JP2005072569A - Organic fet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic FET having an insulating film combinedly having a high capacity, high insulation resistance, and the planarity of an interface with an organic semiconductor. <P>SOLUTION: In a transistor element using an organic semiconductor, a gate insulated film is a laminate, including at least a high-dielectric-constant insulating film which includes a polymer and a low-dielectric-constant insulating film including a polymer. Insulating layers each having a difference in dielectric constants of the low-dielectric-constant insulating film and the high-dielectric-constant insulating film of larger than one are laminated, so as to manufacture an organic FET. By laminating two or more kinds of thin films each having a difference in the dielectric constant of one or larger, the organic FET with performance balance maintained can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic field effect transistor using a gate insulating film having a specific layer structure.

  Gate dielectric materials used in organic field effect transistors include high dielectric constants to achieve high capacitance, dielectric breakdown strength when made into thin films, and organic semiconductors to form good interfaces with organic semiconductors And characteristics such as the flatness of the film surface forming the interface with the semiconductor are required. In addition, the organic field effect transistor may be applied to a flexible element, and it is expected that the flexibility of an insulating film is required for such an element.

  In general, an insulating film is more advantageous as a transistor because the gate voltage can be driven at a lower voltage as the capacitance increases. In order to increase the capacitance, there are methods of using an insulating material having a large dielectric constant or reducing the thickness of the insulator layer. However, there is a limit to thinning the insulator film because pinholes can be formed or a large electric field is applied to easily cause dielectric breakdown. On the other hand, a high dielectric constant film generally cannot be stably operated because charges are accumulated inside or permanent polarization occurs.

Until now, various studies have been made on gate insulating film materials used in organic field effect transistors. The most commonly used gate insulating film is a silicon dioxide film obtained by thermally oxidizing silicon. The inorganic materials other, in order to improve the leakage current of SiO _2, and SiN _x, insulating film or formed by laminating SiO _2, the SiN _x, insulating film formed by laminating organosilsesquioxane has been reported (Non (See Patent Document 1 and Non-Patent Document 2).

  In addition, it has been reported that the use of cyanoethyl pullulan, which is a high dielectric constant polymer, as an insulating film for organic materials improves the mobility, which is a transistor characteristic, but this polymer has a dielectric breakdown strength. It is low and has the disadvantage that the stability of electrical characteristics is not sufficient, such as characteristic hysteresis, and it cannot be said that it is suitable as a material for the gate insulating film as it is (see Non-Patent Document 3). In addition, it has been reported that in a high dielectric constant film, the polarization of the polymer disturbs the interface of the organic semiconductor to cause the localization of carriers and lower the mobility (see Non-Patent Document 4).

  Furthermore, as an insulating film containing a metal oxide in a polymer, an example in which an insulating film having a high dielectric constant is prepared by dispersing particles of barium titanate in an epoxy resin has been reported (see Non-Patent Document 5). . Although the dielectric constant of this insulating film is as high as 40, this film itself has an organic electric field effect because barium titanate is a ferroelectric material and the surface of the insulating film is rougher than a normal polymer thin film. It is unlikely to be suitable as a gate insulating film of a transistor.

  On the other hand, examples of laminating an alignment film or laminating a fluoropolymer layer on an insulating layer for improving the surface properties of the insulating film have been reported (see Patent Documents 1 and 2). These are intended for controlling the solid state of the organic semiconductor film to be further laminated, for example, controlling the crystalline state or the alignment state of the liquid crystal.

In this way, it is an organic material insulating film that has a high dielectric constant that satisfies all of the requirements such as high voltage resistance, surface flatness, insulation strength, high resistance, and electric field stability, which are required for gate insulating films. The insulating film was not known.
Japanese Patent Laid-Open No. 9-232589 JP 2001-94107 A J. et al. Appl. Phys. 89, 9, 5125 (2001) PNAS 98, 9, 4835 (2001) Mol. Cryst. Liq. Cryst. 228, 81 (1993) Adv. Funct. Mater. , 13, 3, 199 (2003) Proc. Electon. Comp. Tech. Conf. , 48, 171 (1998)

  In an organic field effect transistor, although a gate insulating film plays an important role next to an organic semiconductor, a sufficiently practical material has not yet been found.

  Accordingly, there is a demand for an insulating film that can be formed by an easy process such as a coating method from a solution, and that has a high dielectric constant, high insulation resistance, surface flatness, and the like, and its material.

  In view of the above, as a result of various studies, it has been found that in an organic field effect transistor, a gate insulating film obtained by laminating a polymer film having a low dielectric constant on a polymer film having a high dielectric constant exhibits excellent characteristics. It came to.

