JP2004288836A - Organic thin film transistor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film transistor which shows less increase and/or dispersion in threshold voltage and less decrease and/or dispersion in the value of a current between a source and a drain, and a manufacturing method for the organic thin film transistor that improves the yield of the transistor. <P>SOLUTION: The organic thin film transistor comprises an organic semiconductor layer, a gate electrode formed above a channel area in the organic semiconductor layer, and the source/drain electrodes sandwiching the channel area. A thin film layer composed of electron donating organic molecules containing sulfur atoms is formed between the surface area of the source electrode or of the drain electrode and the channel area. The thin film layer of the transistor, which is composed of the electron donating organic molecules, is manufactured by making the organic molecules absorbed to the surface of the source electrode or drain electrode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００９７】
実施例１〜４の素子は、比較例１、２の素子に比べて、移動度、しきい値特性、ドレイン電流値ともに向上していることがわかる。
【００９８】
さらに、素子ごとの特性のばらつきを調べるために、実施例１〜４および比較例１と同様のＴＦＴをそれぞれ４素子ずつさらに作成し、各例について５素子ずつとして、それらのＶ_Ｇ＝−３０Ｖにおけるドレイン電流値を比較した。その結果をまとめると表２に示す通りである。

【００９９】
ソース電極およびドレイン電極表面にチオフェン化合物分子を吸着させた実施例１〜４の素子では、オン電流値が高く、しかも素子ごとの電流値のばらつきが小さかった。一方、比較例１、２の素子ではオン電流値は低かった。また比較例１では素子ごとの電流値のばらつきが大きかった。
【０１００】
実施例６
本実施例では、電子供与性を有する有機半導体としてレジオレギュラ・ポリ（３−ヘキシルチオフェン）を使用したこと、およびＳｉＯ_２ゲート絶縁層３の膜厚が約３５ｎｍでありその静電容量が１００ｎＦ／ｃｍ^２であることを除き、実施例１と同様にしてＴＦＴを作製した。すなわち、この例では、レジオレギュラ・ポリ（３−ヘキシルチオフェン）からなる分子吸着層６を形成させた後、同一物質であるレジオレギュラ・ポリ（３−ヘキシルチオフェン）を用いて有機半導体層７を形成させた。またチャネル長は２μｍ、チャネル幅は１００μｍである。有機半導体層７の形成は以下のようにして行った。
【０１０１】
分子吸着層６の形成に使用したものと同じく、予め２回再沈殿精製したレジオレギュラ・ポリ（３−ヘキシルチオフェン）を用いた。レジオレギュラ・ポリ（３−ヘキシルチオフェン）の４重量％クロロホルム溶液を調整し、溶液を０．２μｍ孔径のＰＴＦＥメンブレンフィルターによりろ過した。ろ過後の溶液を用いて、ゲート絶縁層３、分子吸着層６上にレジオレギュラ・ポリ（３−ヘキシルチオフェン）膜をスピンコートにより成膜し、有機半導体層７とした。スピンコートは基板を回転数２０００回転／分で３０秒間回転させて行った。この有機半導体層は特にパターニングしなかった。この素子を窒素ガス中、室温で２０分間乾燥させた。
【０１０２】
実施例７
本実施例では、分子吸着層６をＦｅＣｌ_３でドーピングしたことを除き、実施例６と同様にしてＴＦＴを作製した。分子吸着層へのドーピングは以下のようにして行った。
【０１０３】
分子吸着層６を吸着させた基板をＦｅＣｌ_３の０．００２重量％アセトニトリル溶液に３０秒間浸漬させたのち、アセトニトリルでリンスし、窒素ガスブローによってアセトニトリルを除去し、窒素ガス中で２時間乾燥させた。
【０１０４】
実施例８
本実施例では、分子吸着層６がレジオレギュラ・ポリ（３−オクチルチオフェン）であることを除き、実施例７と同様にしてＴＦＴを作製した。すなわち、この実施例では、レジオレギュラ・ポリ（３−オクチルチオフェン）からなる分子吸着層にＦｅＣｌ_３をドーピングした。
【０１０５】
比較例３
比較のため、金電極表面に分子吸着層６を形成せずにレジオレギュラ・ポリ（３−ヘキシルチオフェン）を有機半導体層７としたＴＦＴを作成した。金電極表面に分子吸着層を形成させなかったこと以外は、実施例６と同様にＴＦＴの作成を行った。
【０１０６】
実施例９
ＦＥＴ特性の測定
実施例６〜８および比較例３で作成した薄膜トランジスタのＦＥＴ電流−電圧特性を、半導体パラメーターアナライザー（ＨＰ社製：ＨＰ４１４５Ｂ）でそれぞれ測定した。測定はＴＦＴを窒素ガス雰囲気中に配置し、ソース電極を接地しドレイン電圧Ｖ_Ｄを−２０Ｖとした状態で、ゲート電圧Ｖ_Ｇを２Ｖ〜―２０Ｖと変化させた時のドレイン電流Ｉ_Ｄを測定した。実施例４と同様にデバイス特性を求めたところ、移動度μ、しきい値電圧Ｖ_Ｔ、電流オン・オフ比（Ｖ_Ｇ＝０Ｖ〜−２０Ｖの電流変調）、Ｖ_Ｇ＝−２０ＶでのＩ_Ｄはそれぞれ表３に示される通りになった。
【０１０７】

実施例６〜８の素子は比較例３の素子に対して、移動度、およびドレイン電流値がいずれも向上している。
【０１０８】
実施例１０
本実施例では、電子供与性を有する有機半導体としてジベンゾテトラチアフルバレンを使用したこと以外は、実施例４と同様にしてＴＦＴを作製した。有機半導体層７の形成は以下のようにして行った。
【０１０９】
ゲート絶縁層３、ソース電極４及びドレイン電極５上にジベンゾテトラチアフルバレン（レスペケミカル社製）を膜厚１５０ｎｍで蒸着して有機半導体層７を作成した。なおジベンゾテトラチアフルバレンは予めトルエンで再結晶を行い、さらに昇華精製を２回行ったものを使用し、１×１０^−６Ｔｏｒｒ（１．３３×１０^−３Ｐａ）の真空中、基板温度３０℃、蒸着速度０．０５ｎｍ／秒で蒸着した。この有機半導体層は特にパターニングしなかった。
【０１１０】
比較例４
比較のため、金電極表面に分子吸着層６を形成せずにジベンゾテトラチアフルバレンを有機半導体層７としたＴＦＴを作成した。金電極表面に分子吸着層を形成させなかったこと以外は、実施例１０と同様である。
【０１１１】
実施例１１
ＦＥＴ特性の測定
実施例１０および比較例４で作成した薄膜トランジスタのＦＥＴ電流−電圧特性を、実施例５と同様に測定した。実施例１０および比較例４のＴＦＴについてチャネル移動度μ、しきい値電圧Ｖ_Ｔ、３Ｖ〜−３０ＶのＶ_Ｇ変化に対する電流オン・オフ比を求めた結果は、それぞれ表４のようになった。
【０１１２】

実施例１０の素子は比較例４の素子に対して、移動度、およびドレイン電流値がいずれも向上している。
【０１１３】
【発明の効果】
以上説明したように本発明によれば、ソース電極またはドレイン電極と有機半導体層との界面における有機半導体結晶粒の大きさが揃い、かつソース電極またはドレイン電極との密着性が高められる結果、チャネル長が短い場合にもしきい値電圧が低くオン電流値が大きく、また素子毎の電気特性のばらつきが小さい有機薄膜トランジスタを作製することが可能となる。
【図面の簡単な説明】
【図１】本発明の薄膜トランジスタの一例を示す断面図。
【図２】本発明の薄膜トランジスタの製造方法の一例を示す図。
【図３】本発明の薄膜トランジスタの第１の変形例を示す図。
【図４】本発明の薄膜トランジスタの第２の変形例を示す図。
【図５】実施例１の薄膜トランジスタのデバイス特性を示す図。
【図６】実施例１の薄膜トランジスタのデバイス特性を示す図。
【符号の説明】
１ 基板
２ ゲート電極
３ ゲート絶縁層
４ ソース電極
５ ドレイン電極
６ 分子吸着層
７ 有機半導体層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic thin film transistor and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, thin film transistors (hereinafter, referred to as TFTs) using an organic semiconductor material made of a π-conjugated organic polymer or organic low molecule for a channel layer have been actively studied. For example, Jackson et al., A gate electrode layer made of nickel, SiO 2 on a glass substrate or a PET substrate.₂A gate insulating layer made of, a source electrode and a drain electrode made of palladium, and an organic semiconductor thin film made of pentacene on which a channel layer is formed are sequentially laminated to form a bottom-contact TFT having a channel length of 5 µm to 44 µm ( Non-patent document 1).
