JPH04171698A - Electroluminescence display panel - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a luminous film and extend the life of an EL display panel by arranging a barrier film made of an insulating material with little alkaline metal content on the portion of a laminated film structure at least kept in contact with an insulating-substrate. CONSTITUTION:A soda glass plate colorless, transparent and smooth on the surface is used for an insulating substrate 2, and an aluminosilicate barrier film 10 containing an alkaline metal oxide is formed wholly on one face. Many transparent electrode films 3 made of ITO or tin oxide and the like are arranged in a stripe-shaped pattern on the barrier film 10. An insulating film 11 kept in contact with an insulating film 4 made of the same material as that of the barrier film 10 is formed on the whole face as an insulating film to be kept in contact with a luminous film 5 arranged on it. Impurities such as harmful alkaline metal ions are prevented from being moved from the insulating substrate 2 to the luminous film 5, and the deterioration of the EL luminous characteristic is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a display board or display panel that utilizes electroluminescence (hereinafter referred to as EL) light emission, which comprises an EL light-emitting film on an insulating substrate such as transparent glass. It relates to a thin film laminated structure formed by laminating the above together with an insulating film, an electrode film, etc.

[Conventional technology]

As is well known, some EL display boards are of the so-called dispersed type, which use a coating film in which EL luminescent substance powder is dispersed in resin or glass, but recently, those with the above-mentioned thin film laminated structure have been used to display characters, figures, etc. It has become widely adopted due to its suitability for matrix formats that can display variable images, and its practical use has now begun for yellowish monochrome displays, and is expected to have future potential as a self-luminous flat panel. There is. below,
The structure of a typical conventional EL display panel of this matrix type will be briefly explained with reference to FIG.

In FIG. 5, the insulating substrate 1, which is the main body of the EL display board, is usually a transparent and flat glass plate, and the IT
Thin transparent electrode film 3 made of O (indium tin oxide) etc.
A large number of stripes are arranged in a striped pattern extending perpendicular to the plane of the paper as shown in the figure. Next, oxidize intrum over the entire surface.

An insulating film 4 made of alumina, silicon nitride or the like is coated, a luminescent film 5 of zinc sulfide containing about 0.5% manganese is disposed thereon, and the entire surface thereof is covered with the same insulating film 6 as above.

The uppermost back electrode film 7 is usually an aluminum film, and a large number of them are arranged in a striped pattern perpendicular to the transparent electrode film 3, and the ends thereof are used as the connection parts 7a. Note that the insulating film 4
and 6 may be omitted.

When the transparent electrode film 3 and the back electrode film 7 are sequentially scanned and a display voltage is applied between them, the portion corresponding to the intersection of the bipolar films in the light emitting film 5 becomes a pixel on the matrix display,
The display light Ld of each pixel emitting EL light is taken out from the insulating substrate I side as shown. This EL display panel is normally driven with so-called alternating current by switching the display voltage between positive and negative at each scanning period.

(Problems to be Solved by the Invention) In the EL display panel of the conventional structure shown in FIG. It is possible to construct a flat panel with a thickness of about 2 μm or less on an insulating substrate, and by reducing the thickness of the insulating film, it can be driven with a relatively low display voltage. There is a problem that the display brightness tends to gradually decrease over time, and the usable life is not necessarily sufficient.

One of the reasons for this is that the electric field strength in a thin insulating film of 0.3 to 0.5 .mu.l is extremely high, about 105 V/cm, and dielectric breakdown is likely to occur in areas where the electric field is concentrated. For this reason, for example, materials such as the aforementioned yttrium oxide, which has so-called self-healing properties that do not expand even if local dielectric breakdown occurs in the insulating film, are used, but if only the improvement of such an insulating film is enough, the display brightness will gradually decrease. Trends are difficult to stop.

Another reason for this is the deterioration of the EL emission characteristics of the luminescent film itself, and various factors are thought to be related to this deterioration mechanism, but the main one is impurities, especially alkali metal atoms. There is an intrusion into the luminescent film. The impurity source of alkali metals such as Na is of course the glass for the insulating substrate, and EL uses glass with a high Na content as the insulating substrate.
On the display board, the luminance is already low from the initial value, and on the contrary, Na
If a glass with a particularly low content is used, deterioration of the luminescent properties can be reduced.

