JP3958960B2 - EL element - Google Patents

Description

【０１３２】
その結果、非鉛系高誘電率誘電体層を有していない比較例では劣化が５５％と大きいが、本発明のスパッタリング法によって形成されたＢａＴｉＯ₃ 層を有するものは、０．２μm以上の膜厚で到達輝度が１２００cd/m² 前後となり、１４０Ｖ〜１５０Ｖの発光しきい値電圧が得られ、また劣化は小さかった。これに対し０．１μm以下では発光しきい値電圧が上昇すると共に到達輝度が低下し、更に著しい劣化を示した。ＳｒＴｉＯ₃ 層の場合は、わずかに発光しきい値電圧が増加する以外、同膜厚のＢａＴｉＯ₃ 層の場合とほぼ同様の特性が得られた。また、溶液塗布焼成法を用いたＢａＴｉＯ₃ 層の場合もわずかな発光しきい値電圧の増加以外、ほぼスパッタ法で得られた結果と同様の特性が得られた。
【０１３３】
ＴｉＯ₂ 膜の場合、同膜厚のＢａＴｉＯ₃ 膜と比較してしきい値電圧の増大と輝度の低下が見られるとともに劣化が大きかった。
【０１３４】
また、比較例であるＰＺＴ単独の構造では発光しきい値電圧の増大と輝度の低下、劣化が大きく、更に到達輝度付近の印加電圧で絶縁破壊が発生しやすかった。
【０１３５】
これらの結果から明らかなように、非鉛高誘電率ペロブスカイト層を非鉛系高誘電率誘電体層として用いた構造では、膜厚が０．１μm以上からその効果が認められ、特に０．２μm以上では顕著な発光輝度の増加としきい値電圧の低下、信頼性の向上が認められた。
【０１３６】
これは、鉛系誘電体層中の鉛成分の発光層への拡散が効果的に抑制された事を示している。
【０１３７】
また、ＴｉＯ₂ 層の場合、反応防止層としての効果は認められるが、ペロブスカイト層と比較して飽和輝度が低く、発光しきい値電圧が高く、劣化も大きかった。これはＴｉＯ₂ 膜がＰＺＴ層中の過剰鉛と反応し、部分的にＰｂＴｉＯ₃ 化したために反応防止層として完全に機能しなかったと推定される。
【０１３８】
〔実施例２〕
実施例１と同様に、前記下部電極を形成した基板上に、スクリーン印刷法により前記厚膜を形成し、前記ＰＺＴ前駆体溶液をスピンコーティングにて塗布することで実施例１と同様の厚膜セラミックス誘電体層と溶液塗布焼成法によるＰＺＴ層の積層構造体を作製した。
【０１３９】
次に、非鉛系高誘電率誘電体層として、上記鉛系誘電体層上に、スパッタリング法によって形成した（Ｓｒ_0.5Ｂａ_0.5）Ｎｂ₂Ｏ₆ 薄膜、及び実施例１と同様の方法で作成したＢａＴｉＯ₃ 膜、ＴｉＯ₂ 膜を、また比較例として非鉛系高誘電率誘電体層を有していない試料を作製した。
【０１４０】
（Ｓｒ_0.5Ｂａ_0.5）Ｎｂ₂Ｏ₆ 薄膜の形成条件として、マグネトロンスパッタ装置を用い、（Ｓｒ_0.5Ｂａ_0.5）Ｎｂ₂Ｏ₆ セラミックスをターゲットとして、Ａｒガス４Ｐａの圧力で、１３．５６ＭHz高周波電極密度２Ｗ／cm² の条件で成膜を行った。成膜時の基板温度は７５０℃とした。このときの成膜速度は約６nm／min であり、スパッタリング時間を調整することで膜厚４００ｎｍを得た。形成された（Ｓｒ_0.5Ｂａ_0.5）Ｎｂ₂Ｏ₆ 薄膜はタングステンブロンズ型に結晶化していた。さらに誘電特性を向上させるため、この膜を７５０℃空気中で熱処理したところ、比誘電率２００の値が得られた。膜の組成は化学量論比組成であった。
【０１４１】
次にこれらの誘電体基板上に青色発光体であるバリウムチオアルミネート蛍光体層を形成した。蛍光体層としてはＥＬ素子として安定に発光させるため、Ａｌ₂Ｏ₃ 膜、５０nm／ＺｎＳ膜、２００nm／バリウムチオアルミネート蛍光体薄膜、３００nm／ＺｎＳ膜、２００nm／Ａｌ₂Ｏ₃ 膜、５０nmの複合構造体を作製した。ここで、Ａｌ₂Ｏ₃ 膜は酸化雰囲気アニール時の蛍光薄膜への酸素導入量を制御するキャップ層、ＺｎＳは、予めイオウ過剰、または不足で形成することにより、蛍光薄膜中のイオウ量をアニール時に最適化するイオウ制御層として機能する。さらに、素子として形成された場合には、Ａｌ₂Ｏ₃ 膜は、絶縁膜、誘電体層としての機能ではなく、主に発光層への電子注入層として機能する。また、ＺｎＳ層は、注入された電子を加速する注入増強層としても機能する。
【０１４２】
バリウムチオアルミネート蛍光体成膜には、Ｅガン１台と、抵抗加熱セル１台を用いた多元蒸着法を用いた。Ｅｕを５原子％添加したＢａＳペレットを入れたＥＢ源、Ａｌ₂Ｓ₃ 粉を入れたセルをＨ₂Ｓを導入した真空槽内に設け、それぞれのＥＢ源、セルより同時に蒸発させ、５００℃に加熱し、回転させた基板上にバリウムチオアルミネート（ＢａＡｌＯＳ）：Ｅｕ層を形成した。各々の蒸発源の蒸発速度は、（ＢａＡｌＯＳ）：Ｅｕの成膜速度で１nm／sec になるように調節した。このときＨ₂Ｓガスを２０SCCM導入した。
【０１４３】
薄膜形成後７５０℃の大気中で２０分間アニールし、３００nm厚の蛍光体薄膜を得た。
【０１４４】
モニターとしてＳｉ基板上に形成した、バリウムチオアルミネート（ＢａＡｌＯＳ）：Ｅｕ薄膜を蛍光Ｘ線分析により組成分析した結果、原子比でＢａ：Ａｌ：Ｏ：Ｓ：Ｅｕ＝７．７１：１７．６８：８．２３：５１．４：０．４０であった。
【０１４５】
さらに、得られた構造体上にＩＴＯ酸化物ターゲットを用いＲＦマグネトロンスパッタリング法により、基板温度２５０℃で、膜厚２００nmのＩＴＯ透明電極を形成し、ＥＬ素子を完成した。
【０１４６】
このＥＬ素子の発光特性を評価した。得られたＥＬ構造のＩＴＯ上部電極、Ｐｄ上部電極から電極を引き出し、１ｋHzでパルス幅５０μＳの両極性電界を印加した。結果を表２に示す。
【０１４７】
【表２】

【０１４８】
表２から明らかなように、本発明の、ＢａＴｉＯ₃ 非鉛誘電体層を用いたＥＬ素子は、特に膜厚が３００nmで輝度２５０cd/m² 、膜厚４００nmで１４６０cd/m² と著しい高輝度が得られている。これに対し、膜厚２００nmでは９６cd/m² 、膜厚１００nmでは７５cd/m² と輝度は減少するが、その効果は認められた。
【０１４９】
また、本発明のＳＢＮ薄膜を用いた場合も７２０cd/m² とＢａＴｉＯ₃ 誘電体層を用いた場合よりは小さいが、その効果は認められた。
【０１５０】
さらにＴｉＯ₂ 薄膜を形成した場合も、膜厚２００nmでは４０cd/m₂ であるが、膜厚４００nmで８７０cd/m² と輝度はＢａＴｉＯ₃ の場合と比較して低下するが比較的高輝度が得られている。これは、実施例１と同様に、ＴｉＯ₂ 薄膜を用いた場合、反応防止層としての効果は認められるが、ＰＺＴ層中の過剰鉛と反応し、部分的にＰｂＴｉＯ₃ 化したために反応防止層として完全に機能しなかったことと、誘電率が約８０と他の非鉛誘電体層と比較して小さいために、十分な発光が得られなかったためと推定される。
【０１５１】
これに対し、比較例として、非鉛誘電体層を用いない以外全く同条件で作製したＥＬ素子では、１cd／m² とＢａＴｉＯ₃ 非鉛誘電体層を用いた場合と比較して全く輝度が得られておらず、本発明の非鉛誘電体層を積層したＥＬ素子の効果は明らかである。
【０１５２】
なお、本実施例で作成したEL素子の、青色発光は、CIE1931色座標（０．１２８５、０．１３５０）、発光スペクトルのピーク波長は４７３nmであり、極めて良好な青色発光であった。
【０１５３】
また、この実施例と比較例の試料をオージェ分析法により、膜の厚さ方向に不純物分析を行ったところ、比較例では、蛍光体薄膜領域からＰｂ元素が検出された。これは、多層の溶液塗布焼成法によって形成したＰＺＴ誘電体層中のＰｂ元素が拡散したためと考えられる。これに対し、実施例では、蛍光体薄膜領域からはPb元素は検出されなかった。
【０１５４】
これらの結果は、本発明の作用で述べた効果により、飛躍的にＥＬ素子の輝度が向上したものであり、本発明の効果は明らかである。
【０１５５】
【発明の効果】
以上のように、本発明によれば、従来のＥＬ素子において問題とされた誘電体層に生じる欠陥を解決し、特に鉛系誘電体材料を用いた誘電体層を形成したＥＬ素子の発光輝度の低下や輝度ムラ、発光輝度の経時変化を生じる問題を解決し、高い表示品質が得られるＥＬ素子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ＥＬ素子の基本構成を示した一部概略断面図である。
【図２】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。
【符号の説明】
１１ 基板
１２ 下部電極
１３ 鉛系厚膜誘電体層
１４ 鉛系誘電体層
１５ 非鉛系誘電体層
