Abstract:
A display panel includes a pixel array, a light-shielding pattern and a plurality of spacers. The pixel array includes a plurality of sub-pixels. The light-shielding pattern has a first edge and a second edge disposed adjacent to two neighboring sub-pixels, respectively, and a width H exists between the first edge and the second edge. The spacers overlap the light-shielding pattern in a vertical projection direction, and each spacer has a diameter D. Each spacer has a first rim facing the first edge and a second rim facing the second edge. The first rim and the first edge have a first distance A″, the second rim and the second edge have a second distance B″. The width H between the first edge and the second edge, the diameter D of the spacer, the first distance A″ and the second distance B″ satisfy the following relations: B″&gt;0; A″≧0; B″&gt;A″; and 2D≦H≦3D.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a display panel, and more particularly, to a display panel with high contrast ratio. 
         [0003]    2. Description of the Prior Art 
         [0004]    Due to its advantages such as compact size and energy efficiency, liquid crystal display (LCD) panel has been widely used in various types of electronic products such as smart phone, notebook computer, tablet PC and TV. The LCD panel includes a first substrate e.g. an array substrate, a second substrate e.g. a counter substrate, and a liquid crystal layer interposed between the first substrate and the second substrate. In addition, the LCD panel further includes a plurality of main spacers disposed between the first substrate and the second substrate to maintain a constant cell gap. The main spacers are formed on one of the first substrate or the second substrate in advance, and the main spacers will be in contact with the other one of the first substrate and the second substrate to maintain the cell gap after they are assembled. In addition, the LCD panel includes two alignment films disposed on the inner surfaces of the first substrate and the second substrate respectively. The alignment film is used to align liquid crystal molecules, and the aligning effect of the alignment film is achieved by a rubbing alignment process. The existence of the main spacer, however, impedes the rubbing alignment process on the alignment film, which causes light leakage in the proximity to the main spacer. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore one of the objectives of the present invention to provide a display panel with high contrast ratio and low dark state brightness. 
         [0006]    In an embodiment of the present invention, a display panel is provided. The display panel includes a pixel array, a light-shielding pattern and a plurality of spacers. The pixel array includes a plurality of sub-pixels, wherein the sub-pixels are substantially arranged along a first direction to form a plurality of sub-pixel rows, and substantially arranged along a second direction to form a plurality of sub-pixel columns. The light-shielding pattern is disposed between any two adjacent sub-pixel rows, wherein the light-shielding pattern has a first edge and a second edge, the first edge and the second edge are disposed adjoining to the two adjacent sub-pixel rows respectively, and a width H exists between the first edge and the second edge in the second direction. The spacers are disposed between the two adjacent sub-pixel rows, the spacers overlap the light-shielding pattern in a vertical projection direction, wherein each of the spacers has a diameter D, each of the spacers has a first rim facing the first edge and a second rim facing the second edge, a first distance A″ exists between the first rim and the first edge, a second distance B″ exists between the second rim and the second edge, and the width H, the diameter D, the first distance A″ and the second distance B″ satisfy the following relations: 
         [0000]      B″&gt;0;
 
         [0000]      A″≧0;
 
         [0000]      B″&gt;A″; and
 
         [0000]      2D≦H≦3D.
 
         [0007]    The spacer of the display panel of the present invention has shifting design, which can reduce the dark state brightness and increase the contrast ratio without reducing the aperture ratio and increasing the area of the light-shielding pattern. 
         [0008]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic diagram illustrating a display panel according to a first embodiment of the present invention. 
           [0010]      FIG. 2  is a partially enlarged view of the display panel of  FIG. 1 . 
           [0011]      FIG. 3  is a cross-sectional view of the display panel according to the first embodiment of the present invention. 
           [0012]      FIG. 4  is a top view schematically illustrating the display panel of this embodiment when performing a rubbing alignment process. 
           [0013]      FIG. 5  is a cross-sectional view illustrating the display panel of this embodiment when performing a rubbing alignment process. 
           [0014]      FIG. 6  is a schematic diagram illustrating a display panel according to a second embodiment of the present invention. 
           [0015]      FIG. 7  is a partially enlarged view of the display panel of  FIG. 6 . 
           [0016]      FIG. 8  is a cross-sectional view of the display panel according to the second embodiment of the present invention. 
           [0017]      FIG. 9  is a partially enlarged view of a display panel according to an alternative embodiment of the second embodiment of the present invention. 
