JP2012059619A - Protective film, plasma display panel and display device - Google Patents

Abstract

[PROBLEMS] To provide (a) resistance to ion collision required for a protective film (= low sputtering rate), (b) high secondary electron emission (= low voltage characteristics), and (c) charge accumulation. Provided is a protective film for a plasma display panel having sufficient insulation properties (= good phase difference characteristics).
A first protective film 4 containing magnesium oxide MgO as a component is formed so as to further cover a dielectric layer 3 formed so as to cover a front glass substrate 1 and a display electrode 2. A first protective film 4 that protects the dielectric layer 3 is formed, and a second protective film 5 is further formed thereon. The first protective film 4 contains magnesium oxide as a component. The second protective film 5 is composed of a mixture of magnesium oxide and rare earth oxide.
[Selection] Figure 1

Description

  The present invention relates to a plasma display panel used as a display device, and more particularly to a material for forming a protective film and a method for forming the same.

  A plasma display panel is a display device provided with a large number of minute discharge spaces sealed in the gap between two glass substrates. Currently, in a general AC type plasma display panel, a display electrode of a front glass substrate is covered with a dielectric layer, and a protective film is further formed on the dielectric layer.

  The dielectric layer is provided for accumulating 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 discharge start voltage by secondary electron emission.

  The characteristics required for the protective film include (a) being strong against ion collision (= low sputtering rate), (b) having a high secondary electron emission degree (= low voltage characteristics), and the like. (C) that it has sufficient insulating properties to accumulate charges (= good phase difference characteristics).

  Conventionally, as the protective film, a magnesium oxide film having a thickness of about several hundreds nm formed by vapor deposition is mainly used. Based on this, new materials have been proposed to further improve the above-described performances.

  In Japanese Patent Application Laid-Open No. 52-116067 (Patent Document 1), a dielectric that covers an electrode with a material in which a compound such as an oxide or carbonate of strontium Sr is mixed with one or more compounds of alkaline earth or rare earth elements. It is disclosed to form a layer or a protective film layer.

  Japanese Patent Application Laid-Open No. 2000-164143 (Patent Document 2) discloses an AC plasma display panel in which magnesium oxide is made in an amorphous state to reduce the content of impure gas and improve discharge characteristics such as discharge voltage. Has been.

  Japanese Patent Application Laid-Open No. 8-96718 (Patent Document 3) discloses a plasma display panel which is fired from a paste containing a protective film component made of a rare earth oxide.

  Japanese Patent Laying-Open No. 2003-173738 (Patent Document 4) discloses a plasma display panel containing magnesium oxide as a main component and containing at least one rare earth oxide.

  Japanese Patent Laying-Open No. 2006-139999 (Patent Document 5) discloses a plasma display panel including a protective layer containing a rare earth oxide.

JP-A-52-116067 JP 2000-164143 A JP-A-8-96718 JP 2003-1773738 A JP 2006-139999 A

  However, it has not yet been a material that satisfies all the above-mentioned three characteristics and can be used as a substitute for magnesium oxide that is conventionally used for protective films.

  An object of the present invention is to provide a protective film for a plasma display panel having the above three characteristics.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  A protective film according to a representative embodiment of the present invention protects a display electrode disposed on one surface of a front plate and a dielectric layer covering the display electrode, and the protective film is a first protective film layer And the second protective film layer is disposed so as to be sandwiched between the dielectric layer and the second protective film layer, and the second protective film layer is composed of magnesium oxide and rare earth. It is formed of a mixture with an oxide and is exposed to the discharge space.

  In this protective film, the first protective film layer may be made of magnesium oxide.

  The rare earth oxide of the protective film may be europium oxide.

  The protective film may be characterized in that the composition of the mixture of magnesium oxide and europium oxide is Mg: Eu = 90: 10 to 60:40.

  The rare earth oxide of the protective film may be lanthanum oxide.

  This protective film may be characterized in that the composition of the mixture of magnesium oxide and lanthanum oxide is Mg: La = 90: 10 to 40:60.

  The rare earth oxide of the protective film may be gadolinium oxide.

  The protective film may be characterized in that the composition of the mixture of magnesium oxide and the gadolinium oxide is Mg: Gd = 95: 5 to 45:55.

  A plasma display panel using these protective films and a display device using this plasma display panel also fall within the scope of the present invention.

