JP4685253B2 - EL element - Google Patents

Description

【０１２０】
図３から８は、本実施例のＰＺＴゾルゲル液を用い、スパッタ法によって形成したＢａＴｉＯ₃ バッファ層の膜厚を各種変えた条件で、１層目の誘電体層を形成したときのＳＥＭおよび光学顕微鏡写真である。
【０１２１】
ここで、図３：サンプル１（ＳＥＭ写真：長辺=500μm）、図６：サンプル２（ＳＥＭ写真：長辺=250μm）、図７サンプル３（ＳＥＭ写真：長辺=250μm）、図８サンプル６（ＳＥＭ写真：長辺=250μm）、図４：サンプル１０（光学顕微鏡写真：長辺=1000μm）、図３：サンプル１１（光学顕微鏡写真：長辺=1000μm）である。
【０１２２】
図から明らかなように、ＢａＴｉＯ₃ バッファ層が無い場合には、高密度のクラックが生じ、特にＡｕレジネートを用いた電極のサンプルで著しい。また、ＢａＴｉＯ₃ バッファ層が１０nm以上の場合、クラックは等しく減少し、１００nmでは全くクラックが発生しない。
【０１２３】
また、表１から明らかなように、ＢａＴｉＯ₃ バッファ層を持たない場合、下部電極の断線が発生し、さらにパーティクルの発生が確認された。
【０１２４】
これに対し、ＢａＴｉＯ₃ バッファ層が１０nm以上の場合、下部電極の剥離は認められず、さらに膜厚がが１００nmではクラック、パーティクルの発生も全く認められなかった。
【０１２５】
また、バッファ層と誘電体層を合わせた実効誘電率は、バッファ層がある場合もほとんど変化が認められなかった。これは、バッファ層のＢａＴｉＯ₃ 膜が成膜簿点ではアモルフアスで低誘電率であっても、組成が高誘電率誘電体組成であるため、上部の誘電体層を溶液塗布焼成法で形成する際の高温処理で結晶化し、高誘電率化するためと考えられる。
【０１２６】
また、同膜厚のＳｒＴｉＯ₃ バッファ層とＴｉＯ₂ バッファ層を用いた場合も、下部電極の剥離は全く発生せず、パーティクルの発生も認められなかった。
【０１２７】
次に、表１のサンプル１，２，３，６，８，９，１０および１１の誘電体層付基板を用いて、ＥＬ素子を作製した。
【０１２８】
発光層は、２００℃に加熱した状態でＭｎをドープしたＺｎＳ蒸着源を用い、ＺｎＳ発光体薄膜を膜厚０．８μm となるよう真空蒸着法により形成した後、真空中６００℃で１０分間熱処理した。
【０１２９】
次に、絶縁体層としてＳｉ₃Ｎ₄ 薄膜と上部電極層としてＩＴＯ薄膜をスパッタリング法により順次形成することによりＥＬ素子とした。その際、上部電極層のＩＴＯ薄膜はメタルマスクを成膜時に用いることにより、幅１mmのストライプ状にパターニングした。発光特性は、得られた素子構造の下部電極、上部透明電極から電極を引き出し、１kHzのパルス幅５０μｓにて発光輝度が飽和するまでの電界を印加して測定した。また、それぞれのＥＬ素子を所定の個数ずつ作製し評価した。
【０１３０】
その結果、いずれのサンプルも、飽和輝度７０００cd／m² が得られたが、サンプル６，８は、発光しきい値が１６０V であったのに対し、サンプル９は発光しきい値が１７０V と上昇した。これはサンプル９に用いたＴｉＯ₂ 膜の誘電率がサンプル６，８のＢａＴｉＯ₃ とＳｒＴｉＯ₃ に比較して小さいためと考えられる。
【０１３１】
また、サンプル１，２，１０は下部電極層の断線による非発光画素が発生し、特にサンプル１０で顕著であった。また、サンプル１，２，３，１０は、発光部（画素）内に異常発光点や非発光点が発生した。これはパーティクルの発生により、発光層中にピンホールや発光層膜厚の薄い部分が形成されたことが原因と考えられる。
【０１３２】
【発明の効果】
以上のように、本発明によれば、厚膜セラミックス誘電体層の表面平坦性をゾルゲル誘電体層で確保したＥＬ素子において、ゾルゲル誘電体層を付加することによって発生する下部電極層の剥離や断線を防止し、欠陥のない信頼性の高いＥＬ素子を提供することができる。
【図面の簡単な説明】
【図１】本発明のＥＬ素子の基本構成を示した一部概略断面図である。
【図２】本発明のＥＬ素子の他の基本構成を示した一部概略断面図である。
【図３】実施例のＰＺＴ誘電体層（平坦化層）付基板の表面を撮影した図面代用写真である。
【図４】実施例のＰＺＴ誘電体層（平坦化層）付基板の表面を撮影した図面代用写真である。
【図５】実施例のＰＺＴ誘電体層（平坦化層）付基板の表面を撮影した図面代用写真である。
【図６】実施例のＰＺＴ誘電体層（平坦化層）付基板の表面を撮影した図面代用写真である。
【図７】実施例のＰＺＴ誘電体層（平坦化層）付基板の表面を撮影した図面代用写真である。
【図８】実施例のＰＺＴ誘電体層（平坦化層）付基板の表面を撮影した図面代用写真である。
【図９】従来の薄膜ＥＬ素子の基本構成を示した一部概略断面図である。
【図１０】従来の厚膜ＥＬ素子の基本構成を示した一部概略断面図である。
【図１１】従来の誘電体層の焼成時における膜厚変化を示したグラフである。
【符号の説明】
１ 基板
２ 下部電極
３ バッファ層
４ 厚膜誘電体層
５ 誘電体層
６ 薄膜絶縁体層
７ 発光層
８ 薄膜絶縁体層
９ 透明電極層
１０ 交流電源
１１ 基板
１２ 下部電極
１４ 厚膜誘電体層
１５ 誘電体層
１６ 薄膜絶縁体層
１７ 発光層
１８ 薄膜絶縁体層
１９ 透明電極層
２０ 交流電源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EL element having at least a structure in which an electrically insulating substrate, an electrode layer having a pattern on the substrate, and a dielectric layer, a light emitting layer, and a transparent electrode layer are stacked on the electrode layer.
[0002]
[Prior art]
EL elements have been put into practical use as backlights for liquid crystal displays (LCDs) and watches.
[0003]
An EL element is an element that applies a phenomenon in which a substance emits light when an electric field is applied, that is, an electroluminescence (EL) phenomenon.
[0004]
The EL element includes a dispersed EL element having a structure in which a powder luminescent material is dispersed in an organic substance or a hollow and electrode layers are provided on the upper and lower sides, two electrode layers and two thin film insulators on an electrically insulating substrate. There is an EL element using a thin film light emitter formed in a sandwiched manner. Further, there are a DC voltage driving type and an AC voltage driving type for each driving method. Dispersion EL elements have been known for a long time and have the advantage of being easy to manufacture, but their use has been limited because of their low brightness and short lifetime. On the other hand, EL elements have been widely used in recent years because they have characteristics of high luminance and long life.
