JP2004063976A - Field effect transistor - Google Patents

Abstract

Provided is a field-effect transistor using an organic semiconductor, which has higher mobility, high on-current and low leakage current, and high on / off ratio.
An insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, and a source electrode and a drain electrode provided in contact with the organic semiconductor layer are provided. A field effect transistor provided on the insulating support substrate 1. The insulator layer is a layer formed by a coating method using a solvent, and has a residual solvent amount of 1% by weight or less. The insulator layer is a layer formed by applying a monomer and then polymerizing the same, and has a residual monomer and / or oligomer content of 3% by weight or less. Alternatively, the amount of adsorbed moisture in the insulator layer is 1% by weight or less.
[Selection diagram] Fig. 1

Description

【００３２】
上記▲３▼の場合の好適な溶媒Ａと溶媒Ｂの組み合せ又は、上記▲４▼の場合の好適なモノマーＡ’と溶媒Ｂの組み合せとしては、上述した溶解度パラメータの文献値を参照して、それらの差が本発明の特定値以上となるような最適な組み合わせの溶媒及び／又はモノマーを適宜選択することができる。
【００３３】
▲５▼　絶縁体層中の吸着水分量が１重量％以下、好ましくは５０００ｐｐｍ以下、より好ましくは２０００ｐｐｍ以下、特に好ましくは１０００ｐｐｍ以下、とりわけ好ましくは５００ｐｐｍ以下とする。これにより、電荷移動度が向上し、高いｏｎ電流及び低いリーク電流、高いｏｎ／ｏｆｆ比を達成することが可能となる。なお、絶縁体層中の吸着水分量の下限は特に限定されないが、絶縁体層の成膜、精製上の制約等から含有量を０にすることは困難であり０．００１ｐｐｍ以上、更には０．０１ｐｐｍ以上であっても良い。
【００３４】
絶縁体層中の吸着水分量は、絶縁体層の成膜過程で、水分の吸着を低減できるような条件（例えば、露点を下げた条件下のグローブボックス内での製膜）にコントロールする等の方法により、上記好適範囲に低減することができる。
【００３５】
本発明において、絶縁体層は、上記▲１▼の場合において、更に▲３▼，▲５▼の条件も備えていても良い。また、上記▲２▼の場合において、更に▲４▼，▲５▼の条件も備えていても良い。また、上記▲３▼，▲４▼の場合において、上記▲５▼の条件も備えていても良い。
【００３６】
本発明において、電界効果トランジスタの構成材料自体には特に制限はなく、従来電界効果トランジスタに適用されているものをいずれも好適に用いることができる。
【００３７】
絶縁性支持基板の材料としては、絶縁性を示し電界効果トランジスタ及びその上に作成される表示素子、表示パネル等を支持できるものであれば良く、公知のもの、例えば、ガラス、プラスチック、石英等をいずれでも用いることができ、より具体的には、ポリエステル、ポリカーボネート、ポリイミド、ポリエーテルスルフォン、アモルファスポリオレフィン、エポキシ樹脂、ガラス等が挙げられる。中でもポリマー基板が好ましく、強度の点ではポリエステル又はポリカーボネートが好ましく、特にはポリエチレンテレフタレート等のポリエステルが好ましい。絶縁性支持基板の厚みは０．０５　ｍｍから２　ｍｍが好ましく、０．１　ｍｍから１　ｍｍが更に好ましい。
【００３８】
ゲート電極、ソース電極、ドレイン電極の構成材料は、導電性を示すものであれば良く、公知のものをいずれでも用いることができ、例えば白金、金、アルミニウム、クロム、ニッケル、銅、チタン、マグネシウム、カルシウム、バリウム、ナトリウム等の金属、ＩｎＯ_２、ＳｎＯ_２、ＩＴＯ等の導電性酸化物、樟脳スルホン酸がドープされたポリアニリン、パラトルエンスルホン酸がドープされたポリエチレンジオキシチオフェン等のドープされ良好な電気伝導度を示す導電性高分子、カーボンブラック、金属微粒子、グラファイト粉等がバインダーに分散されてなり良好な電気伝導度を示す導電性複合材料などが挙げられる。
【００３９】
ゲート電極、ソース電極、ドレイン電極の形成法としては、真空蒸着法、スパッタ法、塗布法、印刷法、ゾルゲル法等が挙げられ、更にそのパターニング方法としては、フォトレジストのパターニングとエッチング液や反応性のプラズマでのエッチングを組み合わせたフォトリソグラフィー法、インクジェット印刷、スクリーン印刷、オフセット印刷、凸版印刷等の印刷法、マイクロコンタクトプリンティング法等のソフトリソグラフィーの手法及びこれらの手法を複数組み合わせた手法などが挙げられる。また、レーザーや電子線等のエネルギー線を照射して材料を除去することや材料の導電性を変化させることにより、直接パターンを作製することも可能である。
【００４０】
これらゲート電極、ソース電極、ドレイン電極の厚みは０．０１μｍから２μｍが好ましく、０．０２μｍから１μｍが更に好ましい。
【００４１】
なお、ソース電極−ドレイン電極間距離（チャンネル長さＬ）は通常１００μｍ以下、好ましくは５０μｍ以下であり、チャンネル幅Ｗは通常２０００μｍ以下、好ましくは５００μｍ以下であり、Ｌ／Ｗは通常０．１以下、好ましくは０．０５以下である。
【００４２】
