JP2002216954A - Thin film el element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film EL element and its manufacturing method in which a highly displaying quality is obtained without yielding a high cost wherein problems that the reduction of light-emitting luminance, unevenness of the luminance and time-changes of the luminance of the thin film EL element occur are solved wherein a multi-layer dielectric layer is formed by solution coating and baking method using lead series dielectric materials. SOLUTION: This has a multi-layer structure wherein an electrode layer having patterns is formed on the electric insulating substrate, and further wherein the lead series dielectric layer and a non-lead series high dielectric constant dielectric layer are formed by repeating the solution coating and baking method for plural times and laminated as the dielectric layer, and the foremost front layer of the dielectric layer of the multi-layer structure is made to be the non- lead series high dielectric constant dielectric layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film EL device having at least a structure having an electrically insulating substrate, an electrode layer having a pattern on the substrate, a dielectric layer, a light emitting layer and a transparent electrode layer laminated on the electrode layer. About.

[0002]

2. Description of the Related Art An EL element is a liquid crystal display (LCD).
It is used as a backlight for watches and watches. An EL element is an element using a phenomenon in which a substance emits light when an electric field is applied, that is, an electroluminescence (EL) phenomenon.

[0003] The EL element includes a dispersion type EL element having a structure in which a powder luminous body is dispersed in an organic substance or an enamel, and an electrode layer is provided on the upper and lower sides, and two electrode layers are formed on an electrically insulating substrate.
There is a thin-film EL element using a thin-film luminous body formed between two thin-film insulators. Further, there are a DC voltage driving type and an AC voltage driving type depending on the driving method.
Dispersion-type EL elements have been known for a long time and have an advantage of being easy to manufacture, but their use is limited because of their low luminance and short life. On the other hand, thin-film EL elements have been widely used in recent years because of their characteristics of high luminance and long life.

FIG. 2 shows the structure of a typical double-insulation type thin film EL device as a conventional thin film EL device. This thin film EL element is formed on a transparent substrate (21) such as blue plate glass used for a liquid crystal display, a PDP, or the like, in a thickness of 0.2 μm to 0.2 μm.
A transparent electrode layer (22) made of ITO of about 1 μm and having a predetermined stripe pattern, a thin transparent first insulator layer (23), a light emitting layer (24) having a thickness of about 0.2 μm to 1 μm, a thin film An electrode layer (2) such as an Al thin film, which is laminated with a transparent second insulator layer (25) and patterned in a stripe shape so as to be orthogonal to the transparent electrode layer (22).
6) is formed, the transparent electrode layer (22) and the electrode layer (26)
By selectively applying a voltage to a specific luminous body selected by the matrix composed of the above, the luminous body of the specific pixel emits light, and the luminescence is extracted from the substrate side. Such a thin-film insulator layer has a function of restricting a current flowing in the light-emitting layer, can suppress dielectric breakdown of the thin-film EL element, and contributes to obtaining stable light-emitting characteristics. EL elements have been widely and practically used commercially.

The above-mentioned thin film transparent insulator layers (23), (2)
5) is Y ₂ O ₃ , Ta ₂ O ₅ , Al ₃ N ₄ , BaTiO ₃ ,
The transparent dielectric thin film is formed to a thickness of about 0.1 to 1 μm by sputtering or vapor deposition.

As a light emitting material, Mn which emits yellow-orange light is used.
ZnS to which is added has been mainly used from the viewpoint of ease of film formation and light emission characteristics. In order to produce a color display, it is indispensable to use a luminescent material which emits light in three primary colors of red, green and blue. Examples of these materials include ZnS to which SrS or Tm to which blue light emitting Ce is added, ZnS to which Sm to which red light emitting Sm is added, and Ca to which Eu is added.
Known are S, ZnS to which Tb emitting green light is added, and CaS to which Ce is added.

[0007] Also, the monthly display '98 April issue
"Recent Display Technology Trends", Tanaka, p1-10
Include ZnS, Mn / Cd as materials for obtaining red light emission.
As a material for obtaining green light emission such as SSe, ZnS: TbO
F, ZnS: Tb and other materials for obtaining blue light emission
SrS: Cr, (SrS: Ce / ZnS) n, Ca
_TwoGa_TwoS_Four : Ce, Sr_TwoGa_TwoS_Four : Light emitting material such as Ce
Fees are disclosed. In addition, white light emission shall be obtained.
Thus, a light emitting material such as SrS: Ce / ZnS: Mn has been disclosed.
Have been.

Further, among the above materials, SrS: Ce is used for a thin film EL device having a blue light emitting layer.
(International Display Workshop) '97 X.Wu "Mul
ticolor Thin-Film Ceramic Hybrid EL Displays "p593
to 596. Furthermore, this document includes Sr
It is disclosed that when a light emitting layer of S: Ce is formed by an electron beam evaporation method in an H ₂ S atmosphere, a light emitting layer of high purity can be obtained.

However, such a thin film EL device still has a structural problem. That is, since the insulator layer is formed of a thin film, when the display has a large area, the defect of the thin film insulator due to a step portion of the pattern edge of the transparent electrode or dust generated in a manufacturing process is eliminated. And the light-emitting layer is destroyed due to a local decrease in withstand voltage. Since such a defect becomes a fatal problem as a display device, the thin-film EL element has been a serious problem for practical use as a large-area display as compared with a liquid crystal display or a plasma display. .

In order to solve such a problem that a defect of the thin film insulator occurs, an electric insulating ceramic substrate is used as a substrate in Japanese Patent Application Laid-Open No. 7-50197 and Japanese Patent Publication No. 7-44072, and a light emitting device is provided under the light emitting device. A thin film EL device using a thick film dielectric instead of the thin film insulator is disclosed. As shown in FIG. 3, this thin-film EL element is composed of a lower thick-film electrode layer (32), a thick-film dielectric layer (33), a light-emitting layer (34), a thin-film insulator layer on a substrate (31) made of ceramic or the like. (35), a structure in which an upper transparent electrode layer (36) is laminated. As described above, unlike the structure of the thin-film EL element shown in FIG. 2, the transparent electrode layer is formed on the upper side in order to extract the light emitted from the light emitter from the upper side opposite to the substrate.

In this thin-film EL element, the thick dielectric layer is
0 nm to several hundreds μm and several hundreds to several tens of thin film insulator layers
It is formed to a thickness of 00 times. Therefore, there is very little dielectric breakdown caused by a step formed in the electrode or a pinhole formed by dust or the like in a manufacturing process, and there is an advantage that high reliability and a high yield in manufacturing can be obtained.
The use of this thick dielectric layer causes a problem of a drop in the effective voltage applied to the light emitting layer. However, the use of a high dielectric constant material for the dielectric layer solves this problem.

However, the light emitting layer formed on the thick dielectric layer has a thickness of only several hundred nm, which is about 1/100 of that of the thick dielectric layer. Therefore, the surface of the thick-film dielectric layer must be smooth at a level equal to or less than the thickness of the light-emitting layer, but it is difficult to sufficiently smooth the dielectric surface manufactured by the ordinary thick-film process. there were.

That is, since the thick-film dielectric layer is essentially composed of ceramics using a powdered raw material, a volume shrinkage of about 30 to 40% usually occurs for dense sintering. While sintering causes three-dimensional volume shrinkage and densification, in the case of thick-film ceramics formed on a substrate, the thick film is constrained by the substrate,
It cannot shrink in the in-plane direction of the substrate and can only shrink one-dimensionally in the thickness direction. For this reason, the sintering of the thick-film dielectric layer becomes essentially porous with insufficient sintering.

Further, since the densification process is a ceramic solid phase reaction of a powder having a certain particle size distribution, abnormal sintering points such as abnormal crystal growth and formation of huge pores are likely to be formed.
Furthermore, since the surface roughness of the thick film does not become smaller than the crystal grain size of the polycrystalline sintered body, even if there is no defect as described above, the surface has an irregular shape of a submicron size or more.

