JP5125110B2 - Field effect transistor - Google Patents

Description

    The present invention relates to a field effect transistor in which an electrode and a semiconductor layer are formed of a polymer composite having a carbon nanotube and a conjugated polymer.

  Field-effect transistors (hereinafter referred to as FET elements) that are currently used industrially use inorganic semiconductors such as silicon and germanium, and manufacturing costs such as photolithography and vacuum deposition for forming circuit patterns. This process was necessary in many stages. In the semiconductor industry that has adopted such a manufacturing method, there is an increasing demand for a reduction in manufacturing cost and an increase in area of a display device. However, it is difficult to reduce the cost and increase the area of the inorganic semiconductor due to restrictions on the manufacturing apparatus.

  For this reason, an FET element using an organic material having excellent moldability has been proposed. For example, a method using a polythiophene polymer semiconductor as a semiconductor material is known. (See Patent Document 1). Since this organic material can be dissolved in a solvent and used, for example, an ink jet technique, a screen printing technique, a cast coating technique, or a spin coat coating technique, a film can be formed without using a conventional vacuum deposition method.

  Studies on FET elements using organic materials have so far been mainly related to semiconductor materials, and many have been combined with metal electrodes. However, recently, an electrode using an organic material, for example, a polythiophene-based conductive polymer has been shown, and it is known that the threshold voltage when driving an FET can be reduced (see Patent Documents 2 and 3). .

  On the other hand, since carbon nanotubes (hereinafter referred to as CNT) are in the form of aggregates, only a non-uniform and low-conductivity film can be obtained unless the CNTs are uniformly dispersed. Therefore, as a method for deaggregating and uniformly dispersing CNTs, a method of ultrasonically irradiating bundled CNTs in a solution of a conjugated polymer is known, and it has been shown that a semiconductor film having a low sheet resistance can be obtained. (See Patent Document 4).

  Furthermore, it is known that CNTs uniformly dispersed by ultrasonic irradiation are dispersed in a small amount in a conjugated polymer, and the obtained polymer composite is used as a semiconductor layer of a field effect transistor to obtain good transistor characteristics. (See Patent Document 5).

Also known is a method of patterning a CNT film by applying a photosensitive material composed of a photosensitive component such as a resist and CNTs (see Patent Document 6). Although the CNT film formed of the material shows conductivity, the conductivity of CNT cannot be sufficiently exhibited because the resin serving as a binder is an insulator.
JP 2004-83650 A (paragraphs 40 to 42) JP 2006-49577 A (Example 1) Japanese Patent Laying-Open No. 2005-251809 (Example 1) JP 2004-2156 A (Claim 1, Example 1) JP 2004-266272 A (Claims 2, 6, and 7) JP 2006-69848 A (Claims 1 to 7)

This will electrode material of the FET devices using organic materials that have been proposed is susceptible to coating formation, Tei order using a conductive material obtained by mixing an acid to conjugated polymer, the unevenness of the electrode surface There are problems that the film thickness is large and it is difficult to control the film thickness, and that after the element is formed, the acid diffuses into the organic semiconductor layer and the FET characteristics tend to change. An object of the present invention is to provide an FET element in which an electrode is formed of an organic material that can be formed by coating, has small irregularities on the electrode surface, and does not contain an acid component.

  It is another object of the present invention to provide an FET element in which electrodes can be easily patterned and the FET characteristics are not impaired.

In order to achieve the above object, the present invention comprises the following constitution.
(1) the source electrode and / or drain electrode have a conjugated polymer and carbon nanotubes are formed by polymers composites containing no acid, 0.01 to 3 weight carbon nanotubes in the conjugated polymer A field effect transistor in which a semiconductor layer is formed of a polymer composite containing 1%.
(2) The field effect transistor according to (1), wherein the polymer composite used for the source electrode and / or the drain electrode has 10% by weight or more and 10,000% by weight or less of carbon nanotubes with respect to the conjugated polymer.

  According to the present invention, it is possible to reduce the cost by coating formation, and it is possible to obtain an electrode that does not contain an acid component, is highly conductive, has good film uniformity, and has a smooth film surface. Furthermore, since the polymer composite for electrode formation has a conjugated polymer having photocrosslinkable side chains, electrode patterns such as a source electrode and a drain electrode can be formed by a simple photolithography method. it can.

  The FET element of the present invention is a polymer in which the source electrode and / or the drain electrode are formed of a polymer composite having a conjugated polymer and CNT, and 0.01 to 3 wt% of CNT in the conjugated polymer. A semiconductor layer is formed of a composite.

  The polymer composite having a conjugated polymer and CNT used in the electrode and semiconductor layer of the present invention can be dissolved in a solvent, and the electrode can be simply applied by applying this polymer composite solution onto a substrate or film. A film or a semiconductor layer can be formed.

  The electrode of the present invention comprises a polymer composite having a conjugated polymer and CNTs. By using CNT, a low resistance electrode film can be formed, and when an organic material is used for the semiconductor layer, the contact resistance between the electrode and the semiconductor layer can be reduced. Conjugated polymers have the effect of improving the dispersibility of CNTs and, like CNTs, are also effective in reducing contact resistance between electrodes / semiconductor layers when an organic material is used for the semiconductor layer. These effects can also reduce the threshold voltage when the FET element is driven. Further, since no acid component is contained, the FET characteristics are stable over time.

  The weight ratio of the CNT in the polymer composite used for the electrode can be any ratio as long as good FET characteristics can be obtained, but it is preferably 10 wt% or more and 10,000 wt% or less. . In general, a conjugated polymer has a large specific resistance in the absence of a dopant such as an acid and is not suitable for an electrode material, but the specific resistance is drastically reduced by adding 10% by weight or more of CNT to the conjugated polymer. Can be used as an electrode material. If it is 10% by weight or less, the composition of the polymer composite used for the semiconductor layer is close, making it difficult to obtain good transistor characteristics. On the other hand, when the amount is more than 10,000% by weight, there is a high possibility that the CNTs are aggregated and it is difficult to form a uniform electrode. More preferably, they are 50 weight% or more and 1000 weight% or less.

  The film forming the electrode can be formed by applying a polymer composite solution containing a predetermined amount of a conjugated polymer and CNT in a solvent. The electrode obtained by applying the polymer composite solution has a shape in which the CNT in the electrode is uniformly dispersed in the matrix of the conjugated polymer when the weight ratio of CNT to the conjugated polymer is 10 to 30% by weight. Have taken. In the case of 30% by weight or more, a conjugated polymer is present between the entangled CNTs. In any case, the orientation of the CNTs in the polymer composite is substantially parallel to the substrate surface, and adheres to the substrate in a random direction within the substrate plane. By adopting such a form, a film in which CNTs are densely entangled can be formed, and high conductivity can be obtained.

  Furthermore, since the above polymer composite can be used to form a film with a smooth surface, the semiconductor layer or insulating layer provided on this electrode should form a uniform film without being affected by irregularities on the electrode surface. Can do. The thickness of the electrode of the transistor and the semiconductor layer is generally 10 to 100 nm, and the size of the unevenness is preferably 10 nm when the surface roughness Ra is used as an index. The electrode of the present invention can be easily formed with an Ra of 10 nm or less. In the present invention, the surface roughness Ra is measured according to JIS B-0601-1994. A roughness curve is created based on the obtained measurement value, the length l is extracted from the roughness curve in the direction of the average line, and the absolute values of deviations from the average line of the extracted portion to the measurement curve are summed up, The average value.

  The polymer composite used for the electrode of the present invention is composed of a conjugated polymer and CNT, but both are not a mixture, but the conjugated polymer covers at least a part or all of the CNT. it is conceivable that. The reason why the conjugated polymer can coat the CNT is presumed to be that an interaction occurs due to the overlap of π electron clouds derived from the respective conjugated structures. Whether or not the CNT is coated with the conjugated polymer can be determined by approaching the color of the conjugated polymer from the color of the uncoated CNT. Quantitatively, the presence of deposits and the weight ratio of deposits to CNTs can be identified by elemental analysis or X-ray photoelectron spectroscopy (XPS). The conjugated polymer to be attached to the CNTs can be used regardless of the molecular weight, molecular weight distribution, or structure as long as it is a conjugated polymer.

