Abstract:
An in-plane switching mode liquid crystal display device includes a plurality of gate lines and data lines defining a plurality of pixel regions, a driving device disposed within each of the pixel regions, at least one first electrode having a first width and at least one second electrode having a second width both arranged within the pixel region, and at least one third electrode having a third width overlapping at least one of the first and second electrodes to form a storage capacitor.

Description:
[0001]    The present invention claims the benefit of Korean Patent Application No. 78485/2002 filed in Korea on Dec. 10, 2002, 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 device and a method of fabricating a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device and a method of fabricating an in-plane switching mode liquid crystal display device.  
           [0004]    2. Description of the Related Art  
           [0005]    Currently, portable electronic devices, such as mobile phones, personal digital assistants (PDAs), and notebook computers, require various types of flat panel display devices. For example, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices have all been developed for application as a flat panel display. However, the LCD devices are attractive for their simplified production technology, easy driving means, and high image production quality.  
           [0006]    The LCD devices have various display modes according to particular arrangement of liquid crystal molecules. For example, twisted nematic (TN) mode LCD devices are commonly used because of their easy display of black-and-white images, fast response speed, and low driving voltage. During operation of a TN mode LCD device, liquid crystal molecules initially oriented to be parallel with a substrate are oriented nearly perpendicular to the substrate when a voltage is applied thereto. However, when the voltage is applied, the viewing angle is narrowed due to refractive anisotropy of the liquid crystal molecules. Accordingly, various modes of LCD devices having wide viewing angle characteristics have been developed, including in-plane switching (IPS) mode LCD devices.  
           [0007]    [0007]FIG. 1 is a plan view of an in-plane switching mode LCD device according to the related art, FIG. 2A is a cross sectional view along I-I′ of FIG. 1 according to the related art, and FIG. 2B is a cross sectional view along II-II′ of FIG. 1 according to the related art. In FIG. 1, a pixel of a liquid crystal display panel  1  is defined by gate lines  3   a  and  3   b  arranged along a longitudinal direction and data lines  4   a  and  4   b  arranged along a direction traverse to the longitudinal direction. Although only the (n,m) th  pixel of the IPS liquid crystal display panel is shown, an N-number of gate lines (wherein N&gt;n) and an M-number of data lines (where M&gt;m) are arranged on the liquid crystal display panel  1  to form a plurality of pixels across an entire surface of the liquid crystal display panel  1 . A thin film transistor  10  is formed at a region where the gate and data lines  3   a  and  4   a  cross, and includes a gate electrode  12  to which a scan signal is supplied from the gate line  3   a ; a semiconductor layer  13  formed on the gate electrode  12  and is activated as the scan signal is supplied to form a channel layer, and source and drain electrodes  14  and  15 .  
           [0008]    A common electrode  5  and a pixel electrode  7  are arranged in parallel to the data lines  4   a  and  4   b , and are both disposed within the pixel region. In addition, a common line  20  electrically connected to the common electrode  5  is arranged to be in parallel to the gate lines  3   a  and  3   b  on an upper portion of the pixel region. The pixel electrode  7  is electrically connected to a pixel electrode line  22  that includes a portion that overlaps with the gate line  3   b  and common line  20  of an adjacent (n+1) st  pixel. Accordingly, a storage capacitor is formed on the IPS mode LCD device due to the overlap of the pixel electrode line  22 , the gate line  3   b , and the common line  20 .  
           [0009]    In the IPS mode LCD device, liquid crystal molecules are initially oriented to be parallel with the common electrode  5  and the pixel electrode  7 . However, when the thin film transistor  10  is enabled and the signal is supplied to the pixel electrode  7 , a horizontal electric field substantially parallel with the surface of the liquid crystal display panel  1  is generated between the common electrode  5  and the pixel electrode  7 . Accordingly, the liquid crystal molecules are rotated along a same plane of the horizontal electric field, thereby preventing gray inversion due to the refractive anisotropy of the liquid crystal molecules.  
