JP5212596B2 - Organic transistor - Google Patents

Description

  The present invention relates to a coating liquid for a gate insulating film suitable for lowering the manufacturing process in the production of an organic transistor, and a gate insulating film formed thereby, and further, an organic transistor fabricated using this gate insulating film It is related.

  Currently, plastic substrates such as polycarbonate and polyethylene terephthalate are being studied as substrates for flexible devices such as electronic paper, but these have the problem of slightly expanding and contracting when heated, and there is an urgent need to improve heat resistance. Yes. On the other hand, in order to reduce the thermal stress applied to the plastic substrate, lowering the temperature of the manufacturing process of the organic transistor has been studied. One of the processes requiring the highest temperature in manufacturing an organic transistor is a step of forming a gate insulating film, and there is a demand for lowering the film forming process of the gate insulating film.

  As a method for forming the gate insulating film at a low temperature, a method of anodizing the surface of the gate electrode (see Patent Document 1), a method using a chemical vapor deposition method (see Patent Document 2), and the like have been proposed. The process is complicated, and a material that can be easily formed by coating, such as spin coating or printing, is desired.

On the other hand, as an example of creating a gate insulating film by coating, first, an example in which poly-4 (vinylphenol) and poly (melamine-formaldehyde) are cured at 200 ° C. can be cited (Non-patent Document 1). However, in this case, the firing temperature is as high as 200 ° C., and at this temperature, the influence of thermal expansion and contraction of the plastic substrate appears remarkably, making it difficult to produce electronic paper having fine pixels. In addition, there is an example in which a low-temperature curable polyimide precursor is baked at 180 ° C. (Non-patent Document 2). However, this is only a polyimide, and a specific structure of the polyimide is not disclosed. Further, the leakage current density is 1 × 10 ⁻⁹ A / cm ² or more at 2 MV / cm, and the insulation is still insufficient.
Patent Document 3 discloses a polyimide obtained by imidizing a polyimide precursor composed of a specific diamine having a cyclobutenetetracarboxylic dianhydride and a hexafluoropropylidene group in the molecule. It is described that a polyimide film excellent in transparency not only in the visible part but also in the ultraviolet part can be obtained even at a high temperature baking of from ℃ to 350 ℃. For liquid crystal display elements and semiconductor elements, protective films, insulating films, and optical communication It is shown that it is suitable for use in such an optical waveguide material. And in the Example, by baking the polyimide precursor obtained from 2,2'-bis (3-methyl-4-aminophenyl) hexafluoropropane and cyclobutane tetracarboxylic dianhydride at 300 degreeC. A polyimide film is formed. However, this document does not mention at all about the formation of a polyimide film by low-temperature baking suitable for a gate insulating film, and therefore, a polyamide precursor structure and film formation conditions for obtaining a polyimide film having good film quality by low-temperature baking. There is no description suggesting a relationship with the above.
JP 2003-258260 A JP 2004-72029 A International Publication No. 2000/22049 Pamphlet “Journal of Applied Physics” (J. Appl. Phys.), Vol. 93 (Vol. 93), No. 5 (No. 5), March 1, 2003 (1 March 2003), p. 2997-2981 “Applied Physics Letters”, Vol. 84 (Vol. 84), No. 19 (No. 19), May 10, 2004 (10 May 2004), p. 3789-3791

The problem to be solved is that a gate insulating film in an organic transistor with good characteristics can be easily formed by coating and can be fired at a low temperature.
Therefore, an object of the present invention is to be fired at a low temperature, specifically, a coating liquid for a gate insulating film capable of firing at a temperature of 180 ° C. or lower, which is a temperature when considering the heat resistance of a plastic substrate, The film can be easily formed by coating and can be baked at a low temperature. Specifically, the baking can be performed at a temperature of 180 ° C. or lower in consideration of the heat resistance of the plastic substrate. When all the manufacturing processes are performed by coating, it is necessary to stack an organic semiconductor on the upper layer of the gate insulating film, but it has excellent solvent resistance to the solvent used at this time, and also has specific resistance, semiconductor mobility, etc. It is to provide a gate insulating film with good characteristics and to provide an organic transistor to which the gate insulating film is applied.

In order to obtain a high specific resistance by low-temperature firing, it is considered that the best means is to use a material mainly composed of soluble polyimide that does not require thermal imidization. However, since the solubility is lowered when the imidization rate is high, it is necessary to use a polyimide having excellent solubility so that high solubility can be obtained even at a high imidization rate.
Furthermore, if a high boiling point solvent is used as a solvent for dissolving the polyimide, the polyimide must be low because a high baking temperature is required because the baking must be performed at the same temperature as the boiling point in order to completely volatilize the solvent. It is desirable that it can be dissolved in a boiling point solvent.
In addition to these, it is necessary to consider the balance between the solubility in the low boiling point solvent and the resistance to the solvent when the organic semiconductor is applied.

This invention is made | formed in view of such a situation, and this invention first made the polyimide obtained by dehydrating and ring-closing the polyamic acid which has a repeating unit represented by following formula (1). A gate insulating film coating liquid, characterized in that it can be baked at a temperature of 180 ° C. or lower, preferably 150 ° C. or lower.
Second, a gate insulating film made of a polyimide film, which is a film obtained by applying and baking a solution of an organic solvent soluble polyimide, and this organic solvent soluble polyimide is , A polyimide obtained by dehydrating and ring-closing a polyamic acid having a repeating unit represented by the following formula (1), wherein the firing temperature of the polyimide film is 180 ° C. or lower, preferably 150 ° C. or lower. This is a gate insulating film.

[In Formula (1), A represents a tetravalent organic group, B ₁ represents at least one divalent organic group selected from the following (2) to (9), and B ₂ represents (2) Represents a divalent organic group other than (9).

(Here, R ⁵ independently represents hydrogen, a methyl group or a trifluoromethyl group.)
b1 and b2 each represent a composition ratio, and the ratio (mol) of b1 and b2 is 0.5 ≦ (b1 / (b1 + b2)) ≦ 1
Have the relationship. ]
In Formula (1), A is preferably a tetravalent organic group having an alicyclic structure.
Furthermore, the tetravalent organic group having an alicyclic structure is preferably at least one selected from the following (10) to (14).

(In the formula (10), R ¹ , R ² , R ³ and R ⁴ each independently represent hydrogen, fluorine or an organic group having 1 to 4 carbon atoms.)
Furthermore, in the formula (1), B ₁ is preferably the above (2), (4), (6) or (8).
In Formula (1), R ^{5 in} B ₁ is preferably a methyl group or a trifluoromethyl group.
And it is preferable that the baking temperature of a polyimide film is 150 degrees C or less.
Moreover, it is preferable that the imidation ratio of an organic solvent soluble polyimide is 50% or more.
The boiling point of the solvent in the organic solvent-soluble polyimide solution is preferably 200 ° C. or lower.
The organic transistor of the present invention preferably uses such a gate insulating film.

The gate insulating film of the present invention has an advantage that the specific resistance is very high and the gate leakage current is extremely small. Furthermore, according to the coating liquid for a gate insulating film of the present invention, a high-quality insulating film can be obtained at a baking temperature of 180 ° C. or lower. Low temperature processing can be achieved. In this case, the film can be formed even by baking at 150 ° C. by selecting a low boiling point solvent.
Furthermore, there is little outgassing and the organic transistor has excellent long-term reliability. And since it is resistant to solvents such as xylene, trichlorobenzene, and trimethylbenzene, the organic semiconductor layer can be formed by coating.

