JPWO2007135911A1 - Method for forming organic thin film transistor and organic thin film transistor - Google Patents

Abstract

An organic thin film transistor forming method capable of forming an organic thin film transistor having high carrier mobility by a coating method, and an organic thin film transistor formed by the forming method are provided by supplying and applying a coating liquid containing an organic semiconductor material onto a substrate. Then, in the method for forming an organic thin film transistor formed by drying, the organic thin film transistor forming method is characterized in that the channel region of the transistor does not include the center of gravity of the organic semiconductor film, and the organic thin film transistor is formed by the forming method. Achieved by organic thin film transistors.

Description

  The present invention relates to a method for forming an organic thin film transistor and an organic thin film transistor formed by the method.

  In recent years, various organic thin film transistors (organic TFTs) using an organic semiconductor as a semiconductor channel have been studied. Organic semiconductors are easier to process than inorganic semiconductors and have high affinity with plastic supports, making them attractive as thin-layer devices.

  As a method for forming the organic semiconductor film, a vapor deposition method is typical, but various methods are used depending on the characteristics of the material. Among these, a thin film can be obtained more easily than vapor deposition or the like by an atmospheric pressure wet process in which a solution of an organic semiconductor material is applied to a substrate, such as coating or ink jet.

  However, the film formation by the wet process is simple, but it is difficult to stably form a thin film with high mobility, and the method has not been established yet. Therefore, a method for forming a thin film having a desired mobility at a desired position has not been established.

  Conventionally, as a method of forming an organic semiconductor film in an organic thin film transistor manufacturing process, a thin film having a larger area than that required by using an organic semiconductor material is formed, and this is patterned to remove unnecessary portions. A method of forming is widely used. In many cases, the gate electrode is also formed by forming a conductive thin film such as tantalum or aluminum and patterning it.

  A thin film having a fine shape can also be formed by an inkjet method. For example, a method has been proposed in which an organic semiconductor film is formed by discharging a solution containing an organic semiconductor material onto a substrate using an inkjet discharge device. When ejected by an inkjet method, depending on the wettability of the substrate surface, the ejected droplets may spread out and it may be difficult to accurately draw a fine pattern.

In view of this, a method has been proposed in which a bank is formed in advance on the surface of a substrate to control the arrangement of the droplets so that the discharged droplets are arranged according to a desired pattern (see, for example, Patent Documents 1 and 2). ). Furthermore, the peripheral portion (edge portion) of the droplet containing the organic semiconductor material supplied on the substrate dries quickly, and the organic semiconductor material is deposited on the peripheral portion to form an organic semiconductor film, and further to the channel region. A technique for manufacturing an organic thin film transistor by providing an electrode (see, for example, Patent Document 3) is also known.
JP 59-75205 A JP 2000-353594 A JP 2006-49810 A

  The objective of this invention is providing the formation method of an organic thin-film transistor which can form an organic thin-film transistor with high carrier mobility by the apply | coating method, and the organic thin-film transistor formed by this formation method.

  The above object of the present invention is achieved by the following configurations.

  1. A method for forming an organic thin film transistor in which a coating liquid containing an organic semiconductor material is supplied onto a substrate, applied, and dried, and the channel region does not include the center of gravity of the organic semiconductor film. A method for forming a thin film transistor.

  2. 2. The method of forming an organic thin film transistor according to 1 above, wherein the organic semiconductor film forms a thin film having crystallinity on a substrate.

3. 3. The method of forming an organic thin film transistor according to 1 or 2 above, wherein the substrate has a surface energy of 1.0 × 10 ^{−2 to} 7.0 × 10 ⁻² Nm ⁻¹ .

4). 4. The method for forming an organic thin film transistor according to any one of 1 to 3, wherein the area of the organic semiconductor film is 100 nm ² or more and 10 cm ² or less.

  5). 5. The method for forming an organic thin film transistor according to any one of 1 to 4, wherein the organic semiconductor material has a molecular weight of 100 or more and 5000 or less.

  6). 6. The method of forming an organic thin film transistor according to any one of 1 to 5, wherein the organic semiconductor material is a condensed polycyclic aromatic compound containing a hetero atom in the molecule.

  7. 7. The method for forming an organic thin film transistor according to 6 above, wherein the condensed polycyclic aromatic compound containing a hetero atom in the molecule is 6,13-bisalkylsilylethynylpentacene.

  8). 8. An organic thin film transistor formed by the method for forming an organic thin film transistor according to any one of 1 to 7 above.

  According to the present invention, an organic thin film transistor forming method capable of forming an organic thin film transistor having high carrier mobility by a coating method and an organic thin film transistor formed by the forming method can be provided.

It is a figure which shows the structural example of the organic thin-film transistor which concerns on this invention. It is an example of the schematic equivalent circuit diagram of the organic TFT sheet which concerns on this invention. It is a figure which shows typically the source / drain electrode formed in the position of 250 micrometers from the edge part of the circular organic semiconductor film by the microinjector formed on the silicon oxide film. It is a figure which shows typically the source / drain electrode formed in the position of 250 micrometers from the long side edge part of the linear organic semiconductor film by the microinjector formed on the silicon oxide film. It is a figure which shows typically the source / drain electrode formed in the position of 2.5 mm from the short side edge part of the linear organic semiconductor film by the microinjector formed on the silicon oxide film. The figure which shows typically the bottom contact type organic TFT element which forms a source-drain electrode on a silicon oxide film, and a channel area | region is located in the position whose shortest distance from the organic-semiconductor film edge formed on it is about 1 micrometer. It is. The figure which shows typically the bottom contact type organic TFT element which forms a source-drain electrode on a silicon oxide film, and a channel area | region is located in the position whose shortest distance from the organic-semiconductor film edge formed on it is about 1 micrometer. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic-semiconductor layer 2 Source electrode 3 Drain electrode 4 Gate electrode 5 Insulating layer 6 Support body 7 Gate bus line 8 Source bus line 10 Organic TFT sheet 11 Organic TFT
12 Output element 13 Storage capacitor 14 Vertical drive circuit 15 Horizontal drive circuit

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  The present invention is a technique for forming a thin film having a desired mobility at a desired position by forming a direct pattern semiconductor layer such as an ink jet and devising the arrangement of channels in the film.

