Patent Publication Number: US-2016223872-A1

Title: Liquid crystal display device

Description:
CLAIM OF PRIORITY 
     This application claims the priority to and all the benefits of Korean Patent Application No. 10-2015-0015217 filed in the Korean Intellectual Property Office (KIPO) on Jan. 30, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Disclosure 
     The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device capable of increasing transmittance. 
     2. Description of the Related Art 
     A liquid crystal display device, which is one of the flat panel display devices that are currently used widely, includes two display panels on which electric field generating electrodes such as a pixel electrode, a common electrode, and the like, are formed, and a liquid crystal layer interposed between the two display panels, and generates an electric field in the liquid crystal layer by applying a voltage to the electric field generating electrode, thereby determining alignment of liquid crystal molecules of the liquid crystal layer and controls polarization of incident light, thereby displaying an image. 
     The liquid crystal display device has an advantage that thinness is easy, but has a disadvantage that side surface visibility is lower than front surface visibility. Therefore, various methods of arranging and driving a liquid crystal for overcoming this disadvantage have been developed. As a method for implementing a wide viewing angle, a liquid crystal display device in which a pixel electrode and a common electrode are formed on one substrate to form a horizontal electric field has been prominent. 
     In the liquid crystal display device in this horizontal electric field scheme, the pixel electrode or the common electrode are formed so as to have slit patterns having a rod shape, and an interlayer insulating layer is formed between the pixel electrode and the common electrode. Here, the pixel electrode and the common electrode may be made of a transparent metal oxide such as an indium tin oxide (ITO), an indium zinc oxide (IZO), or the like. In addition, the interlayer insulating layer may be made of a silicon oxide (SiO x ) or a silicon nitride (SiN x ). 
     When hydrogen gas (H 2 ) or silane SiN 4  gas is supplied in order to form the interlayer insulating layer on an electrode layer made of a transparent metal oxide such as an indium tin oxide (ITO), an indium zinc oxide (IZO), or the like, oxide of indium is reduced to be precipitated as a metal. Therefore, the electrode layer becomes opaque, such that transmittance is decreased. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a liquid crystal display device having advantages of increasing transmittance. 
     An exemplary embodiment of the present invention provides a liquid crystal display device including: a substrate; a gate line and a data line positioned on the substrate; a thin film transistor connected to the gate line and the data line; a passivation layer positioned on the gate line, the data line, and the thin film transistor; a first electrode positioned on the passivation layer; an interlayer insulating layer positioned on the first electrode; and a second electrode positioned on the interlayer insulating layer, wherein the first electrode includes a first layer made of an indium-zinc oxide in which a weight ratio of an indium oxide is 20 wt % or less or made of a transparent metal oxide that does not contain an indium oxide. 
     The first layer may be made of an aluminum zinc oxide or a gallium zinc oxide. 
     The interlayer insulating layer may be made of a silicon oxide or a silicon nitride. 
     The passivation layer may be made of an organic insulating material. 
     The first electrode may further include a second layer positioned under the first layer. 
     The first layer may be made of an aluminum zinc oxide or a gallium zinc oxide. 
     The second layer may be made of an indium zinc oxide or an indium tin oxide. 
     The first electrode may further include a third layer positioned under the second layer. 
     The third layer may be made of an indium-zinc oxide in which a weight ratio of an indium oxide is 20 wt % or less or be made of a transparent metal oxide that does not contain an indium oxide. 
     The second layer may be made of an indium zinc oxide or an indium tin oxide. 
     The first electrode may further include: a second layer positioned under the first layer; and a first mixed layer positioned between the first layer and the second layer. 
     The first layer may be made of a first material, the second layer may be made of a second material, and the first mixed layer may be made of a mixture of the first material and the second material. 
     In the first mixed layer, ratios of the first material and the second material may be changed in a thickness direction. 
     The closer to the first layer, the higher the ratio of the first material in the first mixed layer, and the closer to the second layer, the higher the ratio of the second material in the first mixed layer. 
     The first material may be an aluminum zinc oxide or a gallium zinc oxide. 
     The second material may be an indium zinc oxide or an indium tin oxide. 
     The first electrode may be formed by an atomic layer deposition method or a plasma enhanced atomic layer deposition method. 
     The first electrode may further include: a third layer positioned under the second layer; and a second mixed layer positioned between the second layer and the third layer. 
     The first layer and the third layer may be made of a first material, the second layer may be made of a second material, and the first mixed layer and the second mixed layer may be made of a mixture of the first material and the second material. 
     In the first mixed layer and the second mixed layer, ratios of the first material and the second material may be changed in a thickness direction. 
     The closer to the first layer, the higher the ratio of the first material in the first mixed layer, and the closer to the second layer, the higher the ratio of the second material in the first mixed layer, and the closer to the third layer, the higher the ratio of the first material in the second mixed layer, and the closer to the second layer, the higher the ratio of the second material in the second mixed layer. 
     The first material may be an indium-zinc oxide in which a weight ratio of an indium oxide is 20 wt % or less or be a transparent metal oxide that does not contain an indium oxide. 
     The second material may be an indium zinc oxide or an indium tin oxide. 
     The first electrode may be formed by an atomic layer deposition method or a plasma enhanced atomic layer deposition method. 
     a predetermined voltage may be applied to the first electrode. 
     The second electrode may be connected to the thin film transistor. 
