JP2007194360A - Organic thin film transistor, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film transistor having high mobility and low threshold voltage. <P>SOLUTION: The organic thin film transistor comprises a gate electrode 102 formed on a substrate 101, a gate insulating film 103 formed on the gate electrode 102, an organic semiconductor layer 105 formed on the gate insulating film 103, and a source electrode 106 and drain electrode 107 formed on the organic semiconductor layer 105 or on the gate insulating film 103 with the organic semiconductor layer 105 in-between. The surface of the gate insulating film 103 is chemically coupled for modification with a second organic molecule having the same main skeleton as that of the first organic molecule constituting the organic semiconductor layer 105. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic thin film transistor and a method for manufacturing the same.

Conventionally, a field effect type organic thin film transistor using an organic semiconductor layer has been developed, and many structures such as a top contact type and a bottom contact type have been studied. In addition, as an organic material for forming the organic semiconductor layer, a large number of substances ranging from low molecules to polymers have been studied.
In order to control the threshold voltage, a method of adding a buffer layer between the gate insulating film and the organic semiconductor layer has been proposed (see, for example, Patent Document 1).
In addition, after a buffer layer made of an organic thin film is formed on the substrate at the first substrate temperature, the same organic material as the buffer layer is used on the buffer layer at a second substrate temperature higher than the first substrate temperature. A method of forming an organic semiconductor layer as a main layer and enlarging the grain size of the organic semiconductor layer is disclosed (for example, see Patent Document 2).

JP 2005-136383 A JP 2005-72068 A

An organic thin film transistor generally has a problem that the mobility of the organic semiconductor layer is low because of a large resistance of the organic semiconductor layer, and a problem that power consumption increases because the threshold voltage is also large. In addition, the organic thin film transistor usually forms an organic semiconductor layer by vapor deposition, but a grain boundary is easily formed, and a channel is interrupted at the grain boundary, so that a resistance value is increased and mobility is reduced.
In the method of Patent Document 1, compatibility is a problem depending on the selection of materials for the organic semiconductor layer and the buffer layer, and it cannot be said that the adhesion is necessarily good.
In the method of Patent Document 2, even if the organic semiconductor layer has a large grain size and good crystallinity, the first substrate temperature at the time of forming the buffer layer is the second substrate temperature at the time of forming the organic semiconductor layer. The density of the buffer layer (organic molecules) on the gate insulating film is lower than the density of the organic semiconductor layer (organic molecules) because of the lower temperature than that, and it is considered that there are many grains near the gate insulating film. . In addition, the gate insulating film and the organic film are in physical contact, and adhesion with the gate insulating film is considered to be a problem.

  The present invention has been made in view of the above-described problems, and has an excellent adhesion between an organic semiconductor layer and a gate insulating film and crystallinity of the organic semiconductor layer, an organic thin film transistor in which a threshold voltage is lowered and mobility is increased. And it aims at providing the manufacturing method.

Thus, according to the present invention, the gate electrode formed on the substrate, the gate insulating film formed on the gate electrode, the organic semiconductor layer formed on the gate insulating film, and the organic semiconductor layer Alternatively, the semiconductor device includes a source electrode and a drain electrode formed on the gate insulating film with an organic semiconductor layer interposed therebetween, and a surface of the gate insulating film includes a main skeleton of the first organic molecule constituting the organic semiconductor layer. An organic thin film transistor is provided that is modified by chemical bonding with a second organic molecule having the same main skeleton.
According to another aspect of the present invention, a step of forming a gate electrode on a substrate, a step of forming a gate insulating film on the gate electrode, and a step of forming an organic semiconductor layer on the gate insulating film And forming a source electrode and a drain electrode on the gate insulating film on the organic semiconductor layer or with the organic semiconductor layer interposed therebetween, and before forming the organic semiconductor layer, the surface of the gate insulating film In contrast, a method of manufacturing an organic thin film transistor is provided that includes a step of chemically bonding and modifying a second organic molecule having the same main skeleton as the main skeleton of the first organic molecule constituting the organic semiconductor layer.