           [0018]      FIG. 10  is a cross-sectional view of the display panel according to the alternative embodiment of the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    To provide a better understanding of the present invention to the skilled users in the technology of the present invention, preferred embodiments will be detailed as follows. The preferred embodiments of the present invention are illustrated in the accompanying drawings with numbered elements to elaborate the contents and effects to be achieved. 
         [0020]    Refer to  FIGS. 1-3 .  FIG. 1  is a schematic diagram illustrating a display panel according to a first embodiment of the present invention,  FIG. 2  is a partially enlarged view of the display panel of  FIG. 1 , and  FIG. 3  is a cross-sectional view of the display panel according to the first embodiment of the present invention, where some components are not drawn in all of the drawings for highlighting the features of the display panel. As shown in  FIGS. 1-3 , the display panel  1  of this embodiment includes a first substrate  10 , a second substrate  20 , a pixel array AR, a light-shielding pattern  22  and a plurality of spacers  24 . The first substrate  10  and the second substrate  20  are disposed opposite to each other, and the first substrate  10  and the second substrate  20  may respectively be a transparent substrate e.g. a glass substrate, a quartz substrate, a plastic substrate or another suitable rigid or flexible substrate. A display medium layer  30  is interposed between the first substrate  10  and the second substrate  20 . In this embodiment, a liquid crystal display (LCD) panel is selected as an example of the display panel  1 , and thus the display medium layer  30  is a liquid crystal layer. The LCD panel may be an in-plane electric field type LCD panel e.g. a fringe field switching (FFS) LCD panel or an in-plane switching (IPS) LCD panel, but not limited thereto. The LCD panel may be other types of LCD panels e.g. a vertical electric field type LCD panel, or other types of display panels e.g. an electroluminescent (EL) display panel. The pixel array AR is disposed on the first substrate  10 , and the pixel array AR includes a plurality of sub-pixels SP. The sub-pixels SP are substantially arranged along a first direction D 1  to form a plurality of sub-pixel rows  12 , and substantially arranged along a second direction D 2  to form a plurality of sub-pixel columns  14 . In this embodiment, the first direction D 1  and the second direction D 2  are substantially perpendicularly to each other, for example, the first direction D 1  is the latitudinal direction in  FIG. 1 , and the second direction D 2  is the longitudinal direction in  FIG. 1 , but not limited thereto. In this embodiment, each of the sub-pixels SP is substantially a rectangular sub-pixel, which has a long axis Lx, and the long axes Lx of all the sub-pixels SP are directed to the same direction e.g. the second direction D 2 , but not limited thereto. The long axes Lx of all the sub-pixels SP may be directed to different directions. In an alternative embodiment, the long axis Lx of each of the sub-pixels SP belonging to the odd rows of the sub-pixel rows  12  and the long axis Lx of each of the sub-pixels SP belonging to the even rows of the sub-pixel rows  12  are arranged in a non-parallel manner so as to provide wide viewing angle display effect. 
         [0021]    Each sub-pixel SP may further include other devices configured to fulfill display function including a switching device e.g. a thin film transistor (TFT) device, a storage capacitor device, electrodes e.g. a pixel electrode and/or a common electrode. The first substrate  10  may be overlaid with various types of signal lines e.g. gate lines (scanning lines), data lines and common lines to provide different driving signals to the sub-pixel SP. In this embodiment, the sub-pixels SP may include sub-pixels configured to provide different colors e.g. green sub-pixels G, blue sub-pixels B and red sub-pixels R. The green sub-pixels G, the blue sub-pixels B and the red sub-pixels R may be alternately and repeatedly arranged in the first direction D 1 , i.e. the sub-pixel columns  14  may include a plurality of green sub-pixel columns  14 G, a plurality of blue sub-pixel columns  14 B and a plurality of red sub-pixel columns  14 R arranged alternately, but not limited thereto. 
