Abstract:
Fringe field switching mode liquid crystal display (FFS LCD) devices are disclosed. A first substrate is disposed opposing a second substrate with a gap therebetween. A liquid crystal layer is interposed between the first and the second substrate. A gate line and data lines are formed on the first substrate in a matrix configuration and defining pixel areas. A counter electrode is disposed on each pixel area of the first substrate. A pixel electrode is disposed above the counter electrode with an insulating layer therebetween. The pixel electrode includes a plurality of parallel electrodes. Each electrode includes a first segment, a second segment, and a third segment, wherein the first segment has an included angle θ from the horizontal direction, the second segment has an included angle φ from the horizontal direction, and the first segment has an included angle θ from the horizontal direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of pending U.S. patent application Ser. No. 11/532,982, filed Sep. 19, 2006 and entitled “LIQUID CRYSTAL DISPLAY DEVICES”. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to liquid crystal display (LCD) devices, and more particularly to fringe field switching mode liquid crystal display (FFS-LCD) devices. 
         [0004]    2. Description of the Related Art 
         [0005]    Liquid crystal display (LCD) devices possess the advantages of small size, light weight and low power consumption, thus increasing portability and applicability in a wide variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and similar. Critical features for large-scale monitors and high-end TV applications, include fast response, high contrast ratio, high transparency, and wide viewing angle without gray scale inversion. In-plane switching (IPS) mode liquid crystal display devices meet the above-mentioned high quality display feature requirements, and solve the viewing angle problems by orienting the liquid crystal molecules to be parallel with a substrate. 
         [0006]    Fringe field switching liquid crystal display (FFS-LCD) devices have pixel and counter electrodes comprise transparent conductors and a narrower distance between electrodes than the distance between the upper and lower substrates to form a fringe field on the electrodes. In operation, the fringe field on the electrodes forces the substantially homogeneous liquid crystal molecules to rotate transversely between the substrates in which a wide viewing angle is accomplished since the light is transmitted through the horizontally arranged liquid crystal molecules. Moreover, since the counter electrode and the pixel electrode comprise transparent conductive materials, the aperture ratio and the transmittance ratio of the display devices can thereby be improved. 
         [0007]    U.S. Pat. No. 6,856,371, the entirety of which is hereby incorporated by reference, discloses electrode structures of a conventional FFS-LCD device. The electrode structures are symmetrical and render high image display quality and high transmittance ratio. 
         [0008]      FIG. 1  is a cross section of a conventional fringe field switching liquid crystal display (FFS-LCD) device. An FFS-LCD  1  comprises a first substrate (an upper substrate)  10 , a second substrate (a lower substrate)  20 , and a liquid crystal layer  30  interposed between the first substrate  10  and the second substrate  20 , serving as an LCD cell. A counter electrode  11  and a plurality of pixel electrodes  13  are disposed on the first substrate  10 . An insulating layer  15  is disposed between the counter electrode  11  and the plurality of pixel electrodes  13 . A lower alignment layer  14  is disposed on the insulating layer  15  and covers the pixel electrodes  15 . A color filter layer  25  and an upper alignment layer  24  are disposed on the inner surface of the second substrate  20  and adjust the liquid crystal layer  30 . 
         [0009]      FIG. 2  is a plan view of the lower substrate structure of a conventional fringe field switching liquid crystal display (FFS-LCD) device. Two parallel gate lines  3  and two parallel data lines  7  are orthogonally intersected, enclosing a pixel area. A counter electrode  11  and pixel electrodes  13  are disposed in the pixel area. The pixel electrodes  15  comprise two electrode bras  13   a  parallel to the data lines  7  and a plurality of inclined electrodes  13   b  with an inclined angle φ. The two ends of each electrode  13   b  are separately connected to the two electrode bras  13   a . Note that the inclined angle φ of the electrodes  13   b  directly affects the operating voltage of the FFS-LCD device. More specifically, the greater the inclination of electrodes  13   b , the higher the voltage required to operate the FFS-LCD device. 