[0003]
However, in the TFTs of Jackson et al., The threshold voltage of the gate voltage greatly varies from element to element, and the range of variation extends to 10 V or more. Therefore, when the operating voltage of the element is as large as several tens of volts, 1 cm²Although the channel mobility of about / Vs is obtained, the source-drain current modulation (current on / off ratio) can be sufficiently obtained at an operating voltage of 10 V or less necessary for application to a liquid crystal display or the like. There is room for improvement because the current value between the source and the drain greatly varies depending on the element, for example, there is no current or the ON current between the source and the drain does not sufficiently flow.
[0004]
In an attempt to improve the source-drain current value, Wang et al. Formed a source electrode and a drain electrode made of gold on a highly doped n-type silicon substrate on which a thermal oxide film was formed, and made these gold electrodes. A TFT is reported in which a channel layer is formed by adsorbing an electron-accepting 2-mercapto-5-nitrobenzimidazole molecule on an electrode surface and then depositing pentacene (Non-Patent Document 2).
[0005]
Wang et al. Formed an electron-transfer complex between an electron-donating pentacene molecule and an electron-accepting 2-mercapto-5-nitrobenzimidazole molecule at the interface between a source electrode and a drain electrode and a pentacene thin film. An attempt was made to reduce the junction resistance between pentacenes. However, the increase of the on-current value between the source and the drain was as low as about 1.5 times. In addition, the device of Wang et al. Has a long channel length of 44 μm, and when thiol having a donor property is used, the effect of reducing the junction resistance of the device is not obtained.
[0006]
For this reason, in an organic TFT having a low operating voltage with a channel length of 30 μm or less, particularly important with a channel length of 10 μm or less, it has been an important issue to improve and stabilize the device performance.
[0007]
By the way, among the organic semiconductor materials used in the organic TFT, a material having a high operating voltage and a high channel mobility is a crystalline low molecular material such as the above-mentioned pentacene or tetracene, or a π-conjugated high molecular material. Also have high crystallinity, such as regioregular poly (3-hexylthiophene), more specifically, there is no cleavage of the π-conjugated system due to twisting of the polymer main chain, and crystalline grains are formed by interaction between polymers. Limited to materials that can develop in the thin film.
[0008]
In order to manufacture a high-performance transistor using such a crystalline organic semiconductor material, it is necessary to grow a crystal grain of an organic thin film layer in a channel region to a large extent and to perform channel movement such as trapping and scattering of carriers by a grain boundary. It is important to improve the channel mobility by reducing the cause of the decrease in the mobility and increasing the adhesion between the organic crystal grains and the surface of the gate insulating layer at the interface between the gate insulating layer and the organic thin film layer, which will be the channel region. is there.
[0009]
Further, it is necessary to reduce the junction resistance between the gate or drain electrode and the organic semiconductor layer in the channel region in order to reduce the threshold voltage and stabilize the device performance. In particular, in the case of the above-described bottom-contact type device, a step of forming an organic semiconductor layer after forming a source electrode and a drain electrode in the device fabrication is included. Alternatively, it is important to make the organic semiconductor crystal grains large at the interface between the drain electrode and the organic semiconductor layer and to improve the adhesion between the crystal grains and the source electrode or the drain electrode.
[0010]
Here, a transistor structure usually adopted for an organic TFT will be described. The transistor structure of an organic TFT is a bottom-contact type element in which a gate electrode, a gate insulating layer, a source electrode and a drain electrode are sequentially stacked on a substrate, and then an organic semiconductor layer is stacked thereon. After the layers and the organic semiconductor layer are sequentially laminated, a top contact element on which a source electrode and a drain electrode are formed, and a source electrode and a drain electrode, an organic semiconductor layer, a gate insulating layer, and a gate electrode are sequentially laminated on a substrate. It is roughly divided into top gate type devices.
[0011]
From the point of device fabrication, it can be adopted depending on the process resistance of the organic material used for the organic semiconductor layer, that is, the resistance of the organic semiconductor material to processes related to formation of an electrode layer and an insulating layer on the organic semiconductor layer. Although the element structure is almost limited, a bottom contact type element having the least process load on the organic semiconductor layer can be applied to many organic semiconductor materials. In terms of element performance, it can be generally expected that a bottom contact element having no current path crossing the thickness direction of the organic semiconductor layer will have excellent performance.
[0012]
However, as described above, in order to improve the device characteristics of the bottom contact type device in which the organic semiconductor layer is formed after the formation of the source electrode and the drain electrode, or to improve the device characteristics of the top gate type device, the channel region must be formed during the formation of the organic semiconductor layer. It is important to control the structure of the organic semiconductor crystal grains in the vicinity of the source electrode or the drain electrode in addition to controlling the structure of the organic semiconductor crystal grains in the above.
[0013]
Such control of the organic crystal grain structure near the source electrode or the drain electrode becomes more important as the channel length of the TFT becomes shorter. That is, in the equivalent circuit of the TFT, the effect of the electrode / organic semiconductor junction resistance becomes remarkable in a short channel, and the disorder of the organic crystal grains at the electrode interface causes the disorder of the crystal grains in a wide portion of the channel region. As a result, the channel mobility itself is reduced.
[0014]
However, in the prior art, the control of the organic crystal grain structure at the electrode interface was not performed, so that the threshold voltage was increased or varied, and the apparent channel mobility was lowered, so that the source-drain current value was reduced. There is a problem in that, in particular, a short channel and a low operating voltage of an organic TFT which is important in application are significant.
