JP6590361B2 - Organic semiconductor film and manufacturing method thereof - Google Patents

Description

  The present invention relates to an organic semiconductor film and a method for manufacturing the same. The present invention also relates to an organic semiconductor device provided with an organic semiconductor film.

  Organic semiconductors have been inferior to inorganic semiconductors such as silicon so far, but recently, materials with excellent electrical characteristics are being developed, and research on crystal states and carrier mobility has progressed. It is out. Organic semiconductors have the advantages of low cost, low environmental load, and large area compared to vacuum technology conventionally used for inorganic semiconductors. In addition, since it can be manufactured near room temperature, a film can be formed by a printing technique on a plastic substrate. Therefore, organic semiconductors are expected to be applied to next-generation electronic devices as post-silicon semiconductors.

  As a method for producing an organic semiconductor film, various methods such as a vapor deposition method, a molecular beam epitaxial method, a solvent evaporation method, a melt method, and a Langmuir-Blodgett method have been conventionally studied. Among these methods, the solvent evaporation method is a method of evaporating a solvent from an organic semiconductor solution to bring the solution into a saturated state and depositing crystals to form an organic semiconductor film. It is excellent in that an organic semiconductor thin film can be obtained.

  Among the solvent evaporation methods, the solvent evaporation method based on the coating method using a solution such as the edge casting method, drop casting method, spin coating method, printing method (inkjet method or gravure printing method) is particularly simple and inexpensive. From the viewpoint that production near room temperature is possible, this is a highly expected method. In particular, the edge casting method is a promising technique in that a single crystal film can be produced as described in WO2011 / 040155.

  In the organic semiconductor film forming process using the solvent evaporation method, it is necessary to dissolve the organic semiconductor in the solvent, but typical organic semiconductors such as acene derivatives and thiophene derivatives generally have poor solubility in the solvent, There is a problem of gelation easily. Thus, many studies have been made to increase the solubility of organic semiconductor materials. In recent years, as described in Patent Document 1, it has been proposed to solve the solubility problem by combining a specific solvent and a specific organic semiconductor.

WO2011 / 040155 JP 2006-287224 A

  It has been difficult to obtain a high-quality single crystal film by conventional organic semiconductor film forming technology. The edge cast method described in Patent Document 1 is certainly promising as a technique capable of forming a single crystal film, but there is still room for improvement. This is thought to be due to the fact that organic semiconductor material development and film formation technology are immature and that the problem of solubility of organic semiconductors in solvents has not been cleared.

  This problem is not sufficiently solved even by the technique described in Patent Document 2. According to the technique described in Patent Document 2, a stable solution of a polythiophene semiconductor can be produced by using a halogen-containing aromatic compound as a solvent. However, although there is specific data regarding the stability of the solution in Patent Document 2, a specific example in which a polythiophene semiconductor is actually formed on a substrate is not described, and there is no description regarding its crystallinity. According to the study results of the present inventors, even when a polythiophene semiconductor is formed on a substrate by the technique described in Patent Document 2, fine cracks are formed in the obtained thin film, and a high-quality single crystal thin film is obtained. I knew that I couldn't get it. Since the presence of cracks adversely affects carrier mobility, which is an important electrical property of semiconductors, it is desirable to provide an organic semiconductor thin film in which cracks are suppressed. In addition, since the quality of the single crystal is higher when the number of domains of the obtained organic semiconductor film is smaller, only the organic semiconductor film having a large number of domains is obtained in the prior art.

  The present invention was created in view of the above circumstances, and an object of the present invention is to provide a single crystal organic semiconductor film with high crack uniformity and high homogeneity. Another object of the present invention is to provide a method suitable for producing such an organic semiconductor film. The present invention also relates to an organic semiconductor device comprising such an organic semiconductor single crystal film.

  As a result of intensive studies to solve the above problems, the present inventor prepared an organic semiconductor solution using 3-chlorothiophene as a solvent and formed an organic semiconductor film by a solvent evaporation method, thereby suppressing the generation of cracks. The present inventors have found that an organic semiconductor film with high homogeneity with a reduced number of domains can be obtained. In particular, when an organic semiconductor solution is prepared by using 3-chlorothiophene as a solvent and an organic semiconductor film is formed by the edge casting method, the generation of cracks is remarkably suppressed and a single crystal film having a high coverage is obtained. I found out. Such an effect could not be obtained with the similar compound 2-chlorothiophene, and further, with other halogenated aromatic solvents and non-halogenated aromatic solvents, This is considered to be a specific effect. The present invention has been completed based on this knowledge.

In one aspect, the present invention is a single crystal organic semiconductor film having 10 or less domains in an area per 1 mm ² .

  In one embodiment of the monocrystalline organic semiconductor film according to the present invention, the coverage is 0.98 or more.

  In another embodiment of the single crystal organic semiconductor film according to the present invention, the distribution range of crystal axes is within 10 °.

  In yet another embodiment of the monocrystalline organic semiconductor film according to the present invention, the standard deviation of the crack angle is 0.5 rad or less.

  In still another embodiment of the monocrystalline organic semiconductor film according to the present invention, the organic semiconductor is polythiophene or thianoacene.

In still another embodiment of the monocrystalline organic semiconductor film according to the present invention, the average mobility is 5 cm ² / Vs or more.

  In still another embodiment of the single crystal organic semiconductor film according to the present invention, the mobility variation coefficient is 40 or less.

  In still another embodiment of the monocrystalline organic semiconductor film according to the present invention, the average film thickness is 1 μm or less.

In another aspect of the present invention, a step 1 of preparing an organic semiconductor solution by dissolving an organic semiconductor in 3-chlorothiophene;
Attaching the organic semiconductor liquid onto the substrate surface;
Evaporating 3-chlorothiophene from the organic semiconductor liquid on the substrate surface; and
The manufacturing method of the organic-semiconductor film containing this.

