Abstract:
A multi-domain liquid crystal display includes a first and a second transparent substrates, a liquid crystal layer interposed between them, a common electrode, a first and a second metal layers, a first and a second dielectric layer, multiple pixel electrodes and multiple auxiliary electrodes. The second metal layer is formed on the first dielectric layer, and the second dielectric layer is formed on the first dielectric layer and covers the second metal layer. The pixel electrodes are formed on the second dielectric layer, each of the pixel electrodes having at least one opening to divide itself into a plurality of sections. The auxiliary electrodes are formed on the second dielectric layer, and each of the auxiliary electrodes extends into the opening of the pixel electrode. The second metal layer is hollowed out at a position overlapping the auxiliary electrode to form at least one opening.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority of application No. 096120626 filed in Taiwan R.O.C on Jun. 8, 2007 under 35 U.S.C. §119; the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a multi-domain liquid crystal display and its array substrate. 
         [0004]    2. Description of the Related Art 
         [0005]    Typically, the display contrast ratio and response speed offered by a VA (vertically-aligned) mode liquid crystal display, which uses negative liquid crystal materials and vertical alignment films, are better than a TN (twisted-nematic) mode LCD, since liquid crystal molecules are aligned in a vertical direction when no voltage is applied. Also, it is known the viewing angle performance of a VA mode LCD is improved by setting the orientation directions of the liquid crystal molecules inside each picture element to a plurality of mutually different directions; that is, forming multiple distinct domains in the liquid crystal display. 
         [0006]      FIG. 11A  shows a schematic diagram illustrating a conventional design of a multi-domain vertically aligned liquid crystal display (MVA LCD). Referring to  FIG. 11A , a top substrate  102  and a bottom substrate  104  are both provided with protrusions  106  having different inclined surfaces and covered by vertical alignment films  108 . Hence, the liquid crystal molecules  112  near the inclined surfaces orientate vertically to the inclined surfaces to have different degrees of pre-tilt angles. In case the pre-tilt liquid crystal molecules exist, surrounding liquid crystal molecules  112  are tilted in the directions of the pre-tilt liquid crystal molecules  112  when a voltage is applied. Thus, multiple domains each having individual orientation direction of liquid crystal molecules  112  are formed. Besides, the domain-regulating structure for providing inclined surfaces includes, but is not limited to, the protrusions  106 , and other structure such as a via structure  114  shown in  FIG. 11B  may also be used. 
         [0007]    However, when one compares the optical path of light I 1  and that of light I 2  shown both in  FIGS. 11A and 11B , it is clearly found the tilted liquid crystal molecules through which the light I 2  passes under a field-off state may result in a non-zero phase difference (□nd≠#0) to cause light leakage. Accordingly, additional compensation films must be provided to eliminate the light leakage. 
         [0008]      FIG. 12  shows a schematic diagram illustrating another conventional design of an MVA LCD. Referring to  FIG. 12 , the transparent electrode  204  on the substrate  202  is provided with slits  206 . Because of the fringe fields produced at edges of transparent electrode  204  and at each slit  206 , the liquid crystal molecules  208  are tilted toward the center of each slit  206  to result in a multi-domain liquid crystal (LC) cell. However, the strength of the fringe fields generated by the formation of the slits  206  is often insufficient, particularly when the widths and the intervals of the slits  206  are not optimized. Besides, since the azimuth in which the liquid crystal molecules tilt due to fringe fields includes all directions of  360  degrees, a disclination region  210  often appears beyond the slits  206  or between two adjacent slits  206  to result in a reduced light transmittance. 
         [0009]    Further, though the protrusion  106 , via structure  114 , or slit  206  may be provided to create multiple domains, the distribution of these structures in a picture element may reduce the active area for display and thus the aperture ratio of the picture element. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The invention provides an a multi-domain liquid crystal display capable of solving the problems of conventional designs and having a high pixel aperture ratio and reduced capacitive coupling effect. 
         [0011]    According to an embodiment of the invention, a multi-domain liquid crystal display includes a first and a second transparent substrates, a liquid crystal layer interposed between them, a common electrode, a first and a second metal layers, a first and a second dielectric layer, multiple pixel electrodes and multiple auxiliary electrodes. The first metal layer is formed on the second transparent substrate, and the first dielectric layer is formed on the second transparent substrate and covers the first metal layer. The second metal layer is formed on the first dielectric layer, and the second dielectric layer is formed on the first dielectric layer and covers the second metal layer. The pixel electrodes are formed on the second dielectric layer, each of the pixel electrodes having at least one opening to divide itself into a plurality of sections. The auxiliary electrodes are formed on the second dielectric layer, and each of the auxiliary electrodes extends into the opening of the pixel electrode and is adjacent to at least one section of the pixel electrode. The second metal layer is hollowed out at a position overlapping the auxiliary electrode to form at least one opening. 