         [0022]    When viewing form a vertical projection direction Z, the light-shielding pattern  22  is disposed between any two adjacent sub-pixel rows  12 , and the light-shielding pattern  22  extends along the first direction D 1 . The light-shielding pattern  22  has a first edge  221  and a second edge  222 , and the first edge  221  and the second edge  222  are disposed adjoining to two sub-pixel rows  12  disposed adjacently in the second direction D 2  respectively. In addition, the light-shielding pattern  22  may be further disposed between any two adjacent sub-pixel columns  14 , and the light-shielding pattern  22  may extend along the second direction D 2  to form a light-shielding grid. A width H exists between the first edge  221  and the second edge  222  in the second direction D 2 , which is equal to the distance between the first edge  221  and the second edge  222 . In this embodiment, the light-shielding pattern  22  is disposed on the second substrate  20 . The light-shielding pattern  22  may be, for example, a black matrix (BM) pattern made of organic material e.g. black photoresist material or inorganic material e.g. metal. In an alternative embodiment, the light-shielding pattern  22  may be disposed on the first substrate  10 , and the material of the light-shielding pattern  22  may be organic material e.g. black photoresist material or inorganic material e.g. metal. The display panel  1  may further optionally include other films such as a color filter pattern CF, a planarization layer  26  and an alignment film  28  disposed on the second substrate  20 . In this embodiment, the spacers  24  may be main spacers and/or sub spacers. The main spacers are in contact with the first substrate  10  and the second substrate  20 , or in contact with the overlying layer of the first substrate  10  and the overlying layer of the second substrate  20  when the display panel  1  is on a normal condition (i.e. when the display panel  1  is not pressed or deformed) to maintain a constant cell gap between the first substrate  10  and the second substrate  20 . The sub spacers are not in contact with the first substrate  10  or not in contact with the overlying layer of the first substrate  10  when the display panel  1  is on a normal condition (i.e. when the display panel  1  is not pressed or deformed). When the display panel  1  is pressed by an external force, the sub spacers will be in contact with the first substrate  10  or in contact with the overlying layer of the first substrate  10  to prevent the display panel  1  from being deformed excessively and damaged. The spacers  24  of this embodiment are preferably sub spacers because the number of the sub spacers is usually more than the number of the main spacers. In such a case, the effect for inhibiting dark state light leakage is more significant. Since the dark state light leakage is inhibited, the contrast ratio is increased and the dark state brightness is decrease (i.e. the dark image is blacker). The spacers  24  are not limited to be sub spacers. In an alternative embodiment, the spacers  24  may be main spacers. In still another alternative embodiment, some of the spacers  24  may be main spacers, while the other spacers  24  may be sub spacers. In addition, the numbers, arrangement densities and locations of the main spacers and the sub spacers may be modified. For example, the spacer  24  may be disposed among any four adjoining sub-pixels SP, or disposed among a portion of four adjoining sub-pixels SP. 
         [0023]    When viewing form a vertical projection direction Z, the spacers  24  are disposed between two adjacent sub-pixel rows  12 , and the spacers  24  overlap the light-shielding pattern  22 . In this embodiment, the spacers  24  are disposed on the second substrate  20 , but not limited thereto. The spacer  24  may be substantially a cylinder structure, a cone structure or other structures. In the second direction D 2 , each of the spacers  24  has a diameter D. In this embodiment, the spacers  24  are disposed between the planarization layer  26  and the alignment film  28 , i.e. the alignment film  28  is disposed on the spacer  24  and covers the surface of the spacer  24  and the surface of the planarization layer  26 . The diameter D is the maximum diameter of the spacer  24  in the second direction D. For example, if the spacer  24  is a cylinder structure or a cone structure, the diameter D is the diameter of the round base of the spacer  24 . 
         [0024]    Refer to  FIGS. 4-5 , as well as  FIGS. 1-3 .  FIG. 4  is a top view schematically illustrating the display panel of this embodiment when performing a rubbing alignment process, and  FIG. 5  is a cross-sectional view illustrating the display panel of this embodiment when performing a rubbing alignment process. As shown in  FIGS. 4-5 , in order to provide the alignment film  28  with aligning effect, the display panel  1  is moved along a rubbing direction X, and a roller  50  with a brush  52  is used to rub the alignment film  28 . During the rubbing alignment process, the roller  50  is immobilized and self-rotated e.g. clockwise at one side of the display panel  1 . The brush  52  is disposed on the roller  50  at an angle of 60 degrees, for example, and the display panel  1  is moved along the rubbing direction X. As shown in  FIG. 5 , at a first time point t 1 , the brush  52  of the roller  50  is in contact with the surface of the alignment film  28  to form an alignment pattern on the surface of the alignment film  28 . At a second time point t 2 , since the roller  50  is rotated clockwise, a dead space between the spacer  24  and the brush  52  will exist when the spacer  24  approaches the roller  50 . Due to the dead space, the brush  52  of the roller  50  is not able to completely contact the second rim  242  of the spacer  24 , and thus the alignment film  28  corresponding to the second edge  222  of the light-shielding pattern  22  cannot be perfectly rubbed and aligned. Consequently, this region forms a weak alignment region  28 B. At the third time point t 3 , since the roller  50  is rotated clockwise, when the display panel  1  continues to move along the rubbing direction X to the first rim  241  of the spacer  24 , the brush  52  of the roller  50  is able to completely contact the first rim  241  of the spacer  24 . Thus, the alignment film  28  corresponding to the first edge  221  of the light-shielding pattern  22  can be perfectly rubbed and aligned, and this region forms a strong alignment region  28 A. 