  The gate insulating film of the present invention is composed of a polyimide film. This polyimide film is formed by using a solution of an organic solvent-soluble polyimide obtained by dehydrating and ring-closing polyamic acid having a repeating unit represented by the following formula (1). It is the film | membrane obtained by apply | coating and baking this as an application | coating liquid.

In formula (1), B ₁ represents at least one divalent organic group selected from the following (2) to (9), and B ₂ is a divalent organic group other than the following (2) to (9). Represents.

In formulas (2) to (9), R ⁵ each independently represents hydrogen, a methyl group or a trifluoromethyl group. Two R ⁵ in these formulas are usually the same, but may be different.
The structural features of (2) to (9) in B ₁ of the formula (1) are characterized in that two phenyl groups present with one carbon atom or oxygen atom in between are 3,3′- or 3,4 ′ It is in the point of bonding to the polymer main chain in the form of-.
These polyimides having a divalent organic group are excellent in solubility, have solubility in low-boiling solvents even at a high imidization rate, and have higher insulation properties.
The 3,3′-bond is preferable because of high solubility.
The phenyl group substituent (R ⁵ ) is a hydrogen atom, a methyl group, or a trifluoromethyl group, and is preferably a methyl group or a trifluoromethyl group for the purpose of increasing the solubility of the polyimide. In consideration of the electrical characteristics of the film, a methyl group is preferred.
The group connecting two phenyl groups is an isopropylidene group, a hexafluoroisopropylidene group, a methylene group, or an ether group. From the viewpoint of solubility, a hexafluoroisopropylidene group is most preferred, followed by an isopropylidene group. From the viewpoint of the electrical characteristics of the gate insulating film, an isopropylidene group or a methylene group is preferable.
In _{B 1} of formula (1), the structure of (2) to (9) may be one kind, or may be plural kinds are mixed.

In the formula (1), b1 and b2 each represent a composition ratio, and the ratio (mol) of b1 and b2 has a relationship of 0.5 ≦ (b1 / (b1 + b2)) ≦ 1. That is, the ratio of the structure (2) to (9) of B _{1 in} the entire B ₁ and B ₂ is 50 to 100 mol%.

The structure of B ₂ occupying the remaining 0 to 50 mol% is one having an alicyclic structure, one having an aromatic ring structure, except that it is a divalent organic group other than (2) to (9), It is not particularly limited, such as an aliphatic group, a group containing a hetero atom, or an appropriate combination thereof. Moreover, the structure may be one type or a plurality of types may be mixed. The structure and ratio of this portion contribute to fine adjustment of the solubility of the polyimide and various characteristics of the gate insulating film, and therefore may be determined in consideration of this.
If these specific examples are given, the following B-1 to B-69 may be mentioned.

  Among those mentioned above, polyimides having high solubility are B-2, B-5, B-7, B-8, B-10, B-11, B-13, B-14, B-17. , B-28, B-30, B-34, B-35, B-36, B-43, B-48, B-49, B-54, B-55 to B69 and the like.

In Formula (1), A is a tetravalent organic group, but the structure of A is not particularly limited. The structure of A may be one type or a plurality of types may be mixed.
Specific examples of A are as follows: an alicyclic structure having an alicyclic structure (A-1 to A-24), an aliphatic one (A-25), and four bonds. Are aromatic types (A-26 to A-36), all others (A-37 to A-46), and the like.

  Among these, those having an alicyclic structure are preferable because they have a high specific resistance when formed as a polyimide film and are excellent in solubility, and the structures shown in the following (10) to (14) are particularly preferable.

In formula (10), R ¹ , R ² , R ³ and R ⁴ are each independently hydrogen, fluorine or an organic group having 1 to 4 carbon atoms (for example, an alkyl group such as methyl or ethyl, or a fluorine-substituted product thereof). Represents. These may be the same or different from each other.

  Polyamic acid can be obtained by reaction of tetracarboxylic dianhydride and diamine. In this reaction, the polyamic acid which has a repeating unit represented by Formula (1) can be obtained by using the diamine shown below for 50-100 mol% of a diamine component.

In these, R < ⁵ > represents hydrogen, a methyl group, or a trifluoromethyl group each independently, and is synonymous with the thing of Formula (2)-(9).

  In order to obtain the polyamic acid in which A in the formula (1) has the above-described (10) to (14) structure, the following compound may be used as the tetracarboxylic dianhydride.

Here, R ¹ , R ² , R ³ , and R ⁴ each independently represent hydrogen, fluorine, or an organic group having 1 to 4 carbon atoms, and have the same meaning as that of formula (10).

As a polymerization reaction for obtaining a polyamic acid, a method of mixing a tetracarboxylic dianhydride, a component, and a diamine component in an organic solvent is simple.
As a method of mixing a tetracarboxylic dianhydride component and a diamine in an organic solvent, a solution in which the diamine component is dispersed or dissolved in the organic solvent is stirred, and the tetracarboxylic dianhydride component is used as it is or in an organic solvent. Dispersing or dissolving in a solution, adding a diamine component to a solution obtained by dispersing or dissolving a tetracarboxylic dianhydride component in an organic solvent, alternating tetracarboxylic dianhydride component and diamine component And the like. When the tetracarboxylic dianhydride component or the diamine component is composed of a plurality of types of compounds, the plurality of types of components may be preliminarily mixed, or may be individually polymerized sequentially.

The temperature at which the tetracarboxylic dianhydride component and the diamine component are polymerized in an organic solvent is usually -20 to 150 ° C, preferably 0 to 80 ° C. When the temperature is higher, the polymerization reaction is completed earlier, but when it is too high, a high molecular weight polyamic acid may not be obtained.
The polymerization reaction can be carried out at any concentration, but if the concentration is too low, it will be difficult to obtain a high molecular weight polymer, and if the concentration is too high, the viscosity of the reaction solution will become too high and uniform stirring will occur. Since it becomes difficult, Preferably it is 1-50 mass%, More preferably, it is 5-30 mass%. The initial stage of the polymerization reaction may be performed at a high concentration, and then an organic solvent may be added.

  The organic solvent used in the above reaction is not particularly limited as long as the produced polyamic acid can be dissolved, but specific examples thereof include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethyl sulfoxide, tetramethyl urea, pyridine, dimethyl sulfone, hexamethyl sulfoxide, γ-butyrolactone and the like can be mentioned. These may be used alone or in combination. Further, even a solvent that does not dissolve the polyamic acid may be used by mixing with the above solvent as long as the produced polyamic acid does not precipitate. In addition, since water in the reaction system inhibits the polymerization reaction and further causes hydrolysis of the produced polyamic acid, it is preferable to use an organic solvent that has been dehydrated and dried as much as possible. Furthermore, it is preferable to keep the reaction system under a nitrogen atmosphere, and it is more preferable to carry out the reaction while bubbling nitrogen through the solvent in the reaction system.

  The ratio of the tetracarboxylic dianhydride component and the diamine component used for the polyamic acid polymerization reaction is preferably 1: 0.8 to 1: 1.2 in molar ratio, and this molar ratio is close to 1: 1. The molecular weight of the resulting polyamic acid increases.

