JP3656608B2 - Organic thin film EL device and driving method thereof - Google Patents

Description

【００９８】
本実施例によれば、色純度が良く、高い発光効率を有し、低い駆動電圧で自発光で視認性に優れた発光が得られ、連続発光試験においても輝度低下が小さく、色度の変化が無い、少ない消費電力で、極めて長期間にわたって安定して使用できる有機薄膜ＥＬ素子を実現できた。
【００９９】
（実施例２）
実施例１の非発光性電子輸送層の形成において、７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）の代わりに、テトラシアノエチレン（関東化学株式会社製）を用いた以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１００】
（実施例３）
実施例１の正孔輸送層と発光層との間に、新たな発光層として１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）とＮ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１０１】
それ以外の構成は全て実施例１と同様にして、有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１０２】
（実施例４）
実施例３の非発光性電子輸送層の形成において、７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）の代わりに、テトラシアノエチレン（関東化学株式会社製）を用いた以外は実施例１と同様にして、有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１０３】
（実施例５）
実施例３の発光層である１，１，４，４−テトラフェニル−１，３−ブタジエン層と、非発光性電子輸送層である７，７，８，８−テトラシアノキノジメタンの代わりに、新たな発光層として、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）と７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１０４】
それ以外の構成は全て実施例３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１０５】
（実施例６）
実施例５の新たな発光層において、７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）の代わりに、テトラシアノエチレン（関東化学株式会社製）を用いた以外は実施例５と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１０６】
（実施例７）
実施例１の発光層の形成において、１，１，４，４−テトラフェニル−１，３−ブタジエン層の代わりに、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）とＣｏｕｍａｒｉｎ５４０（ＬａｍｂｄａＰｈｙｓｉｋ株式会社製）を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１０７】
それ以外の構成は全て実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１０８】
（実施例８）
実施例７の非発光性電子輸送層として、７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）の代わりに、テトラシアノエチレン（関東化学株式会社製）を用いた以外は実施例７と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１０９】
（実施例９）
実施例１の非発光性電子輸送層である７，７，８，８−テトラシアノキノジメタン層の代わりに、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）と７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１１０】
それ以外の構成は全て実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１１】
（実施例１０）
実施例９の７，７，８，８−テトラシアノキノジメタン（関東化学株式会社製）の代わりに、テトラシアノエチレン（関東化学株式会社製）を用いた以外は実施例９と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１２】
（実施例１１）
実施例１の電子輸送層の形成において、トリス（８−キノリノラト）アルミニウム(同仁化学株式会社製)の代わりに、トリス（４−メチル−８−キノリノラト）アルミニウム（ケミプロ化成株式会社製）を用いた以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１３】
（実施例１２）
実施例２の電子輸送層の形成において、トリス（８−キノリノラト）アルミニウム(同仁化学株式会社製)の代わりに、トリス（４−メチル−８−キノリノラト）アルミニウム（ケミプロ化成株式会社製）を用いた以外は実施例２と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１４】
（実施例１３）
実施例３の新たな発光層の形成において、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）の代わりに、Ｎ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ビス（３−メチルフェニル）−１，１’−ビフェニル−４，４’−ジアミン（同仁化学株式会社製）を用いた以外は実施例３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１５】
（実施例１４）
実施例４の新たな発光層の形成において、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）の代わりに、Ｎ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ビス（３−メチルフェニル）−１，１’−ビフェニル−４，４’−ジアミン（同仁化学株式会社製）を用いた以外は実施例４と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１６】
（実施例１５）
実施例７の非発光性電子輸送層として用いた７，７，８，８−テトラシアノキノジメタン層５ｎｍの代わりに、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）を１０ｎｍの膜厚に形成した以外は実施例７と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１７】
（実施例１６）
実施例１の発光層として設けた１，１，４，４−テトラフェニル−１，３−ブタジエン層１０ｎｍの代わりに、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）とＮ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン(保土ヶ谷化学株式会社製)を、各々０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成し、さらに続けて、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）とテトラフェニルエチレン(関東化学株式会社製)を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１１８】
それ以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１１９】
（実施例１７）
実施例１５の発光層として設けた１，１，４，４−テトラフェニル−１，３−ブタジエンとＣｏｕｍａｒｉｎ５４０との共蒸着層１０ｎｍの代わりに、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）とＮ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１２０】
それ以外は実施例１５と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１２１】
（実施例１８）
実施例１５の発光層として設けた１，１，４，４−テトラフェニル−１，３−ブタジエンとＣｏｕｍａｒｉｎ５４０との共蒸着層１０ｎｍの代わりに、１，１，４，４−テトラフェニル−１，３−ブタジエン（関東化学株式会社製）とＮ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ビス（３−メチルフェニル）−１，１’−ビフェニル−４，４’−ジアミン（同仁化学株式会社製）を、それぞれ０．１５ｎｍ／ｓの蒸着速度で共蒸着して膜厚約１０ｎｍに形成した。
【０１２２】
それ以外は実施例１５と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１２３】
（実施例１９）
実施例３の電子輸送層の形成において、トリス（８−キノリノラト）アルミニウム層の膜厚を２５ｎｍの代わりに、２０ｎｍとした以外は実施例３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１２４】
（実施例２０）
実施例３の電子輸送層の形成において、トリス（８−キノリノラト）アルミニウム層の膜厚を２５ｎｍの代わりに、３０ｎｍとした以外は実施例３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１２５】
（実施例２１）
実施例３の正孔輸送層の形成に続いて、発光層形成の前に、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）を０．３ｎｍ／ｓの蒸着速度で膜厚約５ｎｍに形成した以外は実施例３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１２６】
（実施例２２）
実施例４の正孔輸送層の形成に続いて、発光層形成の前に、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）を０．３ｎｍ／ｓの蒸着速度で膜厚約５ｎｍに形成した以外は実施例４と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１に記載のように評価を行った。その結果を（表１）に示す。
【０１２７】
（比較例１）
実施例１において、非発光性電子輸送層（７，７，８，８−テトラシアノキノジメタン層５ｎｍ）を形成せず、また電子輸送層（トリス（８−キノリノラト）アルミニウム層２５ｎｍ）を膜厚１５ｎｍに形成した以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１と同様に評価を行った。その結果を（表１）に示す。
【０１２８】
（比較例２）
実施例１において、非発光性電子輸送層（７，７，８，８−テトラシアノキノジメタン層５ｎｍ）を形成せず、また電子輸送層（トリス（８−キノリノラト）アルミニウム層２５ｎｍ）を膜厚２０ｎｍに形成した以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１と同様に評価を行った。その結果を（表１）に示す。
【０１２９】
（比較例３）
実施例１において、非発光性電子輸送層（７，７，８，８−テトラシアノキノジメタン層５ｎｍ）を形成せず、また電子輸送層（トリス（８−キノリノラト）アルミニウム層２５ｎｍ）を膜厚２５ｎｍに形成した以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１と同様に評価を行った。その結果を（表１）に示す。
【０１３０】
（比較例４）
実施例１において、非発光性電子輸送層（７，７，８，８−テトラシアノキノジメタン層５ｎｍ）を形成せず、また電子輸送層（トリス（８−キノリノラト）アルミニウム層２５ｎｍ）を膜厚３０ｎｍに形成した以外は実施例１と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例１と同様に評価を行った。その結果を（表１）に示す。（表１）において各実施例および比較例の素子構成は略号によって略記されており、
「ＴＰＴ」は、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン、
「ＴＰＤ」は、Ｎ，Ｎ’−ジフェニル−Ｎ，Ｎ’−ビス（３−メチルフェニル）−１，１’−ビフェニル−４，４’−ジアミン、
「ＰＳ」は、４−Ｎ，Ｎ−ジフェニルアミノ−α−フェニルスチルベン、
「ＴＰＢ」は、１，１，４，４−テトラフェニル−１，３−ブタジエン、
「ＴＰＥ」は、テトラフェニルエチレン、
「Ｃ５４０」は、Ｃｏｕｍａｒｉｎ５４０
「ＴＣＮＱ」は、７，７，８，８−テトラシアノキノジメタン、
「ＴＣＮＥ」は、テトラシアノエチレン、
「Ａｌｑ₃」は、トリス（８−キノリノラト）アルミニウム、
「Ａｌｍｑ₃」は、トリス（４−メチル−８−キノリノラト）アルミニウム、
を表し、左から積層構成を表す記号として／で区切ってＩＴＯ電極側から順に記載した。（）内の数字は膜厚をｎｍで示し、＋は共蒸着を示す。
【０１３１】
（実施例２３）
透明基板上に正孔注入電極を形成した基板として、市販のＩＴＯ付きガラス基板（三容真空株式会社製、サイズ１００×１００ｍｍ×ｔ＝０．７ｍｍ、シート抵抗約１４Ω／□）を用い、電子注入電極との重なりにより発光可能面積が７０×７０ｍｍとなるようにフォトリソグラフィーによりパターン化した。フォトリソ後の基板処理は市販のレジスト剥離液（ジメチルスルホキシドとｎメチル２ピロリドンとの混合溶液）に浸漬して剥離を行った後、アセトンでリンスし、さらに発煙硝酸中に１分間浸漬して完全にレジストを除去した。ＩＴＯ表面の洗浄は、基板の裏面表面の両面を十分に行い、テトラメチルアンモニウムハイドロオキサイドの０．２３８％水溶液を十分に供給しながら、ナイロンブラシによる機械的な擦り洗浄を行った。その後、純水で十分にすすぎ、スピン乾燥を行った。
【０１３２】
このようにして作製した正孔注入電極の上に、絶縁層を次のように形成した。ポジ型フォトレジスト（東京応化工業株式会社製ＯＦＰＲ５０００）を専用シンナーで希釈してスピナーで塗布した。露光前のプリベークとして１３０℃１５分間のオーブン加熱を行った後、発光パターンに対応したマスクを用いて露光し、現像して発光パターンに対応したレジスト膜を得た。さらに１８０℃３０分間のオーブン加熱を行って、膜厚約０．１μｍのパターン化されたフォトレジスト層（絶縁層）を得た。
【０１３３】
発光パターンに対応したマスクは、市販のプリンター（アルプス電機株式会社製ＭＤ２０００）でＯＨＰシートに６００ｄｐｉの解像度で黒色プリントしたものを用いた。
【０１３４】
