Patent Application
20100289726
This invention relates to a display device, and relates to a structure of a plasma display panel capable of operating at a reduced discharge voltage and a method for manufacturing the plasma display panel.
The demand for PDP display devices using a plasma display panel (PDP) grows as a flat display capable of large-screen displays. The PDP display device includes a plasma display panel, a front panel placed on the front of the plasma display panel, a drive circuit placed on the back of the plasma display panel, a frame containing them, and the like.
On the front substrate scan electrodes extend from, for example, the left-hand end of the front substrate to the display area, while discharge-sustain electrodes extend from, for example, the right-hand end of the front substrate to the display area. On the back substrate, address electrodes each extend in a direction at right angles to the scan electrode and the discharge-sustain electrode. Sub-pixels are respectively formed in positions corresponding to the intersections of the address electrodes with the scan and discharge-sustain electrodes. The sub-pixels are arranged in matrix form in the display area to form an image.
A discharge is initiated between the scan electrode and the discharge-sustain electrode which are formed on the front substrate, to cause a phosphor in each sub-pixel to emit light for generation of an image. In this regard, in general, a voltage of 180V to 190V is applied between the scan electrode and the discharge-sustain electrode in order to initiate a discharge between the scan electrode and the discharge-sustain electrode. Accordingly, a dielectric layer is deposited to cover the scan electrode and the discharge-sustain electrode for preventing dielectric breakdown from occurring between the scan electrode and the discharge-sustain electrode.
For maintaining a low discharge voltage, it is desirable that a substance having a low secondary electron emission coefficient γ exists in the discharge space. Therefore, the surface of the dielectric layer is coated with an approximately 1-μm thick coating of MgO having a high secondary electron emission coefficient γ as a protective film. However, MgO is deliquescent and therefore exposure of it to the air transforms the surface of the protective film, thus making the surface become clouded or decreasing the secondary electron emission coefficient.
A measure to prevent such transformation of the protective film in the air as described above is described in “Patent Literature 1” in which the protective film is temporarily covered with a protective film such as an SiO2 film (hereinafter referred to as “inert film”), and then the inert film is removed around electrodes by generating a discharge after a plasma display panel is completed. On the other hand, “Patent Literature 2” describes the use of SiOx for an inert film in which x is set to a value ranging from 1.3 to 1.9 to improve the barrier properties against oxygen or moisture vapor.
The protective film placed on the display substrate is required to have a high secondary electron emission coefficient in order to start and sustain a discharge at a lower voltage. In most cases, a magnesium oxide film is used as a material of the protective film to fulfill this requirement. The magnesium oxide is a material sufficiently withstanding practical use. However, a material having a higher secondary electron emission coefficient than that of magnesium oxide is required to reduce the power consumption when driving the plasma display panel, that is, to initiate a discharge at a low voltage.
As materials having a high secondary electron emission coefficient for this purpose, strontium oxide, calcium oxide and the like have been found, but the film of strontium oxide, calcium oxide and/or the like are unstable because, upon exposure to the air, they are converted to carbonate or hydroxide, so that it is impossible to take full advantage of strontium oxide, calcium oxide or the like without any additional process from the viewpoint of the manufacturing process. An approach to address this problem is proposed, in which, as described in “Patent Literature 1”, the surface of the film of strontium oxide, calcium oxide or the like after the film formation process is covered with an inert film to inhibit reaction with the air, and then the inert film is removed after the completion of the panel.
Such an inert film is required (1) to be easily deposited by sputtering and (2) to have the ability to completely seal a high γ material included in the underlayer from carbon dioxide and moisture vapor in the atmosphere (to have outstanding barrier properties). Examples of materials fulfilling the requirement of property (1) include SiO2. However, since SiO2 contains many structural defects, it does not adequately fulfill the requirement of (2) barrier properties. There is “Patent Literature 2” as a method for improving such inadequate barrier properties of SiO2. “Patent Literature 2” employs SiOx (x=1 to 1.9) with a lower number of bonds for oxygen atom than that of SiO2 to improve the barrier properties. However, this method does not offer adequate barrier properties, and also raises problems of the difficulty of controlling the aforementioned value x, and the like.
It is an object of the present invention to form an inert film having outstanding sputtering properties and outstanding barrier properties. Also, it is an object of the present invention to use this inert film thus formed to achieve a stable plasma display panel capable of low discharge voltage operation.
