Abstract:
A plasma display panel (PDP) and the method for manufacturing the same. A method for manufacturing a plasma display panel includes forming electrodes along one direction on a substrate, applying the dielectric paste along the other direction perpendicular to the one direction of the electrodes on the substrate, drying the dielectric paste and firing the dried dielectric paste to form a dielectric layer. Only one swath is needed for the entire dielectric layer, saving time and production costs, while providing a superior quality layer. Accordingly, since the dielectric paste is applied along the direction perpendicular to the longitudinal direction of the display electrodes, it is advantage that tack time and the number of cleaning the nozzle is reduced.

Description:
CLAIM OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application for PLASMA DISPLAY PANEL AND THE METHOD FOR MANUFACTURING THE SAME earlier filed in the Korean Intellectual Property Office on 29 Nov. 2003 and there duly assigned Serial No. 10-2003-0086104. Furthermore, this application claims all benefits accruing under 35 U.S.C. §120 of Applicants&#39; Ser. No. 10/992,354 and is a continuation application of Applicants&#39; Ser. No. 10/992,354 filed in the U.S. Patent &amp; Trademark Office on 19 Nov. 2004 and assigned to the assignee of the present invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a plasma display panel (PDP) and the method for manufacturing the same. More particularly, the present invention relates to a PDP and the method for manufacturing the same in which the formation of dielectric layer is enhanced. 
         [0004]    2. Description of the Related Art 
         [0005]    A PDP is a display device that realizes the display of images through excitation of phosphors by plasma discharge. That is, a predetermined voltage is applied between two electrodes mounted in a discharge region of the PDP to affect plasma discharge therebetween, and ultraviolet rays generated during plasma discharge excite a phosphor layer formed in a predetermined pattern to thus form visible images. 
         [0006]    Traditionally, in such PDPs, the dielectric layer has been formed by a screen printing method. The screen printing method includes a step for applying dielectric paste to a substrate through a screen mask covering the electrodes. With the above method, all the elements of the PDP will be formed by one printer by exchanging screen masks and pastes. In this screen printing method, a dielectric paste is applied to a squeezer and then ejected through the openings of the screen mask while a squeezer reciprocates on the screen mask thus printing a dielectric layer. The printed dielectric layer is then dried and fired. 
         [0007]    However, in order to achieve a desired thickness for the dielectric layer, the above processes must be repeated many times. This produces a multilayered structure for the dielectric layer. This multilayer be problematical and inefficient as vapor develops between each of the dielectric layers having a negative impact on discharging characteristics while producing a dielectric layer whose thickness is difficult to control and whose thickness uniformity is poor. Also, the thickness of the dielectric layers stacked on top of each other becomes uneven thus reducing a brightness characteristic. Further, this multi layered approach can be problematical and inefficient as a mesh shape of the screen mask remains on the dielectric layer thus reducing the smoothness of the surface of the dielectric layer. Also, the screen mask will have to be replaced often because of wear of the squeezer. Therefore, what is needed is an improved and more efficient method for forming the dielectric layer in a PDP. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to provide an improved design for a PDP. 
         [0009]    It is also an object of the present invention to provide an improved and more efficient method for making a PDP. 
         [0010]    These and other objects can be achieved by a PDP where a dielectric layer is formed as a single layer as opposed to many layers. The dielectric layer is applied along a direction perpendicular to the direction of electrodes on the substrate. A method for manufacturing a PDP includes forming electrodes along one direction on a substrate, applying the dielectric paste along the other direction perpendicular to the one direction of electrodes on the substrate, drying and firing the dielectric paste to form a dielectric layer. The dielectric paste may be applied by an application device, the electrodes may be display electrodes. 
         [0011]    The dielectric layer may be formed into a single layer, the dielectric layer may include a region having a thickness between 0 to about 30 μm at the periphery of the display at the start or end of the application device swath and at the side edges of the application device swath and 30 to 40 μm elsewhere. 
         [0012]    Preferably, the dielectric material is applied to another substrate, the mother substrate being much larger than the individual PDPs. After application, drying and firing, the substrate can be cut into individual PDPs. By forming the PDPs this way, mass production is made even easier. Further, when cut, many of the edges of individual PDP&#39;s may not have the roll off effect regarding thickness of the dielectric layer, because the some of the edges of an individual PDP may be in the middle of a mother substrate and thus are in the middle of a swath. 