  That is, the gist of the present invention is a laminated body including a high dielectric constant insulating film containing at least a polymer and a low dielectric constant insulating film containing a polymer in a transistor element using an organic semiconductor, The organic field effect transistor is characterized in that the dielectric constant difference between the dielectric constant insulating film and the high dielectric constant insulating film is larger than 1.

  According to the present invention, by laminating two or more kinds of thin films having a dielectric constant difference of 1 or more, an insulating film having high capacity, high insulation resistance, and flatness of the interface with the organic semiconductor can be produced.

  Hereinafter, embodiments of the present invention will be described in detail.

The organic field effect transistor (FET) of the present invention is an element that controls the current-voltage characteristics between the source and drain electrodes by controlling the carrier density in the semiconductor by the voltage applied to the gate voltage. For example, an element having the structure shown in FIG. Here, 1 is a semiconductor layer, 2 is an insulator layer, 3 and 4 are source and drain electrodes, 5 is a gate electrode, and 6 is a substrate.
(Gate insulation film)
The gate insulating film of the present invention is a laminate including at least a high dielectric constant insulating film containing a polymer and a low dielectric constant insulating film containing a polymer, and a dielectric between the low dielectric constant insulating film and the high dielectric constant insulating film. The rate difference is greater than 1.

The high dielectric constant insulating film contains a polymer and is not particularly limited as long as the difference in dielectric constant from the low dielectric constant insulating film is 1 or more, but the dielectric constant is larger than 6, preferably 7 or more, more preferably It is desirable that it is 10 or more, more preferably 15 or more. When the dielectric constant is 5 or less, the capacitance is small and the source / drain current becomes minute. In addition, in order to increase the capacitance with a low dielectric constant material, it is sufficient to reduce the thickness of the insulator layer. However, due to the appearance of defects and pinholes, the process surface during transistor fabrication is very difficult. Has the disadvantage of becoming.

There are several methods for increasing the dielectric constant of the high dielectric insulating film. One is to insert substituents having large polarization such as cyano group, nitro group, hydroxyl group, carbonyl and ester in the polymer.
Examples of such materials include main chain type or side chain type polymer liquid crystal resins such as cyano resins and polyarylate polymer liquid crystals such as Vectra (trade name of Ticona), and polymethyl methacrylate and the like. Acrylic resin, styrene resin such as polystyrene, polyvinylphenol, polyimide resin represented by Kapton (trade name, manufactured by Du Pont), polycarbonate resin, polyester resin, polyvinyl alcohol, polyvinyl acetate, polyurethane resin, polysulfone resin, epoxy resin, Examples thereof include polymers such as phenol resins and fluororesins, resins in which condensed resins having a heterocyclic ring such as polybenzoxazole and polybenzothiazole are combined, and copolymers in which these are combined.
Among these, a polymer containing a cyano group such as a cyano resin, a styrene resin such as polystyrene, a resin combining a polymer having a hydroxyl group such as polyvinyl phenol, polyvinyl alcohol, an epoxy resin, and a phenol resin, and a resin combining these are preferable.

As another method for increasing the dielectric constant of the high dielectric insulating film, low molecular liquid crystal compounds such as cyanobiphenyl, acrylic resins such as polymethyl methacrylate, styrene resins such as polystyrene, polyvinylphenol, and kapton Polyimide resin, polycarbonate resin, polyester resin, polyvinyl alcohol, polyvinyl acetate, polyurethane resin, polysulfone resin, epoxy resin, phenol resin, fluororesin and other polymers, and polybenzoxazole and polybenzothiazole condensed resins It is also possible to mix with a combined resin and a copolymer obtained by combining them.
Preferably, a low-molecular liquid crystal compound such as cyanobiphenyl is mixed with an acrylic resin such as polymethyl methacrylate, a resin combining polyvinyl phenol and a phenol resin, and a copolymer combining these.

