitor contact hole  57   a.    
           [0019]    Next, referring to FIGS. 4D, 5D and  6 D, exposed portions of the second passivation layer  69  are patterned to form a second gate pad contact hole  59   a  over the gate pad  29  and a second data pad contact hole  61   a  over the data pad  31 . Therefore, the conventional array substrate for the LCD device is complete.  
           [0020]    In the above-mentioned structure, the reason for forming the etching hole  55  corresponding the through-hole “A” is to get the uniform color purity of the light in both the transmissive mode and reflective mode. Namely, by matching the light-passing distances between the transmissive mode and reflective mode, the uniform color purity is achieved regardless of whether the ambient light is reflected in the reflective portion “C” or the artificial light passes through the transmissive portion “A” (i.e., through-hole).  
           [0021]    Further, since the second passivation layer  69  is disposed between the transparent electrode  19   a  and the reflective electrode  19   b,  the electrode corrosion caused by the etching solution (that etches the reflective electrode  19   b ) is prevented. Namely, Galvanic corrosion caused by the etching solution between the transparent electrode  19   a  and the reflective electrode  19   b  does not occur due to the fact that the second passivation layer  69  prevents the corrosion of the transparent electrode  19   a.  Now the mechanism wherein the corrosion is prevented will be described below.  
           [0022]    As well known, the equilibrium potential (oxidation potential) of the anode reaction of aluminum (Al) is lower than the equilibrium potential (reduction potential) of the cathode reaction of the transparent electrode, e.g., ITO or IZO. As a result, when Al and ITO/IZO are brought into contact with each other and immersed in the etching solution for the reflective electrode, the Al and the ITO/IZO exchange electrons therebetween while Galvanic corrosion proceeds in the interfaces between the Al, the etching solution and the ITO.  
           [0023]    However, when forming the passivation layer  69  between the transparent electrode  19   a  and the reflective electrode  19   b,  although Galvanic corrosion is prevented, additional processes, such as mask processes and patterning processes, are required. Namely, the second passivation layer  69 , as shown in FIG. 4D, is patterned to open the gate pad terminal  65  and the data pad terminal  67 .  
           [0024]    Furthermore, if the gate-insulating layer  43  and the first passivation layer  51  are not formed properly, these insulator (the gate-insulating layer  43  and the first passivation layer  51 ) have defects such as cracks and pin-holes therein. Thus, when etching the transparent conductive material (ITO or IZO) to form the transparent electrode  19   a,  the corrosion of the transparent material occurs due to the etching solution for the transparent conductive material. Namely, it is supposed that the transparent conductive material and the etching solution make contacts with the aluminum (patterned first metal) through pin-holes or the like formed in the gate-insulating layer and the first passivation layer.  
           [0025]    Accordingly, as mentioned before, the conventional array substrate needs additional fabricating processes and consumes more time and costs, and the gate line reacts with the transparent conductive material when defects are formed in the insulators, thereby decreasing the manufacturing yield of the LCD device.  
         SUMMARY OF THE INVENTION  
         [0026]    Accordingly, the present invention is directed to a transflective LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0027]    An object of the present invention is to provide a transflective LCD device having decreased manufacturing time and costs without Galvanic corrosion.  
           [0028]    Another object of the present invention is to provide a transflective LCD device having increased manufacturing yield.  
           [0029]    Additional features and advantages of the invention will be set forth in the description that 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.  
           [0030]    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 an array substrate for use in a transflective liquid crystal display device includes the steps of forming a gate line, a gate electrode and a gate pad all having a first layer and a second layer structure on a substrate; forming a gate-insulating layer on the substrate to cover the double-layered gate line, the double-layered gate electrode and the double-layered gate pad; forming an active layer and an ohmic contact layer over the gate electrode; forming a data line, source and drain electrodes on the ohmic contact layer, a capacitor electrode over the gate line and a data pad at the end of the data line; forming a first passivation layer to cover the data line, source and drain electrodes, the capacitor electrode and the data pad, the first passivation layer having a first drain contact hole to the drain electrode, a etching hole corresponding to a transmissive portion, a first capacitor contact hole to the capacitor electrode, a first gate pad contact hole to the gate pad, and a data pad contact hole to the data pad; forming a gate pad terminal, a data pad terminal and a transparent electrode in the transmissive portion, the gate pad terminal contacting the gate pad through the first gate pad contact hole, the data pad terminal contacting the data pad through the first data pad contact hole, and transparent electrode contacting the drain electrode and capacitor electrode through the first drain and capacitor contact holes; forming a second passivation layer to cover the transparent electrode, the gate pad terminal and the data pad terminal, the second passivation layer having a second drain contact hole over the drain electrode, a second capacitor contact hole over the capacitor electrode, a second gate pad contact hole over the gate pad, and a second data pad contact hole over the data pad; forming a corrosion-resistant metal layer on the second passivation layer; forming an aluminum-based layer on the corrosion-resistant metal layer; and patterning the aluminum-based layer and the corrosion-resistant metal layer so as to form a double-layered reflective electrode and expose the gate pad terminal and data pad terminal.  
           [0031]    The first layers of the gate line, gate electrode and gate pad are one of aluminum or aluminum neodymium. The second layers of the gate line, gate electrode and gate pad are titanium. The data line, source and drain electrodes, capacitor electrode and data pad are formed of chromium. The gate-insulating layer is a material selected from a group consisting of silicon oxide or silicon nitride. The gate pad terminal, data pad terminal and transparent electrode are formed of a transparent conductive material selected from a group consisting of indium tin oxide, indium zinc oxide and indium tin zinc oxide. The corrosion-resistant metal is molybdenum, while the aluminum-based layer is aluminum neodymium.  
