Patent Publication Number: US-7211953-B2

Title: Plasma display device having portion where electrical field is concentrated

Description:
This disclosure is a continuation of U.S. patent application Ser. No. 09/533,787, filed Mar. 24, 2000, now U.S. Pat. No. 6,531,820. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a plasma display device, and more particularly, to a plasma display device having an improved dielectric layer in which a maintenance electrode is embedded and a method of manufacturing the same. 
   2. Description of the Related Art 
   A general discharging device includes at least a pair of electrodes and discharge is generated when a voltage is applied to the electrodes. As an example of the discharging device, there is a discharge lamp such as a fluorescent lamp, a gas laser generating apparatus, and a plasma display device. 
   Due to superior display performance such as large display capacity, high brightness, high contrast, and wide viewing angle, the plasma display device is widely recognized as a flat panel display panel having a performance close to a cathode ray tube. 
   Plasma display devices are classified as a direct current plasma display device panel and an alternating current plasma display panel according to operation principle. Also, the plasma display device is divided into an opposing discharge type and a surface discharge type according to the configuration of the electrodes. 
     FIG. 1  is a view showing an example of a surface discharge type plasma display device. 
   As shown in the drawing, a plasma display device includes a substrate  10 , an address electrode  11  on the substrate  10 , a dielectric layer  12  on the substrate  10  where the address electrode  11  is located, a partition  13  on the dielectric layer  12  for maintaining a discharge distance and preventing electrical and optical cross talk between cells, and a front substrate  16  coupled to the substrate where the partition  13  is located and having maintaining electrodes  14  and  15  in a predetermined pattern on the bottom surface, crossing the address electrode  11 . A fluorescent layer  17  is located at at least one side inside a discharge space sectioned by the partition  13 . A dielectric layer  18  and a protective layer  19  in which the electrodes are embedded are located on the bottom surface of the front substrate  16 . A discharge gas mixed with neon (Ne) and xenon (Xe) is injected into the discharge space. 
   In the plasma display device having the above structure, driving methods are divided into driving for an address discharge and driving for a maintaining discharge. The address discharge is generated due to an electrical field between the address electrode  11  and the maintaining electrode  14  (80V−(−170V)=250V). At this time, wall charges are formed. The maintaining discharge is generated due to a difference in electrical potential between the maintaining electrodes  14  and  15  disposed at the discharge space where wall charges are formed. The maintaining discharge becomes a main discharge for displaying an actual image. 
   The maintaining discharge generated due to a difference in electrical potential applied between the maintaining electrodes  14  and  15  becomes weak as time passes. This is because the initial discharge voltage must be over 160 V, in general, since the distance between the maintaining electrodes  14  and  15  is about 80–100 μm in an electrode structure of a conventional surface discharge type AC plasma display panel. 
   When the initial discharge voltage becomes great, much electrical power is consumed and simultaneously the rated capacity of a driving circuit becomes great. Also, induced potential is generated to an adjacent electrode, which causes cross talk. When the distance between the maintaining electrodes  14  and  15  is narrowed to lower the initial discharge voltage, the electrostatic capacity becomes too large. 
   Alternatively, the quantity of Xe in the discharge gas is increased to increase the efficiency of discharge. However, since the initial discharge voltage becomes great, there is a limit in increasing the quantity of Xe. 
   A surface discharge type plasma display device to solve the above problems is disclosed in U.S. Pat. No. 5,742,122. In the surface discharge type plasma display device, as shown in  FIG. 2 , the thickness T 1  of a dielectric layer  23  on an upper surface of a transparent electrode  22  of a first substrate  21  is thinner than the thickness T 2  of the dielectric layer  23  corresponding to a bus electrode  24  on and parallel to the transparent electrode  22 . 
   In the above surface discharge type plasma display device, by removing ineffective discharge on the bus electrode  24 , the efficiency of light emission can be improved while reducing power consumption and preventing cross talk between pixels. However, since the dielectric layer  23  has a uniform thickness on an upper surface of the transparent electrode, there is a limit in reducing the initial discharge voltage. 
   SUMMARY OF THE INVENTION 
   To solve the above problems, it is an objective of the present invention to provide a plasma display device in which an electrical field is concentrated on a predetermined position between maintaining electrodes or at an area corresponding to the maintaining electrode so that the initial discharge voltage is reduced and a method of forming a dielectric layer having a portion where an electrical field is concentrated. 
