Patent Publication Number: US-2007120490-A1

Title: Plasma display panel

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims the benefit of Korean Patent Application No. 10-2005-115870, filed on Nov. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present embodiments relate to a plasma display panel, and more particularly, to a plasma display panel in which yellowing is prevented by changing the composition of a dielectric layer that buries a discharge electrode line.  
      2. Description of the Related Art  
      Conventionally, plasma display panels are flat display devices that display desired numbers, letters, or a graphic by exciting a phosphor material in a phosphor layer by ultraviolet rays generated by a discharge of a discharge gas filled between two substrates on which a plurality of electrodes are formed.  
       FIG. 1  is a partially cutaway exploded perspective view illustrating a conventional plasma display panel  100 . The plasma display panel  100  includes a first substrate  111  and a second substrate  161  facing the first substrate  111 . A first discharge electrode line  112 , which acts as an X electrode, and a second discharge electrode line  113 , which acts as a Y electrode, form a sustain discharge electrode line pair, a first dielectric layer  114  that buries the first and second discharge electrode lines  111  and  113 , and a protective layer  115  are formed on an inner surface of the first substrate  111 . A plurality of address electrode lines  162  crossing the sustain discharge electrode line pair and a second dielectric layer  163  that buries the address electrode lines  162  are formed on an inner surface of the second substrate  161 .  
      The first discharge electrode line  112  is composed of a plurality of first transparent electrode lines  112   a  and a plurality of first bus electrode lines  112   b  disposed along an edge of the first transparent electrode lines  112   a . The second discharge electrode line  113  is composed of a plurality of second transparent electrode lines  113   a  and a plurality of second bus electrode lines  113   b  disposed along an edge of the second transparent electrode lines  113   a.    
      The first transparent electrode lines  112   a  of the first discharge electrode lines  112  and the second transparent electrode lines  113   a  of second discharge electrode lines  113  are formed of a transparent conductive film, and the first bus electrode lines  112   b  of the first discharge electrode line  112  and the second bus electrode lines  113   b  and  113   a  of second discharge electrode line  113  are formed of a metal having high conductivity to increase the conductivity of the first transparent electrode lines  112   a  and the second transparent electrode lines  113   a . Also, the first dielectric layer  114  and the second dielectric layer  163  are formed of a high dielectric material that includes PbO.  
      A plurality of barrier ribs  164  that define discharge cells are disposed between the first and second substrates  111  and  161  and phosphor layers  165  of red, green, and blue color are coated on inner sides of the barrier ribs  164 .  
      In the conventional plasma display panel  100  having the above structure, the discharge cells are selected at intersections of the second discharge electrode line  113  and the address electrode lines  162  by respectively applying electrical signals to the second discharge electrode line  113  and the address electrode lines  162  and a surface discharge is generated from a surface of the first substrate  111  by alternately applying an electrical signal to the first and second discharge electrode lines  112  and  113  in order to generate ultraviolet rays. Visible light is emitted from the red, green, and blue color phosphor layers  165  coated in the selected discharge cells. Therefore, the plasma display panel  100  can display a stationary image or a moving image.  
      In the conventional plasma display panel  100 , in order to avoid blocking of the propagation of the visible light emitted from the phosphor layers  165  towards the first substrate  111 , the first transparent electrode lines  112   a  and the second transparent electrode lines  113   a  are formed of a transparent conductive film such as indium tin oxide (ITO) film. However, the transparent conductive film generally has high resistance, a large voltage drop in a lengthwise direction resulting in high driving power consumption, and a long response time.  
      Therefore, the first bus electrode lines  112   b  and the second bus electrode lines  113   b  which are formed of an opaque metal having high electrical conductivity are respectively formed along edges of the first transparent electrode lines  112   a  and the second transparent electrode lines  113   a.    
      In this way, the plurality of first and second transparent electrode lines  112   a  and  113   a  and the plurality of first and second bus electrode lines  112   b  and  113   b  must be separately formed on the first substrate  111 . Therefore, manufacturing costs increase due to the expensive transparent electrode lines  112   a  and  113   a . Also, the first and second transparent electrode lines  112   a  and  113   a  and the first and second bus electrode lines  112   b  and  113   b  must be separately manufactured, thus, making the manufacturing process complicated, thereby increasing manufacturing time.  
