JP2002203671A - Electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescence element that is superior in reliability. SOLUTION: A transparent electrode 2, a lower part insulating layer 3, a luminous layer 4 by electrolumiescence, an upper part insulating layer 5 and a rear face electrode 6 are laminated in this order on the substrate 1 made of translucent polycrystalline substance that has a perovskite crystal structure as a main crystal phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent (hereinafter, abbreviated as EL) device having excellent reliability.

[0002]

2. Description of the Related Art For a display device using an EL element,
Various types have been developed because they can be made thinner, have little dependence on viewing angle, and have the advantage of being able to display sharp and high contrast because they are self-luminous.

[0003] For example, Japanese Patent Application Laid-Open No. 11-111450 (prior art) discloses that a metal electrode layer, a first insulating layer, a light emitting layer, a second insulating layer, and a transparent electrode are sequentially laminated on an insulating substrate. , A thin film E having an inverted structure emitting light from the transparent electrode side
In the L element, the insulating substrate is a polycrystalline material having higher heat resistance than glass, and has an average surface roughness Ra of 0.02.
A thin-film EL element having a diameter of 1 μm or less and having a diameter of 1 μmφ or less is disclosed.

In the above-mentioned thin film EL device, the heat treatment temperature of the light emitting layer is increased by using a polycrystalline material having higher heat resistance than glass generally used for the insulating substrate, thereby improving the light emission luminance. Alumina is mentioned as such a polycrystal.

Japanese Patent Application Laid-Open No. 9-167686 (prior art) discloses a light emitting structure in which a light emitting layer made of a material obtained by adding a light emitting center to a base material is interposed between a pair of electrodes. In a thin film EL element formed on a light-transmitting substrate, at least one kind of alkaline earth metal sulfide is used as a base material of the light-emitting layer, and the light-transmitting substrate has a thermal expansion coefficient of 8 × 10 ^−6. / ℃ ～ 12 × 10 ^-6 / ℃
Are disclosed. In the above-mentioned thin film EL element, the coefficient of thermal expansion is 8 × 10 ⁻⁶ / ° C. to 12 × 1.
The use of a light-transmitting substrate of 0 ^-6 / ° C suppresses cracks in the light-emitting layer during heat treatment.

Japanese Patent Application Laid-Open No. 7-14678 (prior art) discloses an EL device in which an EL structure including a transparent electrode and a metal electrode disposed on both sides of an EL light emitting layer is formed on a glass substrate surface. Also disclosed is an EL element in which a first ion barrier layer and a second ion barrier layer are formed in this order on the surface of a glass substrate on which the above EL structure is formed.

In the EL device, the provision of each of the barrier layers can prevent the alkali ions contained in the glass substrate from diffusing into the light emitting layer when the light emitting layer is heat-treated.

[0008]

The prior art. However, since the used substrate does not have a light-transmitting property, there is a problem that it can be used only for a thin-film EL element having an inverted structure in which light is emitted from the sealing substrate side.

Further, in the conventional technology. Used a glass substrate (coefficient of thermal expansion: 8 × 10 ⁻⁶ / ° C.) or a single crystal of SrTiO ₃ (coefficient of thermal expansion: 10 × 10 ⁻⁶ / ° C. to 11 × 10 ⁻⁶ / ° C.) as a light-transmitting substrate. Examples are shown, and it is described that no crack occurs in the light emitting layer. However, in the illustrated glass material, the thermal expansion coefficient of the light-emitting layer (thermal expansion coefficient: 11 × 10 ⁻⁶ / ° C. to 14 × 10 ⁻⁶ / ° C.)
In addition, there is a problem that cracks are generated, and that when SrTiO ₃ single crystal is used as a light-transmitting substrate, it becomes expensive.

[0010] Further, the conventional technology. In this case, it is necessary to provide a special barrier layer for preventing diffusion, which causes a problem that the manufacturing process of the EL element becomes complicated.

[0011]

In order to solve the above-mentioned problems, the EL device of the present invention has a light-emitting portion having a light-emitting layer by electroluminescence between a transparent common electrode layer and each scanning electrode layer. Is formed on a substrate, and the substrate is characterized by being a translucent polycrystal having a perovskite crystal structure as a main crystal phase. The light-transmitting ceramic may be any ceramic that is formed by firing and is a light-transmitting polycrystalline material (that is, a material that does not exhibit birefringence).

