Abstract:
An IPS mode LCD device with improved light efficiency by changing a common electrode and a pixel electrode in shape includes first and second substrates facing each other, a plurality of gate and data lines crossing each other on the first substrate for defining a plurality of pixel regions, at least one common electrode formed on the pixel region, wherein the common electrode is formed in shape such that an upper surface area is different than a lower surface area, at least one pixel electrode positioned between each of the common electrode on the pixel region, wherein the pixel electrode is formed in shape such that an upper surface area different larger than a lower surface area, and a liquid crystal layer between the first and second substrates.

Description:
[0001]     This application claims the benefit of the Korean Application No. P2004-40829 filed on Jun. 4, 2004, which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an In-Plane Switching (IPS) mode LCD device and method for manufacturing the same to improve the light efficiency by changing the shape of an electrode.  
         [0004]     2. Discussion of the Related Art  
         [0005]     Demands for various display devices have increased as we develop into an informational society. Accordingly, much effort has been made to research and develop various flat display devices such as liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescent displays (ELDs), and vacuum fluorescent displays (VFDs). Some species of the flat display devices are already being used as displays of various equipments.  
         [0006]     Among the various flat display devices, the liquid crystal display (LCD) device has been most widely used as a substitute for the cathode ray tube (CRT) because of thinness, lightness in weight, low power consumption and other advantageous characteristics. In addition to mobile-type LCD devices, such as displays for notebook computers, LCD devices have been developed to be used as computer monitors and, more recently, as televisions to receive and display broadcasting signals.  
         [0007]     Despite continued technical developments in LCD technology applied to various fields, research in enhancing the picture quality of LCD devices has been lacking as compared to other physical features and advantages of LCD devices. The key to developing LCD devices to be used as general displays for various applications depends on whether high quality pictures, such as high resolution and high luminance, can be implemented on large-sized screens while still maintaining light weight, thin size, and low power consumption.  
         [0008]     Generally, LCD devices include an LCD panel for displaying a picture image and a driving part for applying a driving signal to the LCD panel. The LCD panel includes first and second glass substrates bonded to each other at a predetermined interval, and a liquid crystal layer formed by injecting liquid crystal materials into the space between the first and second glass substrates.  
         [0009]     On the first glass substrate (TFT array substrate), there are a plurality of gate lines arranged in a first direction at fixed intervals, a plurality of data lines arranged in a second direction at fixed intervals and perpendicular to the gate lines, a plurality of pixel electrodes in respective pixel regions defined by the gate lines and the data lines arranged in a matrix, and a plurality of thin film transistors (TFTs) switchable in response to signals on the gate lines to transmit signals on the data line to the pixel electrodes. The second glass substrate (color filter array substrate) has a light-shielding layer for shielding light from areas other than from the pixel regions, a color filter layer (R, G, B) for displaying colors, and a common electrode for generating a picture image.  
         [0010]     The LCD device is driven according to optical anisotropic and polarizable characteristics of the liquid crystal material. Liquid crystal molecules are aligned using directional characteristics because liquid crystal molecules are long and thin. In this respect, an induced electric field is applied to the liquid crystal material to control the alignment direction of the liquid crystal molecules. By controlling the alignment direction of the liquid crystal molecules with the induced electric field, light is polarized and manipulated by the optical anisotropic properties of the liquid crystal, thereby generating a picture image. Currently, an active matrix type LCD, in which a TFT and a pixel electrode are connected and aligned in matrix form, is considered to be the best due to its high resolution and its ability to represent animated images.  
         [0011]     Hereinafter, related art LCD devices will be described with reference to the accompanying drawings.  FIG. 1  is an exploded perspective view of a Twisted Nematic (TN) mode LCD device according to the related art. As shown in  FIG. 1 , the TN mode LCD device according to the related art includes a lower substrate  1 , an upper substrate  2 , and a liquid crystal layer  3 , wherein the liquid crystal layer  3  is formed between the lower substrate  1  and the upper substrate  2 .  