  On the other hand, other organic materials for uniformly dispersing CNTs include insulating materials such as surfactants, sugars, polyvinyl pyrrolidone, and polymethyl methacrylate. These materials are present at the interface between the CNT film and the semiconductor layer. When it is inserted, the contact resistance increases, and the effect of using CNT as an electrode cannot be exhibited sufficiently.

  When a conventionally known polythiophene-based conductive polymer (a mixture of polyethylene dioxythiophene and polystyrene sulfonic acid) is used for the source electrode and drain electrode, the acid contained in the conductive polymer However, there is a problem that after the FET element is formed, the acid diffuses with time into the surrounding semiconductor layer and insulating layer, and the FET characteristics change. However, since the electrode using the above-mentioned CNT does not contain an acid, the change in FET characteristics with time is small.

Since the electrode of the present invention has a low resistivity of about 1 × 10 to 1 × 10 ⁻² Ωcm, it can be used without laminating a metal thin film or the like on the base. Further, even if the CNT film is a thin film having a visible light transmittance of 50% or more, it exhibits a surface resistance value that can be sufficiently used as an electrode, and thus can be used as a transparent conductive film. Therefore, when a transparent glass or transparent film is used for the substrate of the FET element, it is possible to produce a transparent FET element.

  In the semiconductor layer of the FET element of the present invention, a polymer composite containing 0.01 to 3% by weight of CNT in a conjugated polymer is used. Any organic material exhibiting semiconductivity can be used as long as it is a compound having developed a conjugated system, and either a low molecular weight or a high molecular weight can be used. From the viewpoint of the solubility of the organic semiconductor in the solvent and the coating property to the substrate, a conjugated polymer is more preferably used. The semiconductor layer of the FET element of the present invention can improve semiconductor characteristics by containing 0.01 to 3 wt% of CNT. When the amount is less than 0.01% by weight, the effect of addition is small, and only a slight effect can be obtained by replacing the electrode from the metal film to the CNT film. When the content is more than 3% by weight, the threshold value of percolation of CNTs is exceeded, and the electrical conductivity is increased, so that it appears like a conductor rather than a semiconductor. More preferably, it is 0.1 to 1 weight%.

  As the CNT used in the semiconductor layer of the present invention, it is desirable to use a CNT shorter than the distance between the device electrodes in order to prevent a short circuit between the electrodes of the FET device. In addition, since CNTs are generally produced in the form of strings, it is possible to obtain CNTs shorter than the distance between device electrodes by cutting or removing long components using a filter for use in the form of short fibers. it can. In order to cut into short fibers, ultrasonic treatment is effective together with acid treatment with nitric acid, sulfuric acid and the like, and it is more preferable to use separation with a filter in combination for improving purity. In addition, not only the cut CNT but also a CNT prepared in a short fiber shape in advance is preferably used according to the present invention. Such short fibrous CNTs form a catalytic metal such as iron or cobalt on a substrate, and thermally decompose carbon compounds at 700 to 900 ° C. by CVD on the surface thereof to vapor-phase grow the CNTs. It is obtained in a shape oriented in the vertical direction. The short fiber CNTs thus produced can be taken out by a method such as peeling off from the substrate. In addition, the short fibrous CNTs can be obtained by supporting a catalytic metal on a porous support such as porous silicon or an anodic oxide film of alumina and growing the CNTs on the surface by the CVD method. Using oriented molecules such as iron phthalocyanine containing a catalytic metal in the molecule as a raw material and producing CNTs on a substrate by performing CVD in an argon / hydrogen gas flow, producing oriented short fiber CNTs Can do. Furthermore, it is also possible to obtain short fiber CNTs oriented on the SiC single crystal surface by an epitaxial growth method. When the dispersion obtained by applying the solution is used as a semiconductor, the average length of CNT depends on the distance between the electrodes, but is preferably 2 μm or less, more preferably 0.5 μm or less.

  In this invention, it is preferable to provide the process of filtering the CNT dispersion liquid or the polymer composite solution containing CNT with a filter. By obtaining CNT smaller than the filter pore diameter from the filtrate, carbon nanotubes smaller than the distance between the source electrode and the drain electrode can be obtained efficiently.

  As long as the filter used for filtration has a pore size smaller than the channel length, any type of filter such as a membrane filter, cellulose filter paper, or glass fiber filter paper can be used. Among them, the membrane filter can be preferably used because it can reduce the amount of CNT adsorbed inside the filter paper and can recover CNT from the filtrate with a high yield.

  The pore diameter of the filter used for filtration should be smaller than the channel length. For example, when the channel length is 20 μm, a short circuit between the electrodes can be reliably prevented by using a filter having a pore diameter of 10 μm. In practice, a filter having a pore diameter of 0.5 to 10 μm can be preferably used, and can be properly used according to the channel length.

  The film thickness of the semiconductor layer of the FET element is not particularly limited, but is preferably 5 nm or more and 200 nm or less. Within this range, a good on / off ratio can be obtained. If the film thickness is larger than this range, the source-drain current that cannot be controlled by the gate voltage increases, and the on / off ratio of the FET element decreases. Further, below this range, there is a problem that the carrier mobility decreases.

  The fabricated FET element may be annealed under reduced pressure or in an inert atmosphere (nitrogen or argon atmosphere).

  The kind of the conjugated polymer used in the electrode and semiconductor layer of the present invention is not particularly limited, but polythiophene, polythienylene vinylene, polyphenylene vinylene, poly-p-phenylene, polypyrrole, polyaniline, polyacetylene, polydiacetylene, polypyrene, poly Examples thereof include carbazole, polyfuran, and polyindole polymers. Among them, it is preferable to use a polythiophene polymer or a copolymer containing a polythiophene unit as a semiconductor having excellent semiconductor characteristics. The polythiophene polymer is a polyalkylthiophene having a structure in which a polymer having a polythiophene structure skeleton is attached to a side chain. Specific examples include poly-3-alkylthiophene such as poly-3-methylthiophene, poly-3-butylthiophene, poly-3-hexylthiophene, poly-3-octylthiophene, poly-3-dodecylthiophene, poly ( 3,3 ″ -dialkylterthiophene), poly [5,5′-bis (3-alkyl-2-thienyl-2,2′-dithiophene), poly [2,5-bis (2-thienyl) -3, 4-dialkylthiophene], (the carbon number of the alkyl group is not particularly limited, but preferably 1 to 16), poly-3-methoxythiophene, poly-3-ethoxythiophene, poly-3-dodecyloxythiophene, etc. 3-alkoxythiophene (the number of carbon atoms of the alkoxy group is not particularly limited, but preferably 1-12), poly-3-methoxy-4-methylthio Poly-3-alkoxy-4-alkylthiophenes such as phen, poly-3-dodecyloxy-4-methylthiophene (the number of carbons of the alkoxy group and alkyl group is not particularly limited, but preferably 1-12), poly-3 -Poly-3-thioalkylthiophene such as thiohexylthiophene and poly-3-thiododecylthiophene (the number of carbons of the alkyl group is not particularly limited, but preferably 1-12), poly-3,4-ethylenedioxythiophene 1 type or 2 or more types can be used, among which poly-3-alkylthiophene, poly (3,3 ″ -dialkylterthiophene), poly [5,5′-bis (3-alkyl- 2-thienyl-2,2′-dithiophene) and poly-3-alkoxythiophene are preferred. A copolymer containing a polythiophene unit includes an arylene unit, a thienylthiazole unit, a fluorene unit, a carbazole unit, a phthalocyanine unit, or a polymer having a derivative of the above unit sandwiched between thiophene units. Any continuous conjugated system can be used. The polymer here refers to a polymer having a molecular weight of about 800 to 100,000, and includes a polymer having a molecular weight of about 4 to 20 monomer units.

