Abstract:
An element substrate is provided, including a substrate, a metal layer, a planarization layer and a first conductive layer. The metal layer is disposed on the substrate. The planarization layer is located on the metal layer, wherein the planarization layer includes a contact hole, the contact hole has a continuous wall and a bottom, the bottom exposes the metal layer, and the bottom of the contact hole has a first width. The first conductive layer is located on the planarization layer, wherein the first conductive layer includes an opening, the opening exposes the contact hole, and the opening has a second width above the contact hole, wherein the relationship of the first width and the second width is modified to decrease illumination loss and to prevent problems of shot-circuiting and insufficient capacitance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 103131296, filed on Sep. 11, 2014, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a liquid crystal display, and in particular to a liquid crystal display having at least one contact hole. 
     Description of the Related Art 
     In a liquid crystal display, a contact hole is utilized to conduct a pixel electrode and a source electrode. However, with reference to  FIG. 1A , the liquid crystal molecules  2  are arranged along a profile of the contact hole  1 , and the contact hole  1  is like a funnel structure. 
     With reference to  FIG. 1B , conventionally, a bottom conductive layer  3  and a pixel conductive layer  4  surround the contact hole. The bottom conductive layer  3  is insulated from the pixel conductive layer  4  by an insulation layer  5 . When the radius of the contact hole  1  at the location of the bottom conductive layer  3  is decreased, the bottom conductive layer  3  contacts and short-circuits the pixel conductive layer  4 . However, when the radius of the contact hole  1  at the location of the bottom conductive layer  3  is increased, the capacitance between the bottom conductive layer  3  and the pixel conductive layer  4  is insufficient, and the reliability of the liquid crystal display is decreased. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment of the invention, an element substrate is provided, including a substrate, a metal layer, a planarization layer and a first conductive layer. The metal layer is disposed on the substrate. The planarization layer is located on the metal layer, wherein the planarization layer comprises a contact hole, the contact hole has a continuous wall and a bottom, the bottom exposes the metal layer, and the bottom of the contact hole has a first width. The first conductive layer is located on the planarization layer, wherein the first conductive layer comprises an opening, the opening exposes the contact hole, and the opening has a second width above the contact hole, wherein the first width and the second width satisfy the following equation: 
               2   *     {         L   1     2     +         0.95   ⁢           ⁢   h         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ·     ln   ⁡     [       -   0.134         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]           }       ≤     L   2     ≤     2   *     {         L   1     2     +         0.95   ⁢           ⁢   h         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ·     ln   ⁡     [       -   0.00166         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]           }             
wherein L 1  is the first width, L 2  is the second width, h is the thickness of the planarization layer, θ is an included angle between a straight line and an extension surface of the bottom, the straight line connects a reference point and a base point, and the reference point is located on the continuous wall, wherein a vertical distance from the reference point to the bottom is 0.95 h, and the base point is located at the point where the continuous wall is connected to the bottom.
 
     Utilizing the embodiment of the invention, the transmittance loss of the liquid crystal display is less than 1%, which is acceptable for the qualified liquid crystal display, and the problems of short-circuiting and insufficient capacitance between the first conductive layer and the second conductive layer are solved. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIGS. 1A and 1B  shows an element substrate of a conventional liquid crystal display; 
         FIG. 2A  shows the structure of an element substrate of an embodiment of the invention; 
         FIG. 2B  shows the detailed structure of the element substrate of the embodiment of the invention; 
         FIG. 3A  shows the element substrate of the embodiment of the invention utilized in a liquid crystal display; 
         FIG. 3B  shows detailed elements in portion  3 B of  FIG. 3A ; and 
         FIG. 4  shows a liquid crystal display of an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
       FIG. 2A  shows an element substrate  100  of an embodiment of the invention, which comprises a substrate  110 , a metal layer  120 , a planarization layer  130  and a first conductive layer  140 . The metal layer  120  is disposed on the substrate  110 . The planarization layer  130  is located on the metal layer  120 , wherein the planarization layer  130  comprises a top, a bottom, and a contact hole  131 , the contact hole  131  has a continuous wall  132  and a hole bottom, the hole bottom of the contact hole  131  exposes the metal layer  120 , and the hole bottom of the contact hole  131  has a first width L 1 . The first conductive layer  140  is located on the planarization layer  130 , wherein the first conductive layer  140  comprises an opening  141 , the opening  141  exposes the contact hole  131 , and the opening  141  has a second width L 2  above the contact hole  131 . 
     With reference to  FIG. 2A , the applicant has discovered from deriving curve equations that when the first width L 1  and the second width L 2  satisfy the following equation, the transmittance loss of the liquid crystal display is less than 1% (acceptable for the qualified liquid crystal), and the problems of contact short and insufficient capacitance are solved: 
               2   *     {         L   1     2     +         0.95   ⁢           ⁢   h         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ·     ln   ⁡     [       -   0.134         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]           }       ≤     L   2     ≤     2   *     {         L   1     2     +         0.95   ⁢           ⁢   h         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ·     ln   ⁡     [       -   0.00166         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]           }             
wherein L 1  is the first width, L 2  is the second width, h is a thickness of the planarization layer  130  to the bottom of the planarization layer  130 , θ is an included angle between a straight line and an extension surface of the bottom of the planarization layer, the straight line connects a reference point  134  and a base point  135 , and the reference point  134  is located on the continuous wall  132 , wherein a vertical distance from the reference point  134  to the hole bottom  133  of the contact hole  131  is 0.95 h, and the base point  135  is located at the point where the continuous wall  132  is connected to the bottom  133  of the contact hole  131 . By modifying the parameters above, the curvature and the shape of the continuous wall  132  can be modified.
 
