KR102220022B1 - Gate insulator film, organic thin film transistor, and method of manufacturing organic thin film transistor - Google Patents

Abstract

The present invention provides a gate insulating film capable of maintaining high flatness when forming an organic semiconductor layer without changing the film quality by heating or chemical treatment when forming an electrode or the like. In addition, by using such a gate insulating film, there is provided an organic thin film transistor capable of exhibiting high carrier mobility and stable transistor characteristics, and a method of manufacturing the same.
A gate insulating film comprising a cured product obtained by curing a compound obtained by reacting (A) a bisphenol type epoxy compound with an ethylenically unsaturated bond-containing monocarboxylic acid, and (B) a photopolymerization initiator or a composition containing a thermal polymerization initiator as an essential component. A gate insulating film containing 40 to 90 mass% of component (A) and 0.1 to 30 mass% of component (B), and an organic thin film transistor obtained by coating and curing the composition on a gate electrode, and a manufacturing method thereof to be.

Description

A method of manufacturing a gate insulating film, an organic thin film transistor, and an organic thin film transistor {GATE INSULATOR FILM, ORGANIC THIN FILM TRANSISTOR, AND METHOD OF MANUFACTURING ORGANIC THIN FILM TRANSISTOR}

The present invention relates to a gate insulating film, an organic thin film transistor including the same, and a method of manufacturing an organic thin film transistor.

Organic thin-film transistors can be made lightweight and flexible, and are expected to be applied to next-generation displays with excellent impact resistance and portability. The organic thin film transistor can be used as a semiconductor by coating a soluble low molecular organic semiconductor and a high molecular organic semiconductor. By using a printing method, a large area process can be applied, and significant cost reduction can be expected. Since the organic semiconductor can be formed at a low temperature, there is also an advantage that a flexible substrate such as a plastic substrate can be used.

The field of application of an organic thin film transistor is an organic EL display, liquid crystal, display devices such as electronic paper, RFID tags and sensors, and the like, and research is being actively conducted. However, current organic thin film transistors have not reached practical levels in terms of mobility, operating voltage, and driving stability, and it has become an urgent need to improve not only organic semiconductors, but also device configurations and manufacturing processes from various angles.

As illustrated in FIGS. 1 and 3, in an organic thin film transistor using an organic semiconductor, the organic semiconductor layer and the gate insulating layer are generally formed in contact with each other. Therefore, it is known that the semiconductor characteristics of the organic semiconductor layer are affected depending on the material constituting the gate insulating film, and the transistor performance is deteriorated. For example, Patent Document 1 discloses a transistor using a gate insulating layer made of polyimide, but an organic thin film transistor using a gate insulating layer made of such a material has a problem that the threshold voltage of the gate voltage is not stable. In addition, since polyimide requires heating of 250°C or higher to cure, a highly versatile plastic substrate such as PEN (polyethylene naphthalate, heat resistance 150°C) or PET (polyethylene terephthalate, heat resistance 100°C) cannot be used.

As a solution to the above problem, the dielectric breakdown voltage is improved and the threshold voltage is stabilized by using the gate insulating film made of the cardo type resin described in Patent Document 2. However, the carrier mobility of the organic semiconductor layer, which is an important factor in the performance of the organic thin film transistor, is not mentioned. It is known that the carrier mobility of the organic semiconductor layer is affected by the characteristics of the gate insulating film, and since the characteristics of the gate insulating film are not sufficient, there is a concern that the carrier mobility will not be sufficiently high.

Japanese Patent Application Publication No. 2003-304014 Japanese Patent Application Publication No. 2008-166537

Since the carrier moves at the interface between the organic semiconductor layer and the gate insulating film, it is necessary to increase the flatness of the gate insulating film. However, since the film quality of the gate insulating film formed of an organic compound is changed due to heating after film formation, heating, chemical treatment, etc. in the process of forming an electrode or the like, the surface roughness is also increased, and the flatness is significantly reduced.

Therefore, as a preferred gate insulating film used for an organic thin film transistor, a thin film can be formed, and it is necessary to have a high level of flatness even after the formation of the thin film, after the formation of the electrode or the like, and also when the organic semiconductor layer is formed. However, conventionally, there was no gate insulating film satisfying these characteristics.

The present invention has been made in view of these problems, and it is possible to form at a curing temperature of 100 to 150°C, and there is no change in film quality due to heating or chemical treatment when forming electrodes, etc., and formation of an organic semiconductor layer It is an object of the present invention to provide a gate insulating film capable of maintaining high flatness at the time. In addition, by using a gate insulating film capable of maintaining high flatness when forming an organic semiconductor layer as described above, it is an object to provide an organic thin film transistor capable of expressing stable transistor characteristics with high carrier mobility, and a manufacturing method thereof. do. On the other hand, this highly planar insulating film material can also be applied to the planarization film when a planarization film is required in the configuration of an organic transistor.

As a result of careful examination of means for solving the above problems, the present inventors found that by using a predetermined composition, a gate insulating film capable of sufficiently maintaining flatness when forming an organic semiconductor layer can be produced, and the present invention was completed. .

That is, the gist of the present invention is as follows.

(1) The present invention comprises a cured product obtained by curing (A) a compound obtained by reacting a bisphenol-type epoxy compound with an ethylenically unsaturated bond-containing monocarboxylic acid, and (B) a photopolymerization initiator or a composition containing a thermal polymerization initiator as an essential component. As a gate insulating film, it is a gate insulating film characterized by containing 40-90 mass% of (A) component and 0.1-30 mass% of (B) component in a cured product.

