JP4749536B2 - Thin film EL device and manufacturing method thereof - Google Patents

Description

【００８７】
表１中の膜構造とは膜厚×積層回数を表す。例えば試料４の膜構造は０．７μｍを６層積層した構造である。表１から明らかなように、本発明のバッファ層を介して誘電体層を形成した試料はバッファ層を形成することなく同じ構造の誘電体層を形成した比較例に対して高い平均耐圧を有している。また、多層状誘電体層の膜厚が４μｍ未満の試料３は平均耐圧が低く、下部電極膜厚に対し多層状誘電体層の膜厚が４倍以上無い試料４は平均耐圧が十分に得られていないことがわかる。また、この実施例ではバッファ層を形成後あらかじめ熱処理を行った後、溶液塗布焼成法により誘電体層を形成したが、あらかじめ熱処理を行うことなく溶液塗布焼成法により誘電体層を形成したものも誘電率ならびに耐圧は同等であった。このことは溶液塗布焼成法の工程における熱処理はバッファ層に対しても熱処理の効果が与えられことによる。
【００８８】
また、試料９〜１２および試料６を比較するとバッファ層が厚くなることにともなって平均耐圧が向上していることがわかる。図８，９，１０は、それぞれ試料１，１０，６の誘電体層表面の電子顕微鏡（ＳＥＭ）写真である。図より明らかなように、バッファ層を有していない試料１では無数のクラックが観察されているがバッファ層を形成した上に誘電体層を形成した試料６，１２では誘電体層のクラックの発生が抑制されていることがわかる。また、試料１でクラックの発生の核となる欠陥が試料１０では観察されるが試料６では欠陥が埋められておりわずかに痕跡のみが観察される。
基板をガラスとした試料１２はアルミナ基板を用いた同一の膜構造である試料６とほぼ同様の平均耐圧が得られている。さらに、バッファ層をＳｒＴｉＯ₃、ＴｉＯ₃とした試料１３，１４においても実用にされる２００Ｖ以上の平均耐圧が得られている。
【００８９】
表１の試料３〜１４と同様の構成として形成された誘電体層にを２００℃に加熱した状態でＭｎをドープしたＺｎＳ蒸着源を用い、ＺｎＳ発光体薄膜を厚さ０．８μｍ となるよう蒸着法により形成した後、真空中６００℃で１０分間熱処理した。
【００９０】
次に、第２薄膜絶縁体層として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薄膜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のストライプ上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、それぞれの薄膜ＥＬ素子を所定の個数ずつ作製し評価した。
【００９１】
その結果、試料３を用いた薄膜ＥＬ素子は、発光敷居値付近（１４０〜１６０Ｖ）の電圧を印加した時点で約半数の試料において絶縁破壊を起こし破壊した。また、試料４は作製した試料の約１割において最高輝度に達する前に絶縁破壊を起こした。この原因として平均耐圧が低かったことが考えられる。これに対し、その他の試料上に形成された薄膜ＥＬ素子は何れも最高輝度６０００〜１００００ｃｄ／ｍ²が得られ、かつその時の印加電圧でも絶縁破壊が発生しなかった。
（実施例２）
ソーダライムベース高耐熱ガラス基板（軟化点８２０℃）を用い、この基板上にスパッタリング法により薄膜下部電極層としてＡｇ／Ｐｄ（３０％）薄膜を０．５μｍの厚さに形成し、７００℃で熱処理を行って安定化した。この薄膜下部電極層をフォトエッチング法を用いて幅５００μｍ、スペース５０μｍの多数のストライプ状にパターニングした。
【００９２】
次にこの基板にスパッタリング法によりＳｒＴｉＯ₃薄膜を形成し、バッファ層とした。ＳｒＴｉＯ₃薄膜の形成条件は実施例１に示した条件と同様とし、５００℃で熱処理したところ、比誘電率２００の値が得られた。また、熱処理をしたＳｒＴｉＯ₃薄膜はペロブスカイト構造を有することがＸ線回折法により確認された。
【００９３】
この基板に溶液塗布焼成法を用いて誘電体層を形成した。溶液塗布焼成法による誘電体層の形成方法として、以下の方法で形成したゾルゲル液をＢａＴｉＯ₃前駆体溶液として基板にディップコーティング法にて塗布し、最高温度７００℃にて１０分間焼成することを所定回繰り返した。このとき１層当たりの誘電体層の膜厚は１．２μｍであった。
【００９４】
ＢａＴｉＯ₃前駆体溶液の作製方法としては、分子量６３万のＰＶＰ（ポリビニルピロリドン）を２−プロバノールに完全に溶解し、酢酸及びチタンテトライソプロポキシドを攪拌しながら添加し、透明な溶液を得た。この溶液に純水と酢酸バリウムの混合溶液を攪拌しながら滴下し、この状態で攪拌を続けながら所定時間のエージングを行った。各出発原料の組成比は、酢酸バリウム：チタンテトライソプロポキシド：ＰＶＰ：酢酸：純水：２−プロパノール＝１：１：０．５：９：２０：２０である。これによりＢａＴｉＯ₃前駆体溶液が得られた。
【００９５】
上記ＢａＴｉＯ₃前駆体溶液の塗布と焼成を繰り返すことにより表２に示す誘電体層を形成した。
【００９６】
【表２】

【００９７】
表２中の膜構造とは表１と同様に膜厚×積層回数を表す。表２から明らかなように、この実施例においても本発明のバッファ層を形成した後に誘電体層を形成した試料はバッファ層を形成することなく同じ構造の誘電体層を形成した比較例に対して高い平均耐圧を有している。
【００９８】
このようにして形成された試料２１〜２５に実施例１と同様に発光層、薄膜絶縁体層、上部透明電極を形成し薄膜ＥＬ素子を作製し、それぞれ所定の個数ずつ発光特性を評価したところいずれの薄膜ＥＬ素子においても最高輝度６０００〜１００００ｃｄ／ｍ²が得られた。
【００９９】
【発明の効果】
上記のように本発明の効果は明らかである。本発明によれば、従来の薄膜ＥＬ素子において問題とされた誘電体層に生じる欠陥、特に溶液塗布焼成法を用いて形成された誘電体層の焼成時のクラックの発生を抑制し、絶縁耐圧を向上させ、均一かつ信頼性の高い薄膜ＥＬ素子とその製造方法を高コスト化することなく提供することができる。
【図面の簡単な説明】
【図１】本発明の薄膜ＥＬ素子の構造を示す断面図である。
【図２】従来の薄膜ＥＬ素子の構造を示す断面図である。
【図３】従来の薄膜ＥＬ素子の構造を示す断面図である。
【図４】従来の薄膜ＥＬ素子の構造を示す断面図である。
【図５】従来の薄膜ＥＬ素子の誘電体層を形成する工程を示す断面図である。
【図６】従来の誘電体層のの焼結時における膜厚変化を示す図である。
【図７】従来の薄膜ＥＬ素子の断面の電子顕微鏡写真である。
【図８】比較例による薄膜ＥＬ素子の誘電体層の表面の電子顕微鏡写真である。
【図９】本発明による薄膜ＥＬ素子の誘電体層の表面の電子顕微鏡写真である。
【図１０】本発明による薄膜ＥＬ素子の誘電体層の表面の電子顕微鏡写真である。
【符号の説明】
１１ 基板
１２ 下部電極層
１０ バッファ層
１３ 多層状誘電体層
１７ 薄膜絶縁体層
１４ 発光層
１５ 薄膜絶縁体層
１６ 透明電極層
２１ 透明基板
２２ 透明電極層
２３ 薄膜透明第１絶縁体層
２４ 発光層
２５ 薄膜透明第２絶縁体層
２６ 電極層
３１ 基板
３２ 下部厚膜電極
３３ 厚膜誘電体層
３４ 発光層
３５ 薄膜絶縁体層
３６ 上部透明電極層
４１ 基板
４２ 下部電極層
４３ 多層状誘電体層
４４ 発光層
４５ 薄膜絶縁体層
４６ 透明電極層
５１ 基板
５２ 下部電極層
５３−１ 誘電体層第１層
５３−２ 誘電体層第２層
５３−３ 誘電体層第３層
５３−４ 誘電体層第４層
５７ クラック[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrically insulating substrate, an electrode layer having a pattern on the substrate, a thin film EL element having at least a structure in which a dielectric layer, a light emitting layer, and a transparent electrode layer are laminated on the electrode layer, and a method for manufacturing the same.
[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 using 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 a thin film 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, thin film EL elements have been widely used in recent years because of their high brightness and long life.
[0005]
FIG. 2 shows a structure of a typical double insulation type thin film EL element as a conventional thin film EL element. This thin film EL element is a transparent electrode having a predetermined stripe pattern made of ITO having a film thickness of about 0.2 μm to 1 μm on a transparent substrate (21) such as blue plate glass used for liquid crystal displays, PDPs and the like. A layer (22), a thin film transparent first insulator layer (23), a light emitting layer (24) having a thickness of about 0.2 μm to 1 μm, and a thin film transparent second insulator layer (25) are laminated, and further a transparent electrode The electrode layer (26) such as an Al thin film patterned in a stripe shape so as to be orthogonal to the layer (22) is formed, and the specific selected by the matrix composed of the transparent electrode layer (22) and the electrode layer (26) By selectively applying a voltage to the light emitter, the light emitter of the specific pixel emits light, and the emitted light is taken out from the substrate side. Such a thin-film insulator layer has a function of limiting the current flowing in the light-emitting layer, can suppress the dielectric breakdown of the thin-film EL element, and contributes to obtaining stable light-emitting characteristics. EL devices are widely used commercially.
