Abstract:
A rear substrate in a plasma display panel including a first substrate through which an image is transmitted to a viewer, and the rear substrate arranged in facing relation to the first substrate, includes (a) an electrically insulating substrate, (b) a plurality of data electrodes arranged on the substrate and spaced away from one another, (c) a plurality of partition walls formed on the substrate, and (d) a phosphor layer covering the substrate and the data electrodes therewith between adjacent partition walls, wherein at least one partition wall and another partition wall among the partition walls are joined to each other at at least one of opposite ends thereof in a length-wise direction through a curved partition wall, the another partition wall extending in the same direction as a direction in which the at least one partition wall extends.

Description:
This is a continuation of application Ser. No. 10/657,101 filed Sep. 9, 2003. The entire disclosure of the prior application, application Ser. No. 10/657,101 is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a plasma display panel, and more particularly to a plasma display panel which is capable of preventing display defectiveness caused by breakage and/or defective shape of partition walls. 
   2. Description of the Related Art 
   A plasma display panel is recently often used as a flat display, because a plasma display panel has advantages that it is thin and can be readily applied to a big screen, it has a broad viewing angle, and it has a high response speed. 
     FIG. 1  is a perspective view of a display cell in a conventional three-electrode surface-discharge AC type plasma display panel. 
   As illustrated in  FIG. 1 , a front substrate  351  and a rear substrate  352  are arranged parallel to each other in a display cell. 
   The front substrate  351  is comprised of an electrically insulating substrate  302  composed of transparent material such as glass, a plurality of scanning electrodes  303  (only one of them is illustrated in  FIG. 1 ) formed on the substrate  302  in facing relation to the rear substrate  352 , a plurality of common electrodes  304  (only one of them is illustrated in  FIG. 1 ) formed on the substrate  302  in facing relation to the rear substrate  352 , a plurality of trace electrodes  305  each formed on each of the scanning electrodes  303 , a plurality of trace electrodes  306  each formed on each of the common electrodes  304 , a dielectric layer  312  formed on the substrate  302 , covering the scanning electrodes  303 , the common electrodes  304  and the trace electrodes  305  and  306  therewith, and a protection layer  313  formed on the dielectric layer  312 . 
   The scanning electrodes  303  and the common electrodes  304  are arranged alternately, and equally spaced away from adjacent ones in parallel with one another. 
   The trace electrodes  305  and  306  reduce an electrical resistance of the scanning electrode  303  and the common electrode  304 , respectively. 
   The protection layer  313  protects the dielectric layer  312  from discharges. The protection layer  313  is composed of magnesium oxide (MgO), for instance. 
   The rear substrate  352  is comprised of an electrically insulating substrate  301  composed of transparent material such as glass, a plurality of data electrodes  307  formed on the substrate  301  in a direction perpendicular to a direction in which the scanning electrodes  303  and the common electrodes  304  extend, in facing relation to the front substrate  351 , a dielectric layer  341  formed on the substrate  301 , covering the data electrodes  307  therewith, a partition wall  315  formed on the dielectric layer  314 , and a phosphor layer  311  covering an exposed surface of the dielectric layer  314  and sidewalls of the partition wall  315  therewith. 
   The substrate  301  in the rear substrate  352  is comprised of a transparent substrate in the display cell illustrated in  FIG. 1 , however, it is not always necessary for the substrate  301  to be a transparent substrate. 
   The partition wall  315  defines a discharge gas space and a plurality of display cells (pixels)  308 . 
   Viewing perpendicularly to a surface of the substrate  301 , the partition wall  315  is grid-shaped. Specifically, the partition wall  315  is comprised of a vertical partition wall  315   a  extending in parallel with the data electrodes  317 , and a horizontal partition wall  315   b  extending perpendicularly to the vertical partition wall  315   a.    
   The vertical and horizontal partition walls  315   a  and  315   b  are almost equal in height to each other. A height from a surface of the substrate  301  to a summit of the partition wall  315 , that is, a total thickness of the dielectric layer  314  and the partition wall  315  is 120 micrometers, for instance. 
   Each of the display cells  308  is filled with discharge gas composed of noble gas such as helium, neon or xenon singly or in combination. 
   The phosphor layer  311  receives ultra-violet rays generated due to discharges of discharge gas, and thus, emits a visible light  310 . 
   An area between the front substrate  351  and the rear substrate  352  is comprised of a centrally located display area in which images are displayed, and a non-display area located around the display area. A partition wall formed in a non-display area is called a dummy partition wall, which assists a partition wall to be uniformly formed in a display area during fabrication of a plasma display panel, and prevents contaminants from entering a display area for protection of a display area after fabrication of a plasma display panel. A dummy partition wall is formed generally by one or two rows. 
     FIGS. 2A to 4B  show respective step in a method of fabricating the conventional plasma display panel illustrated in  FIG. 1 .  FIGS. 2A ,  3 A and  4 A are plan views of the rear substrate  352 , and  FIGS. 2B ,  3 B and  4 B are cross-sectional views taken along the lines  2 B,  3 B and  4 B in  FIGS. 2A ,  3 A and  4 A, respectively. 
   Hereinbelow is explained a method of fabricating the conventional plasma display panel with reference to  FIGS. 2A to 4B . 
   With reference to  FIG. 1 , the scanning electrodes  303  and the common electrodes  304  are formed on the substrate  302  such that they are alternately arranged and extend in parallel with each other. 
   Then, the trace electrodes  305  and  306  are formed on the scanning and common electrodes  303  and  304 , respectively. 
   Then, the dielectric layer  312  is formed on the substrate  302  such that the dielectric layer  312  covers the scanning and common electrodes  303  and  304  and the trace electrodes  305  and  306  therewith. 
   Then, the protection layer  313  composed of MgO is formed on the dielectric layer  312 . 
   Thus, there is fabricated the front substrate  351 . 
   With reference to  FIGS. 2A and 2B , a plurality of the data electrodes  307  is formed on the substrate  301 . 
   Then, as illustrated in  FIGS. 3A and 3B , the dielectric layer  314  is formed on the substrate  301  such that the dielectric layer  314  covers the data electrodes  307  therewith. 
   Then, as illustrated in  FIGS. 4A and 4B , the partition wall  315  is formed on the dielectric layer  314 . 
   The partition wall  315  can be formed by sand blasting or printing, for instance. The partition wall  315  is formed as follows in the case that the partition wall  315  is formed by sand blasting. 
   First, filler, glass powder, binder and solvent are mixed to thereby have partition wall paste. 
   Then, the partition wall paste is coated on the dielectric layer  314 . Then, the solvent in the paste is evaporated to thereby form a partition wall paste layer (not illustrated). 
   Then, a dry film (not illustrated) is adhered onto a surface of the partition wall paste layer, and then, the dry film is patterned. 
   Then, sand blasting is carried out to the partition wall paste layer with the patterned dry film being used as a mask. As a result, a portion of the partition wall paste layer not covered with the dry film is selectively removed. 