The dehydration ring closure (imidation) reaction for obtaining a soluble polyimide is generally thermal imidation in which the polyamic acid solution obtained above is heated as it is, or chemical imidation in which a catalyst is added to the polyamic acid solution. However, chemical imidation in which the imidization reaction proceeds at a relatively low temperature is preferable because the molecular weight of the resulting soluble polyimide is less likely to decrease.
Chemical imidization is possible by stirring polyamic acid in an organic solvent in the presence of a basic catalyst and an acid anhydride for 1 to 100 hours.
Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine and the like. Of these, pyridine is preferable because it has a suitable basicity for proceeding with the reaction.
Examples of the acid anhydride include acetic anhydride, trimellitic anhydride, pyromellitic anhydride, and the like. Among them, acetic anhydride is preferable because the obtained polyimide can be easily purified after imidization.
As an organic solvent, the solvent used at the time of the polyamic acid polymerization reaction described above can be used.

The soluble polyimide solution obtained as described above may be used as it is for the production of the gate insulating film, but it is preferable to use it after the polyimide is recovered and washed by the following procedure.
The reaction solution is poured into a poor solvent that is being stirred to precipitate the polyimide. Although it does not specifically limit as a poor solvent used in this case, Methanol, hexane, heptane, ethanol, toluene, water etc. can be illustrated. The polyimide obtained by precipitation can be collected by filtration, washed with the above poor solvent, and dried at normal temperature or reduced pressure at room temperature or by heating to obtain a powder. If this powder is further dissolved in a good solvent and re-precipitated, the impurities in the polymer can be further reduced. In addition, it is preferable to use three or more kinds of poor solvents such as alcohols, ketones, and hydrocarbons as the poor solvent at this time because the purification efficiency is further improved.

  The molecular weight of the polyamic acid used in the present invention is a weight average molecular weight from the viewpoint of ease of handling, solvent solubility, solvent resistance against nonpolar solvents, and stability of characteristics when a film is formed. Is preferably 2,000 to 200,000, more preferably 5,000 to 50,000. Most preferably, it is 10,000 to 50,000. The molecular weight is determined by GPC (gel permeation chromatography).

The imidation ratio of the soluble polyimide used in the present invention is not necessarily 100%.
Since the solubility of polyimide may be insufficient when the imidation rate is high, the imidation rate may be lowered in this case.
However, if the portion of the amic acid remains, water may be generated by a dehydration cyclization reaction when heated, and it is desirable that the imidization rate is high. From the viewpoint of high insulating properties, it is preferable that the imidization rate is high.
Therefore, in the present invention, the imidization ratio of the soluble polyimide is preferably 50% or more, more preferably 80% or more, and particularly preferably 90% or more. The imidation ratio is calculated by dissolving ¹ polyimide in d ₆ -DMSO (dimethyl sulfoxide-d ₆ ), measuring ¹ H-NMR, and determining the ratio of the proton peak accumulated value to the amidic acid group in the case where no imidization is performed. The ratio of the remaining amic acid group to the theoretical value was calculated, and all the disappeared amic acid groups were calculated as changed to imide groups.

A soluble polyimide solution, which is a coating solution for the gate insulating film, is prepared as follows.
The soluble polyimide obtained above is dissolved in a suitable solvent. Only 1 type of soluble polyimide may be used, or 2 or more types may be used together.
The solvent of the coating solution is not particularly limited as long as it can dissolve polyimide, but a lower boiling point is preferable for the purpose of reducing the solvent remaining in the polyimide film.
The longer the remaining solvent, the better the long-term reliability of the organic transistor.
The boiling point is preferably 200 ° C. or lower, more preferably 180 ° C. or lower, still more preferably 160 ° C. or lower, and most preferably 150 ° C. or lower.
In the case of amide-based polar solvents, glycols easily remain in the film even at a low boiling point due to interaction with the imide group of soluble polyimide or the amidic acid group remaining without imidization. More preferred are system solvents, lactic acid ester solvents, ketone solvents, and the like.
Examples thereof include ethyl cellosolve (135 ° C.), butyl cellosolve (171 ° C.), ethylene glycol monoethyl ether acetate (156 ° C.), ethyl carbitol (193 ° C.), ethyl carbitol acetate, ethylene glycol (196 to 198 ° C.). Propylene glycol monomethyl ether (119 ° C.), 1-ethoxy-2-propanol (132 ° C.), 1-butoxy-2-propanol (133 ° C.), propylene glycol diacetate (190-191 ° C.), propylene glycol-1 -Monomethyl ether-2-acetate (146 ° C.), propylene glycol-1-monoethyl ether-2-acetate (158 ° C.), dipropylene glycol methyl ether (190 ° C.), 2- (2-ethoxypropoxy) propanol (198 ℃) Glycol derivatives, lactate methyl ester (144 ° C.), lactate ethyl ester (154 ° C.), lactate n-propyl ester, lactate n-butyl ester (185 to 187 ° C.), lactate derivatives such as lactate isoamyl ester, acetone (56 ° C), methyl-n-butyl ketone (144 ° C), methyl-n-amyl ketone (152 ° C), cyclohexanone (156 ° C), and the like. In the above, the values in parentheses are the boiling points of the respective solvents.
Furthermore, in order to ensure the flatness of the coating film, these are a mixture of two or more solvents for the purpose of improving the wettability of the coating solution to the substrate and adjusting the surface tension, polarity, and boiling point of the coating solution. It may be used alone.

  Although there is no restriction | limiting in particular in the density | concentration of a coating liquid, 0.1-30 mass% is preferable as a polymer component, More preferably, it is 4-20 mass%. These are arbitrarily set according to the specifications of the coating apparatus and the film thickness to be obtained.

An additive such as a coupling agent can be added to the coating solution for the purpose of improving the adhesion between the polyimide film and the substrate.
Specific examples of the coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 2-aminopropyltrimethoxysilane, 2-aminopropyltriethoxysilane, N- (2-aminoethyl)- 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, N-ethoxycarbonyl-3-aminopropyl Trimethoxysilane, N-ethoxycarbonyl-3-aminopropyltriethoxysilane, N-trimethoxysilylpropyltriethylenetriamine, N-triethoxysilylpropyltriethylenetriamine, 10-trimethoxysilyl-1,4,7-triazadecane , 10-triethoxysilyl-1,4,7-triazadecane, 9-trimeth Sisilyl-3,6-diazanonyl acetate, 9-triethoxysilyl-3,6-diazanonyl acetate, N-benzyl-3-aminopropyltrimethoxysilane, N-benzyl-3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, N-bis (oxyethylene) -3-aminopropyltrimethoxysilane, N-bis (oxyethylene) -3- Aminopropyltriethoxysilane, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol The Lysidyl ether, glycerin diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, 1,3,5,6-tetraglycidyl-2,4-hexanediol, N, N, N ', N' tetraglycidyl -m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ','N'-tetraglycidyl-4,4'-diaminodiphenylmethane and the like.
The content of the functional silane-containing compound and the epoxy group-containing compound is preferably 0.1 to 30% by mass, more preferably 1 to 20% by volume, based on the total polymer mass in the coating solution. .