Further, as another method for increasing the dielectric constant of the high dielectric insulating film, a structure containing more atoms having a larger atomic weight than carbon atoms, nitrogen atoms, and oxygen atoms can be cited. Examples thereof include typical elements such as sulfur, selenium, tellurium, phosphorus and germanium, transition metals such as copper, zinc, titanium, nickel and lead, and those containing rare earth such as yttrium, hafnium, zirconium, tantalum and lanthanum. Increasing the content of such atoms increases the dielectric constant accordingly. Moreover, as a method including such atoms, it is possible to introduce them into a polymer skeleton, or to mix or disperse these in a polymer with a solid having a large dielectric constant. For example, acrylic resin such as polymethyl methacrylate, styrene resin such as polystyrene, polyvinyl phenol, polyimide resin represented by Kapton (trade name of Du Pont), polycarbonate resin, polyester resin, polyvinyl alcohol, polyvinyl acetate, polyurethane resin, Polymers such as polysulfone resins, epoxy resins, phenol resins, fluororesins, resins combining heterocyclic resins such as polybenzoxazole and polybenzothiazole, cyano resins, liquid crystal polymers, and copolymers combining these , Al ₂ O ₃ , TiO ₂ , Y ₂ O ₃ , ScO ₃ , HfO ₂ , ZrO ₂ , Ta ₂ O ₅ , La ₂ O ₃ , GdO ₃ , SrTiO ₃ , BaTiO ₃ , SrBi ₂ Ta ₂ O ₉ , Pb (Zr _x Ti _1-x ) O ₃ , (Ba _x Sr _{1- x} ) TiO ₃ , Bi ₄ Ti ₃ O ₁₂ , BaMgF ₄ , SrBi ₂ (Ta _1-x N
b _x ) ₂ O ₉ , Ba (Zr _1-x Ti _x ) O ₃ , Bi ₄ Ti ₃ O _{12 and} other oxide films dispersed therein, Si ₃ N _{4 and} other nitride particles dispersed therein A polymer film etc. are mentioned.
Preferably, acrylic resin, styrene resin, polyvinyl phenol, polyvinyl alcohol, phenol resin, cyano resin, and a copolymer thereof are combined with Al ₂ O ₃ , TiO ₂ , Y ₂ O ₃ , ScO ₃ , HfO ₂ , ZrO. ₂ , Ta ₂ O ₅ , La ₂ O ₃ , GdO ₃ , SrTi
O ₃ , BaTiO ₃ , SrBi ₂ Ta ₂ O ₉ , Pb (Zr _x Ti _1-x ) O ₃ , (Ba _x Sr _1-x ) TiO ₃ , Bi ₄ Ti ₃ O ₁₂ , BaMgF ₄ , SrBi ₂ (Ta _1-x Nb _x ) ₂ O ₉ , Ba (Zr _1-x Ti _x ) O ₃ , Bi ₄ Ti ₃ O _{12 and} other polymer films dispersed therein.

The dielectric constant of a system in which inorganic particles having a high dielectric constant are dispersed contributes by the weight fraction of the inorganic particles contained. The higher the content, the higher the dielectric constant. However, if the content is too high, the mechanical properties deteriorate, and film formation by coating becomes difficult. The inorganic particles to be contained preferably have a high dielectric constant, and the relative dielectric constant is 5 or more, preferably 10 or more, more preferably 20 or more. The content is preferably 0.5% by weight or more, and more preferably 1% or more. The upper limit of the content is preferably 20% by weight or less, and desirably 15% or less. When there are too many inorganic particles, a film | membrane will become weak and intensity | strength will fall. Further, the diameter of the particles needs to be smaller than the film thickness to be formed, and in order to obtain a uniform film, 1/2 or less, more preferably 1/5 or less of the film thickness is desirable, and the actual dimension is 500 nm. Hereinafter, it is preferably 100 nm or less, more preferably 20 nm or less.
Moreover, 0.1 nm or more, preferably 0.5 nm or more, more preferably 1 nm or more is desirable.

  The material having a high dielectric constant is preferably a material that can be separately applied to the lower film and the upper film of the high dielectric insulating film so that they can be laminated by a coating process.

  The low dielectric constant insulating film contains a polymer and is not particularly limited as long as the difference in dielectric constant from the high dielectric constant insulating film is 1 or more, but the dielectric constant is preferably 5 or less, more preferably 3 .8 or less, more preferably 3.6 or less. If the dielectric constant is greater than 5, charges are likely to be accumulated near the semiconductor interface, which may cause problems in the stability of transistor characteristics.

  Materials used for the low dielectric constant insulating film include acrylic resins such as polymethyl methacrylate, styrene resins such as polystyrene, polyvinyl phenol, polyimide resins represented by Kapton, polycarbonate resins, polyester resins, polyvinyl acetate, polyurethane resins, Examples thereof include polymers such as polysulfone resin, epoxy resin, fluororesin, polysiloxane oxane and polysiloxane, and copolymers obtained by combining these polymers.

As the low dielectric constant insulating film, a polymer film in which an oxide such as SiO ₂ is dispersed in the above material can also be used.