(2) In the present invention, the composition further comprises (C) a polymerizable monomer having one or more ethylenically unsaturated bonds, and the cured product contains 5 to 60% by mass of (C) component ( It is the gate insulating film described in 1).

(3) The present invention also provides at least one gate electrode, at least one source electrode, at least one drain electrode, at least one organic semiconductor layer, (1) or (2). An organic thin-film transistor comprising the gate insulating film described in ).

(4) The present invention is also the organic thin film transistor according to (3), wherein the gate insulating film has a thickness of 0.05 to 1.0 µm.

(5) The present invention is also a method for manufacturing an organic thin film transistor comprising at least one gate electrode, at least one source electrode, at least one drain electrode, at least one organic semiconductor layer, and a gate insulating film, It is a method for manufacturing an organic thin film transistor, characterized by forming a gate insulating film with a film thickness of 0.05 to 1.0 µm by coating the composition according to claim 1 or 2 on an electrode and curing at a temperature of 100 to 150°C.

Advantageous Effects of Invention According to the present invention, a gate insulating film capable of maintaining high flatness in forming an organic semiconductor layer can be produced, it is possible to improve the carrier mobility of an organic thin film transistor, and stable transistor characteristics can be expressed.

1 is a cross-sectional configuration diagram showing an example of an organic thin film transistor according to a first embodiment.
2 is an explanatory diagram of a method of manufacturing an organic thin film transistor according to the first embodiment. 2(i) is a diagram showing an example of a gate electrode forming process. 2(ii) is a diagram showing an example of a gate insulating film forming process. Fig. 2(iii) is a diagram showing an example of a source/drain electrode formation process. 2(iv) is a diagram showing an example of an organic semiconductor layer forming process.
3 is a cross-sectional configuration diagram showing an example of an organic thin film transistor according to a second embodiment.
FIG. 4 is a characteristic diagram of changes in the square root of the drain current and the drain current to the gate voltage of the organic thin film transistors according to Examples 1 and 2 and Comparative Example 1;
5 is a diagram showing a result of measuring flatness in a gate insulating layer of an organic thin film transistor according to Example 5 and Comparative Example 4;

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[Embodiment 1]

1 is a cross-sectional configuration diagram showing an example of an organic thin film transistor according to Embodiment 1 of the present invention. In FIG. 1, the organic thin film transistor according to Embodiment 1 includes an insulating substrate 10, a gate electrode 20, a gate insulating film 30, a source electrode 40, a drain electrode 41, and an organic semiconductor layer 50. .

In FIG. 1, a gate electrode 20 is formed on an insulating substrate 10 and a gate insulating film 30 is formed on the gate electrode 20. Further, the source electrode 40 and the drain electrode 41 are formed on the surface of the gate insulating film 30 and at a position covering both ends of the gate electrode 20 when viewed from the upper surface. In addition, an organic semiconductor layer 50 is formed on the gate insulating film 30 between the source electrode 40 and the drain electrode 41, and the organic semiconductor layer 50 is formed of the source electrode 40 and the drain electrode 41. It covers the inner end. The structure shown in Fig. 1 is a structure called a bottom gate/bottom contact structure.

The insulating substrate 10 may be composed of various substrates made of an insulating material, for example, glass substrates such as quartz glass and silica glass, polyethylene terephthalate (PET), polyethersulfone (PES), polyethylene naphthalate (PEN). ), polyimide (PI), polyetherimide (PEI), polystyrene (PS), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), nylon, polycarbonate, and other plastic films. have. Further, if the surface is subjected to an insulating treatment, a metal foil or the like can also be used as the insulating substrate 10.

The material of the gate electrode 20 is not limited as long as it can efficiently flow current. For example, it may be made of aluminum. A gate insulating film 30 is formed on the surface of the gate electrode 20, and the surface of the gate electrode 20 preferably has a high surface smoothness as much as possible in order to form a stacked gate insulating film 30.

The gate insulating film 30 covers the periphery of the gate electrode 20 to insulate the gate electrode 20. The gate insulating film 30 of the organic thin film transistor according to the present embodiment comprises (A) a compound obtained by reacting a bisphenol-type epoxy compound with an ethylenically unsaturated bond-containing monocarboxylic acid, and (B) a photopolymerization initiator or a thermal polymerization initiator as essential components. It is a gate insulating film formed by curing the composition described above.

In the organic thin film transistor, when a voltage is applied to the gate electrode 20, a channel is formed in the organic semiconductor layer 50, and the generated carriers move between the source electrode 40 and the drain electrode 41 to conduct (導通) and perform transistor operation. Carriers generated when a voltage is applied to the gate electrode 20 moves through the interface between the gate insulating film 30 and the organic semiconductor layer 50. Therefore, if there are irregularities in the gate insulating film 30, the movement speed becomes slow and the carrier mobility decreases. Therefore, the gate insulating film 30 is required to have flatness.

The gate insulating film 30 of the present invention is formed by forming a coating film of the composition for a gate insulating film, and then photo-processing by exposure or developing an organic solvent (limited to when a photopolymerization initiator is used as (B)), or a coating film of the gate insulating film composition. A photoresist can be laminated on the top, and photo-processing can be performed by removing the insulating film composition from the portion where the photoresist has been removed by exposure, development, reactive ion etching, or the like, and by removing the resist. The gate insulating film of the present invention can be made into a film having very high flatness because there are few irregularities on the surface even through these optical processing steps. Further, the gate insulating film 30 of the present invention exhibits little change in flatness even after the source electrode 40 and the drain electrode 41 are formed on the surface thereof. For this reason, it becomes possible to form an organic semiconductor layer having good carrier mobility. That is, according to the present invention, it is possible to improve the carrier mobility of the organic thin film transistor, and thus stable transistor characteristics can be expressed. Here, the reason for the improvement of carrier mobility is that a gate insulating film having a high level can be obtained by using a predetermined composition for a gate insulating film, and the amount of functional groups such as carboxyl groups that may trap carriers in the insulating film is reduced. It is speculated that less is one of the factors.