The soluble polyimide solution is applied and baked as follows.
The soluble polyimide solution can be applied by dipping, spin coating, transfer printing, roll coating, ink jet, spraying, brushing, etc., and uniform film formation is possible.
Although it does not specifically limit as a baking method after apply | coating a coating liquid to a board | substrate, It carries out in a suitable atmosphere, ie, inert gas, such as air | atmosphere and nitrogen, a vacuum, etc. using a hotplate and oven. Can do.
The baking temperature is 180 ° C. or lower, preferably 150 ° C. or lower, considering the case where the solvent can be evaporated and applied to a plastic substrate. Although there is no restriction | limiting in particular in the minimum of baking temperature, When evaporation of a solvent is considered, it is about 40 degreeC normally. Moreover, what is necessary is just to make baking time normally into about 0.5 hour-5 hours. Firing may be performed at two or more stages. Uniformity of the coating film can be further improved by baking in stages.
When the imidization rate of the soluble polyimide contained in the coating liquid is less than 100%, the imidation rate may be increased by this baking.

The gate insulating film of the present invention is a polyimide film obtained as described above.
When the gate insulating film is too thin, dielectric breakdown occurs in a low electric field and does not operate as a transistor. When the gate insulating film is too thick, a high voltage is required to operate the transistor. 5000 nm is preferable, more preferably 50 nm to 1000 nm, and most preferably 200 nm to 600 nm.
If a polyimide film having a desired thickness cannot be obtained by a single application, it may be applied repeatedly.

FIG. 1 and FIG. 2 show structural examples of organic transistors using the gate insulating film of the present invention.
In the organic transistor of the present invention, a gate electrode 2 is formed on a substrate 1 as shown in the figure, and the gate electrode 2 is covered with the gate insulating film 3 of the present invention.
In the example of FIG. 1, the source electrode 4 and the drain electrode 4 are installed on the gate insulating film 3, and the organic semiconductor layer 5 is formed so as to cover them.
On the other hand, in the example of FIG. 2, the organic semiconductor layer 5 is formed on the gate insulating film 3, and the source electrode 4 and the drain electrode 4 are provided on the organic semiconductor layer 5.
The organic transistor of the present invention is not particularly limited as long as it uses the gate insulating film of the present invention.

As the substrate used in the organic transistor of the present invention, plastics such as polycarbonate and polyethylene terephthalate are suitable because of excellent mechanical flexibility.
Examples of the gate electrode, source electrode, and drain electrode include metals such as gold, silver, copper, aluminum, and calcium, inorganic materials such as carbon black, fullerenes, and carbon nanotubes. Furthermore, polythiophene, polyaniline, polypyrrole, And organic π-conjugated polymers such as polyfluorene and derivatives thereof.
These electrode materials may be used alone or in combination with a plurality of materials, and different materials may be used for the gate electrode, the source electrode, and the drain electrode.
As a method for forming these electrodes, vacuum deposition, sputtering, or the like is generally used. In the case of a nano metal ink or an organic π-conjugated polymer, an electrode can be formed by a coating type such as spin coating, spray coating, printing, inkjet, etc., which is preferable.
In forming the electrode by the coating type, water and various alcohols are preferable as the solvent for the nano metal ink and the organic π-conjugated polymer since damage to the gate insulating film of the present invention is small.
N, N-dimethylformamide, N, N-dimethylacetamide, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methylcaprolactam, dimethyl Polar solvents such as sulfoxide and tetramethylurea are also preferable from the viewpoint of excellent solubility of the organic π-conjugated polymer, but these are preferably used within a range where damage to the gate insulating film of the present invention is small.

Examples of the organic semiconductor material include pentacene, oligothiophene, triphenylamine, polythiophene, and derivatives thereof, and examples of the film formation method include spin coating, spray coating, printing, and inkjet. In this case, the organic semiconductor solvent is not particularly limited as long as it can dissolve or uniformly disperse these organic solvents and causes little damage to the gate insulating film of the present invention.
For example, xylene, trichlorobenzene, trimethylbenzene and the like.

First, the synthesis example of the soluble polyimide of this invention is shown with a comparative synthesis example.
In this example, the molecular weight of the soluble polyimide was measured by a GPC (gel permeation chromatography) apparatus {SSC-7200, manufactured by Senshu Scientific Co., Ltd.}. At this time, the column temperature of the GPC column {KD-803 / KD-805, Showa Denko KK} is 50 ° C.,
As eluent, N, N-dimethylformamide (as additives, lithium bromide-hydrate (LiBr · H ₂ O) 30 mmol / L, phosphoric acid / anhydrous crystal (o-phosphoric acid) 30 mmol / L) And tetrahydrofuran (THF) containing 10 ml / L) under the condition of a flow rate of 1.0 ml / min.
As standard samples for preparing calibration curves, TSK standard polyethylene oxide (molecular weight: about 900,000, 150,000, 100,000, 30,000) manufactured by Tosoh Corporation and polyethylene glycol (molecular weight: about 12,000, 4,000, 1,000) manufactured by Polymer Laboratories were used. .
Moreover, the imidation ratio of the soluble polyimide was determined by dissolving the polyimide in d ₆ -DMSO (dimethyl sulfoxide-d ₆ ), measuring ¹ H-NMR, and determining the ratio of the amic acid group remaining without imidization. It calculated | required and calculated | required from the ratio of the integrated value of a proton peak.

<Synthesis Example 1> Synthesis of Soluble Polyimide (PI-1) In a nitrogen stream, in a 200 mL four-necked flask, 18.45 g (0 of 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane .051 mol), and dissolved in 75.92 g of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), then 1.48 g (0.048 mol) of 1,2,3,4-cyclobutanetetracarboxylic anhydride. And this was stirred at room temperature for 8 hours to carry out a polymerization reaction. The obtained polyamic acid solution was diluted to 10% by mass with NMP. To this solution, 26 g of acetic anhydride and 16.1 g of pyridine were added as imidation catalysts, reacted at room temperature for 30 minutes, and then reacted at 40 ° C. for 90 minutes to obtain a polyimide solution. This solution was put into a large amount of a mixed solution of methanol and water, and the resulting white precipitate was filtered and dried to obtain a white polyimide powder. This polyimide powder was confirmed to be 95% imidized by ¹ H-NMR. 4 g of this powder was dissolved in 46 g of propylene glycol monomethyl ether to obtain an 8% by mass solution of polyimide (PI-1). The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the obtained polyimide (PI-1) were Mn = 8,300 and Mw = 16,900, respectively.

<Synthesis Example 2> Synthesis of Soluble Polyimide (PI-2) In a 200 mL four-necked flask under a nitrogen stream, 2.79 g (0. 2) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane was added. 0068 mol), 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane (9.85 g, 0.027 mol) was dissolved in NMP (75.92 g), and then 1,2,3,4- 6.33 g (0.032 mol) of cyclobutanetetracarboxylic anhydride was added, and this was stirred at room temperature for 8 hours to carry out a polymerization reaction. The obtained polyamic acid solution was diluted with NMP to 5% by mass. To this solution, 12.8 g of acetic anhydride and 9.9 g of pyridine were added as imidization catalysts and reacted at 50 ° C. for 3 hours to obtain a polyimide solution. This solution was put into a large amount of a mixed solution of methanol and water, and the resulting white precipitate was filtered and dried to obtain a white polyimide powder. This polyimide powder was confirmed to be 95% imidized by ¹ H-NMR. 4 g of this powder was dissolved in 46 g of propylene glycol monomethyl ether to obtain an 8% by mass solution of polyimide (PI-2). The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the obtained polyimide (PI-2) were Mn = 8,400 and Mw = 15,100, respectively.