[0005]
FIG. 9 shows the structure of a typical double-insulated thin film EL element as a conventional EL element. This thin film EL element is made of transparent ITO 31 having a film thickness of about 0.2 μm to 1 μm and formed in a predetermined stripe pattern on a transparent substrate 31 such as blue glass used for liquid crystal displays and PDPs. The electrode layer 32, the thin film transparent first insulator layer 33, the light emitting layer 34 having a film thickness of about 0.2 μm to 1 μm, and the thin film transparent second insulator layer 35 are laminated, and further orthogonal to the transparent electrode layer 32. A metal electrode layer 36 such as an Al thin film patterned in a stripe shape is formed. Then, a voltage is selectively applied from a power source 40 to a specific light emitter selected by the matrix of the transparent electrode layer 32 and the metal electrode layer 36 to cause the light emitter of the specific pixel to emit light, and the light emission is transmitted to the substrate 31. Remove from the side. Such thin-film insulator layers 33 and 35 have a function of limiting the current flowing through the light-emitting layer 34, can suppress the dielectric breakdown of the thin-film EL element, and provide stable light-emitting characteristics. Works. For this reason, the thin film EL element having this structure is widely used commercially.
[0006]
The thin film transparent insulator layers 33 and 35 are usually Y ₂ O _Three , Ta ₂ O _Five , Ai _Three N _Four , BaTiO _Three The transparent dielectric thin film such as is formed with a film thickness of about 0.1 to 1 μm by sputtering or vapor deposition.
[0007]
As a light emitting material, ZnS added with Mn which emits yellow-orange light has been mainly used from the viewpoint of easiness of film formation and light emission characteristics. In order to produce a color display, it is indispensable to use a luminescent material that emits light in three primary colors of red, green, and blue. These materials include SrS added with blue light emitting Ce and ZnS added with Tm, ZnS added with red light emitting Sm and CaS added with Eu, ZnS added with green light emitting Tb, and CaS added with Ce. It has been known.
[0008]
In addition, the monthly display '98 April issue “Recent display technology trends”, Tanaka, p. As a material for obtaining blue light emission, such as ZnS: Tb, SrS: Cr, (SrS: Ce / ZnS) n, Ca ₂ Ga ₂ S _Four : Ce, Sr ₂ Ga ₂ S _Four A light emitting material such as Ce is disclosed. In addition, light-emitting materials such as SrS: Ce / ZnS: Mn are disclosed as materials that obtain white light emission.
[0009]
Further, among the above materials, SrS: Ce is disclosed in IDW (International Display Workshop) '97 X.Wu "Multicolor Thin-Film Ceramic Hybrid EL Displays" p593 to 596, which is used for a thin film EL element having a blue light emitting layer. ing. Further, in this document, when a light emitting layer of SrS: Ce is formed, H ₂ It is disclosed that a high-purity light-emitting layer can be obtained when formed by an electron beam evaporation method in an S atmosphere.
[0010]
However, structural problems to be solved still remain in such thin film EL elements. In other words, since the insulator layer is formed of a thin film, there is no defect in the thin film insulator due to the stepped portion of the pattern edge of the transparent electrode or dust generated in the manufacturing process when the display is a large area. However, there is a problem that the light emitting layer is destroyed due to a local decrease in the withstand voltage. Since such defects become a fatal problem as a display device, the thin-film EL element has been a major obstacle to practical application as a large-area display compared to a liquid crystal display or a plasma display. .
[0011]
In order to solve the problem that such a thin-film insulator defect occurs, Japanese Examined Patent Publication No. 7-44072 uses an electrically insulating ceramic substrate as a substrate and uses a thick-film dielectric instead of the thin-film insulator under the light emitter. An EL element using a body is disclosed. Unlike the structure of the conventional thin film EL element, the EL element disclosed in this document takes out light emitted from the light emitter from the upper side opposite to the substrate, and therefore the transparent electrode layer is formed on the upper part.
[0012]
In this EL element, the thick film dielectric layer is formed to have a thickness of several tens to several hundreds of micrometers, which is several hundreds to several thousand times that of the thin film insulator layer. For this reason, there are very few dielectric breakdowns caused by pinholes formed by steps of electrodes or dust in the manufacturing process, and there is an advantage that high reliability and high yield in manufacturing can be obtained. By the way, the use of such a thick film dielectric layer causes a problem that the effective voltage applied to the light emitting layer drops. For example, in the above Japanese Patent Publication No. 7-44072, a composite perovskite high dielectric constant material is used as the dielectric layer. This problem has been improved by using it.
[0013]
However, the light emitting layer formed on the thick dielectric layer is only a few hundreds of nanometers, which is about 1/100 of the thick dielectric layer. For this reason, the surface of a thick film dielectric layer must be smooth at a level below 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. .
[0014]
That is, the thick film dielectric layer is essentially composed of ceramics using a powder raw material. For this reason, when it sinters densely, volume contraction of about 30 to 40% is usually generated. However, while ordinary ceramics shrink and volumetrically shrink three-dimensionally during sintering, thick-film ceramics formed on the substrate are constrained by the substrate, and therefore in the in-plane direction of the substrate. Cannot shrink, and can shrink volume only one-dimensionally in the thickness direction. For this reason, sintering of the thick dielectric layer becomes essentially porous without being sufficient. Furthermore, since the surface roughness of the thick film does not become less than the crystal grain size of the polycrystalline sintered body, the surface has an uneven shape of submicron size or more.
[0015]
If there are defects on the surface of the dielectric layer, porous film quality, or uneven shape, the light-emitting layer formed by vapor deposition such as vapor deposition or sputtering will follow the surface shape. And cannot be formed uniformly. For this reason, an electric field cannot be effectively applied to the light-emitting layer portion formed on the non-flat portion of the substrate, and the effective light-emitting area is reduced or the light-emitting layer is formed due to local nonuniformity of the film thickness. There was a problem that dielectric breakdown partially occurred and the luminance of light emission was lowered. Further, since the film thickness varies greatly locally, the electric field strength applied to the light emitting layer varies greatly locally, and there is a problem that a clear light emission voltage threshold cannot be obtained.
[0016]
In order to solve such problems, for example, in Japanese Patent Application Laid-Open No. 7-50197, a high dielectric constant layer such as lead zirconate titanate formed by a sol-gel method is formed on a thick film dielectric surface made of lead niobate. A method of stacking and improving the flatness of the surface is disclosed.
[0017]
In this way, by using a ceramic high dielectric constant dielectric thick film, it is possible to avoid defects in the thin film insulator due to stepped portions of the pattern edge of the lower electrode layer and dust generated in the manufacturing process, and local dielectric strength It is possible to solve the problem that the light emitting layer is destroyed due to the decrease in the thickness.
[0018]
However, when such a sol-gel method is used, a sol-gel film is also formed in a portion where the lower electrode of the thick ceramic dielectric layer is taken out of the thick film pattern portion. And the sol-gel dielectric layer formed on the electrode part is likely to cause high-density cracks and peeling of the electrode during firing, which may cause disconnection of the underlying electrode, which is a practical problem. It was.
[0019]
[Problems to be solved by the invention]
The object of the present invention is to prevent peeling and disconnection of the lower electrode layer generated by adding the sol-gel dielectric layer in the EL element in which the surface flatness of the thick ceramic dielectric layer is ensured by the sol-gel dielectric layer, An object is to provide a highly reliable EL element free from defects.
[0020]
[Means for Solving the Problems]
Such an object is achieved by any one of the following configurations (1) to (5).