           [0032]    In another aspect, a method of fabricating an array substrate for use in a transflective liquid crystal display device includes the steps of forming a gate line, a gate electrode and a gate pad all having a single-layered structure on a substrate; forming a gate-insulating layer on the substrate to cover the gate line, the gate electrode and the gate pad; forming an active layer and an ohmic contact layer over the gate electrode; forming a data line, source and drain electrodes on the ohmic contact layer, a capacitor electrode over the gate line, and a data pad at the end of the data line, thereby defining intermediate structures; forming a first passivation layer to cover the intermediate structures, the first passivation layer having a first drain contact hole to the drain electrode, a etching hole corresponding to a transmissive portion, a first capacitor contact hole to the capacitor electrode, a gate pad contact hole to the gate pad, and a data pad contact hole to the data pad; forming a gate pad terminal, a data pad terminal and a transparent electrode in the transmissive portion, the gate pad terminal contacting the gate pad through the gate pad contact hole, the data pad terminal contacting the data pad through the first data pad contact hole, and transparent electrode contacting the drain electrode and capacitor electrode through the first drain and capacitor contact holes; forming a second passivation layer to cover the transparent electrode, the gate pad terminal and the data pad terminal, the second passivation layer having a second drain contact hole over the drain electrode and a second capacitor contact hole over the capacitor electrode; forming a reflective electrode having the transmissive portion on the second passivation layer; and patterning the second passivation layer using a dry etching method so as to expose the gate pad terminal and the data pad terminal.  
           [0033]    In another aspect, a method of fabricating an array substrate for use in a transflective liquid crystal display device includes the steps of forming a gate line, a gate electrode and a gate pad on a substrate; forming a gate-insulating layer on the substrate to cover the gate line, the gate electrode and the gate pad; forming an active layer and an ohmic contact layer over the gate electrode; forming a data line, source and drain electrodes on the ohmic contact layer, a capacitor electrode over the gate line, and a data pad at the end of the data line, thereby defining first intermediate structures; forming a first passivation layer to cover the first intermediate structures, the first passivation layer having a first drain contact hole to the drain electrode, a etching hole corresponding to a transmissive portion, a first capacitor contact hole to the capacitor electrode, a first gate pad contact hole to the gate pad, and a first data pad contact hole to the data pad; forming a gate pad terminal, a data pad terminal and a transparent electrode in the transmissive portion, the gate pad terminal contacting the gate pad through the first gate pad contact hole, the data pad terminal contacting the data pad through the first data pad contact hole, and transparent electrode contacting the drain electrode and capacitor electrode through the first drain and capacitor contact holes, thereby defining second intermediate structures; forming a second passivation layer to cover the second intermediate structures, the second passivation layer having a second drain contact hole over the drain electrode, a second capacitor contact hole over the capacitor electrode, a second gate pad contact hole over the gate pad, and a second data pad contact hole over the data pad; forming a corrosion-resistant metal layer on the second passivation layer; forming an aluminum-based layer on the corrosion-resistant metal layer; patterning the aluminum-based layer so as to form a second layer of a double-layered reflective electrode having a transmissive portion; and pattering the corrosion-resistant metal layer so as to form a first layer of the double-layered reflective electrode having the transmissive portion.  
           [0034]    In another aspect, a method of fabricating an array substrate for use in a transflective liquid crystal display device includes the steps of forming a gate line, a gate electrode and a gate pad on a substrate; forming a gate-insulating layer on the substrate to cover the gate line, the gate electrode and the gate pad; forming an active layer and an ohmic contact layer over the gate electrode; forming a data line, source and drain electrodes on the ohmic contact layer, a capacitor electrode over the gate line, and a data pad at the end of the data line, thereby defining first intermediate structures; forming a passivation layer to cover the first intermediate structures, the passivation layer having a drain contact hole to the drain electrode, a etching hole corresponding to a transmissive portion, a capacitor contact hole to the capacitor electrode, a gate pad contact hole to the gate pad, and a data pad contact hole to the data pad; forming a gate pad terminal, a data pad terminal and a transparent electrode in the transmissive portion, the gate pad terminal contacting the gate pad through the gate pad contact hole, the data pad terminal contacting the data pad through the data pad contact hole, and transparent electrode contacting the drain electrode and capacitor electrode through the drain and capacitor contact holes, thereby defining second intermediate structures; laser-treating the transparent electrode; forming a corrosion-resistant metal layer to cover the second intermediate structures; forming an aluminum-based layer on the corrosion-resistant metal layer; patterning the aluminum-based layer so as to form a second layer of a double-layered reflective electrode having a transmissive portion; and pattering the corrosion-resistant metal layer so as to form a first layer of the double-layered reflective electrode having the transmissive portion  
           [0035]    In another aspect, a method of fabricating an array substrate for use in a transflective liquid crystal display device includes the steps of forming a gate line, a gate electrode and a gate pad on a substrate; forming a gate-insulating layer on the substrate to cover the gate line, the gate electrode and the gate pad; forming an active layer and an ohmic contact layer over the gate electrode; forming a data line, source and drain electrodes on the ohmic contact layer, a capacitor electrode over the gate line, and a data pad at the end of the data line, thereby defining first intermediate structures; forming a passivation layer to cover the first intermediate structures, the passivation layer having a drain contact hole to the drain electrode, a etching hole corresponding to a transmissive portion, a capacitor contact hole to the capacitor electrode, a gate pad contact hole to the gate pad, and a data pad contact hole to the data pad; forming a gate pad terminal, a data pad terminal and a transparent electrode in the transmissive portion, the gate pad terminal contacting the gate pad through the gate pad contact hole, the data pad terminal contacting the data pad through the data pad contact hole, and transparent electrode contacting the drain electrode and capacitor electrode through the drain and capacitor contact holes, thereby defining second intermediate structures; laser-treating the transparent electrode; forming a reflective metal layer to cover the second intermediate structures, the reflective metal layer having a enough thickness; forming a photo resist on the reflective metal layer; patterning the photo resist using a photolithography process to expose potions of the reflective metal layer; etching half of the exposed reflective metal layer; removing the photo resist completely using a wet stripper; and etching the residual reflective metal layer so as to form a reflective electrode.  
