JP2006229053A - Field effect organic thin film transistor having organic semiconductor layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect organic thin film transistor having deposition properties, exhibiting sufficient flexibility and generating a drain current with low power consumption. <P>SOLUTION: The organic thin film transistor comprises a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, and an organic semiconductor layer wherein the gate insulating layer comprises a layer of organic insulator having a polar group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a field effect organic thin film transistor having an organic semiconductor layer and a method for manufacturing the same.

As shown in FIG. 1, a conventional silicon-based thin film transistor (TFT) generally forms a source electrode and a drain electrode by performing high-concentration impurity diffusion on a Si substrate, and forms a thermal oxide film as a gate insulating film. (SiO ₂ ) and a structure in which a gate electrode is stacked. By controlling the electric field derived from the gate electrode, a channel is formed between the source and drain electrodes to function as a transistor.

  On the other hand, in recent years, there has been a demand for a flexible sheet display comprising pixels (for example, a display unit such as a liquid crystal, an organic EL, and an electrophoretic microcapsule, and a transistor for driving the same) formed in a matrix arrangement on a substrate. There is. There are various problems when trying to achieve a flexible seed display using conventional silicon-based thin film transistors. (1) Derived from Si contained, sufficient flexibility cannot be secured, and it is destroyed by mechanical stress. (2) Since high temperature is required, usable substrate types are limited. (3) Enormous equipment costs are generated. (4) Advantages of organic semiconductor materials (flexibility, low It is not practical, for example, cost cannot be fully utilized.

  Instead, thin film transistors with organic active layers have attracted much attention in recent years as inexpensive alternatives to conventional silicon-based thin film transistors. By configuring a device using an organic material, a thin film or a circuit can be easily formed by a wet method such as a printing method, a spin coating method, or an immersion method. That is, it is possible to manufacture a device without going through a costly process required in the manufacturing process of the silicon-based TFT, and it is expected that the manufacturing cost is greatly reduced and the area is increased. In addition, the advantages of organic material based devices include mechanical flexibility, process simplification, weight reduction and cost reduction.

  However, when an organic thin film transistor is manufactured using an organic material, an electric field induction type organic thin film transistor that has the original function of the transistor, has excellent film forming properties, and is highly flexible has not been obtained. There's a problem.

  The present invention has been made in order to solve the above-described problems, and provides a field effect organic thin film transistor having film forming properties, high flexibility, and capable of generating drain current with low power consumption. The purpose is to do.

  In view of the above-mentioned problems, intensive studies have resulted in the inventions shown in the following (1) to (8).

(1) A substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, and an organic semiconductor layer,
The organic thin film transistor, wherein the gate insulating layer includes a layer made of an organic insulator having a polar group. Thereby, a high electrostatic capacity is obtained by the organic insulator containing the polar group, and further drain current _IDS is improved by making the film thinner.

(2) The organic thin film transistor according to claim 1, wherein the organic insulator is cyanoethyl pullulan. Thereby, a high electrostatic capacity is obtained by the organic insulator containing the polar group, and further drain current _IDS is improved by thinning the film.

  (3) The organic thin film transistor according to claim 1 or 2, wherein the surface of the gate insulating layer is subjected to silane coupling treatment. Thus, in addition to the above, the transistor operation is changed from the depletion operation to the enhancement operation, thereby achieving a high on / off ratio.

  (4) The organic thin film transistor according to any one of claims 1 to 3, wherein the gate insulating layer further includes an inorganic insulating film. As a result, in addition to the above, it becomes possible to suppress the gate leakage current of the transistor, and further to lower the drive voltage.

  (5) The organic thin film transistor according to claim 4, wherein the inorganic insulating film is a metal oxide or a nitride. As a result, in addition to the above, it becomes possible to suppress the gate leakage current of the transistor, and further to lower the drive voltage.

  (6) The organic thin film transistor according to claim 4, wherein the inorganic insulating film is silicon dioxide. As a result, in addition to the above, it becomes possible to suppress the gate leakage current of the transistor, and further to lower the drive voltage.

  (7) The organic thin film transistor according to any one of claims 1 to 6, wherein the substrate is made of a material selected from the group consisting of glass, silicon, and plastic. Thereby, in addition to the above, it can adapt to the low-cost process of an organic thin-film transistor, and can produce a flexible organic thin-film transistor.

  (8) The organic thin film transistor according to any one of claims 1 to 7, wherein the organic semiconductor layer has a triarylamine skeleton. Thereby, in addition to the above, it can adapt to the low-cost process of an organic thin-film transistor, and can produce a flexible organic thin-film transistor.