(1) A substrate having electrical insulation, an electrode layer having a pattern on the substrate, a dielectric layer covering at least a part of the electrode layer, and at least a light emitting layer and a transparent electrode layer on the dielectric layer Is an EL element having a multilayer structure of a dielectric layer formed by a thick film and a solution coating firing method,
An EL element having a buffer layer on at least the electrode layer.
(2) The EL element according to (1), wherein the buffer layer is a high dielectric constant composition film formed by a sputtering method.
(3) The EL device according to (1) or (2), wherein the high dielectric constant composition film has a perovskite structure dielectric composition and has a relative dielectric constant of 100 or more.
(4) The EL element according to any one of (1) to (3), wherein the buffer layer is disposed at least between an electrode layer and a dielectric layer formed by a solution application baking method.
(5) The EL element according to any one of (1) to (4), wherein the buffer layer has a thickness of 10 nm or more.
[0021]
[Action]
When a high dielectric constant dielectric layer for surface planarization is formed by a solution coating firing method, a solution coating firing dielectric layer (hereinafter referred to as a planarization layer) is used to planarize the entire surface of the thick ceramic dielectric layer. Is required to be larger than the ceramic dielectric. At this time, the planarizing layer 15 is formed directly on a part of the electrode lead-out portion that pulls out the lower electrode 12 shown in FIG. 10 from the thick dielectric layer.
[0022]
The EL element shown in FIG. 10 includes, for example, a lower electrode layer 12 formed in a predetermined pattern on a substrate 11 having electrical insulation, a thick dielectric layer 14 thereon, and a solution thereon. A dielectric layer 15 formed by a coating method is laminated to form a multilayer dielectric layer.
[0023]
A thin film insulator layer 16, a light emitting layer 17, a thin film insulator layer 18, and a transparent electrode layer 19 are laminated on the multilayer dielectric layers 14 and 15, and a lower electrode layer 12 and an upper transparent electrode layer 19. Are formed in stripes in directions orthogonal to each other.
[0024]
On the lower electrode, particularly when a flattening layer thicker than 0.5 μm is baked, high-density cracks 21 are likely to occur due to the reasons described below. The generation of particles due to the peeling 21 and the phenomenon that the electrode peeling 21 occurs simultaneously with the planarization layer frequently occur.
[0025]
Such generation of particles due to the cracks 21, defects due to peeling of the lower electrode layer, and disconnection 21 cause pinhole formation of the light emitting layer due to particles, disconnection of the electrodes, and deterioration of reliability, and are fatal to the EL element. It becomes a flaw.
[0026]
The present inventors have found that the occurrence of such cracks and delamination occurs in common while trying precursor solutions for various planarization layers, and as a result of analyzing the cause, common to solution coating and firing methods. The following estimation was made regarding the cause of the problem in the firing process.
[0027]
The precursor solution used in the solution coating and baking method is composed of a metal organic compound of a metal element constituting the dielectric layer, or a metal alkoxide, a complex of these metal source elements and an organic substance in the solution, and a volatile solvent. .
[0028]
The film formation method of the solution coating and baking method is to form a precursor layer on the substrate by applying the precursor solution to the substrate by spin coating, dip coating, spray coating, or the like, and then the precursor By firing the layer, the organic component in the precursor is removed, an ultrafine oxide layer is formed by the combination of the metal element and oxygen, and this oxide is fired to form the dielectric layer.
[0029]
Here, the change of the film thickness in a baking process is shown in FIG. In the figure, the film thickness immediately after coating is taken as 1, and the change in relative film thickness in the firing process is shown. In this firing process, the following phenomenon occurs. First, the solvent component in the precursor is volatilized to a temperature corresponding to its boiling point at a relatively low temperature (˜200 ° C.), and the thickness of the applied precursor layer is greatly reduced. The film thickness at this point is still considerably larger than the final film thickness, and since many organic substances are present in the film, the film is mechanically soft and cracks and the like are unlikely to occur.
[0030]
When the temperature further increases (˜400 ° C.), the organic component gradually evaporates from the complex of the metal source element and the organic substance (in the solution) due to decomposition or the like, and the film thickness further decreases, and the film mechanically It becomes brittle and a large tensile stress is generated as the film shrinks. At this time, the largest crack is likely to occur.
[0031]
After this stage, the organic component is almost eliminated from the film, and when the remaining oxide of the metal element is sintered, a crystalline dielectric film is formed by sintering. The stress accompanying sintering is generated at the same time as the material is partially relaxed. At this time, a very large crack is not formed.
[0032]
It is presumed that the dielectric layer formed by the solution coating and firing method is usually formed in such a process, and naturally the composition of the precursor solution and the coating and firing conditions are set so that cracks do not occur in such a firing process. However, even when optimized in this manner, the cracks occur on the metal electrode layer at a very high frequency.
[0033]
This is because, in the firing process described above, the metal electrode layer has a thermal expansion coefficient different from that of the substrate, and since this thermal expansion coefficient is usually larger than the thermal expansion coefficient of the substrate, compressive stress is generated in the electrode layer, A minute hilllock is formed in the electrode, and the melting point of the metal constituting the electrode is not sufficiently high, so that a recrystallization phenomenon of the metal electrode occurs. For this reason, it is considered that the cause is that excessive stress is locally applied to the solution-coated fired dielectric layer as compared with a normal ceramic or glass substrate.
[0034]
As a result of estimating and considering the cause of cracks in this way, the present inventors have provided a buffer layer between the dielectric layer and the metal electrode layer, and have a mechanical clamping effect on the surface of the metal electrode layer. It has been found that the generation of cracks can suppress the occurrence of cracks.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
The EL element of the present invention includes an electrically insulating substrate, an electrode layer having a pattern on the substrate, a dielectric layer covering at least a part of the electrode layer, and at least a light emitting layer on the dielectric layer. And an EL element having a multilayer structure of a dielectric layer formed by laminating a transparent electrode layer and the dielectric layer by a thick film and a solution coating firing method, and having a buffer layer on at least the electrode layer is there.
[0036]
Thus, by disposing the buffer layer on the electrode layer, it is possible to prevent cracking and peeling of the dielectric layer formed by the solution coating and baking method formed on the electrode layer, and thus peeling and disconnection of the lower electrode layer are prevented. Can be prevented.
[0037]
The basic structure of the EL element of the present invention is shown in FIG. The EL element of the present invention includes, for example, a lower electrode layer 2 formed in a predetermined pattern on a substrate 1 having electrical insulation, a thick dielectric layer 4 on a buffer layer 3 thereon, and a A dielectric layer 5 formed by a solution coating method is laminated thereon to constitute a multilayer dielectric layer.
[0038]
A thin film insulator layer 6, a light emitting layer 7, a thin film insulator layer 8, and a transparent electrode layer 9 are laminated on the multilayer dielectric layers 4 and 5. The thin film insulator layers 6 and 8 may be omitted. The lower electrode layer 2 and the upper transparent electrode layer 9 are formed in stripes in directions orthogonal to each other. Then, an arbitrary lower electrode layer 2 and upper transparent electrode layer 9 are selected, respectively, and light is emitted from a specific pixel by selectively applying a voltage from the AC power source / pulse power source 10 to the light emitting layer at the orthogonal portion of both electrodes. Obtainable.