  When the semiconductor solution is supplied onto the substrate, the drying starts from the periphery of the droplet, and the drying gradually progresses inside the droplet. In other words, for example, a circular droplet is formed by evaporation of the solvent from the peripheral part toward the center of the circle, and the film formation region that has progressed from all directions is fused in the vicinity of the center of the circle. There is a boundary. It was found that by avoiding this region from the channel, a device with high mobility and stable performance can be manufactured. That is, it has been found that by forming a channel layer at a position other than the position of the center of gravity of the organic semiconductor film, it is possible to fabricate an element with a high mobility performance.

  The method for forming an organic thin film transistor of the present invention can provide an organic thin film transistor that is driven well by coating.

  An organic thin film transistor has a source electrode and a drain electrode connected by an organic semiconductor layer on a support, a top gate type having a gate electrode on the support, and a gate electrode first on the support. And a bottom gate type having a source electrode and a drain electrode connected by an organic semiconductor channel through a gate insulating layer. The organic thin film transistor obtained by the method for forming an organic thin film transistor of the present invention may be either a top gate type or a bottom gate type, and the form thereof is not limited.

  Any organic compound may be selected as the organic semiconductor film constituting the organic semiconductor channel (active layer) in the organic thin film transistor used in the process of the present invention as long as it functions as a low molecular organic semiconductor material. However, it is preferable that a weight average molecular weight is 100 or more and 5000 or less as a molecular weight.

  As the organic semiconductor material used in the present invention, a condensed polycyclic aromatic compound containing a hetero atom in the molecule is preferable, and a hetero atom of Si, S, Sn, O, N, or Ge is particularly preferable. Examples of the condensed polycyclic aromatic compound include anthracene, tetracene, pentacene, hexacene, heptacene, chrysene, picene, fluorene, pyrene, peropyrene, perylene, terylene, quaterylene, coronene, ovalene, thacumanthracene, bisanthene, zeslen, heptazelene. And compounds such as pyranthrene, violanthene, isoviolanthene, cacobiphenyl, phthalocyanine, porphyrin, and derivatives thereof.

  More specifically, a condensed polycyclic aromatic compound represented by the following general formula (OSC1) containing a hetero atom of Si, S, Sn, O, N, and Ge is preferable.

In the formula, R _{1 to} R ₆ represent a hydrogen atom or a substituent, Z ₁ or Z ₂ represents a substituted or unsubstituted aromatic hydrocarbon ring, or a substituted or unsubstituted aromatic heterocyclic ring, and n1 or n2 Represents an integer of 0 to 3.