[0015]
[Non-patent document 1]
1999 International Electron Devices Meetings Technical Digest (1999) 111
[Non-patent document 2]
41^st  Electronic Materials Conference Digest (1999) 16
[0016]
[Problems to be solved by the invention]
As described above, in order to improve the characteristics of the organic TFT, it is important to reduce the junction resistance between the source or drain electrode and the organic semiconductor layer. For that purpose, the interface between the source or drain electrode and the organic semiconductor layer is required. It is considered effective to make the crystal grains of the organic semiconductor layer large in (1) and to improve the adhesion between the crystal grains and the source electrode or the drain electrode. However, in the related art, since the control of the organic crystal grains at the electrode interface is not performed, the decrease and the variation of the source-drain current value appear due to the increase and the variation of the threshold voltage and the apparent decrease of the channel mobility. There was something. Since such a variation causes a reduction in product yield in an actual manufacturing process, it has been desired to reduce the variation.
[0017]
The present invention has been made in view of such a problem, and an organic thin film transistor having a large on-current value between a source and a drain, a large current on / off ratio, and a small variation in characteristics among elements, and It is an object of the present invention to provide a method of manufacturing the same.
[0018]
[Means for Solving the Problems]
The organic thin film transistor of the present invention,
An organic semiconductor layer made of a crystalline organic semiconductor material having an electron donating property,
A gate electrode formed on a channel region in the organic semiconductor layer via a gate insulating layer,
An organic thin-film transistor comprising a source electrode and a drain electrode sandwiching the channel region,
A thin film layer comprising an electron-donating organic molecule containing a sulfur atom between the surface region of the source electrode or the drain electrode and the channel region, wherein the electron-donating organic molecule is a surface region of the source electrode or the drain electrode; Is characterized by being adsorbed to
[0019]
The manufacturing method of the organic thin film transistor of the present invention,
An organic semiconductor layer made of a crystalline organic semiconductor material having an electron donating property,
A gate electrode formed on a channel region in the organic semiconductor layer via a gate insulating layer,
A source electrode and a drain electrode sandwiching the channel region;
A method for manufacturing an organic thin film transistor, comprising: adsorbing a sulfur atom-containing electron-donating organic molecule on a surface region of the source electrode or the drain electrode to convert the sulfur atom-containing electron-donating organic molecule from Forming a thin film layer, and forming the organic semiconductor layer on a surface region of a source electrode or a drain electrode on which the sulfur-containing electron donating organic molecules are adsorbed. Things.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
FIG. 1 is a schematic sectional view showing an example of the organic thin film transistor of the present invention.
[0022]
For example, the organic thin-film transistor shown in FIG. 1 has a gate electrode 2 formed on a substrate 1 and a gate insulating layer 3 formed on the substrate 1 so as to cover the gate electrode 2. . On the gate insulating layer 3, a source electrode 4 and a drain electrode 5 are formed separately so as to avoid a portion immediately above the gate electrode 2. Further, a molecule adsorption layer 6 made of an electron-donating organic molecule containing a sulfur atom is formed on the surface region of the source electrode 4 and the drain electrode 5. Further, an organic semiconductor layer 7 made of a crystalline organic semiconductor material having an electron donating property is formed so as to cover the gate insulating layer 3 and the molecular adsorption layer 6.
[0023]
Among the sulfur-containing electron-donating organic molecules forming the molecular adsorption layer 6, the molecules in contact with the surface of the source electrode 4 or the drain electrode 5 are connected to the source electrode 4 and the source electrode 4 via the sulfur atoms in the molecular skeleton. It is adsorbed on the surface area of the drain electrode 5.
[0024]
The wettability of the surfaces of the source electrode 4 and the drain electrode 5 changes in a hydrophobic direction due to the adsorption of the molecular adsorption layer 6. Alternatively, minute irregularities on the electrode surface are reduced. It is considered that as a result of these effects, the electrode surface is modified into a surface having a strong affinity for the organic semiconductor material, and as a result, an electrode-organic semiconductor interface having high adhesion to the organic semiconductor crystal grains is formed.
[0025]
More specifically, the most important part at the electrode-organic semiconductor interface for improving device characteristics is the surface area of the electrode cross section close to the channel area among the surface areas of the source electrode 4 and the drain electrode 5, and An important part is a surface region of the electrode upper surface close to the electrode cross section. By modifying the surface characteristics of these surface regions, the particle size can be reduced even over the connection region between the channel region and the above-described electrode cross section during the formation of the organic semiconductor layer, and further over the electrode top portion connected to the electrode cross section. Large organic semiconductor crystal grains are formed densely with good adhesion to the electrode.
[0026]
In terms of electrical characteristics, since the organic molecules constituting the molecular adsorption layer 6 have an electron donating property, holes can be easily transferred to the organic semiconductor layer 7 having an electron donating property. Also, the movement of holes between the electrode and the molecule adsorption layer is easy. Therefore, the presence of the molecular adsorption layer 6 does not cause a significant decrease in the current value between the source and the drain. Rather, it is considered that the current value is improved by improving the adhesion between the organic semiconductor layer and the electrode as described above.
[0027]
In particular, it is desirable that the ionization potential of the electron-donating organic molecules constituting the molecule-adsorbing layer 6 in a single-molecule state be 9 electron volts (eV) or less. The fact that the ionization potential in a single-molecule state is 9 eV or less corresponds to approximately 8 eV or less when converted into an ionization potential in an aggregated state such as a solid state. On the other hand, the solid state ionization potential of an organic semiconductor material having an electron donating property is generally 4 eV to 8 eV, and an electrode material having a work function in this range is usually used. Therefore, if the ionization potential of the electron-donating organic molecule in a single-molecule state is 9 eV or less, holes can be easily transferred from the source electrode 4 or the drain electrode 5 to the organic semiconductor layer 7. If the voltage is larger than 9 eV, care must be taken because holes may not be smoothly moved from the source electrode or the drain electrode to the organic semiconductor layer.
[0028]
Specific examples of the organic molecules constituting the molecular adsorption layer 6 include a thiophene compound molecule having an electron donating property and a thiol compound molecule having an electron donating property. More specifically, a thiophene monomer (ionization potential I in one molecular state I = 8.87 eV, hereinafter similarly described), a 3-alkylthiophene monomer (8 eV <I <8.87 eV), bithiophene (8 eV), α- Tarthienyl (7 eV), α-quarterthiophene (5 eV <I <6 eV), α-sexithiophene (5.2 eV), α, ω-dihexylquaterthiophene (5 eV <I <6 eV), α, ω-dihexylsecithiophene ( 5eV), poly (3-alkylthiophene) (5eV), poly (3-phenylthiophene) (5eV), poly (3-phenyl-4-methylthiophene) (5eV), poly (3-cyclohexylthiophene) (5eV) , 4,4'-biphenyldithiol (8 eV <I <9 eV), thiofenthi Lumpur (8eV <I <9eV), p-thiocresol (8eV <I <9eV), and 2,5-diamino-1,4 can be exemplified benzenethiol (7 eV). However, the materials listed here are only examples, and the present invention is not limited to these.
[0029]
Note that the molecular adsorption layer 6 may be doped to increase the conductivity of the molecular adsorption layer 6 and facilitate the movement of holes from the source electrode or the drain electrode to the organic semiconductor layer. For example, when the molecular adsorption layer 6 is made of poly (3-alkylthiophene), iron trichloride (FeCl 3)₃), Iodine, perchloric acid, tetracyanoethylene, dicyanodichlorobenzoquinone, or the like, the molecule-adsorbing layer 6 may be doped to increase the conductivity.