次に、再度基板の裏面表面の両面を、テトラメチルアンモニウムハイドロオキサイドの０．２３８％水溶液を十分に供給しながら、ナイロンブラシによる機械的な擦り洗浄を行った。その後、純水で十分にすすぎ、スピン乾燥を行った。
【０１３５】
また発光機能層の蒸着前には、市販のプラズマリアクター（ヤマト科学株式会社製、ＰＲ４１型）中で、酸素流量２０ｓｃｃｍ、圧力０．２Ｔｏｒｒ、高周波出力３００Ｗの条件で１分間の酸素プラズマ処理を行ってから、蒸着槽内に配置した。
【０１３６】
真空蒸着装置は市販の高真空蒸着装置（日本真空技術株式会社製、ＥＢＶ−６ＤＡ型）を改造した装置を用いた。主たる排気装置は排気速度１５００リットル／ｍｉｎのターボ分子ポンプ（大阪真空株式会社製、ＴＣ１５００）であり、到達真空度は約１×１０^-6Ｔｏｒｒ以下であり、全ての蒸着は２〜３×１０^-6Ｔｏｒｒの範囲で行った。また全ての蒸着はタングステン製の抵抗加熱式蒸着ボートに直流電源（菊水電子株式会社製、ＰＡＫ１０−７０Ａ）を接続して行った。
【０１３７】
このようにして真空層中に配置したＩＴＯ付きガラス基板上に、正孔輸送層として、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）と、４−Ｎ，Ｎ−ジフェニルアミノ−α−フェニルスチルベンを、それぞれ０．３ｎｍ／ｓおよび０．０１ｎｍ／ｓの蒸着速度で共蒸着して膜厚約８０ｎｍに形成した。
【０１３８】
次に、発光層（発光性電子輸送層）としてトリス（８−キノリノラト）アルミニウム（同仁化学株式会社製）を０．３ｎｍ／ｓの蒸着速度で膜厚約４０ｎｍに形成した。
【０１３９】
次に、電子注入電極として、ＡｌＬｉ合金（高純度化学株式会社製、Ａｌ／Ｌｉ重量比９９／１）から低温でＬｉのみを、約０．１ｎｍ／ｓの蒸着速度で膜厚約１ｎｍに形成し、続いて、そのＡｌＬｉ合金をさらに昇温しＬｉが出尽くした状態から、Ａｌのみを、約１．５ｎｍ／ｓの蒸着速度で膜厚約１００ｎｍに形成し、積層型の電子注入電極とした。
【０１４０】
このようにして作成した有機薄膜ＥＬ素子は、蒸着槽内を乾燥窒素でリークした後、乾燥窒素雰囲気下で、コーニング７０５９ガラス製の蓋を接着剤（アネルバ株式会社製、商品名スーパーバックシール９５３−７０００）で貼り付けてサンプルとした。
【０１４１】
このようにして得た有機薄膜ＥＬ素子サンプルは、市販の小型ボタン電池（３Ｖ×２個）で駆動し、明るく視認性に優れ、低消費電力で長寿命なだけでなく、用いた６００ｄｐｉのマスクパターンに極めて忠実な、通常の印刷物に匹敵する優れた解像度のパターン発光を得ることができた。発光輝度は６Ｖで３００ｃｄ／ｍ²、輝度半減寿命は５０００時間以上であった。
【０１４２】
また発光パターン情報は非発光時にはほとんど見えず、判読は極めて困難であり、通電の有無のみで情報の表示・非表示を切りかえれるものであった。
【０１４３】
このように本実施例によれば、高い発光効率で、低い駆動電圧で自発光で視認性に優れた発光が得られ、また極めて高解像度で忠実な発光パターンが再現性良く得られ、且つ連続発光試験においても輝度低下が小さく、少ない消費電力で、極めて長期間にわたって安定して使用できる有機薄膜ＥＬ素子を実現できるものである。
【０１４４】
（比較例５）
実施例２３において、パターン化絶縁層(フォトレジスト)の現像後、１８０℃３０分間の硬化を行わず、代わりに通常のポストベークとして１３５℃３０分の乾燥を行った以外は実施例２３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例２３と同様に発光させた。
【０１４５】
このようにして得た有機薄膜ＥＬ素子サンプルは、同じ電池による駆動ではほとんど発光せず、通常の直流電源による駆動でも発光効率が低く、発光を得るのに極めて高い電圧が必要であった。発光輝度は、１２Ｖで１００ｃｄ／ｍ² であった。
【０１４６】
また発光パターン情報は実施例２３と同様に、非発光時にはほとんど見えず、判読は極めて困難であり、通電の有無のみで情報の表示・非表示を切りかえれるものであった。
【０１４７】
（比較例６）
実施例２３において、パターン化絶縁層（フォトレジスト）の膜厚０．１μｍの代わりに、膜厚０．３μｍに形成を行った以外は実施例２３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例２３と同様に発光させた。
【０１４８】
このようにして得た有機薄膜ＥＬ素子サンプルは、初期においては実施例２３と同様の優れた発光状態が得られるものもあったが、発光を続けていると部分的に陰極が劣化し非発光となる部分が増加し、数時間で相当の部分が非発光となった。またサンプルによっては初期から非発光部分のあるものや、正負電極の短絡により全く発光しないものも多かった。
【０１４９】
また本素子が非発光の時もパターンが容易に判読することが出来る状態であり、通電の有無のみで情報の表示・非表示を切り替えることが出来なかった。
【０１５０】
（比較例７）
実施例２３において、パターン化絶縁層（フォトレジスト）の膜厚０．１μｍの代わりに、膜厚０．０１μｍに形成を行った以外は実施例２３と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例２３と同様に発光させた。
【０１５１】
このようにして得た有機薄膜ＥＬ素子サンプルは、パターンとしては非発光であるべきところの多くが発光し、極めて表示品質が低下した判読しにくいものであった。発光の輝度および寿命においては実施例２３と同様に良好であった。
【０１５２】
また発光パターン情報は実施例２３と同様に、非発光時にはほとんど見えず、判読は極めて困難であったが、前述のように発光時も本来非発光であるべき部分の発光により判読が困難であった。
【０１５３】
（実施例２４）
透明基板として、ガラス基板（コーニング１７３７）を用い、通常の低温ポリシリコンＴＦＴの作製プロセスを用いて、駆動手段を次のように作製した。
【０１５４】
画素数は縦４８０、横６４０のＶＧＡとし、各画素毎に透明電極としてＩＴＯ膜を形成した。ＩＴＯ電極と正電極ライン間には駆動用薄膜トランジスタとしてＷ＝３０μｍ、Ｌ＝３μｍのｐ型低温ポリシリコン薄膜トランジスタを形成して接続した。また、このゲート電極と正電極ライン間には０．２ｐＦのメモリー容量を設けた。
【０１５５】
また、このメモリー容量と並列に前記の駆動用薄膜トランジスタのｐ型チャネル層形成と同時に、同条件で抵抗層を形成した。抵抗層の抵抗値は厚さ、幅、長さが一定であっても移動度の差などの成膜バラツキにより異なるが、全画素の平均値で１０ＧΩとなるように形成した。
【０１５６】
また、各画素の発光情報を一定の時間毎にメモリー容量を充放電させることにより書き込むため、各画素毎に順次情報書き込み用薄膜トランジスタとしてＷ＝３μｍ、Ｌ＝３μｍのｐ型低温ポリシリコン薄膜トランジスタを形成して、同トランジスタのゲートを走査電極に、ソースをデータ（ソース）電極に、ドレインを前記駆動用薄膜トランジスタのゲートに接続した。
【０１５７】
このようにして作製した駆動手段の上に、前記のＩＴＯ電極部のみを開口部として残して絶縁膜を形成した。
【０１５８】
次に、この基板を洗浄した後、市販のプラズマリアクター（ヤマト科学株式会社製、ＰＲ４１型）中で、酸素流量２０ｓｃｃｍ、圧力０．２Ｔｏｒｒ、高周波出力３００Ｗの条件で１分間の酸素プラズマ処理を行ってから、蒸着槽内に配置した。
【０１５９】
真空蒸着装置は市販の高真空蒸着装置（日本真空技術株式会社製、ＥＢＶ−６ＤＡ型）を改造した装置を用いた。主たる排気装置は排気速度１５００リットル／ｍｉｎのターボ分子ポンプ（大阪真空株式会社製、ＴＣ１５００）であり、到達真空度は約１×１０^-6Ｔｏｒｒ以下であり、全ての蒸着は２〜３×１０^-6Ｔｏｒｒの範囲で行った。また全ての蒸着はタングステン製の抵抗加熱式蒸着ボートに直流電源（菊水電子株式会社製、ＰＡＫ１０−７０Ａ）を接続して行った。
【０１６０】
このようにして真空層中に配置した駆動手段形成後のガラス基板上に、正孔輸送層として、Ｎ，Ｎ’−ビス（４’−ジフェニルアミノ−４−ビフェニリル）−Ｎ，Ｎ’−ジフェニルベンジジン（保土ヶ谷化学株式会社製）と、４−Ｎ，Ｎ−ジフェニルアミノ−α−フェニルスチルベンを、それぞれ０．３ｎｍ／ｓおよび０．０１ｎｍ／ｓの蒸着速度で共蒸着して膜厚約８０ｎｍに形成した。
【０１６１】
次に、発光層（発光性電子輸送層）としてトリス（８−キノリノラト）アルミニウム（同仁化学株式会社製）を０．３ｎｍ／ｓの蒸着速度で膜厚約４０ｎｍに形成した。
【０１６２】
次に、電子注入電極として、ＡｌＬｉ合金（高純度化学株式会社製、Ａｌ／Ｌｉ重量比９９／１）から低温でＬｉのみを、約０．１ｎｍ／ｓの蒸着速度で膜厚約１ｎｍに形成し、続いて、そのＡｌＬｉ合金をさらに昇温しＬｉが出尽くした状態から、Ａｌのみを、約１．５ｎｍ／ｓの蒸着速度で膜厚約１００ｎｍに形成し、積層型の電子注入電極とした。
【０１６３】
このようにして作成した有機薄膜ＥＬ素子は、蒸着槽内を乾燥窒素でリークした後、乾燥窒素雰囲気下で、コーニング７０５９ガラス製の蓋を接着剤（アネルバ株式会社製、商品名スーパーバックシール９５３−７０００）で貼り付けてサンプルとした。
【０１６４】
このようにして得た有機薄膜ＥＬ素子サンプルは、電子注入電極を接地し、正電極ラインに７Ｖの直流電圧を印加し、走査電極を順に走査して、データ（ソース）電極に各画素の発光情報に対応した電圧を与えて発光させた。走査は横一行毎に順に縦方向に４８０行の走査を行った。走査の繰り返し周波数（フレームレート）は１００Ｈｚとし、データ（ソース）電極に与える各画素の発光情報に対応した電圧値は発光の階調情報に対応した２５６段階の直流電圧を与えた。
【０１６５】
このようにして発光させたＶＧＡサイズの有機薄膜ＥＬ素子は、全画素に同一のデータを与えた場合には、輝度ムラや発光の不均一が無く、２５６段階の階調信号を与えた場合には、信号に忠実な発光が得られた。また全画素最大輝度で点灯時のパネルの輝度は３００ｃｄ／ｍ² であり、直流７Ｖの駆動で高い発光輝度が得られた。また連続点灯時の寿命は５０００時間以上であった。
【０１６６】
このように本実施例によれば、表示が多くの画素から構成される場合であっても、高い発光効率で、低い駆動電圧で自発光で視認性に優れた発光が得られ、またムラなどの不均一の無い極めて一様性に優れた発光が得られ、また２５６階調の高い階調再現性が得られた。また連続発光試験においても輝度低下が小さく、少ない消費電力で、極めて長期間にわたって安定して使用できる有機薄膜ＥＬ素子を実現できるものである。
【０１６７】
（比較例８）
実施例２４において、メモリー容量と並列に抵抗層を形成しない以外は全て実施例２４と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例２４と同様に発光させた。
【０１６８】
このようにして発光させたＶＧＡサイズの有機薄膜ＥＬ素子は、全画素に同一データを与えた場合にもは、輝度ムラや発光の不均一が認められ、２５６段階の階調信号を与えた場合にも、階調の再現性が悪く、極めて低品質な表示画像しか得られなかった。また全画素最大輝度で点灯時のパネルの輝度は高い部分では５００ｃｄ／ｍ²を超える一方、低い部分は５０ｃｄ／ｍ²以下であった。
【０１６９】
（実施例２５）
実施例２４と駆動手段および有機薄膜ＥＬ素子は同様に作製し、駆動方法も実施例２４と同様に正電極ラインに７Ｖの直流電圧を印加し、走査電極を順に走査して、データ（ソース）電極に各画素の発光情報に対応した電圧を与えて発光させた。階調の表現方法のみ、実施例２４の方法の代わりに、データ（ソース）電極には常に発光または非発光に対応する電圧を与えることとし、走査速度を速くしてサブフィールド法により階調制御を行った。
【０１７０】
このようにして発光させたＶＧＡサイズの有機薄膜ＥＬ素子は、全画素が同じ明るさとなるように駆動した場合には、輝度ムラや発光の不均一が無く、２５６段階の階調をサブフィールド法で与えた場合には信号に忠実な発光が得られた。また全画素最大輝度で点灯時のパネルの輝度は２５０ｃｄ／ｍ² であり、直流７Ｖの駆動で高い発光輝度が得られた。また連続点灯時の寿命は５０００時間以上であった。
【０１７１】
（比較例９）
実施例２５において、メモリー容量と並列に抵抗層を形成しない以外は全て実施例２５と同様にして有機薄膜ＥＬ素子サンプルを作成し、実施例２５と同様に発光させた。
【０１７２】
このようにして発光させたＶＧＡサイズの有機薄膜ＥＬ素子は、全画素に同一の条件で駆動した場合にも、輝度ムラや発光の不均一が認められ、２５６段階の階調をサブフィールド法で与えた場合にも、階調の再現性が悪く、極めて低品質な表示画像しか得られなかった。また全画素をフルフィールドで点灯時のパネルの輝度は高い部分では４００ｃｄ／ｍ²を超える一方、低い部分は５０ｃｄ／ｍ²以下であった。
【０１７３】
【発明の効果】
以上のように本発明によれば、色純度が良く、高い発光効率を有し、低い駆動電圧で自発光で視認性に優れた発光が得られ、連続発光試験においても輝度低下が小さく、色度の変化が無い、少ない消費電力で、極めて長期間にわたって安定して使用できる有機薄膜ＥＬ素子を実現できるものである。
【０１７４】
また、透明基板上に正孔注入電極と電子注入電極と、少なくとも前記正孔注入電極と電子注入電極との間に設けられた絶縁層と発光機能層を有し、前記絶縁層が像情報に対応してパターン形成されたフォトレジスト層としたことによって、高い発光効率で、低い駆動電圧で自発光で視認性に優れた発光が得られ、また極めて高解像度で忠実な発光パターンが再現性良く得られ、且つ連続発光試験においても輝度低下が小さく、少ない消費電力で、極めて長期間にわたって安定して使用できる有機薄膜ＥＬ素子を実現できるものである。
【０１７５】
また、正孔注入電極と電子注入電極との間に電圧を加えることで電流を流し、発光を得る有機薄膜ＥＬ素子の駆動方法であって、電源の片方の極と有機薄膜ＥＬ素子の片方の極を接続するとともに、それぞれの他方の極を薄膜トランジスタを介して接続し、且つ当該トランジスタのゲート電圧保持用のメモリー容量を有し、一定の時間間隔毎に発光強度の情報または発光非発光の情報を当該メモリー容量に充放電させることにより書き込んで、発光状態を制御する駆動方法において、当該メモリー容量と並列に前記薄膜トランジスタのチャネル層と同時に同じ成膜条件で作成した層を抵抗として配置したことによって、表示が多くの画素から構成される場合であっても、高い発光効率で、低い駆動電圧で自発光で視認性に優れた発光が得られ、またムラなどの不均一の無い極めて一様性に優れた発光が得られ、また２５６階調の高い階調再現性が得られた。また連続発光試験においても輝度低下が小さく、少ない消費電力で、極めて長期間にわたって安定して使用できる有機薄膜ＥＬ素子を実現できるものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescence (EL) element and a method for driving the same, which are self-luminous elements that can be used as various light sources for communication, illumination, and other applications including flat-type self-luminous display devices.