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. 2 shows a structure of a typical double-insulated thin film EL element as a conventional EL element. This thin-film EL element is a transparent film formed in 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 and PDPs. The electrode layer 22, the thin film transparent first insulator layer 23, the light emitting layer 24 having a film thickness of about 0.2 μm to 1 μm, and the thin film transparent second insulator layer 25 are laminated, and further orthogonal to the transparent electrode layer 22. A metal electrode layer 26 such as an Al thin film patterned in a stripe shape is formed. Then, by selectively applying a voltage to a specific light emitter selected by the matrix of the transparent electrode layer 22 and the metal electrode layer 26, the light emitter of the specific pixel is caused to emit light, and the light emission is taken out from the substrate 21 side. . Such thin-film insulator layers 23 and 25 have a function of limiting the current flowing in the light-emitting layer 24, can suppress 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 23 and 25 are usually Y₂O_Three , Ta₂O_Five , Al_ThreeN_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, p1-10, ZnS: TbOF as materials for obtaining green light emission, such as ZnS, Mn / CdSSe, etc. As a material for obtaining blue light emission, such as ZnS: Tb, SrS: Cr, (SrS: Ce / ZnS) n, Ca₂Ga₂S_Four: Ce, Sr₂Ga₂S_FourA 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, H₂It 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 to be solved. 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 containing lead is used. This problem is improved by using the dielectric layer.
[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 in volume three-dimensionally and become dense 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 JP-A-7-50197, a high dielectric constant layer such as lead zirconate titanate formed by a sol-gel method is laminated on the surface of a thick film dielectric made of lead niobate. A technique for 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, EL devices using such a conventional ceramic high dielectric constant thick film can be sintered at low temperature as a high dielectric constant thick film layer, and lead-based dielectrics in order to obtain characteristics such as high dielectric constant and high breakdown voltage. It is necessary to use a body layer. However, when a lead-based dielectric material is used as the dielectric layer material, the light emitting layer formed on the dielectric layer reacts with the lead component of the dielectric layer, resulting in a decrease in initial light emission luminance, luminance unevenness and light emission luminance. Changes over time have caused practical problems.
[0019]
[Problems to be solved by the invention]
An object of the present invention is to provide an EL element that solves a decrease in light emission luminance, uneven luminance, and changes with time of an EL element using a lead-based dielectric material, and can provide high display quality without increasing costs. It is to be.
[0020]
[Means for Solving the Problems]
  Such purposes are as follows (1) to (6).
  (1) Electrically insulating substrate and electrode layer on this substrate,Dielectric layer,Light emitting layer and transparent electrode layerIn this order from the side of the boardAn EL device having at least a laminated structure, wherein the dielectric layer isA lead-based thick film dielectric layer whose one surface is in contact with the electrode layer, a ferroelectric layer whose one surface is in contact with the other surface of the lead-based thick film dielectric layer, and a second surface of the ferroelectric layer; The lead-based thick film dielectric layer is composed of a lead-free dielectric layer in contact with one surface, and the lead-based thick film dielectric layer is a material selected from the group consisting of a perovskite structure dielectric, a composite perovskite relaxor ferroelectric, and a tungsten bronze dielectric The ferroelectric layer is formed of a perovskite structure ferroelectric containing at least lead in its composition, and the non-lead-based dielectric layer is formed of perovskite. A structural dielectric or a tungsten bronze dielectric, formed of a material that does not contain lead at least in its compositionEL element.
  (2)Ferroelectric layer and the lead-free dielectric layerIs formed by the solution coating firing method above (1EL element.
  (3)Ferroelectric layerIs formed by a solution coating and baking method,Lead-free dielectric layerIs formed by sputtering method(1)EL element.
