Abstract:
A plasma display panel includes: a first substrate and a second substrate facing the first substrate, the first and second substrates defining a discharge space therebetween; and barrier ribs between the first and second substrates and defining non-discharge and discharge regions at the discharge space. The barrier ribs include: first ribs and second ribs adjacent the first ribs, the first and second ribs defining the non-discharge regions; third ribs adjacent the second ribs, the second and third ribs defining first discharge regions of the discharge regions, the first regions being adjacent the non-discharge regions, and the third ribs having a width different from that of the second ribs; and fourth ribs adjacent the first ribs, the first and fourth ribs defining second discharge regions of the discharge regions, the second regions being adjacent the non-discharge regions, and the fourth ribs having a width different from that of the first ribs.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0030367, filed on Mar. 28, 2007, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a plasma display panel. 
         [0004]    2. Description of the Related Art 
         [0005]    In a conventional plasma display panel, a barrier rib structure formed between upper and lower panels defines a plurality of discharge cells, phosphor layers are coated on walls of the barrier rib structure, and each of the discharge cells is filled with a main discharge gas such as neon (Ne) gas, helium (He) gas, or a mixture gas of Ne gas and He gas, and an inert gas that contains a small amount of xenon (Xe) gas. When a high frequency voltage is applied to the plasma display panel, vacuum ultraviolet rays are generated from the inert gas, and the vacuum ultraviolet rays excite the phosphor layers to emit visible light. Thus, an image is realized using the visible light. Plasma display panels are thin and lightweight, and thus are expected to be the next generation of large screen display apparatuses. 
         [0006]      FIG. 1  is a plan view of the arrangements of a barrier rib structure and discharge electrodes of a conventional plasma display panel. 
         [0007]    Referring to  FIG. 1 , a first barrier rib  181 , a second barrier rib  182 , a third barrier rib  183 , and a fourth barrier rib  184  are horizontally disposed parallel to each other on a lower panel. Fifth barrier ribs  185  are disposed to perpendicularly cross the first through fourth barrier ribs  181  through  184  on the lower panel. 
         [0008]    Non-discharge regions  193  are formed by the first barrier rib  181 , the second barrier rib  182 , and the fifth barrier ribs  185 , a first discharge region  191  is formed by the first barrier rib  181 , the fourth barrier rib  184 , and the fifth barrier ribs  185 , and a second discharge region  192  is formed by the second barrier rib  182 , the third barrier rib  183 , and the fifth barrier ribs  185 . 
         [0009]    An upper panel includes a first electrode  121  and a fourth electrode  124  that generate a discharge in the first discharge region  191 , and a second electrode  122  and a third electrode  123  that generate a discharge in the second discharge region  192 . 
         [0010]    When the lower panel and the upper panel are placed together, the first electrode  121  (a transparent electrode  121   t  and a bus electrode  121   b ) is placed at a location corresponding to the first barrier rib  181 , the second electrode  122  (a transparent electrode  122   t  and a bus electrode  122   b ) is placed at a location corresponding to the second barrier rib  182 , the third electrode  123  (a transparent electrode  123   t  and a bus electrode  123   b ) is placed at a location corresponding to the third barrier rib  183 , and the fourth electrode  124  (a transparent electrode  124   t  and a bus electrode  124   b ) is placed at a location corresponding to the fourth barrier rib  184 . 
         [0011]    However, as the number of discharge regions is increased in order to improve image quality, a cell pitch is reduced, and as a result, misalignments between the barrier ribs and the electrodes may occur frequently. In  FIG. 1 , a size of a first area S 1 , which is an area of the first electrode  121  exposed in the first discharge region  191 , is different from a size of a second area S 2 , which is an area of the second electrode  122  exposed in the second discharge region  192 , since the discharge electrodes are not correctly placed with respect to the barrier ribs. 
         [0012]    Accordingly, a relatively low (or weak) discharge occurs in the second discharge region  192  compared to the first discharge region  191 , that is, a non-uniform discharge occurs in every other line of the conventional plasma display panel. 
       SUMMARY OF THE INVENTION 
       [0013]    An aspect of the present invention is directed to providing a plasma display panel having increased reliability by preventing (or reducing) occurrences of a non-uniform discharge in every other line. 
