JP5913108B2 - Organic semiconductor material, field effect transistor, and method for manufacturing the same - Google Patents

Description

  The present invention relates to a field effect transistor including an organic thin film obtained by applying or printing an organic thin film semiconductor material and drying it, a method for manufacturing the same, and an organic semiconductor material used therefor. More specifically, the present invention relates to a field effect transistor obtained from a semiconductor material comprising an organic heterocyclic compound and a specific additive, and a method for producing the same.

  A field effect transistor generally has a structure in which a semiconductor material on a substrate is provided with a source electrode, a drain electrode, and a gate electrode and the like via these electrodes and an insulator layer. At present, inorganic semiconductor materials centering on silicon are used for field-effect transistors, and thin film transistors created on substrates such as glass using amorphous silicon are used for displays, etc. In addition to being used in integrated circuits as logic circuit elements, it is also widely used in switching elements and the like. Recently, active studies have been made on the use of an oxide semiconductor as a semiconductor material. However, when such an inorganic semiconductor material is used, it is necessary to process the field effect transistor at a high temperature or in a vacuum. As a substrate to be used, films and plastics with poor heat resistance cannot be used, and expensive capital investment and production require a lot of energy, which makes the cost very high and its application range is very Is limited to.

  On the other hand, field effect transistors using organic semiconductor materials that do not require high-temperature treatment when manufacturing the field effect transistors have been actively developed. If it can be applied to organic semiconductor materials, it becomes possible to manufacture field effect transistors by a low temperature process, and the range of usable substrate materials is expanded. As a result, it becomes possible to manufacture a field effect transistor that is more flexible, lightweight, and less likely to break. In the field effect transistor manufacturing process, a large-area field effect transistor can be manufactured at a low cost by applying a solution containing an organic semiconductor material or by a printing method such as inkjet.

  However, conventionally, many organic semiconductor materials used for semiconductor materials are hardly soluble in organic solvents, so that inexpensive methods such as coating and printing cannot be used, and relatively expensive vacuum deposition methods, etc. Therefore, it was necessary to form a thin film on a semiconductor substrate. Currently, devices that have a relatively high carrier mobility can be obtained by dissolving in an organic solvent, forming a film using a coating method, creating a field effect transistor, and moving using a coating or printing process. A field effect transistor using an organic semiconductor having a high degree of durability and excellent durability has not been put into practical use, and development for improving the suitability of each transistor has been actively conducted.

  In general, a semiconductor element using an inorganic material such as silicon is generally an oxidizing or reducing gas such as oxygen or hydrogen, or an oxidizing or reducing liquid in an organic semiconductor layer for the purpose of increasing or decreasing the carrier density in the film. It is necessary to induce a change in properties due to oxidation or reduction. This is because by adding a small amount of elements, atomic groups, molecules, and polymers to the semiconductor layer, the carrier density in the semiconductor layer increases or decreases, and the electrical conductivity and carrier polarity (p-type-n-type conversion), which are semiconductor characteristics, , Fermi level, etc., for example, by contacting gas such as oxygen and hydrogen, soaking in a solution containing acid or Lewis acid, halogen atoms such as iodine, or sodium, potassium, etc. A treatment method using an inorganic compound that electrochemically treats metal atoms and the like, and a method of treating in advance with an electron-accepting or electron-donating organic compound are known. These treatments are performed in processes other than the formation of the semiconductor layer before and after the production of the semiconductor layer, co-evaporated by a vacuum deposition method, mixed in the atmosphere at the time of semiconductor layer production, or ions are accelerated in vacuum. In general, a technique such as collision with a semiconductor layer is used.

  Patent Document 1 discloses a field effect transistor using an alkyl derivative of benzoseleno [3,2-b] [1] benzoselenophene and benzothieno [3,2-b] [1] benzothiophene.

  Patent Document 2 discloses a field effect transistor using a mixed liquid of an alkyl derivative of benzothieno [3,2-b] [1] benzothiophene and a polymer compound having a specific solubility parameter.

  Patent Document 3 discloses a field effect transistor using a material containing an alkyl derivative of benzothieno [3,2-b] [1] benzothiophene and a polymer material.

  Patent Document 4 discloses a technique for amplifying a current value by bringing iodine or a metal into contact with a pentacene thin film.

  Patent Document 5 discloses a technique for improving electrical conductivity by using a thin film obtained by applying and drying a solution obtained by mixing a polyacene compound and excess iodine or butyl lithium.

  Patent Document 6 discloses a technique for changing a threshold voltage by applying an electron-accepting or electron-donating compound in advance and then laminating a polymer semiconductor.

  Non-Patent Document 1 discloses a field effect transistor using an alkyl derivative of benzothieno [3,2-b] [1] benzothiophene.

  Non-Patent Document 2 discloses a field effect transistor prepared by a surface selective deposition method using an alkyl derivative of benzothieno [3,2-b] [1] benzothiophene.

