Patent Publication Number: US-2007103079-A1

Title: Plasma display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0106351 filed in the Korean Intellectual Property Office on Nov. 8, 2005, the entire content of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a plasma display panel, and more particularly, to a plasma display panel having address electrodes, sustain electrodes, and scan electrodes which reduce power consumption.  
      2. Description of the Related Art  
      Plasma display panels (PDPs) display an image typically by using a gas discharge. The PDPs have excellent display capacity, brightness, contrast, viewing angle, and latent image reduction.  
      In a PDP, a front substrate, which has sustain electrodes and scan electrodes with barrier ribs interposed therebetween, is sealed against a rear substrate having address electrodes. The barrier ribs define discharge cells. An inert gas (e.g. neon (Ne) and xenon (Xe)) is filled in the discharge cells.  
      When an address voltage is supplied to the address electrodes, and a scan pulse is supplied to the scan electrodes, the PDP produces wall charges between the two electrodes, and selects the discharge cells to be turned on by an address discharge. In this state, when a sustain pulse is supplied to the sustain electrodes and the scan electrodes, gaseous ions formed in the discharge cells travel between the sustain electrodes and the scan electrodes carrying electrons from one electrode to the other. Accordingly, the address voltage is added to a wall voltage stemming from the wall charges formed by the address discharge. Thus, the address voltage exceeds a discharge ignition voltage, thereby generating a sustain discharge within the selected discharge cells.  
      A vacuum ultraviolet ray generated within the discharge cells by the sustain discharge excites a phosphor material coating inner surface of the discharge cells. The phosphor material relaxes from the excited state, and thus generates a visible light beam. Accordingly, an image is formed on the PDP.  
      Since the PDP has the address electrodes on the rear substrate, and the sustain electrodes and the scan electrodes on the front substrate, the distance between the address electrodes and the scan electrodes increases, thereby disadvantageously raising an address discharge voltage.  
      In order to reduce the address discharge voltage, in one type of PDP the sustain, scan, and address electrodes are all located on a front substrate.  
      In this type of PDP, the sustain electrodes and the scan electrodes are covered with a dielectric layer, and the address electrodes are formed over the dielectric layer. High permittivity of the dielectric layer raises electrostatic capacitance among the sustain electrodes, the scan electrodes, and the address electrodes, thereby disadvantageously increasing power consumption.  
     SUMMARY OF THE INVENTION  
      The embodiments of the present invention provide a plasma display panel capable of lowering an address discharge voltage.  
      The embodiments of the present invention also provide a plasma display panel capable of decreasing electrostatic capacitance among electrodes, thereby reducing power consumption.  
      According to one aspect of the present invention, a plasma display panel is provided having a first substrate and a second substrate facing each other, barrier ribs which are located on the first substrate to define discharge cells, phosphor layers formed on the inner sides of the discharge cells, a third substrate located on the barrier ribs, spacers located between the second substrate and the third substrate, address electrodes which are formed on the third substrate in a first direction, and correspond to the discharge cells, and first electrodes and second electrodes which are formed on the second substrate in a second direction crossing the first direction, and correspond to the discharge cells.  
      The spacers may be located in the second direction corresponding to a boundary position of the discharge cells that are adjacent one another in the first direction. The spacers may be formed of a glass bead. The spacers may be formed of the same material as the third substrate or etched from the substrate.  
      A vacuum space may be formed between the second substrate and the third substrate. The space between the second and third substrates may be formed using the spacers. The space may be filled with a fluid between the second substrate and the third substrate. The fluid may be an inert gas. The fluid may be a liquid material.  
      The third substrate may be formed of a transparent glass. The address electrodes may be formed on one surface of the third substrate facing the first substrate.  
      Each address electrode may include an extended portion which extends in the first direction corresponding to a boundary position of the discharge cells neighboring in the second direction, and a protruded portion which protrudes towards the inner part of the discharge cells in the second direction. The extended portion may be formed of metal, and the protruded portion may be formed of a transparent ITO (Indium tin oxide). The address electrodes may be covered with a dielectric layer. In addition, the dielectric layer may be covered with a protection layer.  
      The first electrode and the second electrode may each include transparent electrodes formed on the second substrate corresponding to the discharge cells, and bus electrodes connecting the transparent electrodes in the second direction.  
      The barrier ribs may include first barrier members which are formed on the first substrate to extend in the first direction. The barrier ribs may further include second barrier members which are formed between the first barrier members to extend in the second direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective exploded view schematically showing a plasma display panel (PDP) according to a first embodiment of the present invention.  
       FIG. 2  is a plan view showing the relationship between layouts of barrier ribs and electrodes of  FIG. 1 .  
