WO2012124666A1

WO2012124666A1 - Thin-film transistor and manufacturing method therefor

Info

Publication number: WO2012124666A1
Application number: PCT/JP2012/056317
Authority: WO
Inventors: 串田　尚
Original assignee: 帝人株式会社
Priority date: 2011-03-14
Filing date: 2012-03-12
Publication date: 2012-09-20
Also published as: TW201304148A

Abstract

The present invention provides a novel thin-film transistor, a manufacturing method therefor, and an electric circuit having such a thin-film transistor. This thin-film transistor has a source electrode, a drain electrode, a gate electrode, a gate insulator, and an organic semiconductor film. The source electrode and the drain electrode are insulated from the gate electrode by the gate insulator, and the electric current that flows from the source electrode to the drain electrode through the semiconductor film is controlled by the voltage applied to the gate electrode. Here, the organic semiconductor film is composed of an organic semiconductor material (1) having an aromatic ring, and is a conformation in which a surface (2) formed by the aromatic ring constituting the organic semiconductor material stands substantially perpendicular to a substrate (10); and the molecular axis in which the mobility of the organic semiconductor material (1) is maximum is oriented in the direction of the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film.

Description

Thin film transistor and manufacturing method thereof

The present invention relates to a novel thin film transistor, a method for manufacturing the same, and an electric circuit having such a thin film transistor.

In recent years, semiconductor films have been used for various applications such as semiconductor elements represented by thin film transistors (TFTs) and solar cells.

An inorganic semiconductor film mainly used at present, especially an inorganic semiconductor film using silicon as a semiconductor material, has a high manufacturing cost because a vacuum process such as chemical vapor deposition (CVD) or sputtering is used at the time of manufacture. In addition, it is difficult to form an inorganic semiconductor film on a polymer film or the like from the viewpoint of process temperature. Furthermore, it is difficult for inorganic semiconductor films to meet low-cost requirements such as lightweight and flexible elements and RF-ID (Radio Frequency IDentification) that are expected to be put to practical use in the future.

In order to solve the above problems, it has been proposed to use an organic semiconductor film made of an organic semiconductor material. A vacuum deposition apparatus and a coating apparatus used for manufacturing an organic semiconductor film are less expensive than a CVD apparatus and a sputtering apparatus used for manufacturing an inorganic semiconductor film. In manufacturing an organic semiconductor film, since the process temperature is low, the organic semiconductor film can be formed on a polymer film, paper, or the like.

Here, as a method of forming the organic semiconductor film, a solution method (for example, a casting method, a spin coating method, a contact printing method, or the like, in which a solution containing an organic semiconductor material is applied to a substrate, a stamp, and the like, and the solvent is removed. Such a printing method, a dip method, and the like) and a vapor deposition method in which an organic semiconductor material is vapor-deposited on a substrate are known. Of these methods, the solution method is generally known to be preferable with respect to production cost, production rate, and the like, and therefore various studies have been made. However, stably obtaining a high-quality organic semiconductor film by a solution method has not always been sufficiently achieved.

It is known that the charge mobility of an organic semiconductor strongly depends on its crystallinity and crystal morphology, and the charge mobility of a single crystal organic semiconductor is known to depend on its crystal orientation. Therefore, in order to maximize the characteristics of the organic semiconductor, it has been proposed to align the crystalline organic semiconductor film in-plane and align the molecular axis that maximizes the mobility in the channel length direction of the organic semiconductor element. Yes.

In this regard, in Patent Document 1 and

Non-Patent Documents

1 and 2, an alignment film such as a polymer layer subjected to rubbing (rubbing) is formed on a substrate, and an organic semiconductor film is formed on the alignment film. And, it is proposed to raise the temperature of the organic semiconductor film to the liquid crystal transition temperature and align the organic semiconductor film by the action of the alignment film, thereby forming an organic semiconductor film having uniaxial anisotropy in the plane. . That is, these documents propose forming an organic semiconductor film on an alignment film for aligning an organic semiconductor material in a plane direction.

In Patent Document 2 and Non-Patent Documents 3 to 7, an organic semiconductor layer having uniaxial anisotropy is formed by forming a film of an organic semiconductor material in a solution state or a molten state while applying strong shear. Has proposed.

In Patent Document 3, an alignment film for aligning the organic semiconductor material in a direction perpendicular to the base material is formed on the base material, and the organic semiconductor film is formed on the alignment film from a releasable substrate such as a stamp. It has been proposed to transfer at the liquid crystal phase temperature and align the organic semiconductor film in the direction perpendicular to the substrate by the action of the alignment film. That is, this document proposes to improve the mobility in the in-plane direction of the organic semiconductor film by orienting the organic semiconductor material in a direction perpendicular to the base material.

JP 2008-192773 A JP 2004-356422 A JP 2009-200479 A

An object of the present invention is to provide a novel thin film transistor and a manufacturing method thereof, and an electric circuit having such a thin film transistor.

The inventors of the present invention have a conformation in which the surface formed by the aromatic ring constituting the organic semiconductor material stands substantially perpendicular to the substrate, and the organic semiconductor material is oriented in the plane of the organic semiconductor film. The present inventors have found that an organic semiconductor film can be formed by a specific method, and have devised the following thin film transistor, a manufacturing method thereof, and an electric circuit.