As described above, when the surface of the dielectric layer is defective or the film quality is porous or irregular, the light emitting layer formed thereon by vapor deposition or sputtering follows the surface shape. It cannot be formed uniformly. For this reason, since an electric field cannot be effectively applied to the light emitting layer formed on such a non-flat portion of the substrate, the light emitting area is reduced, and light emission is caused by local unevenness of film thickness. There is a problem that the light emission luminance is reduced due to partial dielectric breakdown of the layer. Furthermore, since the film thickness locally fluctuates greatly, the intensity of the electric field applied to the light emitting layer fluctuates greatly locally, and there is a problem that a clear light emitting voltage threshold cannot be obtained.

Therefore, in the conventional manufacturing process, it is necessary to remove large irregularities on the surface of the thick film dielectric layer by polishing, and then remove finer irregularities by a sol-gel process.

However, it is technically difficult to polish a large-area substrate for a display or the like, which is a factor that increases the cost. The addition of the sol-gel process was a factor that further increased the cost. Further, when large irregularities that cannot be removed by polishing occur due to abnormal sintering points in the thick dielectric layer, the addition of the sol-gel process cannot be dealt with, causing a reduction in yield. For this reason, it has been extremely difficult to form a low-cost dielectric layer free from light emission defects with a thick-film dielectric.

Further, since the thick-film dielectric layer is formed by a ceramic powder material sintering process, the firing temperature is high. That is, the sintering temperature is 800 ° C. or higher, usually 850 ° C. as in the case of ordinary ceramics. In particular, a sintering temperature of 900 ° C. or higher is required to obtain a dense thick film sintered body. Substrates for forming such a thick dielectric layer are limited to alumina ceramics and zirconia ceramics substrates due to problems with heat resistance and reactivity with the dielectric layer, and it is difficult to use an inexpensive glass substrate. When the above-mentioned ceramic substrate is used for display, it is necessary that the substrate has a large area and good smoothness. However, it is technically extremely difficult to obtain a substrate under such conditions, and this is a factor that increases cost. Met.

Further, the metal film used as the lower electrode layer also needs to use an expensive noble metal such as palladium or platinum because of its heat resistance, which is a factor that increases the cost.

In order to solve such a problem, the present inventor uses a solution coating and firing method as a dielectric layer instead of a conventional thick film dielectric or a thin film dielectric formed by a sputtering method or the like. Japanese Patent Application No. 200-200980 to form a multilayer dielectric layer thicker than a conventional thin film dielectric layer by repeating a plurality of times.
0-299352.

FIG. 4 shows the structure of a thin film EL device using the above-mentioned multilayer dielectric layer. This thin film EL element is a multilayer dielectric formed by repeating a solution coating and firing method a plurality of times on a lower electrode layer (42) having a predetermined pattern on an electrically insulating substrate (41). Layer (4
3) and a structure in which a light emitting layer (44), preferably a thin film insulator layer (45), and a transparent electrode layer (46) are further laminated on a dielectric layer.

The multilayer dielectric layer having such a structure has a higher dielectric strength than a conventional thin-film dielectric, can prevent local insulation defects due to dust and the like during the process, and can have a surface flatness. Is remarkably good.
Furthermore, since the thin-film EL element using the above-mentioned multilayer dielectric layer can form a dielectric layer at a temperature of 700 ° C. or lower, a glass substrate that is less expensive than a ceramic substrate can be used. is there.

However, when a multilayer dielectric layer is formed using such a solution coating and baking method, when a lead-based dielectric is used as the dielectric layer material, the light emitting layer formed on the dielectric layer has a dielectric property. It reacts with the lead component of the body layer and has a problem of a reduction in the initial light emission luminance, luminance unevenness and a change with time of the light emission luminance, and has been a practical problem.

[0024]

SUMMARY OF THE INVENTION It is an object of the present invention to use a glass substrate or the like which is inexpensive and can easily have a large area without restriction on substrate selection which is a problem in a conventional thin film EL device. By the method, the non-flat portion of the dielectric layer due to dust or the like in the electrode layer or the process is corrected, so that the withstand voltage does not decrease, and further, the smoothness of the dielectric layer surface is good,
Further, as described above, the thin-film EL element in which a multilayer dielectric layer is formed using a lead-based dielectric material can solve the problem of reduced luminance unevenness, luminance unevenness, and time-dependent change in emitted luminance, and can achieve high display quality. And a method for manufacturing the same without increasing the cost.

[0025]

That is, the above object is achieved by the following constitution of the present invention. (1) having at least a structure in which a substrate having electrical insulation, a lower electrode layer having a pattern on the substrate, a dielectric layer, a light emitting layer, and an upper electrode layer are laminated on the electrode layer;
A thin-film EL device in which at least one of the lower electrode or the upper electrode is a transparent electrode, wherein the dielectric layer is formed by repeating a solution coating and firing method a plurality of times, and a lead-based dielectric layer and a non-lead-based high dielectric A thin-film EL device having a multilayer structure in which a dielectric constant layer is laminated, wherein the outermost layer of the dielectric layer having the multilayer structure is a lead-free high dielectric constant dielectric layer. (2) The thin-film EL device according to (1), wherein the thickness of the lead-based dielectric layer is 4 μm or more and 16 μm or less. (3) The thin film EL device according to (1), wherein the thickness of the lead-free dielectric layer is more than 0.2 μm. (4) The above (1) to (3), wherein the lead-free high dielectric constant dielectric layer is formed of a perovskite structure dielectric.
The thin film EL device according to any one of the above. (5) The thin film EL device according to any one of (1) to (4), wherein the lead-free high dielectric constant dielectric layer is formed by a sputtering method. (6) The thin film EL device according to any one of the above (1) to (4), wherein the lead-free high dielectric constant dielectric layer is formed by a solution coating and firing method. (7) The dielectric layer having the multilayer structure is formed by the solution coating and baking method.
The thin film EL device according to the above (6), which is formed by repeating at least twice. (8) having at least a structure in which a substrate having electrical insulation, a lower electrode layer having a pattern on the substrate, a dielectric layer, a light emitting layer, and an upper electrode layer are laminated on the electrode layer;
A method of manufacturing a thin-film EL element in which at least one of a lower electrode and an upper electrode is formed of a transparent electrode, wherein a lead-based dielectric layer formed by repeating a solution coating and firing method a plurality of times, and a lead-free high dielectric constant A method for manufacturing a thin-film EL device in which a dielectric layer is laminated to form a multilayer structure, and the outermost layer of the dielectric layer having the multilayer structure is a lead-free high dielectric constant dielectric layer. (9) The method for manufacturing a thin film EL device according to (8), wherein the lead-free high dielectric constant dielectric layer is formed by a sputtering method. (10) The method for producing a thin film EL device according to the above (8), wherein the lead-free high dielectric constant dielectric layer is formed by a solution coating baking method. (11) The method for manufacturing a thin film EL device according to the above (10), wherein the dielectric layer having the multilayer structure is formed by repeating a solution coating and firing method at least three times.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION A thin film EL device according to the present invention comprises a substrate having electrical insulation, a lower electrode layer having a pattern on the substrate, a dielectric layer, a light emitting layer and an upper electrode layer laminated on the electrode layer. A thin film EL element having at least one of a lower electrode and an upper electrode formed of a transparent electrode, wherein the dielectric layer is formed by repeating a solution coating and firing method a plurality of times. It has a multilayer structure in which a dielectric layer and a lead-free high dielectric constant dielectric layer are laminated, and the outermost layer of the dielectric layer of the multilayer structure is a lead-free high dielectric constant dielectric layer. . Here, the lead-based dielectric is a dielectric containing lead in the composition, and the lead-free (high dielectric constant) dielectric layer is a dielectric containing no lead in the composition.