         [0012]     Specifically, the lower substrate  1  includes a plurality of gate lines  4 , a plurality of data lines  5 , a plurality of pixel electrodes  6 , and a plurality of thin film transistors T. The plurality of gate lines  4  are formed on the lower substrate  1  in one direction at fixed intervals, and the plurality of data lines  5  are formed perpendicularly to the plurality of gate lines  4  at fixed intervals, thereby defining a plurality of pixel regions P. Plurality of pixel electrodes  6  are respectively formed in pixel regions P defined by the intersection of the plurality of gate and data lines  4  and  5 , respectively. Plurality of thin film transistors T are respectively formed at intersecting portions of the plurality of gate and data lines  4  and  5 . The upper substrate  2  includes a light-shielding layer  7  that excludes light from regions other than from the pixel regions P, R/G/B color filter layers  8  for displaying various colors, and a common electrode  9  for displaying a picture image.  
         [0013]     Thin film transistor T includes a gate electrode, a gate insulating layer (not shown), an active layer, a source electrode, and a drain electrode. The gate electrode projects from gate line  4 , and the gate insulating layer (not shown) is formed on an entire surface of the lower substrate  1 . Then, the active layer is formed on the gate insulating layer above the gate electrode. The source electrode projects from the data line  5 , and the drain electrode is formed on the opposite side of the source electrode. Also, the aforementioned pixel electrode  6  is formed of a transparent conductive metal having high transmittance, for example, ITO (Indium-Tin-Oxide).  
         [0014]     In the aforementioned LCD device, liquid crystal molecules of the liquid crystal layer  3  on pixel electrode  6  are aligned by a signal from the thin film transistor T. Light transmittance is controlled according to the alignment of the liquid crystal molecules in the liquid crystal layer  3 , thereby displaying a picture image. To align the liquid molecules, an LCD panel drives the liquid crystal molecules by applying an electric field perpendicular to the lower and upper substrates. This method achieves high transmittance and aperture ratio. Damage by static electricity to liquid crystal cells can be prevented since the common electrode  9  of the upper substrate  2  serves as the ground. However, a wide viewing angle is difficult to obtain using this technique.  
         [0015]     To overcome this problem, an in-plane switching (IPS) mode LCD device has been recently proposed. Hereinafter, a related art IPS mode LCD device will be described with reference to the accompanying drawings.  FIG. 2  is a plane view of a related art IPS mode LCD device.  FIG. 3  is a cross sectional view along I-I′ of  FIG. 2 . As shown in  FIG. 2  and  FIG. 3 , the related art IPS mode LCD device mainly includes a lower substrate  10 , an upper substrate  20 , and a liquid crystal layer  25 , wherein the liquid crystal layer  25  is formed between the lower substrate  10  and the upper substrate  20 .  
         [0016]     The lower substrate  10  includes a gate line  11 , a data line  12 , a common electrode  13 , and a pixel electrode  15 . The gate line  11  and the data line  12  cross each other to define a unit pixel region. The common electrode  13  and the pixel electrode  15  are formed at a predetermined interval within the pixel region. Generally, the common electrode  13  is positioned between each pixel electrode  15  with some portions of the common electrode  13  overlapping with the pixel electrode  15  to form a storage capacitor.  
         [0017]     Also, a thin film transistor TFT is formed on the lower substrate  10 , wherein the thin film transistor TFT includes a gate electrode  11   a,  a semiconductor layer  26 , and source and drain electrodes  12   a  and  12   b,  respectively. The gate electrode  1  la projects from the gate line  11 , and the semiconductor layer  26  is overlaps the gate electrode  11   a.  Gate insulating layer  14  is formed on the entire surface of the lower substrate  10  including the gate electrode  11   a.  The source and drain electrodes  12   a  and  12   b  are formed at both sides of the semiconductor layer  26 , wherein the source electrode  12   a  is formed at a predetermined interval from the drain electrode  12   b.  In this state, the drain electrode  12   b  of the thin film transistor TFT is connected with the pixel electrode  15 .  
         [0018]     The common electrode  13  is formed at a predetermined interval from the pixel electrode  15 , wherein the common electrode  13  is formed on the same layer as either the gate line  11  or the data line  12  when forming either respective line. In the drawings, the common electrode  13  is formed on the same layer as the gate line  11 .  
         [0019]     Insulating layer  16  is formed between the data line  12  and the pixel electrode  15 , wherein the insulating layer  16  is formed of the same material as the gate insulating layer  14 . For example, an inorganic insulating material such as SiN x  and SiO x  or an organic insulating material such as acryl, polyimide, BCB (BenzoCycloButene) and photo polymer may be used. Then, a passivation layer  17  and a first alignment layer  18  are sequentially formed on the entire surface of the lower substrate  10  including the insulating layer  16  and the pixel electrode  15 .  