[0006]
The thin film transparent insulator layers (23) and (25) are Y ₂ O _Three , Ta ₂ O _Five , Ai _Three N _Four , BaTiO _Three , Etc. are formed in a 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's works p1 to 10 include ZnS, Mn / CdSSe, etc. as materials for obtaining green light emission, such as ZnS: As materials for obtaining blue light emission, such as TbOF and 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, such a thin film EL element still has structural problems. In other words, since the insulator layer is formed of a thin film, there should be no defects 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 has a large area. It is difficult to destroy the light emitting layer due to a local decrease in withstand voltage. Since such defects become a fatal problem as a display device, the thin film EL element has become a big problem for 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 is defective, an electrically insulating ceramic substrate is used as a substrate in Japanese Patent Application Laid-Open No. 7-50197 and Japanese Patent Publication No. 7-44072. Instead, a thin film EL device using a thick film dielectric is disclosed. As shown in FIG. 3, this thin film EL device has a lower thick film electrode layer (32), a thick film dielectric layer (33), a light emitting layer (34), and a thin film insulator layer on a substrate (31) such as ceramic. (35) The upper transparent electrode layer (36) is laminated. Thus, unlike the structure of the thin-film EL element shown in FIG. 2, the transparent electrode layer is formed on the upper side in order to take out light emitted from the light emitter from the upper side opposite to the substrate.
[0012]
In this thin film EL element, the thick film dielectric layer is formed to have a thickness of several tens (m to several hundred μm, several hundreds to several thousand times that of the thin film insulator layer. There are very few dielectric breakdowns caused by defects formed, and there is an advantage that a high reliability and a high yield during manufacturing can be obtained. However, this problem is improved by using a high dielectric constant material for the dielectric layer.
[0013]
However, the light emitting layer formed on the thick film dielectric layer has a thickness of only several hundreds of nanometers, which is about 1/100 of the thick film dielectric layer. Therefore, the surface of the thick dielectric layer must be smooth at a level below the thickness of the light emitting layer, but it is difficult to sufficiently smooth the dielectric surface produced by the normal thick film process. there were.
[0014]
That is, since the thick film dielectric layer is essentially composed of ceramics using a powder raw material, a volume shrinkage of about 30 to 40% is usually required for dense sintering, but ordinary ceramics are sintered. In some cases, the thick film ceramics formed on the substrate cannot be shrunk in the in-plane direction because the thick film is constrained by the substrate. The volume can be contracted only in one dimension in the thickness direction. For this reason, the thick dielectric layer becomes essentially porous with insufficient sintering.
[0015]
Further, since the densification process is a ceramic solid-phase reaction of powder having a certain particle size distribution, abnormal sintering points such as abnormal crystal growth and formation of giant vacancies are likely to be formed. 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 sub-μm size or more even without the above defects.
[0016]
Thus, if the surface of the dielectric layer has a defect or if the film quality is porous or uneven, a light-emitting layer formed by vapor deposition or sputtering is formed uniformly on the surface following the surface shape. I can't do it. For this reason, since an electric field cannot be effectively applied to the light emitting layer portion formed on the non-flat portion of such a substrate, the effective light emitting area is reduced and light emission is caused by local nonuniformity of the film thickness. There is a problem that the layer partially breaks down to cause a decrease in luminance. Furthermore, since the film thickness greatly fluctuates locally, the electric field intensity applied to the light emitting layer varies greatly locally, and there is a problem that a clear light emission voltage threshold value cannot be obtained.