           [0036]    In another aspect, a transflective liquid crystal display device includes a substrate; at least one gate line and at least one gate electrode formed on the transparent substrate; a gate-insulating layer formed over the at least one gate line and the at least one gate electrode; a silicon layer formed on the gate-insulating layer, the silicon layer being positioned above the at least one gate electrode; a source electrode and a drain electrode formed on the silicon layer and spaced apart from each other with the silicon layer overlapped therebetween, wherein the at least one gate electrode, the source electrode, the drain electrode, and the silicon layer define a thin film transistor (TFT); at least one data line; a first passivation layer covering the at least one data line; a transparent electrode formed on the first passivation layer; and a reflective electrode formed on the transparent electrode.  
           [0037]    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  
       [0038]    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:  
         [0039]    [0039]FIG. 1 is an exploded perspective view illustrating a typical transflective LCD device;  
         [0040]    [0040]FIG. 2 is a schematic cross-sectional view illustrating an operation of a typical transflective LCD device;  
         [0041]    [0041]FIG. 3 is an expanded plan view illustrating a portion of an array substrate for a conventional transflective LCD device;  
         [0042]    [0042]FIGS. 4A to  4 D are sequential cross-sectional views taken along line IV-IV of FIG. 3;  
         [0043]    [0043]FIGS. 5A to  5 D are sequential cross-sectional views taken along line V-V of FIG. 3;  
         [0044]    [0044]FIGS. 6A to  6 D are sequential cross-sectional views taken along line VI-VI of FIG. 3;  
         [0045]    [0045]FIGS. 7A to  7 F are sequential cross-sectional views taken along line VII-VII of FIG. 3 according to a first embodiment of the present invention;  
         [0046]    [0046]FIGS. 8A to  8 F are sequential cross-sectional views taken along line VIII-VIII of FIG. 3 according to the first embodiment of the present invention;  
         [0047]    [0047]FIGS. 9A to  9 F are sequential cross-sectional views taken along line IX-IX of FIG. 3 according to the first embodiment of the present invention;  
         [0048]    [0048]FIGS. 10A to  10 D are sequential cross-sectional views taken along line X-X of FIG. 3 according to a second embodiment of the present invention;  
         [0049]    [0049]FIGS. 11A to  11 D are sequential cross-sectional views taken along line XI-XI of FIG. 3 according to the second embodiment of the present invention;  
         [0050]    [0050]FIGS. 12A to  12 D are sequential cross-sectional views taken along line XII-XII of FIG. 3 according to the second embodiment of the present invention;  
         [0051]    [0051]FIGS. 13A to  13 C are sequential cross-sectional views taken along line XIII-XIII of FIG. 3 according to a third embodiment of the present invention;  
         [0052]    [0052]FIGS. 14A to  14 C are sequential cross-sectional views taken along line XIV-XIV of FIG. 3 according to the third embodiment of the present invention;  
         [0053]    [0053]FIGS. 15A to  15 C are sequential cross-sectional views taken along line XV-XV of FIG. 3 according to the third embodiment of the present invention;  
         [0054]    [0054]FIGS. 16A to  16 C are sequential cross-sectional views taken along line XVI-XVI of FIG. 3 according to a fourth embodiment of the present invention;  
         [0055]    [0055]FIGS. 17A to  17 C are sequential cross-sectional views taken along line XVII-XVII of FIG. 3 according to the fourth embodiment of the present invention; and  
         [0056]    [0056]FIGS. 18A to  18 C are sequential cross-sectional views taken along line XVIII-XVIII of FIG. 3 according to the fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0057]    Reference will now be made in detail to the preferred embodiments of the present invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the principal of the present invention, a plan view and explanation thereof are omitted since a plan view of an inventive array substrate is somewhat similar to that of a conventional art shown in FIG. 3.  
         [0058]    [0058]FIGS. 7A to  7 F,  8 A to  8 F, and  9 A to  9 F are sequential cross-sectional views respectively taken along lines VII-VII, VIII-VIII, IX-IX of FIG. 3 according to a first embodiment of the present invention. In the first embodiment of the present invention, the gate electrode and gate line have double-layered structures using titanium (Ti) and aluminum-based material (e.g., aluminum neodymium (AlNd)). Furthermore, the reflective electrode also has double-layered structure using molybdenum (Mo) and aluminum (Al).  