   Then, the dry film is removed, and the partition wall paste layer is baked. As a result, the binder in the partition wall paste layer is evaporated, and the glass powder is fused and re-cured. Thus, there is formed the partition wall  315  composed of filler and glass. 
   The partition wall  315  is formed in a grid such that the vertical and horizontal partition walls  315   a  and  315   b  are almost equal in height to each other. 
   Then, as illustrated in  FIG. 1 , the phosphor layer  311  is formed on an exposed surface of the dielectric layer  314  and sidewalls of the partition wall  315 . 
   Then, the substrates  301  and  302  are aligned with each other such that the protection layer  313  makes contact with the partition wall  315  and that the data electrodes  307  extend perpendicularly to the scanning and common electrodes  303  and  304 . 
   Then, the substrates  301  and  302  aligned with each other are thermally annealed, resulting in that the substrates  301  and  302  are fused at their ends to each other through flits. Thus, a space surrounded by a sealing layer (not illustrated) comprised of the substrates  301  and  302  and the flits is gas-tightly sealed. 
   Then, the space is exhausted, and thereafter, discharge gas is introduced into the space. 
   Thus, there is completed the plasma display panel illustrated in  FIG. 1 . 
   However, the above-mentioned conventional plasma display panel is accompanied with a problem of poor quality in displaying images which is caused by contraction of a partition wall paste layer generated during being baked. Hereinbelow is explained the problem of contraction of a partition wall paste layer. 
   The above-mentioned poor quality in displaying images is grouped into two types. 
   The first type poor quality is caused by that the vertical partition wall  315   a  is partially raised during the partition wall paste layer is being baked. The first type poor quality is caused because the vertical partition wall  315   a  is longer and thinner than the horizontal partition wall  315   b.    
   Since the vertical partition wall  315   a  is longer and thinner than the horizontal partition wall  315   b , the vertical partition wall  315   a  and the horizontal partition wall  315   b  are different from each other with respect to contraction generated during the partition wall  315  is being baked, and hence, the vertical partition wall  315   a  is partially raised to thereby become higher than the horizontal partition wall  315   b.    
   As a result, when the substrates  301  and  302  are aligned to each other, a raised portion of the vertical partition wall  315   a  is compressed by the protection layer  313 , and resultingly, the vertical partition wall  315   a  is often broken. If the vertical partition wall  315   a  is broken, a portion of the phosphor layer  311  formed on the vertical partition wall  315   a  itself and sidewalls of the vertical partition wall  315   a  is scattered into the display cell  308 , and resultingly, adheres to the scanning electrode  303  and/or the common electrode  304 . This results in that the display cell  308  does not properly operate, that is, the display cell  308  is kept to emit a light regardless of a drive signal or does not emit a light at all. 
   The second type poor quality is caused by that the vertical and horizontal partition walls  315   a  and  315   b  are contracted during the partition wall  315  is being baked, and resultingly, opposite ends of the vertical and horizontal partition walls  315   a  and  315   b  in a length-wise direction are deformed to be higher than centers of them. 
     FIG. 5A  is a cross-sectional view illustrating the partition wall  315  before baked,  FIG. 5B  is a cross-sectional view illustrating the partition wall  315  after baked, and  FIG. 5C  is a cross-sectional view illustrating the substrates  301  and  302  aligned to each other. For simplification, parts other than the substrates  301  and  302  and the partition wall  315  are omitted in  FIGS. 5A to 5C . 
   As illustrated in  FIG. 5A , the partition wall  315  before baked has a uniform height. 
   However, as illustrated in  FIG. 5B , the partition wall  315  is contracted during being baked, and resultingly, opposite ends  315   c  are raised relative to a central portion  315   d.    
   As illustrated in  FIG. 5C , the substrates  301  and  302  are aligned to each other, and then, a discharge gas space is exhausted. The substrates  301  and  302  are bent due to atmospheric pressure. However, the substrates  301  and  302  are bent in a different curvature from the partition wall  315 , and accordingly, gaps  316  are formed between the partition wall  315  and the substrate  302  in the vicinity of the ends  315   c.    
   As a result, a display cell  308  including the gaps  316  would have an increased volume, and hence, a voltage necessary for generating writing discharge in the display cell  308  would be raised. Thus, writing discharge would not be generated by an ordinary drive voltage in the display cell  308 , resulting in writing defectiveness. Thus, the plasma display panel would have a problem of display defectiveness. 
   There have been suggested solutions to the second type poor quality. 
   For instance, Japanese Patent Application Publication No. 2001-319580 has suggested a plasma display panel in which a dielectric layer is not formed in a non-display area on a rear substrate, and a partition wall is formed directly on the rear substrate in order to prevent the above-mentioned second type poor quality. This ensures that a partition wall located in a non-display area is lower in height than a partition wall located in a display area. Hence, even if a partition wall is contracted, and accordingly, opposite ends thereof in a length-wise direction become higher than a central area, it would be possible to prevent formation of gaps between the partition wall and a front substrate. 
   In contrast to the second type poor quality, the first type poor quality is not well recognized, and accordingly, solutions are not much suggested. 
   For instance, the plasma display panel suggested in the above-mentioned Japanese Patent Application Publication No. 2001-319580 prevents the second type poor quality, but cannot prevent the first type poor quality. 
   Japanese Patent Application Publication No. 2000-340123 has suggested a plasma display panel which includes an improved horizontal partition wall in order to prevent the first type poor quality. 
     FIG. 6  is a plan view of a partition wall in the plasma display panel suggested in Japanese Patent Application Publication No. 2000-340123. 
   As illustrated in  FIG. 6 , the partition wall is comprised of a plurality of horizontal partition walls  315 A horizontally extending, and a plurality of vertical partition walls  315 B extending vertically only between adjacent horizontal partition walls  315 A. 
   Each of the horizontal partition walls  315 A is designed to have extensions  315 C extending from opposite ends thereof. Even if the horizontal partition walls  315 A is raised at its opposite ends due to the contraction, such a raise is concentrated to the extensions  315 C. Front and rear substrates are joined to each other between the extensions  315 C formed at opposite ends of the horizontal partition wall  315 A. Accordingly, front and rear substrates can be joined to each other with a constant gap being kept therebetween without being influenced by the raised extensions  315 C. 
   Japanese Patent Application Publication No. 11-339668 has suggested a plasma display panel including a partition wall having opposite tapered ends  315 D, as illustrated in  FIG. 7 , to prevent formation of a raise portion caused by contraction. 
   The plasma display panel suggested in Japanese Patent Application Publication No. 2000-340123 makes it possible for front and rear substrates to join to each other with a constant gap being kept therebetween. However, since the extensions  315 C are raised, if the front and rear substrates are misaligned even slightly, the front substrate aligns with the raised extensions  315 C, resulting in that it would not be possible to keep a constant gap between the front and rear substrates. 
   Accordingly, it is necessary to align the front and rear substrates to each other highly accurately before they join to each other. This causes an additional problem that steps of fabricating a plasma display panel are unavoidably complicated. 
   The partition wall suggested in Japanese Patent Application Publication No. 11-339668 is formed by physically grinding, punching or a process of half-exposing a partition wall to a light. 