If the dielectric breakdown voltage of the gate insulating film 30 is lower than the breakdown voltage required for an actual circuit, the organic thin film transistor cannot be operated as a device in an actual circuit. For example, in the driving circuit of the display, it is necessary to drive it at 20V, so that the gate insulating film 30 capable of being operated is thinned and the dielectric breakdown voltage is required. Since the gate insulating film of the present invention can form a thin film of 1 µm or less and withstand a voltage of 20 V, it is possible to drive with a voltage of 20 V or less. On the other hand, the minimum film thickness of the gate insulating film is generally that the gate electrode is formed in several tens of nm, and since it is necessary to flatten the irregularities caused by the formation of the gate electrode, it is necessary to have a thickness of 0.05 µm or more.

Thus, in the organic thin film transistor according to the present embodiment, by applying the gate insulating film 30 of the present invention, desired flatness and dielectric breakdown voltage can be obtained.

In the composition for a gate insulating film of an organic thin film transistor of the present invention, (A) is a reaction product of an epoxy compound having two glycidyl ether groups derived from bisphenols and a monocarboxylic acid containing an unsaturated group (hereinafter referred to as "bisphenol type epoxy (meta ) It is described as "acrylate compound").

Bisphenols used as raw materials for the bisphenol-type epoxy (meth)acrylate compound (A) include bis(4-hydroxyphenyl)ketone, bis(4-hydroxy-3,5-dimethylphenyl)ketone, and bis(4- Hydroxy-3,5-dichlorophenyl) ketone, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxy-3,5-dimethylphenyl)sulfone, bis(4-hydroxy-3,5-dichloro Phenyl)sulfone, bis(4-hydroxyphenyl)hexafluoropropane, bis(4-hydroxy-3,5-dimethylphenyl)hexafluoropropane, bis(4-hydroxy-3,5-dichlorophenyl) Hexafluoropropane, bis(4-hydroxyphenyl)dimethylsilane, bis(4-hydroxy-3,5-dimethylphenyl)dimethylsilane, bis(4-hydroxy-3,5-dichlorophenyl)dimethylsilane, Bis(4-hydroxyphenyl)methane, bis(4-hydroxy-3,5-dichlorophenyl)methane, bis(4-hydroxy-3,5-dibromophenyl)methane, 2,2-bis( 4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2, 2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, bis(4-hydroxyphenyl)ether, bis(4-hydroxy- 3,5-dimethylphenyl) ether, bis (4-hydroxy-3,5-dichlorophenyl) ether, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy -3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3-chlorophenyl)fluorene, 9,9-bis(4-hydroxy-3-bromophenyl)fluorene, 9,9 -Bis(4-hydroxy-3-fluorophenyl)fluorene, 9,9-bis(4-hydroxy-3,5-dimethylphenyl)fluorene, 9,9-bis(4-hydroxy-3 ,5-dichlorophenyl)fluorene, 9,9-bis(4-hydroxy-3,5-dibromophenyl)fluorene, 4,4'-biphenol, 3,3'-biphenol, etc., and these And derivatives of. Among these, those having a 9,9-fluorenyl group are particularly preferably used.

Next, the bisphenols are reacted with epichlorohydrin to obtain an epoxy compound having two glycidyl ether groups. In general, this reaction involves oligomerization of a diglycidyl ether compound, so that an epoxy compound of the following general formula (I) is obtained.

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom or a phenyl group, and A is -CO-, -SO ₂ -, -C(CF ₃ ) ₂ -, -Si(CH ₃ ) ₂ -, -CH ₂ -, -C(CH ₃ ) ₂ -, -O-, 9,9- Represents a fluorenyl group or a direct bond, l is 0-10 Is the number of.)

Preferred R ₁ , R ₂ , R ₃ and R ₄ are hydrogen atoms, and preferred A is a 9,9-fluorenyl group. In addition, since a plurality of values are usually mixed, 1 is an average value of 0 to 10 (not limited to an integer), but a preferred average value of 1 is 0 to 3. When the value of l exceeds the upper limit, when a composition for gate insulating films using a bisphenol-type epoxy (meth)acrylate compound synthesized using the epoxy compound is used, the viscosity of the composition becomes too large and coating is difficult.

Next, by reacting the compound of the general formula (I) with acrylic acid or methacrylic acid or both as an unsaturated group-containing monocarboxylic acid, a bisphenol type epoxy (meth)acrylate compound represented by the following general formula (II) is obtained. Get

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom or a phenyl group, R ₅ represents a hydrogen atom or a methyl group, and A is -CO- , -SO ₂ -, -C(CF ₃ ) ₂ -, -Si(CH ₃ ) ₂ -, -CH ₂ -, -C(CH ₃ ) ₂ -, -O-, 9,9-fluorenyl group or It represents a direct bond, and l represents the number of 1-10.)

