Patent Publication Number: US-9431437-B2

Title: Display panel and method of manufacturing the same

Description:
This application claims priority to Korean Patent Application No. 10-2013-0103454, filed on Aug. 29, 2013, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field 
     The invention relates to a display panel and a method of manufacturing the same. More particularly, the invention relates to a display panel having a low resistance line structure and a method of manufacturing the display panel. 
     2. Description of the Related Art 
     In general, a liquid crystal display device includes a thin film transistor substrate, a color filter substrate, and a liquid crystal layer interposed between the thin film transistor substrate and the color filter substrate. 
     The thin film transistor substrate includes pixels to display an image. Each pixel includes a thin film transistor and a pixel electrode. The thin film transistor receives gate and data signals provided respectively through gate and data lines, and applies the data signal to the pixel electrode during a turned-on period of the gate signal. 
     SUMMARY 
     One or more exemplary embodiment of the invention provides a display panel capable of widening a range of selecting a material used for a planarization layer in a low resistance line structure, and lowering manufacturing process difficulty thereof. 
     One or more exemplary embodiment of the invention provides a method of manufacturing the display panel. 
     An exemplary embodiment of the invention provides a method of manufacturing a display panel including sequentially stacking a first metal layer, a first insulating layer, an amorphous silicon layer, an n+ amorphous silicon layer and a first photoresist layer on a substrate including a transistor area and a line area, patterning the first photoresist layer using a first mask including a halftone pattern in the transistor area and the line area to form a first photoresist pattern, substantially simultaneously patterning the stacked amorphous silicon, first insulating and first metal layers using the first photoresist pattern as a mask to form an active layer, a gate insulating layer and a gate electrode extended from a gate line, respectively, forming a planarization organic layer including an organic material on the active layer and the substrate after the active layer is formed, removing the planarization organic layer overlapping the active layer to form a planarization layer, forming a second metal layer on the planarization layer and the active layer, patterning the second metal layer using a second mask to form a source electrode, a drain electrode and a data line, forming a protective layer on the planarization layer to cover the source electrode, the drain electrode, and the data line, patterning the protective layer using a third mask to form a contact hole through which the drain electrode is exposed, forming a transparent electrode layer on the protective layer, and patterning the transparent electrode layer using a fourth mask to form a pixel electrode electrically connected to the drain electrode through the contact hole. 
     An exemplary embodiment of the invention provides a display panel including a gate electrode and a gate line, on a substrate, a gate insulating layer and an active layer sequentially on the gate electrode and the gate line, a planarization layer which is on the substrate and compensates a step difference between the substrate, and the gate electrode and the gate line, respectively, source and drain electrodes on the active layer overlapping the gate electrode to be spaced apart from each other, a data line on the active layer and crossing the gate line, a protective layer which covers the planarization layer, the source and drain electrodes, and the data line, a contact hole defined in the protective layer and partially exposing the drain electrode, and a pixel electrode on the protective layer and electrically connected to the drain electrode through the contact hole. 
     According to one or more exemplary embodiment of the invention, when the thickness of the gate electrode and the gate line is increased to reduce the electrical line resistance thereof, the planarization layer disposed thereon prevents the step difference from being generated. In addition, in a method of manufacturing a thin film transistor of a display panel, since the planarization layer is formed after a process of forming the active layer is performed at a high temperature, the planarization layer may not include an organic material with high temperature resistance. Therefore, a range of selecting a material used for the planarization layer may be widened. 
     In addition, the thin film transistor substrate is manufactured using four masks and the portion to which the halftone pattern is applied is not a fine pattern, e.g., a channel area of the transistor, and thus the manufacturing process difficulty may be lowered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other advantages of the invention will become readily apparent by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIGS. 1 to 17  are cross-sectional views showing an exemplary embodiment of a method of manufacturing a display panel according to the invention; 
         FIGS. 18 to 20  are cross-sectional views showing an exemplary embodiment of a process of forming a planarization layer according to the invention; 
         FIGS. 21 and 22  are cross-sectional views showing an exemplary embodiment of a planarization layer according to the invention; 
         FIG. 23  is a plan view showing an exemplary embodiment of a display panel according to the invention; 
         FIG. 24  is a cross-sectional view taken along line I-I′ of  FIG. 23 ; and 
         FIGS. 25 to 29  are cross-sectional views showing another exemplary embodiment of a method of manufacturing a display panel according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. As used herein, “connected” may include in physical and/or electrical connection. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention. 