   If the tapered ends  315 D are formed by grinding, there are newly caused problems that a grinding step has to be additionally carried out, and chips are generated in a grinding step. 
   If the tapered ends  315 D are formed by punching or half-exposing process, there are newly caused problems that an equipment for doing so has to be newly prepared, and hence, punching or half-exposing process cannot be applied to a conventional method of forming a partition wall by sand blasting. 
   SUMMARY OF THE INVENTION 
   In view of the above-mentioned problems in the conventional plasma display panels, it is an object of the present invention to provide a plasma display panel which is capable of preventing a partition wall from partially rising due to contraction during baked, without an increase in fabrication steps and further without an increase in complex in fabrication process. 
   In one aspect of the present invention, there is provided a rear substrate in a plasma display panel including a first substrate through which an image is transmitted to a viewer, and the rear substrate arranged in facing relation to the first substrate, including (a) an electrically insulating substrate, (b) a plurality of data electrodes arranged on the substrate and spaced away from one another, (c) a plurality of partition walls formed on the substrate, and (d) a phosphor layer covering the substrate and the data electrodes therewith between adjacent partition walls, wherein at least one partition wall and another partition wall among the partition walls are joined to each other at at least one of opposite ends thereof in a length-wise direction through a curved partition wall, the another partition wall extending in the same direction as a direction in which the at least one partition wall extends. 
   For instance, the at least one partition wall and the another partition wall are arranged adjacent to each other. 
   For instance, the partition walls include first, second, third and fourth partition walls arranged in this order, and wherein the first and third partition walls are connected at at least one of opposite ends thereof in a length-wise direction to each other through a first curved partition wall, the second and fourth partition walls are connected at at least one of opposite ends thereof in a length-wise direction to each other through a second curved partition wall, and the first and second curved partition walls intersect with each other. 
   For instance, every N partition walls among the partition walls are connected at at least one of opposite ends thereof in a length-wise direction to each other through the curved partition wall, the N being a positive integer equal to or greater than one. 
   For instance, a first pair of partition walls among the partition walls is connected at at least one of opposite ends thereof in a length-wise direction to each other through the curved partition wall, a second pair of partition wall is surrounded by the first pair of partition walls, and the second pair of partition walls among the partition walls is connected at at least one of opposite ends thereof in a length-wise direction to each other through the curved partition wall. 
   For instance, the partition walls are comprised of 2N partition walls, N being a positive integer equal to or greater than two, and wherein a M-th partition wall is connected at at least one of opposite ends thereof in a length-wise direction to an associated end of a (2N−M+1)-th partition wall through the curved partition wall, M being a positive integer in the range of one (1) to N both inclusive. 
   In the above-mentioned case, it is preferable that a curved partition wall connecting the M-th partition wall and the (2N−M+1)-th partition wall to each other therethrough has a width equal to or greater than a width of a curved partition wall connecting a (M+1)-th partition wall and a (2N−M)-th partition wall to each other therethrough. 
   In the above-mentioned case, it is preferable that one of the M-th partition wall and the (2N−M+1)-th partition wall wherein M is equal to one (1) is located outermost of a display area of the plasma display panel. 
   For instance, the curved partition wall is semi-circular. 
   For instance, the partition walls extend in a first direction in parallel with one another. 
   It is preferable that each of the partition walls is comprised of a first partition wall extending in a first direction and a second partition wall extending in a second direction perpendicular to the first direction. 
   It is preferable that each of the partition walls is comprised of a first partition wall extending in a first direction and a second partition wall extending in a second direction perpendicular to the first direction only between adjacent first partition walls. 
   It is preferable that the rear substrate may include a display area in which images are displayed, and a non-display area surrounding the display area, in which images are not displayed, the rear substrate includes flit-stoppers arranged in the non-display area in facing relation to a pair of partition walls connected at at least one of opposite ends thereof in a length-wise direction to each other through the curved partition wall, the flit-stoppers are comprised of curved lines, and the flit-stoppers are arranged each overlapping adjacent flit-stoppers, and surround the display area. 
   For instance, each of the flit-stoppers is circular. 
   In another aspect of the present invention, there is provided a plasma display panel comprising a first substrate through which an image is transmitted to a viewer, and a second substrate arranged in facing relation to the first substrate, the first substrate including (A) a first transparent substrate, (B) at least one scanning electrode formed on the first transparent substrate in facing relation to the second substrate, (C) at least one common electrode formed on the first transparent substrate in facing relation to the second substrate, and (D) a dielectric layer covering the first transparent substrate, the scanning electrode and the common electrode therewith, the second substrate being comprised of the above-mentioned rear substrate. 
   The advantages obtained by the aforementioned present invention will be described hereinbelow. 
   In accordance with the present invention, it is possible to make a gap between a designed total thickness of a dielectric layer and a partition wall and an actual one smaller than the same in a conventional plasma display panel, and further possible to prevent a partition wall from being broken and having an improper shape more surely than a conventional plasma display panel. 
   The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a display cell in a conventional three-electrode surface-discharge AC type plasma display panel. 
       FIG. 2A  is a plan view of a rear substrate in the plasma display panel illustrated in  FIG. 1 , showing respective step of a method of fabricating the plasma display panel illustrated in  FIG. 1 . 
       FIG. 2B  is a cross-sectional view taken along the line  2 B— 2 B in  FIG. 2A . 
       FIG. 3A  is a plan view of a rear substrate in the plasma display panel illustrated in  FIG. 1 , showing respective step of a method of fabricating the plasma display panel illustrated in  FIG. 1 . 
       FIG. 3B  is a cross-sectional view taken along the line  3 B— 3 B in  FIG. 3A . 
       FIG. 4A  is a plan view of a rear substrate in the plasma display panel illustrated in  FIG. 1 , showing respective step of a method of fabricating the plasma display panel illustrated in  FIG. 1 . 
       FIG. 4B  is a cross-sectional view taken along the line  4 B— 4 B in  FIG. 4A . 
       FIG. 5A  is a cross-sectional view illustrating a partition wall before baked. 
       FIG. 5B  is a cross-sectional view illustrating a partition wall after baked. 
       FIG. 5C  is a cross-sectional view illustrating front and rear substrates aligned to each other. 
       FIG. 6  is a plan view illustrating a partition wall in a conventional plasma display panel. 
       FIG. 7  is a plan view illustrating a partition wall in another conventional plasma display panel. 
       FIG. 8  is a plan view illustrating an outline of a rear substrate in accordance with the first embodiment of the present invention. 
       FIG. 9A  is a plan view showing points at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate in accordance with the first embodiment. 
       FIG. 9B  is a table showing the results of measurement. 
       FIG. 10  is a plan view illustrating an outline of a rear substrate in accordance with the second embodiment of the present invention. 
       FIG. 11A  is a plan view showing points at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate in accordance with the second embodiment. 
       FIG. 11B  is a table showing the results of measurement. 
       FIG. 12  is a plan view illustrating an outline of a rear substrate in accordance with the third embodiment of the present invention. 