The drain current _IDS is improved by the high capacitance.

  Hereinafter, the present invention will be described in detail.

  FIG. 2 is a diagram showing an example of an organic thin film transistor according to the present invention, and shows an example in which cyanoethyl pullulan is used as an organic insulator having a polar group, which constitutes the organic thin film transistor. Referring to FIG. 2, the organic thin film transistor according to the present invention includes a gate electrode laminated on a main surface of a glass substrate, a gate insulating layer containing an organic insulator having cyanoethyl pullulan so as to cover the gate electrode, It has a structure in which a semiconductor layer and a source electrode / drain electrode are stacked.

  When a voltage is applied between the source electrode and the drain electrode, a current flows between the source electrode and the drain electrode through the organic semiconductor layer. At this time, when a voltage is applied to the gate electrode separated from the organic semiconductor layer by the insulating layer, the electric conductivity of the organic semiconductor layer changes due to the electric field effect, and therefore the current flowing between the source and drain electrodes can be modulated.

  In general, in a field effect organic thin film transistor operating as described above, the drain current is defined as:

_{I DS = W / 2L × μ} × C i × (V G -V th) 2
C _i = ε ₀ × ε _r / d
I _DS : drain current, W: gate width, L: gate length, μ: mobility, C _i : capacitance of gate insulating film, V _G : gate voltage, V _th : threshold voltage, ε ₀ : vacuum dielectric Ratio, ε _r : relative dielectric constant, d: film thickness

Generally, without depending on the shape of each layer constituting the organic thin film transistor, in order to obtain a high I _DS, or increase mobility, or increasing the operating voltage, or be achieved by either increasing the capacitance . The mobility depends on the semiconductor material, and it is necessary to develop a new material. An increase in voltage causes an increase in power consumption, which is not preferable. On the other hand, increasing the capacitance of the insulating material is relatively easy to achieve.

(Gate insulating layer in the present invention)
Therefore, in the present invention, when focusing on the molecular skeleton of the organic insulating material constituting the gate insulating layer, it was studied the relation between the dependent on the molecular structure relative dielectric constant and a high I _DS of the polar group in the molecular skeleton It has been found that the structure it has is preferable. Further preferably, the organic insulator according to the present invention is cyanoethyl pullulan. Cyanoethyl pullulan is an insulator material having a relatively high dielectric constant among organic insulators, has high solubility in an organic solvent, and can be easily formed at a low temperature by coating. It also has good adhesion properties to substrates such as metal or plastic. The resistance value of cyanoethyl pullulan after film formation is 10 ¹² Ωcm or more, and the dielectric breakdown voltage is 1 MV / cm or more. As the organic insulator having a polar group, in addition to cyanoethyl pullulan, an organic insulator having a hydroxyl group such as polyvinylphenol, polyvinyl alcohol, or polyvinyl butyral may be used.

  Various common coating methods can be used as the gate insulating layer coating method according to the present invention, such as spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, and the like. Examples thereof include a coating method and a die coating method. In addition to these, there are pattern methods such as printing and inkjet.

  The layer made of an organic insulator in the gate insulating layer of the present invention may be subjected to surface modification such as silane coupling treatment in order to improve the stackability. As a suitable silane coupling treatment, a hexamethyldisilazane treatment is particularly effective. As a method for surface modification, a general surface treatment method can be used. For example, a sample is inserted into a sealed container filled with hexamethyldisilazane vapor and left at room temperature for a desired time. This can be done by baking. In addition to hexamethyldisilazane, surface modification may be performed using trimethylchlorosilane, γ-aminopropyltriethoxysilane, vinylethoxysilane, or the like. When these are used, in the dry method, a silane coupling agent solution diluted with an organic solvent or the like is added and dispersed uniformly, and then dried. Further, the silane coupling agent may be directly added by spraying. The thickness of the gate insulating layer in the present invention can be reduced to a thickness that can suppress the gate leakage current, and is preferably 200 to 2000 nm, for example, but is not limited thereto. Not. As a result, high capacitance is expected and transistor performance (drain current) is improved.

