Patent Publication Number: US-2007114936-A1

Title: Plasma display apparatus and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims the benefit of Korean Patent Application No. 10-2005-0112239, filed on Nov. 23, 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 apparatus, and more particularly, to a plasma display apparatus having an improved structure so as to increase luminescence efficiency and uniformity and a method of manufacturing the plasma display apparatus.  
      2. Description of the Related Art  
      Plasma display panels (PDPs) form images using electrical discharge, have good brightness characteristics and a wide viewing angle, etc., leading to an increase in the use of PDPs recently. PDPs display images using visible light emitted through a process of exciting a phosphor material with ultraviolet rays generated from a discharge of a discharge gas between electrodes when a direct current (DC) voltage or an alternating current (AC) voltage is applied to the electrodes. PDPs are classified into DC type panels and AC type panels according to the discharge process (the discharge method). Also, PDPs are classified into facing discharge type panels and surface discharge type panels according to the arrangement of electrodes.  
       FIG. 1  is an exploded perspective view of a conventional plasma display panel (PDP).  
      Referring to  FIG. 1 , the conventional PDP includes a rear substrate  10  and a front substrate  20 , which face each other, and a plurality of barrier ribs  13  interposed between the rear substrate  10  and the front substrate  20  form discharge spaces  15  which are filled with a discharge gas such as Xenon Xe. The barrier ribs  13  partition a plurality of unit discharge cells and prevent electrical and optical crosstalk between the unit discharge cells. The rear substrate  10  includes address electrodes  11  that are covered by a first dielectric layer  12  that is coated with phosphor layers  14  including red R, green G, and blue B phosphor layers. The front substrate  20  includes first and second sustain electrodes  21   a  and  21   b  on which first and second bus electrodes  22   a  and  22   b  are formed, respectively, to reduce line resistance of the first and second sustain electrodes  21   a  and  21   b . A second dielectric layer  23  covers the first and second sustain electrodes  21   a  and  21   b  and the first and second bus electrodes  22   a  and  22   b . A protective layer  24  formed of MgO is formed on the second dielectric layer  23 . The protective layer  24  prevents the second dielectric layer  23  from being damaged due to plasma sputtering, emits secondary electrons during a plasma discharge, and reduces a discharge voltage.  
      The conventional PDP illustrated in  FIG. 1  continuously supplies and accelerates electrons through a discharge, generates excitation particles due to collisions of the accelerated electrons and neutral particles, emits ultraviolet rays owing to the stabilization of the excitation particles, excites a phosphor substance by incidence of the ultraviolet rays to form visible light, emits the visible light through the front substrate  20 , and displays images.  
      However, the density of electron emission contributing to the discharge is not constant in the unit discharge cells, thus reducing luminescence uniformity of the conventional PDP illustrated in  FIG. 1 . In detail, the current density is high inside the first and second sustain electrodes  21   a  and  21   b , resulting in a strong luminescence, and the current density is low outside the first and second sustain electrodes  21   a  and  21   b , resulting in a weak luminescence. That is, an electric field of the unit discharge cells is not constant so that areas having strong luminescence and weak luminescence coexist. As a result, the conventional PDP has a high discharge voltage and a low discharge or luminescence efficiency. Therefore, it is necessary to improve the structure of the PDP so as to increase the luminescence efficiency and uniformity.  
     SUMMARY OF THE INVENTION  
      The present embodiments provide a plasma display apparatus having an improved structure so as to increase luminescence efficiency and uniformity and a method of manufacturing the plasma display apparatus.  
      According to an aspect of the present embodiments, there is provided a plasma display apparatus, comprising: a front substrate and a rear substrate facing each other; a plurality of first and second sustain electrodes formed on the front substrate and spaced apart from each other; and first and second electron emitting layers formed on the first and second sustain electrodes, respectively, emitting electrons received from the first and second sustain electrodes, and having a structure in which their thickness decreases as the first and second electron emitting layers approach a gap between the first and second sustain electrodes.  
      The first and second electron emitting layers may be formed of an oxidized porous polysilicon (OPPS) or an oxidized porous amorphous silicon (OPAS). The first and second sustain electrodes may be formed of one selected from a group consisting of indium tin oxide (ITO), Al, and Ag. The density of electrons emitted from the first and second electron emitting layers may be relatively varied according to the width of the first and second electron emitting layers. The closer the first and second electron emitting layers are to the gap between the first and second sustain electrodes, the lower the density of electrons emitted from the first and second electron emitting layers is. The further the first and second electron emitting layers are from the gap between the first and second sustain electrodes, the higher the density of electrons emitted from the first and second electron emitting layers is. The first emitter electrode may be interposed between the first sustain electrode and the first electron emitting layer, and the second emitter electrode may be interposed between the second sustain electrode and the second electron emitting layer, wherein the first and second emitter electrodes may be formed of a conductive material.  
