Patent Publication Number: US-7595589-B2

Title: Plasma display panel

Description:
CLAIM OF PRIORITY 
   This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for PLASMA DISPLAY PANEL earlier filed in the Korean Intellectual Property Office on 28 Oct. 2004 and there duly assigned Serial No. 10-2004-0086538. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a novel design of a plasma display panel (PDP), and more particularly, to a PDP design that results in improved brightness and luminous efficiency while allowing for a reduced address discharge voltage. 
   2. Description of the Related Art 
   A PDP is a device that produces an image via an electric discharge. PDPs are becoming popular due to its predominant display performance, such as brightness and viewing angle. A principle of the PDP is that strong AC or DC voltage is applied to two electrodes to generate gas discharge that radiates ultraviolet rays, and radiation of the ultraviolet rays excites a phosphor layer within a discharge cell to produce visible rays. 
   PDPs are classified into DC-type and AC-type PDPs according to a discharging manner. The DC-type PDP has a structure in which all electrodes are exposed to a discharge space and electric charges are directly moved between corresponding electrodes. The AC-type PDP has a structure in which at least one electrode is enclosed by a dielectric layer and discharge is caused by wall charge, without direct movement of electric charges between the corresponding electrodes. 
   Also, the PDP can be classified into facing discharge-type and surface discharge-type PDPs according to an arrangement structure of the electrodes. The facing discharge-type PDP includes pairs of sustain electrodes each positioned on upper and lower substrates, where discharge is vertically generated between the substrates. The surface discharge-type PDP includes pairs of sustain electrodes positioned on the same substrate, where discharge is generated parallel to the substrate. In spite of increased luminous efficiency, the facing discharge-type PDP has a disadvantage in that a phosphor layer is easily deteriorated by plasma. Recently, the surface discharge-type PDP has come into wide use. 
   However, surface discharge AC PDPs have limited performance because of their design. For example, the shape of the discharge cells limits the amount of phosphor that can be deposited within, thus limiting the amount of visible light that can be generated. When ultraviolet radiation is produced in the discharge cell, it is not uniformly transmitted to the phosphor, thus limiting brightness and luminance efficiency. Also, the address and the sustain electrodes are separated by a large distance requiring a large voltage to be applied to these electrodes to achieve the requisite address discharge. What is therefore needed is a design for a PDP that overcomes these problems. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide an improved design for a PDP. 
   It is also an object of the present invention to provide a design for a PDP that allows for more phosphor to be deposited in the discharge cells. 
   It is further an object of the present invention to provide a design for a PDP that produces a efficient discharge that can be uniformly transferred to the phosphor. 
   It is still an object of the present invention to provide a PDP where the distance between the address electrodes and the sustain electrodes is small. 
   It is yet an object of the present invention to provide a design for a PDP that results in improved brightness and improved luminous efficiency. 
   These and other objects may be achieved by a PDP that includes a lower substrate and an upper substrate arranged opposite to each other and spaced apart by a distance, with a discharge space being located between the substrates, a plurality of partitions located between the lower substrate and the upper substrate that partitions the discharge space into a plurality of discharge cells, a plurality of address electrodes located on an upper surface of the lower substrate, a first dielectric layer located on the upper surface of the lower substrate and covering the address electrodes, a plurality of first sustain electrodes having a closed loop corresponding to each discharge cell, a plurality of second sustain electrodes having a closed loop corresponding to each discharge cell while corresponding to the first sustain electrodes, and a phosphor layer located on the upper surface of the first dielectric layer and on sidewalls of the partitions. 
   A second dielectric layer can be located on inner sides of the first sustain electrodes, and a protective film can be located on a surface of the second dielectric layer. A protrusion made of a dielectric substance can protrude from the upper surface of the first dielectric layer into each discharge cell, and the second sustain electrode can be located on an upper surface of each protrusion. The protrusion can have a closed-loop that corresponds to a closed loop of the second sustain electrode. 
