JP2010070596A - Organic pigment dispersion, method for forming organic semiconductor layer, method for producing organic transistor and organic transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic semiconductor layer formable by a wet coating method, and having resistance to an organic solvent. <P>SOLUTION: The organic pigment dispersion contains the organic solvent and an organic pigment dispersed in the organic solvent, and is used as a coating liquid when forming the organic semiconductor layer in an organic transistor by the wet coating method. A spin coating method and a droplet-ejecting method for forming dots or a layer by ejecting the organic pigment dispersion as minute droplets can be adopted as the wet coating method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic pigment dispersion used for manufacturing an organic transistor provided with an organic semiconductor layer, a method for forming an organic semiconductor layer using the same, a method for manufacturing an organic transistor, and an organic transistor.

  Thin film transistors (TFTs) with organic active layers are not as good as inorganic semiconductor materials such as silicon from the viewpoint of device characteristics such as carrier mobility, but they can be reduced in weight and area. In recent years, it has attracted a great deal of attention because of its advantages such as high ability and ability to be formed by printing by a wet method.

  As a technique relating to the formation of the organic semiconductor layer, for example, Patent Document 1 describes that an organic semiconductor is dispersed in a resin to form a resin-dispersed organic semiconductor film. However, Patent Document 1 does not describe a specific embodiment, and merely suggests the possibility of realization.

  Patent Document 2 discloses an organic material layer having a mixed layer in which fine particles of a second organic material such as perylene having a second conductivity type are dispersed in a first organic material having a first conductivity type. A transistor is disclosed.

JP 2003-101104 A JP 2005-243731 A

  As described above, an advantage of using an organic material as a semiconductor layer of a transistor is that it can be easily formed by a wet method, and the formed layer has flexibility. Conventionally, such an advantage has been obtained by using a low-molecular or high-molecular organic semiconductor material that can be dissolved in an organic solvent. However, the fact that the organic semiconductor material is soluble in an organic solvent means that the organic semiconductor layer is dissolved depending on the type of the solvent when a protective film or an insulating layer is provided on the upper layer by a wet method after forming the organic semiconductor layer. There is a possibility. For this reason, there is a drawback that the selection of the coating solvent is naturally limited.

  For this reason, the present inventors disperse organic pigment particles that can be produced with a relatively small particle size in a solvent, and use this dispersion as an organic semiconductor production liquid (ink) for producing a semiconductor layer of an organic transistor. Inspired to do. For example, if a liquid in which an azo pigment or a phthalocyanine pigment is dispersed can be used for forming an organic semiconductor layer, the organic semiconductor layer is formed when a protective layer or an insulating layer is provided with a material liquid dissolved in an organic solvent in the upper layer. An advantage is that it does not have to be dissolved. However, there has been no precedent that has been specifically implemented so far to create an organic transistor by applying a liquid in which organic pigment particles already crystallized and dispersed are applied by a wet method before coating. .

  Accordingly, an object of the present invention is to provide an organic semiconductor layer that can be formed by a wet coating method and has resistance to an organic solvent.

This invention is made | formed in view of the said situation, and exists in the following (1)-(10).
(1) An organic pigment dispersion used as a coating liquid for forming an organic semiconductor layer in an organic transistor by a wet coating method, comprising an organic solvent and an azo or phthalocyanine organic pigment dispersed in the organic solvent And an organic pigment dispersion characterized by containing. By using this organic pigment dispersion, it is possible to form an organic semiconductor layer that is difficult to dissolve in an organic solvent by a wet coating method.

(2) The organic pigment dispersion liquid as described in (1) above, wherein the organic pigment is an azo pigment. According to this feature, since the organic pigment is an azo pigment, even an organic semiconductor layer formed from a dispersion exhibits organic transistor characteristics.

(3) The organic pigment dispersion as described in (2) above, wherein the azo pigment is an azo pigment represented by the following general formula (I).

