Abstract:
A touch panel-mounted liquid crystal panel minimizes picture distortion upon driving of the touch panel. In the liquid crystal panel, a lower glass substrate has switching devices provided in the vicinity of intersections between data lines and gate lines. An upper glass substrate has a black matrix joined to it. Patterned clusters of spacers are positioned at an area corresponding to the black matrix in such a manner to enlarge its contact area with the upper glass substrate, thereby keeping a uniform distance between the upper and lower glass substrates. The enlarged contact area allows the patterned clusters of spacers to sufficiently absorb a pressure load of a finger or a stylus pen. Accordingly, uniform distance between the upper and lower glass substrates is maintained even upon driving the touch panel. As a result, light deterioration and local image distortion is prevented or minimized.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a liquid crystal display panel, and more particularly to structures within a liquid crystal display panel with a touch panel to minimize light deterioration and image distortion. 
     2. Description of the Related Art 
     A conventional liquid crystal display panel controls a light transmissivity of liquid crystal cells to display a picture. Liquid crystal cells are formed between two glass substrates. Each liquid crystal cell responds to a video signal, i.e. a pixel signal, to control the transmitted light quantity. 
     Such a liquid crystal display panel maybe mounted with a touch panel to be used as an input device. A user touches the touch panel through a stylus or a finger to input instructions or information. The touch panel generates a voltage or current signal corresponding to a position where the touch panel is touched. 
     The touch panel can be either a capacitive or a resistive type.  FIG. 1  shows a liquid crystal display panel  10  mounted with a capacitive touch panel  12  and  FIG. 2  shows the same liquid crystal display panel  10  mounted with a resistive touch panel  16 . 
     Referring to  FIG. 1 , the liquid crystal display panel  10  includes upper and lower polarizing sheets  14 A and  14 B. Upper and lower glass substrates  20 B and  20 A are positioned below and above the upper and lower polarizing sheets  14 A and  14 B, respectively. Gate lines  23 , insulating film  24 , pixel electrodes  25 A, and a first orientation film  26 A are sequentially provided above the lower glass substrate  20 A. Below the upper glass substrate  20 B, a black matrix  27 , color filter  28 , a common electrode  25 B, and a second orientation film  26 B are sequentially provided. 
     Finally, ball spacers  22  and a liquid crystal material  21  are disposed between the first and second orientation films  26 A and  26 B. The purpose of the ball spacers  22  is to keep the distance between the upper and lower glass substrates  20 B and  20 A as uniform as possible. This in turn keeps the thickness of the liquid crystal material  21  uniform as well. 
     Also referring to  FIG. 1 , the capacitive touch panel  12  includes a glass sheet  30 , an electrode layer  31 , and an insulating layer  32  sequentially disposed above the upper polarizing sheet  14 A. The electrode layer  31  serves as a dielectric layer, and the insulating layer  32  prevents an electrical short from occurring when the touch panel  12  is pressurized by an input device such as a stylus or a finger (not shown). 
     When the touch panel  12  is pressurized, a capacitance value is changed at the pressurized point. The electrode layer  31  detects the capacitance value and generates either a current or a voltage signal corresponding to the capacitance value. 
     Referring to  FIG. 2 , the liquid crystal display panel  10  is the same as the display panel described in FIG.  1 . Thus, detailed description of the display panel  10  is omitted. The touch panel  16  of  FIG. 2  is resistive. The resistive touch panel  16  includes a glass sheet  33 , first and second electrode layers  36 A and  38 B above the glass sheet  33 , touch panel spacers  35  disposed in between the first and second electrode layers  36 A and  36 B, and an insulating sheet  34  above the second electrode layer  36 B. 
     When the touch panel  16  is pressurized, a short is created between the first and second electrode layers  36 A and  36 B at the pressurized point, which generates differing current or voltage corresponding to the pressurized point. 
     As mentioned above, ball spacers  22  are used to maintain a uniform distance between the upper and lower glass substrates  20 B and  20 A in the liquid crystal display panel  10  of  FIGS. 1 and 2 . However, the display image becomes distorted at the points where the touch panel  12  or  16  is pressurized, for example by a stylus or a finger. 
     More specifically, when the stylus is used on the touch panel  12  or  16 , the upper glass substrate  20 B is also pushed corresponding to the position of the stylus on the touch panel. Then the distance between the upper and lower glass substrates  20 B and  20 A is locally narrowed, and thus the electric field intensity applied to the liquid crystal material  21  is locally changed as well. This changes the amount of light transmitted around the pressurized area. 
     Another contributing factor to the distortion is that the pressure created by the stylus or the finger cannot sufficiently be absorbed due to the ball spacers  22  making point contacts with the upper and lower glass substrates  20 B and  20 A. 