FIG. 1 is a structural view of a thin film EL device of the present invention. The thin-film EL element of the present invention comprises a lower electrode layer (1) having a predetermined pattern formed on an electrically insulating substrate (11).
2) and a lead-based dielectric layer (13) and a lead-free high-dielectric-constant dielectric layer (18) formed by repeating the solution coating and firing method a plurality of times. The multilayer dielectric layers are stacked so as to be lead-free high dielectric constant dielectric layers. Further, an insulator layer (17) on the dielectric layer,
It has a structure in which a light emitting layer (14), a thin film insulator layer (15), and a transparent electrode layer (16) are laminated. The insulator layer (1
7) and (15) may be omitted. The lower electrode layer and the upper transparent electrode layer are each formed in a stripe shape, and are arranged in directions orthogonal to each other. By selecting the lower electrode layer and the upper transparent electrode layer, respectively, and selectively applying a voltage to the light emitting layer at a portion orthogonal to both electrodes, light emission of a specific pixel can be obtained.

The substrate is not particularly limited as long as it has electrical insulation and can maintain a predetermined heat resistance without contaminating the lower electrode layer and the dielectric layer formed thereon.

As a specific material, alumina (Al ₂
O ₃ ), quartz glass (SiO ₂ ), magnesia (Mg
O), forsterite (2MgO · SiO _2), steatite (MgO · SiO _2), mullite (3Al ₂ O ₃
・ 2SiO ₂ ), beryllia (BeO), zirconia (ZrO ₂ ), aluminum nitride (AlN), silicon nitride (SiN), silicon carbide (SiC), and other ceramic substrates, crystallized glass, high heat resistant glass, blue plate glass, etc. May be used, and a metal substrate or the like subjected to an enamel treatment may also be used.

Among them, particularly, crystallized glass, high heat-resistant glass, and blue plate glass can be manufactured at low cost, surface property, flatness, and large-area substrate production if they match the firing temperature of the dielectric layer to be formed. It is preferable because of its ease.

The lower electrode layer is formed so as to have a plurality of stripe-shaped patterns. The line width of the lower electrode layer is the width of one pixel, and the space between lines is a non-light emitting area. It is preferable that the line width is about 200 to 500 μm and the space is about 20 μm, depending on the intended display resolution.

As a material for the lower electrode layer, a material which has high conductivity, is not damaged when forming the dielectric layer, and has low reactivity with the dielectric layer and the light emitting layer is preferable. Such lower electrode layer materials include Au, Pt, Pd,
Noble metals such as Ir and Ag, Au-Pd, Au-Pt and A
Noble metal alloys such as g-Pd and Ag-Pt, and Ag-Pd-
An electrode material containing a noble metal such as Cu as a main component and a nonmetal element added thereto is preferable because oxidation resistance to an oxidizing atmosphere during firing of the dielectric layer can be easily obtained. In addition, ITO or SnO ₂
(Nesa film), an oxide conductive material such as ZnO-Al may be used, or a base metal such as Ni or Cu may be used to oxidize the partial pressure of oxygen when firing the dielectric layer. It can also be used by setting it to a range not to be performed. As a method for forming the lower electrode layer, a known technique such as a sputtering method, an evaporation method, and a plating method may be used.

The dielectric layer is preferably made of a material having a high dielectric constant and a high withstand voltage. Here, when the relative dielectric constants of the dielectric layer and the light emitting layer are e1 and e2, the film thicknesses are d1 and d2, and the voltage Vo is applied between the upper electrode layer and the lower electrode layer, the voltage applied to the light emitting layer V2 is represented by the following equation.

V2 / Vo = (e1 × d2) / (e1 × d2 + e2 × d1) ------ (1)

The relative permittivity of the light emitting layer is e2 = 10, and the film thickness is d.
Assuming 2 = 1 μm,

V2 / Vo = e1 / (e1 + 10 × d1) (2)

The effective voltage applied to the light emitting layer is at least 50% or more of the applied voltage, preferably 80% or more, and more preferably 90% or more.

When it is 50% or more, e1 ≧ 10 × d1 (3) When it is 80% or more, e1 ≧ 40 × d1 (4) 90% or more In the case of, e1 ≧ 90 × d1 -------- (5)

That is, the relative dielectric constant of the dielectric layer must be at least 10 times, preferably at least 40 times, more preferably at least 90 times the film thickness when the unit is expressed in μm. For example, when the thickness of the dielectric layer is 5 μm, the relative dielectric constant needs to be 50 to 200 to 450 or more.

Various materials can be considered as such a high dielectric constant material. In particular, a (ferro) dielectric material containing lead as a constituent element is preferable because of its ease of synthesis and low-temperature formability, and PbTiO. ₃ , PZT (= Pb (Zr _x Ti _1-x )
₃ ), perovskite structure dielectric material such as PLZT,
A composite perovskite relaxer type ferroelectric material typified by Pb (Mg _1/3 Ni _2/3 ) O ₃ or a tungsten bronze type ferroelectric material typified by PbNbO ₆ is used. In particular, ferroelectric materials having a perovskite structure, such as PZT and PLZT, have a high relative dielectric constant, and the melting point of lead oxide, which is a main constituent element thereof, is low at 890 ° C., so that synthesis at a relatively low temperature is easy. Therefore, it is preferable.

The dielectric layer is formed by a solution coating and firing method such as a sol-gel method or a MOD method. In the sol-gel method, generally, a predetermined amount of water is added to a metal alkoxide dissolved in a solvent, and a precursor solution of a sol having an MOM bond formed by hydrolysis and polycondensation reaction is applied to a substrate and baked. This is a method of forming a film. MOD (Me
The tallo-organic decomposition method is a method in which a metal salt of a carboxylic acid having an MO bond or the like is dissolved in an organic solvent to form a precursor solution, which is applied to a substrate and fired to form a film. Here, the precursor solution refers to a solution containing an intermediate compound generated by dissolving a raw material compound in a solvent in a film forming method such as a sol-gel method or a MOD method.

The sol-gel method and the MOD method are not completely separate methods, but are generally used in combination with each other. For example, when forming a PZT film, it is common to adjust the solution using lead acetate as a Pb source and alkoxides as Ti and Zr sources. In addition, the sol-gel method and the MOD method are sometimes collectively referred to as a sol-gel method, but in any case, a precursor solution is applied to a substrate and a film is formed by baking to form a film. Then, a solution coating baking method is used. Further, even a solution obtained by mixing a submicron dielectric particle and a dielectric precursor solution is included in the dielectric precursor solution of the present invention. It is included in the solution coating baking method of the invention.

In the sol-gel method and the MOD method, the elements constituting the dielectric are uniformly mixed in the order of submicron or less in both the sol-gel method and the MOD method. Compared with a method using ceramic powder sintering, it is possible to synthesize a dielectric at an extremely low temperature.

For example, taking PZT as an example, a normal ceramic powder sintering method requires a high temperature process of 900 to 1000 ° C. or higher.
It can be formed at a low temperature of about 500 to 700 ° C.

As described above, by forming the dielectric layer by the solution coating and baking method, it is possible to use a high heat resistant glass or crystallized glass which cannot be used from the viewpoint of heat resistance in the conventional thick film method.
In addition, there is an advantage that it is possible to use blue plate glass or the like.

It is widely known that, when synthesizing a lead-based dielectric ceramic, the starting composition must be a lead-excessive composition. It is well known that in order to form a lead-based dielectric having uniform and good dielectric properties at a low temperature, it is necessary to add an excessive amount of lead component (several% to 20%) more than in the case of ceramics. I have.

In the case of the solution coating baking method, the reason that a more excessive lead component is required is that the lead component evaporates during the baking and the effect of avoiding the shortage of lead and the suppression of the crystal growth is reduced. The effect of enabling the reaction at low temperature by facilitating material diffusion during crystal growth to constitute the composition part,
In addition, since the reaction takes place at a lower temperature compared to ordinary ceramics, there is a tendency for excess lead components to be taken into the dielectric crystal grains grown compared to the case of ceramics, and diffusion of excess lead components It is understood that the distance is small and more lead components are needed to maintain a sufficient lead excess state at each site of crystal growth.

For these reasons, a dielectric layer formed of a lead-based dielectric excessively containing a lead component contains a large amount of lead oxide in addition to lead incorporated in the crystal structure. It is characterized by containing excess lead components.