Therefore, it would be sufficient to use glass with as little alkali metal content as possible for the insulating substrate, but it is very expensive and has the problem of increasing material costs and making it impractical. Another possibility is to increase the thickness of the insulating film to prevent impurities from penetrating, but conventional insulating films are not very suitable for this purpose, and the insulating film remains thin until the display voltage exceeds a practical value. A sufficient effect cannot be obtained unless the thickness is increased.

In view of the current situation, it is an object of the present invention to provide an EL display board that effectively prevents alkali metals from entering the light emitting film, has less deterioration of light emitting characteristics, and is economical.

(Means for Solving the Problems) According to the present invention, this object is achieved by providing an E, which is formed by laminating a light emitting film on an insulating substrate together with an insulating film, an electrode film, etc., as described at the beginning.
This is achieved by disposing a barrier film made of an insulating material with a low alkali metal content on at least the portion of the laminated film structure in contact with the insulating substrate for the L display panel.

The alkali metal sound π content of the barrier film in the above structure is preferably 0.1% or less, and it is preferable to use an alumina silicate material, and more preferably a borosilicate alumina material containing boron. In addition to alumina, materials containing divalent metal oxides such as zinc and barium can be used. The content range of each component in such a material suitable for a barrier film is 40 to 8% by weight for silicic acid or silicon oxide.
0%, alumina 5-20%, boric acid 0-20%, and divalent metal oxide 0-30%.

Further, it is most desirable to form this barrier film by a sputtering method, but it can also be formed by a vacuum evaporation method, particularly an electron beam vacuum evaporation method in which a source is heated with an electron beam. Furthermore, when using the sputtering method, it is particularly desirable to form the barrier film in an amorphous state.

In carrying out the present invention, it is possible not only to provide the barrier film on the part of the laminated film structure in contact with the insulating substrate as described in 6-1 above, but also to use it on the insulating film, etc. in contact with the light emitting film. be.

[Effect]

As described in the structure of the previous section, the present invention provides a barrier barrier by forming a dense film with very few defects such as pinballs, which is made of an insulating material such as alumina silicate and has a low alkali metal content, by a sputtering method or the like. By disposing this as a film at least in the part of the laminated film structure including the light-emitting film that is in contact with the insulating substrate, it is possible to prevent impurities such as harmful alkali metal ions from moving from the insulating substrate to the light-emitting film. This prevents deterioration of EL light emission characteristics. Hereinafter, the test results of the ability of this barrier film to inhibit movement of alkali metal ions will be explained with reference to FIGS. 3 and 4.

Figure 3 shows the test sample. The insulating substrate 2 of the sample has approximately 15
A 10 x 10 cm square plate of 1 mm thickness of ordinary soda glass containing % of alkali metal oxide such as Na was used. For the barrier film 10, HOYA's alkali-free aluminosilicate glass NA40 with an alkali metal oxide content of 0.1% or less was used, and a meter targeting the plate was placed in a reduced pressure atmosphere of 5 mTorr containing oxygen. A barrier film 10 was formed on both sides of the insulating substrate 2 to a thickness of 0.1 μl at a sputtering rate of 0.01*/min and a ring speed of 2 by sputtering at room temperature. The barrier film 10 formed in this way has an X
According to the line diffraction results, it is in an amorphous state. Note that by processing the circumferential surface of the insulating substrate 2 obliquely in advance, the entire surface of the sample including the circumferential surface is coated with the barrier film 10 as shown in the figure.
so that it is completely covered by

This sample was immersed in pure water in a pressure vessel and heated at the test temperature for 24 hours, and then trace amounts of Na dissolved in the pure water in the form of Na2O were analyzed by plasma emission spectrometry. As a comparison sample, an insulating substrate 2 made of only soda glass without the barrier film 10 was used. The test results are shown in Figure 4, with the sample with barrier film 10 as A and the sample without as B, where the horizontal axis is the test temperature T and the vertical axis is the elution amount of Na2O at room temperature. This is a relative value with the elution amount of sample B at 1 being 1.