(Inorganic insulating layer)
In the gate insulating layer in the present invention, an inorganic insulating film may be further stacked in addition to the layer made of the organic insulator. As this inorganic insulating film, an insulating material known to those skilled in the art can be used. For example, inorganic materials such as silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, and titanium oxide, or flexibility, light weight, When an inexpensive device is desired, polymer compounds such as polyimide, polyvinyl alcohol, polyvinylphenol, polyester, polyethylene, polyphenylene sulfide, polyparaxylylene, polyacrylonitrile, cyanoethyl pullulan, various insulating LB films, etc. These organic materials may be used, and two or more of these materials may be used in combination. The material is not particularly limited, but among them, a material having a high dielectric constant and a low conductivity is preferable, and silicon oxide is preferable. The metal oxides that can be contained in the inorganic insulating film include various compounds, but those that can be formed at a low temperature, can easily take a stoichiometric composition, and have a stable metal valence are required. Silicon nitride, silicon oxynitride, aluminum oxide, tantalum oxide, titanium oxide, magnesium oxide, and zirconium oxide are preferable.

  There are no particular restrictions on the method for producing these inorganic insulating layers. For example, ion plating, CVD, plasma CVD, plasma polymerization, vapor deposition, spin coating, dipping, sputtering, metal organic compound precursor (TEOS) : Atmospheric pressure plasma treatment method using tetraethoxysilane), printing method, ink jet method, LB method, and the like. Any of them can be used, but sputtering is preferred from the viewpoint of low production cost. The inorganic insulating layer in the present invention can reduce damage caused by a solvent when an organic semiconductor laminated on the inorganic insulating layer is formed by a coating method. This increases the types of solvents that can be used for film formation, which is advantageous in terms of manufacturing process and cost.

(Organic semiconductor in the present invention)
The organic semiconductor layer in the present invention can be variously used as long as it is a layer made of an organic material having semiconductor characteristics. Among them, the following general formula (I)

で示される繰り返し単位を有する重合体を含有する層であることが好ましい。

It is preferable that it is a layer containing the polymer which has a repeating unit shown by these.

In general formula (I), Ar ¹ is a monovalent group of a substituted or unsubstituted aromatic hydrocarbon, and Ar ² and Ar ³ are each independently a divalent group of a substituted or unsubstituted aromatic hydrocarbon. It is a group. Ar ⁴ is a divalent group of a substituted or unsubstituted aromatic hydrocarbon or a substituted or unsubstituted heterocyclic compound. Here, the “aromatic hydrocarbon” includes monocyclic aromatic hydrocarbons, non-condensed polycyclic (ring assembly) hydrocarbons, and condensed polycyclic hydrocarbons.

  The organic semiconductor material of the present invention may have a substituent on the aromatic ring. From the viewpoint of improving solubility, an alkyl group, an alkoxy group, an alkylthio group, and the like can be given. As the number of carbons in these substituents increases, the solubility will improve, but on the other hand, the carrier mobility will decrease, so select a substituent that will provide the desired properties within the range that does not impair the solubility. It is preferable to do. Examples of suitable substituents in that case include linear or branched alkyl groups, alkoxy groups and alkylthio groups having 1 to 25 carbon atoms. More preferably, a linear or branched alkyl group, alkoxy group, and alkylthio group having 2 to 18 carbon atoms are exemplified. A plurality of the same substituents may be introduced, or a plurality of different substituents may be introduced. In addition, these alkyl groups, alkoxy groups and alkylthio groups are further halogen atoms, cyano groups, aryl groups, hydroxyl groups, carboxyl groups, linear, branched or cyclic alkyl groups having 1 to 12 carbon atoms, alkoxy groups, alkylthio groups. It may contain further substituents such as an aryl group substituted with a group.

  Specific examples of the alkyl group include methyl group, ethyl group, n-propyl group, i-propyl group, t-butyl group, s-butyl group, n-butyl group, i-butyl group, pentyl group, hexyl group, Heptyl, octyl, nonyl, decyl, 3,7-dimethyloctyl, 2-ethylhexyl, trifluoromethyl, 2-cyanoethyl, benzyl, 4-chlorobenzyl, 4-methylbenzyl, A cyclopentyl group, a cyclohexyl group, etc. can be mentioned as an example, As an alkoxy group and an alkylthio group, what made the alkoxy group and the alkylthio group by inserting an oxygen atom or a sulfur atom in the bond position of the said alkyl group is mentioned as an example. .

  Specific examples of the aryl group include a phenyl group, a naphthalenyl group, and an anthracenyl group.

  The polymer is further improved in solubility in a solvent due to the presence of an alkyl group, an alkoxy group, or an alkylthio group. It is important to improve the solubility of these materials because the manufacturing tolerance of the film wet film forming process is increased. For example, the choice of coating solvent is expanded, the temperature range during solution preparation is expanded, the temperature and pressure range during solvent drying is expanded, and the high processability results in high purity and high uniformity. The possibility of obtaining a high-quality thin film increases.