Such an excessive lead component easily precipitates from the inside of the dielectric layer due to a heat load after the formation of the dielectric layer, particularly a heat load in a reducing atmosphere. Especially under a heat load under a reducing atmosphere, the production of metallic lead by reduction of lead oxide is likely to occur,
When a light emitting layer as described later is formed directly on such a dielectric layer, it causes a reaction of a lead component with the light emitting layer and contamination of movable metal lead ions in the light emitting layer, resulting in a decrease in light emission luminance and long-term reliability. This will have a significant adverse effect.

In particular, metal lead ions have high ion-migration properties and significantly affect emission characteristics as working ions in a light-emitting layer to which a high electric field is applied, and thus have a particularly large effect on long-term reliability.

Even if lead oxide is not reduced to metallic lead particularly in a reducing atmosphere, if a lead oxide component is contained in the light emitting layer, lead oxide is reduced by electron bombardment due to a high electric field inside the light emitting layer, and metal ions are reduced. Release as a bad influence on reliability.

The thin film EL device of the present invention has a lead-based dielectric layer formed by repeating this solution coating and firing method a plurality of times, and further includes a lead-free high dielectric constant dielectric layer on at least the outermost surface layer. Prepare.

The lead-free high dielectric constant dielectric layer makes it possible to suppress the diffusion of the lead component from the lead-based dielectric layer to the light emitting layer, and to prevent the adverse effect of the excess lead component on the light emitting layer. Becomes

Here, the effect of the addition of the lead-free dielectric layer on the relative dielectric constant of the dielectric layer will be described. The relative dielectric constants of the lead-based dielectric layer and the lead-free dielectric layer are e3 and e4, respectively, and the total thickness of each layer is d3 and d4.
In this case, the effective relative permittivity e5 of the entirety of the lead-based dielectric layer and the lead-free dielectric layer is expressed by the following equation.

E5 = e3 × 1 / [1+ (e3 / e4) × (d4 / d3)] ------- (6)

Lead-based dielectric layer by adding lead-free dielectric layer
/ The effective relative permittivity of the lead-free dielectric layer composite layer
Considering the relationship between the relative dielectric constant of the dielectric layer and the light emitting layer and the effective voltage applied to the light emitting layer, it is necessary that the relative dielectric constant of the composite layer be at least as small as the dielectric layer alone. Is preferably 90% or more, more preferably 95% or more. Therefore, from equation (6)

E3 / d3 ≦ 9 × e4 / d4 in the case of 90% or more (7) e3 / d3 ≦ 19 × e4 / d4 in the case of 95% or more -(8)

For example, assuming that the relative permittivity of the dielectric layer is 1000 and the thickness is 8 μm, the ratio between the relative permittivity and the thickness of the lead-free dielectric layer is 1125 or more, preferably 2375 or more. Therefore, assuming that the thickness of the lead-free dielectric layer is 0.2 μm, the relative dielectric constant needs to be 225 to 475 or more.
Assuming 0.4 μm, a relative dielectric constant of 450 to 950 or more is required.

The thickness of the lead-free dielectric layer is preferably large for the purpose of preventing the diffusion of lead, and is preferably more than 0.2 μm, more preferably 0.3 μm, according to experimental studies by the present inventors. Above, especially 0.4 μm or more is required, and may be even thicker if there is no problem of lowering the effective relative permittivity.

Even when the thickness of the lead-free dielectric layer is 0.2 μm or less, a certain degree of lead diffusion preventing effect itself can be obtained, but it is caused by minute surface defects and surface roughness of the lead-based dielectric layer, and the production process. It becomes susceptible to local surface roughness due to the adhesion of dust and the like, making it difficult to obtain a good diffusion prevention effect, and causing a problem of partial brightness reduction and deterioration of the light emitting layer due to local diffusion of lead components. There is a risk.

Therefore, the thickness of the lead-free dielectric layer is preferably large, and the relative permittivity required for the lead-free dielectric layer is as follows:
It is clear that the relative dielectric constant of the lead-based dielectric layer is preferably 50% or more, more preferably equivalent to that of the lead-based dielectric layer. Therefore, when considering that the relative dielectric constant required for the dielectric layer is preferably 50 to 200 to 450 or more, the relative dielectric constant required for the lead-free dielectric layer is at least 25 or more. , Preferably 100 or more, more preferably 200 or more.

For example, in the above example, when the relative dielectric constant of the dielectric layer is 1000 and the film thickness is 8 μm, the case where a Si ₃ N ₄ film having a relative dielectric constant of about 7 is formed at 0.4 μm is considered. From the equation (6), the effective relative permittivity is 122, and even when a Ta ₂ O ₅ film having a relative permittivity of about 25 is formed at 0.4 μm, the effective relative permittivity becomes 333, which is greatly reduced. Since the applied effective voltage is greatly reduced, when such a lead-free dielectric layer is used, the driving voltage of the EL element is significantly increased, and the practicality is greatly reduced.

On the other hand, when a high dielectric constant material, for example, a TiO ₂ film having a relative dielectric constant of about 80 is formed at 0.4 μm, the effective relative dielectric constant is greatly improved to 615, and the relative dielectric constant is further increased to 200. When the substance is used, an effective relative dielectric constant of 800 is obtained. Further, when a substance having a relative dielectric constant of 500 is used,
The effective relative permittivity is 910, and it is possible to obtain substantially the same characteristics as when there is no lead-free dielectric layer.

Further, as a lead-free high dielectric constant dielectric material which exceeds TiO ₂ having a relative dielectric constant of about 80 and can obtain a relative dielectric constant of 100 to 1000 or more, for example, BaTiO ₃ ,
Perovskite structure dielectrics such as SrTiO ₃ , CaTiO ₃ , BaSnO ₃ , and solid solutions between these materials are particularly preferred.

Further, a tungsten bronze type dielectric material may be used as the lead-free high dielectric constant dielectric material. A tungsten bronze type dielectric material is generally represented by the chemical formula A _x B ₅ O ₁₅ . Here, A and B each represent a cation. A is preferably at least one selected from Mg, Ca, Ba, Sr, rare earth and Cd, and B is at least one selected from Ti, Zr, Ta, Nb, Mo, W, Fe and Ni. It is preferred that Specifically, SBN (= (Sr _1-x Ba _x ) Nb ₂ O ₆ ), Sr
Tungsten bronze type oxides such as Nb ₂ O ₆ and Ba ₃ Nb ₁₀ O ₂₈ .

By using such a lead-free high dielectric constant dielectric layer, the effect of preventing the diffusion of the lead component into the light emitting layer of the present invention can be obtained while keeping the effective relative dielectric constant from being reduced to a minimum. It is easily possible.

According to the study of the present inventors, when using such a lead-free dielectric layer, particularly when a perovskite structure material is used, the composition is changed from the A site atom of the perovskite structure to the B site atom. It is important that the ratio be 1 or more.

That is, as described above, perovskite
Each of the lead-free lead-free dielectric materials has a
Can contain lead ions, such as BaT
iO _Three Taking the composition as an example, BaTiO_Three Layers
When forming, its starting composition is Ba_1-xTiO_3-x In
Ba, which is an A site atom, is a B site atom.
If there is a shortage of Ti_Three Form a layer
The lead-based dielectric layer that contains
BaTiO_Three Excess lead component replaces Ba defect site in layer
And (Ba_1-xPb_x ) TiO_Three A layer is formed.
In such a state, BaTiO_Three Forming a light emitting layer on the layer
In this case, the light emitting layer is in direct contact with the lead
The effect of preventing lead diffusion cannot be obtained.

For this reason, it is preferable that the composition of the lead-free dielectric layer having a perovskite structure is at least on the A-site excess side from the stoichiometric composition. Further, as can be inferred from this description, since the lead-free dielectric material having a perovskite structure can be substituted for a lead component in a crystal structure, even if the composition is changed from the stoichiometric composition to the A-site excess side, the lead-based dielectric material is The portion near the interface with the dielectric layer may possibly partially react with the lead component. For this reason, it is preferable that the thickness of the lead-free dielectric layer is not less than a certain value. According to an experimental study by the present inventors, this thickness is not less than 0.1 μm, preferably more than 0.2 μm.