         [0025]    As shown in  FIGS. 1-3 , the alignment effect of the weak alignment region  20 B is inferior to the alignment effect of the strong alignment region  28 A, and thus the display media e.g. liquid crystal molecules corresponding to the weak alignment region  28 B are not well aligned, which causes light leakage. Consequently, in order to diminish the light leakage in the weak alignment region  28 B, the position of the spacer  24  is shifted toward the strong alignment region  28 A to make the weak alignment region  28 B overlap the light-shielding pattern  22  in the vertical projection direction Z as much as possible. Accordingly, the light leakage can be shielded by the light-shielding pattern  22  without increasing the area of the light-shielding pattern  22 . In another aspect, since the strong alignment region  28 A has good alignment effect, no light leakage will occur even when the strong alignment region  28 A is shifted toward the display region without being partially or entirely shielded by the light-shielding pattern  22  in the vertical projection direction Z. As long as the spacer  24  overlaps the light-shielding pattern  22  in the vertical projection direction Z, the aperture ratio is not affected. Specifically, each spacer  24  has a first rim  241  facing the first edge  221 , and a second rim  242  facing the second edge  222 . A first distance A″ exists between the first rim  241  and the first edge  221 , and a second distance B″ exists between the second rim  242  and the second edge  222 . The width H, the diameter D, the first distance A″ and the second distance B″ satisfy the following relations: 
         [0000]      B″&gt;0;
 
         [0000]      A″≧0;
 
         [0000]      B″&gt;A″; and
 
         [0000]      2D≦H≦3D.
 
         [0026]    Under the above conditions, the spacer  24  is shifted along the second direction D 2  without crossing the boundary of the light-shielding pattern  22 , and the weak alignment region  28 B is disposed within the boundary of the light-shielding pattern  22 . Consequently, the light leakage in the weak alignment region  28 B is shielded by the light-shielding pattern  22 . It is experimentally proved that the shifting design of the spacers  24  of the display panel  1  reduces about 26% of dark state brightness of a dark image and increases about 17.8% of contrast ratio compared to a display panel of a control embodiment in which the spacers are disposed symmetrically, i.e. the spacer is disposed at a symmetric center of four adjacent sub-pixels. 
         [0027]    The display panel is not limited by the aforementioned embodiment, and may have other different preferred embodiments. To simplify the description, the identical components in each of the following embodiments are marked with identical symbols. For making it easier to compare the difference between the embodiments, the following description will detail the dissimilarities among different embodiments and the identical features will not be redundantly described. 
         [0028]    Refer to  FIGS. 6-8 .  FIG. 6  is a schematic diagram illustrating a display panel according to a second embodiment of the present invention,  FIG. 7  is a partially enlarged view of the display panel of  FIG. 6 , and  FIG. 8  is a cross-sectional view of the display panel according to the second embodiment of the present invention, where some components are not drawn in all of the drawings for highlighting the features of the display panel. As shown in  FIGS. 6-8 , in the display panel  2  of this embodiment, the spacers  24  may be shifted in the second direction D 2  toward the strong alignment region  28 A as described in the first embodiment. In this embodiment, the spacers  24  may also be shifted in the first direction D 1 . Specifically, the spacers  24  are disposed between the blue sub-pixel column  14 B and the red sub-pixel column  14 R disposed adjoining to the blue sub-pixel column  14 B; the spacers  24  are not disposed between the blue sub-pixel column  14 B and the green sub-pixel column  14 G disposed adjoining to the blue sub-pixel column  14 B, and the spacers  24  are not disposed between the green sub-pixel column  14 G and the red sub-pixel column  14 R disposed adjoining to the green sub-pixel column  14 G, but not limited thereto. In addition, there is a central reference line (also referred to as a central base line) C between the blue sub-pixel column  14 B and the red sub-pixel column  14 R disposed adjoining to the blue sub-pixel column  14 B. The distance between the central reference line C and the adjoining blue sub-pixel column  14 B in the first direction D 1  is substantially equal to the distance between the central reference line C and the adjoining red sub-pixel column  14 R, and a gap L exists between the blue sub-pixel column  14 B and the red sub-pixel column  14 R in the first direction D 1 . Furthermore, there is a first