      Therefore, a structure in which a transparent electrode line is removed from the substrate and a bus electrode line is only selectively patterned, namely, an ITO-free type of structure has been recently studied. In such a structure where the bus electrode line is only employed as the discharge electrode line, the line width of the bus electrode line is formed to be wider than the bus electrode line in a panel structure in which the bus electrode line overlaps with the transparent electrode line.  
      However, if the bus electrode line is only formed, then Ag, which constitutes the main component of the bus electrode line, diffuses into a dielectric layer that buries the bus electrode line when the bus electrode line is fired, that is, yellowing occurs. The yellowing is caused by PbO included in the dielectric layer since PbO becomes a migration path of a component of an electrode formed of a metal like Ag during firing the dielectric layer.  
      That is, in the prior art, PbO is included in the dielectric layer in order to reduce the melting pint of the dielectric layer. Meanwhile, the size of the Pb 2+  ion in PbO is similar to the size of the Ag 2+  ion. Therefore, the Ag 2+  ion that diffuses into the dielectric layer becomes a neutral metal by replacing the Pb 2+  ion in the dielectric layer through an active electron donor-receiver reaction (mainly a reduction reaction), thereby causing yellowing.  
      Accordingly, in a structure of a plasma display panel that employs a single discharge electrode line, especially, an ITO-free type electrode, the diffusion phenomenon of a metal atom of the single discharge electrode line into a dielectric layer causes a need for yellowing to be minimized.  
     SUMMARY OF THE INVENTION  
      The present embodiments provide a plasma display panel in which yellowing is prevented by forming the dielectric layer without PbO which prevents the diffusion of a metal atom of the discharge electrode into a dielectric layer.  
      According to an aspect of the present embodiments, there is provided a plasma display panel comprising: a first substrate; a second substrate facing the first substrate; a pair of discharge electrode lines that are disposed between the first substrate and the second substrate and comprise a first discharge electrode line formed by connecting the plurality of sub-electrode lines and a second discharge electrode line that faces the first discharge electrode line and is formed by connecting a plurality of sub-electrode lines; and dielectric layers that bury the discharge electrode lines, wherein the dielectric layers comprise B 2 O 3  and BaO.  
      The content of B 2 O 3  in the dielectric layers may be from about 10 to about 60% of the total composition of the dielectric layers.  
      The content of BaO in the dielectric layers may be from about 10 to about 60% of the total composition of the dielectric layers.  
      The dielectric layers may comprise at least one material selected from the group consisting of Al 2 O 3 , ZnO, SnO, and P 2 O 5 .  
      The material selected from the group consisting of Al 2 O 3 , ZnO, SnO, and P 2 O 5  may from about 10 to about 30% of the total composition of the dielectric layers.  
      The discharge electrode lines may be ITO-free type electrodes.  
      According to another aspect of the present embodiments, there is provided a plasma display panel comprising: a first substrate; a second substrate facing the first substrate; barrier ribs disposed between the first and second substrates in order to define a plurality of discharge cells; a pair of sustain discharge electrode lines that comprise a first discharge electrode line that is disposed between the first and second substrates and is formed by connecting a plurality of sub-electrode lines and a second discharge electrode line that faces the first discharge electrode line and is formed by connecting a plurality of sub-electrode lines, and wherein a sustain discharge is generated between the first discharge electrode line and the second discharge electrode line; address electrode lines that are perpendicular to the pair of sustain discharge electrode lines in order to generate address discharges with one of first and second discharge electrode lines of the pair of sustain discharge electrode lines; and dielectric layers that respectively bury the pair of sustain discharge electrode lines and the address electrode lines; and phosphor layers of red, green, and blue color formed in the discharge cells, wherein the dielectric layers comprise B 2 O 3  and BaO.  
      The content of B 2 O 3  in the dielectric layers may from about 10 to about 60% of the total composition of the dielectric layers.  
      The content of BaO in the dielectric layers may be from about 10 to about 60% of the total composition of the dielectric layers.  