     Further, the amount of distortion varies depending on the position of the pressurized point. This is because ball spacers  22  are not uniformly distributed. As shown in  FIG. 3 , the density of ball spacers  22  are not uniformly among the different pixel electrodes  25 A on the lower glass substrate  20 A. As a result, amounts of light deterioration and image distortion are different according to the position of the pressurized point. 
     To prevent image distortion as described above, it has been suggested to densely spread the ball spacers  22 . However, distortion still occurs even if the balls spacers are more densely packed. For example,  FIGS. 4A and 4B  show a display panel where the ball spacer density is increased by three times as described in the above conventional art. It is shown that light deterioration is still generated on the touch panel  12  or  16  at the position pushed by the stylus. Due to the light deterioration, a distorted image with a wave shape is observed around the pressurized position. 
       FIG. 5  shows a liquid crystal display panel according to a Japanese Laid-Open Patent Gazette No. 1985-182414, which has spacers patterned differently from those shown in  FIGS. 1 and 2 .  FIG. 5  is a top view of a lower glass substrate  40  that include gate lines  41  and data lines  42  arranged to cross each other. Pixel electrodes  43  are positioned at cell areas defined by the gate and data lines  41  and  42 . 
     Thin film transistors (TFTs)  44  are provided at each intersection between the gate and data lines  41  and  42  and serve as switches. A column of TFTs  44  respond to a signal from the gate line  41  to selectively connect a column of pixel electrodes  43  to the data lines  42 , which are then used to input display information to each selected pixel electrode. 
     Patterned spacers  45  are formed on TFTs  44 . Like the ball spacers  22  of  FIGS. 1 and 2 , the patterned spacers are formed to keep a uniform distance between the upper glass substrate (not shown in  FIG. 5 ) and lower glass substrate  40 . However, unlike the ball spacers of the previous figures, the patterned spacers  45  are overlapped with each pixel electrode  43 . This allows the liquid crystal display panel to display a high quality picture. 
     However, even the liquid crystal display panel as shown in  FIG. 5  has difficulty in keeping a uniform distance between the upper and lower glass substrates. This is because, like the ball spacers  22 , the contact area of the spacers contacting the upper glass substrate is small. Because of the small contact area, the display panel cannot sufficiently absorb the pressure caused by a stylus or a finger. Thus like the display panels of  FIGS. 1 and 2 , local image distortion occurs, even for the display panel shown in FIG.  5 . 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a liquid crystal display panel mounted with a touch panel that is adapted for minimizing a local image distortion when pressure is applied to the touch panel through a stylus or a finger. 
     In order to achieve these and other objects of the invention, a touch panel-mounted liquid crystal is disclosed that includes a lower glass substrate having switching devices provided in the vicinity of intersections between data lines and gate lines; an upper glass substrate having a black matrix and being joined to the upper glass substrate; and a patterned spacer, being positioned at an area corresponding to the black matrix in such a manner to enlarge its contact area with the upper glass substrate, for constantly keeping a distance between the lower glass substrate and the upper glass substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
         FIG. 1  is a sectional view showing a structure of a conventional liquid crystal display panel mounted with a capacitive touch panel; 
         FIG. 2  is a sectional view showing a structure of a conventional liquid crystal display panel mounted with a resistive touch panel; 
         FIG. 3  is a plan view illustrating a state of the ball spacers spread on the lower glass substrate shown in FIG.  1  and  FIG. 2 ; 
         FIGS. 4A and 4B  show a distorted state of a picture on the liquid crystal display panel having the ball spacers when the touch panel has been pushed by a stylus pen; 
         FIG. 5  is a plan view of the lower glass substrate of another conventional liquid crystal display panel having patterned spacers; 
         FIG. 6  is a sectional view showing a first embodiment of the present invention where a touch panel is mounted to a liquid crystal display panel; 
         FIG. 7  is a plan view showing a layout of the lower glass substrate in  FIG. 6 ; 
         FIGS. 8A and 8B  show a state of a picture displayed on the liquid crystal display panel of  FIG. 6  when the touch panel has been pushed by a stylus pen; 
         FIG. 9  is a detailed sectional view of the structure shown in  FIG. 6 ; 
         FIG. 10  is a sectional view showing a second embodiment of the present invention where a touch panel is mounted to a liquid crystal display panel; 
         FIG. 11  is a detailed view of the touch panel of  FIG. 10 ; 
         FIG. 12  is a sectional view showing a third embodiment of the present invention where a touch panel is integrated with a liquid crystal display panel; and 
         FIG. 13  is a sectional view showing a fourth embodiment of the present invention where a touch panel is integrated with a liquid crystal display panel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 6  shows a liquid crystal display panel  50  according to a first embodiment of the present invention. The liquid crystal display panel  50  includes lower and upper polarizing sheets  52 A and  52 B. A touch panel  54  is disposed above the upper polarizing sheet  52 B. 