[0002]
[Prior art]
In recent years, LCD panels have been widely used as flat display devices, but they still have drawbacks such as a slow response speed and a narrow viewing angle, and many of the new systems that have improved these have insufficient characteristics. There is a problem that the cost as a panel becomes high. Under such circumstances, organic EL elements as new light-emitting elements that are self-luminous, have excellent visibility, have a high response speed, and can be expected to be used in a wide range are expected.
[0003]
An organic EL device is one in which electrons and holes are injected from an electrode into an organic material layer to obtain light emission by recombination. Many studies have been made for a long time, but generally its light emission efficiency is low and it becomes a practical light emitting device. It was far from the application of.
[0004]
Under such circumstances, a device proposed by Tang et al. In 1987 ("Apply Physics Letter" Vol. 51 1987 (CW Tang and SA Vanslyke: Appl. Phys. Lett. 51 (1987)). 913.)) is an element having a transparent hole injection electrode, a light emitting functional layer, and an electron injection electrode on a transparent substrate, and the light emitting functional layer is a laminate of a hole transport layer and a light emitting layer (electron transport layer). In addition, MgAg was used as an alloy of a metal having a low work function and a low electron injection barrier as an electron injection electrode and a metal having a relatively large work function and stability.
[0005]
By using such an electron injection electrode, electrons can be injected with high efficiency and relatively stably, and light emission can be obtained with high efficiency in the vicinity of the interface between the hole transport layer and the light emitting layer (electron transport layer). Became possible. Tang et al. Have a structure of 1000 cd / m at a low voltage of 10 V or less in such a configuration. ² The above high brightness and high efficiency of 1.5 lm / W or more are realized. Tang et al.'S report has led to ongoing active studies.
[0006]
An outline of organic EL devices that are currently being examined generally will be described below.
[0007]
In general, an organic EL element is formed by laminating a hole injection electrode, a light emitting functional layer, and an electron injection electrode in this order on a transparent substrate, and the light emitting functional layer includes a hole transport layer and a light emitting layer (electron transport layer). In many cases, a plurality of laminated films are used. In this way, by making each layer play a role by separating functions, an appropriate material can be selected for each layer, and the characteristics of the element are improved.
[0008]
In general, a glass substrate such as Corning 1737 is widely used as the transparent substrate. A thickness of about 0.7 to 1.1 mm is easy to handle from the viewpoint of strength and weight.
[0009]
As the hole injection electrode, a transparent electrode such as an ITO sputtered film, an electron beam deposited film, or an ion plating film is used. The film thickness is determined from the required sheet resistance value and visible light transmittance. However, since the organic EL element has a relatively high driving current density, it may be used with a thickness of 100 nm or more in order to reduce the sheet resistance. Many.
[0010]
Various configurations of the light emitting functional layer have been studied. A hole transporting layer in which a hole transporting material such as a triphenyldiamine derivative is formed to a thickness of several tens of nanometers by vacuum deposition, tris (8-quinolinolato) aluminum, etc. In many cases, the light emitting material (electron transport material) is formed by stacking layers formed to have a film thickness of several tens of nanometers by vacuum deposition.
[0011]
In general, the part where electrons and holes recombine and emit light is called the light-emitting layer. If this part is in the vicinity of the hole injection electrode or the electron injection electrode, the exciton generated by recombination is deactivated without light emission. Luminous efficiency decreases. In order to prevent this phenomenon and to alleviate the influence of the surface state of the underlying substrate, it is necessary to provide a hole transport layer on the hole injection electrode side and an electron transport layer on the electron injection electrode side It is. Tris (8-quinolinolato) aluminum is a green light-emitting electron transport material, and is used as a layer serving as both a light-emitting layer and an electron transport layer, but the portion on the hole transport layer side is actually a light-emitting layer. It is considered that the portion on the electron injection electrode side functions as an electron transport layer.
[0012]
As the electron injection electrode, an alloy of a metal having a low work function and a low electron injection barrier and a metal having a relatively large work function and a stable metal such as an MgAg alloy or an AlLi alloy proposed by Tang et al. Is often used.
[0013]
Further, if such elements are arranged in a matrix and light is emitted by scanning line-sequentially, it is useful not only as a light emitting element but also as a display device for image information. However, in this case, for example, in the case of driving in which light is emitted by sequentially scanning in the vertical direction in a matrix of vertical 480 pixels × horizontal 640 pixels, the light emission time of each pixel becomes 1/480, for example, the average brightness 100 as the panel brightness. In order to obtain a candela, the actual light emission luminance of each pixel is 480 times and 48000 candela is required. In order to obtain a high instantaneous luminance in this way, a high drive voltage and a high instantaneous current are required, leading to an increase in power consumption such as an increase in power loss due to wiring resistance.
[0014]
Therefore, as a display device for image information, in addition to the simple matrix (passive matrix) driving as described above, a thin film transistor for driving each light emitting element (pixel) and a period until information given by voltage is applied to the next information. An active matrix driving configuration having a memory capacity to be held has been studied (for example, “Proceedings of the 18th International Display Research Conference”, pages 217 to 220 (Processings of 18th International Display Conference, p217). ~ P220)).
[0015]
In such an active matrix driving, an organic thin film EL element, a driving thin film transistor, and a memory capacity are required for each pixel as essential components, and a switching transistor for sequentially writing light emission information given by voltage Writing means such as are required at a minimum. That is, generally, at least two transistors and one capacitance element are required in addition to the organic thin film EL element.
[0016]
As described above, in the active matrix drive, the number of components necessary for displaying the image information is increased. However, unlike the passive matrix drive, each pixel continues to emit light according to the voltage held in the memory capacity even during a period when it is not sequentially selected. As a result, there is no phenomenon in which the light emission luminance of the element itself is remarkably higher than the average luminance of the panel, and the power consumption as the panel is remarkably reduced.
[0017]
[Problems to be solved by the invention]
In this way, a layered device structure separated by function proposed by Tang et al. Is used, and an alloy of a metal having a low work function such as MgAg and a low electron injection barrier and a metal having a relatively large work function and stable as an electron injection electrode. By using this, an element capable of obtaining sufficient luminance of about several hundred candela even at a low voltage of about several volts can be realized. Further, tris (8-quinolinolato) aluminum described above is a green light-emitting electron transport material, and when a green organic thin film EL device is manufactured, it is used as a layer serving as both a light-emitting layer and an electron transport layer. It is possible and convenient.
[0018]
However, when the above-described tris (8-quinolinolato) aluminum or a derivative thereof is used and a material capable of obtaining high efficiency with high characteristics as a light-emitting electron transport layer is used, the light-emitting layer is made of another material and other light emission is achieved. Even if a color is to be obtained, there is a problem that light emission from tris (8-quinolinolato) aluminum or a derivative thereof is mixed.
[0019]
That is, even if it is intended to obtain light emission only from the light emitting layer by laminating the light emitting layer and the electron transport layer, when the electron transport layer is a light emitting material as described above, the holes that have passed through the light emitting layer are formed in the electron transport layer. There is a problem that it is difficult to completely avoid the phenomenon of recombination and light emission in the region.
[0020]
For example, by reducing the thickness of the electron transport layer to about 20 nm, the deactivation rate of the exciton generated by recombination in the electron transport layer is increased, and light emission from the electron transport layer is suppressed. However, there is a natural limit to the optimization of film thickness due to the trade-off between efficiency and color purity, and obtaining an excellent organic thin film EL device that can simultaneously achieve high efficiency, color purity, and long life. Was difficult.
[0021]
In addition, when trying to obtain fixed pattern light emission with a resolution as high as that of printed matter, there is a limit to patterning the cathode or anode, and a method by patterning an insulating layer has been expected. When the lithography process is used, there are problems such as disconnection of the cathode, short-circuit between the cathode and anode, and reduction in light emission efficiency from the beginning, and there are also problems of extremely low reliability during continuous driving. In addition, the light emission pattern can be visually recognized even when no light is emitted, and there is a problem that the display / non-display of information cannot be controlled by electrical control of light emission / no light emission.
[0022]
In addition, in the matrix display device as described above, in particular for a display device with a large number of pixels, an active matrix drive that can greatly reduce power consumption is expected instead of passive matrix drive with large power consumption. A source-drain current characteristic (I-Vg characteristic) with respect to a gate voltage Vg of a thin film transistor used for such an application has a large variation between elements, which is non-uniformity of light emission or a decrease in the number of effective gradations resulting therefrom. There are problems that have been reduced to image quality.