  (4)Lead-free dielectric layer(1) to (1) in which the film thickness is more than 0.2 μm3The thin film EL element of any one of
  (5) Electrically insulating substrate and electrode layer on this substrate,Dielectric layer,Light emitting layer and transparent electrode layerIn this order from the side of the boardAn EL element having at least a laminated structure,The dielectric layer is composed of a lead-based thick film dielectric layer whose one surface is in contact with the electrode layer and a non-lead-based dielectric layer whose one surface is in contact with the other surface of the lead-based thick film dielectric layer. The lead-based thick film dielectric layer is formed of a material selected from the group consisting of a perovskite structure dielectric, a composite perovskite relaxor type ferroelectric, and a tungsten bronze type dielectric, and at least the composition thereof contains lead. The non-lead-based dielectric layer is a perovskite structure dielectric or a tungsten bronze dielectric, and is formed of a material that does not contain lead at least in its composition.
  (6)Lead-free dielectric layerIs formed by the solution coating firing method above (5EL element.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The EL element of the present invention is an EL element having a structure in which at least a substrate having electrical insulation and an electrode layer, a dielectric layer, a light emitting layer, and a transparent electrode layer are laminated on the substrate, The layer is formed by a first dielectric layer composed of a lead-based high dielectric constant thick film ceramic dielectric layer and a solution coating and firing method preferably formed to improve the flatness of the surface of the thick film ceramic. Or the second high dielectric constant layer is further constituted by a laminated structure of a lead-based high dielectric constant film and a lead-free high dielectric constant film, or the second The entire high dielectric constant layer is composed of a dielectric film containing no lead in its composition.
[0022]
Here, the lead-based dielectric is a dielectric containing lead in the composition, and the non-lead-based (high dielectric constant) dielectric layer is a dielectric not containing lead in the composition. In particular, the non-lead-based dielectric means a dielectric material having a perovskite crystal structure and having an element other than lead at the A site.
[0023]
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 12 formed in a predetermined pattern on a substrate 11 having electrical insulation, a lead-based thick film ceramic dielectric layer 13 thereon, and lead on the surface thereof. The system dielectric layer 14 and the lead-free dielectric layer 15 are laminated to constitute a multilayer dielectric layer.
[0024]
Further, 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 laminated dielectric layers 13, 14 and 15. The thin film insulator layers 16 and 18 may be omitted. The lower electrode layer 12 and the upper transparent electrode layer 19 are formed in stripes in directions orthogonal to each other. Then, the arbitrary lower electrode layer 12 and the upper transparent electrode layer 19 are selected, and light is emitted from a specific pixel by selectively applying a voltage from the AC power source / pulse power source 20 to the light emitting layer at the orthogonal part of both electrodes. Obtainable.
[0025]
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.
[0026]
Specific materials include alumina (Al₂O_Three), Quartz glass (SiO₂), Magnesia (MgO), forsterite (2MgO · SiO)₂), Steatite (MgO.SiO)₂), Mullite (3Al₂O_Three・ 2SiO₂), 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.
[0027]
In the case of a simple matrix type, the lower electrode layer is formed so as 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.
[0028]
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 having a precious metal such as a main component and a base metal element added is preferable because oxidation resistance to an oxidizing atmosphere during firing of the dielectric layer can be easily obtained. ITO and SnO₂(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. As a method for forming the lower electrode layer, a known technique such as sputtering, vapor deposition, or plating may be used.
[0029]
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.
[0030]
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.
[0031]
The conditions for the binder removal treatment performed before firing may be normal.
[0032]
The firing atmosphere may be appropriately determined according to the type of the thick dielectric layer, but when firing in an oxidizing atmosphere, ordinary firing may be performed.
[0033]
The holding temperature during firing may be appropriately determined according to the type of the dielectric 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.
[0034]
Moreover, you may anneal-treat as needed.
[0035]
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.
[0036]
V2 / Vo = (e1 * d2) / (e1 * d2 + e2 * d1) ------ (1)
[0037]
Assuming that the relative dielectric constant of the light emitting layer is e2 = 10 and the film thickness is d2 = 1 μm,
[0038]
V2 / Vo = e1 / (e1 + 10 × d1) ------- (2)
[0039]
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,
[0040]
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)
[0041]
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.
[0042]
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.
[0043]
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.
[0044]
Various materials are conceivable as such a high dielectric constant thick film material, but it is necessary to have a high dielectric constant ceramic composition that can be formed at a low temperature in consideration of the heat resistance limitation of the substrate material.
[0045]
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 2₂ And CuO, Bi₂O_Three , Fe₂O_Three Since a liquid phase is formed at a low temperature of about 700 ° C. to 800 ° C. between them, etc., firing is easy at a low temperature and a high dielectric constant is easily obtained._xTi_1-x) O_ThreePerovskite structure dielectric materials such as Pb (Mg_1/3Ni_2/3) O_ThreeComposite perovskite relaxor type ferroelectric materials represented by PbNbO₆A tungsten bronze type ferroelectric material represented by the above is preferably used.
[0046]
Examples of the perovskite type material include Pb-based perovskite compounds such as PZT (lead zircon titanate) and PLZT (lead lanthanum zirconate titanate).
[0047]
Of the perovskite materials, Pb-based perovskite compounds are generally represented by the chemical formula ABO._Three It is represented by Here, A and B each represent a cation. A is Pb, and a part thereof may be substituted with one or more of Ba, Ca and Sr. B is preferably one or more selected from, for example, Ti, Zr, Hf, Ta, Sn and Nb.
[0048]
Specific examples include Pb-based perovskite compounds such as PZT and PLZT containing Pb. Further, these A site and B site may be partially substituted with the above elements. PZT is PbZrO._Three -PbTiO_Three It is a solid solution of the system. The PLZT is a compound in which La is doped into PZT, and ABO_Three (Pb_1-xLa_x ) (Zr_1-yTi_y ) O_Three Indicated by
[0049]
Tungsten bronze type materials include lead niobate, PBN (lead barium niobate), PbNb₂O₆ , PbTa₂O_Five , PbNb_FourO₁₁ Examples thereof include tungsten bronze type oxides.
[0050]
Such a tungsten bronze type material is preferably a tungsten bronze type material described in Landoit-Borenstein Vol. 16 of the ferroelectric material collection. Tungsten bronze type materials generally have the chemical formula A_yB_FiveO₁₅ It is represented by Here, A and B each represent a cation. A is Pb, and a part thereof may be substituted with one or more elements selected from Mg, Ca, Ba, Sr, Rb, Tl, rare earth and Cd. B is preferably at least one selected from Ti, Zr, Ta, Nb, Mo, W, Fe and Ni.
