JP2004006288A - Thin-film el element and composite substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film EL element having high display quality at a low cost by obtaining an excellent luminescent characteristic without using an expensive high-melting-point noble metal for a lower electrode layer even if a lower insulation layer contains a lead-based dielectric material or increasing the thickness of the lower electrode layer, in a thin-film EL element having the lower electrode layer, the lower insulation layer, a luminescent layer and an upper electrode layer in that order. <P>SOLUTION: This thin-film EL element has, on a substrate having an electric insulation property, at least the lower electrode layer, a barrier layer containing a conductive inorganic compound, the lower insulation layer, the luminescent layer and the upper electrode layer in that order. <P>COPYRIGHT: (C)2004,JPO

Description

【００９３】
表１から、本発明の効果が明らかである。すなわち、厚さ５００ｎｍのＡｇ薄膜からなる下部電極層３は、その上に厚さ５００ｎｍのＩＴＯ薄膜からなるバリア層１０を設けた場合、厚膜誘電体層４１を焼成温度８００℃という高温で形成しても、それによる抵抗増大が２倍程度に収まり、電極としての機能が十分に維持されていることがわかる。また、下部電極層３をＡｕから構成した場合、さらに優れた効果が得られている。また、バリア層１０としてＳｎＯ_２薄膜を設けた場合でも、ＩＴＯ薄膜を設けた場合と同等の特性が得られることがわかる。
【００９４】
これに対しバリア層１０を設けずＡｇ電極単独とした場合には、焼成温度６５０℃以上で電極が断線し、電極として機能が全く失われた。また、Ａｕ電極単独の場合も焼成温度８００℃では断線が発生し、電極としての機能が失われた。
【００９５】
ＩＴＯ薄膜の厚さを２５ｎｍとしたサンプルでは、膜厚５００ｎｍの場合と比較して抵抗値変化は大きくなるが、断線は生じていない。バリア層１０を薄くした場合に抵抗変化が大きくなったのは、基板２の表面がアルミナセラミックスの焼き上げ面であるため凹凸が激しく、この上に下部電極層３を介して形成するバリア層１０の膜厚が薄い場合には、スパッタリング時にステップカバレッジが不十分となり、下部電極層３表面に局所的にバリア層１０に覆われていない部分が発生したためと考えられる。
【００９６】
実施例２
実施例１で用いたアルミナ基板２を用い、厚膜誘電体層４１をチタン酸バリウム（ＢａＴｉＯ_３）から構成したほかは実施例１と同様にして、評価用サンプルを得た。厚膜誘電体層４１形成時の焼成温度は９００℃とした。この評価用サンプルについて、実施例１と同様な測定を行った。結果を表２に示す。
【００９７】
【表２】

【００９８】
表２から、下部絶縁体層４に鉛系化合物が含有されない場合でも、バリア層１０が有効であることが明らかである。
【００９９】
なお、厚膜誘電体層４１形成時に９００℃まで加熱したため、バリア層（ＩＴＯ）の比抵抗が１００Ω・ｃｍまで上昇した。しかし、表２に示されるように、バリア層は薄くても（厚さ２００ｎｍでも）十分な効果を示しており、この程度の厚さであれば、厚さ方向におけるバリア層の電気抵抗値は許容範囲にある。
【０１００】
実施例３
以下の手順で図１に示す構成のＥＬ素子を作製した。ただし、薄膜絶縁体層４３は形成しなかった。
【０１０１】
まず、実施例１と同様にして、アルミナからなる基板２上に下部電極層３、バリア層１０および厚膜誘電体層４１を形成した。ただし、下部電極層３を構成する各電極の平面寸法は１ｍｍ×１００ｍｍとし、また、厚膜誘電体層４１の焼成は７５０℃で２０分間行った。厚膜誘電体層４１の誘電率は約２５００であった。下部電極層３およびバリア層１０の構成を、表３に示す。
【０１０２】
次に、溶液塗布焼成法を用いて表面平坦化層４２を形成した。この溶液塗布焼成法では、ＰＺＴのゾルゲル液を前駆体溶液として用いた。この前駆体溶液を、厚膜誘電体層４１の表面にスピンコーティング法にて塗布し、７００℃で１０分間焼成することを繰り返すことにより、膜厚が約３μｍの表面平坦化層４２を形成した。
【０１０３】
前駆体溶液は、以下の手順で調製した。まず、８．４９ｇの酢酸鉛三水和物と４．１７ｇの１，３−プロパンジオールとを混合して約２時間加熱攪拌し、透明な溶液を得た。また、これとは別に３．７０ｇのジルコニウム・ノルマルプロポキシド７０質量％１−プロパノール溶液と１．５８ｇのアセチルアセトンとを乾燥窒素雰囲気中で３０分間加熱攪拌し、これに３．１４ｇのチタニウム・ジイソプロポキシド・ビスアセチルアセトネート７５質量％２−プロパノール溶液と２．３２ｇの１，３プロパンジオールとを加え、さらに２時間加熱攪拌して溶液を調製した。この溶液と前記透明な溶液とを８０℃で混合し、乾燥窒素雰囲気中で２時間加熱攪拌し、褐色透明な溶液を作製した。この溶液を１３０℃で数分間保持することにより副生成物を取り除き、さらに３時間加熱攪拌することにより前駆体溶液を得た。前駆体溶液の粘度調整は、ｎ−プロパノールを用いて希釈することにより行った。
【０１０４】
次に、基板を２００℃に加熱した状態で、ＭｎをドープしたＺｎＳ蒸着源を用い、ＺｎＳ：Ｍｎからなる厚さ０．８μｍの発光層５を蒸着法により形成した後、真空中において５００℃で１０分間熱処理した。
【０１０５】
次に、上部絶縁体層６としてＳｉ_３Ｎ_４薄膜を、上部電極層７としてＩＴＯ薄膜をそれぞれ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素子サンプルを得た。上部電極層７は、メタルマスクを成膜時に用いることにより、幅１ｍｍのライン状電極が並ぶストライプ状にパターニングした。
【０１０６】
これらのサンプルについて、下部電極層３および上部電極層７からそれぞれ電極を引き出して、１ｋＨｚ、パルス幅５０μｓの電界を発光輝度が飽和する強度で印加し、飽和輝度および発光面の面内における発光の均一性を調べた。結果を表３に示す。
【０１０７】
【表３】

【０１０８】
表３から明らかなように、下部電極層３上にバリア層１０を積層した構造を有する本発明サンプルは、高輝度でかつムラのない発光特性を示している。
【０１０９】
これに対し、バリア層を設けず下部電極層３をＡｇ薄膜から構成した比較サンプルは、全く発光しなかった。これは、下部電極層３が厚膜誘電体層４１焼成時に断線し、電極としての機能を失ったためと考えられる。
【０１１０】
一方、バリア層を設けず下部電極層３をＡｕ薄膜から構成した比較サンプルは、飽和輝度は本発明サンプルとほぼ同等であるが、目視でも発光面の均一性が悪いことが認められ、光学顕微鏡を用いて数十μｍオーダーで観察すると、部分的に発光が弱い領域と強い領域とが混在していた。この不均一性は、バリア層を設けないためにＡｕ薄膜の耐熱性が不足し、部分的に電極としての機能が失われていること、および、厚膜誘電体層４１焼成時にアルミナ基板２中のＳｉＯ_２系焼結助剤と鉛系の厚膜誘電体層４１とが部分的に反応し、厚膜誘電体層４１の特性に分布ができたこと、によるものと推定される。
【０１１１】
実施例４
下部電極層３をＡｇから構成し、下部電極層３をリフトオフ法によりパターニングする際にレジスト残渣除去のために酸素プラズマによるアッシングを利用したほかは実施例３と同様な手順で、比較用のＥＬ素子サンプルＮｏ．１を作製した。この比較サンプルＮｏ．１では、Ａｇからなる下部電極層３のリード部３１が、リフトオフ工程において酸素プラズマによって酸化されて黒化したため、表面の導電性が低下して電極構成材としての機能を失った。
【０１１２】
また、下部電極層３形成時に酸素プラズマによるアッシングを行わず、発光層５をＨ_２Ｓガス雰囲気中での蒸着法により形成したＳｒＳ：Ｃｅ層から構成したほかは上記比較サンプルＮｏ．１と同様にして、比較サンプルＮｏ．２を作製した。この比較サンプルＮｏ．２では、Ａｇからなる下部電極層３のリード部３１が、発光層５形成の際にＨ_２Ｓガスによって硫化されて黒化したため、表面の導電性が低下して電極構成材としての機能を失った。
【０１１３】
また、下部電極層３の全面を、ＩＴＯからなる厚さ１００ｎｍのバリア層１０で被覆し、下部電極層３形成時に酸素プラズマによるアッシングを行ったほかは上記比較サンプルＮｏ．２と同様にして、実施例サンプルＮｏ．３を作製した。この実施例サンプルＮｏ．３では、下部電極層３のリード部３１がバリア層１０で被覆されていたため、酸素プラズマおよびＨ_２Ｓガスによるリード部３１の酸化および硫化が生じなかった。
【０１１４】
【発明の効果】
従来の薄膜ＥＬ素子では、下部電極層が薄いと、その上の下部絶縁体層を厚膜法で形成する際の加熱によって下部電極層が島状構造の不連続膜となってしまうため、高価な貴金属を含有する下部電極層を厚くせざるを得なかった。そのため、材料コストが高くなり、また、下部電極層のパターンエッジに起因してＥＬパネル表面に現れる段差が大きくなって表示品位を著しく低下させていた。
【０１１５】
これに対し本発明の薄膜ＥＬ素子では、下部電極層上にバリア層を積層した構造とするので、その上に厚膜法や溶液塗布焼成法により下部絶縁体層を形成する際に加熱されても、下部電極層が島状構造となりにくい。そのため、本発明の素子では下部電極層を薄くすることができ、その結果、材料コストの低減と表示品位の向上とが実現する。
【０１１６】
酸化鉛を含有する誘電体材料は、低温焼成が可能で誘電率も高いことから、下部絶縁体層構成材料として優れている。また、純ＡｇまたはＡｇを含む金属材料は、導電性が高いため電極層を薄くでき、しかも材料コストが低いため、下部電極層構成材料として適している。しかし、Ａｇは酸化鉛との反応性が高いため、下部絶縁体層形成時にその中の酸化鉛と下部電極層中のＡｇとが反応し、下部電極層の抵抗増大や断線を引き起こす。
【０１１７】
これに対し本発明で設けるバリア層は、鉛拡散に対し強固なバリア性を示す。そのため本発明では、鉛系誘電体を含有する下部絶縁体層とＡｇ系材料を含有する下部電極層とを組み合わせることができるので、発光特性および表示品位が良好なＥＬ素子を低コストで実現することができる。また、バリア層は、Ａｇ系材料からなる下部電極の酸化および硫化を防ぐことができる。
【０１１８】
また、基板上に、本発明のＥＬ素子における下部電極層およびバリア層と同様に電極層およびバリア層を設けた複合基板は、ＥＬ素子用としてはもちろん、他の各種表示素子にも好適である。すなわち、この複合基板では電極層の耐熱性が良好なので、形成時および／または形成後に加熱が必要な様々な層を電極層上に設ける場合に、ＥＬ素子に適用した場合と同様な効果が実現する。
【図面の簡単な説明】
【図１】本発明の薄膜ＥＬ素子の構成例を示す断面図である。
【図２】２重絶縁型構造の薄膜ＥＬ素子の構成例を示す斜視図である。
【符号の説明】
２　基板
３　下部電極層
３１　リード部
４　下部絶縁体層
４１　厚膜誘電体層
４２　表面平坦化層
４３　薄膜絶縁体層
５　発光層
６　上部絶縁体層
７　上部電極層
８　前面保護ガラス
９　封止材
１０　バリア層
１１　異方性導電樹脂層
１２　フレキシブルプリント基板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a thin-film EL device having at least a structure in which a lower electrode layer having a predetermined pattern, a lower insulator layer, a light-emitting layer, and an upper electrode layer made of a transparent conductive material are stacked on a substrate having electrical insulation. And a composite substrate used for various display elements such as a thin film EL element.
[0002]
[Prior art]
EL elements have been put to practical use as backlights for liquid crystal displays (LCDs) and watches.
[0003]
An EL element is an element to which a phenomenon in which a substance emits light by application of an electric field, that is, an electroluminescence (EL) phenomenon is applied.
[0004]