     As described above, the liquid crystal display device according to exemplary embodiments of the present invention has the following effect. 
     In the liquid crystal display device according to exemplary embodiments of the present invention, a content of the indium oxide of the electrode positioned under the interlayer insulating layer is decreased to prevent reduction of oxide of indium, thereby making it possible to increase transmittance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a plan view of a liquid crystal display device according to an exemplary embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention taken along line II-II of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
         FIG. 5  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
         FIG. 6  is a view showing a change in a refractive index of a first electrode in a thickness direction in the liquid crystal display device according to an exemplary embodiment of the present invention. 
         FIGS. 7 to 11  are process cross-sectional views showing a method of forming a first layer, a first mixed layer, and a second layer of the first electrode. 
         FIG. 12  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
         FIG. 13  is a view showing a change in a refractive index of a first electrode in a thickness direction in the liquid crystal display device according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described more fully with reference to the accompanying drawings so as to be easily practiced by those skilled in the art to which the present invention pertains. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
     Next, a liquid crystal display device according to an exemplary embodiment of the present invention will be described with reference to  FIGS. 1 to 2 . 
       FIG. 1  is a plan view of a liquid crystal display device according to an exemplary embodiment of the present invention, and  FIG. 2  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention taken along line II-II of  FIG. 1   
     Referring to  FIGS. 1 and 2 , the liquid crystal display device according to an exemplary embodiment of the present invention includes a lower display panel  100  and an upper display panel  200  facing each other, and a liquid crystal layer  3  interposed between the upper and lower display panels  100  and  200 . 
     First, the lower display panel  100  will be described. 
     A gate conductor including a plurality of gate lines  121  and gate electrodes  124  protruding from the gate lines  121  is formed in one direction on a first insulation substrate  110  made of transparent glass, plastic, or the like. 
     The gate lines  121  are mainly extended in a horizontal direction and transfer gate signals. The gate electrodes  124  may be formed in a shape in which they protrude from the gate lines  121  as shown or be formed of portions of the gate lines  121 . 
     Although not shown, sustain electrodes may be further formed so as not to be connected to the gate lines  121  and the gate electrodes  124 . The sustain electrode may be formed in a direction that is in parallel with the gate line  121 , and may have a predetermined voltage such as a common voltage, or the like, applied thereto. 
     A gate insulating layer  140  is formed on the gate lines  121  and the gate electrodes  124 . The gate insulating layer  140  may be made of an inorganic insulating material such as a silicon nitride (SiN x ), a silicon oxide (SiO x ), or the like. In addition, the gate insulating layer  140  may be formed of a single layer or a multilayer. 
     Semiconductors  154  are formed on the gate insulating layer  140 . The semiconductor  154  may be positioned above the gate electrode  124 . The semiconductor  154  may be made of amorphous silicon, polycrystalline silicon, a metal oxide, or the like. 
     Ohmic contact members  163  and  165  may be further positioned on the semiconductors  154 . Each of the ohmic contact members may be made of a material such as silicide or n+ hydrogenated amorphous silicon doped with n-type impurities at a high concentration. 
     Data lines  171  including source electrodes  173  and data conductors including drain electrodes  175  are positioned on the ohmic contact members  163  and  165  and the gate insulating layer  140 . 
     The data lines  171  transfer data signals and are mainly extended in a vertical direction to intersect with the gate lines  121 . The data lines  171  may be periodically bent ( FIG. 1 ). For example, as shown in  FIG. 1 , the respective data lines  171  may be bent at least once at portions corresponding to a horizontal central line CL of one pixel PX. 
     The source electrodes  173  do not protrude from the data lines  171 , but may be positioned on the same line as the data lines  171 , as shown in  FIG. 1 . The drain electrode  175  faces the source electrode  173 . The drain electrode  175  may include a rod shaped part extended substantially in parallel with the source electrode  173  and an extension part  177  disposed at an opposite side to the rod shaped part. 
     The gate electrode  124 , the source electrode  173 , and the drain electrode  175  form one thin film transistor (TFT) together with the semiconductor  154 . The thin film transistor may serve as a switching element SW transferring a data voltage of the data line  171 . Here, a channel of the switching element SW is formed in the semiconductor  154  between the source electrode  173  and the drain electrode  175 . 
     A first passivation layer  180   a  is positioned on exposed portions of the data line  171 , the source electrode  173 , the drain electrode  175 , and the semiconductor  154 . The passivation layer  180   a  may be made of an inorganic insulating material such as a silicon nitride (SiN x ), a silicon oxide (SiO x ), or the like. The first passivation layer  180   a  may include a contact hole  185   a  exposing a part of the drain electrode  175 , for example, the extension part  177 . 
     A second passivation layer  180   b  may be further positioned on the first passivation layer  180   b . The second passivation layer  180   b  may be made of an organic insulating material. The second passivation layer  180   b  may include an opening  185   b  corresponding to the contact hole  185   a  of the first passivation layer  180   a . The opening  185   b  may be larger than the contact hole  185   a , as shown, or substantially coincide with the contact hole  185   a.    
     First electrodes  270  may be positioned on the second passivation layer  180   b . The first electrode  270  has a predetermined voltage such as a common voltage Vcom applied thereto. The first electrodes  270  positioned in a plurality of pixels PX may be connected to each other through a connection leg  276 , or the like, to transfer substantially the same common voltage Vcom. The first electrode  270  may include a plurality of branch electrodes  273 . Slits  73  in which electrodes are removed are formed between neighboring branch electrodes  273 . 