[0017]
For this reason, in the conventional manufacturing process, after the large unevenness | corrugation of the surface of the thick film dielectric layer was removed by grinding | polishing process, the operation | work of removing a further fine unevenness | corrugation by a sol gel process was required.
[0018]
However, it is technically difficult to polish a large-area substrate for a display or the like, which is a factor for increasing the cost. The addition of the sol-gel process was a factor that further increased the cost. In addition, when the thick film dielectric layer has an abnormal sintering point and large irregularities that cannot be completely removed by polishing, the addition of the sol-gel process cannot be dealt with, and this is a factor that decreases the yield. For this reason, it has been extremely difficult to form a dielectric layer free from light emitting defects with a thick film dielectric at low cost.
[0019]
In addition, since the thick film dielectric layer is formed by a ceramic powder material sintering process, its firing temperature is high. That is, the firing temperature is 800 ° C. or higher, usually 850 ° C., as in the case of ordinary ceramics, and a firing temperature of 900 ° C. or higher is required to obtain a particularly dense thick film sintered body. The substrate on which such a thick dielectric layer is formed is limited to an alumina ceramic or zirconia ceramic substrate due to problems of heat resistance and reactivity with the dielectric layer, and it is difficult to use an inexpensive glass substrate. When the ceramic substrate is used for a display, it is a necessary condition to have a large area and good smoothness. However, it is technically difficult to obtain a substrate having such a condition, which increases the cost. Met.
[0020]
Further, the metal film used as the lower electrode layer also needs to use an expensive noble metal such as palladium or platinum because of its heat resistance, which has been a factor in increasing the cost.
[0021]
In order to solve such problems, the present inventor repeats the solution coating and baking method as a dielectric layer a plurality of times instead of a conventional thick film dielectric or a thin film dielectric formed by sputtering or the like. Japanese Patent Application No. 2000-299352 proposed to form a multilayer dielectric layer thicker than the conventional thin film dielectric layer.
[0022]
The structure of a thin film EL element using the above multilayer dielectric layer is shown in FIG. This thin film EL element is a multilayer dielectric formed by repeating a solution coating and firing method a plurality of times on a lower electrode layer (42) having a predetermined pattern on a substrate (41) having electrical insulation. The light emitting layer (44), preferably the thin film insulator layer (45) and the transparent electrode layer (46) are laminated on the layer (43) and further on the dielectric layer.
[0023]
The multi-layered dielectric layer having such a structure can prevent a high insulation breakdown voltage, local insulation defects due to dust in the process, and remarkably good surface flatness as compared with a conventional thin film dielectric. It has the characteristic of being. Furthermore, since the thin film EL element using the multilayer dielectric layer can form the dielectric layer at a temperature of 700 ° C. or lower, it is possible to use a glass substrate that is less expensive than a ceramic substrate. is there.
[0024]
However, when such a solution coating firing method is used, a large number of cracks are likely to occur during firing in the first dielectric layer formed on the lower electrode. Since it is a location with a low withstand voltage and causes dielectric breakdown, it has been a practical problem.
[0025]
Next, a conventional process for forming a dielectric layer formed in a multilayer shape will be described with reference to FIG. In FIG. 5A, a lower electrode layer (52) patterned in a stripe shape on a substrate (51), and a first dielectric layer (53-1) is formed on the electrode layer by a solution coating and firing method.
[0026]
However, in this conventional structure forming process, cracks (57) are likely to be formed in the dielectric layer for some reason during firing after solution application, and this portion becomes a defect and becomes a defective point of insulation of the dielectric layer. . Such cracks are particularly likely to occur at a very high density in the first solution-coated fired dielectric layer formed on the metal electrode layer. Defects in the dielectric layer caused by such cracks, particularly defects formed on the electrodes, directly cause a decrease in the dielectric breakdown voltage of the dielectric layer, which is a fatal defect for the EL element.
[0027]
In FIG. 5B, the dielectric layer is formed in a multilayer shape by repeating the solution coating and firing method four times. Cracks generated during the formation of the first dielectric layer are filled with the second dielectric layer (53-2), and further, the third dielectric layer (54-3) and the fourth layer (54-4) are formed. ing. By repeating the solution coating / firing method in this manner, it is possible to suppress the dielectric breakdown voltage defect portion in the vicinity of the pattern edge portion of the lower electrode and the thickness reduction of the dielectric layer due to the defect in the dielectric layer.
[0028]
By using a multilayer dielectric layer formed by repeating the solution coating and firing method multiple times as a dielectric layer in this way, it is possible to suppress a decrease in breakdown voltage due to cracks occurring in the dielectric layer, but it is not sufficient There wasn't.
[0029]
[Problems to be solved by the invention]
It is an object of the present invention to suppress the occurrence of defects that occur in a dielectric layer, which has been a problem in conventional thin film EL devices, in particular, the generation of cracks during firing of a dielectric layer formed by using a solution coating and firing method, thereby reducing the withstand voltage. An object of the present invention is to provide a uniform and highly reliable thin film EL element and a manufacturing method thereof without increasing the cost.
[0030]
[Means for Solving the Problems]
The above-mentioned problems are solved by the present inventions (1) to (10) below.
(1) A thin film EL element having at least a structure in which a substrate having electrical insulation, an electrode layer having a pattern on the substrate, and a dielectric layer, a light emitting layer, and a transparent electrode layer are laminated on the electrode layer, A thin film EL element comprising a buffer layer on the electrode layer, and the dielectric layer being formed in a multilayer shape by repeating a solution coating and baking method a plurality of times on the buffer layer.
(2) The thin film EL element according to (1), wherein the buffer layer is a high dielectric constant film.
(3) The thin film EL element according to (1) or (2), wherein the buffer layer is a high dielectric constant film having a relative dielectric constant of 100 or more.
(4) The thin film EL element according to any one of (1) to (3), wherein the buffer layer is made of a perovskite structure dielectric.
(5) The thin film EL element according to any one of (1) to (3), wherein the buffer layer is formed by a sputtering method.
(6) The thin film EL element according to any one of (1) to (5), wherein a film thickness of the multilayer dielectric layer is 4 μm or more and 16 μm or less.
(7) The thin film EL element according to any one of (1) to (6), wherein the multilayer dielectric layer is formed by repeating the solution coating and firing method three times or more.
