Patent Publication Number: US-2009230862-A1

Title: Substrate Assembly for Plasma Display Panel and Display Panel

Description:
TECHNICAL FIELD 
     The present invention relates to a substrate assembly for a plasma display panel (hereinafter, referred to as PDP) and a PDP. 
     BACKGROUND ART 
     In  FIG. 4 , a perspective view of a schematic structure of a common PDP is shown. The PDP has a structure formed by sticking a front-side substrate assembly  1  and a rear-side substrate assembly  2  to each other. The front-side substrate assembly  1  comprises a glass substrate  1   a , display electrodes  3  each composed of a transparent electrode  31  and a bus electrode  32  and placed on the substrate  1   a , and a dielectric layer  4  covering the display electrodes  3 . Further, a protective layer  5 , which is a magnesium oxide layer, with a high secondary electron emission coefficient is formed on the dielectric layer  4 . In the rear-side substrate assembly  2 , address electrodes  6  are placed on a glass substrate  2   a , so that the address electrodes  6  cross at a right angle to the display electrodes, and barrier ribs  7  for defining the light emitting regions are formed between neighboring address electrodes  6 , and red-, green-, and blue-emitting phosphor layers  8  are formed on the address electrodes  6  in the regions divided by the barrier ribs  7 . A Ne—Xe gas mixture is introduced in the insides between the front-side substrate assembly  1  and the rear-side substrate assembly  2  stuck to each other. 
     The aspect of discharge of a discharge cell viewed from a cross section is shown in  FIG. 5 . If a voltage is applied between the display electrodes  3  composed of a pair of electrodes X and Y and thereby an electric field is applied to a discharge space, a Xe gas is excited to generate a gas discharge  9  and vacuum ultraviolet rays  10  are emitted from the discharge. The vacuum ultraviolet rays  10  impinge on the phosphors  8  to emit visible light.  11 . The PDP operates as a display by controlling the vacuum ultraviolet rays  10  with an electric field in the cell. In this time, the vacuum ultraviolet rays  10  are irradiated not only to the phosphors  8  but also to the front-side substrate assembly  1 . Though the protective layer (MgO)  5  and the dielectric layer  4  are formed in this order from a discharge surface side on the glass substrate  1   a  of the front-side substrate assembly  1 , a part of the vacuum ultraviolet rays  10  reaches the dielectric layer  4  since MgO transmits a part of the vacuum ultraviolet rays  10  with a wavelength of 165 nm or larger. 
     When the dielectric layer  4  is made of a material which transmits vacuum ultraviolet rays, the vacuum ultraviolet rays  10  pass through the dielectric layer  4 . During this passing, impurity gas mainly containing undecomposed substances (H 2 , NH 3  etc.) in the dielectric layer is generated by energy of the vacuum ultraviolet rays  10 , and this gas may have a detrimental effect on the discharge characteristics or the life of a PDP. 
     In the PDP described in Patent Document 1, the vacuum ultraviolet rays  10  are prevented from reaching the dielectric layer  4  by providing, between the protective layer  5  and the dielectric layer  4 , an intermediate layer made of ZrO 2  or the like having a function of shielding vacuum ultraviolet rays. 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2004-71338 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, good adhesion was not necessarily achieved between the intermediate layer and the protective layer  5  and there might be cases where the protective layer  5  peeled off. 
     The present invention has been achieved in view of the above-mentioned circumstances and provides a substrate assembly for a PDP which can prevent vacuum ultraviolet rays from reaching a dielectric layer and a protective layer from peeling off. 
     Means for Solving the Problems and Effect of the Invention 
     The substrate assembly for a PDP of the present invention includes display electrodes, a first dielectric layer covering the display electrodes, a shield layer for shielding vacuum ultraviolet rays, a second dielectric layer and a protective layer stacked in this order on a substrate. 
     In accordance with the present invention, since the second dielectric layer is provided between the protective layer and the shield layer, the peeling of the protective layer resulting from the low adhesion between the protective layer and the shield layer can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing a structure of a front substrate for a PDP of a first embodiment of the present invention. 