According to the organic thin film transistor of the present invention, since the second organic molecule constituting the organic molecular film is chemically bonded to the surface of the gate insulating film, the organic molecular film is compared with physical adsorption deposited on the gate insulating film. As a result, the adhesion (bonding force) between the gate insulating film and the organic molecular film is increased and the threshold voltage is reduced, and the second organic molecules are bonded to the surface of the gate insulating film at a high density, and in the vicinity of the gate insulating film. Since the grain boundary is reduced, the channel is not interrupted by grains, and the organic molecular film works as a part of effective channel formation and the mobility is improved. Furthermore, since the organic semiconductor layer is formed by the first organic molecule having the same main skeleton (group) as the main skeleton (group) of the second organic molecule constituting the organic molecular film, the first organic molecule and Compared with the case where the second organic molecules have different main skeletons, the physical bonding force (adhesion) between the organic semiconductor layer and the organic molecular film is increased. Therefore, in the organic thin film transistor of the present invention, the gate voltage is uniformly applied without loss, the threshold voltage is lowered, and the power consumption can be reduced.
Moreover, according to the manufacturing method of the organic thin-film transistor of this invention, the organic thin-film transistor which has the above-mentioned effect can be obtained easily.

  The organic thin film transistor of the present invention includes a gate electrode formed on a substrate, a gate insulating film formed on the gate electrode, an organic semiconductor layer formed on the gate insulating film, and the organic semiconductor layer or A source electrode and a drain electrode formed on the gate insulating film with an organic semiconductor layer interposed therebetween, and the surface of the gate insulating film is the same as the main skeleton of the first organic molecule constituting the organic semiconductor layer It is modified by chemical bonding with a second organic molecule having a main skeleton. That is, the surface of the gate insulating film is modified with the organic molecular film made of the second organic molecule for the purpose of improving the adhesion between the gate insulating film and the organic semiconductor layer and suppressing the generation of grains. ing.

The organic thin film transistor of the present invention includes the following two forms.
In the first embodiment, as shown in FIG. 1, a gate electrode 102, a gate insulating film 103, an organic molecular film 104, an organic semiconductor layer 105, a source electrode 106, and a drain electrode 107 are formed in this order on a substrate 101. In the second embodiment, as shown in FIG. 3, a gate electrode 202, a gate insulating film 203, an organic molecular film 204, a source electrode 206, a drain electrode 207, and an organic semiconductor layer are formed on a substrate 201. 205 is formed in this order, and the organic semiconductor layer 205 is disposed between the source and drain electrodes.

As a manufacturing method of the organic thin-film transistor of the above-mentioned 1st and 2nd embodiment, the following five processes can be mentioned, for example. That is, a step (A) of forming a gate electrode on the substrate, a step (B) of forming a gate insulating film on the gate electrode, and a step (C) of forming an organic molecular film on the surface of the gate insulating film. And (D) forming an organic semiconductor layer on the organic molecular film, and forming a source electrode and a drain electrode on the organic molecular film with the organic semiconductor layer or the organic semiconductor layer interposed therebetween ( E), and in the formation of the organic molecular film in the step (C), the second organic molecule having the same main skeleton as the main skeleton of the first organic molecule constituting the organic semiconductor layer with respect to the surface of the gate insulating film Are modified by chemical bonding. Note that the steps (A), (B), (C), (D), and (E) are not limited to this order, and the order of the steps can be changed depending on the transistor structure to be obtained. That is, when the organic thin film transistor of the first embodiment is manufactured, the source electrode is formed on the organic semiconductor layer in the order of steps (A), (B), (C), (D), and (E). In the case of manufacturing the organic thin film transistor of the second embodiment, the order of the steps (A), (B), (C), (E), and (D) A source electrode and a drain electrode are formed on the molecular film, and an organic semiconductor layer is formed on at least the organic molecular film between the source and drain electrodes in the step (D).
Hereafter, each component of the organic thin-film transistor of 1st and 2nd embodiment is demonstrated.

<Board>
The substrate is not particularly limited as long as it is insulative, but is preferably a substrate with little dimensional change at the manufacturing stage of the organic thin film transistor. Specific examples include a synthetic quartz substrate, a glass substrate, a plastic substrate, and a silicon substrate. Moreover, when obtaining the device which reduces board | substrate cost and has flexibility, the plastic substrate which can be bent is preferable, for example, a polyethersulfone board | substrate, a polyimide board | substrate, a polyethylene terephthalate board | substrate etc. are mentioned.

