JP2004192890A - Organic electroluminescent element - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は有機電界発光素子に関し、特には下部電極と光透過性の上部電極との間に有機層を狭持してなる有機電界発光素子に関する。
【０００２】
【従来の技術】
フラットパネルディスプレイ用の表示素子として、有機電界発光素子（以下、有機ＥＬ素子と記す）の実用化を目指した研究開発が精力的に行われている。その中でも、基板と逆方向に発光光を取り出す上面発光型の有機ＥＬ素子は、基板側に画素駆動用のＴＦＴを形成するアクティブマトリックス型のディスプレイにおいて、基板側に発光光を取り出す透過型と比較して開孔率を大きく出来るために、高輝度あるいは高解像度の有機ＥＬディスプレイを製造する上で有利であ
る。
【０００３】
上面発光型の有機ＥＬ素子を作製するためには、まず基板上に、抵抗加熱による真空蒸着法・スパッタ法などの中から適宜選択された方法で金属薄膜を成膜し、これをパターニングすることで反射層を兼ねた下部電極を形成する。次いで、素子分離するための絶縁層を成膜して下部電極を露出開口させるようにパターニングした後に、下部電極上に重ねて有機層および上部電極をこの順に形成する。
【０００４】
ところで、このようにして得られた有機ＥＬ素子においては、下部電極の表面に存在する凹凸によって、有機層の膜厚が局部的に薄くなるため、下部電極−上部電極間に短絡が生じやすいことが問題の一つとなっている。これを解決するための手段として、下記特許文献１では、下部電極上に当該下部電極を構成する金属材料の酸化物からなる緩衝薄膜層を設けた構成が提案されている。
【０００５】
【特許文献１】
特開２００２−２１６９７６号公報
【０００６】
【発明が解決しようとする課題】
しかしながら、緩衝薄膜層を構成する金属酸化物は、ある程度の光透過性を有するものの、可視光領域に光吸収を持つ。このため、有機層で発生させた発光光は、緩衝薄膜層を通過する際に吸収され、光取り出し効率の低下を招く。このような光取り出し効率の低下は、有機ＥＬ素子を用いたディスプレイの消費電力を増大させ、また寿命特性を低下させる要因となっている。
【０００７】
本発明は、かかる点に対処してなされたもので、高効率で素子短絡などの生じない、高信頼性をもつ上面発光型の有機ＥＬ素子を実現することを目的とする。
【０００８】
【課題を解決するための手段】
このような目的を達成するための本発明は、基板上に設けられた下部電極と、この下部電極上に設けられた有機層と、この有機層上に設けられた光透過性の上部電極とからなる有機ＥＬ素子において、下部電極が、金属材料からなる反射層とこの上部の緩衝層とで構成されており、このうち特に緩衝層がＩＴＯ、ＩＺＯ、ＳｎＯ２、ＺｎＯ、ＣｄＯ、ＴｉＯ２およびこれらに類する透明導電性材料のうちの少なくとも１つからなることを特徴としている。
【０００９】
このような構成の有機ＥＬ素子では、下部電極の下層となる反射層が、可視領域の光に対する反射性が良好な金属材料で構成され、この反射層を覆う緩衝層が、ＩＴＯ、ＩＺＯ、ＳｎＯ２、ＺｎＯ、ＣｄＯ、ＴｉＯ２およびこれらに類する透明導電性材料で構成される。これらの透明導電性材料は、金属材料よりも表面粗さが小さくなるように成膜可能なだけではなく、可視領域光に対する光吸収性が極めて小さく光透過性が良好である。このため、この緩衝層によって、反射層の表面粗さが緩和され下部電極の表面平坦性が良好となり、この下部電極上に有機層を介して積層された光透過性の上部電極と、当該下部電極との間隔の面内均一性が確保され、電極間の短絡の発生が防止されるようになる。しかも、有機層においての発光光が、緩衝層を通過することによる光損失が最小限に抑えられる。
【００１０】
【発明の実施の形態】
以下、本発明の有機ＥＬ素子の実施の形態を、図１の断面構成図に基づいて詳細に説明する。
【００１１】
この図に示す有機ＥＬ素子１は、基板２上に、下部電極３、有機層４及び光透過性の上部電極５を順次積層してなり、この素子で発光した発光光ｈを上部電極５側から取り出す、いわゆる上面発光型として構成されている。以下、さらに詳しい構成を、基板２、本発明に特有の構成である下部電極３、上部電極５、および有機層４の順に説明する。