In another aspect of the present invention,
Step 1 of preparing an organic semiconductor solution by dissolving an organic semiconductor in 3-chlorothiophene;
Preparing a substrate on which a contact member having an end surface standing with respect to the substrate surface is placed; and
Solution obtained in step 1 was supplied to the substrate, a step 3 of forming droplets that simultaneously contact the substrate surface and the end face,
Step 4 of evaporating 3-chlorothiophene from the droplets obtained in step 3 ,
The manufacturing method of the organic-semiconductor film containing this.

  In one embodiment of the method for producing an organic semiconductor film according to the present invention, the organic semiconductor is a thiophene derivative.

  In another embodiment of the method for producing an organic semiconductor film according to the present invention, the concentration of the organic semiconductor in the organic semiconductor solution is 0.2% by mass or less.

  In yet another embodiment of the method for producing an organic semiconductor film according to the present invention, the solution is supplied onto the substrate by a printing method.

  In still another embodiment of the method for producing an organic semiconductor film according to the present invention, the organic semiconductor film is monocrystalline.

  In still another aspect, the present invention is an organic semiconductor device comprising a substrate and a single crystal organic semiconductor film according to the present invention formed on the surface of the substrate.

  In still another aspect, the present invention is a transistor including the single crystal organic semiconductor film according to the present invention as a semiconductor channel.

  According to the present invention, there is provided an organic semiconductor film having a low coverage and having a low coverage and having a high coverage. Thereby, an organic semiconductor device having excellent quality stability and high carrier mobility can be manufactured with high yield.

It is a typical perspective view for demonstrating the process of the edge cast method. It is a typical perspective view for demonstrating the process following FIG. It is typical sectional drawing for demonstrating the process of the edge cast method. It is typical sectional drawing for demonstrating the modification of an edge cast method. It is a figure which shows typically the optical system for measuring a crystal axis. It is typical sectional drawing for demonstrating the process of the continuous edge casting method. It is another typical sectional view for explaining the process of the continuous edge casting method. It is an example of the photograph of the organic-semiconductor film which concerns on this invention (experiment number 1). It is an example of the photograph of the organic-semiconductor film which concerns on a comparative example (experiment number 2).

<1. Coverage>
In one embodiment, the single crystal organic semiconductor film according to the present invention has a feature that the film coverage on the substrate is high because cracks of the film are suppressed and a region where the film is missing is also suppressed. If a crack occurs in the film or a defect region occurs in the film formation region, the coverage is lowered. When the coverage is lowered, the yield is lowered and the quality stability of the organic semiconductor device is lowered. According to the present invention, the coverage of the organic semiconductor film can be 0.98 or more, and preferably 0.99 or more. Here, the coverage is defined as the average value of the proportion of the film when a plurality of 10 ⁴ μm ² ranges arbitrarily extracted from the region where the film is formed are observed.

<2. Number of domains>
In addition, since the single crystal organic semiconductor film according to the present invention has high single crystallinity in one embodiment, the number of crystal domains can be extremely reduced. Specifically, the number of domains per mm ² can be 10 or less, preferably 5 or less, and more preferably 1. A domain number of 1 means a so-called single domain single crystal, which means that the crystal orientation is uniform.

<3. Crack angle>
In one embodiment of the single crystalline organic semiconductor film according to the present invention, even if a crack is generated, the cracking direction (angle) is aligned with a crystal axis having high mobility. Usually, current flows along a direction in which the mobility is high, so that an advantage is obtained in that the crack does not significantly affect the mobility or transistor characteristics of the transistor. Specifically, the standard deviation of the crack angle can be 0.5 rad or less, preferably 0.3 rad or less, more preferably 0.2 rad or less, and even more preferably. Can be 0.15 rad or less, for example, 0.1 to 0.5 rad.

<4. Crystal axis>
In one embodiment, the organic semiconductor film according to the present invention is a single crystal film having high crystal axis uniformity. Specifically, the distribution range of crystal axes can be within 10 °, preferably within 8 °, and more preferably within 7 °. Such a single crystal film is advantageous when applied to an electronic device having a large area.

  In the present invention, the distribution range of crystal axes is measured by the following procedure. The optical system shown in FIG. 5 is constructed, and low angle incident X-ray diffraction (GIXD) measurement is performed. Specifically, diffracted light in which X-rays from the light source L (with a beam diameter of about 1.5 cm) are diffracted by the organic semiconductor film is detected while rotating 360 degrees about the axis φ perpendicular to the surface of the semiconductor film. Detector D detects. Thereby, the distribution of diffraction intensity (y-axis) when the thin film is rotated in the φ direction is measured. 2θ (x axis) is set to 22.56 degrees. The standard deviation of the obtained diffraction intensity distribution is defined as the crystal axis distribution range.

<5. Carrier mobility (average value)>
Mobility is an important characteristic that determines the response speed of a semiconductor device. Although the organic semiconductor has a low mobility, which is a problem to be solved for practical use, the organic semiconductor film according to the present invention can have excellent mobility exceeding that of amorphous silicon in one embodiment, which is preferable. In embodiments, it can have movement comparable to polycrystalline silicon. Specifically, in one embodiment, the organic semiconductor film according to the present invention can have an average mobility of 5 cm ² / Vs or more, preferably 7 cm ² / Vs or more, More preferably it can have an average mobility of 8 cm ² / Vs or higher, even more preferably it can have an average mobility of 10 cm ² / Vs or higher, for example an average mobility of 8-12 cm ² / Vs. Can have.

