JPH07122363A - Manufacture of electroluminescence element - Google Patents

Abstract

PURPOSE:To provide a thin film of stable film composition by effectively adding an element of emission center to an emission layer when the emission layer of an EL element is formed by means of sputtering. CONSTITUTION:A first electrode 12, a first insulating layer 13, an emission layer 14, a second insulating layer 15 and a second transparent electrode 16 are laminated on an insulating substrate 11 in this order. A sintered target of no less than 90% in relative density is used for manufacturing this electroluminescence element when an emission layer consisting of alkaline earth metal sulfide, to which a rare earth element is added as an emission center, is formed by sputtering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence element (hereinafter referred to as an EL element) used in, for example, self-luminous segment display or matrix display of instruments or displays of various information terminal devices. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Conventionally, an EL device utilizes a phenomenon of emitting light when an electric field is applied to a light emitting layer in which a light emitting center element is added to a II-VI group compound such as zinc sulfide (ZnS). Has been attracting attention as a component of the flat display of. FIG. 4 shows a cross-sectional structure of the conventional EL element 10.

An EL element 10 is an optically transparent ITO (Indium Tin Oxid) on a glass substrate 1 which is an insulating substrate.
e) a first electrode 2 made of a film or the like, tantalum pentoxide (Ta ₂ O)
₅ ) a first insulating layer 3, a light emitting layer 4, a second insulating layer 5
And the second electrode 6 are sequentially laminated. IT
The O film is a transparent conductive film obtained by doping indium oxide (In ₂ O ₃ ) with tin (Sn), and has been widely used as a transparent electrode from the past.

For the light-emitting layer 4, zinc sulfide (ZnS) is used as a base material, and manganese (Mn), terbium (Tb), and samarium (Sm) are added as emission centers.
A material in which strontium sulfide (SrS) is used as a base material and cerium (Ce) is added as an emission center is used.
The emission color of an EL element is determined by a combination of a base material and an element added as an emission center. When zinc sulfide (ZnS) is used as a base material and manganese (Mn) is added as an emission center, a yellow-orange color and terbium (Tb) are used. ) Is added in green, samarium (Sm) is added in red, strontium sulfide (SrS) is used as a base material, and cerium (Ce) is added as an emission center to obtain blue-green.

[0005]

E composed of the above structure
When the light emitting layer 4 of the L element 10 is formed by the sputtering method,
Powder or sintering targets are used. When a powder target is used, it is difficult to obtain a thin film with stable composition and film quality, because problems such as abnormal discharge during sputtering and instability of the film formation rate may occur depending on the leveling of the powder surface of the target. .

On the other hand, when a sintered target is used,
Reproducibility and controllability are superior to powder targets. Here, a method for manufacturing an EL element having an alkaline earth metal sulfide as a light emitting layer by a sputtering method using a sintered target is described in, for example, Japanese Patent Application Laid-Open No. 4-36992.

However, even if a sintering target is adopted, it is still impossible to obtain a light emitting layer having a stable composition in the film. That is, there are various factors such as the sintering method, the sintering temperature, the sintering time, etc. in the process of producing the sintering target, and in particular, the alkaline earth metal sulfide is unstable itself, This is because the variation in the degree of sintering of the target due to the factor is remarkable. Therefore, even if the luminescent center element is added to the target in the same proportion and sintered, the amount of the luminescent center element that can be added to the light emitting layer greatly varies depending on the sintering condition of the target. .

According to the present invention, when a light emitting layer of an EL device is formed by using the above-mentioned sputtering method, a light emitting center element is efficiently added to the light emitting layer to obtain a light emitting layer having a stable composition in the film. With the goal.

[0009]

Means for Solving the Problems As a result of intensive studies, the inventors of the present invention formed a light emitting layer made of an alkaline earth metal sulfide added with an emission center element by a sputtering method using a sintered target. In doing so, it was discovered for the first time that the degree of stability of the composition of the obtained light emitting layer was largely due to the relative density of the sintered target.

Therefore, as a first feature of the present invention for solving the above-mentioned problems, the first electrode, the first insulating layer, the light emitting layer, the second insulating layer, and the second electrode are formed on the insulating substrate at least as light. In the manufacturing process of the electroluminescence element in which the material on the extraction side is sequentially laminated with an optically transparent material, a light emitting layer made of an alkaline earth metal sulfide to which a rare earth element is added as an emission center is formed by a sputtering method. At this time, a sintering target having a relative density of 90% or more is used.

A second feature is that, in addition to the first feature, the charge concentration of the luminescence center element added to the sintering target is in the range of 0.02 at% to 0.6 at%, That is, the light emitting layer is formed at a temperature of 300 ° C to 500 ° C. Furthermore, the third feature is that the first and second
In addition to the characteristics of 1., the emission center is cerium (Ce) or europium (Eu).