      According to another aspect of the present embodiments, there is provided a plasma display apparatus, comprising: a front substrate and a rear substrate facing each other; a plurality of first and second sustain electrodes formed on the front substrate and spaced apart from each other; first and second electron emitting layers formed on the first and second sustain electrodes, respectively, emitting electrons received from the first and second sustain electrodes; and a dielectric layer covering the first and second electron emitting layers, having a window exposing an upper face of the first and second electron emitting layers, and having a structure in which the closer the first and second electron emitting layers are to a gap between the first and second sustain electrodes, the thinner the window becomes.  
      The first and second electron emitting layers may be formed of an OPPS or an OPAS. The first and second sustain electrode are formed of one selected from a group consisting of ITO, Al, and Ag. A density of electrons emitted from the first and second electron emitting layers may be relatively varied according to the width of the window. The closer the first and second electron emitting layers are to the gap between the first and second sustain electrodes, the lower the density of electrons emitted from the first and second electron emitting layers is. The farther the first and second electron emitting layers are from the gap between the first and second sustain electrodes, the higher the density of electrons emitted from the first and second electron emitting layers is.  
      According to another aspect of the present embodiments, there is provided a method of manufacturing a plasma display apparatus, the method comprising: preparing a front substrate and a rear substrate facing each other; forming a plurality of first and second sustain electrodes on the front substrate to be spaced apart from each other; forming first and second silicon layers on the first and second sustain electrodes, respectively; anodizing the first and second silicon layers and forming first and second electron emitting layers formed of an oxidized porous silicon; and selectively etching and removing a specific area of the first and second electron emitting layers so that the thinner the first and second electron emitting layers are, the closer the first and second electron emitting layers approach a gap between the first and second sustain electrodes.  
      A solution of hydrogen fluoride (HF) and ethanol may be used for the anodizing process. The first and second sustain electrodes may be formed of one selected from a group consisting of ITO, Al, and Ag. A gap between the first and second electron emitting layers may be adjusted to control a discharge start voltage.  
      According to another aspect of the present embodiments, there is provided a method of manufacturing a plasma display apparatus, the method comprising: preparing a front substrate and a rear substrate facing each other; forming a plurality of first and second sustain electrodes on the front substrate to be spaced apart from each other; forming first and second silicon layers on the first and second sustain electrodes, respectively; anodizing the first and second silicon layers and forming first and second electron emitting layers formed of an oxidized porous silicon, using an anodizing process; forming a dielectric layer covering the first and second electron emitting layers; and selectively etching and removing a specific area of the dielectric layer, having a window exposing an upper face of the first and second electron emitting layers, and having a structure in which the thinner the window is, the closer the first and second electron emitting layers are to a gap between the first and second sustain electrodes.  
      A solution of HF and ethanol may be used for the anodizing process. The first and second sustain electrodes may be formed of one selected from a group consisting of ITO, Al, and Ag. A gap between the first and second electron emitting layers may be adjusted to control a discharge start voltage. 
    
    
     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 an exploded perspective view of a conventional plasma display panel (PDP);  
       FIG. 2A  is an exploded perspective view of a plasma display apparatus according to an embodiment;  
       FIG. 2B  is a cross-sectional view of the plasma display apparatus of  FIG. 2A  taken along a line A-A′ in  FIG. 2A ;  
       FIG. 3A  is an exploded perspective view of a plasma display apparatus according to another embodiment;  
       FIG. 3B  is a cross-sectional view of the plasma display apparatus of  FIG. 3A  taken along a line B-B′ in  FIG. 3A  according to an embodiment;  
       FIGS. 4A through 4H  are diagrams illustrating a method of manufacturing a plasma display apparatus, according to an embodiment; and  
       FIGS. 5A through 5I  are diagrams illustrating a method of manufacturing a plasma display apparatus, according to another embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present embodiments will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. In the drawings, the thickness of layers and regions are exaggerated for clarity.  
