Patent Publication Number: US-2006001611-A1

Title: Plasma display panel

Description:
BACKGROUND OF THE INVENTION  
      This application claims the priority of Korean Patent Application No. 10-2004-0050804, filed on Jun. 30, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
      1. Field of the Invention  
      The present invention relates to a plasma display panel, and more particularly, to a plasma display panel having a structure capable of improving a color temperature characteristic.  
      2. Description of the Related Technology  
      In general, in a plasma display panel, a glow discharge is generated by applying a predetermined voltage to electrodes installed in a sealed space filled with a gas. Thereafter, a phosphor layer formed in a predetermined pattern is excited by ultraviolet rays, generated due to the glow discharge, and displays an image.  
      Plasma display panels can be classified into direct current (DC) plasma display panels, alternating current (AC) plasma display panels, and hybrid plasma display panels according to their driving methods. In addition, the plasma display panel can be classified into two-electrode plasma display panels and three-electrode plasma display panels according to the number of electrodes they include. A DC plasma display panel includes an auxiliary electrode in order to induce an auxiliary discharge, and an AC plasma display panel includes an address electrode for improving an address speed by providing an address discharge and a sustain discharge. Also, AC plasma display panels can be classified into opposing discharge plasma display panels and surface discharge plasma display panels according to the arrangement of the electrodes performing the discharge. An AC opposing discharge includes two sustain electrodes for forming the discharge, the sustain electrodes being disposed on two substrates, respectively, to generate the discharge perpendicularly to the panel. An AC surface discharge plasma display panel includes two sustain electrodes that are disposed on one substrate to generate the discharge on a surface of the substrate.  
       FIG. 1  shows an example of a sub-pixel formed on a conventional surface discharge three-electrode type plasma display panel.  
      Referring to  FIG. 1 , in the sub-pixel  10 , pairs of sustain electrodes  12  including X electrodes  13  and Y electrodes  14 , which are separated from each other to form discharge gaps, are formed on a lower surface of an upper substrate  11 . The X and Y electrodes  13  and  14  function as a common electrode and a scan electrode, respectively. The X and Y electrodes  13  and  14 , respectively, include transparent electrodes  13   a  and  14   a  and bus electrodes  13   b  and  14   b  formed on lower surfaces of the transparent electrodes  13   a  and  14   a  to apply voltages. The pairs of sustain electrodes  12  are embedded in an upper dielectric layer  15 , and a protective layer  16  is formed under the upper dielectric layer  15 .  
      A lower substrate  21  faces the upper substrate  11 , and address electrodes  22  are formed on the lower substrate  21 . The address electrodes  22  are embedded in a lower dielectric layer  23 . Barrier ribs  24  are formed on the lower dielectric layer  23 , and a phosphor layer  25  is formed in spaces defined by the barrier ribs  24 . A discharge gas is injected into the sub-pixel  10  having the above structure.  
      Operations of the plasma display panel including the sub-pixels  10  having the above structure will be described.  
      When an address voltage is applied between the address electrode  22  and the Y electrode  14 , an address discharge occurs, and accordingly, predetermined wall charges are generated in the addressed sub-pixel  10 . In addition, a sustain voltage is applied between the X electrode  13  and the Y electrode  14  to generate a sustain discharge. The electric charges generated by the discharge collide with the discharge gas, plasma is generated due to the collisions, and accordingly, ultraviolet rays are generated by the plasma. The phosphor layer  25  is excited by the ultraviolet rays, and then, emits visible lights to display an image.  
      One of red, green, and blue color phosphor materials is disposed in the sub-pixel for displaying colors, thus the sub-pixels  10  can be divided into red sub-pixels  10 R, green sub-pixels  10 G, and blue sub-pixels  10 B as shown in  FIG. 2 . Three of the red, green, and blue sub-pixels  10 R,  10 G, and  10 B form a unit pixel  30 , and various colors can be displayed by combining three primitive colors. In more detail, if brightnesses of the red, green, and blue lights emitted from the red, green, and blue sub-pixels  10 R,  10 G, and  10 B are, respectively, divided into, for example, 256 grades and the divided red, green, and blue lights are combined, about 16,770,000 colors can be displayed from the unit pixel  30 .  