In the general formula (OSC1), examples of the substituent represented by R _{1 to} R ₆ include an alkyl group (for example, methyl group, ethyl group, propyl group, isopropyl group, t-butyl group, pentyl group, t-pentyl group). Group, hexyl group, octyl group, t-octyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group), cycloalkyl group (for example, cyclopentyl group, cyclohexyl group), alkenyl group (for example, vinyl group, allyl group, 1-propenyl group, 2-butenyl group, 1,3-butadienyl group, 2-pentenyl group, isopropenyl group), alkynyl group (for example, ethynyl group, propargyl group), aromatic hydrocarbon group (aromatic carbocyclic group) Also referred to as an aryl group, for example, phenyl group, p-chlorophenyl group, mesityl group, tolyl group, xylyl group, Til group, anthryl group, azulenyl group, acenaphthenyl group, fluorenyl group, phenanthryl group, indenyl group, pyrenyl group, biphenylyl group), aromatic heterocyclic group (also called heteroaryl group, for example, pyridyl group, pyrimidinyl group, furyl group , Pyrrolyl group, imidazolyl group, benzimidazolyl group, pyrazolyl group, pyrazinyl group, triazolyl group (for example, 1,2,4-triazol-1-yl group, 1,2,3-triazol-1-yl group), oxazolyl group , Benzoxazolyl, thiazolyl, isoxazolyl, isothiazolyl, furazanyl, thienyl, quinolyl, benzofuryl, dibenzofuryl, benzothienyl, dibenzothienyl, indolyl, carbazolyl, carbolinyl, dia The carbazolyl group (Indicates that one of the carbon atoms constituting the carboline ring of the carbolinyl group is replaced by a nitrogen atom), quinoxalinyl group, pyridazinyl group, triazinyl group, quinazolinyl group, phthalazinyl group, etc.), heterocyclic group (for example, pyrrolidyl group Imidazolidyl group, morpholyl group, oxazolidyl group, etc.), alkoxy group (for example, methoxy group, ethoxy group, propyloxy group, pentyloxy group, hexyloxy group, octyloxy group, dodecyloxy group), cycloalkoxy group (for example, Cyclopentyloxy group, cyclohexyloxy group), aryloxy group (for example, phenoxy group, naphthyloxy group), alkylthio group (for example, methylthio group, ethylthio group, propylthio group, pentylthio group, hexylthio group, octylthio group, dodecyl group) Thio group), cycloalkylthio group (for example, cyclopentylthio group, cyclohexylthio group), arylthio group (for example, phenylthio group, naphthylthio group), alkoxycarbonyl group (for example, methyloxycarbonyl group, ethyloxycarbonyl group, butyloxycarbonyl) Group, octyloxycarbonyl group, dodecyloxycarbonyl group), aryloxycarbonyl group (for example, phenyloxycarbonyl group, naphthyloxycarbonyl group), sulfamoyl group (for example, aminosulfonyl group, methylaminosulfonyl group, dimethylaminosulfonyl group, Butylaminosulfonyl group, hexylaminosulfonyl group, cyclohexylaminosulfonyl group, octylaminosulfonyl group, dodecylaminosulfonyl group, phenylamino Sulfonyl group, naphthylaminosulfonyl group, 2-pyridylaminosulfonyl group), acyl group (for example, acetyl group, ethylcarbonyl group, propylcarbonyl group, pentylcarbonyl group, cyclohexylcarbonyl group, octylcarbonyl group, 2-ethylhexylcarbonyl group, dodecyl) Carbonyl group, phenylcarbonyl group, naphthylcarbonyl group, pyridylcarbonyl group), acyloxy group (for example, acetyloxy group, ethylcarbonyloxy group, butylcarbonyloxy group, octylcarbonyloxy group, dodecylcarbonyloxy group, phenylcarbonyloxy group) Amide group (for example, methylcarbonylamino group, ethylcarbonylamino group, dimethylcarbonylamino group, propylcarbonylamino group, pentylcarbonylamino group) Mino group, cyclohexylcarbonylamino group, 2-ethylhexylcarbonylamino group, octylcarbonylamino group, dodecylcarbonylamino group, phenylcarbonylamino group, naphthylcarbonylamino group), carbamoyl group (for example, aminocarbonyl group, methylaminocarbonyl group, Dimethylaminocarbonyl group, propylaminocarbonyl group, pentylaminocarbonyl group, cyclohexylaminocarbonyl group, octylaminocarbonyl group, 2-ethylhexylaminocarbonyl group, dodecylaminocarbonyl group, phenylaminocarbonyl group, naphthylaminocarbonyl group, 2-pyridylamino Carbonyl group), ureido group (for example, methylureido group, ethylureido group, pentylureido group, cyclohexylureido group) Octylureido group, dodecylureido group, phenylureido group naphthylureido group, 2-pyridylaminoureido group), sulfinyl group (for example, methylsulfinyl group, ethylsulfinyl group, butylsulfinyl group, cyclohexylsulfinyl group, 2-ethylhexylsulfinyl group, dodecyl) Sulfinyl group, phenylsulfinyl group, naphthylsulfinyl group, 2-pyridylsulfinyl group), alkylsulfonyl group (for example, methylsulfonyl group, ethylsulfonyl group, butylsulfonyl group, cyclohexylsulfonyl group, 2-ethylhexylsulfonyl group, dodecylsulfonyl group) , Arylsulfonyl group (phenylsulfonyl group, naphthylsulfonyl group, 2-pyridylsulfonyl group, etc.), amino group (for example, amino group, Tilamino group, dimethylamino group, butylamino group, cyclopentylamino group, 2-ethylhexylamino group, dodecylamino group, anilino group, naphthylamino group, 2-pyridylamino group), halogen atom (eg, fluorine atom, chlorine atom, bromine) Atom), fluorinated hydrocarbon group (for example, fluoromethyl group, trifluoromethyl group, pentafluoroethyl group, pentafluorophenyl group), cyano group, nitro group, hydroxy group, mercapto group, silyl group (for example, trimethylsilyl group) , Triisopropylsilyl group, triphenylsilyl group, phenyldiethylsilyl group) and the like.

  These substituents may be further substituted with the above substituents. In addition, a plurality of these substituents may be bonded to each other to form a ring.

In the general formula (OSC1), the aromatic hydrocarbon group and aromatic heterocyclic group represented by Z ₁ or Z ₂ are aromatic carbon atoms described as substituents represented by R _{1 to} R ₆ , respectively. It is synonymous with a hydrogen group and an aromatic heterocyclic group, respectively.

  Furthermore, the condensed polycyclic aromatic compound represented by the following general formula (OSC2) containing a hetero atom of Si, S, Sn, O, N, and Ge is preferable.

In the formula, R ₇ or R ₈ represents a hydrogen atom or a substituent, Z ₁ or Z ₂ represents a substituted or unsubstituted aromatic hydrocarbon ring, or a substituted or unsubstituted aromatic heterocyclic ring, and n1 or n2 Represents an integer of 0 to 3.

In the general formula (OSC2), the substituent represented by R ₇ or R ₈ has the same meaning as the substituents represented by R _{1 to} R ₆ in the general formula (OSC1). The aromatic hydrocarbon group and aromatic heterocyclic group represented by Z ₁ or Z ₂ are the aromatic hydrocarbon groups and aromatic groups described as the substituents represented by R _{1 to} R ₆ , respectively. Each has the same meaning as a heterocyclic group.

In the general formula (OSC2), the substituents R ₇ and R ₈ are preferably represented by the general formula (SG1).

In the formula, R _{9 to} R ₁₁ represent substituents, and X represents silicon (Si), germanium (Ge), or tin (Sn). In the said general formula (SG1), the substituent represented by R < ₉ > -R < ₁₁ > is synonymous with the substituent represented by R < ₁ > -R < ₆ > in the said general formula (OSC1).

  Specific examples of the compound represented by the general formula (OSC2) are shown below, but are not limited thereto.

  Among the above exemplified compounds, particularly preferred is 6,13-bisalkylsilylethynylpentacene specifically exemplified by OSC2-1.