         [0059]    Now, referring to FIGS. 7A, 8A and  9 A, a first metal and a second metal are deposited on a substrate  111  and then patterned to form a double-layered gate line  125  arranged transversely upon the substrate  111 , a double-layered gate pad  129  disposed at the end of the double-layered gate line  125  (in FIG. 3), and a double-layered gate electrode  132  extending from the double-layered gated line  125 . The first metal for the first layers  125   a,    129   a  and  132   a  is substantially aluminum-based material, such as aluminum neodymium (AlNd), while the second metal for the second layers  125   b,    129   b  and  132   b  is substantially titanium (Ti). Pure aluminum (Al) is conventionally used as a metal for the gate line  125 , gate pad  129  and gate electrode  132  because of its low resistance and reduced signal delay. However, pure aluminum is chemically weak when exposed to acidic processing and may result in formation of hillocks during high temperature processing. Accordingly, multi-layered aluminum structures, as shown in FIGS. 7A, 8A and  
         [0060]    [0060] 9 A, are used for the gate line  125 , pad  129  and electrode  132 . Since the second layers  125   b,    129   b  and  132   b  are formed of titanium (Ti), these second layers  125   b,    129   b  and  132   b  protect the first layers  125   a,    129   a  and  132   a  from the etching solution for the transparent conductive material although the gate-insulating layer and the passivation layer have cracks or pin-holes in a later steps, in contrast with the conventional art.  
         [0061]    Next, referring to FIGS. 7B, 8B and  9 B, a gate-insulating layer  143  is formed upon the entire surface of the substrate  111  to cover the patterned first and second metal layers. The gate-insulating layer  143  includes at least an inorganic substance, such as silicon oxide (SiO 2 ) or silicon nitride (SiN x ). Thereafter, an amorphous silicon (a-Si) and an impurity-doped amorphous silicon are sequentially formed and subsequently patterned into an island shape to form an active layer  134  and an ohmic contact layer  147  upon the gate-insulating layer  143 , especially over the double-layered gate electrode  132 . Thereafter, a third metal, especially chrome (Cr), is deposited upon the gate-insulating layer  143  to cover the ohmic contact layer  147  and then patterned to form a data line  127 , a source electrode  133 , a drain electrode  135 , a capacitor electrode  149  and a data pad  131 . The source electrode  133  protrudes from the data line  127 , and the drain electrode  135  is spaced apart from the source electrode  133 . The source electrode  133  and the drain electrode  135  overlap end portions of the active layer  134  with a center portion the active layer  134  positioned therebetween.  
         [0062]    As mentioned before, the data line  127  is perpendicular to the double-layered gate line  125 , and the data pad  131  is positioned at the end of the data line  127 . The capacitor electrode  149  overlaps a portion of the double-layered gate line  125 . An exposed portion of the ohmic contact layer  147  is etched away between the source electrode  133  and the drain electrode  135 . At this point, since the top portions of the gate line  125 , gate pad  129  and gate electrode  132  are formed of titanium (Ti), the firstly formed metal (i.e., the gate line  125 , the gate pad  129  and the gate electrode  132 ) are not eroded or deteriorated by the etchant for chrome (i.e., third metal) although the gate-insulating layer  143  has cracks or pin-holes.  
         [0063]    Referring to FIGS. 7C, 8C and  9 C, a first passivation layer  151  is formed upon the source electrode  133 , the drain electrode  135 , the capacitor electrode  149  and the data line  131 . The first passivation layer  151  includes at least one of an organic insulating material and an inorganic material. By patterning the first passivation layer  151 , a first drain contact hole  153  that exposes a portion of the drain electrode  135  is formed. At this time, a first capacitor contact hole  157  and a first data pad contact hole  161  are also formed by patterning the first passivation layer  51 . Furthermore, by patterning both the first passivation layer  151  and the gate-insulating layer  143 , an etching hole  155  corresponding to the through-hole “A” and a first gate pad contact hole  159  are formed. The first capacitor contact hole  157  exposes a portion of the capacitor electrode  149 , the first gate pad contact hole  159  exposes a portion of the gate pad  29 , and the first data pad contact hole  161  exposes a portion of the data pad  131 .  
         [0064]    Thereafter, a transparent conductive material, such as indium tin oxide (ITO), indium zinc oxide (IZO) or indium tin zinc oxide (ITZO), is deposited upon the first passivation layer  151  having the holes and subsequently patterned to form a transparent electrode  119   a,  a gate pad terminal  165  and a data pad terminal  167 . The transparent electrode  119   a  electrically contacts the drain electrode  135  through the first drain contact hole  153 , and the gate pad terminal  165  electrically contacts the double-layered gate pad  129  through the first gate pad contact hole  159 . Additionally, the data pad terminal  167  electrically contacts the data pad  131  through the first data pad contact hole  161 . At this point, the transparent electrode  119   a  preferably overlaps portions of the double-layered gate line  125  and contacts the capacitor electrode  149 , and thus the transparent electrode  119   a  and the capacitor electrode  149  acts as a first capacitor electrode in the storage capacitor “S” (in FIG. 3). Further, a portion of the double-layered gate line  125  acts as a second capacitor electrode in the storage capacitor “S” (in FIG. 3).  
         [0065]    Now referring to FIGS. 7D, 8D and  9 D, an insulating material such as silicon oxide or silicon nitride, for example, is deposited upon the transparent electrode  119   a  and subsequently patterned to form a second passivation layer  169 . The second passivation layer  169  comprises a second drain contact hole  153   a  positioned over the drain electrode  135  and a second capacitor contact hole  157   a  over the capacitor electrode  149 . At this time, a second gate pad contact hole  159   a  and a second data pad contact hole  161   a  are also formed by patterning the second passivation layer  169 . As shown in FIGS. 8D and 9D, the second gate pad contact hole  159   a  exposes a portion of the double-layered gate pad  129 , and the second data pad contact hole  161   a  exposes a portion of the data pad  131 .  