  The side chain bonding mode of the polythiophene polymer used in the present invention preferably has a regioregular structure, and preferably has a regioregularity of at least 80%. The regioregularity is an index indicating how many side chain directions are regularly aligned in one direction in a plurality of monomer units arranged side by side. The regioregularity can be quantified by a nuclear magnetic resonance spectrometer (NMR), and the higher the regioregular ratio, the better the semiconductor properties. In the present invention, the steric structure of the main chain of the conjugated polymer and the arrangement of the side chain substituents may be controlled as described above.

  In the present invention, a polymer composite used for an electrode such as a source electrode or a drain electrode can contain a conjugated polymer having a photocrosslinkable component in the side chain. Since a polymer that is soluble in a solvent before photocrosslinking can be insolubilized in the solvent by photocrosslinking, pattern formation using a photolithography method can be performed. The photolithographic method is a method of irradiating only a desired portion of a polymer film with light, creating a difference in solubility in a solvent between an irradiated portion and an unirradiated portion, and forming a desired pattern through a development process. . In the polymer used for the electrode of the present invention, since the polymer is crosslinked by light irradiation, the irradiated part remains insoluble and the unirradiated part remains soluble. Is removed by immersing in a developing solution or the like, a desired pattern can be obtained.

  Furthermore, the solvent resistance of the polymer irradiated part is improved by crosslinking. Since the densification of the film is promoted by crosslinking of the polymer, the electrode film has improved resistance to swelling and erosion by the solvent. Accordingly, when a semiconductor layer, a protective layer, or the like is to be laminated on the upper layer of the electrode, it can be formed without any problem even if a coating liquid containing a solvent is applied.

  As the main chain skeleton of the conjugated polymer having a photocrosslinkable side chain, any conjugated polymer that exhibits solubility in a solvent and a certain degree of conductivity can be preferably used. Examples include thienylene vinylene, polyphenylene vinylene, poly-p-phenylene, polypyrrole, polyaniline, polyacetylene, polydiacetylene, polypyrene, polycarbazole, polyfuran, and polyindole polymers. Among them, it is preferable to use a polythiophene polymer, and an electrode excellent in moldability, film stability, and transistor characteristics can be obtained. A polythiophene polymer having a photocrosslinkable side chain means that a thiophene ring is bonded at the 2-position and 5-position to form a main chain skeleton, and light is emitted to both the 3-position and 4-position of the thiophene ring, or to either of them. It is a polymer having a crosslinkable side chain. However, thiophene units that do not have photocrosslinkable side chains, such as thiophene units that have no substituents or thiophene units that have alkyl groups or alkoxy groups in the side chains, as long as solubility and photocrosslinkability can be maintained. But you can.

  The photocrosslinkable functional group is preferably a functional group that undergoes an addition reaction by photodimerization. The addition reaction can proceed without using an additive such as a polymerization initiator, and mixing of impurities due to the presence of the polymerization initiator and a by-product of the polymerization initiator can be prevented. Since the semiconductor characteristics of the transistor are greatly influenced by the impurity content in the semiconductor layer, it is preferable to avoid mixing of impurities as much as possible in order to prevent diffusion of impurities from the electrode layer to the semiconductor layer.

  As the functional group that causes a photodimerization reaction, any functional group that causes a photodimerization reaction is preferably used. Examples thereof include cinnamic acid ester groups, chalcone groups, styrylpyridinium groups, α-phenylmaleimide groups, anthryl groups, and coumarin groups. Can be mentioned. In view of the balance between the photosensitivity and thermal stability of the functional group, a cinnamic ester group is more preferably used.

  These functional groups causing the photodimerization reaction may be directly bonded to the main chain unit of the polymer, or may be bonded to a group such as an alkyl group or an alkoxy group provided on the side chain of the polymer. Good. These alkyl groups and alkoxy groups preferably have about 1 to 22 carbon atoms. When the number of carbon atoms is larger than 22, the crosslinkability is not affected, but the transistor characteristics may be deteriorated. By making the number of carbons within the above range, both crosslinkability and transistor characteristics can be achieved.

  The side chain exhibiting photocrosslinking property may be inserted in all the monomer units of the polymer, or a unit having no side chain may be included. It is that the side chain which shows photocrosslinkability is contained in 1/20 or more units in conversion of the number of moles. By doing so, the probability that the photocrosslinkable functional groups react with each other increases, and the crosslinking can be sufficiently performed.

  The main chain of the polythiophene polymer may contain a conjugated polymer other than the thiophene unit. However, the ratio of polythiophene units is preferably 1/10 or more in terms of the number of moles of thiophene units, more preferably 1/6 or more, in terms of film formability, film stability, and conductivity. An excellent electrode layer can be obtained. Units other than thiophene include arylene units, thienylthiazole units, thiazole units, thienothiophene units, thienylthienothiophene units, fluorene units, carbazole units, phthalocyanine units, porphyrin units, vinylene units, phenylene units, naphthylene units, or Derivatives of the above-mentioned units may be mentioned, and any of those having a continuous conjugated system can be preferably used.

  The molecular weight of the polythiophene polymer having a photocrosslinkable side chain is preferably 800 to 200000 in terms of number average molecular weight. Further, it may be an oligomer having a molecular weight of about 800 to 3000. Again, the number average molecular weight and the weight average molecular weight can be determined by measuring with GPC and converting to a polystyrene standard sample. By using the conjugated polymer having the above molecular weight, an electrode layer excellent in film formability, film stability, and conductivity can be obtained.

  The polymer composite used in the electrode of the present invention can contain a conjugated polymer having a photocrosslinkable component in the side chain, but when forming a pattern by photolithography, the total weight of the conjugated polymer is Among them, the polymer having a photocrosslinking component is preferably 50% by weight or more. More preferably, it is 70% by weight or more, and a finer pattern can be formed.

  The conjugated polymer having a photocrosslinkable component in the side chain is excellent in dispersibility of CNTs contained in the polymer composite, but as a polymer having more excellent dispersibility, such as poly-3-hexylthiophene. It is preferable to use a conjugated polymer having no photocrosslinkable side chain. When preparing a polymer composite using both a polymer having a photocrosslinkable side chain and a polymer having no photocrosslinkable side chain, CNTs are first dispersed in a conjugated polymer having no photocrosslinkable side chain, Thereafter, there is a method of adding a conjugated polymer having a photocrosslinkable side chain, and an electrode layer excellent in pattern formability, film stability, and conductivity can be obtained.

  It is preferable that impurities such as raw materials and by-products used in the synthesis process be removed as much as possible from the conjugated polymer used for the semiconductor layer and electrode of the present invention. The purification method is not particularly limited, and a reprecipitation method, a Soxhlet extraction method, a filtration method, an ion exchange method, a chelate method, and the like can be used. Among them, the reprecipitation method or Soxhlet extraction method is preferably used for removing impurities such as monomers and by-products used during the polymerization, dimer deactivated during the polymerization, and the reprecipitation method for removing metal components. The chelate method and the ion exchange method are preferably used. Among these methods, one kind may be used alone, or a plurality may be combined.

  The CNTs used for the electrodes and semiconductor layers of the present invention are produced by arc discharge method, chemical vapor deposition (hereinafter referred to as CVD method), laser ablation method, etc. It may be obtained by the method. In addition, a single-walled CNT (hereinafter referred to as SWCNT) in which one carbon film (graphene sheet) is wound in a cylindrical shape, and a two-layer CNT in which two graphene sheets are wound in a concentric circle ( (Hereinafter referred to as DWCNT) and multi-layer CNT (hereinafter referred to as MWCNT) in which a plurality of graphene sheets are concentrically wound, and in the present invention, SWCNT, DWCNT, and MWCNT can be used alone or in combination, respectively. . In particular, SWCNT and DWCNT and MWCNT having a diameter of 15 nm or less can be preferably used since they have excellent properties in terms of conductivity and semiconductor properties. Among them, SWCNT or DWCNT is particularly preferable.

