JP2004067862A - Organic semiconductor material, field effect transistor using the same - Google Patents

Abstract

To provide an organic semiconductor material capable of obtaining a thin film having a high carrier mobility by a simple method without requiring a special orientation technique. To provide a field-effect transistor having a high density.
An organic semiconductor material is a conjugated oligomer or polymer comprising a main chain having an expanded conjugate bond and a side chain extending in a direction substantially orthogonal to a substantial elongation direction of the main chain.
[Selection diagram] None

Description

【００１２】
【化２】

【００１３】
すなわち３−アルキルチオフェンのオリゴマーまたはポリマーは、接近する分子同士の向きによって、この様に、拡張されたπ軌道面を重ね合わせることができない場合があり、その場合には分子鎖の向きを反転させないかぎりスタックした構造をとることができないという問題を有している。
【００１４】
【発明が解決しようとする課題】
従って本発明の目的は、特殊な配向技術を必要とせず、簡単な方法でキャリア移動度が高い薄膜を得ることができる有機半導体材料を提供することであり、とくに分子の向きが逆になっていてもπ軌道を重ねることができるように主鎖方向と側鎖のなす角度を調節した新規な有機半導体材料を提供することであり、また別の目的は該有機半導体材料を用いて製造容易かつキャリア移動度の高い電界効果トランジスタ（有機薄膜トランジスタ）を提供することにある。
【００１５】
【課題を解決するための手段】
本発明の上記目的は以下の手段により達成された。
【００１６】
１．共役結合が拡張した主鎖と、主鎖の実質的な伸長方向と実質的に直交する方向に伸びた側鎖からなる共役オリゴマーもしくはポリマーであることを特徴とする有機半導体材料。
【００１７】
２．主鎖が少なくとも１種類以上の芳香環を含む繰り返し単位によって構成されていることを特徴とする前記１に記載の有機半導体材料。
【００１８】
３．主鎖が少なくともチオフェン環またはｐ−フェニレン環のいずれかを含む繰り返し単位によって構成されていることを特徴とする前記１または２に記載の有機半導体材料。
【００１９】
４．主鎖が少なくともチオフェン環を含む繰り返し単位によって構成されていることを特徴とする前記１、２または３に記載の有機半導体材料。
【００２０】
５．主鎖に含まれる置換チオフェン環が、チオフェンの３位および４位で芳香族５員環が縮合した構造を有することを特徴とする前記３または４に記載の有機半導体材料。
【００２１】
６．側鎖が直鎖アルキル基であることを特徴とする前記１〜５のいずれか１項に記載の有機半導体材料。
【００２２】
７．前記１〜６のいずれか１項に記載の有機半導体材料を含んでなることを特徴とする電界効果トランジスタ。
【００２３】
８．電荷輸送性材料と、該電荷輸送性材料に直接或いは間接に接するゲート電極から構成され、該ゲート電極及び電荷輸送性材料間に電界を印加することで、電荷輸送性材料中の電流を制御する電界効果トランジスタにおいて、該電荷輸送性材料が前記１〜６のいずれか１項に記載の有機半導体材料であることを特徴とする電界効果トランジスタ。
【００２４】
以下、有機半導体材料および該材料を用いた電界効果トランジスタについて説明する。
【００２５】
本発明に係る有機半導体材料は、共役結合が拡張したオリゴマーもしくはポリマーであって、なおかつ主鎖の実質的な伸長方向に直交する方向へ伸びる側鎖を有するものである。ここでいう主鎖の実質的な伸長方向とは、共役が拡張して形成されるオリゴマーもしくはポリマーが直鎖状構造をとる場合の、主鎖全体が形成する１次元的な方向のことであり、個々の繰り返し単位内部もしくは繰り返し単位間の結合角をいうわけではない。例えばポリ−ｐ−フェニレンの場合、繰り返し単位であるｐ−フェニレンどうしの結合角と同じ方向に繰り返し単位が連続するので、この場合は繰り返し単位どうしの結合角と主鎖の実質的な伸長方向とは同じであるが、ポリチオフェンの場合、分子の熱運動や薄膜を形成した場合の冷却速度や基板の状態、その他の因子によって主鎖が屈曲する場合がある。しかしながらそうした因子がない場合には、やはりポリチオフェン主鎖は直線的に伸びると考えられ、この場合においては個々のチオフェン環どうしの結合角と主鎖が伸びる方向すなわち実質的な伸長方向とは下記のように異なる。
【００２６】
【化３】

【００２７】
本発明に係る材料が有する側鎖は、主鎖の実質的な伸長方向と実質的に直交する方向に伸びている。ここでいう実質的な直交とは、繰り返し単位の共役結合を拡張させる部分構造もしくは共役結合を拡張させる部分構造と縮合した環状構造に側鎖が連結する部分の結合が、主鎖の実質的な伸長方向と直交する角度をなすことであり、該部分における側鎖の結合角が９０度であることではない。またここでいう「実質的に直交」とは、必ずしも正確に９０度をなしている必要はなく、８０〜１００度の範囲に入っていれば実質的に直交しているものとみなすことができる。さらに当業に従事する研究者には周知のとおり、側鎖と主鎖の間の結合は分子の熱運動等により角度を変化させるが、ここでいう方向は分子の幾何的構造を記述する際に用いられる「結合角」と同じく最も安定な、すなわちエネルギー的に低い状態にあると考えられる場合の方向のことである。原子間の結合の角度も熱運動により変化しているが、当業に従事する研究者が「結合角」という用語を用いるときには、その影響をいったん無視して最安定状態の結合角について語るのと同様である。また側鎖は、主鎖が形成する拡張されたπ軌道が形成する面と同一平面内に伸びている必要はなく、拡張されたπ軌道平面の上下いずれかの方向に角度をなしていてよい。すなわち主鎖が形成する拡張されたπ軌道面に平行な平面に対する、分子の最安定状態の構造の写像において、主鎖の実質的な伸長方向と直交する方向に主鎖が伸びていれば、これを本発明に係る有機半導体材料の範疇に含めるものである。
【００２８】
本発明に係る材料は、その繰り返し単位の中に少なくとも１種類以上の芳香族環を含んでいることが好ましい。芳香族環としてはベンゼン環、チオフェン環、フラン環、セレノフェン環、ピロール環、ピリジン環などが挙げられ、これらは置換されていてもよく、また他の芳香族環と縮合して多環式芳香族環を形成していてもよい。これらの芳香族環を含む繰り返し単位とは、これらの芳香族環どうしが共役結合によって連結された構造や、エチレン−１，２−ジイル基やアセチレンジイル基と結合して形成される構造を含む、繰り返し単位内部および繰り返し単位間で共役結合を形成することのできる構造である。これらの繰り返し単位の中で、好ましいのはチオフェン環もしくはベンゼン環を含む繰り返し単位であり、ベンゼン環の場合とくにｐ−フェニレン置換基として繰り返し単位中に組みこまれていることが好ましい。更に好ましくは置換されたチオフェン環が組みこまれた構造を有する繰り返し単位であり、さらに好ましくはチオフェンの３、４位の位置に芳香族５員環が縮合した構造を有する繰り返し単位であり、チオフェン環に対して縮合すべき芳香族環の例としてはイミダゾール環、オキサゾール環、チアゾール環、セレナゾール環、ピロール環などを挙げることができる。
【００２９】