         [0066]    Next, referring to FIGS. 7E, 8E and  9 E, molybdenum (Mo)  166  and aluminum-based material (e.g. aluminum neodymium (AlNd))  168  are formed in series upon the second passivation layer  159  having the second contact holes.  
         [0067]    Thereafter, referring to FIGS. 7F, 8F and  9 F, molybdenum (Mo)  166  and aluminum-based material  168  are patterned using a mixed etching solution with phosphoric acid, acetic acid and nitric acid, thereby forming a first reflective electrode  166   a  and a second reflective electrode  168   a  which have a through-hole “A”. The first reflective electrode  166   a  and the second reflective electrode  168   a  act together as the reflective electrode  19   b  of FIG. 4. The first and second reflective electrodes  166   a  and  168   a  electrically contact the transparent electrode  119   a  via the second drain contact hole  153   a  and second capacitor contact hole  157   a  such that the first and second reflective electrodes  166   a  and  168   a  and the drain electrode  135  are electrically interconnected. Further, the etching hole  155  corresponding to the through-hole “A” is opened to form the transparent portion. Additionally, the gate pad terminal  165  and the data pad terminal  167  are also exposed when forming the first and second reflective electrodes  166   a  and  168   a.  Therefore, the array substrate for the LCD device is complete according to the first embodiment of the present invention.  
         [0068]    As described before, the additional processes for forming the second gate pad contact hole  159   a  and second data pad contact hole  161   a  are not required because these pad contact holes are formed together with the etching hole  155  and second capacitor contact hole  157   a,  thereby decreasing the manufacturing process and increasing the manufacturing yield. Furthermore, although the gate-insulating layer  143  and the first passivation layer  151  have defects such as cracks or pin-holes, the firstly formed metal layer are not deteriorated due to the fact that the top potion thereof is formed of titanium (Ti) having corrosion-resisting characteristics.  
         [0069]    [0069]FIGS. 10A to  10 D,  11 A to  11 D and  12 A to  12 D are sequential cross-sectional views respectively taken along lines X-X, XI-XI and XII-XII of FIG. 3 according to a second embodiment of the present invention. In the second embodiment, the gate line, the gate pad, the gate electrode and the reflective electrode altogether have single-layered structures.  
         [0070]    Referring to FIGS. 10A, 11A and  12 A, a first metal is deposited and patterned upon a transparent substrate  111  such that a gate pad  129 , a gate line  125 , and a gate electrode  132  are formed. As a material for the first metal, aluminum (Al), aluminum neodymium (AlNd), tungsten (W), chromium (Cr) or molybdenum (Mo) is conventionally employed. Alternatively, the gate line  125 , gate pad  129  and the gate electrode  132  can have the double-layered structures as described in the first embodiment (in FIGS. 7A, 8A and  9 A) of the present invention. The gate line  125  extends from and is connected with the gate pad  129 , and the gate electrode  132  protrudes from the gate line  125  (in FIG. 3). Thereafter, a gate-insulating layer  143  is formed on the transparent substrate  111  to cover the metal layer previously formed. The gate-insulating layer  143  may be an inorganic substance, such as silicon nitride (SiN x ) or silicon oxide (SiO 2 ). Subsequently, amorphous silicon (a-Si) and impurity-doped amorphous silicon (n + /p + a-Si) are formed in series on the gate-insulating layer  143 . The amorphous silicon and impurity-doped amorphous silicon are simultaneously patterned into an island shape to form an active layer  134  and an ohmic contact layer  147 , respectively. The active layer  134  is formed on the gate-insulating layer  143 , particularly over the gate electrode  132 , and the ohmic contact layer  147  is formed on the active layer  134 . Also, a source electrode  133  and a drain electrode  135  are formed of a second metal on the ohmic contact layer  147 . By depositing and patterning this second metal, not only are the source electrode  133  and the drain electrode  135  formed, but the data line  127 , a capacitor electrode  149  and a data pad  131  are also formed on the gate-insulating layer  143  such that the source electrode  133  extends from the data line  127 . The source electrode  133  and the drain electrode  135  are spaced apart from each other and respectively overlap opposite ends of the gate electrode  132 . The capacitor electrode  149  overlaps a portion of the gate line  125  to define the storage capacitor “S” of FIG. 3. Moreover, a portion of the ohmic contact layer  147  between the source electrode  33  and drain electrode  35  is eliminated to form a channel region.  
         [0071]    Now referring to FIGS. 10B, 11B and  12 B, a first passivation layer  151  is formed on and over the above-mentioned intermediates by depositing an organic substance, such as BCB (benzocyclobutene) or an acryl-based resin, or an inorganic substance, such as silicon oxide or silicon nitride. By patterning the first passivation layer  151 , a first drain contact hole  153  that exposes a portion of the drain electrode  135  is formed. At this time, a first capacitor contact hole  157  and a first data pad contact hole  161  are also formed by patterning the first passivation layer  151 . Furthermore, by patterning both the first passivation layer  151  and the gate-insulating layer  143 , an etching hole  155  corresponding to the through-hole “A” and a first gate pad contact hole  159  are formed. The first capacitor contact hole  157  exposes a portion of the capacitor electrode  149 ; the first gate pad contact hole  159  exposes a portion of the gate pad  129 ; and the first data pad contact hole  161  exposes a portion of the data pad  131 .  