As shown in the figure, at room temperature, the elution amount of sample A is more than an order of magnitude lower than sample B, and for sample B, the elution amount increases rapidly when the test temperature exceeds 200°C, but for sample A, the rate of increase is much slower. From this, it can be seen that the barrier film 10 has a high blocking effect on the movement of Na ions. It should be noted that EL display boards can of course be used at room temperature, but they can also be used at temperatures of up to 450-500°C during the manufacturing process to improve the characteristics of the light-emitting film.
, undergo heat treatment for about 1 hour. From the test results shown in the figure, it can be seen that the barrier film 10 can prevent the movement of Na ions even during this heat treatment.

〔Example〕

Hereinafter, first and second embodiments of the present invention will be described with reference to FIGS. 1 and 2. Both are partially enlarged sectional views of the EL display board according to the present invention, and the same parts as in FIG. 5 are given the same reference numerals. Also, in the second embodiment, soda glass is used for the insulating substrate 2 in order to reduce material costs.

In the first embodiment shown in FIG. 1, the insulating substrate 2 is a soda glass plate with a thickness of about 1 mm, the surface of which is as smooth as possible and of course colorless and transparent, and the content of alkali metal oxide is 0.00000 on one entire surface. An aluminosilicate barrier film 10 containing 1% or less is formed to a thickness of 0.1 μm under the conditions described in the previous section.

As the material for this barrier film 10, in addition to the above-mentioned Karasu NA40 manufactured by HOYA, the material for this barrier film 10 is NA35. NA45
1729.1733°705 manufactured by Corning, USA
9, AN manufactured by Asahi Glass ■, 0A-2 manufactured by Nippon Electric Glass ■, etc. can be used as appropriate. When using the sputtering method, the target is a glass plate made by adhering these glass plates to a water-cooled copper plate, and when using the vacuum evaporation method, the target is a similar glass plate. By using electron beam heating as an evaporation source, it is possible to create a dense barrier film with very few defects such as pinholes, which contains impurity gas and scattered powder in the film, compared to using a target or source made of sintered powder. can be formed into a film.

Next, on this barrier film 10, a large number of transparent electrode films 3 made of ITO, tin oxide, etc. and having a film thickness of about 0.2 nm are formed in the aforementioned stripe pattern as in the conventional method. Roughly on this entire surface, an insulating film 11 corresponding to the insulating film 4 in FIG. 5 in this first embodiment is formed of the same material as the barrier film 10 to a thickness of about 0.3 nm, and the The insulating film is in contact with the light emitting film 5 provided.

Of course, this is to prevent alkali metal ions from entering the light emitting film 5 from the soda glass of the insulating substrate 2 as much as possible, and if low alkali glass is used for the insulating substrate 2, the conventional method may be used.

The luminescent film 5 is usually ZnS containing 0.3 to 0-5% Mn as an active material for yellow luminescence, and is deposited to a flu thickness of about 0.5 μm by electron beam vacuum evaporation as usual. Then, by photo-etching, a pattern is formed with only the peripheral edge removed as shown in the figure.

Next, the entire surface covering the circumferential surface of this light emitting M5 is insulated It! 6
For example, silicon nitride is 0.3
A film was formed to a thickness of approximately 0.5 mm. The aluminum back electrode film 7 with a thickness of about n is formed into a transparent electrode PIJ as described above.
A large number of stripes are arranged in a striped pattern perpendicular to 3. As in the conventional case, each pixel on the EL display is constituted by the portion of the light emitting film 5 corresponding to the intersection of the back electrode film 7 and the transparent electrode film 3.

Although the EL display board can be used with the back electrode film 7 exposed, in this first embodiment, the barrier film 1 is placed over it.
The connecting portion 7 is covered with a protective film 13 made of the same material as the protective film 13 with a thickness of about 0.3 pm, and the peripheral portion thereof is removed by photo-etching to expose the back electrode film 7.
Let it be a. Patterning of the protective film 13 for this purpose can be easily carried out by chemical etching using an aqueous acid solution or the like using an ordinary photoresist film as a mask.

The second embodiment shown in FIG. 2 is designed to simplify the structure and reduce costs compared to the first embodiment, and the barrier film 10 in FIG. 1 is omitted, and instead, an insulating film 11 made of the same material
and 12 are provided in contact with the light emitting film 5, and the protective film 7 in FIG. 1 is also omitted. The film thickness of both insulating films is, for example, 0 for the insulating film 11.
．． The amount of the insulating film 12 is about 3 μl, and about 0.5 n of the insulating film 12, respectively. Luminescent film 5 of alkali metal ions from insulating substrate 2
The insulating film 11 prevents the intrusion into the insulating film. Although conventional silicon nitride or the like may be used for the insulating film 12 in this embodiment, it is advantageous for mass production of EL display boards to unify the materials of the insulating film as much as possible.