<Synthesis Example 3> Synthesis of Soluble Polyimide (PI-3) In a 200 mL four-necked flask under a nitrogen stream, 5.58 g (0.2.2) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane was added. 014 mol), 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane 7.39 g (0.020 mol) was added and dissolved in 76.7 g of NMP, then 1,2,3,4- 6.20 g (0.032 mol) of cyclobutanetetracarboxylic anhydride was added, and this was stirred at room temperature for 8 hours to carry out a polymerization reaction. The obtained polyamic acid solution was diluted with NMP to 5% by mass. To this solution, 14.8 g of acetic anhydride and 11.5 g of pyridine were added as an imidization catalyst and reacted at 50 ° C. for 3 hours to obtain a polyimide solution. This solution was put into a large amount of methanol, and the resulting white precipitate was filtered and dried to obtain a white polyimide powder. This polyimide powder was confirmed to be 95% imidized by ¹ H-NMR. 4 g of this powder was dissolved in 46 g of propylene glycol monomethyl ether to obtain an 8% by mass solution of polyimide (PI-3). The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the obtained polyimide (PI-3) were Mn = 8,900 and Mw = 16,100, respectively.

<Comparative Synthesis Example 1> Synthesis of Polyamic Acid (PI-4) In a nitrogen stream, 8.01 g (0.040 mol) of 4,4′-diaminodiphenyl ether was placed in a 200 mL four-necked flask, and 91.9 g of NMP. Then, pyromellitic dianhydride 8.20 g (0.038 mol) was added, and this was stirred at 23 ° C. for 2 hours to carry out a polymerization reaction and further diluted with NMP. A 6% by mass solution of 4) was obtained. The number average molecular weight (Mn) and weight average molecular weight (Mw) of the obtained polyamic acid (PI-4) were Mn = 11,200 and Mw = 24,300, respectively.

Here, the structures of the obtained polyimide and polyamic acid are summarized below. Among these, PI-1 is represented by B ₁ = (4) [R ⁵ = CH ₃ ], A = (10) [R ¹ , R ² , R ³ , R ⁴ = H] in the formula (1). It is obtained from something.

In order to investigate the solubility of the polyimides synthesized in Synthesis Examples 1 to 3 and PI-1 to PI-3 in low-boiling solvents, propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), methyl n Experiments were conducted using amyl ketone (MAK), cyclohexanone (CH), and ethyl lactate (EL) under the following conditions.
Any low boiling point solvent was put into a round bottom flask, and 10% by mass of powdered PI-1 was put therein, and stirred for 12 hours while heating in an oil bath so that the temperature of the solvent was 50 ° C. PI-2 and PI-3 were also tested under the same conditions.
The results are shown in Table 1. Table 2 shows the boiling points of the solvents used. The solubility was evaluated by visual observation, and those in which no solid undissolved residue was observed were indicated by ○ in the table, and those in which much undissolved residue was observed were indicated by × in the table. PI-1 and PI-2 showed good solubility in any solvent, and PI-3 hardly dissolved in any solvent except cyclohexanone, but 9% by mass or more with respect to cyclohexanone. It was dissolved and it was confirmed that there was no practical problem in forming a gate insulating film.
It was revealed that the polyimide of the present invention exhibits excellent solubility even in a low boiling point solvent.

In this example, the degassing amount of the polyimide film was determined by using a TDS (Thermal Desorption Spectroscopy) system {WA1000S, manufactured by Electronic Science Co., Ltd.}, a temperature range of 50 ° C. to 300 ° C., and a temperature rising rate of 1 ° C. It was measured as / sec.
<Degassing evaluation of PI-1 (Example)>
The solution of PI-1 prepared in Synthesis Example 1 was dropped on a Si wafer (thickness 0.5 mm) with a syringe with a 0.2 μm pore filter and applied by spin coating. Thereafter, heating is performed for 5 minutes on an 80 ° C. hot plate in the atmosphere to volatilize the organic solvent, and then the Si wafer is cleaved into 1 cm square and then baked on a 150 ° C. hot plate for 60 minutes. A polyimide film of about 200 nm was obtained. Using TDS, the degassing amount from the polyimide and polyamic acid thin film was evaluated at Mw = 16, 18, and 44. The evaluation results are shown in FIGS. Almost no outgassing from the polyimide film has been observed, and it is considered that PI-1 is very unlikely to cause deterioration of the performance of the organic transistor due to outgassing.

<Degassing evaluation of PI-4 (comparative example)>
A solution of PI-4 synthesized in Comparative Synthesis Example 1 was used, a polyimide film was formed in the same manner as in Example 1 except that the film thickness was 220 nm, and the degassing amount was measured using the TDS method. A very large amount of degassing was observed at all Mw = 16, 18, 44. The evaluation results are shown in FIGS. When Mw = 16, an extremely large amount of degassing is observed from around 100 ° C., and there is a concern about adverse effects on device characteristics. In addition, even at Mw = 18 and 44, degassing having a peak near 160 ° C. was observed. In particular, since H ₂ O represented by Mw = 18 is considered to promote the deterioration of the organic semiconductor layer, PI-4 is considered highly likely to cause problems in the long-term reliability and thermal stability of the organic transistor. It is done.

  In this example, the polyimide film thickness was determined by peeling a part of the film with a cutter knife and using a fully automatic fine shape measuring instrument {ET4000A, manufactured by Kosaka Laboratory Co., Ltd.} with a measuring force of 10 μN and a sweep speed of 0. The thickness was determined to be 05 mm / s by measuring the step.

<Solvent resistance of PI-1 (Example)>
In order to investigate the solvent resistance of PI-1 synthesized in Synthesis Example 1, experiments were conducted under the following conditions using xylene, trichlorobenzene, and trimethylbenzene, which are commonly used to dissolve organic semiconductor polymers. It was.
The solution of PI-1 prepared in Synthesis Example 1 was dropped onto a glass substrate with ITO (2.5 cm square, 0.7 mm thick) with a syringe with a 0.2 μm pore filter and applied by spin coating. Thereafter, heating was performed for 5 minutes on an 80 ° C. hot plate in the atmosphere to volatilize the organic solvent, followed by baking for 60 minutes on a 150 ° C. hot plate to obtain a polyimide film having a thickness of 250 nm. Next, 100 mL of any one solvent of xylene, trichlorobenzene, and trimethylbenzene is put into a beaker and heated using an oil bath so that the liquid temperature becomes 80 ° C., and the polyimide substrate is put into this solvent. It was immersed for 30 minutes. Thereafter, the polyimide thin film substrate was dried using an air blower, and the remaining film rate was evaluated.
The remaining film ratio was calculated from the ratio of the film thickness before the solvent treatment and the film thickness after the solvent treatment. The results are shown in Table 3.
The remaining film ratio of PI-1 was 104% with respect to xylene, and a slight swelling was observed, but at a level that does not cause a problem in practice. On the other hand, with respect to trichlorobenzene and trimethylbenzene, the remaining film ratios were 101% and 100%, and it was found that they were not affected at all. Further, no dissolution was observed in any solvent. From this, it became clear that the gate insulating film for organic transistors of the present invention has excellent solvent resistance.