  When producing SWCNT, DWCNT, and MWCNT by the above method, fullerene, graphite, and amorphous carbon are produced as by-products at the same time, and catalyst metals such as nickel, iron, cobalt, yttrium remain, These impurities need to be removed and purified. In order to remove impurities, ultrasonic treatment is effective together with acid treatment with nitric acid, sulfuric acid and the like, and it is more preferable to use separation with a filter in combination in order to improve purity. Although the diameter of CNT used by this invention is not specifically limited, 0.8 nm or more and 100 nm or less are preferable, More preferably, it is 50 nm or less, More preferably, it is 15 nm or less.

  As a method for dispersing CNT in a solvent containing a conjugated polymer, a method in which CNT and a conjugated polymer are mixed with a solvent and then irradiated with ultrasonic waves, and the CNT is previously subjected to ultrasonic irradiation in a solvent. There are a method of adding and dispersing a conjugated polymer after preliminary dispersion, a method of adding and dispersing CNT in a molten conjugated polymer, and the like. In the present invention, any method can be used, but among them, a method of irradiating ultrasonic waves after mixing CNT and a conjugated polymer in a solvent is preferable. The ultrasonic irradiation can be performed using an ultrasonic cleaning machine or an ultrasonic homogenizer. An ultrasonic homogenizer is preferably used when dispersing in a short time with high efficiency.

  When CNT is dispersed in a solvent containing a conjugated polymer, the amount of the conjugated polymer relative to CNT is preferably about 0.5 to 10 times. More preferably, it is 1 to 2 times. By being in this range, while maintaining high dispersibility, a state where there is little excess conjugated polymer can be obtained, and a good CNT dispersion can be obtained.

  The ultrasonic irradiation output is preferably 100 to 500 W in the case of direct irradiation using an ultrasonic homogenizer or the like. When batch processing is performed, 100 to 500 W is preferable, more preferably 100 to 300 W, and when continuous processing is performed, 200 to 750 W, and further 200 to 500 W is preferable. By being in this range, it is possible to obtain a good CNT dispersion while appropriately controlling the rise in liquid temperature due to ultrasonic irradiation of the dispersion. Moreover, the output of the ultrasonic wave in the case of indirect irradiation using an ultrasonic cleaner or the like is preferably 10 to 1000 W. The ultrasonic cleaners that are usually on the market are designed so that the output of the ultrasonic wave and the size of the cleaning tank are approximately proportional, so the output and the size of the cleaning tank are adjusted according to the amount of CNT dispersion treatment. What is necessary is just to select, and it is preferable to use a thing with an output of about 100W / washing tank from about 2 liters and an output of about 300W / washing tank about 10 liters. The frequency of the ultrasonic wave is preferably 20 to 100 kHz. In addition, a conjugated polymer may be added within the range of the above-mentioned blending ratio immediately before the end of the ultrasonic irradiation, thereby suppressing reaggregation of CNTs and improving dispersion stability. it can.

  The polymer composite used in the electrode and semiconductor layer of the present invention is a conjugated polymer much smaller than a predetermined amount and a predetermined amount of CNT in a solvent, and dispersed by ultrasonic irradiation or the like, A predetermined amount of a conjugated polymer is added to this dispersion, and the mixture is prepared by irradiating with ultrasonic waves or stirring with heating. A polymer composite film can be obtained by removing or coating the solvent from the obtained polymer composite solution. Alternatively, a predetermined amount of a conjugated polymer, CNT, and a solvent are directly mixed, and this mixture is subjected to ultrasonic irradiation to prepare a polymer composite solution. Then, the solvent is removed from or applied to the polymer. A composite film can also be obtained.

  As described above, when CNTs are dispersed by irradiating ultrasonic waves in the presence of a conjugated polymer or the like, the aggregation of CNTs is released and can be more finely and uniformly dispersed in the material. The effect of addition can be obtained remarkably. Moreover, the merit that a dispersed state can be stabilized is also acquired.

  The dispersibility of CNT in the polymer composite can be evaluated by applying the polymer composite solution on the substrate and using the atomic force microscope (AFM) on the applied CNT film. For example, the uniformity and the surface roughness Ra can be evaluated by applying the CNT dispersion liquid as it is without observing the thickness and shape of the CNTs in the film, or by observing the unevenness of the film surface. Further, the thickness and shape of the CNTs can be evaluated by further diluting the CNT dispersion liquid by 2 to 20 times and applying it on the substrate, and observing in a state where the overlap between the CNTs is reduced. In the CNT observation by AFM, the thickness in the width direction of the CNT is observed to be larger than the actual CNT thickness due to the characteristics of the apparatus, but the value in the height direction represents an actual numerical value. Can be evaluated as the thickness of In this way, it is possible to evaluate how much the CNTs are deagglomerated. Specifically, it is preferable that CNTs have been unwound into a bundle of about 1 to 10.

  Solvents for dissolving the polymer composite used in the electrode and semiconductor layer of the present invention include methanol, ethanol, butanol, toluene, xylene, o-chlorophenol, acetone, ethyl acetate, ethylene glycol, chloroform, trichloroethane, trichloroethylene, and chlorobenzene. , Dichlorobenzene, trichlorobenzene, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, and the like, but not limited thereto, and a solvent can be selected as necessary.

  The concentration of CNT in the polymer composite used for the electrode and semiconductor layer of the present invention with respect to the solvent is preferably in the range of 0.001 to 30 g / l. When MWCNT, DWCNT, or SWCNT having a diameter of 15 nm or less is used, the CNT concentration is more preferably in the range of 0.001 to 1 g / l. On the other hand, the concentration of the conjugated polymer with respect to the solvent is preferably in the range of 0.001 to 30 g / l. By being in this range, high dispersibility can be maintained and a good CNT dispersion can be obtained.

  When the electrode or semiconductor layer of the FET element of the present invention is applied and formed, the casting method, spin coating method, dip method, bar coater method, dropping method, spray method, blade coating method, slit die coating method, screen printing method, General methods such as a mold application method, a printing transfer method, a dip-up method, and an ink-jet method can be used. What is necessary is just to select the application | coating method according to the coating-film characteristic to obtain, such as coating-film thickness control and orientation control.

  The pattern of the electrode of the FET element or the semiconductor layer of the present invention can be directly formed by an ink jet technique or a screen printing technique. Also, a lift-off method using a photoresist, a method of using photolithography by imparting photosensitivity to electrode components and semiconductor layer components, a method of pattern etching a film, a hydrophilic surface and water repellency on a substrate surface using a photoresist Any method can be used, such as a method of forming a pattern by forming a surface, or a method of forming a pattern by wiping or scraping the removed portion after applying the entire surface. Further, by performing a heat treatment at 50 to 200 ° C. after pattern formation, the denseness of the film can be improved and the solvent resistance can be improved. For the heat treatment, any of a hot plate, a heater oven, a hot air oven, an IR oven and the like can be used.

  When a photocrosslinkable conjugated polymer is used for the electrode of the present invention, an electrode pattern can be formed using a photolithography method. For light irradiation, a method of exposing through a photomask is preferably used. A desired pattern portion is formed transparently on the photomask, and is used by being placed on the polymer film during light irradiation. What is necessary is just to irradiate the wavelength of the light to which the photosensitive group causes an addition reaction, and the wavelength of ultraviolet light to visible light region can be used preferably. A commercially available light irradiation apparatus can be used, and a stepper exposure machine, a proximity exposure machine, etc. can be used. As the light source, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a halogen lamp, a germicidal lamp, an ultraviolet lamp, or the like can be used.

  The removal of the non-irradiated part is performed by a development process. The solvent used for development may be a solvent in which the polymer is soluble, and an organic solvent is used. Moreover, even if it adds water in the range which does not lose the dissolving power, it is used.

For the insulating layer of the FET element of the present invention, inorganic materials such as SiO ₂ film and alumina, polyimide, polyvinyl alcohol, polyvinyl phenol, polyvinyl chloride, polyethylene terephthalate, polyvinylidene fluoride, polymethyl methacrylate, polystyrene, polyparaxylene, etc. A polymer material or a mixture of an inorganic material powder and a polymer material can also be used. Film formation is sputtering, vapor deposition, spin coating method, casting method, dipping method, bar coater method, dropping method, spray method, blade coating method, slit die coating method, screen printing method, mold coating method, printing transfer method, dip pulling up A film can be formed by a method, an inkjet method, or the like.