     Lower and upper glass substrates  60 A and  60 B are positioned above and below the lower and upper polarizing sheets  52 A and  52 B, respectively. Gate lines  63 , insulating film  64 , pixel electrodes  65 A, and a first orientation film  66 A are sequentially provided above the lower glass substrate  60 A. Below the upper glass substrate  60 B, black matrix  67 , color filter  68 , a common electrode  65 B, and a second orientation film  66 B are also sequentially provided. 
     Patterned spacers  62  and a liquid crystal material  61  are disposed between the first and second orientation films  66 A and  66 B. The patterned spacers  62  are formed by photolithographic methods over the pixel electrodes  65 A before the first orientation film  66 A is formed. The patterned spacers  62  are made of an insulating material and are positioned to coincide with areas occupied by the black matrix  67 . The first orientation film  66 A is uniformly formed over the surfaces of the pixel electrodes  65 A as well as on the surfaces of the patterned spacers  62 . 
     The lower and upper glass substrates  60 A and  60 B are joined with each other. The lower and upper glass substrates  60 A and  60 B joined in this manner are spaced uniformly spaced apart through the aid of the patterned spacers  62 . That is, the patterned spacers  62  serve the same function as the ball spacers of  FIGS. 1 and 2 , i.e., they maintain a uniform distance between lower and upper glass substrates  60 A and  60 B. 
     The touch panel  54  generates a voltage or current signal corresponding to the pressurized point just as described above. 
       FIG. 7  shows a layout of the lower glass substrate  60 A provided with the patterned spacers  62 . In  FIG. 7 , the lower glass substrate  60 A includes gate lines  63  and data lines  69  arranged to cross each other. Pixel electrodes  65 A positioned at cells defined by the gate and data lines  63  and  69 . 
     TFTs  74  are provided near each intersection between the gate and data lines  63  and  69  and serve as switches. A column of TFTs  74  respond to a signal from the gate line  63  to selectively connect a column of pixel electrodes  65 A to the data lines  69 , which are then used to input display information to each selected pixel electrode. 
     The data lines  69  are formed on the on the lower glass substrate  60 A before the TFTs  74  are formed, and the TFTs  74  are formed on the surface of the lower glass substrate  60 A before the insulating film  64  is formed. Each gate electrode of the TFTs  74  is formed along with the gate lines  63 . Each source and the drain of the TFTs  74  are electrically connected to the data line  69  and the pixel electrodes  65 A, respectively. 
     The black matrix  67  on the upper glass substrate  60 B overlaps the gate and data lines  63  and  69 . The patterned spacers  62  also are positioned on the lower glass substrate  60 A to coincide with the area of the black matrix area. 
     Each patterned spacer  62  includes first through fourth spacers  62 A to  62 D. The first spacer  62 A is positioned over the gate line  63  between the data lines  69 ; the second spacer  62 B is positioned over the intersection between the gate line  63  and the data line  69 ; the third spacer  62 C is positioned over a contact connecting the source of the TFT  74  to the data line  69 ; and the fourth patterned spacer  62 D is positioned over a portion of a contact connecting the drain of the TFT  74  to the pixel electrode  65 A. 
     Alternately, each patterned spacer can be described as being a cluster of spacers, wherein each cluster includes the first through fourth spacers  62 A to  62 D. And the multiple clusters can be described as being arranged in a matrix. 
     Also the first through fourth spacers can be characterized as being matrices of clusters. For example, a first matrix of first spacers may comprise multiple first spacers  62 A and a second matrix of second spacers may comprise multiple second spacers  62 B. Similarly, a third matrix of third spacers may comprise either multiple third spacers  62 C or multiple fourth spacers  62 D. 
     As noted previously, the spacers  62 A to  62 D keep the lower and upper glass substrates  60 A and  60 B a uniform distance from each other. Also, the spacers  62 A to  62 D enlarge the contact area of the patterned spacer  62  with the upper glass substrate  60 B. The enlarged contact area enables the patterned spacer  62  to sufficiently absorb the load applied to the upper glass substrate  60 B when the touch panel  54  is pressurized. Accordingly, the distance between the upper and lower glass substrates  60 B and  60 A can be kept uniform even when pressure is applied to the touch panel  54 . A result is that the light deterioration as well as the local image distortion is prevented or minimized. 