  The material for the low dielectric constant insulating film is preferably a material that can be separately applied to the lower film and the upper film of the low dielectric insulating film so that they can be laminated by a coating process. Moreover, what shows a high mobility when combined with a semiconductor is preferable. Particularly preferred are polyimide resin, acrylic resin, polyvinylphenol, fluororesin, polycarbonate resin, and siloxane.

  In the present invention, the low dielectric constant insulating film containing a polymer has a dielectric constant difference larger than 1 with respect to the high dielectric constant insulating film. Preferably it is 2 or more. By laminating two or more kinds of thin films having a dielectric constant difference of 1 or more, an insulating film having high capacity, high insulation resistance, and flatness of the interface with the organic semiconductor can be produced. This is because charges can be prevented from being injected into the high dielectric constant film, and the surface roughness and surface properties derived from the high dielectric constant film can be improved. Therefore, if the difference in dielectric constant between the high dielectric constant insulating layer and the low dielectric constant insulating layer is smaller than 1, it is not preferable because the insulation resistance is lowered.

When the dielectric constant of the high dielectric constant layer is 10 or more, it is preferable to further increase the dielectric constant difference from the low dielectric constant insulating layer in order to stabilize the insulating layer. The dielectric constant is preferably 5 or less, more preferably 4 or less.
The dielectric constant of the insulating film is a value specific to the material. In the case of an insulating film composed of a single component, it is generally known, but in the case of a material composed of mixed components or a material whose dielectric constant is unknown, It can be measured using a known method. For example, the capacitance of the insulating layer is measured, and the dielectric constant can be obtained from the thickness of the insulating layer and the electrode area at that time.

  The film thickness of the high dielectric constant film is 5 μm or less, preferably 1 μm or less, more preferably 500 nm or less. Further, it is preferably 6 nm or more, more preferably 10 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more. If it is thicker than 5 μm, the capacitance of the transistor becomes small and the transistor characteristics deteriorate. If it is thinner than 6 nm, pinholes are easily formed and there is a problem in stability.

  The film having a low dielectric constant is 1 μm or less, preferably 500 nm or less. Moreover, 5 nm or more is preferable, More preferably, it is 10 nm or more, More preferably, it is desired that it is 50 nm or more. If it is thicker than 1 μm, the capacitance of the transistor becomes small and the transistor characteristics deteriorate. If the thickness is less than 5 nm, pinholes are easily formed, and there is a problem in stability. Here, in order not to lower the capacitance of the entire laminated film, the low dielectric constant film is preferably thinner than the high dielectric constant film, and the thickness of the high dielectric constant insulating layer is preferably 40% of the normal insulating film thickness. The above is more preferably 50%, more preferably 55% or more, and particularly preferably 60% or more. Most preferably, a thinner low dielectric constant film is laminated on a high dielectric constant film, and an organic semiconductor layer is formed thereon.

  When laminating the high dielectric constant insulating film and the low dielectric constant insulating film, they may be laminated in any order, or three or more layers may be laminated, but the layer configuration according to the purpose can be selected. it can. For example, when a layer using a polymer in which a metal oxide is dispersed is used as a high dielectric constant insulating film, it is desirable that a film having a low dielectric constant is further provided between this layer and the organic semiconductor. Further, when charge injection from the gate electrode to the high dielectric constant insulating film is a problem, it is preferable that a low dielectric constant insulating film is provided between the gate electrode and the high dielectric constant insulating film. Particularly preferably, the semiconductor layer and the low dielectric constant insulating layer are adjacent to each other.

  When laminating a high dielectric constant insulating film and a low dielectric constant insulating film, a lamination method, a lamination condition, and a lamination order are appropriately selected so that a film formed previously is not affected by a solvent for forming a film thereon. You can do that. Specifically, a method of laminating using the difference in solubility of materials, such as making a film to be formed later using a solvent that does not dissolve the previously formed film, curing the previously formed film with light or heat Or the method of laminating | stacking after bridge | crosslinking and converting into a film | membrane insoluble in a solvent, etc. are mentioned.