         [0013]    The PDP manufactured by the above method includes first and second substrates facing each other, and electrodes formed in a first direction on the first substrate and in a second direction on the second substrate. A dielectric layer is applied in a direction perpendicular to the electrodes for one or both substrates. The dielectric layer is applied using only one swath of the application device. The thickness of the dielectric layer is 30 to 40 μm. Along a periphery of the PDP, at the beginning and end and sides of the swath, the thickness of the dielectric layer can be between zero and 30 μm. The portion of the PDP having a dielectric layer of a thickness less than 30 μm is the non-display area where no more than two electrodes reside. Generally, the portion of the PDP having a dielectric layer between 30 and 40 μm is the display region. The portions of the PDP where the dielectric layer is less than 30 μm is about 4 to 8 mm wide. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
           [0015]      FIG. 1  is an exploded perspective view of a PDP; 
           [0016]      FIG. 2  is a perspective view of a mother substrate used in making a plurality of PDPs according to an embodiment of the present invention; 
           [0017]      FIG. 3  is a schematic view illustrating the application process of a dielectric layer according to an embodiment of the present invention; 
           [0018]      FIG. 4A  is a SEM photography of portion “A” of the dielectric layer of  FIG. 2 ; 
           [0019]      FIG. 4B  is a SEM photography of portion “B” of the dielectric layer of  FIG. 2 ; 
           [0020]      FIG. 4C  is a SEM photography of portion “C” of the dielectric layer of  FIG. 2 ; 
           [0021]      FIG. 5A  is a graph illustrating a thickness profile of the dielectric layer of  FIG. 4A ; 
           [0022]      FIG. 5B  is a graph illustrating a thickness profile of the dielectric layer of  FIG. 4B ; and 
           [0023]      FIG. 5C  is a graph illustrating a thickness profile of the dielectric layer of  FIG. 4C . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Turning now to the figures,  FIG. 1  is an exploded perspective view of an AC PDP  100 . As illustrated in  FIG. 1 , the PDP  100  includes a rear substrate  111 , address electrodes  115  formed on the rear substrate  111 , a dielectric layer  119  formed on the rear substrate  111  and covering the address electrodes  115 , a plurality of barrier ribs  123  formed on the dielectric layer  119  to create a discharge space and prevent inter-cell cross talk, and phosphor layers  125  formed on the barrier ribs  123  and on the exposed portions of the dielectric layer  119 . 
         [0025]    A plurality of display electrodes  117  are formed on a front substrate  113  in a direction perpendicular to the address electrodes  115  formed on the rear substrate  111 . A dielectric layer  121  and a MgO protective layer  127  cover the display electrodes  117 . 
         [0026]    Turning now to  FIG. 2 ,  FIG. 2  is a perspective view of a mother substrate used to make a plurality of PDPs according to an embodiment of the present invention. In  FIG. 2 , mother substrate  11  is used to form 4 front substrates for 4 separate PDPs. A dielectric layer is formed on a mother substrate covering electrode previously deposited thereon. As illustrated in  FIG. 2 , with the PDP, a plurality of display electrodes  15  are formed on the mother substrate  11  while extending in a direction (y direction). A dielectric layer  13  is formed on the display electrodes  15  and then a MgO protective layer (not shown) is formed on the dielectric layer  13  to protect the dielectric layer  13  and increase the secondary electron emission coefficient. The mother substrate is later cut to form the front substrates for many PDPs. Although it is shown to make 4 front substrates from one mother substrate, other numbers are also conceivable and within the scope of the present invention. 
         [0027]    Meanwhile, a rear substrate is made to face the front substrate, and a plurality of address electrodes (not illustrated in  FIG. 2 ) are formed on the surface of the rear substrate facing the front substrate in the direction crossing the display electrodes (x direction). 
         [0028]    Pixels are formed at the respective crossed regions of the address electrodes and the display electrodes, and collectively form a display area. The display area may be defined as an area where the display and address electrodes overlap each other. The address and the display electrodes cross each other to cause the display discharge due to the driving voltages applied to those electrodes. In other words, the display area is the region of the PDP where visible images are formed. 
         [0029]    A plurality of barrier ribs (not shown) are formed in the display area to partition the respective pixels each with a separate discharge cell while supporting the two substrates. Phosphors are coated onto the inner wall of the discharge cells to generate visible rays. 
         [0030]    The area external to and surrounding the display area of individual PDPs may be defined as a “non-display area”, not incurring any display discharge. Terminals for the respective electrodes are formed in the non-display area, and are connected to a driving circuit unit (not shown) via an electrical connector, such as a flexible printed circuit (FPC). The dielectric layer  13  is formed without covering the terminal portions of the display electrodes  15  allowing for efficient connectivity with an FPC (not shown). 