[0039]
FIG. 2 shows another configuration example of the EL element of the present invention. In this example, the buffer layer 3 is formed on the thick dielectric layer 4 so as to enclose it. Others are the same as those in FIG. 1, and the same components are denoted by the same reference numerals and the description thereof is omitted. That is, the buffer layer 3 may be formed at any position as long as it is interposed between the lower electrode 2 and the dielectric layer 5 formed by the solution coating method.
[0040]
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.
[0041]
Specific materials include alumina (Al ₂ O _Three ), Quartz glass (SiO ₂ ), Magnesia (MgO), forsterite (2MgO · SiO) ₂ ), Steatite (MgO.SiO) ₂ ), Mullite (3Al ₂ O _Three ・ 2SiO ₂ ), Beryllia (BeO), zirconia (ZrO) ₂ ), Aluminum nitride (AlN), silicon nitride (SiN), ceramic substrate such as silicon carbide (SiC), crystallized glass, high heat-resistant glass, etc., and metal substrates that have been subjected to a brazing treatment are also used. Is possible.
[0042]
When the display device is a simple matrix type, the lower electrode layer is formed to have a plurality of stripe patterns. Further, since the line width is one pixel and the space between the lines is a non-light emitting region, it is preferable to make the space between the lines as small as possible. Specifically, although it depends on the resolution of the target display, for example, a line width of 200 to 500 μm and a space of about 20 to 50 μm are required.
[0043]
A material for the lower electrode layer is preferably a material that has high conductivity, is not damaged when the dielectric layer is formed, and has low reactivity with the dielectric layer and the light emitting layer. Such lower electrode layer materials include noble metals such as Au, Pt, Pd, Ir, and Ag, noble metal alloys such as Au—Pd, Au—Pt, Ag—Pd, and Ag—Pt, and Ag—Pd—Cu. An electrode material containing a precious metal such as a main component and a non-metallic element added is preferable because oxidation resistance to an oxidizing atmosphere during firing of the dielectric layer can be easily obtained. ITO and SnO ₂ (Nesa film), oxide conductive materials such as ZnO-Al may be used, and further, base metals such as Ni and Cu are used, and these non-metals oxidize the partial pressure of oxygen when firing the dielectric layer. It can also be set and used in a range that is not.
[0044]
As a method for forming the lower electrode layer, a known technique such as sputtering, vapor deposition, or plating may be used.
[0045]
In particular, an electrode that can easily exhibit a peeling prevention effect by the buffer layer of the present invention includes an electrode formed of a material called liquid gold, gold resinate, or bright gold. This material called gold liquid or water gold is a brown and viscous liquid in which gold is contained in an organic metal compound in the form of an organometallic compound in an amount of usually 4 to 25%. By using this gold solution, an extremely thin and dense gold film of 50 to 500 nm can be obtained.
[0046]
Since this gold solution is soluble in terpenes and can be freely adjusted in viscosity, an electrode pattern can be formed by various coating and printing methods such as spraying and screen printing.
[0047]
The applied gold solution is dried and then formed into a gold wiring pattern by heat treatment at about 450 to 850 ° C.
[0048]
The thick film 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.
[0049]
Here, the thick film dielectric layer is a ceramic layer formed by firing a powdery insulator material by a so-called thick film method. The thick film dielectric layer is formed, for example, by printing and baking an insulator paste prepared by mixing a binder and a solvent in a powdery insulator material on a substrate on which a lower electrode layer is formed. be able to. Alternatively, a green sheet may be formed by casting an insulator paste and then stacked.
[0050]
The conditions for the binder removal treatment performed before firing may be normal.
[0051]
The atmosphere during firing may be appropriately determined according to the type of the conductive material in the electrode layer paste, but when firing in an oxidizing atmosphere, ordinary firing in the air may be performed.
[0052]
The holding temperature during firing 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. The temperature holding time during firing is preferably 0.05 to 5 hours, particularly preferably 0.1 to 3 hours.
[0053]
Moreover, you may anneal-treat as needed.
[0054]
Here, when the relative dielectric constants of the thick 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 dielectric layer is applied to the light emitting layer. The voltage V2 is expressed by the following equation.
[0055]
V2 / Vo = (e1 * d2) / (e1 * d2 + e2 * d1) ------ (1)
Assuming that the relative dielectric constant of the light emitting layer is e2 = 10 and the film thickness is d2 = 1 μm,
V2 / Vo = e1 / (e1 + 10 × d1) ------- (2)
[0056]
Since the voltage effectively applied to the light emitting layer is at least 50% or more of the applied voltage, preferably 80% or more, more preferably 90% or more,
[0057]
In the case of 50% or more, e1 ≧ 10 × d1 -------- (3)
In the case of 80% or more, e1 ≧ 40 × d1 -------- (4)
In the case of 90% or more, e1 ≧ 90 × d1 -------- (5)
[0058]
That is, the relative dielectric constant of the dielectric layer needs to be at least 10 times, preferably 40 times or more, more preferably 90 times or more of the film thickness when the unit is expressed in μm.
[0059]
The film thickness of the thick film dielectric is required to be thick in order to eliminate pinholes formed by electrode steps or dust in the manufacturing process, and is at least 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more. Necessary.
[0060]
For example, when the thickness of the dielectric layer is 20 μm, the relative dielectric constant needs to be 200 to 800 to 1800 or more, and when the thickness of the dielectric layer is 30 μm, the relative dielectric constant is 300 to 1200. 2700 is required.
[0061]
Various materials can be considered as such a high dielectric constant thick film material, but considering the heat resistance limitation of the substrate material, a high dielectric constant ceramic composition that can be formed at a low temperature is desirable.
[0062]
For example, BaTiO _Three , (Ba _x Ca _1-x ) TiO _Three , (Ba _x Sr _1-x ) TiO _Three , PbTiO _Three , Pb (Zr _x Ti _1-x ) _Three Dielectrics having a perovskite structure, such as ferroelectric materials, Pb (Mg _1/3 Ni _2/3 ) O _Three Composite perovskite relaxor type ferroelectric materials represented by _Four Ti _Three O ₁₂ , SrBi ₂ Ta ₂ O ₉ Bismuth layered compound represented by (Sr _x Ba _1-x Nb ₂ O ₆ , PbNb ₂ O ₆ Tungsten bronze type ferroelectric materials such as the above are preferred because of their high dielectric constant and easy firing.
[0063]
In addition, the dielectric material containing lead in its composition has a low melting point of lead oxide as low as 888 ° C., and lead oxide and other oxide materials such as SiO 2 ₂ And CuO, Bi ₂ O _Three , Fe ₂ O _Three Since a liquid phase is formed at a low temperature of about 700 ° C. to 800 ° C., etc., firing is easy at a low temperature and a high dielectric constant is easily obtained, which is preferable. For example, Pb (Zr _x Ti _1-x ) _Three Perovskite structure dielectric materials such as Pb (Mg _1/3 Ni _2/3 ) O _Three Composite perovskite relaxor type ferroelectric materials represented by PbNbO ₆ Examples thereof include tungsten bronze type ferroelectric materials. These can easily form a dielectric having a relative dielectric constant of 1000 to 10,000 at a firing temperature of 800 to 900 ° C., which is the upper limit heat resistance temperature of a normal ceramic substrate such as alumina ceramics.
[0064]
Since the purpose of the high dielectric constant dielectric layer laminated on the thick film dielectric layer is to improve the surface flatness of the thick film dielectric layer, it is necessary to use a solution coating firing method.