       FIG. 13  is a plan view illustrating an outline of a rear substrate in accordance with the fourth embodiment of the present invention. 
       FIG. 14  is a plan view illustrating an outline of a rear substrate in accordance with the fifth embodiment of the present invention. 
       FIG. 15A  is a plan view showing points at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate in accordance with the fifth embodiment. 
       FIG. 15B  is a table showing the results of measurement. 
       FIG. 16  is a plan view illustrating an outline of a rear substrate in accordance with the sixth embodiment of the present invention. 
       FIG. 17A  is a plan view showing points at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate in accordance with the sixth embodiment. 
       FIG. 17B  is a table showing the results of measurement. 
       FIG. 18  is a plan view illustrating an outline of a rear substrate in accordance with the eighth embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments in accordance with the present invention will be explained hereinbelow with reference to drawings. 
   First Embodiment 
     FIG. 8  is a plan view illustrating an outline of a rear substrate  10  in accordance with the first embodiment of the present invention. For simplification of  FIG. 8 , only a partition wall is illustrated in  FIG. 8 . The rear substrate  10  has the same structure as the rear substrate  352  illustrated in  FIG. 1  except a partition wall. 
   In the rear substrate  10  in accordance with the first embodiment, a partition wall is comprised of a plurality of vertical partition walls  101  extending vertically in  FIG. 8  in parallel with one another, and a plurality of horizontal partition walls  102  extending horizontally in  FIG. 8  in parallel with one another. The vertical partition walls  101  are equally spaced away from one another, and similarly, the horizontal partition walls  102  are equally spaced away from one another. A ratio of a distance between adjacent horizontal partition walls  102  to a distance between adjacent vertical partition walls  101  is set equal to 3:1. The vertical and horizontal partition walls  101  and  102  are arranged in a grid. 
   In the rear substrate  10  in accordance with the first embodiment, the vertical partition walls  101  located adjacent to each other are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103 . 
   Specifically, the rear substrate  10  has sixteen vertical partition walls  101 . A N-th vertical partition wall  101  as viewed from the left in  FIG. 8  is joined at opposite ends thereof to a (N+1)-th vertical partition wall  101  through the semi-circular partition wall  103 . Herein, N indicates a positive odd number in the range of one (1) to fifteen (15). 
   Similarly, the horizontal partition walls  102  located adjacent to each other are joined at their opposite ends in a length-wise direction to each other through the semi-circular partition wall  103 . 
   Specifically, the rear substrate  10  has eight horizontal partition walls  102 . A M-th horizontal partition wall  102  as viewed from the top in  FIG. 8  is joined at opposite ends thereof to a (M+1)-th horizontal partition wall  102  through the semi-circular partition wall  103 . Herein, M indicates a positive odd number in the range of one (1) to seven (7). 
   The inventor had fabricated the rear substrate  10  in accordance with the first embodiment, and measured heights of the vertical partition wall  101 , the horizontal partition wall  102  and the semi-circular partition wall  103  at a plurality of points.  FIG. 9A  shows ten points  1  to  15  at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate  10 , and  FIG. 9B  is a table showing the results of the measurement. 
   A designed total thickness of a dielectric layer and a partition wall is 120 micrometers. The highest total thickness is equal to 133 micrometers at point  5 , and the second highest total thickness is equal to 132 micrometers at point  1 . Considering that measurement error is approximately ±5 micrometers, the total thicknesses measured at points  3 ,  6 ,  12  and  15  are within the measurement error, and the maximum gap between the designed total thickness (120 micrometers) and the measured total thickness is 8 micrometers at point  5  among the total thicknesses measured at points  1 ,  2 ,  5 ,  8 ,  10  and  13  all of which are without the measurement error. 
   In the partition walls in the conventional plasma display panels suggested in the above-mentioned Japanese Patent Application Publications Nos. 2000-340123 and 11-339668, a gap between a designed total thickness and an actual total thickness is in the range of 20 to 30 micrometers. 
   As mentioned above, in accordance with the rear substrate  10 , the vertical or horizontal partition walls  101  and  102  located adjacent to each other are joined at their opposite ends to each other through the semi-circular partition wall  103 , ensuring that contraction force generated during the partition wall is being baked is diffused. Accordingly, it is possible to prevent the vertical and horizontal partition walls  101  and  102  from rising at their ends, and hence, it is also possible to prevent a partition wall from being broken and improperly shaped more surely than the conventional partition walls. 
   The partition wall in the rear substrate  10  can be formed by varying a pattern of a dry film coated onto a surface of a partition wall paste layer, in accordance with a pattern of the partition wall. Accordingly, the number of steps for fabricating the partition wall in the rear substrate  10  is not increased in comparison with the conventional methods of fabricating a partition wall. 
   The vertical and horizontal partition walls  101  and  102  are not limited to the above-mentioned ones with respect to a structure. They may be modified as follows. 
   First, though the vertical and horizontal partition walls  101  and  102  are joined at their opposite ends to each other through the semi-circular partition wall  103  in the rear substrate  10  in accordance with the first embodiment, it is not always necessary to join all of the vertical and horizontal partition walls  101  and  102  to each other. 
   For instance, only a L-th vertical partition wall  101  and a (L+1)-th vertical partition wall  101  may be joined to each other through the semi-circular partition wall  103 , wherein L indicates a positive integer 1, 5, 9 or 13, and the rest of the vertical and horizontal partition walls  101  and  102  may not be joined to each other. That is, it is possible to select the vertical or horizontal partition walls  101  or  102  to be joined to each other through the semi-circular partition wall  103  in accordance with design conditions. 
   It is preferable that a vertical or horizontal partition wall  101  or  102  located outermost of a display area in a plasma display panel is joined to another vertical or horizontal partition wall  101  or  102  through a semi-circular partition wall  103 . 
   Second, the partition wall  103  through which adjacent vertical or horizontal partition walls  101  or  102  are joined to each other is not to be limited to a semi-circular one. 
   For instance, the partition wall  103  may be comprised of an arc as a part of a circle or a combination of curves. The partition wall  103  may be comprised of any curves, if the partition wall  103  does not include two lines joined to each other, forming an angle. 
   Furthermore, the vertical and horizontal partition walls  101  and  102  may be joined to each other only at one of their opposite ends through the semi-circular partition wall  103 . 
   Second Embodiment  
     FIG. 10  is a plan view illustrating an outline of a rear substrate  20  in accordance with the second embodiment of the present invention. For simplification of  FIG. 10 , only a partition wall is illustrated in  FIG. 10 , similarly to  FIG. 8 . The rear substrate  20  has the same structure as the rear substrate  352  illustrated in  FIG. 1  except a partition wall. 
   In the rear substrate  20  in accordance with the second embodiment, a partition wall is comprised of a plurality of vertical partition walls  101   a  extending vertically in  FIG. 10  in parallel with one another, and a plurality of horizontal partition walls  102   a  extending horizontally in  FIG. 10  in parallel with one another. The vertical partition walls  101   a  are equally spaced away from one another, and similarly, the horizontal partition walls  102   a  are equally spaced away from one another. A ratio of a distance between adjacent horizontal partition walls  102   a  to a distance between adjacent vertical partition walls  101   a  is set equal to 3:1. The vertical and horizontal partition walls  101   a  and  102   a  are arranged in a grid. 