International Publication No. 2008/047896 International Publication Pamphlet Japanese Patent Publication “JP 2009-267372 A” Japanese Patent Publication “JP 2009-283786 A” Japanese Patent Publication “JP-A-5-55568” Japanese Patent No. 4219807 Japanese Patent Publication “JP 2009-266865 A”

J. et al. Am. Chem. Soc. 2007, 129, 15732. Applied Physics Letters, 94, 93307 (2009).

  The present invention provides an excellent field effect transistor having not only improved semiconductor characteristics such as a reduction in threshold voltage while maintaining high carrier mobility, but also has printability capable of forming a highly uniform thin film with fewer steps. The purpose is to do.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have obtained an organic semiconductor material obtained by mixing a specific organic heterocyclic compound and an electron-accepting material having a specific substituent as a semiconductor material in an organic solvent. When the field effect transistor used is formed, not only can the semiconductor characteristics such as the reduction of the threshold voltage be improved while maintaining high carrier mobility, but also the printability capable of forming a highly uniform thin film with fewer steps. The present inventors have found that a practical field effect transistor can be provided, and have completed the present invention.

That is, the present invention
(1) An organic semiconductor material obtained by dissolving and / or dispersing a compound represented by the following formula (1) and an electron-accepting compound having a cyano group in at least one organic solvent

(In formula (1), R ₁ and R ₂ each independently represents an unsubstituted or halogeno-substituted C1-C36 aliphatic hydrocarbon group),
About.

  When a field effect transistor is formed using an organic semiconductor material in which a compound represented by the above formula (1) and an electron-accepting compound having a cyano group are dissolved and / or dispersed in at least one organic solvent. A practical field-effect transistor with excellent printability that can not only improve semiconductor characteristics such as threshold voltage reduction while maintaining high carrier mobility, but also can form highly uniform thin films with fewer steps. Can be provided.

AD is the schematic which shows an example of the structure of the field effect transistor of this invention.

  The present invention will be described in detail. The present invention relates to an organic semiconductor material in which a specific organic heterocyclic compound and an electron-accepting compound having a cyano group are dissolved and / or dispersed in at least one organic solvent, a field effect transistor using them, and a method for producing the same About.

First, the compound represented by the formula (1) will be described. In the above formula (1), R ₁ and R ₂ each independently represents an unsubstituted or halogeno-substituted C1-C36 aliphatic hydrocarbon group. The aliphatic hydrocarbon group is a saturated or unsaturated linear, branched or cyclic aliphatic hydrocarbon group, preferably a linear or branched aliphatic hydrocarbon group, more preferably a linear It is an aliphatic hydrocarbon group. Carbon number is C1-C36 normally, Preferably it is C2-C24, More preferably, it is C4-C20, More preferably, it is C6-C12.

Specific examples of the linear or branched saturated aliphatic hydrocarbon group include methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, n-pentyl, iso-pentyl, t- Pentyl, sec-pentyl, n-hexyl, iso-hexyl, n-heptyl, sec-heptyl, n-octyl, n-nonyl, sec-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl , n-eicosyl, docosyl, n-pentacosyl, n-octacosyl , 5- (n-pentyl) decyl, heneicosyl, tricosyl , tetracosyl, hexacosyl, heptacosyl, nonacosyl, n- triacontyl, de door Examples include rear contyle and hexatria contyle. Specific examples of the cyclic saturated aliphatic hydrocarbon group include cyclohexyl, cyclopentyl, adamantyl, norbornyl and the like. Vinyl Specific examples of the linear or branched unsaturated aliphatic hydrocarbon group, A Lil, Eikosajieniru, 11,14 Eikosajieniru, geranyl (trans-3,7-dimethyl-2,6-octadiene-1-yl ), Farnesyl (trans, trans-3,7,11-trimethyl-2,6,10-dodecatrien-1-yl), 4-pentenyl, 1-propynyl, 1-hexynyl, 1-octynyl, 1-decynyl, Examples include 1-undecynyl, 1-dodecynyl, 1-tetradecynyl, 1-hexadecynyl, 1-nonadecynyl and the like.

  Of the linear, branched, and cyclic aliphatic hydrocarbon groups, a linear or branched aliphatic hydrocarbon group is preferable, and a linear aliphatic hydrocarbon group is particularly preferable.

  The saturated or unsaturated aliphatic hydrocarbon group includes a saturated alkyl group, an alkenyl group containing a carbon-carbon double bond, and an alkynyl group containing a carbon-carbon triple bond, and more preferably an alkyl group or an alkynyl group. And more preferably an alkyl group. The aliphatic hydrocarbon residue is a combination of these saturated or unsaturated aliphatic hydrocarbon groups, that is, a carbon-carbon double bond or a carbon-carbon triple bond at a site in the aliphatic hydrocarbon group. All cases are included at the same time.

The halogeno-substituted aliphatic hydrocarbon group means a group in which any kind of halogen atom is substituted at any position on the above-mentioned aliphatic hydrocarbon group. As a halogen atom, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are mentioned, Preferably a fluorine atom, a chlorine atom, a bromine atom, More preferably, a fluorine atom and a bromine atom are mentioned. Specific examples of the halogeno-substituted aliphatic hydrocarbon group include chloromethyl, bromomethyl, trifluoromethyl, pentafluoroethyl, n-perfluoropropyl, n-perfluorobutyl, n-perfluoropentyl, n-perfluorooctyl, and n-perfluorodecyl. , n-(dodecafluoro) -6-iodo-hexyl, 2,2,3,3,3-pentafluoro-propyl, 2,2,3,3-tetrafluoro-flop propyl, and the like.