           [0010]    In FIG. 2A, the common electrode  5  is formed on a first transparent substrate  30 , and the pixel electrode  7  is formed on a gate insulating layer  32 . Since the common electrode  5  and the pixel electrode  7  are connected to the common line  20  and to the pixel electrode line  22 , respectively, it is desirable that the common line  20  and the pixel electrode line  22  are also formed on the first substrate  30  and on the gate insulating layer  32 , as shown in FIG. 2B.  
           [0011]    Although not shown, a gate electrode  12  of the thin film transistor is formed on the first substrate  30 , and the semiconductor layer  13  is formed on the gate insulating layer  32 . In addition, the source electrode  14  and the drain electrode  15  are formed on the semiconductor layer  13 , and a passivation layer  34  is deposited on an entire surface of the first substrate  30 .  
           [0012]    In the liquid crystal display panel  1 , when the scan signal is supplied to the thin film transistor  10  through the gate line  3   a , the thin film transistor  10  is turned ON and an image signal is input to the pixel electrode  7  through the data line  4 . Accordingly, the horizontal electric field in parallel to the first substrate  30  is generated between the common electrode  5  and the pixel electrode  7 . Thus, the liquid crystal molecules are rotated along a direction of with the horizontal electric field.  
           [0013]    A black matrix  42  is formed on a second substrate  40  for preventing light from leaking to the thin film transistor area and between the pixel regions. In addition, a color filter layer  44  is formed on the second substrate for generating colored images, and a liquid crystal material layer  50  is formed between the first substrate  30  and the second substrate  40 .  
           [0014]    The IPS mode LCD device requires use of a storage capacitor to improve stability of gray level images, and to reduce a flicker phenomenon and reduce generation of residual images. In order to form the storage capacitor, the LCD devices commonly include storage-on-gate (SOG) structures and storage-on-common (SOC) structures. In the SOG structures, a pixel electrode line is arranged to overlap a gate line to form a storage capacitor. In the SOC structures, a common line is formed within a pixel region and a pixel electrode line is arranged to overlap the common line to form a storage capacitor.  
           [0015]    However, LCD devices using the SOG and SOC structures have the following problems. First, in the SOG structures, since the gate line is formed having a set width, overlap of the gate line and the pixel electrode line is limited. Accordingly, sufficient amounts of storage capacitance cannot be achieved. Second, in the SOC structures, even though overlap of the common line and the pixel electrode line can be controlled to provide sufficient amounts of storage capacitance by enlarging the widths of the common and pixel electrode lines, the aperture ratio of the LCD device is lowered due to the enlarged widths of the common and pixel electrode lines.  
           [0016]    To resolve these problems, hybrid-type LCD devices have been developed that combine advantages of the SOG and SOC structures to ensure sufficient amounts of the storage capacitance by overlapping the pixel electrode line with the common and gate lines. The IPS mode LCD devices shown in FIGS. 1, 2A, and  2 B include the hydrid-type LCD devices. For example, in FIG. 2B, the common line  20  is arranged near the gate line  3   b  of the adjacent (n+1) st  pixel, and the pixel electrode line  22  overlaps with portions of the gate line  3   b  and the common line  20  of the (n+1) st  pixel. However, first and second widths t1 and t2 (in FIG. 1) of the common line  20  and the pixel electrode line  22  must both be formed having larger widths to ensure sufficient amounts of storage capacitance, thereby limiting the aperture ratio.  
         SUMMARY OF THE INVENTION  
         [0017]    Accordingly, the present invention is directed to an in-plane switching mode liquid crystal display device and method of fabricating an in-plane switching mode liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0018]    An object of the present invention is to provide an in-plane switching (IPS) mode liquid crystal display (LCD) device having sufficient amounts of storage capacitance and improved aperture ratio.  
           [0019]    Another object of the present invention is to provide a method of fabricating an in-plane switching (IPS) mode liquid crystal display (LCD) device having sufficient amounts of storage capacitance and improved aperture ratio.  