絶縁体層の絶縁体としては、ゲート電極への電流の漏れを防ぎかつ低ゲート電圧で電界効果トランジスタを駆動させることができるように絶縁性に優れかつ比較的大きな比誘電率を持つものであれば公知のものをいずれでも用いることができ、例えばポリメチルメタクリレート等のアクリル樹脂、ポリスチレン、ポリビニルフェノール、ポリイミド、ポリカーボネート、ポリエステル、ポリビニルアルコール、ポリ酢酸ビニル、ポリウレタン、ポリスルホン、エポキシ樹脂、フェノール樹脂等のポリマー及びこれらを組み合わせた共重合体、二酸化珪素、酸化アルミニウム、酸化チタン等の酸化物、窒化珪素等の窒化物、ＳｒＴｉＯ_３、ＢａＴｉＯ_３等の強誘電性酸化物、あるいは、上記酸化物や窒化物、強誘電性酸化物等の粒子を分散させたポリマー膜等が挙げられる。中でもエポキシ樹脂、ポリイミド樹脂、アクリル樹脂が好ましい。また、絶縁体の前駆物質としてモノマーを塗布した後、光を照射して硬化させることにより絶縁体を形成する光硬化樹脂も好適に用いられる。
【００４３】
絶縁体層の形成方法としては、スピンコートやブレードコートなどの塗布法、蒸着法、スパッタ法、スクリーン印刷やインクジェット等の印刷法等、材料の特性に合わせた形成方法を採用することができる。
【００４４】
絶縁体を溶媒に溶解して塗布法により絶縁体層を成膜する場合に使用できる溶媒としては、ｎ−ヘプタン、ｎ−ヘキサン、デカリン等の鎖状、又は環状の炭化水素類、四塩化炭素、トリクロロエチレン、クロロホルム、ジクロロメタン等のハロゲン化炭化水素類、ｐ−キシレン、トルエン、ｍ−クレゾール、アニソール等の芳香族化合物類、ジ−ｎ−ブチルエーテル、ジメトキシエタン、テトラヒドロピラン、１，４−ジオキサン、テトラヒドロフラン等の鎖状又は環状のエーテル類、１−ブタノール、ヘキサフルオロ−２−プロパノール等のアルコール類、２−ブタノン、メチルエチルケトン、シクロヘキサノン等のケトン化合物類、Ｎ−メチル−２−ピロリドン、ジメチルホルムアミド等のアミド化合物類、アセトニトリル等のニトリル化合物類などが挙げられる。
【００４５】
このようにして形成される絶縁体層は、前述の如く、ゲート電極への漏れ電流、電界効果トランジスタの低ゲート電圧駆動に関係することから、室温での電気伝導度が１０^−１２　Ｓ／ｃｍ以下、更には１０^−１４　Ｓ／ｃｍ以下、比誘電率が２．０以上、更には２．５以上を示すことが好ましい。
【００４６】
このような絶縁体層の厚みは０．１μｍから４μｍが好ましく、０．２μｍから２μｍが更に好ましい。
【００４７】
有機半導体層は、金属含有量、更には残留溶媒量及び吸着水分量が前述の範囲であれば良く、有機半導体層を形成する有機半導体は特に限定されず、π共役系の低分子及び高分子であれば公知のものをいずれでも用いることができ、例えばペンタセン、オリゴチオフェン、置換基を有するオリゴチオフェン、ビスジチエノチオフェン、置換基を有するジアルキルアントラジチオフェン、金属フタロシアニン、ベンゾポルフィリン、フッ素置換された銅フタロシアニン、Ｎ，　Ｎ’−ジアルキル−ナフタレン−１，　４，　５，　８−テトラカルボン酸ジイミド置換体、３，　４，　９，　１０−ペリレンテトラカルボン酸ジアンハイドライド、Ｎ，　Ｎ’−ジアルキル−３，　４，　９，　１０−ペリレンテトラカルボン酸ジイミド、フラーレンなどのπ共役系低分子やレジオレギュラーポリ（３−ヘキシルチオフェン）に代表されるレジオレギュラーポリ（３−アルキルチオフェン）、ポリ−９，　９’−ジアルキルフルオレンコビチオフェンなどのπ共役系共重合体等のπ共役系高分子が挙げられる。
【００４８】
これらπ共役系低分子、高分子のなかでも、有機半導体層を形成した場合、そのソース電極−ドレイン電極方向の電気伝導度が１０^−４　Ｓ／ｃｍ以下、１０^−１２　Ｓ／ｃｍ以上を示すものが好ましく、特に１０^−６　Ｓ／ｃｍ以下、１０^−１１　Ｓ／ｃｍ以上、とりわけ１０^−７　Ｓ／ｃｍ以下、１０^−１０　Ｓ／ｃｍ以上を示すものがより好ましい。更にまた、これらπ共役系低分子、高分子のなかでも、有機半導体層を形成した場合に電界効果移動度とソース電極−ドレイン電極方向の電気伝導度、及び電荷素量から求めたキャリア密度が１０^７　ｃｍ^−３以上、１０^１８　ｃｍ^−３以下を示すものが好ましく、特に１０^８　ｃｍ^−３以上、１０^１７　ｃｍ^−３以下を示すものがより好ましい。また、これらπ共役系低分子、高分子のなかでも、有機半導体層を形成した場合に電界効果移動度の室温以下での温度依存性から求められる電荷移動に要する活性化エネルギーが０．２ｅＶ以下を示すものが好ましく、特に０．１ｅＶ以下を示すものがより好ましい。
【００４９】
更にまた、これらπ共役系低分子のなかでも分子長が４０Å以下のものにおいては、該電界効果トランジスタに用いた絶縁体層と同じ絶縁体層上に有機半導体層を形成した場合、層表面に対する法線に対して６０°の角度から入射光を入れて測定した偏光吸収において、これらπ共役系低分子の分子軸方向の遷移モーメントに由来する吸収ピーク強度のｐ偏光成分とｓ偏光成分の比であるｐ偏光成分／ｓ偏光成分が１．５以上、更には２．０以上、特には３．０以上を示す特性を持つものが好ましい。
【００５０】
また一方で、分子長が４０Åより大きいπ共役系高分子においては、該電界効果トランジスタに用いた絶縁体層と同じ絶縁体層上に有機半導体層を形成した場合、層表面に垂直方向から入射光を入れて測定した偏光吸収において、これらπ共役系高分子の主鎖方向の遷移モーメントに由来する吸収ピーク強度のソース電極−ドレイン電極方向成分とそれに垂直方向成分の比であるソース電極−ドレイン電極方向成分／垂直方向成分が３．５以上、更には４．５以上、特には５．０以上を示す特性を持つものが好ましい。
【００５１】
更にまた、これらπ共役系低分子、高分子のなかでも、該電界効果トランジスタに用いた絶縁体層と同じ絶縁体層上に有機半導体層を形成した場合、最隣接分子或いは高分子間の距離が３．９Å以下、更には３．８５Å以下、特には３．８Å以下である特性を示すものが好ましい。
【００５２】
このような有機半導体層の膜厚は１　ｎｍから１０　μｍが好ましく、１０　ｎｍから５００ｎｍが更に好ましい。
【００５３】
これらの有機半導体を用いた有機半導体層を形成する方法としては、低分子有機半導体の場合には、真空蒸着により絶縁体層又は絶縁性支持基板上に蒸着して形成する方法、溶媒に溶解してキャスト、ディップ、スピンコートなどにより塗布して形成する方法などが挙げられる。高分子有機半導体の場合は、溶媒に溶解してキャスト、ディップ、スピンコートなどにより塗布して形成する方法などが挙げられる。また、目的とする低分子前駆体或いは目的とする高分子前駆体を用いて前述の適切な方法により層形成し、その後に加熱処理等により目的とする有機半導体層に変換する方法も挙げられる。