<Solvent resistance of PI-2 (Example)>
In order to investigate the solvent resistance of PI-2 synthesized in Synthesis Example 2, an experiment was conducted under the same conditions as described above except that the film thickness of polyimide was 300 nm. The results are shown in Table 3.
The remaining film ratio of PI-2 was 102% with respect to xylene, and a slight swelling was observed. For trichlorobenzene and trimethylbenzene, the remaining film rate was 101% and 100%, and it was found that there was no influence at all. Further, no dissolution was observed in any solvent. From this, it became clear that the gate insulating film for organic transistors of the present invention has excellent solvent resistance.

<Solvent resistance of PI-3 (Example)>
In order to investigate the solvent resistance of PI-3 synthesized in Synthesis Example 3, an experiment was conducted under the same conditions as described above except that the film thickness of polyimide was 230 nm. The results are shown in Table 3.
The remaining film ratio of PI-3 was 105% and 106% with respect to xylene and trichlorobenzene, and although slight swelling was observed, it was a level that does not cause a problem in practice. On the other hand, with respect to trimethylbenzene, the remaining film ratio was 100%, and it was found that there was no influence. Further, no dissolution was observed in any solvent. From this, it became clear that the gate insulating film for organic transistors of the present invention has excellent solvent resistance.

In this example, the specific resistance of the polyimide film (gate insulating film) is {HP4156C, manufactured by Agilent Co., Ltd.], the relative dielectric constant is 100 KHz, 1 V, and {AG-4411B, manufactured by Ando Electric Co., Ltd.} In order to remove the influence of ambient humidity and active substances, the device was immediately transferred to a nitrogen gas atmosphere after completion of the device, and allowed to stand for about 10 minutes until the atmosphere was stabilized, and then measurement was performed.
<Insulation evaluation of PI-1 (Example)>
In order to investigate the insulation of PI-1 synthesized in Synthesis Example 1, the specific resistance of a thin film made of polyimide and polyamic acid was measured by the following experimental procedure.
The solution of PI-1 prepared in Synthesis Example 1 was dropped onto a glass substrate with ITO (2.5 cm square, 0.7 mm thick) with a syringe with a 0.2 μm pore filter and applied by spin coating. Thereafter, in the atmosphere, the organic solvent was volatilized by heating on an 80 ° C. hot plate for 5 minutes, and then baked on a hot plate at 150 ° C. for 60 minutes to obtain a polyimide film having a thickness of about 220 nm. Next, in order to obtain a good contact between the ITO electrode and the probe, a part of the polyimide film is scraped to expose the ITO, and then a vacuum deposition apparatus is used to form a diameter of 0.5 mm and a film thickness of 100 nm on the polyimide film and the ITO. The aluminum electrode was laminated. The conditions for vacuum deposition at this time were room temperature, a degree of vacuum of 3 × 10 ⁻³ Pa or less, and an aluminum deposition rate of 0.3 nm / sec or less. Thus, the sample for the specific resistance measurement of a polyimide thin film was produced by forming an electrode on the upper and lower sides of a polyimide thin film.
The specific resistance is measured in a nitrogen atmosphere, the voltage is set to 19 V so that the applied electric field is 1 MV / cm, and the current density is measured 60 seconds after the voltage is applied. The current value is 0.029 pA. It was -0.070 pA. When the specific resistance was calculated therefrom, the specific resistance was 6.2 × 10 ^{15 to} 1.5 × 10 ¹⁶ Ω · cm, which was sufficient for use as a gate insulating film of an organic transistor even when baked at 150 ° C. Insulation was shown.
Further, in order to investigate the relationship between the leakage current and the electric field in more detail, the relationship between the current density and the electric field when the voltage was increased by 2 V after providing a holding time of 10 seconds from 0 V to 50 V was plotted (FIG. 6). . Even when a high voltage of 50 V (2.3 MV / cm) is applied, the current density is shown to flow only 10 ⁻¹⁰ A / cm ² or less, and even when baked at 150 ° C., as a gate insulating film for organic transistors It showed very good characteristics. The relative dielectric constant of this polyimide film was 3.0.

<Evaluation of insulation of PI-2 (Example)>
A polyimide film was formed by the same method as described above except that the PI-2 solution synthesized in Synthesis Example 2 was used and the film thickness was 210 nm, thereby producing an element for measuring specific resistance. The specific resistance was measured under the same conditions except that the voltage was set to 21 V so that an electric field of 1 MV / cm was applied to the thin film made of PI-2. The current flowing in the insulating film made of polyimide and polyamic acid obtained from the PI-2 solution was 0.024 pA to 0.066 pA, and the specific resistance calculated therefrom was 7.6 × 10 ^{15 to} 2.1 × 10 6. ¹⁶ Ω · cm. Even when baked at 150 ° C., it showed sufficient insulating properties to be used as a gate insulating film of an organic transistor.
Moreover, when the relationship between the current density and the electric field was plotted in the same manner as above (FIG. 6), it was shown that even when a high voltage was applied, the current density flowed only at 10 ⁻¹⁰ A / cm ² or less, at 150 ° C. Even when baked, it showed very excellent characteristics as a gate insulating film for organic transistors.

<Insulation evaluation of PI-3 (Example)>
A polyimide film was formed by the same method as described above except that the PI-3 solution synthesized in Synthesis Example 3 was used and the film thickness was set to 220 nm. Thus, an element for measuring specific resistance was produced. The specific resistance was measured under the same conditions except that the voltage was set to 22 V so that an electric field of 1 MV / cm was applied to the thin film made of PI-3. The current flowing through the insulating film made of polyimide and polyamic acid obtained from the PI-2 solution was 0.020 pA to 0.086 pA, and the specific resistance calculated therefrom was 5.7 × 10 ^{15 to} 2.4 × 10. ¹⁶ Ω · cm. Even when baked at 150 ° C., it showed very good characteristics as a gate insulating film for organic transistors.
Further, when the relationship between the current density and the voltage was plotted in the same manner as above (FIG. 6), it was shown that even when a high voltage was applied, the current density flowed only at 10 ⁻¹⁰ A / cm ² or less, at 150 ° C. Even when baked, it showed very excellent characteristics as a gate insulating film for organic transistors.

<Insulation evaluation of PI-4 (comparative example)>
A polyimide film was formed by the same method as above except that the PI-4 solution synthesized in Comparative Synthesis Example 1 was used and the film thickness was changed to 210 nm, thereby producing an element for measuring specific resistance. The specific resistance was measured under the same conditions except that the voltage was set to 22 V so that an electric field of 1 MV / cm was applied to the thin film made of PI-4. The current flowing through the insulating film made of polyimide and polyamic acid obtained from the PI-4 solution was 7.0 pA, and the specific resistance calculated therefrom was 7.2 × 10 ¹³ Ω · cm. It was shown that when the insulating film made of polyimide and polyamic acid obtained from the PI-4 solution was baked at 150 ° C., the specific resistance was remarkably inferior when used as a gate insulating film of an organic transistor. The relative dielectric constant of this polyimide film was 3.6.

The electrical characteristics of the organic transistor were quickly transferred to vacuum (vacuum degree 5 × 10 ⁻² Pa or less) after the device was completed in order to remove the influence of ambient humidity and active substances by {HP4156C, manufactured by Agilent]. , And measured after allowed to stand for about 30 minutes.