[0012]

By using the present invention, the luminescent center element and other trace elements added to the sintered target can be added very efficiently to the light emitting layer of the EL device. Further, when the present invention is used, the concentration of the emission center element in the emission layer of the EL element is proportional to the concentration of the emission center element added to the sintering target, and therefore the emission center of the emission layer of the EL element is The element concentration can be controlled with good reproducibility.

[0013]

By adopting the present invention, when a light emitting layer of an EL device is formed by using a sputtering method, a light emitting center element is efficiently added to the light emitting layer to stabilize the composition in the film. Can be obtained.

[0014]

EXAMPLES Example 1 The present invention will be described below based on specific examples. FIG. 1 shows an EL device 1 according to the present invention.
It is a schematic diagram of the cross section of 00. The EL element 100 of FIG.
Then the light is extracted in the direction of the arrow.

The thin film EL element 100 is constructed by sequentially laminating the following thin films on a glass substrate 11 which is an insulating substrate. In the following, the film thickness of each layer is described with reference to the central portion thereof. First on the insulating substrate 11
Optically transparent zinc oxide (Zn) as the electrode 12
O) and tantalum pentoxide (Ta) as the first insulating layer 13.
₂ O ₅ ) was sequentially laminated, and strontium sulfide (SrS) to which cerium (Ce) was added as an emission center was formed as a light emitting layer 14 thereon by a sputtering method. Then, tantalum pentoxide (Ta ₂ O ₅ ) was laminated as the second insulating layer 15, and optically transparent zinc oxide (ZnO) was laminated as the second electrode 16 to form an EL device.

Next, a method of manufacturing the above-mentioned thin film EL element 100 will be described. First, the first transparent electrode 12 was formed on the glass substrate 11. As a vapor deposition material, zinc oxide (Z
Gallium oxide (Ga ₂ O ₃ ) was added to and mixed with (nO) powder and molded into pellets, and an ion plating apparatus was used as a film forming apparatus.

Specifically, while the temperature of the glass substrate 11 is kept constant, the inside of the ion plating apparatus is evacuated to a vacuum, and then argon (Ar) gas is introduced to keep the pressure constant, thereby forming a film. The film power was adjusted by adjusting the beam power and the high-frequency power so as to be in the range of 6 to 18 nm / min. Next, a first insulating layer 13 made of tantalum pentoxide (Ta ₂ O ₅ ) was formed on the first transparent electrode 12 by a sputtering method. Specifically, the temperature of the glass substrate 11 was kept constant, a mixed gas of argon (Ar) and oxygen (O ₂ ) was introduced into the sputtering apparatus, and film formation was performed with high-frequency power of 1 kW.

A strontium sulfide: cerium (SrS: Ce) light emitting layer 14 containing strontium sulfide (SrS) as a base material and cerium (Ce) added as an emission center was formed on the first insulating layer 13 by a sputtering method. . Specifically, the glass substrate 11 is kept at a high temperature of 500 ° C., and argon (Ar) gas is added to the glass substrate 11 at a high temperature.
A mixed gas in which hydrogen sulfide (H ₂ S) was mixed at a rate of 100% was introduced, and a film was formed with a high frequency power of 150 W.

At this time, a strontium sulfide (SrS) used in the present invention was used as a sintering target having a relative density of 96%, in which cerium fluoride (CeF ₃ ) was added at a ratio of 0.15 at%. On the light emitting layer 14, tantalum pentoxide (Ta
₂ O ₅ ) and the second insulating layer 15 is replaced by the above-mentioned first insulating layer 13
It was formed in the same manner as. Then, the second transparent electrode 16 made of a zinc oxide (ZnO) film was formed on the second insulating layer 15 by the same method as the above-mentioned first transparent electrode.

The film thickness of each layer is such that the first and second transparent electrodes 12,
16 is 300 nm, and the first and second insulating layers 13 and 15 are 40 nm.
0 nm, and the emission layer 14 is 800 nm. FIG. 2 shows the concentration of cerium (Ce) in the light emitting layer of the EL device of Example 1. In Comparative Examples 1 and 2 of FIG. 2, the above-mentioned film formation was carried out using a sintering target having a relative density of 86% and a relative density of 70% to which the same amount of cerium fluoride (CeF ₃ ) as that of the EL element of Example 1 was added. It is the concentration of cerium (Ce) in the light emitting layer of the EL light emitting device manufactured under the conditions.