      However, generally under the same conditions, the maximum brightness level of the green light is the highest, and the maximum brightness level of blue light is the lowest. Since the blue light has the lowest maximum brightness level, a color temperature of white light that is represented by combining the red, green, and blue lights of maximum brightnesses is low, and thus the maximum brightness of the mixed light is reduced.  
      Therefore, there has been a need to effectively compensate for the lowest maximum brightness level of the blue light.  
     SUMMARY OF CERTAIN INVENTIVE ASPECTS  
      One aspect of the present invention provides a plasma display panel, in which each unit pixel includes a red, a green, and a blue sub-pixel and an additional sub-pixel that has the same brightness level as the sub-pixel having the lowest maximum brightness level among the red, green, and blue sub-pixels, in order to improve color temperature characteristics of the panel and maximize brightness of the light emitted by the unit pixels.  
      Another aspect of the present invention provides a plasma display panel including: an upper substrate, a lower substrate facing the upper substrate, an upper dielectric layer formed on the upper substrate, a lower dielectric layer formed on the lower substrate and facing the upper dielectric layer, barrier ribs formed between the upper and lower substrates, and defining red, green, and blue sub-pixels, each sub-pixel including one of red, green, and blue phosphor layers, upper discharge electrodes embedded in the upper dielectric layer, disposed to correspond to the sub-pixels, extending in the same direction and being separated from each other, lower discharge electrodes embedded in the lower dielectric layer, disposed to correspond to the sub-pixels, extending in a direction crossing the upper discharge electrodes, and being separated from each other; and unit pixels respectively including a set of four sub-pixels, which are divided into two subsets to be disposed at the adjacent two upper discharge electrodes respectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments of the present invention will be described with reference to the attached drawings.  
       FIG. 1  is a cross-sectional view of a sub-pixel according to the conventional art.  
       FIG. 2  is a partial plan view of a unit pixel including sub-pixels according to  FIG. 1 .  
       FIG. 3  is a partial perspective view of a plasma display panel according to an embodiment of the present invention.  
       FIG. 4  is a cross-sectional view of the plasma display panel taken along line IV-IV of  FIG. 3 .  
       FIG. 5  is a partial plan view of an example of an arrangement of the sub-pixels of  FIG. 3  to form a unit pixel.  
       FIG. 6  is a partial plan view of another example of the arrangement of the sub-pixels of  FIG. 3  to form the unit pixel.  
       FIG. 7  is a partial plan view of still another example of the arrangement of the sub-pixels of  FIG. 3  to form the unit pixel. 
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS  
       FIG. 3  is a partial perspective view of a plasma display panel according to an embodiment of the present invention, and  FIG. 4  is a cross-sectional view of the plasma display panel taken along line IV-IV of  FIG. 3 .  
      Referring to  FIGS. 3 and 4 , the plasma display panel  100  includes an upper substrate  111  and a lower substrate  121  facing the upper substrate  111  and coupled to the upper substrate  111 .  
      In one embodiment, the upper substrate  111  is formed of a transparent material such as glass, through which visible lights can be transmitted to display an image.  
      Upper discharge electrodes  112  that are separated from each other are disposed on a lower surface of the upper substrate  111 . In addition, each of the upper discharge electrodes  112  includes transparent electrodes  113  disposed at sub-pixels  130 , and a bus electrode  114  connected to the transparent electrodes  113 .  
      In one embodiment, the transparent electrode  113  has a larger discharge area than that of the bus electrode  114 , and thus the panel  100  can operate with low voltage and a brightness of the panel  100  improves. In one embodiment, the transparent electrodes  113  can be formed of a transparent material such as indium tin oxide (ITO) to allow visible lights emitted from a phosphor layer  125  to be transmitted through the upper substrate  111 .  
      The bus electrode  114 , which receives voltages from a driving unit, supplies voltages to the transparent electrodes  113 . In one embodiment, the bus electrode  114  is formed of a metal having high conductivity, for example, Ag or Cu, in order to improve electric resistances of the transparent electrodes  113  that are formed of the ITO having relatively lower conductivity.  