  The compound represented by the above formula (1) can be synthesized by a known method described in Patent Document 1 and Non-Patent Document 1, for example.

Method for purifying the compound represented by the above formula (1) is not particularly limited, recrystallization, column click chromatography, and can be a known method is employed such as vacuum sublimation purification. Moreover, you may use combining these methods as needed.

  Table 1 below shows specific examples of the compound represented by the above formula (1).

  The electron-accepting compound having a cyano group is an additive for doping an organic semiconductor material, and is not particularly limited, but includes tetracyanoquinodimethane (hereinafter abbreviated as TCNQ) or a derivative thereof, specifically, TCNQ, 2,3,5,6-tetrafluorotetracyano-1,4-benzoquinodimethane (hereinafter abbreviated as F4-TCNQ), trifluoromethyltetracyanoquinodimethane (CF3TCNQ), 2,5-difluorotetracyanoquino Dimethane (F2TCNQ), fluorotetracyanoquinodimethane (FTCNQ), tetracyanoethylene (TCNE), 11,11,12,12-tetracyanonaphth-2,6-quinodimethane (TNAP), and Japanese Patent Publication “ Quinodimethanes having a cyano group described in JP-A-2008-530773 Used to apply. Of these, TCNQ or F4-TCNQ is particularly preferable.

  The organic semiconductor material of the present invention is formed by dissolving or dispersing at least a compound represented by the formula (1) and an electron-accepting compound having a cyano group in an organic solvent, and represented by the formula (1). Even if each of the compound and the electron-accepting compound having a cyano group is contained, one or both of the compound represented by the formula (1) and the electron-accepting compound having a cyano group are mixed. May be used. In the organic semiconductor material containing the compound represented by the formula (1) and the electron-accepting compound having a cyano group, the content of the electron-accepting compound having a cyano group with respect to the compound represented by the formula (1) Is usually in the range of 0.1 to 40% by mass, preferably 0.1 to 20% by mass, and more preferably 0.1 to 10% by mass. If the content exceeds 40% by mass, the characteristic value decreases due to an increase in OFF current. When TCNQ or F4-TCNQ is used, the content is particularly preferably 10% by mass or less.

  As long as the effects of the present invention are not impaired, the organic semiconductor material of the present invention is mixed with other organic semiconductor materials and various additives as necessary in order to improve the characteristics of the field effect transistor and to impart other characteristics. You may do it. Examples of these additives include viscosity modifiers, surface tension modifiers, leveling agents, penetrants, rheology modifiers, alignment agents, and dispersants.

  The content rate of these additives is 0-30 mass% with respect to the total amount of the organic-semiconductor material of this invention, 0-20 mass% is preferable and 0-10 mass% is more preferable.

  The organic semiconductor material of the present invention is obtained by dissolving or dispersing the compound represented by the formula (1) and the electron-accepting compound in a solvent to improve the adaptability of the organic semiconductor material for coating and printing processes. The solvent that can be used is not particularly limited as long as the compound can form a film on the substrate. However, an organic solvent is preferable, and a single organic solvent or a mixture of a plurality of organic solvents can be used. Specifically, halogeno hydrocarbon solvents such as chloroform, methylene chloride and dichloroethane; alcohol solvents such as methanol, ethanol, isopropyl alcohol and butanol; fluorinated alcohol solvents such as octafluoropentanol and pentafluoropropanol; ethyl acetate , Ester solvents such as butyl acetate, ethyl benzoate and diethyl carbonate; aromatics such as toluene, xylene, benzene, chlorobenzene, mesitylene, ethylbenzene, diethylbenzene, triethylbenzene, dichlorobenzene, chloronaphthalene, tetrahydronaphthalene, decalin, cyclohexylbenzene Hydrocarbon solvents; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone; dimethylforma Amide solvents such as dimethylacetamide and N-methylpyrrolidone; Ether solvents such as tetrahydrofuran and diisobutyl ether; Hydrocarbon solvents such as hexane, cyclohexane, octane, decane and tetralin; Acetonitrile, propiononitrile, butyronitrile, benzo Nitrile solvents such as nitrile can be used, and these can be used alone or in combination. The concentration of the compound represented by formula (1) and the electron-accepting compound varies depending on the type of solvent and the film thickness of the semiconductor layer to be produced, but is 0.001 to 50 mass in total with respect to the solvent in the mixed solution. %, Preferably 0.01 to 20% by mass. Further, the semiconductor material of the present invention may be dissolved or dispersed in the above organic solvent, but it is preferable that the semiconductor material is dissolved as a uniform solution in order to form a more uniform thin film.

A field effect transistor (hereinafter sometimes abbreviated as FET) of the present invention has two electrodes, a source electrode and a drain electrode, in contact with a semiconductor layer, and a current flowing between the two electrodes is gated. It is controlled by a voltage applied to another electrode called a gate electrode through an insulator layer. Field effect transistor includes the organic thin film.

  FIG. 1 shows some embodiments of the field effect transistor of the present invention, and the arrangement of each layer and electrode can be appropriately selected depending on the use of the element. In FIG. 1, the same numbers are assigned to the same names.