  The plasma display panel according to the present invention includes a protective film having a two-layer structure of a protective film layer containing a rare earth oxide composed mainly of magnesium oxide MgO and made of lanthanum La and the like, and a protective film layer made of magnesium oxide. It is possible to achieve good results for all the characteristics.

It is a conceptual diagram showing the cross section of the light emitting cell in the plasma display panel concerning this invention. It is a graph showing the relationship of the voltage characteristic of the discharge voltage in the composition ratio with magnesium oxide and rare earth. It is a graph showing the phase difference in the composition ratio with magnesium oxide and rare earth. It is local sectional drawing of the plasma display panel before and behind an acceleration test at the time of using the conventional protective film of one layer. It is local sectional drawing of the plasma display panel before and behind an acceleration test at the time of using the 2 layer protective film concerning this invention. It is a table | surface about the evaluation conditions and evaluation result of an acceleration test.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a conceptual diagram showing a cross section of a light emitting cell in a plasma display panel according to the present invention.

  The plasma display panel is roughly configured to include a front glass substrate 100 and a back glass substrate 200.

  The front glass substrate 100 is a substrate on the side that becomes the display surface when the apparatus is mounted. The front glass substrate 100 includes a front glass plate 1, a display electrode 2, a dielectric layer 3, a first protective film 4, and a second protective film 5. The rear glass substrate 200 is a substrate on the side that is housed in the apparatus when the apparatus is mounted. In the drawing, the rear glass substrate 200 is configured to include ribs 6, phosphor layers 7, dielectric layers 8, address electrodes 9, and rear glass plates 10. However, in reality, a gas exhaust pipe (not shown) or the like whose exposure is a problem on the appearance of the apparatus is often provided on the rear glass substrate 200.

  The front glass plate 1 is a glass substrate that serves as a structural material for the front glass substrate 100. After the device is mounted, the display image of the plasma display pal reaches the eyes of the viewer through the front glass plate 1. Therefore, the material of the front side glass plate 1 is not limited to glass as long as it has a desired structural material strength and visible light transmittance.

  An irregular reflection prevention film or the like may be formed on the display surface side (upward in FIG. 1) of the front glass plate 1, but it is omitted here because it is not directly related to the present invention.

  The display electrode 2 refers to a sustain electrode and a scan electrode provided on the front glass substrate 100. In the present invention, since it is not necessary to distinguish between the two, the display electrodes 2 are combined. The display electrode 2 is often made of ITO or the like having a certain transparency, but the material is not particularly limited.

  The dielectric layer 3 is provided for accumulating charges generated by the voltage applied to the address electrode 9.

  The first protective film 4 is a protective film in contact with the dielectric layer 3. The second protective film 5 is a protective film formed so as to overlap the first protective film 4. In the present invention, it is assumed that the first protective film 4 is composed of magnesium oxide MgO.

  The second protective film 5 is formed having a columnar structure. The material of the second protective film 5 will be described later.

  Further, the performance of the protective film is determined by the components exposed to the discharge space 11. Due to the nature of plasma display panels, the protective film is scraped and lost with use. In the present invention, when the second protective film 5 is shaved and the first protective film 4 is exposed to the discharge space 11, the properties of magnesium oxide MgO, which is a component of the first protective film 4, dominate.

  The rib 6 is a structure for supporting the discharge space 11 which is a light emitting space when the front glass substrate 100 and the rear glass substrate 200 are bonded together. Usually, the rib 6 is formed on the back glass substrate 200 for the convenience of forming the phosphor layer 7.

  The phosphor layer 7 is a phosphor layer that emits RGB light by plasma excited by the display electrode 2 and the address electrode 9. The phosphor used depends on which of the RGB light is emitted, but since the present invention is not directly related, the phosphor material is omitted.

  The dielectric layer 8 is a dielectric layer for emitting plasma in the discharge space 11 defined by the ribs 6 by a voltage applied to the address electrodes 9.

  The address electrode 9 is an address electrode provided on the rear glass substrate 200.

  The back side glass plate 10 is a glass substrate that plays a role as a structural material of the back side glass substrate 200.

  The present invention is characterized by having a protective film formed of two layers and a material used for the two-layer protective film.

  Next, the material used for the second protective film 5 which is this feature will be examined.