   It is another objective of the present invention to provide a method of manufacturing a plasma display device in which the quantity of Xe in a discharge gas is increased to improve the efficiency of light emission and a dielectric layer having a portion where an electrical field is concentrated in the plasma display device. 
   Accordingly, to achieve the above objective, there is provided a plasma display device which comprises a first substrate, an address electrode formed on an upper surface of the fist substrate, a first dielectric layer formed on the upper surface of the first substrate and embedding the address electrode, a second substrate which is transparent and forms a discharge space by being coupled to the first substrate, a plurality of maintaining electrodes formed on a lower surface of the second substrate to form a predetermined angle with the address electrode, each of the maintaining electrodes including first and second electrodes, a second dielectric layer formed on the second substrate where the maintaining electrodes are formed and embedding the maintaining electrodes, at least a portion where an electrical field is concentrated formed between the first and second electrodes constituting the maintaining electrodes, and a partition installed between the first and second substrates for sectioning the discharge space. 
   It is preferred in the present invention that said portion where an electrical field is concentrated includes a groove formed between said first and second electrodes, and that said groove is formed between said first and second electrodes in a discontinuous pattern. 
   To achieve another aspect of the above objective, there is provided a plasma display device which comprises a first substrate, an address electrode formed on an upper surface of the fist substrate, a first dielectric layer formed on the upper surface of the first substrate and embedding the address electrode, a second substrate which is transparent and forms a discharge space by being coupled to the first substrate, a plurality of maintaining electrodes formed on a lower surface of the second substrate to form a predetermined angle with the address electrode, each of the maintaining electrodes including first and second electrodes, a second dielectric layer formed on the second substrate where the maintaining electrodes are formed and embedding the maintaining electrodes, at least one portion where an electrical field is concentrated formed at an area corresponding to the first and second electrodes constituting the maintaining electrodes, and a partition installed between the first and second substrates for sectioning the discharge space. 
   To achieve the second objective, there is provided a method of manufacturing a dielectric layer having a portion where an electrical field is concentrated of a plasma display device, which is accomplished by forming a plurality of maintaining electrodes on an upper surface of a substrate, each of the maintaining electrodes being constituted by a pair of first and second electrodes, forming a lower dielectric layer on an upper surface of the substrate where the maintaining electrodes are formed, printing an upper dielectric layer for forming a groove in a continuous or discontinuous pattern at a portion on an upper surface of the lower dielectric layer and between the first and second electrodes, and curing the upper and lower dielectric layers by burning the same. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objectives and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
       FIG. 1  is an exploded perspective view illustrating a conventional plasma display device having a partially cut-away portion; 
       FIG. 2  is an exploded perspective view illustrating another example of a conventional plasma display device; 
       FIG. 3  is an exploded perspective view illustrating a plasma display device according to the present invention; 
       FIG. 4  is a perspective view showing a state in which a portion where an electrical field is concentrated on a dielectric layer on a second substrate; 
       FIG. 5  is a perspective view showing a state in which another example of the portion where an electrical field is concentrated on a dielectric layer on a second substrate; 
       FIG. 6  is an exploded perspective view illustrating another preferred embodiment of the plasma display device according to the present invention; 
       FIG. 7  is a perspective view showing a state in which a portion where an electrical field is concentrated on the dielectric layer on the second substrate; 
       FIG. 8  is a sectional view showing a state in which a portion where an electrical field is concentrated on the dielectric layer formed on the second substrate; 
       FIGS. 9 through 11  are sectional views showing operational states of a plasma display device according to the present invention; 
       FIGS. 12A through 12C  are sectional views for explaining a method of manufacturing the dielectric layer having a portion where an electrical field is concentrated according to a preferred embodiment of the present invention; and 
       FIGS. 13A through 13C  are sectional views for explaining a method of manufacturing the dielectric layer having a portion where an electrical field is concentrated according to another preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  shows a plasma display device according to a preferred embodiment of the present invention. As shown in the drawing, the plasma display device according to the present invention includes a first substrate  31 , address electrodes  32  in a predetermined pattern on an upper surface of the first substrate  32 , and a first dielectric layer  33  on the first substrate  31  where the address electrodes  32  are embedded. The address electrodes  32 , each having a predetermined width, are parallel strips. 