  Next, although each component of the field effect transistor of the present invention shown in FIG. 1 will be described, the present invention is not limited to this.

  The substrate 1 needs to be able to hold each layer formed thereon without peeling off. For example, insulating material such as resin plate, resin film, paper, glass, quartz, ceramic, etc .; formed by coating an insulating layer on a conductive substrate such as metal or alloy; and various combinations of resin and inorganic material Materials can be used. Among them, the resin film generally used includes, for example, polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyamide, polyimide, polycarbonate, cellulose triacetate, polyetherimide and the like. When a resin film or paper is used, flexibility can be given to the semiconductor element, and the semiconductor element can be flexible and lightweight, thereby improving practicality. The thickness of the substrate is usually 1 μm to 10 mm, preferably 5 μm to 3 mm.

A conductive material is used for the source electrode 2, the drain electrode 3, and the gate electrode 6. For example, platinum, gold, silver, aluminum, chromium, tungsten, tantalum, nickel, cobalt, copper, iron, lead, tin, titanium, indium, palladium, molybdenum, magnesium, calcium, barium, lithium, potassium, sodium, etc. And alloys containing them; conductive oxides such as InO ₂ , ZnO ₂ , SnO ₂ , ITO; conductive polymers such as polyaniline, polypyrrole, polythiophene (such as PEDOT / PSS), polyacetylene, polyparaphenylene vinylene, and polydiacetylene Compounds: Organic charge transfer complexes such as BED-TTF; semiconductors such as silicon, germanium, and gallium arsenide; carbon materials such as carbon black, fullerene, carbon nanotubes, and graphite can be used. Conductive polymer compounds and semiconductors may be doped. Examples of the dopant include acids such as hydrochloric acid, sulfuric acid and sulfonic acid; Lewis acids such as PF ₅ , AsF ₅ and FeCl ₃ ; iodine and the like A halogen atom, a metal atom such as lithium, sodium, potassium, or the like is used. In order to reduce the contact resistance of the electrode, a method of doping with molybdenum oxide or a metal may be treated with thiol or the like. In addition, a conductive composite material in which metal particles such as carbon black, gold, platinum, silver, and copper are dispersed in the above material is also used. A wiring is connected to each electrode 2, 3, 6, and the wiring is also made of substantially the same material as the electrode. Although the film thickness of the source electrode 2, the drain electrode 3, and the gate electrode 6 changes with materials, it is 0.1nm-100micrometer normally, Preferably it is 0.5nm-10micrometer, More preferably, it is 1nm-5micrometer.

The gate insulator layer 5 is an insulating material such as polyparaxylylene, polyacrylate, polymethyl methacrylate, polystyrene, polyvinylphenol, polyamide, polyimide, polycarbonate, polyester, polyvinyl alcohol, polyvinyl acetate, polyurethane, Polymers such as polysulfone, epoxy resin, phenol resin, and copolymers thereof; oxides such as silicon dioxide, aluminum oxide, titanium oxide, and tantalum oxide; ferroelectric oxides such as SrTiO ₃ and BaTiO ₃ ; silicon nitride And nitrides such as aluminum nitride; sulfides; dielectrics such as fluorides; or polymers in which particles of these dielectrics are dispersed. The film thickness of the gate insulator layer 5 varies depending on the material, but is usually 0.1 nm to 100 μm, preferably 0.5 nm to 50 μm, more preferably 5 nm to 10 μm.

  The organic semiconductor material contained in the semiconductor layer 4 is composed of at least the above-described formula (1) and an electron-accepting compound having a cyano group, and several kinds of each of these derivatives may be mixed and used. On the other hand, it is necessary to contain 50% by mass or more, preferably 80% by mass or more, more preferably 95% by mass or more. At this time, in order to improve the characteristics of the field effect transistor and to provide other characteristics, other organic semiconductor materials and various additives may be mixed as necessary. The semiconductor layer 4 may be composed of a plurality of layers. The thickness of the semiconductor layer 4 is preferably as thin as possible without losing necessary functions. In a field effect transistor, if the film thickness exceeds a predetermined value, the characteristics of the semiconductor element do not depend on the film thickness, but as the film thickness increases, the leakage current often increases. On the other hand, if it is too thin, it becomes impossible to form a channel for electric charge (channel), and therefore an appropriate film thickness is necessary. The film thickness of the semiconductor layer for exhibiting a function that requires a semiconductor is usually 0.1 nm to 10 μm, preferably 0.5 nm to 5 μm, more preferably 1 nm to 3 μm.

  Although it does not specifically limit as a material of the protective layer 7, For example, the film | membrane which consists of various resins, such as acrylic resins, such as an epoxy resin and a polymethylmethacrylate, a polyurethane, a polyimide, polyvinyl alcohol, a fluororesin, polyolefin, silicon oxide, aluminum oxide A film made of a dielectric such as an inorganic oxide film or a nitride film, such as silicon nitride, is preferably used, and a resin (polymer) having a low oxygen permeability and a low water absorption is particularly preferable. A protective material developed for organic EL displays can also be used. Although the film thickness of a protective layer can employ | adopt arbitrary film thickness according to the objective, it is 100 nm-1 mm normally. Forming the protective layer has the advantage of stabilizing the electrical characteristics, such as reducing the influence of outside air such as humidity and increasing the ON / OFF ratio of the device.