   Herein, the four vertical partition walls  101   a  arranged at the left end are called, from the left, a first vertical partition wall  101 - 1 , a second vertical partition wall  101 - 2 , a third vertical partition wall  101 - 3 , and a fourth vertical partition wall  101 - 4 , respectively. 
   In the second rear substrate  20  in accordance with the second embodiment, the first and third vertical partition walls  101 - 1  and  101 - 3  are joined at their opposite ends in a length-wise direction to each other through a first semi-circular partition wall  103 - 1 , and the second and fourth vertical partition walls  101 - 2  and  101 - 4  are joined at their opposite ends in a length-wise direction to each other through a second semi-circular partition wall  103 - 2 . 
   The first and second semi-circular partition walls  103 - 1  and  103 - 2  intersect with each other at an immediate point between the second and third vertical partition walls  101 - 2  and  101 - 3 . 
   A distance between the first and third vertical partition walls  101 - 1  and  101 - 3  is equal to a distance between the second and fourth vertical partition walls  101 - 2  and  101 - 4 . Hence, the first semi-circular partition wall  103 - 1  is equal in radius to the second semi-circular partition wall  103 - 2 . 
   Specifically, the rear substrate  20  includes sixteen vertical partition walls  101   a . A vertical partition wall  101   a  located at N-th from the left in  FIG. 10  is joined at their opposite ends to a vertical partition wall  101   a  located at (N+2)-th through the semi-circular partition wall  103 - 1 , and a vertical partition wall  101   a  located at M-th from the left in  FIG. 10  is joined at their opposite ends to a vertical partition wall  101   a  located at (M+2)-th through the semi-circular partition wall  103 - 2 , wherein N indicates a positive odd number 1, 5, 9 or 13, and M indicates a positive even number 2, 6, 10 or 14. 
   The horizontal partition walls  102   a  are arranged in the same way as the vertical partition walls  101   a.    
   The inventor had fabricated the rear substrate  20  in accordance with the second embodiment, and measured heights of the vertical partition wall  101   a , the horizontal partition wall  102   a  and the semi-circular partition wall  103   a  at a plurality of points.  FIG. 11A  shows fifteen points  1  to  20  and A at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate  20 , and  FIG. 11B  is a table showing the results of the measurement. 
   A designed total thickness of a dielectric layer and a partition wall is 120 micrometers. The highest total thickness is equal to 138 micrometers at point  8 , and the second highest total thickness is equal to 134 micrometers at point  5 . Considering that measurement error is approximately ±5 micrometers, the total thicknesses measured at points  2 ,  6 ,  11 ,  12 ,  14 ,  15 ,  16 ,  19  and A are within the measurement error, and the maximum gap between the designed total thickness (120 micrometers) and the measured total thickness is 9 micrometers at point  5  among the total thicknesses measured at points  1 ,  5 ,  7 ,  8 ,  13  and  20  all of which are without the measurement error. 
   In the partition walls in the conventional plasma display panels suggested in the above-mentioned Japanese Patent Application Publications Nos. 2000-340123 and 11-339668, a gap between a designed total thickness and an actual total thickness is in the range of 20 to 30 micrometers. 
   As mentioned above, in accordance with the rear substrate  20 , a pair of the vertical or horizontal partition walls  101   a  and  102   a  is joined at their opposite ends to each other through the semi-circular partition wall  103   a , ensuring that contraction force generated during the partition wall is being baked is diffused. Accordingly, it is possible to prevent the vertical and horizontal partition walls  101   a  and  102   a  from rising at their ends, and hence, it is also possible to prevent a partition wall from being broken and improperly shaped more surely than the conventional partition walls, similarly to the rear substrate  10  in accordance with the first embodiment. 
   Various modifications may be applied to the vertical partition walls  101   a , the horizontal partition walls  102   a  and the partition walls  103   a  in the rear substrate  20 , similarly to the rear substrate  10 . 
   Third Embodiment  
     FIG. 12  is a plan view illustrating an outline of a rear substrate  30  in accordance with the third embodiment of the present invention. For simplification of  FIG. 12 , only a partition wall is illustrated in  FIG. 12 , similarly to  FIG. 8 . The rear substrate  30  has the same structure as the rear substrate  352  illustrated in  FIG. 1  except a partition wall. 
   In the rear substrate  30  in accordance with the third embodiment, a partition wall is comprised of twelve vertical partition walls  101   a  to  101   l  extending vertically in  FIG. 12  in parallel with one another, and eight horizontal partition walls  102   a  to  102   h  extending horizontally in  FIG. 12  in parallel with one another. The vertical partition walls  101   a  to  101   l  are equally spaced away from one another, and similarly, the horizontal partition walls  102   a  to  102   h  are equally spaced away from one another. A ratio of a distance between adjacent horizontal partition walls  102   a  to  102   h  to a distance between adjacent vertical partition walls  101   a  to  101   l  is set equal to 3:1. The vertical and horizontal partition walls  101   a  to  101   l  and  102   a  to  102   h  are arranged in a grid. 
   In the rear substrate  30 , the vertical partition walls  101   a  to  101   l  located every five rows are joined at their opposite ends thereof to each other through a semi-circular partition wall. 
   Specifically, the first and seventh vertical partition walls  101   a  and  101   g  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   a . Similarly, the second and eighth vertical partition walls  101   b  and  101   h  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   b , the third and ninth vertical partition walls  101   c  and  101   i  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   c , the fourth and tenth vertical partition walls  101   d  and  101   j  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   d , the fifth and eleventh vertical partition walls  101   e  and  101   k  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   e , and the sixth and twelfth vertical partition walls  101   f  and  101   l  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   f.    
   The horizontal partition walls  102   a  to  102   h  located every three rows are joined at their opposite ends thereof to each other through a semi-circular partition wall. 
   Specifically, the first and fifth horizontal partition walls  102   a  and  102   e  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   g . Similarly, the second and sixth horizontal partition walls  102   b  and  102   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   h , the third and seventh horizontal partition walls  102   c  and  102   g  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   i , and the fourth and eighth horizontal partition walls  102   d  and  102   h  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   j.    
   That is, the vertical partition walls  101   a  to  101   l  located every S/2 rows are joined at their opposite ends thereof to each other through a semi-circular partition wall, wherein S indicates a total number of vertical partition walls. Similarly, the horizontal partition walls  102   a  to  102   h  located every S/2 rows are joined at their opposite ends thereof to each other through a semi-circular partition wall, wherein S indicates a total number of horizontal partition walls. 
   As mentioned above, in accordance with the rear substrate  30 , a pair of the vertical or horizontal partition walls  101   a  to  101   l  or  102   a  to  102   h  is joined at their opposite ends to each other through the semi-circular partition wall  103   a  to  103   f  or  103   g  to  103   j , ensuring that contraction force generated during the partition wall is being baked is diffused. Accordingly, it is possible to prevent the vertical and horizontal partition walls from rising at their ends, and hence, it is also possible to prevent a partition wall from being broken and improperly shaped more surely than the conventional partition walls, similarly to the rear substrates  10  and  20  in accordance with the first and second embodiments. 
