Abstract:
A plasma display panel has a good productivity of partition formation and air exhaustion process and realizes a bright and stable display. A discharge gas is filled in a gap between two substrates. A mesh-patterned partition is arranged on the inner surface of one of the substrates for dividing the gap into plural squares corresponding to a cell arrangement. The partition has low portions forming a mesh-like air path that travels through all of the gas-filled space enclosed by the partition, in a plan view.A plasma display panel includes two spaced substrates defining a gap therebetween. The gap is divided by intersecting walls into columns and rows of discharge cells. Portions of a wall that are lower in height than remaining portions of the wall define a flow path. The plasma display panel realizes a bright and stable display.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display panel (PDP) having a mesh-patterned partition, each square of which encloses one or more cells for constituting a display surface and a method for manufacturing the PDP. 
     A PDP is commercialized for a wall-hung TV set, whose screen size has reached 60 inches. PDP is a digital display device comprising binary light emission cells, so it is suitable for a display of digital data and is expected as a multimedia monitor. In order to increase applications of a PDP, a new panel structure is under development, which can provide a brighter and more stable display and can be manufactured in a high productivity. 
     2. Description of the Prior Art 
     An AC type PDP for a color display employs a surface discharge format. The surface discharge format has an arrangement of electrodes in which display electrodes that become anodes and cathodes in a display discharge for ensuring a luminance are arranged in parallel on a front or back substrate, and address electrodes are arranged so as to cross a pair of the display electrodes. In the surface discharge format PDP, a partition is necessary for separating a discharge for each column of a matrix display along the longitudinal direction of the display electrode (hereinafter referred to as the row direction). The partition also works as a spacer for defining a discharge space size in the direction of the panel thickness. 
     A partition pattern (a shape of the partition in the plan view) is broadly divided into a stripe pattern and a mesh pattern. The stripe pattern divides the discharge space for cells arranged in the row direction (i.e., in each column). In the stripe pattern, the discharge space of cell included in each column is not separated, so that exhausting of inner air and filling of discharge gas are relatively easy in a manufacturing process of a PDP. The mesh pattern divides the discharge space both in the row direction and in the column direction. A typical mesh pattern is a check pattern. A mesh pattern has an advantage in that the discharge is separated for each cell and that a fluorescent material is arranged on a side face of the partition so as to enclose the cell for increasing a light emission area. The mesh pattern, however, has a disadvantage in that a gap generated by subtle unevenness on the upper surface of the partition becomes an air path in the inner air exhaustion, so a resistance of the air exhaustion is large and it takes a long time for the process. 
     Conventionally, a partition structure of an overlaying form of the mesh-patterned partition and the stripe-patterned partition (this is called a composite pattern structure) is known. In this structure, since the discharge space is continuous as in the case of the stripe pattern, the air exhaustion resistance is smaller than in the case where the stripe-patterned partition is not overlaid. Furthermore, an improved composite pattern structure is disclosed in Japanese unexamined patent publication No. 4-274141, in which a stripe-patterned partition is provided with a hiatus for each cell, so that a grid-shaped air path (air exhaustion path) is formed for the gas to flow not only in the column direction but also in the row direction. 
     The above-explained partition having the composite pattern structure has a mesh-patterned partition whose banding portion in the column direction or the row direction is raised. There was a problem that the partition forming process becomes complicated for forming the above-mentioned structure on the inner surface of one of the substrate pair. Furthermore, if a mesh-patterned partition is disposed at one of the substrates and if a stripe-patterned partition is disposed on the other partition, the fluorescent material should be arranged on both of the substrates for increasing the area in which the fluorescent material is formed. In addition, a registration of the substrate pair in the assembling process is difficult. Thus, the partition having the composite pattern structure is adverse from the viewpoint of the productivity. 
     There is a method of forming the air path by cutting a part of the partition. However, this method may increase the number of manufacturing steps for the cutting process and may reduce the manufacturing yield since the partition can be broken by the cutting process. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a PDP that has a good productivity of partition formation and air exhaustion process and can display more brightly and more stably than a PDP that has a stripe-patterned partition. 
     According to the present invention, a mesh-patterned partition is arranged on the inner surface of one of the substrates. The partition has low portions that form a mesh-like air path that travels through all of the gas-filled space enclosed by the partition in a plan view. For example, in a simple check pattern in which a line along the horizontal direction and a line along the vertical direction cross each other, the portion corresponding to the line along the horizontal direction is made low. In this case, the pattern width (the line width) of the portion corresponding to the line along the horizontal direction is made thicker than the pattern width of the portion corresponding to the line along the vertical direction so as to generate a height difference. The shrink quantity in the thick portion is smaller in the width direction but is larger in the height direction than the thin portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a cell structure of a PDP according to the present invention. 
         FIG. 2  is a plan view showing the arrangement relationship between the display electrode and the partition. 
         FIG. 3  is a plan view showing a partition pattern. 
         FIG. 4  is a diagram showing a solid structure of the partition. 
         FIG. 5  is a schematic diagram showing heat shrink in the partition forming process. 
         FIG. 6  is a diagram showing a baking profile in the partition forming process. 
         FIGS. 7 ,  8 A and  8 B show variations of the partition pattern. 
         FIGS. 9A-12  show variations of the display electrode pattern. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention will be explained in detail with reference to embodiments and accompanied drawings. 
       FIG. 1  is a diagram showing a cell structure of a PDP according to the present invention.  FIG. 2  is a plan view showing the arrangement relationship between the display electrode and the partition.  FIG. 1  is a drawing of an inner structure, which shows a pair of substrate structures being separated from each other. 
     The PDP  1  comprises a pair of substrate structures (a structure including a substrate on which cell elements are arranged)  10 ,  20 , and the display surface ES comprises m×n cells. In each cell, the display electrodes X, Y constituting an electrode pair for generating the display discharge are extending in the row direction (the horizontal direction) of the matrix display, and the address electrodes A are extending in the column direction (the vertical direction). 
     The display electrodes X, Y are arranged on the inner surface of the glass substrate  11  of the front substrate structure  10  as a pair for each row. Herein, the “row” means a set of cells whose positions in the column direction are the same, and the number of the cells is equal to the number of columns (m). Each of the display electrodes X and Y includes a transparent conductive film  41  that forms a surface discharge gap (a discharge slit) and a metal film (a bus conductor)  42  that is overlaid on the edge in the column direction. The display electrodes X, Y are covered with a dielectric layer  17  having the thickness of approximately 20-40 μm, and the surface of the dielectric layer  17  is coated with a protection film  18  made of magnesia (MgO). The electrode gap between rows (that is called a reverse slit) is provided with a dark color layer  65  that is called a black stripe by applying a paint on the outer surface of the glass substrate  11  or by forming a colored glass layer including fillers such as manganese, iron oxide, chromium and other colorant so as to increase contrast (see FIG.  2 ). 
     The address electrodes A are arranged on the inner surface of the glass substrate  21  of the back substrate structure  20  as one for each column and are covered with a dielectric layer  24 . On the dielectric layer  24 , the partition  29  is disposed, which has a grid pattern with partially low profile structure that is unique to the present invention. The partition  29  is made of a baked material of a low melting point glass and includes a portion for dividing the discharge space into columns (hereinafter referred to as a vertical wall)  291  and a portion for dividing a discharge space into rows (hereinafter referred to as a horizontal wall)  292 . The intersection of the vertical wall  291  and the horizontal wall  292  is a common part of them. The horizontal wall  292  is lower in height (i.e., is shorter) than the vertical wall  291  by approximately 10 μm. The upper surface of the dielectric layer  24  and the side face (i.e., side walls) of the partition  29  are covered with red, green and blue colors of fluorescent material layers  28 R,  28 G and  28 B for color display. The italic letters (R, G and B) in  FIG. 1  signify light emission colors of the fluorescent materials. The color arrangement has a repeating pattern of red, green and blue colors in such a way that the cells in a column have the same color. The fluorescent material layers  28 R,  28 G and  28 B are excited by ultraviolet rays generated by the discharge gas in the corresponding cell and emit light. 
     As shown in  FIG. 2 , the metal film  42  of each of the display electrodes X, Y is overlaid on the partition  29  so as to cover the partition  29  partially, for reducing reflection of external light rays, and to avoid overlapping onto the fluorescent material on the partition sidewalls. The transparent conductive film  41  is patterned in such a way that the portion for the surface discharge is substantially separated from the portion overlaid on the metal film  42 , for suppressing discharge current so as to enhance the efficiency of light emission. In the case of 42 inch wide VGA type, the portion for the display discharge of the transparent conductive film  41  is separated from the horizontal wall  292  by a distance more than 30 μm, so that energy loss is largely reduced compared with the case where the distance is less than 30 μm. It is desirable that the distance between the horizontal wall  292  and the transparent conductive film  41  is set so that the discharge current is reduced by more than 5%. 
     The PDP  1  having the above-mentioned structure can be manufactured by the following process.
     (1) Providing the glass substrates  11 ,  21  with a predetermined element separately to make the substrate structures  10 ,  20 .   (2) Overlaying the substrate structures  10 ,  20 , and sealing the rim of the opposing area.   (3) Exhausting the inner air and filling the discharge gas through an air hole that is formed in the back substrate structure  20 .   (4) Closing the air hole.   