[In the formula (I), X is a substituted or unsubstituted aromatic group which may have a hetero atom in the aromatic ring, and R ₁ and R ₂ are the same or different and each represents a hydrogen atom or a halogen atom. , An alkyl group, an alkoxy group, a cyano group, or an amino group. However, a plurality of R ₁ and R ₂ may be bonded to the same benzene ring. ]

  According to this feature, by changing the structure of X, both electron mobility and hole mobility can be achieved.

(4) The organic pigment dispersion according to (1) above, wherein the organic pigment is phthalocyanine.

(5) A method for forming an organic semiconductor layer in an organic transistor, wherein an organic pigment dispersion containing an organic solvent and an azo- or phthalocyanine-based organic pigment dispersed in the organic solvent is formed on the underlayer A method for forming an organic semiconductor layer, which comprises wet coating.

(6) The method for forming an organic semiconductor layer according to (5), wherein the wet coating is performed by a spin coating method.

(7) The wet coating is performed by a droplet discharge method in which the organic pigment dispersion is discharged as fine droplets to form dots or layers on the base layer. Of forming the organic semiconductor layer. According to this feature, by adopting the above-described droplet discharge method, it is possible to create an organic semiconductor layer in an individual form at an individual location directly according to a signal.

(8) A step of forming an organic semiconductor layer by the method for forming an organic semiconductor layer according to any one of (5) to (7) above, and dissolving or dispersing a resin in an organic solvent on the organic semiconductor layer. And a step of forming an insulating layer or a protective layer by adhering a liquid to the organic transistor. According to this feature, the protective layer and the insulating layer can be formed on the upper portion of the organic semiconductor layer by a wet method without destroying the organic semiconductor layer using an organic solvent.

(9) An organic transistor comprising a layer containing a substance represented by the following general formula (I) as an electron transporting material.

[In the formula (I), X is a substituted or unsubstituted aromatic group which may have a hetero atom in the aromatic ring, and R ₁ and R ₂ are the same or different and each represents a hydrogen atom or a halogen atom. , An alkyl group, an alkoxy group, a cyano group, or an amino group. However, a plurality of R ₁ and R ₂ may be bonded to the same benzene ring. According to this feature, an organic transistor in which an organic semiconductor layer that is difficult to dissolve in an organic solvent is formed by a wet coating method can be obtained.

(10) The organic transistor as described in (9) above, wherein in the general formula (I), X is a divalent aromatic group having electron withdrawing performance.

  According to this characteristic, since the electron transport function of the compound of the general formula (I) is exhibited regardless of the film forming method (whether wet or vapor deposition), the organic transistor has excellent electrical characteristics. Can be granted.

  By using the organic pigment dispersion of the present invention, it is possible to form an organic semiconductor layer that is difficult to dissolve in an organic solvent by a wet coating method. Since this organic semiconductor layer has carrier mobility, it is highly useful as an organic semiconductor layer of an organic thin film transistor. In addition, since the organic semiconductor layer obtained using the organic pigment dispersion of the present invention is poorly soluble in organic solvents, an insulating layer or a protective layer can be applied to the upper layer of the organic semiconductor layer using an organic solvent. It becomes possible.

  Next, a preferred embodiment of the present invention will be described with reference to the drawings. First, the structure and operation of an organic thin film transistor (organic TFT) will be described with reference to FIG. 1A to 1D are configuration examples of the organic TFT of the present invention. In FIG. 1, reference numeral 1 is an organic semiconductor layer, reference numeral 2 is a substrate, reference numeral 3 is a gate electrode, reference numeral 4 is a source electrode, reference numeral 5 is a drain electrode, and reference numeral 6 is an insulating layer. In this TFT device, a gate electrode 3, a source electrode 4, and a drain electrode 5 that are spatially separated are provided above a substrate 2, and an insulating layer 6 (gate) is provided between the gate electrode 3 and the organic semiconductor layer 1. Insulating film). In the TFT device, the current flowing in the organic semiconductor layer 1 between the source electrode 4 and the drain electrode 5 is controlled by applying a voltage to the gate electrode 3.