(8) A method of manufacturing a thin film EL device having at least a structure in which a substrate having electrical insulation, an electrode layer having a pattern on the substrate, and a dielectric layer, a light emitting layer, and a transparent electrode layer are laminated on the electrode layer. A method of manufacturing a thin film EL device, comprising: forming a buffer layer on the electrode layer; and forming the dielectric layer in a multilayer shape by repeating a solution coating and baking method on the buffer layer a plurality of times. .
(9) The method for manufacturing a thin film EL element according to (8), wherein the buffer layer is made of a high dielectric material.
(10) The method for manufacturing a thin film EL element according to (8) or (9), wherein the buffer layer is formed by a sputtering method.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor has found that the occurrence of cracks described above commonly occurs while trying various precursor solutions for solution coating and baking methods, and as a result of analyzing the cause, in the baking process common to solution coating and baking methods. It was a problem, and the cause was estimated as follows. Here, the precursor solution refers to a solution containing an intermediate compound produced by dissolving a raw material compound in a solvent in a solution coating and firing method such as a sol-gel method or a MOD method.
[0032]
The precursor solution used in the solution coating firing method is composed of a metal alkoxide or metal organic compound of a metal element constituting the dielectric layer, a complex of these metal element source and organic substance in the solution, and a volatile solvent. . In the film formation method of the solution coating and baking method, the precursor solution layer is formed on the substrate by applying the precursor solution to the substrate by a method such as spin coating, dip coating or spray coating, and then the solution layer is baked. In this step, an organic component in the precursor solution is removed, an ultrafine oxide phase is generated by the combination of the metal element and oxygen, and the oxide is sintered to form a dielectric.
[0033]
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 solution volatilizes to a temperature corresponding to its boiling point at a relatively low temperature (˜200 ° C.), and the film thickness of the solution layer of the applied solution is greatly reduced. At this time, the film thickness 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 not easily generated.
[0034]
When the temperature further increases (up to 400 ° C.), the organic component gradually evaporates from the complex of the metal element source and the organic substance (in the solution) due to decomposition or the like, and the film thickness is further reduced, and the film is mechanically stiff. Thus, a large tensile stress is generated as the film shrinks. At this time, the largest crack is likely to occur.
[0035]
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.
[0036]
It is presumed that the dielectric layer formed by the solution coating and baking method is usually formed in such a process, and naturally the composition of the precursor solution and the coating and baking conditions are set so that cracks do not occur in such a baking process. However, even when optimized in this manner, the cracks occur on the metal electrode layer at a very high frequency.
[0037]
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.
[0038]
As a result of estimating and considering the cause of crack occurrence in this way, the present inventor has provided a buffer layer between the dielectric layer and the metal electrode layer, and has a mechanical clamping effect on the surface of the metal electrode layer. It was found that the generation of cracks can be suppressed by applying the
[0039]
FIG. 1 is a structural diagram of a thin film EL element of the present invention. In the thin film EL device of the present invention, a solution coating and firing method is performed a plurality of times through a lower electrode layer (12) having a predetermined pattern on a substrate (11) having electrical insulation and a buffer layer (10) thereon. A multilayer dielectric layer (13) formed by repeating, and further a thin film insulator layer (17), a light emitting layer (14), a thin film insulator layer (15), and a transparent electrode layer (16) on the dielectric layer. Is a laminated structure. The thin film insulator layer (17) and the thin film insulator layer (15) may be omitted.
[0040]
The thin film EL element of the present invention can suppress the occurrence of cracks in the dielectric layer on the lower electrode layer due to the effect of the buffer layer. For this reason, the cause of the defect is dust or pattern edge caused by the manufacturing process. However, the occurrence of the defect due to such dust or the like is sufficiently small. It becomes possible to suppress by repeating. Therefore, it is possible to extremely reduce the occurrence of a portion having a low local withstand voltage that causes dielectric breakdown.
[0041]
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.
[0042]
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, blue plate glass, etc., or a metal substrate subjected to a brazing process Etc. can also be used.
[0043]
Of these, crystallized glass, high heat resistance glass, and blue plate glass, if matched with the firing temperature of the dielectric layer to be formed, are low in cost, surface property, flatness, and easy to produce a large area substrate. To preferred.
[0044]
The lower electrode layer is formed to have a plurality of stripe patterns, the line width is one pixel width, and the space between the lines becomes a non-light emitting region. Therefore, the space between the lines can be made as small as possible. Desirably, depending on the resolution of the target display, for example, a line width of 200 to 500 μm and a space of about 20 μm are required.
[0045]
The material of 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 having a precious metal such as a main component and a nonmetallic element added is desirable because oxidation resistance to an oxidizing atmosphere during firing of the dielectric layer can be easily obtained. Further, a base metal such as Ni or Cu can be used, and the oxygen partial pressure when firing the dielectric layer can be set within a range in which these non-metals are not oxidized. As a method for forming the lower electrode layer, a known technique such as sputtering, vapor deposition, or plating may be used.
[0046]
In the present invention, the dielectric layer is formed on the multilayer dielectric layer through the buffer layer by a solution coating firing method.
[0047]
The dielectric layer is preferably made of a material having a high dielectric constant and a high withstand voltage. Here, when the dielectric constants of the dielectric layer and the light emitting layer are e1 and e2, respectively, the film thicknesses are d1 and d2, and the voltage Vo is applied between the upper electrode layer and the lower electrode layer, the voltage applied to the light emitting layer V2 is represented by the following equation.
V2 / Vo = (e1 * d2) / (e1 * d2 + e2 * d1) ------ (1)
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)
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,
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)
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. For example, if the film thickness of the dielectric layer is 5 μm, the relative dielectric constant needs to be 50 to 200 to 450 or more.
[0048]
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 (Personal) dielectric materials having a perovskite structure such as 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 compounds represented by _x Ba _1-x Nb ₂ O ₆ , PbNbO ₆ A tungsten bronze type ferroelectric material typified by, etc. is used. 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.
[0049]
The dielectric layer is formed by a solution coating and firing method such as a sol-gel method or a MOD method. In the sol-gel method, generally, a predetermined amount of water is added to a metal alkoxide dissolved in a solvent, and a precursor solution of a sol having an MOM bond formed by hydrolysis and polycondensation reaction is applied to a substrate and baked. This is a method 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.
[0050]
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. 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. In addition, even a solution in which sub-μm dielectric particles and a dielectric precursor solution are mixed is included in the dielectric precursor solution of the present invention, and this solution is applied even when the solution is applied to a substrate and fired. It is included in the solution coating and baking method of the invention.