<Gate electrode>
The constituent material of the gate electrode is not particularly limited as long as it is a conductive material. Specific examples include conductive organic materials, conductive inks, metals, alloys, conductive metal oxides, inorganic semiconductors and organic semiconductors whose conductivity has been improved by doping, and the like. You may use together. For example, a two-layer metal film of titanium and gold can be used. When the gate insulating film is a silicon nitride film, titanium is preferable because it has an effect of improving the adhesion between gold and the SiN _x film or the SiO ₂ film.
The gate electrode can be formed as a thin film having a thickness of about 20 to 200 nm by a physical vapor deposition method such as vacuum vapor deposition, ion sputtering, or electron beam vapor deposition, or a chemical vapor deposition method. Further, the gate electrode is not necessarily patterned, and can operate as an organic semiconductor element even when it is not patterned. However, in consideration of parasitic capacitance and the like, patterning is preferable.

<Gate insulation film>
As a constituent material of the gate insulating film, an insulating material usually used for an organic thin film transistor can be used, but a material that can be surface-treated is preferable, and examples thereof include silicon oxide and silicon nitride.
The gate insulating film can be formed with a thickness of about 10 to 500 nm by a chemical vapor deposition method (CVD), a low pressure chemical vapor deposition method (LPCVD), a plasma chemical vapor deposition method (PCVD), or the like.
Moreover, since it is preferable that the gate insulating film has a functional group for chemically bonding with an organic molecule constituting the organic molecular film on the surface, the gate insulating film is subjected to a surface treatment before the step (C). A plurality of functional groups may be added, for example, the surface of the gate insulating film may be hydrophilized. The method of hydrophilization treatment is not particularly limited. For example, a method of hydrophilizing the surface of the gate insulating film by immersing a laminate of a substrate / gate electrode / gate insulating film in hydrofluoric acid. Alternatively, a method of ashing the surface of the gate insulating film with oxygen plasma and immersing it in water to make it hydrophilic is exemplified.

<Organic semiconductor layer>
The material for forming the organic semiconductor layer is not limited as long as it is an electron-accepting organic material or an electron-donating organic material.
The electron-accepting organic material may be any π-electron conjugated compound as long as the charge carrier is an electron, but is not particularly limited as long as it is a material that exhibits stable n-type semiconductor characteristics in air. Absent. The electron-donating organic material may be any π-electron compound having a conjugated system and any charge carrier as long as it is a hole. However, the electron-donating organic material is not particularly limited as long as the material exhibits stable p-type semiconductor characteristics in air. It is not something.

  The electron-accepting material for forming the organic semiconductor layer includes fullerene and derivatives thereof; oligomers and polymers having pyridine and derivatives thereof as skeletons; oligomers and polymers having quinoline and derivatives thereof as skeletons; benzophenanthrolines and derivatives thereof Ladder polymers according to the above; polymers such as cyanopolyphenylene vinylene; fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and derivatives thereof; perylene and derivatives thereof; naphthalene derivatives; small molecules such as bathocuproine and derivatives thereof can be used.

  Electron donating materials for forming the organic semiconductor layer include oligomers and polymers having thiophene and its derivatives in the skeleton; oligomers and polymers having phenylene vinylene and its derivatives in the skeleton; oligomers and polymers having thienylene vinylene and its derivatives in the skeleton. Polymer: Oligomers and polymers having vinyl carbazole and its derivatives in the skeleton; Oligomers and polymers having pyrrole and its derivatives in the skeleton; Oligomers and polymers having acetylene and its derivatives in the skeleton; Oligomers having isothiaphene and its derivatives Polymers such as oligomers and polymers having skeletons of heptadiene and its derivatives; metal-free phthalocyanines, metal phthalocyanines and their derivatives; diamines, phenyldiamines Derivatives thereof; acenes such as pentacene and derivatives thereof; porphyrin, tetramethylporphyrin, tetraphenylporphyrin, diazotetrabenzporphyrin, monoazotetrabenzporphyrin, diazotetrabenzporphyrin, triazotetrabenzporphyrin, octaethylporphyrin, octa Metal-free porphyrins such as alkylthioporphyrazine, octaalkylaminoporphyrazine, hemiporphyrazine, and chlorophyll, metalloporphyrins and derivatives thereof; cyanine dyes; quinone dyes such as merocyanine, benzoquinone, and naphthoquinone can be used. The central metals of metal phthalocyanine and metal porphyrin include metals such as magnesium, zinc, copper, silver, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, tin, platinum, lead, metal oxide And metal halides are used.