  Examples of substrates for FET elements include glass, silicon wafers, films, and resin substrates. Examples of films and resin substrates include organic materials such as polyimide, polyester, polycarbonate, polysulfone, polyethersulfone, polyethylene, polyphenylene sulfide, and polyparaxylene. Can be used. Further, for the purpose of improving the performance of the FET element, the surface of the substrate may be treated with a surface modifier such as a silane coupling agent.

  The film thickness of the semiconductor layer of the FET element is not particularly limited, but is preferably 5 nm or more and 200 nm or less. Within this range, a good on / off ratio can be obtained. If the film thickness is larger than this range, the source-drain current that cannot be controlled by the gate voltage increases, and the on / off ratio of the FET element decreases. Further, below this range, there is a problem that the carrier mobility decreases.

  The fabricated FET element may be annealed under reduced pressure or in an inert atmosphere (nitrogen or argon atmosphere).

  In the FET element manufactured in this way, the current flowing between the source electrode and the drain electrode can be controlled by changing the gate voltage. From the characteristics, the mobility can be calculated using the following equation (1). Can be calculated.

μ = (δId / δVg) L · D / (W · ε r · ε · Vsd) (1)
However Id is the current between the source and drain, Vsd is the voltage between the source and the drain, Vg is the thickness of the gate voltage, D is the insulating layer, L is the channel length, W is the channel width, epsilon _r is the relative permittivity of the insulating layer (Here, 3.9 of SiO ₂ is used), ε is the dielectric constant of vacuum (8.85 × 10 ⁻¹² F / m).

  Further, the on / off ratio can be obtained from the ratio of the value of Id (on current) at a certain negative gate voltage to the value of Id (off current) at a certain positive gate voltage.

  Hereinafter, the present invention will be described more specifically based on examples. However, the present invention is not limited to the following examples.

Example 1
First, a CNT dispersion was prepared. As the CNT, single-walled carbon nanotubes (manufactured by Science Laboratories, Inc., purity 95%) were used as they were without purification. A conjugated polymer poly-3-hexylthiophene (hereinafter abbreviated as P3HT) (manufactured by Aldrich, regioregular) was used after purification by a reprecipitation method. For reprecipitation, 5 ml of chloroform was added to 20 mg of P3HT, dissolved, and filtered through a membrane filter having a pore size of 0.45 μm. The filtrate was dropped into a mixed solution of 15 ml of methanol and 15 ml of 0.1N hydrochloric acid, and precipitated P3HT Was collected on a membrane filter having a pore size of 0.45 μm by filtration, the solvent was removed by vacuum drying, and this operation was repeated twice for purification.

  Put 1.5 mg of CNT and 1.5 mg of purified P3HT and 30 ml of chloroform into a 50 ml sample tube, prepare a CNT mixture, and use an ultrasonic homogenizer (VCX-502, Tokyo Rika Kikai Co., Ltd., output 250 W, direct irradiation). Used for ultrasonic irradiation. At this time, a probe made of a titanium alloy having a diameter of 13 mm is used as a probe for ultrasonic irradiation, and the probe surface is polished in advance with fine sandpaper so that the surface roughness Ra is 1 μm or less. did. When the ultrasonic irradiation was performed for 30 minutes, the irradiation was stopped once, 1.5 mg of P3HT was added, and the ultrasonic irradiation was further performed for 1 minute to obtain CNT dispersion A (CNT concentration 0.05 g / l with respect to the solvent, solvent Concentration of P3HT to 0.1 g / l, weight ratio of CNT to P3HT: 50% by weight).

  Chloroform is added to CNT dispersion A (CNT concentration 0.05 g / l) to dilute to 1/10 concentration, spin-coated on a 1 cm square silicon wafer, and observed using an atomic force microscope (AFM) did. The CNT in the CNT dispersion A was uniformly dispersed, and the diameter of the CNT was 1 to 10 nm. From this, it was found that single-walled CNTs originally of bundles with a thickness of several tens of nanometers were unraveled to about 1-10.

  Subsequently, 15 ml of CNT dispersion A was filtered using a membrane filter (pore diameter 0.45 μm, diameter 25 mm, Omnipore membrane manufactured by Millipore), and CNTs were collected on the filter. Since the filtrate had a transparent orange color, it was found that the filtrate contained only excess P3HT and no CNT. Next, the collected CNTs were immersed in 15 ml of chloroform together with the filter, and subjected to ultrasonic irradiation for 5 minutes using an ultrasonic cleaner to obtain CNT dispersion B (concentration of CNT to solvent: 0.05 g / l). The concentration of P3HT relative to the solvent is about 0.05 g / l, and the amount of CNT relative to P3HT is 100% by weight).

  The CNT dispersion B was observed with AFM in the same manner as described above. Since the CNTs were uniformly dispersed and the diameter of the CNTs was 1 to 10 nm, the CNTs did not aggregate even when filtration and redispersion steps were added, and the thickness of the CNTs did not change. Here, it was examined whether P3HT was adhered to the CNT in the CNT dispersion B. The dispersion B5 ml was filtered using a membrane filter, and CNTs were collected on the filter. The collected CNTs were quickly transferred onto a silicon wafer before the solvent was dried to obtain dried CNTs. When this CNT was subjected to elemental analysis using X-ray photoelectron spectroscopy (XPS), sulfur element contained in P3HT was detected. Therefore, it was found that P3HT adhered to the CNT in the CNT dispersion B.

  Next, a field effect transistor was produced in the following manner. The structure of this FET element is shown in FIG.

An antimony-doped silicon wafer 1 (with a resistivity of 0.02 Ωcm or less) with a SiO ₂ film 3 (film thickness 300 nm) was used as the substrate of the FET element. Here, the silicon wafer is the substrate and the gate electrode 2 at the same time, and the thermal oxide film is an insulating layer.

The source electrode and the drain electrode were formed on the SiO ₂ film as follows. 0.1 ml of CNT dispersion B is dropped on the entire surface of a 2 cm square silicon wafer, the silicon wafer is tilted to remove excess liquid, and the remaining CNT dispersion B adhered to the substrate is dried to form an electrode. A polymer composite film was obtained. Next, the film on the peripheral edge of the wafer is wiped with a waste so that a film of 3 × 10 mm remains in the center of the wafer, and the center of the film of 3 × 10 mm is scraped with a metal needle having a radius of curvature of about 200 μm at the tip. This was divided into two parts of 3 × 5 mm and 3 × 5 mm. The width of the line scraped by the needle was 30 μm as measured with an optical microscope. The films separated by the lines were used as the source electrode 5 and the drain electrode 6, respectively. Next, the wafer with the electrode polymer composite film was heat-treated on a hot plate at 150 ° C. for 30 minutes. The thickness of the obtained film (source electrode, drain electrode) was 30 nm as measured using AFM. Further, the surface roughness (Ra) of the polymer composite film for electrodes was 4 nm, which was very smooth. An AFM image obtained by observing the surface shape of the obtained film is shown in FIG. In this way, a source electrode and a drain electrode were formed from a polymer composite film for an electrode having a channel length of 30 μm, a channel width of 3 mm, and a thickness of 30 nm.

  Next, a polymer composite solution having CNTs for forming the semiconductor layer 4 was prepared. Chloroform was added to CNT dispersion A having a CNT concentration of 0.05 g / l to dilute to 0.02 g / l, and filtration was performed using a membrane filter (pore size 10 μm, diameter 25 mm, Millipore Omnipore membrane). CNTs having a length of 10 μm or more were removed. The filtrate contained most of the CNTs. The obtained filtrate was designated as CNT dispersion C. CNT dispersion C 0.6 ml, chloroform 0.4 ml, and P3HT 3 mg were put into a sample tube having a volume of 10 ml, and 30 using an ultrasonic cleaner (US-2, Inoue Seieido Co., Ltd., output 120 W, indirect irradiation). Polymer composite solution for semiconductor layer (3g / l P3HT concentration to solvent, about 0.012g / l CNT concentration to solvent, 0.4% by weight CNT concentration to P3HT) by ultrasonic stirring for 5 minutes Got.