         [0014]    According to an exemplary embodiment of the present invention, a plasma display panel includes: a first substrate and a second substrate facing the first substrate, the first and second substrates defining a discharge space therebetween; and a plurality of barrier ribs between the first and second substrates and defining a plurality of non-discharge regions and a plurality of discharge regions at the discharge space. The barrier ribs include: a plurality of first barrier ribs and a plurality of second barrier ribs adjacent to the first barrier ribs, the first and second barrier ribs defining the non-discharge regions; a plurality of third barrier ribs adjacent to the second barrier ribs, the second and third barrier ribs defining first discharge regions of the discharge regions, the first discharge regions being adjacent to the non-discharge regions, and the third barrier ribs having a width different from a width of the second barrier ribs; and a plurality of fourth barrier ribs adjacent to the first barrier ribs, the first and fourth barrier ribs defining second discharge regions of the discharge regions, the second discharge regions being adjacent to the non-discharge regions, and the fourth barrier ribs having a width different from a width of the first barrier ribs. 
         [0015]    The width of the first barrier ribs may be smaller than the width of the fourth barrier ribs. 
         [0016]    The width of the second barrier ribs may be smaller than the width of the third barrier ribs. 
         [0017]    The first barrier ribs, the second barrier ribs, the third barrier ribs, and the fourth barrier ribs may be in parallel to each other. 
         [0018]    The barrier ribs may further include a plurality of fifth barrier ribs crossing the first barrier ribs, the second barrier ribs, the third barrier ribs, and the fourth barrier ribs. 
         [0019]    According to another exemplary embodiment of the present invention, a plasma display panel includes: a first substrate and a second substrate facing the first substrate, the first and second substrates defining a discharge space therebetween; a plurality of barrier ribs between the first and second substrates and defining a plurality of non-discharge regions and a plurality of discharge regions at the discharge space; and a plurality of discharge electrodes for generating discharges at the discharge regions in accordance with an applied voltage. The plurality of barrier ribs include: a plurality of first barrier ribs and a plurality of second barrier ribs adjacent to the first barrier ribs, the first and second barrier ribs defining the non-discharge regions; a plurality of third barrier ribs adjacent to the second barrier ribs, the second and third barrier ribs defining first discharge regions of the discharge regions, the first discharge regions being adjacent to the non-discharge regions, and the third barrier ribs having a width different from a width of the second barrier ribs; and a plurality of fourth barrier ribs adjacent to the first barrier ribs, the first and fourth barrier ribs defining second discharge regions of the discharge regions, the second discharge regions being adjacent to the non-discharge regions, and the fourth barrier ribs having a width different from a width of the first barrier ribs. The plurality of discharge electrodes include: a plurality of first discharge electrodes for generating the discharges at the first discharge regions; and a plurality of second discharge electrodes for generating the discharges at the second discharge regions, the second discharge electrodes being in parallel to the first discharge electrodes, wherein portions of the first discharge electrodes exposed at the first discharge regions have a size different from a size of portions of the second discharge electrodes exposed at the second discharge regions. 
         [0020]    The width of the first barrier ribs may be smaller than the width of the fourth barrier ribs. 
         [0021]    The width of the second barrier ribs may be smaller than the width of the third barrier ribs. 
         [0022]    The first and second discharge electrodes may include Y electrodes to which substantially identical voltage waveforms are applied during a sustain period. 
         [0023]    Portions of the second discharge electrodes may be exposed at the non-discharge regions. 
         [0024]    The plurality of discharge electrodes may further include a plurality of third discharge electrodes for generating the discharges at the second discharge regions. The applied voltage may be alternately applied to the second discharge electrodes and the third discharge electrodes. The third discharge electrodes may include X electrodes. 
         [0025]    The plurality of discharge electrodes may further include a plurality of fourth discharge electrodes for generating the discharges at the first discharge regions. The applied voltage may be alternately applied to the first discharge electrodes and the fourth discharge electrodes. The fourth discharge electrodes may be X electrodes. 