Since this bisphenol-type epoxy (meth)acrylate compound (II) is a resin having an ethylenically unsaturated double bond, as (A) of the composition for a gate insulating film of the present invention, desired physical properties such as excellent light or thermal curing properties and withstand voltage Eggplant is necessary to make a cured film. On the other hand, in the composition using the photoinitiator as (B), the patterning property by organic solvent development can also be provided.

The bisphenol-type epoxy (meth)acrylate compound of the general formula (II) used in the present invention is a known method, for example, Japanese Laid-Open Patent Publication No. Hei 8-278629 or Japanese Laid-Open Patent Publication 2008 by the above-described process. It can be manufactured by the method described in -9401 or the like. That is, as a method of reacting an unsaturated group-containing monocarboxylic acid with an epoxy compound of the general formula (I), for example, an epoxy group of the epoxy compound and a monocarboxylic acid containing an unsaturated group having a sugar mole are added to the solvent, There is a method of reacting by heating and stirring at 90 to 120°C while blowing air in the presence of a catalyst (triethylbenzyl ammonium chloride, 2,6-diisobutylphenol, etc.).

In the composition for a gate insulating film of the present invention, one or more types of polymerizable monomers (C) having at least one ethylenically unsaturated bond can be used in combination as components other than the bisphenol-type epoxy (meth)acrylate compound to be light or thermally cured. . For example, (meth)acrylic esters having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and ethylene glycol di (Meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tetramethylene glycol di(meth)acrylate, trimethylolpropanetri (Meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth) Acrylate, glycerol (meth) acrylate, sorbitol penta (meth) acrylate, dipentaerythritol penta (meth) acrylate, or dipentaerythritol hexa (meth) acrylate, sorbitol hexa (meth) acrylate, phosphazene (Meth)acrylic acid esters, such as alkylene oxide-modified hexa(meth)acrylate and caprolactone-modified dipentaerythritol hexa(meth)acrylate, are mentioned. However, the polymerizable monomer having at least one ethylenically unsaturated bond used in combination does not have a free carboxyl group.

In the cured product comprising the composition for a gate insulating film of the present invention, the component (A) is contained in an amount of 40 to 90% by mass, preferably 50 to 80% by mass. In addition, the polymerizable monomer (C) is preferably used in a range of 60% by mass or less in the cured product, and preferably 5 to 60% by mass is added.

In the composition for a gate insulating film of the present invention, (B) a photopolymerization initiator or a photopolymerization initiator among the thermal polymerization initiators, for example, acetophenone, 2,2-diethoxyacetophenone, p-dimethylacetophenone, p-dimethylamino Acetophenones such as propiophenone, dichloroacetophenone, trichloroacetophenone, p-tert-butylacetophenone, benzophenone, 2-chlorobenzophenone, benzophenones such as p,p'-bisdimethylaminobenzophenone , Benzoin ethers such as benzyl, benzoin, benzoin methyl ether, benzoin isopropyl ether, and benzoin isobutyl ether, 2-(o-chlorophenyl)-4,5-phenylbiimidazole, 2-( o-chlorophenyl)-4,5-di(m-methoxyphenyl)biimidazole, 2-(o-fluorophenyl)-4,5-diphenylbiimidazole, 2-(o-methoxyphenyl) ) Biimidazole compounds such as -4,5-diphenylbiimidazole, 2,4,5-triarylbiimidazole, 2-trichloromethyl-5-styryl-1,3,4-oxa Diazole, 2-trichloromethyl-5-(p-cyanostyryl)-1,3,4-oxadiazole, 2-trichloromethyl-5-(p-methoxystyryl)-1,3, Halomethyldiazole compounds such as 4-oxadiazole, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2-methyl-4,6-bis(trichloromethyl) -1,3,5-triazine, 2-phenyl-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-(4-chlorophenyl)-4,6-bis(trichloro Romethyl)-1,3,5-triazine, 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-(4-methoxy Naphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3, 5-triazine, 2-(3,4,5-trimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-(4-methylthiostyryl )-4,6-bis(trichloromethyl)-1,3,5-triazine, and other halomethyl-S-triazine compounds, 1,2-octanedione, 1-[4-(phenylthio)phenyl ]-,2-(o-benzoyloxime), 1-(4-phenylsulfanylphenyl)butane-1,2-dione-2-oxime-o-benzoate, 1-(4-methylsulfanylphenyl)butane -1,2-dione-2-oxime-o- O-acyloxime compounds such as acetate, 1-(4-methylsulfanylphenyl)butan-1-one oxime-o-acetate, benzyldimethylketal, thioxanthone, 2-chlorothioxanthone, 2,4 -Sulfur compounds such as diethyl thioxanthone, 2-methyl thioxanthone, and 2-isopropyl thioxanthone, 2-ethyl anthraquinone, octamethyl anthraquinone, 1,2-benzanthraquinone, 2,3-di Anthraquinones such as phenylanthraquinone, organic peroxides such as azobisisobutylnitrile, benzoyl peroxide, and cumene peroxide, 2-mercaptobenzoimidazole, 2-mercaptobenzooxazole, 2-mercaptobenzothiazole Thiol compounds such as, and tertiary amines such as triethanolamine and triethylamine. Among these, it is preferable to use o-acyloxime compounds from the viewpoint of easy obtaining a photosensitive composition for a gate insulating film with high sensitivity. Moreover, two or more types of these photoinitiators can also be used. On the other hand, the photoinitiator used in the present invention is used in the sense of including a sensitizer.