         [0072]    Thereafter, a transparent conductive material, such as indium tin oxide (ITO), indium zinc oxide (IZO) or indium tin zinc oxide (ITZO), is deposited upon the first passivation layer  151  having the holes and subsequently patterned to form a transparent electrode  119   a,  a gate pad terminal  165  and a data pad terminal  167 . The transparent electrode  119   a  electrically contacts the drain electrode  135  through the first drain contact hole  153 , and the gate pad terminal  165  electrically contacts the gate pad  129  through the first gate pad contact hole  159 . Additionally, the data pad terminal  167  electrically contacts the data pad  131  through the first data pad contact hole  161 . At this point, the transparent electrode  119   a  preferably overlaps portions of the gate line  125  and contacts the capacitor electrode  149 , and thus the transparent electrode  119   a  and the capacitor electrode  149  acts as a first capacitor electrode in the storage capacitor “S” (in FIG. 3). Further, a portion of the gate line  125  acts as a second capacitor electrode in the storage capacitor “S”.  
         [0073]    Next, as shown in FIGS. 10C, 11C and  12 C, an insulating material such as silicon oxide, for example, is deposited upon the transparent electrode  119   a  and subsequently patterned to form a second passivation layer  169 . The second passivation layer  169  includes a second drain contact hole  153   a  positioned over the drain electrode  135  and a second capacitor contact hole  157   a  over the capacitor electrode  149 .  
         [0074]    Thereafter, a third metal is deposited upon the second passivation layer  169  and subsequently patterned to form a reflective electrode  119   b  having a through-hole “A”. The second metal is preferably aluminum (Al) or aluminum alloy (e.g., aluminum neodymium (AlNd)) which have low resistance and high reflectance properties. Additionally, a photo resist (not shown) is used for patterning the third metal. The reflective electrode  119   b  electrically contacts the transparent electrode  119   a  via the second drain contact hole  153   a  and second capacitor contact hole  157   a  such that the reflective electrode  119   b  and the drain electrode  165  are electrically interconnected. Namely, a first portion of the reflective electrode  119   b  is electrically connected with the drain electrode  135  through the second drain contact hole  153   a,  and a second portion of the reflective electrode  119   b  is electrically connected with the capacitor electrode  149  through the second capacitor contact hole  157   a.    
         [0075]    Next, referring to FIGS. 10D, 11D and  12 D, exposed portions of the second passivation layer  169  are patterned to exposed the gate pad terminal  165  and data pad terminal  167 . At this point, there are two methods of patterning the second passivation layer  169 .  
         [0076]    In the first method of pattering the second passivation layer  169 , the photo resist for forming the reflective electrode  119   b  is first removed and subsequently etches the exposed second passivation layer  169  using a dry etching method. At this time, the reflective electrode  119   b  functions as a etch stopper. Therefore, the third metal for the reflective electrode  119   b  should be very resistant to the dry etching with the low resistance and high reflectance properties.  
         [0077]    In the second method of patterning the second passivation layer  169 , the exposed second passivation layer  169  is first etched using a dry etching method before removing the photo resist for the reflective electrode  119   b.  Further in the second method, an ash process is employed to remove the photo resist for the reflective electrode  119   b.  If the photo resist for the reflective electrode  119   b  is removed by a wet stipper using a wet etching method, Galvanic corrosion occurs between the reflective electrode  119   b  and the transparent electrode  119   a  because the wet stripper is an electrolytic solution. Therefore, when using the ash process for removing the photo resist, Galvanic corrosion does not occur between the reflective electrode  119   b  and the transparent electrode  119   a.    
         [0078]    Accordingly, from one of the above-mentioned methods for patterning the second passivation layer  169 , the gate pad terminal  165  and the data pad terminal are completely exposed. Additionally, the second passivation layer  169  only remains under the reflective electrode  119   b,  as shown in FIGS. 10D, 11D and  12 D.  
         [0079]    In the second embodiment of the present invention, since the second passivation layer is etched using the reflective electrode or photo resist on the reflective electrode as masks, additional mask process is not required to expose the gate and data pad terminals. Therefore, the manufacturing processes are reduced.  
         [0080]    [0080]FIGS. 13A to  13 C,  14 A to  14 C and  15 A to  15 C are sequential cross-sectional views respectively taken along lines XIII-XIII, XIV-XIV and XV-XV of FIG. 3 according to a third embodiment of the present invention. In the third embodiment, the gate line, the gate pad and the gate electrode altogether have single-layered structures, while the reflective electrode has a double-layered structure. Additionally, since FIGS. 13A, 14A and  15 A are the same as FIGS. 10B, 11B and  12 B of the second embodiment, the third embodiment of the present invention is briefly described and some explanation of the third embodiment is omitted.  
         [0081]    Referring to FIGS. 13A, 14A and  15 A, a thin film transistor (TFT) “T” is formed on the substrate  111 . The TFT “T” includes a gate line  132 , an active layer  134 , an ohmic contact layer  147 , a source electrode  133  and a drain electrode  135 . A gate-insulating layer  143  isolates the gate electrode  132  from the active layer  134  and the source and drain electrodes  133  and  135 . A gate line  125  is formed in one direction on the substrate  111 , and a gate pad  129  is positioned at the end of the gate line  125 . The gate electrode  132  extends from the gate line  125 , and the source electrode  133  extends from the data line  127 . When forming the source and drain electrodes  133  and  135 , a capacitor electrode  149  over the gate line  125  and the data pad  131  are also formed. A first passivation layer  151 , such as benzocyclobutene (BCB) or acryl-based resin, covers the TFT “T”, the capacitor electrode  149  and the data pad  131 . As shown in FIGS. 13A, 14A and  15 A, the first passivation layer  151  has a first drain contact hole  153  to the drain electrode  135 , a first capacitor contact hole  157  to the capacitor electrode  149 , a first gate pad contact hole  159  to the gate pad  129 , a first data pad contact hole  161  to the data pad  131 , and an etching hole  155  corresponding to a through-hole (i.e., a transmissive portion) “A”. A transparent electrode  119   a,  a gate pad terminal  165  and a data pad terminal  167  are formed on the first passivation layer  151  by patterning the transparent conductive material, such as ITO or IZO. A first portion of the transparent electrode  119   a  contacts the drain electrode  135  through the first drain contact hole  153 , while a second portion of the transparent electrode  119   a  contacts the capacitor electrode  149  through the first capacitor contact hole  157 . The gate pad terminal  165  and the data pad terminal  167  have island shape, and contact the gate pad  129  through the first gate pad contact hole  159  and the data pad  131  through the first data pad contact hole  161 , respectively.  