         [0026]    Portions of the third discharge electrodes exposed at the second discharge regions may have a surface area different from a surface area of portions of the fourth discharge electrodes exposed at the first discharge regions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The above and other features and aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0028]      FIG. 1  is a plan view of the arrangements of a barrier rib structure and discharge electrodes of a conventional plasma display panel; 
           [0029]      FIG. 2  is a partial cutaway exploded perspective view of a plasma display panel according to an embodiment of the present invention; and 
           [0030]      FIG. 3  is a plan view of the arrangements of a barrier rib structure and discharge electrodes of a plasma display panel according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. 
         [0032]      FIG. 2  is a partial cutaway exploded perspective view of a plasma display panel (PDP) according to an embodiment of the present invention. 
         [0033]    Referring to  FIG. 2 , the plasma display panel includes an upper panel  250  and a lower panel  260 . 
         [0034]    The upper panel  250  includes a first substrate  211 , an upper dielectric layer  213 , a protective layer  215 , and a plurality of discharge electrodes. 
         [0035]    The first substrate  211  is formed of a material having a high optical transmittance, for example, glass or soda lime glass. The first substrate  211  can be colored to increase bright room contrast by reducing external light reflection. 
         [0036]    A plurality of discharge electrodes are formed on the first substrate  211 . 
         [0037]    The discharge electrodes include a first electrode  221 , a second electrode  222 , a third electrode  223 , and a fourth electrode  224  disposed in parallel to each other in an X direction, e.g., an X direction of the PDP (see  FIG. 2 ). The first electrode  221  and the fourth electrode  224  face each other in a first discharge region  291 , and the second electrode  222  and the third electrode  223  face each other in a second discharge region  292 . 
         [0038]    Each of the first through fourth electrodes  221  through  224  includes a transparent electrode and a bus electrode. More specifically, the first electrode  221  includes a first transparent electrode  221   t  and a first bus electrode  221   b , the second electrode  222  includes a second transparent electrode  222   t  and a second bus electrode  222   b , the third electrode  223  includes a third transparent electrode  223   t  and a third bus electrode  223   b , and the fourth electrode  224  includes a fourth transparent electrode  224   t  and a fourth bus electrode  224   b.    
         [0039]    The first through fourth transparent electrodes  221   t ,  222   t ,  223   t , and  224   t  generate discharges and maintain the discharges in discharge regions, and can be formed of a material having high visible light transmittance and low resistance (but relatively high resistance with respect to the bus electrodes), for example, indium tin oxide (ITO). Each of the first through fourth transparent electrodes  221   t ,  222   t ,  223   t , and  224   t  includes a straight line portion that extends in the X direction and protrusion portions extending in a Y direction from the straight line portion. Protrusion portions of a pair of the transparent electrodes that face each other are disposed in each of the discharge regions. That is, the protrusion portions of the first electrode  221  and the fourth electrode  224  face each other in the first discharge region  291 , and the protrusion portions of the second electrode  222  and the third electrode  223  face each other in the second discharge region  292 . 
         [0040]    Substantially equal voltages can be applied to the plurality of discharge regions by the compensation of the first through fourth bus electrodes  221   b ,  222   b ,  223   b , and  224   b  for the relatively high resistance of the first through fourth transparent electrodes  221   t ,  222   t ,  223   t , and  224   t . The first through fourth bus electrodes  221   b ,  222   b ,  223   b , and  224   b  can be formed of, for example, Cr, Cu, or Al. 
         [0041]    The upper dielectric layer  213  is formed on the first substrate  211  to cover the first through fourth electrodes  221 ,  222 ,  223 , and  224 , to sustain a glow discharge, and to reduce a discharge voltage formed through the accumulation of wall charges. The upper dielectric layer  213  may have a high withstanding voltage and a high visible light transmittance to increase discharge efficiency. 
         [0042]    The protective layer  215  is formed on the upper dielectric layer  213  to protect the upper dielectric layer  213  from collision by charged particles and to reduce a discharge voltage by emitting secondary electrons. In one embodiment, the protective layer  215  is formed of magnesium oxide (MgO), or MgO doped with a rare-earth element. 