      The dielectric layers may additionally comprise at least one material selected from the group consisting of Al 2 O 3 , ZnO, SnO, and P 2 O 5 .  
      The content of the material selected from the group consisting of Al 2 O 3 , ZnO, SnO, and P 2 O 5  in the dielectric layers may from about 10 to about 30% of the total composition of the dielectric layers.  
      The pair of sustain discharge electrode lines and the address electrode lines may be ITO-free type of electrodes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a partially cutaway exploded perspective view illustrating a conventional plasma display panel;  
       FIG. 2  is a partially cutaway perspective view of a plasma display panel according to an embodiment;  
       FIG. 3  is a cross-sectional view taken along the line I-I of the plasma display panel of  FIG. 2 , according to an embodiment; and  
       FIG. 4  is a plan view of the plasma display panel of  FIG. 2 , according to an embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A plasma display panel according to the present embodiments will now be described more fully with reference to the accompanying drawings in which exemplary embodiments are shown.  
       FIG. 2  is a partially cutaway perspective view of a plasma display panel  200  according to an embodiment.  FIG. 3  is a cross-sectional view taken along the line I-I of the plasma display panel  200  of  FIG. 2 , and  FIG. 4  is a plan view of the plasma display panel of  FIG. 2 , according to an embodiment.  
      Referring to  FIGS. 2 through 4 , the plasma display panel  200  includes a first substrate  211  and a second substrate  261  facing the first substrate  211 . A sealant (not shown) such as a frit glass is coated on edges of a surface of the first substrate  211  facing the second substrate  261 , and the first and second substrates  211  and  261  are thermally bonded to seal a space therebetween.  
      First discharge electrode lines  212  are disposed in a direction parallel to the X direction of the plasma display panel  200  and, in each discharge cell, second discharge electrode lines  213  are disposed facing the first discharge electrode lines  212  on an inner surface of the first substrate  211 . The second discharge electrode lines  213  are disposed in the same direction as the first discharge electrode lines  212  and have a substantially symmetrical shape. The first discharge electrode lines  212  and the second discharge electrode lines  213  are alternately disposed in a Y direction of the plasma display panel  200 .  
      The first discharge electrode lines  212  and the second discharge electrode lines  213  are buried in a first dielectric layer  214 . A protective layer  215  such as, for example, an MgO film is formed on a surface of the first dielectric layer  214  to protect the first dielectric layer  214  and to increase the emission of secondary electrons.  
      A plurality of address electrode lines  262  crossing the first discharge electrode lines  212  and the second discharge electrode lines  213 , that is, in the Y direction of the plasma display panel  200  are disposed on an inner surface of the second substrate  261 . The address electrode lines  262  are buried in a second dielectric layer  263 .  
      Accordingly, in a unit discharge cell, one sustain discharge electrode pair composed of the first discharge electrode lines  212  and the second discharge electrode lines  213  and the address electrode line  262  crossing the sustain discharge electrode pair are disposed. This structure corresponds to a three-electrode surface discharge type plasma display panel, but the structure of the present embodiments is not limited thereto.  
      Barrier ribs  264  that define a space between the first and second substrates  211  and  261  into a plurality of discharge cells together with the first and second substrates  211  and  261  are formed between the first and second substrates  211  and  261 . The barrier ribs  264  are formed of a dielectric material such as a glass paste to which various fillers are added.  
      The barrier ribs  264  include first barrier ribs  264   a  disposed in an X direction of the plasma display panel  200 , that is, in a direction crossing to the address electrode lines  262  and second barrier ribs  264   b  disposed in a Y direction of the plasma display panel  200 , that is, in a direction parallel to the address electrode lines  262 . The second barrier ribs  264   b  define a discharge cell by extending perpendicular from inner walls of the adjacent first barrier rib  264   a . The first barrier ribs  264   a  and the second barrier ribs  264   b  form a matrix by crossing with each other. Accordingly, the shape of a horizontal cross-section of each of the discharge cells is a rectangular shape.  