   The first substrate  31  is coupled to a transparent second substrate  41  to thereby form a discharge space. A plurality of maintaining electrodes  42 , with several pairs of first and second electrodes  42   a  and  42   b  perpendicular to the address electrodes  32 , are located on a lower surface of the second substrate  41  facing the first substrate  31 . Here, the maintaining electrodes  42  need not be perpendicular to the address electrodes  32  and the distance between the first and second electrodes  42   a  and  42   b  can be adjusted considering the initial discharge voltage or pixels. The first and second electrodes  42   a  and  42   b  are transparent indium tin oxide (ITO) and bus electrodes  42   c  and  42   d  are located along the first and second electrodes  42   a  and  42   b , respectively, to reduce line resistance. The bus electrodes  42   c  and  42   d  are a metal such as silver, silver alloy, or aluminum and are much narrower than the first and second electrodes  42   a  and  42   d.    
   A second dielectric layer  43  covers the lower surface of the second substrate  41  where the maintaining electrodes  42  are embedded. Partitions  45  for sectioning a discharge space are located between the first and second substrates  31  and  41  on which the first and second dielectric layers  33  and  43  are located, respectively. The partitions  45  are parallel to the address electrodes  32 . A fluorescent film  46  is located on a lower surface of a discharge space sectioned by the partitions  45 . The partitions  45  are not limited to the above-described preferred embodiment and any structure in which the discharge space is sectioned in a pixel array pattern is possible. 
   A discharge gas is injected into a discharge space sectioned by the partition  45 . The discharge gas includes Ne and Xe. 
   A portion where an electrical field is concentrated  50  is located between the first and second electrodes  42   a  and  42   b  to lower the initial discharge voltage. The portion  50  where the electrical field is concentrated  50  includes at least one groove  51  having a predetermined depth in the second dielectric layer  43 , between the first and second electrodes  42   a  and  42   b . The groove  51  can have a continuous pattern or a discontinuous pattern, as shown in  FIG. 4 . When the groove  51  has a discontinuous pattern, the groove  51  is preferably disposed inside the discharge space sectioned by the partition  45 . A protective film  44  for protecting the second dielectric layer  43  from ions is located on an upper surface of the second dielectric layer  43  where the groove  51  is located. The protective film  44  is MgO. 
   As another preferred embodiment of the portion  50  where an electrical field is concentrated, as shown in  FIG. 5 , a groove  52  can expose the second substrate  41  between the first and second electrodes  42   a  and  42   b . It is preferable in this embodiment that the protective film  44  on the upper surface of the second dielectric layer  43  be located on the surface of the second dielectric layer  43  and the upper surface of the second substrate  41  be exposed by the groove  52 . Here, although not shown in the drawing, the groove  52  can have a plurality of rows. 
     FIG. 6  shows a plasma display device a portion where an electrical field is concentrated according to another preferred embodiment of the present invention. Here, the same reference numerals as those in the description of the above preferred embodiment indicate the same elements. As shown in the drawing, a portion  60  where an electrical field is concentrated is located on the upper surfaces of the first and second electrodes  42   a  and  42   b . In the portion  60  where an electrical field is concentrated, a groove  61  having a predetermined depth is located at at least one side of the second dielectric layer  43  which corresponds to the first and second electrodes  42   a  and  42   b . The groove  61  can have a continuous pattern or a discontinuous pattern. A protective film  44  is located on the upper surface of the second dielectric layer  43  where the groove  61  is located. 
   As another preferred embodiment of the portion where an electrical field is concentrated, at least one through-hole  62  is located at at least one side of the first dielectric layer  44  to correspond to the first and second electrodes  42   a  and  42   b , such that the first and second electrodes  42   a  and  42   b  are exposed. The through-hole  62  may have a circular or an oval shape. When the portion  60  where an electrical field is concentrated is located in the through-hole  62 , the through-hole  62  should be located inside the discharge space sectioned by the partition. A protective film  44  is located on the upper surface of the second dielectric layer  43  and the upper surfaces of the first and second electrodes  42   a  and  42   b  which are exposed by the through-hole  62 , as shown in  FIG. 8 . 
   The plasma display device having the above structure according to the present invention operates as follows. 