【００５４】
有機半導体を溶媒に溶解して塗布法により有機半導体層を成膜する場合に使用できる溶媒としては、ｎ−ヘプタン、ｎ−ヘキサン等の鎖状炭化水素類、四塩化炭素、トリクロロエチレン、クロロホルム、ジクロロメタン等のハロゲン化炭化水素類、ｐ−キシレン、トルエン、ｍ−クレゾール、アニソール等の芳香族化合物類、ジ−ｎ−ブチルエーテル、テトラヒドロピラン、１，４−ジオキサン、テトラヒドロフラン等の鎖状又は環状のエーテル類、１−ブタノール等のアルコール類、２−ブタノン等のケトン化合物類、Ｎ−メチル−２−ピロリドン、ジメチルホルムアミド等のアミド化合物類、アセトニトリル等のニトリル化合物類、トリフルオロ酢酸等のカルボン酸類等が挙げられる。
【００５５】
本発明の電界効果トランジスタの基本的な構造は、絶縁体層と、この絶縁体層により隔離されたゲート電極及び有機半導体層と、この有機半導体層に接するように設けられたソース電極及びドレイン電極とを絶縁性支持基板上に有するものであり、その具体的な構造としては図１〜３に示すようなものが挙げられるが、本発明の電界効果トランジスタは、何ら図１〜３に示す構造の電界効果トランジスタに限定されず、更に図１〜３に示される層以外の層が形成されていても良い。
【００５６】
例えば、図１，２に示す電界効果トランジスタのように、有機半導体層が表出している電界効果トランジスタにあっては、有機半導体に対する外気の影響を最小限にするために、更にこの上に保護膜を形成しても良く、この場合、保護膜の材料としてはエポキシ樹脂、アクリル樹脂、ポリウレタン、ポリイミド、ポリビニルアルコール等のポリマーや酸化珪素、窒化珪素、酸化アルミニウム等の無機酸化物や窒化物等が挙げられる。保護膜の形成方法としては塗布法や真空蒸着法などが挙げられる。
【００５７】
【発明の効果】
以上詳述した通り、本発明の電界効果トランジスタによれば、絶縁体層中の残留溶媒量、残留モノマー及び／又はオリゴマー量、又は吸着水分量を特定値以下とすることにより、或いは、絶縁体層の形成に用いる溶媒Ａ又はモノマーＡ’と有機半導体層の形成に用いる溶媒Ｂとの溶解度パラメータの差を特定値以上とすることにより、誘起電荷が移動する有機半導体層の有機半導体分子の配列の乱れを効果的に抑制し、より高い移動度と、高いｏｎ電流及び低いリーク電流と、高いｏｎ／ｏｆｆ比とを有する電界効果トランジスタを提供することができる。
【図面の簡単な説明】
【図１】電界効果トランジスタの構造例を示す断面図である。
【図２】電界効果トランジスタの構造例を示す断面図である。
【図３】電界効果トランジスタの構造例を示す断面図である。
【符号の説明】
１　絶縁性支持基板
２　ゲート電極
３　絶縁体層
４　有機半導体層
５　ソース電極
６　ドレイン電極
７　界面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a field effect transistor using an organic semiconductor.
[0002]
[Prior art]
Field effect transistors are widely used as important switches and amplifying elements alongside bipolar transistors. A field-effect transistor has a structure in which a semiconductor material is provided with a source electrode, a drain electrode, and a gate electrode with an insulator layer interposed therebetween. The operating characteristics of the field-effect transistor include the carrier mobility μ of the semiconductor used, the electric conductivity σ, the capacitance Ci of the insulating layer, the configuration of the element (the distance L and the width W between the source electrode and the drain electrode, the film of the insulating layer). The thickness of the semiconductor material is determined by the thickness d or the like. Among them, the semiconductor material having high mobility (μ) shows good characteristics.
[0003]
At present, silicon is widely used as a semiconductor material. Inorganic semiconductors represented by silicon must be processed at a high temperature of 300 ° C. or more during production, so that it is difficult to use a plastic substrate or film as a substrate, and the production requires a lot of energy. is there. In addition, since a device manufacturing process is performed in a vacuum, expensive equipment is required in a manufacturing line, and there is a disadvantage that the cost is high.