<1> It has a source electrode, a drain electrode, a gate electrode, a gate insulating film, and an organic semiconductor film, and the source electrode and the drain electrode are insulated from the gate electrode by the gate insulating film and applied to the gate electrode. A thin film transistor in which the current flowing through the semiconductor film from the source electrode to the drain electrode is controlled by the voltage
The organic semiconductor film is made of an organic semiconductor material having an aromatic ring,
The surface formed by the aromatic ring constituting the organic semiconductor material has a conformation that is substantially perpendicular to the substrate, and the molecular axis that maximizes the mobility of the organic semiconductor material is the organic semiconductor film In the plane, oriented in the direction of the electric field between the source electrode and the drain electrode,
Thin film transistor.
<2> Item <1> above, wherein the direction of the molecular axis of the main chain of the organic semiconductor material is within ± 60 ° of the direction of the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film. A thin film transistor according to 1.
<3> The thin film transistor according to <1> or <2>, wherein the thin film transistor is not in contact with an alignment film that aligns the organic semiconductor material in a plane direction.
<4> Ratio of charge mobility in two directions perpendicular to the plane {(charge mobility in the direction in which the charge mobility is maximum) / (charge mobility in the direction perpendicular to it)} is 1.5 The thin film transistor according to any one of <1> to <3>, which is large.
<5> The thin film transistor according to any one of <1> to <4>, wherein the organic semiconductor film is obtained by a contact printing method.
<6> The thin film transistor according to any one of <1> to <5>, wherein the organic semiconductor material is an organic semiconductor material that can be in a liquid crystal state.
<7> The thin film transistor according to any one of <1> to <6>, wherein the value of the charge mobility ratio is 5 or more.
<8> Any one of <1> to <7> above, wherein the charge mobility in the direction in which the charge mobility of the organic semiconductor film is maximum is 0.01 cm ² / (V · s) or more. A thin film transistor according to 1.
<9> The thin film transistor according to any one of <1> to <8>, wherein the organic semiconductor film is in contact with a substrate or film having a contact angle with water of 50 degrees or more.
<10> An electric circuit having 100 or more thin film transistors,
At least 80% of the thin film transistors are the thin film transistors according to any one of <1> to <9> above,
electric circuit.
<11> providing an organic semiconductor solution in which the organic semiconductor material is dissolved and / or dispersed;
Applying the organic semiconductor solution onto the stamp and drying to obtain an organic semiconductor film on the stamp;
The thin film transistor according to any one of <1> to <9> above, wherein the organic semiconductor film is produced by a method including a step of transferring the organic semiconductor layer at a temperature at which the organic semiconductor material becomes liquid crystal. Production method.
<12> The method according to <11>, wherein the transferring step is performed using a roll having the stamp on the printing surface.
<13> providing an organic semiconductor film made of an organic semiconductor material having an aromatic ring on a substrate or film;
Applying a stress from the outside to the organic semiconductor layer at a temperature at which the organic semiconductor material becomes liquid crystal, and orienting the organic semiconductor material in a plane of the organic semiconductor film;
The method for producing a thin film transistor according to any one of <1 to 9> above, wherein the organic semiconductor film is produced by a method comprising:
<14> The method according to any one of <11> to <13>, wherein the organic semiconductor film is in contact with a substrate or film having a contact angle with water of 50 degrees or more.

The thin film transistor of the present invention can function at a relatively high speed. Moreover, according to the method of the present invention for producing an organic semiconductor film, the organic semiconductor film used in the thin film transistor of the present invention can be produced.

FIG. 1 is a diagram for conceptually explaining an organic semiconductor film used in the present invention. FIG. 2 is a diagram for conceptually explaining a conventional organic semiconductor film. FIG. 3 is a diagram for conceptually explaining the organic semiconductor film used in the present invention. FIG. 4 is a diagram illustrating a thin film transistor of the present invention. FIG. 5 is a diagram showing the results of in-plane X-ray diffraction (XRD) analysis of the organic semiconductor film obtained in Example 1. FIG. 6 is a diagram showing the results of in-plane X-ray diffraction (XRD) analysis of the organic semiconductor film obtained in Example 3. FIG. 7 is a diagram for conceptually explaining the method of the present invention for producing an organic semiconductor film. FIG. 8 is a diagram showing the direction dependency of mobility for the organic semiconductor films of Examples 1A and 8A.

<< Thin Film Transistor >>
The thin film transistor of the present invention includes a source electrode, a drain electrode, a gate electrode, a gate insulating film, and an organic semiconductor film, the source electrode and the drain electrode are insulated from the gate electrode by the gate insulating film, and the gate electrode The current flowing through the organic semiconductor film from the source electrode to the drain electrode is controlled by the voltage applied to.

In the thin film transistor of the present invention, the organic semiconductor film is made of an organic semiconductor material having an aromatic ring. Here, in this organic semiconductor film, the surface formed by the aromatic ring constituting the organic semiconductor material has a conformation that stands substantially perpendicular to the substrate.

Further, in this organic semiconductor film, the molecular axis that maximizes the mobility of the organic semiconductor material is the channel length direction of the organic semiconductor element, that is, the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film. Oriented in the direction. Specifically, for example, in this organic semiconductor film, the direction of the molecular axis of the main chain of the organic semiconductor material is within ± 60 ° of the direction of the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film. , Within ± 45 °, within ± 30 °, within ± 20 °, or within ± 10 °.

The organic semiconductor film may not be in contact with the alignment film that aligns the organic semiconductor material in the plane direction. For example, such an alignment film may not be provided directly below.

(Conformation standing almost vertically)
In the organic semiconductor film used in the thin film transistor of the present invention, as shown in FIG. 1, the surface (2) formed by the aromatic ring constituting the organic semiconductor material (1) is substantially perpendicular to the substrate (10). The organic semiconductor material (1) is oriented in the plane of the organic semiconductor film.