本発明に係る有機半導体材料が有する側鎖としては、主鎖の実質的な伸長方向に対して実質的に直交していれば格別の制限はないが、分岐や立体的にかさ高い置換基を有していないものが好ましい。なかでも好ましいのは直鎖アルキル基であるが、これは置換されていてもよい。側鎖中のメチレン（−ＣＨ_２−）部分が酸素原子や硫黄原子に置き換わりエーテル結合やチオエーテル結合となっていてもよいし、ベンゼン環と置き換わっていてもよい。アルキル鎖中の水素原子の一部または全部がハロゲン原子と置き換わっていてもよく、この場合の好ましいハロゲン原子としては塩素原子もしくはフッ素原子が挙げられる。さらに側鎖末端部分には置換されていてもよい芳香族基（フェニル基、ナフチル基、トリル基、ピリジル基、ピラゾリル基、キノリル基、イミダゾリル基、ベンズチアゾリル基など）やシアノ基が結合していてもよい。
【００３０】
以下に本発明に係る拡張共役オリゴマーもしくはポリマーの例を挙げるが、本発明の態様がこの化合物例によって制限されるものではない。なお以下の化合物例に記されたｍは重合度を示し、いずれもゲル泳動クロマトグラフィー（ポリスチレン基準）によって求めたものである。
【００３１】
【化４】

【００３２】
【化５】

【００３３】
【化６】

【００３４】
【化７】

【００３５】
本発明に係る有機半導体材料は、Ｊ．Ｈｅｔｅｒｏｃｙｃｌ．Ｃｈｅｍ．，１９９１，１４４９−１４５１、Ｃｈｅｍ．Ｂｅｒ．，１９８６，３１９８−３２０３、Ｊ．Ｏｒｇ．Ｃｈｅｍ．，１９９４，３０７７−３０８１、Ｐｈｏｓｐｈｏｒｏｕｓ，Ｓｕｌｆｕｒ，Ｓｉｌｉｃｏｎ，Ｒｅｌ．Ｅｌｅｍ．，１９９４，５０７−５０８、Ｈｅｔｅｒｏｃｙｃｌｅｓ，１９９５，２６９１、Ｔｅｔｒａｈｅｄｒｏｎ　Ｌｅｔｔ．，１９８９，７２４９−７２５２、同２００１，７４３５−７４３８、同５３２７−５３２９、同６８７７−６８８１、Ｊ．Ｏｒｇ．Ｃｈｅｍ．，１９８３，４７１３−４７１４、Ｊ．Ｃｈｅｍ．Ｓｏｃ．Ｐｅｒｋｉｎ　Ｔｒａｎｓ２．，１９９９，５０５−５０４、Ｊ．Ｍｅｄ．Ｃｈｅｍ．，１９９１，２９２２−２９２５、同１９９２，４３８−４５０、同１９９２，３７９２−３８０２、Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．，１９５４，１０６８−１０７２、Ｓｙｎｔｈｅｓｉｓ，１９７５，４５１、Ｍｏｎａｔｓｈ．Ｃｈｅｍ．，１９７６，２９９−３０５、高分子論文集，２００１，２２１−２２６、Ｃｈｅｍ．Ｒｅｖ．，２００２，１３５９−１４６９に記載の内容をはじめとする、既知の化学反応を用いることで合成が可能であるほか、ポリマーを合成するにあたっては基質に応じて気相重合法や電解重合法等の既知の重合方法を用いることも可能である。反応は連続的に行っても、段階をおって中間生成物を単離精製しながら行ってもよい。以下に典型的な合成例として、例示化合物３の合成経路を示すが、前述の通りこの化合物合成の各段階の反応はいずれも当業に従事する研究者には周知の反応である。
【００３６】
〈合成例〉例示化合物３
【００３７】
【化８】

【００３８】
（中間体２の合成）
メタノール１００ｍｌに溶解したチエノメルカプトイミダゾール（１）１０ｇにクロルヘキサン（６．３ｇ）を加え、ナトリウムメトキシドの２８％メタノール溶液を１５ｍｌ加えて３時間還流温度にて撹拌した。得られた混合溶液を水３００ｍｌ中に注ぎ入れ、酢酸エチルにて抽出した有機物をシリカゲルカラムクロマトグラフィーにて精製し、中間体２（ヘキシルチオチエノイミダゾール）４．９ｇを得た。（収率３３％）
（中間体３の合成）
４．５ｇの中間体２を、１，２−ジクルロエタン溶液とし、これにＮ−ブロモコハク酸イミド７ｇを固体のまま加え、室温下３時間撹拌を行った。得られた混合物を濃縮後、酢酸エチルにより有機物を抽出し、シリカゲルカラムクロマトグラフィーにより精製して、中間体３（ヘキシルチオジブロモチエノイミダゾール）７．１ｇを得た。（収率９５％）
（例示化合物３の合成）
窒素雰囲気下、テトラヒドロフラン中に置いたマグネシウム粒（０．５ｇ）に、中間体３を７ｇテトラヒドロフラン３０ｍｌに溶解した溶液を徐々に滴下して、マグネシウム粒からの細かい発泡が持続する状態を維持しつつ、中間体３の溶液の滴下を続けた。滴下終了後、得られた溶液を５０℃にて１時間撹拌して中間体３とマグネシウムの反応を完結させた。反応混合物を放冷後、この溶液をシリンジにて反応容器から抜き取り、（１，３−ビス（ジフェニルホスフィノ）プロパン）ニッケル塩化物０．４ｇがテトラヒドロフラン１５ｍｌ中に分散した懸濁液が入った窒素雰囲気の反応容器に加えた。混合物を５０℃に加熱して撹拌を１２時間行った。得られた反応混合物を希塩酸に注いで反応を停止し、不溶物を濾取して水、メタノールおよびエチレンジアミン４酢酸水溶液にて洗浄し、例示化合物３の暗褐色固体１．２ｇを得た。
【００３９】
本発明に係わる有機半導体材料は、溶媒として例えばエタノール、メタノール、テトラヒドロフラン、ジオキサン、メチルエチルケトン、クロロホルム、塩化メチレン、Ｎ−メチルピロリドン、Ｎ，Ｎ−ジメチルホルムアミド等の溶剤に溶解して塗布することもできるし、必要に応じてさらに適切な添加剤を加えた水性もしくは油性インクを調製してスクリーン印刷、インクジェット法などにより印刷を行うこともできる。さらには該有機半導体材料を塗布した基板と適切な光熱変換材料を用いて、アブレーション法により電気素子を形成したい基板に転写を行ってもよい。
【００４０】
この様にして形成した薄膜に対してアニーリングを、例えば塗布後の乾燥時に２００℃を越えない温度で処理してもよい。アニーリングは空気中で行ってもよいが、窒素やアルゴンといった不活性雰囲気下にて行うこともできるし、水素雰囲気下で行ってもよい。
【００４１】
また、本発明に係わる有機半導体材料には、ルイス酸（塩化鉄、塩化アルミニウム、臭化アンチモン等）やハロゲン（ヨウ素や臭素など）およびハロゲン化水素酸もしくはその塩、スルホン酸もしくはその塩（ポリスチレンスルホン酸のナトリウム塩やｐ−トルエンスルホン酸カリウム等）などをドープしてもよく、ドーピングにより伝導性を調整することも出来る。
【００４２】
これらの有機半導体材料を含んでなる電界効果トランジスタは、薄膜の電界効果トランジスタとしてスイッチング素子等、各種デバイスの製造に有利に用いることができる。
【００４３】
即ち、これらの有機半導体材料からなる有機薄膜を用いた電界効果トランジスタは、本発明に係わる上記有機半導体材料を電荷輸送性材料とし、該電荷輸送性材料層に、例えば誘電体からなるゲート絶縁層を介して接するゲート電極、更に、該電荷輸送性材料層に接して設けられたソース電極、およびドレイン電極から構成され、該ゲート電極及びソース電極間に電界を印加することで、ソース、ドレイン電極間の電流（即ち電荷輸送性材料層中の電流）を制御する。
【００４４】
次いで、これらの有機半導体材料やその薄膜を用いた電界効果トランジスタについて述べる。
【００４５】
上記電界効果トランジスタに用いられるゲート電極、ソース電極、ドレイン電極としては、導電性材料であれば特に限定されず、白金、金、銀、ニッケル、クロム、銅、鉄、錫、アンチモン鉛、タンタル、インジウム、パラジウム、テルル、レニウム、イリジウム、アルミニウム、ルテニウム、ゲルマニウム、モリブデン、タングステン、酸化スズ・アンチモン、酸化インジウム・スズ（ＩＴＯ）、フッ素ドープ酸化亜鉛、亜鉛、炭素、グラファイト、グラッシーカーボン、銀ペースト及びカーボンペースト、リチウム、ベリリウム、ナトリウム、マグネシウム、カリウム、カルシウム、スカンジウム、チタン、マンガン、ジルコニウム、ガリウム、ニオブ、ナトリウム、ナトリウム−カリウム合金、マグネシウム、リチウム、アルミニウム、マグネシウム／銅混合物、マグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム混合物、リチウム／アルミニウム混合物等が用いられるが、特に、白金、金、銀、銅、アルミニウム、インジウム、ＩＴＯ及び炭素が好ましい。あるいはドーピング等で導電率を向上させた公知の導電性ポリマー、例えば導電性ポリアニリン、導電性ポリピロール、導電性ポリチオフェン、ポリエチレンジオキシチオフェンとポリスチレンスルホン酸の錯体等も好適に用いられる。ソース電極、ドレイン電極は、上に挙げた中でも有機半導体材料層との接触面において電気抵抗が少ないものが好ましい。