  FIG. 1A is a cross-sectional view of a typical organic TFT. A description of a structure other than the material will be given with reference to FIG. When a voltage is applied between the pair of electrodes (source electrode 4 and drain electrode 5) in FIG. 1A, a current flows between the source electrode 4 and the drain electrode 5 through the organic semiconductor layer 1. At this time, when a voltage is applied to the gate electrode 3 separated from the organic semiconductor layer 1 by the insulating layer 6, the electric conductivity of the organic semiconductor layer 1 changes due to the field effect, and thus the current flowing between the source and drain electrodes is modulated. be able to. This is considered to be because the width of the storage layer in the organic semiconductor layer 1 adjacent to the insulating layer changes depending on the gate voltage, and the channel cross-sectional area changes.

  FIG. 1A is called a bottom contact type in which source or drain electrodes 4 and 5 are provided on an insulating layer 6 and the organic semiconductor layer 1 is formed thereon. 1B is said to be a top contact type in which source or drain electrodes 4 and 5 are formed on an organic semiconductor layer 1. FIG. 1C and 1D show an example in which an insulating layer 6 and a gate electrode 3 are provided on an organic semiconductor layer 1.

  In the organic TFT of the present invention, the organic semiconductor layer 1 is sandwiched between the source electrode 4 and the drain electrode 5 in any structure as shown in FIGS. The thickness of the organic semiconductor layer 1 is preferably about 1000 nm to about 5 nm. Accordingly, a dispersion of a pigment having a very large particle size is not preferable. The average particle size in the solution is preferably 1000 nm or less, and more preferably 300 nm or less.

  The organic TFT of the present invention is usually formed on a substrate 2 made of, for example, glass, silicon, plastic or the like. When the device is desired to have flexibility, light weight, and low cost, a plastic substrate is usually used. In the case of the transistor structure shown in FIGS. 1A and 1B, by using a conductive substrate as the substrate 2, it can also serve as the gate electrode 3.

  The device of the present invention has three spatially separated electrodes (source electrode 4, drain electrode 5, gate electrode 3). The gate electrode 3 is in contact with the insulating layer 6. Each electrode can be formed on the substrate 2 using a known conventional technique. The material of the source electrode 4, the drain electrode 5, and the gate electrode 3 is not particularly limited as long as it is a conductive material. For example, platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony, lead, tantalum, Indium, aluminum, zinc, magnesium, and alloys thereof, conductive metal oxides such as indium / tin oxide, or inorganic and organic semiconductors whose conductivity has been improved by doping, such as silicon single crystals, polysilicon, Examples include amorphous silicon, germanium, graphite, polyacetylene, polyparaphenylene, polythiophene, polypyrrole, polyaniline, polythienylene vinylene, and polyparaphenylene vinylene. Of the conductive materials, the source electrode 4 and the drain electrode 5 are preferably connected in ohmic contact with the organic semiconductor layer 1.

  The insulating layer 6 is disposed between the gate electrode 3 and the organic semiconductor layer 1. Suitable insulating materials are well known to those skilled in the art. As an insulating material, for example, inorganic materials such as silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, and titanium oxide, or when a flexible, lightweight, and inexpensive device is desired, for example, polyimide, polyvinyl Examples include various organic materials such as high molecular compounds such as alcohol, polyvinylphenol, polyester, polyethylene, polyphenylene sulfide, polyparaxylylene, polyacrylonitrile, cyanoethyl pullulan, polycarbonate, and various insulating LB films. it can. Two or more of these materials may be used in combination. In the present invention, the type of the insulating material is not particularly limited, but a material having low conductivity is preferable. When silicon is used for both the gate electrode 3 and the substrate 2, silicon oxide obtained by thermal oxidation of silicon can also be used as the insulating layer 3.