[0065]
The solution coating and firing method refers to a method in which a dielectric material precursor solution such as a sol-gel method or a MOD method is applied to a substrate and a dielectric layer is formed by firing.
[0066]
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 for forming a film. The MOD (Metal-Organic Decomposition) method forms a film by dissolving a metal salt of a carboxylic acid having an MO bond in an organic solvent to form a precursor solution, and applying and baking the substrate. Is the method. Here, the precursor solution refers to a solution containing an intermediate compound produced by dissolving a raw material compound in a solvent in a film forming method such as a sol-gel method or a MOD method.
[0067]
The sol-gel method and the MOD method are not completely separate methods and are generally used in combination with each other. For example, when forming a PZT film, it is common to use lead acetate as the Pb source and adjust the solution using the alkoxide as the Ti and Zr sources. In addition, the two methods of the sol-gel method and the MOD method may be collectively referred to as the sol-gel method, but in any case, a film is formed by applying a precursor solution to a substrate and baking it. Then, it is set as the solution application baking method. Moreover, even if the solution is a mixture of submicron-sized dielectric particles and a dielectric precursor solution, it is included in the dielectric precursor solution of the present invention, and the solution is applied to a substrate and fired. It is included in the solution coating firing method of the present invention.
[0068]
In the solution coating and firing method, in both the sol-gel method and the MOD method, the elements constituting the dielectric are uniformly mixed in the order of sub-μm or less. Compared with the method using powder sintering, it is characterized in that a dense dielectric can be synthesized at an extremely low temperature.
[0069]
The main purpose of using the solution coating and baking method is that the dielectric layer formed by this method is formed through the step of applying and baking the precursor solution. Since a thin layer is formed on the surface, the step on the substrate surface is flattened, and the surface flatness of the thick ceramic dielectric layer of the EL element is remarkably improved, and the thin film light emission formed thereon The layer uniformity can be greatly improved.
[0070]
Therefore, the thickness of the dielectric layer formed by the solution coating and firing method is desired to be 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm or more in order to sufficiently flatten the unevenness of the thick film surface.
[0071]
Here, the influence on the relative dielectric constant of the entire dielectric layer due to the lamination of the dielectric layers by this solution coating and firing method will be described. When the relative dielectric constants of the thick dielectric layer and the high dielectric constant dielectric layer formed by the solution coating firing method are e3 and e4, respectively, and the total film thickness of each layer is d3 and d4, the laminated dielectric The effective relative dielectric constant e5 of the entire layer is expressed by the following equation. (Here, the film thickness of the entire laminated dielectric layer is converted into a dielectric constant assuming that it does not change as d3)
[0072]
e5 = e3 × 1 / [1+ (e3 / e4) × (d4 / d3)] ------- (6)
If this equation is transformed,
e4 / d4 = e3 * e5 / (d3 * (e3-e5)) ------- (7)
[0073]
Based on the above discussion, the effective relative dielectric constant of the entire laminated dielectric layer formed by the solution coating and baking method is preferable when the thickness of the thick film layer is 30 μm. Is 1200-2700 or more. Therefore, for example, when a thick film having a relative dielectric constant of 4000 is used to obtain an effective dielectric constant of 2700, the ratio of the relative dielectric constant to the film thickness of the dielectric layer formed by the solution coating and baking method needs to be 277 or more. If the dielectric constant of the thick dielectric layer is 3000, the ratio is 900.
[0074]
As described above, the film thickness of the dielectric layer formed by the solution coating firing method is at least 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm or more. For this reason, the relative dielectric constant is desirably as high as possible, and is at least 250 or more, preferably 500 or more.
[0075]
As described above, the high dielectric constant layer formed by the solution coating firing method needs to have a large film thickness and a high dielectric constant. Examples of such a high dielectric constant material include BaTiO. _Three , (Ba _x Ca _1-x ) TiO _Three , (Ba _x Sr _1-x ) TiO _Three , PbTiO _Three , Pb (Zr _x Ti _1-x ) _Three Dielectrics having a perovskite structure, such as ferroelectric materials, Pb (Mg _1/3 Ni _2/3 ) O _Three Composite perovskite relaxor type ferroelectric materials represented by _Four Ti _Three O ₁₂ , SrBi ₂ Ta ₂ O ₉ Bismuth Bismuth Layered Compound (Sr _x Ba _1-x Nb ₂ O ₆ , PbNbO ₆ Examples thereof include tungsten bronze type ferroelectric materials. Among these, BaTiO _Three A ferroelectric material having a perovskite structure such as PZT is preferable because it has a high dielectric constant and can be easily formed at a relatively low temperature.
[0076]
The buffer layer itself does not generate cracks on the metal electrode and needs to have a sufficient mechanical clamping effect. Therefore, excessive volume shrinkage does not occur in the buffer layer even during the formation of the buffer layer or in the baking process by the solution coating baking method after the buffer layer is formed, and it is sufficiently hard and has an appropriate film thickness compared to the metal electrode. It is necessary to have.
[0077]
As a method for forming such a buffer layer, the density of the buffer layer is sufficiently high at the time when the buffer layer is formed, and the volume shrinkage of the buffer layer is small during the firing of the solution-coated fired layer after the buffer layer is formed. A method that can exert a clamping effect is preferable. That is, as a method for forming the buffer layer, a method in which significant volume shrinkage occurs in the process of forming the desired structure such as the above-described solution coating and baking method is not preferable, and a dense film formation method without causing volume shrinkage is preferable. Needed.
[0078]
As such a film formation method, a vacuum deposition method, a sputtering method, a CVD method, or the like is used, and a film close to the composition and density of the target composition can be directly formed on the substrate without performing post-heat treatment or the like. A membrane method is needed.
[0079]
In particular, the sputtering method is particularly preferable because a thin film having the same composition as the target composition can be easily formed. A thin film having a density of 95% or more is easily formed in a crystallized state, and a thin film having a density of 80% or more is easily formed even in an amorphous state. Can be formed.
[0080]
Next, the influence of the dielectric constant of the buffer layer will be described.
[0081]
Here, when the relative dielectric constants of the dielectric layer and the buffer layer are e7 and e6, respectively, and the film thicknesses of the respective layers are d7 and d6, the effective relative dielectric constant e8 of the laminated dielectric layer and the buffer layer is It is shown by the formula.
[0082]
e8 = e6 × 1 / [1+ (e6 / e7) × (d7 / d6)] ------- (8)
[0083]
The decrease in effective dielectric constant of the dielectric layer / buffer layer composite layer due to the insertion of the buffer layer is based on the relationship between the relative dielectric constant between the dielectric layer and the light emitting layer and the effective voltage applied to the light emitting layer. In view of this, it is necessary that the amount be small, and it is preferable that the relative dielectric constant of the composite layer is at least 90%, preferably 95% or more that of the dielectric layer alone. Therefore, from equation (8)
[0084]
When it is 90% or more, e6 / d6 ≦ 1/9 × e7 / d7 -------- (9)
When 95% or more, e6 / d6 ≦ 1/19 × e7 / d7 -------- (10)
[0085]
For example, assuming that the dielectric layer has a relative dielectric constant of 2700 and a film thickness of 30 μm, the ratio of the relative dielectric constant to the film thickness of the buffer layer is 810 or more, preferably 1710 or more.