  The field effect transistor of the present invention is a substrate surface cleaning treatment, such as acid treatment with hydrochloric acid, sulfuric acid, acetic acid, etc., alkali treatment with sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, etc., ozone treatment, fluorination treatment, oxygen Excellent print suitability by performing plasma processing such as argon and argon, Langmuir / Blodgett film forming process, other insulator and semiconductor thin film forming process, mechanical process, corona discharge and other electrical processes However, other layers may be provided between the above layers or on the outer surface of the semiconductor element as necessary. In addition, by performing surface treatment in advance on a substrate or an insulator layer on which a semiconductor layer is laminated, control of molecular orientation and crystallinity of the interface portion between the substrate, electrode, etc. and a semiconductor layer to be subsequently formed, an electrode By improving the properties such as carrier mobility by reducing trap sites on the interface and insulator layer, and adjusting the hydrophilic / hydrophobic balance of the substrate surface, It is possible to further improve the uniformity of the device by improving the paintability to the substrate. Examples of such a substrate treatment include a silane coupling treatment with phenylethyltrichlorosilane and the like, a thiol treatment, a rubbing treatment using fibers, and the like.

  As a method for providing each layer in the present invention, for example, a vacuum deposition method, a sputtering method, a coating method, a printing method, a sol-gel method and the like can be used as appropriate. preferable.

  Next, the manufacturing method of the field effect transistor of this invention is demonstrated below based on the example of an aspect of FIG.

(Substrate and substrate processing)
The field effect transistor of the present invention is produced by providing necessary electrodes and various layers on the substrate 1 (see FIG. 1). It is also possible to perform the above-described surface treatment on this substrate. The thickness of the substrate 1 is preferably as thin as possible without interfering with necessary functions. Although it varies depending on the material, it is usually 1 μm to 10 mm, preferably 5 μm to 3 mm.

(Formation of source electrode and drain electrode)
A source electrode 2 and a drain electrode 3 are formed on the substrate 1 using the above electrode material or the like. The material of the source electrode 2 and the drain electrode 3 may be the same or different. Examples of the method for forming the electrode include a vacuum deposition method, a sputtering method, a coating method, a thermal transfer method, a printing method, and a sol-gel method. It is preferable to perform patterning as necessary so as to obtain a desired shape during or after film formation. Various methods can be used as the patterning method, and examples thereof include a photolithography method in which patterning and etching of a photoresist are combined. Further, it is possible to perform patterning using a printing method such as ink jet printing, screen printing, offset printing, letterpress printing or the like, a soft lithography method such as a micro contact printing method, or a method combining a plurality of these methods. Although the film thickness of the source electrode 2 and the drain electrode 3 changes with materials, it is 0.1 nm-100 micrometers normally, Preferably it is 0.5 nm-10 micrometers, More preferably, it is 1 nm-5 micrometers. The film thickness of the source electrode 2 and the drain electrode 3 may be the same or different.

(Formation of semiconductor layer)
The semiconductor layer is an organic thin film formed by a coating printing process using the organic semiconductor material described above. In other words, an organic thin film can be referred to as an organic semiconductor thin film. The coating printing process, the organic semiconductor material having a Solvent soluble, dissolved or dispersed in advance an organic solvent electron-accepting compound having the compound and a cyano group represented by the formula (1) of example the present invention, obtained A method for manufacturing a semiconductor layer, in which a semiconductor layer having excellent semiconductor characteristics can be easily formed by applying or printing a solution of an organic semiconductor material and drying the solution. The manufacturing method by coating or printing, that is, the coating printing process is industrially advantageous because a large area field effect transistor can be manufactured at a low cost without the need for making the environment during device manufacturing vacuum or high temperature. Among the methods for manufacturing a semiconductor layer, it is particularly preferable.

  Specifically, the organic semiconductor material of the present invention is prepared by dissolving or dispersing a compound represented by the above formula (1) and an electron-accepting compound having a cyano group in a solvent. The compound represented by the formula (1) and the electron-accepting compound having a cyano group may be dissolved or dispersed at the same time, or may be prepared by individually dissolving or dispersing in a solvent and then mixing. The concentration of the compound represented by the formula (1) and the electron-accepting compound having a cyano group in the organic semiconductor material of the present invention (when these compounds are used in plural types, the total concentration of the plural types of compounds) is Although it varies depending on the type of solvent and the film thickness of the semiconductor layer to be produced, it is usually 0.001 to 50% by mass and preferably 0.01 to 20% by mass with respect to the total amount of the solution. In order to improve the film formability of the semiconductor layer, the field effect transistor characteristics, and other characteristics, additives and other types of semiconductor materials can be mixed.

  In order to prepare the organic semiconductor material, it is necessary to dissolve or disperse the compound represented by the above formula (1) and the electron-accepting compound having a cyano group in a solvent. Good. Further, the obtained organic semiconductor material may be filtered using a filter to remove impurities and the like. When this is coated on a substrate, the film-forming property of the semiconductor layer is improved and can be suitably used.