[0051]
Specifically, (Ba, Pb) Nb₂O₆ , PbNb₂ O₆ , PbTa₂O₆ , PbNb_FourO₁₁, PbNb₂O₆ Tungsten bronze oxides such as lead niobate and the like, and solid solutions thereof are preferable.
[0052]
As a composite perovskite relaxor ferroelectric material, PFN: Pb (Fe_1/2Nb_1/2) O_Three , PFW: Pb (Fe_1/3W_2/3) O_Three , PMN: Pb (Mg_1/3Ni_2/3) O_Three , PNN: Pb (Ni_1/3Nb_2/3) O_Three , PMW: Pb (Mg_1/2W_1/2) O_Three , PT: PbTiO_Three , PZ: PbZrO_Three , PZN: Pb (Zn_1/3Nb_2/3) O_Three , Ferroelectric materials such as lead lanthanum zirconate titanate PLZT, Proceedings of 1990 Ultrasonic Symposium 711-720 pages Shrout and other “Relaxor Ferroelectric Materials” and Japanese Journal of Applied Physics, Vol. 28, No. 4 (1989) Pp. 653-661, April 1994) Other modified “Large Piezoelectric Effect Induced by Direct Current Bias in PMN: PT Relaxor Ferroelectric Ceramics” modified lead magnesium niobate Pb (Mg_1/3Nb_2/3) O_Three-PbTiO_Three Doped or modified relaxors such as modified PMN or PMN-PT can be used.
[0053]
If these materials are used, a dielectric layer having a relative dielectric constant of 1000 to 10000 can be easily formed 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.
[0054]
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.
[0055]
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.
[0056]
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 precursor solution by dissolving a metal salt of a carboxylic acid having an MO bond in an organic solvent, coating the substrate, and baking it. 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.
[0057]
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.
[0058]
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.
[0059]
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.
[0060]
Therefore, the thickness of the dielectric layer formed by the solution coating and firing method is preferably 0.5 μm or more, more preferably 1 μm or more, and further preferably 2 μm or more in order to sufficiently flatten the unevenness of the thick film surface. .
[0061]
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)
[0062]
e5 = e3 × 1 / [1+ (e3 / e4) × (d4 / d3)] ------- (6)
[0063]
If this equation is transformed,
[0064]
e4 / d4 = e3 * e5 / (d3 * (e3-e5)) ------- (7)
[0065]
From the above discussion, the effective relative dielectric constant of the entire laminated dielectric layer by adding the high dielectric constant dielectric layer formed by the solution coating and firing method is preferably 1200 when the thickness of the thick film layer is 30 μm. 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 firing method is 277. The above is necessary, and if the dielectric constant of the thick film dielectric layer is 3000, the ratio is 900.
[0066]
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. Desirably, at least 250 or more, preferably 500 or more.
[0067]
As described above, the high dielectric constant layer formed by the solution coating and baking method needs to have a large film thickness and a high dielectric constant. In consideration of consistency with the lead-based thick film dielectric layer and low-temperature synthesis. Conventionally, a ferroelectric material having a perovskite structure such as PZT is mainly used.
[0068]
By the way, when synthesizing a lead-based dielectric ceramic thick film, it is widely known that the starting composition needs to be a lead-excess composition. In order to sinter lead-based dielectric ceramic thick film at a low temperature of 800 ° C. to 900 ° C., it is essential to add a sintering aid that forms a liquid phase at this temperature, As described above, the sintering aid uses a low-temperature liquid phase formation reaction between lead oxide and other oxide-based materials, and the lead component may evaporate during sintering. .
[0069]
In addition, when forming a dielectric layer having a lead-based perovskite structure such as PZT by a solution coating firing method, it is often necessary to add an excessive amount of lead component (about 5% to 20%) more than in the case of ceramics. Are known.
[0070]
In the case of the solution coating firing method, the reason why a more excessive lead component is necessary is that the lead component evaporates during firing, and in addition to the effect of preventing lead from becoming insufficient and suppressing crystal growth, the lead excess component has a low melting point composition part. Because of its structure, it has the effect of facilitating material diffusion during crystal growth and enabling reaction at a low temperature, and because it reacts at a low temperature compared to ordinary ceramics, it grows dielectric compared with ceramics. There is a tendency for excessive lead components to be incorporated into the body crystal grains, and the diffusion distance of excess lead components is small, and more lead components are necessary to maintain a sufficient lead excess state at each site of crystal growth It is understood that
[0071]
For this reason, a dielectric layer formed of a lead-based dielectric with an excessive amount of lead component added contains a large amount of excess lead component in the state of lead oxide in addition to the lead component incorporated in the crystal structure in the layer. It is the feature that contains.
[0072]
Such an excessive lead component easily deposits from the inside of the dielectric layer due to a heat load after the formation of the dielectric layer, particularly a heat load in a reducing atmosphere. In particular, the formation of metallic lead due to reduction of lead oxide tends to occur under a heat load in a reducing atmosphere. When a light emitting layer as described later is formed directly on such a dielectric layer, reaction of the lead component with the light emitting layer and light emission. This leads to contamination of the movable metal lead ions in the layer, and has a significant adverse effect on the decrease in light emission luminance and long-term reliability.
[0073]
In particular, metallic lead ions have a high ion migration property, and as a mobile ion within the light emitting layer to which a high electric field is applied, have a significant effect on the light emission characteristics, and thus have a particularly large effect on long-term reliability.
[0074]
In addition, even if lead oxide is not reduced to metallic lead by a reducing atmosphere in particular, if a lead oxide component is contained inside the light emitting layer, lead oxide is reduced and released as metal ions by electron impact due to a high electric field inside the light emitting layer. It adversely affects reliability.
[0075]
In addition to the formed lead-based dielectric layer, the EL device of the present invention further has a non-lead-based high dielectric constant dielectric layer at least on the outermost surface layer. Here, the lead-free dielectric layer refers to a dielectric layer formed of a dielectric material that does not substantially contain Pb. Specifically, it is a dielectric material such as a perovskite type or a tungsten bronze type, and in the case of the perovskite type, it is a dielectric material having an element other than lead, preferably other than monovalent, at the A site. Specifically, the A site contains one or more of Ba, Sr, Ca, and Cd, and the B site contains one or more of Ti, Zr, Sn, and Hf. .
[0076]
More specifically, for example, the following materials and a mixture of two or more of the following materials are suitable.
[0077]
(A) Of the perovskite materials, BaTiO_Three And SrTiO_Three Compounds such as are generally represented by the chemical formula ABO_Three It is represented by Here, A and B each represent a cation. A is preferably one or more selected from Ca, Ba, Sr and Cd, and B is preferably one or more selected from Ti, Zr and Hf.
[0078]
Specifically, CaTiO_Three , SrTiO_Three , BaTiO_Three , BaZrO_Three , CaZrO_Three , SrZrO_Three , CdHfO_Three , CdZrO_Three , SrSnO_Three And solid solutions thereof. In order to adjust the characteristics of these compounds, a part of the composition thereof may be substituted with the above elements, or a trace amount of preferably a trivalent element may be added.