[0086]
Therefore, for example, assuming that the thickness of the buffer layer is 0.1 μm, the relative dielectric constant needs to be 1 to 171 or more, and if it is assumed to be 0.01 μm, the relative dielectric constant needs to be 8.1 to 17.1 or more. Become.
[0087]
The thickness of the buffer layer is not limited as long as the effect of suppressing the generation of cracks during the formation of the dielectric layer due to the interaction between the electrode layer and the dielectric layer can be obtained. The effect is expected to become remarkable. According to the experimental study by the present inventors, in the case of an oxide thin film formed by a sputtering method, a crack suppression effect is sufficiently recognized from a thickness of 10 nm or more, and the crack suppression effect improves as the film thickness increases. And when it became 100 nm or more, it became clear that the crack on an electrode disappeared completely.
[0088]
Therefore, the required film thickness is at least 10 nm or more, preferably 100 nm or more. This effect is similarly observed up to a thickness of about 1 μm, but overhangs can cause overhangs. For this reason, an upper limit becomes like this. Preferably it is 1 micrometer or less, More preferably, it is 1/2 or less of electrode layer thickness.
[0089]
As the material of the buffer layer, alumina (relative dielectric constant: 8), zirconia (relative dielectric constant: about 10), Ta ₂ O _Five An insulating material such as (relative dielectric constant of about 25) can be used, but high dielectric constant is preferable from the viewpoint of the relationship between the relative dielectric constant and the film thickness, the crack suppression effect, and the reactivity with the dielectric layer. Rate material, eg TiO ₂ A material having a relative dielectric constant of 100 or more, for example, Pb ₂ (Zr _1-y Ti _y ) ₂ O ₆ Pyrochlore type dielectric such as Bi _Four Ti _Three O ₁₂ , SrBi ₂ Ta ₂ O ₉ Materials such as Bi layered compound type dielectrics typified by, etc., barium titanate (BaTiO _Three ), Strontium titanate (SrTiO) _Three ), Calcium titanate (CaTiO) _Three ), Lead titanate (PbTiO _Three ), Lead zirconate (PbZrO) _Three ) And other perovskite-type high dielectric constant materials, and mixtures and solid solution compositions thereof ((Ba _1-x Sr _x ) TiO _Three , PZT, etc.) and perovskite type relaxor oxides are preferred. Especially among these, BaTiO _Three A ferroelectric material having a perovskite structure such as PZT is preferable because it has a high relative dielectric constant and can be easily synthesized at a relatively low temperature. Such a material can easily have a dielectric constant suitable for the buffer layer of 100 or more.
[0090]
Further, by using a material having the same crystal structure as that of the dielectric layer formed by the solution coating and firing method, the reaction between the dielectric layer and the buffer layer, the formation of a different phase of the dielectric layer, and the like can be easily avoided. Furthermore, if the same composition is used, it is possible to completely eliminate the decrease in effective relative permittivity of the buffer layer / dielectric layer composite layer due to the use of the buffer layer, and the effective voltage value applied to the light emitting layer can be reduced. Degradation can be avoided.
[0091]
As a result of detailed experiments by the present inventors, it has been recognized that the above-described effects are particularly effective under the following conditions.
[0092]
First, a buffer layer is formed on the surface of the lower electrode where there is a possibility that the dielectric layer and the lower electrode layer are in direct contact with each other by a solution coating and firing method. This buffer layer can prevent the occurrence of cracks in the solution-coated fired dielectric layer formed directly on the lower electrode, and eliminate the peeling of the dielectric layer and the peeling and defects of the lower electrode layer that accompany this peeling. . Accordingly, pinholes in the light emitting layer due to generation of particles and defects or disconnection in the lower electrode layer can be prevented, so that a high-quality and highly reliable EL element can be manufactured with a high yield. In particular, when manufacturing a high-definition display panel, the size of individual pixels is reduced and the line width of the lower electrode is also reduced, so the reliability of the lower electrode and the importance of particle prevention increase. In this case, the insertion of the buffer layer is particularly effective.
[0093]
Secondly, a high dielectric composition film in which the buffer layer is formed by sputtering is used. Since a high-density buffer layer can be formed by using a high dielectric constant composition film formed by sputtering, a mechanical clamping effect of the metal electrode is generated from a very thin film thickness of 10 nm, and solution coating and baking are performed. The crack generation of the dielectric first layer by the method can be suppressed. By using such a thin buffer layer and using a high dielectric constant composition, it is possible to minimize a decrease in the effective dielectric constant of the dielectric layer due to the buffer layer being interposed. Become.
[0094]
Thirdly, the high dielectric constant composition film uses a perovskite structure dielectric composition, and the relative dielectric constant is 100 or more. By setting the relative dielectric constant to 100 or more, it is possible to minimize a decrease in the effective dielectric constant of the dielectric layer due to the interposition of the buffer layer.
[0095]
Although it does not specifically limit as a material of a light emitting layer, Well-known materials, such as ZnS which doped Mn mentioned above, can be used. Among these, SrS: Ce is 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 light emission efficiency decreases. Specifically, although it depends on the light emitting material, it is preferably about 100 to 2000 nm.
[0096]
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 sputtering or vapor deposition or a chemical vapor deposition method such as CVD is preferable. Further, as described above, particularly when a light emitting layer of SrS: Ce is formed, H ₂ When the substrate temperature during film formation is maintained at 500 ° C. to 600 ° C. by an electron beam evaporation method in an S atmosphere, a high-purity light emitting layer can be obtained.
[0097]
After the light emitting layer is formed, heat treatment is preferably performed. Heat treatment may be performed after laminating the electrode layer, dielectric layer, and light emitting layer from the substrate side, or the electrode layer, dielectric layer, light emitting layer, insulator layer, or electrode layer is formed on the substrate side from the substrate side. Then, heat treatment (cap annealing) may be performed. The temperature of the heat treatment depends on the light emitting layer to be formed, but is preferably 300 ° C. or higher, more preferably 400 ° C. or higher, which is lower than the firing temperature of the dielectric layer. The treatment time is preferably 10 to 600 minutes. The atmosphere during the heat treatment includes air, N, depending on the composition and formation conditions of the light emitting layer. ₂ , He and Ar may be selected.
[0098]
The thin-film insulator layer (6) and / or (8) may be omitted as described above, but preferably has this.
[0099]
This thin-film insulator layer functions as a function of adjusting the electronic state of the interface between the light emitting layer and the dielectric layer to stabilize and improve electron injection into the light emitting layer, and this electronic state is The main purpose is to improve the positive / negative objectivity of the light emission characteristics during AC drive by constructing it on both sides, and it is necessary to consider the function of maintaining the dielectric strength that is the role of the light emitting dielectric layer Since there is no film thickness, the film thickness may be small.
[0100]
This thin-film insulator layer has a resistivity of 10 ⁸ Ω · cm or more, especially 10 ^Ten -10 ¹⁸ About Ω · cm is preferable. Further, it is preferably a substance having a relatively high relative dielectric constant, and the relative dielectric constant ε is preferably ε = 3 or more. As a constituent material of the thin film insulator layer, for example, silicon oxide (SiO 2 ₂ ), Silicon nitride (SiN), tantalum oxide (Ta ₂ O _Five ), Yttrium oxide (Y ₂ O _Three ), Zirconia (ZrO ₂ ), Silicon oxynitride (SiON), alumina (Al ₂ O _Three ), Etc. can be used. As a method for forming the thin film insulator layer, a sputtering method, a vapor deposition method, or a CVD method can be used. The film thickness of the thin film insulator layer is preferably about 10 to 1000 nm, particularly preferably about 20 to 200 nm.