         [0031]    In the PDP of the exemplary embodiment described above, application of a drive voltage is applied to the address electrodes and the display electrodes to affect address discharge therebetween, resulting in the formation of a wall charge on the dielectric layer. Further, a sustain discharge is applied to a pair of the display electrodes by an AC signal alternately supplied to the pair of the display electrodes. The sustain discharge occurs at the discharge cells selected by the address discharge. As a result, ultraviolet rays are generated while discharge gas filled in discharge spaces formed by the discharge cells is excited. The ultraviolet rays excite the phosphor layer material so that it emits visible light, thus realizing the formation of images. 
         [0032]    In  FIG. 2 , four PDPs according to an embodiment of the present invention are formed on one mother substrate. Each of PDPs formed on one mother substrate is defined as a “unit”, each of electrode groups is defined as an “electrode unit”. Accordingly, in  FIG. 3 , the total number of PDP units is four, also the number of electrode units formed on the top substrate is four. As described above, when it is desired to form a plurality of PDPs from one mother substrate, it involves forming a plurality of PDP units on one mother substrate, forming entirely the dielectric layer, cutting them and then sealing each of PDP unit with the rear substrates. Therefore, the present invention is suitable for a mass production of a PDP. 
         [0033]    The number of PDP units of  FIG. 2  is only an example. Accordingly, the present invention may be applied on forming one PDP unit or a plurality of PDP units. 
         [0034]      FIG. 3  is a schematic view illustrating the deposition process of a dielectric layer according to an embodiment of the present invention. With reference to  FIG. 3 , in a process of manufacturing a plurality of PDPs according to the present invention, a dielectric paste is applied to the substrates in a direction perpendicular to a longitudinal direction of display electrodes  25  to form a dielectric layer  23 . At this time, the dielectric layer may be formed by using an application device  300 . The application device moves in the −x direction, which is perpendicular to the y-direction that the display electrodes  25  run. The dielectric paste is applied uniformly on the substrate  21  from nozzles in the application device  300  by controlling the air pressure of the application device  300 . 
         [0035]    By having the swath of the application device  300  move in a direction that is orthogonal to and not parallel to the direction of the display electrodes, the tack time and the number of times the nozzles of the application device needs to be cleaned is reduced due to the continuous application of the dielectric paste. Also, the thickness of the dielectric layer may be formed uniformly over the entire of the substrate when the swath direction of the application device is orthogonal to the electrodes. 
         [0036]    “Tack time” is the time taken for changing direction or changing position of the coater or application device. The tack time of the application device can be reduced by not changing often the position or direction of the application device. This reduction of tack time of the application device is achieved by having the direction of the swath of the application device perpendicular to the lengthwise direction of the electrodes on the substrate and by using a mother substrate that is very long in the swath direction. 
         [0037]    The PDP according to an embodiment of the present invention is manufactured by a method for manufacturing as followed. This method involves first forming electrodes on the substrate (in  FIG. 3 , display electrodes formed on the mother substrate are illustrated, address electrodes formed on a rear substrate may be illustrated), applying a dielectric paste along a direction perpendicular to the longitudinal direction of the formed electrodes. The dielectric paste can be formed with combination of two more of the following materials: PbO, B 2 O 3 , SiO 2 , Al 2 O 3 , BaO, or ZnO. The paste on the substrate is then dried, preferably in a heating room. Then, the dried dielectric paste is fired in a firing room at a temperature between 350° C. and 580° C. thus completing the formation of the dielectric layer on the substrate. 
         [0038]    Accordingly, it is advantageous to form the dielectric layer as a single layer instead of as many layers stacked on top of each other. To begin with, there is better control over the thickness of the resultant dielectric layer when only one layer is present. In other words, since the result thickness of the dielectric layer may be controlled by determining an amount of the paste ejected from the application device, it is advantageous that a dielectric layer having a predetermined thickness can be formed at one time. In addition, by forming the dielectric layer from one swath of the application device, process time and process cost can be minimized. Also, the invention is suitable for forming a front substrate that requires good optical transmission characteristics. That is, the present invention can produce a dielectric layer that satisfies all the requirements for a dielectric layer on a front substrate of a PDP, such as insulating property, smoothness, high transmissivity, low vaporization and low reactivity. 
         [0039]    Turning now to  FIGS. 4A through 4C ,  FIG. 4A  and  FIG. 4C  illustrate SEM (scanning electron microscope) photographs of partial sectional views “A” through “C” respectively of dielectric layer  13  of  FIG. 2 . In more detail,  FIG. 4A  is a SEM photograph at “A” in  FIG. 2 , “A” being the dielectric layer  13  at the beginning of a swath taken in the direction of the swath.  FIG. 4B  is a SEM photograph at “B” in  FIG. 2 , “B” being at a side edge of a swath and taken in a direction parallel to display electrodes  15 .  FIG. 4C  is an SEM photograph at “C” in  FIG. 2 , “C” being partial sectional view of the dielectric layer  13  at an end of a swath of the application device  300  taken in the x direction parallel to the direction the application device travels. 