As can be seen from this figure, in the case of the EL element of Example 1, cerium (Ce) can be efficiently added to the light emitting layer of the EL element, but in Comparative Examples 1 and 2, almost no cerium (Ce) can be added. . Particularly, in Comparative Example 2, it was below the detection limit of the analyzer. (Examples 2 and 3) Next, EL elements were manufactured in the same manner as in Example 1 by changing the concentration of cerium fluoride (CeF ₃ ) added to the sintering target.

FIG. 3 shows an EL manufactured by changing the concentration of cerium fluoride (CeF ₃ ) added to the sintering target.
It is the concentration of cerium (Ce) in the light emitting layer of the device. At this time, the light emitting layer was formed at a substrate temperature of 300 ° C. in Example 2 and at 500 ° C. in Example 3. As shown in FIG. 3, when the substrate temperature is increased, the concentration of cerium (Ce) in the light emitting layer tends to increase. In Comparative Example 3 shown in FIG. 3, a sintering target having a relative density of 70% to 80% is used, and the substrate temperature at this time is 500 ° C.

From FIG. 3, by using the present invention,
Cerium fluoride (CeF ₃ ) added to the sintering target
Since the cerium (Ce) concentration in the EL light emitting layer also increases in proportion to the concentration of, the cerium (Ce) concentration in the EL light emitting layer can be easily controlled. On the other hand, in the case of a sintered target having a relative density of 70% to 80%, cerium (Ce) which is a luminescent center in the EL light emitting layer was changed despite changing the concentration of cerium fluoride (CeF ₃ ) in the target. ) Can hardly be added.

Table 1 shows the light emission results of the above Examples and Comparative Examples.

[0025]

[Table 1]

When a sintering target having a relative density of 90% or more is used, the target charging amount is 0.02 at% to 0.3 at% at a substrate temperature of 500 ° C., and 0.15 at 300 ° C.
Further high-luminance light emission was confirmed between at% and 0.6 at%. In particular, when the light emitting layer was formed at a substrate temperature of 500 ° C., the crystallinity of the light emitting layer was very good, and an EL device with higher brightness was obtained among the examples.

As can be seen from Table 1, by using the present invention, the luminescent center element can be efficiently added to the luminescent layer, and the charge amount of the luminescent center element in the sintering target can be adjusted corresponding to the substrate temperature. With this, higher brightness can be achieved. As described above, when the light emitting layer of the EL element is formed by the sputtering method, by using the present invention, the luminescent center element can be added very efficiently to the light emitting layer, which has high brightness and reliability. An EL element can be manufactured.

Furthermore, in the above embodiment, since the high-density target is adopted, the high-density target is less likely to be broken during film formation, and the generation of particles during film formation can be suppressed.

[Brief description of drawings]

FIG. 1 is a schematic view showing a vertical cross section of an electroluminescent element according to a specific example of the present invention.

FIG. 2 is a characteristic diagram showing the concentration of cerium (Ce) in the light emitting layer of the electroluminescence element according to Example 1.

FIG. 3 shows the concentration of cerium (Ce) added to the sintered target used for forming the light emitting layer of the electroluminescent elements according to Examples 2 and 3, and the concentration of cerium (Ce) in the light emitting layer after the formation of the light emitting layer. It is a characteristic diagram showing.

FIG. 4 is a schematic diagram showing a vertical cross section of a conventional electroluminescence element.

[Explanation of symbols]

 1 Glass Substrate (Insulating Substrate) 2 First Transparent Electrode (First Electrode) 4 Light-Emitting Layer 6 Second Transparent Electrode (Second Electrode) 10 EL Element (Electroluminescence Element) 11 Glass Substrate (Insulating Substrate) 12 First Transparent electrode (first electrode) 14 Light emitting layer 16 Second transparent electrode (second electrode) 100 EL element (electroluminescence element)

Claims (3)

[Claims] 1. A first electrode, a first insulating layer, and
A method for manufacturing an electroluminescence device, in which a light emitting layer, a second insulating layer and a second electrode are sequentially laminated at least with a material on the light extraction side being optically transparent, wherein an alkali containing a rare earth element as a luminescence center is added. A method for manufacturing an electroluminescent element, which comprises using a sintered target having a relative density of 90% or more when a light emitting layer made of an earth metal sulfide is formed by a sputtering method. 2. The light emitting layer is formed at a substrate temperature of 300 ° C. to 500 ° C., in which the concentration of the luminescent center element added to the sintering target is in the range of 0.02 at% to 0.6 at%. The method for manufacturing an electroluminescent element according to claim 1, wherein. 3. The emission center of the emission layer is cerium (C
e) and europium (Eu), The manufacturing method of the electroluminescent element of Claim 1 characterized by the above-mentioned.