【００１２】
先ず、基板２は、ガラス、シリコン、プラスチック基板、さらにはＴＦＴ（ｔｈｉｎ ｆｉｌｍ ｔｒａｎｓｉｓｔｏｒ）が形成されたＴＦＴ基板などからなる。
【００１３】
そして、下部電極３は、陽極または陰極として用いられるものである一方、上部電極５は、下部電極３が陽極である場合には陰極として用いられ、下部電極３が陰極である場合には陽極として用いられる。
【００１４】
ここで、下部電極３は、有機ＥＬ素子１の駆動方式によって適する形状にパターニングされていることとする。例えば、この有機ＥＬ素子１を用いた表示装置の駆動方式が単純マトリックス型である場合には、この下部電極３は例えばストライプ状に形成される。また、表示装置の駆動方式が画素毎にＴＦＴを備えたアクティブマトリックス型である場合には、下部電極３は複数配列された各画素に対応させてパターン形成され、同様に各画素に設けられたＴＦＴに対して、これらのＴＦＴを覆う層間絶縁膜に形成されたコンタクトホール（図示省略）を介してそれぞれが接続される状態で形成されることとする。そして、下部電極３は、発光領域７ａのみを露出開口させる形状の絶縁膜７によって、その周縁が覆われている。
【００１５】
一方、上部電極５は、この有機ＥＬ素子１を用いた表示装置が、単純マトリックス型である場合には、下部電極３のストライプと交差するストライプ状に形成され、これらが交差して積層された部分が有機ＥＬ素子１となる。また、この表示装置が、アクティブマトリックス型である場合には、この上部電極５は、基板２上の一面を覆う状態で成膜されたベタ膜状に形成され、各画素に共通の電極として用いられることとする。尚、表示装置の駆動方式としてアクティブマトリックス型を採用する場合には、本発明が適用される上面発光型の有機ＥＬ素子１を用いることで素子の開口率の向上が図られる。
【００１６】
そして、本発明に特徴的な構成である下部電極３は、反射層３ａおよびこの上部に積層された緩衝層３ｂとの積層構造で構成されている。
【００１７】
このうち反射層３ａは、金属材料、特には可視領域の光に対する反射性の良好なＣｒ（クロム）、Ａｌ（アルミニウム）、Ａｇ（銀）およびこれらを主成分とする合金を用いて構成され、特には好ましく光反射性およびプロセスの安定性に優れたＡｇ（銀）およびＡｇを主成分とする合金を用いて構成されることとする。
【００１８】
また、緩衝層３ｂは、ＩＴＯ（Ｉｎｄｉｕｍ Ｔｉｎ Ｏｘｉｄｅ）、ＩＺＯ（Ｉｎｄｉｕｍ Ｚｉｎｃ Ｏｘｉｄｅ）、ＳｎＯ２、ＺｎＯ、ＣｄＯおよびＴｉＯ２およびこれらに類する透明導電性材料のうちの少なくとも１つからなることとする。特に、緩衝層３ｂがＩＴＯからなる場合には、２ｎｍより厚く３０ｎｍより薄く、好ましくは５ｎｍ〜２０ｎｍの範囲で緩衝層３ｂを構成することが好ましい。
【００１９】
尚、下部電極３が陽極、陰極のどちらとして用いられるかは、緩衝層３ｂを構成する材料の仕事関数と緩衝層３ｂとの界面に配置される有機層４の材料によって決定される。例えば下部電極３を陽極として用いる場合には、緩衝層３ｂはＩＴＯ（Ｉｎｄｉｕｍ Ｔｉｎ Ｏｘｉｄｅ）、ＩＺＯ（Ｉｎｄｉｕｍ Ｚｉｎｃ Ｏｘｉｄｅ）、ＳｎＯ２、ＺｎＯ、ＣｄＯおよびＴｉＯ２が用いられ、例えば陰極として用いる場合には、緩衝層３ｂは上記透明導電性材料の上に例えばＬｉ２ＯやＭｇ、Ｌｉ、Ｃａ等のアルカリ金属とその酸化物、弗化物、窒化物などの低仕事関数材料を１ｎｍ以下積層する必要がある。
【００２０】
一方、光透過性の上部電極５は、光透過性に優れた導電性材料のうちから、当該上部電極５が陽極、陰極のどちらとなるかによって適宜選択して用いられる。例えば、上部電極５が陰極となる場合、Ｍｇ（マグネシウム）とＡｇ（銀）との共蒸着層が用いられる。一方、上部電極５が陽極となる場合、例えばＩＴＯ（Ｉｎｄｉｕｍ Ｔｉｎ Ｏｘｉｄｅ）、ＩＺＯ（Ｉｎｄｉｕｍ Ｚｉｎｃ Ｏｘｉｄｅ）、ＳｎＯ２、ＺｎＯ、ＣｄＯおよびＴｉＯ２が用いられる。
【００２１】