[0023]
Regarding the variation in the gate voltage Vth at which the current starts to flow, a technique for correcting the voltage that automatically cancels this by storing it in a capacity different from the memory capacity of the light emission information for each pixel (each driving thin film transistor) is examined. Has been. (SID98Digest, p11-p14).
[0024]
However, the realization of such a method requires four transistors and two capacitors for each pixel, and current variation in the gate voltage region during actual driving (corresponding to variation in the slope of the I-Vg characteristic). However, there is still a problem that the image quality is lowered in the form of large non-uniform light emission or a decrease in the number of effective gradations resulting therefrom.
[0025]
[Means for Solving the Problems]
In view of such a situation, the authors use materials having various physical properties, laminate functional thin films with various characteristics in various configurations, and perform evaluation in terms of luminous efficiency, color purity, and life, The inventors have found that the recombination region of holes and electrons can be effectively controlled by using a specific functional layer or a combination of specific materials, and have completed the present invention.
[0026]
In addition, in order to realize a fixed pattern display with a resolution as high as that of a printed material with high luminous efficiency and reliability, the authors and others have made prototypes of patterned light emitting elements with various insulating layers, and by using specific insulating layers, It is possible to obtain high luminous efficiency, and it is possible to improve reliability by suppressing cathode disconnection, cathode anode-to-cathode short circuit, efficiency reduction, etc. The present invention has been completed by finding that display non-display can be controlled by electrical light emission / non-light emission.
[0027]
In addition, the authors studied driving means using various combinations of thin film transistors, and examined how actual light emission changes when the channel mobility changes. The present inventors have completed the present invention by finding that the combination of resistors provides high emission uniformity of each pixel, that is, a high level of gradation can be realized.
[0028]
Specifically, the organic thin film EL element of the first invention includes a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting layer provided at least between the hole injection electrode and the electron injection electrode. An electron injecting and transporting layer is provided, and a non-light emitting electron transporting layer is provided between the light emitting layer and the electron injecting and transporting layer.
[0029]
The organic thin film EL device according to the second aspect of the invention includes a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting layer provided between at least the hole injection electrode and the electron injection electrode, and an electron injection transport. And a non-light emitting hole blocking layer between the light emitting layer and the electron injecting and transporting layer.
[0030]
The organic thin film EL device according to the third aspect of the invention includes a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting layer provided between at least the hole injection electrode and the electron injection electrode, and an electron injection transport. And the light emitting layer has both a hole transporting capability and an electron transporting capability.
[0031]
According to a fourth aspect of the present invention, there is provided an organic thin film EL device comprising: a hole injection electrode and an electron injection electrode on a transparent substrate; and a light emitting layer provided at least between the hole injection electrode and the electron injection electrode; And a thin layer made of an acceptor organic molecule between the light emitting layer and the electron injecting and transporting layer.
[0032]
An organic thin film EL device according to a fifth aspect of the invention includes a hole injection electrode and an electron injection electrode on a transparent substrate, at least a light emitting layer provided between the hole injection electrode and the electron injection electrode, and an electron injection transport. And the light emitting layer is mainly composed of an organic light emitting molecule and an acceptor organic molecule.
[0033]
The organic thin film EL element of the sixth invention is characterized in that the acceptor organic molecule is mainly composed of 7,7,8,8-tetracyanoquinodimethane.
[0034]
The organic thin film EL element of the seventh invention is characterized in that the acceptor organic molecule is mainly composed of tetracyanoethylene.
[0035]
The organic thin film EL element of the eighth invention is characterized in that the electron injecting and transporting layer is luminescent and the emission wavelength is different from the emission wavelength of the emission layer.
[0036]
The organic thin film EL element of the ninth invention is characterized in that the electron injecting and transporting layer is luminescent, and the emission wavelength of the light emitting layer is shorter than the emission wavelength.
[0037]
In the organic thin film EL element according to the tenth invention, the electron injecting and transporting layer is mainly composed of tris (8-quinolinolato) aluminum or a derivative thereof.
[0038]
The organic thin film EL element of the eleventh invention has a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting layer provided at least between the hole injection electrode and the electron injection electrode, The light emitting layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl- It consists of 4,4'-diamine.
[0039]
The organic thin film EL element of the twelfth invention has a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting layer provided at least between the hole injection electrode and the electron injection electrode, The light emitting layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine. It is characterized by.
[0040]
An organic thin film EL device according to a thirteenth aspect of the present invention includes a hole injection electrode and an electron injection electrode on a transparent substrate, at least a light emitting layer provided between the hole injection electrode and the electron injection electrode, and hole blocking. And the hole blocking layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene.
[0041]
According to a fourteenth aspect of the present invention, there is provided an organic thin film EL device comprising: a hole injection electrode and an electron injection electrode on a transparent substrate; and a light emitting layer provided at least between the hole injection electrode and the electron injection electrode; And the hole blocking layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene and tetraphenylethylene.
[0042]
In the organic thin film EL element according to the fifteenth aspect, the light emitting layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-diphenyl-N, N′-bis ( 3-methylphenyl) -1,1′-biphenyl-4,4′-diamine.
[0043]
In the organic thin film EL element according to the sixteenth aspect of the present invention, the light emitting layer mainly comprises 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-bis (4′-diphenylamino-4). -Biphenylyl) -N, N'-diphenylbenzidine.
[0044]
According to a seventeenth aspect of the present invention, there is provided an organic thin film EL device comprising: a hole injection electrode and an electron injection electrode on a transparent substrate; and a light emitting layer continuously provided at least between the hole injection electrode and the electron injection electrode. The light-emitting layer mainly comprises 1,1,4,4-tetraphenyl-1,3-butadiene and N, N'-diphenyl-N, N'- It is made of bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine, and the hole blocking layer is mainly made of 1,1,4,4-tetraphenyl-1,3-butadiene. It is characterized by.
[0045]
An organic thin film EL element according to an eighteenth aspect of the present invention includes a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting layer provided continuously between at least the hole injection electrode and the electron injection electrode. A hole-blocking layer and a non-light-emitting electron transport layer, wherein the light-emitting layer mainly comprises 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-bis (4′-diphenylamino- 4-biphenylyl) -N, N′-diphenylbenzidine, and the hole blocking layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene.
[0046]
In the organic thin film EL element according to the nineteenth invention, the non-light emitting electron transport layer is mainly composed of 7,7,8,8-tetracyanoquinodimethane.
[0047]
The organic thin film EL element of the twentieth invention is characterized in that the non-light emitting electron transport layer is mainly composed of tetracyanoethylene.
[0048]
An organic thin film EL device according to a twenty-first aspect includes a hole injection electrode and an electron injection electrode on a transparent substrate, and an insulating layer and a light emitting functional layer provided at least between the hole injection electrode and the electron injection electrode. And the insulating layer is a photoresist layer patterned in accordance with image information.
[0049]
In the organic thin film EL element of the 22nd invention, the photoresist layer has a film thickness of 0.02 μm or more and 0.2 μm or less, and is completely cured at a temperature of 150 ° C. or more after pattern formation. Features.
[0050]
The organic thin film EL device of the twenty-third aspect of the present invention is the vapor phase on the surface of the hole injection electrode after forming the photoresist layer on the hole injection electrode and completely curing it, and before forming the light emitting functional layer. It is characterized by performing cleaning.
[0051]
According to a twenty-fourth aspect of the invention, there is provided a driving method of an organic thin film EL element that obtains light emission by applying a voltage between a hole injection electrode and an electron injection electrode, wherein one pole of the power source and the organic thin film One side of the EL element is connected, and the other side is connected via a thin film transistor, and has a memory capacity for holding the gate voltage of the transistor. In a driving method in which information on light emission and non-light emission is written by charging / discharging the memory capacity and the light emission state is controlled, a layer created under the same film formation conditions simultaneously with the channel layer of the thin film transistor in parallel with the memory capacity It is characterized by arranging as follows.
[0052]
In a twenty-fifth aspect of the invention, a time constant obtained from a product of the memory capacity and the average value of resistance is at least smaller than the predetermined time interval and larger than 1/100 of the time interval. And
[0053]
DETAILED DESCRIPTION OF THE INVENTION
The organic thin film EL element according to the embodiment of the present invention will be described below.
[0054]
The organic thin film EL device of the present invention is composed of a hole injection electrode and an electron injection electrode on a transparent substrate, and a light emitting functional layer provided at least between the hole injection electrode and the electron injection electrode. Here, the light emitting functional layer is a collective term for each layer involved in the process of emitting light by holes and electrons injected from both electrodes, and as is generally known, in fact, a hole transport layer and an electron are actually used. A laminated structure with a transporting light-emitting layer, a laminated structure of a hole-transporting layer, a light-emitting layer, and an electron-transporting layer, or a structure in which layers such as a hole-injecting layer and an electron-injecting layer are laminated To do.
[0055]
The transparent substrate is not particularly limited as long as it can carry an organic thin film EL element, and a normal glass substrate such as Corning 1737 glass is often used, but a polyester or other resin film can also be used. In general, one of the electron injection electrode and the hole injection electrode needs to be transparent. In many cases, the transparent electrode is provided on the transparent substrate to extract the emitted light to the outside. It is also possible to extract light emission by forming a film and using the upper electrode as a transparent electrode. Usually, a transparent ITO (indium tin oxide) film is often used for the hole injection electrode, and the electron injection electrode is made of a metal having a low work function and a low electron injection barrier, such as MgAg alloy or AlLi alloy proposed by Tang et al. An alloy with a stable metal having a relatively large work function is often used.
[0056]
The electron injection electrode may have a layered structure of a layer that substantially contributes to the injection of electrons into the light emitting functional layer and a layer that is responsible for electrical conductivity as an electrode. An electron injection electrode having a laminated structure of a lithium layer or a lithium oxide layer and an aluminum layer is used. In this case, it is known that the driving voltage is lowered and the luminous efficiency is improved as compared with the case where only the aluminum layer is used for the electron injection electrode.
[0057]
ITO film is formed by sputtering, electron beam evaporation, ion plating, etc. for the purpose of improving its transparency or decreasing the resistivity, and various post-treatments for the purpose of resistivity and shape control. Is often performed. The film thickness is determined from the required sheet resistance value and visible light transmittance. However, since the organic EL element has a relatively high driving current density, it should be used with a thickness of 100 nm or more in order to reduce the sheet resistance. There are many.
[0058]
As the hole injection electrode, these normal ITO films can be used, and a coating film of a transparent conductive paint in which conductive powder is dispersed and other electrodes can be used. In addition to the alloy of the above-mentioned MgAg, AlLi and other metals having a low work function and a low electron injection barrier and a metal having a relatively high work function and a stable metal, a thin Li film was first formed on the electron injection electrode. Laminated electrodes that later form a relatively thick Al film, LiF films, Al ₂ O _Three A laminated electrode in which the Al film is formed relatively thick after the film is formed into a thin layer, and other various electrode configurations can be used.
[0059]
In the first invention, the main part is a unique structure in which a non-light emitting electron transport layer is provided between the light emitting layer and the electron injection transport layer, and the materials constituting each layer are widely known materials. Can be used.
[0060]
In the second invention, the main part is a unique structure in which a non-light-emitting hole blocking layer is provided between the light emitting layer and the electron injecting and transporting layer, and the material constituting each layer is a generally known material. Can be widely used.
[0061]
In the third invention, the main part has a unique structure using a light emitting layer capable of transporting both electrons and holes, and generally known materials can be widely used as materials constituting each layer. .