In the present invention, the mobility is calculated based on the FET mobility evaluation method (FET method) that is generally performed. That is, FET current formula
Id = (W / 2L) · μ · Cox (Vg−Vt) ^ 2... Saturation region (where, Id: drain current, Vg: gate voltage, Vt: threshold voltage, μ: mobility, Cox : Represents oxide film capacity, W: channel width, L: channel length)
From the measured value of IdVg of the FET, and the mobility is determined.

<6. Carrier mobility (coefficient of variation)>
A high homogeneity of the organic semiconductor film is an important characteristic for realizing a high yield, and a small coefficient of variation in mobility is advantageous from the viewpoint of homogeneity. In this regard, in one embodiment, the organic semiconductor film according to the present invention has a controlled variation coefficient of mobility. Specifically, in one embodiment, the organic semiconductor film according to the present invention has a mobility variation coefficient of 40 or less, preferably a mobility variation coefficient of 35 or less, more preferably a mobility variation coefficient. Is 30 or less, and even more preferably, the mobility variation coefficient is 30 or less, for example, the mobility variation coefficient is 20 to 30.

In the present invention, the variation coefficient of mobility is obtained from the mobility data obtained when the average value of mobility is obtained by the following equation.
(Variation coefficient of mobility) = (Standard deviation of mobility) / (Average value of mobility) × 100

<7. Film thickness>
The film thickness required for the organic semiconductor film varies depending on the application and is not particularly limited. The organic semiconductor film according to the present invention can have an average film thickness of 1 μm or less in one embodiment, 100 nm or less in another embodiment, and 50 nm or less in another embodiment. It can be. The organic semiconductor film according to the present invention can have an average film thickness of 20 nm or less in a preferred embodiment, 15 nm or less in another embodiment, and 10 nm or less in another embodiment. It can be.

<8. Organic semiconductor>
Although there is no restriction | limiting in particular about the kind of organic semiconductor which comprises the organic-semiconductor film based on this invention, It is desirable that it is a material with a high self-condensing function. The self-condensation function means a tendency to easily aggregate and crystallize when molecules are precipitated from the solvent. Moreover, a thiophene derivative is preferable in view of compatibility with the solvent 3-chlorothiophene. Examples of the thiophene derivative include polythiophene and thienoacene (thiophene-containing condensed polycyclic aromatic compound), and examples thereof include compounds represented by the following chemical structure. From the viewpoint of obtaining a single crystal, it is necessary to use an organic semiconductor alone, and it is not desirable to use a mixture of a plurality of types of organic semiconductors.

式（ｉ）中、Ｒ¹及びＲ²はそれぞれ独立に水素原子又は炭素数が４〜１０のアルキル基である。アルキル基はヘテロ原子（典型的には酸素原子及び硫黄原子から選択される。）を含んでもよい。また、Ｒ¹及びＲ²は一緒になって環を形成することもできる。自己凝集能の理由により、好ましくは、Ｒ¹及びＲ²はそれぞれ独立に水素原子又は炭素数が５〜８のアルキル基である。より好ましくはＲ¹及びＲ²はそれぞれ独立に水素原子又はヘキシル基である。 (A. Polythiophene semiconductor)
A polythiophene semiconductor has a high on / off ratio (on-state conductivity with respect to off-state conductivity) and high mobility, and thus can be suitably applied to a semiconductor device such as a transistor.

In formula (i), R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 4 to 10 carbon atoms. The alkyl group may contain heteroatoms (typically selected from oxygen and sulfur atoms). R ¹ and R ² can also form a ring together. For reasons of self-aggregation ability, preferably R ¹ and R ² are each independently a hydrogen atom or an alkyl group having 5 to 8 carbon atoms. More preferably, R ¹ and R ² are each independently a hydrogen atom or a hexyl group.

  n represents an integer of 5 to 100. n represents the average number of thiophene monomer units in the polythiophene semiconductor, that is, the length of the polythiophene chain. From the viewpoint of forming a single crystal film, n is preferably 50 or less.

In one embodiment of the polythiophene semiconductor, in the above formula (i), R ¹ is a hydrogen atom, and R ² is an alkyl group having 4 to 10 carbon atoms. For reasons of self-aggregation ability, preferably, in the above formula (i), R ¹ is a hydrogen atom and R ² is an alkyl group having 5 to 8 carbon atoms. More preferably, in the above formula (i), R ¹ is a hydrogen atom and R ² is a hexyl group.

  Specific examples of preferable polythiophene include P3HT (poly (3-hexylthiophene)), P3OT (poly (3-octylthiophene)), and P3DT (poly (3-decylthiophene)).

式（ｉｉ）中、Ｒ³、Ｒ⁴、Ｒ⁵及びＲ⁶はそれぞれ独立に、水素原子又は炭素数が１〜１４のアルキル基である。アルキル基はヘテロ原子（典型的には酸素原子及び硫黄原子から選択される。）を含んでもよく、アルキル基中の水素原子はハロゲン原子等の置換基で置換されていてもよい。自己凝集能の理由により、Ｒ⁴＝Ｒ⁵であることが好ましく、Ｒ³＝Ｒ⁶であることが好ましい。溶解性の観点から、好ましくは、Ｒ⁴及びＲ⁵が水素原子であり、Ｒ³及びＲ⁶がそれぞれ独立に炭素数が１〜１４のアルキル基であるか、又は、Ｒ³及びＲ⁶が水素原子であり、Ｒ⁴及びＲ⁵がそれぞれ独立に炭素数が１〜１４のアルキル基である。より好ましくは、Ｒ³及びＲ⁶が水素原子であり、Ｒ⁴及びＲ⁵がそれぞれ独立に炭素数が１〜１４のアルキル基である。自己凝集能の理由により、アルキル基の好ましい炭素数は４〜１２であり、より好ましくは６〜１０である。 (B. Thienoacene)
Thienoacenes represented by the following formulas (ii) to (ix) are preferable because of high atmospheric stability and high mobility.