そして、有機層４は、陽極側（図面においては一例として下部電極３側）から順に、正孔注入層４ａ、正孔輸送層４ｂ、電子輸送性発光層４ｃをこの順に積層してなる。尚、有機層４の構成はこのような構成に限定されることはなく、正孔輸送層と電子輸送層との間に発光層を設けた構成や、電子輸送層と陰極との間に電子注入層を設けた構成であっても良く、必要に応じた積層構造として良い。
【００２２】
尚、光透過性の上部電極５と反射層３ａとは、電子輸送性発光層４ｃで発生した光ｈを共振させる共振器の共振部を構成していることとする。
【００２３】
この場合、反射層３ａ及び光透過性の上部電極５で生じる反射光の位相シフトをΦ、反射層３ａと光透過性の上部電極５との光学的距離をＬ、光透過性の上部電極５の側から取り出す光ｈのスペクトルのピーク波長をλとすると、光学的距離Ｌは、下記式（１）を満たす正の最小値となっていることとする。
【数２】
以上のように構成された有機ＥＬ素子では、下部電極３の下層となる反射層３ａが、可視領域の光に対する反射性が良好な金属材料で構成され、この反射層３ａを覆う緩衝層３ｂが、ＩＴＯ、ＩＺＯ、ＳｎＯ２、ＺｎＯ、ＣｄＯ、ＴｉＯ２及びこれらに類する透明導電性材料で構成される。これらの透明導電性材料は、金属材料よりも表面粗さが小さくなるように成膜可能なだけではなく、可視領域光に対する光吸収性が極めて小さく、光透過性が良好である。
【００２５】
中でも、ＩＴＯは、その膜厚を２ｎｍより厚く３０ｎｍより薄く、さらに好ましくは５ｎｍ〜２０ｎｍの範囲とすることで、ＩＴＯ膜自体の凹凸を発現させることなく下地となる反射層３ａの凹凸を緩和可能である。またＩＺＯは、もともと非結晶性の材料であるため、このＩＺＯを緩衝膜３ｂとして形成することで下地となる反射層３ａの凹凸を緩和可能である。
【００２６】
以上のように、緩衝層３ｂによって、反射層３ａの表面粗さが緩和され下部電極の表面平坦性が良好となり、この下部電極３上に有機層４を介して積層された上部電極５と、下部電極３との間隔の面内均一性が確保される。しかも、有機層４において生じた発光光ｈが、緩衝層３ｂを通過することによる光損失を最小限に抑えることが可能になる。
【００２７】
この結果、本構成の有機ＥＬ素子によれば、下部電極３−上部電極５間の短絡の発生なく高信頼性を維持でき、しかも光取り出し効率の向上によって消費電力の低下と寿命特性の向上とを実現することが可能になる。
【００２８】
【実施例】
以下、本発明の具体的な実施例１とこの実施例１に対する比較例の有機ＥＬ素子の製造手順を図１に基づいて説明し、さらに実施例１と比較例とについて行った評価結果を説明する。またその後、実施例２とその評価結果を説明する。
【００２９】
＜実施例１＞
まず、ガラス板からなる基板２上に、Ｃｒ（膜厚約１５０ｎｍ）をスパッタ法によって成膜し、さらに成膜装置の真空状態を維持したまま連続してＩＴＯを１０ｎｍの膜厚に成膜した。その後、通常のリソグラフィー法によって形成したレジストパターンをマスクに用いたエッチングによって、Ｃｒからなる反射層３ａ上にＩＴＯからなる緩衝層３ｂを積層してなる下部電極３を陽極としてパターン形成した。
【００３０】
次いで、ＣＶＤ法によって、ＳｉＯ２膜からなる絶縁膜７を６００ｎｍの膜厚で形成してこれをパターニングし、下部電極３表面の２ｍｍ×２ｍｍの発光領域７ａを露出開口させてそれ以外を絶縁膜７でマスクした有機ＥＬ素子用のセルを作製した。
【００３１】
次に、純水洗浄を行った後、下部電極３をＯ２プラズマに晒す前処理を行った。これに引き続き、基板２を大気暴露することなく有機層４を成膜するための成膜チャンバ内に搬送した。
【００３２】
次いで、発光領域７ａよりも一回り大きい開口部を有するメタルマスク（図示省略）を所定の位置にアライメントした状態で、１０−４Ｐａ以上の真空度で、正孔注入層４ａ、正孔輸送層４ｂ、および電子輸送性発光層４ｃを順次成膜した。尚、正孔輸送層４ａとして膜厚３０ｎｍのＭＴＤＡＴＡを成膜し、正孔輸送層４ｂとして膜厚２０ｎｍのα−ＮＰＤを成膜し、電子輸送性発光層４ｃとして膜厚５０ｎｍのＡｌｑ３を成膜した。これらの各層４ａ−４ｃは、それぞれ蒸着用ボートに０．２ｇ程度ずつ充填し、蒸着用ボートの両端に電圧を印加することで蒸着成膜した。
【００３３】