     With reference to  FIG. 2A , the derivative of the curve equation is presented in the following description. 
     First, curve fitting, assuming a curve equation of the continuous wall of the contact hole is:
 
 y=f ( R )=− A ′exp(− R )  (1)
 
     Next, the curve fitting (relative to reference point  134 , base point  135  and included angle θ), assuming that a distance between the reference point  134  and the top of the planarization layer  130  is p (p=0.05) times the thickness h of the planarization layer  130 , then the curve equation of the continuous wall of the contact hole satisfies: 
     
       
         
           
             
               f 
               ⁡ 
               
                 ( 
                 r 
                 ) 
               
             
             = 
             
               
                 - 
                 h 
               
               ⁢ 
               
                   
               
               ⁢ 
               
                 exp 
                 ⁡ 
                 
                   ( 
                   
                     
                       - 
                       r 
                     
                     α 
                   
                   ) 
                 
               
             
           
         
       
     
     The horizontal distance between the reference point  134  and the base point  135  is R′. When the curve passes through the reference point  134 , that means f(r=R′), the following two equations are satisfied: 
     
       
         
           
             
               f 
               ⁡ 
               
                 ( 
                 
                   R 
                   ′ 
                 
                 ) 
               
             
             = 
             
               
                 - 
                 ph 
               
               = 
               
                 
                   - 
                   h 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   exp 
                   ⁡ 
                   
                     ( 
                     
                       
                         - 
                         
                           R 
                           ′ 
                         
                       
                       α 
                     
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             
               tan 
               ⁢ 
               
                   
               
               ⁢ 
               θ 
             
             = 
             
               
                 
                   ( 
                   
                     1 
                     - 
                     p 
                   
                   ) 
                 
                 ⁢ 
                 h 
               
               
                 R 
                 ′ 
               
             
           
         
       
     
     Next, an included angle β between a cut line L′ at base point  135  and the horizontal line defines the angle of the curve of the planarization layer  130 , and the included angle β substantially equals 1.5θ. Therefore, by revising the curve equation (angle revising) further, we get: 
                     f   ⁡     (   r   )       =       ⁢           -   h     ·   exp     ⁢     {       -   r     /   α     }       =       h   ·   exp     ⁢     {     r   ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (   β   )           0.95   ⁢           ⁢   h         }                     =       ⁢         -   h     ·   exp     ⁢     {     r   ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h         }                   
The curve equation of the contact hole is achieved.
 
     Next, by bringing this equation into the above equation (moving the base point to the center of the contact hole  131 ), we get: 
               ∵   r     =     R   -       R   0     ⁢           ⁢   …   ⁢           ⁢     (   displacement   )                             ⇒     f   ⁡     (   r   )         =       ⁢         -   h     ·   exp     ⁢     {       -     (     R   -     R   0       )       /   α     }                   =       ⁢         -   h     ·   exp     ⁢     {       (     R   -     R   0       )     ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h         }                   
The actual curve equation of the contact hole is achieved.
 
     Next, the radius of the opening of the first conductive layer  140  should be deduced. The first conductive layer  140  is commonly located on a planar area of the planarization layer  130 . Because the planar area of the planarization layer  130  is not perfectly planar, the tilt angle of the liquid crystal molecule is about 0.1°, and δ=0.1° is the inferior limit of the acceptable tilt angle. 
                     ⁢         ∂     f   ⁡     (     R   ′     )           ∂     R   ′         =       tan   ⁢           ⁢   δ     =           ∂     ∂     R   ′         ⁢     {       -   h     ·     exp   ⁡     [       R   ′     ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h         ]         }       ⁢     
     ⇒       -   h     ·     exp   ⁡     [       R   ′     ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h         ]       ·       ∂     ∂     R   ′         ⁡     [       R   ′     ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h         ]           =         tan   ⁢           ⁢   δ     ⁢     
     ⁢           ⇒     exp   ⁡     [       R   ′     ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h         ]         =               -   0.95     ·   tan     ⁢           ⁢   δ         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ⁢     
     ⁢           ⇒       R   ′     ·         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           0.95   ⁢           ⁢   h           =         ln   ⁡     [           -   0.95     ·   tan     ⁢           ⁢   δ         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]       ⁢     
     ⁢           ⇒     R   ′       =             0.95   ⁢           ⁢   h         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ·     ln   ⁡     [           -   0.95     ·   tan     ⁢           ⁢   δ         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]         ⁢     
     ⁢           ⇒   R     =       R   0     +         0.95   ⁢           ⁢   h         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ·     ln   ⁡     [           -   0.95     ·   tan     ⁢           ⁢   δ         ln   ⁡     (   0.05   )       ·     tan   ⁡     (     1.5   ⁢   θ     )           ]                               
The radius of the opening of the first conductive layer  140  is achieved.
 