[0004]
On the other hand, most of transistors using an organic semiconductor can be manufactured by a lower temperature process than an inorganic semiconductor, so that a plastic substrate or a film can be used as a substrate, and a lightweight and hard-to-break element can be manufactured. Can be. Some devices can be manufactured by applying a solution or using a printing method, and thus a large-area device can be manufactured at low cost. Furthermore, since there is a wide variety of materials, and it is possible to fundamentally change the material properties easily by changing the molecular structure, functions and elements that cannot be achieved with inorganic semiconductors by combining different functions It is also possible to realize.
[0005]
As for a transistor using an organic semiconductor as a semiconductor, Japanese Patent Application Laid-Open No. 61-202467 discloses a transistor using a conductive polymer and a conjugated polymer, and Japanese Patent No. 2984370 uses a low molecular compound. Things are listed.
[0006]
A typical structure of a transistor using an organic semiconductor as a conventional semiconductor is shown in FIGS.
[0007]
In the field-effect transistor of FIG. 1, a gate electrode 2 is provided on an insulating support substrate 1, and an insulator layer 3 and an organic semiconductor layer 4 are further provided thereon. A source electrode 5 and a drain electrode 6 are provided on the insulator layer 3 so as to be in contact with the organic semiconductor layer 4. This field effect transistor is called a bottom gate / bottom contact type.
[0008]
The field effect transistor of FIG. 2 is different from the field effect transistor shown in FIG. 1 in that a source electrode 5 and a drain electrode 6 are provided on an organic semiconductor layer 4 on an insulator layer 3, and the others are the same. The configuration is as follows. This field effect transistor is called a bottom gate / top contact type.
[0009]
In the field-effect transistor shown in FIG. 3, a source electrode 5 and a drain electrode 6 are provided on an insulating support substrate 1, an organic semiconductor layer 4 and an insulator layer 3 are stacked on the insulating support substrate 1, The gate electrode 2 is provided on the insulator layer 3. This field effect transistor is called a top gate / bottom contact type.
[0010]
In such a field-effect transistor, when a voltage is applied to the gate electrode 2, the carrier density of the organic semiconductor layer near the interface between the organic semiconductor layer 4 and the insulator layer 3 is changed to change the source-drain electrodes 5, 6 The amount of current flowing between them is changed.
[0011]
Active research has been made on various types of organic semiconductors in transistors having such various structures. Research on residual solvents etc. is by no means sufficient, and how problems with residual solvents etc. affect the performance (mobility, leakage current value, on / off ratio, etc.) of organic field effect transistors It is not clear.
[0012]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned conventional situation, and can achieve higher mobility, higher on-current and lower leakage current, and higher on / off ratio, and can improve the transistor performance of these transistors. It is an object of the present invention to provide a stable organic transistor.
[0013]
[Means for Solving the Problems]
The field effect transistor of the present invention includes an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided to be in contact with the organic semiconductor layer, In a field effect transistor having a substrate, the insulator layer has one of the following characteristics (1) to (5).
[0014]
{Circle around (1)} The insulator layer is a layer formed by a coating method using a solvent, and the amount of the residual solvent in the insulator layer is 1% by weight or less. In this case, particularly, when the insulator layer is a layer formed by a coating method using a solvent A and the organic semiconductor layer is a layer formed by a coating method using a solvent B, the solvent A and the solvent A are used. It is preferable that the difference between the solubility parameters of the solvent B is 1.1 or more. Further, the amount of adsorbed water in the insulator layer is preferably 1% by weight or less.
{Circle around (2)} The insulator layer is a layer formed by applying a monomer and then polymerizing the same, and the amount of the residual monomer and / or oligomer in the insulator layer is 3% by weight or less. In this case, when the insulator layer is a layer formed by applying the monomer A ′ and then polymerizing the same, and when the organic semiconductor layer is a layer formed by a coating method using the solvent B, the monomer A It is preferable that the difference between the solubility parameter of '′ and the solvent B is 0.5 or more. Further, the amount of adsorbed water in the insulator layer is preferably 1% by weight or less.
{Circle around (3)} The insulator layer is a layer formed by a coating method using a solvent A, and the organic semiconductor layer is a layer formed by a coating method using a solvent B. The difference is 1.1 or more. Further, the amount of adsorbed water in the insulator layer is preferably 1% by weight or less.
{Circle around (4)} The insulator layer is a layer formed by applying the monomer A ′ and then polymerizing the same, and the organic semiconductor layer is a layer formed by a coating method using the solvent B, and the monomer A ′ and the solvent B Are not less than 0.5. Further, the amount of adsorbed water in the insulator layer is preferably 1% by weight or less.
(5) The amount of adsorbed water in the insulator layer is 1% by weight or less.
[0015]
The present inventors have conducted intensive studies on the instability of transistor performance in a conventional field-effect transistor, and found that a solvent remaining in the insulator layer during the process of forming the insulator layer, or a monomer and / or oligomer, or adsorption Moisture degrades the performance of the insulator layer itself, disturbs the orientation, arrangement, or morphology of the organic semiconductor molecules in the organic semiconductor layer adjacent to the insulator layer, disrupting the arrangement of the organic semiconductor molecules, and Disordered arrangement weakens the interaction of π orbitals between organic semiconductor molecules, resulting in a negative effect on induced charge transfer, and impairs transistor performance (mobility, leak current value, on / off ratio, etc.). I found it.