         [0012]    According to another embodiment of the invention, an array substrate includes a transparent substrate, a plurality of metallic signal lines, at least one dielectric layer, multiple pixel electrodes, multiple auxiliary electrodes and multiple storage capacitors. The dielectric layer is formed on the transparent substrate and covers the metallic signal lines. The pixel electrodes is formed on the dielectric layer, each of the pixel electrodes having at least one opening that extends from the periphery to the inside of the pixel electrode. The auxiliary electrodes are formed on the dielectric layer, and each of the auxiliary electrodes extends into the opening of the pixel electrode to produce fringe fields. Each of the storage capacitors has a first capacitor conductor beside the auxiliary electrode and a second capacitor conductor opposite the first capacitor conductor. The first capacitor conductor is hollowed out at a position overlapping the auxiliary electrode to form at least one opening. 
         [0013]    According to the above embodiments, a multi-domain profile of a LC cell is formed by providing auxiliary electrodes that spread over the spacing regions and extend into the openings, and this can be easily achieved through typical TFT fabrication processes. Hence, compared with the conventional design where a protrusion or via structure is used to cause tilted liquid crystal molecules, the residue phase difference is eliminated to avoid light leakage according to this embodiment since all liquid crystal molecules are vertically aligned under a field-off state. Further, compared with another conventional design where slits are formed to produce fringe fields, the biased auxiliary electrodes allow for stronger field strength to tilt liquid crystal molecules so as to reduce the areas of a disclination region and thus increase the light-transmittance of an LCD. Further, since the second metal layer is hollowed out at a position overlapping the auxiliary electrode, the overlap between each auxiliary electrode and the second metal layer is considerably reduced to effectively reduce the capacitive coupling effect and minimize the variations in gray-level voltages as a result. 
     
    
     
       BRIEF DESCRIPTION OF TIE DRAWINGS 
         [0014]      FIG. 1  is a top view observed from the normal direction of an array substrate, and  FIG. 2  is a cross-section taken along line A-A′ in  FIG. 1 . 
           [0015]      FIG. 3  show schematic diagrams of patterns of transparent electrodes and a second metal layer according to an embodiment of the invention. 
           [0016]      FIG. 4  shows a top view of a multi-domain liquid crystal display according to another embodiment of the invention, and  FIG. 5  is a cross-section taken along line B-B′ in  FIG. 5 . 
           [0017]      FIG. 6  shows a top view of a multi-domain liquid crystal display according to another embodiment of the invention, and  FIG. 7  is a cross-section taken along line C-C′ in  FIG. 6 . 
           [0018]      FIG. 8  shows a top view of a multi-domain liquid crystal display according to another embodiment of the invention, and  FIG. 9  is a cross-section taken along line D-D′ in  FIG. 8 . 
           [0019]      FIG. 10  shows a polarity diagram of the embodiment shown in  FIG. 8 . 
           [0020]      FIG. 11A  shows a schematic diagram illustrating a conventional design of a multi-domain vertically aligned liquid crystal display. 
           [0021]      FIG. 11B  shows a schematic diagram illustrating another conventional design of a multi-domain vertically aligned liquid crystal display. 
           [0022]      FIG. 12  shows a schematic diagram illustrating another conventional design of a multi-domain vertically aligned liquid crystal display. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology is used with reference to the orientation of the Figure(s) being described. The components of the present invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components is between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
         [0024]      FIGS. 1 and 2  show schematic diagrams illustrating a multi-domain liquid crystal display according to an embodiment of the invention, where  FIG. 1  is a top view observed from the normal direction of an array substrate, and  FIG. 2  is a cross-section taken along line A-A′ in  FIG.1 . 
         [0025]    Referring to  FIG. 1 , a plurality of pixel units  12  that constitute the multi-domain liquid crystal display  10  are shown. Each pixel unit  12  has a pixel electrode  14  and an auxiliary electrode  16 , and each auxiliary electrode  16  positioned next to one side of a first pixel electrode  14  is connected to a second pixel electrode  14 P that is vertically adjacent to the first pixel electrode  14  and controlled by a preceding scan line. Further, the non-active area, which is spread with opaque devices such as thin film transistors and storage capacitors and fails to effect display, is provided in the center portion of each pixel unit  12  to divide its active area into two display regions  18   a  and  18   b.  Further, in this embodiment, the pixel electrode  14  has a lateral opening S that extends from the periphery to the inside of the pixel electrode  14  to divide the pixel electrode  14  into two sections. Also, the auxiliary electrode  16  has a main part  16   a  that extends in parallel with data lines  28  and two extension parts  16   b  and  16   c  that extend in parallel with scan lines  22  and into the opening S of the pixel electrode  14 . 