           [0020]    Additional features and advantages of the invention will be set froth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0021]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an in-plane switching mode liquid crystal display device includes a plurality of gate lines and data lines defining a plurality of pixel regions, a driving device disposed within each of the pixel regions, at least one first electrode having a first width and at least one second electrode having a second width both arranged within the pixel region, and at least one third electrode having a third width overlapping at least one of the first and second electrodes to form a storage capacitor.  
           [0022]    In another aspect, an in-plane switching mode liquid crystal device includes a plurality of gate lines and data lines defining a plurality of pixel regions, a driving device disposed with each of the pixel regions, at least a pair of electrodes arranged within each of the pixel regions for generating a horizontal electric field, and at least one storage capacitor electrode having a first width overlapping at least one electrode between the pair of electrodes for forming a storage capacitor.  
           [0023]    In another aspect, a method of fabricating an in-plane switching mode liquid crystal display device includes forming a plurality of gate lines and data lines on a first substrate to define a plurality of pixel regions, forming a driving device disposed within each of the pixel regions, forming at least one first electrode having a first width and at least one second electrode having a second width within the pixel region, and forming at least one third electrode having a third width to overlap at least one of the first and second electrodes to form a storage capacitor.  
           [0024]    In another aspect, a method of fabricating an in-plane switching mode liquid crystal device includes forming a plurality of gate lines and data lines to define a plurality of pixel regions, forming a driving device disposed with each of the pixel regions, forming at least a pair of electrodes arranged within each of the pixel regions for generating a horizontal electric field, and forming at least one storage capacitor electrode having a first width to overlap at least one electrode between the pair of electrodes for forming a storage capacitor.  
           [0025]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    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:  
         [0027]    [0027]FIG. 1 is a plan view of an in-plane switching mode LCD device according to the related art;  
         [0028]    [0028]FIG. 2A is a cross sectional view along I-I′ of FIG. 1 according to the related art;  
         [0029]    [0029]FIG. 2B is a cross sectional view along II-II′ of FIG. 1 according to the related art;  
         [0030]    [0030]FIG. 3A is a plan view of an exemplary in-plane switching mode LCD device according to the present invention;  
         [0031]    [0031]FIG. 3B is a cross sectional view along III-III′ of FIG. 3A according to the present invention;  
         [0032]    [0032]FIG. 4 is a cross sectional view of another exemplary in-plane switching mode LCD device according to the present invention; and  
         [0033]    [0033]FIG. 5 is a cross sectional view of another exemplary in-plane switching mode LCD device according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0035]    [0035]FIG. 3A is a plan view of an exemplary in-plane switching mode LCD device according to the present invention, and FIG. 3B is a cross sectional view along III-III′ of FIG. 3A according to the present invention. In FIG. 3A, an exemplary in-plane switching mode LCD device may include a thin film transistor  110  formed at a region where a gate line  103  and a data line  104  cross each other. The thin film transistor  110  may include a gate electrode  112  that extends from the gate line  103 , a semiconductor layer  113  formed on the gate electrode  112 , and source and drain electrodes  114  and  115  that extend from the data line  104  and are disposed on the semiconductor layer  113 .  
         [0036]    In addition, a common electrode  105  and a pixel electrode  107  may be arranged in parallel to each other within a pixel region. The common electrode  105  may be connected to a common line  120  that overlaps the gate line  103 , and a storage capacitor electrode  106  may be formed to overlap with the pixel electrode  107  within the pixel region. Accordingly, the storage capacitor electrode  106  and the pixel electrode may have an insulating layer disposed therebetween, thereby forming a storage capacitor.  
         [0037]    In FIG. 3A, a width (t3) of the storage capacitor electrode  106  may be smaller than a corresponding width of the pixel electrode  107 . Accordingly, if the width t3 of the storage capacitor electrode  106  is larger than the corresponding width of the pixel electrode  107 , the storage capacitor electrode  106  may block any transmitted light and lower the aperture ratio.  