  Among the above-mentioned organic materials forming the organic semiconductor layer, fullerene or fullerene derivatives are preferable as the electron-accepting material.

The organic semiconductor layer can be formed with a film thickness of 30 to 200 nm by vacuum deposition or spin coating.
In the vacuum deposition method, an organic semiconductor layer can be formed by depositing an organic material on the organic molecular film while heating the substrate having the organic molecular film to a substrate temperature of 50 to 250 ° C. in a vacuum chamber. . If the substrate temperature is lower than 50 ° C., the grain size of the organic semiconductor layer tends to be small and the mobility tends to be low, while if it exceeds 250 ° C., it becomes difficult to form the organic semiconductor layer.

In the spin coating method, a solution in which an organic material is dissolved can be applied onto an organic molecular film by spin coating, and baked at 100 to 250 ° C. to form an organic semiconductor layer. A thin film can be formed at low cost by forming an organic semiconductor layer by spin coating. When the firing temperature is lower than 100 ° C., a thin film remains in the organic semiconductor layer and the resistance value is increased. On the other hand, when the temperature exceeds 250 ° C., the organic molecules themselves are damaged and the characteristics are deteriorated.
Examples of the solvent used for spin coating include alcohols (methanol, ethanol, t-butanol, benzyl alcohol, etc.), nitriles (acetonitrile, propionitrile, 3-methoxypropionitrile, etc.), nitromethane, halogenated carbonization, and the like. Hydrogen (dichloromethane, dichloroethane, chloroform, chlorobenzene, etc.), ethers (diethyl ether, tetrahydrofuran, etc.), dimethyl sulfoxide, amides (N, N-dimethylformamide, N, N-dimethylacetamide, etc.), N-methylpyrrolidone 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, esters (ethyl acetate, butyl acetate, etc.), carbonates (diethyl carbonate, ethylene carbonate, propylene carbonate, etc.), ketones (acetone, 2-butanone) Cyclohexanone), hydrocarbons (hexane, petroleum ether, benzene, toluene, etc.), but mixtures of these solvents, is not limited as long as having these properties.

<Organic molecular film>
The organic molecule (the second organic molecule) as a material for forming the organic molecular film is the same main skeleton as the main skeleton of the organic molecule (the first organic molecule) described above, which is a material for forming the organic semiconductor layer. Those having (group) are used. In other words, organic materials for organic molecular films include: fullerene derivatives; pyridine derivatives; quinoline derivatives; benzophenanthroline derivatives; polymers such as cyanopolyphenylene vinylene; fluorinated metal-free phthalocyanines and fluorinated metal phthalocyanines. Perylene derivatives; naphthalene derivatives; electron-accepting materials such as bathocuproine derivatives, or thiophene derivatives; phenylene vinylene derivatives; thienylene vinylene derivatives; vinyl carbazole derivatives; pyrrole derivatives; acetylene derivatives; Derivatives of isothiaphene; derivatives of heptadiene; derivatives of metal-free phthalocyanines and metal phthalocyanines; derivatives of diamines; derivatives of phenyldiamines; induction of acenes such as pentacene Porphyrin, tetramethylporphyrin, tetraphenylporphyrin, diazotetrabenzporphyrin, monoazotetrabenzporphyrin, diazotetrabenzporphyrin, triazotetrabenzporphyrin, octaethylporphyrin, octaalkylthioporphyrazine, octaalkylaminoporphyrazine, hemiporphyrazine Electron-donating materials such as metal-free porphyrins such as chlorophyll, derivatives of metalloporphyrins, derivatives of cyanine dyes; derivatives of quinone dyes such as merocyanine, benzoquinone, and naphthoquinone. An organic molecule having the same main skeleton (group) as the organic molecule selected to form is selected.