An EL element using a phosphor made of an inorganic substance includes a dispersion type EL element having a structure in which a powdered phosphor is dispersed in an organic substance or an enamel and an electrode layer is provided above and below, and a thin film light emitting body is sandwiched between a pair of thin film insulators. Further, there is a thin-film EL element in which a laminate obtained by sandwiching this between a pair of electrode layers is provided on an electrically insulating substrate. Further, each of them has a DC voltage driving type and an AC voltage driving type depending on the driving method. Dispersion type EL elements have been known for a long time and have an advantage that they are easy to manufacture, but their use is limited because of their low luminance and short life. On the other hand, thin film EL elements have been widely used in recent years because of their characteristics of high luminance and long life.
[0005]
FIG. 2 shows the structure of a typical double-insulation thin-film EL element as a conventional EL element. This thin film EL element has a structure in which a lower electrode layer 3, a lower insulator layer 4, a light emitting layer 5, an upper insulator layer 6, and an upper electrode layer 7 are laminated in this order on a substrate 2 having electrical insulation. . The substrate 2 is transparent and is made of blue plate glass used for a liquid crystal display, a PDP, or the like. The lower electrode layer 3 is an ITO (Indium Tin Oxide) layer having a thickness of about 0.2 to 1 μm. The lower insulator layer 4 and the upper insulator layer 6 are thin films having a thickness of about 0.1 to 1 μm formed by sputtering, vapor deposition, or the like.₂O₃, Ta₂O₅, Ai₃N₄, BaTiO₃Etc. The light emitting layer 5 has a thickness of about 0.2 to 1 μm. The upper electrode layer 7 is made of a metal such as Al. Each of the lower electrode layer 3 and the upper electrode layer 7 is patterned in a stripe shape such that one is a row electrode and the other is a column electrode, and is arranged orthogonal to each other. The intersection of the row electrode and the column electrode forms a pixel, and the matrix electrode selectively applies an AC voltage or a pulse voltage to a specific pixel to emit light, and the light is extracted from the substrate 2 side. .
[0006]
In this thin-film EL device, the lower insulator layer 4 and the upper insulator layer 6 have a function of limiting the current flowing in the light-emitting layer 5, and can suppress the dielectric breakdown of the thin-film EL device, and provide stable light emission. It works so that characteristics are obtained. For this reason, the thin film EL device having this structure has been widely used commercially.
[0007]
As a phosphor material constituting the light-emitting layer 5, ZnS to which Mn exhibiting yellow-orange emission is added has been mainly used from the viewpoint of ease of film formation and light emission characteristics. In order to produce a color display, it is indispensable to use a luminescent material that emits light in three primary colors of red, green and blue. Examples of these materials include ZnS to which SrS or Tm to which Ce emitting blue light is added, ZnS or CaS to which Sm to which red light emission is added, and CaS to which ZnS or Ce to which green light emitting Tb is added. Etc. are known.
[0008]
Non-Patent Document 1 (Monthly Display '98 April, “Recent Display Technology Trends”, Tasaku Tanaka, pp. 1-10) states that as a material for emitting red light, green light such as ZnS or Mn / CdSSe is obtained. Materials for obtaining blue light emission, such as ZnS: TbOF and ZnS: Tb, are SrS: Cr, (SrS: Ce / ZnS) n, and CaGa.₂S₄: Ce, SrGa₂S₄: A light emitting material such as Ce is disclosed. In addition, a light-emitting material such as SrS: Ce / ZnS: Mn is disclosed as a device for obtaining white light emission.
[0009]
Further, among the above materials, SrS: Ce is used for a thin film EL device having a blue light emitting layer in Non-Patent Document 2 (IDW (International Display Workshop) '97 XW. to $ 596). Further, in this document, when a light emitting layer of SrS: Ce is formed, H₂It is disclosed that when formed by an electron beam evaporation method in an S atmosphere, a high-purity light-emitting layer can be obtained.
[0010]
However, such a thin film EL device still has a structural problem to be solved. That is, since the lower insulator layer 4 is a thin film, when the display has a large area, there is no defect of the lower insulator layer 4 due to a step portion of the pattern edge of the lower electrode layer 3 or dust generated in a manufacturing process. However, there is a problem that the light-emitting layer 5 is broken due to a local decrease in withstand voltage. Since such a problem is fatal as a display device, the thin-film EL element has a great obstacle to its practical use as a large-area display as compared with a liquid crystal display or a plasma display.
[0011]
In order to solve the problem that defects are likely to occur in the thin-film insulator layer, Patent Document 1 (Japanese Patent Publication No. 7-44072) discloses that an electrically insulating ceramic substrate is used as the substrate 2 and a thin film is used as the lower insulator layer 3. An EL device using a thick-film dielectric layer instead of an insulator layer is disclosed. The EL element disclosed in this document differs from the structure of a conventional thin film EL element in that the upper electrode 7 is a transparent electrode layer in order to extract light emitted from the light emitting layer 5 from the side opposite to the substrate 2. .
[0012]
Thick film dielectric layers are formed in thicknesses of tens to hundreds of micrometers, hundreds to thousands times the thickness of thin film insulator layers. Therefore, there is an advantage that dielectric breakdown due to a step formed in the lower electrode layer 3 or a pinhole formed by dust or the like in a manufacturing process is extremely small, and high reliability and high yield in manufacturing can be obtained. ing. 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 5 drops. For example, Patent Document 1 (Japanese Patent Publication No. 7-44072) contains lead. This problem has been remedied by constructing the thick film dielectric layer from a composite perovskite high dielectric constant material.
[0013]
However, the light emitting layer formed on the thick dielectric layer has a thickness of only several hundred nanometers, which is about 1/100 of the thickness of the thick dielectric layer. For this reason, the thick-film dielectric layer must have a smooth surface at a level equal to or less than the thickness of the light-emitting layer. However, as described below, the surface of the dielectric layer produced by a normal thick-film forming process is It was difficult to make it sufficiently smooth.