         [0082]    Now, referring to FIGS. 13B, 14B and  15 B, an insulating material is deposited upon the transparent electrode  119   a  and subsequently patterned to form a second passivation layer  169 . Here, the insulating material is an inorganic substance, such as silicon oxide or silicon nitride, or an organic substance, such as benzocyclobutene (BCB) or acryl-based resin. The second passivation layer  169  comprises a second drain contact hole  153   a  positioned over the drain electrode  135  and a second capacitor contact hole  157   a  positioned over the capacitor electrode  149 . At this time, a second gate pad contact hole  159   a  and a second data pad contact hole  161   a  are also formed by patterning the second passivation layer  169 . The second gate pad contact hole  159   a  exposes a portion of the gate pad  129 , and the second data pad contact hole  161   a  exposes a portion of the data pad  131 .  
         [0083]    Thereafter, a corrosion-resistant metal layer (a first layer)  166 , such as a chromium (Cr) layer, is formed on the second passivation layer  169  having the second contact holes  153   a,    157   a,    159   a  and  161   a.  Subsequently, aluminum-based layer (a second layer)  168 , such as Al or AlNd layer, is formed on the corrosion-resistant metal layer  166 . Thereafter, the corrosion-resistant metal layer  166  and aluminum-based layer  168  are patterned using a mixed etching solution with phosphoric acid, acetic acid and nitric acid. If the corrosion-resistant metal layer  166  is formed of chromium (Cr), the etching solution includes a ceric ammonium nitrate solution. Additionally, during this etching process, the corrosion-resistant metal layer  166  protects the gate and data pad terminals  165  and  167  from the etching solution for the aluminum-based layer  168 .  
         [0084]    From this etching process, formed are a first reflective electrode  166   a  and a second reflective electrode  168   a  both having a through-hole “A”, as shown in FIG. 13C. The first reflective electrode  166   a  and the second reflective electrode  168   a  act together as the reflective electrode  119   b  of FIG. 10D.  
         [0085]    As shown in FIGS. 13C, 14C and  15 C, the double-layered reflective electrodes  166   a  and  168   a  contact the transparent electrode  119   a  via the second drain contact hole  153   a  and second capacitor contact hole  157   a  such that the double-layered reflective electrodes  166   a  and  168   a  and the drain electrode  165  are electrically interconnected. Further, the etching hole  155  corresponding to the through-hole “A” is opened to form the transparent portion. Additionally, the gate pad terminal  165  and the data pad terminal  167  are also exposed when forming the double-layered reflective electrodes  166   a  and  168   a.  Therefore, the array substrate for the LCD device is complete according to the third embodiment of the present invention.  
         [0086]    In the third embodiment described above, the second layer  168  of the double-layered reflective electrode is first etched, and then the first layer  166  of the double-layered reflective electrode is etched. Namely, aluminum-based layer  168  which causes Galvanic corrosion with the transparent conductive material is etched before etching the corrosion-resistant metal layer  166  which does not cause Galvanic corrosion with the transparent conductive material. Therefore, the gate pad terminal  165  and the data pad terminal  167  are not deteriorated and corroded when forming the double-layered reflective electrode. Furthermore, the additional processes are not required to expose the gate pad terminal  165  and the data pad terminal  167 , unlike the conventional art.  
         [0087]    [0087]FIGS. 16A to  16 C,  17 A to  17 C and  18 A to  18 C are sequential cross-sectional views respectively taken along lines XVI-XVI, XVII-XVII and XVIII-XVIII of FIG. 3 according to a fourth embodiment of the present invention. In the fourth embodiment, the second passivation layer between the transparent electrode and the reflective electrode is not necessary, unlike the conventional art. Additionally, since FIGS. 16A, 17A and  18 A are the same as FIGS. 10B, 11B and  12 B of the second embodiment, the fourth embodiment of the present invention is briefly described and some explanation of the fourth embodiment is omitted.  