       FIG. 3  is a plan view showing a partition pattern.  FIG. 4  is a diagram showing a solid structure of the partition. 
     As shown in  FIG. 3 , the partition pattern is a grid pattern in which each square of the grid pattern encloses a cell C individually. However, it is not a simple check pattern. Namely, the inter-row portion  293  (the portion between the cells aligned in the column direction) of the partition  29  includes two horizontal walls  292  and a part of the vertical wall  291 . The plan view pattern of the inter-row portion  293  is made of a ladder pattern, and a space  33  is formed between the gas-filled space  32  that corresponds to each of the cells C aligned in the column direction. Since the dielectric constant of the discharge gas is approximately one eighth of that of a low melting point glass that is a common material of the partition, capacitance between the display electrodes of the neighboring rows is reduced, so that a waste of power consumption can be reduced and response of drive control can be improved. In the check pattern, the side face of the vertical wall  291  and the side face of the horizontal wall  292  respectively are provided with a fluorescent material, so that the light emission area is enlarged and the light emission efficiency can be improved. 
     In the PDP  1  of this embodiment, the inter-row portion  293  of the partition  29  is made approximately 10 μm lower than other portions, i.e., made approximately 7% lower, relative to the maximum height (140 μm) of the partition  29 . Thereby, an air exhaustion path  90  is formed which has a grid shape in the plan view for enabling air exhaustion both in the column direction and in the row direction. The width W 20  of the inter-row portion  293  is substantially large, and the inter-row portion  293  is substantially lowered, relative to the other portions, and therefor, the air exhaustion conductance is substantially the same as the stripe pattern. Concrete dimension of the partition  29  is as follows.
         row pitch P 1 : 1080 μm   column pitch P 2 : 360 μm   width W 11  of the upper surface of the vertical wall  291 : approximately 70 μm
           width W 12  of the bottom surface of the vertical wall  291 : approximately 140 μm   height H 1  of the vertical wall  291 : approximately 140 μm   width W 21  of the upper surface of the horizontal wall  292 : approximately 100 μm   width W 22  of the bottom surface of the horizontal wall  292 : approximately 200 μm   height H 2  of the horizontal wall  292 : approximately 130 μm   column direction size D 11  of the space  32 : approximately 680 μm   row direction size D 22  of the space  32 : approximately 290 μm   column direction size D 12  of the space  33 : approximately 200 μm   width W 20  of the inter-row portion  293 : approximately 400 μm   
               