  Next, 0.01 ml of the polymer composite solution for the semiconductor layer is dropped on the channel formed by the source electrode and the drain electrode, and a thin film having a film thickness of 25 nm is formed by a spin coating method (rotation speed: 1000 rpm, 0.3 seconds). Formed. At this time, neither the source electrode nor the drain electrode was eluted or eroded by chloroform contained in the polymer composite solution, and it was confirmed from observation with an optical microscope that the original shape was maintained. After the lead wires were attached to the source and drain electrodes using silver wire and silver paste, they were left in a vacuum dryer at 110 ° C. for 2 hours, slowly cooled to 50 ° C. or lower, and taken out from the dryer. . Thus, an FET element was produced.

  The obtained FET element was moved to a measurement box, left in a vacuum for 18 hours, and then the current-voltage characteristics were measured to examine the FET characteristics. As a measuring device, a semiconductor characteristic evaluation system 4200-SCS manufactured by Keithley Instruments Inc. was used, and the measurement box kept a reduced pressure state of 1 torr or less.

The source-drain current (Isd) -source-drain voltage (Vsd) characteristics are measured when the gate voltage (Vg) of the FET element is changed, and Vsd = − when Vg = 0 to −50V is changed. When the mobility was determined from the change in Isd value at 5 V, the mobility was as high as 1.1 × 10 ⁻² cm ² / V · sec, and a good value was obtained. The on / off ratio was found to be 2.0 × 10 ³ from the ratio of the Isd value at Vsd = −5V when Vg = −50V and the Isd value at Vsd = −5V when Vg = + 50V. Good values were obtained.

The FET element was vacuum-stored and the FET characteristics were measured again after 30 days. The mobility was 1.2 × 10 ⁻² cm ² / V · sec, the on / off ratio was 1.2 × 10 ³ , and the characteristics were almost the same. It did not change.

Example 2
Example except that the coating solution for the film used for the source electrode and the drain electrode was changed from the CNT dispersion B (weight ratio of CNT to P3HT was 100 wt%) to the CNT dispersion A (CNT amount to P3HT was 50 wt%) The same operation as in No. 1 was performed to produce an FET element. The electrode shape was such that the electrode thickness was 30 nm, the channel length was 30 μm, the channel width was 3 mm, and the electrode surface roughness (Ra) was 4.5 nm. When the characteristics of the fabricated FET element were examined, the mobility was 9.0 × 10 ⁻³ cm ² / V · sec, the on / off ratio was 1.2 × 10 ³ , and good values were obtained.

The FET element was stored in a vacuum and the FET characteristics were measured again after 30 days. The mobility was 9.0 × 10 ⁻³ cm ² / V · sec, the on / off ratio was 2.0 × 10 ³ , and the characteristics were almost the same. It did not change.

Example 3
Example 1 except that the coating solution for the film used for the source electrode and the drain electrode was changed from the CNT dispersion B to a polymer composite solution having a CNT amount of 10 wt% with respect to P3HT, and the coating method was changed to the spin coating method. An FET device was fabricated by performing the same operation as described above.

  The polymer composite solution was prepared as follows. Put CNT 9mg and purified P3HT 9mg and chloroform 30ml into a 50ml sample tube, irradiate ultrasonically using an ultrasonic homogenizer, stop irradiation once when ultrasonic irradiation was performed for 30 minutes, add 9mg of P3HT, Furthermore, ultrasonic irradiation was performed for 1 minute to obtain a CNT dispersion D (CNT concentration 0.3 g / l). Next, 2.4 mg of P3HT is added to 1 ml of the CNT dispersion D, and ultrasonic irradiation is performed with an ultrasonic cleaner for 30 minutes. The concentration of P3HT is 3 g / l, and the CNT concentration is 0.3 g / l (the CNT amount with respect to P3HT is 10% by weight). A polymer composite solution was prepared.

Next, 0.1 ml of the polymer composite solution was dropped onto the substrate, spin-coated by rotating at a rotation speed of 1000 rpm for 0.3 seconds, and a polymer composite film for an electrode having a film thickness of 30 nm was obtained. Subsequently, a source electrode and a drain electrode pattern were formed in the same manner as in Example 1 to obtain an electrode film having a thickness of 30 nm, a channel length of 30 μm, a channel width of 3 mm, and an electrode surface roughness Ra = 2.1 nm. Next, the same operation as in Example 1 was performed to form a semiconductor layer, and an FET element was produced. When the FET characteristics were examined, it was found that the mobility was 4.5 × 10 ⁻³ cm ² / V · sec and the on / off ratio was 1.5 × 10 ³ .

The FET element was stored in vacuum, and the FET characteristics were measured again after 30 days. The mobility was 4.6 × 10 ⁻³ cm ² / V · sec, the on / off ratio was 2.2 × 10 ³ , and the characteristics were almost the same. It did not change.

Example 4
Example 1 except that the substrate was changed from a silicon wafer to a polyethylene terephthalate (PET) film, the insulating film was changed from an SiO ₂ film to polyvinylphenol (PVP), and the gate electrode was changed from antimony doped silicon to an electrode made of CNT dispersion A. The same operation was performed to produce an FET element.

  The PET film is a polyester film (trade name “Lumirror S10”, thickness 100 μm) manufactured by Toray Industries, Inc., cut into 2 cm square, and PVP is manufactured by Aldrich, mixed with a crosslinking agent and a solvent, Used by dissolving. Poly (melamine-co-formaldehyde) methacrylate (manufactured by Aldrich) was used as the crosslinking agent, and tetrahydrofuran (THF) was used as the solvent. The amount of the crosslinking agent was 25% by weight with respect to PVP, and the amount of solvent was adjusted so that the PVP concentration was 40 g / L.

  First, 0.1 ml of CNT dispersion D was dropped on the entire surface of the PET film and spin-coated under the conditions of 1000 rpm and 10 seconds. The periphery of the substrate was wiped off with a waste cloth containing a solvent so as to have a shape of 1 mm × 20 mm, and a P3HT film in which CNTs with a thickness of 20 nm were dispersed was formed as a gate electrode.

  Next, 0.1 mL of the above PVP solution containing a crosslinking agent was dropped on a PET film with a gate electrode, and spin-coated under conditions of 3000 rpm and 30 seconds. Next, heat treatment was performed in an oven at 120 ° C. for 3 minutes to form an insulating layer having a thickness of 300 nm.

  On the insulating layer thus formed, a source electrode, a drain electrode, and a semiconductor layer were formed in the same manner as in Example 1 to produce an FET element. Only the heat treatment method for forming the source electrode and the drain electrode was changed, and an oven (120 ° C., 3 minutes) was used without using a hot plate. Thus, an FET element made of an organic material was produced.

The electrode of the obtained FET element has a thickness of 30 nm, a channel length of 30 μm, a channel width of 3 mm, an electrode surface roughness (Ra) of 4.2 nm, and the FET characteristics have a mobility of 3.2 × 10 ⁻³ cm. ² / V · sec and an on / off ratio of 1.2 × 10 ³ were obtained.

The FET element was stored in a vacuum and the FET characteristics were measured again after 30 days. The mobility was 4.0 × 10 ⁻³ cm ² / V · sec, the on / off ratio was 1.0 × 10 ³ , and the characteristics were almost the same. It did not change.

Comparative Example 1
The source electrode and drain electrode were replaced with a film of a polythiophene-based conductive polymer polyethylenedioxythiophene / polystyrenesulfonate (hereinafter abbreviated as PEDOT / PSS) (Denatron G-115S manufactured by Nagase ChemteX). An FET element was fabricated in the same manner as in Example 1 except for the above. The PEDOT / PSS electrode was formed as follows.