[0079]
(B) Tungsten bronze type materials include tungsten bronze type oxides represented by SBN (strontium barium niobate), and solid solutions thereof. In order to adjust the characteristics of these compounds, a part of the composition thereof may be substituted with the above elements, or a trace amount of preferably a trivalent element may be added.
[0080]
This lead-free high dielectric constant dielectric layer can suppress the diffusion of the lead component from the lead-based dielectric layer to the light emitting layer, and can prevent the adverse effects that occur in the light emitting layer due to the excess lead component.
[0081]
Here, the influence on the dielectric constant of the dielectric layer by adding this lead-free dielectric layer will be considered again. When the relative dielectric constants of the lead-based dielectric layer and the lead-free dielectric layer are e6 and e7, respectively, and the total film thickness of each layer is d6 and d7, the lead-based dielectric layer and the lead-free dielectric layer as a whole The effective relative dielectric constant e8 of is expressed by the following equation.
[0082]
e8 = e6 × 1 / [1+ (e6 / e7) × (d7 / d6)] ------- (8)
[0083]
The effective relative dielectric constant of the lead-based dielectric layer / lead-free dielectric layer composite layer due to the addition of the lead-free dielectric layer is reduced by the relative dielectric constant between the dielectric layer and the light-emitting layer. In view of the relationship with the effective voltage applied to the dielectric layer, it is necessary that it be small, and it is preferable that the relative dielectric constant of the composite layer is at least 90%, preferably 95% or more of the dielectric layer alone. . Therefore, from equation (6)
[0084]
In the case of 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 relative dielectric constant of the lead-based dielectric layer is 2700 and the film thickness is 30 μm, the ratio of the relative dielectric constant to the film thickness of the non-lead dielectric layer is 810 or more, preferably 1710 or more. Therefore, assuming that the film thickness of the lead-free dielectric layer is 0.2 μm, the relative dielectric constant needs to be 162 to 342 or more, and if it is assumed to be 0.4 μm, the relative dielectric constant needs to be 324 to 684 or more.
[0086]
The thickness of the lead-free dielectric layer is preferably larger for the purpose of preventing lead diffusion, and is preferably more than 0.2 μm, more preferably 0.4 μm or more in the experimental study by the present inventor. If there is no problem of a decrease in effective relative dielectric constant, it may be thicker.
[0087]
Even if the thickness of the lead-free dielectric layer is 0.2 μm or less, a certain degree of lead diffusion prevention effect can be obtained, but minute surface defects and surface roughness of the lead-based dielectric layer, dust caused by the manufacturing process, etc. It is easily affected by local surface roughness due to adhesion, and it is difficult to obtain a good anti-diffusion effect, and there is a risk of causing a partial decrease in luminance or deterioration of the light emitting layer due to local diffusion of lead components. is there.
[0088]
For this reason, it is preferable that the lead-free dielectric layer is thick, and the relative dielectric constant required for the lead-free dielectric layer is at least 100, preferably 200 or more, more preferably 400 or more.
[0089]
For example, in the above example, when the relative dielectric constant of the lead-based dielectric layer is 2700 and the film thickness is 30 μm, the relative dielectric constant is about 7._ThreeN_FourConsidering the case where the film is formed to have a thickness of 0.4 μm, the effective relative dielectric constant is 440 from the equation (8), and the relative dielectric constant is about 25 Ta.₂O_FiveEven when the film is formed to have a thickness of 0.4 μm, the effective relative dielectric constant is significantly reduced to 1107, and the effective voltage applied to the light emitting layer is greatly reduced. Therefore, when such a lead-free dielectric layer is used As a result, the driving voltage of the EL element is remarkably increased and the practicality is greatly reduced.
[0090]
In contrast, high dielectric constant materials, such as TiO with a relative dielectric constant of about 80₂When the film is formed to have a thickness of 0.4 μm, the effective relative permittivity is greatly improved to 1862. Further, when a material having a relative permittivity of 200 is used, an effective relative permittivity of 2288 is obtained, and a material having a relative permittivity of 400 is further obtained. Is used, the effective relative permittivity is 2477, which can obtain characteristics of 90% or more when there is almost no lead-free dielectric layer.
[0091]
TiO with a relative dielectric constant of about 80₂As a lead-free high dielectric constant dielectric material with a relative dielectric constant exceeding 100 to 1000 or more, for example, as described above, BaTiO_Three, SrTiO_Three, CaTiO_Three, BaSnO_Three, CdHfO_Three Perovskite structure dielectrics such as Ba_1-xSr_xTiO_ThreeA solid solution between these materials is preferred.
[0092]
By using the lead-free dielectric layer having the perovskite structure in this way, it becomes possible to easily obtain the effect of preventing diffusion of the lead component of the present invention into the light emitting layer while minimizing the decrease in effective dielectric constant. .
[0093]
By the way, according to the study by the present inventor, when using such a perovskite structure lead-free dielectric layer, it is important that the composition has a ratio of A site atoms of the perovskite structure to 1 or more with respect to B site atoms. It is.
[0094]
That is, as described above, the perovskite structure lead-free dielectric material can contain lead ions at the A site in terms of crystal structure, for example, BaTiO._ThreeTaking the composition as an example, BaTiO_ThreeWhen the layer is formed, the starting composition is Ba_1-xTiO_3-xWhen Ba, which is an A-site atom, is deficient with respect to Ti, which is a B-site atom, BaTiO_ThreeThe lead-based dielectric layer forming the layer has an excessive lead component, so this BaTiO_ThreeThe excess lead component replaces the Ba defect site of the layer, and (Ba_1-xPb_x) TiO_ThreeWill form a layer. In this state, BaTiO_ThreeWhen the light emitting layer is formed on the layer, since the light emitting layer is in direct contact with the lead component, a sufficient lead diffusion preventing effect cannot be obtained.
[0095]
For this reason, the composition of the perovskite structure lead-free dielectric layer is preferably at least on the A site side from the stoichiometric composition. In addition, as can be inferred from this explanation, since the lead-free dielectric material of perovskite structure can replace the lead component in the crystal structure, even if the composition is changed from the stoichiometric composition to the A-site excess side, the lead-based material A portion near the interface with the dielectric layer may slightly react with the lead component. For this reason, it is preferable that the film thickness of the lead-free dielectric layer is not less than a certain value, and this film thickness is 0.1 [mu] m or more, preferably more than 0.2 [mu] m, according to an experimental study by the inventors.
[0096]
Also, SBN (Sr_1-xBa_x Nb₂O₆ In the case of a tungsten bronze type dielectric represented by the same formula as in the case of the perovskite type dielectric, its composition is generally expressed by the chemical formula A_xB_FiveO₁₅ Since it is possible to substitute Pb as the A ion, it is desirable that the cation located at A be equal to or higher than the stoichiometric ratio.