   A phosphor layer can be located on inner and outer walls of the protrusion, and a phosphor layer can be located at a lower surface of the upper substrate. A third dielectric layer can be located on the upper surface of the protrusion to cover the second sustain electrode, and a protective film can be located on a surface of the third dielectric layer. The first sustain electrode can have a cylindrical shape. The second sustain electrode can have a plate shape with an aperture located at a center thereof. The address electrode can have a band shape or a plate shape with an aperture located at a center thereof. 
   According to another aspect of the present invention, there is provided a PDP that includes a lower substrate and an upper substrate arranged opposite to each other and spaced apart by a distance, with a discharge space being located between the substrates, a plurality of partitions located between the lower substrate and the upper substrate that partitions the discharge space into a plurality of discharge cells, a plurality of address electrodes located on an upper surface of the lower substrate, a first dielectric layer located on the upper surface of the lower substrate that covers the address electrodes, a plurality of first sustain electrodes having a shape of a closed loop corresponding to each discharge cell, a second dielectric layer located on the lower surface of the upper substrate and covering the first sustain electrodes, a plurality of second sustain electrodes having a closed loop, each closed loop corresponding to each discharge cell while corresponding to the first sustain electrodes, and a phosphor layer located on the upper surface of the first dielectric layer and on sidewalls of the partitions. 
   The first and second sustain electrodes can have a plate shape with an aperture located at a center thereof. The address electrode can have a band shape or a plate shape with an aperture located at a center thereof. A bus electrode can be made of a non-transparent metal and can be located at an outer periphery of the first sustain electrode. The first sustain electrode can be made of indium tin oxide (ITO). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
       FIG. 1  is an exploded perspective view of a PDP; 
       FIGS. 2A and 2B  are transverse and vertical sectional views of the PDP of  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of a PDP according to a first embodiment of the present invention; 
       FIG. 4  is a cross-sectional view of the PDP of  FIG. 3 ; 
       FIG. 5  is a perspective view depicting the electrodes in the PDP of  FIG. 3 ; 
       FIG. 6  is a perspective view depicting a variation of electrode design that can be used in the PDP of  FIG. 3 ; 
       FIG. 7  is a perspective view depicting another variation of electrode design that can be used in the PDP of  FIG. 3 ; 
       FIG. 8  is a perspective view depicting yet another variation of electrode design that can be used in the PDP of  FIG. 3 ; 
       FIG. 9  is an exploded perspective view of a PDP according to a second embodiment of the present invention; 
       FIG. 10  is a cross-sectional view of the PDP of  FIG. 9 ; 
       FIG. 11  is a perspective view depicting the electrodes in the PDP of  FIG. 9 ; 
       FIG. 12  is a perspective view depicting a variation of electrode design that can be used in the PDP of  FIG. 9 ; 
       FIG. 13  is a perspective view depicting another variation of electrode design that can be used in the PDP of  FIG. 9 ; and 
       FIG. 14  is a perspective view depicting yet another variation of electrode design that can be used in the PDP of  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning now to the FIGURES,  FIGS. 1 ,  2 A and  2 B illustrate a surface discharge-type PDP  30 .  FIGS. 2A and 2B  are transverse and vertical sectional views of the PDP  30  of  FIG. 1 . Referring to  FIGS. 1 ,  2 A, and  2 B, the PDP  30  includes an upper substrate  20  and a lower substrate  10  arranged opposite to each other and spaced apart from each other. Discharge occurs in a discharge space located between the upper substrate  20  and the lower substrate  10 . 
   A plurality of address electrodes  11  having a stripe shape are arranged on an upper surface of the lower substrate  10 . A first dielectric layer  12  covers the address electrodes  11 . A discharge space between the upper substrate  20  and the lower substrate  10  is partitioned into discharge cells  14  on an upper surface of the first dielectric layer  12 . A plurality of partitions  13  are located on the first dielectric layer  12  at constant intervals, so as to prevent electrical and optical interference between the discharge cells  14 . A phosphor layer  15  of red R, green G and blue B is coated on an inner surface of the discharge cells  14  to a desired thickness, and the discharge cells  14  are filled with a discharge gas. 