The present invention is made to solve the problems as described above, and the following is the specific means.
(1) A plasma display panel includes a front substrate on which a dielectric layer is formed to cover first discharge electrodes and second discharge electrodes and a protective film is formed to cover the dielectric layer, and a back substrate on which a dielectric layer is formed to cover address electrodes and partition walls are formed on the dielectric layer, the front and back substrates being sealed together by a sealing material formed along a periphery. An inert film is formed of a metal oxide and a metal on the protective film, and portions of the inert film corresponding to the discharge electrodes are removed.
(2) The plasma display panel described in (1), wherein, when the amount of metal oxide is x and the amount of metal is y, y/(x+y) ranges from 0.5 mol % to 50 mol %.
(3) The plasma display panel described in (1), wherein the metal oxide is any of metal oxides of SiO2, Al2O3, TiO2, MgO and ZrO, and the metal is a rare-earth metal such as Tb, La, Ce, Eu, Yb, Y or Sc, an alkaline-earth metal such as Mg, Ca, Sr or Ba, or an alkali metal such as K or Na.
(4) The plasma display panel described in (1), wherein the protective film includes MgO, SrO, CaO, BaO or a mixture including them.
(5) The plasma display panel described in (1), wherein the inert film has a film thickness ranging from 10 nm to 500 nm.
(6) A method of manufacturing a plasma display panel including a front substrate on which a dielectric layer is formed to cover first discharge electrodes and second discharge electrodes, a protective film is formed to cover the dielectric layer and an inert film is formed on the protective film, and a back substrate on which a dielectric layer is formed to cover address electrodes and partition walls are formed on the dielectric layer, the front and back substrates being sealed together by a sealing material formed along a periphery. The method comprises the steps of simultaneous film formation of a metal oxide and a metal by vapor deposition to form the inert film, and removal of a portion of the inert film exposed to a plasma display in an aging step.
(7) The method of manufacturing a plasma display panel described in (6), wherein the vapor deposition includes heating, by electron beam heating, of vapor deposition materials which are a metal oxide and a metal placed in a single hearth.
(8) The method of manufacturing a plasma display panel described in (6), wherein the vapor deposition is performed by placing a metal oxide and a metal in different hearths, and then separately heating and controlling the metal oxide and the metal.
(9) A method of manufacturing a plasma display panel including a front substrate on which a dielectric layer is formed to cover first discharge electrodes and second discharge electrodes, a protective film is formed to cover the dielectric layer and an inert film is formed on the protective film, and a back substrate on which a dielectric layer is formed to cover address electrodes and partition walls are formed on the dielectric layer, the front and back substrates being sealed together by a sealing material formed along a periphery. The method comprises the steps of simultaneous film formation of a metal oxide and a metal by sputtering to form the inert film, and removal of a portion of the inert film exposed to a plasma display in an aging step.
Since a metal such as a rare-earth metal has a high affinity for oxygen, it traps carbon dioxide and moisture vapor in the atmosphere to prevent the carbon dioxide and the moisture vapor from penetrating the underlayer surface of materials having a high secondary electron emission coefficient. As a result, a high y material surface is kept clean after the inert film has been removed. Since the secondary electron emission from a clean high y material occurs in a low voltage, a reduction in drive voltage of the PDP is made possible.
In addition, since the present invention allows formation of an inert film having outstanding barrier properties, SrO, CaO, BaO or a mixture including them, which cannot be conventionally easily used for a protective film, can be used for the protective film. Since these films of them have a higher secondary electron emission coefficient than that of MgO, a plasma display panel in which the discharge voltage is low can be achieved.
The contents of the present invention will be described below in detail with reference to examples.
The scan electrode 20 in turn includes a scan discharge electrode which is made of ITO (Indium Tin Oxide) and operates actually as a discharge electrode, and a scan bus electrode which is provided for supplying voltage from a terminal. In the following, the scan bus electrode is also called a Y bus electrode 22, and the scan discharge electrode is also called a Y discharge electrode 21. Note that if the “Y electrode 20” is simply described, this means the Y electrode 20 including the Y bus electrode 22 and the Y discharge electrode 21.
The discharge sustain electrode 10 in turn includes a discharge sustain electrode 10 which is made of ITO (Indium Tin Oxide) and operates actually as a discharge electrode, and a discharge-sustain bus electrode which is provided for supplying voltage from a terminal. In the following, the discharge sustain bus electrode is also called an X bus electrode 12, and the discharge sustain electrode 10 is also called an X discharge electrode 11. Note that if the “X electrode 10” is simply described, this means the X electrode 10 including the X bus electrode 12 and the X discharge electrode 11.