(Organic field effect transistor)
An organic semiconductor film is used for the organic field effect transistor of the present invention. The organic semiconductor is not particularly limited, but specifically, condensed aromatic hydrocarbons such as naphthacene, pentacene, pyrene, and fullerene, oligomers such as α-sexithiophene, and macrocyclic compounds such as phthalocyanine and porphyrin. Oligothiophenes represented by α-sexithiophene and dialkylsexithiophene, including four or more thiophene rings, or thiophene ring, benzene ring, fluorene ring, naphthalene ring, anthracene ring, thiazole ring, thiadiazole ring, Concatenated 4 or more benzothiazole rings. Condensed aromatic hydrocarbons such as naphthalene, pentacene, pyrene, perylene, fullerene; Condensed thiophenes such as anthradithiophene, dibenzothienobisthiophene, α, α′-bis (dithieno [3,2-b ′: 2 ′, 3′-d] thiophene) and derivatives thereof; Aromatic carboxylic acid anhydrides and imidized products thereof such as naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, and perylenetetracarboxylic acid diimide. Macrocyclic compounds such as copper phthalocyanine, perfluoro copper phthalocyanine, tetrabenzoporphyrin and metal salts thereof. Polythiophene, polyfluorene, polythienylene vinylene, polyphenylene vinylene, polyphenylene, polyacetylene, polypyrrole, polyaniline. In particular, those exhibiting self-organization such as regioregular polythiophene, and polymers exhibiting liquid crystallinity represented by polyfluorene and copolymers thereof are exemplified.

  In the case of the field effect transistor exemplified above, the thickness of the organic semiconductor film does not depend on the film thickness as long as the element characteristics are equal to or greater than the required film thickness. As the film thickness increases, the leakage current often increases. Therefore, a preferable film thickness is 1 nm or more, preferably 10 nm or more. Further, it is 10 μm or less, preferably 500 nm or less. In addition, the organic semiconductor can be used alone, but can also be used in a mixture with other materials, or can be used in a laminated structure with other layers.

  As the substrate of the organic field effect transistor of the present invention, a polymer plate, a film, glass, or a metal-coated insulating film formed by coating, a composite material of a polymer and an inorganic material, or the like can be used.

  An organic semiconductor film or an insulating film can be formed by a coating process or a vacuum process to manufacture a device. A coating process is preferred.

  Application methods include casting by simply dropping the solution and drying, coating methods such as spin coating, dip coating, blade coating, wire bar coating, spray coating, ink jet printing, screen printing, offset printing, letterpress printing, etc. A printing lithography method, a soft lithography method such as a microcontact printing method, and a combination of these methods can be used. Furthermore, as a technique similar to coating, a Langmuir-Blodgett method in which a monomolecular film formed on a water surface is transferred to a substrate and laminated, a liquid crystal or a melt state is sandwiched between two substrates, or introduced between substrates by capillary action A method etc. are also mentioned.

For film formation in a vacuum process, a vacuum deposition method in which an organic compound is placed in a crucible or a metal boat and heated in a vacuum to adhere to the substrate can be used. At this time, the degree of vacuum is 1 × 10 ⁻³ Torr or less, preferably 1 × 10 ⁻⁵ Torr or less. Further, since the device characteristics change depending on the substrate temperature, it is necessary to select an optimum substrate temperature, but a range of 0 ° C. to 200 ° C. is preferable. The deposition rate is 0.01 Å / second to 100 Å / second, preferably 0.1 Å / second to 10 Å / second. As a method for evaporating the material, a sputtering method in which ions such as accelerated argon collide can be used in addition to heating.

  The produced film can be improved in properties by post-treatment. For example, the heat treatment can relieve distortion in the film generated during film formation, and can improve and stabilize characteristics. Furthermore, a change in characteristics due to oxidation or reduction can be induced by exposure to an oxidizing or reducing gas or liquid such as oxygen or hydrogen. This can be used for the purpose of increasing or decreasing the carrier density in the film, for example.

Electrodes and wiring for manufacturing electronic devices include metals such as gold, aluminum, copper, chromium, nickel, cobalt, titanium, platinum, magnesium, calcium, barium, sodium, and conductive materials such as InO ₂ , SnO ₂ , and ITO. Oxides, polyaniline, polypyrrole, polythiophene, polyacetylene, polydiacetylene, and other conductive polymers, and acids such as hydrochloric acid, sulfuric acid, and sulfonic acid, Lewis acids such as PF ₆ , AsF ₅ , and FeCl ₃ , and halogens such as iodine Conductive material in which atoms, metal atoms such as sodium potassium are doped, semiconductors such as silicon, germanium, gallium arsenide, and the like, carbon materials such as fullerenes, carbon nanotubes, graphite, and metal particles are dispersed. Conductive materials such as composite materials are used. . As a method for forming them, a vacuum deposition method, a sputtering method, a coating method, a printing method, a sol-gel method, or the like can be used. The patterning method is also a photolithography method combining photoresist patterning and etching with an etchant or reactive plasma, ink-jet printing, screen printing, offset printing, letterpress printing and other printing methods, micro-contact printing method, etc. The soft lithography method and a combination of these methods can be used. It is also possible to directly produce a pattern by irradiating an energy beam such as a laser or an electron beam to remove the material or change the conductivity of the material.