Furthermore, the organic molecule as a material for forming the organic molecular film has a substituent capable of reacting with the functional group so that it can chemically bond to the surface of the gate insulating film by reacting with the functional group on the surface of the gate insulating film. It is preferable to have at the terminal of the group of the organic molecule.
When the surface of the gate insulating film is hydrophilized as described above, a functional group such as —OH (hydroxyl group) or —NH ₂ (amino group) is added to the surface of the gate insulating film. In order to react with the active hydrogen of the group, the organic molecule that is the material of the organic molecular film is represented by —COOH (carboxyl group) or —COOR (R is an alkyl group, preferably a lower alkyl group having 1 to 3 carbon atoms). An alkoxycarbonyl group, a halogen atom such as —Cl, —F, and —Br, an alkoxysilyl group represented by —SiOR (where R is an alkyl group, preferably a lower alkyl group having 1 to 3 carbon atoms), —SiCl ₃ It is preferable to have a substituent such as a halogenated silyl group such as —SiF ₃ or an atom at the end of the main skeleton. Combinations of these substituents or halogen atoms and —OH or —NH ₂ functional groups added to the surface of the gate insulating film are —COOH and —NH ₂ , —COOH and —OH, —Cl and —OH. , Si (OCH ₃ ) ₃ and —OH, and —SiCl ₃ and —OH.

When forming the organic molecular film, that is, modifying the surface of the gate insulating film, it is preferable to react until the organic molecule is sufficiently chemically bonded to the gate insulating film. The occupation area ratio is preferably 80% or more. If this occupied area ratio is less than 80%, the density of organic molecules on the surface of the gate insulating film is insufficient, so that many grains are likely to be generated, and the threshold voltage as an organic thin film transistor tends to increase.
As a method of forming an organic molecular film by chemically bonding to the surface of the gate insulating film, there is a method of immersing a substrate having a hydrophilized gate insulating film in a solution containing organic molecules as an organic molecular film forming material. Can be mentioned. At this time, the area ratio of the organic molecules bonded to the surface of the gate insulating film to the surface of the gate insulating film is 80% or more, and the substrate is immersed in a solution containing the organic molecules at 40 to 200 ° C. for 10 to 120 minutes. More preferably, it is 70-150 degreeC for 20 to 90 minutes, Most preferably, it is 100 degreeC for 40 minutes. When the reaction temperature is less than 40 ° C. and / or the reaction time is less than 10 minutes, the occupied area ratio is hardly 80% or more, whereas when the reaction temperature is more than 200 ° C. and / or more than 120 minutes, the occupied area ratio is If it is 80% or more, energy and / or time is wasted.

  The organic molecule occupied area ratio of the organic molecular film to the surface of the gate insulating film is as follows: (1) For example, when the organic molecular film is chemically bonded to the surface of the quartz substrate by the same method and the absorbance is saturated, the occupied area ratio is 100 Therefore, when the absorbance at that time is 80%, the occupied area ratio is also 80%, or (2) the absorbance of the ultraviolet absorption spectrum of the organic molecular film is measured, and the surface of the gate insulating film is determined from the absorption peak intensity. The number of organic molecules per unit area can be estimated, and the reciprocal of this number can be used to determine the number of organic molecules.

<Source electrode and drain electrode>
The material constituting the source electrode and the drain electrode is not particularly limited as long as it is a conductive material. For example, the same material as that of the gate electrode can be used. Materials that are in ohmic contact with the layer are preferred. Even a material that becomes a Schottky junction with the semiconductor layer can be used as long as its barrier is low. For example, a two-layer metal film of titanium and gold is preferable because titanium has an effect of improving the adhesion between gold and a SiN _x film or a SiO ₂ film.
The source electrode and the drain electrode may be formed as a thin film having a thickness of about 20 to 200 nm by a physical vapor deposition method such as a vacuum vapor deposition method, an ion sputtering method, an electron beam vapor deposition method, or a chemical vapor deposition method. it can.

  Hereinafter, the manufacturing method of each embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment.

(First embodiment)
When the field effect organic thin film transistor of the first embodiment shown in FIG. 1 is manufactured, first, the substrate 101 is cleaned, and then a gate having a predetermined pattern shape is formed on the substrate 101 by vacuum evaporation using a mask. The electrode 102 is formed as a thin film with a thickness of about 20 to 200 nm, and then the gate insulating film 103 is formed as a thin film with a thickness of about 10 to 500 nm on the gate electrode 102 and the substrate 101 by a CVD method or the like.

Thereafter, before the organic molecular film 104 is formed on the gate insulating film 103, the surface of the gate insulating film 103 is subjected to a hydrophilic treatment, and —OH or —NH ₃ is added to the surface of the gate insulating film 103. Embodiment 1 illustrates the case where —OH is added. As for the hydrophilization treatment method, there are a method of immersing the substrate in hydrofluoric acid or a method using oxygen plasma as described above.