Further, SBN (Sr_1-xBa_x ) Nb_TwoO₆ 
In the case of tungsten bronze type dielectric represented by
As with lobskite-type dielectrics, their composition is generally
Formula A _xB_FiveO₁₅ Where Pb is represented as A ion
A cation located at A because it can be substituted
Is preferably not less than the stoichiometric ratio.

As described above, as a method of forming the lead-free dielectric layer by sufficiently controlling the composition thereof, it is preferable to use a sputtering method or a solution coating baking method because the controllability of the composition is high.

The lead-free dielectric layer formed by the sputtering method can easily form a thin film having the same composition as the target composition, and is a dense thin film which can be expected to have a higher density and an effect of preventing the diffusion of the lead component. This is a preferable film forming method because it can be easily formed.

The solution coating and baking method can form a dielectric layer whose composition is more strictly controlled than the sputtering method by controlling the blend ratio of the precursor solution. This lead-free dielectric layer itself has the effect of repairing defects, which is a feature of the method, and the unevenness of the substrate generated when a thick layer is formed by sputtering is emphasized. It does not cause the problem of surface roughness due to being formed, and can easily form a thick layer, does not require expensive film forming equipment, and is formed by the same equipment and process as the lead-based dielectric layer This is a more preferable formation method from the possible viewpoint.

As a result of a detailed study by the present inventors, the above effects were found to be particularly effective under the following conditions.

First, the dielectric layer has a composite structure of a lead-based dielectric layer and a lead-free high-permittivity dielectric layer, and at least the lead-based dielectric layer is formed by repeating a solution coating and firing method a plurality of times. In addition, at least the outermost layer of the composite structure is constituted by a lead-free high dielectric constant dielectric layer. With this structure, it is possible to prevent the excess lead component of the lead-based dielectric layer from affecting the light emitting layer as described above.

Second, the lead-free dielectric layer is formed of a high dielectric constant film, particularly preferably a lead-free perovskite structure dielectric material having a relative dielectric constant of 100 or more. By making the lead-free dielectric layer a high dielectric constant composition film, the effective relative dielectric constant of the composite dielectric layer is prevented from lowering due to the intervention of the lead-free dielectric layer, and a lead-free high dielectric having a perovskite structure is particularly preferably used. This is preferable because the effective lowering of the relative permittivity of the dielectric layer can be reduced to a minimum, and a good lead diffusion preventing effect can be obtained. In particular, when the composition of the lead-free high dielectric layer having a perovskite structure is used, the composition is set to be on the A site excess side from the stoichiometric ratio. This makes it possible to effectively complete the effect of preventing the lead component from diffusing into the light emitting layer.

Third, the lead-free high dielectric constant dielectric layer is formed by a sputtering method or a solution coating baking method. By using the sputtering method, it is possible to easily control the composition and form a dense and dense lead-free high dielectric constant dielectric layer. Further, by using the solution coating and baking method, it is possible to more strictly control the composition and to easily form a thicker lead-free high dielectric constant dielectric layer having no problem of surface irregularities. Furthermore, since the effect of repairing defects such as dust generated in a single layer, which is a feature of the solution coating and firing method, can be expected even when a lead-free high dielectric constant dielectric layer is formed, a lead-based dielectric layer and a lead-free high dielectric constant dielectric can be expected. All the body layers are formed by the solution coating and baking method, and the number of times is set to three or more times, so that it is possible to avoid a problem such as a dielectric breakdown even in a local withstand voltage lowering portion caused by the above-described defect. Become.

When the thickness of the dielectric layer is at least four times the thickness of the lower electrode layer, the coverage of the pattern edge portion caused by patterning of the lower electrode layer and the flatness of the surface of the dielectric layer are sufficiently improved. It can be improved.

Fourth, the thickness of the multilayer dielectric layer should be set to 4 μm or more and 16 μm or less. According to the study of the present inventors, the particle size of dust and the like generated in a process in a normal clean room is 0.1 to 2 μm, particularly 1 μm.
When the average film thickness is 4 μm or more, preferably 6 μm or more, the dielectric withstand voltage of the dielectric layer defective portion due to a defect such as dust can be set to 2/3 or more of the average withstand voltage. .

If the film thickness is 16 μm or more, the number of repetitions of the solution coating and sintering method becomes too large, resulting in an increase in cost. Further, as shown in equations (3) to (5), it is necessary to increase the relative dielectric constant of the dielectric layer when the thickness of the dielectric layer is increased. For example, when the thickness is 16 μm or more, Relative dielectric constant is 160 to 640 to 144
It becomes 0 or more. However, it is generally technically difficult to form a dielectric layer having a relative dielectric constant of 1500 or more using a solution coating baking method. Further, in the present invention, since a dielectric layer having a high withstand voltage and having no defect can be easily formed, it is not necessary to form a dielectric layer having a thickness of 16 μm or more. For this reason, the upper limit of the film thickness is 16 μm or less, preferably 12 μm or less.

When the thickness of the dielectric layer is four times or more the thickness of the lower electrode layer, the coverage of the pattern edge caused by the patterning of the lower electrode layer and the flatness of the surface of the dielectric layer are sufficiently improved. It can be improved.

The combination of the stack of the lead-based dielectric layer and the lead-free high-permittivity dielectric layer of the present invention may be any as long as the outermost surface is a lead-free high-permittivity dielectric layer. The layers may be alternately stacked, and the outermost layer may be a lead-free high dielectric constant dielectric layer. With such a configuration, the excessive lead component present in the lead-based dielectric layer is effectively prevented from being diffused to each other by the alternately stacked lead-free high-permittivity dielectric layers, and moreover to the outermost surface. The lead-free diffusion effect of the non-lead-based high-k dielectric layer located is improved. In such a configuration, particularly when forming a lead-free high dielectric constant dielectric layer using a sputtering method, irregularities on the film surface become severe when a thick layer is formed, which is a problem of the sputtering method. Effective to avoid problems.

Further, in order to clearly explain the function of the present invention, a lead-based dielectric layer formed by repeating the solution coating and baking method of the present invention a plurality of times and a lead-free dielectric layer formed on at least the outermost surface layer thereof are formed. A case in which a high dielectric constant dielectric layer is not formed as a multilayer dielectric layer but is formed by a sputtering method will be described using an electron micrograph. FIG. 5 is an electron micrograph of a case in which a BaTiO ₃ thin film of 8 μm is formed on a patterned substrate by forming a 3 μm lower electrode layer and by sputtering. As is clear from FIG. 5, when the dielectric layer is formed by the sputtering method, the surface of the dielectric film is formed in such a manner that the step of the substrate is emphasized, so that the dielectric surface has significant unevenness and overhang. . Such unevenness of the surface shape is similarly recognized when a dielectric layer is formed by an evaporation method other than the sputtering method. It is impossible at all to form and use a functional thin film such as an EL light emitting layer on such a dielectric layer. As described above, in the present invention, defects caused by steps or dust in the lower electrode layer, which were impossible with a dielectric layer formed by a conventional sputtering method or the like, are completely eliminated by repeating the solution coating and firing method a plurality of times. Cover and planarize the dielectric layer surface.

The material of the light-emitting layer is not particularly limited, but known materials such as Mn-doped ZnS described above can be used. Among them, SrS: Ce and a barium thioaluminate phosphor layer which is a blue light-emitting material are particularly preferable because excellent characteristics can be obtained. The thickness of the light emitting layer is not particularly limited, but if it is too thick, the driving voltage increases, and if it is too thin, the luminous efficiency decreases. Specifically, although it depends on the luminescent material, it is preferably 100 to 20.
It is about 00 nm.

As a method for forming the light emitting layer, a vapor phase deposition method can be used. As the vapor deposition method, a physical vapor deposition method such as a sputtering method or a vapor deposition method or a chemical vapor deposition method such as a CVD method is preferable. In addition, as described above, in particular, SrS:
When a Ce light emitting layer is formed, the substrate temperature during film formation is set to 50 in an H ₂ S atmosphere by electron beam evaporation.
When formed at a temperature of 0 ° C. to 600 ° C., a high-purity light-emitting layer can be obtained.