  In the organic field effect transistor of the present invention, a protective film can be formed to minimize the influence of outside air. Examples thereof include polymer films such as epoxy resin, acrylic resin, polyurethane, polyimide, and polyvinyl alcohol, inorganic oxide films such as silicon oxide, silicon nitride, and aluminum oxide, and nitride films. Examples of the polymer film include a method of applying and drying a solution, and a method of polymerizing by applying or vapor-depositing a monomer, and it is also possible to form a crosslinking treatment or a multilayer film. For the formation of the inorganic film, a formation method using a vacuum process such as a sputtering method or a vapor deposition method, or a formation method using a solution process typified by a sol-gel method can be used.

  The organic field effect transistor of the present invention can be used as an active matrix switching element of a display. This utilizes the fact that the current between the source and drain can be switched by the voltage applied to the gate, so that the switch is turned on only when a voltage is applied to or supplied to a certain display element, and the circuit is disconnected at other times. By doing so, a high-speed, high-contrast display is performed.

  Examples of the display element to be applied include a liquid crystal display element, a polymer dispersed liquid crystal display element, an electrophoretic display element, an electroluminescent element, and an electrochromic element.

  In particular, the organic field effect transistor of the present invention can be manufactured by a low-temperature process, and a substrate such as a plastic substrate, a plastic film, or paper that cannot withstand high-temperature processing can be used. In addition, since the device can be manufactured by a coating or printing process, it is suitable for application to a large area display. Further, as an alternative to the conventional active matrix, it is advantageous as an element capable of an energy saving process and a low cost process.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
(Example 1)
A glass substrate (2.5 × 2.5 cm ² , manufactured by Furuuchi Chemical Co., Ltd .: trade name Pyrex (registered trademark)) is covered with a shadow mask having a width of 1 mm, and a vacuum deposition machine EX-400 (vacuum degree: 10 ⁻⁶ ) manufactured by Ulvac. Torr) was used to deposit aluminum with a thickness of 1000 mm to produce a gate electrode.

CYPPL (manufactured by Shinetsu co., Trade name: Cyanoresin CR-S, dielectric constant: 18.5) was dissolved in a mixed solvent of dimethylformamide (DMF): acetonitrile (1: 1 weight ratio) at a concentration of 5 wt%, and a 0.45 μm filter And filtered. 1 mL of this CEYPL solution was developed on a 2.5 × 2.5 cm ² glass substrate with a gate electrode, and 3500 r
Spin coating was performed for pm and 120 sec. Thereafter, polycarbonate / PC (manufactured by Aldrich, Mw = 64,000 (GPC method), dielectric constant 2.85) was dissolved in chloroform at a concentration of 5 wt% on this CEYPL layer, and filtered through a 0.45 μm filter. 1 mL of the polymer solution was developed, and spin coating was performed at 3000 rpm for 120 seconds. As a result of measuring the film thickness of each insulator layer with a film thickness meter (Alpha-Step 500: manufactured by Tencor), it was found that CEYPL: 4000 mm and PC: 4000 mm.

With respect to the substrate having the two-layer insulating film prepared above, pentacene (manufactured by Tokyo Chemical Industry, subjected to sublimation purification twice) as a semiconductor layer is a vacuum deposition machine EX-400 (vacuum degree: 10 ⁻⁶ ) manufactured by Ulvac. Torr) was deposited from the crucible at a rate of 1 kg / sec with a thickness of 1000 mm. In order to produce a source / drain electrode on this semiconductor layer, gold was deposited in a thickness of 1000 mm using a shadow mask of a channel (L: 1000 μm, W: 50 μm) to produce a top contact type organic transistor.

The transistor element produced above was measured with a semiconductor parameter analyzer 4155 manufactured by Agilent, and the current (I _ds ) _-voltage (V _ds ) characteristics between the source electrode and the drain electrode were measured under each gate voltage (V _g ). Then, a voltage-current curve was obtained and the transistor characteristics were evaluated. The measurement conditions were a source-drain voltage (V _ds ): 0 to −60 to 0 V and a gate voltage (V _g ): 30 to −60 V. Field effect mobility μ is about 0.12-
It was 0.3 cm ² / Vs.