After the surface of the gate insulating film 103 is hydrophilized, the substrate / gate electrode / gate insulating film is dissolved in a solution in which organic molecules for forming an organic molecular film having a substituent that reacts with —OH at the molecular end are dissolved in a solvent. The laminated body is laminated and heated at 40 to 200 ° C. for 10 to 120 minutes to chemically bond organic molecules on the gate insulating film 103 to form the organic molecular film 104. In the case of the first embodiment shown in FIG. 2, the organic molecule that is the material of the organic molecular film 104 is one in which —Si (OCH ₃ ) ₃ is substituted at the end of the group (main skeleton) X. The organic molecule -Si (OCH ₃ ) ₃ reacts with -OH on the gate insulating film and -Si (OCH ₃ ) _{3 of} other adjacent organic molecules, so that the organic molecular film 104 and the gate insulating film 103 become While being chemically bonded by the Si—O bond, adjacent organic molecules are two-dimensionally chemically bonded (siloxane bond) by the Si—O—Si bond. At this time, the reaction is performed under the reaction conditions of the heating temperature and the heating time so that the occupied area ratio of the organic molecules to the surface of the gate insulating film is 80% or higher. The relationship between the occupied area ratio and the reaction condition is as follows. By measuring in advance through experiments, it is possible to control the organic molecules to be bonded to the surface of the gate insulating film at an occupation area ratio of 80% or more by controlling the reaction conditions.

After the organic molecular film 104 is formed on the gate insulating film 103, the organic semiconductor layer 105 is formed with a thickness of about 30 to 200 nm on the organic molecular film 104 by the above-described vacuum deposition method or the method of baking after spin coating.
After the organic semiconductor layer 105 is formed, the source electrode 106 and the drain electrode 107 are formed with a film thickness of about 20 to 200 nm by vacuum deposition or the like using a mask.
In order to prevent photo-oxidation, a series of steps from the formation of the gate electrode 102 to the formation of the source / drain electrodes 106 and 107 are preferably performed in a vacuum and in an inert gas such as nitrogen. It is more preferable to carry out the above step without being exposed to the atmosphere even once.

(Second Embodiment)
In the method of manufacturing the field effect organic thin film transistor of the second embodiment shown in FIG. 3, except that the order of the organic semiconductor layer forming step and the source / drain electrode forming step in the first embodiment is reversed. It can be performed in the same manner as the manufacturing method of the first embodiment. In this case, the entire source electrode 206 and drain electrode 207 may be covered with the organic semiconductor layer 205.

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

Example 1
In Example 1, an organic thin film transistor having the structure shown in FIG. 1 was produced as follows.
First, ashing with O ₂ plasma was performed on a synthetic quartz substrate (3 inches in length and width, thickness 0.6 mm) under conditions of 150 ° C. and RF power 50 W for 15 minutes to remove organic contamination. Next, the synthetic quartz substrate was immersed in hydrofluoric acid for 1 minute and then washed twice for 6 minutes in ultrapure water. After cleaning, the ultrapure water was blown off with N ₂ gas.

Titanium and gold were sequentially deposited on the surface of the cleaned substrate using an electron beam deposition apparatus, and a gate electrode made of a two-layer metal film of titanium having a thickness of 5 nm and gold having a thickness of 100 nm was formed by lift-off.
Next, as a gate insulating film, an SiO ₂ film having a thickness of 300 nm was formed on the gate electrode and the substrate based on a sputtering method. Thereafter, the surface of the gate insulating film was subjected to an ashing process using oxygen plasma to expose the clean surface, and then immersed in ultrapure water for 10 minutes to hydroxylate the oxygen radical surface.

Next, the carbonyl group portion at the terminal of the alkyl chain of [6,6] -phenylene C ₆₁ -butyric acid ester (PCBM: manufactured by Frontier Carbon), which is a derivative of fullerene (C ₆₀ ), was substituted with a trichlorosilyl group. An organic molecule is prepared as an organic material for forming an organic molecular film, and a laminate in which a gate electrode and a gate insulating film are laminated on a substrate is immersed in a 2 wt% xylene solution of the fullerene derivative and heated at 100 ° C. for 40 minutes. Then, a fullerene derivative was chemically bonded to the surface of the gate insulating film (SiO ₂ ) to form an organic molecular film (monomolecular film) having a thickness of 2 nm.