[0016]
According to the present invention, the amount of the residual solvent in the insulating layer is set to 1% by weight or less, and the amount of the residual monomer and / or oligomer in the insulating layer is set to 3% by weight or less. The water content is set to 1% by weight or less, or the solubility parameter difference between the solvent A or the monomer A ′ used for forming the insulator layer and the solvent B used for forming the organic semiconductor layer is set to a specific value or more. Accordingly, an organic transistor having higher mobility, high on-current and low leak current, and high on / off ratio can be realized.
[0017]
That is, by setting the amount of residual solvent, the amount of residual monomer and / or oligomer, or the amount of adsorbed moisture in the insulator layer to the above-mentioned specific value or less, the characteristics of the insulator layer are enhanced, and the organic semiconductor in which these are in contact with the insulator layer. The effect of the layer on the orientation, arrangement, or morphology of organic semiconductor molecules can be reduced, and an organic transistor having higher mobility, high on-current and low leakage current, and high on / off ratio can be realized. .
[0018]
Note that the amount of residual solvent (% by weight) in the insulator layer can be measured by, for example, a gas chromatograph method in which the insulator layer of the organic transistor is separated by physical peeling or solvent dissolution. Further, the amount of adsorbed moisture (% by weight) in the insulating layer can be measured by, for example, a physical method of physically separating or dissolving the insulating layer of the organic transistor or dissolving the solvent by a drying weight loss method or a near infrared absorption method. The amount (% by weight) of the residual monomer and / or oligomer in the insulator layer can be measured, for example, by separating the insulator layer of the organic transistor by physical peeling or dissolving in a solvent, and by gas chromatography.
[0019]
Further, the solubility parameter is a numerical value of the solubility when the resin is dissolved in the solvent, and is calculated from the latent heat of vaporization and the heat of vaporization of the resin and the solvent. It indicates that the compound has compatibility, and the larger the value, the smaller the compatibility. And the solubility parameter is prescribed | regulated about various resins and various solvents.
[0020]
If the difference between the solubility parameter of the solvent A or the monomer A ′ forming the insulator layer and the solubility parameter of the solvent B forming the organic semiconductor layer is equal to or greater than a specific value, the compatibility between the two is poor. At the interface with the layer, the solvent A or the monomer A ′ in the insulator layer is prevented from penetrating into the organic semiconductor layer, and the solvent B in the organic semiconductor layer is prevented from penetrating into the insulator layer. Thus, it is possible to realize an organic transistor having higher mobility, higher on-current and lower leak current, and higher on / off ratio by preventing the disorder of the arrangement of the organic semiconductor in the organic semiconductor layer.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the field effect transistor of the present invention will be described below in detail with reference to the drawings.
[0022]
The field effect transistor of the present invention includes an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, and a source electrode and a drain electrode provided in contact with the organic semiconductor layer. It is provided on a support substrate, and its structure is not particularly limited. The bottom gate / bottom contact type shown in FIG. 1, the bottom gate / top contact type shown in FIG. 2, and the top gate / bottom contact type shown in FIG. And the like.
[0023]
In the present invention, such a field effect transistor has the following characteristics as an insulator layer.
[0024]
{Circle around (1)} In the insulator layer formed by a coating method using a solvent, the amount of the residual solvent in the insulator layer is 1% by weight or less, preferably 5000 ppm or less, more preferably 2000 ppm or less, particularly preferably 1000 ppm or less. Or less, particularly preferably 500 ppm or less. Thereby, the charge mobility is improved, and a high on-current, a low leak current, and a high on / off ratio can be achieved. The lower limit of the amount of the residual solvent in the insulator layer is not particularly limited, but it is difficult to reduce the content to 0 due to restrictions on film formation of the insulator layer and the content is 0.001 ppm or more, further 0.01 ppm. It may be above.
[0025]
The amount of residual solvent in the insulator layer can be reduced to the above preferred range by strictly controlling drying conditions (temperature, time, and the like) when forming the insulator layer by a coating method.
[0026]
{Circle around (2)} In the insulator layer formed by applying the monomer and then polymerizing, the amount of the residual monomer and / or oligomer in the insulator layer is 3% by weight or less, preferably 2% by weight or less, more preferably Is 1% by weight or less. Thereby, the charge mobility is improved, and a high on-current, a low leak current, and a high on / off ratio can be achieved. The lower limit of the amount of the residual monomer and / or oligomer in the insulator layer is not particularly limited, but it is difficult to reduce the content to 0 due to restrictions on the formation of the insulator layer and the content is 0.001 ppm or more. May be 0.01 ppm or more.
[0027]
The amount of residual monomers and / or oligomers in the insulator layer can be reduced to the above preferred range by increasing the polymerization efficiency by adjusting the polymerization conditions such as the reaction temperature and the amount of catalyst during the formation of the insulator layer. .
[0028]
{Circle around (3)} In the case where the insulator layer is a layer formed by a coating method using a solvent A and the organic semiconductor layer is a layer formed by a coating method using a solvent B, the solubility of the solvents A and B The parameter difference (hereinafter referred to as “solubility parameter difference | AB |”) is 1.1 or more, preferably 1.5 or more, more preferably 2.0 or more, and particularly preferably 2.5 or more. Next, a combination of the solvent A and the solvent B is selected. Thereby, the charge mobility is improved, and a high on-current, a low leak current, and a high on / off ratio can be achieved. The upper limit of the solubility parameter difference | AB | is not particularly limited, but is generally 10 or less, particularly 8 or less.
[0029]
{Circle around (4)} When the insulator layer is a layer formed by applying the monomer A ′ and then polymerizing the same, and the organic semiconductor layer is a layer formed by a coating method using the solvent B, the monomer A ′ The difference in the solubility parameter of the solvent B (hereinafter, referred to as "solubility parameter difference | A'-B |") is 0.5 or more, preferably 1 or more, more preferably 1.5 or more, and particularly preferably 2.0 or more. The combination of the solvent A and the solvent B is selected so that Thereby, the charge mobility is improved, and a high on-current, a low leak current, and a high on / off ratio can be achieved. The upper limit of the solubility parameter difference | A'-B | is not particularly limited, but is generally 10 or less, particularly 8 or less.