The substituted or unsubstituted aromatic hydrocarbon (monovalent) group Ar ¹ in the general formula (I) may be a monocyclic group or a polycyclic group (a condensed polycyclic group or a non-condensed polycyclic group), The following can be mentioned as an example. Examples thereof include a phenyl group, a naphthyl group, a pyrenyl group, a fluorenyl group, an azulenyl group, an anthryl group, a triphenylenyl group, a chrycenyl group, a biphenyl group, and a terphenyl group.

Examples of the substituted or unsubstituted aromatic hydrocarbon divalent groups Ar ² and Ar ³ include divalent groups of benzene, naphthalene, pyrene, fluorene, azulene, anthracene, triphenylene, chrysene, biphenyl, and terphenyl as an example. Is mentioned.

Furthermore, examples of the divalent group Ar ⁴ of the substituted or unsubstituted aromatic hydrocarbon or the substituted or unsubstituted heterocyclic compound include divalent groups of benzene, anthracene, biphenyl, and thiophene.

  In addition, these aromatic hydrocarbon (monovalent) and divalent groups, and the divalent group of the heterocyclic compound may have the following substituents.

  (1) Halogen atom, trifluoromethyl group, cyano group, nitro group.

  (2) A linear or branched alkyl group or alkoxy group having 1 to 25 carbon atoms. These alkyl groups and alkoxy groups may be further substituted with a halogen atom, a cyano group, a phenyl group, a hydroxyl group, a carboxyl group, an alkoxy group, or an alkylthio group.

  (3) Aryloxy group. (Aryloxy groups having a phenyl group or a naphthyl group as the aryl group may be mentioned. These aryloxy groups may contain a halogen atom as a substituent, and are linear or branched having 1 to 25 carbon atoms. An alkyl group, an alkoxy group or an alkylthio group may be contained as a substituent, specifically, a phenoxy group, a 1-naphthyloxy group, a 2-naphthyloxy group, a 4-methylphenoxy group, or a 4-methoxyphenoxy group. , 4-chlorophenoxy group, 6-methyl-2-naphthyloxy group and the like).

  (4) An alkylthio group or an arylthio group. (Specific examples of the alkylthio group or arylthio group include a methylthio group, an ethylthio group, a phenylthio group, and a p-methylphenylthio group).

  (5) An alkyl-substituted amino group. (Specifically, diethylamino group, N-methyl-N-phenylamino group, N, N-diphenylamino group, N, N-di (p-tolyl) amino group, dibenzylamino group, piperidino group, morpholino group And a urolidyl group).

  (6) Acyl group. (Specific examples of the acyl group include an acetyl group, a propionyl group, a butyryl group, a malonyl group, and a benzoyl group).

  Specific examples of the repeating unit of the polymer represented by the general formula (I) in the present invention are listed. These specific examples do not limit the present invention.

  The production method of the polymer containing the repeating unit represented by the above general formula includes, for example, Wittig-Horner reaction using aldehyde and phosphonate, Wittig reaction using aldehyde and phosphonium salt, Heck reaction using vinyl substituent and halide Ullmann reaction using an amine and a halide can be used, and can be produced by a known method.

  In particular, the Wittig-Horner reaction and the Wittig reaction are effective for the convenience of the reaction operation.

  The preferred molecular weight of the polymer represented by the above general formula is 1000 to 1000000 in terms of polystyrene-reduced number average molecular weight by GPC, more preferably 2000 to 500000. If the molecular weight is too small, the film formability such as the generation of cracks is deteriorated and the practicality becomes poor. On the other hand, if the molecular weight is too large, the solubility in a general organic solvent becomes poor, the viscosity of the solution becomes high, and the coating becomes difficult, which also causes a problem in practical use.

  The semiconductor material of the present invention exhibits good solubility in various common organic solvents such as dichloromethane, tetrahydrofuran, dioxane, chloroform, toluene, dichlorobenzene and xylene. Therefore, a solution having an appropriate concentration can be prepared using an appropriate solvent capable of dissolving the polymer material of the present invention, and a semiconductor thin film can be prepared by a wet film forming method using the solution. Particularly preferred is a solvent containing tetrahydrafuran as a main component and at least one of toluene, xylene, dioxane, chloroform and dichloromethane.