  Examples of organic semiconductor materials include polythiophene and its oligomer, polypyrrole and its oligomer, polyaniline, polyphenylene and its oligomer, polyphenylene vinylene and its oligomer, polythienylene vinylene and its oligomer, polyacetylene, polydiacetylene, tetrathiafulvalene compound, quinone compound Further, cyano compounds such as tetracyanoquinodimethane, fullerenes and derivatives thereof can be used in addition to the condensed polycyclic aromatic compound containing a hetero atom according to the present invention. In particular, among polythiophene and oligomers thereof, thiophene hexamer α-seccithiophene α, ω-dihexyl-α-sexithiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (3-butoxypropyl) ) -Α-secthiothiophene and the like can be suitably used.

  Further, metal phthalocyanines such as copper phthalocyanine and fluorine-substituted copper phthalocyanine described in JP-A-11-251601, naphthalene 1,4,5,8-tetracarboxylic acid diimide, N, N′-bis (4-trifluoromethyl) Benzyl) naphthalene 1,4,5,8-tetracarboxylic acid diimide, N, N'-bis (1H, 1H-perfluorooctyl), N, N'-bis (1H, 1H-perfluorobutyl) and N, N '-Dioctylnaphthalene 1,4,5,8-tetracarboxylic acid diimide derivative, naphthalene tetracarboxylic acid diimides such as naphthalene 2,3,6,7-tetracarboxylic acid diimide, and anthracene 2,3,6,7- Condensed ring tetracarbos such as tetracarboxylic diimides and other anthracene tetracarboxylic diimides Acid diimides, C60, C70, C76, C78, fullerenes, etc. C84, carbon nanotubes SWNT like, merocyanine dyes, and dyes such as hemicyanine dyes.

  Among these π-conjugated materials, at least one selected from the group consisting of condensed polycyclic aromatic compounds such as pentacene, fullerenes, condensed ring tetracarboxylic acid diimides, and metal phthalocyanines is preferable.

  Other organic semiconductor materials include tetrathiafulvalene (TTF) -tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene (BEDTTTTF) -perchloric acid complex, BEDTTTTF-iodine complex, TCNQ-iodine complex. Organic molecular complexes such as can be also used. Furthermore, (sigma) conjugated polymers, such as polysilane and polygermane, and organic-inorganic hybrid material as described in Unexamined-Japanese-Patent No. 2000-260999 can also be used.

  The present invention provides an organic thin film transistor forming method in which an organic semiconductor film is formed by a coating method, and a channel layer is formed on the organic semiconductor film, wherein the channel layer is formed at a position other than the center of gravity of the organic semiconductor film. To do.

  In the present invention, the organic semiconductor film forms a thin film having crystallinity on the substrate. A thin film having crystallinity means that there is a region that periodically changes in luminance when the film is rotated by a polarizing microscope, or that a peak appears in the X-ray reflection spectrum.

Further, the present invention is characterized in that the area of the organic semiconductor film is 100 nm ² or more and 10 cm ² or less. Below 100 nm ² , even if any organic solvent is used, the droplets are very small and the solvent volatilization rate is very fast, which is an insufficient time scale for high-quality crystal growth. If it is 10 cm ² or more, the volatilization rate of the solvent is slow and suitable for crystal growth, but the productivity is low, and when the substrate has low surface energy, the accuracy of the film forming position is lowered.

  The insulator surface on which the organic semiconductor film is to be formed is, for example, the surface of a silicon wafer substrate with an oxide film in the case of a bottom gate type organic thin film transistor. A bottom-gate organic thin film transistor can be formed by forming an electrode and a drain electrode and connecting organic semiconductor layers. The silicon wafer also serves as a gate, and an oxide film (silicon oxide film) formed on the surface forms a gate insulating layer.

  Further, in the case of the top gate type, for example, an organic semiconductor layer is first formed on a support which is an insulator, a source electrode and a drain electrode are formed thereon, and a gate electrode is further formed thereon via a gate insulating layer. To form an organic thin film transistor. In this case, the organic semiconductor material solution is first applied, and the support (insulator) surface on which the organic semiconductor film (layer) is formed constitutes the insulator surface.

  In any case, it is necessary to form an organic semiconductor film having a high carrier mobility on the substrate, that is, on the surface of the insulator serving as the substrate, and in order to form a TFT sheet having a fine structure, These organic semiconductor material solutions must be fine and can be applied to the substrate with high patterning accuracy.

  When these organic semiconductor films constitute an organic thin film transistor, they are formed on a substrate having a gate insulating film, for example, a highly hydrophobic insulating film such as a thermal oxide film of silicon, so that the organic semiconductor material is dissolved. The solvent is preferably a solvent having an affinity for the surface to be applied, and has a boiling point of 70 ° C. or higher and 250 ° C. or lower. For example, aromatic hydrocarbons such as toluene, chain fatty acids such as hexane and heptane Aromatic hydrocarbons, cycloaliphatic hydrocarbons such as cyclohexane and cyclopentane, aliphatic hydrocarbons, halogenated hydrocarbons such as chloroform and 1,2-dichloroethane, chain ethers such as diethyl ether and diisopropyl ether, Examples include cyclic ethers such as tetrahydrofuran and dioxane, and ketones such as acetone and methyl ethyl ketone. These solvents may be used as a mixture. In order to promote dissolution of the organic semiconductor material, another solvent having high solubility in the organic semiconductor material may be mixed and used.

  The content of the organic semiconductor material in the solvent varies depending on the type of solvent used and the selection of the organic semiconductor material. However, in order to form a thin film by applying these liquid materials on the substrate by coating, The organic semiconductor material is preferably dissolved in the range of 0.01 to 10.0% by mass, preferably 0.1 to 5.0% by mass. If the concentration is too high, uniform spreading on the substrate cannot be achieved, and if it is too low, pinholes of the coating film due to liquid breakage on the substrate tend to occur.