         [0026]    According to the arrangement of pixel electrodes shown in  FIG. 1 , since each auxiliary electrode  16  positioned next to one side of a first pixel electrode  14  is connected to a second pixel electrode  14 P controlled by a preceding scan line under a row inversion drive scheme, the auxiliary electrode  16  and neighboring pixel electrode  14  have opposite polarities to produce fringe fields. More specifically, taking the display region  18   a  with a negative polarity as an example, the pixel electrode  14 P with a positive polarity controlled by a preceding scan line is placed adjacent to the top of the display region  18   a,  the main part  16   a  of the auxiliary electrode  16  extended from the pixel electrode  14 P to have a positive polarity is placed adjacent to the left of the display region  18   a,  the extension part  16   b  of the auxiliary electrode  16  with a positive polarity is placed adjacent to the bottom of the display region  18   a,  and the main part  26   a  of the auxiliary electrode  26  extended from the pixel electrode  24 P to have a positive polarity is placed adjacent to the right of the display region  18   a.  Hence, a voltage difference existing between the display region  18   a  with a negative polarity and surrounding electrodes with positive polarities produces fringe fields, and the orientations of liquid crystal molecules within one display region are divided into different tilt directions. Similarly, the orientations of liquid crystal molecules within the display region  18   b  with a negative polarity are divided into different tilt directions. In addition, under a column inversion drive scheme, each auxiliary electrode positioned next to one side of a first pixel electrode is connected to a second pixel electrode controlled by a preceding data line to produce fringe fields. The principle is similar to the embodiment mentioned above; therefore, the detail description and figures can be omitted. 
         [0027]    Next, as shown in  FIG. 2 , in the color filter substrate  30 , a color filter  33  and a common electrode  35  are formed on a transparent substrate  31 . In the array substrate  20 , a first metal layer M 1  is deposited on the transparent substrate  32  and patterned to define scan lines (not shown), gate regions  34  of TFTs, and lower capacitor electrodes  36 . A dielectric gate insulation layer  38  is formed on the transparent substrate  32  and covers the first metal layer M 1 . A second metal layer M 2  is deposited on the gate insulation layer  38  and patterned to define data lines  28 , source/drain regions  42  of TFTs, and upper capacitor electrodes  44 . A flattened layer  46  is formed on the gate insulation layer  38  and covers the source/drain regions  42  and the upper capacitor electrodes  44 . A transparent conductive film is deposited on the flattened layer  46  and patterned to define pixel electrodes  14  and auxiliary electrodes  16 . In this embodiment, each lower capacitor electrodes  36  formed from the first metal layer M 1  and each upper capacitor electrodes  44  formed from the second metal layer M 2  together form a storage capacitor for each pixel unit  12 . Further, the upper capacitor electrode  44  formed from the second metal layer M 2  is hollowed out at a position overlapping the extension part  16   b  of the auxiliary electrode  16  to form an opening  52 . As can be more clearly seen in  FIG. 3 , the left side diagram shows a pattern of transparent electrodes, where an opening S is formed within each pixel electrode  14  to divide it into two sections, a spacing region G is formed between two adjacent pixel electrodes  14 , and each auxiliary electrode  16  spreads over the spacing region G and extends into the opening S. The right side diagram shows a pattern of the second metal layer M 2 , where each upper capacitor electrode  44  formed from the second metal layer M 2  is hollowed out at a position corresponding to the extension part  16   b  of the auxiliary electrode  16  to form an opening  52 . 
         [0028]    According to the above embodiment, a multi-domain profile of a LC cell is formed by providing auxiliary electrodes  16  that spread over the spacing regions G and extend into the openings S, and this can be easily achieved through typical TFT fabrication processes. Hence, compared with the conventional design where a protrusion or via structure is used to cause tilted liquid crystal molecules, the residue phase difference is eliminated to avoid light leakage according to this embodiment since all liquid crystal molecules are vertically aligned under a field-off state. Further, compared with another conventional design where slits are formed to produce fringe fields, the biased auxiliary electrodes  16  allow for stronger field strength to tilt liquid crystal molecules so as to reduce the areas of a disclination region and thus increase the light-transmittance of an LCD. Further, under the design that the pixel electrodes  14  cooperate with the auxiliary electrodes  16  to produce fringe fields, the auxiliary electrode  16  that extends to the inside of each pixel unit  12  often overlaps the second metal layer M to create coupling capacitances. Hence, according to the above embodiment, since part of the upper capacitor electrode  44  which overlaps the extension part  16   b  of the auxiliary electrode  16  is hollowed out, the overlap between each auxiliary electrode  16  and the second metal layer M 2  is considerably reduced to effectively reduce the capacitive coupling effect and minimize the variations in gray-level voltages as a result. 