[0030]
Literature values of solubility parameters (δ) of solvents and monomers are provided in polymer handbooks and the like. Representative solvent solubility parameters are shown in Table 1 below. Further, in the present invention, when two or more mixed solvents are used as the solvent, the solubility parameter of the mixed solvent is specified by taking the molar average of the solubility parameter of each used solvent.
[0031]
[Table 1]

[0032]
As a suitable combination of the solvent A and the solvent B in the case of the above (3) or a preferable combination of the monomer A ′ and the solvent B in the case of the above (4), with reference to the literature value of the solubility parameter described above, An optimum combination of solvents and / or monomers can be appropriately selected such that the difference is equal to or more than the specific value of the present invention.
[0033]
{Circle around (5)} The amount of adsorbed water in the insulator layer is 1% by weight or less, preferably 5000 ppm or less, more preferably 2000 ppm or less, particularly preferably 1000 ppm or less, particularly preferably 500 ppm or less. Thereby, the charge mobility is improved, and a high on-current, a low leak current, and a high on / off ratio can be achieved. Although the lower limit of the amount of adsorbed moisture in the insulator layer is not particularly limited, it is difficult to reduce the content to 0 due to restrictions on film formation and purification of the insulator layer. It may be at least 0.01 ppm.
[0034]
The amount of adsorbed moisture in the insulator layer is controlled under conditions that can reduce the adsorption of moisture during the process of forming the insulator layer (for example, film formation in a glove box with a reduced dew point). By the method described above, the content can be reduced to the preferable range described above.
[0035]
In the present invention, the insulator layer may further satisfy the conditions (3) and (5) in the case of the above (1). In the case of the above (2), the conditions of (4) and (5) may be further provided. In the cases of (3) and (4), the condition of (5) may be provided.
[0036]
In the present invention, the constituent materials of the field-effect transistor are not particularly limited, and any of the materials conventionally applied to the field-effect transistor can be suitably used.
[0037]
The material of the insulating support substrate may be any material as long as it has an insulating property and can support a field-effect transistor and a display element and a display panel formed thereon, and known materials such as glass, plastic, and quartz. Can be used, and more specifically, polyester, polycarbonate, polyimide, polyethersulfone, amorphous polyolefin, epoxy resin, glass and the like can be used. Among them, a polymer substrate is preferable, and polyester or polycarbonate is preferable in terms of strength, and particularly, polyester such as polyethylene terephthalate is preferable. The thickness of the insulating support substrate is preferably from 0.05 mm to 2 mm, more preferably from 0.1 mm to 1 mm.
[0038]
The constituent materials of the gate electrode, the source electrode, and the drain electrode are not particularly limited as long as they show conductivity, and any known materials can be used, for example, platinum, gold, aluminum, chromium, nickel, copper, titanium, and magnesium. Metal, such as calcium, barium, and sodium; conductive oxides such as InO ₂ , SnO ₂ , and ITO; polyaniline doped with camphorsulfonic acid, and polyethylenedioxythiophene doped with paratoluenesulfonic acid; Conductive polymers exhibiting good electrical conductivity, such as a conductive polymer having excellent electrical conductivity, carbon black, metal fine particles, and graphite powder are dispersed in a binder.
[0039]
Examples of a method for forming the gate electrode, the source electrode, and the drain electrode include a vacuum deposition method, a sputtering method, a coating method, a printing method, and a sol-gel method. Methods such as photolithography combined with etching with an inactive plasma, printing methods such as inkjet printing, screen printing, offset printing, letterpress printing, soft lithography methods such as microcontact printing, and methods combining a plurality of these methods. No. Further, it is also possible to directly form a pattern by irradiating an energy beam such as a laser or an electron beam to remove the material, or by changing the conductivity of the material.
[0040]
The thickness of the gate electrode, source electrode, and drain electrode is preferably 0.01 μm to 2 μm, more preferably 0.02 μm to 1 μm.
[0041]
The distance between the source electrode and the drain electrode (channel length L) is usually 100 μm or less, preferably 50 μm or less, the channel width W is usually 2000 μm or less, preferably 500 μm or less, and L / W is usually 0.1 μm or less. Or less, preferably 0.05 or less.
[0042]
As the insulator of the insulator layer, any insulator having an excellent insulating property and a relatively large relative permittivity so as to prevent current leakage to the gate electrode and to drive the field effect transistor at a low gate voltage can be used. Any known one can be used, for example, acrylic resin such as polymethyl methacrylate, polystyrene, polyvinyl phenol, polyimide, polycarbonate, polyester, polyvinyl alcohol, polyvinyl acetate, polyurethane, polysulfone, epoxy resin, phenol resin and the like. Polymers and copolymers thereof, oxides such as silicon dioxide, aluminum oxide, and titanium oxide; nitrides such as silicon nitride; ferroelectric oxides such as SrTiO ₃ and BaTiO _3; Particles such as materials and ferroelectric oxides Polymer film, and the like. Among them, epoxy resin, polyimide resin and acrylic resin are preferable. In addition, a photocurable resin that forms an insulator by applying a monomer as a precursor of the insulator and then irradiating light to cure the monomer is also preferably used.
[0043]
As a method for forming the insulator layer, a formation method suitable for the characteristics of the material, such as a coating method such as spin coating or blade coating, a vapor deposition method, a sputtering method, a printing method such as screen printing or inkjet printing, can be employed.