   Fourth Embodiment  
     FIG. 13  is a plan view illustrating an outline of a rear substrate  40  in accordance with the fourth embodiment of the present invention. For simplification of  FIG. 13 , only a partition wall is illustrated in  FIG. 13 , similarly to  FIG. 8 . The rear substrate  40  has the same structure as the rear substrate  352  illustrated in  FIG. 1  except a partition wall. 
   In the rear substrate  40  in accordance with the fourth embodiment, a partition wall is comprised of eighth vertical partition walls  101   a  to  101   h  extending vertically in  FIG. 13  in parallel with one another, and eight horizontal partition walls  102   a  to  102   h  extending horizontally in  FIG. 13  in parallel with one another. The vertical partition walls  101   a  to  101   h  are equally spaced away from one another, and similarly, the horizontal partition walls  102   a  to  102   h  are equally spaced away from one another. A ratio of a distance between adjacent horizontal partition walls  102   a  to  102   h  to a distance between adjacent vertical partition walls  101   a  to  101   h  is set equal to 3:1. The vertical and horizontal partition walls  101   a  to  101   h  and  102   a  to  102   h  are arranged in a grid. 
   In the substrate  40 , a first pair of partition walls is joined at their opposite ends thereof to each other through a semi-circular partition wall, and second and third pairs of partition walls are arranged inside the first pair of partition walls. Each of the second and third pairs of partition walls is joined at their opposite ends thereof to each other through a semi-circular partition wall. 
   Specifically, the first and sixth vertical partition walls  101   a  and  101   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   a . The second and third vertical partition walls  101   b  and  101   c  both surrounded by the first and sixth vertical partition walls  101   a  and  101   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   b , and the fourth and fifth vertical partition walls  101   d  and  101   e  both surrounded by the first and sixth vertical partition walls  101   a  and  101   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   c.    
   The semi-circular partition wall  103   a  has a radius five times greater than radiuses of the semi-circular partition walls  103   b  and  103   c . The semi-circular partition wall  103   b  has a radius equal to a radius of the semi-circular partition walls  103   c.    
   Similarly, the first and sixth horizontal partition walls  102   a  and  102   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   e . The second and third horizontal partition walls  102   b  and  102   c  both surrounded by the first and sixth horizontal partition walls  102   a  and  102   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   f , and the fourth and fifth horizontal partition walls  102   d  and  102   e  both surrounded by the first and sixth horizontal partition walls  102   a  and  102   f  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   g.    
   The semi-circular partition wall  103   e  has a radius five times greater than radiuses of the semi-circular partition walls  103   f  and  103   g . The semi-circular partition wall  103   f  has a radius equal to a radius of the semi-circular partition walls  103   g.    
   The seventh and eighth vertical partition walls  101   g  and  101   h  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   d , and the seventh and eighth horizontal partition walls  102   g  and  102   h  are joined at their opposite ends in a length-wise direction to each other through a semi-circular partition wall  103   h . The seventh and eighth vertical partition walls  101   g  and  101   h  are located outside the semi-circular partition wall  103   a , and the seventh and eighth horizontal partition walls  102   g  and  102   h  are located outside the semi-circular partition wall  103   e.    
   In the rear substrate  40  in accordance with the fourth embodiment, two pairs of vertical partition walls, that is, a pair of the second and third vertical partition walls  101   b  and  101   c  and a pair of the fourth and fifth vertical partition walls  101   d  and  101   e  are arranged inside the first and sixth vertical partition walls  101   a  and  101   f  and the semi-circular partition walls  103   a . However, the number of pairs of vertical partition walls arranged inside of the first and sixth vertical partition walls  101   a  and  101   f  and the semi-circular partition walls  103   a  is not to be limited to two. Any number may be selected. The same is applied to the horizontal partition wall. 
   As mentioned above, in accordance with the rear substrate  40 , a pair of the vertical or horizontal partition walls is joined at their opposite ends to each other through the semi-circular partition walls, ensuring that contraction force generated during the partition wall is being baked is diffused. Accordingly, it is possible to prevent the vertical and horizontal partition walls from rising at their ends, and hence, it is also possible to prevent a partition wall from being broken and improperly shaped more surely than the conventional partition walls, similarly to the rear substrates  10  and  20  in accordance with the first and second embodiments. 
   Fifth Embodiment  
     FIG. 14  is a plan view illustrating an outline of a rear substrate  50  in accordance with the fifth embodiment of the present invention. For simplification of  FIG. 14 , only a partition wall is illustrated in  FIG. 14 , similarly to  FIG. 8 . The rear substrate  50  has the same structure as the rear substrate  352  illustrated in  FIG. 1  except a partition wall. 
   In the rear substrate  50  in accordance with the fifth embodiment, a partition wall is comprised of a plurality of vertical partition walls  101  extending vertically in  FIG. 14  in parallel with one another, and a plurality of horizontal partition walls  102  extending horizontally in  FIG. 14  in parallel with one another. The vertical partition walls  101  are equally spaced away from one another, and similarly, the horizontal partition walls  102  are equally spaced away from one another. A ratio of a distance between adjacent horizontal partition walls  102  to a distance between adjacent vertical partition walls  101  is set equal to 3:1. The vertical and horizontal partition walls  101  and  102  are arranged in a grid. 
   Herein, the four vertical partition walls  101  arranged at the left end are called, from the left, a first vertical partition wall  101 - 1 , a second vertical partition wall  101 - 2 , a third vertical partition wall  101 - 3 , and a fourth vertical partition wall  101 - 4 , respectively. 
   In the rear substrate  50  in accordance with the fifth embodiment, the first and fourth vertical partition walls  101 - 1  and  101 - 4  are joined at their opposite ends in a length-wise direction to each other through first semi-circular partition walls  103   a , and the second and third vertical partition walls  101 - 2  and  101 - 3  are joined at their opposite ends in a length-wise direction to each other through second semi-circular partition walls  103   b.    
   The first semi-circular partition wall  103   a  has a radius three times greater than a radius of the second semi-circular partition wall  103   b.    
   In the rear substrate  50 , a first pair of the vertical partition walls  101 - 1  and  101 - 4  is joined at their opposite ends thereof to each other through the first semi-circular partition walls  103   a , and a second pair of the vertical partition walls  101 - 2  and  101 - 3  are arranged inside the first pair of vertical partition walls  101 - 1  and  101 - 4 . The second pair of the vertical partition walls  101 - 2  and  101 - 3  is joined at their opposite ends thereof to each other through the second semi-circular partition wall  103   b.    
   The partition wall configuration as mentioned above is repeated every four vertical partition walls  101 . 
   The horizontal partition walls  102  are arranged in the same way as the vertical partition walls  101 . 