[0014]
That is, the thick-film dielectric layer is composed of ceramics obtained by sintering a powder material. For this reason, dense sintering usually causes a volume shrinkage of about 30 to 40%. However, while ordinary ceramics shrink in volume by three-dimensional shrinkage during sintering, the thick-film ceramics formed on the substrate are constrained by the substrate and shrink in the in-plane direction of the substrate. It is not possible to perform volume contraction only one-dimensionally in the thickness direction. For this reason, the thick film dielectric layer becomes essentially porous with insufficient sintering. Further, since the surface roughness of the thick film does not become smaller than the crystal grain size of the polycrystalline sintered body, the surface thereof has an irregular shape of a submicron size or more.
[0015]
Since the thick-film dielectric layer is porous or has an uneven surface as described above, when a light-emitting layer is formed thereon by a vapor deposition method such as an evaporation method or a sputtering method, the light-emitting layer becomes thicker. Since it cannot follow the surface shape of the film dielectric layer, it is not formed as a uniform thin film. Therefore, an electric field cannot be effectively applied to the light emitting layer in the uneven portion of the thick dielectric layer, and the effective light emitting area is reduced, and the light emitting layer is partially broken down due to local unevenness of the film thickness. This causes a problem that light emission luminance is lowered. Furthermore, since the film thickness locally largely fluctuates, the intensity of the electric field applied to the light emitting layer is locally largely fluctuated, so that a clear light emission voltage threshold cannot be obtained.
[0016]
In order to solve such a problem, for example, in Patent Document 2 (Japanese Patent Application Laid-Open No. 7-50197), lead zirconate titanate or the like formed on a surface of a thick dielectric layer made of lead niobate by a sol-gel method is disclosed. For improving the surface flatness by stacking high dielectric constant layers.
[0017]
As described above, by using a thick dielectric layer having a high dielectric constant, it is possible to avoid a step of a pattern edge of the lower electrode layer and a defect of the thin film insulator layer due to dust or the like generated in a manufacturing process. It is possible to solve the problem that the light emitting layer is destroyed due to a large decrease in dielectric strength.
[0018]
For the thick-film dielectric layer, a lead-based dielectric is usually used in order to enable sintering at a low temperature and obtain characteristics such as high dielectric constant and high withstand voltage. However, even if a lead-based dielectric material is used, the sintering temperature must be at least 700 ° C. or higher, usually 800 ° C. or higher. Further, since the firing of the thick-film dielectric layer is generally performed in a high-temperature oxidizing atmosphere, the lower electrode layer formed before the thick-film dielectric layer needs to have both heat resistance and oxidation resistance. Further, when the thick film dielectric layer is composed of a lead-based dielectric, the reactivity of lead oxide, which is a constituent compound thereof, is extremely high. Low reactivity with lead oxide at high temperatures is required. In addition, since the lower electrode layer is used after being patterned, if the film thickness is large, a step due to the electrode pattern occurs on the surface of the thick dielectric layer, and the display quality as a display deteriorates. The thickness is preferably smaller. Therefore, it is necessary that the lower electrode layer be made of a material that can provide sufficient conductivity even if it is thin.
[0019]
In order to satisfy such required characteristics, conventionally, it has been general to use a noble metal having a high melting point as a constituent material of the lower electrode layer. Among the noble metal electrode materials, Ag is remarkably low in material cost as compared with other noble metals such as Au, Pt, Pd, Ir, Ru, and Rh, and has the lowest electric resistance among all metals, and therefore has high conductivity and low cost. Very attractive as an electrode material. However, Ag is difficult to use alone because it has a lower melting point and lower heat resistance than other noble metals. Therefore, for example, Patent Document 1 (Japanese Patent Publication No. 7-44072) and Patent Document 2 (Japanese Unexamined Patent Application Publication No. It is used as an alloy like Ag-Pd and Ag-Pt described in JP-A-7-50197), and is particularly generally used as an Ag-Pd alloy (Pd content: 10 to 70%).
[0020]
However, Pd is a very expensive noble metal, and even if used as an Ag-Pd alloy, it becomes a very expensive material as compared with Ag alone. In addition, a noble metal alloy electrode layer containing Ag such as an Ag-Pd alloy or an Ag-Pt alloy has remarkably low heat resistance when thinned, so that the content of a high melting point noble metal such as Pd or Pt is increased to increase the heat resistance. It is necessary to increase the cost, which increases the cost and is a problem. Further, when an alloy is formed with Ag using Pd, Pt, or the like, there is a problem in that as the content of Pd or Pt increases, the electric resistance increases, and the performance as an electrode decreases. In this case, it is necessary to increase the film thickness in order to form a low-resistance electrode, so that the amount of material used increases and the manufacturing cost of the electrode increases, resulting in higher cost and display quality as a display. Is a problem.
[0021]
Further, Ag has a very high reactivity with a lead-based dielectric material, and is not only difficult to use alone for the above-mentioned reason, but also when the Ag component in the electrode is alloyed with other high melting point noble metal, the Ag component in the electrode becomes lead-based. It reacts when the dielectric material is fired, causing a remarkable increase in the electrode resistance and, in some cases, disconnection. Therefore, it has been very difficult to use a thin film having a thickness of 1 μm or less.
[0022]
Even when a high melting point noble metal such as Pt or Pd is used alone as an electrode, when a ceramic substrate such as alumina is used as the substrate, the substrate surface is not flat. However, there is a problem that the heat resistance is deteriorated and the electrode resistance is increased by a high-temperature process at the time of forming the dielectric layer.
[0023]
[Patent Document 1]
Japanese Patent Publication No. 7-44072
[Patent Document 2]
JP-A-7-50197
[Non-patent document 1]
Monthly Display '98 April, “Recent Display Technology Trends”, Tanaka Shosaku, p1-10
[Non-patent document 2]
IDW (International Display Workshop) '97 {X. Wu “Multicolor Thin-Film Ceramic Hybrid EL Display” p593 to 596
[0024]
[Problems to be solved by the invention]
An object of the present invention is to provide a thin-film EL device having a lower electrode layer, a lower insulator layer, a light-emitting layer, and an upper electrode layer in this order on a substrate, even when the lower insulator layer contains a lead-based dielectric material. By using a high-melting precious metal that is not expensive for the lower electrode layer and obtaining good light-emitting characteristics without increasing the thickness of the lower electrode layer, a thin-film EL element with high display quality can be realized at low cost. is there.
[0025]
[Means for Solving the Problems]
The above object is achieved by the present invention described below.
The EL element of the present invention has at least a lower electrode layer, a barrier layer containing a conductive inorganic compound, a lower insulator layer, a light emitting layer, and an upper electrode layer in this order on a substrate having electrical insulation. The conductive inorganic compound is preferably an oxide, particularly an oxide containing indium and / or tin. The lower electrode layer is preferably a metal electrode containing Ag. The lower insulator layer preferably contains an oxide dielectric containing lead. The barrier layer preferably has a specific resistance of 100 Ω · cm or less. The barrier layer usually has a specific resistance of 10^-4Ω · cm or more. The lower electrode layer has a specific resistance of 2 × 10^-5It is preferably Ω · cm or less. The barrier layer preferably has a thickness of 0.02 to 0.5 μm, particularly preferably 0.02 to 0.2 μm.
The composite substrate of the present invention is obtained by providing an electrode layer containing Ag and a barrier layer containing a conductive inorganic compound in this order on a substrate having electrical insulation.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a configuration example of the thin film EL element of the present invention. This thin-film EL element has a lower electrode layer 3, a lower insulator layer 4, a light-emitting layer 5, an upper insulator layer 6, and an upper electrode layer 7 in this order on a substrate 2 having electrical insulation. A barrier layer 10 is provided between the layer 3 and the lower insulator layer 4. The lower insulator layer 4 is formed by laminating a thick film dielectric layer 41, a surface flattening layer 42, and a thin film insulator layer 43.
[0027]
In this EL element, the lower electrode layer 3 and the upper electrode layer 7 are patterned in a stripe shape similarly to the EL element shown in FIG. 2, and are driven similarly.
[0028]
Although the light emitting layer 5 has a single-layer structure in the illustrated thin film EL element, the present invention is not limited to such an element, and can be applied to, for example, an element having a structure in which a plurality of light emitting layers are stacked in the film thickness direction. Can be applied to an element having a structure in which different light emitting layers (pixels) are arranged in a matrix in a plane.
[0029]
The main part of the thin film EL element is hermetically sealed using a panel front protective glass 8 and a sealing material 9 in order to prevent deterioration of the light emitting layer 5 due to outside air, particularly moisture.
[0030]
An end portion of the lower electrode layer 3 is a lead portion 31 for electrically connecting to the outside of the element. The lead portion 31 is electrically connected to the flexible printed circuit board 12 via, for example, the anisotropic conductive resin layer 11 and further to an external drive circuit (not shown).
[0031]
Hereinafter, the configuration of each part of the thin film EL element of the present invention will be described with reference to the drawings.