【００４６】
電極の形成方法としては、上記を原料として蒸着やスパッタリング等の方法を用いて形成した導電性薄膜を、公知のフォトリソグラフ法やリフトオフ法を用いて電極形成する方法、アルミニウムや銅等の金属箔上に熱転写、インクジェット等によるレジストを用いてエッチングする方法がある。また導電性ポリマーの溶液あるいは分散液，導電性微粒子分散液を直接インクジェットによりパターニングしてもよいし、塗工膜からリソグラフやレーザーアブレーション等により形成してもよい。さらに導電性ポリマーや導電性微粒子を含むインク、導電性ペースト等を凸版、凹版、平版、スクリーン印刷等の印刷法でパターニングする方法も用いることができる。
【００４７】
また、これらをＴＦＴシートとして作製する場合の信号線、走査線、表示電極の材料、形成方法等も上記と同様である。
【００４８】
また、これらの有機半導体材料や薄膜の電界効果トランジスタに用いられるゲート絶縁層には、種々の絶縁膜を用いることができるが、特に、比誘電率の高い無機酸化物皮膜が好ましい。無機酸化物としては、酸化ケイ素、酸化アルミニウム、酸化タンタル、酸化チタン、酸化スズ、酸化バナジウム、チタン酸バリウムストロンチウム、ジルコニウム酸チタン酸バリウム、ジルコニウム酸チタン酸鉛、チタン酸鉛ランタン、チタン酸ストロンチウム、チタン酸バリウム、フッ化バリウムマグネシウム、チタン酸ビスマス、チタン酸ストロンチウムビスマス、タンタル酸ストロンチウムビスマス、タンタル酸ニオブ酸ビスマス、トリオキサイドイットリウム等が挙げられる。それらのうち好ましいのは、酸化ケイ素、酸化アルミニウム、酸化タンタル、酸化チタンである。窒化ケイ素、窒化アルミニウム等の無機窒化物も好適に用いることができる。
【００４９】
上記皮膜の形成方法としては、真空蒸着法、分子線エピタキシャル成長法、イオンクラスタービーム法、低エネルギーイオンビーム法、イオンプレーティング法、ＣＶＤ法、スパッタリング法、大気圧プラズマ法等のドライプロセスや、スプレーコート法、スピンコート法、ブレードコート法、デイップコート法、キャスト法、ロールコート法、バーコート法、ダイコート法等の塗布による方法、印刷やインクジェット等のパターニングによる方法等のウェットプロセスが挙げられ、材料に応じて使用できる。ウェットプロセスは、無機酸化物の微粒子を、任意の有機溶剤あるいは水に必要に応じて界面活性剤等の分散補助剤を用いて分散した液を塗布、乾燥する方法や、酸化物前駆体、例えばアルコキシド体の溶液を塗布、乾燥する、いわゆるゾルゲル法が用いられる。これらのうち好ましいのは、大気圧プラズマ法とゾルゲル法である。
【００５０】
大気圧下でのプラズマ製膜処理は、大気圧または大気圧近傍の圧力下で放電し、反応性ガスをプラズマ励起し、基材上に薄膜を形成する処理をさし、その方法については特開平１１−１３３２０５号、特開２０００−１８５３６２、特開平１１−６１４０６号、特開２０００−１４７２０９、同２０００−１２１８０４等に記載されている（以下、大気圧プラズマ法とも称する）。これによって高機能性の薄膜を、生産性高く形成することができる。
【００５１】
また絶縁層として用いられる有機化合物皮膜としては、ポリイミド、ポリアミド、ポリエステル、ポリアクリレート、光ラジカル重合系、光カチオン重合系の光硬化性樹脂、あるいはアクリロニトリル成分を含有する共重合体、ポリビニルフェノール、ポリビニルアルコール、ノボラック樹脂、及びシアノエチルプルラン、ポリマー体、エラストマー体を含むホスファゼン化合物等がある。有機化合物皮膜の形成法としては、前記ウェットプロセスが好ましい。
【００５２】
無機酸化物皮膜と有機酸化物皮膜は積層して併用することができる。またこれら絶縁膜の膜厚としては、一般に５０ｎｍ〜３μｍ、好ましくは、１００ｎｍ〜１μｍである。
【００５３】
本発明においては、有機半導体材料層に、例えばアクリル酸、アセトアミド、ジメチルアミノ基、シアノ基、カルボキシル基、ニトロ基等の官能基を有する材料や、ベンゾキノン誘導体、テトラシアノエチレン及びテトラシアノキノジメタンやそれらの誘導体等のように電子を受容するアクセプターとなる材料や、例えばアミノ基、トリフェニル基、アルキル基、水酸基、アルコキシ基、フェニル基等の官能基を有する材料、フェニレンジアミン等の置換アミン類、アントラセン、ベンゾアントラセン、置換ベンゾアントラセン類、ピレン、置換ピレン、カルバゾール及びその誘導体、テトラチアフルバレンとその誘導体等のように電子の供与体であるドナーとなるような材料を含有させ、いわゆるドーピング処理を施してもよい。
【００５４】
前記ドーピングとは電子授与性分子（アクセクター）または電子供与性分子（ドナー）をドーパントとして薄膜に導入することを意味する。本発明に用いるドーパントとしてアクセプター、ドナーのいずれも使用可能である。このアクセプターとしてＣｌ_２、Ｂｒ_２、Ｉ_２、ＩＣｌ、ＩＣｌ_３、ＩＢｒ、ＩＦ等のハロゲン、ＰＦ_５、ＡｓＦ_５、ＳｂＦ_５、ＢＦ_３、ＢＣ１_３、ＢＢｒ_３、ＳＯ_３等のルイス酸、ＨＦ、ＨＣ１、ＨＮＯ_３、Ｈ_２ＳＯ_４、ＨＣｌＯ_４、ＦＳＯ_３Ｈ、ＣｌＳＯ_３Ｈ、ＣＦ_３ＳＯ_３Ｈ等のプロトン酸、酢酸、蟻酸、アミノ酸等の有機酸、ＦｅＣｌ_３、ＦｅＯＣｌ、ＴｉＣｌ_４、ＺｒＣｌ_４、ＨｆＣｌ_４、ＮｂＦ_５、ＮｂＣｌ_５、ＴａＣｌ_５、ＭｏＣｌ_５、ＷＦ_５、ＷＣｌ_６、ＵＦ_６、ＬｎＣｌ_３（Ｌｎ＝Ｌａ、Ｃｅ、Ｎｄ、Ｐｒ、等のランタノイドとＹ）等の遷移金属化合物、Ｃｌ⁻、Ｂｒ⁻、Ｉ⁻、ＣｌＯ_４ ⁻、ＰＦ_６ ⁻、ＡｓＦ_５ ⁻、ＳｂＦ_６ ⁻、ＢＦ_４ ⁻、スルホン酸アニオン等の電解質アニオン等を挙げることができる。またドナーとしては、Ｌｉ、Ｎａ、Ｋ、Ｒｂ、Ｃｓ等のアルカリ金属、Ｃａ、Ｓｒ、Ｂａ等のアルカリ土類金属、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｙｂ等の希土類金属、アンモニウムイオン、Ｒ_４Ｐ^＋、Ｒ_４Ａｓ^＋、Ｒ_３Ｓ^＋（Ｒはアルキル基、アリール基等）、アセチルコリン等を挙げることができる。これらのドーパントのドーピングの方法として予め有機半導体材料の薄膜を作製しておき、ドーパントを後で導入する方法、有機半導体材料の薄膜作製時にドーパントを導入する方法のいずれも使用可能である。前者の方法のドーピングとして、ガス状態のドーパントを用いる気相ドーピング、溶液あるいは液体のドーパントを薄膜に接触させてドーピングする液相ドーピング、固体状態のドーパントを薄膜に接触させてドーパントを拡散ドーピングする固相ドーピングの方法を挙げることができる。また液相ドーピングにおいては電解を施すことによってドーピングの効率を調整することができる。後者の方法では、有機半導体化合物とドーパントの混合溶液あるいは分散液を同時に塗布、乾燥してもよい。例えば真空蒸着法を用いる場合、有機半導体化合物とともにドーパントを共蒸着することによりドーパントを導入することができる。またスパッタリング法で薄膜を作製する場合、有機半導体化合物とドーパントの二元ターゲットを用いてスパッタリングして薄膜中にドーパントを導入させることができる。さらに他の方法として、電気化学的ドーピング、光開始ドーピング等の化学的ドーピング及び例えば刊行物｛工業材料、３４巻、第４号、５５頁、１９８６年｝に示されたイオン注入法等の物理的ドーピングの何れも使用可能である。
【００５５】
有機半導体材料薄膜の作製法としては、前記の塗布、スクリーン印刷、インクジェット法等の印刷による方法の他、真空蒸着法、分子線エピタキシャル成長法、イオンクラスタービーム法、低エネルギーイオンビーム法、イオンプレーティング法、ＣＶＤ法、スパッタリング法、プラズマ重合法、電解重合法、化学重合法、スプレーコート法、スピンコート法、ブレードコート法、デイップコート法、キャスト法、ロールコート法、バーコート法、ダイコート法及びＬＢ法等も挙げられ、材料に応じて使用できる。ただし、この中で生産性の点で、有機半導体材料溶液を用いて簡単かつ精密に薄膜が形成できるスピンコート法、ブレードコート法、デイップコート法、ロールコート法、バーコート法、ダイコート法等の塗布法が好ましい。これら有機半導体材料からなる薄膜の膜厚としては、特に制限はないが、得られたトランジスタの特性は、有機半導体材料からなる活性層の膜厚に大きく左右される場合が多く、その膜厚は有機半導体材料の種類によっても異なるが、一般に１μｍ以下、特に１０〜３００ｎｍが好ましい。