     The first electrode  270  may be formed of a single layer. 
     The first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     Both of the indium zinc oxide (IZO) and the indium tin oxide (ITO) contain the indium oxide (In 2 O 3 ). When weight ratios of the indium oxide (In 2 O 3 ) and the zinc oxide (ZnO) in the indium zinc oxide are 90 wt % and 10 wt %, respectively, atomic weight ratios of the indium oxide (In 2 O 3 ) and the zinc oxide (ZnO) are 73 at % and 27 at %, respectively. When weight ratios of the indium oxide (In 2 O 3 ) and the tin oxide (SnO 2 ) in the indium tin oxide are 90 wt % and 10 wt %, respectively, atomic weight ratios of the indium oxide (In 2 O 3 ) and the tin oxide (SnO 2 ) are 83 at % and 17 at %, respectively. That is, when weight ratios of the indium oxides in the indium zinc oxide and the indium tin oxide are the same as each other, an atomic weight ratio of the indium oxide in the indium-zinc oxide is relatively less than that of the indium oxide in the indium-tin oxide. It is more preferable that the first electrode  270  is made of the indium zinc oxide in which the atomic weight ratio of the indium oxide is less, than that the first electrode  270  is made of the indium-tin oxide. 
     For example, the first electrode  270  may be made of an indium-zinc oxide in which a weight ratio of the indium oxide (In 2 O 3 ) is 20 wt % and a weight ratio of the zinc oxide (ZnO) is 80 wt %. Here, in the indium-zinc oxide, an atomic weight ratio of the indium oxide (In 2 O 3 ) is 7 at %, and an atomic weight ratio of the zinc oxide (ZnO) is 93 at %. In addition, the first electrode  270  may be made of an indium-zinc oxide in which a weight ratio of the indium oxide (In 2 O 3 ) is 10 wt % and a weight ratio of the zinc oxide (ZnO) is 90 wt %. Here, in the indium-zinc oxide, an atomic weight ratio of the indium oxide (In 2 O 3 ) is 3 at %, and an atomic weight ratio of the zinc oxide (ZnO) is 97 at %. 
     An interlayer insulating layer  180   c  is formed on the first electrode  270 . The interlayer insulating layer  180   c  may be made of an inorganic insulating material such as a silicon nitride (SiN x ), a silicon oxide (SiO x ), or the like. 
     In order to deposit the interlayer insulating layer  180   c  made of the silicon nitride (SiN x ) or the silicon oxide (SiO x ), hydrogen gas (H 2 ) or silane (SiH 4 ) gas is used. A hydrogen radical is generated from this reaction gas to allow a reduction reaction to be generated while taking away oxygen of the first electrode  270  made of the transparent metal oxide. A material in which the reduction reaction is most highly generated among transparent metal oxides is the indium oxide (In 2 O 3 ). In an exemplary embodiment of the present invention, the first electrode  270  is made of a transparent metal oxide that contains a low content of the indium oxide (In 2 O 3 ) or does not contain the indium oxide (In 2 O 3 ), thereby making it possible to prevent the generation of the reduction reaction in a process of depositing the interlayer insulating layer  180   c . Therefore, it is possible to prevent an indium metal from being precipitated, and transmittance is increased. 
     Second electrodes  191  are formed on the interlayer insulating layer  180   c . The second electrodes  191  of the respective pixels PX may have a planar shape. The second electrode  191  is overlapped with the plurality of branch elements  273  of the first electrode  270 . The second electrode  191  and the first electrode  270  are separated from each other by the interlayer insulating layer  180   c . The interlayer insulating layer  180   c  serves to insulate the second electrode  191  and the first electrode  270  from each other. 
     The second electrode  191  may include a protrusion part  193  for connection to another layer. The protrusion part  193  of the second electrode  191  is physically and electrically connected to the drain electrode  175  through the contact hole  185   a  to receive a voltage applied from the drain electrode  175 . The second electrode  191  may be made of a transparent metal oxide such as an indium tin oxide (ITO), an indium zinc oxide (IZO), or the like. 
     The second electrode  191  may include a side bent along a bent shape of the data line  171 . For example, the second electrode  191  may be formed of a polygon including a side bent at least once in the portion corresponding to the horizontal central line CL of the pixel PX. 
     The second electrode  191  receiving the data voltage through the switching element SW and the first electrode  270  receiving the common voltage Vcom, which are two electric field generating electrodes, generate an electric field in the liquid crystal layer  3  together with each other, thereby determining a direction of liquid crystal molecules  31  of the liquid crystal layer  3  and displaying an image. Particularly, the branch electrodes  273  of the first electrode  270  form a fringe field in the liquid crystal layer  3  together with the second electrode  191 , thereby making it possible to determine an alignment direction of the liquid crystal molecules  31 . The liquid crystal display device according to an exemplary embodiment of the present invention may further include at least one polarizer, and be operated in a normally black mode or a normally white mode depending on a polarization axis direction of the polarizer. 