[0032]
Barrier layer 10
A feature of the present invention is that a barrier layer 10 containing a conductive inorganic compound is provided between the lower electrode layer 3 and the lower insulator layer 4.
[0033]
The present inventors have conducted various studies on the heat resistance of the lower electrode layer 3 as described above, particularly when the lower insulator layer 4 laminated on the lower electrode layer 3 contains lead. Was obtained.
[0034]
When a metal thin film is heated to a high temperature close to its melting point, the metal thin film aggregates due to the growth of crystal grains of the metal and becomes a discontinuous film having an island structure, thereby losing the function as an electrode. In particular, this phenomenon occurs when the thickness of the metal thin film is small, or when the substrate used as the base for forming the metal thin film has irregularities like a ceramic substrate such as alumina, and the irregularities cannot be ignored with respect to the thickness of the metal thin film. , It was found to occur at lower temperatures.
[0035]
Further, Pb reacts with most noble metal elements such as Au, Pt, Pd, and Ag to form a low melting point alloy. Therefore, a dielectric material containing lead is laminated on a metal thin film electrode containing such an element to form a high-temperature alloy. It has been found that when the thick insulator layer is formed through a thermal process, the above phenomenon occurs at a lower temperature, and particularly a remarkable reaction occurs with Ag. This is presumably because Pb atoms released from the lead oxide react with the metal thin-film electrode to cause the above phenomenon at a lower temperature, resulting in a remarkable decrease in the heat resistance of the metal thin-film electrode.
[0036]
Further, a substrate serving as a base for the metal thin-film electrode is coated with SiO 2.₂It has also been found that the above-described phenomenon is likely to occur when a substance which easily forms a low melting point oxide with PbO is contained. This phenomenon is probably due to the fact that the Pb component in the thick-film dielectric layer diffuses through the defects of the metal thin-film electrode during baking to form a low-melting oxide in the substrate, and this low-melting oxide is This is presumed to be due to interaction with the substrate-side interface of the thin film electrode. SiO₂Is, for example, a glass substrate or forsterite (2MgO.SiO₂), Steatite (MgO.SiO)₂), Mullite (3Al₂O₃・ 2SiO₂), Etc., and as a sintering aid material for alumina ceramic substrates, the above problem occurs in practically most heat-resistant insulating substrates.
[0037]
Based on the analysis of these phenomena, the present inventors have adopted a structure in which a barrier layer 10 containing a conductive inorganic compound is provided in close contact with the lower electrode layer 3. By forming the barrier layer 10 having a higher melting point and a higher rigidity than the lower electrode layer 3 on the lower electrode layer 3, the lower electrode layer 3 aggregates at a high temperature due to the interaction at the interface with the lower electrode layer 3. The phenomenon can be suppressed.
[0038]
When the lower electrode layer 3 contains Ag and the thick-film dielectric layer 41 contains lead, the barrier layer 10 having low reactivity with lead oxide and having a high barrier effect against lead diffusion is laminated. Thus, when the thick dielectric layer 41 is formed, diffusion of lead oxide, which lowers the heat resistance of the lower electrode layer 3, is prevented, and the function of the lower electrode layer 3 as an electrode is maintained. That is, since the reaction between the constituent material of the lower electrode layer 3 or the substrate 2 and the lead component in the dielectric material is prevented, higher heat resistance can be given to the lower electrode layer 3.
[0039]
In the present invention, providing the barrier layer 10 is effective for preventing the lower electrode layer 3 from being sulfurized and oxidized. Here, an example of a method for manufacturing the thin film EL device of the present invention will be described. First, the lower electrode layer 3 and the barrier layer 10 having a predetermined pattern are formed on the substrate 2 by a lift-off method or the like. Next, the lower insulator layer 4 having a predetermined pattern is formed by a screen printing method or the like. Next, the light emitting layer 5 and the upper insulator layer 6 having a predetermined pattern are formed by a vacuum evaporation method or a sputtering method using a mask. Next, the upper electrode layer 7 having a predetermined pattern is formed by a lift-off method or the like. When the lift-off method is used to form the lower electrode layer 3 and / or the upper electrode layer 7 and ashing with oxygen plasma is used to remove the resist residue at that time, if the barrier layer 10 is not present, the lower electrode layer 3 The exposed lead portion 31 is irradiated with oxygen plasma. When the electrode is made of Ag or an alloy thereof, the electrode is oxidized by irradiation with oxygen plasma, the conductivity is reduced, and the electrode function is lost. In addition, when the luminescent layer 5 containing sulfide is formed by using a vapor deposition method in a sulfur-containing gas such as hydrogen sulfide gas or sulfur vapor, if the barrier layer 10 is not present, the lead portion 31 may not contain sulfur. Exposure to gas. When the electrode is made of Ag or an alloy thereof, the electrode is sulfided by the sulfur-containing gas, the conductivity is reduced, and the electrode function is lost. As described above, by providing the barrier layer 10 covering the entire surface of the lower electrode layer 3 including the lead portion 31, it is possible to prevent the lower electrode layer 3 from being deteriorated due to oxidation, sulfurization, and the like. Also, after the thin-film EL element is manufactured, the sulfur atoms in the light emitting layer 5 may diffuse with time and reach the lower electrode layer 3 to deteriorate the lower electrode layer 3. Can be. Therefore, by providing the barrier layer 10, the reliability of the thin film EL element is also improved.
[0040]
The barrier layer 10 needs to be conductive so as not to cause a decrease in the capacity of the lower insulator layer 4, but since the lower electrode layer 3 only has to function as an electrode, the conductivity is a single. It may be lower than when used as an electrode.
[0041]
First, consider the electrical resistance required for the electrodes of the EL display. Assuming that the column electrode has a width of, for example, 300 μm and a length of 20 cm, the electrode resistance when the column electrode has a thickness of 0.5 μm is 2 × 10 2^-6Ω · cm, about 27Ω, 2 × 10^-5In the case of Ω · cm, it is 267Ω, which is a resistance value that cannot be ignored. Therefore, the specific resistance of the electrode is at least 2 × 10^-5Ω · cm or less, preferably 1 × 10^-5Ω · cm or less.
[0042]
However, in the present invention, since the lower electrode layer 3 functions as an electrode, the conductivity of the barrier layer 10 may be within a range that does not cause a decrease in the capacity of the lower insulator layer 4 in contact with the lower electrode layer 3. For example, it is considered that the barrier layer 10 is inserted between the lower insulator layer 4 having a dielectric constant of 2000 and a film thickness of 20 μm and the lower electrode layer 3. The impedance in the thickness direction of the lower insulator layer 4 without the barrier layer 10 is 1 / F × 1.8 × 10⁶Ω / cm²It becomes. In the case of a normal EL display, since the driving frequency of the EL element forming the individual pixel does not usually exceed 30 kHz, the impedance of the lower insulator layer 4 may be considered to be 60Ω or more. The effect on the lower insulator layer 4 due to the insertion of the barrier layer 10 is considered to be almost negligible if the impedance is 1% (0.6Ω) or less. For example, the thickness of the barrier layer 10 is set to 0.5 μm. Assuming that, the specific resistance of the barrier layer 10 may be 12000 Ω · cm or less. Further, considering the electrical connection to the outside through the laminate of the lower electrode layer 3 and the barrier layer 10, the area of the portion of the lead portion 31 of the lower electrode layer 3 used for connection to the outside of the element (differing). Assuming that the area of the isotropic conductive resin layer 11 is 300 μm × 1 mm and the resistance of the contact portion is 1 Ω or less, the specific resistance of the barrier layer 10 may be 60 Ω · cm or less. Therefore, the specific resistance of the barrier layer 10 is generally 100 Ω · cm or less, preferably 10 Ω · cm or less, although it depends on the film thickness.
[0043]
As described above, the barrier layer 10 needs to have a function of improving the heat resistance of the lower electrode layer 3 and needs to have a specific resistance that is low to some extent. Further, when a lead-containing compound is used for the lower insulator layer 4, it is preferable to have a barrier function against lead diffusion. The present inventors have searched for a conductive inorganic compound that satisfies such requirements, and as a result, have found that each of the oxides and / or nitrides has a conductivity, more specifically, an oxide containing indium and / or tin. , Zinc oxide, aluminum-doped zinc oxide, titanium nitride, chromium nitride, zirconium nitride and hafnium nitride. Therefore, in the present invention, a barrier layer containing at least one of these conductive inorganic compounds, preferably a barrier layer substantially composed of at least one of these conductive inorganic compounds, is provided. Among these conductive inorganic compounds, oxides are preferable because of good heat resistance in a high-temperature oxidizing atmosphere, and oxides containing indium and / or tin are particularly preferable. Such a barrier layer 10 is particularly effective when combined with the lower electrode layer 3 containing Ag. When a lead-containing compound is used for the lower insulator layer 4, it is particularly effective to use an oxide containing indium and / or tin as the conductive inorganic compound.