<Evaluation of electrical characteristics of organic transistor (Example)>
In order to evaluate the characteristics of polyimide as a gate insulating film, an organic transistor was fabricated. The solution of PI-1 prepared in Synthesis Example 1 was dropped onto a glass substrate with ITO (2.5 cm square, 0.7 mm thick) with a syringe with a 0.2 μm pore filter and applied by spin coating. Thereafter, in the air, the organic solvent was volatilized by heating on an 80 ° C. hot plate for 5 minutes, and then baked on a 150 ° C. hot plate for 60 minutes to obtain a polyimide film having a film thickness of about 425 nm. Moreover, the electrostatic capacitance C of this insulating film was 6.25 × 10 ⁻⁹ (F / cm ² ) when calculated from the relative dielectric constant and the film thickness of the polyimide. Next, after sufficiently purifying poly (3-hexylthiophene-2,5-diyl) (hereinafter abbreviated as P3HT) containing 98.5% or more of HT bonds purchased from Sigma-Aldrich, 1% by mass in xylene After dissolving, a coating solution of P3HT was prepared. This coating solution was applied onto polyimide to form a P3HT thin film. The film forming method was a spin coating method, and was performed in a nitrogen atmosphere with an oxygen concentration of 0.5 ppm or less. Next, in order to completely volatilize the solvent, heat treatment was performed in a vacuum state at 100 ° C. for 90 minutes. Next, about 60 nm of gold was laminated on the P3HT film using a vacuum deposition apparatus, and source / drain electrodes having a channel length L of 90 μm and a channel width W of 2 mm were formed. The conditions during vacuum deposition were room temperature, a degree of vacuum of 3 × 10 ⁻³ Pa or less, and a gold deposition rate of 0.1 nm / sec or less. The organic transistor thus produced was left to stand overnight in a nitrogen atmosphere with an oxygen concentration of 0.5 ppm or less, and then was exposed to the atmosphere once to be installed in a measuring apparatus, and then the electrical characteristics were evaluated.

Electrical characteristics were measured using a vacuum chamber while maintaining a degree of vacuum of 5 × 10 ⁻² Pa or less. In order to measure the modulation of the drain current with respect to the gate voltage, the source-drain voltage (V _D ) is set to −60 V, and the gate voltage (V _G ) is changed from +20 V to −60 V in 2 V steps until the current is sufficiently stabilized. The value after holding the voltage for 3 seconds was taken as the measured drain current. Characteristics of the drain current versus gate voltage measured in this way the (V _G -I _D characteristic) shown in FIG. By applying the gate voltage in the negative direction, the drain current _ID was significantly increased, and it was confirmed that P3HT operates as a p-type semiconductor. In general, the drain current _ID in a saturated state can be expressed by the following formula. That is, the mobility μ of the organic semiconductor can be obtained from the slope of the graph when the square root of the absolute value of the drain current _ID is plotted on the vertical axis and the gate voltage V _G is plotted on the horizontal axis.
_{I D = WCμ (V G -V} T) 2 / 2L
In the above equation, W is the channel width of the transistor, L is the channel length of the transistor, C is the capacitance of the gate insulating film, V _T is the threshold voltage of the transistor, and μ is the mobility. When the mobility μ of P3HT was calculated based on this formula, it was 9.1 × 10 ⁻⁴ cm ² / Vs. Further, the threshold voltage V _T was 15 V, the current flowing when the organic transistor was in the off state, the off current was 0.65 nA, and the ratio of the on state to the off state (on / off ratio) was 580 (Table 4). Thus, the gate insulating film of the present invention exhibited sufficiently excellent characteristics as an organic transistor.

<Evaluation of electrical characteristics of organic transistor (comparative example)>
An organic transistor was prepared in the same manner as described above except that the PI-4 solution synthesized in Comparative Synthesis Example 1 was used and the film thickness was changed to 370 nm, and the electrical characteristics were measured. The results are shown in FIG. The capacitance C of this insulating film was calculated from the relative dielectric constant and the film thickness of the polyimide, and was 8.56 × 10 ⁻⁹ (F / cm ² ). The mobility of P3HT was 8.7 × 10 ⁻⁴ cm ² / Vs, the off current was 38.9 nA, and the on / off ratio was 15. Further, the threshold voltage could not be measured because the organic transistor did not take a complete off state. Thus, it was shown that an organic transistor using PI-4 cannot be used as an organic transistor because of a very large leakage current and a normal off state.

<Synthesis Example 4> Synthesis of Soluble Polyimide (PI-5) In a 200 mL four-necked flask under a nitrogen stream, 5.435 g of 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane (0 0.15 mol) and dissolved in 36.75 g of NMP, then 3.753 g (0.015 mol) of bicyclo [3.3.0] -octane-2,4,6,8-tetracarboxylic anhydride was added. This was stirred at 80 ° C. for 48 hours to carry out a polymerization reaction. The obtained polyamic acid solution was diluted to 8% by mass with NMP. To this solution, 19.55 g of acetic anhydride and 9.09 g of pyridine were added as imidization catalysts and reacted at 100 ° C. for 3 hours to obtain a polyimide solution. This solution was poured into a large amount of a water / methanol mixed solution, and the resulting white precipitate was filtered and dried to obtain a white polyimide powder containing a repeating unit represented by the following formula. This polyimide powder was confirmed to be 90% imidized by 1H-NMR. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of this polyimide powder were Mn = 11,400 and Mw = 18,000, respectively.

<Synthesis Example 5> Synthesis of soluble polyimide (PI-6)

In a nitrogen stream, 2.029 g (0.0056 mol) of 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane was placed in a 200 mL four-necked flask and dissolved in 24.67 g of NMP. 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride (3.36 g, 0.0112 mol) was added and stirred at 50 ° C. for 15 hours, and then NMP 37 0.04 g, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride 5.045 g (0.0168 mol), 4,4-diaminodiphenyl ether 3.925 g (0 1.096 mol), 1.055 g (0.0028 mol) of 1-octadecyloxy-2,4-diaminobenzene was added, and this was stirred at 50 ° C. for 24 hours for polymerization. Reaction was performed. The obtained polyamic acid solution was diluted to 8% by mass with NMP. To this solution, 28.55 g of acetic anhydride and 13.28 g of pyridine were added as imidization catalysts and reacted at 50 ° C. for 3 hours to obtain a polyimide solution. This solution was poured into a large amount of methanol, and the resulting white precipitate was filtered off and dried to obtain a white polyimide powder containing a repeating unit represented by the following formula. This polyimide powder was confirmed to be 95% imidized by 1H-NMR. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of this polyimide powder were Mn = 13,500 and Mw = 28,200, respectively.
(Here, the ratio of l, k, j is expressed by the following equation: l / (l + k + j) = 0.2, k / (l + k + j) = 0.7)

<Synthesis Example 6> Synthesis of soluble polyimide (PI-7)

In a 200 mL four-necked flask under a nitrogen stream, 2.79 g (0.00689 mol) of 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane and 2,2-bis (3-amino- 4.85 g (0.0272 mol) of 4-methylphenyl) hexafluoropropane was added and dissolved in 76.48 g of NMP, and then 6.59 g (0.0337 mol) of 1,2,3,4-cyclobutanetetracarboxylic anhydride. And this was stirred at room temperature for 8 hours to carry out a polymerization reaction. The obtained polyamic acid solution was diluted with NMP to 5% by mass. To this solution, 12.8 g of acetic anhydride and 9.9 g of pyridine were added as imidization catalysts and reacted at 50 ° C. for 3 hours to obtain a polyimide solution. This solution was poured into a mixed solution of a large amount of methanol and water, and the resulting white precipitate was filtered and dried to obtain a white polyimide powder containing a repeating unit represented by the following formula. This polyimide powder was confirmed to be 95% imidized by 1H-NMR. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of this polyimide powder were Mn = 24,000 and Mw = 42,000, respectively.

