JP2002163988A - Plasma display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma display panel in which the secondary electron discharge is efficiently made and which is equipped with a protecting film having a high durability for ion bombardment in the electric discharge. SOLUTION: The specific surface area of a metal oxide film formed as the further protecting film of the dielectric layer formed on a display electrode is made to be not less than 50 m2 per 1 g of the film weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is Purazumade _Lee spray panel used as a display device (hereinafter, PDP
).

[0002]

2. Description of the Related Art A PDP is a display device having a large number of minute discharge spaces sealed in a gap between two glass substrates.

For example, a matrix display type PDP
In this example, a large number of electrodes are arranged in a lattice pattern, and an image is displayed by selectively causing the discharge cells at the intersections of the electrodes to emit light. In a typical surface discharge type AC PDP, the display electrodes on the front substrate are covered with a dielectric layer, and a protective film is formed on the dielectric layer. Here, the dielectric layer is provided to accumulate charges generated by applying a voltage to the electrodes. The protective film is provided to prevent damage to the dielectric layer due to collision of ions in the discharge gas, and to reduce the firing voltage by emitting secondary electrons. Conventionally, as a protective film, a magnesium oxide film having a thickness of about several hundred nm formed using a thin film method such as evaporation has been mainly used.

Japanese Patent Laid-Open Publication No. Hei 7-37510 discloses a plasma display panel in which the amount of secondary electrons emitted is increased by increasing the surface area of a protective layer of magnesium oxide with irregularities.

[0005]

Problems to be solved by the protective film in the AC type PDP are to reduce the firing voltage by increasing the secondary electron emission coefficient and to reduce the damage of the protective film due to ion sputtering during discharge. Various characteristics such as extending the life are given.

The protective film is formed by an electron beam evaporation method or the like. However, the relationship between the physical properties of the protective film and the above-mentioned characteristics is not always clear, and it has been difficult to improve the protective film.

An object of the present invention is to provide a PDP having a protective film having a high secondary electron emission coefficient and high durability against ion sputtering.

[0008]

The present invention is characterized in that the protective film has physical properties of 100 m ² or more per gram as a specific surface area defined by, for example, gas adsorption.

Conventionally, an oxide film mainly composed of magnesium oxide has been used as a protective film, and a thin film having a thickness of about several hundred nm has been formed by an electron beam evaporation method or the like.
The relation between the physical properties of the protective film, the discharge characteristics and the sputter resistance is not clear, and there is no guideline for improving the performance of the film at present.

The present inventors have examined the relationship between the physical properties of the protective film and the above characteristics in detail, and found that there is a correlation between the specific surface area of the protective film, the secondary electron emission coefficient, and the ion sputtering resistance. Based on the findings and the findings, the present inventors have made repeated studies and thoughts, and have reached the present invention.

The current protective film is polycrystalline, has fine irregularities on the surface, and has many fine holes in the film. It is considered that the greater the degree of the surface irregularities, the more easily secondary electrons are emitted, and the higher the durability against sputtering by ions. The surface of the protective film is gradually scraped by ion sputtering at the time of discharge. In this case, it is considered that, after the film having many fine holes is shaved, the degree of unevenness of the re-exposed surface is large.

As a method for quantifying the degree of development of the fine uneven surface and the fine pores in the film, there is a specific surface area measuring method by gas adsorption. The present inventors have evaluated in detail the physical properties and characteristics of a magnesium oxide film formed by various methods. As a result, it was confirmed that the larger the specific surface area of the protective film, the higher the secondary electron emission coefficient and the higher the durability against ion sputtering, and the characteristics were quantitatively understood.

Specifically, in terms of 1 g of the protective film,
A film having a specific surface area of 50 m ² or more, preferably 100 m ² or more is superior to a conventional protective film. The conventional protective film is mainly formed by an electron beam evaporation method, but usually has a specific surface area of less than 50 m ² / g. It was also found that no significant effect was obtained.

In the present invention, an oxide is used for the protective film for PDP, but a film containing magnesium oxide as a main component is particularly preferable. Needless to say, components such as calcium oxide, strontium oxide, silica, alumina, and rare earth oxides may be added in order to control the physical properties of the film and improve the characteristics.

[0015]

FIG. 1 is an enlarged view showing a portion constituting one pixel of a PDP to which a protective film of the present invention is applied. FIG. 1A is a perspective view, and FIG.
FIG. 2 is a cross-sectional view of FIG.

