JP2007026794A - Raw material for protective layer - Google Patents

Abstract

Disclosed is a plasma display panel that has a protective layer having a stable film quality and is excellent in display quality with little change over time over a long period of time.
A protective layer for forming a protective layer 15 of a plasma display panel 1 in which a display electrode 12 formed on a front glass substrate 11 is covered with a dielectric layer 14 and the dielectric layer 14 is covered with a protective layer 15. The raw material is made of a mixture of magnesium oxide and metallic magnesium, and the oxygen atom / magnesium atom ratio is set to 0.3 to 1.0, so that both the denseness of the film quality and the light transmittance can be achieved.
[Selection] Figure 1

Description

  The present invention relates to a plasma display panel used for an image display device or the like, and more particularly to a protective layer raw material for forming a protective layer.

  Plasma display panels (hereinafter referred to as PDPs) are attracting attention as large-screen display devices because they can display at higher speed than liquid crystal panels and are easy to increase in size. The development of PDPs aimed at improving display quality and high reliability has become increasingly important.

  In general, an AC drive surface discharge type PDP adopts a three-electrode structure, and this type of PDP has a structure in which two glass substrates of a front plate and a back plate are arranged to face each other at a predetermined interval. The front plate has a pair of display electrodes formed of a stripe-shaped scan electrode and a sustain electrode formed on a glass substrate, a dielectric layer that covers the display electrode and accumulates electric charge and functions as a capacitor, The protective layer is formed on the dielectric layer and has a thickness of about 1 μm.

  On the other hand, the back plate has a plurality of stripe-shaped address electrodes formed on a glass substrate, a base dielectric layer covering the address electrodes, barrier ribs formed thereon, and display cells formed by the barrier ribs. It is comprised by the fluorescent substance layer which light-emits each applied red, green, and blue.

  The front plate and the back plate are hermetically sealed with their electrode forming surfaces facing each other, and a discharge gas such as neon and xenon is sealed at a pressure of 400 Torr to 600 Torr in the discharge space formed by the barrier ribs.

  By selectively applying a video signal voltage to the display electrodes, the discharge gas is discharged, and the ultraviolet rays generated thereby excite each color phosphor layer to emit red, green, and blue colors, thereby producing a color image. it's shown.

  The protective layer that covers the dielectric layer of the front plate is formed using a material having high sputtering resistance due to ion bombardment, and protects the dielectric layer from sputtering due to discharge, and also from the surface of the protective layer. It has a function of reducing the drive voltage for discharging electrons and discharging the discharge gas. Therefore, the protective layer is subjected to ion bombardment as the lighting time of the PDP increases, and the film thickness becomes thin, and the emission characteristics of secondary electrons from the surface of the protective layer change. As a result, a time delay occurs between the application of a voltage to the display electrode and the occurrence of the write discharge, which causes a flickering of the display screen of the PDP and significantly deteriorates the display quality.

In general, the protective layer is formed by a vacuum film forming technique using a single crystal magnesium oxide (MgO) material. Secondary electron emission performance is related to the refractive index of the protective layer, and by adjusting the film formation conditions during the formation of the protective layer, the refractive index is limited to a certain range and a stable discharge without flickering is realized. A method has been proposed (see, for example, Patent Document 1).
JP 2003-317631 A

  However, since MgO is a highly hygroscopic material, when the protective layer is formed by a vacuum film forming technique, a large amount of moisture adsorbed on the MgO raw material is desorbed in vacuum, so that the crystallinity is not stable and stable. It becomes difficult to form a quality protective layer. For this reason, the ion bombardment resistance and secondary electron emission characteristics of the protective layer become unstable, which adversely affects the life and discharge characteristics of the PDP. That is, the PDP has a problem that the surface quality exposed to the discharge space changes as the lighting time increases and the display quality changes with time, resulting in a large variation in life. In addition, there is a problem that the ion impact resistance is satisfied and the light transmittance cannot be satisfied.

  It is an object of the present invention to provide a protective layer raw material that can realize both ion bombardment resistance and light transmittance as a protective layer, and that does not impose a burden on production facilities and processes.