     Only considering the tilt angle without considering the twisting angle of the liquid crystal panel, the transparent ratio of the liquid crystal panel satisfies the following equation: T∝sin 2 (Γ), wherein Γ is a phase retardation angle, T is the transparent ratio of the liquid crystal panel, and the transparent ratio of the liquid crystal panel is directly proportionate with a sine square function. When the tilt angle is between 0.1 and 8 degrees, the illumination loss is less than 1%, which is acceptable for qualified liquid crystal display. According to the parameters above, the following function is achieved: 
     
       
         
           
             
               2 
               * 
               
                 { 
                 
                   
                     
                       L 
                       1 
                     
                     2 
                   
                   + 
                   
                     
                       
                         0.95 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         h 
                       
                       
                         
                           ln 
                           ⁡ 
                           
                             ( 
                             0.05 
                             ) 
                           
                         
                         · 
                         
                           tan 
                           ⁡ 
                           
                             ( 
                             
                               1.5 
                               ⁢ 
                               θ 
                             
                             ) 
                           
                         
                       
                     
                     · 
                     
                       ln 
                       ⁡ 
                       
                         [ 
                         
                           
                             - 
                             0.134 
                           
                           
                             
                               ln 
                               ⁡ 
                               
                                 ( 
                                 0.05 
                                 ) 
                               
                             
                             · 
                             
                               tan 
                               ⁡ 
                               
                                 ( 
                                 
                                   1.5 
                                   ⁢ 
                                   θ 
                                 
                                 ) 
                               
                             
                           
                         
                         ] 
                       
                     
                   
                 
                 } 
               
             
             ≤ 
             
               L 
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             ≤ 
             
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               * 
               
                 { 
                 
                   
                     
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                       1 
                     
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                         0.95 
                         ⁢ 
                         
                             
                         
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                           ln 
                           ⁡ 
                           
                             ( 
                             0.05 
                             ) 
                           
                         
                         · 
                         
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                           ⁡ 
                           
                             ( 
                             
                               1.5 
                               ⁢ 
                               θ 
                             
                             ) 
                           
                         
                       
                     
                     · 
                     
                       ln 
                       ⁡ 
                       
                         [ 
                         
                           
                             - 
                             0.00166 
                           
                           
                             
                               ln 
                               ⁡ 
                               
                                 ( 
                                 0.05 
                                 ) 
                               
                             
                             · 
                             
                               tan 
                               ⁡ 
                               
                                 ( 
                                 
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                                   ⁢ 
                                   θ 
                                 
                                 ) 
                               
                             
                           
                         
                         ] 
                       
                     
                   
                 
                 } 
               
             
           
         
       
     
     In one embodiment, the included angle θ is between 20 and 40 degrees, such as between 25 and 35 degrees. 
     With reference to  FIG. 2A , in one embodiment, the metal layer  120  is a source electrode or a drain electrode of a driving element. In one embodiment, the element substrate  100  further comprises a semiconductor layer  137  located between the metal layer  120  and the substrate  110 . The semiconductor layer  137  can be made of polycrystalline silicon, amorphous silicon or metal oxide. 
     With reference to  FIG. 2B , in one embodiment, the element substrate  100  further comprises an insulation layer  160  and a second conductive layer  170 , wherein at least a portion of the insulation layer  160  is disposed between the first conductive layer  140  and the second conductive layer  170 , and the second conductive layer  170  is electrically connected to the metal layer  120  via the contact hole  131 . 
       FIG. 3A  shows the element substrate of the embodiment of the invention utilized in a liquid crystal display  200  which comprises an active area (pixel area) A and an non-active area (B).  FIG. 3B  shows detailed structures of portion  3 B of  FIG. 3A , wherein the liquid crystal display  200  further comprises scan lines  201 , data lines  202 , a semiconductor layer  203 , source electrodes  240 , a contact hole  231  (equivalent to the contact hole  131  of  FIG. 2A ), a bottom  233  of the contact hole (equivalent to the bottom  133  of  FIG. 2A ), a common electrode opening  234  (equivalent to the opening  141  of  FIG. 2A ), drain electrodes  204 , common electrodes  205  and pixel electrodes  210 , which are located in the active area A. In an embodiment of the invention, the metal layer  120  comprises the source electrodes  240  and the drain electrodes  204 . The liquid crystal display can be a fringe field switching display or in-place switching display. 
       FIG. 4  shows a liquid crystal display  200  of an embodiment of the invention, which comprises an opposite substrate  260 , a liquid crystal layer  250  and the element substrate  100 . 
     Utilizing the embodiment of the invention, the illumination loss of the liquid crystal display is less than 1%, which is acceptable for the qualified liquid crystal display, and the problems of contact short and insufficient capacitance between the first conductive layer  140  and the second conductive layer  170  are solved. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having the same name (but for use of the ordinal term). 
     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. On 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.