         [0088]    Referring to FIGS. 16A, 17A and  18 A, a thin film transistor (TFT) “T” is formed on the substrate  111 . The TFT “T” includes a gate line  132 , an active layer  134 , an ohmic contact layer  147 , a source electrode  133  and a drain electrode  135 . A gate-insulating layer  143  isolates the gate electrode  132  from the active layer  134  and the source and drain electrodes  133  and  135 . A gate line  125  is formed in one direction on the substrate  111 , and a gate pad  129  is positioned at the end of the gate line  125 . The gate electrode  132  extends from the gate line  125 , while the source electrode  133  extends from the data line  127 . When forming the source and drain electrodes  133  and  135 , a capacitor electrode  149  over the gate line  125  and the data pad  131  are also formed. A passivation layer  151 , such as benzocyclobutene (BCB) or acryl-based resin, is formed to cover the TFT “T”, the capacitor electrode  149  and the data pad  131 . As shown in FIGS. 16A, 17A and  18 A, the passivation layer  151  has a drain contact hole  153  to the drain electrode  135 , a capacitor contact hole  157  to the capacitor electrode  149 , a gate pad contact hole  159  to the gate pad  129 , a data pad contact hole  161  to the data pad  131 , and an etching hole  155  corresponding to a through-hole (i.e., a transmissive portion) “A”. A transparent electrode  119   a,  a gate pad terminal  165  and a data pad terminal  167  are formed on the passivation layer  151  by patterning the transparent conductive material, such as ITO or IZO. A first portion of the transparent electrode  119   a  contacts the drain electrode  135  through the drain contact hole  153 , while a second portion of the transparent electrode  119   a  contacts the capacitor electrode  149  through the capacitor contact hole  157 . The gate pad terminal  165  and the data pad terminal  167  have island shape, and contact the gate pad  129  through the first gate pad contact hole  159  and the data pad  131  through the first data pad contact hole  161 , respectively.  
         [0089]    Now, referring to FIGS. 16B, 17B and  18 B, a corrosion-resistant metal layer (a first layer)  166 , such as a chromium (Cr) or molybdenum (Mo) layer, is formed on the passivation layer  151  to cover the patterned transparent conductive material. Subsequently, aluminum-based layer (a second layer)  168 , such as Al or AlNd layer, is formed on the corrosion-resistant metal layer  166 . Therefore, a double-layered structure is complete for the double-layered reflective electrode.  
         [0090]    Thereafter, a photolithography process is performed as follows. First, a photo resist is formed on the second layer  168  and exposed to the light. The light-exposed portions of the photo resist is stripped to form a photo resist pattern  170 , thereby exposing the second layer  168  except for a portion for reflective electrode.  
         [0091]    When removing the exposed portion of the second layer (the aluminum-based layer)  168 , a mixed etching solution including phosphoric acid, acetic acid and nitric acid is used. However, when removing the first layer (the corrosion-resistant metal layer, e.g., chromium or molybdenum)  166  to form the double-layered reflective layer, a mixed solution with a ceric ammonium nitrate solution and nitric acid is used as an etching solution.  
         [0092]    In this fourth embodiment of the present invention, the first layer  166  should be thick enough to protect the transparent conductive material therebelow from the mixed etching solution for the second layer  168 . Namely, the first layer  166  prevents the etching solution for the second layer  168  from affecting the transparent electrode  119   a,  gate pad terminal  165  and data pad terminal  167 . The first layer  166  formed of Cr or Mo does not cause Galvanic corrosion with the transparent conductive material (e.g., ITO or IZO), thereby not deteriorating the electrode  119   a  and terminals  165  and  167  formed of transparent conductive material when etching the first layer  166 .  
         [0093]    Accordingly, since the first layer  166  and the second layer  168  are etched respectively in the fourth embodiment of the present invention, Galvanic corrosion does not occur between the aluminum-based layer  168  and the layers formed of transparent conductive material. Furthermore, although chromium and molybdenum are mentioned for the first layer  166  in this reference, other metal layers that do not corrosively reacts with the transparent conductive material can be employed as a first layer  166 .  
         [0094]    [0094]FIGS. 16C, 17C and  18 C are cross-sectional views showing an array substrate according to the present invention after forming the double-layered reflective electrode  166   a  and  168   a.  In accordance with the fourth embodiment of the present invention, since the double-layered reflective electrode  166   a  and  168   a  is formed on and contacts the transparent electrode  119   a,  some additional processes may be required. Namely, the processes for removing the defects may be necessary because the electrons may be trapped in the interface between the transparent electrode  119  and the first layer  166   a  of the reflective electrode and these trapped electrons cause the defects. In order to overcome this problem, the transparent electrode  119   a  is laser-treated to improve electrical and optical characteristics thereof.  
         [0095]    Although the reflective electrode has the double-layered structure in the fourth embodiment of the present invention, a single-layered structure can be employed in the reflective electrode. At this point, the reflective electrode is relatively thicker than the conventional art, and a dry etching method is used for patterning the thick reflective electrode. Namely, the opaque metal having high reflectance is deposited on the transparent electrode, and then the photolithography process proceeds using a photo resist. At this time, half of the thick opaque metal layer, which is exposed for etching, is removed by the dry etching method. Thereafter, the photo resist patterned for the reflective electrode is stripped completely. Although the wet stripper for the photo resist is an electrolytic solution, the transparent electrode and pad terminals are not affected by this wet stripper because half-etched opaque metal layer covers the transparent electrode and pad terminals. After stripping the photo resist, the half-etched opaque metal layer is removed using the dry etching method. At this time, a portion of the opaque metal layer where the photo resist pattern remained becomes the reflective electrode. Although the portion for reflective electrode is half-etched, this properly functions as a reflective electrode.  
         [0096]    In the fourth embodiment of the present invention, the second passivation layer is not formed on the patterned transparent conductive material, and the reflective electrode is directly disposed on the transparent electrode. Since the second passivation layer is omitted, the manufacturing processes are reduced in the fourth embodiment. Additionally, although the reflective electrode is formed on the surface of the transparent electrode, Galvanic corrosion does not occur in the fourth embodiment of the present invention.  
         [0097]    It will be apparent to those skilled in the art that various modifications and variation can be made in the method of manufacturing a thin film transistor 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 they come within the scope of the appended claims and their equivalents.

Technology Category: 3