  The organic semiconductor material prepared as described above is applied to the substrate (exposed portions of the source electrode and the drain electrode). Coating methods such as casting, spin coating, dip coating, blade coating, wire bar coating, spray coating, etc .; inkjet printing, screen printing, offset printing, letterpress printing, gravure printing, etc .; microcontact printing method A soft lithography method such as the above, and a method combining a plurality of these methods can be employed. In addition, as a method similar to the coating method, the Langmuir-Blodgett method, in which a monomolecular film of a semiconductor layer produced by dropping the above organic semiconductor material onto the water surface is transferred to a substrate and laminated, a material in a liquid crystal or melt state It is also possible to adopt a method of sandwiching between two substrates and introducing them between the substrates by capillary action. The thickness of the semiconductor layer manufactured by these methods is preferably thin as long as the function is not impaired. As the film thickness increases, the leakage current may increase. The film thickness of the semiconductor layer is the same as that of the semiconductor layer 4 described above.

  The semiconductor layer thus manufactured can improve semiconductor characteristics by post-processing. For example, by heat-treating the substrate after forming the semiconductor layer, the distortion in the film generated during film formation is alleviated, and the alignment and orientation in the film can be controlled, so that the semiconductor characteristics can be improved and stabilized. And pinholes can be reduced. The heat treatment may be performed at any stage as long as the semiconductor layer is formed. The temperature of the heat treatment is not particularly limited, but is usually room temperature to 150 ° C, preferably 40 to 120 ° C, more preferably 45 to 100 ° C. The heat treatment time is not particularly limited, but is usually 1 second to 24 hours, preferably 1 minute to 1 hour. The atmosphere during the heat treatment may be in the air, but may be an inert atmosphere such as nitrogen or argon.

(Formation of gate insulator layer)
A gate insulator layer 5 is formed on the semiconductor layer 4 using the above insulator material or the like (see FIG. 1). Examples of the method for forming the gate insulator layer 5 include spin coating, spray coating, dip coating, casting, bar coating, blade coating, and the like; screen printing, offset printing, inkjet printing, and the like; vacuum deposition, molecular Examples thereof include a line epitaxial growth method, an ion cluster beam method, an ion plating method, a sputtering method, an atmospheric pressure plasma method, a dry process method such as a CVD method, and the like. Further, a method of forming an oxide film on the metal surface such as a sol-gel method or anodized on aluminum can also be used.

The film thickness of the gate insulator layer 5 is preferably as thin as possible without impairing its function, and is usually 0.1 nm to 100 μm, preferably 0.5 nm to 50 μm, more preferably 5 nm to 10 μm.
(Formation of gate electrode)
The gate electrode 6 can be formed by the same method as the method for forming the source electrode 2 and the drain electrode 3. The film thickness varies depending on the material, but is usually 1 nm to 100 μm, preferably 0.5 nm to 10 μm, and more preferably 1 nm to 5 μm.

(Protective layer)
When the protective layer 7 is formed using the protective layer material, there is an advantage that the influence of outside air can be minimized and the electric characteristics of the field effect transistor can be stabilized (see FIG. 1). Although the film thickness of the protective layer 7 can employ | adopt arbitrary film thickness according to the objective, it is 100 nm-1 mm normally. Various methods can be employed to form the protective layer. When the protective layer is made of a resin, for example, a method of drying a resin-containing solution after application to form a resin film, or applying or depositing a resin monomer The method of superposing | polymerizing after performing etc. is mentioned, You may perform a crosslinking process after film-forming. When the protective layer is made of an inorganic material, for example, a forming method in a vacuum process such as a sputtering method or a vapor deposition method or a forming method in a coating printing process such as a sol-gel method can be used. In the field effect transistor of the present invention, a protective layer can be provided between the layers as needed in addition to the surface of the semiconductor layer. The installed protective layer may help to stabilize the electrical characteristics of the field effect transistor.

  In general, the operating characteristics of a field effect transistor are determined by carrier mobility of a semiconductor layer, conductivity, capacitance of an insulating layer, element configuration (distance and width between source and drain electrodes, film thickness of the insulating layer, and the like). The organic material used for the semiconductor layer of the field effect transistor requires high carrier mobility, but the compound represented by the above formula (1) of the present invention that can be manufactured at low cost is high in carrier mobility as an organic semiconductor material. Express degree. The field effect transistor of the present invention can be manufactured by a relatively low temperature process, and a flexible material such as a plastic plate or a plastic film that cannot be used under high temperature conditions can be used as the substrate. As a result, it is possible to manufacture a light, flexible, and hard-to-break element, and it can be used as a switching element for an active matrix of a display. Examples of the display include a liquid crystal display, a polymer dispersion type liquid crystal display, an electrophoretic display, an EL display, an electrochromic display, a particle rotation type display, and the like. Furthermore, since the field effect transistor of the present invention has good film formability, it can be manufactured by a coating printing process such as coating, and the field effect for a large area display application at a very low cost compared to a conventional vacuum deposition process. It can also be applied to the manufacture of transistors.