[0051]
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 to the method using powder sintering, it is possible to synthesize the dielectric at an extremely low temperature.
[0052]
For example, BaTiO _Three Taking a perovskite structure ferroelectric such as PZT or the like as an example, a normal ceramic powder sintering method requires a high-temperature process of 900 to 1000 ° C. or more, but if a solution coating and firing method is used, 500 to 700 ° C. is used. Can be formed at low temperatures
Thus, by forming a dielectric layer by a solution coating and firing method, it is possible to use high heat-resistant glass, crystallized glass, blue plate glass, etc. that could not be used from the viewpoint of heat resistance by the conventional thick film method. It becomes possible.
[0053]
Further, the thicknesses of the layers constituting the multilayer dielectric layer may be formed equal, or the layers may be formed with different thicknesses. Each layer may be made of the same material, or may be made of different materials.
[0054]
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. 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 a large 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 necessary. It is said.
[0055]
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. Among these, the sputtering method is a particularly preferable method 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 in a crystallized state and a thin film having a density of 80% or more even in an amorphous state. It can be easily formed.
[0056]
Next, the influence of the relative dielectric constant of the buffer layer will be described. When the relative dielectric constants of the dielectric layer and the buffer layer are e3 and e4, respectively, and the film thicknesses are d3 and d4, the effective relative dielectric constant e5 of the dielectric layer and the buffer layer composite is expressed by the following equation.
e5 = e3 × 1 / [1+ (e3 / e4) × (d4 / d3)] ------- (6)
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 desirable 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 (6)
In the case of 90% or more, e3 / d3 ≦ 9 × e4 / d4 -------- (7)
When 95% or more, e3 / d3 ≦ 19 × e4 / d4 -------- (8)
For example, assuming that the relative dielectric constant of the dielectric layer is 1000 and the film thickness is 8 μm, the ratio between the relative dielectric constant and the film thickness of the buffer layer is 1125 or more, preferably 2375 or more. Therefore, assuming that the thickness of the buffer layer is 0.1 μm, the relative dielectric constant needs to be 112.5 to 237.5 or more. If the thickness of the buffer layer is assumed to be 0.01 μm, the relative dielectric constant is 11. 25-23.75 or more is required.
[0057]
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, and according to the present inventors' experimental investigation, in the case of an oxide thin film formed by sputtering, the crack suppressing effect is sufficiently recognized from a thickness of 10 nm or more. As the thickness increased, the crack suppression effect was improved, and it became clear that the cracks on the electrode disappeared completely when the thickness was 100 nm or more. Therefore, the required film thickness is at least 10 nm or more, preferably 100 nm or more. This effect is similarly recognized up to a thickness of about 1 μm, but if the thickness is larger than that, overhang may occur as described later. Therefore, the upper limit is preferably 1 μm or less, more preferably 1/2 or less of the electrode layer thickness.
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-x (Zr _1-y Ti _y ) ₂ O _6-z 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.
[0058]
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.
[0059]
Usually, these materials can obtain a high dielectric constant by performing a heat treatment after film formation. In the present invention, heat treatment at about 500 to 700 ° C. is performed in the step of forming the dielectric layer by the solution coating and baking method. This heat treatment step can give the heat treatment effect to the buffer layer. Therefore, heat treatment may be performed in advance after forming the buffer layer. However, even if heat treatment is not performed, the buffer layer can have a high dielectric constant by a heat treatment step in the solution coating and firing method.
[0060]
Furthermore, in order to clearly explain the operation of the present invention, an electron micrograph of a case where the dielectric layer is not formed on the multilayer dielectric layer by the solution coating and baking method via the buffer layer according to the present invention but is formed by the sputtering method. Will be described. In FIG. 7, a 3 μm lower electrode layer is formed, and BaTiO 3 is sputtered on the patterned substrate. _Three It is an electron micrograph at the time of forming 8 micrometers of thin films. As is apparent from FIG. 6, when the dielectric layer is formed by sputtering, the surface of the dielectric film is formed in such a way as to emphasize the step of the substrate, so that the surface of the dielectric has significant irregularities and overhangs. . Such surface irregularities are recognized in the same way when the dielectric layer is formed by vapor deposition in addition to sputtering. It is impossible to form and use a functional thin film such as an EL light emitting layer on such a dielectric layer.
[0061]
That is, according to the present invention, by forming the solution coating and baking method on the lower electrode layer through the buffer layer a plurality of times, the crack of the first dielectric layer that has been generated on the lower electrode in the past can be prevented. In addition to being able to be suppressed by the effect of the conventional method, it is possible to completely cover defects caused by steps and dust in the lower electrode layer, which was not possible with a dielectric layer formed by a conventional method such as sputtering, by repeating the solution coating and firing method multiple times. Furthermore, the surface of the dielectric layer can be flattened and the portion having a weak withstand voltage can be extremely reduced.
[0062]
As a result of detailed experiments by the present inventor, the above effects were particularly recognized under the following conditions.
[0063]
First, the dielectric layer is formed on the lower electrode layer by repeating the solution coating and baking method a plurality of times through the buffer layer. This effect is as described above, and can solve the problem of crack generation in the first dielectric layer, which is particularly problematic. Furthermore, when the number of repetitions is 3 times or more, the film thickness of the defective portion caused by dust or the like in the single dielectric layer should be at least 2/3 or more of the average film thickness of the multilayer dielectric layer. Is possible. In general, the dielectric breakdown voltage design value of the dielectric layer is expected to have a margin of about 50% of the expected applied voltage, so it is possible to avoid problems such as dielectric breakdown even at local voltage drop portions caused by the above-mentioned defects. It becomes.
[0064]
Second, the buffer layer is made of a high dielectric constant film, particularly preferably a substance having a relative dielectric constant of 100 or more. By making the buffer layer a high dielectric constant film, it is possible to prevent the effective relative dielectric constant of the dielectric layer from being lowered due to the interposition of the buffer layer, and in particular, by setting the relative dielectric constant to 100 or more, the effective ratio of the dielectric layer It is possible to reduce the dielectric constant drop to a negligible range. Particularly preferably, the buffer layer is composed of a dielectric film having a perovskite structure as the high dielectric constant film. By making the buffer layer a dielectric film having a perovskite structure, the relative dielectric constant can be easily increased to 100 or more.