[0044]
Examples of the oxide containing indium and / or tin include indium oxide (In).₂O₃), Tin oxide (SnO)₂) And ITO (Indium Tin Oxide), which are known as materials for forming a transparent electrode such as the upper electrode layer 7, for example. In₂O₃And SnO₂Are considered to be oxygen-defective N-type semiconductors, and these thin films are usually formed by a sputtering method or the like. When used as an electrode layer, by controlling the film formation conditions to create oxygen vacancies,^-1-10^-3It is known that the specific resistance can be reduced to about Ω · cm, but since the specific resistance is extremely large as compared with the metal electrode, in order to obtain a lower resistance,₂O₃SnO₂Doped with ITO and SnO₂Is used in a form doped with Sb or F. In this case, the specific resistance is 10^-3-10^-4It can be reduced to about Ω · cm.
[0045]
However, it is known that the resistivity of any of these conductive oxides increases when a high-temperature treatment at 600 ° C. or higher is performed in an oxidizing atmosphere. Therefore, using these conductive oxides as the constituent material of the lower electrode layer provided below the thick film dielectric layer sintered by high-temperature treatment in an oxidizing atmosphere constitutes a very small display. It is difficult except in special cases.
[0046]
On the other hand, in the case of the thin-film EL device of the present invention, although it is preferable that the specific resistance of the barrier layer is low, this is not essential as described above, and the specific resistance of the barrier layer is generally 100 Ω · cm or less, preferably It may be 10 Ω · cm or less. Therefore, there is no problem even if characteristic deterioration (specific resistance rise) occurs due to high temperature treatment in an oxidizing atmosphere at the time of forming the thick film dielectric layer. Further, unlike the case where the barrier layer is used alone as an electrode, the barrier layer can be used without introducing a special dopant or the like. When ITO is used, SnO in ITO is used.₂The content is not limited, and may be any value between 0 and 100% by mass. However, in order to lower the specific resistance, SnO in ITO should be used.₂The content is preferably 1 to 20% by mass, more preferably 5 to 12% by mass.
[0047]
Zinc oxide, titanium nitride, chromium nitride, zirconium nitride, and hafnium have a stoichiometric atomic ratio (metal / nitrogen, etc.) even if they have the required conductivity, even if they have the stoichiometric composition. The composition may deviate from the composition.
[0048]
Note that the barrier layer preferably does not contain any other than the above-described conductive compound in order to obtain sufficient conductivity, and in order not to have reactivity with lead, but other barriers may be included as unavoidable impurities or trace additives. It may contain an element. However, it is preferable that other elements be 10 atomic% or less of the barrier layer.
[0049]
If the thickness of the barrier layer 10 is too small, the effect of suppressing the aggregation phenomenon of the lower electrode layer 3 at a high temperature is insufficient, and the lead diffusion barrier effect and the effect of preventing sulfuration and oxidation of the lower electrode layer 3 are sufficient. In particular, when a substrate 2 having a surface irregularity such as ceramics is used as the substrate 2, the coating of the lower electrode layer 3 with the barrier layer 10 becomes incomplete, and This is not preferable because lead-based dielectric material may enter the film dielectric layer 41 and react with the lower electrode layer 3. The inventors' experimental studies show that if the thickness of the barrier layer 10 is 0.02 μm or more, particularly 0.1 μm or more, a sufficient lead diffusion barrier effect and an effect of preventing sulfuration and oxidation can be obtained. Was.
[0050]
On the other hand, if the thickness of the barrier layer 10 is too large, it is not preferable particularly when used for a display. That is, the lower electrode layer 3 is patterned in a stripe shape or the like, and the barrier layer 10 needs to be patterned in the same manner as the lower electrode layer 3 in order to prevent a short circuit. Is formed, and the surface property of each layer formed thereon is affected by this step, and finally the unevenness due to the step occurs on the EL panel surface, and the display quality as a display is reduced. Significant damage. Therefore, it is desired that the total thickness of the lower electrode layer 3 and the barrier layer 10 is as small as possible. Specifically, the total thickness is preferably 2 μm or less, more preferably 1 μm or less, and still more preferably 0.5 μm or less. is there.
Therefore, it is preferable to determine the thickness of the barrier layer 10 in consideration of the thickness of the lower electrode layer 3 so that the total thickness falls within this range. The thickness of the lower electrode layer 3 is preferably 0.3 μm or more in view of its specific resistance. When the surface of the substrate 2 has irregularities, such as a sintered substrate of alumina, if the lower electrode layer 3 is thin, its heat resistance is significantly reduced. If it is 3 μm or more, such a problem hardly occurs.
[0051]
In the above-described electrical connection to the outside via the barrier layer 10, in order to obtain sufficient conductivity, the barrier layer 10 is preferably thinner, specifically, 0.5 μm or less, particularly, 0.5 μm or less. Preferably it is 0.2 μm or less.
[0052]
As a method for forming the barrier layer 10, a known film forming method for forming a transparent conductive film, for example, a PVD method (physical vapor deposition method) such as an ion plating method or a sputtering method, a solution coating baking method (a sol-gel method, MOD method) and spray pyrolysis method.
[0053]
By using the PVD method, a high-density thin film can be formed. Therefore, a barrier layer having a high lead diffusion barrier effect and a high effect of preventing oxidation and sulfidation can be formed with a small film thickness. This is suitable when the barrier layer 10 is formed on the lower electrode layer 3 formed on a flat substrate.
[0054]
On the other hand, a solution coating baking method and a spray pyrolysis method are known as methods capable of forming a transparent conductive film at low cost. Conventionally, the transparent conductive film formed by these methods has a specific resistance about one digit higher than that of the transparent conductive film formed by the PVD method. However, even if the barrier layer 10 in the thin film EL device of the present invention has a relatively high specific resistance as described above, no problem occurs. In addition, these methods, particularly the solution coating and baking method, make it easy to form a coating film without any defect on a base having irregularities or steps, so that the lower electrode layer 3 formed on a ceramic substrate having irregularities on the surface can be easily formed. This is an excellent method for forming the barrier layer 10 on the substrate.
[0055]
Lower electrode layer 3
The constituent material of the lower electrode layer 3 is a metal (including a semi-metal) or an alloy thereof (including an intermetallic compound), provides high conductivity, and has a high-temperature oxidizing atmosphere when the thick-film dielectric layer 41 is formed. Must not be damaged by Examples of such materials include high melting point noble metals such as Pt, Pd, and Ir; other noble metals such as Au and Ag; alloys of noble metals such as Au-Pd, Au-Pt, Ag-Pd, and Ag-Pt; An alloy containing a noble metal such as -Pd-Cu as a main component and a base metal element added thereto, and a metal silicide such as titanium silicide can be used.
[0056]
By increasing the thickness of the lower electrode layer 3, the electrode resistance is reduced and the heat resistance of the lower electrode layer 3 is also improved. However, as described above, if the patterned lower electrode layer 3 is thick, the display quality as a display is significantly impaired, which is not preferable. Therefore, it is desirable that the thickness of the lower electrode layer 3 be as small as possible. Also, increasing the thickness of the lower electrode layer 3 is not preferable in terms of film formation cost and material cost, and directly increases the cost particularly when a noble metal having a large material cost is used. It is desirable to make it thin.
[0057]
From these points, it is preferable that the lower electrode layer 3 contains Ag, which can provide a low electrode resistance even if the film thickness is small and which is significantly lower in cost than other noble metals. Is advantageous if it can be composed of Ag alone.
[0058]
In the thin-film EL device of the present invention, since the barrier layer 10 is provided on the lower electrode layer 3, even when the lower electrode layer 3 is thin, the lower electrode layer 3 has an island structure when the thick dielectric layer 41 is formed. A uniform continuous structure is maintained without becoming. When the barrier layer 10 contains an oxide containing indium and / or tin, the barrier effect against the diffusion of lead is high. Therefore, even when a lead-based dielectric material is used for the thick The lower electrode layer 3 can be made of pure Ag or a low-cost metal material containing Ag, which has been conventionally difficult to use because of its high reactivity with lead. Specifically, even when a pure Ag electrode having the lowest melting point among the noble metals is used, the thickness of the lower electrode layer 3 can be set to 1 μm or less, and more preferably 0.5 μm or less. Therefore, a great effect can be obtained with respect to the improvement of the display quality of the display using the EL element and the reduction of the manufacturing cost. Since the metal silicide also has high reactivity with lead, the present invention exhibits a high effect even when a metal silicide electrode is provided.
[0059]
The method for forming the lower electrode layer 3 is not particularly limited, and a known technique such as a sputtering method, an evaporation method, a plating method, and a printing method using an organic metal paste (resinate metal paste) can be used.
[0060]
In the case of a simple matrix type, the lower electrode layer 3 has a stripe pattern composed of a large number of linear electrodes. In that case, the width of each electrode is the width of one pixel, and the space between two adjacent electrodes is a non-light emitting region. Therefore, it is preferable to minimize the space between the electrodes. Specifically, depending on the intended resolution of the display, for example, an electrode width of about 200 to 500 μm and a space width of about 20 to 50 μm are required.