     It is important that the width W 20  of the inter-row portion  293  is substantially larger than the width W 11  of the vertical wall  291 , so that the difference between the widths makes a height difference between the inter-row portion  293  and other portions. Namely, in a baking process of a material such as a general low melting point glass having a heat shrink property, as shown schematically in  FIG. 5 , the shrink quantity in the height direction depends on the width of the pattern. The shrink can be generated both in the width direction and in the height direction as a whole in the portion  29 A having a small pattern width. In contrast, in the portion  29 B having a large pattern width, the shrink in the width direction is suppressed more at the portion closer to the center in width direction, so that the shrink is generated more in the height direction, compensating for the suppression in the width direction. Therefore, the thick portion  29 B becomes lower in height than the thin portion  29 A. In addition, an isotropic shrink occurs in the upper portion of the wall material layer since the shrink can easily occur in any direction, while the shrink in the direction of the substrate surface is suppressed in the bottom portion due to the bond of the substrate. Therefore, the shrink quantity in the height direction becomes larger than the shrink quantity in the direction of the substrate surface. Namely, even if the width of the upper surface is substantially uniform before baking, and if the widths of the bottom surface are different, the height after baking of the material layer having larger width of the bottom surface becomes lower than the material layer having smaller width of the bottom surface. Considering this fact, the pattern width of the partition is defined as the dimension at the position whose distance from the bottom surface is 10% of the height in this specification. It is desirable that the pattern width of the thick portion is set to be more than 130% of the pattern width of the thin portion so that a difference of height is generated that is sufficient for air exhaustion. In the case of the above-mentioned partition size, two horizontal walls  292  and the portion between them (a part of the vertical wall  291 ) are shrunk in the same way in the height direction, and a partition  29  is obtained that has two inter-row portions  293  having low profile as a whole in the inter-row portion  293  of the ladder pattern. 
     The composition of the low melting point glass that is a material of the partition  29  is shown in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Composition of the low melting point glass 
               