   The upper substrate  20  is a transparent substrate mainly made of glass through which visible rays can transmit through. The upper substrate  20  is coupled to the lower substrate  10  with the partitions  13  located on top of the upper substrate  20 . Pairs of sustain electrodes  21   a  and  21   b  are located in the shape of stripe along a direction perpendicular to the address electrodes  11  and under the upper substrate  20 . The sustain electrodes  21   a  and  21   b  are made of transparent conductive material, such as indium tin oxide (ITO) allowing for visible rays to pass through. In order to reduce a line resistance along the sustain electrodes  21   a  and  21   b , bus electrodes  22   a  and  22   b  made of metal material are located under a lower surface of each sustain electrode  21   a  and  21   b , and have a width narrower than that of the sustain electrodes  21   a  and  21   b . The sustain electrodes  21   a  and  21   b  and the bus electrodes  22   a  and  22   b  are covered by a second dielectric layer  23 . A protective layer  24  is formed over the second dielectric layer  23  and is generally made of MgO. Protective layer  24  serves to prevent the second dielectric layer  23  from being sputtered by plasma particles. Protective layer  24  also serves to lower a discharge voltage by emitting secondary electrons. 
   The PDP  30  configured as described is limited in the amount of phosphor material that can be deposited in the discharge cells. In addition, there is a problem in that since the ultraviolet rays produced in the discharge cell can not be uniformly transmitted to the phosphor layer, thus limiting brightness and luminous efficiency of the PDP  30 . Also, there is another problem in that since the distance between the address electrode and the sustain electrode is relatively large, the voltage applied to the address electrode must be high to achieve an address discharge. 
   Turning now to  FIGS. 3 through 5 ,  FIG. 3  is an exploded perspective view of a PDP  100  according to a first embodiment of the present invention,  FIG. 4  is a cross-sectional view of the PDP  100  of  FIG. 3  and  FIG. 5  is a perspective view depicting electrodes employed in the PDP  100  of  FIG. 3 . For the sake of clarity, a second dielectric layer  123 , a phosphor layer  115 , and a line connecting the electrodes are not illustrated in  FIG. 3  even though these features are part of the design of PDP  100 . 
   Referring to  FIGS. 3 through 5 , a lower substrate  110  and an upper substrate  120  are arranged opposite to each and spaced apart by a certain distance. A discharge space is located between the lower substrate  110  and the upper substrate  120 . The lower substrate  110  and the upper substrate  120  are generally made of glass. 
   A plurality of address electrodes  111  are located on an upper surface of the lower substrate  110 . The address electrodes  111  can have the shape of a band (or stripe) as illustrated of  FIG. 5 . Alternatively, an address electrode  111 ′ can have a rectangular plate shape with an aperture located at the center thereof, as illustrated of  FIG. 6 . The address electrodes  111  are covered by a first dielectric layer  112  located on the upper surface of the lower substrate  110 . 
   A plurality of partitions  113  are located on an upper surface of the first dielectric layer  112  and are formed to have a desired height to partition the discharge space between the lower substrate  110  and the upper substrate  120  into a plurality of discharge cells  114 . The partitions  113  serve to prevent electrical and optical interference between neighboring discharge cells  114 . 
   A plurality of first sustain electrodes  121  are sandwiched between the upper surfaces of the partitions  113  and the lower surface of the upper substrate  120 . The first sustain electrodes  121  form closed loops above the upper surfaces of the partitions  113 , each closed loop corresponding to a discharge cell  114 . Dielectric substance is interposed between the first sustain electrodes  121 . The first sustain electrode  121  can be have a rectangular case shape electrode, as illustrated of  FIG. 5 . 
   A second dielectric layer  123  is located between the upper surface of the partitions  113  and the lower surface of the upper substrate  120 . The second dielectric layer  123  also covers inner surfaces of the first dielectric electrodes  121 . A protective film (not illustrated) covers the second dielectric layer  123  to prevent the second dielectric layer  123  from being exposed to and damaged by plasma particles. This protective film that covers second dielectric layer  123  also allows for application of a lower discharge voltage by emitting secondary electrons. Preferably, the protective film is made of MgO. 