       FIG. 3  is a cross-sectional view taken along line III-III of  FIG. 1 .  
       FIG. 4  is a cross-sectional view showing a PDP according to a second embodiment of the present invention.  
       FIG. 5  is a plan view of a PDP according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIG. 1 ,  FIG. 2 , and  FIG. 3 , the PDP of the first embodiment of the present invention includes a first substrate  10  (hereinafter referred to as a “rear substrate”) and a second substrate  20  (hereinafter referred to as a “front substrate”). The rear and front substrates  10 ,  20 , face each other and are sealed against each other while being spaced apart.  
      A third substrate  40  (hereinafter referred to as a “intermediate substrate”) is located between the rear substrate  10  and the front substrate  20 . Barrier ribs  16  are located between the rear substrate  10  and the intermediate substrate  40 . Spacers  26  are located between the intermediate substrate  40  and the front substrate  20 .  
      The barrier ribs  16  that are located between the rear substrate  10  and the intermediate substrate  40  have predetermined heights to define a plurality of discharge cells  17 . The discharge cells  17  are filled with a discharge gas (for example, a gas mixture including neon (Ne) and xenon (Xe)) to generate vacuum ultraviolet rays through gas discharge. The discharge cells  17  include phosphor layers  19  which absorb the vacuum ultraviolet ray to emit visible light.  
      To form an image by gas discharge, the PDP includes address electrodes  11  respectively corresponding to the discharge cells  17 , and first electrodes  31  (hereinafter referred as “sustain electrodes”), and second electrodes  32  (hereinafter referred to as “scan electrodes”).  
      The address electrodes  11  are formed on the intermediate substrate  40  to extend in a first direction (y-axis direction in the drawings, hereinafter referred to as “y”). Each address electrode  11  corresponds to the discharge cells  17  that are adjacent one another and formed along the first direction y. The address electrodes  11  are parallel to one another and two adjacent address electrodes  11  correspond to two rows of discharge cells  17  neighboring in a second direction (x-axis direction in the drawing, hereinafter referred to as “x”) crossing the first direction y.  
      Each of the address electrodes  11  includes an extended portion  11   a  and a protruded portion  11   b . The extended portion  11   a  extends in the first direction y corresponding to a boundary between the discharge cells  17  neighboring in the second direction x. The extended portion  11   a  is located in a non-emissive region of the discharge cell  17 , thereby not interfering with a forward emission of the visible light beam toward the front substrate  20 . The extended portion  11   a  may be formed of metal having an excellent conductivity, for example, aluminum (Al). The protruded portion  11   b  protrudes from the extended portion  11  a towards the inner part of the discharge cell  17  in the second direction x. The protruded portion  11   b  is therefore located in an emissive region of the discharge cell  17 . In order to minimize blockage of the visible light beam, the protruded portion  11   b  may be formed of a transparent material, for example, ITO (indium tin oxide).  
      As described above, the address electrodes  11  are formed on one surface of the intermediate substrate  40 , for example, a surface facing the rear substrate  10 . The address electrodes  11  are covered with a dielectric layer  13 . During discharge, the dielectric layer  13  protects the address electrodes  11  against a direct collision with positive ions or electrons, thereby reducing damage to the address electrodes  11 . Further, the dielectric layer  13  accumulates wall charges.  
      The dielectric layer  13  is covered with a protection layer  14 . The protection layer  14  is formed of a transparent MgO, thereby transmitting a visible light beam. The protection layer  14  protects the dielectric layer  13  against discharge, and increases a secondary electron emission factor to reduce a discharge ignition voltage during discharge.  
      To permit the forward transmission of the visible light beam emitted from the discharge cells  17 , the intermediate substrate  40  is formed of a transparent material such as glass like the front substrate  20 .  
      The barrier ribs  16  are located between the intermediate substrate  40 , where the address electrodes  11  are formed, and the rear substrate  10 . For example, the barrier ribs  16  are formed with first barrier members  16   a  extending in the first direction y and second barrier members  16   b  extending in the second direction x. The second barrier members  16   b  are located between each two neighboring first barrier members  16   a , and are arranged in the second direction x crossing the first barrier members  16   a.    
      As described above, the first barrier members  16   a  and the second barrier members  16   b  cross each other between the rear substrate  10  and the intermediate substrate  40 . Accordingly, each discharge cell  17  is enclosed between the two substrates with two sets of intersecting first and second barrier members  16   a  and  16   b . The closed barrier structure around a discharge cell  17  effectively prevents cross-talk between the discharge cells.  
      The closed barrier structure is not limited to a rectangular parallelepiped shape as shown in the drawing. Thus, variations in shape may be made to obtain another shape such as a hexagonal prism or an octagonal prism.  