After the formation of the light emitting layer, a heat treatment is preferably performed. The heat treatment may be performed after the electrode layer, the dielectric layer, and the light-emitting layer are stacked from the substrate side, or the electrode layer, the dielectric layer, the light-emitting layer, the insulator layer, or the electrode layer is formed therefrom from the substrate side. After that, heat treatment (cap annealing) may be performed. The temperature of the heat treatment depends on the light emitting layer to be formed.
In the case of Ce, the temperature is preferably 500 ° C. to 600 ° C. or higher, the firing temperature of the dielectric layer or lower, and the processing time is preferably 10 to 600 minutes. The atmosphere during the heat treatment is preferably in Ar.

As described above, the conditions for forming a light-emitting layer having excellent characteristics such as SrS: Ce and barium thioaluminate phosphor are as follows under vacuum or under reducing atmosphere.
A film formation at a high temperature such as 0 ° C. or higher and a subsequent high-temperature heat treatment process under the atmospheric pressure are required. In the conventional technology, the problem due to the reaction and diffusion between the lead component of the dielectric layer and the light emitting layer cannot be avoided. On the other hand, the thin-film EL device of the present invention is particularly effective because the adverse effect of the lead component on the light emitting layer can be completely prevented.

The thin-film insulator layer (17) and / or (1)
5) may be omitted as described above, but is preferably provided.

The function of the thin-film insulator layer is to adjust the electronic state at the interface between the light-emitting layer and the dielectric layer to stabilize and improve the electron injection into the light-emitting layer. The main purpose is to improve the positive-negative symmetry of the light emission characteristics during AC driving by symmetrically configuring both surfaces of the light-emitting layer. The dielectric breakdown voltage, which is the role of the dielectric layer formed by the solution coating baking method, is It is not necessary to consider the function of maintaining the thickness, so that the film thickness may be small.

This thin film insulator layer has a resistivity of 10 ⁸
Ωcm or more, particularly preferably about 10 ¹⁰ to 10 ¹⁸ Ωcm. Further, it is preferable that the material has a relatively high relative dielectric constant, and the relative dielectric constant ε thereof is preferably ε =
3 or more. As a constituent material of this thin film insulator layer,
For example, silicon oxide (SiO ₂ ), silicon nitride (Si
N), tantalum oxide (Ta ₂ O ₅ ), yttrium oxide (Y ₂ O ₃ ), zirconia (ZrO ₂ ), silicon oxynitride (SiON), alumina (Al ₂ O ₃ ),
Etc. can be used. In addition, as a method for forming the thin film insulator layer, a sputtering method or an evaporation method can be used. In addition, the thickness of the thin-film insulator layer is preferably about 50 to 1000 nm, particularly preferably about 50 to 200 nm.

The transparent electrode layer has a thickness of 0.2 μm to 1 μm.
An oxide conductive material such as TO, SnO ₂ (Nesa film), or ZnO—Al is used. As a method for forming the transparent electrode layer, a known technique such as a vapor deposition method other than the sputtering method may be used.

Although the above-mentioned thin-film EL element has only a single light-emitting layer, the thin-film EL element of the present invention is not limited to such a structure, and a plurality of light-emitting layers are stacked in the film thickness direction. Alternatively, different types of light emitting layers (pixels) may be combined in a matrix and arranged in a plane.

In the above-described thin-film EL device, the configuration in which light from the light-emitting layer is extracted from the upper ITO electrode side has been described. However, the thin-film EL device of the present invention is not limited to such a configuration. The light of the light emitting layer may be extracted from the conductive substrate side. In this case, a light-transmitting substrate such as heat-resistant glass may be used as the insulating substrate, and a transparent electrode such as ITO may be used as the lower electrode.

The thin film EL device of the present invention can be easily identified by observation with an electron microscope. That is, in the present invention, a dielectric layer formed in a multilayer by repeating the solution coating and firing method a plurality of times is different from a dielectric layer formed by another method only in that the dielectric layer is formed in a multilayer. However, a difference in film quality is also observed. Further, there is a feature that the smoothness of the surface of the dielectric layer is extremely good.

As described above, the thin film EL device of the present invention
The surface of the dielectric layer on which the light-emitting layer is laminated has extremely good smoothness, high dielectric strength, no defects, and complete damage to the light-emitting layer due to the excess lead component of the dielectric layer, which was a conventional problem. Since the display can be prevented, a display with high luminance, high long-term reliability of luminance, high performance and high definition can be easily formed. Further, the manufacturing process is easy, and the manufacturing cost can be reduced.

[0096]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically shown below and described in more detail.

[Example 1] A 99.6% pure alumina substrate was polished on its surface, an Au thin film to which a trace amount of additive was added was formed to a thickness of 1 µm on this substrate by a sputtering method, and heat treatment was performed at 700 ° C. Went and stabilized. This Au thin film was patterned into a large number of stripes having a width of 300 μm and a space of 30 μm by photoetching.

A PZT dielectric layer, which is a lead-based dielectric layer, was formed on this substrate by using a solution coating baking method. As a method for forming a dielectric layer by a solution coating and baking method, a method of applying a sol-gel solution prepared by the following method as a PZT precursor solution to a substrate by a spin coating method and baking it at 700 ° C. for 15 minutes was repeated a predetermined number of times.

A basic method for preparing a sol-gel liquid is described in 8.4.
9 g of lead acetate trihydrate and 4.17 g of 1.3 propanediol were heated and stirred for about 2 hours to obtain a clear solution. Separately, 3.70 g of a zirconium normal propoxide 70 wt% 1-propanol solution and 1.58 g of acetylacetone were heated and stirred in a dry nitrogen atmosphere for 30 minutes, and 3.14 g of titanium diisopropoxide. Bisacetylacetonate 75 wt% 2-propanol solution and 2.32 g of 1.3 propanediol were added,
The mixture was further heated and stirred for 2 hours. These two solutions were mixed at 80 ° C., and heated and stirred in a dry nitrogen atmosphere for 2 hours to produce a brown transparent solution. This solution was kept at 130 ° C. for several minutes to remove by-products, and further heated and stirred for 3 hours to prepare a PZT precursor solution.

The viscosity of the sol-gel solution was adjusted by diluting it with n-propanol. The thickness of the dielectric layer per single layer was set to 0.7 μm by adjusting the spin coating conditions and the viscosity of the sol-gel solution. The PZT layer formed under these conditions contained an excess of about 10% of the lead component with respect to the stoichiometric composition.

The above sol-gel solution was used as a PZT precursor solution, and spin coating and baking were repeated 10 times to form a lead-based dielectric layer having a thickness of 7 μm. The relative dielectric constant of this PZT film was 600.

Next, as a lead-free high dielectric constant dielectric layer, lead-based
Ba formed on the dielectric layer by a solution coating baking method
TiO_Three BaT formed by sputtering method
iO _Three Film and SrTiO_Three Film, TiO_Two Membrane and ratio
Sample without lead-free high dielectric constant dielectric layer as comparative example
Was prepared.

The conditions for forming the BaTiO ₃ thin film were as follows: a magnetron sputtering apparatus was used, BaTiO ₃ ceramic was used as a target, and Ar gas was applied at a pressure of 4 Pa.
Film formation was performed under the conditions of a 3.56 MHz high frequency electrode density of 2 W / cm ² . At this time, the film formation rate is about 5 nm / min, and the film thickness is 50 nm to 400 nm by adjusting the sputtering time.
I got The BaTiO ₃ thin film formed at this time was in an amorphous state, and when this film was heat-treated at 700 ° C., a value of a relative dielectric constant of 500 was obtained. Further, it was confirmed by an X-ray diffraction method that the heat-treated BaTiO ₃ thin film had a perovskite structure. In addition, this BaTiO ₃
The composition of the film was such that Ba was 5% excess with respect to the stoichiometric composition.