[0030]
As an electrode material of the source electrode 4 and the drain electrode 5, it is preferable to use gold, silver, copper, platinum or palladium in order to facilitate the adsorption of electron donating organic molecules. However, the material is not limited to these, and any material may be used as long as the electron-donating organic molecule can be adsorbed on the electrode surface via a sulfur atom in the molecule.
[0031]
Further, an electrode material in which an electron-donating organic molecule can be adsorbed via a sulfur atom in the molecule and an electrode material in which the electron-donating organic molecule cannot be adsorbed may be used in the electrode layer. In this case, it is sufficient that the electrode material capable of adsorbing the adsorbed molecules is exposed on the surface of the electrode. In particular, it is desirable that a material capable of adsorbing an electron donating organic molecule via a sulfur atom is exposed on the surface of the electrode cross section. For example, as a two-layer structure of an electrode material capable of adsorbing electron-donating organic molecules and an electrode material capable of not adsorbing, an electrode material capable of adsorbing electron-donating organic molecules is exposed only at the electrode cross section, and a molecular adsorption layer is formed only at the electrode cross section. 6 may be formed.
[0032]
Further, regarding the shape of the electrode, in FIG. 1, the cross section of the electrode close to the channel region is almost perpendicular to the surface of the gate insulating layer. In order to grow the electrode with good adhesion, the electrode cross section may be tapered. That is, the angle between the gate insulating layer surface in the channel region and the electrode cross section may be larger than 90 degrees. Further, the electrode cross section need not be a flat surface, but may be a curved surface having a substantially tapered shape.
[0033]
The contact angle of the electrode surface on which the molecular adsorption layer 6 is formed with pure water is desirably 55 degrees or more.
[0034]
Examples of the electron-donating crystalline organic semiconductor material constituting the organic semiconductor layer 7 include polycyclic aromatic molecular materials such as pentacene, tetracene, anthracene, perylene, pyrene, coronene, chrysene, decacyclene, and biolanthrene, phthalocyanine, triphenylene, and thiophene. Oligomers and their derivatives, tetrathiafulvalenes such as dibenzotetrathiafulvalene, tetrathiotetracene, and regioregular poly (3-alkylthiophene) can be mentioned. However, the present invention is not limited thereto, and any crystalline organic semiconductor material having an electron donating property may be used as the electron donating crystalline organic semiconductor material constituting the organic semiconductor layer 7 of the present invention. Can be.
[0035]
Next, an example of a method for manufacturing an organic thin film transistor of the present invention will be described with reference to the drawings.
[0036]
FIG. 2 is a process chart showing an example of a manufacturing process of the transistor shown in FIG.
[0037]
A gate electrode 2, a gate insulating layer 3, a source electrode 4, and a drain electrode 5 are sequentially formed on a substrate 1 (FIG. 2A).
[0038]
The gate electrode layer is made of a known conductive material such as a metal material such as Cr, Al, Ta, Mo, Nb, Cu, Ag, Au, Pt, Pd, In, Ni or Nd, an alloy material thereof, or a carbon material. Any film can be used without any particular limitation. For example, the film may be formed to a thickness of about 10 nm to about 500 nm by a sputtering method, an evaporation method, or the like. Alternatively, a gate electrode layer may be formed by removing a liquid component by drying or the like using a polymer mixture in which conductive particles such as silver ink or graphite ink are dispersed together with a polymer in a liquid. An electrode layer having a thickness of about 30 nm to about 1000 nm can be formed. As the conductive material, a soluble conductive polymer such as polyaniline salt, poly (3,4-ethylene-dioxythiophene) polystyrene sulfonate, or doped polypyrrole can be used for the electrode layer material. Also in this case, an electrode layer having a thickness of about 30 nm to about 1000 nm can be formed by coating.
[0039]
Furthermore, a method in which a solvent in which metal fine particles having a particle size of several nm to several tens nm are dispersed is applied, and a metal thin film is obtained by a process at a substrate temperature of less than 400 ° C. may be used. Examples of materials that enable such a method include Au paste (trade name Perfect Gold, manufactured by vacuum metallurgy), Ag paste (trade name Perfect Silver, manufactured by vacuum metallurgy), and Cu paste (trade name Perfect Copper, manufactured by vacuum metallurgy) ). The above-mentioned electrode materials may be used alone, or a plurality of types may be used in combination.
[0040]
Furthermore, the gate electrode layer 2 may be made of highly doped silicon. In particular, when a silicon substrate used in a normal LSI process is used, the region near the surface of the silicon substrate where the gate insulating layer is formed or the entire silicon substrate only needs to be highly doped. In this case, the silicon substrate is used as the gate electrode layer. 2 and the substrate 1 may be used, or a silicon substrate may be separately attached to a plastic substrate or a glass substrate.
[0041]
As the material used for the gate insulating layer 3, various insulating materials such as inorganic or organic materials can be used. The method of forming a thin film also depends on the material, such as vapor deposition, sputtering, anodic oxidation of the electrode layer 2, coating, and solution. Various film formation methods, such as adhesion from the surface, can be adopted.
[0042]
Specifically, for example, SiO 2 is used as the inorganic material.₂, SiO, Al₂O₃, Ta₂O₅, ZrO₂And a composite oxide such as strontium titanate and strontium barium titanate, and a nitride such as SiNx. These materials can be formed into a film by a commonly used method such as a sputtering method, an evaporation method, and a CVD method.
[0043]
Various complex oxides and single metal oxides can also be formed into a film by a sol-gel method utilizing hydrolysis of an alcoholate. As a material that enables such a method, for example, a MOD coat material (trade name, manufactured by Kojundo Chemical Co., Ltd.) can be mentioned.
[0044]
Furthermore, Ta₂O₅And Al₂O₃Can be formed by anodizing the Ta or Al electrode layer using an electrolyte such as an aqueous solution of ammonium borate with the gate electrode layer 2 being Ta or Al, respectively.
[0045]
When a single metal oxide or a composite oxide is used as the inorganic material, a hydrophilic oxide surface is coated with an alkyltrichlorosilane such as octadecyltrichlorosilane in order to enhance the adhesion between the oxide surface and the organic semiconductor material. It is desirable to modify the hydrophobic surface with octadecyltrimethoxysilane and other alkyltrimethoxysilanes, fluorinated alkyltrimethoxysilanes, hexamethyldisilazane, and other silylating agents.
[0046]
Note that the inorganic materials mentioned here are merely examples, and the present invention is not limited to these.
[0047]
Organic materials that can be used for the gate insulating layer 3 include polyvinyl phenol, polymethyl methacrylate, polystyrene, polyimide, benzocyclobutene, cyanoethyl pullulan (trade name Cyanoresin, manufactured by Shin-Etsu Chemical Co., Ltd.), polyvinylidene fluoride, and vinylidene-4. Examples include fluorinated ethylene copolymers and other polymer materials. For these materials, a solution dissolved in an appropriate solvent or a solution in which a precursor is dissolved is applied by a spin coating method, a screen printing method, or the like, and then the solvent is removed by volatilization, or the solvent is removed by volatilization. By converting the precursor into a desired polymer by heating, an insulating layer having a thickness of about 50 nm to about 500 nm can be formed. A cross-linking agent may be mixed into a solvent, and the film may be cross-linked by heating after film formation to improve process resistance.