  In the present invention, the organic semiconductor film can be formed on the substrate by applying the organic semiconductor material solution to the surface of the insulator (on the substrate) by cast coating, spin coating, printing, ink jetting, or the like, and drying.

  In the present invention, heat treatment may be performed at a predetermined temperature for a predetermined time after the organic semiconductor film (layer) is installed. As a result, it is possible to further strengthen and promote the molecular orientation or arrangement of the organic semiconductor material formed.

The heat treatment is preferably performed at a temperature below the melting point of the organic semiconductor material. In particular, when the organic semiconductor material has an exothermic peak in the differential scanning calorimetry (DSC) measurement, it is preferable to perform the treatment for a certain period of time at a temperature below the melting point and above the exothermic starting temperature. For example, the heat treatment is preferably performed for a certain period of time of 10 seconds to 1 week, preferably 10 seconds to 1 day, more preferably 10 seconds to 1 hour. This is because the heat treatment at a temperature equal to or higher than the melting point melts the organic semiconductor material, so that the formed oriented or crystallized film is melted and destroyed. Moreover, it is not preferable to expose to an excessively high temperature because decomposition and alteration of the organic semiconductor material itself occur. These heat treatments are preferably carried out in an inert gas such as nitrogen or helium or argon. Further, the pressure of these inert gases is preferably in the range of 0.7 × 10 ^{2 to} 1.3 × 10 ² kPa, that is, near atmospheric pressure.

  In the present invention, the substrate having an insulator surface on which the organic semiconductor film is formed varies depending on the manufacturing procedure such as a top gate type and a bottom gate type, which will be described later. Examples thereof include a gate insulating film (thermal oxide film formed on a polysilicon substrate) formed on the gate electrode. A top gate thin film transistor or the like is a substrate having an insulator surface on which an organic semiconductor film (layer) is first formed.

  In order to obtain a surface with high wettability with the liquid containing the organic semiconductor material to be applied, for example, the gate insulating film is preferably subjected to a surface treatment. Examples of such treatment include treatment for changing the surface roughness of the gate insulating film by polishing, orientation treatment such as rubbing for forming a self-aligned thin film, and surface treatment with a silane coupling agent. Preferred examples of the silane coupling agent include octadecyltrichlorosilane, octyltrichlorosilane, hexamethyldisilane, hexamethyldisilazane, and the like. The present invention is not limited to these, but treatment with a silane coupling agent is preferred.

In addition, the contact angle measurement of the substrate surface to which the organic semiconductor material solution is applied in the present invention is performed in an environment of 20 ° C. and 50% RH using a contact angle meter CA-VorCA-DT · A type manufactured by Kyowa Interface Science Co., Ltd. It is to measure with. Further, the surface energy of the substrate is preferably 1.0 × 10 ^{−2 to} 7.0 × 10 ⁻² Nm ⁻¹ , and if it is smaller than 1.0 × 10 ⁻² Nm ⁻¹ , there is a problem in coating, If it is larger than 7.0 × 10 ⁻² Nm ⁻¹ , high carrier mobility cannot be obtained.

  The film thickness of the organic semiconductor layer thus formed is not particularly limited, but the characteristics of the obtained organic thin film transistor (TFT) are often greatly influenced by the film thickness of the organic semiconductor layer. Although it varies depending on the organic semiconductor material, it is generally 1 μm or less, particularly preferably 10 to 300 nm.

  Further, when the condensed polycyclic aromatic compound containing a heteroatom according to the present invention is used as an organic semiconductor material, not only the organic semiconductor material but also, for example, acrylic acid, acetamide, dimethylamino group, cyano group in the organic semiconductor layer , A material having a functional group such as a carboxyl group, a nitro group, a material serving as an acceptor such as a benzoquinone derivative, tetracyanoethylene and tetracyanoquinodimethane or a derivative thereof, for example, an amino group, Materials having functional groups such as triphenyl group, alkyl group, hydroxyl group, alkoxy group, phenyl group, substituted amines such as phenylenediamine, anthracene, benzoanthracene, substituted benzoanthracene, pyrene, substituted pyrene, carbazole and derivatives thereof, Electrons such as tetrathiafulvalene and its derivatives Materials such as the donor is a donor is contained, it may be performed so-called doping treatment. The method of forming an organic semiconductor film according to the present invention is also useful in structuring the organic semiconductor material molecules such as the orientation of the doped organic semiconductor film.

  In the present invention, the production of an organic thin film transistor will be described by taking a bottom gate type organic thin film transistor which is one of preferred embodiments as an example.

  An organic thin film transistor is configured by optimally arranging a gate electrode, a gate insulating film, an active layer, a source electrode, and a drain electrode on a support.

  Therefore, for example, after forming the gate electrode on the support, forming the gate insulating film, and forming the active layer (organic semiconductor film (layer)) on the gate insulating film by the above-described method, the source, By forming the drain electrode, the organic thin film transistor according to the present invention is formed. For example, after forming the gate insulating film, a source / drain electrode pattern may be formed on the gate insulating film, and an organic semiconductor layer may be formed by patterning between the source / drain electrodes.

  As described above, the gate electrode, the gate insulating film, the organic semiconductor film (layer), the source electrode, and the drain electrode are appropriately patterned on the support as necessary, and optimally arranged to obtain the organic thin film transistor of the present invention. It is done.

  Hereinafter, other components constituting the organic thin film transistor other than the organic semiconductor layer in the present invention will be described.