As the conditions for forming the SrTiO ₃ thin film, a magnetron sputtering apparatus was used, the target was SrTiO ₃ ceramics, and the pressure of Ar gas was 4 Pa.
Film formation was performed under the conditions of a 56 MHz high frequency electrode density of 2 W / cm ² . At this time, the film formation rate was about 4 nm / min, and a film thickness of 400 nm was obtained by adjusting the sputtering time. The SrTiO ₃ thin film formed at this time was in an amorphous state, and when subjected to a heat treatment at 700 ° C., a value of 250 was obtained. Further, it was confirmed by an X-ray diffraction method that the SrTiO ₃ thin film heat-treated at a temperature of 500 ° C. or more had a perovskite structure. In addition, this SrTiO
The composition of the _three thin films was such that Sr was 3% excess with respect to the stoichiometric composition.

As the conditions for forming the TiO ₂ thin film, a magnetron sputtering apparatus was used, TiO ₂ ceramic was used as a target, and a pressure of 1 Pa of Ar gas was applied.
Film formation was performed under the conditions of a 56 MHz high frequency electrode density of 2 W / cm ² . At this time, the film formation rate was about 2 nm / min, and a film thickness of 400 nm was obtained by adjusting the sputtering time. When this film was heat-treated at 600 ° C., a value of 76 was obtained.

The BaTiO ₃ film is formed by the solution coating and baking method by using a sol-gel liquid formed by the following method.
The process of applying the O ₃ precursor solution to the substrate by a spin coating method, increasing the temperature in steps of 200 ° C. to a maximum temperature of 700 ° C. in steps, and baking at the maximum temperature for 10 minutes was repeated a predetermined number of times.

A BaTiO ₃ precursor solution was prepared by completely dissolving PVP (polyvinylpyrrolidone) having a molecular weight of 630,000 in 2-propanol, and adding acetic acid and titanium tetraisopropoxide with stirring to obtain a transparent solution. I got A mixed solution of pure water and barium acetate was added dropwise to this solution with stirring, and aging was performed for a predetermined time while stirring was continued in this state. The composition ratio of each starting material is barium acetate: titanium tetraisopropoxide: PVP: acetic acid: pure water: 2-propanol = 1: 1: 0.5: 9: 2
0:20. As a result, a BaTiO ₃ precursor solution was obtained.

The BaTiO ₃ precursor solution was applied and baked in one and two layers to form a BaTiO ₃ dielectric layer having a thickness of 0.5 μm and a thickness of 1.0 μm. The relative dielectric constant of this film was 380, and the composition matched the stoichiometric composition.

On a substrate on which a lead-based dielectric layer and a lead-free high-permittivity dielectric layer were laminated, a SrS: Ce light-emitting layer was formed under an H ₂ S atmosphere by electron beam evaporation under a substrate temperature during film formation. Was formed at a temperature of 500 ° C. After the formation of the light emitting layer, a heat treatment was performed in vacuum at 600 ° C. for 30 minutes.

Next, an Si ₃ N ₄ thin film as an insulator layer and an ITO thin film as an upper electrode layer were sequentially formed by a sputtering method to obtain a thin film EL device. At that time, the ITO thin film of the upper electrode layer was patterned on a stripe having a width of 1 mm by using a metal mask at the time of film formation. The emission characteristics were measured by extracting electrodes from the lower electrode and the upper transparent electrode of the obtained device structure and applying an electric field until the emission luminance was saturated with a 1 kHz pulse width of 50 μS.

As evaluation items, degradation of the emission threshold voltage, saturation luminance, and the reached luminance after continuous light emission for 100 hours were evaluated.

[0112]

[Table 1]

As a result, in the comparative example having no lead-free high dielectric constant dielectric layer, the deterioration was as large as 50%, but in the comparative example having the BaTiO ₃ layer formed by the sputtering method of the present invention, the degradation was 0.1%. With a film thickness of 2 μm or more, the ultimate brightness is 12
The light emission threshold voltage was about 140 V, and the deterioration was small. 0.1 μm
In the following, as the emission threshold voltage increases, the achievable luminance decreases, and further significant deterioration is shown. In the case of the SrTiO ₃ layer, except that the emission threshold voltage slightly increases,
Almost the same characteristics as those of the aTiO ₃ layer were obtained. Also, in the case of the BaTiO ₃ layer using the solution coating baking method, almost the same characteristics as those obtained by the sputtering method were obtained except for a slight increase in the light emission threshold voltage.

In the case of a TiO ₂ film, the same thickness of BaTiO ₃
Compared with the film, an increase in threshold voltage and a decrease in luminance were observed, and the deterioration was large. In the case of an Al ₂ O ₃ film, at 0.1 μm, the threshold voltage is increased and the luminance is significantly reduced, and furthermore, the deterioration is large. Before the breakdown occurred.

Further, in the structure of PZT alone, which is a comparative example, the emission threshold voltage is increased and the luminance is greatly reduced and deteriorated.
Furthermore, dielectric breakdown was likely to occur at an applied voltage near the ultimate luminance.

As is clear from these results, in the structure using the lead-free high dielectric constant perovskite layer as the lead-free high dielectric constant dielectric layer, the effect is recognized from the film thickness of 0.1 μm or more. At 0.2 μm or more, a remarkable increase in light emission luminance, a decrease in threshold voltage, and an improvement in reliability were observed.

This indicates that the diffusion of the lead component in the lead-based dielectric layer into the light emitting layer was effectively suppressed.

In the case of the TiO ₂ layer, the effect as a reaction preventing layer was recognized, but the saturation luminance was lower, the light emission threshold voltage was higher, and the deterioration was larger than in the perovskite layer. This is presumably because the TiO ₂ film reacted with excess lead in the PZT layer and was partially converted to PbTiO ₃ , so that it did not completely function as a reaction preventing layer.

Example 2 As in Example 1, the PZT precursor solution was spin-coated and baked 10 times on the substrate on which the lower electrode had been formed, thereby obtaining a lead-based dielectric layer having a thickness of 7 μm. Was formed. The relative dielectric constant of this PZT film was 600.

Next, a (Sr _0.5 Ba _0.5 ) Nb ₂ O ₆ thin film formed by a sputtering method on the lead-based dielectric layer as a lead-free high-permittivity dielectric layer, and a method similar to that of the first embodiment. A sample not having the BaTiO ₃ film and the TiO ₂ film prepared as described above and a sample having no lead-free high dielectric constant dielectric layer was prepared as a comparative example.

As a condition for forming the (Sr _0.5 Ba _0.5 ) Nb ₂ O ₆ thin film, using a magnetron sputtering apparatus,
Film formation was performed using _0.5 Ba _0.5 ) Nb ₂ O ₆ ceramics as a target and a pressure of 13.56 Mz high frequency electrode density of 2 W / cm ² at a pressure of 4 Pa of Ar gas. The substrate temperature during film formation was 750 ° C. The deposition rate at this time is about 6 nm /
The thickness was 400 nm by adjusting the sputtering time. Formed (Sr _0.5 Ba _0.5 ) Nb
_{The 2} O ₆ thin film was crystallized in a tungsten bronze type. To further improve the dielectric properties, this film is 750
After heat treatment in air at ℃, a value of relative dielectric constant of 200 was obtained. The composition of the film was a stoichiometric composition.

Next, a blue light-emitting body is formed on these dielectric substrates.
A barium thioaluminate phosphor layer was formed. firefly
In order to emit light stably as an EL element as a light body layer,
Al _TwoO_Three Film, 50 nm / ZnS film, 200 nm / barium
Thioaluminate phosphor thin film, 300 nm / ZnS film, 2
00nm / Al_TwoO_Three Fabricate 50nm composite structure
Was. Where Al_TwoO_Three The film is fired during annealing in an oxidizing atmosphere.
Cap layer for controlling the amount of oxygen introduced into the optical thin film, ZnS
Is formed in advance with sulfur excess or shortage.
To optimize the amount of sulfur in the fluorescent thin film during annealing.
Functions as an aux control layer. In addition, formed as an element
Al_TwoO_Three The film is an insulating film and a dielectric layer.
Function as an electron injection layer into the light emitting layer, not
Works. Further, the ZnS layer accelerates the injected electrons.
Also functions as an injection enhancing layer.

For the barium thioaluminate phosphor film formation, a multiple vapor deposition method using two E guns was used. EB source containing BaS powder containing 5 atomic% of Eu, Al ₂ S ₃
An EB source containing the powder is provided in a vacuum chamber into which H ₂ S is introduced,
The respective EB sources were evaporated at the same time, heated to 500 ° C., and a BaAl ₂ O ₃ S: Eu layer was formed on the rotated substrate. The evaporation rate of each evaporation source is BaAl ₂ O ₃ S: E
The film formation rate of u was adjusted to 1 nm / sec. At this time, ₂₀ SCCM of H ₂ S gas was introduced.

After forming the thin film, the film was annealed in the air at 750 ° C. for 20 minutes to obtain a phosphor thin film having a thickness of 300 nm.

As a monitor, B formed on a Si substrate
As a result of composition analysis of the aAl ₂ O ₃ S: Eu thin film by X-ray fluorescence analysis, Ba: Al: O: S: Eu = 7.4 in atomic ratio.
1: 19.20: 60.18: 13.0: 0.32.

Further, a 200 nm-thick ITO transparent electrode was formed on the obtained structure at a substrate temperature of 250 ° C. by an RF magnetron sputtering method using an ITO oxide target to complete an EL device.

The light emitting characteristics of this EL device were evaluated. Electrodes were drawn out from the obtained ITO upper electrode and Pd upper electrode of the EL structure, and a bipolar electric field having a pulse width of 50 μS was applied at 1 kHz. Table 2 shows the results.

[0128]

[Table 2]

As is clear from Table 2, Ba of the present invention
TiO_Three EL devices using lead-free dielectric layers have a particular thickness.
Is 650 cd / m at 300 nm^Two , 102 at 400 nm thickness
0cd / m^Two And a remarkably high luminance is obtained. In contrast,
230 cd / m at 200 nm thickness ^Two 90 for a film thickness of 100 nm
cd / m^Two And the brightness decreased, but the effect was recognized.

Also, when the SBN thin film of the present invention was used, the effect was recognized at 550 cd / m ^2, which is smaller than that when the BaTiO ₃ dielectric layer was used.

[0131] may further form a TiO ₂ thin film, but a film thickness of 200nm at ^{110cd / m 2, 600cd / m} 2 and the brightness in the thickness 400nm decreases as compared with the case of BaTiO ₃ is relatively high Brightness is obtained. This is because, as in Example 1, when a TiO ₂ thin film was used, the effect as a reaction prevention layer was recognized, but it reacted with excess lead in the PZT layer and was partially converted to PbTiO ₃ , so that the reaction prevention layer was used. It is presumed that sufficient light emission was not obtained due to the complete lack of function and the dielectric constant of about 80, which was smaller than that of other lead-free dielectric layers.

On the other hand, as a comparative example, an EL device manufactured under exactly the same conditions except that no lead-free dielectric layer was used was 1
No luminance was obtained compared to the case where cd / m ² and BaTiO ₃ lead-free dielectric layers were used, and the effect of the EL element of the present invention in which the lead-free dielectric layers were laminated was clear.

The blue light emission of the EL device prepared in this embodiment was measured by the CIE1931 color coordinates (0.1295, 0.135).
7), the peak wavelength of the emission spectrum is 471 nm,
Very good blue light emission.

Further, when the impurities of the samples of this example and the comparative example were analyzed in the thickness direction of the film by Auger analysis, the Pb element was detected from the phosphor thin film region in the comparative example. This is presumably because the Pb element in the PZT dielectric layer formed by the multi-layer solution coating and firing method was diffused. On the other hand, in the embodiment, from the phosphor thin film region,
Pb element was not detected.

These results indicate that the luminance of the EL element is remarkably improved by the effects described in the operation of the present invention, and the effects of the present invention are clear.

[0136]

The effects of the present invention are apparent as described above. According to the present invention, a defect occurring in a dielectric layer, which has been a problem in a conventional thin film EL element, is solved, and in particular, a thin film EL element in which a multilayer dielectric layer is formed using a lead-based dielectric material by a solution coating and firing method. It is possible to provide a thin-film EL element capable of achieving high display quality and a method of manufacturing the thin-film EL element without increasing the cost, by solving the problems of reduced luminance, uneven luminance, and temporal change in luminance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a thin film EL device according to the present invention.

FIG. 2 is a cross-sectional view showing the structure of a conventional thin film EL device.

FIG. 3 is a cross-sectional view showing the structure of a conventional thin film EL device.

FIG. 4 is a cross-sectional view showing the structure of a conventional thin film EL device.

FIG. 5 is an electron micrograph of a cross section of a conventional thin film EL device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Lower electrode layer 13 Lead-based dielectric layer 18 Lead-free high dielectric constant dielectric layer 17 Thin-film insulator layer 14 Light-emitting layer 15 Thin-film insulator layer 16 Transparent electrode layer 21 Transparent substrate 22 Transparent electrode layer 23 Thin-film transparent Reference Signs List 1 insulator layer 24 light emitting layer 25 thin transparent second insulator layer 26 electrode layer 31 substrate 32 lower thick electrode 33 thick dielectric layer 34 light emitting layer 35 thin insulator layer 36 upper transparent electrode layer 41 substrate 42 lower electrode layer 43 multilayer dielectric layer 44 light emitting layer 45 thin film insulator layer 46 transparent electrode layer

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Katsuto Nagano 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Yoshihiko Yano 1-13-1 Nihonbashi, Chuo-ku, Tokyo F-term in DK Corporation (reference) 3K007 AB02 AB04 AB06 AB11 AB17 AB18 BA06 CA02 CB01 DA02 DA05 DB01 DB02 DC04 EA02 EA04 EC01 EC03 FA01

Claims (11)

[Claims] A substrate having electrical insulation, a lower electrode layer having a pattern on the substrate, a dielectric layer, a light emitting layer, and an upper electrode layer laminated on the electrode layer; A thin-film EL element in which at least one of the electrode and the upper electrode is a transparent electrode, wherein the dielectric layer is formed by repeating a solution coating and firing method a plurality of times; A thin-film EL device having a multilayer structure in which a body layer is stacked, wherein the outermost layer of the dielectric layer having the multilayer structure is a lead-free high dielectric constant dielectric layer. 2. The lead-based dielectric layer has a thickness of at least 4 μm.
2. The thin film EL device according to claim 1, wherein the thickness is 6 μm or less. 3. The lead-free dielectric layer has a thickness of 0.2 μm.
2. The thin-film EL device according to claim 1, which is super. 4. The lead-free high dielectric constant dielectric layer is composed of a perovskite structure dielectric.
The thin film EL device according to any one of the above. 5. The thin film EL device according to claim 1, wherein said lead-free high dielectric constant dielectric layer is formed by a sputtering method. 6. The thin-film EL device according to claim 1, wherein said lead-free high dielectric constant dielectric layer is formed by a solution coating baking method. 7. The thin film EL device according to claim 6, wherein the dielectric layer having a multilayer structure is formed by repeating a solution coating and firing method three times or more. 8. A lower electrode having at least a structure in which an electrically insulating substrate, a lower electrode layer having a pattern on the substrate, a dielectric layer, a light emitting layer, and an upper electrode layer are laminated on the electrode layer. Alternatively, a method of manufacturing a thin-film EL element in which at least one of the upper electrodes is formed of a transparent electrode, wherein a lead-based dielectric layer formed by repeating a solution coating and firing method a plurality of times, and a lead-free high dielectric constant dielectric A method for manufacturing a thin-film EL device in which layers are stacked to form a multilayer structure, and the outermost layer of the dielectric layer having the multilayer structure is a lead-free high dielectric constant dielectric layer. 9. The method according to claim 8, wherein the lead-free high dielectric constant dielectric layer is formed by a sputtering method. 10. The method for manufacturing a thin film EL device according to claim 8, wherein said lead-free high dielectric constant dielectric layer is formed by a solution coating baking method. 11. The multi-layered dielectric layer is formed by repeating a solution coating baking method three times or more.
A method for manufacturing a thin film EL device.