         [0029]      FIG. 4  shows a top view of a multi-domain liquid crystal display according to another embodiment of the invention, and  FIG. 5  is a cross-section taken along line B-B′ in  FIG. 5 . The embodiment shown in  FIG. 4  and  FIG. 5  is similar to that shown in  FIG. 1 , where the upper capacitor electrode  44  formed from the second metal layer M 2  is hollowed out at a position overlapping the extension part  16   b  of the auxiliary electrode  16  to form an opening  52 , except the lower half of the main part  16   a  adjacent to the longitudinal side of the display region  18   b  is removed. The elimination of the lower half of the main part  16   a  may reduce the overlap between the auxiliary electrode  16  and the date line  28  formed from the second metal layer M 2  to further reduce the capacitive coupling effect. Besides, since the former lower half of the main part  16   a  is not provided, the display region I  8   b  may extend to the left side farther to cover vacant region, thus improving the aperture ratio of the pixel unit  12 . Note that even the lower half of the main part  16   a  adjacent to the longitudinal side of the display region  18   b  is removed, the voltage differences exist between the display region  18   b  and its horizontally-adjacent pixel electrodes  14  under a line inversion scheme, and the voltage differences exist between the display region  18   b  and surrounding pixel electrodes  14  under a dot inversion scheme all allow for the formation of fringe fields. 
         [0030]      FIG. 6  shows a top view of a multi-domain liquid crystal display according to another embodiment of the invention, and  FIG. 7  is a cross-section taken along line C-C′ in  FIG. 6 . Referring to  FIG. 6 , the pixel electrode  14  is provided with an opening S that extends from the periphery to the inside of the pixel electrode  14 , and the auxiliary electrode  56  has a main part  56   a  and a single extension part  56   b  that extends into the opening S. In this embodiment, voltage differences exist between the extension part  56   b  (positive polarity) and display regions  18   a  and  18   b  (negative polarity) to produce fringe fields. Further, as shown in  FIG. 7 , the upper capacitor electrode  44  formed from the second metal layer M 2  is also hollowed out at a position overlapping the single extension part  56   b  to form an opening  52  and as a result reduce the capacitive coupling effect. 
         [0031]      FIG. 8  shows a top view of a multi-domain liquid crystal display according to another embodiment of the invention, and  FIG. 9  is a cross-section taken along line D-D′ in  FIG. 8 . In this embodiment, a single horizontally-extending section protruding from the center portion of a pixel electrode  14  form a complete auxiliary electrodé  66 ; more specifically, each auxiliary electrode  66  that is positioned next to one side and extends into the opening of a first pixel electrode is connected to a second pixel electrode controlled by a preceding data line. Hence, the auxiliary electrode  66  is not formed to overlap the data line  28  formed from the second metal layer M 2  to further reduce the capacitive coupling effect. Besides, the display region of the pixel electrode  14  may extend to the right and left sides farther to cover the vacant region, thus improving the aperture ratio of the pixel unit  12 . Also, as shown in  FIG. 9 , the upper capacitor electrode  44  formed from the second metal layer M 2  is also hollowed out at a position overlapping the auxiliary electrode  66  to form an opening  52 . Besides, as shown in  FIG. 10 , when the pattern of transparent electrodes shown in  FIG. 8  is driven by a dot inversion scheme, each display region  18   a  or  18   b  has an opposite polarity in relation to surrounding auxiliary electrodes  66  or surrounding display regions to produce fringe fields. 
         [0032]    Also, a reflective metallic film may be provided in the multi-domain pixel structure shown in the above embodiments to effect reflective display, and the reflective metallic film may spread over the non-active area, which is spread with opaque devices such as thin film transistors and storage capacitors, to maintain a high aperture ratio. Further, the capacitive coupling effect can be reduced as long as part of the second metal layer M 2  that overlaps the auxiliary electrode is hollowed out, and it is not limited to remove part of the capacitor electrode to achieve such purpose. For example, the capacitive coupling effect may also be reduced by forming a longitudinal opening on the data line  28  to reduce the overlap between each auxiliary electrode  16  and the second metal layer M 2 . Besides, each auxiliary electrode  16  may be formed only in the opening S of the pixel electrode  14  or only in the spacing region G to produce fringe fields, and, in that case, the capacitive coupling effect can be also reduced as part of the second metal layer M 2  that overlaps the auxiliary electrode  16  is hollowed out. 
         [0033]    The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “the present invention” or the like is not necessary limited the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims. Moreover, no element and component in the present disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.