[0101]
The transparent electrode layer is made of ITO or SnO having a thickness of 0.2 μm to 1 μm. ₂ (Nesa film), oxide conductive materials such as ZnO-Al, and the like are used. As a method for forming the transparent electrode layer, a known technique such as vapor deposition as well as sputtering may be used.
[0102]
Although the above-described EL element has only a single light emitting layer, the EL element of the present invention is not limited to such a configuration, and a plurality of light emitting layers may be stacked in the film thickness direction, A configuration may be adopted in which different types of light emitting layers (pixels) are combined and arranged in a matrix.
[0103]
As described above, the EL device of the present invention has extremely good smoothness on the surface of the dielectric layer on which the light emitting layer is laminated, has high withstand voltage, and has no defects. Therefore, a high-performance and high-definition display can be easily configured with high luminance and high luminance long-term reliability. Further, the manufacturing process is easy and the manufacturing cost can be kept low.
[0104]
【Example】
Examples of the present invention are specifically shown below and described in more detail.
On a 96% purity alumina substrate, as samples 1 to 9, an Au thin film to which a trace amount of additive was added was formed by sputtering to a thickness of 1 μm and stabilized by heat treatment at 850 ° C. This Au lower electrode layer was patterned into a large number of stripes having a width of 300 μm and a space of 30 μm by using a photoetching method.
[0105]
Similarly, on the alumina substrate, Herus RP2003 / 237-22% resinate gold paste was used as samples 10 and 11, and screen printing and drying were repeated in the same pattern as described above so that the film thickness after firing was 1 μm. It was. Thereafter, firing was performed at 850 ° C. for 20 minutes in an atmosphere supplied with sufficient air.
[0106]
A dielectric ceramic thick film was further formed on the substrate on which the lower electrode was formed by screen printing. As the thick film paste, ESL 4210C thick film dielectric paste was used, and screen printing and drying were repeated so that the film thickness after firing was 30 μm.
[0107]
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. The dielectric constant of this thick film alone was about 4000.
[0108]
Next, BaTiO _Three , SrTiO _Three , TiO ₂ Each thin film was formed on the substrate by a sputtering method to form each buffer layer.
[0109]
BaTiO _Three As a thin film formation condition, a magnetron sputtering apparatus was used, and BaTiO 3 was used. _Three Targeting ceramics, Ar gas 3Pa pressure, 13.56MHz High frequency power density 2W / cm ² Film formation was performed under the conditions of:
[0110]
The deposition rate at this time was about 5 nm / min, and a buffer layer having a thickness of 100 nm was obtained by adjusting the sputtering time. BaTiO formed at this time _Three The thin film was in an amorphous state, and the film density was 80 to 90%. The sputtered film had a relative dielectric constant of about 20. When this film was heat treated at 700 ° C., a relative dielectric constant of 500 was obtained. In addition, heat-treated BaTiO _Three It was confirmed by X-ray diffraction that the thin film had a perovskite crystal structure.
[0111]
SrTiO _Three As the conditions for forming the thin film, SrTiO _Three Using BaTiO as a target with ceramics _Three Same as thin film. The deposition rate was about 4 nm / min, and a buffer layer with a thickness of 100 nm was obtained by adjusting the sputtering time. SrTiO formed at this time _Three The thin film was in an amorphous state, and the film density was 80 to 90%. The relative dielectric constant of the sputtered film could not be measured because the film was highly conductive. When this film was heat-treated at 600 ° C., a relative dielectric constant of 200 to 300 was obtained. Also, heat-treated SrTiO _Three It was confirmed by X-ray diffraction that the thin film had a perovskite crystal structure. This film was heat-treated at a temperature of 600 ° C., but the results were the same even when heat-treated at a temperature of 500 to 700 ° C.
[0112]
TiO ₂ As a thin film formation condition, a magnetron sputtering apparatus is used and TiO 2 is used. ₂ Targeting ceramics, Ar gas 1Pa pressure, 13.56MHz High frequency power density 2W / cm ² Film formation was performed under the conditions of:
[0113]
The deposition rate at this time was about 2 nm / min, and a buffer layer having a thickness of 100 nm was obtained by adjusting the sputtering time. BaTiO formed at this time _Three The thin film was in an amorphous state, and the film density was 80 to 90%. Further, the relative dielectric constant of the sputtered film could not be measured because of the high conductivity of the film, but when this film was heat-treated at 600 ° C., a relative dielectric constant of 80 was obtained. This film was heat-treated at a temperature of 600 ° C., but the results were the same even when heat-treated at a temperature of 500 to 700 ° C.
[0114]
A dielectric layer was formed on these substrates using a solution coating and firing method. A PZT sol-gel solution prepared by the following method was prepared as a method for forming a dielectric layer by a solution coating and baking method, and used as a solution coating and baking method precursor solution. First, the operation of applying the precursor solution to the substrate on which the buffer layer was formed by spin coating and baking at 700 ° C. for 15 minutes was repeated a predetermined number of times.
[0115]
The basic sol-gel solution was prepared by heating and stirring 8.49 g of lead acetate trihydrate and 4.17 g of 1.3 propanediol for about 2 hours to obtain a transparent solution. Separately, 3.70 g of zirconium / normal propoxide 70 mass%, 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 Isopropoxide bisacetylacetonate 75 mass%, 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 prepare a brown transparent solution. By keeping this solution at 130 ° C. for several minutes, by-products were removed, and the mixture was further heated and stirred for 3 hours to prepare a PZT precursor solution.
[0116]
The viscosity of the PZT precursor solution was adjusted by diluting with n-propanol. The thickness of the dielectric layer per single layer was adjusted to about 0.7 μm per layer by adjusting the spin coating conditions and the viscosity of the sol-gel solution. Using the sol-gel solution as a PZT precursor solution, application and baking by spin coating were repeated four times to form a PZT dielectric layer having a thickness of about 3 μm.
[0117]
Further, the dielectric constant in the laminated structure of the thick ceramic dielectric layer and the PZT layer formed by the solution coating and firing method was about 2800 when it was assumed that the total film thickness did not change at 30 μm.
[0118]
About the obtained board | substrate with a PZT dielectric material layer (flattening layer), it evaluated about a crack, peeling, a disconnection rate, and a particle. The evaluation was based on visual observation except for disconnection, and the presence or absence of disconnection was determined using a HP3456A digital meter, and the resistance from one end to the other end of one electrode pattern was determined to be 1 MΩ or more. The results are shown in Table 1.
[0119]
[Table 1]

[0120]
3 to 8 show BaTiO formed by sputtering using the PZT sol-gel solution of this example. _Three It is SEM and an optical microscope photograph when the 1st dielectric layer is formed on the conditions which changed the film thickness of the buffer layer variously.
[0121]
Here, FIG. 3: Sample 1 (SEM photograph: long side = 500 μm), FIG. 6: Sample 2 (SEM photograph: long side = 250 μm), FIG. 7 Sample 3 (SEM photograph: long side = 250 μm), FIG. 8 sample 6 (SEM photograph: long side = 250 μm), FIG. 4: sample 10 (optical micrograph: long side = 1000 μm), and FIG. 3: sample 11 (optical micrograph: long side = 1000 μm).