In formula (ii), R ³ , R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom or an alkyl group having 1 to 14 carbon atoms. The alkyl group may contain a hetero atom (typically selected from an oxygen atom and a sulfur atom), and a hydrogen atom in the alkyl group may be substituted with a substituent such as a halogen atom. For reasons of self-aggregation ability, R ⁴ = R ⁵ is preferred, and R ³ = R ⁶ is preferred. From the viewpoint of solubility, preferably, R ⁴ and R ⁵ are hydrogen atoms, R ³ and R ⁶ are each independently an alkyl group having 1 to 14 carbon atoms, or R ³ and R ⁶ are It is a hydrogen atom, and R ⁴ and R ⁵ are each independently an alkyl group having 1 to 14 carbon atoms. More preferably, R ³ and R ⁶ are hydrogen atoms, and R ⁴ and R ⁵ are each independently an alkyl group having 1 to 14 carbon atoms. For the reason of self-aggregation ability, the alkyl group preferably has 4 to 12 carbon atoms, more preferably 6 to 10 carbon atoms.

Specific examples of suitable compounds represented by formula (ii) include 3,9-didecyldinaphtho [2,3-b: 2 ′, 3′-d] thiophene represented by the following formula (iii). .

式（ｉｖ）中、Ｒ⁷、Ｒ⁸、Ｒ⁹及びＲ¹⁰はそれぞれ独立に、水素原子又は炭素数が１〜１４のアルキル基である。アルキル基はヘテロ原子（典型的には酸素原子及び硫黄原子から選択される。）を含んでもよく、アルキル基中の水素原子はハロゲン原子等の置換基で置換されていてもよい。自己凝集能の理由により、Ｒ⁷＝Ｒ⁹であることが好ましく、Ｒ⁸＝Ｒ¹⁰であることが好ましい。溶解性の観点から、好ましくは、Ｒ⁷及びＲ⁹が水素原子であり、Ｒ⁸及びＲ¹⁰がそれぞれ独立に炭素数が１〜１４のアルキル基であるか、又は、Ｒ⁸及びＲ¹⁰が水素原子であり、Ｒ⁷及びＲ⁹がそれぞれ独立に炭素数が１〜１４のアルキル基である。より好ましくは、Ｒ⁸及びＲ¹⁰が水素原子であり、Ｒ⁷及びＲ⁹がそれぞれ独立に炭素数が１〜１４のアルキル基である。自己凝集能の理由により、アルキル基の好ましい炭素数は６〜１３であり、より好ましくは８〜１０である。

In formula (iv), R ⁷ , R ⁸ , R ⁹ and R ¹⁰ are each independently a hydrogen atom or an alkyl group having 1 to 14 carbon atoms. The alkyl group may contain a hetero atom (typically selected from an oxygen atom and a sulfur atom), and a hydrogen atom in the alkyl group may be substituted with a substituent such as a halogen atom. For reasons of self-aggregation ability, R ⁷ = R ⁹ is preferred, and R ⁸ = R ¹⁰ is preferred. From the viewpoint of solubility, preferably, R ⁷ and R ⁹ are hydrogen atoms, R ⁸ and R ¹⁰ are each independently an alkyl group having 1 to 14 carbon atoms, or R ⁸ and R ¹⁰ are It is a hydrogen atom, and R ⁷ and R ⁹ are each independently an alkyl group having 1 to 14 carbon atoms. More preferably, R ⁸ and R ¹⁰ are hydrogen atoms, and R ⁷ and R ⁹ are each independently an alkyl group having 1 to 14 carbon atoms. For reasons of self-aggregation ability, the alkyl group preferably has 6 to 13 carbon atoms, more preferably 8 to 10 carbon atoms.

Specific examples of suitable compounds represented by formula (iv) include 2,9-didecyldinaphtho [2,3-b: 2 ′, 3′-f] thieno [3, represented by the following formula (v): 2-b] thiophene (C ₁₀ -DNTT) and the like.

式（ｖｉ）中、Ｒ¹¹、Ｒ¹²、Ｒ¹³及びＲ¹⁴はそれぞれ独立に、水素原子又は炭素数が１〜１４のアルキル基である。アルキル基はヘテロ原子（典型的には酸素原子及び硫黄原子から選択される。）を含んでもよく、アルキル基中の水素原子はハロゲン原子等の置換基で置換されていてもよい。自己凝集能の理由により、Ｒ¹¹＝Ｒ¹³であることが好ましく、Ｒ¹²＝Ｒ¹⁴であることが好ましい。溶解性の観点から、好ましくは、Ｒ¹¹及びＲ¹³が水素原子であり、Ｒ¹²及びＲ¹⁴がそれぞれ独立に炭素数が１〜１４のアルキル基であるか、又は、Ｒ¹²及びＲ¹⁴が水素原子であり、Ｒ¹¹及びＲ¹³がそれぞれ独立に炭素数が１〜１４のアルキル基である。より好ましくは、Ｒ¹²及びＲ¹⁴が水素原子であり、Ｒ¹¹及びＲ¹³がそれぞれ独立に炭素数が１〜１４のアルキル基である。自己凝集能の理由により、アルキル基の好ましい炭素数は５〜１２であり、より好ましくは８〜１０である。

In the formula (vi), R ¹¹ , R ¹² , R ¹³ and R ¹⁴ are each independently a hydrogen atom or an alkyl group having 1 to 14 carbon atoms. The alkyl group may contain a hetero atom (typically selected from an oxygen atom and a sulfur atom), and a hydrogen atom in the alkyl group may be substituted with a substituent such as a halogen atom. For reasons of self-aggregation ability, R ¹¹ = R ¹³ is preferred, and R ¹² = R ¹⁴ is preferred. From the viewpoint of solubility, preferably, R ¹¹ and R ¹³ are hydrogen atoms, R ¹² and R ¹⁴ are each independently an alkyl group having 1 to 14 carbon atoms, or R ¹² and R ¹⁴ are It is a hydrogen atom, and R ¹¹ and R ¹³ are each independently an alkyl group having 1 to 14 carbon atoms. More preferably, R ¹² and R ¹⁴ are hydrogen atoms, and R ¹¹ and R ¹³ are each independently an alkyl group having 1 to 14 carbon atoms. For reasons of self-aggregation ability, the alkyl group preferably has 5 to 12 carbon atoms, more preferably 8 to 10 carbon atoms.