[0065]
Third, the buffer layer is formed by a sputtering method. Since a high-density buffer layer can be formed by sputtering, a mechanical clamping effect of the metal electrode is generated from a very thin region having a film thickness of 10 nm, and the generation of cracks in the first dielectric layer due to the solution coating and baking method is suppressed. be able to. By using such a thin buffer layer and using a high dielectric constant, it is possible to minimize a decrease in the effective relative dielectric constant of the dielectric layer due to the buffer layer interposed. .
[0066]
Fourth, the thickness of the multilayer dielectric layer is 4 μm or more and 16 μm or less. According to the inventor's study, the particle size of dust and the like generated in a process in a normal clean room is concentrated in the range of 0.1 to 2 μm, particularly around 1 μm, and the average film thickness is 4 μm or more, preferably 6 μm. In this way, the dielectric breakdown voltage of the dielectric layer defect due to defects such as dust can be set to 2/3 or more of the average breakdown voltage.
[0067]
When the film thickness is 16 μm or more, the number of repetitions of the solution coating and baking method increases excessively, resulting in an increase in cost. Furthermore, as shown in the formulas (3) to (5), when the film thickness of the dielectric layer is increased, it is necessary to increase the relative dielectric constant itself of the dielectric layer, for example, when the film thickness is 16 μm or more. The relative dielectric constant is 160 to 640 to 1440 or more. However, it is generally technically difficult to form a dielectric layer having a relative dielectric constant of 1500 or more by using a solution coating and firing method. In the present invention, since a dielectric layer having a high breakdown voltage and no defects can be easily formed, it is not necessary to form a dielectric layer of 16 μm or more. For this reason, the upper limit of the film thickness is 16 μm or less, preferably 12 μm or less.
[0068]
Also, by making the thickness of the dielectric layer at least four times the thickness of the lower electrode layer, it is possible to sufficiently improve the coverage of the pattern edge portion and the flatness of the surface of the dielectric layer caused by the patterning of the lower electrode layer. .
[0069]
Although the thin film insulator layer (17) may be omitted as described above on the multilayer dielectric layer, it is preferable to have it. This thin film insulator layer has a resistivity of 10 ⁸ Ωcm or more, especially 10 ^Ten -10 ¹⁸ About Ωcm is preferable. Moreover, it is preferable that it is a substance which has a comparatively high dielectric constant, As the dielectric constant (epsilon), Preferably (epsilon) = about 3 to 1000. 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 ), Strontium titanate (SrTiO) _Three ), Yttrium oxide (Y ₂ O _Three ), Barium titanate (BaTiO) _Three ), Lead titanate (PbTiO _Three ), Zirconia (ZrO ₂ ), Silicon oxynitride (SiON), alumina (Al ₂ O _Three ), Lead niobate (PbNb) ₂ O ₆ ) Etc. can be used. The thin film insulator layer is preferably composed of the same material as the multilayer dielectric layer. As a method for forming the thin film insulator layer, a sputtering method or a vapor deposition method can be used. The film thickness of the thin film insulator layer is preferably about 50 to 1000 nm, particularly preferably about 50 to 500 nm.
[0070]
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.
[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 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 formed by an electron beam evaporation method in an S atmosphere, a high-purity light emitting layer can be obtained.
[0072]
After the light emitting layer is formed, heat treatment is preferably performed. The heat treatment may be performed after laminating the electrode layer, the dielectric layer, and the light emitting layer from the substrate side, or the electrode layer, the dielectric layer, the light emitting layer, the thin film insulator layer, or the electrode layer on the substrate side from the substrate side. Heat treatment (cap annealing) may be performed after the formation. Although the temperature of the heat treatment depends on the light emitting layer to be formed, it is preferably 300 ° C. or higher, more preferably 400 ° C. or higher, and the dielectric layer firing temperature or lower, and the processing time is 10 to 600 minutes. The atmosphere during the heat treatment may be Air, N depending on the composition of the light emitting layer and the formation conditions. ₂ , Ar, He or the like may be selected.
[0073]
Although the thin film insulator layer (15) formed on the light emitting layer may be omitted as described above, it is preferable to have it. The thin-film insulator layer (15) is composed of the same material as the thin-film insulator layer (17) on the multilayer dielectric layer, but is preferably composed of the same material as the multilayer dielectric layer. The method for forming the thin film insulator layer (15) is the same as that for the thin film insulator layer (17). Moreover, as a film thickness of a thin film insulator layer (15), Preferably it is 50-1000 nm, Most preferably, it is about 50-500 nm.
[0074]
The transparent electrode layer is made of ITO or SnO having a film 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.
[0075]
Although the thin film EL element described above has only a single light emitting layer, the thin film 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. However, a configuration may be adopted in which different types of light emitting layers (pixels) are combined and arranged in a matrix.
[0076]
In addition, the thin film EL element of the present invention is easily identified by observation with an electron microscope. That is, in the present invention, there is a buffer layer on the electrode layer, and the dielectric layer is formed in a multilayer shape by repeating the solution coating and firing method on the buffer layer a plurality of times. In addition to the feature that the dielectric layer is formed in a multilayer shape, a difference in film quality from the dielectric layer formed using other methods is also observed. Furthermore, there is a feature that the smoothness of the surface of the dielectric layer is very good. In addition, since the generation of cracks in the first dielectric layer is suppressed by the effect of the buffer layer, a dielectric layer with few defects is formed from the first dielectric layer.
[0077]
As described above, the thin film EL element of the present invention has a very smooth surface of the dielectric layer on which the light emitting layer is laminated, has a high dielectric strength, and has extremely few defects. It can also be configured easily. Further, the manufacturing process is easy and the manufacturing cost can be kept low.
[0078]
【Example】
Examples of the present invention are specifically shown below and described in more detail.
(Example 1)
Using a 99.6% pure alumina substrate and a soda lime-based high heat-resistant glass substrate (softening point 820 ° C.), an Au thin film with a small amount of additive was formed on this substrate to a thickness of 1.2 μm by sputtering. And stabilized by heat treatment at 700 ° C. This Au thin film was patterned into a large number of stripes having a width of 300 μm and a space of 30 μm by using a photoetching method.
[0079]
Next, BaTiO _Three , SrTiO _Three , TiO ₂ A thin film was formed by sputtering to form a buffer layer.
[0080]
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, 13.56Mz high frequency electrode density 2W / cm ² Film formation was performed under the conditions of: At this time, the film formation rate was about 5 nm / min, and a buffer layer having a film thickness of 5 to 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%. Moreover, the relative dielectric constant of the sputtered film was about 20, and when this film was heat-treated at 600 ° C., a value of a relative dielectric constant of 400 was obtained. In addition, heat-treated BaTiO _Three It was confirmed by X-ray diffraction that the thin film had a perovskite structure. In this example, the heat treatment was performed at a temperature of 600 ° C., but the effect was the same even if the heat treatment was performed at a temperature of 500 to 700 ° C.