【００５６】
また、その形成に高温を必要とせず、ガラス基板等耐熱性の基板がいらないので、各種のプラスチックフィルム等の絶縁性支持体上に有機半導体材料薄膜、これを用いた電界効果トランジスタ、スイッチング素子等が形成でき、各種表示パネルに用いる各画素単位で表示材料を駆動するための駆動素子となるＴＦＴシートをフレキシブルなものにできる。
【００５７】
フレキシブルな絶縁性シートとしては、例えばプラスチックフィルムをシートとして用いることができる。プラスチックフィルムとしては、例えばポリエチレンテレフタレート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、ポリエーテルスルホン（ＰＥＳ）、ポリエーテルイミド、ポリエーテルエーテルケトン、ポリフェニレンスルフィド、ポリアリレート、ポリイミド、ポリカーボネート（ＰＣ）、セルローストリアセテート（ＴＡＣ）、セルロースアセテートプロピオネート（ＣＡＰ）等からなるフィルム等が挙げられる。このように、プラスチックフィルムを用いることで、ガラス基板を用いる場合に比べて軽量化を図ることができ、可搬性を高めることができるとともに、衝撃に対する耐性を向上できる。
【００５８】
更にこれらのプラスチックフィルムには、トリオクチルホスフェートやジブチルフタレート等の可塑剤を添加してもよく、ベンゾトリアゾール系やベンゾフェノン系等の公知の紫外線吸収剤を添加してもよい。また、テトラエトキシシラン等の無機高分子の原料を添加し、化学触媒や熱、光等のエネルギーを付与することにより高分子量化する、いわゆる有機−無機ポリマーハイブリッド法を適用して作製した樹脂を原料として用いることもできる。
【００５９】
【発明の実施の形態】
以下に、本発明に係わる導電性材料からなる有機半導体材料薄膜を用いた電界効果トランジスタについて説明する。
【００６０】
図１は、本発明の有機半導体性材料を用いた電界効果トランジスタの概略構成例を示す。同図（ａ）は、支持体６上に金属箔等によりソース電極２、ドレイン電極３を形成し、両電極間に本発明の導電性材料からなる有機半導体材料層１を形成し、その上に絶縁層５を形成し、更にその上にゲート電極４を形成して電界効果トランジスタを形成したものである。同図（ｂ）は、有機半導体材料層１を、（ａ）では電極間に形成したものを、コート法等を用いて電極及び支持体表面全体を覆うように形成したものを表す。（ｃ）は、支持体６上に先ずコート法等を用いて、有機半導体材料層１を形成し、その後ソース電極２、ドレイン電極３、絶縁層５、ゲート電極４を形成したものを表す。
【００６１】
同図（ｄ）は、支持体６上にゲート電極４を金属箔等で形成した後、絶縁層５を形成し、その上に金属箔等で、ソース電極２及びドレイン電極３を形成し、該電極間に本発明の導電性材料により形成された有機半導材料体層１を形成する。その他同図（ｅ）、（ｆ）に示すような構成をとることもできる。
【００６２】
以下実施例を用いて本発明を更に具体的に説明するが、本発明はこれにより限定されるものではない。
【００６３】
【実施例】
以下、実施例により本発明を説明するが、本発明の実施態様はこれらに限定されるものではない。
【００６４】
実施例１
ポリ（３−ｎ−ヘキシルチオフェン−２，５−ジイル）のｒｅｇｉｏｒｅｇｕｌａｒ体（アルドリッチ社製、ゲル泳動クロマトグラフィーで測定した平均分子量９００００）１ｇをクロロホルム１０ｍｌに溶解し、これをポリエーテルスルホン（ＰＥＳ）フィルム上に、アプリケータ（厚み１２０μｍ）にて塗布し自然乾燥することでポリマー膜を形成し、有機半導体材料Ａを得た。
【００６５】
前記合成経路にしたがって合成した例示化合物３（ゲル泳動クロマトグラフィーで測定した平均重合度６）の１００ｍｇをクロロホルム１ｍｌに溶解した溶液を用いて、有機半導体材料Ａと同様にしてポリマー膜を形成し、有機半導体材料Ｂを得た。
【００６６】
有機半導体材料Ａ及びＢをそれぞれ２ｍｏｌ／Ｌの塩酸水溶液に２０℃で１２時間浸漬して、４０℃にて真空乾燥した後、試料の電気導電性を測定した結果、有機半導体材料Ａの電気導電性を１００とした有機半導体材料Ｂの電気導電性の相対値は１６１であり、本発明の有機半導体材料Ｂは大きく電気導電性が向上していることが確認できた。
【００６７】
実施例２
ｎ型ドープシリコン基板上に厚さ３００ｎｍの熱酸化膜を形成した後、酸化膜上に厚さ５０ｎｍの金を蒸着し、フォトリソグラフ法により１０μｍのギャップを有するソース、ドレイン電極を形成した。次に、良く精製した本発明の例示化合物３のクロロホルム溶液をスピンコートすることで厚さ３０ｎｍの有機半導体材料層を形成し、有機電界効果トランジスタ（薄膜トランジスタ）を得た。
【００６８】
作製した有機電界効果トランジスタは、ゲート、ソース電極間の電圧（ゲート電圧）のＯＮ／ＯＦＦによって、スイッチング機能を示し、また、低いゲート電圧でのスイッチングＯＮ状態で電流値が高い、従って電流のＯＮ／ＯＦＦ比が高く良好なスイッチング機能を有することが確認された。
【００６９】
本発明に従って形成された有機電界効果トランジスタ（薄膜トランジスタ）は、従来の方法によって形成されたものよりも、塗布等を用いて、効率よく、単純なプロセスでパターニング形成できるので、そのために製造工程にも多大な設備が必要なく効率的に低コストで高精度パターン化が可能である。
【００７０】
また、塗布法等簡便な方法により有機半導体材料層等の構成層を形成するにも拘わらず、電極パターン形成の精度がよいため、素子全体として構成したときに各トランジスタ間の電極・有機半導体材料間の障壁となるバラツキが少ない。
【００７１】
【発明の効果】
簡単なプロセスで形成可能な有機半導体材料が得られ、該有機半導体材料薄膜を用いた有機電界効果（薄膜トランジスタ）、スイッチング素子が構成出来、ディスプレイパネル等の回路に使用可能なことが実証できた。
【図面の簡単な説明】
【図１】有機導電性材料を用いた電界効果トランジスタの概略構成例を示す図である。
【符号の説明】
１　有機半導体材料層
２　ソース電極
３　ドレイン電極
４　ゲート電極
５　絶縁層
６　支持体[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic semiconductor material that can be formed by a simple process, and a field-effect transistor using the organic semiconductor material thin film.
[0002]
[Prior art]
With the spread of information terminals, needs for flat panel displays as displays for computers are increasing. In addition, with the progress of computerization, information provided in the form of paper has been provided electronically, and the number of opportunities to provide the information has increased, and electronic paper or digital media has become a thin, light, and portable mobile display medium. The need for paper is also growing.