         [0020]     The common electrode  13  is electrically connected with a common line  19 , whereby the common electrode  13  receives a voltage signal. When a voltage signal is applied to the pixel electrode  15  through the drain electrode  12   b,  the common electrode  13  generates an IPS mode electric field, thereby driving the liquid crystal molecules of the liquid crystal layer  25 .  
         [0021]     On the upper substrate  20 , there is a light-shielding layer  21  to prevent light leakage on the remaining portions of the lower substrate  10  except the pixel region. Upper substrate  20  further includes, a color filter layer  22  for obtaining colors red R, green G and blue B, an overcoat layer  23  for planarizing the color filter layer  22  having color films, and a second alignment layer  24  for defining the initial alignment of liquid crystal molecules. The first and second alignment layers  18  and  24  are rubbed at a pretilt angle of 2° to 5° such that the liquid crystal molecules are initially aligned in parallel to the lower and upper substrates  10  and  20 .  
         [0022]     The aforementioned drawings show an optical mode of a general IPS mode. In an initial state, light is not transmitted unit a voltage is applied (i.e. normally in a black state). On applying a voltage to the pixel electrode  15  and the common electrode  13 , an electric field is generated between the two electrodes  13  and  15  formed on the same substrate. The liquid crystal molecules of the liquid crystal layer  25  are aligned along the electric field formed between the two electrodes  13  and  15 . The internal light is then transmitted along the aligned liquid crystal molecules of the liquid crystal layer  25 , thereby representing a white state.  
         [0023]     During operation, aligning the liquid crystal molecules in a predetermined direction is difficult when applying the voltage to each electrode because the liquid crystal molecules corresponding to the common and pixel electrodes  13  and  15  are positioned in the area where the electric field is divided. Accordingly, in the display mode, disclination is generated at the portion where the electric field is divided. To prevent light leakage on the portions forming the common electrode  13  and the pixel electrode  15 , the common electrode  13  and the pixel electrode  15  are formed using metal or an alloy of ITO and metal.  
         [0024]     Both the common electrode  13  and the pixel electrode  15  are formed on the lower substrate  10 . The liquid crystal layer  25  is formed between the lower and upper substrates  10  and  20  at a predetermined interval therebetween, and the liquid crystal layer  25  is driven by the electric field formed between the common electrode  13  and the pixel electrode  15  on the lower substrate. The liquid crystal layer  25  is formed of liquid crystal molecules having positive dielectric anisotropic characteristics, whereby the longitudinal axes of liquid crystal molecules are aligned along the direction of the electric field.  
         [0025]     In the turn-off state, the IPS mode electric field is not applied to the common electrode  13  or the pixel electrode  15 , and the alignment direction of liquid crystal molecules in the liquid crystal layer  25  is not changed. In the turn-on state, the IPS mode electric field is applied to the common electrode  13  or the pixel electrode  15 , and the alignment direction of liquid crystal molecules in the liquid crystal layer  25  is changed, wherein the liquid crystal molecules are twisted at an angle of 45°.  
         [0026]      FIG. 4  is a cross sectional view for explaining an operation of the related art IPS mode LCD device. Referring to  FIG. 4 , the common electrode  13  and the pixel electrode  15  are alternately positioned in the related art IPS mode LCD device.  
         [0027]     In the related art IPS mode LCD device, the different voltages are respectively applied to the common electrode  13  and the pixel electrode  15 , whereby the IPS mode electric field is generated between the two electrodes  13  and  15 . Due to the liquid crystal molecules having the liquid crystal molecules having positive dielectric anisotropic characteristic, the liquid crystal molecules are aligned in parallel along the IPS mode electric field formed between the two electrodes. As shown in  FIG. 4 , a complete IPS mode electric field is formed in region A between the common electrode  13  and the pixel electrode  15 . This field causes the liquid crystal molecules to become aligned in parallel to the field. However, in region B above the common electrode  13  and the pixel electrode  15 , only a partial IPS mode electric field is formed. Consequently, the liquid crystal molecules in Region B do not become completely aligned in parallel.  