(Example 2)
Example 1 is the same as Example 1 except that the PC of Example 1 is changed to polystyrene / PS (manufactured by Aldrich, Mw = 230,000 (GPC method), dielectric constant 2.6), and the coating solution is changed from a chloroform solution to toluene. Similarly, a top contact type organic transistor was fabricated. The film thickness of each insulator layer was found to be CEYPL: 4000 mm and PS: 3000 mm. The transistor characteristics are shown in Table 1.

(Example 3)
A top contact type organic material was obtained in the same manner as in Example 1 except that the PC of Example 1 was changed to polyvinyl cinnamate / PVCN (manufactured by Aldrich, Mw = 200,000 (GPC method), dielectric constant 3.8). A transistor was fabricated. The film thickness of each insulator layer was found to be CEYPL: 4000 mm and PVCN: 4000 mm. The transistor characteristics are shown in Table 1.

Example 4
In Example 3, a transistor element was fabricated in the same manner as in Example 3 except that the semiconductor was changed from pentacene to tetrabenzoporphyrin to be a semiconductor in the coating process and heated at 180 ° C. for 10 minutes. The transistor characteristics are shown in Table 1.

(Example 5)
In Example 3, the semiconductor was changed from pentacene to poly (3-hexylthiophene-2,5-diyl): P3HT, Regioregular (manufactured by Aldrich, Mw = 87,000 (GPC method)) which becomes a semiconductor in the coating process. A transistor element was fabricated in the same manner as in Example 3. The transistor characteristics are shown in Table 1.

(Example 6)
In Example 1, CEYPL was changed to polyvinyl alcohol / PVA (—OH, 99%, manufactured by Aldrich, Mw = 50,000 (GPC method), dielectric constant 7.8), and the coating solution was pure water at a concentration of 10 wt%. Was changed to a mixed solvent of n-propanol (1: 1 weight ratio), spin-coated, and dried for 48 hours under a reduced pressure of 10 ⁻⁴ Torr. In addition, the PC of Example 1 was changed to polyvinyl cinnamate / PVCN (manufactured by Aldrich, Mw = 200,000 (GPC method), dielectric constant 3.8), and the spin coat speed was changed to 3500 rpm. A transistor element was fabricated in the same manner as in Example 1. The film thickness of each insulating layer was found to be PVA: 4000 mm and PVCN: 4000 mm. Table 1 shows the properties of the transistor.

(Comparative Example 1)
In Example 1, a transistor element was formed in the same manner as in Example 1 except that the insulating film was changed from the two layers of CEYPL and PC to a CEYPL single layer. The thickness of the CEYPL layer was found to be 4000 mm. Table 1 shows the properties of the transistor. As for the transistor performance, in the CIEPL single layer having a large dielectric constant, I _ds has a large capacitance component, so a large current flows, but a very large hysteresis is observed, and the variation in transistor characteristics is remarkable. The field effect mobility μ was about 0.12 to 0.3 cm ² / Vs.

(Comparative Example 2)
In Example 1, a transistor element was fabricated in the same manner as in Example 1 except that the insulating film was changed from CYPPL and PC to a PC single layer. The thickness of the PC layer was 4000 mm. Table 1 shows the properties of the transistor. As transistor performance, I _ds was lower than that of Example 1 because the electrostatic capacitance component was small. No hysteresis was observed in the I _ds -V _ds characteristics when applying / removing the V _g voltage. The field effect mobility μ is about 0.12 to 0.3 cm ^2.
/ Vs.

In the CEYPL / PC laminated film of Example 1, a larger I _ds than that of the PC alone is observed and the hysteresis derived from CEYPL is observed although the film thickness increases and the capacitance decreases due to the lamination. Was not.

(Comparative Example 3)
In Example 2, a transistor element was formed in the same manner as in Example 2 except that the insulating film was changed from the CYPPL and PS two layers to the PS single layer. The thickness of the PS layer was 3000 mm. Table 1 shows the properties of the transistor. As for transistor performance, I _ds was lower than that of Example 2 because the capacitance component was small. No hysteresis was observed in the I _ds -V _ds characteristics when applying / removing the V _g voltage. The field effect mobility μ is about 0.12 to 0.3 cm ^2.
/ Vs.

(Comparative Example 4)
In Example 3, a transistor element was produced in the same manner as in Example 3 except that the insulating film was changed from the two layers of CEYPL and PVCN to a single layer of PVCN. The film thickness of the PVCN layer was 4000 mm. Table 1 shows the properties of the transistor. As transistor performance, I _ds was lower than that of Example 3 because the capacitance component was small. No hysteresis was observed in the I _ds -V _ds characteristics when applying / removing the V _g voltage. The field effect mobility μ is about 0.12 to 0.12.
It was 0.3 cm ² / V _s .