  In the present invention, the material for forming the source electrode, the drain electrode, and the gate electrode is not particularly limited as long as it is a conductive material, and various metal materials can be used. Platinum, gold, silver, nickel, chromium, Copper, iron, tin, antimony lead, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin oxide / antimony, indium tin oxide (ITO), fluorine-doped zinc oxide, zinc , Carbon, graphite, glassy carbon, silver paste and carbon paste, lithium, beryllium, sodium, magnesium, potassium, calcium, scandium, titanium, manganese, zirconium, gallium, niobium, sodium, sodium-potassium alloy, magne Lithium, aluminum, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide mixture, lithium / aluminum mixture, etc., in particular, platinum, gold, silver, Copper, aluminum, indium, ITO, carbon and the like are preferable.

  The source and drain electrodes are preferably linear.

  As an electrode forming method, there are a method of patterning a conductive fine particle dispersion, or a solution or dispersion of a conductive polymer directly by an ink jet method, and a method of forming a coating film by lithography, laser ablation, or the like. Furthermore, a method of patterning an ink containing a conductive polymer or conductive fine particles, a conductive paste, or the like by a printing method such as relief printing, intaglio printing, planographic printing, or screen printing can also be used.

  Alternatively, a known conductive polymer whose conductivity is improved by doping or the like, for example, conductive polyaniline, conductive polypyrrole, conductive polythiophene, a complex of polyethylenedioxythiophene and polystyrenesulfonic acid, or the like is also preferably used. Especially, a thing with little electrical resistance in a contact surface with an organic-semiconductor layer is preferable.

  Examples of conductive fine metal materials (metal fine particles) include platinum, gold, silver, cobalt, nickel, chromium, copper, iron, tin, antimony, lead, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium. Germanium, molybdenum, tungsten, zinc, and the like can be used, and platinum, gold, silver, copper, cobalt, chromium, iridium, nickel, palladium, molybdenum, and tungsten having a work function of 4.5 eV or more are particularly preferable.

  As a method for producing such a metal fine particle dispersion, metal ions can be reduced by reducing metal ions in a liquid phase such as a gas phase evaporation method, a sputtering method, a metal vapor synthesis method, or a liquid phase such as a colloid method or a coprecipitation method. Examples of the chemical production method for producing fine particles include colloidal methods described in JP-A-11-76800, JP-A-11-80647, JP-A-11-319538, JP-A-2000-239853, and the like. Dispersion of fine metal particles produced by a gas evaporation method described in JP-A Nos. 2001-254185, 2001-53028, 2001-35255, 2000-124157, 2000-123634, etc. It is a thing.

  The average particle diameter of the dispersed metal fine particles is preferably 20 nm or less.

  In addition, it is preferable to contain a conductive polymer in the metal fine particle dispersion. If the source electrode and the drain electrode are formed by patterning and pressing, heating, etc., ohmic contact with the organic semiconductor layer is possible with the conductive polymer. And can. That is, the effect of the present invention can be further enhanced by interposing a conductive polymer on the surface of the metal fine particles, reducing the contact resistance to the semiconductor, and thermally fusing the metal fine particles.

  As the conductive polymer, a known conductive polymer whose conductivity has been improved by doping or the like is preferably used. For example, conductive polyaniline, conductive polypyrrole, conductive polythiophene, polyethylenedioxythiophene and polystyrenesulfonic acid complex Etc. are preferably used.

  The content of the metal fine particles is preferably 0.00001 to 0.1 in terms of mass ratio with respect to the conductive polymer. If this amount is exceeded, fusion of the metal fine particles may be inhibited.

  When forming electrodes with these metal fine particle dispersions, it is preferable to heat-fuse the metal fine particles by heating after forming the source and drain electrodes. Further, at the time of electrode formation, a pressure of about 1 to 50000 Pa, and further about 1000 to 10000 Pa may be applied to promote fusion.

  In the case of patterning directly by an ink jet method as a method of patterning like an electrode using the fine metal particle dispersion, the ejection method of the ink jet head may be an on-demand type such as a piezo method or a bubble jet (registered trademark) method or an electrostatic method. A known method such as a continuous jet type ink jet method such as a suction method can be used.

  As a method of heating or pressurizing, a known method including a method used for a heating laminator or the like can be used.

  Various insulating films can be used as the gate insulating layer, and an inorganic oxide film having a high relative dielectric constant is particularly preferable.

  Examples of inorganic oxides include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead lanthanum titanate, strontium titanate, Examples thereof include barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, and trioxide yttrium. Of these, silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide are preferable. Inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.

  The inorganic oxide film can be formed by vacuum deposition, molecular beam epitaxy, ion cluster beam, low energy ion beam, ion plating, CVD, sputtering, atmospheric pressure plasma (atmospheric pressure) Plasma CVD method), dip coating method, casting method, reel coating method, bar coating method, method of forming by coating such as die coating method, and wet process such as a method of patterning such as printing or inkjet, etc. Can be used.

  The wet process is a method of applying and drying a liquid in which inorganic oxide fine particles are dispersed in an arbitrary organic solvent or water using a dispersion aid such as a surfactant as required, or an oxide precursor, for example, A so-called sol-gel method in which a solution of an alkoxide body is applied and dried is used.

  Of these, the atmospheric pressure plasma method and the sol-gel method are preferable.

  The method for forming an insulating film by the atmospheric pressure plasma method is a process in which a thin film is formed on a substrate by discharging at atmospheric pressure or a pressure in the vicinity of atmospheric pressure to excite a reactive gas to form a thin film on a substrate. 11-61406, 11-133205, JP-A 2000-121804, 2000-147209, 2000-185362, and the like. Thereby, a highly functional thin film can be formed with high productivity.

  These insulating films may be subjected to surface treatment in advance, and preferred examples of these treatments include treatment with a silane coupling agent as described above and alignment treatment such as rubbing.

  The organic compound film can be formed by using polyimide, polyamide, polyester, polyacrylate, photo radical polymerization system, photo cation polymerization system photo-curing resin, or copolymer containing acrylonitrile component, polyvinyl phenol, polyvinyl alcohol. , Novolak resin, cyanoethyl pullulan, and the like can also be used. As a method for forming the organic compound film, a wet process is preferable.