[0081]
SrTiO _Three As a thin film formation condition, a magnetron sputtering apparatus is used, and SrTiO is used. _Three Targeting ceramics, Ar gas 3Pa pressure, 13.56Mz high frequency electrode density 2W / cm ² Film formation was performed under the conditions of: At this time, the deposition rate was about 4 nm / min, and a buffer layer having 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%. In addition, 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 value of 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 structure. In this example, the heat treatment was performed at a temperature of 600 ° C., but the effect was the same even if the heat treatment was performed at a temperature of 500 to 700 ° C.
[0082]
TiO ₂ As a thin film formation condition, a magnetron sputtering apparatus is used and TiO 2 is used. ₂ Using ceramics as a target, Ar gas 1Pa pressure, 13.56Mz high frequency electrode density 2W / cm ² Film formation was performed under the conditions of: At this time, the deposition rate was about 2 nm / min, and a buffer layer having a thickness of 100 nm was obtained by adjusting the sputtering time. 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 value of a relative dielectric constant of 80 was obtained. In this example, the heat treatment was performed at a temperature of 600 ° C., but the effect was the same even if the heat treatment was performed at a temperature of 500 to 700 ° C.
[0083]
A dielectric layer was formed on this substrate using a solution coating firing method. As a method for forming a dielectric layer by a solution coating and baking method, a sol-gel solution of PZT prepared by the following method was prepared and used as a solution coating and baking method precursor solution. In the baking method, the precursor solution was applied to the substrate on which the buffer layer was formed by a spin coating method, and baking at 700 ° C. for 15 minutes was repeated a predetermined number of times.
[0084]
A basic PZT 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 wt% 1-propanol solution and 1.58 g of acetylacetone were heated and stirred in a dry nitrogen atmosphere for 30 minutes, and then 3.14 g of titanium diisopropoxide, A bisacetylacetonate 75 wt% 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.
[0085]
The viscosity of the PZT sol-gel solution was adjusted by diluting with n-propanol. The thickness of the dielectric layer per single layer was adjusted to 0.4 μm and 0.7 μm per layer by adjusting the spin coating conditions and the viscosity of the sol-gel solution. The dielectric layer shown in Table 1 was formed by repeating spin coating and baking using the sol-gel solution as a PZT precursor solution. Subsequently, a predetermined number of each sample was evaluated for pressure resistance, and an average pressure resistance was obtained.
[0086]
[Table 1]

[0087]
The film structure in Table 1 represents film thickness × number of laminations. For example, the film structure of Sample 4 is a structure in which six layers of 0.7 μm are stacked. As is clear from Table 1, the sample in which the dielectric layer is formed via the buffer layer of the present invention has a higher average breakdown voltage than the comparative example in which the dielectric layer having the same structure is formed without forming the buffer layer. is doing. Sample 3 with a multilayer dielectric layer thickness of less than 4 μm has a low average breakdown voltage, and sample 4 with a multilayer dielectric layer thickness not more than four times the lower electrode thickness has a sufficient average breakdown voltage. You can see that it is not. In this embodiment, after the buffer layer is formed and heat-treated in advance, the dielectric layer is formed by the solution coating and firing method. However, the dielectric layer is formed by the solution coating and firing method without performing the heat treatment in advance. The dielectric constant and withstand voltage were equivalent. This is because the heat treatment in the step of the solution coating and baking method gives the heat treatment effect to the buffer layer.
[0088]
Further, comparing Samples 9 to 12 and Sample 6, it can be seen that the average breakdown voltage is improved as the buffer layer becomes thicker. 8, 9, and 10 are electron microscope (SEM) photographs of the dielectric layer surfaces of Samples 1, 10, and 6, respectively. As is clear from the figure, innumerable cracks are observed in Sample 1 that does not have a buffer layer, but in Samples 6 and 12 in which a dielectric layer is formed on the buffer layer, cracks in the dielectric layer are observed. It turns out that generation | occurrence | production is suppressed. Further, a defect that becomes a nucleus of occurrence of cracks in the sample 1 is observed in the sample 10, but the defect is buried in the sample 6, and only a trace is observed.
The sample 12 with the substrate made of glass has almost the same average withstand voltage as the sample 6 having the same film structure using the alumina substrate. Furthermore, the buffer layer is made of SrTiO. _Three TiO _Three The average breakdown voltage of 200 V or more which is put into practical use is obtained also in the samples 13 and 14.
[0089]
Using a ZnS vapor deposition source doped with Mn in a state where the dielectric layers formed in the same manner as Samples 3 to 14 in Table 1 are heated to 200 ° C., the ZnS phosphor thin film has a thickness of 0.8 μm. After forming by vapor deposition, it was heat-treated at 600 ° C. for 10 minutes in a vacuum.
[0090]
Next, Si as the second thin film insulator layer _Three N _Four A thin film EL element was formed by sequentially forming an ITO thin film as a thin film and an upper electrode layer by a sputtering method. At that time, the ITO thin film of the upper electrode layer was patterned on a stripe having a width of 1 mm by using a metal mask 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 thin film EL element was produced and evaluated.
[0091]
As a result, the thin film EL element using the sample 3 was broken due to dielectric breakdown in about half of the samples when a voltage in the vicinity of the light emission threshold value (140 to 160 V) was applied. Sample 4 caused dielectric breakdown before reaching the maximum luminance in about 10% of the produced samples. This may be because the average breakdown voltage was low. On the other hand, the thin film EL elements formed on other samples all have a maximum luminance of 6000 to 10000 cd / m. ² In addition, dielectric breakdown did not occur even at the voltage applied at that time.
(Example 2)
Using a soda lime-based high heat-resistant glass substrate (softening point 820 ° C.), an Ag / Pd (30%) thin film having a thickness of 0.5 μm is formed on this substrate as a thin film lower electrode layer by sputtering, at 700 ° C. Heat treatment was performed for stabilization. This thin film lower electrode layer was patterned into a large number of stripes having a width of 500 μm and a space of 50 μm by using a photoetching method.
[0092]
Next, this substrate is sputtered by SrTiO. _Three A thin film was formed as a buffer layer. SrTiO _Three The conditions for forming the thin film were the same as those shown in Example 1. When heat treatment was performed at 500 ° C., a relative dielectric constant of 200 was obtained. Also, heat-treated SrTiO _Three It was confirmed by X-ray diffraction that the thin film had a perovskite structure.