そしてさらに、成膜チャンバ内の真空状態を保持したままで、上部電極５用のマスクを所定の位置にアライメントし、１０−４Ｐａ以上の真空度で、陰極となる上部電極５としてＭｇ（マグネシウム）とＡｇ（銀）との共蒸着層［Ｍｇ：Ａｇ＝１０：１（体積比）］を１０ｎｍの膜厚で形成した。
【００３４】
その後、さらに成膜チャンバ内の真空状態を保持したままで、保護膜用のマスクを所定の位置にアライメントし、保護膜（図示省略）としてＳｉＮｘをＣＶＤ法により１μｍの膜厚で形成した。
【００３５】
以上により、実施例の有機ＥＬ素子を作製した。
【００３６】
＜実施例２＞
本実施例２においては、陽極となる下部電極３の反射層３ａとして、膜厚１５０ｎｍのＡｇ（銀）を形成したこと以外は、実施例１と同様の手順で有機ＥＬ素子を作製した。
【００３７】
＜比較例＞
比較例においては、陽極となる下部電極３の緩衝層３ｂとして、膜厚１０ｎｍのＣｒＯ２を形成したこと以外は、実施例１と同様の手順で有機ＥＬ素子を作製した。
【００３８】
―評価結果―
以上の様にして作製した各４０個の実施例１、実施例２および比較例の有機ＥＬ素子について、上部電極３−下部電極５間の▲１▼短絡発生数（個）、８．０Ｖの電圧を印加した場合の▲２▼電流密度および▲３▼発光輝度を計測した。この結果を表１に示す。
【００３９】
【表１】
表１に示されるように、実施例１、実施例２、比較例の有機ＥＬ素子ともに、▲１▼短絡発生数は０［個］、▲２▼電流密度も２０［ｍＡ／ｃｍ２］であった。一方、▲３▼発光輝度に関しては、比較例の有機ＥＬ素子の値に対して、本発明を適用した実施例１の有機ＥＬ素子の値が１．２倍程度高く、また本発明を適用した実施例２の有機ＥＬ素子の値が２．１倍以上高く、発光効率を上昇させる効果が確認できた。
【００４１】
尚、本実施例２と同様の手順において、ＩＴＯからなる緩衝層３ｂの膜厚がそれぞれ異なる各有機ＥＬ素子をそれぞれ４０個づつ作製し、これらの有機ＥＬ素子に関して上部電極３−下部電極５間の短絡発生数（個）を計測した。この結果を図２のグラフに示す。
【００４２】
このグラフに示したように、ＩＴＯからなる緩衝層３ｂについては、その膜厚が２ｎｍ〜３０ｎｍの範囲であれば、有機ＥＬ素子の短絡個数を２／４０［個］以下に抑えられる効果が確認できた。これは、従来の技術において、示した特許文献１第６頁に示される発光素子▲２▼と同等の結果である。したがって、ＩＴＯからなる緩衝膜３ｂの膜厚が２ｎｍよりも厚く、３０ｎｍよりも薄い範囲であれば、この結果を超える効果が得られることなる。さらに、ＩＴＯからなる緩衝層３ｂの膜厚が５ｎｍ〜２０ｎｍの範囲であれば、有機ＥＬ素子の短絡個数を１／４０［個］以下に抑えられる効果が確認できた。またさらに、ＩＴＯからなる緩衝層３ｂの膜厚が１０ｎｍであれば、有機ＥＬ素子の短絡個数を０／４０［個］に抑えられる効果が確認できた。
【００４３】
【発明の効果】
以上説明したように本発明の有機ＥＬ素子によれば、金属材料からなる反射層上に、ＩＴＯ、ＩＺＯ、ＳｎＯ２、ＺｎＯ、ＣｄＯ及びＴｉＯ２等の可視領域光に対する光吸収性が極めて小さい透明導性材料からなる緩衝層を設けた下部電極構成とすることで、上部電極−下部電極間の面内均一性を確保しつつも、緩衝層を通過することによる光損失を最小限に抑えることが可能になる。この結果、下部電極−上部電極間の短絡を防止して高信頼性を維持でき、しかも光取り出し効率の向上によって消費電力の低下と寿命特性の向上とを実現することが可能になる。
【図面の簡単な説明】
【図１】実施形態の有機ＥＬ素子の断面構成図である。
【図２】実施例２で作製した各４０個の有機ＥＬ素子の短絡発生個数のグラフである。
【符号の説明】
１…有機ＥＬ素子（有機電界発光素子）、２…基板、３ａ…反射層、３ｂ…緩衝層、３…下部電極、５…有機層、６…上部電極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent device having an organic layer sandwiched between a lower electrode and a light-transmitting upper electrode.