      The phosphor layers  19  are formed on the lateral sides of the barrier ribs  16  and the surface of the rear substrate  10  surrounded by the barrier ribs  16 . That is, the phosphor layers  19  are formed on the lateral sides of the first barrier members  16   a , the lateral sides of the second barrier members  16   b , and the surface of the rear substrate  10  that is surrounded by these barrier members.  
      The sustain electrodes  31  and the scan electrodes  32  are formed on the inner surface of the front substrate  20  facing the discharge cells  17 . The sustain electrodes  31  and the scan electrodes  32  form a surface discharge structure. The sustain electrodes  31  and the scan electrodes  32  are arranged extending in the second direction x crossing the direction y of the address electrodes  11 .  
      The sustain and scan electrodes  31 ,  32  are formed each with a respective transparent electrode  31   a ,  32   a  and a respective bus electrode  31   b ,  32   b . The transparent electrodes  31   a ,  32   a  protrude towards the center of the discharge cells  17 , and form a surface discharge structure. To supply voltage to the transparent electrodes  31   a ,  32   a , the bus electrodes  31   b ,  32   b  are formed on the transparent electrodes  31   a ,  32   a  to extend in the second direction x.  
      In an alternative embodiment, the transparent electrodes  31   a ,  32   a  may extend in the second direction x like the bus electrodes  31   b ,  32   b  (not shown).  
      The transparent electrodes  31   a ,  32   a  produce a surface discharge within the discharge cells  17 . In order to ensure an adequate aperture ratio for the discharge cells  17 , the transparent electrodes  31   a ,  32   a  are formed of a transparent material, for example, ITO (Indium tin oxide). The bus electrodes  31   b ,  32   b  are formed of metal having an excellent conductivity, so as to ensure conductivity by compensating for high electrical resistance of the transparent electrodes  31   a ,  32   a.    
      In the first embodiment that is described above, the address electrodes  11  are formed on the intermediate substrate  40  facing the rear substrate  10 , and the sustain electrodes  31  and the scan electrodes  32  are formed on the front substrate  20 .  
      However, the present invention is not limited to the above-mentioned layout, and thus the locations of the address electrodes  11 , the sustain electrodes  31 , and the scan electrodes  32  may change from one embodiment to the other. For example, the sustain electrodes  31  and the scan electrodes  32  may be formed on the intermediate substrate  40 , and the address electrodes  11  may be formed on the front substrate  20 .  
      The spacers  26  are interposed between the intermediate substrate  40  and the front substrate  20 , and form a predetermined gap CC between the intermediate substrate  40  and the front substrate  20  (see  FIG. 3 ). The spacer  26  may be formed of a glass bead. The spacers  26  are located along the second direction x corresponding to a boundary of the neighboring discharge cells  17  (see  FIG. 2 ).  
      That is, the spacers  26  are located between the bus electrodes  31   b  of the sustain electrodes  31  and the bus electrodes  32   b  of the scan electrodes  32 , and remain parallel to these bus electrodes  31   b ,  32   b . Therefore, the spacers  26  are located at locations corresponding to the second barrier members  16   b  of the barrier ribs  16  that in turn correspond to non-emissive regions.  
      The spacers  26  may be formed by etching one surface of the intermediate substrate  40 . In this case, the spacers  26  are formed of the same material as the intermediate substrate  40 .  
      A space is formed between the front substrate  20  and the intermediate substrate  40  by the spacers  26 . A substantial vacuum is established in this space. Thus, the sustain electrodes  31  and the scan electrodes  32  are covered with a vacuum insulation layer having a relative permittivity ε of 1. In one embodiment, the space between the front substrate  20  and the intermediate substrate  40  has the same vacuum pressure as the interior of the discharge cell  17  formed between the intermediate substrate  40  and the rear substrate  10 .  
      For example, if it is assumed that a discharge gap formed between the sustain electrode  31  and the scan electrode  32  is 100-200 μm at a discharge ignition voltage of 400-600V, and a dielectric breakdown voltage of air is 3(V/μm), then if the space between the front and intermediate substrates  20 ,  40  is not under vacuum, discharge does not occur in the space between the front substrate  20  and the intermediate substrate  40 . Instead, discharge first occurs in the discharge cells  17  between the intermediate substrate  40  and the rear substrate  10  where a vacuum has been established.  
      The spacers  26  allow the gap CC to be formed between the front substrate  20  and the intermediate substrate  40 . This gap may be under vacuum and has a lower permittivity than a dielectric layer that would have been there if the spacers were not being used. As a result the permittivity between the address electrode  11  and the scan electrode  32  is reduced thereby enabling an address discharge at a lower voltage. Further, having the intermediate substrate  40  between the front and rear substrates  20 ,  10  and forming the address electrodes on the intermediate substrates  40 , as opposed to the rear substrate, allows a reduced distance between the address electrodes and the sustain and scan electrodes which also helps reduce the address discharge voltage.  