     Spatially relative terms, such as “lower,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “lower” relative to other elements or features would then be oriented “upper” relative to the other elements or features. Thus, the exemplary term “lower” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms, “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Embodiments of the invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     All methods described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”), is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as used herein. 
     As a liquid crystal display device increases in size and resolution, signal lines, e.g., gate and data lines, are formed to have a low electrical resistance line structure in order to reduce a line electrical resistance in the signal lines. As the low line electrical resistance structure, a method of increasing a thickness of the gate line has been suggested. However, when the gate line increases in thickness, a step difference is generated in the thin film transistor substrate. Therefore, there remains a need for an improved low line electrical resistance structure and a display panel including the same. 
     Hereinafter, the invention will be explained in detail with reference to the accompanying drawings. 
       FIGS. 1 to 17  are cross-sectional views showing an exemplary embodiment of a method of manufacturing a display panel according to the invention. 
     Referring to  FIG. 1 , a first metal material layer  103  is formed on a substrate  101 . In detail, the first metal material layer  103  includes a first lower metal layer  103   a  formed of titanium (Ti) and a first upper metal layer  103   b  formed of copper (Cu), which are sequentially stacked on the substrate  101  such as by a deposition process. Besides the above-mentioned materials, the first metal material layer  103  may include various materials, such as aluminum (Al), chromium (Cr), etc. 
     As an exemplary embodiment, the first metal material layer  103  has a total cross-sectional thickness of about 1 micrometer to about 3 micrometers to reduce a line resistance of a signal line formed therefrom, such as a gate line. 
     A first insulating layer  105 , an amorphous silicon layer  107   a , an n+ amorphous silicon layer  107   b  and a first photoresist layer  109  are sequentially stacked on the first upper metal layer  103   b  of the first metal material layer  103 . 
     The first insulating layer  105  includes silicon nitride (SiNx) or silicon oxide (SiOx) and has a cross-sectional thickness of about 1000 angstroms. The amorphous silicon layer  107   a  and the n+ amorphous silicon layer  107   b  are deposited on the first insulating layer  105  such as by a chemical vapor deposition (“CVD”) process. 
     The first photoresist layer  109  is formed on the n+ amorphous silicon layer  107   b  and a first mask  111  is disposed on the first photoresist layer  109 . The first mask  111  has a halftone pattern  111   a  in a transistor area TFTA and first and second line areas GLA and DLA, and a slit pattern  111   b  in a first pad area GPA. 
     The first photoresist layer  109  is exposed and developed when the first mask  111  is disposed on the first photoresist layer  109 , and then the exposed first photoresist layer  109  is removed. As a result, a first photoresist pattern  110  is formed on the n+ amorphous silicon layer  107   b  as shown in  FIG. 2 . 
     Referring to  FIG. 2 , the first photoresist pattern  110  includes a first part  110   a  corresponding to a center portion of the transistor area TFTA and the first and second line areas GLA and DLA, and a second part  110   b  formed along an end portion of the transistor area TFTA and the first and second line areas GLA and DLA. 
     The first part  110   a  of the first photoresist pattern  110  has a first cross-sectional thickness t 1  and the second part  110   b  of the first photoresist pattern  110  has a second cross-sectional thickness t 2  smaller than the first thickness t 1 . 
     The first photoresist pattern  110  has the second thickness t 2  in the first pad area GPA and is completely excluded in the second pad area DPA where the first photoresist layer  109  has been removed. 
     Then, the first insulating layer  105 , the amorphous silicon layer  107   a , and the n+ amorphous silicon layer  107   b  are dry-etched using the first photoresist pattern  110  as a mask, and thus the first insulating layer  105 , the amorphous silicon layer  107   a , and the n+ amorphous silicon layer  107   b  are removed except for the area in which the first photoresist pattern  110  is formed. Accordingly, as shown in  FIG. 3 , a gate insulating layer  113  and an active layer  115  are formed on the first metal material layer  103 . The active layer  115  includes a semiconductor layer  115   a  and an ohmic contact layer  115   b.    
     Here, a condition of the dry etching process may be controlled such that an edge of the gate insulating layer  113  and the active layer  115  has a forward taper shape. 