  As a wet film forming method for forming the organic semiconductor layer, the film is thinned by a known wet film forming technique such as a spin coating method, a dipping method, a blade coating method, a spray coating method, a casting method, an ink jet method, or a printing method. be able to. For these various film forming methods, an appropriate solvent is selected from the solvent types described above.

  The organic semiconductor material according to the present invention is not substantially oxidized even in air in a solid or solution state.

  In the organic thin film transistor of the present invention, the organic semiconductor material layer formed of the polymer has a uniform thickness (that is, a thin film having no gap or hole that adversely affects the carrier transport property of the material). The thickness is selected. The thickness of the organic semiconductor layer is preferably about 200 nm to about 5 nm, particularly about 100 nm to about 5 nm.

(Substrate in the present invention)
The organic thin film transistor of the present invention may be an insulating substrate, and is formed on a substrate made of glass, silicon, or plastic. In consideration of flexibility, it may be a thin-strained tempered glass substrate, a plastic sheet or a nickel electroformed sheet insulated, and a plastic substrate is preferred when characteristics such as flexibility, light weight, and low cost are desired. Used.

(Source electrode, drain electrode and gate electrode in the present invention)
The device of the present invention has three spatially separated electrodes (source, drain, gate electrode). The gate electrode is in contact with the insulating layer. Each electrode is formed on the substrate using well-known conventional techniques.

  The material of the source electrode, drain electrode, and gate electrode is not particularly limited as long as it is a conductive material. Platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony, lead, tantalum, indium, aluminum, Zinc, magnesium, and alloys thereof, conductive metal oxides such as indium and tin oxide, or inorganic and organic semiconductors whose conductivity has been improved by doping, such as silicon single crystal, polysilicon, amorphous silicon, germanium Graphite, polyacetylene, polyparaphenylene, polythiophene, polypyrrole, polyaniline, polythienylene vinylene, polyparaphenylene vinylene, and the like. Of the conductive materials, the source electrode and the drain electrode are preferably connected in ohmic contact with the semiconductor layer.

(Comparative example)
[Formation of gate electrode on Si substrate]
The Si substrate (thermal oxide film: 100 nm) was subjected to hexamethyldisilazane (HMDS) vapor treatment for 5 minutes and dried at 120 ° C. for 5 minutes. A photoresist (TSMR8800; manufactured by Tokyo Ohka Kogyo Co., Ltd.) was spin coated on the treated Si substrate surface to protect only the surface. The obtained Si substrate (thermal oxide film: 100 nm) was immersed in buffered hydrofluoric acid (BHF63U; manufactured by Daikin Industries) for 100 seconds, and the oxide film on the back surface was removed. Thereafter, cleaning was performed using ultrasonic waves. Further, an Al film having a thickness of 300 nm was formed on the back surface of the Si substrate by a vacuum deposition method, and the surface resist was removed.

[Organic semiconductor layer formation]
The Si substrate surface obtained above was subjected to HMDS vapor treatment for 1 minute and dried at 120 ° C. for 5 minutes. A triarylamine represented by the above formula (1) was used as a semiconductor material, and an organic semiconductor layer having a thickness of 30 nm was formed by spin coating.

[Source / drain electrode formation]
On the organic semiconductor layer formed as described above, an Au film having a thickness of 100 nm was formed by vacuum deposition as shown in FIG. The transistor static characteristics of the silicon organic thin film transistor 1 are shown in FIG. As can be seen from FIG. 4, the organic thin film transistor 1 based on silicon exhibits a negative threshold voltage Vth and performs an enhancement operation.

Example 1
[Formation of gate electrode on glass substrate]
A Cr film having a thickness of 300 nm was formed on an optically polished glass substrate by a vacuum deposition method, and photolithography / etching was performed to form a gate electrode.

[Gate insulation film formation]
After forming the gate electrode as described above, a cyanoethyl pullulan insulating film (cyanoresin CR-S; manufactured by Shin-Etsu Chemical Co., Ltd.) was spin-coated and dried at 100 ° C. for 30 minutes using a hot plate to form a gate insulating layer having a thickness of 900 nm. Formed.

[Semiconductor layer formation]
A triarylamine represented by the above formula (1) was used as a semiconductor material, and an organic semiconductor layer having a thickness of 30 nm was formed by spin coating.