[0093]
A dielectric layer was formed on this substrate using a solution coating firing method. As a method for forming a dielectric layer by a solution coating and firing method, a sol-gel solution formed by the following method is used as BaTiO. _Three Application as a precursor solution to the substrate by dip coating and baking for 10 minutes at a maximum temperature of 700 ° C. were repeated a predetermined number of times. At this time, the film thickness of the dielectric layer per layer was 1.2 μm.
[0094]
BaTiO _Three As a method for preparing the precursor solution, PVP (polyvinylpyrrolidone) having a molecular weight of 630,000 was completely dissolved in 2-propanol, and acetic acid and titanium tetraisopropoxide were added with stirring to obtain a transparent solution. A mixed solution of pure water and barium acetate was added dropwise to this solution while stirring, and aging was performed for a predetermined time while stirring was continued in this state. The composition ratio of each starting material is barium acetate: titanium tetraisopropoxide: PVP: acetic acid: pure water: 2-propanol = 1: 1: 0.5: 9: 20: 20. As a result, BaTiO _Three A precursor solution was obtained.
[0095]
BaTiO _Three Dielectric layers shown in Table 2 were formed by repeating the application and firing of the precursor solution.
[0096]
[Table 2]

[0097]
The film structure in Table 2 represents the film thickness × the number of laminations as in Table 1. As is apparent from Table 2, in this example, the sample in which the dielectric layer was formed after forming the buffer layer of the present invention was also compared with the comparative example in which the dielectric layer having the same structure was formed without forming the buffer layer. And has a high average withstand voltage.
[0098]
A light emitting layer, a thin film insulator layer, and an upper transparent electrode were formed on the samples 21 to 25 thus formed in the same manner as in Example 1 to produce a thin film EL device, and a predetermined number of each was evaluated for light emission characteristics. In any thin film EL element, the maximum luminance is 6000 to 10000 cd / m. ² was gotten.
[0099]
【The invention's effect】
As described above, the effect of the present invention is clear. According to the present invention, it is possible to suppress the occurrence of defects occurring in a dielectric layer, which has been a problem in conventional thin film EL elements, particularly cracks during firing of a dielectric layer formed by using a solution coating and firing method. Thus, it is possible to provide a uniform and highly reliable thin film EL element and its manufacturing method without increasing the cost.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of a thin film EL element of the present invention.
FIG. 2 is a cross-sectional view showing the structure of a conventional thin film EL element.
FIG. 3 is a cross-sectional view showing the structure of a conventional thin film EL element.
FIG. 4 is a cross-sectional view showing the structure of a conventional thin film EL element.
FIG. 5 is a cross-sectional view showing a process of forming a dielectric layer of a conventional thin film EL element.
FIG. 6 is a diagram showing a change in film thickness during sintering of a conventional dielectric layer.
FIG. 7 is an electron micrograph of a cross section of a conventional thin film EL element.
FIG. 8 is an electron micrograph of the surface of a dielectric layer of a thin film EL device according to a comparative example.
FIG. 9 is an electron micrograph of the surface of a dielectric layer of a thin film EL device according to the present invention.
FIG. 10 is an electron micrograph of the surface of a dielectric layer of a thin film EL device according to the present invention.
[Explanation of symbols]
11 Substrate
12 Lower electrode layer
10 Buffer layer
13 Multi-layer dielectric layer
17 Thin insulator layer
14 Light emitting layer
15 Thin insulator layer
16 Transparent electrode layer
21 Transparent substrate
22 Transparent electrode layer
23 Thin film transparent first insulator layer
24 Light emitting layer
25 Thin film transparent second insulator layer
26 Electrode layer
31 substrates
32 Lower thick film electrode
33 Thick film dielectric layer
34 Light emitting layer
35 Thin insulator layer
36 Upper transparent electrode layer
41 Substrate
42 Lower electrode layer
43 Multi-layer dielectric layers
44 Light emitting layer
45 Thin film insulator layer
46 Transparent electrode layer
51 substrates
52 Lower electrode layer
53-1 Dielectric Layer First Layer
53-2 Dielectric Layer Second Layer
53-3 Dielectric Layer 3rd Layer
53-4 Dielectric Layer 4th Layer
57 crack

Claims (12)

A substrate having an electrically insulating, and an electrode layer having a pattern on the substrate, a dielectric layer on the electrode layer, a light emitting layer and the transparent electrode layer are laminated, the A thin film EL device having at least ,
A buffer layer on the electrode layer;
The dielectric layer is formed in a multilayer shape by repeating the solution coating and firing method a plurality of times on the buffer layer ,
The thin film EL device , wherein the buffer layer has a density that does not cause volume shrinkage when a dielectric layer coated with a solution on the buffer layer is fired .   2. The thin film EL device according to claim 1, wherein the buffer layer is a high dielectric constant film.   3. The thin film EL device according to claim 1, wherein the buffer layer is a high dielectric constant film having a relative dielectric constant of 100 or more.   4. The thin film EL element according to claim 1, wherein the buffer layer is made of a perovskite structure dielectric.   The thin film EL device according to claim 1, wherein the buffer layer is formed by a sputtering method.   The thin film EL element according to claim 1, wherein the multilayer dielectric layer has a thickness of 4 μm to 16 μm.   7. The thin film EL device according to claim 1, wherein the multilayer dielectric layer is formed by repeating the solution coating and firing method three times or more. A substrate having an electrically insulating, and an electrode layer having a pattern on the substrate, a manufacturing method of the electrode layer dielectric layer on a thin film EL device having at least a light emitting layer and the transparent electrode layer are laminated, the Because
Forming a buffer layer on the electrode layer;
Forming the dielectric layer on the buffer layer in multiple layers by repeating a solution coating and firing method a plurality of times ;
Have
The method for manufacturing a thin film EL device , wherein the buffer layer has a density that does not cause volume shrinkage when a dielectric layer coated with a solution on the buffer layer is baked .   The method for manufacturing a thin film EL element according to claim 8, wherein the buffer layer is made of a high dielectric material.   The method of manufacturing a thin film EL element according to claim 8 or 9, wherein the buffer layer is formed by a sputtering method. The thin film EL element according to claim 1, wherein the electrode layer having the pattern is made of metal. The method for manufacturing a thin film EL element according to claim 8, wherein the electrode layer having the pattern is made of metal.

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