The PDP is as shown in FIG.
The front plate 9 and the back plate 4 are provided so as to face each other. On the back substrate 4, three types of phosphors 1 </ b> R (red), 1 </ b> G (green), and 1 </ b> B (blue) for displaying one pixel are provided separated by a partition wall 2. The three types of phosphors 1R, 1G, and 1B are configured so that one pixel can be displayed in each color.

The back substrate 4 is provided with address electrodes 3 wired along the Y-axis direction. The display electrodes 7 are wired on the front substrate 9 along the X-axis direction so as to be orthogonal to the address electrodes. Further, a bus electrode 8 is wired along the display electrode 7. The display electrode 7 and the bus electrode 8 are covered with the dielectric layer 6. This dielectric layer 6 is located on the side facing back substrate 4. Further, a protective film 5 is provided on the surface of the dielectric layer 6. This protective film 5 is located on the side facing the back substrate 30. The front plate 9 and the back plate 4 are integrated into one piece.

A rare gas having a predetermined pressure is sealed as a discharge gas in a gap between the front plate 9 and the back plate 4. The space in which the rare gas is sealed becomes a discharge space.

When a predetermined voltage is applied to the address electrode 3, the display electrode 7, and the bus electrode 8, the phosphor emits light due to the ultraviolet light generated by the rare gas plasma discharge.
Visible light is emitted from the front plate 9 to the outside, and display is performed by the pixel.

According to the protective film having a high specific surface area according to the present invention, the secondary electron emission coefficient from the protective film is improved, and as a result, the discharge starting voltage of the PDP can be reduced. In addition, durability against sputtering due to ion bombardment at the time of discharge can be increased.

Conventionally, the protective film has a thickness of 700
Although a thickness of about m is used, since the film of the present invention has high sputter resistance, the thickness of the protective film can be reduced.

The protective film for a PDP in the present invention is not particularly limited to a film forming method as long as the predetermined specific surface area value intended in the present invention is obtained. Electron beam deposition, sputtering, ion plating _Lee ring method and the like can be used. However, in order to obtain a film having physical properties according to the present invention, it is necessary to devise a method such as optimizing film forming conditions.

In the PDP of the present invention, a gas medium is sealed in the discharge space. As the gas medium, a mixture of rare gas elements is usually used. Specifically, helium,
At least one gas selected from neon, argon, xenon, and krypton is used.

The sealing pressure is not particularly limited.
Desirably, the pressure is between 0 Torr and 760 Torr.

Next, a method for forming the protective film will be described.

In the present invention, an example in which a film is formed by an ion plating method will be described. That is, the protective film 5 of the present invention was formed using an ion plating type vacuum film forming apparatus in which a film material evaporated by electron beam irradiation passes through a high-frequency coil and is deposited on a substrate. As the film material, magnesium oxide particles were used, and oxygen gas was supplied into the vacuum apparatus to form the protective film 5 made of magnesium oxide. Various films having different physical properties were formed by changing the heating temperature of the substrate and the supply amount of oxygen gas during the film formation. As a comparative example, a protective film was also formed by an electron beam evaporation method.

As a method for measuring the specific surface area of the film, there are a gravimetric method, a gas adsorption method, a liquid adsorption method and the like. Here, the gas adsorption method which is relatively easy to measure and has high accuracy is used. The surface area S per unit weight determined by the adsorption method is represented by the following equation.

S = Nmσ (1) Nm: adsorbed amount of monolayer, σ: occupied cross-sectional area of adsorbed molecules. The area of the base is determined from the cross-sectional area occupied by the adsorbed molecules. It is desired that the adsorption probe molecule is inert, does not cause a chemical reaction with the surface, and has a sufficiently small molecular diameter so as to be able to reflect surface irregularities. To calculate the surface area, it is necessary to evaluate the number of molecules occupying the surface. This number is obtained from the adsorption equation.

Here, a typical BET equation was used as the adsorption equation. This is a formula derived when forming a multimolecular adsorption layer, and is often used as a physical adsorption type. V = VmCX / (1-X ) (1-X + CX) (2) V: adsorption number of molecules, Vm: monomolecular adsorption, X = P (suction pressure) / P ₀ (saturated vapor pressure), C: Constant 1 the / _{V (P 0 / P-1} ) = 1 / VmC + (C-1) / VmC x (P / P 0) (3) this method, although the specific surface area of the entire sample is determined,
Since the MgO film is formed on a glass substrate, it is necessary to correct the actual MgO film weight. Here, the weight of the MgO film in the sample was calculated by treating the sample with a 1N dilute hydrochloric acid solution, dissolving and extracting the entire amount of MgO, and quantifying the amount of Mg ions in the liquid by ICP emission spectrometry.

Next, the process of forming the protective film will be described in more detail. This will be described with reference to actual examples (1 to 5).