[0062]
In the fourth invention, the main part is a unique structure in which a thin layer made of an acceptor organic molecule is provided between a light emitting layer and an electron injecting and transporting layer, and materials constituting each layer are generally known materials. Can be widely used.
[0063]
In the fifth aspect of the invention, the main part is that the light emitting layer has a unique structure composed of organic light emitting molecules and acceptor organic molecules, and generally known materials can be widely used as materials constituting each layer.
[0064]
In particular, when a material such as light-emitting tris (8-quinolinolato) aluminum or a derivative thereof is used as the electron injecting and transporting layer, a remarkable improvement in color purity and an improvement in life are recognized by using these materials.
[0065]
This is because the recombination region of holes and electrons is controlled by these unique configurations, the light emission of the light-emitting electron injecting and transporting layer is suppressed, and recombination and light emission are effectively performed in the light emitting layer. is there.
[0066]
The electron injecting and transporting layer refers to a layer in which electrons are injected from the electron injecting electrode and plays a role of transporting electrons, and is used as a general term for a part having this function as a single layer or a laminated film. The hole blocking layer may be a layer that prevents the movement of holes and has a function of accumulating holes on the hole injection electrode side, but has a higher ionization potential than the layer in contact with the hole injection electrode side. Even if it is difficult to inject holes or they can be injected, a layer having extremely low hole mobility can serve such a role. Having both hole transport ability and electron transport ability means that the transport ability of both carriers is not a big difference. The organic light-emitting molecule refers to a material that exhibits fluorescence inherent in the molecule, and in particular, in the present invention, emits fluorescence by electrical excitation (recombination of electrons and holes) in a solid thin film state.
[0067]
In the eleventh aspect, the light-emitting layer is mainly 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-diphenyl-N, N′-bis (3-methylphenyl). It consists of -1,1'-biphenyl-4,4'-diamine, and the hole injection / transport layer, the electron injection / transport layer, and other layers can use a wide variety of ordinary materials. These two materials are formed as a light emitting layer by co-evaporation or application from a mixed paint, but the mixing ratio may be 1: 9 or more and 9: 1 or less by weight. By using the light emitting layer made of this mixed material, high light emission efficiency can be stably obtained.
[0068]
In the twelfth aspect of the invention, the light-emitting layer is mainly 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-bis (4′-diphenylamino-4-biphenylyl) -N. , N′-diphenylbenzidine, and the hole injecting and transporting layer, the electron injecting and transporting layer, and other layers can use a wide variety of ordinary materials. These two materials are formed as a light emitting layer by co-evaporation or application from a mixed paint, but the mixing ratio may be 1: 9 or more and 9: 1 or less by weight. By using the light emitting layer made of this mixed material, high light emission efficiency can be stably obtained.
[0069]
In the thirteenth invention, the main part is that the hole blocking layer provided in contact with the light emitting layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene, and the hole injection transport. The layers, the light emitting layer, the electron injecting and transporting layer, and other layers can use a wide variety of ordinary materials. 1,1,4,4-Tetraphenyl-1,3-butadiene is characterized by an extremely high ionization potential and a high hole injection barrier. As a result, it increases the recombination probability in the light emitting layer in contact with it. It is something to do.
[0070]
In the fourteenth invention, the main part is that the hole blocking layer provided in contact with the light emitting layer is mainly composed of 1,1,4,4-tetraphenyl-1,3-butadiene and tetraphenylethylene, For the hole injecting and transporting layer, the light emitting layer, the electron injecting and transporting layer, and other layers, ordinary materials can be widely used. By mixing a suitable amount of tetraphenylethylene, black spots (non-luminous defects) due to crystallization of 1,1,4,4-tetraphenyl-1,3-butadiene can be suppressed. The effect as a blocking layer is impaired. The mixing ratio of tetraphenylethylene to 1,1,4,4-tetraphenyl-1,3-butadiene is 0.5% or more and 60% or less by weight.
[0071]
In the seventeenth invention, the main part has a light emitting layer, a hole blocking layer, and a non-light emitting electron transport layer provided continuously, and the light emitting layer mainly comprises 1,1,4,4-tetra The hole blocking layer is composed of phenyl-1,3-butadiene and N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine. It consists mainly of 1,1,4,4-tetraphenyl-1,3-butadiene, and the hole injection / transport layer, the light emitting layer, the electron injection / transport layer, and other layers can use a wide variety of ordinary materials. For the non-light emitting electron transport layer, materials such as 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene can be used.
[0072]
This 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′- The light-emitting layer material of diamine is formed as a light-emitting layer by co-evaporation or coating from a mixed paint. The mixing ratio may be 1: 9 or more and 9: 1 or less by weight. By using the light-emitting layer made of this mixed material and the hole blocking layer mainly made of 1,1,4,4-tetraphenyl-1,3-butadiene, the hole-electron recombination region is formed in the light-emitting layer. The light emission efficiency is high and the light emission efficiency is high and the light emission efficiency is stably obtained.
[0073]
In the seventeenth invention, the main part has a light emitting layer, a hole blocking layer, and a non-light emitting electron transport layer provided continuously, and the light emitting layer is mainly 1,1,4,4-tetraphenyl. -1,3-butadiene and N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine, the hole blocking layer being mainly 1,1,4,4- It consists of tetraphenyl-1,3-butadiene, and the hole injecting and transporting layer, the light emitting layer, the electron injecting and transporting layer, and other layers can use a wide variety of ordinary materials.
[0074]
For the non-light emitting electron transport layer, materials such as 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene can be used. The light-emitting layer material of 1,1,4,4-tetraphenyl-1,3-butadiene and N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine is a common material. The light-emitting layer is formed by vapor deposition or application from a mixed paint, but the mixing ratio may be 1: 9 or more and 9: 1 or less by weight. By using the light-emitting layer made of this mixed material and the hole blocking layer mainly made of 1,1,4,4-tetraphenyl-1,3-butadiene, the hole-electron recombination region is formed in the light-emitting layer. The light emission efficiency is high and the light emission efficiency is high and the light emission efficiency is stably obtained.
[0075]
In the twenty-first aspect, the main part is to pattern light emission using a patterned photoresist layer as an edge layer, and a wide range of light emitting functional layers can be used.
[0076]
In the twenty-second aspect, in addition to the above, the main part is that the film thickness of the photoresist is 0.02 μm or more and 0.2 μm or less and that the photoresist is completely cured at a temperature of 150 ° C. or more. When the photoresist film thickness is 0.02 μm or less, it becomes difficult to obtain a uniform film, and problems such as light emission from film defects such as repellency become prominent. When the thickness is 0.2 μm or more, the step between the portion where the photoresist is formed and the portion where the photoresist is not formed becomes large, and the problem that the conduction of the electrode formed on the light emitting functional layer at the step portion becomes insufficient is remarkable. There is a problem that the stepped portion is conspicuous and the light emission pattern can be easily visually recognized even when there is no light emission. In addition, if the curing temperature of the photoresist layer is less than 150 ° C. and insufficient, there is a problem that the luminous efficiency is remarkably lowered due to redeposition of uncured organic resist molecules to the light emitting portion.
[0077]
In the twenty-third aspect, in addition to the above, the main part is to perform vapor phase cleaning of the surface of the hole injection electrode after completely curing the photoresist layer and before forming the light emitting functional layer. A widely used method such as oxygen plasma treatment or UV ozone treatment can be used as the method for vapor phase cleaning. By this cleaning treatment, a small amount of organic substance layer remaining on the surface is removed, and high luminous efficiency can be stably obtained.
[0078]
In the twenty-fourth aspect of the invention, the main part is arranged in parallel with the capacity for storing the gate voltage of the driving thin film transistor element of the organic thin film EL element, and the layer formed under the same film formation conditions as the resistance at the same time as the channel layer of the transistor. There is. As a result, even if characteristics such as channel layer mobility and carrier concentration change due to local variations such as substrate conditions and film formation conditions, the mobility and carrier concentration of the resistance layer also change in the same way. Become. That is, for example, a constant voltage is given to each pixel as light emission information, stored in the memory capacity, and according to the voltage, a current flows through each driving thin film transistor, and the organic thin film EL element emits light. In pixels where the current for the same gate voltage increases due to reasons such as high mobility, the current flowing through the resistor arranged in parallel with the memory capacity also increases, and the gate voltage decreases faster than other pixels. As a result, the light emission time is shortened.
[0079]
In other words, in a pixel with a large current flowing through the driving thin film transistor of the pixel, the luminance of light emission increases according to the flowing current, but the current flowing through the resistor created under the same conditions simultaneously with the channel of the driving thin film transistor also increases at the same rate. Therefore, the discharge of the memory capacity is faster by that amount, and the actual light emission time in the time interval (one frame time) from writing to writing of light emission information is shortened, and the average luminance observed as a panel Means compensated to be equal.
[0080]
On the other hand, for a pixel with a small current flowing through the driving thin film transistor for the same gate voltage, the luminance of the light emission decreases according to the flowing current. Since the flowing current also decreases at the same rate, the discharge of the memory capacity is delayed accordingly, and the actual light emission time in one frame time becomes longer, and the average luminance observed as a panel is compensated for each other. Means to be equivalent.
[0081]
In the twenty-fifth aspect of the invention, in addition to the above-described structure, the main part has at least the time constant obtained from the product of the memory capacity and the average value of each pixel of the resistance created under the same conditions simultaneously with the channel of the driving thin film transistor. Is smaller than one frame time and larger than 1/100 time of one frame time. The resistance value described above varies due to variations in mobility, etc., but if the product of the average value and the memory capacity (discharge time constant) is longer than one frame time, substantially the frame time is one frame time. Light emission continues throughout, and effective compensation of current variation cannot be expected.
[0082]
On the other hand, when the coincidence constant is 1/100 or less of one frame time, the compensation functions effectively, but the actually required peak luminance is 100 times or more of the panel luminance and is consumed in the same manner as the passive matrix driving described above. The power becomes large and the merit of active matrix driving cannot be obtained. That is, in view of these phenomena, the driving means of the present invention has a memory capacity and a width of the resistance layer so that the average of the time constant is smaller than one frame time and larger than 1/100 time of one frame time. By setting the length, it is possible to suppress variations in luminance because the light emission time is inversely proportional to the luminance of the pixels having a larger time constant than the average and smaller pixels.
[0083]
The compensation effect of the characteristic variation of the driving thin film transistor due to the resistance layer arranged in parallel with the memory capacity provided by this driving means is extremely remarkable, and normal driving means in which the resistance layer described here is not provided in parallel with the memory capacity Then, even when the luminance variation of one digit or more is caused by the characteristic variation of the transistor, the luminance variation can be suppressed to a level where the luminance variation cannot be recognized by visual observation. As a result, high gradation reproducibility can be obtained regardless of the gradation control by the gate voltage value itself or the subfield method.
[0084]
On the other hand, in the method using the normal driving means, the memory capacity is only discharged with a slight leakage current, and normally the light emission is always continued except for a short time of data writing by scanning. When the driving means is used, the light emission time is shortened depending on the pixel according to the variation in transistor characteristics, and the light emission efficiency is lowered accordingly. However, this drawback can be minimized by appropriately setting the above-described discharge time constant according to the uniformity and gradation level required for the display image.
[0085]
Next, it demonstrates further in detail based on a specific Example.
[0086]
(Example 1)
As a substrate having a hole injection electrode formed on a transparent substrate, a commercially available glass substrate with ITO (manufactured by Sanyo Vacuum Co., Ltd., size 100 × 100 mm × t = 0.7 mm, sheet resistance of about 14Ω / □) is used. Patterning was performed by photolithography so that the light emitting area was 10 × 10 mm by overlapping with the injection electrode. Substrate treatment after photolithography is performed by immersing in a commercially available resist stripping solution (mixed solution of dimethyl sulfoxide and N-methyl-2-pyrrolidone), rinsing with acetone, and then immersing in fuming nitric acid for 1 minute. Then, the resist was completely removed.