   When a predetermined pulse voltage is applied to any of the address electrode  32  and the first and second electrodes  42   a  and  42   b  constituting the maintaining electrode  42 , an address discharge is generated therebetween and wall charges are formed on the inner surface of the discharge space. The generated wall charges fill the groove  51  in the second dielectric layer  43  between the first and second electrodes  42   a  and  42   b  or in the second dielectric layer  43  on the first and second electrodes. In this condition, when a voltage is applied to the first and second electrodes  42   a  and  42   b , a maintaining discharge is generated therebetween. The initial discharge voltage for the maintaining voltage can be lowered by the groove  51  and the charges therein. 
   In particular, when the distance between the first and second electrodes  42   a  and  42   b  decreases, the electrostatic capacitance becomes greater, whereas, when the distance between the first and second electrodes  42   a  and  42   b  increases, the initial discharge voltage becomes higher. As shown in  FIGS. 9 and 10 , when the groove  51  is formed and the second dielectric layer  43  between the first and second electrodes  42   a  and  42   b  is removed or becomes thinner, the electrical field between the first and second electrodes  42   a  and  42   b  is concentrated on the groove  51 . Then, a discharge is generated from the groove  51  which is filled with charge and gas so that the initial discharge voltage can be lowered without increasing the electrostatic capacitance. When the groove  51  is formed without a decrease in the distance between the first and second electrodes  42   a  and  42   b , the effect is a decrease in the distance between the first and second electrodes  42   a  and  42   b  and thus the initial discharge voltage is lowered. In particular, a discharge gas including Xe in a concentration of 0.1–10% which is injected into the discharge space to achieve a highly efficient discharge causes an increase in the initial discharge voltage. Such an increase can be compensated for by the structure of the groove  51  located between the first and second electrodes  42   a  and  42   b . Ultraviolet light generated during the maintaining discharge excites the fluorescent material to emit light so that an image is formed. 
   It is obvious that the same operation and function as described above can be obtained when grooves  61  and  62  are located above the first and second electrodes  42   a  and  42   b , as shown in  FIG. 11 . 
   The method of manufacturing a plasma display device according to the present invention includes forming the second dielectric layer  43  where the portion where an electrical field is concentrated is formed. 
     FIGS. 12A through 12C  show the method of forming the dielectric layer at the portion where an electrical field is concentrated. As shown in the drawing, the transparent substrate  41  is prepared (Step  1 ). A plurality of maintaining electrodes  42 , each including a pair of the first and second electrodes, is formed on the upper surface of the substrate  41  (Step  2 ; see  FIG. 12A ). A lower dielectric layer  43   a  is formed on the upper surface of the substrate  41  where the maintaining electrodes  42  are located (Step  3 ; see  FIG. 12B ). An upper dielectric layer  43   b  is printed on the upper surface of the lower dielectric layer  43   a  such that a groove can be formed between the first and second electrodes or on the first and second electrodes (Step  4 ; see  FIG. 12C ). The upper and lower dielectric layers  43   a  and  43   b  are cured after being completely formed (Step  5 ). The above method of forming the portion where an electrical field is concentrated on the dielectric layer makes it possible for the groove in the portion where an electrical field is concentrated to have a fine pattern. 
     FIGS. 13A through 13C  show another preferred embodiment of the method of forming the dielectric layer including a portion where an electrical field is concentrated. 
   As shown in the drawing, a transparent substrate  41  is prepared (Step  1 ). A plurality of maintaining electrodes  42 , each including a pair of the first and second electrodes, are formed on the upper surface of the substrate  41  (Step  2 ; see  FIG. 13A ). A dielectric layer is formed on the upper surface of the substrate  41  where the maintaining electrodes  42  are located (Step  3 ; see  FIG. 13B ). The dielectric layer  43  is made soft by being heated to a predetermined temperature (Step  4 ). A groove is formed in the softened dielectric layer by pressing with a mold  70 , including a protrusion  71  of a pattern corresponding to that of the desired groove is formed, against the upper surface of the softened dielectric layer (Step  5 ; see  13 C). The above method is suitable for mass production since the groove can be formed by pressing a mold against the softened dielectric layer. 
   As described above, in the method of manufacturing a plasma display device according to the present invention, the portion where an electrical field is concentrated is formed in the dielectric layer between the first and second electrodes. Thus, the initial discharge voltage according to the maintaining discharge can be lowered. As a result, power consumption of the plasma display device can be reduced. 
   It is noted that the present invention is not limited to the preferred embodiment described above, and it is apparent that variations and modifications by those skilled in the art can be effected within the spirit and scope of the present invention defined in the appended claims.