Here, the fact that the surface (2) is a conformation standing substantially perpendicular to the substrate (10) and being uniaxially oriented is, for example, in in-plane X-ray diffraction (XRD) analysis. This can be confirmed by observing only the peaks due to the spacing between the surfaces.

On the other hand, as in Patent Document 2 and Non-Patent Documents 3 to 5, when an organic semiconductor material in a solution state or a molten state is formed while applying strong shearing, an organic film is used without using an alignment film. Although the orientation of the semiconductor material can be achieved, as shown in FIG. 2, the surface (2 ′) formed by the aromatic ring (1) constituting the organic semiconductor material is substantially parallel to the substrate (10). It is known that the film is oriented so as to have a stacked structure (Non-patent Document 5).

The fact that this surface (2 ′) is a layered structure substantially parallel to the substrate (10) is, for example, in the out-of-plane X-ray diffraction (XRD) analysis, this surface ( 2 ′) diffraction peaks are confirmed, and in the in-plane X-ray diffraction (XRD) analysis, a plurality of lamellar peaks due to the crystallization direction along the alkyl side chain (C ₁₂ H ₂₅ ) This can be confirmed by observation.

In this regard, the relationship between the conformation of organic semiconductors having aromatic rings and semiconductor properties has been extensively studied. Specifically, the surface (2) formed by the aromatic ring constituting the organic semiconductor material (1) has a conformation (edge-on-conformation (FIG. 1)) in which the surface (2) stands substantially perpendicular to the substrate (10). In the case of having the surface (2 ′) formed by the aromatic ring (1) constituting the organic semiconductor material, the conformation (face-on conformation (FIG. 2) in which the surface (2 ′) is laminated substantially parallel to the substrate (10). It is generally known that the semiconductor characteristics including charge mobility are superior to those of (ii)) (Patent Document 3, Non-Patent Documents 1, 6, etc.).

(Direction of molecular axis of main chain)
In the organic semiconductor film used in the thin film transistor of the present invention, the molecular axis direction of the main chain of the organic semiconductor material is uniaxially oriented in the direction of the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film. Thus, a large charge mobility can be achieved in the direction of this electric field. Note that an unoriented organic semiconductor film has a large variation in the orientation direction of the organic semiconductor material, which causes a problem that characteristic variations of thin film transistors using such an organic semiconductor film are likely to occur. On the other hand, since the organic semiconductor film used in the present invention is uniaxially oriented, such variation in characteristics is reduced.

Therefore, as in the thin film transistor of the present invention, the surface formed by the aromatic ring constituting the organic semiconductor material has a conformation standing substantially perpendicular to the substrate, and the molecular axis of the main chain of the organic semiconductor material Is oriented in the direction of the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film, a thin film transistor that functions at a relatively high speed can be obtained.

Furthermore, when the organic semiconductor film used in the present invention is not in contact with an alignment film that aligns the organic semiconductor material in the plane direction, such an alignment film may have an undesirable effect on the organic semiconductor film, for example, alignment. When a defect occurs in the film and / or when the alignment film deteriorates, it is possible to avoid a decrease in the characteristics of the organic semiconductor film. Still further, polyimide, which is mainly used for the alignment film for aligning the organic semiconductor material in the plane direction, has a relatively high surface energy, so that the organic semiconductor film in contact therewith is disadvantageous in terms of electrical characteristics, and the organic semiconductor aromatic ring is a substrate. However, in the organic semiconductor film of the present invention that is not in contact with the alignment film, such a problem can be avoided.

The organic semiconductor film used in the thin film transistor of the present invention can be manufactured by the method of the present invention for manufacturing an organic semiconductor film.

(Charge mobility)
In the organic semiconductor film used in the present invention, the ratio of charge mobility in two directions perpendicular to the surface {(charge mobility in the direction in which the charge mobility is maximum) / (charge mobility in the direction perpendicular thereto)} Or the maximum value of the ratio of the charge mobility in any two directions in the plane {(charge mobility in the direction in which the charge mobility is maximum) / (charge mobility in the direction in which the charge mobility is minimum) } May be greater than 1.5. That is, for example, as shown in FIG. 3, in the organic semiconductor film (20) of the present invention disposed on the substrate (10), the charge mobility in the direction (arrow 22) in which the charge mobility is maximum. However, it may be larger than 1.5 times the charge mobility in the direction (arrow 24) in which the charge mobility is minimum.

Here, the ratio value or maximum value of the charge mobility is, for example, 2 or more, 10 or more, 20 or more, and may be 50 or less, 30 or less, 20 or less, or 15 or less.

In the organic semiconductor film used in the present invention, the charge mobility in the direction in which the mobility is maximum is, for example, 0.01 cm ² / (V · s) or more, 0.05 cm ² / (V · s) or more, or 0 It may be 10 cm ² / (V · s) or more. Here, in the present invention, the charge mobility {cm ² / (V · s)} is the charge mobility on the surface of the organic semiconductor film, and represents the ease of movement of charges that are holes or electrons. .

(thickness)
The organic semiconductor film used in the present invention can have an arbitrary thickness, for example, a thickness of 1 nm to 1 μm, or 10 nm to 500 nm.