Further, examples of the thermal polymerization initiator in (B) include benzoyl peroxide, lauroyl peroxide, di-t-butylperoxyhexahydroterephthalate, t-butylperoxy-2-ethylhexanoate, 1 Organic peroxides such as ,1-t-butylperoxy-3,3,5-trimethylcyclohexane, azobisisobutyronitrile, azobis-4-methoxy-2,4-dimethylvaleronitrile, azobiscyclo Azo compounds such as hexanone-1-carbonitrile, azodibenzoyl, 2,2-azobis(1-acetoxy-1-phenylethane), water-soluble catalysts such as potassium persulfate and ammonium persulfate, and peroxides or persulfates Any one that can be used for conventional radical polymerization, such as a redox catalyst obtained by combining a reducing agent and a reducing agent, can be used. It can be selected in consideration of the storage stability of the composition for a gate insulating film of the present invention and conditions for forming a cured product. Thermal polymerization initiators may be used alone or in combination of two or more, and can be used in combination with a photoinitiator and a sensitizer.

In the composition for a gate insulating film of the present invention, the (B) photopolymerization initiator or the thermal polymerization initiator makes the component (B) in the resulting cured product 0.1 to 30 mass%, preferably 1 to 20 mass%. If the component (B) is less than 0.1% by mass, the speed of photopolymerization or thermal polymerization is slowed, and sensitivity tends to decrease in photopolymerization, which is not preferable.If it exceeds 30% by mass, the sensitivity is too strong in photopolymerization and the pattern line width is patterned. It is not preferable because it tends to become thicker with respect to the mask, making it difficult to reproduce the line width faithful to the mask. In addition, if the amount of the photo or thermal polymerization initiator is too large, it is likely to cause gas generation during heating in a post process.

In the composition for a gate insulating film of the present invention, it is preferable to adjust the viscosity using a solvent other than the above (A) to (B) (other than (A) to (C) in some cases). Examples of the solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, and propylene glycol, terpenes such as α- or β-terpineol, and acetone, Ketones such as methyl ethyl ketone, cyclohexanone, and N-methyl-2-pyrrolidone, aromatic hydrocarbons such as toluene, xylene, and tetramethylbenzene, cellosolve, methyl cellosolve, ethyl cellosolve, carbitol, Methylcarbitol, ethylcarbitol, butylcarbitol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl Glycol ethers such as ether, ethyl acetate, butyl acetate, cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, carbitol acetate, ethyl carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, And acetic acid esters such as propylene glycol monoethyl ether acetate, and the like, and dissolving and mixing them using them to obtain a uniform solution-like composition.

The composition for imparting the gate insulating film of the present invention contains a bisphenol-type epoxy (meth)acrylate compound (A) having an ethylenically unsaturated bond group as an essential component, but in order to design it with desired properties, including photocuring properties and thermosetting properties. Other resin components can be included. For example, in order to impart alkali solubility, an ethylenically unsaturated bond-containing alkali-soluble resin (D) obtained by reacting a bisphenol-type epoxy (meth)acrylate compound (A) with an acid dianhydride and an acid monoanhydride may coexist. do. The ratio (A)/(D) with the component (A) that can coexist the component (D) is in the range of 70/30 to 40/60, and if the component (D) is less than 70/30, it is alkali-soluble in the composition. It becomes difficult to give. In addition, if the component (D) is more than 40/60, when the composition is used to form a gate insulating film, there is a concern about an adverse effect on transistor characteristics due to residual carboxyl groups. In order to reduce the amount of this residual carboxyl group, it is possible to further coexist (E) epoxy resin, but if the (D) component is more than (A)/(D)=40/60, post-baking at a temperature of 150°C or less In the case of doing so, it is difficult to sufficiently reduce the remaining carboxyl groups.

Examples of the acid dianhydride used when deriving from component (A) to component (D) include pentanetetracarboxylic acid, cyclohexanetetracarboxylic acid, benzophenonetetracarboxylic acid, biphenyltetracarboxylic acid, and biphenylethertetracarboxylic acid. And acid dianhydrides such as, and examples of the acid monoanhydride include acid monoanhydrides such as adipic acid, hexahydrophthalic acid, tetrahydrophthalic acid, phthalic acid, and trimellitic acid.

(D) As the molecular weight range of the alkali-soluble resin containing an ethylenically unsaturated bond group, the weight average molecular weight (Mw) is preferably between 2,000 and 10,000, and particularly preferably between 3,000 and 7,000. In addition, (D) preferably has an acid value in the range of 30 to 200 KOHmg/g.

(E) As the epoxy resin, a phenol novolak type epoxy resin, a bisphenol A type epoxy resin, a biphenyl type epoxy resin, an alicyclic epoxy resin, etc. can be mentioned, and an epoxy resin or an epoxy compound having two or more epoxy groups is used. I can.

The source electrode 40 and the drain electrode 41 can be made of various materials. As a material of the source electrode 40 and the drain electrode 41, for example, a solution in which colloidal metal particles such as gold, silver, and nickel are dispersed, or a paste using metal particles such as silver as a conductive material may be mentioned. In addition, for example, a metal, an alloy, or a transparent conductive film material is formed on the entire surface by a sputtering method or a vapor deposition method, and then a desired resist pattern is formed by a photolithography method or a screen printing method using a resist material. , A desired pattern can be formed by etching with an etching solution such as an acid. In addition, a desired pattern can also be directly formed by a sputtering method or a vapor deposition method using a metal, an alloy, or a transparent conductive film material using a mask. Metal materials that can be used in these sputtering and vapor deposition methods include aluminum, molybdenum, chromium, titanium, tantalum, nickel, copper, silver, gold, platinum, palladium, and the like, and transparent conductive film materials include ITO.