Each of the X and Y bus electrodes 12 and 22 has a metal multilayer structure in which chromium, copper and chromium are laminated in this order from the front substrate 1. The chromium deposited on the front substrate 1 has an outstanding adhesion property to glass and has an effect of improving the contrast because the chromium surface is black. Copper is used to reduce the resistance of the bus electrode. The copper is further covered with chromium. The chromium is provided for preventing the copper surface from being oxidized to effect a change in resistance.
In some cases, the chromium on the front glass may have a multilayer structure of chromium oxide and chromium. Since chromium oxide is black and has a lower reflectance than chromium, it is possible to more improve the image contrast. Chromium oxide also has an outstanding adhesion property to glass. In addition, the contact face with copper is chromium, the copper is not oxidized.
In
A dielectric layer 5 is deposited to cover the X electrodes 10 and the Y electrodes 20. For the dielectric layer 5, a low-melting-point glass with a softening point of about 500° C. is used. A protective film 6 is deposited on the dielectric layer 5. The protective film 6 is deposited by mainly using magnesium oxide (MgO) through sputtering or vapor deposition techniques. In the present invention, since an inert film 60 is formed on the protective film 6 as described below, rather than MgO, SrO, CaO, BaO or an alloy of them can be employed.
In
Note that, in
On the back substrate 2, address electrodes 30 (hereinafter also called “A electrode(s)”) are formed to extend at right angles to the X bus electrode 12 or the Y bus electrode 22. The structure of the address electrode 30, which is similar to the structure of the X bus electrode 12 or the Y bus electrode 22, is a chromium-copper-chromium multilayer structure. The address electrodes 30 are covered with a dielectric layer 5. Typically, the dielectric layer 5 deposited on the back substrate 2 is formed by use of the same material as that of the dielectric layer 5 deposited on the front substrate 1.
Partition walls 7 are formed on the dielectric layer 5 of the back substrate 2 to extend in the same direction as that of the address electrode 30 such that the address electrode 30 is located between adjacent partition walls 7. In
The spaces surrounded with the front substrate 1, the back substrate 2 and the partition walls 7 are discharge spaces filled with discharge gas. A range between a pair of the bus wirings and between the partition walls corresponds to one discharge cell (sub-pixel), and in the case of color display, the three sub-pixels respectively correspond to three primary colors (R, G, B) to form one pixel.
The principle of light emission of the plasma display panel will be described below. First, a voltage of about 100V to 200V (a discharge breakdown voltage) is applied between the address electrode 30 corresponding to a cell intended for light emission and the scan electrode 20 corresponding to this cell. Because the address electrode 30 and the bus wiring interest at right angles, a single cell located at the intersection of them can be selected. In the selected cell, a weak discharge is generated between the discharge electrode (the Y electrode 20 in this case) and the address electrode 30 to which the voltage is applied, whereupon electric charge (wall charge) accumulates on the protective film 6 laid on the dielectric layer 5 on the front substrate 1. In this manner, writing is performed on all the cells in the display area using the electric charge. This period is a writing period during which an image is not generated.
Then, in a discharge sustaining period (sustain period), a high frequency pulse is applied between the X electrode 10 and the Y electrode 20 to initiate a sustaining discharge. At this stage, a sustaining discharge is generated only in the cells with the accumulation of wall charge. As a result of this sustaining discharge, ultraviolet light is generated, and the ultraviolet light causes the phosphor 8 to emit light. The visible light produced from the phosphor 8 is emitted from the front substrate 1, which is visibly recognized by a human being. Since the phosphors 8 located in only the cells in which electric charge has accumulated in the writing period emit light, an image is formed.
In
If the inert film 60 has a small thickness, the barrier properties cannot be ensured, whereas if it has a large thickness, the time required for a subsequent discharge removal process is increased. A lower limit film-thickness required for obtaining the minimum level of the barrier properties is approximately 10 μm, and an upper limit film-thickness required for allowing the removal process to be terminated within a realistic time period is approximately 500 nm. Ideally, the inert film 60 is desirably formed in a minimum film-thickness offering ensured barrier properties. Accordingly, an ideal film-thickness depends on types or concentrations of mixed metal.