  An inorganic oxide film and an organic oxide film can be laminated and used together. The thickness of these insulating films is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.

  Moreover, a support body is comprised with glass or a flexible resin-made sheet | seat, for example, a plastic film can be used as a sheet | seat. Examples of the plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), Examples thereof include films made of cellulose triacetate (TAC), cellulose acetate propionate (CAP), and the like. By using a plastic film in this manner, the weight can be reduced as compared with the case of using a glass substrate, the portability can be improved and the resistance to impact can be improved.

  FIG. 1 is a cross-sectional view showing a configuration example of an organic thin film transistor (TFT) of the present invention.

  In FIG. 6A, a mask is used on a glass support 6 and, for example, a pattern is formed by vapor deposition of gold, a source electrode 2 and a drain electrode 3 are formed, and an organic semiconductor material layer 1 is formed between them. An organic TFT is formed by forming a gate insulating layer 5 thereon and further forming a gate electrode 4 thereon.

  2B and 2C show other configuration examples of the top gate type organic thin film transistor.

  2D to 2F show configuration examples of bottom gate type organic TFTs. In FIG. 4D, after the gate electrode 4 is formed on the support 6, the gate insulating layer 5 is formed, the source electrode 2 and the drain electrode 3 are formed thereon, and the gate between the source and drain electrodes is formed. A bottom gate type organic TFT is formed by forming an organic semiconductor material layer 1 on an insulating layer. Similarly, other configuration examples are shown in FIGS. In FIG. 5 (f), a gate electrode 4 is formed on a support 6, a gate insulating layer 5 is formed, an organic semiconductor material layer 1 is formed thereon, and further a source electrode 2 and a drain electrode 3 are formed. Thus, an organic TFT is formed.

  FIG. 2 is an example of a schematic equivalent circuit diagram of a TFT sheet configured like an output element such as a liquid crystal or an electrophoretic element using the organic thin film transistor.

  The TFT sheet 10 has a large number of organic TFTs 11 arranged in a matrix. 7 is a gate bus line of each organic TFT 11, and 8 is a source bus line of each organic TFT 11. For example, an output element 12 such as a liquid crystal or an electrophoretic element is connected to the source electrode of each organic TFT 11 to constitute a pixel in the display device. The pixel electrode may be used as an input electrode of the photosensor. In the illustrated example, a liquid crystal as an output element is shown by an equivalent circuit composed of a resistor and a capacitor. 13 is a storage capacitor, 14 is a vertical drive circuit, and 15 is a horizontal drive circuit.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Comparative Example 1
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film.

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. This solution was discharged and applied to the surface of the silicon oxide film using a microinjector (Narishige). The organic semiconductor layer deposition region formed at this time was a circle having a diameter of 500 μm, and the average film thickness was 50 nm. All of the solution preparation, film formation and drying steps were performed in nitrogen.

Furthermore, gold is vapor-deposited on the surface of this film, and source and drain electrodes are formed in a region where the shortest distance from the coating film end of the center of the channel region is 250 μm as shown in FIG. A field effect transistor having a channel width of 10 μm was fabricated. Carrier mobility (cm ² / V · s) was determined from the saturation region of the IV characteristics of the produced organic thin film transistor. The mobility at this time is shown in Table 1.

Examples 1 and 2
In the same manner as in Comparative Example 1, channels were formed on the organic semiconductor layer in regions where the shortest distance from the coating film end of the center of the channel region to 180 μm in FIG. 3 was 180 and 25 μm, respectively. The mobility at this time is shown in Table 1.

Comparative Example 2
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film. The surface energy of this surface was measured and found to be 5.5 × 10 ⁻² Nm ⁻¹ .

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. A linear organic semiconductor layer having a line width of 500 μm, a length of 5 mm, and an average film thickness of 50 nm was formed on the surface of the silicon oxide film using a microinjector (manufactured by Narishige) equipped with a manipulator. All of the solution preparation, film formation and drying steps were performed in nitrogen.

  Further, gold is deposited on the surface of this film, and the shortest distance from the coating film end of the center of the channel region is 250 μm and the distance from the short side end is 2.5 mm as shown in FIG. A source / drain electrode was formed on the substrate to produce a field effect transistor having a channel length of 10 μm and a channel width of 10 μm. The mobility at this time is shown in Table 1.

Examples 3 and 4
On the organic semiconductor layer formed in the same manner as in Comparative Example 2, channels were formed in regions where the shortest distance from the coating film end of the center of the channel region to 180 μm in FIG. 4 was 180 μm and 25 μm, respectively. The mobility at this time is shown in Table 1.

Comparative Example 3, Examples 5 and 6
In the same manner as in Comparative Example 2, an organic semiconductor layer was formed, and a channel was formed in a region where the distance from the coating film end of the center of the channel region was 2.5 mm and the distance from the long side end was 250 μm as shown in FIG. Similarly, a channel was formed in a region where the distance from the coating film edge was 1.8 mm and 0.25 mm and the distance from the long side edge part was 250 μm. The mobility at this time is shown in Table 1.

Comparative Example 4, Examples 7-8
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film.

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. This solution was discharged and applied to the surface of the silicon oxide film using an organic solvent inkjet head. The organic semiconductor layer deposition region formed at this time was circular with a diameter of 50 μm, and the average film thickness was 50 nm. From the above solution preparation, the film forming and drying steps were all carried out in nitrogen.

  Further, gold is vapor-deposited on the surface of this film, and source / drain electrodes are formed in regions where the shortest distance from the coating film edge of the channel region center of gravity is 25 μm, 12 μm, and 5 μm as shown in FIG. A field effect transistor having a thickness of 10 μm and a channel width of 10 μm was manufactured. The mobility at this time is shown in Table 1.