   A protrusion  116  made of a dielectric material extends to a desired height from the upper surface of the first dielectric layer  112 . The protrusion  116  can be have a closed loop shape, and a second sustain electrode  117  of a closed loop corresponding to the first sustain electrode  121  is located on an upper surface of the protrusion  116 . Alternatively, the protrusion  116  can be omitted and the second sustain electrode  117  can be located directly on the upper surface of the first dielectric layer  112  and still be within the scope of the present invention. 
   The second sustain electrode  117  can have a rectangular plate shape with an aperture located at the center thereof, as illustrated of  FIG. 5 . A third dielectric layer  118  is located on the upper surface of the protrusion  116  to cover the second sustain electrode  117 . A protective film (not illustrated) can be located on top of the third dielectric layer  118 . 
   A phosphor layer  115  is located on the upper surface of the first dielectric layer  112  and on sidewalls of partitions  113  used to form an inner wall of the discharge cells  114 . The phosphor layer  115  can also be located on inner and outer walls of the protrusion  116 . Further, phosphor layer  115  can be located at a lower surface of the upper substrate  120 . As a result, there is much more surface area for phosphor material to be deposited on for each discharge cell  114  of PDP  100  than in the PDP  30  of  FIGS. 1 ,  2 A and  2 B 
   Turning now to  FIG. 7 ,  FIG. 7  is a perspective view depicting electrodes of a different shape that can be employed in a PDP  100  according to a variation of the first embodiment of the present invention. Referring to  FIG. 7 , a first sustain electrode  121 ′ can have a cylindrical shape instead of the rectangular case shape of  FIGS. 5 and 6 . Second sustain electrode  117 ′ can have a disk shape instead of the rectangular plate shape of  FIGS. 5 and 6 . The address electrode  111  can have a band shape. Meanwhile, as illustrated of  FIG. 8 , the address electrode  111 ″ can have a disk shape having an aperture located at the center thereof. 
   Although the variations of the first embodiment show the first sustain electrode as having either a rectangular case shape or a cylindrical shape, in no way is the present invention so limited to these designs. Likewise, the second sustain electrode can also have other various shapes of a plate with an aperture located at the center thereof, besides the rectangular plate shape electrode  117  or the disk shape electrode  117 ′. Similarly, the address electrode can also have other various shapes of a plate with an aperture located at the center thereof instead of the band shape electrode  111 , the rectangular plate shape electrode  111 ′ and the disk shape electrode  111 ″. 
   With the PDP  100  configured as described above, a sustain discharge is generated between the first sustain electrode  121  or  121 ′ and the second sustain electrode  117  or  117 ′. With the designs of  FIGS. 3 through 8  according to the first embodiment of the present invention, since the first sustain electrodes  121  and  121 ′ have a case or a cylindrical shape, and the second sustain electrodes  117  and  117 ′ have a plate shape with an aperture located at the center thereof, the characterization of the sustain discharge is a combination of both the facing type and the surface type. As a result, ultraviolet rays produced by this hybrid type discharge uniformly transmits to the phosphor layer  115  located on the inner wall of the discharge cell  114 , resulting in improved brightness and improved luminous efficiency over the PDP  30  design of  FIGS. 1 ,  2 A and  2 B. 
   Also, with the designs of  FIGS. 3 through 8  according to the first embodiment of the present invention, the address discharge is generated between the address electrode  111 ,  111 ′ or  111 ″ and the second sustain electrode  117  or  117 ′ of a pair of sustain electrodes. When the address electrode takes on a band shape as in  FIGS. 5 and 7 , the address discharge is generated between the center region of the second sustain electrode  117  or  117 ′ and the address electrode  111 . When the address electrodes have a plate-like shape as in  FIGS. 6 and 8 , the address discharge is generated in the same shape as that of the second sustain electrode  117  or  117 ′ and the address electrode  111 ′ or  111 ″. In either case, the distance between the address electrode  111 ,  111 ′ or  111 ″ and the second sustain electrode  117  or  117 ′ in the PDPs according to the first embodiment of the present invention is smaller than that of PDP  30  of  FIGS. 1 ,  2 A and  2 B. By decreasing this distance between the address electrode and the second sustain electrode, an address discharge can occur with less applied voltage than in the case of the PDP  30  of  FIGS. 1 ,  2 A and  2 B. Also, reset discharge can be generated between the address electrode  111 ,  111 ′ or  111 ″ and the second sustain electrode  117  or  117 ′, which can improve contrast. 