  A positive resist solution was dropped onto a silicon wafer with a thermal oxide film, applied using a spin coater, and then dried on a hot plate at 90 ° C. to form a resist film. Next, using an exposure machine, UV irradiation is performed through a photomask, and then the wafer with the resist film is immersed in an alkaline aqueous solution, the UV irradiation section is removed, and the resist film has a shape in which the comb-shaped electrode is removed. Got. Next, a water / alcohol dispersion of PEDOT / PSS is spin-coated on the resist film substrate, dried at 90 ° C. for 30 seconds, then immersed in acetone together with the wafer, and ultrasonically irradiated with an ultrasonic cleaner. Excess PEDOT / PSS on the resist was removed. Next, heat treatment was performed on a hot plate at 150 ° C. for 10 minutes. Thus, a PEDOT / PSS comb-shaped electrode having a channel width of 0.5 cm and a channel length of 20 μm was formed on the wafer. The surface roughness (Ra) of this electrode was 20 nm, and the unevenness was large. Further, the thickness of the electrode was 20 nm when it was thin, and 90 nm when it was thick, and the thickness was about 40 nm on average.

Next, a semiconductor layer was formed by the same operation as in Example 1 to produce an FET element. When the FET characteristics were examined, the mobility was 1.1 × 10 ⁻³ cm ² / V · sec, the on / off ratio was 5.5 × 10 ² , and the characteristics were low.

The FET element was vacuum-stored and the FET characteristics were measured again 30 days later. The mobility was 5.2 × 10 ⁻³ cm ² / V · sec, the on / off ratio was 6.4 × 10, and the characteristics changed greatly. Was.

Example 5
The CNT dispersion B 15 ml prepared in Example 1 was filtered once again using a membrane filter (pore diameter 0.45 μm, diameter 25 mm), and CNTs were collected on the filter. Next, the collected CNTs were immersed in 15 ml of chloroform together with the filter, and subjected to ultrasonic irradiation for 1 minute in an ultrasonic cleaning machine to obtain a CNT dispersion E (CNT concentration 0.05 g / l with respect to the solvent). When the CNT dispersion E was filtered using a membrane filter, the filtrate was almost colorless and transparent, and all the CNTs were collected on the filter. After sufficiently drying the CNTs on the filter, elemental analysis of the CNTs was performed. As a result, sulfur element derived from P3HT was detected, and the weight ratio of CNT to P3HT was determined from the ratio to carbon. The weight ratio of CNT to P3HT was 900% by weight.

Next, the coating solution for the film used for the source electrode and drain electrode was changed from CNT dispersion B (weight ratio of CNT to P3HT was 100 wt%) to CNT dispersion E (CNT amount to P3HT was 900 wt%). The same operation as in Example 1 was performed to produce an FET element. As for the electrode shape, the electrode thickness was 30 nm, the channel length was 30 μm, the channel width was 3 mm, and the electrode surface roughness (Ra) was 10 nm. When the characteristics of the manufactured FET element were examined, the mobility was 7.5 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 4.5 × 10 ³ .

When the FET element was stored in vacuum and the FET characteristics were measured again after 30 days, the mobility was 7.1 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 4.6 × 10 ³ .

Example 6
A polythiophene polymer a having a photocrosslinkable side chain represented by the following formula (1) was synthesized. The synthesis method is shown below.

  First, 5 g of 2- (3-thienyl) ethanol and 20.8 g of N-bromosuccinimide (NBS) were stirred in 150 ml of dimethylformamide (DMF) at room temperature under a nitrogen stream for 10 hours. Chloroform 100 ml and pure water 100 ml were added in this order to extract the product into chloroform, and the by-product and dimethylformamide were dissolved and removed on the pure water side. Next, magnesium sulfate was added to the chloroform solution to remove water, and then the chloroform was distilled off, followed by purification by silica gel column chromatography (solvent: chloroform: methanol = 10: 1 (weight ratio)), and 2- (2,5 -Dibromo-3-thienyl) -ethanol (yield 8.9 g, yield 80%) was obtained.

  Next, 8.9 g of 2- (2,5-dibromo-3-thienyl) -ethanol was dissolved in 25 ml of diethyl ether, 2.5 g of pyridine was added, and the mixture was stirred while cooling with ice. A solution prepared by dissolving 5.4 g of cinnamoyl chloride in 20 ml of diethyl ether was slowly added dropwise thereto, followed by stirring for 1 hour under ice-cooling and 7 hours at room temperature. 100 ml of ethyl acetate and 100 ml of pure water were added in this order to extract the product into ethyl acetate, and the by-product and pyridine were dissolved and removed on the pure water side. Next, sodium sulfate was added to the ethyl acetate solution to remove water, and then ethyl acetate and diethyl ether were distilled off, followed by purification by silica gel column chromatography (solvent: chloroform: n-hexane = 2: 1 (weight ratio)). The monomer cinnamoyl-2- (2,5-dibromo-3-thienyl) -ethyl ester (yield 12.9 g, yield 77%) was obtained.

Next, 0.26 g of bis- (1,5-cyclooctadiene) nickel (Ni (COD) ₂ ) and 0.15 g of 2,2′-bipyridine (bpy) are dissolved in 3 ml of dimethylformamide. A solution prepared by dissolving 0.6 g in 2 ml of dimethylformamide was slowly added dropwise. The mixture was refluxed at 100 ° C. for 96 hours under a nitrogen stream, cooled to room temperature, and then dimethylformamide was distilled off using an evaporator until the amount of the solution reached 10 ml. The obtained polymer solution was dropped into a 1: 1 mixture of methanol and 0.1N hydrochloric acid, and the precipitated solid was collected using a membrane filter having a pore size of 1 μm. This solid was transferred to a Soxhlet extractor and refluxed with 200 ml of methanol for 3 hours and then with 200 ml of hexane for 2 hours to remove components soluble in each solvent. Subsequently, 200 ml of chloroform was used to dissolve and recover the solid, and the solution was distilled off using an evaporator until the amount of the solution became 2 ml. This chloroform solution was dropped into methanol, and the precipitated solid was collected using a membrane filter having a pore size of 0.45 μm and dried in vacuo to obtain a polythiophene polymer a. N of the polymer a represented by the general formula (1) was 30.

The obtained polymer was yellow granular. When the molecular weight of the obtained polymer was determined by gel permeation chromatography (high-speed GPC device HLC-8220 GPC manufactured by TOSOH Co., Ltd., liquid feeding solvent: chloroform, absolute calibration curve method), the number average molecular weight was 7700, weight. The average molecular weight was 16000. Next, the results of analysis using ¹ H-NMR (manufactured by JEOL Ltd., superconducting FTNMR “EX-270”, sample dissolution solvent: deuterated chloroform) were as follows.
¹ H-NMR (CDCl ₃ (d = ppm)): 2.95 (s, 2H), 4.36 (s, 2H), 6.37-6.42 (d, 1H), 7.13 (s, 1H), 7.32 (s, 3H) , 7.41 (s, 2H), 7.62-7.68 (d, 1H).

  Next, 0.6 mg of the polythiophene polymer a obtained by the above method and 2.4 ml of CNT dispersion A (CNT concentration: 0.05 mg / ml, P3HT concentration: 0.1 mg / ml) are mixed, and ultrasonic waves are mixed. A polymer composite solution was prepared by stirring for 5 minutes with a washing machine. At this time, the ratio of the polythiophene polymer a having a photocrosslinkable side chain to the total amount of the conjugated polymer is 71% by weight, and the ratio of CNT to the conjugated polymer is 14% by weight.