position P 1  in the central reference line C. Each of the spacers  24  is shifted from the first position P 1  toward the blue sub-pixel column  14 B to be disposed at a second position P 2 , an offset S exists between the first position P 1  and the second position P 2 , and the offset S, the gap L and the diameter D satisfy the following relation: S≧0.5(D−L). Also, each of the sub-pixels SP has a side E substantially parallel to the first direction D 1 , and each of the spacers  24  is disposed between the sides E of two adjoining sub-pixels SP (e.g. blue sub-pixels B) of the corresponding blue sub-pixel column  14 B. In this embodiment, each of the spacers  24  partially overlaps the side E of the sub-pixel SP (e.g. blue sub-pixel B) of the corresponding blue sub-pixel column  14 B in the second direction D 2 , and an overlapping portion of the spacer  24  and the side E of the sub-pixel SP (e.g. blue sub-pixel B) of the corresponding blue sub-pixel column  14 B has a first overlapping length O 1  in the first direction D 1 . Each of the spacers  24  is disposed between the sides E of two adjoining sub-pixels (e.g. red sub-pixels R) of the corresponding red sub-pixel column  14 R, each of the spacers  24  partially overlaps the side E of the sub-pixel (e.g. red sub-pixel R) of the corresponding red sub-pixel column  14 R in the second direction D 2 , an overlapping portion of the spacer  24  and the side E of the sub-pixel SP (e.g. red sub-pixel R) of the corresponding red sub-pixel column  14 R has a second overlapping length O 2  in the first direction D 1 , and the first overlapping length O 1  is greater than the second overlapping length O 2 . In other words, the spacer  24  is shifted from the first position P 1  toward the blue sub-pixel column  14 B to be disposed at the second position P 2 , but the spacer  24  still partially overlaps the blue sub-pixel B and the red sub-pixel R respectively in the second direction D 2 . 
         [0029]    Since the spacer  24  is shifted from the first position P 1  toward the blue sub-pixel column  14 B to the second position P 2 , the weak alignment region  28 B is shifted toward the blue sub-pixel B as well so that the light leakage in the blue sub-pixel B is more than the light leakage in the red sub-pixel R. In other words, without increasing the area of the light-shielding pattern  22 , the weak alignment region  28 B is shifted toward the blue sub-pixel B and away from the red sub-pixel R, and thus the light leakage in the blue sub-pixel B is more than the light leakage in the red sub-pixel R. Normally, the brightness of red light is higher than the brightness of blue light, and thus the light leakage in the blue sub-pixel B is less significant and less noticeable than the light leakage in the red sub-pixel R. Accordingly, the dark state brightness of a dark image can be reduced. In this embodiment, the spacers  24  may be only the sub spacers, only the main spacers or a combination of main spacers and sub spacers. 
         [0030]    Refer to  FIGS. 9-10 .  FIG. 9  is a partially enlarged view of a display panel according to an alternative embodiment of the second embodiment of the present invention, and  FIG. 10  is a cross-sectional view of the display panel according to the alternative embodiment of the second embodiment of the present invention. As shown in  FIGS. 9-10 , in the display panel  3  of this alternative embodiment, each of the spacers  24  is shifted from the first position P 1  toward the blue sub-pixel column  14 B to the second position P 2 , where an offset S exists between the first position P 1  and the second position P 2 , and the offset S, the gap L and the diameter D satisfy the following relation: S≧0.5(D−L). Different from the second embodiment, in this alternative embodiment, each of the spacers  24  partially overlaps the side E of the sub-pixel SP (e.g. blue sub-pixel B) of the corresponding blue sub-pixel column  14 B in the second direction D 2 , but each of the spacers  24  does not overlap the side E of the sub-pixel SP (red sub-pixel R) of the corresponding red sub-pixel column  14 R in the second direction D 2 . In this alternative embodiment, the spacers  24  may be only the sub spacers, only the main spacers or a combination of main spacers and sub spacers. 
         [0031]    In conclusion, the spacer of the display panel of the present invention is shifted to make the weak alignment region overlap the light-shielding pattern without reducing the aperture ratio since the area of the light-shielding pattern is unchanged. Thus, the dark state brightness of a dark image is reduced, and the contrast ratio is increased. In addition, the spacer of the display panel of the present invention is shifted toward the sub-pixel with specific color (e.g. blue sub-pixel), and thus the dark state brightness of a dark image is reduced. 
         [0032]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.