According to the above configuration, since the substrate is made of a translucent ceramic, the substrate is excellent in heat resistance and can be subjected to a high-temperature heat treatment of the light emitting layer, and the heat treatment can improve the luminous efficiency of the light emitting layer.

In addition, in the above configuration, the substrate made of a translucent ceramic can have high surface smoothness (Ra ≦ 10).
nm), surface defects can be extremely reduced (area ratio of surface defects is 0.1% or less). Thereby, the adhesion between the transparent electrode layer formed on the substrate and the transparent electrode layer can be improved, and inconveniences such as separation between the substrate and the transparent electrode layer can be suppressed. Display quality can be improved.

Further, the substrate has a thermal expansion coefficient of 10 ×.
Because it to ^{10 -6 / ℃ ~11 × 10 -6} / ℃, and possible to reduce the difference between the thermal expansion coefficient of the light-emitting layer, it is possible to suppress the occurrence of peeling at the cracks and substrate in the light emitting layer during the heat treatment.

Further, since the linear transmittance of the substrate can be set high, light can be emitted through the substrate, and the invention can be applied to EL elements other than the inverted structure. In addition, in the above configuration, since it can be manufactured without expensive and complicated steps such as hot pressing, the cost can be reduced.

Therefore, with the above configuration, reliability can be improved and the cost can be reduced as compared with the conventional configuration.

In the above EL device, Ba (Mg, T
It is preferably a) O ₃ system. According to the above configuration,
Since the coefficient of thermal expansion is 10 × 10 ⁻⁶ / ° C. to 11 × 10 ⁻⁶ / ° C., the difference between the coefficient of thermal expansion and the coefficient of thermal expansion of the light emitting layer can be further reduced. It can be suppressed more reliably.

The substrate may be of a Ba (Zn, Ta) O ₃ type. According to the above configuration, the coefficient of thermal expansion is 10 ×
Since it is 10 ⁻⁶ / ° C. to 11 × 10 ⁻⁶ / ° C., the difference from the thermal expansion coefficient of the light emitting layer can be further reduced, and the generation of cracks and peeling during the heat treatment in the light emitting layer can be suppressed more reliably.

In the above EL device, the substrate has a refractive index of 1.
It is desirable that the thickness be 9 or more and a paraelectric substance. A paraelectric is a substance whose permittivity does not change even when an electric field is applied, and therefore does not cause birefringence.

According to the above configuration, since the material is paraelectric,
Does not show birefringence, even if used on the display screen side of the display device of the substrate, the display on the display surface is distorted due to birefringence, it can be avoided that it is corrected, suitable as a display device It becomes something. Furthermore, in the above configuration, since the refractive index is 1.9 or more, the viewing angle on the display screen can be increased, and the viewing angle visibility can be improved.

In the above EL device, it is preferable that the base material of the light emitting layer is a sulfide of an alkaline earth metal. According to the above configuration, since the sulfide of the alkaline earth metal is used as the base material of the light emitting layer, the difference in the coefficient of thermal expansion between the light emitting layer and the substrate can be set much smaller. The occurrence of cracks and peeling at the time can be suppressed more reliably.

As the translucent ceramic, the A site contains one or more of Ba, Sr and Ca, and the B site contains Zr, Sn, Hf, Ta, Zn, Nb, Mg, T
General formula ABO containing at least one of i, Al and rare earths
It is desirable to have a perovskite crystal structure represented by ₃ . The perovskite-type crystal structure includes a composite perovskite-type crystal structure.

[0023]

FIG. 1 shows an embodiment of the present invention.
The following is a description based on FIG.

In the EL device according to the present invention, as shown in FIG. 1, a light-transmitting substrate 1 made of a light-transmitting ceramic has a plate shape, a surface roughness Ra of 0.005 μm, and a surface of the substrate 1. Is formed to have a defect area of 0.1%. On this substrate 1, for example, ITO (Indium Tin Oxid
The transparent electrode layer 2 of e) is formed to a thickness of, for example, 200 nm by a sputter link method or the like. The transparent electrode layer 2 is a common electrode layer.

On the transparent electrode layer 2, a lower insulating layer 3, a light emitting layer 4, and an upper insulating layer 5 are formed in this order. As the lower insulating layer 3, a laminated film of silicon oxide and silicon nitride was used. The layer thickness at this time is, for example, 50 nm, respectively.
It was 200 nm. As the upper insulating layer 5, a laminated film of silicon nitride and silicon oxide was used. The layer thickness at this time was, for example, 200 nm and 50 nm, respectively.