     According to another exemplary embodiment of the present invention, positions of the second electrode  191  and the first electrode  270  may also be exchanged with each other. That is, although the case in which the interlayer insulating layer  180   c  is formed on the first electrode  270  and the second electrode  191  is formed on the interlayer insulating layer  180   c  has been described in the present exemplary embodiment, the interlayer insulating layer  180   c  may be formed on the second electrode  191 , and the first electrode  270  may be formed on the interlayer insulating layer  180   c . In addition, the second electrode  191  may include branch electrodes and slits, and the first electrode  270  may have a planar shape. 
     Although not shown, a first alignment layer may be formed on an inner surface of the lower display panel  100 . The first alignment layer may be positioned on the second electrode  191 . 
     Next, the upper display panel  200  will be described. 
     A light blocking member  220  is formed on a second insulation substrate  210  made of transparent glass, plastic, or the like. The light blocking member  220  is also called a black matrix and prevents light leakage. The light blocking member  220  may be formed at boundary parts of pixel areas, such as the gate lines  121 , the data lines  171 , and the thin film transistors, and the like. 
     A plurality of color filters  230  are also formed on the second insulation substrate  210 . The color filters  230  may be mainly present in regions enclosed by the light blocking member  220 , and may be lengthily extended in the vertical direction along a column of the second electrode  191 . Each of the color filters  230  may display one of primary colors such as three primary colors including a red, a green, and a blue. An example of the primary colors may include three primary colors of a red, a green, and a blue, and a yellow, a cyan, a magenta, and the like. Although not shown, the color filters may further include a color filter displaying a mixed color of the primary colors or a white in addition to the primary colors. 
     An overcoat  250  may be formed on the color filters  230  and the light blocking member  220 . The overcoat  250  may be made of an organic insulating material, prevent the color filters  230  from being exposed, and provide a flat surface. The overcoat  250  may also be omitted. 
     Although not shown, a second alignment layer may be formed on an inner surface of the upper display panel  200 . The second alignment layer may be positioned on the overcoat  250 . 
     The liquid crystal layer  3  may include the liquid crystal molecules  31  having a dielectric anisotropy. The liquid crystal molecule  31  may have a positive dielectric anisotropy or a negative dielectric anisotropy. The liquid crystal molecule  31  may be arranged so that a long side thereof is in parallel with the display panels  100  and  200  in a state in which the electric field is not present in the liquid crystal layer  3 . That is, the liquid crystal molecule  31  may be horizontally aligned. The liquid crystal molecule  31  may also be aligned so as to have a pre-tilt in a predetermined direction. 
     Next, the liquid crystal display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 3 . 
     Since the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 3  is substantially similar to the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIGS. 1 and 2 , a description therefor will be omitted. The liquid crystal display device according to the present exemplary embodiment is partially different from the liquid crystal display device according to the previous exemplary embodiment in that a first electrode is configured of a double layer, which will be described in detail. 
       FIG. 3  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
     Similar to the previous exemplary embodiment, the liquid crystal display device according to an exemplary embodiment of the present invention includes a lower display panel  100  and an upper display panel  200  facing each other, and a liquid crystal layer  3  interposed between the upper and lower display panels  100  and  200 . 
     The lower display panel  100  includes gate lines  121  and data lines  171  positioned on a first insulation substrate  110  and thin film transistors connected to the gate lines  121  and the data lines  171 . A first passivation layer  180   a  and a second passivation layer  180   b  are positioned on the gate lines  121 , the data lines  171 , and the thin film transistors. First electrodes  270  are positioned on the second passivation layer  180   b , an interlayer insulating layer  180   c  is positioned on the first electrodes  270 , and second electrodes  191  are positioned on the interlayer insulating layer  180   c.    
     The first electrode  270  is formed of the single layer in the previous exemplary embodiment, while the first electrode  270  is formed of a double layer in the present exemplary embodiment. The first electrode  270  includes a first layer  270   a  and a second layer  270   b  positioned under the first layer  270   a.    
     The first layer  270   a  of the first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The first layer  270   a  of the first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the first layer  270   a  of the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the first layer  270   a  of the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     The second layer  270   b  of the first electrode  270  may be made of an indium zinc oxide (IZO) or an indium tin oxide (ITO). Here, a weight ratio of an indium oxide (In 2 O 3 ) in the indium zinc oxide (IZO) or the indium tin oxide (ITO) may be 80 wt % or more. That is, the second layer  270   b  of the first electrode  270  may contain a large amount of indium-zinc oxide. 
     The interlayer insulating layer  180   c  is positioned on the first electrode  270 , and the first layer  270   a  of the first electrode  270  is exposed in a process of forming the interlayer insulating layer  180   c . That is, the interlayer insulating layer  180   c  contacts the first layer  270   a  of the first electrode  270 , and does not contact the second layer  270   b  of the first electrode  270 . A reduction reaction may be generated by hydrogen gas (H 2 ) or silane (SiH 4 ) gas used in order to deposit the interlayer insulating layer  180   c  made of a silicon nitride (SiN x ) or a silicon oxide (SiO x ). In an exemplary embodiment of the present invention, the first layer  270   a  of the first electrode  270  exposed in the process of forming the interlayer insulating layer  180   c  is made of a transparent metal oxide that contains a low content of the indium oxide (In 2 O 3 ) or does not contain the indium oxide (In 2 O 3 ), thereby making it possible to prevent the generation of the reduction reaction in a process of depositing the interlayer insulating layer  180   c.    