         [0043]    The lower panel  260  includes a second substrate  271 , a lower dielectric layer  273 , address electrodes  275 , a plurality of barrier ribs, and a plurality of phosphor layers. 
         [0044]    Similar to the first substrate  211 , the second substrate  271  can be formed of a material having high optical transmittance, for example, glass or soda lime glass. Also, the second substrate  271  can be colored to increase bright room contrast by reducing external light reflection. 
         [0045]    The lower dielectric layer  273  is formed on the second substrate  271  to cover the address electrodes  275 . The lower dielectric layer  273  can be formed of a material having high dielectric breakdown strength, and, in the case of a top emission type PDP, can be formed of a material having high optical reflectance to increase light emission efficiency. The lower dielectric layer  273  can protect the address electrodes  275  from collision by charged particles. 
         [0046]    The address electrodes  275  extend in the Y direction, e.g., the Y direction of the PDP (see  FIG. 2 ) on the second substrate  271 , and a voltage is applied to the address electrodes  275  to generate address discharges by which discharge regions, where light is to be emitted, are selected. The address electrodes  275  can be formed of a metal having high electrical conductivity such as Cr, Cu, or Al so that substantially equal voltages can be applied to the plurality of discharge regions together with the first through fourth bus electrodes  221   b ,  222   b ,  223   b , and  224   b.    
         [0047]    In a PDP according to an embodiment of the present invention, the barrier ribs are disposed on the lower dielectric layer  273  to form a plurality of non-discharge regions and a plurality of discharge regions. 
         [0048]    The barrier ribs include first barrier ribs  281  and second barrier ribs  282 , and further include fourth barrier ribs  284  that define the first discharge regions  291  of the plurality of discharge regions together with the first barrier ribs  281 . The first discharge regions  291  are disposed adjacent to non-discharge regions  293 . Also, the barrier ribs include third barrier ribs  283  that define the non-discharge regions  293  and the second discharge regions  292  adjacent to the non-discharge regions  293  together with the second barrier ribs  282 . The first barrier ribs  281 , the second barrier ribs  282 , the third barrier ribs  283 , and the fourth barrier ribs  284  are disposed in parallel to each other in the X direction. 
         [0049]    Also, the barrier ribs further include fifth barrier ribs  285  that cross the first through fourth barrier ribs  281  through  284 , and more specifically, extend in the Y direction. Accordingly, the barrier ribs in the present embodiment are disposed in a matrix format, and, thus, form non-discharge regions  293  and the first and second discharge regions  291  and  292  having rectangular shapes. 
         [0050]    When the upper panel  250  and the lower panel  260  are placed together, the discharge electrodes are disposed on the barrier ribs. The arrangements of the barrier ribs and the discharge electrodes, according to one embodiment, will now be described with reference to  FIG. 3 . 
         [0051]    Referring to  FIG. 3 , the first barrier rib  281 , the second barrier rib  282 , the third barrier rib  283 , and the fourth barrier rib  284  are disposed in parallel to each other, and the fifth barrier ribs  285  that cross the first through fourth barrier ribs  281  through  284  are disposed to form a matrix type barrier rib structure. 
         [0052]    The first barrier rib  281  and the second barrier rib  282  form the non-discharge region  293 , the first barrier rib  281  and the fourth barrier rib  284  form the first discharge region  291 , and the second barrier rib  282  and the third barrier rib  283  form the second discharge region  292 . Accordingly, the non-discharge region  293  is disposed between the first discharge region  291  and the second discharge region  292 . 
         [0053]    A plurality of discharge electrodes are disposed at the discharge regions defined by the barrier ribs. More specifically, the first electrode  221  and the fourth electrode  224  are disposed at the first discharge region  291 , and the second electrode  222  and the third electrode  223  are disposed at the second discharge region  292 . As such, a discharge is generated in the first discharge region  291  by applying a voltage to the first electrode  221  and the fourth electrode  224 , and a discharge is generated in the second discharge region  292  by applying a voltage to the second electrode  222  and the third electrode  223 . 