In any of these examples, heat treatment is performed at a temperature of 450 to 500° C. for about 1 hour in order to increase the luminous efficiency of the light emitting M5. At this time, of course, the barrier film 10 and the insulating film 11. Although this temperature is applied to the insulating film 12 in some cases, it has been confirmed that the luminance of the light emitting film 2 is not reduced due to the intrusion of alkali metal ions such as Na ions from the soda glass of the insulating substrate 2.

Of course, the EL display panel configured as described above may be driven for display in exactly the same manner as the conventional display.

Note that when an alumina-silicate material for a barrier film is used as an insulating film in contact with a light-emitting film, its dielectric constant is about the same as silicon nitride and alumina, which have traditionally been widely used, so it has no effect on the EL luminance of the light-emitting film. There is no inferiority, and the display voltage may be the same.

According to the results of a heating deterioration acceleration test at a temperature of 100°C of the EL display board according to the first example, it is recognized that the deterioration rate of luminance is low, at a fraction of the conventional rate.
It is estimated that its usable life will be improved several times over that of conventional products.

As can be seen from the description of the first and second embodiments, the present invention is not limited to these embodiments and can be implemented in various ways. In the embodiment, the case where soda glass is used for the insulating substrate has been described, but even when conventional electrical glass is used, it can be applied with a simpler structure to increase the effect of inhibiting the movement of alkali metal ions. In addition, the material composition of each part in the EL display board described in the examples.

The film thickness, film-forming conditions, etc. are merely examples, and the present invention can be implemented in an appropriately selected manner within the scope of the invention according to specifications, usage conditions, etc.

〔Effect of the invention〕

As explained above, in the present invention, for an EL display panel formed by laminating a luminescent film on an insulating substrate together with an insulating film, an electrode film, etc., the alkali metal content is reduced in at least the portion of the laminated film structure that is in direct contact with the insulating substrate. By providing a barrier film made of a small insulating material, the following effects can be obtained.

(a) Preventing alkali metal ions from entering the light-emitting film from the insulating substrate by using a dense film with few defects such as pinholes as a barrier film made of an insulating material such as alumina silicate with a small alkali metal content. Accordingly, deterioration of the light emitting film can be prevented and the life of the EL display panel can be extended several times or more compared to the conventional one.

(b) Soda glass, which has a high alkali metal content, is used for the insulating substrate because a barrier film can be placed in the part of the laminated film structure that is in contact with the insulating substrate to effectively prevent the movement of alkali metal ions from the insulating substrate. The material cost can be reduced to one-tenth that of alkali-free glass, and the economic efficiency of the EL display board can be greatly improved.

(C) If the barrier film is also used as an insulating film in contact with the light-emitting film, the effect of preventing alkali metal ions from entering the light-emitting film will be further enhanced, and its defect-free property will improve the insulation performance, resulting in an EI55 Deterioration of the light emitting characteristics of the display board can be further reduced.

Note that the barrier film can be easily formed within a short time by sputtering or the like, and an EL display board incorporating this film is no inferior to conventional products in terms of display characteristics such as luminance and display voltage.

As described above, the present invention can be very effective in improving the usable life and economical efficiency of EL display panels, and is particularly effective when applied to matrix-type EL display panels having a laminated thin film structure.
It is expected that this technology will make a major contribution to the development and spread of this segment.

[Brief explanation of drawings]

Claims (1)

[Scope of Claims] 1) A display board comprising an electroluminescent film laminated on an insulating substrate together with an insulating film, an electrode film, etc.,
An electroluminescent display board characterized in that a barrier film made of an insulating material with a small content of alkali metal is disposed at least in a portion of the laminated film structure that contacts an insulating substrate. 2) The electroluminescent display board according to claim 1, wherein the barrier film is made of an alumina silicate material. 3) The electroluminescent display board according to claim 1, wherein a barrier film is used for the insulating film in contact with the light emitting film in the laminated structure.