(Organic semiconductor materials)
The organic semiconductor material constituting the organic semiconductor film used in the present invention is an arbitrary organic semiconductor having an aromatic ring, and particularly an organic semiconductor material that can be in a liquid crystal state. Examples of such organic semiconductor materials include low molecular organic semiconductor molecules such as pentacene, thiophene, perylene, and fullerene materials, polyalkylthiophene, polyphenylene vinylene, polyfluorene-thiophene copolymers, and the like. Mention may be made of molecular organic semiconductor molecules.

For reference, the temperature at which the organic semiconductor material can be in a liquid crystal state is exemplified below:

In addition, the meaning of the symbol in Table 1 is as follows:
PQT: Poly [bis (3-dodecyl-2-thienyl) -2,2′-dithiophene-5,5′-diyl]
F8T2: Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co-bithiophene]
F8BT: Poly [(9,9-dioctylfluorenyl-2,7-diyl) -alt-benzo [2,1,3] thiadiazole-4,8-diyl]
pBTTT (C10): poly (2,5-bis (3-decylthiophen-2-yl) thieno [3,2, b] thiophene)
pBTTT (C12): poly (2,5-bis (3-dodecylthiophen-2-yl) thieno [3,2, b] thiophene)
pBTTT (C14): poly (2,5-bis (3-tetradecylthiophen-2-yl) thieno [3,2, b] thiophene)

Here, the phase transition temperature can be obtained as follows. That is, using a differential scanning calorimeter, the differential scanning calorimetry (DSC) in accordance with JIS K7121-1987 “Testing Methods for Transition Temperature Plastics” than the expected transition temperature. After holding the device at about 50 ° C. until it stabilizes, it is heated at a heating rate of 10 ° C./min to a temperature about 30 ° C. higher than the expected end of the transition to obtain a differential scanning calorimetry curve. Thereafter, for the obtained differential scanning calorimetry curve, the peak of liquid crystallization and melting peaks are specified as the liquid crystal phase transition temperature and melting temperature, respectively. As the differential scanning calorimeter, for example, trade name: DSC Q10 manufactured by TA Instruments Inc. can be used.

(Production method)
The organic semiconductor film used in the present invention can be produced by any method. It may be preferable in terms of productivity to manufacture the organic semiconductor film by a solution method, that is, a printing method such as a casting method, a spin coating method, or a contact printing method, or a dipping method. When the organic semiconductor film of the present invention is a film obtained by a solution method, it is distinguished from those produced by other methods by the presence of a trace amount of solvent remaining in the organic semiconductor film, the shape and physical properties of the film, etc. be able to. The organic semiconductor film of the present invention can be produced, for example, by the method of the present invention for producing an organic semiconductor film.

In addition, layers other than the organic semiconductor film of the thin film transistor of the present invention, for example, other layers such as an electrode layer and a dielectric layer, may be made of an inorganic material or an organic material.

For example, as shown in FIG. 4, the thin film transistor of the present invention includes (a) bottom gate / top contact type (BGTC type), (b) bottom gate / bottom contact type (BGBC type), and (c) top gate / top contact. Any of a type (TGTC type) and (d) a top gate / bottom contact type (TGBC type) may be used. In these

thin film transistors

130, 140, 150 and 160 of the present invention,

source electrodes

134, 144, 154, 164,

drain electrodes

135, 145, 155, 165,

gate electrodes

131, 141, 151, 161, a

gate insulating film

132, 142, 152, 162, and

semiconductor films

133, 143, 153, 163, the source electrode and the drain electrode are insulated from the gate electrode by the gate insulating film, and the source is applied by the voltage applied to the gate electrode. The current flowing through the semiconductor film from the electrode to the drain electrode is controlled.

"electric circuit"
The electric circuit of the present invention has 100 or more, 1,000 or more, 10,000 or more, or 100,000 or more thin film transistors, and at least 80%, at least 90%, at least of these thin film transistors. 95% is the thin film transistor of the present invention.

According to such an electric circuit of the present invention, the characteristics of the thin film transistor of the present invention that operates at high speed can be used effectively.

<< Method for Manufacturing Organic Semiconductor Film-First Method >>
A first inventive method for producing an organic semiconductor film comprises providing an organic semiconductor solution in which an organic semiconductor material is dissolved and / or dispersed, applying the organic semiconductor solution onto a stamp and drying, Obtaining an organic semiconductor film on the stamp, and transferring the organic semiconductor layer at a temperature at which the organic semiconductor material becomes liquid crystal.

According to the method of the present invention for producing an organic semiconductor film, the organic semiconductor film used in the thin film transistor of the present invention can be produced.

Specifically, according to the method of the present invention for producing an organic semiconductor film, the organic semiconductor layer is transferred at a temperature at which the organic semiconductor material becomes liquid crystal, thereby enabling transfer by the stamp and the base material. By applying stress to the organic semiconductor film in the liquid crystal state, the surface formed by the aromatic ring constituting the organic semiconductor material can be aligned in a conformation that is substantially perpendicular to the substrate Become.

Although not limited by theory, it is thought that the reason why the surface of the present invention can be oriented in a conformation that is substantially perpendicular to the substrate is as follows.

1. When the organic semiconductor film is formed on the stamp using the solution method, the aromatic ring of the organic semiconductor material is self-organized in a conformation that is substantially perpendicular to the stamp at the air side interface. This is presumably because air is theoretically superhydrophobic and therefore has little influence on the organic semiconductor, whereby the organic semiconductor material itself takes the most stable conformation at least on the air side of the organic semiconductor film.