      The bus electrode  114 , which has generally a width narrower than that of the transparent electrode  113 , is connected to center portions of the transparent electrodes  113  and extends in a direction of crossing lower discharge electrodes  122 . In one embodiment, the bus electrode  114  is disposed at the center portion of the transparent electrodes  113 . In another embodiment, the bus electrode can be disposed at end portions of the transparent electrodes  113 .  
      The upper discharge electrodes  112  are embedded in an upper dielectric layer  115  formed of a dielectric material such as PbO, B 2 O 3 , or SiO 2 . The upper dielectric layer  115  prevents charged particles from directly colliding onto the upper discharge electrodes  112  during a discharge and the upper discharge electrodes  112  from being damaged by the collision, and induces the charged particles. In one embodiment, the lower surface of the upper dielectric layer  115  is covered by an upper protective layer  116  formed of, for example, MgO. The upper protective layer  116  prevents the charged particles from directly colliding onto the upper dielectric layer  115  during the discharge, and emits secondary electrons when the charged particles collide thereto in order to improve discharge efficiency.  
      The lower discharge electrodes  122  extend perpendicularly to the upper discharge electrodes  112  on the upper surface of the lower substrate  121  facing the upper substrate  111  and are separated predetermined distances from each other, and thus these are arranged in stripes. The lower discharge electrodes  122  are embedded in a lower dielectric layer  123 , and barrier ribs  124  are formed on the lower dielectric layer  123  in a predetermined pattern.  
      The barrier ribs  124  define sub-pixels  130 , and prevent cross talk from being generated between neighboring sub-pixels  130 . The barrier ribs  124  include first barrier ribs  124   a  that are parallel to and separated from each other, and second barrier ribs  124   b  that are perpendicular to the first barrier ribs  124   a , and parallel to and separated from each other on the same plane as that of the first barrier ribs  124   a . Thus, the sub-pixels  130  are of a closed type. Here, the first barrier ribs  124   a  extend parallel to the lower discharge electrodes  122 , and the lower discharge electrodes  122  can be disposed between the first barrier ribs  124   a  one by one. The barrier ribs  24  are not limited to the above example, and can be formed to have various shapes such as stripe.  
      The phosphor layer  125  that is excited by the ultraviolet rays generated during the discharge to emit the visible lights is disposed in the sub-pixels  130  defined by the barrier ribs  124 . In one embodiment, the phosphor layer  125  is formed on side surfaces of the barrier ribs  124 . In another embodiment, the phosphor layer  125  can be formed on other portions, for example, the bottom of each discharge cell. The phosphor layer  125  can be formed of one of red, green, and blue color phosphor materials for realizing the colors, and accordingly, the phosphor layer  125  can be classified into red, green, and blue phosphor layers.  
      In the lower dielectric layer  123 , on which the barrier ribs  124  and the phosphor layer  125  are formed in a predetermined pattern, a lower protective layer  126  is formed on the upper surface of the lower dielectric layer  123  where the barrier ribs  124  and the phosphor layer  125  are not formed. Like the upper protective layer  116 , the lower protective layer  126  prevents the charged particles from colliding onto the lower dielectric layer  123  and the lower dielectric layer  123  from being damaged by the collision, and emits secondary electrons when the charged particles collided thereto, thus improving the discharge efficiency. In one embodiment, the lower protective layer  126  can be formed of MgO. Otherwise, the lower protective layer  126  can be formed on entire upper surface of the lower dielectric layer  123 , and accordingly, the barrier ribs  124  and the phosphor layer  125  can be formed on the lower protective layer  126 . The discharge gas, a mixture of, for example, Ne and Xe is filled in the sub-pixels  1 - 30 .  
      Referring to  FIG. 5 , the sub-pixels  130  can be classified into red sub-pixels  130 R, green sub-pixels  130 R, and blue sub-pixels  130 B according to the emitting color of phosphor layer  125  disposed in that sub-pixels. The red, green, and blue sub-pixels  130 R,  130 G, and  130 B are included in a unit pixel  131  to display various colors by combining the three primitive colors.  