(Here, the ratio of n and m is expressed by the following equation: n / (n + m) = 0.8)

<Comparative Synthesis Example 2> Synthesis of Soluble Polyimide (PI-8)

In a 200 mL four-necked flask under a nitrogen stream, 2.79 g (0.00689 mol) of 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane and 2,2-bis (3-amino- 4.85 g (0.0272 mol) of 4-methylphenyl) hexafluoropropane was added and dissolved in 76.48 g of NMP, and then 6.67 g (0.034 mol) of 1,2,3,4-cyclobutanetetracarboxylic anhydride. And this was stirred at room temperature for 8 hours to carry out a polymerization reaction. The obtained polyamic acid solution was diluted with NMP to 5% by mass. To this solution, 12.8 g of acetic anhydride and 9.9 g of pyridine were added as imidization catalysts and reacted at 50 ° C. for 3 hours to obtain a polyimide solution. This solution was put into a mixed solution of a large amount of methanol and water, and the resulting white precipitate was filtered and dried to obtain a white polyimide powder represented by the following formula. This polyimide powder was confirmed to be 95% imidized by 1H-NMR. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of this polyimide powder were Mn = 29,000 and Mw = 60,000, respectively.

<Solvent solubility of PI-5 (Example)>
In order to investigate the solvent solubility of PI-5, experiments were conducted under the following conditions using propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), cyclohexanone, and γ-butyrolactone.
Any low boiling point solvent was put in a round bottom flask, and 10% by mass of powdered PI-6 was put therein, and stirred for 3 hours while heating in an oil bath so that the temperature of the solvent was 50 ° C.
PI-5 showed good solubility in any solvent.
<Solvent solubility of PI-6 (Example)>
In order to investigate the solvent solubility of PI-6, an experiment was conducted using cyclohexanone and γ-butyrolactone under the following conditions.
Any low boiling point solvent was put in a round bottom flask, and 10% by mass of powdered PI-6 was put therein, and stirred for 3 hours while heating in an oil bath so that the temperature of the solvent was 50 ° C.
PI-6 showed good solubility in any solvent.
<Solvent solubility of PI-7 (Example)>
In order to investigate the solvent solubility of PI-7, cyclohexanone was put into a round bottom flask, and 10% by mass of powdered PI-7 was put therein, and heated with an oil bath so that the temperature of the solvent became 50 ° C. Stir for 3 hours.
PI-7 showed good solubility in cyclohexanone.
<Solvent solubility of PI-8 (comparative example)>
In order to investigate the solvent solubility of PI-8, experiments were conducted using propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), and cyclohexanone under the following conditions.
Any low-boiling solvent was put into a round bottom flask, and 10% by mass of powdered PI-8 was put therein, and stirred for 3 hours while heating in an oil bath so that the temperature of the solvent was 50 ° C.
PI-8 did not dissolve in all solvents.
The results so far are summarized in Table 5.

<Solvent resistance of PI-5 (Example)>
In order to examine the solvent resistance of PI-5 to xylene, a polyimide film having a thickness of 307 nm was formed in the same manner as in Example 4, and immersed in a xylene solvent heated to 50 ° C. for 5 minutes. Next, the solvent was dried on a hot plate at 180 ° C., and the remaining film ratio was measured. The residual film ratio of the polyimide film made of PI-5 was 100%, indicating good solvent resistance.

  The gate insulating film according to the present invention can reduce the manufacturing process of the organic transistor, and can provide an inexpensive and high-performance organic transistor.

It is a schematic sectional drawing of the organic transistor which shows the usage example of the gate insulating film of this invention. It is a schematic sectional drawing of the organic transistor which shows the usage example of the gate insulating film of this invention. It is a graph which shows the desorption gas intensity | strength (Intensity) in the molecular weight 16 of the thin film obtained from the solution of PI-1 (Example) and PI-4 (comparative example). It is a graph which shows the desorption gas intensity | strength in the molecular weight 18 of the thin film obtained from the solution of PI-1 (Example) and PI-4 (comparative example). It is a graph which shows the desorption gas intensity | strength in the molecular weight 44 of the thin film obtained from the solution of PI-1 (Example) and PI-4 (comparative example). Current density (CurrentDensity) and voltage (ElectricField) of thin films obtained from solutions of PI-1 (Example), PI-2 (Example), PI-3 (Example) and PI-4 (Comparative Example) It is a graph which shows a relationship. It is a graph which shows the relationship between the drain current (DrainCurrent) and gate voltage (GateVoltage) of the organic transistor which used the thin film obtained from the solution of PI-1 (Example) and PI-4 (comparative example) as a gate insulating film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulating film 4 Source electrode, drain electrode 5 Organic semiconductor layer

Claims (7)

Formula solution is that the organic solvent-soluble polyimide to obtain a polyamic acid by cyclodehydration with a repeating unit represented by formula (1), applied to a film obtained by baking, the baking temperature of the polyimide film An organic transistor using a gate insulating film, characterized by being 180 ° C. or lower and a boiling point of a solvent in an organic solvent-soluble polyimide solution being 200 ° C. or lower.



[In Formula (1), A represents a tetravalent organic group, B ₁ represents at least one divalent organic group selected from the following (2) to (9), and B ₂ represents (2) Represents a divalent organic group other than (9).



(Here, R ⁵ independently represents hydrogen, a methyl group or a trifluoromethyl group.)
b1 and b2 each represent a composition ratio, and the ratio (mol) of b1 and b2 is 0.5 ≦ (b1 / (b1 + b2)) ≦ 1
Have the relationship. ] In the formula (1), A is an organic transistor having a gate insulating film is used according to claim 1 which is a tetravalent organic group having an alicyclic structure. The organic transistor using the gate insulating film according to claim 1 or 2 , wherein the tetravalent organic group having an alicyclic structure is at least one selected from the following (10) to (14).



(In the formula (10), R ¹ , R ² , R ³ and R ⁴ each independently represent hydrogen, fluorine or an organic group having 1 to 4 carbon atoms.) In the formula (1), _{B 1} is the (2), (4), (6) or (8) an organic transistor having a gate insulating film is used according to any one of claims 1 to 3. In the formula (1), an organic transistor having a gate insulating film is used according to any one of claims 1 ~ 4 R ⁵ is a methyl group or a trifluoromethyl group in B _1. Organic transistor gate insulating film is used according to any one of claims 1 to 5, the firing temperature of the polyimide film is 0.99 ° C. or less. Organic transistor gate insulating film is used according to any one of claims 1 to 6, the imidization ratio of the organic solvent-soluble polyimide is 50% or more.