[0061]
Substrate 2
The substrate 2 has an electrical insulating property, does not contaminate the lower electrode layer 3 and the thick dielectric layer 41 formed thereon, and can maintain a predetermined heat-resistant strength. There is no particular limitation. In the EL device of the present invention, as described above, SiO 2 is contained in the composition of the substrate.₂And B₂O₃Since the heat resistance of the lower electrode layer 3 can be maintained even when a compound having a high reactivity with lead oxide is contained, the constituent material of the substrate 2 can be selected from a wide range.
[0062]
As a specific material, for example, alumina (Al₂O₃), Quartz glass (SiO₂), Magnesia (MgO), forsterite (2MgO.SiO)₂), Steatite (MgO.SiO)₂), Mullite (3Al₂O₃・ 2SiO₂), Beryllia (BeO), zirconia (ZrO)₂), Aluminum nitride (AlN), silicon nitride (Si₃N₄), Ceramics such as silicon carbide (SiC), crystallized glass, and high heat-resistant glass. In addition, a metal substrate that has been subjected to an enamel treatment can also be used.
[0063]
Thick dielectric layer 41
The lower insulator layer 4 needs to have a high dielectric constant and a high withstand voltage. By forming most of the lower insulating layer 4 from the thick-film dielectric layer 41, a high dielectric constant 100 times or more as compared with the case of using the thin-film dielectric layer can be achieved.
[0064]
Here, the thick film dielectric layer is a dielectric layer formed by a so-called thick film method, that is, a ceramic layer formed by firing a powdery insulating material. The thick film dielectric layer 41 can be formed, for example, by printing and firing an insulating paste in which a powdery insulating material, a binder and a solvent are mixed, on the substrate 2 on which the lower electrode layer 3 is formed. Alternatively, it can be formed by forming a green sheet by casting a film of an insulator paste, laminating the green sheet on the substrate 2 on which the lower electrode layer 3 is formed, and firing.
[0065]
The constituent material of the thick film dielectric layer 41 is not particularly limited.₃, (Ba_xCa_1-x) TiO₃, (Ba_xSr_1-x) TiO₃, PbTiO₃(Ferroelectric) material having a perovskite structure, such as PZT, PZT, or Pb (Mg_1/3Nb_2/3) O₃Perovskite relaxor type ferroelectric material represented by₄Ti₃O₁₂, SrBi₂Ta₂O₉Bismuth layered compound represented by (Sr_xBa_1-x) Nb₂O₆, PbNbO₆And the like are preferable. Note that PZT is Pb (Zr_xTi_1-x)₃It is. Among them, BaTiO₃A ferroelectric material having a perovskite structure such as PZT or PZT is preferable because of its high dielectric constant and easy firing.
[0066]
In particular, a dielectric material containing lead in its composition has a low melting point of lead oxide of 888 ° C., and contains lead oxide and another oxide-based material such as SiO 2.₂And CuO, Bi₂O₃, Fe₂O₃Since a liquid phase is formed at a low temperature of about 700 ° C. to 800 ° C. between them and the like, baking is easy at a low temperature and a high dielectric constant is easily obtained, which is preferable. Examples of the dielectric material containing lead include PZT and PLZT (PbZrO to which La is added).₃-PbTiO₃Perovskite structure dielectric material such as solid solution), Pb (Mg_1/3Nb_2/3) O₃Perovskite relaxer type ferroelectric material represented by PbNbO₆And the like are preferable. Among these, Pb (Mg_1/3Nb_2/3) O₃A lead-containing composite perovskite relaxor-type ferroelectric material represented by, for example, is preferable because a dielectric layer having a relative dielectric constant of 1000 to 10000 can be easily formed at a firing temperature of 700 to 900 ° C.
[0067]
The thickness of the thick dielectric layer 41 is required to be large in order to eliminate pinholes formed by steps of the electrodes and dusts in the manufacturing process, and is at least 10 μm or more, preferably 20 μm or more. However, in order to prevent an increase in the light emission threshold voltage, the total thickness of the thick film dielectric layer 41 and the surface flattening layer 42 is preferably set to 100 μm or less.
[0068]
Surface flattening layer 42
Since the surface flattening layer 42 is provided for the purpose of reducing the deterioration of the surface properties of the lower insulating layer 4 due to the surface unevenness of the thick film dielectric layer 41, the solution flattening method is used for forming the surface flattening layer 42. It is necessary to use
[0069]
The solution coating and sintering method refers to a method in which a precursor solution of a dielectric material is applied to a substrate and a dielectric layer is formed by sintering. For example, a sol-gel method and a MOD (Metallo-Organic Decomposition) method are known.
[0070]
The sol-gel method is generally a method in which a predetermined amount of water is added to a metal alkoxide dissolved in a solvent, and a precursor solution of a sol having an M-O-M bond formed by hydrolysis and polycondensation reaction is applied to a substrate and baked. This is a method of forming a film. The MOD method is a method in which a metal salt of a carboxylic acid having an MO bond or the like is dissolved in an organic solvent to form a precursor solution, which is applied to a substrate and baked to form a film. Here, the precursor solution refers to a solution containing an intermediate compound generated by dissolving a raw material compound in a solvent in a film forming method such as a sol-gel method or a MOD method.
[0071]
The sol-gel method and the MOD method are not completely separate methods, but are generally used in combination with each other. For example, when forming a PZT film, it is common to prepare a solution using lead acetate as a Pb source and alkoxides as Ti and Zr sources. In addition, the sol-gel method and the MOD method may be collectively referred to as a sol-gel method, but in any case, a precursor solution is applied to a substrate and baked to form a film. In the book, these are collectively referred to as a solution coating firing method. In addition, a solution obtained by mixing a submicron-sized dielectric particle and a precursor solution of a dielectric is also referred to as a precursor solution in the present specification, and a case where the solution is applied to a substrate and fired is also referred to as a solution coating firing method. .
[0072]
In both the sol-gel method and the MOD method, the solution coating and baking method involves the uniform mixing of the compounds composing the dielectric material on the order of submicron or less. The feature is that a dense dielectric can be synthesized at an extremely low temperature, as compared with the method using. The main reason for using the solution coating baking method is that the precursor solution is applied and baked, so that a thick film is formed on the concave portion of the base and a thin film is formed on the convex portion. The point is that unevenness and steps on the surface are not reflected, and a film having a flat surface is obtained. Therefore, by forming the surface flattening layer 42 using the solution coating and baking method, the surface roughness of the thick dielectric layer 41 is not reflected on the surface properties of the lower insulating layer 4, and The uniformity of the light emitting layer 5 formed on the substrate can be greatly improved.
[0073]
The thickness of the surface flattening layer 42 may be determined so as to sufficiently fill the irregularities on the surface of the thick dielectric layer 41, but is usually 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm. That is all. When the purpose is to fill irregularities on the surface of the thick film dielectric layer 41, the thickness of the surface flattening layer 42 does not need to exceed 10 μm.
[0074]
The relative permittivity of the surface flattening layer 42 is desirably as high as possible, preferably 100 or more, and more preferably 500 or more. As a dielectric material that can provide such a high dielectric constant, for example, BaTiO₃, (Ba_xCa_1-x) TiO₃, (Ba_xSr_1-x) TiO₃, PbTiO₃(Ferroelectric) material having a perovskite structure, such as PZT, PZT, PLZT, or Pb (Mg_1/3Nb_2/3) O₃Perovskite relaxor-type ferroelectric material represented by₄Ti₃O₁₂, SrBi₂Ta₂O₉Bismuth layered compound represented by (Sr_xBa_1-x) Nb₂O₆, PbNbO₆Tungsten bronze-type ferroelectric materials represented by, for example, are preferable. Among them, a ferroelectric material having a lead-based composite perovskite structure such as PZT or PLZT, particularly containing lead oxide in its basic composition, has a dielectric constant of It is preferable because the synthesis at a high temperature and a relatively low temperature of 700 ° C. or less is easy.
[0075]
The configuration example shown in FIG. 1 is a configuration in which a surface flattening layer 42 formed by a solution coating baking method is laminated on a thick film dielectric layer 41. In the EL device of the present invention, a thick film dielectric layer is provided. Instead, only the dielectric layer formed by the solution coating baking method may be provided. Since the heating process in an oxidizing atmosphere also exists in the solution coating and baking method as in the thick film method, the effect of providing the barrier layer can be realized even when only the dielectric layer is provided by the solution coating and baking method. .
[0076]
Thin-film insulator layer 43 and upper insulator layer 6
The thin-film insulator layer 43 and the upper insulator layer 6 that are in contact with and sandwich the light-emitting layer 5 are not necessarily provided, but are preferably provided.
[0077]
By providing these insulator layers, the electronic state at the interface between these insulator layers and the light emitting layer 5 can be controlled, so that the electron injection into the light emitting layer 5 can be stabilized and the efficiency can be improved. . Further, by providing these insulator layers symmetrically on both sides of the light emitting layer 5 with the light emitting layer 5 as a center, the electronic state becomes symmetric at both interfaces of the light emitting layer 5, so that the light emission characteristics during AC driving are symmetrical. Performance can be improved. These insulator layers do not need to have a function of maintaining dielectric strength, and thus may have a small thickness, preferably 10 to 1000 nm, more preferably about 20 to 200 nm.