Strontium sulfide (SrS) is used as a light emitting base material of the light emitting layer 4, and cerium sulfide (Ce ₂ S ₃ ) is used as a light emitting center of the light emitting layer 4 on the substrate 1 heated to 500 ° C. by an electron beam evaporation method. , 0.8 μm to 1.8 μm.

The light-emitting layer 4 is annealed in vacuum, for example, at 600 ° C. for 2 hours in order to improve the crystallinity of the light-emitting layer 4 and to distribute the light-emitting centers more uniformly to increase the light-emitting efficiency. ing.

Finally, on the upper insulating layer 5, aluminum electrodes in the form of stripes are formed in parallel with and separated from each other as back electrodes 6 by using an etching process. Each of the back electrodes 6 is a scanning electrode for displaying an image. Thus, a thin-film EL element is obtained.

The transparent ceramics may have any refractive index as long as it is formed by firing and has a linear transmittance of light of 20% or more, more preferably 50% or more. Although it may have birefringence, it is preferable that the material has a refractive index of 1.9 or more and is a paraelectric material (having no birefringence).

Next, Ba (M
The translucent ceramic having a g, Ta) O ₃ -based composite perovskite crystal structure as a main crystal phase will be described below.

First, as raw material powder, high purity BaCO
_Three, SnO_Two, ZrO_Two, MgCO _ThreeAnd Ta_TwoO_Five
Was prepared. Subsequently, each of the raw material powders was
[(Sn_uZr_1-u)_xMg_yTa_z]_vO_wComposition
In the equation, u = 0.67, x = 0.16, y = 0.2
9, a composition of z = 0.55 and v = 1.02 is obtained.
And weigh them together in a ball mill for 16 hours
The mixture was obtained by wet mixing. In addition, about w,
Later, it is almost 3. About x, y, z
Satisfies the relationship x + y + z = 1.00.

After the mixture has been dried,
After calcining for a time, a calcined product was obtained. The calcined product was put into a ball mill together with water and an organic binder, and wet-pulverized for 16 hours to obtain a pulverized product. As an organic binder, it has a function as a binder, and at the time of sintering, before it reaches the sintering temperature, it reacts with oxygen in the air at, for example, about 500 ° C. in the air to produce gas such as carbon dioxide gas or water vapor. Any substance may be used as long as it is converted and disappears, and examples thereof include ethyl cellulose.

After the pulverized product is dried, it is granulated through a 50-mesh net (sieve), and the obtained granulated powder is formed into a predetermined rectangular parallelepiped shape at a pressure of, for example, 2000 kg / cm ² . I got Next, this molded product was embedded in the same composition powder.

The above-mentioned powder of the same composition is obtained by pulverizing a calcined product obtained by calcining a powder having the same composition as that of the above-mentioned molded product, and does not need to have a particular light-transmitting property. As the same composition system, if the molded product and each component are the same,
Although their composition ratio may be different, substantially the same one is preferable. Therefore, the molded article embedded in the powder of the same composition is disposed close to the same composition system as the molded article and fired.

The molded product is heated together with the powder of the same composition in a firing furnace in an atmosphere having an atmospheric composition to raise the temperature to remove the organic binder contained in the molded product by heating. After the temperature is raised to a temperature range where the temperature rises, and after removing the binder, oxygen is injected into the air while raising the temperature, and the oxygen concentration is increased from the oxygen concentration in the air, for example, to 95% (volume%). The inside firing atmosphere was adjusted.

Thereafter, while maintaining the firing atmosphere, the inside of the firing furnace is heated to a firing temperature of, for example, 1600 ° C., and the molded product is fired for 20 hours while maintaining the firing atmosphere and the firing temperature. A sintered body was obtained from the molded product.

As described above, as shown in FIG. 1, the translucent body according to the present embodiment is a sintered body having a Ba (Mg, Ta) O ₃ -based composite perovskite-type crystal structure as a main crystal phase. A substrate 1 made of a conductive ceramic was produced.

The translucent ceramic thus obtained was analyzed by X-ray diffraction (XRD) to find that Ba (M
g, Ta) It was confirmed to have an O ₃ -based crystal structure. Here, Ba enters the A site of the complex perovskite type crystal structure, and the entry of Mg and Ta into the B site is restricted by their ionic radius and valence.