  The field effect transistor of the present invention can be used as a digital element or an analog element such as a memory circuit element, a signal driver circuit element, and a signal processing circuit element, and an IC card or an IC tag can be manufactured by combining these elements. Furthermore, since the field effect transistor of the present invention can change its characteristics by an external stimulus such as a chemical substance, it can be expected to be used as an FET sensor.

The present invention includes the following forms (2) to (7).
(2) The organic semiconductor material according to (1), wherein R ₁ and R ₂ in formula (1) are each independently a C12 or lower linear aliphatic hydrocarbon group,
(3) The organic semiconductor material according to (1) or (2), wherein the electron-accepting compound having a cyano group is tetracyanoquinodimethane or a derivative thereof,
(4) The organic semiconductor material according to any one of (1) to (3), wherein the content of the electron-accepting compound having a cyano group with respect to the compound represented by the formula (1) is 10% by mass or less,
(5) A field effect transistor comprising an organic thin film obtained from the organic semiconductor material according to any one of (1) to (4),
(6) A method for producing a field effect transistor, in which an organic thin film is formed by applying or printing the organic semiconductor material according to any one of (1) to (4) and drying,
(7) A method of manufacturing a field effect transistor comprising a gate electrode, a gate insulator layer, a semiconductor layer, a source electrode, and a drain electrode, wherein (1 ) To (4) A method for producing a field effect transistor, wherein an organic thin film is formed by coating or printing the organic semiconductor material according to any one of (4) and drying the material.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these. In the examples, unless otherwise specified, parts represent parts by mass, and% represents mass%. Note that everything from the preparation of semiconductor materials to the evaluation of semiconductor characteristics was performed in the air.

(Preparation of stock solution)
The compound (11) described in Table 1 was dissolved in chloroform so as to be 2% to prepare a stock solution of the compound (11). On the other hand, TCNQ (manufactured by Tokyo Chemical Industry Co., Ltd.) and F4-TCNQ (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in acetonitrile so as to be 0.2%, respectively, thereby preparing TCNQ and F4-TCNQ stock solutions.

[Example 1]
(Preparation of semiconductor materials)
100 parts of the stock solution of compound (11), 20 parts of TCNQ stock solution, and 80 parts of chloroform were mixed, respectively, and chloroform-acetonitrile (9: 1) containing 1% of compound (11) and 0.02% of TCNQ A mixed solution 1 of organic semiconductor materials was prepared.

(Creation of transistor elements)
A mixed solution 1 containing the compound (11) and TCNQ prepared in advance on a 300 nm UV-ozone-treated n-doped silicon wafer with a SiO ₂ thermal oxide film was applied by spin coating, and then the substrate was placed on a hot plate at 80 After heating at 0 ° C. for 10 minutes, the organic thin film was formed by drying at 120 ° C. for 1 minute. Gold was deposited on the organic thin film as a source electrode and a drain electrode (channel length 50 μm, channel width 2 mm) by a vacuum deposition method using a metal mask, and a bottom gate-top contact element was produced.

(Characteristic evaluation)
Using the semiconductor parameters (Agilent 4155C) for the obtained organic field effect transistor, the four semiconductor characteristics on one substrate were changed under the condition that the drain voltage was changed to −60V and the gate voltage Vg was changed from +20 to −80V. evaluated. As a result, the average value of the mobility of the four electrodes on the calculated standard deviation is an index showing the variation of 0.31 cm ² / Vs, the substrate was 0.02 cm ² / Vs. The threshold voltage is -29 V on average and 1.3 V on standard deviation, the ON current is 2.3 × 10 ⁻⁴ A, the standard deviation is 2.6 × 10 ⁻⁵ A, high semiconductor characteristics and uniformity within the substrate. showed that. The OFF current was on the order of 10 ⁻¹¹ A, and no increase in OFF current was observed when an electron accepting material was added. Further, even when exposed to the atmosphere for 1 week, the mobility was 0.32 cm ² / Vs, the threshold voltage was −31 V, the ON current was 2.2 × 10 ⁻⁴ A, and excellent semiconductor characteristics were maintained.

[Example 2]
(Preparation of semiconductor materials)
100 parts of the stock solution of compound (11), 10 parts of the stock solution of TCNQ, 80 parts of chloroform and 10 parts of acetonitrile were mixed, respectively, and chloroform-acetonitrile (1% of compound (11) and 0.01% of TCNQ ( 9: 1) mixed solution 2 of organic semiconductor materials was prepared.

(Creation of transistor elements)
A bottom gate-top contact element was fabricated in the same manner as in Example 1 except that the semiconductor material was changed from the mixed solution 1 to the mixed solution 2.

(Characteristic evaluation)
The semiconductor characteristics were evaluated under the same conditions as in Example 1. Mean value of the mobility of the four electrodes is the standard deviation is an index showing 0.58cm ² / Vs, the variation in the substrate was 0.038 cm ² / Vs. The threshold voltage is the average -26V, the standard deviation 0.9V, ON current is 4.5 × ^{10 -4} A, standard deviation 3.7 × ^{10 -6} A, high semiconductor characteristics and in the substrate It showed uniformity. Further, the OFF current was on the order of 10 ⁻¹¹ A, and the OFF current did not increase even when the electron accepting material was added. Further, even when exposed to the atmosphere for 1 week, the mobility was 0.59 cm ² / Vs, the threshold voltage was −30 V, the ON current was 4.1 × 10 ⁻⁴ A, and excellent semiconductor characteristics were maintained.