         [0028]     In the IPS mode LCD device, the common electrode  13  and the pixel electrode  15 , positioned in the pixel region, are formed of the light-shielding metal material. The light shielding material blocks about 15% of light emitted from a backlight unit.  
         [0029]     As compared with a non-IPS mode LCD device, the IPS mode LCD device has lower light efficiency. In order to overcome this problem, the backlight unit uses more power. However, high power consumption by the backlight unit is disadvantageous for small-sized mobile products, such as mobile phones, notebook computers, PDAs and the like. Accordingly, the related art IPS mode LCD device has the following disadvantages.  
         [0030]     First, the common electrode and the pixel electrode have rectangular cross sections. Accordingly, even though a complete IPS mode electric field is formed between the common electrode and the pixel electrode, the rectangular cross sections prevent IPS mode electric field from being formed above the common electrode and the pixel electrode. This non-IPS region formed above the common electrode and the pixel electrode prevents the liquid crystal molecules from becoming completely aligned above the common electrode and the pixel electrode.  
         [0031]     Secondly, the common electrode and the pixel electrode of the related art IPS mode LCD device are formed of the light-shielding metal material in the pixel region. This configuration blocks about 15% of the light emitted from the backlight unit. Accordingly, even though the IPS mode LCD device has a wider viewing angle in compared to the non-IPS mode LCD device, the IPS mode LCD device has lower light efficiency. In order to overcome this problem, the backlight unit for the IPS mode LCD device uses more power. High power consumption of the backlight unit is disadvantageous for small-sized mobile products, such as, mobile phones, notebook computers, PDAs and the like. Without the appropriate amount of power provided to these products, proper luminance is difficult to obtain in the mobile products. Accordingly, even though the IPS mode LCD device has a wide viewing angle, its low light efficiency hinders the competitiveness of the IPS mode LCD device over non-IPS mode LCD devices.  
       SUMMARY OF THE INVENTION  
       [0032]     Accordingly, the present invention is directed to an IPS mode LCD device that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0033]     An object of the present invention is to provide an IPS mode LCD device and method for manufacturing the same, to improve the light efficiency by changing the shape of a common electrode and a pixel electrode.  
         [0034]     Additional advantages, objects, and features of the invention will become apparent to one of ordinary skill in the art as set forth in part in the description which follows and in part upon examination of the following, or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0035]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an exemplary embodiment of an IPS mode LCD device of the present invention includes first and second substrates facing each other, a plurality of gate and data lines crossing each other on the first substrate for defining a plurality of pixel regions, at least one common electrode formed on the pixel region, wherein the common electrode is formed in shape such that an upper surface area is different than a lower surface area, at least one pixel electrode positioned between each of the common electrode on the pixel region, wherein the pixel electrode is formed in shape such that an upper surface area is different than a lower surface area, and a liquid crystal layer between the first and second substrates.  
         [0036]     In another aspect, an IPS mode LCD device includes first and second substrates facing each other, a plurality of gate and data lines crossing each other on the first substrate for defining a plurality of pixel regions, at least one common electrode formed on the pixel region, at least one pixel electrode positioned between each of the common electrode, a transparent dielectric layer for covering the common electrode and the pixel electrode, wherein the transparent dielectric layer is formed in shape such that an upper surface area is different than a lower surface area, and a liquid crystal layer between the first and second substrates.  
         [0037]     In yet another aspect, a method for manufacturing an IPS mode LCD device includes the steps of forming a gate line on a substrate, forming at least one common electrode in a pixel region on the substrate, the at least one common electrode having a shape such that an upper surface area is different than a lower surface area, forming a data line in perpendicular with the gate line, to define pixel regions, forming a thin film transistor at a crossing portion of the gate and data lines, and forming at least one pixel electrode in parallel with the common electrodes, the at least one pixel electrode having a shape such that an upper surface area is different than a lower surface area.  
         [0038]     In yet another aspect, a method for manufacturing an IPS mode LCD device includes the steps of forming a gate line on a substrate, forming at least one common electrode in a pixel region on the substrate, forming a data line in perpendicular with the gate line, to define pixel regions, forming a thin film transistor at a crossing portion of the gate and data lines, forming at least one pixel electrode in parallel with the common electrodes, and forming a transparent dielectric layer for covering the at least one common electrode and the at least one pixel electrode, wherein the transparent dielectric layer is formed in shape such that an upper surface area is different than a lower surface area.  