[0044]
Solvents that can be used when an insulator is dissolved in a solvent to form an insulator layer by a coating method include chain or cyclic hydrocarbons such as n-heptane, n-hexane, and decalin, and carbon tetrachloride. , Trichloroethylene, chloroform, halogenated hydrocarbons such as dichloromethane, p-xylene, toluene, m-cresol, aromatic compounds such as anisole, di-n-butyl ether, dimethoxyethane, tetrahydropyran, 1,4-dioxane, Chain or cyclic ethers such as tetrahydrofuran, alcohols such as 1-butanol and hexafluoro-2-propanol, ketone compounds such as 2-butanone, methyl ethyl ketone and cyclohexanone, N-methyl-2-pyrrolidone, dimethylformamide and the like Amide compounds, nitriles such as acetonitrile Such as compounds such, and the like.
[0045]
As described above, the insulator layer formed in this manner has an electric conductivity at room temperature of 10 ⁻¹² S / cm since it is related to the leakage current to the gate electrode and the low gate voltage driving of the field effect transistor. In the following, it is more preferable to show 10 ⁻¹⁴ S / cm or less, and to show a relative dielectric constant of 2.0 or more, and more preferably 2.5 or more.
[0046]
The thickness of such an insulator layer is preferably from 0.1 μm to 4 μm, more preferably from 0.2 μm to 2 μm.
[0047]
The organic semiconductor layer may have a metal content, furthermore, a residual solvent amount and an adsorbed water amount within the above-mentioned range, and the organic semiconductor forming the organic semiconductor layer is not particularly limited, and may be a π-conjugated low-molecular or high-molecular compound. Any known compounds can be used, for example, pentacene, oligothiophene, oligothiophene having a substituent, bisdithienothiophene, dialkylanthratithiophene having a substituent, metal phthalocyanine, benzoporphyrin, and fluorine-substituted. Copper phthalocyanine, N, N'-dialkyl-naphthalene-1,4,5,8-tetracarboxylic diimide-substituted product, 3,4,9,10-perylenetetracarboxylic dianhydride, N, N'-dialkyl- Π-conjugated system such as 3,4,9,10-perylenetetracarboxylic diimide, fullerene Π-conjugated polymers such as molecules and regioregular poly (3-alkylthiophene) typified by regioregular poly (3-hexylthiophene) and π-conjugated copolymers such as poly-9,9′-dialkylfluorencobithiophene Molecules.
[0048]
Among these π-conjugated low-molecular and high-molecular compounds, when an organic semiconductor layer is formed, the electric conductivity in the direction from the source electrode to the drain electrode is 10 ⁻⁴ S / cm or less and 10 ⁻¹² S / cm or more. Those having a value of 10 ⁻⁶ S / cm or less, 10 ⁻¹¹ S / cm or more, particularly 10 ⁻⁷ S / cm or less, and 10 ⁻¹⁰ S / cm or more are more preferable. Furthermore, among these π-conjugated low-molecular and high-molecular compounds, when an organic semiconductor layer is formed, the electric field effect mobility, the electric conductivity in the direction from the source electrode to the drain electrode, and the carrier density obtained from the charge element amount are higher. Those exhibiting 10 ⁷ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less are preferable, and those exhibiting 10 ⁸ cm ⁻³ or more and 10 ¹⁷ cm ⁻³ or less are more preferable. Among these π-conjugated low-molecular and high-molecular compounds, the activation energy required for charge transfer determined from the temperature dependence of the field-effect mobility at room temperature or lower when an organic semiconductor layer is formed is 0.2 eV or less. Are preferable, and those showing 0.1 eV or less are more preferable.
[0049]
Furthermore, among these π-conjugated small molecules, those having a molecular length of 40 ° or less, when the organic semiconductor layer is formed on the same insulator layer as the insulator layer used in the field-effect transistor, the The ratio of the p-polarized component to the s-polarized component of the absorption peak intensity derived from the transition moment in the direction of the molecular axis of these π-conjugated small molecules in the polarized light absorption measured by entering the incident light at an angle of 60 ° with respect to the normal. It is preferable that the p-polarized light component / s-polarized light component has a characteristic of 1.5 or more, more preferably 2.0 or more, and especially 3.0 or more.
[0050]
On the other hand, in the case of a π-conjugated polymer having a molecular length of greater than 40 °, when an organic semiconductor layer is formed on the same insulator layer as the insulator layer used for the field-effect transistor, light is incident on the layer surface in a vertical direction. In polarized light absorption measured with light, the ratio between the source-drain electrode direction component and the vertical direction component of the absorption peak intensity derived from the transition moment in the main chain direction of these π-conjugated polymers is measured. It is preferable to use a material having a property of exhibiting an electrode direction component / vertical direction component of 3.5 or more, more preferably 4.5 or more, and especially 5.0 or more.
[0051]
Further, among these π-conjugated low-molecular and high-molecular compounds, when an organic semiconductor layer is formed on the same insulator layer as the insulator layer used in the field-effect transistor, the distance between the nearest molecule or the polymer is reduced. Is preferably 3.9 ° or less, more preferably 3.85 ° or less, and particularly preferably 3.8 ° or less.
[0052]
The thickness of such an organic semiconductor layer is preferably from 1 nm to 10 μm, more preferably from 10 nm to 500 nm.
[0053]
As a method of forming an organic semiconductor layer using these organic semiconductors, in the case of a low molecular weight organic semiconductor, a method of forming by vapor deposition on an insulator layer or an insulating support substrate by vacuum vapor deposition, dissolving in a solvent Cast, dipping, spin coating, etc. In the case of a polymer organic semiconductor, a method of dissolving in a solvent and applying by casting, dipping, spin coating, or the like may be used. Further, there is also a method in which a layer is formed by a suitable method as described above using a target low molecular precursor or a target polymer precursor, and then converted into a target organic semiconductor layer by heat treatment or the like.