  There is no restriction | limiting in particular as a preparation method of the insulating layer 6, For example, CVD method, plasma CVD method, plasma polymerization method, vapor deposition method, spin coating method, dipping method, printing method, inkjet method, LB method etc. are mentioned, All It can be used.

  In the organic TFT having the above configuration, when an organic semiconductor that is easily dissolved in an organic solvent is used as the material of the organic semiconductor layer 1, in the structure of FIGS. 1C and 1D, insulation is performed with the material dissolved in the organic solvent. When the layer 6 is applied, there is a disadvantage that the organic semiconductor layer 1 is dissolved. However, in the case of an organic semiconductor layer made of an ink (organic pigment dispersion) in which a hardly soluble pigment is dispersed in an organic solvent as in the present invention, the organic semiconductor layer 1 is dissolved even in contact with the organic solvent. For this reason, even when the insulating layer 6 is made of, for example, a solution obtained by dissolving polycarbonate or the like in an organic solvent, wet deposition can be performed without affecting the organic semiconductor layer 1.

  1A and 1B, the organic semiconductor layer 1 made of an organic pigment dispersion that is difficult to dissolve in an organic solvent as in the present invention is not affected by the organic solvent. A protective layer (not shown) can be formed by a wet method using a material that is easily dissolved in an organic solvent and an organic solvent.

[Organic pigment dispersion]
The organic pigment dispersion of the present invention is a composition containing an organic solvent and an organic pigment dispersed in the organic solvent.

  In the present invention, the organic pigment may not have absorption in the visible region, and is defined as a crystalline organic powder having high mobility of carriers (electrons and holes) inside the crystal. Any powder can be included. In addition, the organic pigment used in the present invention is preferably an organic semiconductor material that is difficult to dissolve in an organic solvent, and examples thereof include azo pigments, bisazo pigments, perylene pigments, metal phthalocyanine pigments, metal-free phthalocyanine pigments, ansanthrone pigments, and the like. it can. As the organic pigment, those having a solubility in an organic solvent of 0.1% by weight or less are more preferable.

  An example of an organic pigment that can be preferably used in the present invention is a disazo compound represented by the following general formula (I).

[In the formula (I), X is a substituted or unsubstituted aromatic group which may have a hetero atom in the aromatic ring, and R ₁ and R ₂ are the same or different and each represents a hydrogen atom or a halogen atom. , An alkyl group, an alkoxy group, a cyano group, or an amino group. However, a plurality of R ₁ and R ₂ may be bonded to the same benzene ring. ]

  In the compound of the general formula (I), as a result of experiments, by selecting a divalent aromatic group having an electron-withdrawing property, such as a fluorenone, anthraquinone, benzophenone, thioxanthone structure, as the group X, an electron-transporting organic transistor A characteristic is obtained. Electron transporting materials are rare, and these materials are effective not only for wet methods but also for forming an organic semiconductor layer by vapor deposition.

  Moreover, when the group X had the following structure, hole mobility was shown (in the structure below, the aromatic ring may have a substituent).

  As another example of the organic pigment, a trisazo pigment having the following structure may be used.

  Further, the organic pigment may be a phthalocyanine pigment having the following structure.

[Wherein Z represents a metal atom of copper, nickel, iron, titanium oxide or a metal-free atom, and Y ₁ , Y ₂ , Y ₃ , Y ₄ represent a halogen group, an alkyl group, or an alkylsulfonyl group. And k, l, m, and n independently represent a number from 0 to 4. ]

  The disazo pigment has a thread shape of several tens of nanometers or less when viewed with an electron microscope, and the layer seems to be a structure in which the yarn is folded, creating a thinner film than expected from the average particle size in the solution. It is advantageous to do. The phthalocyanine pigment tends to have a large particle size, but it can be made amorphous with a relatively small particle size by being dropped into water after being dissolved in sulfuric acid.

