JPH0744074B2 - Thin film EL device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a thin film EL device that emits EL (electroluminescence) light when an alternating electric field is applied.

[Prior art]

As a conventional thin film EL element, for example, Japanese Patent Application No. 1958, 1983.
Some are listed in No. 128.

FIG. 2 is a sectional view of the above-mentioned thin film EL device.

In FIG. 2, a transparent conductive film 2 such as In ₂ O ₃ and SnO ₂ and a first dielectric film 3 such as Y ₂ O ₃ and Si ₃ N ₄ on a glass substrate 1 and ZnS containing a small amount of Mn. And the second dielectric film 5 made of the same material as the first dielectric film 3 are sequentially laminated by electron beam evaporation or sputtering, and the transparent multilayer film 100 is formed by these 2-5. There is.

The film thickness of each of the above parts is about 5000Å for the dielectric film and about 6000Å for the light emitting film.

Further, on the second dielectric film 5, M having a mass film thickness of 50 to 300Å
The island-shaped absorber film 6 made of a film is formed by electron beam evaporation or sputtering. The above Mo is a substance having a low reflectance, and has a structure in which it is scattered in an island shape.

The island-shaped absorber film 6 can be replaced by another metal film or semiconductor film having an island-shaped structure, such as Ta, Cr, Si.

Further, a transparent dielectric film 7 of Al ₂ O ₃ or the like having a film thickness of about 500Å is formed on the island-shaped absorber film 6. At this time, the dielectric film 7 is formed so as to fill the gaps and Mo on the island-shaped structure. That is, the dielectric film 7 is interspersed with Mo.
The unevenness of is filled in and flattened. Further, a metal film 8 of Al or the like is sequentially laminated thereon by vapor deposition or sputtering.
These 6 to 8 form the blackened back electrode 200.

The transparent conductive film 2 and the blackened back electrode 200 are patterned into an appropriate shape by ordinary photolithography.

In the above device, the transparent conductive film 2 and the blackened back electrode 20
When an AC voltage is applied between 0 and 0, the electric field in the light emitting film 4 becomes 1 to
When the voltage reaches 2 × 10 ⁶ V / cm, the portion sandwiched between the two electrodes emits light, and the above-described patterned shape is displayed as light emission.

Therefore, it is desirable to use a material having a large dielectric constant as the first and second dielectric films.

In the element of FIG. 2, since the blackened back electrode 200 is used as described above, the external light entering through the transparent multilayer film 100 is absorbed by the island-shaped absorber film 6 and the transparent dielectric film 7. To be done. That is, a part of the external light enters the transparent dielectric film 7 through the Mo gaps scattered on the island-shaped absorber film 6, and is repeatedly reflected between the metal film 8 and the Mo, and is attenuated each time it is reflected. To do. In addition, external light that directly strikes scattered Mo is absorbed and attenuated by Mo having a low reflectance. As described above, the structure in which the light is repeatedly absorbed by utilizing the repeated reflection can significantly reduce the reflectance.
Therefore, the contrast in a bright environment is significantly improved as compared with an element using a high-reflectance metal such as Al as the back electrode.

Further, as an element for maintaining a high display contrast under a high illuminance environment, for example, an element having a structure shown in FIG. 3 has been proposed (Japanese Patent Laid-Open Publication No. 104788, 1979).

In the device shown in FIG. ₃ , a transparent conductive film 300 made of ITO (In ₂ O ₃ with a few% of SnO ₂ added) or In ₂ O ₃ or SnO ₂ is formed on the second dielectric film 5. The transparent multi-layered film 100 is formed in a thickness of about 2000Å and a black background plate 10 is provided behind it.

In the element of FIG. 3, since each constituent film is composed of a transparent film, external light incident from the rear of the glass substrate 1 passes through each transparent layer and is absorbed by the black background plate 10, High contrast can be obtained regardless of the intensity of extraneous light.

[Problems to be solved by the invention]

However, the elements shown in FIGS. 2 and 3 have the following problems.

First, in the device of FIG. 2, since the transparent dielectric film 7 (Al ₂ O ₃ ) is provided between the island-shaped absorber film 6 and the metal film 8, the driving voltage increases by about 5%, Therefore, it is necessary to increase the withstand voltage of the driving element, which causes a problem of increasing the manufacturing cost of the driving circuit.

Further, since the transparent dielectric film 7 is itself very thin and is formed on the island-shaped absorber film 6 having large irregularities, the dielectric characteristics are extremely unstable and dielectric breakdown easily occurs. Therefore, there is a problem that the yield at the time of manufacturing is deteriorated.

On the other hand, in the element shown in FIG. 3, since the metal film is not provided on the transparent conductive film 300 and the transparent conductive film 300 itself serves as an electrode, it is necessary to realize a low resistance required as an electrode. Needs to have a considerably large film thickness, and is required to have sufficient transparency.

In order to form such a transparent conductive film, it is necessary to maintain the substrate on which the transparent multilayer film 100 of 1 to 5 is formed at 200 ° C. or higher, preferably about 300 ° C. during the manufacturing.
There is a problem that cracks and film peeling occur due to the difference in the thermal expansion coefficient of each of the No. 00 films 1 to 5 and the yield decreases.

Further, in etching for forming a pattern of thick ITO or the like, it is necessary to use an acid such as HCl, but the light emitting film 4 is very weak against acid, and the acid is generated through defects such as pinholes in the second dielectric film 5. The entry of the element causes the light emitting film 4 to be dissolved, which also causes a decrease in yield.