         [0010]    For small FFS-LCD panels, the inclined angle φ of the electrodes  13   b  must be reduced to lower the operating voltage of the FFS-LCD device. A low inclined angle φ of electrodes  13   b  (e.g., less than 7°) can cause the disclination effect deteriorating display image quality. Conversely, high inclined angle φ of the electrodes  13   b  requires a high driving voltage such that the physical area of the thin film transistor (TFT) must be increased to provide adequate charge storage capability. The TFT structure comprises a gate electrode  3 , a channel and source/drain regions  4 , and source contact  6   a  and drain contact  6   b . The drain contact  6   b  connects the pixel electrodes  13  via a contact plug  9 . When the physical area of the thin film transistor (TFT) increases, however, the area of the pixel electrodes  13  must be reduced, thus, a small aperture ratio and a low transmittance ratio occur. 
         [0011]    Thus, low operating voltage FFS-LCD devices with improved aperture and transmittance ratios, capable of preventing the disclination effect are desirable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
         [0013]    The invention is directed to electrode structures of an FFS-LCD device. The electrode structures comprise multiple deflected electrodes thereby providing an FFS-LCD device having low operating voltage, preventing the disclination effect and improving aperture and transmittance ratios. 
         [0014]    Liquid crystal display devices are provided. An exemplary embodiment of a liquid crystal display device comprises oppositely disposed first and second substrates with a predetermined gap therebetween. A liquid crystal layer is interposed between the first and the second substrates. A gate line and a scan line are disposed on the first substrate in a matrix configuration and defining pixel areas. A counter electrode is disposed on each pixel area of the first substrate. A first pixel electrode is disposed on the counter electrode with at least one insulating layer therebetween. The first pixel electrode comprises a plurality of parallel electrodes, and each electrode comprises a first segment, a second segment, and a third segment; the first segment includes an angle of θ from the horizontal, the second segment includes an angle of φ from the horizontal, and the third segment includes an angle of θ from the horizontal, and wherein the angle of θ is greater than the angle of φ. 
         [0015]    Note that the liquid crystal display device further comprises a second pixel electrode disposed on the counter electrode with at least one insulating layer therebetween. The second pixel electrode comprises a plurality of parallel electrodes, and each electrode comprises a sixth segment, a seventh segment, and a eighth segment. The sixth segment includes an angle of −θ from the horizontal. The seventh segment includes an angle of −φ from the horizontal. The eighth segment includes an angle of −θ from the horizontal, and the angle of −θ is greater than the angle of −φ. 
         [0016]    Another exemplary embodiment of a liquid crystal display device comprises: oppositely disposed first and second substrates with a predetermined gap therebetween; a liquid crystal layer interposed between the first and the second substrates; a gate line and a scan line disposed on the first substrate in a matrix configuration and defining pixel areas; a counter electrode disposed on each pixel area of the first substrate; a pixel electrode disposed on the counter electrode with at least one insulating layer therebetween; wherein the pixel electrode comprises a plurality of parallel electrodes, and each electrode comprises a first segment, a second segment, and a third segment; wherein the first segment includes an angle of θ from the horizontal, the second segment includes an angle of φ from the horizontal, and the third segment includes an angle of θ from the horizontal, wherein the angle of θ is greater than the angle of φ; the pixel electrode further comprises a fourth segment connecting the first segment of the odd electrodes and the third segment of the even electrodes, and fifth segment connecting the third segment of the odd electrodes and the first segment of the even electrodes. 