Specific examples of suitable compounds represented by formula (vi) include 2,7-dioctyl [1] benzothieno [3,2-b] [1] benzothiophene (C ₈ ) represented by the following formula (vii): -BTBT).

式（ｖｉｉｉ）中、Ｒ¹⁵、Ｒ¹⁶、Ｒ¹⁷及びＲ¹⁸はそれぞれ独立に、水素原子又は炭素数が１〜１４のアルキル基である。アルキル基はヘテロ原子（典型的には酸素原子及び硫黄原子から選択される。）を含んでもよく、アルキル基中の水素原子はハロゲン原子等の置換基で置換されていてもよい。自己凝集能の理由により、Ｒ¹⁵＝Ｒ¹⁷であることが好ましく、Ｒ¹⁶＝Ｒ¹⁸であることが好ましい。溶解性の観点から、好ましくは、Ｒ¹⁶及びＲ¹⁸が水素原子であり、Ｒ¹⁵及びＲ¹⁷がそれぞれ独立に炭素数が１〜１４のアルキル基であるか、又は、Ｒ¹⁵及びＲ¹⁷が水素原子であり、Ｒ¹⁶及びＲ¹⁸がそれぞれ独立に炭素数が１〜１４のアルキル基である。より好ましくは、Ｒ¹⁶及びＲ¹⁸が水素原子であり、Ｒ¹⁵及びＲ¹⁷がそれぞれ独立に炭素数が１〜１４のアルキル基である。自己凝集能の理由により、アルキル基の好ましい炭素数は５〜１２であり、より好ましくは８〜１０である。

In the formula (viii), R ¹⁵ , R ¹⁶ , R ¹⁷ and R ¹⁸ are each independently a hydrogen atom or an alkyl group having 1 to 14 carbon atoms. The alkyl group may contain a hetero atom (typically selected from an oxygen atom and a sulfur atom), and a hydrogen atom in the alkyl group may be substituted with a substituent such as a halogen atom. For reasons of self-aggregation ability, R ¹⁵ = R ¹⁷ is preferred, and R ¹⁶ = R ¹⁸ is preferred. From the viewpoint of solubility, preferably, R ¹⁶ and R ¹⁸ are hydrogen atoms, R ¹⁵ and R ¹⁷ are each independently an alkyl group having 1 to 14 carbon atoms, or R ¹⁵ and R ¹⁷ are It is a hydrogen atom, and R ¹⁶ and R ¹⁸ are each independently an alkyl group having 1 to 14 carbon atoms. More preferably, R ¹⁶ and R ¹⁸ are hydrogen atoms, and R ¹⁵ and R ¹⁷ are each independently an alkyl group having 1 to 14 carbon atoms. For reasons of self-aggregation ability, the alkyl group preferably has 5 to 12 carbon atoms, more preferably 8 to 10 carbon atoms.

Specific examples of suitable compounds represented by the formula (viii) include 3,11-didecyldinaphtho [2,3-d: 2 ′, 3′-d ′] benzo [1 represented by the following formula (ix): , 2-b: 4,5-b ′] dithiophene (C ₁₀ -DNBDT).

  The organic semiconductor film according to the present invention can be applied as a semiconductor layer of various organic semiconductor devices. In one embodiment of the organic semiconductor device, a substrate and a single crystalline organic semiconductor film layer, various electrode layers, an insulating film layer, and the like are provided on the substrate. Here, the substrate refers to a member for forming a semiconductor layer on the surface thereof, and examples thereof include a glass substrate, a silicon substrate, a plastic substrate, a ceramic substrate, a metal substrate, and the like. A substrate in which various device components such as an electrode layer and an insulating film layer are appropriately formed on the substrate is also exemplified. The substrate may be hard (rigid) or soft (flexible). The types of semiconductor devices include, but are not limited to, semiconductor elements (diodes, rectifier elements, transistors, thermistors, varistors, thyristors, photoelectric conversion elements, etc.) and integrated circuits (linear ICs, digital ICs, etc.). For example, in one embodiment, the organic semiconductor device according to the present invention can be a transistor including the organic semiconductor film according to the present invention as a semiconductor channel.

  Products that use transistors include active matrix elements and drive circuits for driving flexible display pixels, logic circuits that can be fabricated on plastic, low-cost RF-ID tags, signal processing elements for flexible sensors, and high-speed response. A pressure sensor etc. are mentioned.

<9. Film formation method>
The suitable manufacturing method of the organic-semiconductor film based on this invention is demonstrated. In producing a high-quality single crystal organic semiconductor film, an organic semiconductor solution preparation step is extremely important. As organic semiconductor solvents, halogen solvents such as chloroform, halogen aromatic solvents such as chlorobenzene and o-dichlorobenzene, and non-halogen aromatic solvents such as toluene and tetralin have been used. There is a problem that a semiconductor has poor solubility in a solvent or easily gels. Even these solvents can be dissolved by heating the organic semiconductor, but due to the large difference in solubility depending on temperature, crystallization is likely to occur rapidly, making it difficult to produce a homogeneous single crystal film. Met.