             
          
           
               
                   
                 Components 
                 Content (wt %) 
               
               
                   
                   
               
               
                   
                 PbO 
                 50-60 
               
               
                   
                 B 2 O 3   
                  5-10 
               
               
                   
                 SiO 2   
                 10-20 
               
               
                   
                 Al 2 O 3   
                 15-25 
               
               
                   
                 CaO 
                 −5 
               
               
                   
                   
               
             
          
         
       
     
     Concerning optical characteristics of the partition  29 , it is desirable that it is semitransparent having the absorptance of visual light at approximately 80% per 30 μm of film thickness. If it is semitransparent, light rays generated at the vicinity of the top of the partition pass the partition and contribute to improvement of the luminance, while external rays that entered the partition are reflected by the bottom surface of the partition and are absorbed by the partition before reaching the front surface. Therefore, a display having a good contrast can be realized. 
     The process of forming the partition  29  is as follows.
     (1) Forming the partition material layer having the thickness of approximately 200 μm made of a uniform paste mixture of a low melting point glass powder having the components shown in Table 1 and a vehicle so as to cover the dielectric layer  24 . The partition material layer may be formed by any method such as a screen printing method, a laminating method in which a green sheet is transferred, or other method.   (2) Drying the partition material layer, and then sticking thereto a photosensitive dry film (or a resist material is applied), and forming a cut mask of the grid pattern corresponding to the partition  29  by using photolithography, including exposure and development. The mask pattern size is set larger that the desired partition size considering the heat shrink quantity.   (3) Grinding the non-masking portion of the partition material layer by a sandblaster until the dielectric layer  24  is exposed (the partition material layer is patterned).   (4) Performing a heating process according to the baking profile shown in  FIG. 6  to bake the partition material layer so that the partition  29  is formed.   