An oxygen gas at a pressure of ² × 10 ⁻² Pa was introduced into the vacuum film forming apparatus, and the glass substrate was heated at 100 ° C., 150 ° C., 200 ° C., 250 ° C., and 300 ° C. by the substrate heater.
Each is heated to form a film, and an actual protective film,
, The deposition rate was 1.5 nm per second. A high frequency of 1.5 kW was applied to the high frequency coil. The substrate has a negative DC bias voltage of 100 to 400
kV was applied.

The specific surface area determined by the krypton gas adsorption test at the temperature of liquid nitrogen is as follows.
0 m ² / g, Illustrative protective film of 190 m ² / g, illustrative protective layer of 160 m ² / g, illustrative protective film of 130m ² /
g, the protective film in the example was 110 m ² / g.

On the other hand, the protective film of the comparative example was formed by an electron beam evaporation method in order to compare with the actual example of the present invention. Oxygen gas was introduced at a pressure of 2.times.10.sup.- ² Pa, and the glass substrate was heated to 100.degree. C., 200.degree. C., and 300.degree. C., respectively, to form a film.
The deposition rate was 1 nm per second.

The specific surface area determined by the krypton gas adsorption test at the temperature of liquid nitrogen was 4% for the protective film of the comparative example.
9 m ² / g, the protective film of the comparative example was 41 m ² / g, and the protective film of the comparative example was 36 m ² / g.

The secondary electron emission coefficient, which is a parameter closely related to the discharge characteristics of the PDP, was measured as follows. In addition, the measurement is based on the IEICE TECHNICICAL
REPORT OF IEICE. EID98-108
The measurement method described in (1999-01) was used.

FIG. 2A is a diagram showing a schematic configuration of a secondary electron emission coefficient measuring device used for the measurement. According to this secondary electron emission coefficient measuring apparatus, as shown in FIG. 2A, the surface of a protective film 11 made of MgO formed on a stainless steel substrate 10 is irradiated with an ion beam 12 of Ne. The secondary electrons 13 are emitted, and the secondary electrons 13 are collected by the collector electrode 14 arranged on the front surface of the protective film 11.
The secondary electron emission ratio is determined from the current value generated in the collector electrode 14.

A bias voltage Vc is applied between the collector electrode 14 and the stainless steel substrate 10 so that the collector electrode 14 becomes a positive electrode, and all the secondary electrons 13 emitted from the MgO protective film 11 are captured. To be gathered. A value saturated when the voltage Vc applied to the collector electrode 14 is increased is defined as a secondary electron emission coefficient.

In measuring the secondary electron emission characteristics, a Ne ion beam was irradiated at an acceleration energy of 500 eV.

FIG. 2B is a diagram showing an example of the measurement result, showing the dependence of the secondary electron emission coefficient on the collector voltage. In FIG. 2B, the characteristic A represents the characteristic of the protective film 1 of the example, and the characteristic B represents the characteristic of the protective film 1 of the comparative example. The horizontal axis in the figure corresponds to the collector voltage, and the vertical axis corresponds to the secondary electron emission coefficient (γ).

From FIG. 2B, the secondary electron emission coefficient (γ) of the protective film 1 of the embodiment is 0.55, while the secondary electron emission coefficient of the protective film 1 of the comparative example is 0.35. It was found that the secondary electron emission coefficient of Example 1 was much larger than that of Comparative Example 1. Further, the secondary electron emission coefficients of the protective films of Examples 1 and 2 were all between 0.5 and 0.6, while the films of Comparative Example and 3 were 0.33 and 0.31, respectively. Was.

From these results, it can be seen that the MgO film of this example having a large specific surface area has a much higher secondary electron emission coefficient than the MgO film of the comparative example having a small specific surface area.

From this, the PD using the protective film of the embodiment is
P is expected to reduce the firing voltage.

Next, the spatter resistance of the protective film, which is a parameter closely related to the life of the PDP, was measured as follows.

For the protective film of the embodiment and the protective film of the comparative example, the sputter resistance was measured by argon plasma. High-frequency magnetron sputtering was used for the sputtering apparatus, and argon gas was introduced at 0.5 Pa. The sample was covered with a tungsten mask having a slit having a width of 1 mm, and arranged at the same location of the discharge electrode. High frequency power 10
It was exposed to argon plasma at 0 W for 1 hour. An atomic force microscope was used to measure the amount of spatter, and the amount of spatter was evaluated by measuring the step at the boundary of the mask.

As a result, the sputter amount of the actual example was 45% and 55% of the sputter amount of the comparative example, respectively. From this, it was found that the protective films of Examples and Examples had about twice the sputter durability as compared with the conventional protective film.