2. As shown in FIG. 6A, when the aligned organic semiconductor film (210) in the liquid crystal state is transferred from the stamp (220) to the base material (250) using a roller (230), for example, 220) and the substrate (250) are subjected to stress, particularly shear stress, on the organic semiconductor film (210). According to this, as shown in FIG. 6B, the aromatic ring of the organic semiconductor material of the organic semiconductor film (210) maintains a conformation that is preliminarily standing substantially perpendicular to the stamp. For example, it is considered to be oriented with respect to the rotation direction (261) of the roller indicated by the arrow (231) or the vertical direction (262) thereof. At this time, by setting the transfer temperature within the liquid crystal phase temperature range of the organic semiconductor film, the organic semiconductor film becomes a liquid crystal phase, and molecular orientation is facilitated even with a slight shear stress.

(Organic semiconductor materials and solvents)
For the organic semiconductor material used in the method of the present invention, the description relating to the organic semiconductor film of the present invention can be referred to.

The solvent contained in the organic semiconductor solution used in the method of the present invention may be any solvent that can dissolve and / or disperse the organic semiconductor material. Examples of such a solvent include toluene, xylene, tetralin, decalin, chloroform, monochlorobenzene, dichlorobenzene, trichlorobenzene, and combinations thereof.

(Base material)
In the method of the present invention, the organic semiconductor layer can be transferred from the stamp to a substrate or film. Such a substrate or film may be any substrate or film that is intended to have an organic semiconductor film disposed thereon. Thus, for example, examples of such a substrate include an inorganic material such as a silicon wafer and glass, and an organic material such as a polymer film.

Further, this substrate or film may have a contact angle with water of 50 degrees or more, 60 degrees or more, 70 degrees or more, 80 degrees or more, 90 degrees or more, or 100 degrees or more. That is, this substrate or film may be a substrate or film having a low surface energy. When the organic semiconductor film is transferred to the substrate or film having a low surface energy by the method of the present invention, the surface formed by the aromatic ring constituting the organic semiconductor material is substantially perpendicular to the substrate. It becomes easy to take formation.

(stamp)
The stamp to which the organic semiconductor solution is applied in the method of the present invention is an arbitrary stamp that can form an organic semiconductor film thereon and transfer the organic semiconductor film from the organic semiconductor film to a substrate or the like, that is, It may be a contact print stamp for forming an organic semiconductor film. Such a stamp can be attached to a roll so that the stamp is arranged on the printing surface, and the stamp can be pressed against a substrate or the like while the roll is rotated to perform transfer.

The stamp to which the organic semiconductor solution is applied in the method of the present invention has a surface having a relatively large contact angle with water, that is, for example, a contact angle with water of 40 ° or more, 50 ° or more, 60 ° or more, 70 ° or more, 80 You may have the surface which is (degree) or more, 90 degree or more, 100 degree or more, or 105 degree or more. Thus, a relatively large contact angle of the surface of the substrate with water means that the surface is relatively lyophobic, that is, the surface energy of the surface is relatively small.

The contact print stamp that can be used in the method of the present invention is a contact print stamp in which the transfer portion is more lyophobic than the peripheral portion. Here, being lyophobic means that the surface energy is low, so this contact printing stamp has a transfer portion-peripheral portion structure in which the surface energy of the transfer portion is small and the surface energy of the peripheral portion is large. It can be said that it is a stamp for contact printing having.

When an organic semiconductor film is formed from an organic semiconductor solution on the contact print stamp transfer portion, the transfer is relatively difficult to wet due to the presence of a lyophilic peripheral portion around the lyophobic transfer portion. By holding the film of the organic semiconductor solution on the surface of the part, it is possible to promote the formation of the organic semiconductor film from the organic semiconductor solution on the surface of the transfer part. That is, according to this stamp, the organic semiconductor film can be formed even on the surface of the transfer portion that is relatively difficult to wet.

Further, when an organic semiconductor film is formed from an organic semiconductor solution on the transfer portion of the contact print stamp, the adhesion between the obtained organic semiconductor film and the transfer portion is relatively weak, and therefore, a relatively lyophobic substrate. The organic semiconductor film can be transferred onto the surface of the material, that is, the surface of the substrate having a contact angle with water of 50 ° or more, for example.

It should be noted that the transfer part of a general contact print stamp is generally a lyophilic solution in order to improve the wettability with respect to the organic semiconductor solution thereon, thereby enabling the stable formation of a film of the organic semiconductor solution. Have been sexed. Therefore, when an organic semiconductor film is formed from an organic semiconductor solution on a transfer portion of a conventional contact print stamp, the adhesion between the obtained organic semiconductor film and the transfer portion is relatively strong, and therefore relatively lyophobic. It has been difficult to transfer the organic semiconductor film onto the surface of the substrate, that is, the surface of the substrate having a contact angle with water of 50 ° or more, for example.

With respect to the present invention, the contact angle with respect to water is that at 25 ° C., 50 μL of water is dropped on the surface for measuring the contact angle, the shape of the dropped droplet is observed from the side, and the angle between the droplet and the surface is determined. It can be determined by measuring.

As described above, when the stamp to which the organic semiconductor solution is applied in the method of the present invention has a low surface energy surface, the organic semiconductor material in the organic semiconductor film can be formed on the surface of the stamp even on the surface in contact with the stamp. It is not easily affected, and therefore it becomes easy to rearrange due to the crystallinity of the organic semiconductor material itself.

A stamp having a surface with a relatively large contact angle with water can be obtained, for example, by treating the surface of the stamp with a lyophobic material. Examples of such lyophobic materials include silane, silazane, fluorine compounds, polyimide, polyester, polyethylene, polyphenylene sulfide, polyparaxylene, polyethylene terephthalate, polyethylene naphthalate, polydimethylsiloxane, and combinations thereof. it can.