     In addition, in the present exemplary embodiment, the second layer  270   b  of the first electrode  270  that does not directly contact the interlayer insulating layer  180   c  may be made of a transparent metal oxide in which a content of the indium oxide (In 2 O 3 ) is high. The higher the content of the indium oxide (In 2 O 3 ), the higher the electrical conductivity. Since the second layer  270   b  of the first electrode  270  is not exposed in the process of forming the interlayer insulating layer  180   c , the reduction reaction is not generated in the second layer  270   b . Therefore, in the present exemplary embodiment, precipitation of the indium metal is prevented, thereby making it possible to increase transmittance and improve electrical conductivity of the first electrode  270 . 
     Next, the liquid crystal display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 4 . 
     Since the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 4  is substantially similar to the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 3 , a description therefor will be omitted. The liquid crystal display device according to the present exemplary embodiment is partially different from the liquid crystal display device according to the previous exemplary embodiment in that a first electrode is configured of a triple layer, which will be described in detail. 
       FIG. 4  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
     Similar to the previous exemplary embodiment, the liquid crystal display device according to an exemplary embodiment of the present invention includes a lower display panel  100  and an upper display panel  200  facing each other, and a liquid crystal layer  3  interposed between the upper and lower display panels  100  and  200 . 
     The lower display panel  100  includes gate lines  121  and data lines  171  positioned on a first insulation substrate  110  and thin film transistors connected to the gate lines  121  and the data lines  171 . A first passivation layer  180   a  and a second passivation layer  180   b  are positioned on the gate lines  121 , the data lines  171 , and the thin film transistors. First electrodes  270  are positioned on the second passivation layer  180   b , an interlayer insulating layer  180   c  is positioned on the first electrodes  270 , and second electrodes  191  are positioned on the interlayer insulating layer  180   c.    
     The first electrode  270  is formed of the double layer in the previous exemplary embodiment, while the first electrode  270  is formed of a triple layer in the present exemplary embodiment. The first electrode  270  includes a first layer  270   a , a second layer  270   b  positioned under the first layer  270   a , and a third layer  270   c  positioned under the second layer  270   b.    
     The first layer  270   a  of the first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The first layer  270   a  of the first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the first layer  270   a  of the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the first layer  270   a  of the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     The second layer  270   b  of the first electrode  270  may be made of an indium zinc oxide (IZO) or an indium tin oxide (ITO). Here, a weight ratio of an indium oxide (In 2 O 3 ) in the indium zinc oxide (IZO) or the indium tin oxide (ITO) may be 80 wt % or more. That is, the second layer  270   b  of the first electrode  270  may contain a large amount of indium-zinc oxide. 
     The third layer  270   c  of the first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The third layer  270   c  of the first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the third layer  270   c  of the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the third layer  270   c  of the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     Next, the liquid crystal display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 5 . 
     Since the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 5  is substantially similar to the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 3 , a description therefor will be omitted. The liquid crystal display device according to the present exemplary embodiment is partially different from the liquid crystal display device according to the previous exemplary embodiment in that a mixed layer is further positioned between first and second layers of a first electrode, which will be described in detail 
       FIG. 5  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
     Similar to the previous exemplary embodiment, the liquid crystal display device according to an exemplary embodiment of the present invention includes a lower display panel  100  and an upper display panel  200  facing each other, and a liquid crystal layer  3  interposed between the upper and lower display panels  100  and  200 . 
     The lower display panel  100  includes gate lines  121  and data lines  171  positioned on a first insulation substrate  110  and thin film transistors connected to the gate lines  121  and the data lines  171 . A first passivation layer  180   a  and a second passivation layer  180   b  are positioned on the gate lines  121 , the data lines  171 , and the thin film transistors. First electrodes  270  are positioned on the second passivation layer  180   b , an interlayer insulating layer  180   c  is positioned on the first electrodes  270 , and second electrodes  191  are positioned on the interlayer insulating layer  180   c.    
     The first electrode  270  includes a first layer  270   a  and a second layer  270   b  positioned under the first layer  270   a . In addition, the first electrode further includes a first mixed layer  270   m  positioned between the first and second layers  270   a  and  270   b.    
     The first layer  270   a  of the first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The first layer  270   a  of the first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the first layer  270   a  of the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the first layer  270   a  of the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     The second layer  270   b  of the first electrode  270  may be made of an indium zinc oxide (IZO) or an indium tin oxide (ITO). Here, a weight ratio of an indium oxide (In 2 O 3 ) in the indium zinc oxide (IZO) or the indium tin oxide (ITO) may be 80 wt % or more. That is, the second layer  270   b  of the first electrode  270  may contain a large amount of indium-zinc oxide. 
     The first mixed layer  270   m  of the first electrode  270  is made of a mixture of a first material configuring the first layer  270   a  and a second material configuring the second layer  270   b . Here, ratios of the first material and the second material are changed in a thickness direction. The closer to the first layer  270   a , the higher the ratio of the first material in the first mixed layer  270   m , and the closer to the second layer  270   b , the higher the ratio of the second material in the first mixed layer  270   m . That is, a ratio of the first material is higher than that of the second material in an upper region of the first mixed layer  270   m , a ratio of the second material is higher than that of the first material in a lower region of the first mixed layer  270   m , and ratios of the first material and the second material are similar to each other in an intermediate region of the first mixed layer  270   m.    