Next, the obtained polymer composite solution was cast-coated on an antimony-doped silicon wafer substrate with a ₂ cm square SiO ₂ film (film thickness 300 nm) to form an electrode film. Next, a stainless steel mask in which a comb pattern having a channel length of 100 μm and a channel width of 5 mm is hollowed is overlaid on the electrode film, and a UV lamp (a handy UV lamp SLUV-4 manufactured by AS ONE Co., Ltd., wavelength 254 nm) is formed on the mask. , Intensity 614 μW / cm ² , irradiation distance 2 cm) and irradiation with ultraviolet rays for 2 minutes to carry out photocrosslinking. Next, the substrate was immersed in chloroform, and irradiated with ultrasonic waves for 30 seconds with an ultrasonic cleaner to dissolve and remove unexposed portions. Thus, an electrode made of a comb-shaped polymer composite having a channel length of 100 μm and a channel width of 5 mm was formed. When the obtained electrode was observed using AFM, the film thickness was 20 nm and the surface roughness (Ra) was 8 nm.

Next, the same operation as in Example 1 was performed to obtain a semiconductor layer (having P3HT and CNT, the weight concentration of CNT with respect to P3HT was 0.4% by weight, and the film thickness was 25 nm). Thereafter, lead wires were attached in the same manner as in Example 1, heat treatment was performed, and FET characteristics were measured. As for FET characteristics, the mobility was 6.6 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 4.2 × 10 ³ . When the FET element was stored in vacuum and the FET characteristics were measured again after 30 days, the mobility was 7.1 × 10 ⁻³ cm ² / V · sec and the on / off ratio was 4.8 × 10 ³ .

Example 7
0.24 mg of the polythiophene polymer a obtained in Example 5 above and 2.4 ml of CNT dispersion A (CNT concentration: 0.05 mg / ml, P3HT concentration: 0.1 mg / ml) were mixed. A polymer composite solution was prepared by stirring with a sonic cleaner for 5 minutes. At this time, the ratio of the polythiophene polymer a having a photocrosslinkable side chain to the total amount of the conjugated polymer is 50% by weight, and the ratio of CNT to the conjugated polymer is 25% by weight.

  Next, the obtained polymer composite solution was subjected to the same operation as in Example 5 to form an electrode composed of a comb-shaped polymer composite having a channel length of 100 μm and a channel width of 5 mm. However, the number of times of cast application was increased from 5 times to 10 times. When the obtained electrode was observed using AFM, the film thickness was 20 nm and the surface roughness (Ra) was 9 nm.

Next, the same operation as in Example 1 was performed to obtain a semiconductor layer (having P3HT and CNT, the weight concentration of CNT with respect to P3HT was 0.4% by weight, and the film thickness was 25 nm). Thereafter, lead wires were attached in the same manner as in Example 1, heat treatment was performed, and FET characteristics were measured. As for the FET characteristics, the mobility was 7.9 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 1.1 × 10 ³ . When the FET element was stored in vacuum and the FET characteristics were measured again after 30 days, the mobility was 8.0 × 10 ⁻³ cm ² / V · sec and the on / off ratio was 2.1 × 10 ³ .

Example 8
Using the method described in Example 6 above, a conjugated system of polythiophene polymer a having a photocrosslinkable side chain on an antimony-doped silicon wafer substrate with a ₂ cm square SiO ₂ film (film thickness 300 nm) An electrode for FET containing the total amount of polymer and CNTs was formed. The electrode shape was a comb pattern with a channel length of 100 μm and a channel width of 5 mm, as in Example 6.

  Next, chloroform was added to the CNT dispersion A used in Example 1 to dilute to 0.005 g / l, and filtration was performed using a membrane filter (pore size 10 μm, diameter 25 mm, Omnipore membrane manufactured by Millipore). The obtained filtrate was designated as CNT dispersion F. CNT dispersion F 0.6 ml, chloroform 0.4 ml, and P3HT 3 mg are placed in a sample tube with a volume of 10 ml, and 30 using an ultrasonic cleaner (US-2, Inoue Seieido Co., Ltd., output 120 W, indirect irradiation). Polymer composite solution for semiconductor layer (P3HT concentration 3g / l with respect to solvent, CNT concentration 0.003g / l with respect to solvent, and CNT weight concentration with respect to P3HT 0.1% by weight) by ultrasonic stirring for minutes Obtained. Subsequently, the polymer composite solution for semiconductor layers was spin-coated on the above-mentioned electrode, and the thin film with a film thickness of 25 nm was obtained.

Thereafter, lead wires were attached in the same manner as in Example 1, heat treatment was performed, and FET characteristics were measured. As for the FET characteristics, the mobility was 2.2 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 1.2 × 10 ⁴ . The FET element was stored in a vacuum and the FET characteristics were measured again 30 days later. The mobility was 2.4 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 1.9 × 10 ⁴ .

Example 9
Using the method described in Example 6 above, a conjugated system of polythiophene polymer a having a photocrosslinkable side chain on an antimony-doped silicon wafer substrate with a ₂ cm square SiO ₂ film (film thickness 300 nm) An electrode for FET containing the total amount of polymer and CNTs was formed. The electrode shape was a comb pattern with a channel length of 100 μm and a channel width of 5 mm, as in Example 6.

  Subsequently, the CNT dispersion A used in Example 1 (CNT concentration 0.05 g / l with respect to the solvent) was directly filtered using a membrane filter (pore size 10 μm, diameter 25 mm, Omnipore membrane manufactured by Millipore). The filtrate obtained was designated as CNT dispersion G. CNT dispersion G 0.6 ml, chloroform 0.4 ml, and P3HT 3 mg are put into a sample tube with a volume of 10 ml, and 30 using an ultrasonic cleaner (US-2, Inoue Seieido Co., Ltd., output 120 W, indirect irradiation). By ultrasonically stirring for a minute, a polymer composite solution for semiconductor layer (P3HT concentration 3 g / l with respect to the solvent, CNT concentration 0.03 g / l with respect to the solvent, and CNT weight concentration with respect to P3HT 1 wt%) was obtained. . Subsequently, the polymer composite solution for semiconductor layers was spin-coated on the above-mentioned electrode, and the thin film with a film thickness of 25 nm was obtained.

Thereafter, lead wires were attached in the same manner as in Example 1, heat treatment was performed, and FET characteristics were measured. As for FET characteristics, the mobility was 9.6 × 10 ⁻³ cm ² / V · sec, and the on / off ratio was 1.1 × 10 ³ . When the FET element was stored in vacuum and the FET characteristics were measured again after 30 days, the mobility was 9.4 × 10 ⁻³ cm ² / V · sec and the on / off ratio was 1.0 × 10 ³ .

  The organic FET of the present invention can be used for a thin film transistor for a liquid crystal display or an electroluminescence (EL) display, which can use a low-cost process such as a coating method and can provide an element having a small characteristic change with time. It is done.

Schematic sectional view of the field effect transistor of the present invention Atomic force microscope image observing surface shape of electrode of field effect transistor of the present invention

Explanation of symbols

1 Silicon wafer 2 Gate electrode (silicon wafer)
3 SiO ₂ film 4 Semiconductor layer 5 Source electrode 6 Drain electrode

Claims (7)

The source electrode and / or drain electrode have a conjugated polymer and carbon nanotubes, is formed of a polymer composite containing no acid, semiconductor layer comprises 0.01 to 3 wt% of carbon nanotubes in the conjugated polymer Field effect transistor made of polymer composite. The field effect transistor according to claim 1, wherein the polymer composite used for the source electrode and / or the drain electrode has 10% by weight or more and 10,000% by weight or less of carbon nanotubes with respect to the conjugated polymer. 2. The field effect transistor according to claim 1, wherein the conjugated polymer used for the polymer composite of the electrode and / or semiconductor layer is a polythiophene polymer. 2. The field effect transistor according to claim 1, wherein the carbon nanotube used in the polymer composite of the electrode and / or semiconductor layer is a single-walled carbon nanotube. 2. The field effect transistor according to claim 1, wherein the polymer composite used for the source electrode and / or drain electrode has a conjugated polymer having a photocrosslinkable side chain. 6. The field effect transistor according to claim 5, wherein the conjugated polymer having a photocrosslinkable side chain is a polythiophene conjugated polymer. 7. The field effect transistor according to claim 6, wherein the photocrosslinkable side chain is a functional group that undergoes an addition reaction by photodimerization.

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