After the formation of the organic molecular film, an organic semiconductor layer made of fullerene (C ₆₀ ) was formed with a film thickness of 50 nm using a vacuum deposition apparatus. At this time, the fullerene is put into the vapor deposition source and evacuated to 4 × 10 ⁻⁶ Torr or less by using a vacuum exhaust system. Thereafter, the temperature is gradually increased, and the vapor deposition source shutter is opened at about 250 ° C. It was raised. Evaporation started from about 300 ° C., and deposition was performed until the film thickness reached 50 nm while adjusting the temperature so that the deposition rate was about 0.1 nm / sec. The substrate temperature was kept at 30 ° C.

Thereafter, a source electrode and a drain electrode were formed with a film thickness of 50 nm by vacuum deposition (vacuum degree: about 4.0 × 10 ⁻⁴ Pa) using a mask on the surface of the organic semiconductor layer. As a material of the source / drain electrode, a magnesium alloy in which Mg and Ag were mixed so as to have an atomic ratio of 10: 1 was used.

Part of the gate insulating film of the organic thin film transistor of Example 1 produced in this way was peeled to expose the gate electrode, and a silver paste was applied to the exposed gate electrode and dried. Thereafter, the obtained organic thin film transistor is fixed to a metal stage, a prober probe is brought into contact with the gate electrode, the source electrode, and the drain electrode, and a gate voltage Vg and a drain voltage Vd are applied, and Vg−Id ^{1 / Two} curves were measured. From these, the mobility μ (cm ² / Vs) and the threshold voltage V _th (V) were calculated.

(Example 2)
In Example 2, an organic thin film transistor was produced in the same manner as in Example 1 except that the substrate temperature during the formation of the organic semiconductor layer in Example 1 was maintained at 200 ° C., and Vg-Id ¹ was obtained in the same manner as in Example ^{1. The / 2} curve was measured, and the mobility μ (cm ² / Vs) and the threshold voltage V _th (V) were calculated.

(Comparative Example 1)
In Comparative Example 1, an organic thin film transistor was prepared in the same manner as in Example 1 except that the organic molecular film was not formed in Example 1, and the Vg-Id ^1/2 curve was measured and transferred as in Example 1. Degree μ (cm ² / Vs) and threshold voltage V _th (V) were calculated.

(Example 3)
In Example 3, an organic thin film transistor having the structure shown in FIG. 3 was produced. In Example 3, an organic thin film transistor was produced under the same conditions as in Example 1 except that the organic semiconductor layer forming process and the source / drain electrode forming process in Example 1 were reversed. Similarly, the Vg-Id ^1/2 curve was measured, and the mobility μ (cm ² / Vs) and the threshold voltage V _th (V) were calculated.

(Comparative Example 2)
In Comparative Example 2, an organic thin film transistor was produced in the same manner as in Example 3 except that the organic molecular film in Example 3 was not formed, and the Vg-Id ^1/2 curve was measured and transferred as in Example 1. Degree μ (cm ² / Vs) and threshold voltage V _th (V) were calculated.

(Comparative Example 3)
In Comparative Example 3, an organic thin film transistor was prepared in the same manner as in Example 3 except that a 2 wt% xylene solution of a fullerene derivative was heated at 100 ° C. for 20 minutes during the formation of the organic molecular film in Example 3. Similarly, the Vg-Id ^1/2 curve was measured, and the mobility μ (cm ² / Vs) and the threshold voltage V _th (V) were calculated.

The results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1.

  From Table 1, it was found that Examples 1 to 3 had high mobility and low threshold voltage. On the other hand, Comparative Example 1 has a slightly better mobility than Example 3, but is not preferred because the threshold voltage is the highest, and Comparative Examples 2 and 3 are both less in mobility and threshold voltage than Examples 1-3. It turned out to be inferior.