[0097]
Thus, as a method for forming the lead-free dielectric layer by sufficiently controlling its composition, it is preferable to use a sputtering method or a solution coating firing method because of its high controllability of the composition.
[0098]
The lead-free dielectric layer formed by sputtering can easily form a thin film with the same composition as the target composition, and it can easily form a dense thin film that can be expected to prevent diffusion of lead components at a higher density. This is a preferable film forming method because it can be used.
[0099]
In addition, the solution coating and baking method can form a dielectric layer whose composition is controlled more strictly than the sputtering method by controlling the preparation ratio of the precursor solution, and the dielectric formed by the solution coating and baking method. It is advantageous that the effect of planarizing the unevenness of the underlayer, which is a characteristic of the layer, can be obtained. In particular, if a high dielectric constant equivalent to that of a lead-based dielectric layer formed by a solution-coating and firing method formed on a base can be obtained, this lead-based dielectric layer is omitted, and a non-lead formed by a solution-coating and firing method. It is effective that only the lead-based dielectric layer can serve as both a flat surface unevenness of the lead-based thick film ceramic dielectric layer and a lead diffusion preventing effect.
[0100]
The combination of the lamination of the lead-based dielectric layer and the non-lead-based high dielectric constant dielectric layer formed on the lead-based thick film ceramic dielectric layer of the present invention has a lead-free high dielectric constant dielectric on the outermost surface. Any body layer may be used, and these layers may be alternately stacked, and the outermost layer may be a lead-free high dielectric constant dielectric layer. If such a configuration is adopted, the lead-free dielectric layer in which the excessive lead component existing in the lead-based dielectric layer is alternately laminated can be effectively prevented from diffusing to each other, and the outermost surface can be further improved. The lead component diffusion preventing effect of the located lead-free high dielectric constant dielectric layer is improved. With such a configuration, when forming a lead-free high dielectric constant dielectric layer using a sputtering method, the film surface becomes uneven when a thick layer, which is a problem with the sputtering method, is formed. It is effective to avoid the problem.
[0101]
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 and a barium thioaluminate phosphor layer which is a blue light emitter are particularly preferable because excellent characteristics can be obtained. The thickness of the light emitting layer is not particularly limited, but if it is too thick, the driving voltage increases, and if it is too thin, the light emission efficiency decreases. Specifically, although it depends on the light emitting material, it is preferably about 100 to 2000 nm.
[0102]
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, H₂When 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.
[0103]
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 in the case of SrS: Ce, it is preferably 500 ° C. to 600 ° C. or higher, lower than the firing temperature of the dielectric layer, and the processing time is 10 to 600 minutes. The atmosphere during the heat treatment is preferably in Ar.
[0104]
As described above, the conditions for forming a light emitting layer capable of obtaining excellent characteristics such as SrS: Ce and barium thioaluminate phosphors are film formation at a high temperature of 500 ° C. or higher in a vacuum or in a reducing atmosphere, A subsequent high-temperature heat treatment step under atmospheric pressure is required, and in the conventional technology, problems due to reaction and diffusion between the lead component of the dielectric layer and the light-emitting layer cannot be avoided, whereas in the EL device of the present invention, the light-emitting layer This is particularly effective because it can completely prevent the adverse effects caused by the lead component.
[0105]
The thin-film insulator layer (16) and / or (18) may be omitted as described above, but preferably has this.
[0106]
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 The film thickness may be small because there is no such film.
[0107]
This thin-film insulator layer has a resistivity of 10⁸Ω · cm or more, especially 10^Ten-10¹⁸About 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 2₂), Silicon nitride (SiN), tantalum oxide (Ta₂O_Five), Yttrium oxide (Y₂O_Three), Zirconia (ZrO₂), Silicon oxynitride (SiON), alumina (Al₂O_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.
[0108]
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.
[0109]
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.
[0110]
As described above, the EL element 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, is free from defects, and has excessive dielectric layers, which has been a problem in the past. Since damage to the light-emitting layer due to the lead component can be completely prevented, 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.
[0111]
【Example】
Examples of the present invention are specifically shown below and described in more detail.
[Example 1]
A commercially available Ag—Pd paste was printed on a 99.6% purity alumina substrate by screen printing so that the film thickness after firing was 3 μm and fired at 850 ° C. This 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.
[0112]
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.
[0113]
The thick film paste is Pb (Mg_1/3Nb_2/3) O_Three It is based on a perovskite-based dielectric composition and contains excess lead oxide as a sintering aid.
[0114]
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.
[0115]
A PZT dielectric layer, which is a lead-based 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 produced by the following method is applied as a PZT precursor solution to a substrate by a spin coating method, and baking at 700 ° C. for 15 minutes is repeated a predetermined number of times. It was.
[0116]
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 wt% 1-propanol solution and 1.58 g of acetylacetone were heated and stirred in a dry nitrogen atmosphere for 30 minutes, and 3.14 g of titanium diisopropoxy was added thereto. A 75 wt% 2-propanol solution of de bisacetylacetonate 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.
[0117]
This precursor solution was diluted with n-propanol to adjust the concentration, and a PZT layer having a thickness of 2 μm was formed on the thick film by repeating application and baking by spin coating a plurality of times.
[0118]
The PZT layer formed under these conditions contained a lead component in excess of about 10% with respect to the stoichiometric composition. The relative dielectric constant of this PZT film alone was 600.
[0119]
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.
[0120]
Next, as a lead-free high dielectric constant dielectric layer, BaTiO formed on the lead dielectric layer by a solution coating and firing method_Three Film, BaTiO formed by sputtering method_Three Film and SrTiO_Three Film, TiO₂ As a comparative example, a sample having no lead-free high dielectric constant dielectric layer was prepared.
[0121]
BaTiO_ThreeAs a thin film formation condition, a magnetron sputtering apparatus was used, and BaTiO 3 was used._ThreeUsing ceramics as a target, with Ar gas pressure of 4 Pa, 13.56 MHz, high frequency power density 2 W / cm² Film formation was performed under the conditions of: At this time, the film formation rate was about 5 nm / min, and the film thickness of 50 nm to 400 nm was obtained by adjusting the sputtering time. BaTiO formed at this time_Three The thin film was in an amorphous state, and when this film was heat-treated at 700 ° C., a value of a relative dielectric constant of 500 was obtained. In addition, heat-treated BaTiO_Three It was confirmed by X-ray diffraction that the thin film had a perovskite structure. This BaTiO_Three The composition of the film was a 5% excess composition of Ba with respect to the stoichiometric composition.