         [0017]    Some embodiments of a liquid crystal display device comprise: oppositely disposed first second substrates with a predetermined gap therebetween; a liquid crystal layer interposed between the first and the second substrates; a gate line and a scan line disposed on the first substrate in a matrix configuration and defining pixel areas; a counter electrode disposed on each pixel area of the first substrate; a pixel electrode disposed on the counter electrode with at least one insulating layer therebetween; wherein the pixel electrode with a first portion comprising a plurality of parallel electrodes, and each electrode comprises a first segment, a second segment, and a third segment; wherein the first segment includes an angle of θ from the horizontal, the second segment includes an angle of φ from the horizontal, and the third segment includes an angle of θ from the horizontal, and wherein the angle of θ is greater than the angle of φ; wherein the pixel electrode with a second portion comprising a plurality of parallel electrodes, and each electrode comprises a sixth segment, a seventh segment, and an eighth segment; wherein the sixth segment includes an angle of −φ from the horizontal, the seventh segment includes an angle of −φ from the horizontal, and the eighth segment includes an angle of −θ from the horizontal, and wherein the angle of −θ is greater than the angle of −φ. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a cross section of a conventional fringe field switching liquid crystal display (FFS-LCD) device; 
           [0020]      FIG. 2  is a plan view of the lower substrate structure of a conventional fringe field switching liquid crystal display (FFS-LCD) device; 
           [0021]      FIG. 3  is a plan view of an electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention; 
           [0022]      FIGS. 4A-4F  are cross sections of the steps of fabricating the electrode structure of an FFS-LCD device according to a first embodiment of the invention; 
           [0023]      FIG. 5  is a cross section of the electrode structure in each pixel area of an FFS-LCD device taken along the line A-A′ of  FIG. 3 ; 
           [0024]      FIG. 6  is an equivalent circuit of the electrode structure in each pixel area of an FFS-LCD device of  FIGS. 3 and 5 ; 
           [0025]      FIG. 7  is a plan view of a variation of the electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention; 
           [0026]      FIG. 8  is a plan view of another variation of the electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention; 
           [0027]      FIG. 9  is a plan view of another variation of the electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention; 
           [0028]      FIG. 10  is a plan view of an electrode structure in each pixel area of an FFS-LCD device according to a second embodiment of the invention; and 
           [0029]      FIG. 11  is a plan view of an electrode structure in each pixel area of an FFS-LCD device according to a third embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0031]    FFS-LCD devices comprising electrode structures with multiple deflected electrodes are provided. The provided FFS-LCD devices have low operating voltage, thus, the disclination effect is prevented and the aperture ratio and transmittance ratio are improved. 
       First Embodiment 
       [0032]      FIG. 3  is a plan view of an electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention. In the active matrix array substrate  101   a  of  FIG. 3 , a unit electrode structure comprises a plurality orthogonally intersecting gate lines  103  and scan lines  107  disposed on a substrate  100 . A plurality of pixel areas are defined by two adjacent gate lines  103  and scan lines  107 . A counter electrode  105  is disposed on the substrate  100  and in each pixel area. A first pixel electrode  113  is disposed on the counter electrode  105  with at least one insulating layer (referring to the first insulating layer  109  and the second insulating layer  110  of  FIG. 5 ) therebetween, wherein the first pixel electrode  113  comprises two electrode bars  113   a  parallel to the scan lines  107  and a plurality of parallel electrodes  113   b . Each electrode  113   b  comprises a first segment  113   b   1 , a second segment  113   b   2 , and a third segment  113   b   3 . The first segment  113   b   1  includes an angle of θ from the horizontal. The second segment  113   b   2  includes an angle of φ from the horizontal. The third segment  113   b   3  includes an angle of θ from the horizontal. The angle of θ is greater than the angle of φ. For example, the angle of θ is approximately in a range between 1° and 80° and the angle of φ is approximately in a range between 0° and 79°. Since in the region D neighboring the electrode bar  113   a , the angle of θ of the third segment  113   b   3  deviating from the horizontal is greater than the angle of φ, the disclination effect can thus be prevented. 
         [0033]      FIG. 3  shows a TFT device disposed at the intersection of each gate line  103  and scan line  107  electrically coupled to the first pixel electrode  113 . The TFT device comprises a gate electrode  103 , a channel and source/drain regions  104 , and source contact  106   a  and drain contact  106   b . The drain contact  106   b  connects the first pixel electrodes  113  via a contact plug  109 . By deflecting the angle of θ of the third segment  113   b   3  greater than the angle of φ, the physical area of TFT device can be reduced, and the area of the first pixel electrodes  113  can nonetheless be increased resulting in improved high aperture ratio and high transmittance ratio. 
         [0034]    Note that an alignment layer (not shown) which is horizontally rubbed is optionally formed on the pixel electrode  113  of the substrate structure  101   a.    
         [0035]      FIGS. 4A-4F  are cross sections of the steps of fabricating the electrode structure of an FFS-LCD device according to a first embodiment of the invention. Referring to  FIG. 4A , a substrate  100  such a transparent glass substrate or a plastic substrate is provided. A patterned counter electrode is formed on the substrate  100 . Referring to  FIG. 4B , a patterned first metal layer including gate lines  103  and common electrode lines  108  is formed on the substrate  100 , wherein the common electrode lines  108  and the counter electrode  105  are operatively electrically connected. The gate lines  103  and common electrode line  108  are parallel and made from metal materials such as aluminum (Al), molybdenum (Mo), or other conductive materials. A gate insulating layer  109  is subsequently formed on the substrate  100  and covering the counter electrode  105 , gate lines  107 , and the common electrode lines  108 . 