  The organic solvent contained in the organic pigment dispersion of the present invention may be any solvent that can disperse the organic pigment, but when the organic pigment is, for example, a disazo pigment, an anone-based solvent is preferable. Further, when the organic pigment is a phthalocyanine pigment, for example, a ketone solvent or an ether solvent is preferable.

  In the organic pigment dispersion of the present invention, in addition to the organic solvent and the organic pigment, a dispersion resin (which may be conductive), or a surfactant for imparting leveling properties in some cases, an antioxidant, Optional components such as an antifoaming agent can also be blended.

  The organic pigment dispersion can be prepared, for example, by mixing an organic pigment and an organic solvent and dispersing the organic pigment in the organic solvent. The dispersion method is not limited, and for example, ball mill dispersion may be performed using zirconia balls or the like. Moreover, you may use a wet disperser [For example, dyno mill KDL A type (made by WAB company)]. When dispersing the organic pigment powder in the organic solvent, the average particle diameter of the organic pigment is preferably 1000 nm or less (for example, 1000 nm or less and 1 nm or more) from the viewpoint of making the organic semiconductor layer as thin as possible, and 50 nm or less. More preferably (for example, 50 nm or less and 1 nm or more). In addition, the blending ratio of the organic solvent and the organic pigment in the organic pigment dispersion of the present invention is preferably 5 to 200 parts to 1 part from the viewpoint of dispersibility. In some cases, from the viewpoint of film forming properties, 0 to 1 part of the dispersion resin is added to 1 part of the organic pigment.

[Wet coating process]
The organic pigment dispersion of the present invention is applied onto an object by a wet method and then dried. As for the wet method, the film can be formed by a known printing method such as spin coating, stencil printing, offset printing, and ink jet printing. Spin coating is a method of forming a coating film on a substrate using, for example, centrifugal force due to rotation. However, in spin coating, due to the relative position change at the rotating body (substrate) and the air interface due to rotation, the so-called wind causes drastic drying of the solvent, and uniform coating cannot be formed. There's a problem. Therefore, it is preferable to form a film by a cup spin method.

The cup spin method is performed by the following steps (1) and (2).
(1) The substrate is fixed to the bottom surface of the cup (container), and the coating solution is disposed.
(2) Thereafter, the container is sealed (covered), and the whole container is rotated to form a film.
The advantages of the cup-spin method are that the relative position of the rotating body and air does not change in the enclosed space and is not affected by the wind, and the enclosed space is saturated with the vapor of the solvent, so that rapid drying is possible. The point which can be prevented is mentioned. However, in the method of the present invention, the organic semiconductor layer 1 can be formed without using the cup spin method.

  On the other hand, it is possible to perform printing by a droplet discharge method in which dots or layers can be formed on an underlying layer by applying an inkjet printing technique and discharging an organic pigment dispersion as fine droplets. In that case, in order to improve paintability, various surfactants may be added to the organic pigment dispersion. In particular, fluorine and silicon nonionic surfactants are preferred.

[Drying process]
After the wet coating, the organic solvent is removed to form an organic semiconductor layer and then dried. Although there is no restriction | limiting in particular in the drying method, Heat drying is preferable. Regarding the formation of the organic semiconductor layer of the present invention, since the heating temperature affects the mobility of carriers, it is not preferable to set the treatment temperature for solvent drying too high, for example, drying at a treatment temperature of 200 ° C. or less. Is desirable.

  In the present invention, it was confirmed that an organic semiconductor layer capable of exhibiting organic transistor characteristics can be formed by applying a material that does not dissolve in a solvent such as an azo pigment as a dispersion, as shown in Examples below. It was done. From this, an organic thin film transistor excellent in cost performance can be easily manufactured by a wet film forming technique. In addition, there is an advantage that printing can be easily performed by a droplet discharge method that applies an inkjet printing technique.