     After that, as shown in  FIG. 4 , the first lower metal layer  103   a  and the first upper metal layer  103   b  of the first metal material layer  103  are wet-etched to form a gate electrode GE in the transistor area TFTA, a gate line GL in the first line area GLA, and a light blocking line BL in the second line area DLA. In addition, a gate pad GP is formed in the first pad area GPA. The gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP are in a same layer. While the lead line points to only one layer in the structure, the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP include both the first lower metal layer  103   a  and the first upper metal layer  103   b  of the first metal material layer  103 . 
     When the first metal material layer  103  is wet-etched, an under-cut occurs, in which an upper surface of the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP has a size (e.g., width parallel to the substrate  101 ) smaller than that of a lower surface of the overlying gate insulating layer  113 . Due to the under-cut, an outer edge of the gate insulating layer  113  and the active layer  115  is protruded further outward than an outer edge of each of the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP. Here, the portion of the gate insulating layer  113  and the active layer  115 , which is protruded further outward than the edge of each of the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP, is called a protrusion portion PP. 
     Then, as shown in  FIG. 5 , the second part  110   b  of the first photoresist pattern  110  is removed by an etchback process. Therefore, only the first part  110   a  of the first photoresist pattern  110  remains in the transistor area TFTA and the first and second areas GLA and DLA, and the first photoresist pattern  110  is completely removed in the first pad area GPA. 
     When the active layer  115  and the gate insulating layer  113  are dry-etched using the first part  110   a  as a mask, the protrusion portion PP is removed as shown in  FIG. 6 . The active layer  115  and the gate insulating layer  113  are completely removed on the gate pad GP in the first pad area GPA. 
     As the first metal material layer  103  increases in thickness, the under-cut is intensified, and thus the protrusion portion PP increases in width. Thus, a width of the second part  110   b  is determined depending on the thickness of the first metal material layer  103 , so that the halftone pattern  111   a  of the first mask  111  may be controlled. 
     Referring to  FIG. 7 , the first part  110   a  of the first photoresist pattern  110  is removed by a strip process. 
     Referring to  FIG. 8 , a planarization organic layer  117  is formed on the active layer  115  and the substrate  101 . The planarization layer  117  includes an organic material. In the illustrated exemplary embodiment, the planarization layer  117  may have a negative photosensitivity, but the invention is not limited thereto. 
     As shown in  FIG. 9 , when a rear surface exposing process is performed on the planarization organic layer  117  from a rear of the substrate  101  as indicated by the open shape arrows, and a development process is performed, portions of the planarization organic layer  117 , which are not exposed, may be removed. In particular, the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP do not transmit the light during the rear surface exposing process since the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP are formed of a metal material. Therefore, the planarization organic layer  117  on the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP may be completely removed. 
     Thus, the planarization organic layer  117  may be removed in the areas, in which the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP are formed, without using any mask. 
     When a curing process is performed, a planarization layer  119  is formed as shown in  FIG. 10 . In detail, the planarization layer  119  exposes the upper surface of the active layer  115  in the transistor area TFTA and the first and second line areas GLA and DLA, and exposes the upper surface of the gate pad GP in the first pad area GPA. 
     Referring to  FIG. 11 , a second metal material layer  121  is formed on the planarization layer  119 , the exposed active layer  115  and the exposed gate pad GP. The second metal material layer  121  includes a second lower metal layer  121   a  formed of titanium (Ti) and a second upper metal layer  121   b  formed of copper (Cu), which are sequentially deposited such as by a deposition process. Besides the above-mentioned materials, the second metal material layer  121  may include various materials, such as aluminum (Al), chromium (Cr), etc. 
     In addition, a second photoresist layer  123  is formed on the second metal material layer  121 . 
     Then, the second photoresist layer  123  is exposed and developed using a second mask  125  to form a second photoresist pattern (not shown). When the second lower metal layer  121   a  and the second upper metal layer  121   b  of the second metal material layer  121  are etched using the second photoresist pattern as a mask, a source electrode SE, a drain electrode DE, a data line DL and a data pad DP are formed as shown in  FIG. 12 . The source electrode SE, the drain electrode DE, the data line DL and the data pad DP are in a same layer. While the lead line points to only one layer in the structure, the source electrode SE, the drain electrode DE, the data line DL and the data pad DP include both the second lower metal layer  121   a  and the second upper metal layer  121   b  of the second metal material layer  121 . 