     A change in a refractive index of the first electrode  270  depending on a mixed ratio of the first and second materials will be described below with reference to  FIG. 6 . 
       FIG. 6  is a view showing a change in a refractive index of a first electrode in a thickness direction in the liquid crystal display device according to an exemplary embodiment of the present invention. 
     The first layer  270   a  of the first electrode  270  may be made of the aluminum zinc oxide (AZO), and the second layer  270   b  thereof may be made of the indium tin oxide (ITO). Here, the first mixed layer  270   m  may be made of a mixture of the aluminum zinc oxide (AZO) and the indium tin oxide (ITO). 
     A refractive index of the first layer  270   a  made of the aluminum zinc oxide (AZO) is about 1.8, and a refractive index of the second layer  270   b  made of the indium tin oxide (ITO) is about 1.6. A refractive index of the first mixed layer  270   m  may be between about 1.6 and about 1.8. Since a ratio of the aluminum zinc oxide (AZO) is higher than that of the indium tin oxide (ITO) in the upper region of the first mixed layer  270   m , the upper region of the first mixed layer  270   m  has a refractive index close to 1.8. Since a ratio of the indium tin oxide (ITO) is higher than that of the aluminum zinc oxide (AZO) in the lower region of the first mixed layer  270   m , the lower region of the first mixed layer  270   m  has a refractive index close to 1.6. Since ratios of the aluminum zinc oxide (AZO) and the indium tin oxide (ITO) are similar to each other in the intermediate region of the first mixed layer  270   m , the intermediate region of the first mixed layer  270   m  has a refractive index of about 1.7. 
     In the first mixed layer  270   m , ratios of the first material and the second material are gradually changed, such that a refractive index is gradually changed. In a region in which the refractive index is rapidly changed, interface reflection is generated. In the present exemplary embodiment, since the first mixed layer  270   m  in which the refractive index is gradually changed is present between the first layer  270   a  and the second layer  270   b  of the first electrode  270 , it is possible to prevent the interface reflection from being generated. 
     Next, a method of forming the first layer  270   a , the first mixed layer  270   m , and the second layer  270   b  of the first electrode  270  will be described with reference to  FIGS. 7 and 11 . 
       FIGS. 7 to 11  are process cross-sectional views showing a method of forming a first layer, a first mixed layer, and a second layer of the first electrode. 
     The first electrode may be formed by an atomic layer deposition (ALD) method or a plasma enhanced atomic layer deposition (PEALD) method. 
     The atomic layer deposition (ALD) method is a kind of thin film deposition method. First, a reactant A including a metal source of a thin film that is to be formed is injected onto and adsorbed on a surface of a substrate mounted in a reaction chamber for a predetermined time, and purge gas of nitrogen (N2), argon (Ar), helium (H), or the like, which is inert gas, is injected to remove the reactant A in a gas state that remains without reacting. Then, a reactant B is injected as reaction gas for exchange with the reactant A adsorbed on the substrate to induce an exchange reaction in the reactant A adsorbed on the substrate, thereby forming the thin film. One cycle of deposition process of forming one layer of thin film through the injection of the reactant A→the injection of the purge gas→the injection of the reactant B→the injection of the purge gas as described above is performed plural times, thereby forming a thin film having a desired thickness. 
     The plasma enhanced atomic layer deposition (PEALD) method is similar to the atomic layer deposition (ALD) method, and one cycle of deposition process configured of the injection of the reactant A→the injection of the purge gas→the injection of the reactant B→the injection of the purge gas is repeated in the plasma enhanced atomic layer deposition (PEALD) method. Here, plasma is generated at the time of injecting the reactant B or the reactant B is injected in a plasma state to form a thin film. 
     First, as shown in  FIG. 7 , the second layer  270   b  made of a second material  274  is formed. The second material  274  may be an indium tin oxide (ITO). The second material  274  is deposited by an atomic layer deposition method or a plasma enhanced atomic layer deposition method. 
     The second material  274  is deposited through one cycle configured of injection of cyclopentadienyl indium (InCp)→injection of purge gas→injection of ozone (O 3 )→injection of purge gas→injection of tetrakis-dimethyl-amine tin (TDMASn)→injection of purge gas→injection of hydrogen peroxide (H 2 O 2 ). A process of depositing the second material  274  is repeated plural times. 
     Then, as shown in  FIG. 8 , a lower region  270   m   1  of the first mixed layer  270   m  made of a mixture of the second material  274  and a first material  275  is formed on the second layer  270   b  made of the second material  274 . The first material  275  may be an aluminum zinc oxide (AZO). The first material  275  and the second material  274  are deposited by an atomic layer deposition method or a plasma enhanced atomic layer deposition method. 
     The second material  274  is deposited through one cycle configured of injection of cyclopentadienyl indium (InCp)→injection of purge gas→injection of ozone (O 3 )→injection of purge gas→injection of tetrakis-dimethyl-amine tin (TDMASn)→injection of purge gas→injection of hydrogen peroxide (H 2 O 2 ). 
     The first material  275  is deposited through one cycle configured of injection of diethyzinc (DEZn)→injection of purge gas→injection of water vapor (H 2 O)→injection of purge gas→injection of trimethylaluminum (TMAl)→injection of purge gas→injection of water vapor (H 2 O)→injection of purge gas. 