[0002]
[Prior art]
Research and development for the practical use of organic electroluminescent elements (hereinafter, referred to as organic EL elements) as display elements for flat panel displays are being vigorously conducted. Among them, the top emission type organic EL element that emits emitted light in the direction opposite to the substrate is compared with the transmission type that emits emitted light to the substrate side in an active matrix type display in which TFTs for driving pixels are formed on the substrate side. In this case, the aperture ratio can be increased, which is advantageous in manufacturing a high-brightness or high-resolution organic EL display.
[0003]
In order to manufacture a top emission type organic EL element, first, a metal thin film is formed on a substrate by a method appropriately selected from a vacuum deposition method, a sputtering method, or the like by resistance heating, and is patterned. To form a lower electrode also serving as a reflective layer. Next, after an insulating layer for element isolation is formed and patterned so as to expose and expose the lower electrode, an organic layer and an upper electrode are formed in this order on the lower electrode.
[0004]
By the way, in the organic EL element thus obtained, the thickness of the organic layer is locally reduced due to the unevenness existing on the surface of the lower electrode, so that a short circuit is likely to occur between the lower electrode and the upper electrode. Is one of the problems. As a means for solving this problem, Japanese Patent Application Laid-Open No. H11-163,073 proposes a configuration in which a buffer thin film layer made of an oxide of a metal material constituting the lower electrode is provided on the lower electrode.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-216976
[Problems to be solved by the invention]
However, although the metal oxide constituting the buffer thin film layer has a certain degree of light transmittance, it has light absorption in the visible light region. For this reason, the emitted light generated in the organic layer is absorbed when passing through the buffer thin film layer, resulting in a decrease in light extraction efficiency. Such a decrease in light extraction efficiency causes an increase in power consumption of a display using an organic EL element and a decrease in life characteristics.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to realize a highly reliable top emission type organic EL element which is highly efficient and does not cause element short-circuiting.
[0008]
[Means for Solving the Problems]
The present invention for achieving such an object includes a lower electrode provided on a substrate, an organic layer provided on the lower electrode, and a light-transmitting upper electrode provided on the organic layer. The lower electrode is composed of a reflective layer made of a metal material and a buffer layer thereabove, and particularly the buffer layer is made of ITO, IZO, SnO 2 , ZnO, CdO, TiO 2 and It is characterized by being made of at least one of transparent conductive materials similar to these.
[0009]
In the organic EL element having such a configuration, the reflective layer, which is the lower layer of the lower electrode, is made of a metal material having good reflectivity to light in the visible region, and the buffer layer covering this reflective layer is made of ITO, IZO, SnO. 2 , ZnO, CdO, TiO 2 and similar transparent conductive materials. These transparent conductive materials can not only be formed into a film so as to have a smaller surface roughness than a metal material, but also have a very low light absorption for visible region light and a good light transmission. Therefore, the buffer layer reduces the surface roughness of the reflective layer and improves the surface flatness of the lower electrode. The light-transmitting upper electrode laminated on the lower electrode via the organic layer, In-plane uniformity of the interval between the electrodes is ensured, and the occurrence of a short circuit between the electrodes is prevented. In addition, light loss due to light emitted from the organic layer passing through the buffer layer can be minimized.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the organic EL device of the present invention will be described in detail with reference to the cross-sectional configuration diagram of FIG.
[0011]
The organic EL device 1 shown in FIG. 1 has a lower electrode 3, an organic layer 4, and a light-transmissive upper electrode 5 sequentially laminated on a substrate 2, and emits light h emitted by this device on the upper electrode 5 side. So-called top emission type. Hereinafter, a more detailed configuration will be described in the order of the substrate 2, the lower electrode 3, the upper electrode 5, and the organic layer 4, which are configurations specific to the present invention.