  In the case of the organic semiconductor layer of the present invention, since the organic pigment is not dissolved in the organic solvent, a coating solution containing an organic solvent can be used when an insulating layer or a protective layer is provided on the upper layer. That is, for example, various polycarbonates, polyesters, polystyrene resins and the like can be dissolved in an organic solvent and applied. In this case, an inorganic material for adjusting the dielectric constant may be added and dispersed in the coating solution.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not restrict | limited by this. First, a transistor performance evaluation method performed in Examples and the like will be described with reference to FIGS. The carrier mobility due to the electric field effect of the organic semiconductor is calculated using the following equation.

[Where C _in is the capacitance per unit area of the gate insulating film, W is the channel width, L is the channel length, V _g is the gate voltage, I _ds is the source / drain current, μ is the carrier mobility, and V _th is The threshold voltage of the gate where the channel begins to form. ]

  FIG. 2 is an example of a graph showing the characteristics of the organic TFT at the source-drain voltage Vds = −20 [V] (note that this is merely an example and not the data of the organic TFT of the present invention).

  As shown in FIG. 2, -20 [V] is applied between the source and the drain, and the source / drain current when the gate voltage is subtracted from 10 to -20 [V] is measured. In the graph shown in FIG. 2, the Ids value at Vg = −20 [V] is the ON current of the organic TFT.

  Further, as shown in FIG. 3, the square root of the source / drain current measured under the above conditions is plotted against the gate voltage to perform linear approximation (FIG. 3 is also an example). The gate voltage value at which the square root of the source / drain current in the approximate curve becomes 0 [A] is defined as the threshold voltage Vth.

[Example 1]
Preparation of organic semiconductor coating solution:
A disazo pigment having the following structural formula was synthesized. This disazo pigment is a known compound (for example, see JP-A-3-230168).

  The operation of dispersing 8.0 g of the obtained crude crystals in 800 ml of N, N-dimethylformamide (DMF) and stirring and washing at 80 ° C. for 2 hours was repeated three times. Thereafter, the crystals were washed twice with 1000 ml of ion exchange water and dried at 120 ° C. under reduced pressure.

  In a glass pot with a diameter of 6 cm, a 5 mm diameter YTZ (partially stabilized zirconia) ball is placed so that the volume is approximately ½ of the volume. Further, 1.0 g of the above disazo pigment, polyvinyl butyral (Union Carbide) (XYHL manufactured) 0.1 g and cyclohexanone 22.9 g were added and dispersed with a ball mill for 4 days. After the completion of dispersion, 24 g of cyclohexanone was added and stirred, and then 30 g of mill base was taken out and diluted dropwise with methyl ethyl ketone / cyclohexanone (27.6 g / 34.8 g) while stirring to obtain a coating ink. The average particle size of the dispersed particles in this coating ink was about 110 nm as a result of measurement using a particle size measuring device CAPA-500 (trade name) manufactured by Horiba.

Board creation:
A substrate was prepared in which the silicon substrate surface was thermally oxidized to form an SiO ₂ insulating film having a thickness of 300 nm. This substrate was washed with sulfuric acid: hydrogen peroxide = 4: 1 until no bubbles were generated, washed with water, surface-treated with hexamethyldisilazane, and dried at 110 ° C. After drying, a pattern of source / drain electrodes was formed on the substrate by a photoresist method with a thickness of 1 angstrom (0.1 nm) of chromium and a thickness of 500 angstrom (50 nm) of gold. The channel length was 25 μm and the channel width was 7.6 mm. On top of this, the coating ink was applied by spin coating (1500 rpm; 30 seconds). This was dried at 120 ° C. for 15 minutes.

  The field effect mobility, which is a characteristic of the organic thin film transistor thus fabricated, was measured. In addition, the following formula | equation was used for calculation of the field effect mobility of an organic thin-film transistor.