     In detail, the source electrode SE and the drain electrode DE are formed in the transistor area TFTA to be spaced apart from each other by a predetermined distance in a width direction. The ohmic contact layer  115   b  is removed in an area between the source electrode SE and the drain electrode DE, and thus a channel layer  115   c  is formed. 
     In addition, the data line DL is formed on the active layer  115  in the second line area DLA and the data pad DP is formed on the planarization layer  119  in the second pad area DPA. 
     As shown in  FIG. 12 , the active layer  115 , the gate insulating layer  113  and the light blocking line BL are formed under the data line DL. When the active layer  115  and the gate insulating layer  113  are disposed under the data line DL, the light blocking line BL blocks the light provided from the rear of the substrate  101  and traveling toward to the active layer  115 . 
     However, when the active layer  115  and the gate insulating layer  113  are excluded under the data line DL as the first and second pad areas GPA and DPA, the light blocking line BL may also be excluded. 
     Then, as shown in  FIG. 13 , a protective layer  127  is formed on the planarization layer  119  to cover the source electrode SE, the drain electrode DE, the data line DL and the data pad DP. The protective layer  127  includes a protective inorganic layer  127   a  and a protective organic layer  127   b , which are sequentially stacked. In the illustrated exemplary embodiment, the protective inorganic layer  127   a  includes silicon nitride or silicon oxide and has a cross-sectional thickness of about 1000 angstroms. The protective organic layer  127   b  includes acrylic-containing material such as a photosensitive resin. 
     Referring to  FIG. 14 , when the protective organic layer  127   b  is exposed and developed after a third mask  129  is disposed on the protective organic layer  127   b , portions of the protective organic layer  127   b , which correspond to the drain electrode DE in the transistor area TFTA and the gate pad GP and the data pad DP respectively disposed in the first and second pad areas GPA and DPA, are partially removed. 
     When the protective inorganic layer  127   a  is etched using the protective organic layer  127   b  as a mask, a contact hole CH, a first pad opening PO 1  and a second pad opening PO 2  are formed through the protective layer  127  to respectively expose the drain electrode DE, the gate pad GP and the data pad DP as shown in  FIG. 15 . 
     Referring to  FIG. 16 , a transparent electrode material layer  131  is formed on the protective layer  127 . The transparent electrode material layer  131  may include a transparent conductive oxide (“TCO”), e.g., indium tin oxide (“ITO”), indium zinc oxide (“IZO”), etc. 
     When the transparent electrode material layer  131  is patterned using a fourth mask  132 , a pixel electrode  133  is formed to be electrically connected to the drain electrode DE through the contact hole CH as shown in  FIG. 17 . In addition, first and second pad electrodes  134   a  and  134   b  are respectively formed in the first and second pad areas GPA and DPA. The first pad electrode  134   a  makes contact with the gate pad GP through the first pad opening PO 1  and the second pad electrode  134   b  makes contact with the data pad DP through the second pad opening PO 2 . 
     According to the above-described processes, the display panel is manufactured. For the convenience of explanation, only the manufacturing process of the thin film transistor substrate of the display panel has been shown in  FIGS. 1 to 17 . Although not shown in figures, the manufacturing process of the display panel may further include a process of coupling the thin film transistor substrate to an opposite substrate and a process of forming a display device, e.g., disposing a liquid crystal layer, between the thin film transistor substrate and the opposite substrate. 
     Hereinafter, a liquid crystal display panel configured to include the thin film transistor, the opposite substrate and the liquid crystal layer will be described in detail as the display panel. 
       FIGS. 18 to 20  are cross-sectional views showing an exemplary embodiment of process of forming a planarization layer according to the invention. 
     Referring to  FIG. 18 , a planarization organic layer  135  is formed on the active layer  115  and the substrate  101  using an organic material. Processes performed before the planarization organic layer  135  is formed are the same as those shown in  FIGS. 1 to 7 , and thus details thereof will be omitted. In addition, the planarization organic layer  135  shown in  FIG. 18  may not have photosensitivity. 
     Referring to  FIG. 19 , the planarization organic layer  135  is partially removed through an ashing process. The ashing process is performed until the planarization organic layer  135  is completely removed on the active layer  115 , the gate electrode GE, the gate line GL, the light blocking line BL and the gate pad GP. 
     After the ashing process is performed, a surface roughness of the planarization organic layer  135  may be increased as illustrated by the wavy upper surface in  FIG. 19 . Accordingly, when a hard bake process is performed, a planarization layer  137  in which the surface roughness is decreased may be formed as shown in  FIG. 20 . 