(Apply)
In the method of the present invention for producing an organic semiconductor film, in order to apply the organic semiconductor solution to the stamp, any method such as a casting method, a spin coating method, or a dipping method can be used.

(Dry)
In the method of the present invention for producing an organic semiconductor film, the organic semiconductor solution applied on the stamp is dried to obtain the organic semiconductor film on the stamp. Here, this drying can be performed, for example, by exposing the organic semiconductor solution on the stamp to an atmosphere of more than 40 ° C., 50 ° C., 70 ° C. or 100 ° C. This drying can also be performed by removing the solvent from the organic semiconductor solution under reduced pressure.

(Transcription)
The method of the present invention for producing an organic semiconductor film includes the step of transferring the organic semiconductor layer on the stamp, for example, to a substrate or other stamp, at a temperature at which the organic semiconductor material becomes liquid crystal.

That is, for example, the organic semiconductor film on the stamp can be directly transferred onto a substrate such as a silicon wafer or a polymer film. Also, the organic semiconductor film on the stamp can be transferred to another stamp and transferred from the other stamp to the substrate.

The transfer of the organic semiconductor film from the first stamp to the base material or another stamp can be achieved by bringing the stamp holding the organic semiconductor film into contact with the base material or another stamp. Here, the transfer conditions such as the contact time, the stamp, and the temperature of the base material can be arbitrarily determined so that the organic semiconductor material becomes liquid crystal and can be transferred.

Specifically, this transfer can be performed such that the temperature of the base material or other stamp is higher than the temperature of the stamp. This transfer also treats the surface of the stamp to reduce adhesion to the organic semiconductor film and / or treats the surface of the substrate or other stamp to increase adhesion to the organic semiconductor film. Can be achieved. Still further, this transfer can be achieved by a combination of the above.

The other stamp used in the method of the present invention is an arbitrary stamp that can transfer an organic semiconductor film formed on the stamp, and from which the organic semiconductor film can be transferred to a substrate, That is, it may be a contact print stamp. Such other stamps can be made of, for example, polysiloxane. Further, the transfer of the organic semiconductor film from another stamp to the base material can be performed as described for the transfer of the organic semiconductor film from the stamp to the base material or another stamp.

<< Method for Manufacturing Organic Semiconductor Film-Second Method >>
The method of the second present invention for producing an organic semiconductor film includes a step of providing an organic semiconductor film made of an organic semiconductor material having an aromatic ring on a substrate or film, and a temperature at which the organic semiconductor material is liquid crystallized. Applying an external stress to the layer to orient the organic semiconductor material in the plane of the organic semiconductor film. Here, the provision of the organic semiconductor film on the substrate or film can be performed by any method, for example, a casting method, a spin coating method, a printing method such as a contact printing method, a solution method such as a dipping method, and the like. It can be provided using a vapor deposition method in which an organic semiconductor material is vapor-deposited on a substrate.

According to the method of the present invention for producing an organic semiconductor film, an external stress is applied to the organic semiconductor layer at a temperature at which the organic semiconductor material becomes liquid crystal, particularly a shear stress, for example, the stamp is pressed against the base material By applying stress to the organic semiconductor film in a liquid crystal state between the substrate and the substrate, the organic semiconductor material can be aligned in the plane of the organic semiconductor film.

In particular, according to the method of the present invention for producing an organic semiconductor film, the organic semiconductor film of the present invention can be produced.

For the organic semiconductor material, stamp, substrate, etc. that can be used in this method, the above description relating to the method of the first invention can be referred to.

The present invention will be described in detail using the following examples, but the present invention is not limited thereto. In the following examples, a bottom gate / top contact type (BGTC type) transistor was formed.

Water contact angle:
The water contact angle was measured with pure water at 25 ° C. using a water contact angle meter CA-X manufactured by Kyowa Interface Science.

Charge mobility:
The charge mobility of the organic semiconductor film was evaluated using a 4200-SCS type semiconductor evaluation apparatus manufactured by Keithley. The standard deviation of charge mobility was calculated by evaluating the characteristics of 10 or more elements.

In-plane X-ray diffraction (XRD) analysis:
Using Rigaku SmartLab, X-rays were incident in parallel and perpendicular to the transfer direction at an incident angle of 0.2 ° under the conditions of CuKα ray, tube voltage 45 kW, and tube current 200 mA. .

<< Example 1 >>
(Production of stamps for contact printing)
A silicone rubber (SIM-260 manufactured by Shin-Etsu Chemical Co., Ltd.) was cured into a flat plate shape, and oligomers were removed using hexane as a stamp material.

The stamp material is cut into 20 mm square, a mask corresponding to the transfer portion is placed on the stamp material, the transfer portion is masked, and the stamp material in which the transfer portion is thus masked is subjected to UV (ultraviolet) -ozone treatment. Performed for 30 minutes. That is, the transfer portion was not subjected to UV-ozone treatment, and the peripheral portion was subjected to UV-ozone treatment. This UV-ozone treatment provided a lyophilic surface at the periphery.

The water contact angle of the transfer part not subjected to UV-ozone treatment was 110 °, and the water contact angle of the peripheral part subjected to UV-ozone treatment for 30 minutes was 44 °. Further, twelve transfer portions exist on the stamp, and the size of each transfer portion was 100 μm × 2 mm.