         [0054]    The first electrode  221  and the second electrode  222 , to which substantially identical voltage waveforms are applied during a sustain period, can be Y electrodes (e.g., scan electrodes). Also, the third electrode  223  and the fourth electrode  224 , to which substantially identical voltage waveforms are applied during the sustain period, can be X electrodes (e.g., sustain electrodes). Since sustain discharges are generated by alternately applying a voltage to the X electrode and the Y electrode during the sustain period, the voltage is alternately applied to the first electrode  221  and the fourth electrode  224 , and the voltage is alternately applied to the second electrode  222  and the third electrode  223 . 
         [0055]    The first through fourth electrodes  221 ,  222 ,  223 , and  224  respectively include the first through fourth transparent electrodes  221   t ,  222   t ,  223   t , and  224   t  and respectively include the first through fourth bus electrodes  221   b ,  222   b ,  223   b , and  224   b . Each of the first through fourth transparent electrodes  221   t ,  222   t ,  223   t , and  224   t  includes straight line portions that extend in parallel to the first through fourth barrier ribs  281  through  284  and protrusion portions protruding from the straight line portions. The protrusion portions that are disposed in (or at) the first discharge region  291  face each other, and the protrusion portions that are disposed at the second discharge region  292  face each other. More specifically, the protrusion portions of the first electrode  221  and the protrusion portions of the fourth electrode  224  are symmetrically disposed at the first discharge region  291 , and the protrusion portions of the second electrode  222  and the protrusion portions of the third electrode  223  are symmetrically disposed at the second discharge region  292 . 
         [0056]    In order to increase the light emission efficiency of the PDP, the first electrode  221 , particularly, the first bus electrode  221   b , is located at a location corresponding to the first barrier rib  281 , the second bus electrode  222   b  is located at a location corresponding to the second barrier rib  282 , the third bus electrode  223   b  is located at a location corresponding to the third barrier rib  283 , and the fourth bus electrode  224   b  is located at a location corresponding to the fourth barrier rib  284 . As a result, the protrusion portions of the first electrode  221  and the protrusion portions of the fourth electrode  224  are symmetrically disposed at the first discharge region  291 , and the protrusion portions of the second electrode  222  and the protrusion portions of the third electrode  223  are symmetrically disposed at the second discharge region  292 . 
         [0057]    However, due to a misalignment between the first through fourth electrodes  221 ,  222 ,  223 , and  224  and the first through fourth barrier ribs  281  through  284 , respective areas of the first through fourth electrodes  221 ,  222 ,  223 , and  224  exposed in (or at) the first and second discharge regions  291  and  292  can be different. More specifically, a first area, which is an area of the first electrode  221  exposed in the first discharge region  291 , can be different from (e.g., larger or smaller than) a second area, which is an area of the second electrode  222  exposed in the second discharge region  292 . When the misalignment, as described above, is severe, the second electrode  222  can become exposed in the non-discharge region  293 . 
         [0058]    In particular, when the number of pixels is increased in order to realize a full high definition (FHD) image quality, a cell pitch is reduced, and thus, the misalignment can frequently occur. For example, if the first area is larger than the second area, that is, a portion (e.g., a considerable portion) of the second electrode  222  is covered by the second barrier rib  282 , the discharge characteristics of the first discharge region  291  become superior to those of the second discharge region  292 , and thus, a non-uniform discharge on every other line occurs. In contrast, the second area can be larger than the first area. Here, a non-uniform discharge in every other line can similarly be caused. 
         [0059]    Also, if a portion of the fourth electrode  224  is covered by the fourth barrier rib  284 , a fourth area which is an area of the fourth electrode  224  exposed at the first discharge region  291  can be smaller than a third area which is an area of the third electrode  223  exposed in the second discharge region  292 . 
         [0060]    In a PDP according to one embodiment, a first width W 1  of the first barrier rib  281  corresponding to the first electrode  221  and a second width W 2  of the second barrier rib  282  corresponding to the second electrode  222  are formed to be relatively small. More specifically, when the third barrier rib  283  corresponding to the third electrode  223  has a third width W 3  and the fourth barrier rib  284  corresponding to the fourth electrode  224  has a fourth width W 4 , the first width W 1  is formed to be smaller than the fourth width W 4 , and the second width W 2  is formed to be smaller than the third width W 3 . In one embodiment, the first width W 1  can be formed to be equal to the second width W 2 , and/or the third width W 3  can be formed to be equal to the fourth width W 4 . 