  As the performance of the protective film, it is necessary to consider three factors: 1) discharge voltage, 2) phase difference, and 3) sputter rate. FIG. 2 is a graph showing the relationship of the voltage characteristics of the discharge voltage at the composition ratio of magnesium oxide and rare earth. FIG. 3 is a graph showing the phase difference in composition ratio between magnesium oxide and rare earth.

  In the present invention, first, a first protective film 4 having a thickness of 250 nm is formed from magnesium oxide MgO. Subsequently, a second protective film 5 made of a composition in which magnesium oxide MgO and rare earth are mixed is formed to a thickness of 300 nm. Here, the 2nd protective film 5 shall be formed by the electron beam vapor deposition method by 2 source | sauce vapor deposition.

For example, when a magnesium oxide MgO single film is formed, both sources are generated as a source of magnesium oxide MgO. When a mixture of magnesium oxide MgO and rare earth is formed, the film is formed simultaneously using one as the source of magnesium oxide MgO and the other as the source of rare earth. More specifically, when forming a protective film with a gadolinium Gd mixture, Gd ₂ O ₃ is used as a source. Further, when forming a protective film with a lanthanum La mixture, La ₂ O ₃ is used as a source. When forming a protective film with a europium Eu mixture, Eu ₂ O ₃ is used as a source.

  When the composition of magnesium oxide MgO and rare earth oxide is changed, the measurement conditions are confirmed by changing the film formation rate, forming the film, and checking the composition by EDX analysis.

The protective film formation process measured by the present invention is performed by introducing an oxidizing gas having a pressure of 5 × 10 ⁻² (Pa) into a vacuum apparatus and heating the glass substrate to 300 ° C. with a substrate heater. ing. The sealed gas conditions are neon Ne-20% Xe and 66.7 KPa.

  In the present invention, lanthanum La, gadolinium Gd, and europium Eu are used as rare earths.

  Even if any rare earth is mixed, the effect becomes almost constant when the mixing ratio exceeds 10%, depending on the object.

  In the case of the magnesium oxide MgO-gadolinium Gd mixture, the discharge voltage is reduced by about 10 volts from that of 100% MgO.

  In the case of a magnesium oxide MgO-lanthanum La mixture, a reduction in discharge voltage of about 45-55 volts can be expected.

  In the case of the magnesium oxide MgO-europium Eu mixture, a reduction in discharge voltage of about 50-55 volts can be expected.

  As described above, it can be seen that all the rare earth mixtures used in the verification have low voltage characteristics as compared with 100% magnesium oxide MgO.

  On the other hand, what was examined from the point of phase difference is FIG. The phase difference shown in this figure is a value measured using a digital LCR meter.

  As is apparent from the graph, although depending on the rare earth material, it can be seen that the phase difference deteriorates when the ratio of the rare earth is about 60% from the middle of 30%. In any rare earth material, the phase difference is most aggravated when the rare earth is 100%.

  When gadolinium Gd is 100%, the phase difference is −88 °. In the case of the magnesium oxide MgO-gadolin Gd mixture, a situation in which the wall charge cannot be retained due to the deterioration of the phase difference, that is, the generation of the resistance of the direct current component, starts to appear around 55% of the gadolin Gd.

  With lanthanum La 100%, although the phase difference performance is slightly worse than that of gadolin Gd 100%, it is −88 °. However, the onset of the deterioration of the phase difference in the magnesium oxide MgO-lanthanum La mixture lasts until the lanthanum La becomes close to 60%.

  On the other hand, the phase difference at 100% europium is -86 °, which is the worst compared to the other two types. Moreover, the deterioration of the phase difference of the magnesium oxide MgO-europium Eu mixture is also started to about 35%.

  Considering the above two points of 1) discharge voltage and 2) phase difference, the material used as the second protective film 5, that is, a sufficiently low voltage compared with MgO and sufficient insulation capable of accumulating wall charges. The following can be considered as things that can maintain the property.

* Gadolinium mixture Mg-Gd composition: Mg: Gd = 95: 5-45: 55
Lanthanum mixture Mg-La composition: Mg: La = 90: 10-40: 60
Europium mixture Mg-Eu composition: Mg: Eu = 90: 10-60: 40
Next, 3) Consider the sputtering rate. Here, a case where magnesium oxide MgO-europium Eu is used as the second protective film is examined.