(Inking of organic semiconductors)
Poly [bis (3-dodecyl-2-thienyl) -2,2′-dithiophene-5,5′-diyl] (“PQT”) (American Dye Source, ADS12PQT, MW = 18,000) 0.5 A mass part was dissolved by heating in 99.5 parts by mass of toluene to obtain a PQT solution as an organic semiconductor solution. This PQT solution was spin coated (1800 rpm, 20 seconds) onto the patterned stamp material. Thereafter, the PQT solution was aged and dried for about 10 minutes as it was, thereby forming an organic semiconductor film on the stamp.

(Silicon base)
An n-type silicon wafer with a 300 nm thermal oxide film (plane orientation <100>, specific resistance 0.05Ω) was treated with hot concentrated sulfuric acid for 30 minutes, and then several times using pure water, acetone, toluene, and hexane. Ultrasonic cleaning was performed twice. Further, after cleaning for 30 minutes with a UV ozone cleaning device, surface treatment was performed with octadecyltrichlorosilane (OTS).
In addition, the process of the base material by OTS was performed as follows.

A 20 mM toluene solution of OTS was prepared. The above silicon substrate was immersed in the obtained OTS solution and held for 7 days. After soaking, the substrate was washed with toluene and ethanol and ultrasonically washed in ethanol for 30 minutes. All the steps so far were performed in a glove box in which the humidity was controlled to 3% or less. Thereafter, the substrate was washed with pure water and heat-treated at 100 ° C. for 5 minutes to obtain an OTS-treated substrate.

(Transcription)
The stamp which has an organic-semiconductor film was fixed to the roller, and the roller with a stamp was obtained. The silicon substrate was heated and held at 135 ° C., the above-mentioned stamped roller was brought into contact therewith, and rotated to transfer the entire organic semiconductor film to the substrate.

For this transfer film, in-plane X-ray diffraction measurement was performed in a direction parallel to and perpendicular to the transfer direction. The results are shown in FIG. In FIG. 5, a peak in the (010) direction is observed, but the X-ray diffraction intensity is clearly different between the parallel direction A and the vertical direction B, indicating that the PQT film is uniaxially oriented. Further, in FIG. 5, only the (010) peak is observed, and it is clear that the thiophene ring has a conformation that stands perpendicular to the substrate.

(Production of thin film transistor)
Gold is vacuum-deposited by a mask vapor deposition method at a position corresponding to the transfer part of the obtained organic semiconductor film to form a source electrode and a drain electrode (L / w = 50 μm / 1.5 mm), and a silicon substrate is formed. A thin film transistor was obtained using the gate electrode and the oxide film on the surface of the silicon substrate as the gate insulating film. That is, a thin film transistor having a configuration as indicated by 130 in FIG. 4 was obtained.

At this time, an element in which the moving direction of the roller is in the channel length direction (maximum mobility) and an element in which the channel direction is perpendicular to the channel direction were produced. The evaluation results are shown in Table 2.

<< Example 1A >>
In the same manner as in Example 1, a PQT film was formed, and a source electrode and a drain electrode were formed to obtain a thin film transistor. However, in this example, the moving direction of the roller (the direction in which the mobility is maximum, that is, the direction of the molecular axis of the main chain of the organic semiconductor material) and the direction of the electric field between the source electrode and the drain electrode The angle between them was set to 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, and 90 °.

The evaluation results for mobility are shown in FIG.

Example 2
The same procedure as in Example 2 was performed except that the transfer temperature was 140 ° C. The evaluation results are shown in Table 2.

Example 3
The same procedure as in Example 1 was performed except that the transfer temperature was 130 ° C. The evaluation results are shown in Table 2.
FIG. 6 shows the result of in-plane X-ray diffraction measurement of the transfer film in the direction parallel to and perpendicular to the transfer direction. In FIG. 6, a peak in the (010) direction is observed, but the X-ray diffraction intensity is clearly different between the parallel direction A and the vertical direction B, indicating that the PQT film is uniaxially oriented. Further, in FIG. 6, only the (010) peak is observed, and it is clear that the thiophene ring has a conformation that stands perpendicular to the substrate.

Example 4
The same procedure as in Example 1 was performed except that the transfer temperature was 125 ° C. The evaluation results are shown in Table 2.

Example 5 (Comparison)
In the same manner as in Example 1, a PQT thin film was formed on the stamp. Same as Example 1 except that the solvent was dried by allowing it to stand for 10 minutes, and then the PQT thin film was heat-treated at 130 ° C. for 10 minutes under reduced pressure and transferred to the substrate at a transfer temperature of 80 ° C. Implemented. The evaluation results are shown in Table 2.

Example 6 (Comparison)
The same procedure as in Example 1 was performed except that the transfer temperature was 80 ° C. The evaluation results are shown in Table 2.

Example 7 (Comparison)
The device fabricated in Example 6 was heat-treated at 135 ° C. for 5 minutes under vacuum. The evaluation results are shown in Table 2.

Example 8 (Comparison)
The same procedure as in Example 7 was performed, except that a PQT film was directly formed on the substrate by spin coating using a 0.5% toluene solution of PQT. The evaluation results are shown in Table 2.

<< Example 8A (comparison) >>
In the same manner as in Example 8, a PQT film was formed, and a source electrode and a drain electrode were formed to obtain a thin film transistor. However, in this example, the moving direction of the roller (the direction in which the mobility is maximum, that is, the direction of the molecular axis of the main chain of the organic semiconductor material) and the direction of the electric field between the source electrode and the drain electrode The angle between them was set to 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, and 90 °.