[0012]
First, the substrate 2 includes a glass, silicon, plastic substrate, and a TFT substrate on which a thin film transistor (TFT) is formed.
[0013]
The lower electrode 3 is used as an anode or a cathode, while the upper electrode 5 is used as a cathode when the lower electrode 3 is an anode, and as an anode when the lower electrode 3 is a cathode. Used.
[0014]
Here, it is assumed that the lower electrode 3 is patterned into an appropriate shape according to the driving method of the organic EL element 1. For example, when the driving method of the display device using the organic EL element 1 is a simple matrix type, the lower electrode 3 is formed in a stripe shape, for example. When the driving method of the display device is an active matrix type having a TFT for each pixel, the lower electrode 3 is formed in a pattern corresponding to each of a plurality of arranged pixels, and is similarly provided for each pixel. The TFTs are formed to be connected to each other via contact holes (not shown) formed in an interlayer insulating film covering these TFTs. The periphery of the lower electrode 3 is covered with an
[0015]
On the other hand, when the display device using the organic EL element 1 is of a simple matrix type, the upper electrode 5 is formed in a stripe shape that intersects with the stripe of the lower electrode 3, and these are intersected and stacked. The portion becomes the organic EL element 1. When the display device is of an active matrix type, the upper electrode 5 is formed as a solid film formed so as to cover one surface of the substrate 2 and is used as an electrode common to each pixel. Shall be In the case where the active matrix type is adopted as the driving method of the display device, the aperture ratio of the element is improved by using the top emission type organic EL element 1 to which the present invention is applied.
[0016]
The lower electrode 3, which is a characteristic feature of the present invention, has a laminated structure of a reflective layer 3a and a buffer layer 3b laminated thereon.
[0017]
The reflective layer 3a is made of a metal material, in particular, Cr (chromium), Al (aluminum), Ag (silver), and an alloy containing these as main components, which have good reflectivity to light in the visible region. Particularly, it is preferable to use Ag (silver) and an alloy containing Ag as a main component, which are preferably excellent in light reflectivity and process stability.
[0018]
The buffer layer 3b is made of at least one of ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), SnO 2 , ZnO, CdO, TiO 2 and a transparent conductive material similar thereto. In particular, when the buffer layer 3b is made of ITO, it is preferable that the buffer layer 3b be configured to be thicker than 2 nm and thinner than 30 nm, preferably in the range of 5 nm to 20 nm.
[0019]
Whether the lower electrode 3 is used as an anode or a cathode is determined by the work function of the material forming the buffer layer 3b and the material of the organic layer 4 disposed at the interface between the buffer layer 3b. For example, when the lower electrode 3 is used as an anode, the buffer layer 3b is made of ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), SnO 2 , ZnO, CdO, and TiO 2. For the buffer layer 3b, it is necessary to laminate, for example, an alkali metal such as Li 2 O, Mg, Li, or Ca and a low work function material such as an oxide, a fluoride, or a nitride of 1 nm or less on the transparent conductive material. is there.
[0020]
On the other hand, the light transmissive upper electrode 5 is appropriately selected and used from conductive materials having excellent light transmissivity depending on whether the upper electrode 5 is an anode or a cathode. For example, when the upper electrode 5 serves as a cathode, a co-deposited layer of Mg (magnesium) and Ag (silver) is used. On the other hand, when the upper electrode 5 serves as an anode, for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), SnO 2 , ZnO, CdO, and TiO 2 are used.
[0021]
The organic layer 4 is formed by laminating a hole injection layer 4a, a
[0022]
Note that the light-transmissive upper electrode 5 and the reflective layer 3a constitute a resonator of a resonator that resonates the light h generated in the electron transporting light emitting
[0023]
In this case, the phase shift of the reflected light generated by the reflection layer 3a and the light-transmitting upper electrode 5 is Φ, the optical distance between the reflection layer 3a and the light-transmitting upper electrode 5 is L, and the light-transmitting upper electrode 5 Let λ be the peak wavelength of the spectrum of the light h extracted from the side of, and the optical distance L is a positive minimum value satisfying the following equation (1).
(Equation 2)
In the organic EL element configured as described above, the reflective layer 3a, which is the lower layer of the lower electrode 3, is made of a metal material having good reflectivity to light in the visible region, and the buffer layer 3b that covers the reflective layer 3a is formed. , ITO, IZO, SnO 2 , ZnO, CdO, TiO 2 and similar transparent conductive materials. These transparent conductive materials can not only be formed into a film having a surface roughness smaller than that of a metal material, but also have a very low light absorption for visible region light and a good light transmission.