   Herein, the four horizontal partition walls  102  arranged at the top end are called, from the top, a first horizontal partition wall  102 - 1 , a second horizontal partition wall  102 - 2 , a third horizontal partition wall  102 - 3 , and a fourth horizontal partition wall  102 - 4 , respectively. 
   In the rear substrate  50 , a first pair of the horizontal partition walls  102 - 1  and  102 - 4  is joined at their opposite ends thereof to each other through the first semi-circular partition walls  103   c , and a second pair of the horizontal partition walls  102 - 2  and  102 - 3  are arranged inside the first pair of horizontal partition walls  102 - 1  and  102 - 4 . The second pair of the horizontal partition walls  102 - 2  and  102 - 3  is joined at their opposite ends thereof to each other through the second semi-circular partition wall  103   d.    
   The semi-circular partition wall  103   c  has a radius three times greater than a radius of the semi-circular partition wall  103   d.    
   In the rear substrate  50 , a first pair of the horizontal partition walls  102 - 1  and  102 - 4  is joined at their opposite ends thereof to each other through the semi-circular partition walls  103   c , and a second pair of the horizontal partition walls  102 - 2  and  102 - 3  are arranged inside the first pair of horizontal partition walls  102 - 1  and  102 - 4 . The second pair of the horizontal partition walls  102 - 2  and  102 - 3  is joined at their opposite ends thereof to each other through the semi-circular partition wall  103   d.    
   The partition wall configuration as mentioned above is repeated every four horizontal partition walls  102 . 
   The inventor had fabricated the rear substrate  50  in accordance with the fifth embodiment, and measured heights of the vertical partition wall  101 , the horizontal partition wall  102  and the semi-circular partition wall  103  at a plurality of points.  FIG. 15A  shows sixteen points  1  to  20 , A and B at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate  50 , and  FIG. 15B  is a table showing the results of the measurement. 
   A designed total thickness of a dielectric layer and a partition wall is 120 micrometers. The highest total thickness is equal to 136 micrometers at point  13 , and the second highest total thickness is equal to 131 micrometers at point  1 . Considering that measurement error is approximately ±5 micrometers, the total thicknesses measured at points  2 ,  3 ,  5 ,  9 ,  14 ,  20  and B are within the measurement error, and the maximum gap between the designed total thickness (120 micrometers) and the measured total thickness is 11 micrometers at point  13  among the total thicknesses measured at points  1 ,  4 ,  8 ,  12 ,  13 ,  15 ,  16 ,  17  and A all of which are without the measurement error. 
   In the partition walls in the conventional plasma display panels suggested in the above-mentioned Japanese Patent Application Publications Nos. 2000-340123 and 11-339668, a gap between a designed total thickness and an actual total thickness is in the range of 20 to 30 micrometers. 
   As mentioned above, in accordance with the rear substrate  50 , a pair of the vertical or horizontal partition walls is joined at their opposite ends to each other through the semi-circular partition wall, ensuring that contraction force generated during the partition wall is being baked is diffused. Accordingly, it is possible to prevent the vertical and horizontal partition walls from rising at their ends, and hence, it is also possible to prevent a partition wall from being broken and improperly shaped more surely than the conventional partition walls. 
   Various modifications may be applied to the vertical partition walls  101 , the horizontal partition walls  102  and the partition walls  103  in the rear substrate  50 , similarly to the rear substrate  10 . 
   A partition wall located outside is likely to be side-etched during sand blasting in comparison with a partition wall located inside. Accordingly, as illustrated in  FIG. 15A , the semi-circular partition wall  103   a  is designed to have a width W 1  greater than a width W 2  of the semi-circular partition wall  103   b , and, the semi-circular partition wall  103   c  is designed to have a width W 3  greater than a width W 4  of the semi-circular partition wall  103   d.    
   Furthermore, since the semi-circular partition walls  103   a  and  103   c  located outside can have a curvature greater than a curvature of the semi-circular partition walls  103   b  and  103   d  located inside, the vertical or horizontal partition walls joined to each other through the semi-circular partition walls  103   a  and  103   c  can diffuse contraction forces exerted thereon to a much degree, preventing them from rising at their opposite ends. 
   In the rear substrate  50  in accordance with the fifth embodiment, the pair of the vertical or horizontal partition walls joined at their opposite ends thereof to each other through the semi-circular partition wall is arranged in another pair of the vertical or horizontal partition walls joined at their opposite ends thereof to each other through the semi-circular partition walls. As a modification of the fifth embodiment, a structure where a pair of the vertical or horizontal partition walls joined at their opposite ends thereof to each other through the semi-circular partition wall is arranged in another pair of the vertical or horizontal partition walls joined at their opposite ends thereof to each other through the semi-circular partition walls may be repeated N times, wherein N is a positive integer equal to or greater than two (2). 
   Hereinbelow is shown an example in which three pairs of vertical or horizontal partition walls are arranged similarly to and coaxially with one another, as the sixth embodiment. 
   Sixth Embodiment  
     FIG. 16  is a plan view illustrating an outline of a rear substrate  60  in accordance with the sixth embodiment of the present invention. For simplification of  FIG. 16 , only a partition wall is illustrated in  FIG. 16 , similarly to  FIG. 8 . The rear substrate  60  has the same structure as the rear substrate  352  illustrated in  FIG. 1  except a partition wall. 
   In the rear substrate  60  in accordance with the sixth embodiment, a partition wall is comprised of a plurality of vertical partition walls  101  extending vertically in  FIG. 16  in parallel with one another, and a plurality of horizontal partition walls  102  extending horizontally in  FIG. 16  in parallel with one another. The vertical partition walls  101  are equally spaced away from one another, and similarly, the horizontal partition walls  102  are equally spaced away from one another. A ratio of a distance between adjacent horizontal partition walls  102  to a distance between adjacent vertical partition walls  101  is set equal to 3:1. The vertical and horizontal partition walls  101  and  102  are arranged in a grid. 
   Herein, the six vertical partition walls  101  arranged at the left end are called, from the left, a first vertical partition wall  101 - 1 , a second vertical partition wall  101 - 2 , a third vertical partition wall  101 - 3 , a fourth vertical partition wall  101 - 4 , a fifth vertical partition wall  101 - 5 , and a sixth vertical partition wall  101 - 6 , respectively. 
   In the rear substrate  60  in accordance with the sixth embodiment, the first and sixth vertical partition walls  101 - 1  and  101 - 6  are joined at their opposite ends in a length-wise direction to each other through first semi-circular partition walls  103   a , the second and fifth vertical partition walls  101 - 2  and  101 - 5  are joined at their opposite ends in a length-wise direction to each other through second semi-circular partition walls  103   b , and the third and fourth vertical partition walls  101 - 3  and  101 - 4  are joined at their opposite ends in a length-wise direction to each other through third semi-circular partition walls  103   c.    
   The first semi-circular partition wall  103   a  has a radius five times greater than a radius of the third semi-circular partition wall  103   c , and the second semi-circular partition wall  103   b  has a radius three times greater than a radius of the third semi-circular partition wall  103   c.    