         [0061]    Therefore, the area of the second electrode  222  covered by the second barrier rib  282  can be reduced. That is, occurrences of the non-uniform discharge between the first discharge region  291  and the second discharge region  292  can be prevented (or reduced) by reducing the difference in size between the first area of the first electrode  221  exposed in the first discharge region  291  and the second area of the second electrode  222  exposed in the second discharge region  292 . 
         [0062]    More specifically, since the first electrode  221  and the second electrode  222  correspond to Y electrodes that generate reset discharges and address discharges, a non-uniformity of the reset discharges and the address discharges can be prevented (or reduced) by reducing the difference in size between the first area of the first electrode  221  exposed in the first discharge region  291  and the second area of the second electrode  222  exposed in the second discharge region  292 . 
         [0063]    The phosphor layer  277  (see, for example,  FIG. 2 ) emits R, G and B visible light by receiving vacuum ultraviolet rays generated due to the discharge. In one embodiment, the phosphor layer  277  includes a red light emitting layer  277 R formed of Y(V,P)O 4 :Eu, a green light emitting layer  277 G formed of Zn 2 SiO 4 :Mn or YBO 3 :Tb, and a blue light emitting layer  277 B formed of BAM:Eu. 
         [0064]    The first and second discharge regions  291  and  292  are filled with a discharge gas such as Ne gas, Xe gas, or He gas, or a mixture of these gases. 
         [0065]    Hereinafter, the improvement of non-uniform discharge characteristics in every other line of a PDP according to an embodiment of the present invention is presented. The conventional PDP has barrier ribs having equal width as depicted in  FIG. 1 . In a PDP according to an embodiment of the present invention, widths of a first barrier rib and a second barrier rib are formed smaller than widths of a third barrier rib and a fourth barrier rib, the width of the first barrier rib is formed to be equal to the width of the second barrier rib, and the width of the third barrier rib is formed to be equal to the width of the fourth barrier rib. Discharge cells that generate a non-uniform discharge in every other line were visually observed by driving the PDP according to the present embodiment and the conventional PDP at room temperature (25° C.), low temperature (−5° C.), and high temperature (55° C.), respectively. The results are summarized in Table 1. The numbers in Table 1 are the percentage ratios of discharge cells that generate a non-uniform discharge in every other line with respect to all discharge cells. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 PDP of present embodiment 
               
               
                 Temperatures 
                 Conventional PDP (%) 
                 (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Room temperature 
                 4.3 
                 0.9 
               
               
                 Low temperature 
                 28 
                 7.2 
               
               
                 High temperature 
                 16 
                 3.4 
               
               
                   
               
             
          
         
       
     
         [0066]    Referring to Table 1, it is seen that the PDP according to the present invention has a reduced non-uniform discharge ratio of more than 3 percentage points. In particular, at low temperature, the reduction is more than 20 percentage points lower than the conventional PDP. 
         [0067]    As described above, embodiments of the present invention provide a PDP having double barrier ribs to form non-discharge regions between the discharge regions. Thus, the exhaustion of a discharge can be effectively performed. 
         [0068]    Also, since discharge electrodes are formed on the double barrier ribs and, in particular, the discharge electrodes, to which substantially identical voltage waveforms are applied during a sustain period, are respectively disposed on the adjacent barrier ribs, the power consumption of the PDP can be reduced. For example, Y electrodes or X electrodes are respectively disposed on the adjacent barrier ribs that form the non-discharge regions, thereby reducing the power consumption of the PDP. 
         [0069]    In embodiments of the present invention, since widths of the first and second barrier ribs that correspond to the Y electrodes are formed relatively smaller than widths of the third and fourth barrier ribs that correspond to the X electrodes, a difference in size between the areas of the discharge electrodes exposed in the first and second discharge regions can be reduced when a misalignment of the discharge electrodes with respect to the barrier ribs occurs. Accordingly, the occurrences of a non-uniform discharge in every other line due to such a difference in size can be reduced, thereby increasing the reliability of the PDP. 
         [0070]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents.