JP2004079372A - El element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL element with stable luminous characteristics, for one securing a surface smoothness of a thick-film ceramic dielectric layer with a sol-gel dielectric layer. <P>SOLUTION: With the EL element with at least a first electrode layer, a dielectric layer, a luminous layer and a second electrode layer laminated (in turn) on a substrate with the dielectric layer consisting of a first dielectric layer and a second dielectric layer formed by a solution coating and baking method, a protection layer is fitted at a part where an electrode pattern of the second electrode layer is not formed on the surface of a layer at least adjacent to the second electrode layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an EL element and a method for manufacturing an EL element, and more particularly to an EL element having stable light emission characteristics and a method for manufacturing an EL element.
[0002]
[Prior art]
EL devices include a dispersion type EL device having a structure in which a powdered light emitter is dispersed in an organic substance or an enamel and an electrode layer is provided on the upper and lower sides thereof, and a thin film light emitter formed on an electrically insulating substrate by two thin film insulators. There is a thin-film EL element in which a structure is sandwiched and further sandwiched between two electrode layers. In each case, the driving method includes a DC voltage driving type and an AC voltage driving type.
[0003]
Dispersion type EL elements have been known for a long time and have an advantage that they are 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.
[0004]
FIG. 5 shows the structure of a typical double-insulation type thin film EL device as an example of a conventional thin film EL device. This thin-film EL element is composed of a transparent electrode layer 12 having a film thickness of about 0.2 to 1 μm and a predetermined stripe pattern formed on a transparent substrate 11 such as blue plate glass used for a liquid crystal display or a PDP. A thin-film transparent first insulator layer 13, a light-emitting layer 14 having a thickness of about 0.2 to 1 μm, and a thin-film transparent second insulator layer 15 are laminated, and further patterned in a stripe shape so as to be orthogonal to the transparent electrode layer 12. The metal electrode layer 16 is formed. Then, by applying a voltage from a power supply 17 to a specific luminous body selected in the matrix of the transparent electrode layer 12 and the metal electrode layer 16, the luminous body of the specific pixel emits light, and the luminescence is transmitted from the transparent substrate 11 side. Take out.
[0005]
The thin-film insulator layers 13 and 15 have a function of restricting a current flowing in the light-emitting layer 14, can suppress dielectric breakdown of the thin-film EL element, and provide stable light-emitting characteristics. Thin-film EL devices have been widely used commercially.
[0006]
However, in the thin-film EL device as shown in FIG. 5, since the insulator layer is formed of a thin film, when a large-area display is formed, a step portion of a pattern edge of a transparent electrode, dust generated in a manufacturing process, and the like are generated. It is difficult to eliminate defects of the thin film insulator layer due to the above, and there is a problem that 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 major obstacle to widespread practical use as a large-area display as compared with a liquid crystal display or a plasma display. .
[0007]
In order to solve the problem that such a defect of the thin film insulator layer occurs, Japanese Patent Publication No. 7-44072 discloses that an electrically insulating ceramic substrate is used as a substrate, and a thin film insulator is formed instead of the thin film insulator below the light emitting body. An EL device using a film dielectric is disclosed. The EL element disclosed in this publication differs from the structure of a conventional thin-film EL element in that the light emission of the luminous body is extracted from the upper side opposite to the substrate, so that the transparent electrode layer is formed on the upper side.
[0008]
In this EL device, the thick-film dielectric layer is formed to have a thickness of several tens to several hundreds μm, which is several hundreds to several thousand times the thickness of the thin-film insulator layer. Therefore, there is very little dielectric breakdown due to a defect formed due to a step of an electrode or dust in a manufacturing process, and there is an advantage that high reliability and a high yield in manufacturing can be obtained.
[0009]
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 the thickness of the thick dielectric layer. For this reason, 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 has been difficult to sufficiently smooth the dielectric surface produced by the normal thick-film process. .
[0010]
That is, the thick-film dielectric layer is essentially composed of ceramics sintered using a powder material. For this reason, dense sintering usually causes a volume shrinkage of about 30 to 40%. However, while ordinary ceramics shrink three-dimensionally in volume during sintering and become denser, the thick-film ceramics formed on the substrate are constrained by the substrate, so that the in-plane direction of the substrate is It cannot shrink, 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 surface roughness of the thick film does not become smaller than the crystal grain size of the polycrystalline sintered body, the surface thereof has an irregular shape of a submicron size or more.
[0011]
If the surface of such a thick dielectric layer has a defect or a porous film or irregularities, the light emitting layer formed thereon by a vapor deposition method such as a vapor deposition method or a sputtering method follows the surface shape. However, it cannot be formed smoothly. For this reason, an electric field cannot be effectively applied to the light emitting layer portion formed on such a non-flat portion of the substrate, and the light emitting layer is reduced due to a decrease in the effective light emitting area or local unevenness of the film thickness. There has been a problem that the dielectric breakdown occurs partially and the emission luminance decreases.
[0012]
Furthermore, since the film thickness locally largely fluctuates, the intensity of the electric field applied to the light-emitting layer varies greatly locally, so that there is a problem that a clear light-emitting voltage threshold cannot be obtained.
[0013]
In order to solve such a problem, Japanese Patent Application Laid-Open No. 7-50197 discloses a method of laminating a high dielectric constant layer such as lead zirconate titanate formed by a sol-gel method on the surface of a thick-film dielectric made of lead niobate. However, a technique for improving the flatness of the surface is disclosed.
[0014]
FIG. 6 shows an example of a conventional thin film EL device having improved flatness. As shown in the figure, a lower electrode layer 22 formed in a predetermined pattern on an electrically insulating substrate 21, a thick dielectric layer (first dielectric layer) 23 thereon, and further thereon And a second dielectric layer 24 formed by a sol-gel method to form a multilayer dielectric layer. Then, a thin-film insulator layer 25, a light-emitting layer 26, a thin-film insulator layer 27, and a transparent electrode layer 28 are sequentially laminated on the second dielectric layer 24.
[0015]
[Problems to be solved by the invention]
However, even in the case of an EL device having a dielectric layer formed by the sol-gel method, when the light-emitting layer is formed by a vapor deposition method, it is not possible to suppress the generation of splash during the formation of the light-emitting layer. Here, the splash is an abnormal particle of about 1 to 2 μm generated during the formation of the light emitting layer and attached to the film (attachment in a cluster state in which some atoms or molecules are aggregated). Although the shape is rounded as a whole, the shape of the dense portion is uneven.
[0016]
Due to the occurrence of the splash, the resist or the solvent soaked in the splash portion is likely to remain in the photoresist forming step performed when patterning the upper electrode. When such organic substances remain, there is a problem that in a high-temperature continuous operation test of the EL element, ZnS: Mn or the like, which is a light emitting layer, is deteriorated and light emitting characteristics are remarkably deteriorated.
[0017]
In addition, the interface to which the splash has adhered may have microcracks.
[0018]
Further, materials such as ZnS: Mn and SrS: Ce are known for the light-emitting layer, but generally have a problem that they are deteriorated by moisture, moisture, and adhesion of organic substances.
[0019]
Accordingly, an object of the present invention is to provide an EL device having a thick-film ceramic dielectric layer whose surface is flattened by a sol-gel method and having high reliability in light emission characteristics, and a method of manufacturing the same.
[0020]
[Means for Solving the Problems]
Such an object is achieved by means (1) to (8).
[0021]
(1) At least a first electrode layer, a dielectric layer, a light-emitting layer, and a second electrode layer are provided on a substrate, and the dielectric layer and the first dielectric layer are coated with a solution and fired. In an EL element comprising a second dielectric layer formed by a method, a protective layer is formed on at least a surface of a layer adjacent to the second electrode layer and where the electrode pattern of the second electrode layer is not formed. An EL element comprising:
[0022]
(2) The EL device according to (1), wherein the protective layer is formed on a lower surface of the second electrode layer.
[0023]
(3) The EL device according to (1) or (2), wherein the protective layer is formed of an inorganic material having electrical insulation.
[0024]
(4) The EL device according to any one of (1) to (3), having a thin-film insulator layer on at least one surface of the light-emitting layer.
[0025]
(5) The EL device according to (4), wherein the thin-film insulator layer is made of aluminum oxide or yttrium oxide.
[0026]
(6) The display panel according to any one of (1) to (5), including the EL element.
[0027]
(7) a step of forming a first electrode layer on the substrate, a step of forming a first dielectric layer on the first electrode layer, and a solution coating and baking method on the first dielectric layer Forming a second dielectric layer, forming a light emitting layer on the second dielectric layer, forming a protective layer material on the entire surface of the light emitting layer, and then forming a lift-off for forming a second electrode. Forming a resist pattern for use with a resist, etching a protective layer material in a second electrode forming portion by a dry etching method, and forming a second electrode layer in the etched portion.
[0028]
(8) The method of manufacturing an EL element according to (7), further comprising a step of forming an insulator layer before, after, or both before and after the step of forming the light emitting layer.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a specific configuration of the present invention will be described in detail.
[0030]
FIG. 1 shows a schematic sectional view of a first embodiment of the EL device according to the present invention.
[0031]
In the EL device according to the present invention, a first electrode layer 2 having a predetermined pattern is provided on one surface of a substrate 1, and a thick film dielectric is formed so as to cover at least a part of the first electrode layer 2. Layer 3 is provided. The thick-film dielectric layer 3 includes a first dielectric layer 31 and a second dielectric layer 32, and the second dielectric layer 32 is provided by a solution coating baking method. Here, the solution coating baking method is a method in which a precursor solution of a dielectric material is applied to a substrate by a sol-gel method, a MOD (Metallo-Organic Decomposition) method, or the like, and a dielectric layer is formed by baking.
[0032]
Then, the light emitting layer 4 is provided on the second dielectric layer side of the thick dielectric layer 3. A thin film dielectric layer may be provided on at least one of the upper and lower surfaces of the light emitting layer 4 (FIG. 1 shows an embodiment in which the thin film dielectric layers 5 and 6 are provided on both the upper and lower surfaces of the light emitting layer). Further, when the thin film dielectric layer 6 is provided on the side opposite to the light emitting layer 4 or the dielectric layer side, the second electrode layer 7 having a predetermined pattern is provided on the surface thereof, and the thin film dielectric layer 6 is adjacent to the second electrode layer. When the light emitting layer 4 or the thin film dielectric layer 6 is provided on the surface of the layer to be formed, that is, on the surface thereof and on a portion where the predetermined pattern of the electrode layer 7 is not provided, the protective layer 8 is provided.
[0033]
The second electrode layer 7 is formed in a stripe shape in a direction orthogonal to the first electrode layer when viewed from the upper surface of the EL element. Then, an arbitrary stripe electrode of the first electrode layer 2 and an arbitrary stripe electrode of the second electrode layer 7 are respectively selected, and an AC power supply 9 is provided in a part of the light emitting layer where both electrodes in the light emitting layer intersect. By selectively applying a voltage, light emission of a specific pixel can be obtained.
[0034]
FIG. 2 shows a schematic sectional view of a second embodiment of the EL device according to the present invention.
[0035]
The structure of the element is basically the same as that of the first embodiment. However, it differs from the first embodiment in that the protective layer 8 is also formed on the lower surface of the electrode layer 7.
[0036]
By forming the protective layer 8 also on the lower surface of the electrode layer 7, the same effect as that of the thin film insulator layer can be obtained, and the influence of a defect of the laminated film due to splash or the like can be reduced.
[0037]
Hereinafter, members constituting the EL element according to the present invention, a forming method, and the like will be described in more detail.
[0038]
<Substrate>
The substrate is not particularly limited as long as it has electrical insulation properties and can maintain a predetermined heat-resistant strength without contaminating the adjacent first electrode layer or thick film dielectric layer.
[0039]
As a specific material, alumina (Al₂O₃), Quartz glass (SiO₂), Magnesia (MgO), forsterite (2MgO.SiO)₂), Steatite (MgO.SiO)₂), Mullite (3Al₂O₃・ 2SiO₂), Beryllia (BeO), zirconia (ZrO)₂), Aluminum nitride (AlN), silicon nitride (SiN), silicon carbide (SiC), etc., a ceramic substrate, crystallized glass, high heat resistant glass, or the like, or a metal substrate that has been subjected to an enamel treatment can also be used. .
[0040]
<First electrode layer>
When the display device is a simple matrix type, the first electrode layer is formed to have a plurality of stripe-shaped patterns. In addition, the line width is the width of one pixel, and the space between lines is a non-light emitting region. Therefore, it is preferable to minimize the space between lines. Specifically, for example, a line width of about 200 to 500 μm and a space of about 20 to 50 μm are required, depending on the resolution of the target display.
[0041]
Further, the thickness of the first electrode layer is preferably about 0.1 to 3 μm, and particularly preferably about 0.5 to 1 μm. If it is too thick, a step between the electrodes will cause irregularities in the thick dielectric layer formed thereon, making it impossible to form a flat light emitting layer. On the other hand, if the thickness is too small, the electrode resistance increases, the voltage applied to the light emitting layer decreases, and the luminance decreases.
[0042]
As the material of the first electrode layer, high conductivity is obtained, the reactivity with the dielectric layer and the light emitting layer is low, and the first electrode layer is not damaged at the time of forming the dielectric layer covering the material electrode layer. Those which are hardly oxidized in an oxidizing atmosphere at the time of layer firing are preferable.
[0043]
Specifically, precious metals such as Au, Pt, Pd, Ir, and Ag, precious metal alloys such as Au-Pd, Au-Pt, Ag-Pd, and Ag-Pt, and precious metals such as Ag-Pd-Cu are used as main components. An electrode material to which a nonmetallic element is added is preferable.
[0044]
In addition, ITO, SnO₂(Nesa film), an oxide conductive material such as ZnO-Al may be used, or a base metal such as Ni or Cu can be used if the firing atmosphere of the dielectric layer is adjusted.
[0045]
As a method for forming the first electrode layer, a known technique such as a sputtering method, an evaporation method, or a plating method may be used.
[0046]
Alternatively, a material formed of a material called a liquid (liquid @ gold, gold @ resinate, bright @ gold) may be used. The material referred to as the gold liquid is a terpene-based solvent containing gold in the form of an organometallic compound, usually about 4 to 25%, and is a brown viscous liquid. By using this gold solution, a very thin and dense gold film of 50 to 500 nm can be obtained.
[0047]
Since this gold solution is soluble in terpene and its viscosity can be freely adjusted, an electrode pattern can be formed by various coating and printing methods such as spraying and screen printing.
[0048]
The applied gold solution is dried to form a gold wiring pattern by a heat treatment at about 450 to 850 ° C.
[0049]
<Thick dielectric layer>
The thick dielectric layer needs to have a high dielectric constant and a high withstand voltage, and is required to be a material that can be fired at a low temperature in consideration of the heat resistance of the substrate.
[0050]
The thick dielectric layer according to the present invention comprises a first dielectric layer and a second dielectric layer.
[0051]
The first dielectric layer is a ceramic layer formed by firing a powdery insulating material by a so-called thick film method.
[0052]
The thickness of the first dielectric layer is not particularly limited as long as it has a thickness that can eliminate pinholes formed by steps of the electrodes and dust in the manufacturing process, but is not particularly limited. And preferably about 20 to 40 μm. If it is too thick, it will be difficult to densify it, and if it is too thin, it will not be possible to eliminate the effect of the step between the electrodes.
[0053]
Further, the relative dielectric constant is preferably 1000 or more when the above film thickness is secured. If the relative dielectric constant is too low, the effective voltage applied to the light emitting layer decreases, and the luminance in light emission decreases. Therefore, to efficiently supply the voltage applied to the light emitting layer, it is preferable that the dielectric constant of the thick film dielectric layer is higher.
[0054]
Various materials can be used as the material of the first dielectric constant layer. However, considering the heat resistance of the substrate material, a high dielectric constant ceramic composition that can be fired at a low temperature is preferable.
[0055]
For example, BaTiO₃, (Ba_xCa_1-x) TiO₃, (Ba_xSr_1-x) TiO₃, PbTiO₃, Pb (Zr_xTi_1-x) O₃(Hereinafter, PZT) and other dielectric materials having a perovskite structure, ferroelectric materials, Pb (Mg_1/3Nb_2/3) O₃Perovskite relaxor type ferroelectric material represented by₄Ti₃O₁₂, SrBi₂Ta₂O₉Bismuth layer compound represented by (Sr_xBa_1-x) Nb₂O₆, PbNb₂O₆For example, a tungsten bronze type ferroelectric material or the like can be used.
[0056]
Further, the dielectric material containing lead in the composition has a low melting point of lead oxide of 886 ° C., and the lead oxide and other oxide-based materials such as SiO 2₂, CuO, Bi₂O₃, Fe₂O₃Since a liquid phase is formed at a low temperature of about 700 ° C. to 800 ° C. between them and the like, baking is easy at a low temperature and a high dielectric constant is easily obtained, which is preferable.
[0057]
For example, a perovskite structure dielectric material such as PZT or Pb (Mg_1/3Ni_2/3) O₃Perovskite relaxer type ferroelectric material represented by PbNbO₆Tungsten bronze type ferroelectric materials and the like represented by the above are particularly preferable examples. These can easily form a dielectric having a relative dielectric constant of 1,000 to 10,000 at a firing temperature of 800 to 900 ° C., which is the upper limit heat-resistant temperature of a normal ceramic substrate such as alumina ceramics.
[0058]
The first dielectric layer is formed by a so-called thick film forming method.
[0059]
For example, the insulating paste can be formed by printing and firing an insulating paste prepared by mixing a powdery insulating material, a binder, and a solvent over a substrate on which the first electrode layer is formed. Alternatively, a green sheet may be formed by casting an insulator paste to form a film, and the green sheet may be formed by lamination.
[0060]
Thereafter, a first electrode layer is formed by performing binder removal processing and firing. The conditions for the binder removal treatment may be appropriately selected according to the type of the binder, the solvent, and the like. The atmosphere at the time of firing may be appropriately determined according to the type of the conductive material in the electrode layer paste. When firing is performed in an oxidizing atmosphere, normal firing in the atmosphere may be performed. The firing temperature may be appropriately determined according to the type of the insulator layer, but is usually about 700 to 1200 ° C, preferably 1000 ° C or less. Further, the temperature holding time during firing is preferably 0.05 to 5 hours, particularly preferably 0.1 to 3 hours. Further, an annealing treatment may be performed as necessary.
[0061]
A second dielectric layer is formed on the first dielectric layer by a solution coating baking method.
[0062]
The solution coating and baking method is a method of forming a dielectric layer by applying a precursor solution of a dielectric material to a substrate by a sol-gel method or a MOD method and baking the solution.
[0063]
By using the solution coating and baking method, a layer is formed thicker in the concave portion and thinner in the convex portion with respect to the unevenness on the surface of the first dielectric layer, so that the step on the surface of the dielectric layer is flattened. And the uniformity of the thin film light emitting layer formed thereon can be greatly improved.
[0064]
The sol-gel method generally involves adding a predetermined amount of water to a metal alkoxide dissolved in a solvent, applying a precursor solution of a sol having an M-O-M bond formed by hydrolysis and polycondensation reaction to a substrate, and firing. This is a method of forming a film. The MOD 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 baked to form a film. Here, the precursor solution is 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.
[0065]
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 two methods of the sol-gel method and the MOD method may be collectively referred to as a sol-gel method. A solution coating firing method is used. Further, even a solution obtained by mixing a submicron-size dielectric particle and a dielectric precursor solution is included in the dielectric precursor solution of the present invention, and the solution is applied to the substrate and fired. Are also included in the solution coating baking method of the present invention.
[0066]
In both the sol-gel method and the MOD method, since the elements constituting the dielectric are uniformly mixed in the order of submicron or less, the solution coating and baking method uses a ceramic powder such as a dielectric film formed by a thick film method. The feature is that a dense dielectric can be formed at an extremely low temperature as compared with the sintering method.
[0067]
The thickness of the dielectric layer formed by the solution coating and baking method is preferably 0.5 to 3 μm, particularly preferably 1 to 2 μm in order to sufficiently flatten the unevenness on the surface of the thick film.
[0068]
Like the first dielectric layer, the relative dielectric constant of this layer is desirably as high as possible to secure the effective voltage of the light emitting layer, and is at least 250 or more, preferably 500 or more.
[0069]
As such a high dielectric constant material, for example, BaTiO₃, (Ba_xCa_1-x) TiO₃, (Ba_xSr_1-x) TiO₃, PbTiO₃, PZT and other dielectric materials having a perovskite structure, ferroelectric materials, and Pb (Mg_1/3Nb_2/3) O₃Perovskite relaxor-type ferroelectric material represented by₄Ti₃O₁₂, SrBi₂Ta₂O₉Bismuth layer compound represented by (Sr_xBa_1-x) Nb₂O₆, PbNbO₆Tungsten bronze-type ferroelectric materials, etc., represented by the same. Among them, BaTiO₃A ferroelectric material having a perovskite structure such as PZT or PZT is preferable because it has a high relative dielectric constant and can be easily fired at a relatively low temperature.
[0070]
<Light-emitting layer>
The material of the light emitting layer is not particularly limited, but ZnS doped with Mn (ZnS: Mn), ZnS doped with Tb (ZnS: Tb), ZnMgS doped with Mn (ZnMgS: Mn), and SrS doped with Ce ( Known materials such as SrS: Ce) can be used. 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, the thickness is preferably about 100 to 2000 nm, though it depends on the luminescent material.
[0071]
As a method for forming the light emitting layer, a vapor deposition method can be used. As the vapor deposition method, a physical vapor deposition method such as a sputtering method or an electron beam evaporation method or a chemical vapor deposition method such as a CVD method is preferable.
[0072]
After the formation of the light emitting layer, 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 may be formed on the substrate side from the substrate side. You may go after doing. The heat treatment temperature depends on the material of the light emitting layer to be formed, but is preferably 300 ° C. or more, more preferably 400 ° C. or more, and is lower than the firing temperature of the dielectric layer. The processing time is preferably from 10 to 600 minutes. The atmosphere during the heat treatment may be air, N 2 depending on the composition of the light emitting layer and the forming conditions.₂, He or Ar may be selected.
[0073]
<Thin insulator layer>
The thin film insulator layer can be omitted, but is preferably formed on at least one surface of the light emitting layer.
[0074]
This thin-film insulator layer can adjust the electronic state of the interface between the light-emitting layer and the dielectric layer, stabilize and improve the efficiency of electron injection into the light-emitting layer, and can be formed on both surfaces of the light-emitting layer. For example, by forming the electronic state symmetrically on both surfaces of the light emitting layer, it is possible to improve the positive / negative symmetry of the light emission characteristics during AC driving.
[0075]
Further, since it is not necessary to consider a function of maintaining a dielectric strength like a dielectric layer formed on the first electrode, the film thickness may be small. Specifically, it is preferably from 10 to 1000 nm, particularly preferably from 20 to 200 nm.
[0076]
This thin film insulator layer has a resistivity of 10⁸Ω · cm or more, preferably 10¹⁰-10¹⁸Ω · cm is particularly preferred. Further, the substance is preferably a substance having a relatively high relative permittivity, and the relative permittivity is preferably 3 or more.
[0077]
As a material of the thin film insulator layer, for example, silicon oxide (SiO 2)₂), Silicon nitride (SiN), tantalum oxide (Ta)₂O₅), Yttrium oxide (Y₂O₃), Zirconia (ZrO)₂), Silicon oxynitride (SiON), alumina (Al₂O₃) Etc. can be used. As a method for forming the thin-film insulator layer, a sputtering method, an evaporation method, or a CVD method can be used.
[0078]
Further, in the present invention, the protective layer is dry-etched as described later, and a material which is not etched by an etching stopper at that time, that is, a material which is not etched by a gas at the time of etching, or a material having an extremely low etching rate is preferable. Specifically, yttrium oxide (Y₂O₃), Alumina (Al₂O₃Is preferred.
[0079]
<Protective layer>
The protective layer is preferably an inorganic material having an insulating property that can be dry-etched.
[0080]
For example, silicon oxide (SiO₂), Silicon oxynitride (SiON), silicon nitride (SiN), titanium oxide (TiO)₂), Tantalum oxide (Ta)₂O₅), Zirconia (ZrO)₂), Niobium oxide (Nb₂O₅Is preferred. Among them, when the protective layer material is formed under the second electrode, titanium oxide (TiO 2) having a high dielectric constant is used.₂), Tantalum oxide (Ta)₂O₅Is preferred.
[0081]
Since the resistivity is arranged between the upper electrodes, the larger the resistivity, the better.⁸Ω · cm or more, especially 10¹⁰-10¹⁸Ω · cm is preferred.
[0082]
The thickness of the protective layer is preferably 1 to 2 μm which can cover the surface of the splash portion. Specifically, it is preferably from 0.2 to 3 μm, particularly preferably from 0.5 to 2 μm. If the thickness is too thin, the surface of the splash portion cannot be sufficiently covered, and the effect of the protective layer cannot be obtained. On the other hand, if it is too thick, the amount of etching must be increased to form an electrode, which is inefficient. That is, when the etching amount is small, the effective driving voltage applied to the light emitting layer is reduced due to the thickness of the protective layer. In addition, when the etching amount is increased, damage due to the etching occurs in the lift-off resist, which causes a problem that the subsequent lift-off becomes difficult. In addition, by making the protective layer thicker than the second electrode layer, an effect of preventing a short circuit between the electrodes can be obtained.
[0083]
<Second electrode layer>
When the display device is a simple matrix type like the first electrode layer, the second electrode layer has a plurality of striped patterns so as to be orthogonal to the electrode pattern of the first electrode layer. It is formed. In addition, the line width is the width of one pixel, and the space between lines is a non-light emitting region. Therefore, it is preferable to minimize the space between lines. Specifically, for example, a line width of 200 to 500 μm and a space of 20 to 50 μm are required, depending on the resolution of the target display.
[0084]
The second electrode layer must be a transparent electrode because it is necessary to transmit light emitted from the light emitting layer. Specifically, ITO or SnO₂(Nesa film), an oxide conductive material such as ZnO-Al, or the like can be used. The thickness is preferably from 0.2 to 1 μm.
[0085]
<Method of forming protective layer and electrode layer>
First, as described above, the first electrode layer / dielectric layer / (thin film insulator layer) / light emitting layer / (thin film insulator layer) are sequentially formed on the substrate (however, the formation of the thin film insulator layer is optional). When a thin film insulator layer is formed on the surface of the light emitting layer or on the surface of the layer, a material to be a protective layer is formed by a film forming method such as an evaporation method or a sputtering method.
[0086]
Next, a lift-off resist pattern for forming a second electrode is formed on the surface of the film, and the material of the protective layer at the portion where the second electrode is to be formed is etched by a dry etching method. As a result, the portion where the resist has once adhered is removed, and the residue of the resist can be removed. Specific examples of the dry etching include an RIE (reactive ion etching) method using a fluorine-based gas and an ion etching method using an Ar gas.
[0087]
At the time of etching, the protective layer material at the relevant portion may be entirely removed, or a film thickness that does not affect the EL element characteristics, specifically, about 20 to 200 nm so as to function as a thin film insulator layer. You may leave it. By dry-etching the protective layer, there is no residue such as an organic substance which has conventionally been a problem at the interface between the light-emitting layer or the thin-film insulator layer and the second electrode layer, and the reliability of the element is improved. .
[0088]
In the case of removing all, it is preferable to form a thin film insulator layer. Further, it is preferable to use a material that functions as an etching stopper.
[0089]
Next, a second electrode is formed by a film forming method such as a sputtering method or a vapor deposition method, and then lift-off is performed to form a second electrode layer having a stripe pattern and a protective layer between the patterns. can do.
[0090]
【Example】
Hereinafter, examples of the present invention will be specifically described, and further details will be described.
[0091]
Screen printing and drying were repeated on a 96% pure alumina substrate using Heraus RP2003 / 237-22% resinate gold paste so that the film thickness after firing was 0.6 μm. Thereafter, firing was performed at 850 ° C. for 20 minutes in an atmosphere in which sufficient air was supplied. The obtained first electrode layer was patterned into a large number of striped patterns each having a width of 250 μm and a space of 30 μm by a photoetching technique.
[0092]
Next, a dielectric ceramic thick film was formed as a first dielectric layer by a screen printing method. As the thick film paste, a 4210C thick film dielectric paste manufactured by ESL was used, and screen printing and drying were repeated so that the film thickness after firing became 20 μm.
[0093]
After printing and drying, the thick film was baked at 850 ° C. for 20 minutes in an atmosphere supplied with sufficient air using a belt furnace.
[0094]
A second dielectric layer of PZT was formed on this substrate by using a solution coating and baking method.
[0095]
Specifically, using a PZT sol-gel solution prepared by the method described below as a precursor solution, applying the precursor solution to the dielectric layer by a spin coating method, and baking at 700 ° C. for 15 minutes. Repeated predetermined times.
[0096]
In the method for producing the PZT precursor solution, a transparent solution was obtained by heating and stirring 8.49 g of lead acetate trihydrate and 4.17 g of 1,3-propanediol for about 2 hours. Separately, 3.70 g of zirconium normal propoxide 70% by mass, a 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 was added thereto. -75 mass% of diisopropoxide bisacetylacetonate, a 2-propanol solution, and 2.32 g of 1,3-propanediol were added, and 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.
[0097]
The viscosity of the PZT precursor solution was adjusted by diluting the solution with n-propanol. The thickness of the dielectric layer per single layer was set to about 0.5 μm by adjusting the spin coating conditions and the viscosity of the PZT precursor solution. The PZT precursor solution was spin-coated and baked three times to form a PZT dielectric layer having a thickness of about 1.5 μm.
[0098]
The luminescent layer was formed by vacuum deposition using a ZnS deposition source doped with Mn while the substrate was heated to 200 ° C., so that a ZnS luminous body thin film had a thickness of 0.8 μm.
[0099]
Further, an alumina thin film of a thin film insulator layer was continuously formed by a vacuum evaporation method so as to have a thickness of 0.1 μm, and the light emitting layer was annealed in air at 600 ° C. for 20 minutes. In addition, as a result of observing the surface of the obtained thin film, a splash of about 1 to 2 μm was confirmed.
[0100]
Next, Ta₂O₅Was formed as a protective layer material to a thickness of 0.5 μm by a sputtering method. The film forming conditions at this time were as follows.
[0101]
Protective layer material: Tantalum oxide (Ta₂O₅)
Target: Ta₂O₅
Sputtering gas: Ar @ 100 SCCM
Reactive gas: O₂15SCCM
Pressure during film formation: 0.4 Pa
Next, a second electrode pattern was formed. First, a resist is applied, and after exposure through a mask, washing is performed to form a resist pattern. The resist pattern was formed in a stripe shape having a width of 250 μm and a space of 30 μm.
[0102]
Before the formation of the second electrode layer, the Ta of the upper electrode forming portion is formed by a reactive etching method.₂O₅Was completely removed. The etching conditions at this time were as follows.
[0103]
Etching equipment: RIE (reactive ion etching)
Reaction gas: SF₆$ 50 SCCM
O₂20 SCCM
Reaction pressure: 3Pa
Reaction output: 150W
An ITO thin film having a thickness of 0.4 μm was formed as an upper electrode layer by a sputtering method, and then the previously formed resist was lifted off to complete the device.
[0104]
This sample was used as a sample 1, and a sample having a conventional structure without a protective layer was made as a sample for comparison to make a sample 2.
[0105]
Then, Samples 1 and 2 were sealed in dry nitrogen.
[0106]
The obtained device was driven in a constant temperature layer at 85 ° C. for 1000 hours. The measurement of the LV characteristic was performed at the initial stage, 250 hours, 500 hours, 750 hours, and 1000 hours.
The driving conditions were as follows.
[0107]
Voltage: 180V
Pulse: 75Hz-100μs
Initial luminance: about 600 cd / m²
FIG. 3 shows the result of Sample 1 according to the present invention, and FIG. 4 shows the result of Sample 2 according to the conventional structure.
[0108]
As is clear from these figures, the sample 1 according to the present invention has a smaller change in the LV characteristic curve due to the accumulation of the driving time as compared with the sample 2 having the conventional structure. In particular, the sample 1 does not show a rise in luminance that pulls a tail as the light emission time on the low voltage side increases.
[0109]
This indicates that the EL device according to the present invention can obtain stable characteristics even in a continuous high-temperature operation test.
[0110]
【The invention's effect】
As described above, the EL element and the method for manufacturing the EL element according to the present invention can provide an EL element with stable emission characteristics.
[0111]
In addition, the protective layer covers a splash portion generated when a light emitting layer such as ZnS: Mn is formed by a vacuum evaporation method, so that the surface shape can be made smooth.
[0112]
In addition, by protecting the light emitting layer with the protective layer material, it is possible to reduce the moisture and the like from the outside air and the damage received from the process.
[0113]
In addition, by forming a lift-off resist for patterning the upper electrode and etching the protective layer material before forming the upper electrode, there is no residue such as organic matter at the interface between the base and the upper electrode. improves.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a first embodiment of an EL panel of the present invention.
FIG. 2 is a schematic cross-sectional view of a second embodiment of the EL panel of the present invention.
FIG. 3 is a graph showing an LV characteristic of Sample 1 according to the present invention.
FIG. 4 is a graph showing the LV characteristics of Sample 2 having a conventional structure.
FIG. 5 is a schematic sectional view showing an example of a conventional EL element.
FIG. 6 is a schematic sectional view showing another example of a conventional EL element.
[Explanation of symbols]
1, 11, 21 substrate
2, 12, 22} first electrode layer
3 dielectric layer
23, 31 {first dielectric layer
24, 32} second dielectric layer
4, 14, 26 ° light-emitting layer
5, 6, 13, 15, 25, 27} thin-film insulator layer
7, 16, 28} Second electrode layer
8 Protective layer
9, 17, 29 AC power supply

Claims (8)

On a substrate, at least a first electrode layer, a dielectric layer, a light emitting layer, and a second electrode layer are formed, and the dielectric layer is formed with the first dielectric layer by a solution coating firing method. In the EL device comprising the second dielectric layer, a protective layer is provided on at least a surface of the layer adjacent to the second electrode layer and where the electrode pattern of the second electrode layer is not formed. An EL device, characterized in that: The EL device according to claim 1, wherein the protective layer is formed on a lower surface of the second electrode layer. The EL device according to claim 1, wherein the protective layer is formed of an inorganic material having electrical insulation. The EL device according to claim 1, further comprising a thin-film insulator layer on at least one surface of the light-emitting layer. The EL device according to claim 4, wherein the thin-film insulator layer is made of aluminum oxide or yttrium oxide. The display panel according to claim 1, comprising the EL element. Forming a first electrode layer on the substrate, forming a first dielectric layer on the first electrode layer, and forming a second dielectric layer on the first dielectric layer by solution coating and firing; Forming a light emitting layer on the second dielectric layer, forming a protective layer material on the entire surface of the light emitting layer, and then forming a lift-off resist for forming a second electrode. Forming a pattern, etching a protective layer material in a second electrode formation portion by a dry etching method, and forming a second electrode layer in the etched portion. The method for manufacturing an EL device according to claim 7, further comprising a step of forming an insulator layer before, after, or both before and after the step of forming the light emitting layer.

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