   In the rear substrate  60 , a first pair of the vertical partition walls  101 - 1  and  101 - 6  is joined at their opposite ends thereof to each other through the first semi-circular partition walls  103   a , a second pair of the vertical partition walls  101 - 2  and  101 - 5  are arranged inside the first pair of vertical partition walls  101 - 1  and  101 - 6 , and is joined at their opposite ends thereof to each other through the second semi-circular partition wall  103   b , and further, a third pair of the vertical partition walls  101 - 3  and  101 - 4  are arranged inside the second pair of vertical partition walls  101 - 2  and  101 - 5 , and is joined at their opposite ends thereof to each other through the third semi-circular partition wall  103   c.    
   The partition wall configuration as mentioned above is repeated every six vertical partition walls  101 . 
   The horizontal partition walls  102  are arranged in the same way as the vertical partition walls  101 . 
   The inventor had fabricated the rear substrate  60  in accordance with the sixth embodiment, and measured heights of the vertical partition wall, the horizontal partition wall and the semi-circular partition wall at a plurality of points.  FIG. 17A  shows twenty points  1  to  18  and A to T at which a total thickness of a dielectric layer and a partition wall is measured in the rear substrate  60 , and  FIG. 17B  is a table showing the results of the measurement. 
   A designed total thickness of a dielectric layer and a partition wall is 120 micrometers. The highest total thickness is equal to 133 micrometers at points  1 ,  3 ,  6  and  10 , and the second highest total thickness is equal to 131 micrometers at point A. Considering that measurement error is approximately ±5 micrometers, the total thicknesses measured at points  2 ,  4 ,  12 ,  17 ,  18 , P and S are within the measurement error, and the maximum gap between the designed total thickness (120 micrometers) and the measured total thickness is 8 micrometers at points  1 ,  3 ,  6  and  10  among the total thicknesses measured at points  1 ,  3 ,  5 ,  6 ,  10 , A, D, F, H, I, M, N and T all of which are without the measurement error. 
   In the partition walls in the conventional plasma display panels suggested in the above-mentioned Japanese Patent Application Publications Nos. 2000-340123 and 11-339668, a gap between a designed total thickness and an actual total thickness is in the range of 20 to 30 micrometers. 
   As mentioned above, in accordance with the rear substrate  60 , a pair of the vertical or horizontal partition walls is joined at their opposite ends to each other through the semi-circular partition wall, ensuring that contraction force generated during the partition wall is being baked is diffused. Accordingly, it is possible to prevent the vertical and horizontal partition walls from rising at their ends, and hence, it is also possible to prevent a partition wall from being broken and improperly shaped more surely than the conventional partition walls. 
   As illustrated in  FIG. 17A , the semi-circular partition wall  103   a  is designed to have a width W 1  greater than a width W 2  of the semi-circular partition wall  103   b , and the semi-circular partition wall  103   b  is designed to have a width W 2  greater than a width W 3  of the semi-circular partition wall  103   c.    
   With respect to a width of the semi-circular partition walls connecting a pair of the horizontal partition walls to each other, the same as mentioned above is applied. 
   By designing a width of each of the semi-circular partition walls in such a manner as mentioned above, the advantages obtained in the fifth embodiment can be obtained. 
   In the sixth embodiment, three pairs of vertical or horizontal partition walls are arranged similarly to and coaxially with one another. However, the number of pairs of vertical or horizontal partition walls to be arranged similarly to and coaxially with one another is not to be limited to three. The vertical or horizontal partition walls may be comprised of 2N ones wherein N is a positive integer equal to or greater than two, in which case, a M-th vertical or horizontal partition wall is joined at opposite ends thereof in a length-wise direction to a (2N−M+1)-th vertical or horizontal partition wall through a semi-circular partition wall wherein M is a positive integer in the range of one (1) to N both inclusive. 
   In the above-mentioned first to sixth embodiments, a partition wall is comprised of a plurality of vertical partition walls and a plurality of horizontal partition walls. However, a partition wall may be comprised of either a plurality of vertical partition walls or a plurality of horizontal partition walls. 
   As an alternative, as illustrated in  FIG. 6 , a partition wall may be comprised of a plurality of horizontal partition walls and a plurality of vertical partition walls extending only between adjacent horizontal partition walls. 
   Seventh Embodiment  
     FIG. 18  is a plan view illustrating an outline of a rear substrate  70  in accordance with the seventh embodiment. 
   The rear substrate  70  includes a partition wall having the same structure as that of the partition wall in the rear substrate  10  in accordance with the first embodiment, illustrated in  FIG. 8 . 
   As illustrated in  FIG. 18 , the rear substrate  70  has a display area  71 , illustrated as a hatched area, in which images are displayed, and a non-display area  72  surrounding the display area  71 , in which images are not displayed. 
   The vertical and horizontal partition walls  101  and  102  are formed entirely in the display area  71  and around a boundary between the display area  71  and the non-display area  72 . In the non-display area  72 , the vertical and horizontal partition walls  101  and  102  are formed each by two rows such that they surround the display area  71 . These two rows of the vertical and horizontal partition walls  101  and  102  are dummy partition walls. The formation of dummy partition walls makes it possible to uniformly form the vertical and horizontal partition walls  101  and  102  in the display area  71  during fabrication of a plasma display panel, and prevent contaminants from invading into the display area  71  after fabrication of a plasma display panel. 
   In the rear substrate  70 , flit-stoppers  73  are formed on the substrate  301  in the non-display area  72  in facing relation to opposite ends of a pair of the vertical and horizontal partition walls  101  and  102  joined to each other through the semi-circular partition wall  103 . 
   Each of the flit-stoppers  73  is circular, and is located on a line passing through a center between a pair of the vertical or horizontal partition walls  101  or  102  joined to each other through the semi-circular partition wall  103 , in a width-wise direction of the vertical or horizontal partition walls  101  or  102 . 
   The flit-stoppers  73 A located in facing relation to pairs of the vertical partition walls  101  have a common diameter, and similarly, the flit-stoppers  73 B located in facing relation to pairs of the horizontal partition walls  102  have a common diameter. 
   Assuming that each of the flit-stoppers  73  has a diameter D, the flit-stoppers  73  located adjacent to each other overlap each other by D/3. The flit-stoppers  73  thus overlapping adjacent flit-stoppers are arranged in a rectangle such that they surround the display area  71 . 
   Conventional flit-stoppers are arranged in the form of a frame in the non-display area  72  such that they surround the display area  71 . By designing flit-stoppers to be circular as in the seventh embodiment, it would be possible to reduce a space occupied by the flit-stoppers. Furthermore, by arranging the flit-stoppers  73  in facing relation to a pair of the vertical or horizontal partition walls  101  or  102 , it would be possible to surely adhere the front substrate  351  and the rear substrate  352  to each other around the vertical and horizontal partition walls  101  and  102 . 
   The flit-stoppers  73  are not to be limited to circular in shape. The flit-stoppers  73  may be comprised of any curves. For instance, the flit-stoppers  73  may be designed to be elliptic. 
   While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
   The entire disclosure of Japanese Patent Application No. 2002-264352 filed on Sep. 10, 2002 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.