The organic semiconductor layer 50 is an active semiconductor region that forms a channel during transistor operation, and is formed of an organic semiconductor film. The organic semiconductor layer 50 may be made of various materials, for example, polycyclic aromatic hydrocarbons such as pentacene, anthracene, and rubrene, low molecular compounds such as tetracyanoquinodimethane (TCNQ), Polymers such as polyacetylene, poly-3-hexylthiophene (P3HT), and polyparaphenylenevinylene (PPV) may be used.

On the other hand, although not shown in Fig. 1, the organic thin film transistor according to the present embodiment may be provided with a sealing layer, a light-shielding layer, or the like, if necessary.

Next, a method of manufacturing an organic thin film transistor according to Embodiment 1 of the present invention will be described with reference to Fig. 2. 2 is a diagram for explaining a method of manufacturing an organic thin film transistor according to the first embodiment. Meanwhile, in FIG. 2, an example using the above-described gate insulating film will be described.

2(i) is a diagram showing an example of a gate electrode forming process. In the gate electrode formation process, the gate electrode 20 is formed on the insulating substrate 10.

2(ii) is a diagram showing an example of a gate insulating film forming process. In the gate insulating film formation process, a composition for a gate insulating film is applied on the gate electrode 20, a photoresist is applied on the coating film, and after forming a desired pattern by exposure and development, the photoresist is removed by reactive ion etching. After removing the partial gate insulating film, peeling off the photoresist, it is formed by thermosetting. (Pattern formation of the gate insulating film is also possible by using a photopolymerization initiator as the component (B) of the gate insulating film composition and performing exposure and developing with an organic solvent.) Thereby, the gate insulating film 30 is completed.

Fig. 2(iii) is a diagram showing an example of a source/drain electrode formation process. In the source/drain electrode formation process, the source electrode 40 and the drain electrode 41 are formed on the gate insulating film 30. The source electrode 40 and the drain electrode 41 are formed above both ends of the gate electrode 20 so that the central region of the gate electrode 20 becomes an opening, and are partially overlapped with both ends of the gate electrode 20. Is formed. On the other hand, since the source electrode 40 and the drain electrode 41 are made of the same material, the source electrode 40 and the drain electrode 41 may be formed by changing them. The method of forming the source electrode 40 and the drain electrode 41 is not considered. For example, in addition to the photolithography method and the dispenser method, it may be formed by a printing method such as a screen printing method, an inkjet method, a flexo printing method, and a reverse offset printing method. As described above, a film may be formed using a sputtering method or an evaporation method, and then a predetermined pattern may be formed by photolithography or screen printing, or a film may be formed in a predetermined pattern by a sputtering method or a vapor deposition method using a mask. As the material to be used, various materials may be used as described in FIG. 1. On the other hand, it is necessary that the surface smoothness of the gate insulating film 30 after the formation of the source electrode 40 and the drain electrode 41 is maintained.

2(iv) is a diagram showing an example of an organic semiconductor layer forming process. In the organic semiconductor layer forming process, an organic semiconductor film is formed in the opening portion of the source electrode 40 and the drain electrode 41, where the gate insulating film 30 is exposed. The method of forming the organic semiconductor layer 50 is not considered, and may be formed by various methods. The organic semiconductor layer 50 is formed on the gate insulating layer 30 and is formed to cover the end portions of each of the source electrode 40 and the drain electrode 41 on the opening side. The organic semiconductor layer 50 may also be made of various materials, as described in FIG. 1.

[Embodiment 2]

3 is a cross-sectional configuration diagram showing an example of an organic thin film transistor according to Embodiment 2 of the present invention. The organic thin film transistor according to the second embodiment includes an insulating substrate 10, a gate electrode 20, and a gate insulating film 30, and the fact that they are stacked in order from the bottom is the organic thin film transistor according to the first embodiment. Is the same as Therefore, these constituent elements are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted.

In the organic thin film transistor according to the second embodiment, the organic semiconductor layer 51 is formed on the entire surface of the gate insulating film 30, and the source electrode 42 and the drain electrode 43 are formed on the organic semiconductor layer 51 In that it is different from the organic thin film transistor according to the first embodiment.

The organic thin film transistor according to Embodiment 2 has a structure called a bottom gate-top contact structure. As described above, the organic thin film transistor according to the present invention may have a top contact structure as long as the gate insulating film 30 is formed on the gate electrode 20.

On the other hand, the source electrode 42 and the drain electrode 43 are formed on the organic semiconductor layer 50 in the thickness direction, and are different from the first embodiment, but the positions when viewed from the top surface are at both ends of the gate electrode 20 It is the same as that of the organic thin film transistor according to the first embodiment in that it is a position to cover.

Regarding the method of manufacturing the organic thin film transistor according to the second embodiment, the order of forming the source/drain electrode described in FIG. 2(iii) and the process of forming the organic semiconductor layer described in FIG. 2(iv) are changed to form an organic semiconductor layer. In the process, the organic semiconductor layer 51 may be formed on the entire surface of the gate insulating film 30, and the other processes are the same as the manufacturing method of the organic thin film transistor according to the first embodiment, and thus a description thereof will be omitted.

As described above, as described in Embodiments 1 to 2, if the organic thin film transistor according to the present invention has a bottom gate structure in which the gate insulating film 30 is formed on the gate electrode 20, it can be applied to organic thin film transistors of various structures. I can.