  In order to solve the above-described problems, the protective layer raw material of the present invention is a protective layer raw material for forming a protective layer of a PDP, and the protective layer raw material has an oxygen atom / magnesium atomic ratio of 0. .3 to 1.0.

  According to such raw materials, it is possible to realize a protective layer having a dense and stable crystal structure and a large light transmittance, and having a long life and excellent display quality.

  Further, the raw material for the protective layer may be a mixture of magnesium oxide and magnesium metal. According to such a raw material for a protective layer, it becomes possible to set the ratio of oxygen atoms and magnesium atoms with high accuracy and easily.

  Further, the protective layer raw material may be magnesium oxide produced in an overreduced state. According to such a protective layer raw material, it becomes possible to easily reduce the ratio of oxygen atoms when producing the protective layer raw material.

  As described above, according to the raw material for a protective layer of the present invention, a protective layer having a dense and stable crystal structure can be formed for the protective layer covering the dielectric layer formed on the front plate. By increasing the crystallinity of the protective layer, uniform display quality can be maintained over a long period of time. Therefore, it is possible to provide a long-life and high-quality PDP with little change with time.

  Hereinafter, the raw material for protective layers and the manufacturing method of a protective layer using the same in embodiment of this invention are demonstrated using drawing.

(Embodiment)
An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a partial perspective view showing a basic structure of an AC surface discharge type PDP, FIGS. 2 and 3 are schematic configuration diagrams of a vacuum vapor deposition apparatus for forming a protective layer 15 of the PDP, and FIG. 4 is for a protective layer. It is a figure which shows the relationship between the characteristic of a raw material, and a refractive index. FIG. 5 is a diagram showing the relationship between the properties of the protective layer raw material and the screen display quality of the PDP.

  As shown in FIG. 1, the AC surface discharge type PDP 1 includes a front plate 10 and a back plate 20 that are arranged to face each other. The front plate 10 forms a display electrode 12 by forming a plurality of pairs of scan electrodes 12 a and sustain electrodes 12 b in a stripe shape on a front glass substrate 11. A black stripe 13 is formed between the display electrodes 12. Furthermore, a dielectric layer 14 is formed on the scan electrode 12a, the sustain electrode 12b, and the black stripe 13, and a protective layer 15 made of MgO is formed so as to cover the dielectric layer 14. .

  On the other hand, the back plate 20 is provided with a striped address electrode 22 on a back glass substrate 21 so as to be orthogonal to the scan electrode 12a and the sustain electrode 12b. A base dielectric layer 23 is formed so as to cover the address electrodes 22, and a partition wall 24 is formed on the base dielectric layer 23 so as to sandwich the address electrodes 22 in the same direction as the address electrodes 22. The phosphor layer 25 is formed.

  The front plate 10 and the back plate 20 are arranged to face each other, and the periphery is sealed with a sealing member (not shown) to form the discharge space 30. The discharge space 30 is formed between adjacent barrier ribs 24 and forms a cell related to image display in an area where a pair of adjacent display electrodes 12 and one address electrode 22 intersect. The discharge space 30 is filled with a discharge gas such as a mixed gas of neon (Ne) or xenon (Xe) at a pressure of 53200 Pa (400 Torr) to 79800 Pa (600 Torr).

  In the PDP 1 having such a configuration, a pulsed voltage is applied between the scan electrode 12a and the sustain electrode 12b to discharge the discharge gas in the discharge space 30 to generate ultraviolet rays, and the phosphor layer 25 is irradiated with ultraviolet rays. To do. As a result, visible light is emitted from the phosphor layers 25 of the respective colors and transmitted from the surface of the front plate 10 to perform color image display.

  Next, as an embodiment of the present invention, a method for forming the protective layer 15 and a raw material for the protective layer will be described. The protective layer 15 is formed by physical vapor deposition. The physical vapor deposition method is a method of forming a thin film on a substrate by heating and evaporating or sublimating a solid raw material under a low pressure, and specific forming methods include a vacuum deposition method and a sputtering method. Method and ion plating method. In the embodiment of the present invention, the protective layer 15 is formed by vacuum deposition.