A lower limit of a mixing ratio of required metal is determined based on a lower limit concentration allowing the inert film 60 to have a required level of the barrier properties, and an upper limit of the same is determined such that the inert film 60 does not have electrical conductivity which affects a discharge. A range of metal concentration meeting such requirements is from 0.5 mol % to 50 mol %.
In
Then, the phosphors 8 are formed in the recesses surrounded with the partition walls 7. Then, the back substrate 2 is coated with frit glass which is to be a sealing layer by use of a dispenser or the like. Then, the front glass 1 and the back glass 2 are combined together and then heated in a baking furnace in order to melt and solidify the frit glass which is a sealing material.
The sealing material is melted and the inside is evacuated through a sealing pipe to produce a vacuum up to about some Pa. Then, for example, a Xe-10%+Ne-90% discharge gas is sealed under about 50 kPa, and then the sealing pipe is tipped off.
The aging discharge results in removal of the inert film 60, in this case, the Tb—SiO2 layer, on the surface of the protective film 6. The determination whether or not the inert film 60 is removed can be made by monitoring the discharge voltage.
The inert film 60 is not entirely removed from the protective film 6, and only the portions of the inert film 60 corresponding to the discharge electrodes are removed. Since of most of the inert film 60 removed by sputtering adheres to the structures, including the remaining inert film 60, located around the removed portions of the inert film 60, the discharge gas is not contaminated.
The mixing of metal into the inert film 60 in this manner allows the metal to trap carbon dioxide and water in the atmosphere to prevent the carbon dioxide and the water from penetrating the underlying protective film 6 even when the back substrate 2 is exposed to the atmosphere before the sealing process so that degradation of the protective film 6 can be prevented.
The foregoing has described the simultaneous deposition of SiO2 and Tb to form an inert film 60 as an example. Materials for the inert film 60 are not limited to the SiO2 and Tb, and an oxide-metal mixture film, which is obtained by simultaneous deposition of SiO2 and another metal, can be used. Metals that can be used in combination with SiO2 include, in addition to Tb, a rare-earth metal such as La, Ce, Eu, Yb, Y and Sc, an alkaline-earth metal such as Mg, Ca, Sr, Ba and the like, and an alkali metal such as K and Na.
The foregoing has described the use of SrO+Cao as a material for the protective film 6 by way of example. However, materials for the protective film 6 are not limited to this, and Ba, MgO or a mixture including them can be used. At present, MgO is most widely used for the protective film 6, and application of the present invention to an MgO protective film 6 makes it possible to prevent transformation of MgO to achieve a narrower range of variation in discharge breakdown voltage.
The use of SrO, CaO, BaO or a mixture including them which has a large value as a secondary electron emission coefficient and exhibits outstanding properties as a protective film 6 has been previously impossible because they are transformed by oxygen, water and the like in the atmosphere, but the use of them is made possible by the present invention, thus achieving a reduction in the discharge voltage of the plasma display panel.
A plasma display panel made in the example is similar in structure to the plasma display panel made in Example 1. This example differs in a method of producing an inert film 60 from Example 1.
SiO2 and Tb differ in vapor deposition rate. In this example, however, since SiO2 and Tb can be independently controlled for vapor deposition, a mixing ratio of two types of vapor-deposition components can be accurately controlled. The front substrate 1 with an evaporated inert film 60 is moved in the direction shown by the arrow in
In
A plasma display panel made in the example is similar in structure to the plasma display panel made in Example 1. This example differs in a method of producing an inert film 60 from Examples 1 and 2. In Examples 1 and 2, vacuum vapor deposition is used to form the inert film 60. In this example, however, sputtering is used to form the inert film 60.
In
In the aforementioned example, as a sputtering target 300, one with Tb implanted in a SiO2 target is used. It is possible to use a SiO2 target with a rare-earth metal such as La, Ce, Eu, Yb, Y or Sc, a SiO2 target with an alkaline-earth metal such as Mg, Ca, Sr, Ba or the like, and a SiO2 target with an alkali metal such as K or Na, instead of Tb. In this case, it is possible to form an inert film 60 of an SiO2 film and each metal.
The aforementioned examples have described taking SiO2 as an example of metal oxide. However, the metal oxide is not limited to SiO2, and the present invention can apply in the case of using Al2O3, TiO2, MgO, ZrO or the like.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/003524 | 11/28/2008 | WO | 00 | 7/20/2010 |