Example

Next, an organic thin film transistor according to an embodiment of the present invention will be described. In the organic thin film transistor according to the present embodiment, an organic thin film transistor having a bottom contact structure according to Embodiment 1 shown in FIG. 1 was fabricated using pentacene, which is a low molecular weight semiconductor, for the organic semiconductor layer 50, and The characteristics of the organic thin film transistor were compared. On the other hand, in each of the following examples, the same reference numerals are assigned to the same components as those of the organic thin film transistor according to the first embodiment, and description thereof is omitted.

[Example 1]

An organic thin film transistor according to Example 1 of the present invention was fabricated as follows. First, a glass substrate (20 mm square) was used as the insulating substrate 10, and Al serving as the gate electrode 20 was formed on the insulating substrate 10 to a film thickness of 50 nm by vacuum evaporation. The film thickness was measured using a stylus type surface shape measuring device (Dektak3030, manufactured by ULVAC, Inc.), and the level difference between the film-forming part and the non-film-forming part was measured. The measurement of the film thickness formed in each of the following steps was performed in the same manner.

Next, the gate insulating film composition 1 (composition shown in Table 1) was applied by a spin coating method, and then prebaked on a hot plate at 90°C for 90 seconds. Thereafter, the entire surface of the coating film was irradiated with ultraviolet rays having a wavelength of 365 nm of 800 mJ/cm 2 with an ultra-high pressure mercury lamp of 4.5 mW/cm 2 to perform a photocuring reaction. Then, heat curing treatment was performed at 150° C. for 60 minutes using a hot plate to form a gate insulating film 30 having a thickness of 480 nm.

Subsequently, Au was completely formed on the gate insulating film 30 by vacuum evaporation to a film thickness of 50 nm, and then, a positive photoresist (OFPR800, manufactured by Tokyo Okakogyo Co., Ltd.) was applied by a spin coat method. After pre-baking for 90 seconds at °C, UV rays having a wavelength of 365 nm were irradiated with a 4.5mW/cm2 ultra-high pressure mercury lamp through a photomask for pattern formation. Thereafter, a 2.38 wt% aqueous solution of tetramethylammonium hydroxide (TMAH) was used to develop for 25 seconds by dip development, followed by dip washing for 60 seconds to remove the exposed portion of the photoresist. Next, this sample was immersed in an Au etching solution (AURUM-302 Kanto Chemical Co., Ltd.) for 60 seconds to perform patterning. Thereafter, it was washed with ultrapure water for 60 seconds, and _{dried by blowing N 2} to form a source electrode 40 and a drain electrode 41.

Next, 50 nm of pentacene was formed on the gate insulating film 30 at the openings of the source electrode 40 and the drain electrode 41 by using a vacuum vapor deposition apparatus to form the organic semiconductor layer 50.

As described above, organic transistor 1 was formed. Transistor characteristics were measured for this organic transistor 1.

[Example 2]

As the insulating substrate 10, a fluoropolymer (product name: EPRIMA (registered trademark)) as a planarizing film on a 125 μm-thick PEN film (product name: Teonex (registered trademark) Q65FA, manufactured by Teijin DuPont Film Co., Ltd.) ) AL-X6, manufactured by Asahi Glass Co., Ltd.) were laminated to a thickness of 600 nm, and each layer was formed in the same manner as in Example 1 to form an organic transistor 2. Transistor characteristics were measured for this organic transistor 2.

[Example 3]

Each layer was formed in the same manner as in Example 1 except for the formation of the gate insulating layer 30 to form the organic transistor 3.

The gate insulating film 30 was formed as follows. After applying the gate insulating film composition 2 (composition shown in Table 1) by a spin coating method, it was prebaked on a hot plate at 90°C for 90 seconds. Thereafter, through a photomask for pattern formation, an ultraviolet ray having a wavelength of 365 nm was irradiated with an ultra-high pressure mercury lamp of 4.5 mW/cm 2 and a photocuring reaction of the exposed portion was performed. Then, the exposed coating was developed for 20 seconds by dip development using a 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution, followed by dip washing for 60 seconds to remove the unexposed part of the coating film. . Thereafter, as a post-baking, a hot plate was used to heat cure at 150° C. for 60 minutes to form the gate insulating film 30.

The transistor characteristics were measured for the organic transistor 3 formed as described above.

[Example 4]

As the insulating substrate 10, each layer was formed in the same manner as in Example 3, except that a PEN film having a thickness of 125 μm in which 600 nm of the fluoropolymer used in Example 2 was stacked was used to form an organic transistor 4. Transistor characteristics were measured for this organic transistor 4.

[Comparative Example 1]

Each layer was formed in the same manner as in Example 1, except that the gate insulating film formation step was performed as shown below, to form the organic transistor 3. In the gate insulating film formation step, polyimide varnish (CT4112, manufactured by Kyocera Chemical) was applied by a spin coating method, heated and dried at 100°C for 10 minutes in a nitrogen atmosphere, and heated at 180°C for 1 hour. Thus, a gate insulating film having a thickness of 680 nm was formed. Transistor characteristics were measured for this organic transistor 5.

[Comparative Examples 2 and 3]

Organic transistors 6 (Comparative Example 2) and 7 (Comparative Example 3) were formed in the same manner as in Examples 3 and 4, except that the gate insulating film composition 3 (composition shown in Table 1) was used instead of the gate insulating film composition 2. ) Was formed. On the other hand, the thickness of the gate insulating film 30 was 400 nm. Transistor characteristics were measured for the organic transistors 5 and 6.

* All numbers in the table are parts by mass.