[0078]
The specific resistance of these insulator layers is 10⁸Ω · cm or more, especially 10¹⁰-10¹⁸It is preferably about Ω · cm. Further, it is preferable that the material be composed of a substance having a relatively high relative permittivity, specifically, a substance having a relative permittivity of preferably 3 or more. As a constituent material of these insulator layers, for example, silicon oxide (SiO 2)₂), Silicon nitride (Si₃N₄), Tantalum oxide (Ta)₂O₅), Yttrium oxide (Y₂O₃), Zirconia (ZrO)₂), Silicon oxynitride (SiON), alumina (Al₂O₃) Etc. can be used. These insulator layers can be formed by a sputtering method, an evaporation method, or a CVD method.
[0079]
Light emitting layer 5
The effect of the present invention is realized irrespective of the constituent material of the light emitting layer 5. Therefore, the phosphor material constituting the light emitting layer 5 is not particularly limited, and any phosphor material such as the above-described Mn-doped ZnS may be used. The thickness of the light emitting layer is not particularly limited, but if it is too thick, the driving voltage increases, and if it is too thin, the luminous efficiency decreases. Specifically, the thickness is preferably about 100 to 2000 nm, though it depends on the luminescent material.
[0080]
The light emitting layer 5 can be formed by a vapor deposition method. As the vapor deposition method, a PVD method such as a sputtering method or a vapor deposition method or a CVD method (chemical vapor deposition method) is preferable. As described above, when forming the light emitting layer composed of SrS: Ce, H₂When the substrate is formed at a temperature of 500 to 600 ° C. during film formation by an electron beam evaporation method in an S atmosphere, a high-purity light-emitting layer can be obtained.
[0081]
After forming the light emitting layer 5, it is preferable to perform annealing. The annealing may be performed in a state where the light emitting layer 5 is exposed, or the cap annealing may be performed after forming the upper insulator layer 6 on the light emitting layer 5 or after forming the upper electrode layer 7. The optimum annealing temperature varies depending on the constituent materials of the light emitting layer. In the case of SrS: Ce, the annealing temperature is 500 ° C. or more, particularly 600 ° C. or more and the firing temperature of the thick film dielectric layer 41, and the processing time is 10 to 600 minutes. It is preferable that Annealing is preferably performed in an Ar atmosphere.
[0082]
Upper electrode layer 7
In the thin-film EL device of the present invention, since light is extracted from the upper electrode layer 7 side, the upper electrode layer 7 is made of a transparent conductive material. As the transparent conductive material, In used in the barrier layer 10₂O₃, SnO₂In addition to ITO and ITO, an oxide conductive material such as ZnO-Al can be used. For the upper electrode layer 7, a known technique such as a sputtering method or a vapor deposition method may be used. The thickness of the upper electrode layer 7 may be 0.2 to 1 μm.
[0083]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.
[0084]
Example 1
In the configuration shown in FIG. 1, each layer up to the thick film dielectric layer 41 was formed on the substrate 2 by the following procedure to obtain a sample for evaluation.
[0085]
Commercially available 96% purity alumina substrate (SiO 2 as sintering aid)₂/ MgO containing 4%) or a high strain point heat-resistant glass substrate (softening point: 850 ° C.) was used as the substrate 2, and a resist film for lift-off patterning was formed on the substrate 2 using a positive resist.
[0086]
Next, an Ag thin film or an Au thin film was formed as the lower electrode layer 3. Next, as the barrier layer 10, an ITO thin film or SnO₂A thin film was formed. As a comparative example, a sample without the barrier layer 10 was manufactured. Table 1 shows the configurations of the lower electrode layer 3 and the barrier layer 10. Each thin film was formed under the following conditions.
[0087]
The Ag thin film and the Au thin film were formed using a magnetron sputtering apparatus, using Ag as a target, in an Ar gas atmosphere at a pressure of 0.5 Pa, at a frequency of 13.56 MHz, and a high frequency power density of 3 W / cm.²Under the following conditions. The film formation rate was about 50 nm / min for the Ag thin film and about 33 nm / min for the Au thin film, and the thickness was as shown in Table 1 by adjusting the sputtering time. The specific resistance of the Ag thin film is 2 × 10^-6Ω · cm and Au thin film is 3 × 10^-6It was about Ω · cm.
[0088]
ITO (SnO) is deposited on the ITO thin film using a magnetron sputtering device.₂10% by mass) Using a ceramic as a target, a frequency of 13.56 MHz and a high-frequency power density of 4 W / cm in an Ar gas atmosphere at a pressure of 1 Pa²Under the following conditions. The film formation rate was about 15 nm / min, and a film having the thickness shown in Table 1 was obtained by adjusting the sputtering time. The specific resistance of the ITO thin film is 10^-3It was about Ω · cm. SnO₂The thin film was formed by using a magnetron sputtering apparatus, targeting a Sn + Sb1% alloy as a target and Ar + O at a pressure of 1 Pa.₂(20%) In a gas atmosphere, frequency 13.56 MHz, high frequency power density 4 W / cm²Under the following conditions. The film formation rate was about 30 nm / min, and a film having the thickness shown in Table 1 was obtained by adjusting the sputtering time. SnO₂The specific resistance of the thin film is 10^-2It was about Ω · cm.
[0089]
Next, unnecessary portions of the lower electrode layer 3 and the barrier layer 10 were separated by a lift-off method to be patterned to form a striped electrode layer in which a large number of electrodes having a plane dimension of 1 mm × 50 mm were arranged.
[0090]
Next, using a 4210C thick film dielectric paste manufactured by ESL, a thick film dielectric layer 41 was formed on the substrate 2 on which the barrier layer 10 was formed by a screen printing method. This thick film dielectric paste is composed of Pb (Mg_1/3Nb_2/3) O₃It is mainly composed of a perovskite-based dielectric composition and contains excess lead oxide as a sintering aid. At the time of screen printing, the operation of coating and drying was repeated until the total thickness of the coating film became 20 μm in the fired film thickness. Note that, for the measurement of the resistance value, regions of 5 mm at both ends of the striped barrier layer 10 were exposed without applying paste. After forming the coating film, the film was fired at 650 to 800 ° C. for 30 minutes in a belt furnace under an atmosphere supplied with sufficient air. Table 1 shows the firing temperature for each sample.
[0091]
With respect to each of the samples thus obtained, the electric resistance value of the laminate including the lower electrode layer 3 and the barrier layer 10 was measured. This electric resistance value is shown in Table 1 as an electrode resistance. The electrode resistance shown in Table 1 is a relative value when the electrode resistance of each sample before forming the thick film dielectric layer 41 is 1.
[0092]
[Table 1]

[0093]
Table 1 clearly shows the effect of the present invention. That is, when the lower electrode layer 3 made of an Ag thin film having a thickness of 500 nm is provided thereon and the barrier layer 10 made of an ITO thin film having a thickness of 500 nm is provided thereon, the thick film dielectric layer 41 is formed at a high firing temperature of 800 ° C. Even so, it can be seen that the increase in resistance due to this is about twice, and the function as an electrode is sufficiently maintained. Further, when the lower electrode layer 3 is made of Au, more excellent effects are obtained. In addition, as the barrier layer 10, SnO₂It can be seen that even when the thin film is provided, the same characteristics as when the ITO thin film is provided can be obtained.
[0094]
In contrast, when the Ag electrode was used alone without the barrier layer 10, the electrode was broken at a firing temperature of 650 ° C. or higher, and the function as an electrode was completely lost. Also, in the case of the Au electrode alone, disconnection occurred at a firing temperature of 800 ° C., and the function as an electrode was lost.
[0095]
In the sample in which the thickness of the ITO thin film was 25 nm, the change in the resistance value was larger than that in the case of the film thickness of 500 nm, but no disconnection occurred. The reason why the resistance change was increased when the barrier layer 10 was made thinner was that the surface of the substrate 2 was a baked surface of alumina ceramics, so that the surface of the substrate 2 was very uneven, and the barrier layer 10 formed thereover with the lower electrode layer 3 interposed therebetween. If the film thickness is small, it is considered that step coverage becomes insufficient during sputtering, and a portion not covered by the barrier layer 10 locally occurs on the surface of the lower electrode layer 3.
[0096]
Example 2
Using the alumina substrate 2 used in Example 1, the thick film dielectric layer 41 was formed of barium titanate (BaTiO 3).₃) Was obtained in the same manner as in Example 1 except that the sample for evaluation was used. The firing temperature at the time of forming the thick film dielectric layer 41 was 900 ° C. For this evaluation sample, the same measurement as in Example 1 was performed. Table 2 shows the results.
[0097]
[Table 2]

[0098]
From Table 2, it is clear that the barrier layer 10 is effective even when the lower insulating layer 4 does not contain a lead-based compound.
[0099]
In addition, since it heated to 900 degreeC at the time of formation of the thick film dielectric layer 41, the specific resistance of the barrier layer (ITO) rose to 100 ohm * cm. However, as shown in Table 2, even if the barrier layer is thin (even at a thickness of 200 nm), the barrier layer has a sufficient effect, and if the barrier layer has such a thickness, the electric resistance value of the barrier layer in the thickness direction becomes large. It is acceptable.