         [0038]    A first storage capacitor may be formed by an overlap of the gate line  103  and the common line  120 , and a second storage capacitor may be formed by an overlap of the pixel electrode  107  and the storage capacitor electrode  106 . Accordingly, a sum of the capacitance of the first and second storage capacitors Cst 1  and Cst 2  may be a total storage capacitance (Cst) of the LCD device. The storage capacitance Cst may vary depending upon the amount of overlap between the storage capacitor electrode  106  and the pixel electrode  107 . In addition, the storage capacitance (Cst) may vary depending upon the amount of overlap between the gate line  103  and the common line  120 . However, since the gate line  103  may have a predetermined width and the common line  120  may have a length longer than a set length, the amount of overlap between the gate line  103  and the common line  120  may be limited. Likewise, since a width of the storage capacitor electrode  106  may be set to a width not larger than a width of the pixel electrode  107 , the length of the storage capacitor electrode  106  may be adjusted. Thus, the storage capacitance (Cst) may be controlled by adjusting the width t3 and length 1 of the storage capacitor electrode  106 .  
         [0039]    In FIG. 3B, the gate electrode  112  of the thin film transistor  110  may be formed on the first substrate  130 , the semiconductor  113  may be formed on the gate insulating layer  132  that may be deposited on entire surface of the first substrate  130 . In addition, the source electrode  114  and the drain electrode  115  of the thin film transistor  110  may be formed on the semiconductor layer  113 , and a passivation layer  134  may be deposited upon an entire surface of the first substrate  130 .  
         [0040]    The storage capacitor electrode  106  may be formed on the first substrate  130  as a single layer or as a plurality of layers by evaporating or depositing metal materials, such as Cu, Mo, Ta, Ti, Al, or an Al alloy, using a sputtering method and etching the metal material(s). In addition, the storage capacitor electrode  106  may be formed using a process different from a process for forming the gate electrode  112  on the thin film transistor  110 . However, the storage capacitor electrode  106  may be formed by using similar processes (i.e., using the same photo mask) and by using similar metal material(s) in order to simplify the fabricating processes.  
         [0041]    The pixel electrode  107  may be formed on the gate insulating layer  132 , and may include a single layer or a plurality of layers made by depositing metal material(s), such as Cr, Mo, Cu, Ta, Ti, Al, or an Al alloy, using sputtering or evaporation methods and etching the metal material(s) using an etchant. In addition, the pixel electrode  107  may be formed using a process different from a process for forming the source electrode  114  and the drain electrode  15  of the thin film transistor  110 . However, the pixel electrode  107  may be formed using similar processes and by using similar metal material(s) in order to simplify the fabricating processes.  
         [0042]    The pixel electrode  107  and the storage capacitor electrode  106  may be arranged and overlap each other. Accordingly, since the gate insulating layer  132  may be located between the pixel electrode  107  and the storage capacitor electrode  106 , the second storage capacitor Cst 2  may be formed between the pixel electrode  107  and the storage capacitor electrode  106 . Since the width t3 of the storage capacitor electrode  106  may be smaller than the corresponding width of the pixel electrode  107 , the storage capacitor electrode  106  may be completely covered by the pixel electrode  107 . Thus, any transmitted light may not be shielded by the storage capacitor electrode  106 , wherein a sufficient amount of storage capacitance may be generated by the storage capacitor electrode  106  such that reduction of the aperture ratio may be prevented.  
         [0043]    The common electrode  105  may be formed on the passivation layer  134 , and together with the pixel electrode  107  they may form a horizontal electric field. The common electrode  105  may be formed using the material(s) used to form the gate electrode  112 , such as Cu, Mo, Ta, Ti, Al, or and Al alloy, or by using the material(s) used to form the source electrode  114 , such as Cr, Mo, Cu, Ta, Ti, Al, or and Al alloy. In addition, the common electrode  105  may be formed using transparent material(s), such as indium tin oxide (ITO) or indium zinc oxide (IZO), for improving aperture ratio.  
         [0044]    A black matrix  142  may be formed on the second substrate  140  for preventing light from leaking into non-display regions, and a color filter layer  144  may be formed on the second substrate  140  to provide colored images. Although not shown, an overcoat layer may be formed on the color filter layer  144  for improving flatness of the second substrate  140 . In addition, alignment layers (not shown) for orienting liquid crystal molecules may be formed on the first substrate  130  and on the second substrate  140  for providing initial orientation of liquid crystal moles of a liquid crystal material layer  150 .  