Regarding the above-mentioned firing temperature and firing time,
It is set depending on the composition to be used.
The firing time may be 10 hours or more within the range of 1 to 1650 ° C. By firing under the above conditions, a translucent ceramic which is a sintered body having high translucency can be obtained. The translucent ceramic is a paraelectric polycrystalline body and does not exhibit birefringence.

The linear transmittance and the refractive index of the translucent ceramic used for the substrate 1 were measured. The refractive index was 2.1. As shown in FIG. 2, the linear transmittance is 40% or more when the light wavelength is in a range from 300 nm to 900 nm, 60% or more in a range from 350 nm to 900 nm, and 70% or more in a range from 380 nm to 900 nm. Met.

The linear transmittance was measured using a spectrophotometer (UV-
200S) and the measurement wavelength λ is 180 nm to 900 n.
m and the refractive index is measured by a prism coupler (Metric
on Model, MODEL 2010), and the measurement wavelength λ is 633 nm
Was measured.

The fact that the linear transmittance of the substrate 1 made of the translucent ceramic used is substantially a theoretical value will be described below. First, at the time of measuring the linear transmittance, light is perpendicularly incident on the sample from the air. Therefore, when the refractive index (n) is 2.1, the sum of the reflectances on the front surface and the back surface of the substrate 1 is 23%. Therefore, the theoretical value (theoretical maximum value) of the linear transmittance of the substrate 1 is 77%.

The substrate 1 has a linear transmittance of 400.
Above nm, it was almost 75%, showing a value equivalent to the theoretical value. This indicates that there is almost no defect in the crystal of the light-transmitting ceramic as the substrate 1, and supports that this light-transmitting ceramic can be used as an optical component. By applying an AR (anti-reflection film) coating on the surface of such a translucent ceramic, it is possible to obtain an almost 100% linear transmittance.

In such an EL element, since the substrate 1 made of the above-mentioned translucent ceramic is used, SrS
Even if the thickness of the light emitting layer 4 was changed variously, peeling or cracking of the light emitting layer 4 after annealing was not observed. Also, no defects such as disconnection during the formation of each thin film were observed. This is because the thermal expansion coefficient of the used substrate 1 is 10 × 10 ⁻⁶ / ° C. to 11 × 10
⁻⁶ / ° C., the thermal expansion coefficient of the light emitting layer 4 is 11 × 10 ^−6.
/ ° C ~ 14 × 10 ^-6 / ° C)
This is because cracking and peeling of the light emitting layer 4 could be avoided.

In addition, in the above EL device, SrT
The same effect can be exerted without using an expensive material such as iO ₃ single crystal as the substrate 1, and a method using an expensive device such as HP or HIP can be avoided, so that the device can be made inexpensive.

Next, the effect of the oxygen concentration of the above-mentioned firing atmosphere on the linear transmittance was examined. First, translucent ceramics were prepared by changing the oxygen concentration in the firing atmosphere in various ways. Subsequently, the linear transmittance of each translucent ceramic was examined, and the results are shown in FIG. In this result, the relationship between the oxygen concentration and the linear transmittance shows a positive correlation, and the oxygen concentration in the firing atmosphere is preferably 45% or more (a range where the linear transmittance is 20% or more), and is preferably 75% or more ( (A range in which a linear transmittance of 60% or more is obtained), and more preferably 90% or more.

In the above description, the transparent ceramic of the substrate 1 is used.
Ba (Mg, Ta) O _ThreeExamples using the system
However, other translucent ceramics may be used.
a (Zn, Ta) O_ThreeUsing transparent ceramics
You can also. Based on this translucent ceramics manufacturing method,
The description is as follows. First, as raw material
And high purity BaCO_Three, ZrO_Two, ZnO and Ta
_TwoO_FiveWas prepared.

Subsequently, these raw materials were converted to Ba (Zr _x
In Zn _y Ta _{z) a} O _w a composition formula, x = 0.0
3, y = 0.32, z = 0.65, a = 1.02 were weighed so as to obtain a composition, and they were wet-mixed together in a ball mill for 16 hours to obtain a mixture. In addition, w is substantially 3 after firing.