     In the lower region  270   m   1  of the first mixed layer  270   m , the repetition number of cycle of depositing the second material  274  is more than that of cycle of deposing the first material  275 . For example, after the cycle of depositing the second material  274  is repeated about ten times, the cycle of depositing the first material  275  is performed about once. Therefore, in the lower region  270   m   1  of the first mixed layer  270   m , a thin film thickness of the second material  274  is thicker than that of the first material  275 . 
     Then, as shown in  FIG. 9 , the cycle of depositing the second material  274  and the cycle of depositing the first material  275  are repeated, respectively, to form the first mixed layer  270   m . Here, the repetition number of cycle of depositing the second material  274  is gradually decreased, and the repetition number of cycle of depositing the first material  275  is gradually increased. 
     In an intermediate region  270   m   2  of the first mixed layer  270   m , the repetition number of cycle of depositing the second material  274  is similar to that of cycle of deposing the first material  275 . For example, after the cycle of depositing the second material  274  is repeated about five times, the cycle of depositing the first material  275  is repeated about five times. Therefore, in the intermediate region  270   m   2  of the first mixed layer  270   m , a thin film thickness of the second material  274  is similar to that of the first material  275 . 
     Then, as shown in  FIG. 10 , the cycle of depositing the second material  274  and the cycle of depositing the first material  275  are repeated, respectively, to form the first mixed layer  270   m . Here, the repetition number of cycle of depositing the second material  274  is gradually decreased, and the repetition number of cycle of depositing the first material  275  is gradually increased. 
     In an upper region  270   m   3  of the first mixed layer  270   m , the repetition number of cycle of depositing the second material  274  is less than that of cycle of deposing the first material  275 . For example, after the cycle of depositing the second material  274  is performed about once, the cycle of depositing the first material  275  is performed about ten times. Therefore, in the upper region  270   m   3  of the first mixed layer  270   m , a thin film thickness of the second material  274  is thinner than that of the first material  275 . 
     Then, as shown in  FIG. 11 , the cycle of depositing the first material  275  is repeated to form the first layer  270   a.    
     As described above, a layer made of only the second material, a layer made of only the first material, and a layer made of a mixture of the first and second materials may be formed using the atomic layer deposition method or the plasma enhanced atomic layer deposition method. In addition, in the layer made of the mixture of the first and second materials, thin film thicknesses of the first and second materials may be adjusted to adjust ratios of the first and second materials and allow the ratios of the first and second materials to be changed in the thickness direction. 
     Next, the liquid crystal display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 12 . 
     Since the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 12  is substantially similar to the liquid crystal display device according to an exemplary embodiment of the present invention shown in  FIG. 5 , a description therefor will be omitted. The liquid crystal display device according to the present exemplary embodiment is partially different from the liquid crystal display device according to the previous exemplary embodiment in that a third layer is further positioned under a second layer of a first electrode and a mixed layer is further positioned between the second and third layers of a first electrode, which will be described in detail 
       FIG. 12  is a cross-sectional view of the liquid crystal display device according to an exemplary embodiment of the present invention. 
     Similar to the previous exemplary embodiment, the liquid crystal display device according to an exemplary embodiment of the present invention includes a lower display panel  100  and an upper display panel  200  facing each other, and a liquid crystal layer  3  interposed between the upper and lower display panels  100  and  200 . 
     The lower display panel  100  includes gate lines  121  and data lines  171  positioned on a first insulation substrate  110  and thin film transistors connected to the gate lines  121  and the data lines  171 . A first passivation layer  180   a  and a second passivation layer  180   b  are positioned on the gate lines  121 , the data lines  171 , and the thin film transistors. First electrodes  270  are positioned on the second passivation layer  180   b , an interlayer insulating layer  180   c  is positioned on the first electrodes  270 , and second electrodes  191  are positioned on the interlayer insulating layer  180   c.    
     The first electrode  270  includes a first layer  270   a , a second layer  270   b  positioned under the first layer  270   a , and a third layer  270   c  positioned under the second layer  270   b . In addition, the first electrode  27  further includes a first mixed layer  270   m  positioned between the first layer  270   a  and the second layer  270   b  and a second mixed layer  270   n  positioned between the second layer  270   b  and the third layer  270   c.    
     The first layer  270   a  of the first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The first layer  270   a  of the first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the first layer  270   a  of the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the first layer  270   a  of the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     The second layer  270   b  of the first electrode  270  may be made of an indium zinc oxide (IZO) or an indium tin oxide (ITO). Here, a weight ratio of an indium oxide (In 2 O 3 ) in the indium zinc oxide (IZO) or the indium tin oxide (ITO) may be 80 wt % or more. That is, the second layer  270   b  of the first electrode  270  may contain a large amount of indium-zinc oxide. 
     The third layer  270   c  of the first electrode  270  may be an indium zinc oxide (IZO). The indium zinc oxide (IZO) is made of an indium oxide (In 2 O 3 ) and a zinc oxide (ZnO). Here, it is preferable that a weight ratio of the indium oxide is 20 wt % or less. The third layer  270   c  of the first electrode  270  may also be made of a transparent metal oxide that does not contain the indium oxide (In 2 O 3 ). For example, the third layer  270   c  of the first electrode  270  may be made of an aluminum zinc oxide (AZO) or a gallium zinc oxide (GZO). That is, it is preferable that the third layer  270   c  of the first electrode  270  does not contain the indium zinc oxide or contains a small amount of indium zinc oxide. 