         [0036]    Referring to  FIG. 4C , a patterned semiconductor layer is formed covering part of the gate lines  103 . For example, a semiconductor island  104  including an amorphous silicon island or polysilicon island is formed part of the gate line  103  to serve as a carrier channel region. A source region and a drain region are separately formed on both sides of the carrier channel region. Referring to  FIG. 4D , a patterned second metal layer is formed on the substrate  100 . The patterned second metal layer comprises scan lines  107 , source contact  106   a  and drain contact  106   b . The second metal layer is preferably comprises metal materials such as aluminum (Al), molybdenum (Mo), or other conductive materials. A second insulating layer  110  (referring to  FIG. 5 ) is deposited and patterned creating a contact plug  109  on the drain contact  106   b.    
         [0037]    Referring to  FIG. 4F , a patterned pixel electrode structure is formed on the second insulating layer  110  and operatively coupled the drain contact  106   b . The pixel electrode structure is disposed corresponding to the counter electrode  105  with the second insulating layer sandwiched therebetween. The first pixel electrode structure  113  comprises two electrode bars  113   a  parallel to the scan lines  107  and a plurality of parallel electrodes  113   b . Each electrode  113   b  comprises a first segment  113   b   1 , a second segment  113   b   2 , and a third segment  113   b   3 . The first segment  113   b   1  includes an angle of θ from the horizontal. The second segment  113   b   2  includes an angle of φ from the horizontal. The third segment  113   b   3  includes an angle of θ from the horizontal. The angle of θ is greater than the angle of φ. 
         [0038]      FIG. 5  is a cross section of the electrode structure in each pixel area of an FFS-LCD device taken along the line A-A′ of  FIG. 3 .  FIG. 6  is an equivalent circuit of the electrode structure in each pixel area of an FFS-LCD device of  FIG. 3  and  FIG. 5 . Referring to  FIG. 5 , a storage capacitor C st  and a fringe capacitor C f  are induced between the electrode  131   b  of the pixel electrode structure  131  and the counter electrode  105 . The capacitances of the storage capacitor C st  and the fringe capacitor C f  are increased as the overlying area between the electrode  131   b  of the pixel electrode structure  131  and the counter electrode  105 . The larger overlying area between the electrode  131   b  of the pixel electrode structure  131  and the counter electrode  105  is, the larger the TFT devices are required to be to provide adequate charge storage capacity. When the physical area of the thin film transistor (TFT) device increases, however, the aperture ratio and low transmittance ratio of the FFS-LCD device are decreased. By deflecting the angle of θ greater than the angle of φ, the physical area of TFT device can be reduced by improving the aperture ratio and high transmittance ratio. 
         [0039]      FIG. 7  is a plan view of a variation of the electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention. In the active matrix array substrate  101   b  of  FIG. 7 , the electrode structure in each pixel area is nearly identical to the electrode structure in each pixel area of the first embodiment in  FIG. 3  and for simplicity its detailed description is omitted. The electrode structure in each pixel area in  FIG. 7  is different from the electrode structure in each pixel area in  FIG. 3  in that a second pixel electrode  123  comprises a plurality of electrodes  113   b . Each electrode  113   b  comprises a first segment, a second segment, and a third segment. The first segment includes an angle of −θ from the horizontal. The second segment includes an angle of φ from the horizontal. The third segment includes an angle of −θ from the horizontal. The angle of −θ is greater than the angle of −φ. 
         [0040]      FIG. 8  is a plan view of another variation of the electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention. In  FIG. 8 , the first pixel electrode  113  and the second pixel electrode  123  are mirror symmetrical horizontally. 
         [0041]      FIG. 9  is a plan view of another variation of the electrode structure in each pixel area of an FFS-LCD device according to a first embodiment of the invention. In  FIG. 9 , the first pixel electrode  113  and the second pixel electrode  123  are vertically and symmetrically mirrored. 