[0003]
Generally, in a flat panel display device, a display medium is formed using elements utilizing liquid crystal, organic EL, electrophoresis, or the like. Further, in such a display medium, in order to ensure the uniformity of the screen luminance and the screen rewriting speed, a technique using an active drive element (TFT element) as an image drive element has become mainstream. For example, in a general computer display, these TFT elements are formed on a glass substrate, and a liquid crystal, an organic EL element, and the like are sealed.
[0004]
Here, semiconductors such as a-Si (amorphous silicon) and p-Si (polysilicon) can be mainly used for the TFT element, and these Si semiconductors (and a metal film if necessary) are multi-layered to form a source. , A drain, and a gate electrode are sequentially formed on a substrate to manufacture a TFT element. The production of such a TFT element usually requires sputtering and other vacuum-based production processes.
[0005]
However, in the manufacture of such a TFT element, each layer has to be formed by repeating the manufacturing process of a vacuum system including a vacuum chamber many times, and the apparatus cost and the running cost are extremely enormous. For example, in the case of a TFT device, it is usually necessary to repeatedly perform processes such as vacuum deposition, doping, photolithography, and development for forming each layer, and the device is formed on a substrate through dozens of processes. I have. A plurality of semiconductor layers such as a p-type semiconductor layer and an n-type semiconductor layer are stacked on a semiconductor portion which is a key for a switching operation. In such a conventional manufacturing method using a Si semiconductor, it is not easy to change the equipment, for example, a large design change of a manufacturing apparatus such as a vacuum chamber is required to meet the need for a large display screen.
[0006]
Further, since formation of such a conventional TFT element using a Si material involves a high-temperature process, a restriction is imposed on a substrate material that can withstand the process temperature. For this reason, glass must be used in practice, and when a thin display such as the electronic paper or digital paper described above is constructed using such a conventionally known TFT element, the display is heavy and flexible. Chipped, resulting in a product that may be broken by the impact of falling. These characteristics resulting from the formation of TFT elements on a glass substrate are undesirable in meeting the need for a portable thin display with the progress of computerization.
[0007]
On the other hand, in recent years, research on organic semiconductor materials as organic compounds having a high charge transporting property has been energetically advanced. These compounds include a charge transporting material for an organic EL device, an organic laser oscillation device as discussed in, for example, Science, 289, 599 (2000), and a large number of such as, for example, Nature, 403, 521 (2000). Is expected to be applied to the organic thin film transistor reported in the paper of No. If these organic semiconductor devices can be realized, the possibility of obtaining a semiconductor that can be made into a solution by simplifying the manufacturing process by vapor deposition at a relatively low temperature under a vacuum or a low pressure, and by appropriately improving the molecular structure of the device. It is considered that the organic semiconductor solution is made into an ink, and the production by a printing method including an ink-jet method is also considered. Manufacturing by these low-temperature processes has been considered impossible with conventional Si-based semiconductor materials, but there is a possibility in devices using organic semiconductors, and thus the above-mentioned restrictions on substrate heat resistance are relaxed. There is also a possibility that, for example, a TFT element can be formed on a transparent resin substrate. If a TFT element can be formed on a transparent resin substrate and a display material can be driven by the TFT element, the display is lighter and more flexible than conventional ones, and does not crack even if dropped (or very hard to crack). It can be a display.
[0008]
As organic semiconductors for realizing such a TFT element, acenes such as pentacene and tetracene disclosed in JP-A-5-55568, and phthalocyanine containing lead phthalocyanine disclosed in JP-A-5-190877 have been used. , Low molecular weight compounds such as perylene and its tetracarboxylic acid derivative, aromatic oligomers represented by thiophene hexamers called α-thienyl or sexithiophene disclosed in JP-A-8-264805, and polythiophenes And high molecular compounds such as polythienylenevinylene and poly-p-phenylenevinylene. (Many of these are described in Advanced @ Material, 2002, No. 2, pp. 99-117.)
Among them, an organic transistor element having an organic semiconductor layer composed of a pentacene thin film has attracted much attention because of its high carrier (charge carrier) mobility as an organic transistor, but pentacene has poor solubility in a solvent. Since it is a compound, it is poorly suitable for forming a semiconductor thin film by a printing process including coating or an inkjet method. In most cases, a vacuum deposition process is used for forming a pentacene thin film. On the other hand, an oligomer or polymer having a solubilizing group introduced therein, for example, an oligomer or polymer having a 3-alkylthiophene as a repeating unit, has relatively high carrier mobility and relatively good solvent solubility, so that it can be applied or printed. It is considered that a high quality organic semiconductor thin film can be obtained by a wet process such as a process.
[0009]
Oligomers or polymers of 3-alkylthiophenes are thought to move carriers by stacking some or all of the molecules in a π-orbital plane overlapping another molecule or part of a polymer chain. When stacking, the alkyl side chain extending from the 3-position of the thiophene ring is considered to overlap between the molecules or between parts of the polymer chain so as to fill the gap between them. Since this structure is stable, these oligo or It appears that poly-3-alkylthiophenes can form thin films with relatively high carrier mobilities. This is because a thin film formed of oligo- or polythiophene having a regio specificity in which the 2-position of the 3-alkylthiophene is bonded to the 5-position of the adjacent 3-alkylthiophene molecule is called a head-to-tail type. This is consistent with the fact well known to those skilled in the art that they have higher carrier mobilities than thin films formed by oligo or polythiophenes with a random mode of attachment without any.
[0010]
However, these 3-alkylthiophene oligomers or polymers have side chains extending at an acute angle with respect to the direction in which the conjugated main chain extends, so that even if the oligomers or polymers have the same molecule or partial structure, the molecules are the same. In the case of the orientation (that is, the following formula (a)), a good stack structure in which the π orbitals overlap without side chain repulsion can be obtained. In the following formula (b)), the side chains repel each other and the π orbitals cannot be overlapped with each other.
[0011]
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[0012]
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[0013]
That is, depending on the directions of approaching molecules, the oligomer or polymer of 3-alkylthiophene may not be able to overlap the extended π orbital plane in such a case, in which case the direction of the molecular chain is not reversed. There is a problem that a stacked structure cannot be obtained as far as possible.
[0014]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide an organic semiconductor material which does not require a special orientation technique and can obtain a thin film having a high carrier mobility by a simple method, and in particular, the orientation of molecules is reversed. It is another object of the present invention to provide a novel organic semiconductor material in which the angle between the main chain direction and the side chain is adjusted so that the π orbitals can be overlapped. An object of the present invention is to provide a field effect transistor (organic thin film transistor) having high carrier mobility.
[0015]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following means.
[0016]
1. An organic semiconductor material comprising a conjugated oligomer or polymer comprising a main chain having an extended conjugate bond and a side chain extending in a direction substantially perpendicular to the direction in which the main chain extends substantially.
[0017]
2. 2. The organic semiconductor material as described in 1 above, wherein the main chain is composed of a repeating unit containing at least one kind of aromatic ring.
[0018]
3. 3. The organic semiconductor material according to the above 1 or 2, wherein the main chain is constituted by a repeating unit containing at least either a thiophene ring or a p-phenylene ring.
[0019]
4. 4. The organic semiconductor material according to the above 1, 2, or 3, wherein the main chain is constituted by a repeating unit containing at least a thiophene ring.
[0020]
5. 5. The organic semiconductor material according to the above item 3 or 4, wherein the substituted thiophene ring contained in the main chain has a structure in which a 5-membered aromatic ring is fused at the 3- and 4-positions of the thiophene.
[0021]
6. 6. The organic semiconductor material according to any one of 1 to 5, wherein the side chain is a straight-chain alkyl group.
[0022]
7. A field effect transistor comprising the organic semiconductor material according to any one of the above items 1 to 6.
[0023]
8. A charge transporting material and a gate electrode that is in direct or indirect contact with the charge transporting material, and controls an electric current in the charge transporting material by applying an electric field between the gate electrode and the charge transporting material. 7. A field-effect transistor, wherein the charge-transporting material is the organic semiconductor material according to any one of the above items 1 to 6.
[0024]
Hereinafter, an organic semiconductor material and a field-effect transistor using the material will be described.