[0048]
Furthermore, cholic acid, methyl cholate, and other organic low molecular weight amorphous materials may be used for the gate insulating layer 3. In this case, an insulating layer having a thickness of about 10 nm to about 500 nm can be easily formed by a vacuum evaporation method.
[0049]
Note that the organic materials mentioned here are merely examples, and the present invention is not limited to these.
[0050]
As a method for forming the source electrode 4 and the drain electrode 5, a photoetching process or a lift-off process usually used in a semiconductor process can be used. Thereby, an electrode pattern having a short channel length, preferably 30 μm or less, more preferably 0.5 μm to 10 μm can be formed. By shortening the channel length, the effect of the present invention is more strongly exhibited.
[0051]
Further, as described above with respect to the gate electrode layer forming method, a method in which a solvent in which metal fine particles having a particle size of about several nm to several tens of nm are dispersed is applied and a metal thin film is obtained by a process at a substrate temperature of less than 400 ° C. The source electrode 4 and the drain electrode 5 may be formed. Materials that enable such a method include, for example, Au paste (trade name: Perfect Gold, manufactured by vacuum metallurgy), Ag paste (trade name: Perfect Silver, manufactured by vacuum metallurgy), and Cu paste (trade name: Perfect Copper, manufactured by vacuum metallurgy) ).
[0052]
As a method of forming the electrode patterns of the source electrode 4 and the drain electrode 5 with such a solvent, for example, a solvent adhesion method such as a screen printing method, an ink jet printing method, and a microcontact printing method may be mentioned. An electrode pattern having a channel length of about 10 μm to about 20 μm can be formed by screen printing or inkjet printing. Also, an electrode pattern having a channel length of about 1 μm to about 10 μm can be formed by microcontact printing.
[0053]
In particular, when an electrode pattern is formed using an inkjet printing method, the surface of the gate insulating layer 3 is patterned into a hydrophilic portion and a hydrophobic portion, and a solvent is selectively attached to the surface of the gate insulating layer 3. This is effective for forming a clear electrode pattern. It is also effective to form a clear electrode pattern by patterning the surface of the gate insulating layer 3 with irregularities and selectively attaching a solvent to the recesses on the surface of the gate insulating layer 3.
[0054]
Note that the electrode materials and the formation methods described here are merely examples, and the present invention is not limited to these.
[0055]
Next, a molecular adsorption layer 6 is formed on the electrode surfaces of the source electrode 4 and the drain electrode 5 (FIG. 2B).
[0056]
The method for forming the molecule adsorption layer 6 is not particularly limited, but it can be performed by bringing a liquid, gas or solid containing adsorbed molecules into contact with the electrode surface. In particular, when the adsorbed molecule is a solid or liquid at normal temperature and normal pressure, it is preferable to dissolve the adsorbed molecule in an appropriate solvent and bring the solution into contact with the electrode surface for adsorption. Alternatively, after the solid-state adsorbed molecules are attached to the electrode surface, the temperature of the electrode surface may be raised to make the adsorbed molecules in a molten state and adsorbed on the electrode surface. Further, it is also possible to form a molecular adsorption layer by rubbing a solid composed of adsorbed molecules on the electrode surface. Further, it is also possible to form the adsorbed molecular layer 6 on a liquid surface such as water and transfer it to the electrode surface, that is, the so-called Langmuir-Blodgett method. Further, in order to effectively perform the adsorption, the molecules may be adsorbed while applying a potential to the electrode surface. However, the method described here is an example, and the present invention is not limited to these methods.
[0057]
In order to increase the conductivity of the molecule adsorption layer 6 and facilitate the transfer of holes from the source electrode or the drain electrode to the organic semiconductor layer, the molecule adsorption layer 6 can be doped with electron donating molecules. As a specific method, a method of exposing the molecule-adsorbing layer 6 to a gas of electron-donating molecules serving as a dopant, or a method of immersing the molecule-adsorbing layer 6 in a solution containing electron-donating molecules serving as a dopant can be considered. . However, any method can be used as long as it can bring the molecule-adsorbing layer 6 into contact with an electron-donating molecule serving as a dopant, and is not limited to the method described here.
[0058]
Next, an organic semiconductor layer 7 is formed (FIG. 2C).
[0059]
Examples of a method for forming the organic semiconductor layer 7 include a vapor deposition method and other dry processes, a spin coating method, a casting method, a screen printing method, an inkjet printing method, a microcontact printing method, and other wet processes. Further, after forming a thin film of a precursor of the organic semiconductor material constituting the organic semiconductor layer by a dry process or a wet process, the organic semiconductor layer is formed by converting into a desired organic semiconductor material by a treatment such as heating. Is also good.
[0060]
Next, a modified example of the transistor of the present invention will be described with reference to FIGS. Note that the materials, shapes, film formation methods, and the like of the components are the same as those of the transistor illustrated in FIG. 1, and thus detailed description is omitted.
[0061]
The transistor shown in FIG. 3 has a source electrode 4 and a drain electrode 5 formed on a substrate 1, and a molecular adsorption layer 6 formed on the surface of the source electrode 4 and the drain electrode 5. Further, an organic semiconductor layer 7 is formed so as to cover the source electrode 4 and the drain electrode 5 on which the surface of the substrate 1 and the molecular adsorption layer 6 are formed. Further, a gate insulating layer 3 is formed immediately above the organic semiconductor layer portion sandwiched between the source electrode 4 and the drain electrode 5. Even with this structure, the formation of the molecular adsorption layer 6 improves the junction characteristics between the source electrode 4 and the drain electrode 5 and the organic semiconductor layer 7, thereby improving the device characteristics. can get.
[0062]
In the transistor shown in FIG. 4, a gate electrode 2 and a gate insulating layer 3 are sequentially formed on a substrate 1, and a source electrode 4 is formed on the gate insulating layer 3 so as to avoid a portion immediately above the gate electrode 2. . Further, a molecule adsorption layer 6 is formed on the surface of the source electrode 4. Further, an organic semiconductor layer 7 is formed so as to cover the source electrode 4 on which the molecular adsorption layer 6 is formed and the gate insulating layer 3. Further, a drain electrode 5 is formed on the organic semiconductor layer 7. In this element, a region near the surface of the gate insulating layer 3 in the organic semiconductor layer between the source electrode and the drain electrode becomes a channel region, and an electric field effect appears.
[0063]
Even with this structure, the effect of the present invention that the junction characteristics between the source electrode 4 and the organic semiconductor layer 7 are improved and the device characteristics are improved due to the formation of the molecular adsorption layer 6 can be obtained. .
[0064]
In FIG. 4, the drain electrode 5 is formed up to just above the source electrode 4 via the organic semiconductor layer 7 and the molecular adsorption layer 6. It is excellent in that fine positioning of the electrode pattern is not required when forming the drain electrode 5. In this case, an insulating layer is formed only on the upper surface of the source electrode 4 to reduce an off-current flowing through an overlapping portion between the source electrode 4 and the drain electrode 5, and a section of the source electrode close to the channel region is exposed. An element structure in which the molecular adsorption layer 6 is formed only in the surface region of the cross section may be used.
[0065]
Of course, the drain electrode 5 may be separately formed so as to avoid the portion immediately above the source electrode 4. Further, a structure in which the source electrode 4 and the drain electrode 5 are replaced in FIG. 4 may be used.