[Where C _in is the capacitance per unit area of the gate insulating film, W is the channel width, L is the channel length, V _g is the gate voltage, I _ds is the source / drain current, μ is the mobility, and V _th is the channel. This is the threshold voltage of the gate that begins to form. ]

When the characteristics of the thin film transistor thus fabricated were evaluated, the field effect mobility was 2.7 × 10 ⁻⁵ cm ² / Vs, the threshold voltage was 7 V, the on / off ratio was 1.2 × 10 ³ , and the electron mobility was exhibited. It was. Hall mobility was small. FIG. 4 shows the transfer characteristics of the manufactured transistor when Vds = −40 V, and FIG. 5 shows the output characteristics. As described above, those having an electron-withdrawing property such as fluorenone and anthraquinone having a central skeleton of a disazo compound can be used for a transistor as a good electron transfer agent. Note that this disazo pigment has an average particle size of 110 nm in the solvent, which is still large, but when viewed with an electron microscope, it has a thread shape with a diameter of several tens of nm or less. It was also confirmed that there is an advantage that a thin film can be easily formed after coating.

[Example 2]
Zirconia beads having a diameter of 2 mm were placed in a sample bottle, 3 parts by weight of cycloheptanone, 0.84 parts by weight of methyl ethyl ketone, and 0.043 parts by weight of an azo pigment having the following structure were added and milled for 1 hour.

To the mixture after milling, 0.21 part by weight of a 4% by weight solution of butyral resin (Sekisui Chemical Co., Ltd., trade name: BM-S) (solvent is methyl ethyl ketone) was added and milled for another 5 hours. The average particle size of the dispersed particles was 350 nm. This was applied to the substrate by spin coating as in Example 1, and dried at 120 ° C. for 15 minutes to produce an organic thin film transistor. The mobility was 1.2 × 10 ⁻⁶ cm ² / Vs, indicating hole mobility. FIG. 6 shows the transfer characteristics of the manufactured transistor, and FIG. 7 shows the output characteristics.

[Example 3]
1.8 parts by weight of oxytitanium phthalocyanine (having a strong peak at 27.1 ° of diffraction angle 2θ ± 0.2 ° in X-ray diffraction using CuKα), 1.2 parts by weight of butyral resin, 97 parts by weight of methyl ethyl ketone The milling solution was spin coated on the substrate as in Example 1. The average particle diameter of the dispersed particles was approximately 1 μm. An organic thin film transistor was produced in the same manner as in Example 1, and the electrical characteristics were examined. As a result, the mobility was 5 × 10 ⁻⁷ cm ² / Vs and the hole mobility was shown.

[Example 4]
After mixing and dissolving 1 part by weight of polycarbonate resin [Polycarbonate Z Polyca (manufactured by Teijin Chemicals Ltd.)] and 100 parts by weight of tetrahydrofuran, this was coated on the organic semiconductor layer produced in Example 1 by spin coating, and 2 parts at 80 ° C. A protective layer was prepared by drying for 15 minutes at 140 ° C. for 15 minutes. However, the organic semiconductor layer prepared with the lower organic pigment dispersion did not dissolve. If a gate electrode is provided on the polycarbonate layer, this layer can also be used as an insulating layer.

[Comparative Example 1]
Instead of the organic pigment dispersion of Example 1, the coating liquid containing the polycarbonate of Example 4 was applied on the layer coated with the organic polymer semiconductor having the following structure. Since the organic polymer semiconductor is dissolved in tetrahydrofuran, the channel portion is dissolved and broken. Therefore, an insulating layer or protective layer could not be formed on such an organic semiconductor layer by a wet coating method using an organic solvent solution.

[Wherein q means a number of 1 to 10,000]
Further, in this comparative example, a q number having a molecular weight of about 100,000 was used.