Example 3
(Preparation of semiconductor materials)
100 parts of a stock solution of compound (11), 20 parts of a stock solution of F4-TCNQ, and 80 parts of chloroform were mixed, respectively, and chloroform-acetonitrile (1% of compound (11) and 0.02% of F4-TCNQ ( 9: 1) mixed solution 3 of organic semiconductor materials was prepared.

(Creation of transistor elements)
A bottom gate-top contact element was fabricated in the same manner as in Example 1 except that the semiconductor material was changed from the mixed solution 1 to the mixed solution 3.

(Characteristic evaluation)
The semiconductor characteristics were evaluated under the same conditions as in Example 1. The average value of the mobility of the four electrodes was 0.42 cm ² / Vs, and the standard deviation as an index indicating the variation in the substrate was 0.007 cm ² / Vs. The threshold voltage is the average -20 V, the standard deviation 0.3V, ON current is 4.0 × ^{10 -4} A, standard deviation 9.1 × ^{10 -6} A, high semiconductor characteristics and in the substrate It showed uniformity. Further, the OFF current was on the order of 10 ⁻¹¹ A, and the OFF current did not increase even when the electron accepting material was added. Furthermore, even when exposed to the atmosphere for 1 week, the mobility was 0.42 cm ² / Vs, the threshold voltage was −20 V, the ON current was 3.9 × 10 ⁻⁴ A, and excellent semiconductor characteristics were maintained.

[Comparative Example 1]
(Preparation of semiconductor materials)
100 parts of the stock solution of the compound (11), 80 parts of chloroform, and 20 parts of acetonitrile were mixed, and the compound (11) containing no electron accepting compound was mixed with 1% chloroform-acetonitrile (9: 1). A mixed solution 4 of organic semiconductor materials was prepared.

(Creation of transistor elements)
A bottom gate-top contact element was fabricated in the same manner as in Example 1 except that the semiconductor material was changed from the mixed solution 1 to the mixed solution 4.

(Characteristic evaluation)
The semiconductor characteristics were evaluated under the same conditions as in Example 1. The average mobility of the four electrodes was 0.22 cm ² / Vs, and the standard deviation, which is an index indicating variation within the substrate, was 0.062 cm ² / Vs. The threshold voltage is the average -44V, the standard deviation 1.5V, the ON current is 8.3 × ^{10 -5} A, the standard deviation 2.9 × ^{10 -5} A, the mobility and ON current practice Compared with Examples 1 and 2, the threshold voltage was higher. Further, it was shown that the standard deviation indicating the variation of each characteristic was larger than that of the example.

  From the above evaluation results of semiconductor characteristics, it was found that the field effect transistor made of the organic semiconductor material of the present invention operates stably in the atmosphere and has high semiconductor characteristics and durability. Further, it was found that not only the semiconductor characteristics of mobility, threshold voltage, and ON current can be improved, but also the in-plane uniformity can be improved as compared with the comparative example not including the electron accepting material. Furthermore, when the semiconductor layer is manufactured, not only does it need to use a vacuum deposition method that requires special equipment, but also the purpose is to perform complicated operations such as patterning in substrate surface treatment and functions such as trap reduction. It was confirmed that a semiconductor layer can be easily and inexpensively produced by a coating method or the like without requiring a layer forming step, and the semiconductor characteristics can be improved. Therefore, it can be said that the field effect transistor using the organic semiconductor material of the present invention is extremely useful having excellent transistor performance.

1 substrate 2 source electrode 3 drain electrode 4 semiconductor layer 5 gate insulator layer 6 gate electrode 7 protective layer

Claims (6)

A compound represented by the following formula (1) and an electron-accepting compound having 1 to 10% by mass of a cyano group with respect to the compound represented by the following formula (1) are dissolved in at least one organic solvent and An organic semiconductor material obtained by dispersing an organic semiconductor material , wherein the electron-accepting compound having a cyano group is tetracyanoquinodimethane or a derivative thereof .

(In formula (1), R ₁ and R ₂ each independently represents an unsubstituted or halogeno-substituted C1-C36 aliphatic hydrocarbon group) The organic semiconductor material according to claim 1, wherein R ₁ and R ₂ in formula (1) are each independently a C12 or lower linear aliphatic hydrocarbon group. The organic semiconductor material according to claim 1 or 2 , wherein the content of the electron-accepting compound having a cyano group with respect to the compound represented by the formula (1) is 1 to 2% by mass. Field effect transistor comprising the organic thin film obtained from an organic semiconductor material according to any one of claims 1 to 3. The manufacturing method of the field effect transistor which forms an organic thin film by apply | coating or printing the organic-semiconductor material as described in any one of Claims 1 thru | or 3 , and drying. A gate electrode, a gate insulator layer, a semiconductor layer, a method of manufacturing a field effect transistor having a source electrode and a drain electrode, claims 1 to 3 between the source electrode and the drain electrode on the substrate or the gate insulator layer A method for producing a field effect transistor, wherein an organic thin film is formed by applying or printing the organic semiconductor material according to any one of the above and drying it.

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