     The first mixed layer  270   m  of the first electrode  270  is made of a mixture of a first material configuring the first layer  270   a  and a second material configuring the second layer  270   b . Here, ratios of the first material and the second material are changed in the thickness direction. The closer to the first layer  270   a , the higher the ratio of the first material in the first mixed layer  270   m , and the closer to the second layer  270   b , the higher the ratio of the second material in the first mixed layer  270   m . That is, a ratio of the first material is higher than that of the second material in an upper region of the first mixed layer  270   m , a ratio of the second material is higher than that of the first material in a lower region of the first mixed layer  270   m , and ratios of the first material and the second material are similar to each other in an intermediate region of the first mixed layer  270   m.    
     The second mixed layer  270   n  of the first electrode  270  is made of a mixture of the second material configuring the second layer  270   b  and the first material configuring the third layer  273   c . Here, ratios of the second material and the first material are changed in the thickness direction. The closer to the second layer  270   b , the higher the ratio of the second material in the second mixed layer  270   n , and the closer to the third layer  270   c , the higher the ratio of the first material in the second mixed layer  270   n . That is, a ratio of the second material is higher than that of the first material in an upper region of the second mixed layer  270   n , a ratio of the first material is higher than that of the second material in a lower region of the second mixed layer  270   n , and ratios of the first material and the second material are similar to each other in an intermediate region of the second mixed layer  270   n.    
     A change in a refractive index of the first electrode  270  depending on a mixed ratio of the first and second materials will be described below with reference to  FIG. 13 . 
       FIG. 13  is a view showing a change in a refractive index of a first electrode in a thickness direction in the liquid crystal display device according to an exemplary embodiment of the present invention. 
     The first layer  270   a  and the third layer  270   c  of the first electrode  270  may be made of the aluminum zinc oxide (AZO), and the second layer  270   b  thereof may be made of the indium tin oxide (ITO). Here, the first mixed layer  270   m  and the second mixed layer  270   n  may be made of a mixture of the aluminum zinc oxide (AZO) and the indium tin oxide (ITO). 
     Refractive indices of the first layer  270   a  and the third layer  270   c  made of the aluminum zinc oxide (AZO) are about 1.8, and a refractive index of the second layer  270   b  made of the indium tin oxide (ITO) is about 1.6. Refractive indices of the first mixed layer  270   m  and the second mixed layer  270   n  may be between about 1.6 and about 1.8. Since a ratio of the aluminum zinc oxide (AZO) is higher than that of the indium tin oxide (ITO) in the upper region of the first mixed layer  270   m  and the lower region of the second mixed layer  270   n , the upper region of the first mixed layer  270   m  and the lower region of the second mixed layer  270   n  have a refractive index close to 1.8. Since a ratio of the indium tin oxide (ITO) is higher than that of the aluminum zinc oxide (AZO) in the lower region of the first mixed layer  270   m  and the upper region of the second mixed layer  270   n , the lower region of the first mixed layer  270   m  and the upper region of the second mixed layer  270   n  have a refractive index close to 1.6. Since ratios of the aluminum zinc oxide (AZO) and the indium tin oxide (ITO) are similar to each other in the intermediate region of the first mixed layer  270   m  and the intermediate region of the second mixed layer  270   n , the intermediate region of the first mixed layer  270   m  and the intermediate region of the second mixed layer  270   n  have a refractive index of about 1.7. 
     In the first mixed layer  270   m  and the second mixed layer  270   n , ratios of the first and second materials are gradually changed, such that a refractive index is gradually changed. In a region in which the refractive index is rapidly changed, interface reflection is generated. In the present exemplary embodiment, since the first mixed layer  270   m  in which the refractive index is gradually changed is present between the first layer  270   a  and the second layer  270   b  of the first electrode  270  and the second mixed layer  270   n  in which the refractive index is gradually changed is present between the second layer  270   b  and the third layer  270   c  of the first electrode  270 , it is possible to prevent the interface reflection from being generated 
     The first electrode  270  may be formed using an atomic layer deposition (ALD) method or a plasma enhanced atomic layer deposition (PEALD) method. The cycle of depositing the first material may be repeated to form a layer made of only the first material, and the cycle of depositing the second material may be repeated to form a layer made of only the second material. In addition, the cycle of depositing the first material and the cycle of depositing the second material may be repeated, respectively, to form a layer made of a mixture of the first material and the second material. Here, the repetition number of cycle of depositing the first material and the repetition number of cycle of depositing the second material are adjusted to adjust thin film thicknesses of the first material and the second material, thereby making it possible to adjust ratios of the first material and the second material. Therefore, the ratios of the first material and the second material may be changed in the thickness direction. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     DESCRIPTION OF SYMBOLS 
     
         
           110 : first insulation substrate 
           121 : gate line 
           171 : data line 
           180   a : first passivation layer 
           180   b : second passivation layer 
           180   c : interlayer insulating layer 
           191 : second electrode 
           210 : second insulation substrate 
           270 : first electrode 
           270   a : first layer of first electrode 
           270   b : second layer of first electrode 
           270   c : third layer of first electrode 
           270   m : first mixed layer of first electrode 
           270   m   1 : lower region of first mixed layer 
           270   m   2 : intermediate region of first mixed layer 
           270   m   3 : upper region of first mixed layer 
           270   n : second mixed layer of first electrode