     Furthermore, because the spacers  62 A to  62 D are positioned to coincide with the black matrix area, this allows the liquid crystal display panel to achieve a uniform display contrast throughout. The uniform contrast, in turn, improves the quality of the image displayed. For example,  FIGS. 8A and 8B  show a display device according to the first embodiment. It is seen that the wave shape as shown in  FIG. 4  does not appear around the position pushed by the stylus pen. In other words, the touch panel-mounted liquid crystal display panel according to the first embodiment is capable of preventing light deterioration and image distortion. 
       FIG. 9  shows the touch panel  54  of  FIG. 6  in more detail. As shown, the touch panel  54  includes lower and upper glass sheets  70 A and  70 B; first and second electrode layers  72 A and  72 B disposed above and below the lower and upper glass sheets, respectively; and touch panel spacers  71  disposed in between the first and second electrode layers  72 A and  72 B. This is the same resistive touch panel shown in FIG.  2 . However, the capacitive touch panel shown in  FIG. 1  may be mounted on the liquid crystal display panel  50  as well. 
       FIG. 10  is a sectional view of a combined touch panel and liquid crystal display panel according a second embodiment of the present invention. In this embodiment, a polarizing sheet is made to be a part of a touch panel  73 . In  FIG. 10 , the liquid crystal display panel  50  is the same as shown in  FIG. 6  except that the display panel  50  does not include the upper polarizing sheet. That is, the liquid display panel  50  of  FIG. 10  includes the upper glass substrate  60 B and the lower polarizing sheet  52 B. Because the parts of the liquid display panel  50  have been described above, detailed discussion of the display panel  50  is omitted. 
     As shown in  FIG. 10 , the touch panel  73  is mounted above the upper glass substrate sheet  52 B. In this second embodiment, an upper polarizing sheet  75  is made to be a part of the touch panel  73  as shown in FIG.  11 . This simplifies the structure of the liquid crystal display panel  50  of FIG.  10 . 
       FIG. 11  is a detailed view of the touch panel  73  of FIG.  10 . As shown, the touch panel  73  includes a glass sheet  74  disposed above the upper glass substrate  60 B (shown in FIG.  10 ), a first and second electrode layers  77 A and  77 B above the glass sheet  74 , panel ball spacers  76  in between the first and second electrode layers  77 A and  77 B, and the upper polarizing sheet  75  above the second electrode layer  77 B. 
     When pressure is applied to the touch panel  73 , the first and second electrode layers  77 A and  77 B are shorted at the pressurized point. As discussed previously, this generates a voltage or a current signal corresponding to the pressurized position. 
       FIG. 12  shows a liquid crystal display panel according to a third embodiment of the present invention. Like the second embodiment, a polarizing sheet is made integral with the touch panel  78  in this third embodiment. Again, the detailed discussion of the liquid crystal display panel  50  is omitted. 
     As shown, the resistive touch panel  78  is disposed above the upper glass substrate  60 B and include in sequence a first electrode  81 A, panel spacers  80 , a second electrode  81 B, a glass sheet  79 , and a polarized sheet  82 . Note that the lower glass sheet  70 A of  FIG. 9  is not included in this embodiment. Again, this resistive touch panel  78  functions like other resistive touch panels described previously in that when pressure is applied, the first and second electrodes  81 A and  81 B are shorted to create a voltage or a current signal corresponding to the pressurized point. 
     In this third embodiment, the touch panel  78  and the liquid crystal display panel  50  are integrated with each other by removing the lower glass sheet. Accordingly, the integrated structure of the liquid crystal display panel  50  and the touch panel  78  is made simpler. 
       FIG. 13  shows a liquid crystal display panel according to a fourth embodiment of the present invention. The fourth embodiment is like the third embodiment, except that the touch panel is capacitive. Because of the integration, the entire structure is made simpler. 
     As before, the detailed discussion of the liquid crystal display panel  50  is omitted. As shown, the capacitive touch panel  83  is integrated on top of the upper glass substrate  60 B. The touch panel  83  includes a transparent electrode layer  84  formed on an upper glass substrate  60 B and a polarizing sheet  85  disposed on the transparent electrode layer  84 . Like other capacitive touch panels, varying capacitance is detected at the pressurized points and a corresponding voltage or current signal is generated. 
     As describe above, according to the present invention, the contact area between the patterned spacers and the upper glass substrate is enlarged, which increases the capability to absorb the pressure load of a stylus or a finger. Accordingly, the distance between the upper and lower glass substrates can be kept uniform even when pressure on the touch panel is applied. As a result, a light deterioration of the light panel and local image distortion is prevented or minimized. Furthermore, the patterned spacers are positioned at the black matrix area, so that a uniform contrast and a high quality images can be obtained. 
     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.