In the above embodiment, magnesium oxide has been described, but oxides other than magnesium oxide include calcium oxide, strontium oxide, barium oxide, aluminum oxide, silicon dioxide, lanthanum oxide, cerium oxide, and cerium oxide. Yttrium, gadolinium oxide and the like can be used. Further, a mixture of these and a composite oxide can also be used. Mixtures and composite oxides of magnesium oxide and these oxides can also be used.

As for the specific surface area, as is apparent from the results shown in the examples of the present inventors, a film having a secondary electron emission coefficient and a sputter resistance of 100 m ² or more is smaller than a film of less than 50 m ^2. It is much better. It is considered that this tendency does not essentially change even if the value exceeds 230 m ² shown in the example. That is, considering the correlation between the secondary electron emission coefficient, the ion sputter resistance and the specific surface area, it is considered that these characteristics are improved as the specific surface area is increased. Of course, when the specific surface area is increased to a certain degree or more, the improvement of these effects is reduced and it is considered that the effect is saturated, but the upper limit of the specific surface area is not limited to 230 m ² or less.

[0048]

As described above, by using the protective film according to the present invention as a protective film of an AC type PDP, the secondary electron emission coefficient can be increased, and the durability against sputter impact due to ions during discharge can be increased. There is an effect that can be.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a portion corresponding to one pixel of an AC type PDP. FIG. 2 (b) is the same as FIG. 1 (a)
FIG.

FIG. 2A is a schematic diagram of a secondary electron emission coefficient measuring device. FIG. 2B is a diagram illustrating a measurement result of a secondary electron emission coefficient characteristic.

[Explanation of symbols]

1R: red phosphor, 1G: green phosphor, 1B: blue phosphor, 2 ... partition, 3 ... address electrode, 4 ... back plate, 5 ... protective film, 6 ... dielectric layer, 7 ... display electrode, 8 ... Bus electrode, 9
... Front plate, 10 ... Stainless steel substrate, 11 ... Protective film, 12
... Ne ion beam, 13 ... secondary electrons, 14 ... collector electrode.

Continued on the front page (72) Inventor Kenichi Onizawa 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Tetsuro Minemura 7-1-1, Omikamachi, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Kazuo Uetani 1-5-5 Kosone-cho, Nishinomiya-shi, Hyogo Prefecture Inside Shin-Meiwa Industry Co., Ltd. No. 25 Inside Shin Meiwa Kogyo Co., Ltd. (72) Inventor Shiro Takikawa 1-5-5 Kosone-cho, Nishinomiya-shi, Hyogo Prefecture Inside Shin Meiwa Kogyo Co., Ltd. No. 25 New Meiwa Kogyo Co., Ltd. (72) Inventor Yasushi Yasushi 1-chome, Kosone-cho, Nishinomiya City, Hyogo Prefecture No.5-25 New Meiwa Kogyo Co., Ltd. F-term (reference) 5C040 FA01 FA04 GE01 GE07 GJ08 JA07 KA04 KB19 LA14 MA10 MA17

Claims (5)

[Claims] 1. A plasma display device comprising: a front substrate provided with display electrodes; and a rear substrate provided with address electrodes. The plasma display displays an image by discharge discharged into a minute discharge space formed between the two substrates. in _Lee spray panel, the display of the dielectric layer formed on the electrode, provided on the dielectric layer, and a protective film disposed on the side opposite to the rear substrate is formed of a metal oxide, the metal oxide Purazumade _Lee spray panel protective film of things and having per weight 1g, the 100 m ² or more specific surface area. Wherein Purazumade _Lee spray panel according to claim 1, wherein the protective film is characterized by comprising the oxide composed mainly of magnesium oxide. 3. A minute discharge space formed between a front substrate provided with display electrodes and a rear substrate provided with address electrodes and provided so as to be aligned with the front substrate. in Purazumade _Lee spray panel for displaying an image in discharge shoot, said display electrodes on the front substrate a dielectric layer provided on the side opposite to the rear substrate, the dielectric layer protects the rear substrate which faces The protective film is formed of a metal oxide, and the protective film of the metal oxide is 100 g / g.
m has ^two or more specific surface area, the the rear substrate, Purazumade _Lee spray panel in which a plurality color phosphors provided is characterized in that a partition wall so as to be arranged by color. 4. Purazumade _Lee spray panel according to claim 3, wherein the encapsulating mixture of rare gas elements in the discharge space. 5. The pressure of the mixture is set to about 760 Torr to 400 Torr.
Purazumade _Lee spray panel described.