[0100]
Example 3
An EL device having the configuration shown in FIG. 1 was manufactured by the following procedure. However, the thin film insulator layer 43 was not formed.
[0101]
First, a lower electrode layer 3, a barrier layer 10, and a thick dielectric layer 41 were formed on a substrate 2 made of alumina in the same manner as in Example 1. However, the planar dimensions of each electrode constituting the lower electrode layer 3 were 1 mm × 100 mm, and the baking of the thick film dielectric layer 41 was performed at 750 ° C. for 20 minutes. The dielectric constant of the thick dielectric layer 41 was about 2500. Table 3 shows the configurations of the lower electrode layer 3 and the barrier layer 10.
[0102]
Next, the surface flattening layer 42 was formed by using a solution coating baking method. In this solution coating and firing method, a sol-gel solution of PZT was used as a precursor solution. This precursor solution was applied to the surface of the thick-film dielectric layer 41 by spin coating, and repeatedly baked at 700 ° C. for 10 minutes to form a surface flattening layer 42 having a thickness of about 3 μm. .
[0103]
The precursor solution was prepared according to the following procedure. First, 8.49 g of lead acetate trihydrate and 4.17 g of 1,3-propanediol were mixed and heated and stirred for about 2 hours to obtain a transparent solution. Separately, 3.70 g of a zirconium normal propoxide 70% by mass 1-propanol solution and 1.58 g of acetylacetone were heated and stirred in a dry nitrogen atmosphere for 30 minutes. A solution of isopropoxide bisacetylacetonate 75 mass% in 2-propanol and 2.32 g of 1,3 propanediol were added, and the mixture was further heated and stirred for 2 hours to prepare a solution. This solution and the transparent solution were mixed at 80 ° C., and heated and stirred in a dry nitrogen atmosphere for 2 hours to produce a brown transparent solution. This solution was kept at 130 ° C. for several minutes to remove by-products, and further heated and stirred for 3 hours to obtain a precursor solution. The viscosity of the precursor solution was adjusted by diluting with n-propanol.
[0104]
Next, while the substrate is heated to 200 ° C., a 0.8 μm-thick luminescent layer 5 made of ZnS: Mn is formed by an evaporation method using a Mn-doped ZnS evaporation source, and then 500 ° C. in vacuum. For 10 minutes.
[0105]
Next, Si is used as the upper insulator layer 6.₃N₄A thin film EL element sample was obtained by sequentially forming an ITO thin film as the upper electrode layer 7 by a sputtering method. The upper electrode layer 7 was patterned into a stripe shape in which linear electrodes having a width of 1 mm were arranged by using a metal mask during film formation.
[0106]
With respect to these samples, electrodes were respectively extracted from the lower electrode layer 3 and the upper electrode layer 7, and an electric field of 1 kHz and a pulse width of 50 μs was applied at an intensity at which the emission luminance was saturated, and the saturation luminance and the emission of light in the plane of the emission surface were measured. The uniformity was investigated. Table 3 shows the results.
[0107]
[Table 3]

[0108]
As is clear from Table 3, the sample of the present invention having the structure in which the barrier layer 10 is laminated on the lower electrode layer 3 has high luminance and uniform light emission characteristics.
[0109]
On the other hand, the comparative sample in which the lower electrode layer 3 was formed of an Ag thin film without providing a barrier layer did not emit light at all. This is presumably because the lower electrode layer 3 was disconnected during firing of the thick dielectric layer 41 and lost its function as an electrode.
[0110]
On the other hand, the comparative sample in which the lower electrode layer 3 was made of an Au thin film without a barrier layer had almost the same saturation luminance as that of the sample of the present invention, but was visually observed to have poor uniformity of the light emitting surface. When observed on the order of several tens of μm using, a region where light emission was weak and a region where light emission was strong were mixed partially. This non-uniformity is due to the lack of heat resistance of the Au thin film due to the absence of the barrier layer, the partial loss of the function as an electrode, and the fact that the alumina thin film 2 SiO₂It is presumed that this is because the system-based sintering aid partially reacted with the lead-based thick film dielectric layer 41, and the characteristics of the thick film dielectric layer 41 were distributed.
[0111]
Example 4
The lower electrode layer 3 was made of Ag, and the lower electrode layer 3 was patterned by the lift-off method, except that ashing with oxygen plasma was used to remove the resist residue when removing the resist residue. Element sample No. 1 was produced. This comparative sample No. In No. 1, the lead portion 31 of the lower electrode layer 3 made of Ag was oxidized by the oxygen plasma in the lift-off process and was blackened, so that the conductivity of the surface was lowered and the function as an electrode constituent material was lost.
[0112]
Further, when the lower electrode layer 3 is formed, ashing with oxygen plasma is not performed, and₂The comparative sample No. 1 was composed of a SrS: Ce layer formed by a vapor deposition method in an S gas atmosphere. In the same manner as in Comparative Sample No. 1, 2 was produced. This comparative sample No. 2, the lead portion 31 of the lower electrode layer 3 made of Ag is₂Since it was sulfided and blackened by the S gas, the conductivity of the surface was reduced and the function as an electrode constituent material was lost.
[0113]
Further, except that the entire surface of the lower electrode layer 3 was covered with a barrier layer 10 made of ITO and having a thickness of 100 nm, and the lower electrode layer 3 was formed, ashing by oxygen plasma was performed. In the same manner as in Example 2, 3 was produced. In this example sample no. 3, since the lead portion 31 of the lower electrode layer 3 was covered with the barrier layer 10, oxygen plasma and H₂Oxidation and sulfidation of the lead portion 31 by S gas did not occur.
[0114]
【The invention's effect】
In a conventional thin film EL element, if the lower electrode layer is thin, the lower electrode layer becomes a discontinuous film having an island-like structure due to heating when forming the lower insulator layer thereover by a thick film method, which is expensive. The lower electrode layer containing the noble metal had to be thickened. As a result, the material cost is increased, and a step appearing on the EL panel surface due to the pattern edge of the lower electrode layer is increased, thereby significantly lowering the display quality.
[0115]
On the other hand, the thin-film EL device of the present invention has a structure in which the barrier layer is laminated on the lower electrode layer, so that it is heated when the lower insulator layer is formed thereon by a thick film method or a solution coating baking method. Also, it is difficult for the lower electrode layer to have an island structure. Therefore, in the device of the present invention, the thickness of the lower electrode layer can be reduced, and as a result, reduction in material cost and improvement in display quality can be realized.
[0116]
A dielectric material containing lead oxide can be fired at a low temperature and has a high dielectric constant. In addition, pure Ag or a metal material containing Ag is suitable as a lower electrode layer constituent material because the electrode layer is thin because of high conductivity and the material cost is low. However, since Ag has high reactivity with lead oxide, the lead oxide in the lower insulator layer reacts with Ag in the lower electrode layer when the lower insulator layer is formed, which causes an increase in resistance and disconnection of the lower electrode layer.
[0117]
On the other hand, the barrier layer provided in the present invention exhibits a strong barrier property against lead diffusion. Therefore, in the present invention, a lower insulator layer containing a lead-based dielectric and a lower electrode layer containing an Ag-based material can be combined, thereby realizing an EL element having good emission characteristics and display quality at low cost. be able to. Further, the barrier layer can prevent oxidation and sulfidation of the lower electrode made of the Ag-based material.
[0118]
A composite substrate in which an electrode layer and a barrier layer are provided on a substrate in the same manner as the lower electrode layer and the barrier layer in the EL element of the present invention is suitable not only for an EL element but also for various other display elements. . That is, since the heat resistance of the electrode layer is good in this composite substrate, when various layers requiring heating at the time of formation and / or after the formation are provided on the electrode layer, the same effect as when applied to the EL element is realized. I do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration example of a thin-film EL device of the present invention.
FIG. 2 is a perspective view illustrating a configuration example of a thin-film EL element having a double insulation structure.
[Explanation of symbols]
2 substrate
3 Lower electrode layer
31mm lead
4 Lower insulator layer
41 thick dielectric layer
42 surface flattening layer
43 thin film insulator layer
5 Light emitting layer
6 Upper insulator layer
7 Upper electrode layer
8 mm front protective glass
9 Sealant
10 barrier layer
11 anisotropic conductive resin layer
12mm flexible printed circuit board

Claims (6)

A thin-film EL element having at least a lower electrode layer, a barrier layer containing a conductive inorganic compound, a lower insulator layer, a light-emitting layer, and an upper electrode layer in this order on an electrically insulating substrate. 2. The thin film EL device according to claim 1, wherein the conductive inorganic compound is an oxide. 2. The thin-film EL device according to claim 1, wherein the conductive inorganic compound is an oxide containing indium and / or tin. 4. The thin film EL device according to claim 1, wherein said lower electrode layer contains Ag. 5. The thin-film EL device according to claim 1, wherein said lower insulator layer contains an oxide dielectric containing lead. A composite substrate having, in this order, an electrode layer containing Ag and a barrier layer containing a conductive inorganic compound on a substrate having electrical insulation.

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