[0087]
Cleaning of the ITO surface was performed by mechanical rubbing with a nylon brush while sufficiently supplying both sides of the back surface of the substrate and sufficiently supplying a 0.238% aqueous solution of tetramethylammonium hydroxide. Thereafter, it was sufficiently rinsed with pure water and spin-dried. In addition, before vapor deposition of the organic thin film EL element, oxygen plasma treatment for 1 minute was performed in a commercially available plasma reactor (manufactured by Yamato Scientific Co., Ltd., PR41 type) under the conditions of an oxygen flow rate of 20 sccm, a pressure of 0.2 Torr, and a high frequency output of 300 W. Then, it was placed in a vapor deposition tank.
[0088]
As the vacuum deposition apparatus, a device obtained by modifying a commercially available high vacuum deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd., EBV-6DA type) was used. The main exhaust device is a turbo molecular pump (TC 1500, manufactured by Osaka Vacuum Co., Ltd.) with an exhaust speed of 1500 liters / min, and the ultimate vacuum is about 1 × 10 ^-6 Less than Torr, all deposition is 2-3 × 10 ^-6 Performed in the range of Torr. All the vapor depositions were performed by connecting a direct current power source (manufactured by Kikusui Electronics Co., Ltd., PAK10-70A) to a resistance heating vapor deposition boat made of tungsten.
[0089]
Thus, on the glass substrate with ITO arranged in the vacuum layer, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (Hodogaya) was used as a hole transport layer. Chemical Co., Ltd.) and 4-N, N-diphenylamino-α-phenylstilbene were co-deposited at a deposition rate of 0.3 nm / s and 0.01 nm / s, respectively, to form a film thickness of about 80 nm.
[0090]
Next, 1,1,4,4-tetraphenyl-1,3-butadiene (manufactured by Kanto Chemical Co., Inc.) was formed as a light emitting layer to a thickness of about 10 nm at a deposition rate of 0.3 nm / s.
[0091]
Next, a non-light emitting electron transport layer 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Inc.) was formed to a film thickness of about 5 nm at a deposition rate of 0.1 nm / s.
[0092]
Next, tris (8-quinolinolato) aluminum (manufactured by Dojin Chemical Co., Ltd.) was formed as an electron transport layer to a film thickness of about 25 nm at a deposition rate of 0.3 nm / s.
[0093]
Next, as an electron injection electrode, only Li is formed at a low temperature from an AlLi alloy (manufactured by High-Purity Chemical Co., Ltd., Al / Li weight ratio 99/1) at a deposition rate of about 0.1 nm / s to a film thickness of about 1 nm. Then, from the state where the temperature of the AlLi alloy was further raised and Li was exhausted, only Al was formed at a film thickness of about 100 nm at a deposition rate of about 1.5 nm / s to obtain a stacked electron injection electrode. .
[0094]
The organic thin film EL device thus prepared leaks the inside of the vapor deposition tank with dry nitrogen, and then, in a dry nitrogen atmosphere, attaches a lid made of Corning 7059 glass (made by Anelva Co., Ltd., trade name Super Back Seal 953). -7000) to prepare a sample.
[0095]
The organic thin film EL element sample thus obtained was evaluated as follows. The DC drive power supply uses a DC constant current power supply (trade name: Multichannel Current Voltage Controller TR6163, manufactured by Advantest Corporation), and the spectrum measurement of the emission wavelength and the CIE chromaticity measurement are instantaneous multiphotometry systems (manufactured by Otsuka Electronics Co., Ltd., MCPD5000). The luminance was measured with a luminance meter (trade name Topcon Luminescence Meter BM-8, manufactured by Tokyo Optical Machinery Co., Ltd.). Luminous image quality such as luminance unevenness and black spots (non-light emitting portion) was observed with a 50 × optical microscope.
[0096]
The initial evaluation was performed in a normal laboratory environment at normal temperature and humidity 12 hours after the glass lid was adhered after vapor deposition of the device, and the emission chromaticity CIE (X, Y), luminous efficiency (cd / A), 100 cd / m ² The driving voltage during light emission was evaluated. The initial luminance is 100 cd / m ² A continuous light emission test was performed by driving at a constant DC current in a normal laboratory environment at normal temperature and humidity. From this test, the chromaticity changes or the brightness is reduced by half (50 cd / m ² ) Was evaluated as the lifetime. The evaluation results are shown in (Table 1).
[0097]
[Table 1]

[0098]
According to this example, the color purity is good, the light emission efficiency is high, the light emission is excellent due to the self-light emission at a low driving voltage, the luminance decrease is small even in the continuous light emission test, and the chromaticity changes. Thus, an organic thin film EL element that can be used stably for an extremely long time with low power consumption can be realized.
[0099]
(Example 2)
In the formation of the non-light-emitting electron transport layer of Example 1, tetracyanoethylene (manufactured by Kanto Chemical Co., Inc.) was used instead of 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Ltd.). An organic thin film EL element sample was prepared in the same manner as in Example 1 except that the sample was evaluated and evaluated as described in Example 1. The results are shown in (Table 1).
[0100]
(Example 3)
Between the hole transport layer and the light-emitting layer of Example 1, 1,1,4,4-tetraphenyl-1,3-butadiene (manufactured by Kanto Chemical Co., Inc.) and N, N′- Bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (Hodogaya Chemical Co., Ltd.) was co-deposited at a deposition rate of 0.15 nm / s to form a film thickness of about 10 nm. .
[0101]
All other configurations were made in the same manner as in Example 1, and organic thin film EL element samples were prepared and evaluated as described in Example 1. The results are shown in (Table 1).
[0102]
(Example 4)
In the formation of the non-light-emitting electron transport layer of Example 3, tetracyanoethylene (manufactured by Kanto Chemical Co., Inc.) was used instead of 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Ltd.). An organic thin film EL element sample was prepared in the same manner as in Example 1 except that the sample was evaluated and evaluated as described in Example 1. The results are shown in (Table 1).
[0103]
(Example 5)
Instead of the 1,1,4,4-tetraphenyl-1,3-butadiene layer, which is the light emitting layer of Example 3, and 7,7,8,8-tetracyanoquinodimethane, which is the non-light emitting electron transport layer In addition, 1,1,4,4-tetraphenyl-1,3-butadiene (manufactured by Kanto Chemical Co., Inc.) and 7,7,8,8-tetracyanoquinodimethane (Kanto Chemical Co., Ltd.) are used as new light emitting layers. Were manufactured by co-evaporation at a deposition rate of 0.15 nm / s to a thickness of about 10 nm.
[0104]
Other than that, organic thin film EL element samples were prepared in the same manner as in Example 3 and evaluated as described in Example 1. The results are shown in (Table 1).
[0105]
(Example 6)
Implementation was performed except that tetracyanoethylene (manufactured by Kanto Chemical Co., Ltd.) was used in place of 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Ltd.) in the new light-emitting layer of Example 5. An organic thin film EL device sample was prepared in the same manner as in Example 5 and evaluated as described in Example 1. The results are shown in (Table 1).
[0106]
(Example 7)
In the formation of the light emitting layer of Example 1, 1,1,4,4-tetraphenyl-1,3-butadiene (Kanto Chemical) was used instead of the 1,1,4,4-tetraphenyl-1,3-butadiene layer. Co., Ltd.) and Coumarin 540 (Lambda Physik Co., Ltd.) were co-deposited at a deposition rate of 0.15 nm / s to form a film thickness of about 10 nm.
[0107]
In all other configurations, an organic thin film EL element sample was prepared in the same manner as in Example 1 and evaluated as described in Example 1. The results are shown in (Table 1).
[0108]
(Example 8)
As the non-light emitting electron transport layer of Example 7, tetracyanoethylene (manufactured by Kanto Chemical Co., Ltd.) was used instead of 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Ltd.). Prepared an organic thin film EL element sample in the same manner as in Example 7, and evaluated as described in Example 1. The results are shown in (Table 1).
[0109]
Example 9
In place of the 7,7,8,8-tetracyanoquinodimethane layer, which is the non-light emitting electron transport layer of Example 1, 1,1,4,4-tetraphenyl-1,3-butadiene (Kanto Chemical Co., Inc.) Company) and 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Inc.) were co-deposited at a deposition rate of 0.15 nm / s to form a film thickness of about 10 nm.
[0110]
In all other configurations, an organic thin film EL element sample was prepared in the same manner as in Example 1 and evaluated as described in Example 1. The results are shown in (Table 1).
[0111]
(Example 10)
Instead of 7,7,8,8-tetracyanoquinodimethane (manufactured by Kanto Chemical Co., Inc.) in Example 9, tetracyanoethylene (manufactured by Kanto Chemical Co., Ltd.) was used in the same manner as in Example 9 Organic thin film EL device samples were prepared and evaluated as described in Example 1. The results are shown in (Table 1).
[0112]
(Example 11)
In the formation of the electron transport layer of Example 1, tris (4-methyl-8-quinolinolato) aluminum (manufactured by Chemipro Kasei Co., Ltd.) was used instead of tris (8-quinolinolato) aluminum (manufactured by Dojin Chemical Co., Ltd.). Except for the above, an organic thin film EL element sample was prepared in the same manner as in Example 1 and evaluated as described in Example 1. The results are shown in (Table 1).
[0113]
(Example 12)
In formation of the electron transport layer of Example 2, tris (4-methyl-8-quinolinolato) aluminum (made by Chemipro Kasei Co., Ltd.) was used instead of tris (8-quinolinolato) aluminum (made by Dojin Chemical Co., Ltd.). Except for the above, an organic thin film EL element sample was prepared in the same manner as in Example 2 and evaluated as described in Example 1. The results are shown in (Table 1).
[0114]
(Example 13)
In the formation of a new light-emitting layer of Example 3, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (manufactured by Hodogaya Chemical Co., Ltd.) Except that N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (manufactured by Dojin Chemical Co., Ltd.) was used, the same procedure as in Example 3 was performed. Organic thin film EL device samples were prepared and evaluated as described in Example 1. The results are shown in (Table 1).
[0115]
(Example 14)
In the formation of the new light-emitting layer of Example 4, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (manufactured by Hodogaya Chemical Co., Ltd.) The same as in Example 4 except that N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (manufactured by Dojindo) was used. Organic thin film EL device samples were prepared and evaluated as described in Example 1. The results are shown in (Table 1).
[0116]
(Example 15)
Instead of the 7,7,8,8-tetracyanoquinodimethane layer 5 nm used as the non-light emitting electron transport layer in Example 7, 1,1,4,4-tetraphenyl-1,3-butadiene (Kanto) An organic thin film EL element sample was prepared in the same manner as in Example 7 except that Chemical Chemical Co., Ltd. was formed to a film thickness of 10 nm and evaluated as described in Example 1. The results are shown in (Table 1).
[0117]
(Example 16)
Instead of the 1,1,4,4-tetraphenyl-1,3-butadiene layer 10 nm provided as the light-emitting layer of Example 1, 1,1,4,4-tetraphenyl-1,3-butadiene (Kanto Chemical) Co., Ltd.) and N, N'-bis (4'-diphenylamino-4-biphenylyl) -N, N'-diphenylbenzidine (Hodogaya Chemical Co., Ltd.) at a deposition rate of 0.15 nm / s. Vapor deposition forms a film with a thickness of about 10 nm, followed by 1,1,4,4-tetraphenyl-1,3-butadiene (manufactured by Kanto Chemical Co., Ltd.) and tetraphenylethylene (manufactured by Kanto Chemical Co., Ltd.). The films were co-deposited at a deposition rate of 0.15 nm / s to form a film thickness of about 10 nm.