[0122]
SrTiO_ThreeAs a thin film formation condition, a magnetron sputtering apparatus is used, and SrTiO is used._Three Using ceramics as a target, with Ar gas pressure of 4 Pa, 13.56 MHz, high frequency power density 2 W / cm² Film formation was performed under the conditions of: At this time, the deposition rate was about 4 nm / min, and a film thickness of 400 nm was obtained by adjusting the sputtering time. SrTiO formed at this time_Three The thin film was in an amorphous state, and when it was heat-treated at 700 ° C., a value of a relative dielectric constant of 250 was obtained. Also, SrTiO that has been heat-treated at a temperature of 500 ° C. or higher._Three It was confirmed by X-ray diffraction that the thin film had a perovskite structure. In addition, this SrTiO_Three The composition of the thin film was a 3% excess composition with respect to the stoichiometric composition.
[0123]
TiO₂ 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 at 1 Pa pressure, 13.56 MHz, high frequency power density 2 W / cm² Film formation was performed under the conditions of: At this time, the deposition rate was about 2 nm / min, and a film thickness of 400 nm was obtained by adjusting the sputtering time. When this film was heat-treated at 600 ° C., a relative dielectric constant of 76 was obtained.
[0124]
BaTiO by solution coating and baking method_Three The film is formed by using a sol-gel solution formed by the following method with BaTiO_Three The precursor solution was applied to the substrate by a spin coating method, the temperature was increased stepwise every 200 ° C. up to a maximum temperature of 700 ° C., and firing for 10 minutes at the maximum temperature was repeated a predetermined number of times.
[0125]
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_ThreeA precursor solution was obtained.
[0126]
BaTiO_Three By applying and baking the precursor solution, a BaTiO film with a thickness of 0.5 μm is obtained._Three A dielectric layer was formed. The relative dielectric constant of this film was 380, and the composition matched the stoichiometric composition.
[0127]
This BaTiO_Three The film is formed on a PZT film with a thickness of 2 μm and 1.5 μm formed by the solution coating and baking method, and is formed directly on the thick film ceramic substrate with a thickness of 2 μm without forming the PZT film. Also made.
[0128]
On the substrate on which the thick ceramic dielectric layer, the lead-based dielectric layer, and the lead-free high-dielectric-constant dielectric layer formed as described above are stacked, a light-emitting layer of SrS: Ce is formed by an electron beam evaporation method.₂In the S atmosphere, the substrate temperature during film formation was maintained at 500 ° C. After forming the light emitting layer, heat treatment was performed in vacuum at 600 ° C. for 30 minutes.
[0129]
Next, Si as an insulator layer_ThreeN_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 1 mm wide stripe 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.
[0130]
As evaluation items, emission threshold voltage, saturation luminance, and deterioration of luminance reached after 100 hours of continuous emission were evaluated.
[0131]
[Table 1]

[0132]
As a result, in the comparative example having no lead-free high dielectric constant dielectric layer, the deterioration is as large as 55%, but the BaTiO formed by the sputtering method of the present invention_Three Those having a layer have a film thickness of 0.2 μm or more and an ultimate luminance of 1200 cd / m.² The emission threshold voltage of 140V to 150V was obtained, and the deterioration was small. On the other hand, when the thickness is 0.1 μm or less, the emission threshold voltage is increased and the luminance reached is lowered, and further remarkable deterioration is shown. SrTiO_Three In the case of the layer, except that the emission threshold voltage slightly increases, the BaTiO of the same film thickness_Three Almost the same characteristics as in the case of the layer were obtained. In addition, BaTiO using a solution coating firing method_Three In the case of the layer, the same characteristics as those obtained by the sputtering method were obtained except for a slight increase in the light emission threshold voltage.
[0133]
TiO₂ In the case of a film, the same thickness of BaTiO_Three Compared with the film, an increase in threshold voltage and a decrease in luminance were observed and the deterioration was large.
[0134]
In addition, in the structure of PZT alone as a comparative example, the emission threshold voltage is increased, the luminance is decreased, and the deterioration is large. Furthermore, dielectric breakdown is likely to occur at an applied voltage near the ultimate luminance.
[0135]
As is clear from these results, in the structure using the lead-free high-permittivity perovskite layer as the lead-free high-permittivity dielectric layer, the effect is recognized from a thickness of 0.1 μm or more, particularly 0.2 μm. As described above, a remarkable increase in emission luminance, a decrease in threshold voltage, and an improvement in reliability were observed.
[0136]
This indicates that the diffusion of the lead component in the lead-based dielectric layer to the light emitting layer was effectively suppressed.
[0137]
TiO₂ In the case of the layer, the effect as the reaction preventing layer was recognized, but the saturation luminance was low, the emission threshold voltage was high, and the deterioration was large as compared with the perovskite layer. This is TiO₂ The film reacts with excess lead in the PZT layer and partially PbTiO_Three It is presumed that it did not function completely as a reaction preventing layer because
[0138]
[Example 2]
As in Example 1, the thick film is formed on the substrate on which the lower electrode has been formed by screen printing, and the PZT precursor solution is applied by spin coating, which is the same as in Example 1. A laminated structure of a ceramic dielectric layer and a PZT layer by a solution coating firing method was produced.
[0139]
Next, a lead-free high dielectric constant dielectric layer was formed on the lead-based dielectric layer by sputtering (Sr_0.5Ba_0.5Nb₂O₆ Thin film and BaTiO prepared by the same method as in Example 1_Three Film, TiO₂ As a comparative example, a sample having no lead-free high dielectric constant dielectric layer was prepared.
[0140]
(Sr_0.5Ba_0.5Nb₂O₆ As a thin film formation condition, a magnetron sputtering apparatus is used, and (Sr_0.5Ba_0.5Nb₂O₆ Using ceramics as the target, Ar gas at 4 Pa pressure, 13.56 MHz high-frequency electrode density 2 W / cm² Film formation was performed under the conditions of: The substrate temperature during film formation was set to 750 ° C. The film formation rate at this time was about 6 nm / min, and a film thickness of 400 nm was obtained by adjusting the sputtering time. Formed (Sr_0.5Ba_0.5Nb₂O₆ The thin film was crystallized into a tungsten bronze type. Further, when this film was heat-treated in air at 750 ° C. in order to improve the dielectric characteristics, a value of a relative dielectric constant of 200 was obtained. The composition of the film was a stoichiometric composition.
[0141]
Next, a barium thioaluminate phosphor layer as a blue light emitter was formed on these dielectric substrates. As a phosphor layer, in order to emit light stably as an EL element, Al₂O_Three Film, 50 nm / ZnS film, 200 nm / barium thioaluminate phosphor thin film, 300 nm / ZnS film, 200 nm / Al₂O_Three A film, 50 nm composite structure was prepared. Where Al₂O_Three The film is a cap layer that controls the amount of oxygen introduced into the fluorescent thin film during annealing in an oxidizing atmosphere, and the sulfur control layer that optimizes the amount of sulfur in the fluorescent thin film during annealing by forming ZnS in advance in the presence or absence of excess or insufficient sulfur. Function as. Further, when formed as an element, Al₂O_Three The film mainly functions as an electron injection layer into the light emitting layer, not as an insulating film or a dielectric layer. The ZnS layer also functions as an injection enhancement layer that accelerates injected electrons.