  FIG. 4 is a local cross-sectional view of the plasma display panel before and after the acceleration test when a conventional single-layer protective film is used. FIG. 5 is a local sectional view of the plasma display panel before and after the acceleration test when the two-layer protective film according to the present invention is used. (A) is a cross-sectional view before the acceleration test, and (b) is a cross-sectional view after the acceleration test.

  FIG. 6 is a table of evaluation conditions and evaluation results of the acceleration test.

  The evaluation conditions for the acceleration test of the present invention are a voltage of 270 V and a frequency of 15 KHz. The acceleration time is 307 hours for the conventional plasma display panel and 261 hours for the plasma display panel according to the present invention.

  In FIG. 4, before the acceleration test, a magnesium oxide single-layer protective film (protective film of the conventional embodiment) 12 of 451 nm is provided. On the other hand, after the acceleration test, only a thickness of 92 nm remains.

  On the other hand, in FIG. 5 according to the present invention, the thickness of the first protective film 4 and the second protective film prepared assuming that the first protective film 4 is 250 nm and the second protective film 5 is 300 nm is 545 nm. It is. As can be seen from the figure, the second protective film 5 is assumed to be Mg-30% Eu-O having a columnar structure. On the other hand, the thickness after the acceleration test is 362 nm.

Since it is not the same test time, when comparing with the sputter rate,
-Conventional plasma display panel:
Lost amount (digged amount) 451-92 = 359 nm
Acceleration time 307h
Sputter rate 359/307 = 1.17 nm / h
-Plasma display panel of the present invention Amount lost (amount dug) 545-362 = 183 nm
Acceleration time 261h
Sputter rate 183/261 = 0.70nm / h
As described above, even when compared with the sputtering rate, a clear difference of about 60% (0.70 / 1.17 = 0.598) can be grasped. This is because magnesium oxide MgO is formed as the first protective film 4, and Mg-30% Eu—O is formed as the second protective film 5 on the basis of the magnesium oxide MgO, so that the second protective film 5 is strong. It is estimated that

  As described above, by forming two layers, it is possible to obtain better characteristics than the conventional one in terms of 3) sputtering rate.

  From this, good results could be obtained in three points: 1) discharge voltage, 2) phase difference, and 3) sputtering rate. As a result, it is possible to provide a means for practical use of a rare earth mixture that is resistant to ion bombardment, has low voltage characteristics, and can be expected to have sufficient insulating properties to accumulate electric charges.

  The present invention is assumed to be used for a protective film applied to a front glass substrate of an AC type plasma display panel.

DESCRIPTION OF SYMBOLS 1 ... Front side glass plate, 2 ... Display electrode, 3 ... Dielectric layer, 4 ... 1st protective film, 5 ... 2nd protective film,
6 ... rib, 7 ... phosphor layer, 8 ... dielectric layer, 9 ... address electrode, 10 ... back side glass plate,
11 ... discharge space, 12 ... protective film (protective film of the conventional embodiment),
100 ... front side glass substrate, 200 ... back side glass substrate.

Claims (10)

A protective film for protecting a display electrode disposed on one surface of the front plate and a dielectric layer covering the display electrode,
The protective film includes a first protective film layer and a second protective film layer,
The first protective film layer is disposed so as to be sandwiched between the dielectric layer and the second protective film layer,
2. The protective film according to claim 1, wherein the second protective film layer is formed of a mixture of magnesium oxide and rare earth oxide and is exposed to the discharge space. The protective film according to claim 1,
The protective film according to claim 1, wherein the first protective film layer is made of magnesium oxide. The protective film according to claim 1,
The protective film, wherein the rare earth oxide is europium oxide. The protective film according to claim 3,
The composition of the mixture of the said magnesium oxide and the said europium oxide is Mg: Eu = 90: 10 to 60:40, The protective film characterized by the above-mentioned. The protective film according to claim 1,
The protective film according to claim 1, wherein the rare earth oxide is a lanthanum oxide. The protective film according to claim 5,
A composition of a mixture of the magnesium oxide and the lanthanum oxide is Mg: La = 90: 10 to 40:60. The protective film according to claim 1,
The protective film, wherein the rare earth oxide is gadolinium oxide. The protective film according to claim 7,
A protective film, wherein the composition of the mixture of magnesium oxide and gadolinium oxide is Mg: Gd = 95: 5 to 45:55.   A plasma display panel using the protective film according to claim 1.   A display device using the plasma display panel according to claim 9.