[0118]
Otherwise, an organic thin film EL element sample was prepared in the same manner as in Example 1 and evaluated as described in Example 1. The results are shown in (Table 1).
[0119]
(Example 17)
Instead of the co-evaporated layer of 1,1,4,4-tetraphenyl-1,3-butadiene and Coumarin 540 provided as the light emitting layer of Example 15, 10 nm, 1,1,4,4-tetraphenyl-1, 3-butadiene (manufactured by Kanto Chemical Co., Inc.) and N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (manufactured by Hodogaya Chemical Co., Ltd.) were each 0.15 nm / Co-deposited at a deposition rate of s to form a film thickness of about 10 nm.
[0120]
Otherwise, an organic thin film EL element sample was prepared in the same manner as in Example 15 and evaluated as described in Example 1. The results are shown in (Table 1).
[0121]
(Example 18)
Instead of the co-evaporated layer of 1,1,4,4-tetraphenyl-1,3-butadiene and Coumarin 540 provided as the light emitting layer of Example 15, 10 nm, 1,1,4,4-tetraphenyl-1, 3-butadiene (manufactured by Kanto Chemical Co., Inc.) and N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (manufactured by Dojin Chemical Co., Ltd.) ) Were co-deposited at a deposition rate of 0.15 nm / s to form a film thickness of about 10 nm.
[0122]
Otherwise, an organic thin film EL element sample was prepared in the same manner as in Example 15 and evaluated as described in Example 1. The results are shown in (Table 1).
[0123]
(Example 19)
An organic thin-film EL element sample was prepared in the same manner as in Example 3 except that the film thickness of the tris (8-quinolinolato) aluminum layer was changed to 20 nm instead of 25 nm in the formation of the electron transport layer of Example 3. Evaluation was performed as described in Example 1. The results are shown in (Table 1).
[0124]
(Example 20)
In the formation of the electron transport layer of Example 3, an organic thin film EL element sample was prepared in the same manner as in Example 3 except that the thickness of the tris (8-quinolinolato) aluminum layer was changed to 30 nm instead of 25 nm. Evaluation was performed as described in Example 1. The results are shown in (Table 1).
[0125]
(Example 21)
Following the formation of the hole transport layer of Example 3, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (Hodogaya Chemical Co., Ltd.) was formed prior to the formation of the light emitting layer. An organic thin film EL element sample was prepared in the same manner as in Example 3 except that the film thickness was about 5 nm at a deposition rate of 0.3 nm / s, and evaluation was performed as described in Example 1. . The results are shown in (Table 1).
[0126]
(Example 22)
Following the formation of the hole transport layer of Example 4, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (Hodogaya Chemical Co., Ltd.) was formed before the light emitting layer was formed. An organic thin film EL element sample was prepared in the same manner as in Example 4 except that the film thickness was about 5 nm at a deposition rate of 0.3 nm / s, and evaluation was performed as described in Example 1. . The results are shown in (Table 1).
[0127]
(Comparative Example 1)
In Example 1, the non-light-emitting electron transport layer (7,7,8,8-tetracyanoquinodimethane layer 5 nm) was not formed, and the electron transport layer (Tris (8-quinolinolato) aluminum layer 25 nm) was formed as a film. An organic thin film EL element sample was prepared in the same manner as in Example 1 except that the thickness was 15 nm, and evaluation was performed in the same manner as in Example 1. The results are shown in (Table 1).
[0128]
(Comparative Example 2)
In Example 1, the non-light-emitting electron transport layer (7,7,8,8-tetracyanoquinodimethane layer 5 nm) was not formed, and the electron transport layer (Tris (8-quinolinolato) aluminum layer 25 nm) was formed as a film. An organic thin film EL element sample was prepared in the same manner as in Example 1 except that the thickness was 20 nm, and evaluation was performed in the same manner as in Example 1. The results are shown in (Table 1).
[0129]
(Comparative Example 3)
In Example 1, the non-light-emitting electron transport layer (7,7,8,8-tetracyanoquinodimethane layer 5 nm) was not formed, and the electron transport layer (Tris (8-quinolinolato) aluminum layer 25 nm) was formed as a film. An organic thin film EL element sample was prepared in the same manner as in Example 1 except that the thickness was 25 nm, and evaluation was performed in the same manner as in Example 1. The results are shown in (Table 1).
[0130]
(Comparative Example 4)
In Example 1, the non-light-emitting electron transport layer (7,7,8,8-tetracyanoquinodimethane layer 5 nm) was not formed, and the electron transport layer (Tris (8-quinolinolato) aluminum layer 25 nm) was formed as a film. An organic thin film EL element sample was prepared in the same manner as in Example 1 except that the thickness was 30 nm, and evaluation was performed in the same manner as in Example 1. The results are shown in (Table 1). In (Table 1), the device configurations of the examples and comparative examples are abbreviated by abbreviations,
“TPT” means N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine,
“TPD” means N, N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine,
“PS” means 4-N, N-diphenylamino-α-phenylstilbene,
“TPB” is 1,1,4,4-tetraphenyl-1,3-butadiene,
“TPE” is tetraphenylethylene,
"C540" is the Coumarin 540
“TCNQ” is 7,7,8,8-tetracyanoquinodimethane,
“TCNE” is tetracyanoethylene,
"Alq _Three "Is tris (8-quinolinolato) aluminum,
"Almq _Three Is tris (4-methyl-8-quinolinolato) aluminum,
From the left, it is divided by / as a symbol representing the laminated structure, and is described in order from the ITO electrode side. The numbers in parentheses indicate the film thickness in nm, and + indicates co-evaporation.
[0131]
(Example 23)
As a substrate having a hole injection electrode formed on a transparent substrate, a commercially available glass substrate with ITO (manufactured by Sanyo Vacuum Co., Ltd., size 100 × 100 mm × t = 0.7 mm, sheet resistance of about 14Ω / □) is used. Patterning was performed by photolithography so that the light-emitting area was 70 × 70 mm by overlapping with the injection electrode. Substrate treatment after photolithography is completed by immersing in a commercially available resist stripping solution (mixed solution of dimethyl sulfoxide and n-methyl 2-pyrrolidone), rinsing with acetone, and further immersing in fuming nitric acid for 1 minute. The resist was removed. Cleaning of the ITO surface was performed by mechanical rubbing with a nylon brush while sufficiently supplying both sides of the back surface of the substrate and sufficiently supplying a 0.238% aqueous solution of tetramethylammonium hydroxide. Thereafter, it was sufficiently rinsed with pure water and spin-dried.
[0132]
On the hole injection electrode thus produced, an insulating layer was formed as follows. A positive photoresist (OFPR5000 manufactured by Tokyo Ohka Kogyo Co., Ltd.) was diluted with a special thinner and applied with a spinner. As prebake before exposure, oven heating at 130 ° C. for 15 minutes was performed, and then exposure was performed using a mask corresponding to the light emission pattern, and development was performed to obtain a resist film corresponding to the light emission pattern. Further, oven heating at 180 ° C. for 30 minutes was performed to obtain a patterned photoresist layer (insulating layer) having a thickness of about 0.1 μm.
[0133]
As a mask corresponding to the light emission pattern, a commercially available printer (MD2000 manufactured by Alps Electric Co., Ltd.) was used which was printed black on an OHP sheet at a resolution of 600 dpi.
[0134]
Next, mechanical scrubbing with a nylon brush was performed again while sufficiently supplying a 0.238% aqueous solution of tetramethylammonium hydroxide on both sides of the back surface of the substrate. Thereafter, it was sufficiently rinsed with pure water and spin-dried.
[0135]
Further, before vapor deposition of the light emitting functional layer, oxygen plasma treatment for 1 minute was performed in a commercially available plasma reactor (PR41 type, manufactured by Yamato Kagaku Co., Ltd.) under conditions of an oxygen flow rate of 20 sccm, a pressure of 0.2 Torr, and a high frequency output of 300 W. After that, it was placed in a vapor deposition tank.
[0136]
As the vacuum deposition apparatus, a device obtained by modifying a commercially available high vacuum deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd., EBV-6DA type) was used. The main exhaust device is a turbo molecular pump (TC 1500, manufactured by Osaka Vacuum Co., Ltd.) with an exhaust speed of 1500 liters / min, and the ultimate vacuum is about 1 × 10 ^-6 Less than Torr, all deposition is 2-3 × 10 ^-6 Performed in the range of Torr. All the vapor depositions were performed by connecting a direct current power source (manufactured by Kikusui Electronics Co., Ltd., PAK10-70A) to a resistance heating vapor deposition boat made of tungsten.
[0137]
Thus, on the glass substrate with ITO arranged in the vacuum layer, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenylbenzidine (Hodogaya) was used as a hole transport layer. Chemical Co., Ltd.) and 4-N, N-diphenylamino-α-phenylstilbene were co-deposited at a deposition rate of 0.3 nm / s and 0.01 nm / s, respectively, to form a film thickness of about 80 nm.
[0138]
Next, tris (8-quinolinolato) aluminum (manufactured by Dojin Chemical Co., Ltd.) was formed to a film thickness of about 40 nm at a deposition rate of 0.3 nm / s as a light emitting layer (light emitting electron transport layer).
[0139]
Next, as an electron injection electrode, only Li is formed at a low temperature from an AlLi alloy (manufactured by High-Purity Chemical Co., Ltd., Al / Li weight ratio 99/1) at a deposition rate of about 0.1 nm / s to a film thickness of about 1 nm. Then, from the state where the temperature of the AlLi alloy was further raised and Li was exhausted, only Al was formed at a film thickness of about 100 nm at a deposition rate of about 1.5 nm / s to obtain a stacked electron injection electrode. .
[0140]
The organic thin film EL device thus prepared leaks the inside of the vapor deposition tank with dry nitrogen, and then, in a dry nitrogen atmosphere, attaches a lid made of Corning 7059 glass (made by Anelva Co., Ltd., trade name Super Back Seal 953). -7000) to prepare a sample.
[0141]
The organic thin film EL element sample thus obtained was driven by a commercially available small button battery (3V × 2), bright and excellent in visibility, low power consumption and long life, as well as the 600 dpi mask used. It was possible to obtain a pattern emission with an excellent resolution comparable to that of a normal print, which was extremely faithful to the pattern. Luminance is 6cd and 300cd / m ² The luminance half-life was 5000 hours or more.
[0142]
In addition, the light emission pattern information is hardly visible when light is not emitted, and is extremely difficult to read. Information display / non-display can be switched only by the presence or absence of energization.
[0143]
As described above, according to this embodiment, light emission with high luminous efficiency, low driving voltage, and self-luminous emission with excellent visibility can be obtained, and an extremely high resolution and faithful light emission pattern can be obtained with good reproducibility, and continuous. Even in a light emission test, a decrease in luminance is small, and an organic thin film EL element that can be used stably for a very long time can be realized with low power consumption.
[0144]
(Comparative Example 5)
In Example 23, after development of the patterned insulating layer (photoresist), curing was not performed at 180 ° C. for 30 minutes, but instead drying was performed at 135 ° C. for 30 minutes as a normal post-bake, instead. Then, an organic thin film EL element sample was prepared, and light was emitted in the same manner as in Example 23.
[0145]
The organic thin film EL element sample thus obtained hardly emitted light when driven by the same battery, had low light emission efficiency even when driven by a normal DC power source, and required a very high voltage to obtain light emission. Luminance is 100cd / m at 12V ² Met.
[0146]
Similarly to Example 23, the light emission pattern information was hardly visible when no light was emitted, and it was extremely difficult to read, and the display / non-display of information could be switched only by the presence or absence of energization.