         [0039]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:  
         [0041]      FIG. 1  is an exploded perspective view of a TN mode LCD device according to the related art;  
         [0042]      FIG. 2  is a plane view of an IPS mode LCD device according to the related art;  
         [0043]      FIG. 3  is a cross sectional view of the IPS mode LCD device along I-I′ of  FIG. 2 ;  
         [0044]      FIG. 4  is a cross sectional view for explaining an operation of an IPS mode LCD device according to the related art;  
         [0045]      FIG. 5A -C are cross sectional views of an IPS mode LCD device according to exemplary embodiments of the present invention;  
         [0046]      FIG. 6A -C are cross sectional views of an IPS mode LCD device according to exemplary embodiments of the present invention;  
         [0047]      FIG. 7  is a plane view of an IPS mode LCD device according to the present invention;  
         [0048]      FIG. 8  is a cross sectional view of an IPS mode LCD device along II-II′ of  FIG. 7 , according to the first embodiment of the present invention; and  
         [0049]      FIG. 9  is a cross sectional view of an IPS mode LCD device along II-II′ of  FIG. 7 , according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Hereinafter, an IPS mode LCD device according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.  
         [0051]      FIG. 5A  is a cross sectional view of an IPS mode LCD device according to a first embodiment of the present invention. As shown in  FIG. 5A , a pixel electrode  104  and a common electrode  105  are alternately formed on a lower substrate  100  of the IPS mode LCD device. In particular, the pixel electrode  104  and the common electrode  105  are shaped such that an upper surface area is different than a lower surface area. Accordingly, when a voltage is applied to the pixel electrode  104  and the common electrode  105 , an IPS mode electric field is formed uniformly around the electrodes except at the top points of the two electrodes  104  and  105 . This allows the liquid crystal molecules to be aligned smoothly regardless of the division of regions.  
         [0052]     In this embodiment, the cross sectional view of  FIG. 5A  shows the pixel electrode  104  and the common electrode  105  are formed in shape of a semicircle. However, the pixel electrode  104  and the common electrode  105  may be formed in shape of a triangle or a trapezoid as shown in  FIG. 5B  and  FIG. 5C , respectively.  
         [0053]     Also, the pixel electrode  104  and the common electrode  105  are formed of a metal material having high reflectivity, such as, aluminum (Al) or silver (Ag). Accordingly, when the external light is incident on the pixel electrode  104  and the common electrode  105 , the light is reflected from the top points of the pixel electrode  104  and the common electrode  105 . In other words, the external light is used as a partial light source in conjunction with the light emitted from a backlight unit (not shown) to improve the light efficiency. In this case, like the related art, the light emitted from the backlight unit incident with the flat surface of the pixel electrode  104  and the common electrode  105  are shielded. However, the external light incident with the top points of the pixel electrode  104  and the common electrode  105  are reflected back. This allows the reflected light to be used as a light source, thereby improving the light efficiency.  
         [0054]      FIG. 6A  is a cross sectional view of an IPS mode LCD device according to a second embodiment of the present invention. As shown in  FIG. 6A , a pixel electrode  104  and a common electrode  105  are alternately formed on a lower substrate  100  of the IPS mode LCD device according to the second embodiment of the present invention. In addition, a transparent dielectric layer  140  covers an upper surface of the pixel electrode  104  and the common electrode  105 . The transparent dielectric layer  140  is shaped such that an upper surface area is different than a lower surface area.  
         [0055]     Like the related art LCD device, the pixel electrode  104  and the common electrode  105  in the IPS mode LCD device according to the second embodiment of the present invention have an upper surface area having the same size as a lower surface area. The cross sectional shape is that of a rectangle. However, a transparent dielectric layer  140  is formed to cover the upper surfaces of each of the pixel electrode  104  and the common electrode  105 . The transparent dielectric layer  140  is formed of a material having a dielectric constant that is the same as, or similar to that of the liquid crystal material. The transparent dielectric layer  140  may be formed of an inorganic material layer or an organic material layer.  