       FIG. 2A  is an exploded perspective view of a plasma display apparatus according to an embodiment.  FIG. 2B  is a cross-sectional view of the plasma display apparatus of  FIG. 2A  taken along a line A-a′ in  FIG. 2A  according to an embodiment. A plasma display panel (PDP) is realized as an example of the plasma display apparatus according to the current embodiment.  
      Referring to  FIGS. 2A and 2B , the plasma display apparatus according to the current embodiment includes a front substrate  120  and a rear substrate  110  which face each other, and a plurality of barrier ribs  113  interposed between the front substrate  120  and the rear substrate  110 , forming discharge spaces  115  filled with a discharge gas such as, for example, Neon Ne or Xenon Xe. The barrier ribs  113  partition a plurality of unit discharge cells. The discharge gas generates a visible light in the unit discharge cells during a plasma discharge. The barrier ribs  113  prevent electrical or optical crosstalk between the unit discharge cells.  
      The rear substrate  110  includes address electrodes  111  and a first dielectric layer  112  that covers the address electrodes  111 . The first dielectric layer  112  is coated with phosphor layers  114  including red R, green G, and blue B phosphor layers. The front substrate  120  includes first and second sustain electrodes  121   a  and  121   b  which are spaced apart from each other. A second dielectric layer  123  covers the first and second sustain electrodes  121   a  and  121   b . First and second emitter electrodes  124   a  and  124   b  formed of conductive materials such as indium tin oxide (ITO), Al, Ag, etc. are formed on the second dielectric layer  123 , and correspond to the first and second sustain electrodes  121   a  and  121   b , respectively. First and second electron emitting layers  128   a  and  128   b  formed of an oxidized porous silicon (OPS) material are formed on the first and second emitter electrodes  124   a  and  124   b , respectively. The OPS material is an oxidized porous polysilicon (OPPS) or an oxidized porous amorphous silicon (OPAS).  
      If a specific alternating current (AC) voltage is applied to the first and second sustain electrodes  121   a  and  121   b , an electric field having a specific magnitude is formed between the first and second sustain electrodes  121   a  and  121   b  so that the first and second emitter electrodes  124   a  and  124   b  supply electrons to the first and second electron emitting layers  128   a  and  128   b , respectively. The electrons are accelerated through the first and second emitting layers  128   a  and  128   b  and emitted to the discharge spaces  115 . More specifically, silicon nano-crystallization particles forming the first and second electron emitting layers  128   a  and  128   b  have a diameter of about 5 nm. The diameter of the silicon nano-crystallization particles is much smaller than a means free path of about 50 nm of the electrons. Therefore, the electrons are not likely to collide with each other in the silicon nano-crystallization particles, and most of the electrons reach the interface of the silicon nano-crystallization particles through the silicon nano-crystallization particles. A very thin oxidization film is formed between the silicon nano-crystallization particles forming an electric field area in the first and second electron emitting layers  128   a  and  128   b  when a specific voltage is applied to the first and second sustain electrodes  121   a  and  121   b . The electrons tunnel through the oxidization film, are accelerated in the electric field area formed in the first and second electron emitting layers  128   a  and  128   b , and are emitted to the discharge spaces  115 . Therefore, the first and second electron emitting layers  128   a  and  128   b  of the plasma display apparatus according to the current embodiment can improve discharge and brightness characteristics of the plasma display apparatus.  
      In particular, the closer the first and second electron emitting layers  128   a  and  128   b  are to a gap between the first and second emitter electrodes  124   a  and  124   b , the thinner the first and second electron emitting layers  128   a  and  128   b  are. The first and second emitter electrodes  124   a  and  124   b  may have the same structure as the first and second electron emitting layers  128   a  and  128   b . In this case, the density of the electrons emitted from the first and second electron emitting layers  128   a  and  128   b  is changed according to the width of the first and second electron emitting layers  128   a  and  128   b . For example, the closer the first and second electron emitting layers  128   a  and  128   b  are to the gap between the first and second emitter electrodes  124   a  and  124   b , the lower the density of the electrons emitted from the first and second electron emitting layers  128   a  and  128   b  is, and vice versa. Since the density of the electrons is changed according to the width of the first and second electron emitting layers  128   a  and  128   b , the width of the first and second electron emitting layers  128   a  and  128   b  is controlled according to the location thereof so that the electric field can be uniformly distributed in the unit discharge cells.  