[0147]
(Comparative Example 6)
In Example 23, an organic thin film EL element sample was prepared in the same manner as in Example 23 except that the patterned insulating layer (photoresist) was formed to a thickness of 0.3 μm instead of the thickness of 0.1 μm. In the same manner as in Example 23, light was emitted.
[0148]
Some of the organic thin-film EL device samples obtained in this way had an excellent light emission state similar to that in Example 23 in the initial stage. However, when the light emission continued, the cathode partially deteriorated and the light emission did not occur. The number of parts increased, and a considerable part became non-luminescent in a few hours. Some samples had a non-light emitting portion from the beginning, and many samples did not emit light at all due to a short circuit between the positive and negative electrodes.
[0149]
In addition, even when this element is not emitting light, the pattern can be easily read, and it has not been possible to switch between displaying and hiding information only by energization.
[0150]
(Comparative Example 7)
In Example 23, an organic thin film EL element sample was prepared in the same manner as in Example 23 except that the patterned insulating layer (photoresist) was formed to a thickness of 0.01 μm instead of the thickness of 0.1 μm. In the same manner as in Example 23, light was emitted.
[0151]
The organic thin-film EL element sample thus obtained had a lot of light that should be non-light-emitting as a pattern, and the display quality was extremely deteriorated. The luminance and lifetime of light emission were good as in Example 23.
[0152]
In addition, the light emission pattern information was hardly visible at the time of non-light emission as in Example 23 and was difficult to interpret. It was.
[0153]
(Example 24)
A glass substrate (Corning 1737) was used as a transparent substrate, and a driving means was manufactured as follows using a normal low-temperature polysilicon TFT manufacturing process.
[0154]
The number of pixels was VGA of 480 vertical and 640 horizontal, and an ITO film was formed as a transparent electrode for each pixel. A p-type low-temperature polysilicon thin film transistor having W = 30 μm and L = 3 μm was formed and connected between the ITO electrode and the positive electrode line as a driving thin film transistor. A memory capacity of 0.2 pF was provided between the gate electrode and the positive electrode line.
[0155]
In parallel with the memory capacity, a p-type channel layer of the driving thin film transistor was formed and a resistance layer was formed under the same conditions. The resistance value of the resistance layer was formed so that the average value of all the pixels would be 10 GΩ, although the thickness, width, and length differ depending on the film formation variation such as the difference in mobility.
[0156]
In addition, in order to write the light emission information of each pixel by charging and discharging the memory capacity at regular intervals, a p-type low-temperature polysilicon thin film transistor having W = 3 μm and L = 3 μm is sequentially formed for each pixel as an information writing thin film transistor. The gate of the transistor was connected to the scan electrode, the source was connected to the data (source) electrode, and the drain was connected to the gate of the driving thin film transistor.
[0157]
On the driving means thus produced, an insulating film was formed leaving only the ITO electrode portion as an opening.
[0158]
Next, after cleaning the substrate, oxygen plasma treatment for 1 minute was performed in a commercially available plasma reactor (PR41 type, manufactured by Yamato Scientific Co., Ltd.) under the conditions of an oxygen flow rate of 20 sccm, a pressure of 0.2 Torr, and a high frequency output of 300 W. After that, it was placed in a vapor deposition tank.
[0159]
As the vacuum deposition apparatus, a device obtained by modifying a commercially available high vacuum deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd., EBV-6DA type) was used. The main exhaust device is a turbo molecular pump (TC 1500, manufactured by Osaka Vacuum Co., Ltd.) with an exhaust speed of 1500 liters / min, and the ultimate vacuum is about 1 × 10 ^-6 Less than Torr, all deposition is 2-3 × 10 ^-6 Performed in the range of Torr. All the vapor depositions were performed by connecting a direct current power source (manufactured by Kikusui Electronics Co., Ltd., PAK10-70A) to a resistance heating vapor deposition boat made of tungsten.
[0160]
As a hole transport layer, N, N′-bis (4′-diphenylamino-4-biphenylyl) -N, N′-diphenyl is formed as a hole transport layer on the glass substrate after forming the driving means arranged in the vacuum layer. Benzidine (Hodogaya Chemical Co., Ltd.) and 4-N, N-diphenylamino-α-phenylstilbene were co-deposited at a deposition rate of 0.3 nm / s and 0.01 nm / s, respectively, to a film thickness of about 80 nm. Formed.
[0161]
Next, tris (8-quinolinolato) aluminum (manufactured by Dojin Chemical Co., Ltd.) was formed to a film thickness of about 40 nm at a deposition rate of 0.3 nm / s as a light emitting layer (light emitting electron transport layer).
[0162]
Next, as an electron injection electrode, only Li is formed at a low temperature from an AlLi alloy (manufactured by High-Purity Chemical Co., Ltd., Al / Li weight ratio 99/1) at a deposition rate of about 0.1 nm / s to a film thickness of about 1 nm. Then, from the state where the temperature of the AlLi alloy was further raised and Li was exhausted, only Al was formed at a film thickness of about 100 nm at a deposition rate of about 1.5 nm / s to obtain a stacked electron injection electrode. .
[0163]
The organic thin film EL device thus prepared leaks the inside of the vapor deposition tank with dry nitrogen, and then, in a dry nitrogen atmosphere, attaches a lid made of Corning 7059 glass (made by Anelva Co., Ltd., trade name Super Back Seal 953). -7000) to prepare a sample.
[0164]
In the organic thin film EL device sample thus obtained, the electron injection electrode is grounded, a DC voltage of 7 V is applied to the positive electrode line, the scan electrode is sequentially scanned, and the light emission of each pixel is applied to the data (source) electrode. A voltage corresponding to the information was applied to emit light. The scanning was performed for 480 lines in the vertical direction in order for every horizontal line. The scanning repetition frequency (frame rate) was 100 Hz, and the voltage value corresponding to the light emission information of each pixel applied to the data (source) electrode was a 256-step DC voltage corresponding to the light emission gradation information.
[0165]
The VGA-sized organic thin-film EL element that emits light in this way has no luminance unevenness and non-uniformity of light emission when giving the same data to all pixels, and gives a 256-level gradation signal. The light emission faithful to the signal was obtained. The panel brightness is 300 cd / m when all the pixels are at maximum brightness. ² A high luminance was obtained by driving at a direct current of 7V. Moreover, the lifetime at the time of continuous lighting was 5000 hours or more.
[0166]
As described above, according to this embodiment, even when the display is composed of many pixels, light emission with high luminous efficiency, self-luminous emission with low driving voltage, and excellent visibility can be obtained. Light emission with excellent uniformity was obtained, and high gradation reproducibility with 256 gradations was obtained. Further, even in a continuous light emission test, a decrease in luminance is small, and an organic thin film EL element that can be used stably for a very long time with a small amount of power consumption can be realized.
[0167]
(Comparative Example 8)
In Example 24, an organic thin film EL element sample was prepared in the same manner as in Example 24 except that the resistance layer was not formed in parallel with the memory capacity, and light was emitted in the same manner as in Example 24.
[0168]
The VGA-sized organic thin-film EL element that emits light in this way has a luminance unevenness and non-uniform light emission even when the same data is given to all pixels, and gives a 256-level gradation signal. In addition, the reproducibility of gradation was poor and only a display image with extremely low quality was obtained. In addition, when the luminance of the panel is high at the maximum luminance of all pixels, the luminance is 500 cd / m. ² While the lower part is 50 cd / m ² It was the following.
[0169]
(Example 25)
In Example 24, the driving means and the organic thin-film EL element were produced in the same manner, and the driving method was applied in the same manner as in Example 24 by applying a DC voltage of 7 V to the positive electrode line, scanning the scan electrodes in order, and data (source). A voltage corresponding to the light emission information of each pixel was applied to the electrode to emit light. Only in the gradation expression method, instead of the method of the embodiment 24, a voltage corresponding to light emission or non-light emission is always applied to the data (source) electrode, and the gradation control is performed by the subfield method by increasing the scanning speed. Went.
[0170]
The VGA-sized organic thin-film EL element that emits light in this way has 256 levels of gradation with no sub-field method when there is no luminance unevenness or non-uniform light emission when all pixels are driven to have the same brightness. When given in, light emission faithful to the signal was obtained. In addition, the brightness of the panel when lit at the maximum brightness of all pixels is 250 cd / m. ² A high luminance was obtained by driving at a direct current of 7V. Moreover, the lifetime at the time of continuous lighting was 5000 hours or more.
[0171]
(Comparative Example 9)
In Example 25, an organic thin film EL element sample was prepared in the same manner as in Example 25 except that a resistance layer was not formed in parallel with the memory capacity, and light was emitted in the same manner as in Example 25.
[0172]
The VGA-sized organic thin-film EL element thus made to emit light has uneven luminance and non-uniform light emission even when all pixels are driven under the same conditions, and 256 gradations can be obtained by the subfield method. Even in this case, the reproducibility of the gradation was poor and only a display image with extremely low quality was obtained. In addition, the panel has a high luminance of 400 cd / m when all pixels are lit in full field. ² While the lower part is 50 cd / m ² It was the following.
[0173]
【The invention's effect】
As described above, according to the present invention, light emission with good color purity, high light emission efficiency, self-light emission and excellent visibility with a low driving voltage can be obtained, and a decrease in luminance is small even in a continuous light emission test. It is possible to realize an organic thin film EL element that can be used stably over an extremely long period of time with little power consumption and no change in degree.
[0174]
Further, a transparent substrate has a hole injection electrode and an electron injection electrode, and at least an insulating layer and a light emitting functional layer provided between the hole injection electrode and the electron injection electrode. The corresponding patterned photoresist layer provides high luminous efficiency, low emission voltage and self-luminous emission with excellent visibility, and extremely high resolution and faithful emission pattern with good reproducibility. The organic thin-film EL element that can be obtained and can be used stably over a very long period of time can be realized with little power consumption even in a continuous light emission test.
[0175]
Also, there is provided a driving method of an organic thin film EL element in which a current is applied by applying a voltage between a hole injection electrode and an electron injection electrode to obtain light emission. Connects the other pole to each other via a thin film transistor, and has a memory capacity for holding the gate voltage of the transistor, and information on light emission intensity or light emission non-light emission at regular time intervals In the driving method for controlling the light emission state by charging / discharging the memory capacity, the layer formed under the same film formation conditions as the resistance of the thin film transistor channel layer in parallel with the memory capacity is arranged as a resistance. Even when the display is composed of many pixels, it is possible to obtain light emission with high luminous efficiency and excellent visibility due to self-emission with a low driving voltage. The light emission was obtained with excellent very uniformity without unevenness such as uneven and high gradation reproducibility of 256 gradations is obtained. Further, even in a continuous light emission test, a decrease in luminance is small, and an organic thin film EL element that can be used stably for a very long time with a small amount of power consumption can be realized.

Claims (3)

A driving method of an organic thin film EL element that emits light by applying a voltage between a hole injection electrode and an electron injection electrode, and connects one pole of a power source and one pole of the organic thin film EL element In addition, each of the other poles is connected via a thin film transistor, and has a memory capacity for holding the gate voltage of the transistor, and information on light emission intensity or light emission non-light emission is stored in the memory at regular time intervals. In the driving method for controlling the light emission state by writing by charging / discharging the capacitor, a layer formed under the same film formation conditions as the channel layer of the thin film transistor is arranged as a resistor in parallel with the memory capacitor. Driving method of organic thin film EL element. The time constant calculated from the product of the memory capacity and the average value of the resistance is at least smaller than the certain time interval and larger than 1/100 of the time interval. Driving method of organic thin film EL element. An organic thin film EL element driven by the driving method according to claim 1.