         FIG. 2  is a sectional view showing a structure of a front substrate for a PDP of a second embodiment of the present invention 
         FIG. 3  is a graph showing the results of a test of the changes in intensity in Example 1 and Comparative Example 2 of the present invention. 
         FIG. 4  is a schematic perspective view of a conventional PDP. 
         FIG. 5  is a schematic view showing the aspect of discharge of a gas discharge panel according to the conventional PDP. 
     
    
    
     DESCRIPTION OF THE REFERENCE NUMERALS AND SYMBOLS 
       1 : front-side substrate assembly  1   a : front glass substrate  2 : rear-side substrate assembly  2   a : rear glass substrate  3 : display electrodes  31 : transparent electrodes  32 : bus electrodes  4 : dielectric layer  5 : protective layer  6 : address electrodes  7 : barrier ribs  8 : phosphor layers  9 : gas discharge  10 : vacuum ultraviolet rays  11 : visible light  12 : substrate  13 : display electrodes  15 : first dielectric layer  17 : shield layer  19 : second dielectric layer  21 : protective layer X and Y: pair of display electrodes 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described with reference to drawings. The drawings are used for convenience sake of description and accordingly, the present invention is not to be considered as being limited by the embodiments shown in drawings. 
     In the following embodiments, the present invention will be described by exemplifying the case where display electrodes, a dielectric layer and a protective layer are provided on a front-side substrate. In the following embodiments and Examples, the front-side substrate assembly is also referred to as a front substrate. 
     The present invention can be embodied primarily in two embodiments described below. 
     1. First Embodiment 
       FIG. 1  is a sectional view showing a structure of a front substrate for a PDP of a first embodiment of the present invention. The front substrate of this embodiment includes display electrodes  13 , a first dielectric layer  15  covering the display electrodes  13 , a shield layer  17  for shielding vacuum ultraviolet rays, a second dielectric layer  19  and a protective layer  21  stacked in this order on a substrate  12 . In this embodiment, the second dielectric layer  19  acts as an adhesive layer between the shield layer  17  and the protective layer  21 . Therefore, a material of the second dielectric layer  19  is selected so as to have high adhesion to both the shield layer  17  and the protective layer  21 . By sandwiching the second dielectric layer  19  between the shield layer  17  and the protective layer  21 , the adhesion among the shield layer  17 , the second dielectric layer  19  and the protective layer  21  is enhanced and the peeling of the protective layer  21  can be prevented. 
     The substrate  12  is not particularly limited, and any substrate which is known in the art can be used. Specific examples of the substrate include transparent substrates such as a glass substrate, a plastic substrate and the like. 
     As the display electrodes  13 , electrodes made of transparent electrode materials such as ITO, and SnO 2  and electrodes made of metal electrode materials such as Ag, Au, Al, Cu, and Cr, or the like, may be employed. Specifically, electrodes each composed of a transparent electrode  13   a  with a wide width made of materials such as ITO, or SnO 2  and a bus electrode  13   b  with a narrow width made of a metal such as Ag, Au, Al, Cu, Cr or laminates thereof (for example, Cr/Cu/Cr laminate structure) for reducing the resistance of the electrode are employed. Desired number of the display electrodes  13  with desired thickness, width, and spacing may be formed by employing a printing method for Ag and Au and combining a film formation method such as a vapor deposition method, a sputtering method or the like with an etching method for the other materials. 
     The first dielectric layer  15  can be formed from silicon oxide (SiO 2 ), magnesium fluoride (MgF 2 ), lithium fluoride (LiF), potassium chloride (KCl) or the like. Since these materials transmit the vacuum ultraviolet rays, the problem of impurity gas described in a paragraph of BACKGROUND ART can arise, but in accordance with the present invention, it is possible to prevent the occurrence of such a problem. The first dielectric layer  15  is formed, for example, in a thickness of 5 to 15 μm. The first dielectric layer  15  can be formed by a chemical vapor deposition (CVD) method, a sputtering method, or the like. 