  In addition, this invention is not limited to said each embodiment, A various change is possible. For example, a material that is easily dissolved in an organic solvent and that exhibits high mobility when crystallized can be dissolved in an organic solvent, applied, and crystallized on an insulating layer as in the past. In this case, there is an adverse effect that crystals are inevitably made non-uniform. Even in such a case, there is a method in which an organic solvent is selected, and a solid material that has already crystallized is dispersed in a poor solvent that is difficult to dissolve, and coating is performed. In this case, a grain boundary is formed between the crystals, but since there are not a few points where charges are transmitted between the crystals, there is no current at all due to a wide and wide break such as when crystallizing on the insulating layer. Is not difficult to pass, and the characteristics of each transistor element can be made uniform.

It is drawing which shows the structural example of an organic thin-film transistor. It is a graph which shows an example of the correlation with the gate voltage of an organic thin-film transistor, and source-drain current. It is a graph which shows the approximated curve of the correlation of the gate voltage of an organic thin-film transistor, and source-drain current. 6 is a graph showing a relationship between a gate voltage and a drain current of the thin film transistor manufactured in Example 1. FIG. 6 is a graph showing a relationship between a source-drain voltage and a drain current of the thin film transistor manufactured in Example 1. FIG. 6 is a graph showing a relationship between a gate voltage and a drain current of a thin film transistor manufactured in Example 2. FIG. 6 is a graph showing the relationship between the source-drain voltage and the drain current of the thin film transistor fabricated in Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic semiconductor layer 2 ... Substrate 3 ... Gate electrode 4 ... Source electrode 5 ... Drain electrode 6 ... Insulating layer

Claims (10)

An organic pigment dispersion used as a coating liquid when an organic semiconductor layer in an organic transistor is formed by a wet coating method,
An organic pigment dispersion comprising at least an organic solvent and an organic pigment dispersed in the organic solvent.   The organic pigment dispersion according to claim 1, wherein the organic pigment is an azo-based or phthalocyanine-based organic pigment. The organic pigment dispersion according to claim 2, wherein the azo organic pigment is an azo pigment represented by the following general formula (I).

[In the formula (I), X is a substituted or unsubstituted aromatic group which may have a hetero atom in the aromatic ring, and R ₁ and R ₂ are the same or different and each represents a hydrogen atom or a halogen atom. , An alkyl group, an alkoxy group, a cyano group, or an amino group. However, a plurality of R ₁ and R ₂ may be bonded to the same benzene ring. ]   The organic pigment dispersion according to claim 1, wherein the organic pigment is phthalocyanine. A method for forming an organic semiconductor layer in an organic transistor,
A method for forming an organic semiconductor layer, comprising wet-coating an organic pigment dispersion containing an organic solvent and an azo- or phthalocyanine-based organic pigment dispersed in the organic solvent on an underlayer.   The method for forming an organic semiconductor layer according to claim 5, wherein the wet coating is performed by a spin coating method.   6. The organic semiconductor layer according to claim 5, wherein the wet coating is performed by a droplet discharge method in which the organic pigment dispersion is discharged as fine droplets to form dots or layers on the base layer. Forming method. Forming an organic semiconductor layer by the method for forming an organic semiconductor layer according to any one of claims 5 to 7,
A step of forming an insulating layer or a protective layer by adhering a liquid obtained by dissolving or dispersing a resin in an organic solvent to the upper layer of the organic semiconductor layer;
A method for producing an organic transistor, comprising: An organic transistor comprising a layer containing a substance represented by the following general formula (I) as an electron transporting material.

[In the formula (I), X is a substituted or unsubstituted aromatic group which may have a hetero atom in the aromatic ring, and R ₁ and R ₂ are the same or different and each represents a hydrogen atom or a halogen atom. , An alkyl group, an alkoxy group, a cyano group, or an amino group. However, a plurality of R ₁ and R ₂ may be bonded to the same benzene ring. ]   10. The organic transistor according to claim 9, wherein in the general formula (I), X is a divalent aromatic group having electron withdrawing performance.

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