[0122]
As is apparent from the figure, BaTiO _Three In the absence of the buffer layer, high density cracks occur, particularly in the electrode samples using Au resinate. BaTiO _Three When the buffer layer is 10 nm or more, the cracks are equally reduced, and at 100 nm, no cracks are generated.
[0123]
As is clear from Table 1, BaTiO _Three When the buffer layer was not provided, disconnection of the lower electrode occurred, and further generation of particles was confirmed.
[0124]
In contrast, BaTiO _Three When the buffer layer was 10 nm or more, peeling of the lower electrode was not observed, and when the film thickness was 100 nm, no cracks or particles were observed.
[0125]
Further, the effective dielectric constant of the buffer layer and the dielectric layer was hardly changed even when the buffer layer was present. This is because the buffer layer BaTiO _Three Even if the film is amorphous and has a low dielectric constant, the composition is a high dielectric constant dielectric composition, so that the upper dielectric layer is crystallized by high-temperature treatment when formed by a solution coating firing method, This is considered to increase the dielectric constant.
[0126]
Also, SrTiO with the same film thickness _Three Buffer layer and TiO ₂ Even when the buffer layer was used, no peeling of the lower electrode occurred and no generation of particles was observed.
[0127]
Next, EL elements were fabricated using the dielectric layer-coated substrates of Samples 1, 2, 3, 6, 8, 9, 10 and 11 in Table 1.
[0128]
The light-emitting layer was formed by a vacuum evaporation method using a ZnS vapor deposition source doped with Mn while being heated to 200 ° C. to a film thickness of 0.8 μm, and then heat-treated at 600 ° C. for 10 minutes in a vacuum. did.
[0129]
Next, Si as an insulator layer _Three N _Four An ITO thin film was sequentially formed as a thin film and an upper electrode layer by a sputtering method to obtain an EL element. At that time, the ITO thin film of the upper electrode layer was patterned into a stripe shape having a width of 1 mm by using a metal mask during film formation. The light emission characteristics were measured by extracting an electrode from the lower electrode and the upper transparent electrode of the obtained element structure and applying an electric field until the light emission luminance was saturated at a 1 kHz pulse width of 50 μs. Further, a predetermined number of each EL element was produced and evaluated.
[0130]
As a result, all samples had a saturation luminance of 7000 cd / m. ² However, in Samples 6 and 8, the emission threshold value was 160V, whereas in Sample 9, the emission threshold value increased to 170V. This is the TiO used in Sample 9 ₂ BaTiO of samples 6 and 8 whose dielectric constant is film _Three And SrTiO _Three This is probably because it is smaller than
[0131]
In Samples 1, 2, and 10, non-luminous pixels were generated due to disconnection of the lower electrode layer, and this was particularly noticeable in Sample 10. In Samples 1, 2, 3, and 10, abnormal light emission points and non-light emission points occurred in the light emitting portion (pixel). This is considered due to the formation of pinholes or thin portions of the light emitting layer in the light emitting layer due to the generation of particles.
[0132]
【The invention's effect】
As described above, according to the present invention, in the EL element in which the surface flatness of the thick ceramic dielectric layer is ensured by the sol-gel dielectric layer, peeling of the lower electrode layer generated by adding the sol-gel dielectric layer, It is possible to provide a highly reliable EL element which is free from defects and has no defects.
[Brief description of the drawings]
FIG. 1 is a partial schematic cross-sectional view showing a basic configuration of an EL element of the present invention.
FIG. 2 is a partial schematic cross-sectional view showing another basic configuration of the EL element of the present invention.
FIG. 3 is a drawing-substituting photograph in which the surface of a substrate with a PZT dielectric layer (flattening layer) is photographed.
FIG. 4 is a drawing-substituting photograph in which the surface of a substrate with a PZT dielectric layer (flattening layer) is photographed.
FIG. 5 is a drawing-substituting photograph in which the surface of a substrate with a PZT dielectric layer (flattening layer) is photographed.
FIG. 6 is a drawing-substituting photograph in which the surface of a substrate with a PZT dielectric layer (flattening layer) is photographed.
FIG. 7 is a drawing-substituting photograph in which the surface of a substrate with a PZT dielectric layer (flattening layer) is photographed.
FIG. 8 is a drawing-substituting photograph in which the surface of a substrate with a PZT dielectric layer (flattening layer) is photographed.
FIG. 9 is a partial schematic cross-sectional view showing a basic configuration of a conventional thin film EL element.
FIG. 10 is a partial schematic cross-sectional view showing a basic configuration of a conventional thick film EL element.
FIG. 11 is a graph showing a change in film thickness during firing of a conventional dielectric layer.
[Explanation of symbols]
1 Substrate
2 Lower electrode
3 Buffer layer
4 Thick film dielectric layer
5 Dielectric layer
6 Thin insulator layer
7 Light emitting layer
8 Thin insulator layer
9 Transparent electrode layer
10 AC power supply
11 Substrate
12 Lower electrode
14 Thick film dielectric layer
15 Dielectric layer
16 Thin insulator layer
17 Light emitting layer
18 Thin film insulator layer
19 Transparent electrode layer
20 AC power supply

Claims (6)

A substrate having electrical insulation;
A metal electrode layer formed on the substrate and having a pattern on the substrate;
A buffer layer formed on the metal electrode layer and having a thickness of 10 nm or more;
A first dielectric layer formed by firing powder on the buffer layer;
A second dielectric layer formed on the first dielectric layer by a solution coating firing method;
A light emitting layer formed directly or via an insulator layer on the second dielectric layer;
A transparent electrode layer formed directly on the light emitting layer or via an insulator layer;
With
The buffer layer extends over the metal electrode layer beyond an end of the first dielectric layer, and the second dielectric layer is at least partially from the end of the first dielectric layer. An EL element that protrudes in the lateral direction, and the protruding portion only contacts the buffer layer and does not contact the metal electrode layer. A substrate having electrical insulation;
A metal electrode layer formed on the substrate and having a pattern on the substrate;
A first dielectric layer formed by firing powder on the metal electrode layer;
A buffer layer formed on the first dielectric layer and having a thickness of 10 nm or more;
A second dielectric layer formed on the buffer layer by a solution coating firing method;
A light emitting layer formed directly or via an insulator layer on the second dielectric layer;
A transparent electrode layer formed directly on the light emitting layer or via an insulator layer;
With
The buffer layer extends over the metal electrode layer beyond an end of the first dielectric layer, and the second dielectric layer is at least partially from the end of the first dielectric layer. An EL element that protrudes in the lateral direction, and the protruding portion only contacts the buffer layer and does not contact the metal electrode layer. The buffer layer, EL element according to claim 1 or 2 is formed by sputtering. The EL device according to claim 1, wherein the buffer layer has a perovskite structure dielectric composition and has a relative dielectric constant of 100 or more. The EL element according to claim 1, wherein the buffer layer has a thickness of 100 nm or more. The buffer layer is made of alumina, zirconia, Ta ₂ O ₅ Insulating material selected from the above, or TiO ₂ The EL device according to claim 1, wherein the EL device is formed of a dielectric material selected from a pyrochlore dielectric, a Bi layered compound dielectric, and a perovskite structural dielectric.

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