      Due to the spacers  26 , a vacuum space is formed between the sustain electrodes  31 , the scan electrodes  32 , and the address electrodes  11  that has a permittivity ε of 1, lower than the permittivity of other dielectric materials. Thus, power consumption between electrodes are reduced in comparison with the case that additional dielectric layer is provided.  
      In the PDP configured as described above, a reset discharge occurs during a reset period in response to a reset pulse supplied to the scan electrodes  31 . An address discharge then occurs during an addressing period following the reset period in response to a scan pulse supplied to the scan electrodes  32  and an address pulse supplied to the address electrodes  11 . Thereafter, a sustain discharge occurs during a sustain period in response to a sustain pulse supplied to the sustain electrodes  31  and the scan electrodes  32 .  
      The sustain electrodes  31  and the scan electrodes  32  function as electrodes for supplying the sustain pulse required for the sustain discharge. The scan electrodes  32  function as electrodes for supplying the reset pulse and the scan pulse. The address electrodes  11  function as electrodes for supplying the address pulse. Functions of these electrodes  31 ,  32 ,  11  may be different according to waveforms of voltages respectively supplied thereto. Thus, the present invention is not limited to the aforementioned functions.  
      In the PDP, the discharge cells  17  are selected to be turned on by the address discharge stemming from the interaction of the address electrodes  11  and the scan electrodes  32 . The selected discharge cells  17  are driven while the sustain discharge occurs due to the interaction of the sustain electrodes  31  and the scan electrodes  32 . As a result, an image is formed.  
       FIG. 4  is a cross-sectional view of a PDP according to a second embodiment of the present invention.  
      The second embodiment is similar to the first embodiment in terms of overall structure and operations. Thus, description of like elements is omitted.  
      As described above, the space between the front substrate  20  and the intermediate substrate  40  is under a substantial vacuum in the first embodiment. However, according to the second embodiment, the space between the front substrate  20  and the intermediate substrate  40  is filled with a fluid  42 . The fluid  42  electrically insulates the sustain electrodes  31  and the scan electrodes  32 .  
      The fluid  42  exemplifies that although the space between the front substrate  20  and the intermediate substrate  40  may be under vacuum, the space may alternatively be formed with a fluid dielectric layer different from the conventional solid dielectric layer. That is, an inert gas having a high breakdown voltage may be filled in this space. For example, the space may be filled with a gas containing Xe. In this case, the Xe contained in the gas has a partial pressure that is different from the partial pressure of Xe in a discharge gas injected within a discharge cell. A fluid  42  may be a liquid material. The liquid material may have a high working voltage. The dielectric oil generally used in a capacitor or a transformer may be used as the liquid material. Silicon oil may also be used because it has a high working voltage, low permittivity and because it is transparent. In addition, Dimethyl silicon oil having the following molecular formula may be used.  
                 
 
       FIG. 5  is a plan view of a PDP according to a third embodiment of the present invention.  
      The third embodiment is similar to the first embodiment. However, the barrier ribs  116  of the third embodiment do not include first and second barrier members  16   a ,  16   b  of the first embodiment. In the third embodiment, the barrier ribs  116  are similar to the first barrier members  16   a  of the first embodiment and extend in one direction alone.  
      The barrier ribs  116  extend in the first direction y between the rear substrate  10  and the intermediate substrate  40 , and are parallel to one another and spaced apart along the second direction x. Accordingly, the barrier ribs  116  form an open-type barrier structure. Discharge cells  117  of the third embodiment, are enclosed only along one direction y.  
      In the third embodiment, the sustain electrodes  31  and the scan electrodes  32  are located on the front substrate  20 , and the address electrodes  11  are located on the intermediate substrate  40 . This arrangement indicates that various barrier ribs can be located between the intermediate substrate  40  and the rear substrate  10 .  
      In a plasma display panel according to the embodiments of the present invention, an intermediate substrate is located between a rear substrate and a front substrate. Address electrodes are formed on the intermediate substrate. Sustain electrodes and scan electrodes are formed on the front substrate. A space between the front substrate and the intermediate substrate may be under vacuum or may be filled with liquid. Thus, the distance between the scan electrodes and the address electrodes is reduced, thereby lowering an address discharge voltage. The vacuum or fluid-filled space between electrodes results in a low permittivity. Thus, electrostatic capacitance decreases, thereby advantageously reducing power consumption.  
      Although certain exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments, but may be modified in various forms without departing from the scope of the invention set forth in the detailed description, the accompanying drawings, the appended claims, and their equivalents.