      Alternately, the barrier ribs  264  can be formed in various types such as for example, a meander type, a delta type, or a honeycomb type. However, the present embodiments are not limited to those types. Also, the discharge cells defined by the barrier ribs  264  can have any shape that can define the discharge cells other than the rectangular shape, such as, for example, a hexagonal shape, a circle shape, or an oval shape. However, the present embodiments are not limited to those shapes.  
      A discharge gas such as, for example, a Ne—Xe gas mixture or a He—Xe gas mixture is filled into the discharge cells defined by the first substrate  211 , the second substrate  261 , and the barrier ribs  264 .  
      Phosphor layers  265  of red, green, and blue colour are formed in each discharge cell to emit visible light when the phosphor layers  265  are excited by ultraviolet rays generated from the discharge gas. The phosphor layers  265  can be coated in any region of the discharge cell. However, in the present embodiment, the phosphor layers  265  are coated on inner walls of the barrier ribs  264  and on an upper surface of the second dielectric layer  263  to a predetermined thickness.  
      The red, green, and blue color phosphor layers  265  are respectively coated in each discharge cell. The phosphor layer  265  of red color may be formed of (Y,Gd)BO 3 ;Eu +3 , the phosphor layer  265  of green colour may be formed of Zn 2 SiO 4 :Mn 2+ , and the phosphor layer  265  of blue color may be formed of BaMgAl 10 O 17 :Eu 2+ .  
      In the present embodiment, the first discharge electrode lines  212  have a structure in which a plurality of sub-electrode lines that are connected to each other, and the second discharge electrode lines  213  which are disposed alternately with the first discharge electrode lines  212  also have a structure in which a plurality of sub-electrode lines are connected to each other. The first dielectric layer  214  that buries the first and second discharge electrode lines  212  and  213  includes a component of a particular material. The structures of the electrodes will now be described.  
      The first discharge electrode lines  212  extend along the X direction of the first substrate  211 . Each of first discharge electrode lines  212  has a structure in which a plurality of sub-electrode lines  212   a  through  212   c  are connected to each other.  
      That is, the first discharge electrode lines  212  include first through third sub-electrode lines  212   a  through  212   c  disposed parallel and a predetermined distance apart from each other from a central region toward outside of each discharge cell.  
      The first through third sub-electrode lines  212   a  through  212   c  are formed in a strip shape, but the present embodiments are not limited thereto. Also, in the current embodiment, the first discharge electrode lines  212  include the first through third sub-electrode lines  212   a  through  212   c , but the present embodiments are not limited thereto.  
      The first through third sub-electrode lines  212   a  through  212   c  are electrically connected to each other by a first bridge  212   d  disposed between the first and second sub-electrode lines  212   a  and  212   b  and a second bridge  212   e  disposed between the second and third sub-electrode lines  212   b  and  212   c.    
      The first and second bridges  212   d  and  212   e  are respectively disposed in each discharge cell, but the present embodiments are not limited thereto. Also, the first and second bridges  212   d  and  212   e  are disposed linearly in a direction perpendicular to the first through third sub-electrode lines  212   a  through  212   c , that is, along the Y direction of the first substrate  211 .  
      The second discharge electrode lines  213  also extend along the X direction of the first substrate  211 . The second discharge electrode lines  213  substantially have the same shape as the first discharge electrode lines  212 , and are substantially symmetrically disposed in unit discharge cells.  
      The second discharge electrode lines  213  include stripe shaped fourth through sixth sub-electrode lines  213   a  through  213   c  disposed a predetermined distance apart from each other from a central region towards outside of each discharge cell  
      The fourth through sixth sub-electrode lines  213   a  through  213   c  are electrically connected to each other by a third bridge  213   d  disposed between the fourth sub-electrode line  213   a  and the fifth sub-electrode line  213   b  and a fourth bridge  213   e  disposed between the fifth sub-electrode line  213   b  and the sixth sub-electrode line  213   c.    
      The third and fourth bridges  213   d  and  213   e  are disposed linearly in a direction perpendicular to the fourth through sixth sub-electrode lines  213   a  through  213   c , and each of the third and fourth bridges  213   d  and  213   e  is disposed in each discharge cell, but the present embodiments are not limited thereto.  