  The organic thin film transistor of the present invention is used in various applications, for example, as a semiconductor device such as a memory, a logic element or a logic circuit, as a personal computer, a notebook, a laptop, a personal assistant / transmitter, a minicomputer, a workstation, a mainframe, Data processing systems such as multiprocessor computers or all other types of computer systems; electronic components comprising data processing systems such as CPUs, memories, data storage devices; communication devices such as telephones, PHS, modems, routers; displays Image display equipment such as panels and projectors; office equipment such as printers, scanners, and copiers; sensors; imaging equipment such as video cameras and digital cameras; entertainment equipment such as game machines and music players; portable information terminals, watches, electronic dictionaries Information equipment such as car In-vehicle devices such as navigation systems and car audio; AV devices for recording and playing back information such as videos, still images and music; electrification of washing machines, microwave ovens, refrigerators, rice cookers, dishwashers, vacuum cleaners, air conditioners, etc. Products; Health management equipment such as massagers, weight scales, blood pressure monitors, etc .; Wide application to electronic devices such as portable storage devices such as IC cards and memory cards.

It is a fragmentary sectional view which shows the structure of the organic thin-film transistor of the 1st Embodiment of this invention. It is the schematic of the molecular level which shows the organic molecular film in 1st Embodiment. It is a fragmentary sectional view which shows the structure of the organic thin-film transistor of the 2nd Embodiment of this invention.

Explanation of symbols

101, 201 Substrate 102, 202 Gate electrode 103, 203 Gate insulating film 104, 204 Organic molecular film 105, 205 Organic semiconductor layer 106, 206 Source electrode 107, 207 Drain electrode

Claims (11)

  A gate electrode formed on the substrate; a gate insulating film formed on the gate electrode; an organic semiconductor layer formed on the gate insulating film; and the organic semiconductor layer or the organic semiconductor layer interposed therebetween And a source electrode and a drain electrode formed on the gate insulating film, wherein the surface of the gate insulating film has the same main skeleton as the main skeleton of the first organic molecule constituting the organic semiconductor layer. An organic thin film transistor, which is modified by chemical bonding with an organic molecule.   2. The organic thin film transistor according to claim 1, wherein an occupation area ratio of the second organic molecule to the surface of the gate insulating film is 80% or more.   The organic thin film transistor according to claim 1 or 2, wherein the first organic molecule is fullerene or a derivative thereof, and the second organic molecule is a fullerene derivative.   The organic thin film transistor according to any one of claims 1 to 3, wherein a chemical bond between the second organic molecular film and the gate insulating film is a Si-O bond.   Forming a gate electrode on the substrate, forming a gate insulating film on the gate electrode, forming an organic semiconductor layer on the gate insulating film, and forming the organic semiconductor layer or the organic semiconductor layer on the gate insulating film; Forming a source electrode and a drain electrode on the gate insulating film with a sandwich therebetween, and forming the organic semiconductor layer on the surface of the gate insulating film before forming the organic semiconductor layer A method for producing an organic thin film transistor, comprising a step of chemically bonding and modifying a second organic molecule having the same main skeleton as the main skeleton of the organic molecule.   Before modifying the surface of the gate insulating film, the gate insulating film is surface-treated to add a plurality of functional groups, and then a substituent that reacts with the functional group on the surface of the gate-treated film is treated with a substituent. 6. The method of manufacturing an organic thin film transistor according to claim 5, wherein the surface of the gate insulating film is modified using the second organic molecule at the end.   The organic material according to claim 6, wherein when modifying the surface of the gate insulating film, the substrate having the surface-treated gate insulating film is immersed in a solution containing the second organic molecule at 40 to 200 ° C for 10 to 120 minutes. A method for manufacturing a thin film transistor. The combination of a functional group substituent and the surface of the gate insulating film of the second organic molecules, -COOH and -NH _2, -COOH and -OH, -Cl and -OH or -Si (OCH _{3) 3} and - It is OH, The manufacturing method of the organic thin-film transistor of Claim 6 or 7.   The method for producing an organic thin film transistor according to any one of claims 5 to 8, wherein the first organic molecule is a fullerene derivative or a derivative thereof, and the second organic molecule is a fullerene derivative.   The method for producing an organic thin film transistor according to any one of claims 5 to 9, wherein the organic semiconductor layer is formed at a substrate temperature of 50 to 250 ° C by a vacuum deposition method.   The organic semiconductor layer is formed by applying a solution containing the first organic molecule on the modified surface of the gate insulating film by a spin coating method and baking the applied film. The manufacturing method of the organic thin-film transistor as described in one.

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