[0066]
1 and 3, the molecular adsorption layer 6 may be formed only on one of the surfaces of the source electrode 4 and the drain electrode 5. Among the source electrode-organic semiconductor junction or the drain electrode-organic semiconductor junction, the effect of the present invention is exerted if a molecular adsorption layer is formed at the junction that is rate-limiting with respect to the electrical characteristics of the device.
[0067]
Further, a passivation layer can be formed on the surface of the transistor as shown in FIG. 1, FIG. 3, or FIG. 4, so that the element can be protected from water vapor, oxygen, or the like existing in the use atmosphere.
[0068]
For the passivation layer, various insulating inorganic materials and insulating organic materials can be used. For example, it is conceivable to form a passivation layer with a UV curable resin in a nitrogen dry atmosphere. Examples of the organic material include polymers such as polyvinyl alcohol and ethylene vinyl alcohol copolymer. Examples of the inorganic material include SiOx, SiNx, and SiOxNy formed by a sputtering method. However, it is not limited to these materials.
[0069]
【Example】
Hereinafter, examples of the present invention will be described as follows.
[0070]
Example 1
In the present invention, the method shown in FIG. 2 is adopted, wherein pentacene having an electron donating property is used as an organic semiconductor, a gold thin film is used as a source electrode and a drain electrode, and a regioregular compound having an electron donating molecule as a molecule adsorbed on the gold thin film is used. A thin film transistor was formed on a silicon substrate using poly (3-hexylthiophene) as follows.
[0071]
About 50 nm thick thermally oxidized SiO2 on the surface of a highly doped n + type Si wafer (resistance value 0.03 Ωcm)₂A film was formed, and a Cr layer having a thickness of 3 nm and an Au layer having a thickness of 100 nm were continuously deposited on the back surface in a vacuum. SiO serving as gate insulating layer 3₂Has a capacitance of 70 nF / cm²Met.
[0072]
Next, SiO₂A source electrode 4 and a drain electrode 5 made of gold were formed on the gate insulating layer 3 by lift-off. Each of the source electrode 4 and the drain electrode 5 includes a stripe-shaped portion having a width of 100 μm and a length of 2 mm and a 1-mm square pad portion for making electrical contact. The short sides are arranged at intervals of 2 μm. That is, the TFT has a channel length of 2 μm and a channel width of 100 μm. In forming the source electrode 4 and the drain electrode 5, a gate insulating layer of SiO₂2 × 10^-6Torr (2.66 × 10^-3After evaporating Cr to a thickness of 3 nm in a vacuum of Pa), Au was subsequently evaporated to a thickness of 50 nm in a vacuum. The deposition rates were Cr: 0.1 nm / s and Au: 0.5 nm / s. In order to measure the contact angle on the gold surface, a pad-shaped gold thin film portion of 5 mm square was formed near the source electrode 4 and the drain electrode 5 simultaneously with the formation of the source electrode 4 and the drain electrode 5.
[0073]
Next, SiO₂In order to hydrophobize the surface of the channel region on the gate insulating layer 3, the surface of the channel region was exposed to vapor of hexamethyldisilazane (trade name: OAP, manufactured by Tokyo Ohka) for 24 hours.
[0074]
Next, in order to remove unreacted hexamethyldisilazane adhering to the surfaces of the source electrode and the drain electrode, the substrate was ultrasonically washed in acetone for 40 minutes, and then dried at 100 ° C. for 10 minutes on a hot plate. Removal of unreacted hexamethyldisilazane was confirmed by a change in contact angle of the gold surface with pure water. That is, the contact angle before the ultrasonic cleaning was about 66 degrees, while the contact angle after the cleaning was about 52 degrees. This value was close to the actually measured contact angle of about 48 degrees before the hexamethyldisilazane treatment of the gold surface.
[0075]
Next, a molecular adsorption layer 6 made of regioregular poly (3-hexylthiophene) (manufactured by Aldrich) was formed on the surfaces of the source electrode and the drain electrode. Poly (3-hexylthiophene) used was obtained by performing reprecipitation purification twice using chloroform as a good solvent and methanol as a poor solvent in advance. The substrate was immersed in a 0.1% by weight chloroform solution of regioregular poly (3-hexylthiophene) for 15 hours, rinsed with chloroform, and further immersed in chloroform for 20 minutes. Thereafter, chloroform was removed by blowing nitrogen gas, and drying was performed in nitrogen gas for 2 hours. The contact angle of the gold surface with the pure water after the formation of the molecular adsorption layer 6 was about 95 degrees.
[0076]
Next, pentacene (manufactured by Aldrich), which is an organic semiconductor material having an electron donating property, was deposited to a thickness of 80 nm on the gate insulating layer 3, the source electrode 4, and the drain electrode 5 to form an organic semiconductor layer 7. Note that pentacene, which had been subjected to sublimation purification twice, was used.^-6Torr (1.33 × 10^-3In a vacuum of Pa), vapor deposition was performed at a substrate temperature of 80 ° C. and a vapor deposition rate of 0.03 nm / sec. This organic semiconductor layer was not particularly patterned.
[0077]
The pentacene thin film of the manufactured TFT was observed by AFM. In a channel region having a channel length of 2 μm and a channel width of 100 μm, pentacene crystal grains having a grain size of about 1 to about 2 μm and having a substantially uniform size were densely grown up to the contact portions with the source electrode and the drain electrode. The number of pentacene crystal grains in the channel length (2 μm) direction was about 1 to 2.
[0078]
Example 2
A thin film transistor was manufactured in the same manner as in Example 1, except that 3-n-dodecylthiophene, which is an electron donating molecule, was used as a molecule adsorbed on the surface of the source electrode and the drain electrode made of a gold thin film. The adsorption of 3-n-dodecylthiophene on the surface of the gold electrode was performed as follows. The substrate was immersed in a 1 mM ethanol solution of 3-n-dodecylthiophene (Tokyo Kasei) for 10 hours, rinsed with ethanol, and further immersed in ethanol for 10 minutes. After that, ethanol was removed by blowing nitrogen gas, and dried in nitrogen gas for 2 hours. The contact angle of the gold surface after the formation of the molecular adsorption layer 6 with pure water was about 90 degrees.
[0079]
In order to ensure the same conditions as in Example 1, the deposition of Cr and Au and the deposition of a pentacene thin film during the formation of the source and drain electrodes were performed simultaneously with Example 1.
[0080]
When the pentacene thin film of the manufactured TFT was observed by AFM, a pentacene thin film almost similar to that of Example 1 was formed.
[0081]
Example 3
A thin film transistor was manufactured in the same manner as in Example 1, except that α-terthienyl, which is an electron donating molecule, was used as a molecule adsorbed on the surface of the source electrode and the drain electrode composed of a gold thin film. The adsorption of α-terthienyl on the surface of the gold electrode was performed as follows. The substrate was immersed in a 1 mM ethanol solution of α-tarthienyl (manufactured by Aldrich) for 20 hours, rinsed with ethanol, and further immersed in ethanol for 10 minutes. After that, ethanol was removed by blowing nitrogen gas, and dried in nitrogen gas for 2 hours. The contact angle of the gold surface after the formation of the molecular adsorption layer 6 with pure water was about 70 degrees.
[0082]
In order to ensure the same conditions as in Example 1, the deposition of Cr and Au and the deposition of a pentacene thin film during the formation of the source and drain electrodes were performed simultaneously with Example 1.