         [0056]     The transparent dielectric layer  140  is positioned on each of the pixel electrode  104  and the common electrode  105 , to compensate for the path of light reflected from the pixel electrode  104  and the common electrode  105 , in order to form a parallel electric field on the upper surfaces of the pixel electrode  104  and the common electrode  105 . Accordingly, when a voltage is applied to the pixel electrode  104  and the common electrode  105 , an IPS mode electric field is formed uniformly around the electrodes except at the top points of the two electrodes  104  and  105 . This allows the liquid crystal molecules to be aligned smoothly regardless of the division of regions.  
         [0057]     In the embodiment, the cross sectional view of  FIG. 6A  shows the transparent dielectric layer  140  is formed in shape of a semicircle. However, the transparent dielectric layer  140  may be formed in shape of a triangle or a trapezoid as shown in  FIG. 6B  and  FIG. 6C , respectively.  
         [0058]     Hereinafter, a method for manufacturing an IPS mode LCD device according to the preferred exemplary embodiments of the present invention will be described with reference to the accompanying drawings.  FIG. 7  is a plane view of an IPS mode LCD device according to the preferred embodiments of the present invention.  FIG. 8  is a cross sectional view of an IPS mode LCD device along II-II′ of  FIG. 7 , according to the first embodiment of the present invention.  
         [0059]     As shown in  FIG. 7  and  FIG. 8 , the IPS mode LCD device according to the first embodiment of the present invention includes a lower substrate  100 . A gate line  101  and a data line  102  are formed on the lower substrate  100 , wherein the gate line  101  and the data line  102  cross each other to define a unit pixel region. Then, a pixel electrode  104  and a common electrode  105  are formed at a predetermined interval from each other within the pixel region. As mentioned above, the pixel electrode  104  and the common electrode  105  are shaped such that an upper surface area is different than a lower surface area.  
         [0060]     After that, a thin film transistor TFT is formed on the lower substrate  100 . The thin film transistor TFT is comprised of a gate electrode  101   a,  a semiconductor layer  103 , and source and drain electrodes  102   a  and  102   b.  At this time, the gate electrode  101   a  projects from the gate line  101 , and the semiconductor layer  103  is overlaps the gate electrode  101   a  with a gate insulating layer  107  formed on an entire surface of the lower substrate  100  including the gate electrode  101   a.  Also, the source and drain electrodes  102   a  and  102   b  are formed on both sides of the semiconductor layer  103 , wherein the source and drain electrodes  102   a  and  102   b  are formed at a predetermined interval therebetween. Also, the drain electrode  102   b  of the thin film transistor TFT is connected with the pixel electrode  104 .  
         [0061]     The pixel electrode  104  is formed at the same layer as the data line  102 , and the common electrode  105  and a common line  106  are formed at the same layer as the gate line  101 . The gate line  101  and the data line  102  may be formed of a radioactive metal or a metal coated with a radioactive material. The common electrode  105  is positioned between each of the pixel electrode  104 , wherein the common electrode  105  is electrically connected with the common line  106  for receiving a common voltage. The common electrode  105  is formed at the same layer as the common line  106 , thereby improving the integration of components.  
         [0062]     Then, the gate insulating layer  107  is formed on the gate line  101  having the gate electrode  101   a,  the common line  106 , and the common electrode  105 , wherein the gate insulating layer  107  is insulated from the gate line  101  having the gate electrode  101   a,  the common line  106  and the common electrode  105 . The gate insulating layer  107  may be formed of an inorganic insulating layer such as SiN x  and SiO x , or an organic insulating layer, such as acryl, polyimide, BCB (BenzoCycloButene) and photo polymer.  
         [0063]     After that, a passivation layer  108  is formed on the gate insulating layer  107  including the pixel electrode  104 . The passivation layer  108  is formed with the same material as the gate insulating layer  107  (i.e., the inorganic insulating layer such as SiN x  and SiO x  or the organic insulating layer such as acryl, polyimide, BCB (BenzoCycloButene) and photo polymer). Then, a first alignment layer  121  is formed on an entire surface of the passivation layer  108  for initially aligning the liquid crystal molecules, and a rubbing process is performed on the first alignment layer  121 .  