     As shown in  FIG. 18 , a cross-sectional thickness of the planarization organic layer  135  on the gate pad GP is larger than a cross-sectional thickness of the planarization organic layer  135  on the active pattern  115 . Therefore, a portion of the planarization organic layer  135  may remain on the gate pad GP after the ashing process is formed, but the invention is not limited thereto. 
     However, although a portion of the planarization organic layer  135  remains on the gate pad GP, such remaining portion of the planarization organic layer  135  may be removed by the process of forming the contact hole CH and the first and second pad openings PO 1  and PO 2  through the protective layer  127  shown in  FIGS. 15 and 16 . That is, when the protective inorganic layer  127   a  is etched using the protective organic layer  127   b  as the mask in order to form the first pad opening PO 1 , the portion of the planarization organic layer  135  remaining on the gate pad GP may be removed. 
       FIGS. 21 and 22  are cross-sectional views showing an exemplary embodiment of a planarization layer according to the invention. 
     Referring to  FIG. 21 , a planarization layer  139  includes red, green and blue color pixels R, G and B. Each of the red, green and blue color pixels R, G and B is formed in a corresponding pixel area of the display panel. 
     As shown in  FIG. 22 , processes performed after the planarization layer  139  is formed are the same as those shown in  FIGS. 11 to 17 , and thus details thereof will be omitted. 
       FIG. 23  is a plan view showing an exemplary embodiment of a display panel according to the invention and  FIG. 24  is a cross-sectional view taken along line I-I′ of  FIG. 23 . 
     Referring to  FIGS. 23 and 24 , an exemplary embodiment of a pixel according to the invention includes the thin film transistor (“TFT”) and the pixel electrode  133 . 
     The substrate  101  includes the transistor area TFTA in which the thin film transistor is disposed, the first and second line areas GLA and DLA in which the gate line GL and the data line DL are respectively disposed, and a pixel area PA in which the pixel electrode  133  is disposed. 
     The gate line GL extends in a stripe shape along a first direction, and the data line DL extends along a second direction to cross the gate line GL. Here, the gate line GL extends to be substantially perpendicular to the data line DL, but the invention is not limited thereto. In addition, the gate line GL is electrically insulated from the data line DL by the gate insulating layer  113  and the active layer  115 . 
     The thin film transistor is electrically connected to the data line DL and the gate line GL. In detail, the thin film transistor includes the gate electrode GE branched from the gate line GL, the source electrode SE branched from the data line DL, and the drain electrode DE disposed to be spaced apart from the source electrode SE and electrically connected to the pixel electrode  133 . The thin film transistor may further include the gate insulating layer  113  and the active layer  115  with respect to the gate, source and drain electrodes GE, SE and DE. The pixel electrode  133  is electrically connected to the drain electrode DE through the contact hole CH in the transistor area TFTA. 
     The pixel electrode  133  includes a trunk portion  133   a , and a plurality of branch portions  133   b  protruding from the trunk portion  133   a  and extending in a radial shape. 
     The trunk portion  133   a  may have a cross shape, and thus the pixel electrode  133  is divided into a plurality of domains by the trunk portion  133   a . The branch portions  133   b  are disposed in each domain and extend in different directions according to the domains. In the illustrated exemplary embodiment, the pixel electrode  133  is divided in four domains as shown in  FIG. 23 , but the number of the domains should not be limited to four. The branch portions  133   b  are spaced apart from each other and extend to be substantially in parallel to each other in each domain. A distance between two adjacent branch portions  133   b  to each other is measured in terms of micrometers. The branch portions  133   b  are extended in an elongation direction, and the distance between adjacent branch portions  133   b  is taken perpendicular to the elongation direction. The branch portions  133   b  align liquid crystal molecules of the liquid crystal layer in a specific azimuth on a surface substantially in parallel to the substrate  101 . 
     According to another exemplary embodiment, the pixel electrode  133  may include first and second sub-pixel electrodes applied with voltages having different levels, and each of the first and second sub-pixel electrodes may be divided into a plurality of domains. Where each of the first and second sub-pixel electrodes may be divided into a plurality of domains, the liquid crystal molecules are aligned in different directions according to the domains and an alignment angle of the liquid crystal molecules are changed, and thus a viewing angle of the liquid crystal display panel may be improved. 