   In the PDP  100  of  FIGS. 3 through 8 , since the phosphor layer  115  can be located on the inner and outer walls of the protrusion  116 , on the lower surface of the upper substrate  120 , on the upper surface of the first dielectric layer  112  and on the side of the partitions  113 , more phosphor material can be placed inside each discharge cell  114  compared to the PDP  30  of  FIGS. 1 ,  2 A and  2 B. This increase in the amount of phosphor material in each discharge cell results in an increase in the amount of visible rays produced during a discharge. Another benefit of the PDP according to the first embodiment is that a larger percentage of visible light produced can be actually viewed. This improvement in luminance efficiency is brought about by having no dielectric layer formed on the upper substrate  120 , allowing for a larger percentage of visible rays produced within the discharge cells  114  to transmit through the upper substrate  120  where they can be viewed without having to go through a separate dielectric layer. 
   Comparing the PDP  100  of  FIGS. 3 through 5  and variations thereof in  FIGS. 6 through 8  according to the first embodiment of the present invention with the PDP  30  of  FIGS. 1 ,  2 A and  2 B, the luminous efficiency of the present PDP  100  is improved by about 38% compared to that of PDP  30 . Also, the discharge start voltage of the present PDP  100  is lowered by about 32% compared to that of PDP  30 . 
   Turning now to  FIGS. 9 through 11 ,  FIGS. 9 through 11  illustrate views of PDP  200  according to a second embodiment of the present invention, where  FIG. 9  is an exploded view of PDP  200 ,  FIG. 10  is a cross sectional view of PDP  200  and  FIG. 11  is a perspective view of the electrodes used in PDP  200  of  FIGS. 9 and 10 . 
   Referring to  FIGS. 9 through 11 , a lower substrate  210  and an upper substrate  220  are arranged opposite to each other and separated from each other by a certain distance. A discharge space is located between the lower substrate  210  and the upper substrate  220 . A plurality of address electrodes  211  are located on an upper surface of the lower substrate  210 , and a first dielectric layer  212  is formed over the address electrodes  211  to cover the address electrodes  211 . The address electrodes  211  can have the shape of a band, as illustrated of  FIG. 11 . Alternatively, an address electrode  211 ′ can have a rectangular plate shape having an aperture located at the center thereof, as illustrated of  FIG. 12 . A plurality of partitions  213  are located on an upper surface of the first dielectric layer  212  to partition the discharge space between the two substrates into a plurality of discharge cells  214 . 
   A plurality of first sustain electrodes  221  are located on a lower surface of the upper substrate  220 . The first sustain electrodes  221  is formed to have the shape of a closed loop and are formed on top of an upper surface of the partitions  213 , each closed loop corresponding to a different discharge cell  214 . The first sustain electrodes  221  can have a rectangular plate shape with an aperture located at the center thereof, as illustrated of  FIG. 11 . The first sustain electrode  221  can be made of indium tin oxide (ITO), which is a transparent conductive material. A plurality of bus electrodes  222  made of an opaque, highly conductive metal can be located at an outside edge of the first sustain electrode  221  to reduce a line resistance of the first sustain electrode  221  that is made of a lesser conductive but transparent ITO. 
   A second dielectric layer  223  is formed on the lower surface of the upper substrate  220  and covers both the first sustain electrodes  221  and the bus electrodes  222 . Preferably, the second dielectric layer  223  is made of transparent material to allow visible rays generated in the discharge cells to pass through and be viewed by a viewer on the outside. A protective film  224  can be formed over the second dielectric layer  223  to prevent the second dielectric layer  223  from being sputtered and thus damaged by plasma particles. Protective film  224  also serves to reduce a discharge voltage by emitting secondary electrons. Preferably, the protective film  224  is made of MgO. 