[0083]
When the pentacene thin film of the manufactured TFT was observed by AFM, a pentacene thin film almost similar to that of Example 1 was formed.
[0084]
Example 4
A thin film transistor was fabricated in the same manner as in Example 1 except that α, ω-dihexylquaterthiophene, which is an electron donating molecule, was used as a molecule adsorbed on the surface of the source electrode and the drain electrode composed of a gold thin film. The adsorption of α, ω-dihexylquaterthiophene on the surface of the gold electrode was performed as follows. The substrate was immersed in a 0.1% by weight solution of α, ω-dihexylquaterthiophene (manufactured by Wako Pure Chemical Industries, Ltd.) in chloroform for 20 hours, rinsed with chloroform, and further immersed in chloroform for 15 minutes. Thereafter, chloroform was removed by blowing nitrogen gas, and drying was performed in nitrogen gas for 2 hours. The contact angle of the gold surface with the pure water after the formation of the molecular adsorption layer 6 was about 80 degrees.
[0085]
In order to ensure the same conditions as in Example 1, the deposition of Cr and Au and the deposition of a pentacene thin film during the formation of the source and drain electrodes were performed simultaneously with Example 1.
[0086]
When the pentacene thin film of the manufactured TFT was observed by AFM, a pentacene thin film almost similar to that of Example 1 was formed.
[0087]
Comparative Example 1
For comparison, a TFT using pentacene as an organic semiconductor layer without forming a molecular adsorption layer on the surface of a gold electrode was prepared. A TFT was prepared in the same manner as in Example 1, except that the monomolecular layer was not adsorbed on the surface of the gold electrode.
[0088]
In order to ensure the same conditions as in Example 1, the deposition of Cr and Au and the deposition of a pentacene thin film during the formation of the source and drain electrodes were performed simultaneously with Example 1.
[0089]
When the pentacene thin film of the manufactured TFT was observed by AFM, the pentacene crystal grain size in the channel region was approximately 1 to 2 μm. However, turbulence of pentacene crystal grains was observed in some places in a channel region near a contact with the source electrode or the drain electrode. That is, there is a portion where crystal grains having a small crystal grain size of 0.1 μm to 0.5 μm are growing, and there is a gap between the crystal grains, that is, pentacene is not attached to the surface of the gate insulating layer in the channel region. There was a part.
[0090]
Comparative Example 2
For comparison, a TFT was prepared in the same manner as in Example 1 except that a molecular adsorption layer made of 1-hexanethiol as an insulating material was formed on the surface of the gold electrode. Here, since the ionization potential of n-hexane in the single-molecule state is 10.2 eV, the ionization potential of 1-hexanethiol in the single-molecule state is larger than 9 eV.
[0091]
The adsorption of 1-hexanethiol on the surface of the gold electrode was performed as follows. The substrate was immersed in a 1 mM ethanol solution of 1-hexanethiol (manufactured by Tokyo Kasei) for 12 hours, rinsed with ethanol, immersed in ethanol for 10 minutes, and then ethanol was removed by blowing nitrogen gas. And dried in the oven for 2 hours.
[0092]
In order to ensure the same conditions as in Example 1, the deposition of Cr and Au and the deposition of a pentacene thin film during the formation of the source and drain electrodes were performed simultaneously with Example 1.
[0093]
When the pentacene thin film of the manufactured TFT was observed by AFM, a pentacene thin film almost similar to that of Example 1 was formed.
[0094]
Example 5
Measurement of FET characteristics
The FET current-voltage characteristics of the thin film transistors prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were measured using a semiconductor parameter analyzer (HP4145B, manufactured by HP). For the measurement, the TFT was placed in a nitrogen gas atmosphere, the source electrode was grounded, and the drain voltage V_DIs -30 V, and the gate voltage V_GCurrent I when the voltage is changed from 5V to -30V_DWas measured. Also, the source electrode is grounded and the gate voltage V_GIs fixed, and the drain voltage V_DThe drain current I when I was changed from 0V to -30V_DWas measured. Where V_GWere fixed to 0 V, -5 V, -10 V, -15 V, -20 V, -25 V, and -30 V, respectively.
[0095]
FIGS. 5 and 6 are graphs showing typical device characteristics of the TFT of Example 1. FIG. As described above, this TFT has a channel length of 2 μm, a channel width of 100 μm, and a capacitance of the gate insulating layer of 70 nF / cm.²It is. FIG. 5 shows that when the source electrode is grounded, V_D= I under -30V_DV_G(Left axis) and the square root of the absolute value (√ | I_D|) Vs. V_GThe plot (right axis) is shown. FIG. 6 shows various V_GI for value_DV_DThe plot of is shown. V in FIG._G= I at -30V_DIs I_D= -476 [mu] A. √ | I in FIG._D| V_GIn the plot of, a tangent is drawn at a portion where the slope of the graph is almost constant, and the channel mobility μ is μ = 0.44 cm²/ Vs. The threshold voltage V is determined from the intersection of the tangent and the horizontal axis._TWas determined to be -4V. Also, I in FIG._DV_GFrom the plot, the current on / off ratio is 3V to -30V._GAbout 10 for change⁵Met.
[0096]
Similarly, the TFTs of Examples 2 to 4 and Comparative Examples 1 and 2 have the channel mobility μ and the threshold voltage V_TV from 3V to -30V_GThe current on / off ratio for the change was determined. The results are summarized in Table 1.

[0097]
It can be seen that the devices of Examples 1 to 4 have improved mobility, threshold characteristics, and drain current values as compared with the devices of Comparative Examples 1 and 2.
[0098]
Further, in order to investigate the variation in the characteristics of each element, four TFTs each similar to those in Examples 1 to 4 and Comparative Example 1 were further formed, and five elements were set for each example, and the V_G= −30 V were compared. The results are summarized in Table 2.

[0099]
In the devices of Examples 1 to 4 in which the thiophene compound molecules were adsorbed on the surfaces of the source electrode and the drain electrode, the on-current value was high and the variation in the current value for each device was small. On the other hand, in the devices of Comparative Examples 1 and 2, the on-current value was low. Further, in Comparative Example 1, the variation of the current value for each element was large.
[0100]
Example 6
In this embodiment, regioregular poly (3-hexylthiophene) was used as an organic semiconductor having an electron donating property,₂The thickness of the gate insulating layer 3 is about 35 nm, and its capacitance is 100 nF / cm.²A TFT was fabricated in the same manner as in Example 1, except that That is, in this example, after forming the molecular adsorption layer 6 made of regioregular poly (3-hexylthiophene), the organic semiconductor layer 7 is formed using regioregular poly (3-hexylthiophene), which is the same substance. Formed. The channel length is 2 μm and the channel width is 100 μm. The formation of the organic semiconductor layer 7 was performed as follows.
[0101]
Regioregular poly (3-hexylthiophene), which was previously reprecipitated and purified twice, was used in the same manner as used for forming the molecular adsorption layer 6. A 4 wt% chloroform solution of regioregular poly (3-hexylthiophene) was prepared, and the solution was filtered through a PTFE membrane filter having a pore size of 0.2 μm. Using the solution after filtration, a regioregular poly (3-hexylthiophene) film was formed on the gate insulating layer 3 and the molecular adsorption layer 6 by spin coating to form an organic semiconductor layer 7. The spin coating was performed by rotating the substrate at 2000 revolutions / minute for 30 seconds. This organic semiconductor layer was not particularly patterned. The device was dried in a nitrogen gas at room temperature for 20 minutes.