       FIGS. 7 ,  8 A and  8 B show variations of the partition pattern. 
     The partition  29 b shown in  FIG. 7  includes a vertical wall  291  and a horizontal wall  292 b. The partition  29 b corresponds to such that the inter-row portion  293  of the partition  29  shown in  FIG. 3  is replaced with the horizontal wall  292 b. The partition  29 c shown in  FIG. 8A  includes a vertical wall  291 c and a horizontal wall  292 c. The pattern thereof in a plan view is a mesh pattern in which the positions of cells of the neighboring rows are shifted by a half pitch from each other. In the partition  29 c, the pattern width of the horizontal wall  292 c is set larger than the pattern width of the vertical wall  291 c, so that the horizontal wall  292 c is lower than the vertical wall  291 c, and a mesh-like air exhaustion path  90 c is formed. The partition  29 d shown in  FIG. 8B  includes a vertical wall  291 d and a horizontal wall  292 d, and the pattern thereof in a plan view is a honeycomb mesh pattern. In the partition  29 d, too, the pattern width of the zigzag banding horizontal wall  292 d is set larger than the pattern width of the vertical wall  291 d, so that the horizontal wall  292 d is lower than the vertical wall  291 d, and a mesh-like air exhaustion path  90 d is formed. In a PDP having the partitions  29 c and  29 d, the address electrodes A can be arranged so that the address electrode A weaves in and out of the cells shifted from each other by a half pitch, or that a linear address electrode A is arranged being overlaid on the vertical walls  291 c and  291 d. The display electrodes X, Y can be arranged so that a pair of display electrodes is arranged for each row as shown in  FIG. 2 , or that three display electrodes are arranged for two rows as a display electrode is shared by two neighboring rows for display. In any way, the entire bus conductor is overlaid on the horizontal walls  292 c and  292 d, so that shading can be avoided. 
       FIGS. 9A-12  show variations of the display electrode pattern. 
     Each of the display electrodes Xb and Yb shown in  FIG. 9A  includes a transparent conductive film  41 b and a metal film  42 b and corresponds to such display electrodes wherein the pattern of the transparent conductive film  41  of the display electrodes X, Y shown in  FIG. 2  is changed. In the display electrodes Xb and Yb, the portion of the transparent conductive film  41  to be a discharge surface is connected to the portion that is overlaid on the metal film  42 b at the position where it is not overlaid on the vertical wall of the partition  29 . Each of the display electrodes Xc and Yc shown in  FIG. 9B  includes a transparent conductive film  41 c and a metal film  42 c. The metal film  42 c is arranged at the position where it is not overlaid on the horizontal wall of the partition  29 . In the display electrodes Xd and Yd shown in  FIG. 10A , the portion of the transparent conductive film  41 d that forms the surface discharge gap to be the discharge surface is divided into columns to be a T-shape. The portion of the transparent conductive film  41 d that is overlaid on the metal film  42 b is straddling over plural columns. Each of the display electrodes Xe and Ye shown in  FIG. 10B  includes a T-shaped transparent conductive film  41 e that is divided for each column and a metal film  42 b for supplying electricity to the transparent conductive film. The structures of  FIGS. 10A and 10B  in which the transparent conductive film is divided are effective for suppressing a discharge current and for reducing a capacitance between electrodes. 
     In the example shown in FIG.  11  and in the example shown in  FIG. 12 , a bus conductor is provided for hiding the reverse slit, so that the process of forming the black stripe can be omitted. In  FIGS. 11 and 12 , the partition  29 e includes a vertical wall  291  and a horizontal wall  292 e and corresponds to such partition wherein the inter-row portion  293  of the partition  29  shown in  FIG. 3  is replaced with three horizontal walls  292 e. However, the following electrode structure can be applied both to the partition  29  shown in FIG.  2  and to the partition  29 b shown in FIG.  7 . 
     In  FIG. 11 , each of the display electrodes Xf and Yf includes a transparent conductive film  41 f and a metal film  42 d and is arranged so that the neighboring electrodes of the neighboring rows are the same kind (e.g., in the order of X, Y, Y, X, X, Y, . . . ). The transparent conductive film  41 f is patterned in the same way as the transparent conductive film  41 b shown in  FIG. 9A  except for the size of the portion that is overlaid on the metal film  42 d. The display electrodes Xf and Yf have a feature in that the metal film  42 d as a bus conductor has a large width over two neighboring horizontal walls  292 e. Since an element close to the display surface is drawn at the upper in the figure, a part of the metal film  42 d is covered with the transparent conductive film  41 f. However, actually in the observation from the display surface side, the metal film  42 d can be seen through the transparent conductive film  41 f. Namely, the entire metal film  42 d works as a shading member for hiding the structure thereunder. Therefore, it is not necessary to provide another shading member (a black stripe) to the inter-row portion (the reverse slit), so that the manufacturing steps of a PDP can be reduced. In addition, since the width of the metal film  42 d is enlarged, a line resistance of each of the display electrodes Xf and Yf decreases. Thus, the generation of Joule heat can be reduced, and the voltage drop is also reduced when the discharge current flows. 
     In  FIG. 12 , each of the display electrodes Xg and Yg includes a transparent conductive film  41 g and a metal film  42 e and three display electrodes are arranged for two rows so that a display electrode is shared by two neighboring rows for display (in the order of X, Y, X, Y, . . . ). The metal film  42 e of the display electrodes Xg and Yg have a large width over three neighboring horizontal walls  292 e. The example of  FIG. 12  has the same advantage as the example of  FIG. 11  in that the manufacturing steps can be reduced, and that the line resistance can be reduced. 
     In the above-mentioned embodiment, the dimension and the material of the partition  29  are not limited to the examples. The plan-view pattern of the partitions  29 ,  29 b- 29 e is not limited to that enclosing a cell. It can be a mesh pattern enclosing plural cells as a unit. 
     According to the present invention, a PDP that has a good productivity of partition formation and air exhaustion process and can display more brightly and more stably than a PDP that has a stripe-patterned partition can be realized. 
     While the presently preferred embodiments of the present invention have been shown and described, it will be understood that the present invention is not limited thereto, and that various changes and modifications may be made by those skilled in the art without departing from the scope of the invention as set forth in the appended claims.