[0025]
The organic semiconductor material according to the present invention is an oligomer or polymer having an expanded conjugate bond, and has a side chain extending in a direction orthogonal to a substantial extension direction of the main chain. The substantial extension direction of the main chain referred to here is a one-dimensional direction formed by the entire main chain when the oligomer or polymer formed by expanding the conjugation has a linear structure. It does not mean the bonding angle within each repeating unit or between repeating units. For example, in the case of poly-p-phenylene, the repeating units are continuous in the same direction as the bonding angle between p-phenylenes, which are the repeating units. In this case, the bonding angle between the repeating units and the substantial elongation direction of the main chain are determined. However, in the case of polythiophene, the main chain may be bent depending on the thermal motion of molecules, the cooling rate when a thin film is formed, the state of the substrate, and other factors. However, in the absence of such factors, the polythiophene main chain is considered to extend linearly, and in this case, the bond angle between the individual thiophene rings and the direction in which the main chain extends, that is, the substantial extension direction, are as follows. So different.
[0026]
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[0027]
The side chain of the material according to the present invention extends in a direction substantially orthogonal to the substantial extension direction of the main chain. The term “substantially orthogonal” as used herein means that the bond of the portion where the side chain is connected to the cyclic structure condensed with the partial structure that extends the conjugate bond of the repeating unit or the partial structure that expands the conjugate bond is substantially the same as the main chain. This is to make an angle perpendicular to the elongation direction, and it does not mean that the bond angle of the side chain in this portion is 90 degrees. The term “substantially orthogonal” as used herein does not necessarily mean that the angle is exactly 90 degrees, but can be regarded as substantially orthogonal if the angle is in the range of 80 to 100 degrees. . Furthermore, as is well known to those skilled in the art, the bond between the side chain and the main chain changes the angle due to the thermal motion of the molecule, etc., but the direction mentioned here is used when describing the geometric structure of the molecule. Is the most stable direction, that is, the direction in which it is considered that the state is energetically low. The angle of the bond between atoms also changes due to thermal motion, but when researchers in the field use the term "bond angle", they ignore the effect once and talk about the most stable state bond angle. Is the same as Further, the side chain does not need to extend in the same plane as the plane formed by the extended π orbit formed by the main chain, and may form an angle in any direction above or below the extended π orbit plane. . That is, in the mapping of the structure of the molecule in the most stable state with respect to a plane parallel to the extended π orbital plane formed by the main chain, if the main chain extends in a direction orthogonal to the substantial extension direction of the main chain, This is included in the category of the organic semiconductor material according to the present invention.
[0028]
The material according to the present invention preferably contains at least one or more aromatic rings in its repeating unit. Examples of the aromatic ring include a benzene ring, a thiophene ring, a furan ring, a selenophene ring, a pyrrole ring, a pyridine ring and the like, which may be substituted, or which is condensed with another aromatic ring to form a polycyclic aromatic ring. It may form a group ring. The repeating unit containing these aromatic rings includes a structure in which these aromatic rings are connected by a conjugate bond, and a structure formed by bonding to an ethylene-1,2-diyl group or an acetylenediyl group. And a structure capable of forming a conjugated bond inside the repeating unit and between the repeating units. Among these repeating units, a repeating unit containing a thiophene ring or a benzene ring is preferable, and in the case of a benzene ring, it is particularly preferable that the repeating unit is incorporated in the repeating unit as a p-phenylene substituent. More preferably, it is a repeating unit having a structure in which a substituted thiophene ring is incorporated, more preferably a repeating unit having a structure in which a 5-membered aromatic ring is condensed at positions 3 and 4 of thiophene. Examples of the aromatic ring to be condensed to the ring include an imidazole ring, an oxazole ring, a thiazole ring, a selenazole ring, a pyrrole ring and the like.
[0029]
The side chain of the organic semiconductor material according to the present invention is not particularly limited as long as it is substantially orthogonal to the substantial extension direction of the main chain, but a branched or sterically bulky substituent may be used. Those which do not have are preferred. Of these, a straight-chain alkyl group is preferred, but this may be substituted. Methylene in the side chain (-CH₂The-) portion may be replaced by an oxygen atom or a sulfur atom to form an ether bond or a thioether bond, or may be replaced by a benzene ring. Some or all of the hydrogen atoms in the alkyl chain may be replaced by halogen atoms, and preferred halogen atoms in this case include a chlorine atom or a fluorine atom. Further, an aromatic group which may be substituted (phenyl group, naphthyl group, tolyl group, pyridyl group, pyrazolyl group, quinolyl group, imidazolyl group, benzothiazolyl group, etc.) and a cyano group are bonded to the terminal portion of the side chain. Is also good.
[0030]
Examples of the extended conjugated oligomer or polymer according to the present invention are described below, but the embodiments of the present invention are not limited by these compound examples. In addition, m described in the following compound examples indicates the degree of polymerization, and all are determined by gel electrophoresis chromatography (polystyrene standard).
[0031]
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[0032]
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[0033]
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[0034]
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[0035]
The organic semiconductor material according to the present invention is described in J. Heterocycl. Chem. Chem., 1991, 1449-1451, Chem. Ber. 1986, 3198-3203; Org. Chem. , 1994, 3077-3081, Phosphorous, Sulfur, Silicon, Rel. Elem. , 1994, 507-508, Heterocycles, 1995, 2691, Tetrahedron @ Lett. 1989, 7249-7252, 2001, 7435-7438, 5327-5329, 6877-6881; Org. Chem. 1983, 4713-4714; Chem. Soc. Perkin @ Trans2. , 1999, 505-504; Med. Chem. , 1991, 922-2925, 1992, 438-450, 1992, 3792-3802, J. Am. Am. Chem. Soc. , 1954, 1068-1072, Synthesis, 1975, 451, Monatsh. Chem. Chem., 1976, 299-305, Journal of Polymers, 2001, 221-226, Chem. Rev .. , 2002, 1359-1469, and the like, and can be synthesized using known chemical reactions. In synthesizing a polymer, a gas phase polymerization method, an electrolytic polymerization method, or the like may be used depending on a substrate. It is also possible to use known polymerization methods. The reaction may be performed continuously or may be performed while isolating and purifying the intermediate product through steps. As a typical synthesis example, the synthetic route of Exemplified Compound 3 is shown. As described above, the reactions at each stage of the synthesis of the compound are all well known to researchers engaged in the art.
[0036]
<Synthesis Example> Exemplified Compound 3
[0037]
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[0038]
(Synthesis of Intermediate 2)
Chlorohexane (6.3 g) was added to 10 g of thiomercaptoimidazole (1) dissolved in 100 ml of methanol, and 15 ml of a 28% methanol solution of sodium methoxide was added, followed by stirring at reflux for 3 hours. The obtained mixed solution was poured into 300 ml of water, and the organic matter extracted with ethyl acetate was purified by silica gel column chromatography to obtain 4.9 g of intermediate 2 (hexylthiothienoimidazole). (33% yield)
(Synthesis of Intermediate 3)
4.5 g of Intermediate 2 was used as a 1,2-diculoethane solution, to which 7 g of N-bromosuccinimide was added as a solid, followed by stirring at room temperature for 3 hours. After concentrating the obtained mixture, the organic matter was extracted with ethyl acetate and purified by silica gel column chromatography to obtain 7.1 g of intermediate 3 (hexylthiodibromothienoimidazole). (95% yield)
(Synthesis of Exemplified Compound 3)
Under a nitrogen atmosphere, a solution prepared by dissolving 7 g of Intermediate 3 in 30 ml of tetrahydrofuran was gradually added dropwise to magnesium particles (0.5 g) placed in tetrahydrofuran to maintain a state in which fine foaming from the magnesium particles was maintained. The addition of the solution of Intermediate 3 was continued. After completion of the dropwise addition, the resulting solution was stirred at 50 ° C. for 1 hour to complete the reaction between Intermediate 3 and magnesium. After allowing the reaction mixture to cool, the solution was drawn out of the reaction vessel with a syringe, and a suspension in which 0.4 g of (1,3-bis (diphenylphosphino) propane) nickel chloride was dispersed in 15 ml of tetrahydrofuran was contained. It was added to the reaction vessel in a nitrogen atmosphere. The mixture was heated to 50 ° C. and stirred for 12 hours. The obtained reaction mixture was poured into dilute hydrochloric acid to stop the reaction, and the insolubles were collected by filtration and washed with water, methanol and an aqueous solution of ethylenediaminetetraacetic acid to obtain 1.2 g of a dark brown solid of Exemplified Compound 3.