[0025]
Above all, the thickness of ITO is more than 2 nm and less than 30 nm, more preferably 5 nm to 20 nm, so that the unevenness of the underlying reflective layer 3 a can be reduced without causing the unevenness of the ITO film itself. It is. In addition, since IZO is originally a non-crystalline material, forming this IZO as the buffer film 3b can alleviate the unevenness of the underlying reflective layer 3a.
[0026]
As described above, the buffer layer 3b reduces the surface roughness of the reflective layer 3a and improves the surface flatness of the lower electrode, and the upper electrode 5 laminated on the lower electrode 3 with the organic layer 4 interposed therebetween. In-plane uniformity of the gap with the lower electrode 3 is ensured. Moreover, it is possible to minimize the light loss caused by the emission light h generated in the organic layer 4 passing through the buffer layer 3b.
[0027]
As a result, according to the organic EL element of this configuration, high reliability can be maintained without occurrence of a short circuit between the lower electrode 3 and the upper electrode 5, and the power consumption is reduced and the life characteristics are improved by improving the light extraction efficiency. Can be realized.
[0028]
【Example】
Hereinafter, a specific example 1 of the present invention and a manufacturing procedure of an organic EL element of a comparative example with respect to the example 1 will be described with reference to FIG. 1, and evaluation results performed on the example 1 and the comparative example will be described. I do. Then, Example 2 and its evaluation result will be described.
[0029]
<Example 1>
First, Cr (thickness: about 150 nm) was deposited on a substrate 2 made of a glass plate by a sputtering method, and further, ITO was deposited to a thickness of 10 nm continuously while the vacuum state of the deposition apparatus was maintained. . Thereafter, a pattern was formed by etching using a resist pattern formed by ordinary lithography as a mask, with the lower electrode 3 formed by laminating the buffer layer 3b made of ITO on the reflective layer 3a made of Cr as an anode.
[0030]
Next, an insulating
[0031]
Next, after performing pure water cleaning, a pretreatment of exposing the lower electrode 3 to O 2 plasma was performed. Subsequently, the substrate 2 was transferred into a film forming chamber for forming an organic layer 4 without exposing the substrate 2 to the atmosphere.
[0032]
Next, a hole injection layer 4a and a hole transport layer are formed at a degree of vacuum of 10 −4 Pa or more with a metal mask (not shown) having an opening slightly larger than the light emitting region 7a aligned at a predetermined position. 4b and an electron transporting light emitting
[0033]
Further, while maintaining the vacuum state in the film forming chamber, the mask for the upper electrode 5 is aligned at a predetermined position, and a vacuum of 10 −4 Pa or more is used as the upper electrode 5 serving as a cathode. ) And Ag (silver) to form a co-evaporated layer [Mg: Ag = 10: 1 (volume ratio)] with a thickness of 10 nm.
[0034]
Thereafter, while maintaining the vacuum state in the film forming chamber, a mask for a protective film was aligned at a predetermined position, and SiN x was formed as a protective film (not shown) to a thickness of 1 μm by a CVD method.
[0035]
Thus, the organic EL device of the example was manufactured.
[0036]
<Example 2>
In Example 2, an organic EL device was manufactured in the same procedure as in Example 1, except that Ag (silver) having a thickness of 150 nm was formed as the reflective layer 3a of the lower electrode 3 serving as an anode.
[0037]
<Comparative example>
In the comparative example, an organic EL element was manufactured in the same procedure as in Example 1, except that a 10 nm-thick CrO 2 was formed as the buffer layer 3b of the lower electrode 3 serving as an anode.
[0038]
-Evaluation results-
For each of the 40 organic EL devices of Example 1, Example 2 and Comparative Example manufactured as described above, {circle around (1)} (number) When a voltage was applied, (2) current density and (3) emission luminance were measured. Table 1 shows the results.
[0039]
[Table 1]
As shown in Table 1, in each of the organic EL devices of Example 1, Example 2, and Comparative Example, (1) the number of occurrences of short-circuit was 0 [number], and (2) the current density was 20 [mA / cm 2 ]. there were. On the other hand, with respect to (3) emission luminance, the value of the organic EL element of Example 1 to which the present invention was applied was about 1.2 times higher than the value of the organic EL element of the comparative example, and the present invention was applied. The value of the organic EL device of Example 2 was 2.1 times or more higher, and the effect of increasing the luminous efficiency was confirmed.
[0041]
In the same procedure as in the second embodiment, forty organic EL elements each having a different thickness of the buffer layer 3b made of ITO were manufactured, and the upper electrode 3 and the lower electrode 5 were formed with respect to these organic EL elements. The number (number) of occurrences of short circuits was measured. The results are shown in the graph of FIG.