      Also, in the current embodiment, the second discharge electrode lines  213  include the fourth through sixth sub-electrode lines  213   a  through  213   c  and of the third and fourth bridges  213   d  and  213   e , but the present embodiments are not limited thereto. The first through third sub-electrode lines  212   a  through  212   c  and the fourth through sixth sub-electrode lines  213   a  through  213   c  may respectively have a line width of from about 20 to about 150 micrometers.  
      As the area of the first through third sub-electrode lines  212   a  through  212   c  and the fourth through sixth sub-electrode lines  213   a  through  213   c  increases, discharges can be generated smoothly, thus, the generation of visible light increases. However, as the area of the first through third sub-electrode lines  212   a  through  212   c  and the fourth through sixth sub-electrode lines  213   a  through  213   c  excessively increases, the aperture ratio decreases, thereby reducing overall brightness and unnecessarily increasing power consumption.  
      Also, the first discharge electrode lines  212  that include the first through third sub-electrode lines  212   a  through  212   c  and the first and second bridges  212   d  and  212   e  formed between the first through third sub-electrode lines  212   a  through  212   c  and the second discharge electrode lines  213  that include the fourth through sixth sub-electrode lines  213   a  through  213   c  and the third and fourth bridges  213   d  and  213   e  formed between the fourth through sixth sub-electrode lines  213   a  through  213   c  can be formed in a single layer structure as in the current embodiment, but may be formed in a double layer structure.  
      When the first discharge electrode lines  212  and the second discharge electrode lines  213  have a double layer structure, each layer can be formed of different material. Also, to simplify a manufacturing process, the first through third sub-electrode lines  212   a  through  212   c  and the first and second bridges  212   d  and  212   e  formed therebetween and the fourth through sixth sub-electrode lines  213   a  through  213   c  and the third and fourth bridges  213   d  and  213   e  formed therebetween may be simultaneously formed to a thick film using a printing method that uses a photosensitive paste or to a thin film using a sputtering method or a deposition method.  
      The first discharge electrode lines  212  and the second discharge electrode lines  213  can be formed of various conductive metals, that is, at least one selected from the group consisting of Ag, Pt, Ni, Cu, Pd or an alloy of these metals.  
      Alternately, the first discharge electrode lines  212  and the second discharge electrode lines  213  can be formed of a conductive ceramic material or a material including carbon nanotubes in order to increase the emission of secondary electrons.  
      In non-discharge regions between the discharge cells adjacent in the Y direction of the plasma display panel  200 , light absorbing layers  216  such as black stripe layers are formed to increase a bright room contrast ratio, and thus, to increase optical characteristics of the plasma display panel  200 . The light absorbing layers  216  extend along the X direction of the plasma display panel  200 , and are disposed on the non-discharge regions corresponding to the first barrier ribs  264   a.    
      The first discharge electrode lines  212 , the second discharge electrode lines  213 , and the light absorbing layer  216  are buried in the first dielectric layer  214 . The first dielectric layer  214  is formed of a material that can prevent direct connection between the first discharge electrode lines  212  and the second discharge electrode lines  213 , can prevent the first discharge electrode lines  212  and the second discharge electrode lines  213  from being damaged by direct collision with positive ions or electrons, and can accumulate wall charges by inducing charges.  
      The first dielectric layer  214  is formed of a high dielectric material that includes B 2 O 3  and BaO in order to minimize the occurrence of yellowness by the diffusion of the metal ion such as Ag 2+  included in the first discharge electrode lines  212  and the second discharge electrode lines  213  into the first dielectric layer  214 . B 2 O 3  and BaO are respectively mixed in the first dielectric layer  214  in the range from about 10 to about 60% of the total composition of the first dielectric layer  214 .  
      Also, the first dielectric layer  214  may preferably include at least two materials selected from the group consisting of Al 2 O 3 , ZnO, SnO, and P 2 O 5 . At least one materials selected from the group consisting of Al 2 O 3 , ZnO, SnO, and P 2 O 5  can be mixed in the first dielectric layer  214  in the range from about 10 to about 30% of the total composition of the first dielectric layer  214 .  