Example 9
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film. Gold was deposited on the surface of the insulating film, and source / drain electrodes having a channel length of 2 μm and a channel width of 30 μm were formed by photolithography.

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. This solution was continuously discharged onto the substrate on which the source and drain were formed using an electrostatic suction type ink jet head, and an element as shown in FIG. 6 was produced. The average film thickness of the organic semiconductor film was 50 nm. All of the solution preparation, film formation and drying steps were performed in nitrogen. The mobility at this time is shown in Table 1.

Example 10
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film. Gold was deposited on the surface of the insulating film, and source / drain electrodes having a channel length of 2 μm and a channel width of 30 μm were formed by photolithography.

  The substrate surface was cleaned using an oxygen plasma apparatus and then immersed and cleaned in an octyltrichlorosilane (OTS) solution to form an OTS SAM film on the insulating film surface. Furthermore, this substrate was immersed in an octanethiol solution and washed to form a SAM film on the surface of the source / drain electrodes.

  Next, using a mask having an opening of 30 μm × 5 μm on the substrate surface-treated in the previous stage, the region surrounded by the dotted line in FIG. 7 was irradiated with ultraviolet rays.

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. This solution was continuously discharged onto the substrate on which the source / drain electrodes were formed using an electrostatic suction type ink jet head, and an element as shown in FIG. 7 was produced. The average film thickness of the organic semiconductor film was 100 nm. The above solution preparation, film formation and drying steps were all carried out in nitrogen. The mobility at this time is shown in Table 1.

Example 11
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film. Gold was deposited on the surface of the insulating film, and source / drain electrodes having a channel length of 2 μm and a channel width of 30 μm were formed by photolithography.

  The substrate surface was cleaned using an oxygen plasma apparatus and then immersed and cleaned in an octyltrichlorosilane (OTS) solution to form an OTS SAM film on the insulating film surface. Furthermore, this substrate was immersed in an octanethiol solution and washed to form a SAM film on the surface of the source / drain electrodes.

  Next, using a mask having an opening of 30 μm × 5 μm on the substrate surface-treated in the previous stage, the region surrounded by the dotted line in FIG. 7 was irradiated with ultraviolet rays.

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. This solution was discharged onto the substrate on which the source / drain electrodes were formed using an ink jet head to produce an element as shown in FIG. The average film thickness of the organic semiconductor film was 100 nm. All of the solution preparation, film formation and drying steps were performed in nitrogen. The mobility at this time is shown in Table 1.

Example 12
A thermal oxide film having a thickness of 200 nm was formed on an n-type Si wafer having a specific resistance of 0.02 Ω · cm to form a gate insulating film. Gold was deposited on the surface of the insulating film, and source / drain electrodes having a channel length of 2 μm and a channel width of 30 μm were formed by photolithography.

  The substrate surface was cleaned using an oxygen plasma apparatus and then immersed and washed in an octyltrichlorosilane (OTS) solution to form an OTS SAM film on the insulating film surface. Furthermore, this substrate was immersed in an octanethiol solution and washed to form a SAM film on the surface of the source / drain electrodes.

  Next, using a mask having an opening of 30 μm × 5 μm on the substrate surface-treated in the previous stage, the region surrounded by the dotted line in FIG. 7 was irradiated with ultraviolet rays.

  Next, the exemplary compound OSC2-1 was bubbled with nitrogen gas to prepare a 0.1 mass% toluene solution. Using this solution, the substrate as shown in FIG. 7 was produced by dip coating the substrate. The average film thickness of the semiconductor film was 100 nm. The above solution preparation, film formation and drying steps were all carried out in nitrogen. The mobility at this time is shown in Table 1.

Example 13
In Example 7, an element was manufactured by replacing the semiconductor with OSC2-2.

Example 14
In Example 7, the organic semiconductor solution was replaced with a 0.1 mass% o-dichlorobenzene dispersion of the comparative compound (1) having an average molecular weight of 20000 (Exemplary compound (15) of JP-A-2004-140359). Formed an organic semiconductor layer and a channel in the same manner. The mobility at this time is shown in Table 1.

  From Table 1, it can be seen that the shortest distance from the end of the organic semiconductor layer deposition region in the channel region shows high carrier mobility within the scope of the present invention.

Claims (8)

A method for forming an organic thin film transistor in which a coating liquid containing an organic semiconductor material is supplied onto a substrate, applied, and dried, and the channel region does not include the center of gravity of the organic semiconductor film. A method for forming a thin film transistor. 2. The method of forming an organic thin film transistor according to claim 1, wherein the organic semiconductor film forms a thin film having crystallinity on a substrate. 3. The method of forming an organic thin film transistor according to claim ¹ , wherein the surface energy of the substrate is 1.0 × 10 ^{−2 to} 7.0 × 10 ⁻² Nm ⁻¹ . 4. The method of forming an organic thin film transistor according to claim 1, wherein an area of the organic semiconductor film is 100 nm ² or more and 10 cm ² or less. The method for forming an organic thin film transistor according to any one of claims 1 to 4, wherein the organic semiconductor material has a molecular weight of 100 or more and 5000 or less. 6. The method for forming an organic thin film transistor according to any one of claims 1 to 5, wherein the organic semiconductor material is a condensed polycyclic aromatic compound containing a hetero atom in a molecule. The method for forming an organic thin film transistor according to claim 6, wherein the condensed polycyclic aromatic compound containing a hetero atom in the molecule is 6,13-bisalkylsilylethynylpentacene. An organic thin film transistor formed by the method for forming an organic thin film transistor according to any one of claims 1 to 7.