The evaluation results for mobility are shown in FIG.

Example 9 (Comparison)
A device was fabricated in the same manner as in Example 1 except that polyhexylthiophene (P3HT: Poly (3-HexylThiophene)) (Plexcores Inc. Plexcore OS1100) was used as the organic semiconductor. Thereafter, heat treatment was performed at 100 ° C. for 30 minutes under vacuum, and the characteristics were measured. The evaluation results are shown in Table 2.

Example 10
Poly [(9,9-dioctylfluorenyl-2,7-diyl) -co-bithiophene] (“F8T2”) (ADS2008P molecular weight 43000, dispersion 2.8, manufactured by American Dye Source) was used as an organic semiconductor, and was transferred. The same operation as in Example 1 was conducted except that the temperature was 280 ° C. The evaluation results are shown in Table 2.

Example 11 (Comparison)
The same procedure as in Example 10 was performed except that the transfer temperature was 70 ° C. The evaluation results are shown in Table 2.

Example 12 (Comparison)
The same procedure as in Example 10 was performed except that a F8T2 0.5% toluene solution was used to directly form an F8T2 film on the substrate by spin coating. The evaluation results are shown in Table 2.

<< Example 12A (Comparison) >>
As an organic semiconductor, poly [(9,9-dioctylfluorenyl-2,7-diyl) -co-bithiophene] (“F8T2”) (ADS2008P, molecular weight 43000, dispersion 2.8, manufactured by American Dye Source) was used. A thin film transistor was prepared in accordance with Non-Patent Document 7, except that the transfer temperature was 280 ° C., that is, an organic semiconductor layer was formed while applying strong shearing. The evaluation results are shown in Table 2.

Example 13
Except that poly (2,5-bis (3-tetradecylthiophen-2-yl) thieno [3,2, b] thiophene) (“pBTTT-C14”) was used as the organic semiconductor and the transfer temperature was 150 ° C. The same procedure as in Example 1 was performed. The evaluation results are shown in Table 2.

DESCRIPTION OF SYMBOLS 1 Organic semiconductor material 2, 2 'The surface formed by the aromatic ring which comprises organic-semiconductor material 2 The surface formed by the aromatic ring which comprises organic-semiconductor material 10 Substrate

Claims

A source electrode, a drain electrode, a gate electrode, a gate insulating film, and an organic semiconductor film, wherein the source electrode and the drain electrode are insulated from the gate electrode by the gate insulating film, and the voltage applied to the gate electrode A thin film transistor in which the current flowing through the semiconductor film from the source electrode to the drain electrode is controlled,
The organic semiconductor film is made of an organic semiconductor material having an aromatic ring,
The surface formed by the aromatic ring constituting the organic semiconductor material is a conformation that is substantially perpendicular to the substrate, and the molecular axis that maximizes the mobility of the organic semiconductor material is the organic semiconductor film In the plane, oriented in the direction of the electric field between the source electrode and the drain electrode,
Thin film transistor.
The thin film transistor according to claim 1, wherein the direction of the molecular axis of the main chain of the organic semiconductor material is within ± 60 ° of the direction of the electric field between the source electrode and the drain electrode in the plane of the organic semiconductor film.
The thin film transistor according to claim 1 or 2, wherein the thin film transistor is not in contact with an alignment film that orients the organic semiconductor material in a plane direction.
The ratio of charge mobility in two directions perpendicular to the plane {(charge mobility in the direction in which the charge mobility is maximum) / (charge mobility in the direction perpendicular thereto)} is greater than 1.5. Item 4. The thin film transistor according to any one of Items 1 to 3.
The thin film transistor according to any one of claims 1 to 4, wherein the organic semiconductor film is obtained by a contact printing method.
The thin film transistor according to any one of claims 1 to 5, wherein the organic semiconductor material is an organic semiconductor material that can be in a liquid crystal state.
The thin film transistor according to any one of claims 1 to 6, wherein a value of the charge mobility ratio is 5 or more.
The thin film transistor according to any one of claims 1 to 7, wherein a charge mobility in a direction in which the charge mobility of the organic semiconductor film is maximized is 0.01 cm 2 / (V · s) or more.
The thin film transistor according to any one of claims 1 to 8, wherein the organic semiconductor film is in contact with a substrate or film having a contact angle with water of 50 degrees or more.
An electric circuit having 100 or more thin film transistors,
At least 80% of the thin film transistors are the thin film transistors according to any one of claims 1 to 9.
electric circuit.
Providing an organic semiconductor solution in which the organic semiconductor material is dissolved and / or dispersed;
Applying the organic semiconductor solution onto a stamp and drying to obtain an organic semiconductor film on the stamp;
The method of manufacturing a thin film transistor according to any one of claims 1 to 9, wherein the organic semiconductor film is manufactured by a method including a step of transferring the organic semiconductor layer at a temperature at which the organic semiconductor material becomes liquid crystal.
The method according to claim 11, wherein the transferring step is performed using a roll having the stamp on a printing surface.
Providing an organic semiconductor film made of an organic semiconductor material having an aromatic ring on a substrate or film;
Applying a stress from the outside to the organic semiconductor layer at a temperature at which the organic semiconductor material becomes liquid crystal, and orienting the organic semiconductor material in a plane of the organic semiconductor film;
The method for producing a thin film transistor according to any one of claims 1 to 9, wherein the organic semiconductor film is produced by a method comprising:
The method according to any one of claims 11 to 13, wherein the organic semiconductor film is in contact with a substrate or film having a contact angle with water of 50 degrees or more.