      In comparison with the structure in which the width of the first and second electron emitting layers  128   a  and  128   b  is gradually changed and the structure in which the electron emitting layers  128   a  and  128   b  has a uniform width in the unit discharge cells, the density of the electrons contributing to the discharge is more uniform than the discharge spaces  115 . The plasma display apparatus of the current embodiment can provide an improved distribution of the electric field in the unit discharge cells compared to the conventional PDP. The conventional PDP has a strong luminescence since the current density is high inside the first and second sustain electrodes  21   a  and  21   b , and has a weak luminescence since the current density is low outside the first and second sustain electrodes  21   a  and  21   b . However, the plasma display apparatus of the current embodiment has a weak current density by relatively decreasing the width of the first and second electron emitting layers  128   a  and  128   b  inside the first and second sustain electrodes  121   a  and  121   b , and has a strong current density by relatively increasing the width of the first and second electron emitting layers  128   a  and  128   b  outside the first and second sustain electrodes  121   a  and  121   b . Therefore, the unit discharge cells have a uniformly distributed electric field, thereby increasing luminescence efficiency and uniformity in the unit discharge cells and improving the voltage and brightness characteristics of the plasma display apparatus.  
       FIG. 3A  is an exploded perspective view of a plasma display apparatus according to another embodiment.  FIG. 3B  is a cross-sectional view of the plasma display apparatus of  FIG. 3A  taken along a line B-B′ in  FIG. 3A  according to an embodiment. A PDP is realized as an example of the plasma display apparatus according to the current embodiment.  
      Like reference numerals in  FIGS. 3A and 3B  denote like elements illustrated in  FIGS. 2A and 2B , and thus descriptions thereof will be omitted. A front substrate  220  of the plasma display apparatus of  FIGS. 3A and 3B  is different from the front substrate  120  of the plasma display apparatus of  FIGS. 2A and 2B .  
      Referring to  FIGS. 3A and 3B , the plasma display apparatus includes the front substrate  220  and a rear substrate  110  which face each other, and a plurality of barrier ribs  113  interposed between the front substrate  220  and the rear substrate  110 , forming discharge spaces  115  filled with a discharge gas such as Neon Ne or Xenon Xe. The barrier ribs  113  partition a plurality of unit discharge cells.  
      The rear substrate  110  includes address electrodes  111  and a first dielectric layer  112  that covers the address electrodes  111 . The first dielectric layer  112  is coated with phosphor layers  114  including red R, green G, and blue B phosphor layers. The front substrate  220  includes first and second sustain electrodes  221   a  and  221   b  which are spaced apart from each other. First and second electron emitting layers  228   a  and  228   b  formed of an OPS material are formed on the first and second sustain electrodes  221   a  and  221   b , respectively. A second dielectric layer  229  covers the first and second electron emitting layers  228   a  and  228   b . The second dielectric layer  229  includes a window that exposes upper faces of the first and second electron emitting layers  228   a  and  228   b  to the discharge spaces  115 . The closer the first and second electron emitting layers  228   a  and  228   b  are to a gap between the first and second sustain electrodes  221   a  and  221   b , the thinner the window becomes. In this case, a density of electrons emitted from the first and second electron emitting layers  228   a  and  228   b  is changed according to the thickness of the window. For example, the closer the first and second electron emitting layers  228   a  and  228   b  are to the gap between the first and second sustain electrodes  221   a  and  221   b , the lower the density of the electrons emitted from the first and second electron emitting layers  228   a  and  228   b  is, and vice versa. As described in  FIGS. 2A and 2B , the plasma display apparatus of the current embodiment can increase luminescence efficiency and uniformity in the unit discharge cells and thus improve voltage and brightness characteristics of the plasma display apparatus. The first and second sustain electrodes  221   a  and  221   b  can be formed of a material selected from the group consisting of ITO, Al, and Ag.  
       FIGS. 4A through 4H  are diagrams illustrating a method of manufacturing a plasma display apparatus according to an embodiment. A PDP is realized as an example of the plasma display apparatus according to the current embodiment. Material layers can be formed using various widely known thin film deposition methods. Such thin film deposition methods include physical vapor deposition (PVD), chemical vapor deposition (CVD), spray coating, screen printing, etc.  
      Referring to  FIGS. 4A and 4B , a front substrate  120  and a rear substrate  110  are prepared facing each other Address electrodes  111  and a first dielectric layer  112  that covers the address electrodes  111  are formed on the rear substrate  110 . First and second sustain electrodes  121   a  and  121   b  formed on the front substrate  120  to be spaced apart from each other, are formed of a conductive material such as ITO, Al, or Ag. A second dielectric layer  123  covers the first and second sustain electrodes  121   a  and  121   b.    