         [0064]     Next, an upper substrate  200  is formed opposite to the lower substrate  100 . The upper substrate  200  includes a light-shielding layer (not shown), a color filter layer  112 , an overcoat layer  113 , and a second alignment layer  122 . The light-shielding layer (not shown) prevents the light leakage on the remaining portions (in correspondence with the gate line, the data line and the thin film transistor) of the lower substrate excluding the pixel region. The color filter layer  112  represents colors of red R, green G and blue B. The overcoat layer  113  is formed on an entire surface of the upper substrate  200 , and the second alignment layer  122  is formed on an entire surface of the overcoat layer  113 . At this time, the second alignment layer  122  is rubbed to define the initial alignment of liquid crystal molecules.  
         [0065]     In the IPS mode LCD device according to the first embodiment of the present invention, the liquid crystal layer of the liquid crystal molecules is formed between the lower substrate  100  and the upper substrate  200 . The liquid crystal molecules have positive dielectric anisotropic characteristics. When a voltage is applied to the common electrode  105  and the pixel electrode  104 , an IPS mode electric field is generated between the common electrode  105  and the pixel electrode  104 . Since the common electrode  105  and the pixel electrode  104  are formed in shape of a hemisphere, for example, the reflectivity of external light higher as compared to the common electrode  105  and the pixel electrode  104  having a cross sectional shape of a rectangle. Moreover, a parallel electric field is formed on the upper surfaces of the common electrode  105  and the pixel electrode  104 , whereby the liquid crystal molecules of the liquid crystal layer are smoothly aligned regardless of the division of regions.  
         [0066]      FIG. 9  is a cross sectional view of an IPS mode LCD device along II-II′ of  FIG. 7 , according to the second exemplary embodiment of the present invention.  
         [0067]     As shown in  FIG. 7  and  FIG. 9 , the IPS mode LCD device according to the second embodiment of the present invention includes a lower substrate  100 . A gate line  101  and a data line  102  are formed on the lower substrate  100 , wherein the gate line  101  and the data line  102  cross each other to define a unit pixel region. Then, a pixel electrode  104  and a common electrode  105  are formed at a predetermined interval from each other within the pixel region. A transparent dielectric layer  140  is additionally formed on each of the pixel electrode  104  and the common electrode  105 . The transparent dielectric layer  140  is formed in shape such that an upper surface area is different than a lower surface area.  
         [0068]     After that, a thin film transistor TFT is formed on the lower substrate  100 . The thin film transistor TFT is comprised of a gate electrode  101   a,  a semiconductor layer  103 , and source and drain electrodes  102   a  and  102   b.  At this time, the gate electrode  101   a  projects from the gate line  101 , and the semiconductor layer  103  is overlaps the gate electrode  101   a  with a gate insulating layer  107  formed on an entire surface of the lower substrate  100  including the gate electrode  101   a.  Also, the source and drain electrodes  102   a  and  102   b  are formed on both sides of the semiconductor layer  103 , wherein the source and drain electrodes  102   a  and  102   b  are formed at a predetermined interval therebetween. The drain electrode  102   b  of the thin film transistor TFT is connected with the pixel electrode  104 .  
         [0069]     The pixel electrode  104  is formed at the same layer as the data line  102 , and the common electrode  105  and a common line  106  are formed at the same layer as the gate line  101 . The gate line  101  and the data line  102  may be formed of a radioactive metal or a metal coated with radioactive material. The transparent dielectric layer  140  may be formed of an organic layer or an inorganic layer, wherein the transparent dielectric layer  140  is formed of a material having a dielectric constant that is the same as, or similar to that of the liquid crystal material. The common electrode  105  is formed at a predetermined interval from the pixel electrode  104 , and the common electrode  105  is electrically connected with the common line  106  for receiving a common voltage. In this case, the common electrode  105  and the common line  106  are formed at the same layer, thereby improving the integration of components.  
         [0070]     After that, the gate insulating layer  107  is formed on the gate line  101  having the gate electrode  101   a,  the common line  106 , and the common electrode  105 , wherein the gate insulating layer  107  is insulated from the gate line  101  having the gate electrode  101   a,  the common line  106  and the common electrode  105 . The gate insulating layer  107  may be formed of an inorganic insulating layer such as SiN x  and SiO x  or an organic insulating layer such as acryl, polyimide, BCB (BenzoCycloButene) and photo polymer.  