     The shield layer  17  is formed from a material which does not transmit the vacuum ultraviolet rays, specifically light with a wavelength of 190 nm or less. For example, the shield layer  17  is made of at least one selected from the group consisting of zirconium (Zr) compounds, aluminum (Al) compounds, titanium (Ti) compounds, yttrium (Y) compounds, zinc (Zn) compounds, low melting point glass, silicon carbide (SiC), and silicon nitride (SiN). That is, the shield layer  17  may be made of any one of these substances, or may be made of a mixture of any two or more of these substances. Examples of the Zr compounds include zirconium oxide (ZrO 2 ), zirconium nitride, and the like, examples of the Al compounds include alumina, aluminum nitride, and the like, examples of the Ti compounds include titania, titanium nitride, and the like, examples of the Y compounds include yttrium oxide, yttrium nitride, and the like, and examples of the Zn compounds include zinc oxide, zinc nitride, zinc sulfide, and the like. The shield layer  17  is formed, for example, in a thickness of 0.1 to 1 μm, and preferably in a thickness of 0.3 to 0.4 μm. The shield layer  17  can be formed by a sputtering method, a vapor deposition method, a sol-gel method, a binder method, or the like. 
     The second dielectric layer  19  can be formed from the same materials and method as those in the descriptions of the first dielectric layer  15 . The materials for forming the second dielectric layer  19  may be identical to or different from those of the first dielectric layer  15 . Since the second dielectric layer  19  is exposed to the vacuum ultraviolet rays, the second dielectric layer  19  is preferably formed in a thickness smaller than the first dielectric layer  15  in order to inhibit the generation of impurity gas, and it is preferably formed in a thickness of one-tenth or less (for example, one-twentieth or less, fiftieth or less) of that of the first dielectric layer  15 . The second dielectric layer  19  preferably has a thickness of 1 μm or less (for example, 0.5 μm or less, 0.2 μm or less). The second dielectric layer  19  is preferably formed in a thickness of 0.01 μm or more (for example, 0.02 μm or more, 0.05 μm or more). The reason for this is that when this thickness is too small, the second dielectric layer  19  may not properly exert its function. 
     By the way, in this embodiment, the substrate assembly has two dielectric layers, but in another embodiment, it may have three or more dielectric layers. 
     The protective layer  21  has a function of protecting the second dielectric layer  19  from damages caused by impingement of ions produced by discharge generated in displaying. The protective layer  21  is composed of, for example, MgO, CaO, SrO, BaO or the like. A thickness of the protective layer  21  is selected to be, for example, 0.5 to 1.5 μm. The protective layer  21  can be formed by a sputtering method, a vapor deposition method, or the like. 
     2. Second Embodiment 
       FIG. 2  is a sectional view showing a structure of a front substrate for a PDP of a second embodiment of the present invention. In the front substrate of this embodiment, a shield layer  17  is formed in a smaller area than areas of the first dielectric layer  15  and the second dielectric layer  19  so that the shield layer  17  is enveloped in the first dielectric layer  15  and the second dielectric layer  19 . Accordingly, the first dielectric layer  15  contacts the second dielectric layer  19  outside the periphery of the shield layer  17 . Put another way, the shield layer  17  is embedded in a dielectric layer composed of the first dielectric layer  15  and the second dielectric layer  19 . The first dielectric layer  15  is in close contact with the second dielectric layer  19  and the shield layer  17  is held between both dielectric layers. Materials of the first dielectric layer  15  and the second dielectric layer  19  are selected so as to have high adhesion to each other. From this viewpoint, the first dielectric layer  15  is preferably formed from the same material as that of the second dielectric layer  19 . Further, in order to effectively prevent the peeling of the protective layer  21 , a material having high adhesion to the protective layer  21  is selected as the material of the second dielectric layer  19 . 
     The materials and the production methods of the respective layers described in the first embodiment hold true in principle for the second embodiment. 
     (Others) 
     The various characteristics described in the above embodiments may be combined. In the case where a plurality of characteristics are included in one embodiment, one or a plurality of these characteristics may be appropriately picked up and employed alone or in combination for the present invention. 
     In the above embodiment, the present invention has been described by exemplifying the case where the display electrodes, the dielectric layer, the protective layer, and the like, are formed on the front-side substrate, but in a inverted panel configuration in which these members are formed on the rear-side substrate, the present invention can also be embodied. 