      Referring to  FIGS. 4C through 4E , first and second emitter electrodes  124   a  and  124   b  are formed on the second dielectric layer  123  so as to correspond to the first and second sustain electrodes  121   a  and  121   b , respectively. The first and second emitter electrodes  124   a  and  124   b  are formed of a conductive material such as ITO, Al, or Ag. First and second silicon layers  125   a  and  125   b  are formed on the first and second emitter electrodes  124   a  and  124   b , respectively. The first and second silicon layers  125   a  and  125   b  are formed of a polycrystalline silicon or an amorphous silicon.  
      The first and second silicon layers  125   a  and  125   b  are anodized to form first and second electron emitting layers  128   a  and  128   b , which are formed of an OPS material. Any anodizing process is known in the art can be used. In the current embodiment, a solution of hydrogen fluoride (HF) and ethanol is used for the anodizing process, thereby obtaining an OPS layer.  
      Referring to  FIGS. 4F through 4H , a specific area of the first and second electron emitting layers  128   a  and  128   b  is etched and removed in order to decrease the thickness of the first and second electron emitting layers  128   a  and  128   b  when the first and second electron emitting layers  128   a  and  128   b  are close to a gap between the first and second emitter electrodes  124   a  and  124   b , thereby obtaining a plasma display apparatus having improved luminescence efficiency and uniformity.  
      A gap between the first and second electron emitting layers  128   a  and  128   b  can influence a discharge start voltage of the plasma display apparatus. Therefore, the gap between the first and second electron emitting layers  128   a  and  128   b  may be controlled in order to minimize the discharge start voltage. For example, the gap between the first and second electron emitting layers  128   a  and  128   b  can be increased or decreased during the etching process.  
       FIGS. 5A through 5I  are diagrams illustrating a method of manufacturing a plasma display apparatus according to another embodiment. A PDP is realized as an example of the plasma display apparatus according to the current embodiment.  
      Referring to  FIGS. 5A through 5C , a front substrate  220  and a rear substrate  110  are prepared facing each other. Address electrodes  111  and a first dielectric layer  112  that covers the address electrodes  111  are formed on the rear substrate  110 . First and second sustain electrodes  221   a  and  221   b  are formed on the front substrate  220  and spaced apart from each other. First and second silicon layers  225   a  and  225   b  are formed on the first and second sustain electrodes  221   a  and  221   b , respectively. The first and second silicon layers  225   a  and  225   b  are formed of a polycrystalline silicon or an amorphous silicon. The first and second sustain electrodes  221   a  and  221   b  are formed of a conductive material such as ITO, Al, or Ag.  
      Referring to  FIGS. 5D and 5E , the first and second silicon layers  225   a  and  225   b  are anodized to form first and second electron emitting layers  228   a  and  228   b , which are formed of an OPS material. The anodizing process is the same as that described with reference to  FIGS. 4A through 4H , and thus a description thereof will be omitted.  
      Referring to  FIGS. 5F through 5I , a second dielectric layer  229  covers the first and second electron emitting layers  228   a  and  228   b . A specific area of the second dielectric layer  229  is etched and removed to form a window that exposes an upper face of the first and second electron emitting layers  228   a  and  228   b  to the discharge spaces  115 . The closer the first and second electron emitting layers  228   a  and  228   b  are to a gap between the first and second sustain electrodes  221   a  and  221   b , the thinner the window becomes, thereby obtaining the PDP having improved luminescence efficiency and uniformity.  
      As described with reference to  FIGS. 4A through 4I , the gap between the first and second electron emitting layers  228   a  and  228   b  can influence a discharge start voltage of the plasma display apparatus. Therefore, the gap between the first and second electron emitting layers  228   a  and  228   b  may be controlled in order to minimize the discharge start voltage. For example, the gap between the first and second electron emitting layers  228   a  and  228   b  can be increased or decreased during the etching process of the second dielectric layer  229 .  
      According to an embodiment, a plasma display apparatus, e.g., a PDP, having improved luminescence efficiency and uniformity in discharge cells can be obtained. In detail, the thickness of electron emitting layers is changed according to their position relative to unit discharge cells so that the density of emitted electrons contributed to a discharge can be uniformly distributed, thereby optimizing discharge efficiency. The unit discharge cells can be controlled to have a uniform distribution of electric field so that the plasma display apparatus has high discharge efficiency at a low voltage, thereby improving brightness and voltage characteristics of the plasma display apparatus.  
      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.