[Source / drain electrode formation]
An Au film having a thickness of 100 nm is formed on the semiconductor layer by a vacuum deposition method using a shadow mask, and a substrate / gate electrode (Cr) / cyanoethyl pullulan / organic semiconductor / source / drain electrode (Au) (FIG. 2). The organic thin film transistor 1 having the structure of the reference was obtained. The static characteristics of the organic thin film transistor 1 are shown in FIG. As shown in FIG. 5, the subthreshold voltage (voltage required to increase the drain current by one digit) is a small value, and low voltage driving is possible. In addition, a depletion operation in which a current flows even at a gate voltage of 0 V is shown. As a result, when the display pixel is driven, the dynamic range is reduced, and an increase in off current (drain current at a gate voltage of 0 V) reduces battery life. This is considered to be caused by the occurrence of polarization by the hydroxyl group present on the cyanoethyl pullulan surface and the formation of a negative surface potential, which is synonymous with the negative gate bias applied to the organic semiconductor layer. It is done.

(Example 2)
After forming a gate insulating layer with cyanoethyl pullulan, the surface of the gate insulating layer containing cyanoethyl pullulan was subjected to hexamethyldisilazane vapor treatment for 5 minutes and dried at 120 ° C. for 5 minutes, as in Example 1. The organic thin film transistor 2 having a structure of glass substrate / gate electrode (Cr) / cyanoethyl pullulan / organic semiconductor / source / drain electrode (Au) was obtained. The static characteristics of the organic thin film transistor 2 are shown in FIG. As can be seen from FIG. 7, the organic thin film transistor 2 showed an enhancement operation (Vth <0 V), and an on / off ratio was improved due to a decrease in off current. Further, the subthreshold voltage is small, and the performance higher than that of the silicon organic thin film transistor 1 can be obtained, and a high performance transistor can be fabricated even on a glass substrate.

(Example 3)
After forming a gate insulating layer containing cyanoethyl pullulan, an inorganic insulating film having a film thickness of 50 nm is further formed by RF magnetron sputtering using a SiO ₂ target at a sputtering gas Ar + O 2 (Ar 95%) at a substrate temperature of room temperature. Except that, an organic thin film transistor 3 having a structure of substrate / gate electrode (Cr) / cyanoethyl pullulan / SiO ₂ / organic semiconductor / source / drain electrode (Au) (see FIG. 3) was obtained. .

In the organic thin film transistor 2 provided with only cyanoethyl pullulan as a gate insulating layer obtained in Example 2, the gate leakage current is 50 nA (L = 30 μm, W = 10 mm) when V _DS = −20 V and V _G = −20 V. On the other hand, in the organic thin film transistor 3 obtained in Example 3, when V _DS = −20 V and V _G = −20 V, the gate leakage current is 20 nA (L = 30 μm, W = 10 mm), and the gate leakage current is reduced. did.

Moreover, in the silicon organic thin-film transistor 1 obtained in the above comparative example, the on / off ratio when VDS = −20 V was applied was 300 (V _G = −20 V / V _G = 0 V), while obtained in Example 3. In the organic thin film transistor 3, the on / off ratio when V _DS = −20V was applied was 600 (V _G = −20V / V _G = 0V), and an improvement in the on / off ratio was observed.

It is a silicon-based thin film transistor structure. It is an organic transistor structure using cyanoethyl pullulan as an organic insulator. This is an organic transistor structure using an organic / inorganic laminated insulating film. This is a static characteristic of an organic thin film transistor using a Si substrate and a SiO ₂ insulator. This is a static characteristic of an organic thin film transistor using a glass substrate and a cyanoethyl pullulan insulating film. It is an organic transistor structure subjected to hexamethyldisilazane treatment. It is the static characteristic of the organic transistor which performed the silane coupling process to the cyanoethyl pullulan.

Claims (8)

It consists of a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, and an organic semiconductor layer,
The organic thin film transistor, wherein the gate insulating layer includes a layer made of an organic insulator having a polar group.   2. The organic thin film transistor according to claim 1, wherein the organic insulator is cyanoethyl pullulan.   The organic thin film transistor according to claim 1 or 2, wherein a surface of the gate insulating layer is subjected to a silane coupling treatment.   The organic thin film transistor according to any one of claims 1 to 3, wherein the gate insulating layer further includes an inorganic insulating film.   The organic thin film transistor according to claim 4, wherein the inorganic insulating film is a metal oxide or a nitride.   The organic thin film transistor according to claim 4, wherein the inorganic insulating film is silicon dioxide.   The organic thin film transistor according to any one of claims 1 to 6, wherein the substrate is made of a material selected from the group consisting of glass, silicon, and plastic.   The organic thin film transistor according to any one of claims 1 to 7, wherein the organic semiconductor layer has a triarylamine skeleton.

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