[0039]
The organic semiconductor material according to the present invention can be applied by dissolving in a solvent such as ethanol, methanol, tetrahydrofuran, dioxane, methyl ethyl ketone, chloroform, methylene chloride, N-methylpyrrolidone, N, N-dimethylformamide as a solvent. If necessary, an aqueous or oil-based ink to which a suitable additive is further added may be prepared, and printing may be performed by screen printing, an inkjet method, or the like. Further, the substrate to which an electric element is to be formed may be transferred by an ablation method using a substrate coated with the organic semiconductor material and a suitable photothermal conversion material.
[0040]
The thin film thus formed may be subjected to annealing, for example, at a temperature not exceeding 200 ° C. during drying after coating. Annealing may be performed in air, but may be performed in an inert atmosphere such as nitrogen or argon, or may be performed in a hydrogen atmosphere.
[0041]
The organic semiconductor material according to the present invention includes a Lewis acid (such as iron chloride, aluminum chloride, and antimony bromide), a halogen (such as iodine and bromine), a hydrohalic acid or a salt thereof, and a sulfonic acid or a salt thereof (polystyrene). (A sodium salt of sulfonic acid, potassium p-toluenesulfonate, and the like), and the conductivity can be adjusted by doping.
[0042]
A field-effect transistor containing these organic semiconductor materials can be advantageously used as a thin-film field-effect transistor for manufacturing various devices such as a switching element.
[0043]
That is, a field-effect transistor using an organic thin film made of these organic semiconductor materials is characterized in that the organic semiconductor material according to the present invention is used as a charge-transporting material, and the charge-transporting material layer includes, for example, a gate insulating layer made of a dielectric. And a source electrode provided in contact with the charge-transporting material layer, and a drain electrode. The source and drain electrodes are formed by applying an electric field between the gate electrode and the source electrode. Current (i.e., current in the charge transporting material layer).
[0044]
Next, a field effect transistor using these organic semiconductor materials and thin films thereof will be described.
[0045]
The gate electrode, source electrode, and drain electrode used in the field-effect transistor are not particularly limited as long as they are conductive materials. Platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony lead, tantalum, Indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin / antimony oxide, indium / tin oxide (ITO), fluorine-doped zinc oxide, zinc, carbon, graphite, glassy carbon, silver paste and Carbon paste, lithium, beryllium, sodium, magnesium, potassium, calcium, scandium, titanium, manganese, zirconium, gallium, niobium, sodium, sodium-potassium alloy, magnesium, lithium, aluminum A magnesium / copper mixture, a magnesium / silver mixture, a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide mixture, a lithium / aluminum mixture, and the like are used. In particular, platinum, gold, silver, copper, aluminum, indium, ITO and carbon are preferred. Alternatively, a known conductive polymer whose conductivity is improved by doping or the like, for example, conductive polyaniline, conductive polypyrrole, conductive polythiophene, a complex of polyethylene dioxythiophene and polystyrene sulfonic acid, or the like is also preferably used. Among the above, the source electrode and the drain electrode preferably have low electric resistance at the contact surface with the organic semiconductor material layer.
[0046]
As a method of forming an electrode, a method of forming an electrode using a known photolithographic method or a lift-off method on a conductive thin film formed using a method such as evaporation or sputtering using the above as a raw material, or a metal foil such as aluminum or copper There is a method of etching using a resist by thermal transfer, ink jet or the like. A solution or dispersion of a conductive polymer or a dispersion of conductive fine particles may be directly patterned by ink jet, or may be formed from a coating film by lithography or laser ablation. Furthermore, a method of patterning an ink, a conductive paste, or the like containing a conductive polymer or conductive fine particles by a printing method such as letterpress, intaglio, lithographic, or screen printing can also be used.
[0047]
In addition, the signal lines, scanning lines, display electrode materials, forming methods, and the like when these are manufactured as a TFT sheet are the same as those described above.
[0048]
Various insulating films can be used for the gate insulating layer used for these organic semiconductor materials and thin-film field-effect transistors. In particular, an inorganic oxide film having a high relative dielectric constant is preferable. As the inorganic oxide, silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead lanthanum titanate, strontium titanate, Examples include barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, and yttrium trioxide. Among them, preferred are silicon oxide, aluminum oxide, tantalum oxide and titanium oxide. Inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.
[0049]
Examples of the method of forming the film include a vacuum deposition method, a molecular beam epitaxial growth method, an ion cluster beam method, a low energy ion beam method, an ion plating method, a CVD method, a sputtering method, a dry process such as an atmospheric pressure plasma method, and a spray process. Wet processes such as a coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, a bar coating method, a coating method such as a die coating method, and a method by patterning such as printing or inkjet, Can be used depending on the material. The wet process is a method in which fine particles of an inorganic oxide are dispersed in an optional organic solvent or water using a dispersing agent such as a surfactant as needed, and a method of drying the oxide precursor or an oxide precursor, for example. A so-called sol-gel method of applying and drying a solution of an alkoxide body is used. Of these, the atmospheric pressure plasma method and the sol-gel method are preferred.
[0050]
The plasma film forming process under atmospheric pressure is a process of discharging under the atmospheric pressure or a pressure close to the atmospheric pressure, exciting the reactive gas into plasma, and forming a thin film on the base material. These are described in Kaihei 11-133205, JP-A-2000-185362, JP-A-11-61406, JP-A-2000-147209, and 2000-121804 (hereinafter also referred to as atmospheric pressure plasma method). Thereby, a highly functional thin film can be formed with high productivity.
[0051]
As the organic compound film used as the insulating layer, polyimide, polyamide, polyester, polyacrylate, photo-radical polymerization type, photo-cationic polymerization type photo-curable resin, or copolymer containing acrylonitrile component, polyvinyl phenol, polyvinyl Examples include alcohols, novolak resins, and phosphazene compounds including cyanoethyl pullulan, polymers, and elastomers. As the method for forming the organic compound film, the above-mentioned wet process is preferable.
[0052]
The inorganic oxide film and the organic oxide film can be laminated and used together. The thickness of these insulating films is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.
[0053]
In the present invention, for example, a material having a functional group such as acrylic acid, acetamido, dimethylamino group, cyano group, carboxyl group, or nitro group in the organic semiconductor material layer, a benzoquinone derivative, tetracyanoethylene, and tetracyanoquinodimethane Or a material serving as an acceptor such as a derivative thereof, or a material having a functional group such as an amino group, a triphenyl group, an alkyl group, a hydroxyl group, an alkoxy group, or a phenyl group; and a substituted amine such as phenylenediamine. , Anthracene, benzoanthracene, substituted benzoanthracenes, pyrene, substituted pyrene, carbazole and its derivatives, tetrathiafulvalene and its derivatives, etc. Processing may be performed.
[0054]
The doping means that an electron donating molecule (acsector) or an electron donating molecule (donor) is introduced into a thin film as a dopant. Either an acceptor or a donor can be used as the dopant used in the present invention. Cl as the acceptor₂, Br₂, I₂, ICl, ICl₃, IBr, IF and other halogens, PF₅, AsF₅, SbF₅, BF₃, BC1₃, BBr₃, SO₃Lewis acids such as HF, HC1, HNO₃, H₂SO₄, HClO₄, FSO₃H, ClSO₃H, CF₃SO₃H or other protonic acids, acetic acid, formic acid, organic acids such as amino acids, FeCl₃, FeOCl, TiCl₄, ZrCl₄, HfCl₄, NbF₅, NbCl₅, TaCl₅, MoCl₅, WF₅, WCl₆, UF₆, LnCl₃(Ln = La, Ce, Nd, Pr, etc. Lanthanoids and Y) and transition metal compounds such as Y, Cl⁻, Br⁻, I⁻, ClO₄ ⁻, PF₆ ⁻, AsF₅ ⁻, SbF₆ ⁻, BF₄ ⁻And electrolyte anions such as sulfonic acid anions. Examples of the donor include alkali metals such as Li, Na, K, Rb, and Cs; alkaline earth metals such as Ca, Sr, and Ba; Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy. , Ho, Er, Yb and other rare earth metals, ammonium ions, R₄P⁺, R₄As⁺, R₃S⁺(R is an alkyl group, an aryl group, etc.), acetylcholine and the like. As a method of doping these dopants, any of a method of preparing a thin film of an organic semiconductor material in advance and introducing the dopant later and a method of introducing a dopant at the time of forming the thin film of the organic semiconductor material can be used. As the doping in the former method, gas phase doping using a gaseous dopant, liquid phase doping in which a solution or liquid dopant is brought into contact with a thin film, and solid doping in which a solid state dopant is brought into contact with a thin film and diffusion doping is performed. A method of phase doping can be mentioned. In liquid phase doping, the efficiency of doping can be adjusted by performing electrolysis. In the latter method, a mixed solution or dispersion of the organic semiconductor compound and the dopant may be simultaneously applied and dried. For example, when a vacuum evaporation method is used, the dopant can be introduced by co-evaporating the dopant together with the organic semiconductor compound. When a thin film is formed by a sputtering method, a dopant can be introduced into the thin film by sputtering using a binary target of an organic semiconductor compound and a dopant. Still other methods include chemical doping, such as electrochemical doping and photo-initiated doping, and physical doping, such as the ion implantation method described in the publication {Industrial Materials, Vol. 34, No. 4, p. 55, 1986}. Any of the conventional dopings can be used.