         [0071]     Then, the transparent dielectric layer  140  is formed on the gate insulating layer  107  covering the common electrode  105  and the pixel electrode  104 . In this case, since the transparent dielectric layer  140  is formed of a material having the dielectric constant that is the same as, or similar to the liquid crystal material, the electric field is induced on the surface of the transparent dielectric layer  140 , as shown in  FIG. 6A , when forming the parallel electric field between the common electrode  105  and the pixel electrode  104 .  
         [0072]     A passivation layer  108  is formed on the gate insulating layer  107  including the transparent dielectric layer  140 . The passivation layer  108  is formed with the same material as the gate insulating layer  107  (i.e., the inorganic insulating layer such as SiN x  and SiO x , or the organic insulating layer such as acryl, polyimide, BCB (BenzoCycloButene) and photo polymer). Then, a first alignment layer  121  is formed on an entire surface of the passivation layer  108  for initially aligning the liquid crystal molecules, and a rubbing process is performed on the first alignment layer  121 .  
         [0073]     Next, an upper substrate  200  is formed opposite to the lower substrate  100 . The upper substrate  200  includes a light-shielding layer (not shown), a color filter layer  112 , an overcoat layer  113  and a second alignment layer  122 . The light-shielding layer (not shown) prevents the light leakage on the remaining portions (in correspondence with the gate line, the data line and the thin film transistor) of the lower substrate excluding the pixel region. The color filter layer  112  represents colors of red R, green G and blue B. The overcoat layer  113  is formed on an entire surface of the upper substrate  200 , and the second alignment layer  122  is formed on an entire surface of the overcoat layer  113 . At this time, the second alignment layer  122  is rubbed to define the initial alignment of liquid crystal molecules.  
         [0074]     In the IPS mode LCD device according to the second embodiment of the present invention, the liquid crystal layer of the liquid crystal molecules is formed between the lower substrate  100  and the upper substrate  200 . The liquid crystal molecules have positive dielectric anisotropic characteristics. When a voltage is applied to the common electrode  105  and the pixel electrode  104 , the liquid crystal molecules are aligned along the IPS mode electric field on the transparent dielectric layer  140  for the surface of the common electrode  105  and the pixel electrode  104 .  
         [0075]     In the IPS mode LCD device according to the exemplary embodiments of the present invention, the electrode may be shaped such that the upper surface area is different than the lower surface area. Alternatively, a transparent dielectric layer, having a dielectric constant that is the same as, or similar to the liquid crystal material, may be formed on each of the electrodes and shaped such that the upper surface area is different than the lower surface area. Accordingly, it is possible to generate a parallel electric field, so that the same level of luminance as that of the related art can be maintained with a lower voltage applied to the common electrode and the pixel electrode. Therefore, the IPS mode LCD device according to the exemplary embodiments of the present invention decreases the power consumption without affecting performance. Also, it is possible to improve the reflectivity of external light, whereby the IPS mode LCD device can be used as a trans-reflective type LCD device.  
         [0076]     As mentioned above, the IPS mode LCD device according to the exemplary embodiment of the present invention has the following advantages. First, in the IPS mode LCD device according to the present invention, the electrode may be shaped such that the upper surface area is different than the lower surface area. Alternatively, the transparent dielectric layer, having the dielectric constant that is the same as, or similar to the liquid crystal material, may be formed on each of the electrodes and shaped such that the upper surface area is different than the lower surface area. Accordingly, it is possible to generate parallel electric field between the common electrode and the pixel electrode, so that the liquid crystal molecules positioned above the common electrode and the pixel electrode are normally aligned along the parallel electric field, thereby increasing the portions driven by the parallel electric field. Thus, it is possible to decrease the power consumption by improving the light efficiency.  
         [0077]     Also, the IPS mode LCD device according to the exemplary embodiments of the present invention improves the reflectivity of external light, so that the external light can be used as a light source in conjunction with the light emitted from the backlight unit. That is, the IPS mode LCD device according to the present invention may be used as a trans-reflective type LCD device.  
         [0078]     Furthermore, as the power consumption decreases, the IPS mode LCD device according to the exemplary embodiments of the present invention may be used in mobile products thereby producing mobile products having a wide viewing angle.  
         [0079]     In addition, the IPS mode LCD device according the exemplary embodiments of the present invention can improve light efficiency by changing the shape of the electrodes without additional fabrication processes.  
         [0080]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.