[0054]
Solvents that can be used when an organic semiconductor is dissolved in a solvent to form an organic semiconductor layer by a coating method include chain hydrocarbons such as n-heptane and n-hexane, carbon tetrachloride, trichloroethylene, chloroform, and dichloromethane. Such as halogenated hydrocarbons, aromatic compounds such as p-xylene, toluene, m-cresol, and anisole; and linear or cyclic ethers such as di-n-butyl ether, tetrahydropyran, 1,4-dioxane, and tetrahydrofuran. , Alcohols such as 1-butanol, ketone compounds such as 2-butanone, amide compounds such as N-methyl-2-pyrrolidone and dimethylformamide, nitrile compounds such as acetonitrile, carboxylic acids such as trifluoroacetic acid, etc. Is mentioned.
[0055]
The basic structure of the field-effect transistor of the present invention includes an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, and a source electrode and a drain electrode provided in contact with the organic semiconductor layer. Are provided on an insulating support substrate, and specific examples thereof include those shown in FIGS. 1 to 3. The field-effect transistor of the present invention has a structure shown in FIGS. Not limited to the field effect transistor described above, a layer other than the layers shown in FIGS. 1 to 3 may be further formed.
[0056]
For example, in a field-effect transistor in which an organic semiconductor layer is exposed as in the field-effect transistors shown in FIGS. 1 and 2, further protection is performed on the organic semiconductor to minimize the influence of the outside air on the organic semiconductor. A film may be formed. In this case, as a material of the protective film, a polymer such as an epoxy resin, an acrylic resin, polyurethane, polyimide, or polyvinyl alcohol, or an inorganic oxide or a nitride such as silicon oxide, silicon nitride, or aluminum oxide is used. Is mentioned. Examples of a method for forming the protective film include a coating method and a vacuum evaporation method.
[0057]
【The invention's effect】
As described above in detail, according to the field-effect transistor of the present invention, the amount of residual solvent, the amount of residual monomer and / or oligomer, or the amount of adsorbed moisture in the insulator layer is set to a specific value or less, or By setting the difference between the solubility parameter of the solvent A or the monomer A ′ used for forming the layer and the solvent B used for forming the organic semiconductor layer to be a specific value or more, the arrangement of the organic semiconductor molecules of the organic semiconductor layer to which the induced charge moves. Can be effectively suppressed, and a field effect transistor having higher mobility, higher on-current and lower leakage current, and higher on / off ratio can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structural example of a field-effect transistor.
FIG. 2 is a cross-sectional view illustrating a structural example of a field-effect transistor.
FIG. 3 is a cross-sectional view illustrating a structural example of a field-effect transistor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Insulating support substrate 2 Gate electrode 3 Insulator layer 4 Organic semiconductor layer 5 Source electrode 6 Drain electrode 7 Interface

Claims (15)

In a field-effect transistor including an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided to be in contact with the organic semiconductor layer, and an insulating support substrate. ,
The field effect transistor, wherein the insulator layer is a layer formed by a coating method using a solvent, and the amount of a residual solvent in the insulator layer is 1% by weight or less. 2. The solvent according to claim 1, wherein the insulator layer is a layer formed by a coating method using a solvent A, and the organic semiconductor layer is a layer formed by a coating method using a solvent B; A field effect transistor, wherein the difference in solubility parameter of B is 1.1 or more. In a field-effect transistor including an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided to be in contact with the organic semiconductor layer, and an insulating support substrate. ,
A field effect transistor, wherein the insulator layer is a layer formed by applying a monomer and then polymerizing the same, and the amount of residual monomer and / or oligomer in the insulator layer is 3% by weight or less. 4. The monomer according to claim 3, wherein the insulator layer is a layer formed by applying a monomer A ′ and then polymerizing the same, and the organic semiconductor layer is a layer formed by a coating method using a solvent B. A field effect transistor, wherein the difference between the solubility parameters of A ′ and the solvent B is 0.5 or more. In a field-effect transistor including an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided to be in contact with the organic semiconductor layer, and an insulating support substrate. ,
The insulator layer is a layer formed by a coating method using a solvent A, the organic semiconductor layer is a layer formed by a coating method using a solvent B, and the solubility parameter of the solvent A and the solvent B A field effect transistor wherein the difference is 1.1 or more. In a field-effect transistor including an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided to be in contact with the organic semiconductor layer, and an insulating support substrate. ,
The insulator layer is a layer formed by applying the monomer A ′ and then polymerizing the same, and the organic semiconductor layer is a layer formed by a coating method using the solvent B, and the monomer A ′ and the solvent B Wherein the difference in the solubility parameter is 0.5 or more. 7. The field effect transistor according to claim 1, wherein the amount of water adsorbed in the insulator layer is 1% by weight or less. In a field-effect transistor including an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided to be in contact with the organic semiconductor layer, and an insulating support substrate. ,
A field-effect transistor, wherein the amount of adsorbed water in the insulator layer is 1% by weight or less. 9. The device according to claim 1, wherein the gate electrode is provided on the insulating support substrate, and an organic semiconductor layer is provided on the gate electrode via an insulator layer. Field-effect transistor. 10. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are in contact with the insulator layer. The field effect transistor according to any one of claims 1 to 9, wherein the source electrode and the drain electrode are provided on the organic semiconductor layer. 9. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are provided on the insulating support substrate. 13. The method according to claim 1, wherein the insulating support substrate is a plastic substrate selected from the group consisting of polyester, polycarbonate, polyimide, Amosphas polyolefin, polyether sulfone, and epoxy resin. Field effect transistor. 14. The field effect transistor according to claim 1, wherein a relative dielectric constant of the insulator layer is 2.0 or more. The field-effect transistor according to any one of claims 1 to 14, wherein the electrical conductivity of the insulator layer is 10 ^-12 S / cm or less.

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