   A protrusion  216  made of dielectric material extends to a desired height in each discharge cell  214  from the upper surface of the first dielectric layer  212 . The protrusion  216  can have the shape of a closed loop, and a second sustain electrode  217  can be formed on top of the protrusion and thus also have the shape of a closed loop that corresponds to the closed loops of the first sustain electrode  221 . Alternatively, the second sustain electrode  217  can be formed directly on the first dielectric layer  212 . In such a scenario, no protrusion  216  is formed on the first dielectric layer  212 . This is to say, the second sustain electrodes are arranged between the upper substrate  220  and the lower substrate  210 . 
   The second sustain electrode  217  can have the shape of a rectangular plate with an aperture located at the center thereof, as illustrated of  FIG. 11 . A third dielectric layer  218  can be formed on the upper surface of the protrusion  216  to cover the second sustain electrode  217 . A protective film (not illustrated) can be further be formed to cover the third dielectric layer  218 . 
   In the second embodiment of the present invention, a phosphor layer  215  can be located on the upper surface of the first dielectric layer  212  and on sidewalls of the partitions  213  that forms an inner walls of the discharge cells  214 . The phosphor layer  215  can also be located on inner and outer walls of the protrusions  216 , allowing for more surface area and thus more phosphor material to be deposited in each discharge cell  214  than in the PDP  30  of  FIGS. 1 ,  2 A and  2 B. 
   Turning now to  FIG. 13 ,  FIG. 13  is a perspective view depicting a variation in design of the shape of the electrodes that can be used in the PDP  200  of  FIG. 9  according to the present invention. Referring to  FIG. 13 , a first sustain electrode  221 ′ has a disk shape with an aperture located at the center thereof. With the configuration of  FIG. 13 , a bus electrode  222 ′ can be located at an outer periphery of the first sustain electrode  221 ′. A second sustain electrode  217 ′ also has a disk shape with an aperture located at the center thereof. The address electrode  211  can have a band shape. However, in another variant as illustrated of  FIG. 14 , the address electrode  211 ″ can instead have a disk shape with an aperture located at the center thereof. 
   Although the first sustain electrode is described as having either a rectangular plate shape or a disk shape, the present invention is in no way so limited, as the first sustain electrode can have other shapes and still be within the scope of the present invention. Likewise, although the present invention describes the second sustain electrode as having either a rectangular plate shape or a disk shape, the present invention is in no way so limited, as the first sustain electrode can have other shapes and still be within the scope of the present invention. Again likewise, although the present invention describes the address electrode as having either a band shape, a rectangular plate shape or a disk shape, the present invention is in no way so limited as the address electrode can have other shapes and still be within the scope of the present invention. 
   With the PDP  200  configured as described above, a sustain discharge is generated between the first sustain electrode  221  or  221 ′ and the second sustain electrode  217  or  217 ′. Because the sustain discharge is generated in a surface-type manner for this second embodiment, luminous efficiency is improved. With the PDP  200  as designed according to this second embodiment, the address discharge voltage can be lowered, and more phosphor material can be placed within each discharge cell  214 . 
   In conclusion, the PDPs according to the present invention have the following beneficial effects. First, since a sustain discharge is generated between the first and second sustain electrodes in either a mixed facing and surface discharge manner or in just a surface-type discharge manner, the ultraviolet radiation generated by these discharges uniformly transmits to the phosphor layer located on the inner wall of the discharge cell, which leads to improved brightness and improved luminous efficiency. Second, since a distance between the address electrode and the second sustain electrode in the embodiments of the present invention is smaller than that of PDP  30  of  FIGS. 1 ,  2 A and  2 B, the address discharge voltage can be lowered. Also, reset discharge is also generated between the address electrode and the second sustain electrode, which can improve contrast. Finally, since more phosphor material can be arranged inside each discharge cell in the embodiment of the present invention as opposed to the PDP  30  of  FIGS. 1 ,  2 A and  2 B, more visible rays are generated. 
   While the present invention has been particularly illustrated and described with reference to exemplary embodiments depicted in the drawings, it will be understood by those of ordinary skill in the art that various changes and modifications in form and details can be made therein without departing from the spirit and scope of the present invention.