[0102]
Example 7
In this embodiment, the molecular adsorption layer 6 is made of FeCl₃A TFT was fabricated in the same manner as in Example 6, except that the TFT was doped. The doping of the molecular adsorption layer was performed as follows.
[0103]
The substrate on which the molecule adsorption layer 6 has been adsorbed is₃Was immersed in a 0.002% by weight acetonitrile solution for 30 seconds, rinsed with acetonitrile, acetonitrile was removed by blowing nitrogen gas, and dried in nitrogen gas for 2 hours.
[0104]
Example 8
In this example, a TFT was manufactured in the same manner as in Example 7, except that the molecular adsorption layer 6 was regioregular poly (3-octylthiophene). That is, in this embodiment, the molecular adsorption layer made of regioregular poly (3-octylthiophene) contains FeCl 2.₃Was doped.
[0105]
Comparative Example 3
For comparison, a TFT was formed in which regioregular poly (3-hexylthiophene) was used as the organic semiconductor layer 7 without forming the molecular adsorption layer 6 on the surface of the gold electrode. A TFT was prepared in the same manner as in Example 6, except that no molecular adsorption layer was formed on the surface of the gold electrode.
[0106]
Example 9
Measurement of FET characteristics
The FET current-voltage characteristics of the thin film transistors prepared in Examples 6 to 8 and Comparative Example 3 were measured using a semiconductor parameter analyzer (HP4145B, manufactured by HP). For the measurement, the TFT was placed in a nitrogen gas atmosphere, the source electrode was grounded, and the drain voltage V_DIs set to −20 V, and the gate voltage V_GCurrent I when the voltage is changed from 2V to -20V_DWas measured. When the device characteristics were determined in the same manner as in Example 4, the mobility μ, the threshold voltage V_T, Current on / off ratio (V_G= 0V to -20V current modulation), V_G= I at -20V_DWere as shown in Table 3, respectively.
[0107]

The devices of Examples 6 to 8 have improved mobility and the drain current value as compared with the device of Comparative Example 3.
[0108]
Example 10
In this example, a TFT was manufactured in the same manner as in Example 4, except that dibenzotetrathiafulvalene was used as the organic semiconductor having an electron donating property. The formation of the organic semiconductor layer 7 was performed as follows.
[0109]
Dibenzotetrathiafulvalene (manufactured by Respe Chemical Co.) was deposited on the gate insulating layer 3, the source electrode 4, and the drain electrode 5 to a thickness of 150 nm to form an organic semiconductor layer 7. Note that dibenzotetrathiafulvalene was recrystallized with toluene in advance, and was further subjected to sublimation purification twice.^-6Torr (1.33 × 10^-3In a vacuum of Pa), vapor deposition was performed at a substrate temperature of 30 ° C. and a vapor deposition rate of 0.05 nm / sec. This organic semiconductor layer was not particularly patterned.
[0110]
Comparative Example 4
For comparison, a TFT was prepared in which dibenzotetrathiafulvalene was used as the organic semiconductor layer 7 without forming the molecular adsorption layer 6 on the surface of the gold electrode. It is the same as Example 10 except that no molecular adsorption layer was formed on the gold electrode surface.
[0111]
Example 11
Measurement of FET characteristics
The FET current-voltage characteristics of the thin film transistors prepared in Example 10 and Comparative Example 4 were measured in the same manner as in Example 5. Channel mobility μ and threshold voltage V for the TFTs of Example 10 and Comparative Example 4_TV from 3V to -30V_GTable 4 shows the results of determining the current on / off ratio with respect to the change.
[0112]

The device of Example 10 is improved in both the mobility and the drain current value as compared with the device of Comparative Example 4.
[0113]
【The invention's effect】
As described above, according to the present invention, the size of the organic semiconductor crystal grains at the interface between the source or drain electrode and the organic semiconductor layer is uniform, and the adhesion to the source or drain electrode is increased, resulting in a channel. Even when the length is short, it is possible to manufacture an organic thin film transistor having a low threshold voltage, a large on-current value, and a small variation in electric characteristics of each element.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an example of a thin film transistor of the present invention.
FIG. 2 is a diagram illustrating an example of a method for manufacturing a thin film transistor of the present invention.
FIG. 3 is a diagram showing a first modification of the thin film transistor of the present invention.
FIG. 4 is a diagram showing a second modification of the thin film transistor of the present invention.
FIG. 5 is a view showing device characteristics of the thin film transistor of Example 1.
FIG. 6 is a view showing device characteristics of the thin film transistor of Example 1.
[Explanation of symbols]
1 substrate
2 Gate electrode
3 Gate insulation layer
4 Source electrode
5 Drain electrode
6 Molecular adsorption layer
7 Organic semiconductor layer

Claims (9)

An organic semiconductor layer made of a crystalline organic semiconductor material having an electron donating property,
A gate electrode formed on a channel region in the organic semiconductor layer via a gate insulating layer,
An organic thin-film transistor comprising a source electrode and a drain electrode sandwiching the channel region,
A thin film layer comprising an electron-donating organic molecule containing a sulfur atom between the surface region of the source electrode or the drain electrode and the channel region, wherein the electron-donating organic molecule is a surface region of the source electrode or the drain electrode; An organic thin-film transistor characterized by being adsorbed on a substrate. 2. The organic thin-film transistor according to claim 1, wherein the ionization potential of the electron-donating organic molecule containing a sulfur atom in one molecule state is 9 electron volts or less. The organic thin-film transistor according to claim 1, wherein the electron-donating organic molecule containing a sulfur atom is a thiophene compound. 4. The crystalline organic semiconductor material is at least one selected from the group consisting of pentacene, dibenzotetrathiafulvalene, and poly (3-alkylthiophene). 4. The organic thin film transistor according to claim 1. The organic thin film transistor according to claim 1, wherein the thin film layer is doped with an electron accepting molecule. The organic thin-film transistor according to claim 1, wherein a distance between the source electrode and the drain electrode is 30 μm or less. An organic semiconductor layer made of a crystalline organic semiconductor material having an electron donating property,
A gate electrode formed on a channel region in the organic semiconductor layer via a gate insulating layer,
A method for manufacturing an organic thin film transistor comprising a source electrode and a drain electrode sandwiching the channel region, wherein the surface region of the source electrode or the drain electrode is made to adsorb an electron-donating organic molecule containing a sulfur atom, and Forming a thin film layer comprising a sulfur atom-containing electron donating organic molecule, and forming the organic semiconductor layer on a surface region of a source electrode or a drain electrode on which the sulfur atom-containing electron donating organic molecule is adsorbed. Forming an organic thin film transistor. By contacting a liquid containing the sulfur-containing electron-donating organic molecule with the surface region of the source electrode or the drain electrode, an electron-donating organic molecule containing a sulfur atom in the surface region of the source or drain electrode The method for producing an organic thin film transistor according to claim 7, wherein the organic thin film transistor is adsorbed. 9. The method according to claim 7, wherein after forming the thin film layer made of the electron donating organic molecule, the thin film layer is doped with an electron accepting molecule.

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