[0042]
As shown in this graph, with respect to the buffer layer 3b made of ITO, if the film thickness is in the range of 2 nm to 30 nm, the effect of suppressing the number of short-circuited organic EL elements to 2/40 or less was confirmed. did it. This is a result equivalent to that of the light emitting element (2) shown on page 6 of Patent Document 1 shown in the prior art. Therefore, if the thickness of the buffer film 3b made of ITO is more than 2 nm and less than 30 nm, an effect exceeding this result can be obtained. Furthermore, when the thickness of the buffer layer 3b made of ITO is in the range of 5 nm to 20 nm, the effect of suppressing the number of short-circuited organic EL elements to 1/40 [number] or less was confirmed. Furthermore, when the thickness of the buffer layer 3b made of ITO was 10 nm, the effect of suppressing the number of short-circuits of the organic EL elements to 0/40 [pieces] was confirmed.
[0043]
【The invention's effect】
As described above, according to the organic EL device of the present invention, a transparent layer having a very small light absorption for visible region light such as ITO, IZO, SnO 2 , ZnO, CdO, and TiO 2 is formed on a reflective layer made of a metal material. By using a lower electrode configuration provided with a buffer layer made of a conductive material, it is possible to ensure in-plane uniformity between the upper electrode and the lower electrode while minimizing light loss caused by passing through the buffer layer. Becomes possible. As a result, high reliability can be maintained by preventing a short circuit between the lower electrode and the upper electrode, and a reduction in power consumption and an improvement in the life characteristics can be realized by improving the light extraction efficiency.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an organic EL element according to an embodiment.
FIG. 2 is a graph showing the number of short circuits occurring in each of 40 organic EL elements manufactured in Example 2.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Organic EL element (organic electroluminescent element), 2 ... Substrate, 3a ... Reflection layer, 3b ... Buffer layer, 3 ... Lower electrode, 5 ... Organic layer, 6 ... Upper electrode
Claims (5)
前記下部電極が、金属材料からなる反射層とこの上部の緩衝層とで構成され、
前記緩衝層は、ＩＴＯ、ＩＺＯ、ＳｎＯ２、ＺｎＯ、ＣｄＯ、ＴｉＯ２およびこれらに類する透明導電性材料のうちの少なくとも１つからなる
ことを特徴とする有機電界発光素子。Organic electroluminescence comprising a lower electrode provided on a substrate, one or more organic layers including a light emitting layer provided on the lower electrode, and a light-transmitting upper electrode provided on the organic layer. In the element
The lower electrode includes a reflective layer made of a metal material and a buffer layer on the reflective layer,
The buffer layer, ITO, IZO, SnO 2, ZnO, CdO, TiO 2 and the organic electroluminescent device, characterized in that of at least one of the transparent conductive material similar thereto.
前記緩衝層は、３０ｎｍよりも薄く２ｎｍよりも厚い膜厚のＩＴＯからなる
ことを特徴とする有機電界発光素子。The organic electroluminescent device according to claim 1,
The organic electroluminescent device according to claim 1, wherein the buffer layer is made of ITO having a thickness smaller than 30 nm and larger than 2 nm.
前記反射層は、銀を主成分として含む
ことを特徴とする有機電界発光素子。The organic electroluminescent device according to claim 1,
The organic electroluminescent device, wherein the reflection layer contains silver as a main component.
前記光透過性の上部電極と前記反射層とは、前記発光層で発生した光を共振させる共振器の共振部を構成している
ことを特徴とする請求項１記載の有機電界発光素子。The organic electroluminescent device according to claim 1,
The organic electroluminescent device according to claim 1, wherein the light-transmitting upper electrode and the reflective layer constitute a resonator of a resonator that resonates light generated in the light emitting layer.
前記反射層及び前記光透過性の上部電極で生じる反射光の位相シフトをΦ、前記反射層と前記光透過性の上部電極との光学的距離をＬ、前記光透過性の上部電極の側から取り出す光のスペクトルのピーク波長をλとすると、
前記光学的距離Ｌは、下記式（１）を満たす正の最小値であることを特徴とする有機電界発光素子。
The phase shift of the reflected light generated in the reflective layer and the light-transmissive upper electrode is Φ, the optical distance between the reflective layer and the light-transmissive upper electrode is L, from the side of the light-transmissive upper electrode. If the peak wavelength of the spectrum of the light to be extracted is λ,
The organic electroluminescent device, wherein the optical distance L is a positive minimum value satisfying the following equation (1).
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