  The present inventor has discovered that 3-chlorothiophene not only exhibits higher solubility in organic semiconductors than other solvents, but also has a small solubility difference due to temperature. Therefore, it has been found that crystallization hardly occurs even at a relatively low temperature (60 to 70 ° C.), and coating at a low temperature is possible. In addition, the application at a low temperature can improve the yield and increase the area of the device. Most surprisingly, when an organic semiconductor solution is prepared using 3-chlorothiophene as a solvent, and an organic semiconductor film is formed by a solvent evaporation method, particularly an edge casting method, the generation of cracks is remarkably suppressed. In other words, a highly uniform single crystal film with a small number of domains can be obtained.

  The organic semiconductor solution can be prepared by putting the organic semiconductor into a heated solvent, or by heating after putting the organic semiconductor into the solvent. Although there is no restriction | limiting in particular in the form of the organic semiconductor thrown in in a solvent, For example, it can be set as a powder form. From the viewpoint of the stability of the compound, the heating temperature of the solvent is preferably not more than the boiling point, more preferably not more than 10 ° C. than the boiling point, and even more preferably not more than 30 ° C. than the boiling point. Further, from the viewpoint of the stability of the compound and the solubility of the compound, the temperature is preferably from room temperature to 135 ° C, more preferably from 50 to 135 ° C, and even more preferably from 70 to 90 ° C.

  In addition, the organic semiconductor concentration in the organic semiconductor solution is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, from the viewpoint of obtaining a homogeneous thin film with good reproducibility, and 0.025%. It is still more preferable that it is -0.05 mass%.

  The edge casting method itself is a known organic semiconductor film forming method, and is described, for example, in WO2011 / 040155 (the entire text of the method is incorporated herein). A preferred embodiment will be described below with reference to FIGS.

  As shown in FIG. 1, an organic semiconductor solution (hereinafter also referred to as “raw material solution”) is formed with electrodes and insulating films as necessary so as to contact the end face of the contact member 2 and the surface of the substrate 1 simultaneously. The liquid droplets 3 are formed by supplying on the substrate 1. The organic semiconductor film 4 is formed on the substrate 1 by drying the droplet 3 in this state.

  The contact member 2 has an end face 2a that stands at a predetermined angle from the surface of the contact member 2 placed on the surface of the substrate 1. The end surface 2a typically has a planar shape. The droplet 3 is supplied so as to come into contact with the end surface 2 a of the contact member 2. The contact member 2 can be formed of, for example, a resin, but any material other than a resin may be used as long as it appropriately performs the functions described below.

  As the manufacturing process of the organic semiconductor film, first, as shown in FIG. 1, the contact member 2 is placed on the substrate so that the end surface 2a crosses the predetermined A direction of the substrate 1, and preferably the end surface 2a is orthogonal to the A direction. Place on top of 1. Examples of the material of the substrate 1 include, but are not limited to, glass, plastic, ceramic, and metal. Further, it is desirable to perform treatment with a self-assembled monolayer containing functional groups exemplified by an alkyl group, an aryl group and an amino group so as to enhance the wettability of the surface of the substrate 1. This is because during crystal growth, a uniform single crystal film is obtained when the contact angle between the far end of the raw material solution and the substrate 1 with respect to the contact member 2 is smaller. This contact angle is preferably 10 ° or less. The substrate 1 may be hard (rigid) or soft (flexible). When a soft substrate is used, a curved organic semiconductor film can be formed. In this state, the raw material solution is supplied onto the surface of the substrate 1 so as to be in contact with the end face 2a. The supplied raw material solution droplets 3 are held by the end surface 2a, and a certain force is applied. The cross-sectional shape in this state is shown in FIG.

  A drying process is performed in a state where the droplet 3 is held by the end face 2a, and the solvent in the droplet 3 is evaporated. As a result, as shown in FIG. 3, in the droplet 3, the raw material solution becomes saturated by evaporation of the solvent sequentially at the far end edge from the end surface 2 a in the A direction, and organic semiconductor crystals begin to precipitate. The movement of the far end edge of the droplet 3 accompanying the evaporation of the solvent is indicated by broken lines e1 and e2. As the solvent evaporates, the crystallization of the organic semiconductor material advances, and the organic semiconductor film 4 grows as shown in FIG. That is, crystal growth proceeds toward the end face 2a along the A direction of the substrate 1, and the organic semiconductor film 4 is gradually formed.

  In this drying process, the action of defining the crystal growth direction through contact with the end surface 2a works depending on the state in which the droplet 3 of the raw material solution adheres to the end surface 2a. Thereby, the crystallinity control effect is obtained, the regularity of the arrangement of molecules of the organic semiconductor is improved, and it is considered that it contributes to the improvement of the electron conductivity (mobility).

  Although depending on the type of organic semiconductor, the drying process can be performed in the atmosphere at a substrate temperature of 60 to 90 ° C., typically 70 to 80 ° C. The deposition rate can be about 15 to 25 μm / s, although it depends on the type of organic semiconductor. Further, the film thickness can be adjusted by changing the substrate temperature or the concentration of the organic semiconductor in the solution. Furthermore, in the case of the continuous edge casting method described later, the film thickness changes depending on the moving speed of the contact member.