     Referring to  FIG. 24 , the gate insulating layer  113  is not formed in (e.g., excluded from) each pixel area PA. That is, since the gate insulating layer  113  and the active layer  115  are substantially simultaneously patterned, the gate insulating layer  113  is disposed on the patterns formed by patterning the metal material layer  103 , e.g., the gate electrode GE, the gate line GL, the light blocking line BL, etc., in the transistor area TFTA and the first and second line areas GLA and DLA. 
     When the gate insulating layer  113  is excluded in the pixel area PA, a transmittance of the liquid crystal display panel may be improved compared with a conventional liquid crystal display panel in which the gate insulating layer  113  is disposed in the pixel area PA. 
     In addition, edges of the gate insulating layer  113  and the active layer  115  are disposed more inward than edges of the gate electrode GE and the gate line GL. 
       FIGS. 25 to 29  are cross-sectional views showing another exemplary embodiment of a method of manufacturing a display panel according to the invention. In  FIGS. 25 to 29 , the same reference numerals denote the same elements in  FIGS. 1 to 17 , and thus detailed descriptions of the same elements will be omitted. 
     Referring to  FIG. 25 , a first metal material layer  103  is formed on the substrate  101  and the first metal material layer  103  includes a first lower metal layer  103   a  and a first upper metal layer  103   b , which are sequentially stacked. A first insulating layer  105 , an amorphous silicon layer  107   a , an n+ amorphous silicon layer  107   b , and a first photoresist layer  109  are sequentially stacked on the first upper metal layer  103   b.    
     A first mask  111  is disposed on the first photoresist layer  109 . The first mask  111  has a halftone pattern  111   a  in a transistor area TFTA, first and second line areas GLA and DLA, and a first pad area GPA. 
     When the first photoresist layer  109  is exposed and developed using the first mask  111  as a mask and the exposed first photoresist layer  109  is removed, a first photoresist pattern  110  is formed on the n+ amorphous silicon layer  107   b  as shown in  FIG. 26 . 
     Referring to  FIG. 26 , the first photoresist pattern  110  includes a first part  110   a  corresponding to a center portion of the transistor area TFTA, the first and second line areas GLA and DLA, and the first pad area GPA, and a second part  110   b  formed along an end portion of the transistor area TFTA, the first and second line areas GLA and DLA, and the first pad area GPA. 
     The first part  110   a  of the first photoresist pattern  110  has a first cross-sectional thickness t 1  and the second part  110   b  of the first photoresist pattern  110  has a second cross-sectional thickness t 2  smaller than the first thickness t 1 . 
     The first photoresist pattern  110  is completely removed in the second pad area DPA. 
     Then, the first insulating layer  105 , the amorphous silicon layer  107   a  and the n+ amorphous silicon layer  107   b  are dry-etched using the first photoresist pattern  110  as a mask, and thus the first insulating layer  105 , the amorphous silicon layer  107   a  and the n+ amorphous silicon layer  107   b  are removed except for the area in which the first photoresist pattern  110  is formed. 
     When the processes similar to those shown in  FIGS. 4 to 6  are performed, a gate electrode GE is formed in the transistor area TFTA, a gate line GL is formed in the first line area GLA, and a light blocking line BL is formed in the second line area DLA as shown in  FIG. 27 . In addition, a gate pad GP is formed in the first pad area GPA. Different from  FIG. 7 , the gate insulating layer  113  and the active layer  115  remain on the gate pad GP shown in  FIG. 27 . 
     When the processes similar to those shown in  FIGS. 8 to 13 , a contact pattern and first and second opening patterns may be formed through a protective organic layer  127   b  using a third mask  129  as shown in  FIG. 28 . 
     When the protective inorganic layer  127   a  is etched using the protective organic layer  127   b , a contact hole CH is formed in the transistor area TFTA and first and second pad openings PO 1  and PO 2  are respectively formed in the first and second pad areas GPA and DPA. 
     When the first pad opening PO 1  is formed, the gate insulating layer  113  and the active layer  115 , which remain on the gate pad GP, may be removed. Thus, the upper surface of the gate pad GP is exposed through the first pad opening PO 1 . 
     Then, the thin film transistor substrate is manufactured by performing the processes similar to those shown in  FIGS. 16 and 17 . 
     Although exemplary embodiments of the invention have been described, it is understood that the invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the invention as hereinafter claimed.