         [0040]    As shown in  FIG. 4A , at first, the thickness of the dielectric layer is unstable at the left hand side of  FIG. 4A , which represents the starting edge of the swath. However, the thickness becomes gradually more stable as the dielectric paste is applied from the left to right towards a center of the mother substrate, after the paste is dried and then fired. Turning now to  FIG. 4B , the thickness of the dielectric layer reduces towards a right edge of the photograph, representing an edge of a swath. Turning now to  FIG. 4C , the thickness of the dielectric layer has an unstable and reduced thickness at the left portion of the photograph, representing a back edge of the mother substrate where the swath of application device  300  ends. As shown in  FIG. 4A through 4C , the dielectric layer  13  can be formed as a single layer with a single swath of application device  300  by application of the dielectric paste, drying and then firing. By forming dielectric layer  13  as a single layer, the thickness of the dielectric layer is controlled and uniform, thus enhancing the discharge characteristics. 
         [0041]    Turning now to  FIGS. 5A through 5C ,  FIGS. 5A through 5C  are graphs illustrating a thickness of dielectric layer  13  at “A” through “C” respectively in  FIG. 2 .  FIG. 5A  corresponds to  FIG. 4A  and to “A” in  FIG. 2  at a beginning edge of a swath.  FIG. 5B  corresponds to  FIG. 4B  and to “B” of  FIG. 2  at a lateral edge of a swath. Likewise,  FIG. 4C  corresponds to  FIG. 5C  and to “C” of  FIG. 2  at a finishing edge of a swath.  FIG. 5A  is a graph illustrating the thickness of the dielectric layer  13  near a starting edge of the mother substrate at “A” in  FIG. 2 .  FIG. 5B  is a graph illustrating the thickness of the dielectric layer at the side or lateral edge of a region that the application device is applying a dielectric paste at “B” in  FIG. 2 .  FIG. 5C  is a graph illustrating the thickness of the dielectric layer at an edge of the mother substrate where the swath ends at “C” in  FIG. 2 . 
         [0042]    In  FIGS. 5A and 5C , the dielectric layer includes one region having a thickness between 0 and 30 μm at the beginning or ending point of a swath of application device  300 . Since the process for forming a dielectric layer is optimized, the one region having a thickness of 0 to 30 μm of the dielectric layer is only 4 to about 8 mm wide. Since these beginning and ending regions correspond to the upper or lower end portions of the PDP substrate where the non-display area is formed, the thickness variations does not result in faulty discharge characteristics. These edges of the PDP are used for a region that frit is adhered to enhance close adhesion of upper and lower substrates. 
         [0043]    As shown in  FIG. 5A  through  FIG. 5C , most portions of dielectric layer  13  has a thickness between 30 and 40 μm. In a case that more than one PDP is formed from a single mother substrate, many of the edge portions of the PDP have uniform thickness dielectric layers right to the edge of the PDP, especially when an edge of the PDP is formed in the middle and not at the edge of the mother substrate. 
         [0044]    In the PDP of the exemplary embodiment of the present invention, since the dielectric paste is applied along the direction perpendicular to the longitudinal direction of the display electrodes, it is advantageous that tack time and the number of cleaning of the nozzle is reduced due to continuous application of the dielectric paste compared to the scenario where the dielectric paste is applied in a direction that is parallel the display electrodes. Also, the thickness of the dielectric layer may be formed uniformly over the entire of the substrate. 
         [0045]    Also, since the thickness of the dielectric layer may be controlled by varying an amount of the paste ejected from the application device, it is advantageous that a dielectric layer having a predetermined thickness can be formed at one time, resulting in a uniform thickness while reducing processing time and manufacturing costs. 
         [0046]    Further, the invention is suitable for forming a front substrate desired to have a good optical transmission characteristics. That is, the dielectric layer  13  formed on the front substrate will have good insulating characteristics, good smoothness, a high transmissivity, low vaporization and a low reactivity, all features that a front substrate of PDP requires. Thus, the process described herein is compatible and can be used to make front substrates for PDPs. In addition, in the PDP of the exemplary embodiment of the present invention, the dielectric layer can be formed continuously at one time so that it is suitable to form a plurality of PDPs at once on one mother substrate allowing for easier mass production of PDPs. Finally, in the PDP of the exemplary embodiment of the present invention, the dielectric layer is formed into a single layer to enable the inter-structure thereof to elaborate and to prevent the vapor from generating, thus enhancing the discharge characteristics of PDP. 
         [0047]    Although embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.