[0055]
As a method for producing an organic semiconductor material thin film, in addition to the above-mentioned methods such as coating, screen printing, and printing by an ink-jet method, a vacuum evaporation method, a molecular beam epitaxial growth method, an ion cluster beam method, a low energy ion beam method, and an ion plating method. Method, CVD method, sputtering method, plasma polymerization method, electrolytic polymerization method, chemical polymerization method, spray coating method, spin coating method, blade coating method, dip coating method, casting method, roll coating method, bar coating method, die coating method and The LB method and the like are also mentioned, and can be used depending on the material. However, in terms of productivity, spin coating, blade coating, dip coating, roll coating, bar coating, and die coating can be used to easily and accurately form thin films using organic semiconductor material solutions. The coating method is preferred. The thickness of the thin film made of these organic semiconductor materials is not particularly limited, but the characteristics of the obtained transistor are often largely influenced by the thickness of the active layer made of the organic semiconductor material. Although it depends on the type of the organic semiconductor material, it is generally preferably 1 μm or less, particularly preferably 10 to 300 nm.
[0056]
In addition, since high temperature is not required for the formation and a heat-resistant substrate such as a glass substrate is not required, an organic semiconductor material thin film, a field effect transistor using the same, a switching element, etc. using the same on an insulating support such as various plastic films. Can be formed, and a TFT sheet serving as a driving element for driving a display material in each pixel unit used for various display panels can be made flexible.
[0057]
As the flexible insulating sheet, for example, a plastic film can be used as the sheet. Examples of the plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyether imide, polyether ether ketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), and cellulose triacetate. (TAC), cellulose acetate propionate (CAP) and the like. As described above, by using a plastic film, the weight can be reduced as compared with the case of using a glass substrate, portability can be improved, and resistance to impact can be improved.
[0058]
Further, a plasticizer such as trioctyl phosphate or dibutyl phthalate may be added to these plastic films, or a known ultraviolet absorber such as benzotriazole or benzophenone may be added. In addition, a resin prepared by applying a so-called organic-inorganic polymer hybrid method, in which a raw material of an inorganic polymer such as tetraethoxysilane is added, and a high molecular weight is obtained by applying energy such as a chemical catalyst, heat, and light. It can also be used as a raw material.
[0059]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a field effect transistor using an organic semiconductor material thin film made of a conductive material according to the present invention will be described.
[0060]
FIG. 1 shows a schematic configuration example of a field effect transistor using the organic semiconductor material of the present invention. FIG. 3A shows that a source electrode 2 and a drain electrode 3 are formed on a support 6 by a metal foil or the like, and an organic semiconductor material layer 1 made of the conductive material of the present invention is formed between the two electrodes. An insulating layer 5 is formed thereon, and a gate electrode 4 is further formed thereon to form a field effect transistor. FIG. 2B shows the organic semiconductor material layer 1 formed between the electrodes in FIG. 2A and formed so as to cover the entire surface of the electrodes and the support using a coating method or the like. (C) shows that the organic semiconductor material layer 1 is first formed on the support 6 by a coating method or the like, and then the source electrode 2, the drain electrode 3, the insulating layer 5, and the gate electrode 4 are formed.
[0061]
FIG. 3D shows that after forming the gate electrode 4 on the support 6 with a metal foil or the like, the insulating layer 5 is formed, and the source electrode 2 and the drain electrode 3 are formed thereon with the metal foil or the like. An organic semiconductor material layer 1 made of the conductive material of the present invention is formed between the electrodes. In addition, a configuration as shown in FIGS.
[0062]
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.
[0063]
【Example】
Hereinafter, the present invention will be described with reference to examples, but embodiments of the present invention are not limited thereto.
[0064]
Example 1
1 g of a poly (3-n-hexylthiophene-2,5-diyl) (Reggioregular form, average molecular weight measured by gel electrophoresis chromatography, 90000) was dissolved in 10 ml of chloroform, and this was dissolved in polyethersulfone (PES). A polymer film was formed on the film by applying with an applicator (120 μm in thickness) and air-dried to obtain an organic semiconductor material A.
[0065]
Using a solution in which 100 mg of Exemplified Compound 3 (average degree of polymerization measured by gel electrophoresis chromatography 6) synthesized in accordance with the above synthesis route was dissolved in 1 ml of chloroform, a polymer film was formed in the same manner as the organic semiconductor material A, Organic semiconductor material B was obtained.
[0066]
Each of the organic semiconductor materials A and B was immersed in a 2 mol / L hydrochloric acid aqueous solution at 20 ° C. for 12 hours and dried at 40 ° C. under vacuum, and the electrical conductivity of the sample was measured. The relative value of the electric conductivity of the organic semiconductor material B was 161 when the property was set to 100, and it was confirmed that the organic semiconductor material B of the present invention had significantly improved electric conductivity.
[0067]
Example 2
After a thermal oxide film having a thickness of 300 nm was formed on an n-type doped silicon substrate, gold having a thickness of 50 nm was deposited on the oxide film, and source and drain electrodes having a gap of 10 μm were formed by photolithography. Next, an organic semiconductor material layer having a thickness of 30 nm was formed by spin coating a well-purified chloroform solution of Exemplified Compound 3 of the present invention to obtain an organic field-effect transistor (thin film transistor).
[0068]
The produced organic field effect transistor exhibits a switching function by ON / OFF of a voltage (gate voltage) between a gate and a source electrode, and has a high current value in a switching ON state at a low gate voltage. It was confirmed that the / OFF ratio was high and a good switching function was provided.
[0069]
The organic field effect transistor (thin film transistor) formed according to the present invention can be more efficiently and simply patterned by using a coating process and the like than those formed by a conventional method. High-precision patterning can be efficiently performed at low cost without requiring a large amount of equipment.
[0070]
In addition, despite the formation of a constituent layer such as an organic semiconductor material layer by a simple method such as a coating method, the accuracy of electrode pattern formation is high. There is little variation that acts as a barrier between them.
[0071]
【The invention's effect】
An organic semiconductor material that can be formed by a simple process was obtained, and an organic field effect (thin film transistor) and a switching element using the organic semiconductor material thin film could be constructed, and it was proved that the organic semiconductor material could be used for a circuit such as a display panel.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration example of a field-effect transistor using an organic conductive material.
[Explanation of symbols]
1) Organic semiconductor material layer
2 source electrode
3 Drain electrode
4 gate electrode
5 Insulation layer
6 support

Claims (8)

An organic semiconductor material comprising a conjugated oligomer or polymer comprising a main chain having an extended conjugate bond and a side chain extending in a direction substantially perpendicular to the direction in which the main chain extends substantially. The organic semiconductor material according to claim 1, wherein the main chain is composed of a repeating unit containing at least one kind of aromatic ring. 3. The organic semiconductor material according to claim 1, wherein the main chain is constituted by a repeating unit containing at least either a thiophene ring or a p-phenylene ring. The organic semiconductor material according to claim 1, 2 or 3, wherein the main chain is constituted by a repeating unit containing at least a thiophene ring. 5. The organic semiconductor material according to claim 3, wherein the substituted thiophene ring contained in the main chain has a structure in which a 5-membered aromatic ring is fused at the 3- and 4-positions of thiophene. The organic semiconductor material according to any one of claims 1 to 5, wherein a side chain is a straight-chain alkyl group. A field effect transistor comprising the organic semiconductor material according to claim 1. A charge transporting material, and a gate electrode that is in direct or indirect contact with the charge transporting material, and controls an electric current in the charge transporting material by applying an electric field between the gate electrode and the charge transporting material. A field-effect transistor, wherein the charge-transporting material is the organic semiconductor material according to claim 1.

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