After drying this mixture, the mixture was dried at 1200 ° C. for 3 hours.
After calcining for a time, a calcined product was obtained. The calcined product was put into a ball mill together with water and an organic binder, and wet-pulverized for 16 hours to obtain a pulverized product. Using this pulverized material, a substrate 1 was prepared in the same manner as in the above-described Ba (Mg, Ta) O ₃ system, except that the firing temperature was changed to 1500 ° C. and the firing time was changed to 10 hours.

Regarding the above-mentioned firing temperature and firing time,
It is set depending on the composition to be used.
What is necessary is just to be in the range of ℃ to 1600 ℃, and the firing time is 5 hours or more. By firing under the above conditions, a sintered body having high translucency can be obtained.

The translucent ceramics are similarly directly
The linear transmittance and the refractive index were measured respectively. The above translucent sera
The refractive index of the mix was 2.1. Also, linear transmittance
The results are shown in FIG. In the above result,
The excess ratio is more than 50% from 400 nm to 900 nm.
there were. As described above, in the above, Ba (Zn, Ta)
O_ThreeExamples of translucent ceramics are shown,
Ba (Mg, Ta) O _ThreeComplex perovska different from the system
Even in a material system with a main crystal phase of
That linear transmittance and high refractive index are obtained
I understand.

Further, another EL device using a translucent ceramic having a Ba (Mg, Ta) O ₃ -based composite perovskite-type crystal structure as a main crystal phase will be described below.

First, high purity BaCO ₃ ,
MgCO ₃ and Ta ₂ O ₅ were prepared. Subsequently, each of the above raw materials, Ba in _{(Mg y Ta z) v O} w a composition formula, y = 0.33, z = 0.67 , v = 1.03 and consisting, respectively, as the composition is obtained weighed did.

Subsequently, an EL element was manufactured in the same manner as the substrate 1 using the above-mentioned Ba (Mg, Ta) O ₃ system. The linear transmittance of the translucent ceramic was measured, and the results are shown in FIG. From the results, the linear transmittance is 2
Although it is about 0% and has a slightly lower linear transmittance than the above-mentioned translucent ceramics, it can be used as a material of the substrate 1 by applying an antireflection coat.

In each of the above examples, examples of each translucent ceramic having a specific composition ratio have been described.
The translucent ceramic used for the L element is not limited to these.

Further, in each of the above examples, the example in which the molded article is embedded in the powder of the same composition in order to dispose the molded article in close proximity to the same composition system as the molded article has been described. The present invention is not limited thereto. For example, a sintered body plate or sheath having the same composition as the above-mentioned molded product may be used. In the case of using the above-mentioned plate, the molded product may be placed on the plate and firing, and in the case of using the above-mentioned sheath, the molded product may be placed in the sheath and fired. I just need.

[0057]

As described above, the EL device of the present invention has a
A light emitting portion having a light emitting layer of L between the transparent common electrode layer and each scanning electrode layer is formed on the substrate, and the substrate has a light-transmitting property having a perovskite crystal structure as a main crystal phase. The structure is a crystal.

Therefore, in the above structure, since the heat treatment for the light emitting layer can be performed at a high temperature when the substrate is made of a polycrystalline material having a light transmitting property, the light emitting efficiency of the light emitting layer can be increased. Also, there is an effect that conventional expensive materials and methods can be avoided and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an EL device of the present invention.

FIG. 2 is a graph showing the linear transmittance at each wavelength for each translucent ceramic used for the substrate of the EL element of the present invention.

FIG. 3 is a graph showing the relationship between the oxygen concentration in a firing atmosphere and the linear transmittance of the translucent ceramic used for the EL element.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 transparent electrode (transparent common electrode layer) 4 light emitting layer 6 back electrode (scanning electrode layer)

Claims (5)

[Claims] 1. An electroluminescent light-emitting layer,
A light emitting portion having between the transparent common electrode layer and each scanning electrode layer is formed on a substrate, and the substrate has a perovskite crystal structure as a main crystal phase.
An electroluminescent element, which is a light-transmitting polycrystalline body. 2. The electroluminescent device according to claim 1, wherein the substrate is based on Ba (Mg, Ta) O ₃ . 3. The electroluminescent device according to claim 1, wherein the substrate is based on Ba (Zn, Ta) O ₃ . 4. The electroluminescent device according to claim 1, wherein the substrate has a refractive index of 1.9 or more and is a paraelectric material. 5. The electroluminescent device according to claim 1, wherein the base material of the light emitting layer is a sulfide of an alkaline earth metal.