  As a modification of the above manufacturing method, as shown in FIG. 4, the substrate 1 is maintained at a predetermined angle, and the contact member 2 is desirably end surface 2 a so that the end surface 2 a crosses the inclined direction of the substrate 1. Is placed on the substrate 1 so as to be orthogonal to the tilt direction. In this state, the raw material solution is supplied onto the surface of the substrate 1 so as to come into contact with the end surface 2a. The supplied droplet 3 of the raw material solution is held by the end surface 2 a and is suspended in the tilt direction of the substrate 1. By tilting the substrate 1, it becomes easy to control the size of the wetted surface by the droplet 3 and obtain an organic semiconductor film having desired characteristics.

  Note that the method of forming the droplet 3 is not limited to the above-described method. For example, by removing the substrate 1 together with the contact member 2 from a state where the substrate 1 is immersed in the raw material solution, it is possible to form droplets attached to the end surface 2a.

  As another modified example, a method by a continuous edge casting method can be given. The continuous edge casting method was introduced in “Inch-Size Solution-Processed Single-Crystaline Films of High-Mobility Organic Semiconductors”, Junshi Soeda et al., Applied Physics Express 6, The Japan Society of Applied Physics, 2013, 076503. This is an advantageous method for increasing the area of the single crystal film. In the continuous edge casting method, as shown in FIGS. 6A and 6B, the direction in which the contact member 2 is separated from the droplet 3 in the direction parallel to the surface of the substrate 1 (directions of arrows X1 and X2 in the drawing). On the substrate 1 after the contact member 2 is moved by evaporating the solvent in the droplet 3 by continuously supplying the raw material solution 5 while relatively moving the substrate 1 and the contact member 2 to each other. Forming the organic semiconductor film 4 continuously. Supply of the raw material solution 5 can be performed using the solution supply nozzle 6, for example. As shown in FIGS. 6A and 6B, the contact member 2 is provided with a slight gap between the surface of the substrate 1 and the bottom surface of the contact member 2, and the tip of the nozzle 6 is disposed on the surface opposite to the end surface 2a of the contact member. The raw material solution 5 can be supplied toward the gap.

  According to this method, since the raw material solution 5 is continuously supplied, the crystal growth does not end due to evaporation of the solvent from the raw material solution 5. Therefore, the size of the formed organic semiconductor film 4 can be formed in a desired large area according to the width of the end surface 2a of the contact member 2 and the movement distance.

  During the relative movement, it is desirable to keep supplying the raw material solution 5 so that the size of the droplet 3 is maintained within a predetermined range from the viewpoint of keeping the film thickness of the organic semiconductor film 4 constant. That is, by supplying the raw material solution 5 at a rate equivalent to the evaporation rate of the solvent, the droplets 3 are maintained at the same size. Since the speed of crystallization from the raw material solution 5 is about 1 mm / min to several cm / min according to the normal setting, the relative speed of the substrate 1 and the contact member 2 may be adjusted to the same speed. By these operations, the organic semiconductor film 4 is continuously formed with a uniform film thickness on the surface of the substrate 1 after the contact member 2 moves when the state shown in FIG. 6A progresses to the state shown in FIG. 6B, for example. Is done.

  EXAMPLES Examples (invention examples) of the present invention are shown below together with comparative examples, which are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention. .

<Organic semiconductor>
The following materials were prepared as organic semiconductors.
(1A) 3,11-didecyldinaphtho [2,3-d: 2 ′, 3′-d ′] benzo [1,2-b: 4,5-b ′] dithiophene powder (TM026)
(1B) 3,9-Dihexyldinaphtho [2,3-b: 2 ′, 3′-d] thiophene powder (1C) 6,13-bis (triisopropylsilylethynyl) pentacene powder

<Solvent>
The following were prepared as the solvent.
(2A) 3-chlorothiophene (2D) 2-chlorothiophene (2E) 3-phenoxytoluene (2F) 1,2-dimethoxybenzene (2G) 1,2-dimethoxybenzene (2H) orthodichlorobenzene (ODCB)
(2I) Tetralin (2J) Butoxybenzene (2K) Thioanisole

<Formation of organic semiconductor film>
The organic semiconductor powder was put into a solvent in a beaker so as to have a predetermined concentration, and was completely dissolved by heating to a predetermined temperature (dissolution temperature) with a hot plate. The obtained organic semiconductor solution was applied onto a glass substrate with a thin film electrode on a hot plate by an edge casting method, heated to a predetermined temperature (film formation temperature) to evaporate the solvent, and an organic semiconductor thin film was formed. The combination of the organic semiconductor and the solvent, the conditions for dissolving the organic semiconductor, and the temperature condition of the hot plate when forming the organic semiconductor thin film are as shown in Table 1.