     3. PDP 
     A PDP can be produced by sticking the rear-side substrate assembly (rear substrate) and the front-side substrate assembly (front substrate) to each other with a sealing material and introducing/encapsulating a discharge gas in a discharge spaces. The PDP can be produced according to, for example, the method described in Patent Document 1. By employing the substrate assembly of the present invention, it is possible to obtain the PDP of the present invention, for example an AC type PDP, including display electrodes  13  for generating surface-discharge, a first dielectric layer  15  covering the display electrodes  13 , and a protective layer  21  for protecting the surface of the first dielectric layer  15 , which are formed on the front-side substrate  12 , characterized in that a shield layer  17  for shielding vacuum ultraviolet rays is formed between the first dielectric layer  15  and the protective layer  21  and a second dielectric layer  19  is formed between the shield layer  17  and the protective layer  21  to sandwich the above-mentioned shield layer  17  between the first dielectric layer  15  and the second dielectric layer  19 . 
     EXAMPLES 
     3-1. Preparation of Front Substrate 
     Example 1 
     (1) After forming transparent electrodes and bus electrodes on a glass substrate, a first dielectric layer made of SiO 2  was formed in a thickness of 10 μm under the following conditions. 
     Apparatus: parallel plate plasma CVD apparatus 
     Species of gas/flow rate: SiH 4 /8000 sccm, N 2 O/110000 sccm 
     RF power: 17 kW 
     Substrate temperature: 450° C. 
     Degree of vacuum: 2.5 Torr 
     (2) Next, a shield layer made of ZrO 2  was formed in a thickness of 0.3 μm under the following conditions. 
     Apparatus: electron beam vapor deposition apparatus 
     Degree of vacuum: 10 −6  Torr 
     Power source: 1.5 kW, 150 mA 
     (3) Then, a second dielectric layer made of SiO 2  was formed in a thickness of 0.1 μm under the following conditions. 
     Apparatus: parallel plate plasma CVD apparatus 
     Species of gas/flow rate: SiH 4 /3000 sccm, N 2 O/40000 sccm 
     RF power: 7 kW 
     Substrate temperature: 450° C. 
     Degree of vacuum: 3 Torr 
     (4) Next, a protective layer made of MgO was formed in a thickness of 0.8 μm under the following conditions to prepare a front substrate. 
     Degree of vacuum: 4×10 −7  Torr 
     Power source: 1.5 kW, 150 mA 
     Temperature: 150° C. 
     (5) The shield layer was formed so as to be enveloped in the first dielectric layer and the second dielectric layer like the second embodiment. The peeling of the protective layer did not occur immediately after the film formation. 
     Comparative Example 1 
     A Second Dielectric Layer is not Provided 
     A first dielectric layer, a shield layer and a protective layer were formed under the same conditions as in Example 1 to prepare a front substrate. A second dielectric layer was not formed. As a result of this, the peeling of the protective layer occurred immediately after the film formation. 
     Comparative Example 2 
     A Shield Layer is not Provided 
     A first dielectric layer and a protective layer were formed under the same conditions as in Example 1 to prepare a front substrate. A shield layer and a second dielectric layer were not formed. The peeling of the protective layer did not occur immediately after the film formation. 
     3-2. Preparation of PDP and Test of Changes in Intensity 
     A PDP was prepared according to the method described in Patent Document 1 using the front substrates in Example 1 and Comparative Example 2. A test of the changes in intensity was carried out on each of the prepared PDPs. The results of the test are shown in  FIG. 3 . It is found from  FIG. 3  that the intensity in using the substrate in Example 1 is decreased significantly more slowly than that in using the substrate in Comparative Example 2. The reason for this is thought to be by virtue of inhibiting the generation of impurity gas by the shield layer provided in Example 1. 
     3-3. Add-Up 
     From the above descriptions, it has been found that in accordance with the PDP of the present invention, it is possible to prevent the peeling of the protective layer and to inhibit the generation of impurity gas from the dielectric layer due to the vacuum ultraviolet rays.