      When the above materials are added to the first dielectric layer  214 , during a firing process of the first dielectric layer  214 , a thermal treatment temperature is reduced and, at the same time, firing viscosity is reduced, and thus, fine air bubbles in the first dielectric layer  214  can be removed. When air bubbles are removed, the dispersion rate of incident light into the first dielectric layer  214  decreases. Therefore, light transmittance of the first dielectric layer  214  increases, thereby increasing operation brightness of the plasma display panel  200 .  
      A protective layer  215  is formed on a surface of the first dielectric layer  214  to prevent the first dielectric layer  214  from being damaged by collisions with positive ions and electrons during discharges, to increase light transmittance, and to be able to emit larger amounts of secondary electrons during discharges. The protective layer  215  is formed as a thin film type using a sputtering method or an electron beam deposition method.  
      In the case of the address electrode lines  262  disposed on the second substrate  261  and the second dielectric layer  263  that buries the address electrode lines  262 , in order to prevent the diffusion of a metal atom that constitutes the address electrode lines  262  into the second dielectric layer  263 , the second dielectric layer  263  also employs the same composition as the first dielectric layer  214 .  
      An operation of the plasma display panel  200  having the above structure according to an embodiment will now be described.  
      When a predetermined voltage is applied between the second discharge electrode lines  213 , which corresponds to the Y electrode, and the address electrode lines  262 , wall charges are accumulated on the surface of the first dielectric layer  214 . In this state, a sustain discharge is generated by applying an alternate current between the first discharge electrode lines  212 , which corresponds to the X electrode, and the second discharge electrode lines  213 .  
      The sustain discharge between the first discharge electrode lines  212  and the second discharge electrode lines  213  will be described in detail. When an alternating current voltage of about 180V is applied between the first discharge electrode lines  212  and the second discharge electrode lines  213 , an initial discharge is generated between the first sub-electrode line  212   a  of the first discharge electrode lines  212  and the fourth sub-electrode line  213   a  of the second discharge electrode lines  213  disposed closest to the central region of the discharge cell where the discharge distance is relatively short. The discharge consecutively expands to the second and third sub-electrode lines  212   b  and  212   c  and the fifth and sixth sub-electrode lines  213   b  and  213   c  consecutively disposed toward the outside of the discharge cell. To ensure a stable initial discharge, the line width of the first sub-electrode line  212   a  and the fourth sub-electrode line  213   a  can be in the range from about 20 to about 150 micrometers.  
      In a state where charges are formed in a discharge space due to the initial discharge, a main discharge is generated by an alternating current voltage applied between the first discharge electrode lines  212  and the second discharge electrode lines  213 . The formed charges and ultraviolet rays formed during the initial discharge facilitate the generation of the main discharge by accelerating an insulation breakage action of the discharge gas filled between the second and third sub-electrode lines  212   b  and  212   c  and the fifth and sixth sub-electrode lines  213   b  and the  213   c  consecutively disposed towards outside of the discharge cell.  
      The main discharge is generated by an alternate current voltage applied between the first discharge electrode lines  212  and the second discharge electrode lines  213  and ultraviolet rays are generated from the discharge gas while the energy level of the discharge gas is reduced due to level of the main discharge. The generated ultraviolet rays excite phosphor layers  265  formed at least on a surface of the discharge space defined by the barrier ribs  264  in order to emit visible light, and the emitted visible light displays predetermined numbers, letters, or graphics.  
      The plasma display panel according to the present embodiments provides the following advantages.  
      First, dielectric layers that bury discharge electrode lines include B 2 O 3  and BaO, and thus, yellowing caused by the migration of a metal component included in the discharge electrode lines into the dielectric layers during a firing process can be prevented.  
      Second, the discharge electrode lines use an ITO-free type of electrode structure. Therefore, a manufacturing process is simple, thereby reducing manufacturing costs.  
      Third, since discharge electrode lines include a plurality of sub-electrode lines and bridges that electrically connect the discharge electrode lines, the initiation of a discharge is easy. An optimum brightness can be maintained by controlling thicknesses and widths of the discharge electrode lines.  
      While the present embodiments have 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 embodiments as defined by the following claims.