<Evaluation of organic semiconductor film>
The produced thin film was evaluated according to the following method.
(1) Coverage The thin film was observed in a crossed Nicol state using an ECLIPSE LV100N POL type microscope manufactured by Nikon Corporation. Photographing was performed under the conditions of an ISO sensitivity of 200 and an exposure time of 1.3 seconds using a 10 × objective lens and a SONY NEX-5R type camera at the angle at which most of the thin film became the brightest. Based on the definition described above for the crystal coverage based on the color information of the polarization micrograph, a plurality of arbitrary 10 ⁴ μm ² ranges were observed and the average value was calculated.
Specifically, in the above-mentioned polarization micrograph, the calculation was made based on the green brightness information in which the relationship between the film thickness and the brightness is most prominent. The decrease in coverage is mainly due to very thin cracks. In this case, the crack present in the thick film tends to appear brighter than the color of the thin film because the light of the film that appears brightly spreads in the crack portion. For this reason, in order to obtain the coverage rate, it is necessary to compare the brightness of the pixel with the surrounding portion. First, the average of the average crack interval is calculated from the photograph. For photos with cracks in the vertical direction, the average of the green brightness is calculated by half the crack spacing on the left and right of each pixel. If the average of the left and right sides of the target pixel is 3 or more darker, the pixel is judged to be a crack.
In the case of Experiment No. 13, the coverage was clearly low visually, and the evaluation method described above was not applicable, so evaluation was performed by another method. In the obtained photograph, green brightness information is recorded in 256 steps from 0 to 255. Therefore, in the case of Experiment No. 13, the portion where the green brightness is less than 30 as the substrate is the substrate portion, and the brighter portion is the crystal.
(2) Average film thickness The pixel color information in the crystal taken at the brightest angle in the polarizing microscope photograph mentioned above, the color information in the reflection microscope photograph, and the thickness of the crystal measured by the atomic force microscope are highly correlated. Confirmed that. Using this relationship, the average film thickness of a thin film having a uniform crystal direction was estimated by histogram analysis of a polarizing microscope photograph. For thin films with irregular crystal directions, the average film thickness was estimated by histogram analysis of photographs taken with a reflection microscope.
(3) Carrier mobility A large number of field effect transistors were fabricated using the deposited crystal as an active layer, and the mobility was estimated from the transfer characteristics. First, accept the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane 2 nm and the gold 30 nm, which are acceptor molecules, using a shadow mask designed to have a channel length of 50 μm on the thin film. Evaporated as an electrode. In order to prevent current from flowing outside the channel, etching was performed with a pulsed laser having a wavelength of 355 nm so that the channel width was precisely 50 μm. As the insulating layer, silicon dioxide having a relative dielectric constant of 3.9 and a thickness of 200 nm was used. Using a 4200-SCS semiconductor parameter analyzer manufactured by Keithley, the gate voltage was swept in the range of +10 V to −50 V under a drain voltage of −50 V, and the transfer characteristics were measured. By fitting a gate voltage range of −25V to −50V in the obtained transfer characteristics, the carrier mobility in the saturation region was obtained from the measured value of IdVg of the FET described above. Note that the measured mobility value varies depending on the direction of the current flowing through the active layer. Here, the channel direction is set so that the current flows in the direction in which the mobility is highest.

  The evaluation results are shown in Table 2. From Table 2, the organic semiconductor film according to the present invention is a homogeneous single crystal film having a high coverage. It can also be seen that the organic semiconductor film according to the present invention stably exhibits high mobility. That is, it will be understood that a high-performance organic semiconductor device can be manufactured with high yield by using the organic semiconductor film according to the present invention.

(4) Number of Domains For Experiment No. 1 (solvent: 3-chlorothiophene) and Experiment No. 2 (solvent: 2-chlorothiophene), multiple thin films were observed in the same manner as the coverage measurement (per field of view). 10 ⁴ range of [mu] m ^2), was measured number of domains crystals present per 1 mm ² by using a particle analysis capabilities WeveMetrics Co. Igor Pro based on the green color information. An area where the green brightness is continuously larger than 60 is defined as one domain. As a result, in Experiment No. 1, it was 1 domain / mm ² , whereas in Experiment No. 2 it was 5000 domains / mm ² .

(5) Crack angle For Experiment No. 1 (solvent: 3-chlorothiophene) and Experiment No. 2 (solvent: 2-chlorothiophene), the thin film was observed by the same method as the measurement of the coverage (arbitrary 10 ⁴ range of [mu] m ^2), was determined the angle of each crack. FIG. 7 shows a polarizing microscope photograph obtained in Experiment No. 1 and FIG. 8 shows a polarizing microscope photograph obtained in Experiment No. 2, respectively. The streaks were cracks, and the length and angle of the cracks were measured by tracing over the cracks using an Adobe Photoshop ruler. The standard deviation was calculated by weighting the crack angle by the crack length. As a result, in Experiment No. 1, it was 0.15 rad, whereas in Experiment No. 2, it was 0.83 rad. 7 and 8, it can be seen that the color of the thin film changes, but this represents a change in the thickness of the thin film, not a crack.

(6) Distribution of crystal axes For Experiment No. 1 (solvent: 3-chlorothiophene), the distribution range of crystal axes was examined using a Rigaku model StartLab GIXD apparatus according to the method described above. CuKα ray (1.5418 線) was used as the light source. The standard deviation of the diffraction intensity distribution was obtained by fitting a Gaussian curve to the measured intensity distribution. As a result, the distribution range of the crystal axes was 7 °.

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Contact member 2a End surface 3 Droplet 4 Organic-semiconductor film 5 Raw material solution 6 Solution supply nozzle L Light source D Detector

Claims (5)

Step 1 of preparing an organic semiconductor solution by dissolving an organic semiconductor that is thienoacene in 3-chlorothiophene;
Attaching the organic semiconductor liquid onto the substrate surface;
Evaporating 3-chlorothiophene from the organic semiconductor liquid on the substrate surface; and
A method for producing a single crystalline organic semiconductor film of thienoacene containing Step 1 of preparing an organic semiconductor solution by dissolving an organic semiconductor that is thienoacene in 3-chlorothiophene;
Preparing a substrate on which a contact member having an end surface standing with respect to the substrate surface is placed; and
Supplying the solution obtained in step 1 to the substrate to form droplets that simultaneously contact the end surface and the substrate surface; and
Step 4 of evaporating 3-chlorothiophene from the droplets obtained in step 3,
A method for producing a single crystalline organic semiconductor film of thienoacene containing The method for manufacturing a single-crystal organic semiconductor film according to claim 1 or 2 organic semiconductor concentration of the organic semiconductor solution is not more than 0.2 mass%. The method for producing a single crystalline organic semiconductor film according to any one of claims 1 to 3 , wherein the solution is supplied onto the substrate by a printing method. The method for producing a single crystal organic semiconductor film according to any one of claims 1 to 4 , wherein the number of domains existing in an area per 1 mm ^{2 of the} organic semiconductor film is 5 or less.

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