      According to one embodiment of the present invention, the unit pixel  131  includes four sub-pixels  130  that are disposed adjacent to each other. That is, the four sub-pixels  130  constituting the unit pixel  131  are arranged around a crossing point of the first barrier rib  124   a  and the second barrier rib  124   b . The four sub-pixels  130  are divided into two units or subsets, which correspond to two adjacent upper discharge electrodes  112 , respectively.  
      In one embodiment, the four sub-pixels  130  are the red, green, and blue sub-pixels  130 R,  130 G, and  130 B, and another sub-pixel  130  that has the same brightness level with the sub-pixel  130  having the lowest maximum brightness level among the red, green, and blue sub-pixels  130 R,  130 G, and  130 B. When the sub-pixel  130  having the lowest maximum brightness level is further added in the unit pixel  131 , the maximum brightness of the visible light having the lowest maximum brightness level can be increased. Accordingly, the color temperature characteristic of white light that is represented by combining the red, green, and blue lights of maximum brightnesses from the unit pixel can be improved, and the maximum brightness characteristic of the unit pixel  131  can be improved.  
      Generally, under the same conditions, the maximum brightness level of the green light is the highest, and the maximum brightness level of the blue light is the lowest. Thus, the other sub-pixel  130  having the lowest maximum brightness level can be the blue sub-pixel  130 B. As described above, if two blue sub-pixels  130 B are included in the unit pixel  131 , the maximum brightness of the blue light can be increased. Therefore, the color temperature of the white light that is represented by combining the red, green, and blue lights of maximum brightnesses from the unit pixel  31  can be increased, and the maximum brightness of the unit pixel  131 _can also be increased.  
      Depending on embodiments, the four sub-pixels  130  constituting the unit pixel  131  can be arranged in various patterns. For example, in one embodiment as shown in  FIG. 5 , the red sub-pixel  130 R, green sub-pixel  130 G, blue sub-pixel  130 B, and another blue sub-pixel  130 B are arranged around the crossing point of the first barrier rib  124   a  and the second barrier rib  124   b  in a clockwise direction.  
      In another embodiment as shown in  FIG. 6 , the sub-pixels  130  can be arranged in the order of the red sub-pixel  130 R, blue sub-pixel  130 B, green sub-pixel  130 G, and another blue sub-pixel  130 B around the crossing point of the first barrier rib  124   a  and the second barrier rib  124   b  in the clockwise direction. In another embodiment as shown in  FIG. 7 , the sub-pixels  130  can be arranged in the order of the red sub-pixel  130 R, blue sub-pixel  130 B, another blue sub-pixel  130 B, and green sub-pixel  130 G around the crossing point of the first barrier rib  124   a  and the second barrier rib  124   b  in the clockwise direction.  
      The operation of a plasma display panel having the above structure is as follows.  
      One of the upper discharge electrode  112  and the lower discharge electrode  122  functions as a scan and sustain electrode, and the other functions as an address and sustain electrode. When the upper discharge electrode  112  functions as the scan and sustain electrode and the lower discharge electrode  122  functions as the address and sustain electrode, the scan voltage is applied to the upper discharge electrode  112  and the address voltage is applied to the lower discharge electrode  122 . Then, the address discharge occurs at the sub-pixel corresponding to the crossing point between the upper and lower discharge electrodes  112  and  122 . After the address discharge, when a sustain voltage is alternately applied between the upper and lower discharge electrodes  112  and  122 , the charged particles reciprocate in an up-and-down direction and the sustain discharge occurs. The discharge gas emits ultraviolet rays by the sustain discharge, and the phosphor layer  125  disposed in the sub-pixel  130  is excited by the ultraviolet rays. As such, the excited phosphor layer  125  emits visible light.  
      As described above, according to embodiments of the present invention, each unit pixel in a plasma display panel includes red, green, and blue sub-pixels, and an additional sub-pixel that has the same maximum brightness level as the sub-pixel having the lowest maximum brightness level, and thus the color temperature of white light emitted by the unit pixel can be improved. In addition, the brightness of the plasma display panel can be maximized.  
      While the above description has pointed out novel features of the invention as applied to various embodiments, the skilled person will understand that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made without departing from the scope of the invention. Therefore, the scope of the invention is defined by the appended claims rather than by the foregoing description. All variations coming within the meaning and range of equivalency of the claims are embraced within their scope.