(Comparative Example 5)
In Example 4, a transistor element was fabricated in the same manner as in Example 4 except that the insulating film was changed from the two layers of CEYPL and PVCN to a CEYPL single layer. The film thickness of the PVCN layer was 4000 mm. Table 1 shows the properties of the transistor. As for transistor performance, a large current flows because I _ds has a large capacitance component, but very large hysteresis was observed, and variation in transistor characteristics was remarkable. I _ds in applying and removing V _g voltage
No hysteresis was observed in the −V _ds characteristic. The field effect mobility μ was about 0.02 to 0.04 cm ² / V _s .

(Comparative Example 6)
In Example 4, a transistor element was formed in the same manner as in Example 4 except that the insulating film was changed from the two layers of CEYPL and PVCN to a single layer of PVCN. The film thickness of the PVCN layer was 4000 mm. Table 1 shows the properties of the transistor. As for transistor performance, I _ds was lower than that of Example 4 because the capacitance component was small. No hysteresis was observed in the I _ds -V _ds characteristics when applying / removing the V _g voltage. The field effect mobility μ is about 0.02 to 0.02.
It was 0.04 cm ² / V _s .

(Comparative Example 7)
In Example 5, a transistor element was produced in the same manner as in Example 4 except that the insulating film was changed from CYPPL and PVCN to a CEYPL single layer. The film thickness of the PVCN layer was 4000 mm. Table 1 shows the properties of the transistor. As for transistor performance, a large current flows because I _ds has a large capacitance component, but very large hysteresis was observed, and variation in transistor characteristics was remarkable. No hysteresis was observed in the I _ds -V _ds characteristics when applying / removing the V _g voltage. The field effect mobility μ is about 0.01 to
It was 0.02 cm ² / V _s .

(Comparative Example 8)
In Example 5, a transistor element was fabricated in the same manner as in Example 4 except that the insulating film was changed from the two layers of CEYPL and PVCN to a single layer of PVCN. The film thickness of the PVCN layer was 4000 mm. Table 1 shows the properties of the transistor. As transistor performance, I _ds was lower than that of Example 5 because the capacitance component was small. No hysteresis was observed in the I _ds -V _ds characteristics when applying / removing the V _g voltage. The field effect mobility μ is about 0.01 to
It was 0.02 cm ² / V _s .

(Comparative Example 9)
In Example 6, a transistor element was formed in the same manner as in Example 6 except that the insulating film was changed from the two layers of PVA and PVCN to a single layer of PVA. The film thickness of the PVCN layer was 4000 mm. Table 1 shows the properties of the transistor. As for transistor performance, a large current flows because I _ds has a large capacitance component, but very large hysteresis was observed, and variation in transistor characteristics was remarkable. I _ds -V _ds in applying / removing V _g voltage
No hysteresis was observed in the characteristics. The field effect mobility μ was about 0.12 to 0.3 cm ² / V _s .

It is a figure which shows the organic electrolysis effect transistor of this invention. 4 is a diagram illustrating a voltage-current curve of a transistor in Example 1. FIG. 6 is a diagram illustrating a voltage-current curve of a transistor in Comparative Example 1. FIG. 10 is a diagram illustrating a voltage-current curve of a transistor in Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic-semiconductor layer 2 Insulator layer 3 Source or drain electrode 4 Source or drain electrode 5 Gate electrode 6 Support substrate

Claims (6)

In a transistor element using an organic semiconductor, a gate insulating film is a laminated body including a high dielectric constant insulating film containing at least a polymer and a low dielectric constant insulating film containing a polymer, the low dielectric constant insulating film and the high dielectric constant An organic field effect transistor having a dielectric constant difference greater than 1 with respect to a dielectric constant insulating film. 2. The organic field effect transistor according to claim 1, wherein the dielectric constant of the low dielectric constant insulating film is 5 or less. The organic field effect transistor according to claim 1 or 2, wherein the high dielectric constant insulating film has a thickness of 6 nm or more. 4. The organic field effect transistor according to claim 1, wherein the high dielectric constant insulating film has a thickness of 5 [mu] m or less. The organic field effect transistor according to any one of claims 1 to 4, wherein the low dielectric constant insulating film has a thickness of 5 nm or more. 6. The organic field effect transistor according to claim 1, wherein the low dielectric constant insulating film has a thickness of 1 μm or less.

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