  FIG. 2 is a schematic configuration diagram showing an example of a vacuum deposition apparatus. As shown in FIG. 2, the vacuum vapor deposition apparatus 40 includes a vacuum pump 41, a sealed container 42 and an electron gun 43, and the vacuum pump 41 is connected to the sealed container 42. Further, an MgO evaporation unit is provided in the lower part of the sealed container 42, and a substrate holding part is provided in the upper part. The MgO evaporating section is composed of an electron gun 43 and a water-cooled hearth 44. A protective layer raw material 45 is supplied to the hearth 44 by a raw material supply means (not shown) and arranged at a predetermined position. On the other hand, a front plate holding member (not shown) and a front plate heating heater 47 are provided in the substrate holding portion, and the front plate 10 is held facing the hearth 44 by the front plate holding member. In the embodiment of the present invention, for the protective layer raw material 45, for example, a pellet-shaped vapor deposition material obtained by molding and sintering a material obtained by mixing high-purity MgO powder and Mg powder under high temperature and high pressure is used. Moreover, the mixing ratio of the MgO powder and the Mg powder is adjusted so that this pellet-shaped vapor deposition material has an oxygen atom / magnesium atom ratio of 0.3 to 1.0.

  Next, the inside of the sealed container 42 is placed in an oxygen atmosphere, and the front plate 10 is heated to a predetermined temperature by the front plate heater 47. Thereafter, an electron beam 46 is emitted from the electron gun 43 and irradiated to the protective layer raw material 45 accommodated in the hearth 44. Thereby, the raw material 45 for protective layers is heated and MgO is evaporated. The evaporated MgO adheres so as to cover the dielectric layer 14 (not shown) formed on the front plate 10, and the protective layer 15 of the MgO thin film is formed. An example of film forming conditions for forming these protective layers 15 is as follows.

Ultimate pressure before vapor deposition in sealed container 42: 5.0 × 10 ⁻⁴ Pa or less Heating temperature of front plate 10 during vapor deposition: 250 ° C.
Emission current of electron gun 43: 250 mA
Supply pressure of oxygen gas in the sealed container 42: 2.0 × 10 ⁻² Pa
In the embodiment of the present invention, the case of using the vacuum deposition method as the film forming method for forming the protective layer 15 has been described. However, the present invention is not limited to the vacuum deposition method, and a sputtering method, an ion plating method, or the like is used. The protective layer 15 can be formed. Also in this case, the same effect as that of the embodiment of the present invention can be obtained by controlling the components of the target material and the raw material and forming a film using the material.

  Further, in the embodiment of the present invention, a mixture of MgO powder and Mg powder is used as the protective layer raw material 45, but the protective layer raw material is manufactured in an overreduced state, that is, oxygen atom Less magnesium oxide crystals may be used.

  Further, as an application example of the vacuum deposition method in the embodiment of the present invention, as shown in FIG. 3, the raw material supplied to the hearth 44 is divided into, for example, two systems of magnesium oxide 50a and metal magnesium 50b. Film formation can be performed by controlling the conditions of vapor deposition. By using this method, various controls can be performed on the deposition conditions.

Further, in the embodiment of the present invention, the MgO film is used as the protective layer raw material 45, but Al ₂ O ₃ , CaO, BaO, TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , HfO _{2 are used.} The same effect as that of the present invention can be expected by using a material such as a metal oxide or mixed oxide having excellent ion bombardment resistance and a large secondary electron emission coefficient and applying the method according to the present invention. be able to.

  Next, characteristics and effects of the protective layer 15 formed by the above method will be described.

  In the embodiment of the present invention, the protective layer 15 made of an MgO thin film is formed by changing the oxygen atom / magnesium atomic ratio in the protective layer raw material 45, and the refractive index and extinction of the MgO thin film in the visible light region (wavelength 550 nm). The coefficient was measured. The measurement results are shown in FIGS. The protective layer raw material 45 is a vapor-deposited mixture of high-purity MgO powder and metallic magnesium so that the oxygen atom / magnesium atomic ratio is 0.1, 0.3, 0.5, 0.7, 1.0. Material used. For these evaluations, an MgO thin film was formed on a silica substrate and measured.