*1 PGMEA solution of bisphenol-type epoxy acrylate in which A is a 9,9-fluorenyl group in the general formula (II) (ASF-400 (Shinnittetsu Sumikin Chemical Co., Ltd. product, resin solid content concentration 50% by mass)

*2 Aronix M-360 (manufactured by Toagosei Co., Ltd.)

*3 Mixture of dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate (manufactured by Nippon Kayaku Co., Ltd.)

*4 Propylene glycol monomethyl ether acetate solution of epoxy acrylate acid adduct with fluorene skeleton (resin solid content 56.5%, manufactured by Shinnittetsu Sumikin Chemical Co., Ltd.)

*5 jER YX4000HK (made by Mitsubishi Chemical Co., Ltd.)

[Example 5]

An organic transistor was formed in the same manner as in Example 1, and the surface roughness of the gate insulating film before and after the formation of the source electrode 40 and the drain electrode 41 was measured. The surface roughness was calculated in a 5 µm×5 µm area using an atomic force microscope system (BrukerAXS, Inc., Nano Scope Dimension Icon).

[Comparative Example 4]

An organic transistor was formed in the same manner as in Comparative Example 1, and the surface roughness of the gate insulating film before and after the formation of the source electrode 40 and the drain electrode 41 was measured in the same manner as in Example 5.

4 is a diagram showing one of the transistor characteristics of the organic thin film transistors according to Examples 1 and 2 and Comparative Example 1, and is a view showing the change characteristics of the drain current to the gate voltage of the organic thin film transistor. 4 shows characteristic curves of organic thin film transistors according to Examples 1 and 2 and Comparative Example 1, respectively. All of the typical p-type characteristics are obtained, and Examples 1 and 2 have no current hysteresis, carrier mobility is 0.1 cm 2 or more, current on-off ratio is 10 ⁶ or more, and the threshold voltage is in the vicinity of 0 V. It showed good switching performance. On the other hand, in Comparative Example 1, some current hysteresis was confirmed. Further, from the transistor characteristic curve, the on-off ratio was 1 digit lower than in Examples 1 and 2, the carrier mobility decreased by 1 digit, and the threshold voltage was significantly shifted toward the positive side.

5 is a view showing a result of measuring flatness in a gate insulating layer of an organic thin film transistor according to Example 5 and Comparative Example 4;

In Example 5, the surface roughness of the gate insulating film was 0.6 nm or less even after the Au electrode was formed, and the surface roughness after the Au electrode was formed in Comparative Example 4 was increased to 0.9 nm, but it was found that good surface flatness was maintained. .

The above evaluation results are put together in Table 2 and shown.

On the other hand, for the transistor characteristics of Examples 3 and 4 and Comparative Examples 2 and 3, each characteristic value read through the characteristic diagram shown in FIG. 4 for Examples 1 and 2 and Comparative Example 1 is described in Table 2, and the characteristic diagram Omitted itself. In addition, the flatness measurements in the gate insulating film of the organic thin film transistors according to Examples 2, 3 and 4 and Comparative Examples 2 and 3 were also carried out in the same manner as in Examples 5 and 4, but drawings are omitted for these as well, Table 2 shows only the measured values of the surface roughness after formation.

As described above, the gate insulating film 30 according to the present invention has high flatness after formation of a thin film and after formation of an electrode or the like by photolithography (when forming an organic semiconductor layer). In addition, the carrier mobility of the organic thin film transistor using the same is high, and there is no shift in threshold voltage or current hysteresis, so that the driving stability and responsiveness of the transistor can be improved.

As described above, preferred embodiments of the present invention have been described in detail, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention.

The present invention can be used for organic transistors and various electronic circuits using organic transistors.

10 Insulation board
20 gate electrode
30 gate insulating film
40, 42 source electrode
41, 43 drain electrode
50, 51 organic semiconductor layers

Claims (5)

A gate insulating film comprising a cured product obtained by curing (A) a compound obtained by reacting a bisphenol-type epoxy compound with an ethylenically unsaturated bond-containing monocarboxylic acid, and (B) a photopolymerization initiator or a thermal polymerization initiator as an essential component, wherein the ( A) is a bisphenol-type epoxy (meth)acrylate compound represented by the following general formula (II), contains 40 to 90 mass% of the component (A) in the cured product, and 0.1 to 30 mass% of the component (B) Gate insulating film comprising a.

(In the formula, R ₁ , R ₂ , R ₃ and R ₄ each independently represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom or a phenyl group, R ₅ represents a hydrogen atom or a methyl group, and A represents 9,9 -Represents a fluorenyl group, and l represents the number of 1-10.) The method of claim 1,
The composition further comprises (C) a polymerizable monomer having one or more ethylenically unsaturated bonds, and a gate insulating film containing 5 to 60 mass% of the component (C) in the cured product. An organic thin film transistor comprising at least one gate electrode, at least one source electrode, at least one drain electrode, at least one organic semiconductor layer, and the gate insulating film according to claim 1 or 2 . The method of claim 3,
An organic thin film transistor having a gate insulating film having a thickness of 0.05 to 1.0 µm. A method of manufacturing an organic thin film transistor including at least one gate electrode, at least one source electrode, at least one drain electrode, at least one organic semiconductor layer, and a gate insulating film,
Preparation of an organic thin film transistor, characterized in that the composition of claim 1 or 2 is coated on the gate electrode and cured at a temperature of 100 to 150°C to form a gate insulating film with a thickness of 0.05 to 1.0 μm. Way.

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