         [0045]    The liquid crystal material layer  150  may be formed between the first substrate  130  and the second substrate  140  using a vacuum liquid crystal injecting method, wherein the liquid crystal material is injected between the attached first and second substrates  130  and  140  in a vacuum chamber. Alternatively, the liquid crystal material layer  150  may be formed between the first substrate  130  and the second substrate  140  using a liquid crystal dispensing method, wherein the liquid crystal material may be directly dropped onto one or both of the first substrate  130  or the second substrate  140 . Accordingly, the liquid crystal material may be uniformly dispersed between the first and second substrates  130  and  140  during processes for attaching the first and second substrates  130  and  140  together.  
         [0046]    [0046]FIG. 4 is a cross sectional view of another exemplary in-plane switching mode LCD device according to the present invention. The exemplary in-plane switching mode LCD device of FIG. 4 has a similar structure as that of FIG. 3B except for positioning of the pixel electrode. Accordingly, descriptions for similar elements in FIG. 3B have been omitted.  
         [0047]    In FIG. 4, a first storage capacitor electrode  206  may be formed on a first substrate  230 , and a second storage capacitor electrode  208  may be formed on a gate insulating layer  232 . In addition, a common electrode  205  and a pixel electrode  207  may be formed in parallel to each other on a passivation layer  234 . Accordingly, the common and pixel electrodes  205  and  207  may induce a horizontal electric field to a liquid crystal material layer  250 .  
         [0048]    The pixel electrode  207  may be electrically connected to the second storage capacitor electrode  208  through a contact hole formed in the passivation layer  234 , and a storage capacitor may be created with the first storage capacitor electrode  206 , the gate insulating layer  232 , and the second storage capacitor electrode  208 . The first storage capacitor electrode  206  and the second storage capacitor electrode  208  may be formed to have similar widths, or may be formed having widths less than a width of the pixel electrode  207 . Accordingly, the first storage capacitor electrode  206  and the second storage capacitor electrode  208  may be completely covered by the pixel electrode  207 . Thus, the aperture ratio is not reduced by the first and second storage capacitor electrodes  206  and  208 .  
         [0049]    Alternatively, the second storage capacitor electrode  208  may not be formed. Accordingly, the first storage capacitor electrode  206  may directly contact the pixel electrode  207  through the gate insulating layer  232  and the contact hole formed in the passivation layer  234 . However, storage capacitance between the first storage capacitor electrode  205  and the pixel electrode  207  may be too small. Thus, the second storage capacitor electrode  208  may be incorporated as shown in FIG. 4.  
         [0050]    [0050]FIG. 5 is a cross sectional view of another exemplary in-plane switching mode LCD device according to the present invention. In FIG. 5, storage capacitor electrodes  306   a  and  306   b  may be formed to overlap with two pixel electrodes  307  arranged within a pixel region. Accordingly, a total number of storage capacitor electrodes may vary depending upon a needed amount of storage capacitance. In addition, a total number of storage capacitor electrodes may vary depending upon a total number of blocks in the IPS mode LCD device.  
         [0051]    Accordingly, in the IPS mode LCD device according to the present invention, the storage capacitor electrode may overlap with the pixel electrode to obtain a desired amount of storage capacitance and prevent reduction of the aperture ratio. However, the present invention may not be limited to the structures described above. For example, the storage capacitor electrode may be arranged to overlap the common electrode to create a storage capacitance nearly similar to the storage capacitance of the IPS mode LCD device according to the present invention. The IPS mode LCD device according to the present invention may be applied to all LCD devices, as well as 4-block, 6-block or 8-block IPS mode LCD devices.  
         [0052]    It will be apparent to those skilled in the art that various modifications and variations can be made in the in-plane switching mode liquid crystal display device and method of fabricating an in-plane switching mode liquid crystal display device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.