The present invention is intended to solve the problems of the prior art as described above.

[Means for solving problems]

In order to achieve the above object, in the present invention, the blackened back electrode is formed of a multilayer thin film composed of an island-shaped absorber film, a transparent conductive film, and a metal film to prevent an increase in driving voltage, and also to manufacture the film. It is configured so that the yield can be improved easily.

Example of Invention

FIG. 1 is a sectional view of an embodiment of the present invention, and the same reference numerals as those in FIG. 2 indicate the same parts.

In the embodiment shown in FIG. 1, the blackened back electrode 400 has a laminated structure of the island-shaped absorber film 6, the transparent conductive film 11 and the metal film 8.

When manufacturing the device shown in FIG. 1, for example, the second dielectric film 5 is used.
An island-shaped absorber film 6 composed of a Mo film having a mass film thickness of 50 to 300 Å is formed on the above by electron beam evaporation or sputtering, and a transparent conductive film 11 such as ITO is formed thereon to a thickness of 100 to 1000 Å. Then, a metal film 8 of Al or the like is formed thereon by vapor deposition or sputtering. The above structure uses a transparent conductive film 11 instead of the transparent dielectric film 7 in the conventional example of FIG. 2, and the other structures are the same as those of FIG.

The island-shaped absorber film 6 can be replaced with another metal film or a semiconductor film such as Ta or Cr.

Further, as the transparent conductive film 11, it is possible to use, in addition to ITO, a semiconductor such as In ₂ O ₃ , SnO ₂ , or Si doped with impurities so as to have conductivity.

Next, the operation will be described.

External light that has entered from the outside through the transparent multilayer film 100 is absorbed by the island-shaped absorber film 6 and the transparent conductive film 11. That is, part of the external light enters the transparent conductive film 11 through the Mo gaps scattered on the island-shaped absorber film 6, and is repeatedly reflected between the metal film 8 and the Mo, and is attenuated each time it is reflected. . In addition, external light that directly strikes scattered Mo is absorbed and attenuated by Mo having a low reflectance. The reflectance can be significantly reduced by adopting the structure in which the light is repeatedly absorbed by utilizing the repeated reflection as described above.

Therefore, a black back electrode that hardly reflects extraneous light can be realized, and an EL panel having excellent display contrast can be provided.

The above operation is similar to that of the conventional element shown in FIG.

However, in the conventional element shown in FIG. 2, since the transparent dielectric film 7 is provided between the island-shaped absorber film 6 and the metal film 8, the driving voltage is increased and the dielectric breakdown is likely to occur. Although there was a problem, in the case of this embodiment, since the transparent conductive film 11 is provided between the island-shaped absorber film 6 and the metal film 8, the island-shaped absorber film 6 and the metal film 8 are different from each other. As a result, the potentials are practically the same, and therefore there is no possibility of causing the problems such as the above-mentioned increase in drive voltage and easy dielectric breakdown.

Further, when the transparent conductive film 300 is used alone as an electrode as in the conventional example shown in FIG. 3, it is necessary to make the film thickness extremely large, and therefore it is necessary to maintain a high temperature state during manufacturing. However, there is a problem that etching for pattern formation must be performed by using an acid. However, in the case of the present embodiment, since it is used together with the metal film 8, the film thickness of the transparent conductive film 11 is the third.
It can be made much thinner than the film thickness of the transparent conductive film 300 in the figure.

Therefore, even if the transparency of the film itself is lowered to some extent, no problem occurs, so that the film can be formed at a low temperature.
The pattern formation is also very thin, so
It can be removed with an alkaline etchant together with Mo.

Therefore, unlike the conventional element shown in FIG. 3, there is no risk of obstacles for keeping at a high temperature during production and obstacles for using acid.

In the embodiment shown in FIG. 1, the island-shaped absorber film 6 and the transparent conductive film 11 are provided one each, but by stacking them in layers, the light absorption effect can be further improved. It can be increased.

〔The invention's effect〕

As described above, in the present invention, since the back electrode is configured to form the multilayer thin film including the island-shaped absorber film, the transparent conductive film, and the metal film, it is possible to obtain an excellent display cost last performance. Since it is possible to prevent the drive voltage from rising without damaging it, it is possible to reduce the cost of the thin film EL display system including the drive system, and there is no need to keep it at a high temperature or to use an acid during manufacturing. It is possible to further improve the yield and reliability during manufacturing.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIGS. 2 and 3 are sectional views of an example of a conventional element, respectively. DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent conductive film 3 ... First dielectric film, 4 ... Light emitting film 5 ... Second dielectric film, 6 ... Island absorber film 7 ... Transparent dielectric film, 8 ... Metal Film 11 ... Transparent conductive film, 100 ... Transparent multilayer film 400 ... Blackened back electrode

Claims (1)

[Claims] 1. A thin-film EL device comprising a transparent light emitting layer formed between a front electrode made of a transparent conductive film provided on the display side and a back electrode provided on the back side, wherein Are arranged so as to fill the gap between the island-shaped absorber film and the island-shaped absorber film, and the island-shaped absorber film having a structure in which low-reflectance minute objects are scattered in an island shape in order from the one closer to A thin film EL element characterized in that the back electrode is formed by a multi-layered thin film in which at least one laminated film with a transparent conductive film is formed, and a metal film is provided on the outside thereof.