  FIG. 4 shows the relationship between the properties of the raw material for the protective layer and the refractive index. As shown in FIG. 4, it can be seen that the refractive index of the MgO thin film increases as the oxygen atom / magnesium atom ratio decreases. The refractive index is closely related to the packing density of the thin film. In general, the higher the refractive index, the higher the packing density. Therefore, a dense MgO thin film can be formed by reducing the ratio of oxygen atoms in the protective layer raw material. In the embodiment of the present invention, the protective layer raw material 45 is mixed with magnesium oxide and metal magnesium so that the oxygen atom / magnesium atomic ratio is 0.3 to 1.0, and the protective layer 15 is also within this range. Has a high refractive index of 1.5 to 1.7.

  On the other hand, FIG. 5 shows the relationship between the characteristics of the protective layer raw material and the extinction coefficient. The extinction coefficient is a numerical value indicating the degree of light absorption. When the extinction coefficient is large, the light absorption increases and the transmitted light decreases. As shown in FIG. 5, when the oxygen atom / magnesium atom ratio is 0.3 or less, the extinction coefficient increases rapidly. This is because, when the ratio of oxygen atoms in the protective layer raw material is reduced, even if oxygen gas is introduced during vacuum deposition, magnesium atoms are not oxidized and oxygen vacancies increase in the thin film, even in the visible light region. This is presumably because the film has a low transmittance. Therefore, when such an MgO film is used as the protective layer 15, the light transmittance is lowered, the luminance is lowered, and the display quality is lowered, so that it cannot be used for the PDP 1. However, in the embodiment of the present invention, since the oxygen atom / magnesium atom ratio of the raw material for the protective layer is 0.3 or more, a good display quality can be obtained without causing a decrease in luminance of the display image of the PDP 1. Can do.

  From the above results, by setting the oxygen atom / magnesium atom ratio in the raw material for the protective layer, which is the vapor deposition material, to 0.3 to 1.0, the dense protective layer 15 having good crystallinity can be formed. Therefore, the ion impact resistance of the protective layer 15 is improved, and the life of the PDP 1 can be extended. Moreover, since the protective layer 15 has high transparency, display quality can be improved.

  According to the raw material for the protective layer of the present invention, a long-life and high-quality protective layer can be realized with high productivity without imposing a special burden on manufacturing equipment and processes.

  As described above, the PDP using the raw material for the protective layer of the present invention is particularly useful as a large-screen display device because of its high quality and long life.

Partial perspective view showing basic structure of AC surface discharge type PDP The schematic block diagram of the vacuum evaporation system which forms a protective layer using the raw material for protective layers in embodiment of this invention The schematic block diagram which shows the other example of the vacuum evaporation system which forms a protective layer using the raw material for protective layers in embodiment of this invention The figure which shows the relation between the characteristic and refractive index of the raw material for the same protective layer Figure showing the relationship between the properties of the protective layer and the extinction coefficient

Explanation of symbols

1 PDP
DESCRIPTION OF SYMBOLS 10 Front plate 11 Front glass substrate 12 Display electrode 12a Scan electrode 12b Sustain electrode 13 Black stripe 14 Dielectric layer 15 Protection layer 20 Back plate 21 Rear glass substrate 22 Address electrode 23 Base dielectric layer 24 Partition 25 Phosphor layer 30 Discharge space DESCRIPTION OF SYMBOLS 40 Vacuum evaporation apparatus 41 Vacuum pump 42 Airtight container 43 Electron gun 44 Hearth 45 Raw material for protective layers 46 Electron beam 47 Heater for front plate heating 50a Magnesium oxide 50b Metal magnesium

Claims (3)

A protective layer raw material for forming a protective layer of a plasma display panel, wherein the protective layer raw material has an oxygen atom / magnesium atom ratio of 0.3 to 1.0. . 2. The protective layer raw material according to claim 1, wherein the protective layer raw material is a mixture of magnesium oxide and metallic magnesium. The raw material for a protective layer according to claim 1, wherein the raw material for the protective layer is magnesium oxide produced in an overreduced state.

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