       Second Embodiment 
       [0042]      FIG. 10  is a plan view of an electrode structure in each pixel area of an FFS-LCD device according to a second embodiment of the invention. Referring to  FIG. 10 , in order to improve the aperture ratio and transmittance ratio of the FFS-LCD device, the active matrix array substrate  101   c  of the second embodiment of the invention comprises a plurality of orthogonally intersecting gate lines  103  and scan lines  107  disposed on a substrate  100 . A plurality of pixel areas are defined by two adjacent gate lines  103  and scan lines  107 . A counter electrode  105  is disposed on the substrate  100  and in each pixel area. A pixel electrode  133  is disposed on the counter electrode  105  with at least one insulating layer therebetween. The pixel electrode  133  comprises an upper portion which comprises a plurality of parallel electrodes. Each electrode comprises a first segment, a second segment, and a third segment. The first segment includes an angle of θ from the horizontal. The second segment includes an angle of φ from the horizontal. The third segment includes an angle of θ from the horizontal. The angle of θ is greater than the angle of φ. The pixel electrode  133  further comprises a lower portion which comprises a plurality of parallel electrodes. Each electrode comprises a sixth segment, a seventh segment, and an eighth segment. The sixth segment includes an angle of −θ from the horizontal. The seventh segment includes an angle of −φ from the horizontal. The eighth segment includes an angle of −θ from the horizontal. The angle of −θ is greater than the angle of −φ. Note that the first portion of the pixel electrode and the second portion of the pixel electrode are vertically and symmetrically mirrored. 
       Third Embodiment 
       [0043]      FIG. 11  is a plan view of an electrode structure in each pixel area of an FFS-LCD device according to a third embodiment of the invention. Referring to  FIG. 11 , in order to improve the aperture ratio and transmittance ratio of the FFS-LCD device, the active matrix array substrate  101   d  of the third embodiment of the invention comprises a plurality of orthogonally intersecting gate lines  203  scan lines  207  disposed on a substrate  200 . A plurality of pixel areas are defined by two adjacent gate lines  203  and scan lines  207 . A counter electrode  205  is disposed on the substrate  200  and in each pixel area. A pixel electrode  213  is disposed on the counter electrode  205  with at least one insulating layer therebetween. The pixel electrode  213  comprises a plurality of parallel electrodes  213   b . Each electrode  213   b  comprises a first segment  213   b   1 , a second segment  213   b   2 , and a third segment  213   b   3 . The first segment  213   b   1  includes an angle of θ from the horizontal. The second segment  213   b   2  includes an angle of φ from the horizontal. The third segment  213   b   3  includes an angle of θ from the horizontal. The angle of θ is greater than the angle of φ. The pixel electrode  213  further comprises a fourth segment  213   a   1  connecting the third segment  213   b   3  of the odd electrodes and the third segment  213   b   3  of the even electrodes, and fifth segment  213   a   2  connecting the first segment  213   b   1  of the odd electrodes and the first segment  213   b   1  of the even electrodes. More specifically, the pixel electrode  213  is an S-shaped continuous zigzag line or an inverted S-shaped continuous zigzag line. Preferably the angle of θ is approximately in a range between 1° and 80° and the angle of φ is approximately in a range between 0° and 79°. Since in the region D neighboring the electrode bar  113   a , the angle of θ of the third segment  113   b   3  deviated from the horizontal is greater than the angle of φ, the disclination effect can thus be prevented. 
         [0044]    Furthermore, since a first opening  213   c  is formed between each adjacent fourth segments  213   a   1  and a second opening  213   c  between each adjacent fifth segments  213   a   2  of the pixel electrode  213  to increase aperture ratio and transmittance ratio of the FFS-LCD device. Preferably the width of the first and the second openings  213   c  is about 0.1 μm to 10 μm. 
         [0045]    Referring to  FIG. 11 , a TFT device is disposed at the intersection of each gate line  203  and scan line  207  and electrically coupled to the pixel electrode  213 . The TFT device comprises a gate electrode  203 , a channel and source/drain regions  204 , and source contact  206   a  and drain contact  206   b . The drain contact  206   b  connects the pixel electrodes  213  via a contact plug  209 . By deflecting the angle of θ of the third segment  213   b   3  greater than the angle of φ, the physical area of TFT device can be reduced, and the area of the pixel electrodes  213  can nonetheless be increased resulting in improved high aperture ratio and high transmittance ratio. 
         [0046]    Note that an alignment layer (not shown) which is horizontally rubbed is optionally formed on the pixel electrode  213  of the substrate structure  101   d.    
         [0047]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.