[0142]
For the deposition of the barium thioaluminate phosphor, a multi-source deposition method using one E gun and one resistance heating cell was used. EB source containing BaS pellets with 5% Eu added, Al₂S_Three H with powdered cell₂A barium thioaluminate (BaAlOS): Eu layer was formed on a substrate which was provided in a vacuum chamber into which S was introduced and was simultaneously evaporated from each EB source and cell, heated to 500 ° C., and rotated. The evaporation rate of each evaporation source was adjusted to be 1 nm / sec at the deposition rate of (BaAlOS): Eu. At this time H₂20 SCCM of S gas was introduced.
[0143]
After forming the thin film, it was annealed in the atmosphere at 750 ° C. for 20 minutes to obtain a phosphor thin film having a thickness of 300 nm.
[0144]
The composition of barium thioaluminate (BaAlOS): Eu thin film formed on a Si substrate as a monitor was analyzed by X-ray fluorescence analysis. As a result, Ba: Al: O: S: Eu = 7.71: 17.68 in atomic ratio. : 8.23: 51.4: 0.40.
[0145]
Further, an ITO transparent electrode having a film thickness of 200 nm was formed at a substrate temperature of 250 ° C. by an RF magnetron sputtering method using an ITO oxide target on the obtained structure, thereby completing an EL element.
[0146]
The light emission characteristics of this EL element were evaluated. Electrodes were drawn from the obtained ITO upper electrode and Pd upper electrode of EL structure, and a bipolar electric field with a pulse width of 50 μS was applied at 1 kHz. The results are shown in Table 2.
[0147]
[Table 2]

[0148]
As is apparent from Table 2, the BaTiO of the present invention._Three An EL element using a lead-free dielectric layer has a film thickness of 300 nm and a luminance of 250 cd / m.² 1460cd / m at 400nm thickness² A remarkably high brightness is obtained. In contrast, at a film thickness of 200 nm, it is 96 cd / m.² , 75cd / m at 100nm thickness² The brightness decreased, but the effect was recognized.
[0149]
Further, when the SBN thin film of the present invention is used, it is 720 cd / m.² And BaTiO_Three The effect was observed although it was smaller than when the dielectric layer was used.
[0150]
TiO₂ Even when a thin film is formed, it is 40 cd / m at a film thickness of 200 nm.₂ However, 870 cd / m at a film thickness of 400 nm² And the brightness is BaTiO_Three As compared with the case of, a relatively high luminance is obtained. This is similar to Example 1 in that TiO₂ When a thin film is used, the effect as a reaction preventing layer is recognized, but it reacts with excess lead in the PZT layer and partially PbTiO._Three This is presumably because the layer did not function completely as an anti-reaction layer because of the formation of a sufficient amount of light, and because it had a dielectric constant of about 80 compared with other lead-free dielectric layers, sufficient light emission could not be obtained.
[0151]
On the other hand, as a comparative example, in an EL device manufactured under exactly the same conditions except that no lead-free dielectric layer is used, 1 cd / m² And BaTiO_Three Luminance is not obtained at all as compared with the case of using the lead-free dielectric layer, and the effect of the EL element in which the lead-free dielectric layer of the present invention is laminated is clear.
[0152]
Note that the EL device produced in this example had blue light emission of CIE1931 color coordinates (0.1285, 0.1350) and a peak wavelength of the emission spectrum of 473 nm, which was very good blue light emission.
[0153]
Further, when the samples of this example and the comparative example were subjected to impurity analysis in the film thickness direction by Auger analysis, in the comparative example, Pb element was detected from the phosphor thin film region. This is presumably because the Pb element in the PZT dielectric layer formed by the multilayer solution coating firing method diffused. In contrast, in the examples, no Pb element was detected from the phosphor thin film region.
[0154]
These results show that the luminance of the EL element is drastically improved by the effect described in the operation of the present invention, and the effect of the present invention is clear.
[0155]
【The invention's effect】
As described above, according to the present invention, the defects generated in the dielectric layer, which is a problem in the conventional EL element, are solved, and in particular, the light emission luminance of the EL element in which the dielectric layer using the lead-based dielectric material is formed. Can be provided without increasing the cost, by solving the problems that cause deterioration of brightness, uneven brightness, and changes in emission brightness over time, and providing high display quality.
[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 a basic configuration of a conventional thin film EL element.
[Explanation of symbols]
11 Substrate
12 Lower electrode
13 Lead-based thick film dielectric layer
14 Lead-based dielectric layer
15 Lead-free 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)

An EL element having at least a structure in which an electrically insulating substrate and an electrode layer , a dielectric layer , a light emitting layer, and a transparent electrode layer are laminated on the substrate in this order from the substrate side ;
The dielectric layer includes a lead-based thick film dielectric layer whose one surface is in contact with the electrode layer , a ferroelectric layer whose one surface is in contact with the other surface of the lead-based thick film dielectric layer, and the ferroelectric Consisting of a lead-free dielectric layer with one surface in contact with the other surface of the body layer,
The lead-based thick film dielectric layer is formed of a material selected from the group consisting of a perovskite structure dielectric, a composite perovskite relaxor type ferroelectric, and a tungsten bronze type dielectric, and at least a composition thereof containing lead. ,
The ferroelectric layer is formed of a perovskite structure ferroelectric containing at least lead in its composition,
The EL element in which the non-lead-based dielectric layer is a perovskite structure dielectric or a tungsten bronze type dielectric and does not contain lead at least in its composition . The EL device according to claim 1, wherein the ferroelectric layer and the lead-free dielectric layer are formed by a solution coating firing method. The EL device according to claim 1, wherein the ferroelectric layer is formed by a solution coating firing method , and the lead-free dielectric layer is formed by a sputtering method. The thin film EL element according to claim 1, wherein a film thickness of the lead-free dielectric layer is more than 0.2 μm. An EL element having at least a structure in which an electrically insulating substrate and an electrode layer , a dielectric layer , a light emitting layer, and a transparent electrode layer are laminated on the substrate in this order from the substrate side ;
The dielectric layer is a laminate of a lead-based thick film dielectric layer whose one surface is in contact with the electrode layer and a non-lead-based dielectric layer,
The lead-based thick film dielectric layer is formed of a material selected from the group consisting of a perovskite structure dielectric, a composite perovskite relaxor type ferroelectric, and a tungsten bronze type dielectric, and at least a composition thereof containing lead. ,
The EL element in which the non-lead-based dielectric layer is a perovskite structure dielectric or a tungsten bronze type dielectric and does not contain lead at least in its composition . The EL device according to claim 5, wherein the lead-free dielectric layer is formed by a solution coating firing method.

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