JP2010074188A - Field-effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible high-performance organic field-effect transistor manufacturable inexpensively through a simple process by combining a specific plastic substrate with a specific resin insulation layer. <P>SOLUTION: The organic field-effect transistor includes, on an insulating support substrate 1, the insulation layer 3, a gate electrode 2 and an organic semiconductor layer 4 isolated from each other by the insulation layer 3, and a source electrode 5 and a drain electrode 6 formed to contact the semiconductor layer 4. The insulating support substrate 1 is formed of polyethylene terephthalate. The insulation layer 3 is formed of one or more kinds selected among polystyrene, polyvinyl phenol, polycarbonate, polyester, polyvinyl acetate, polyurethane, polysulfone, methacrylic resin, epoxy resin, hydrocarbon resin having a cyano group, and phenol resin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a field effect transistor using an organic semiconductor.

  Field effect transistors are widely used as important switches and amplifying elements along with bipolar transistors. A field effect transistor has a structure in which a source electrode and a drain electrode are provided in a semiconductor material, and a gate electrode is provided via an insulator layer. The operational characteristics of the field effect transistor are as follows: carrier mobility μ, electric conductivity σ of the semiconductor used, capacitance Ci of the insulating layer, device configuration (source electrode-drain electrode distance L and width W, insulating layer film) Among them, the semiconductor material having a high mobility (μ) exhibits good characteristics.

  Currently, silicon is widely used as a semiconductor material. Inorganic semiconductors typified by silicon need to be processed at a high temperature of 300 ° C. or higher at the time of production, so that it is difficult to use a plastic substrate or film for the substrate, and a lot of energy is required for production. is there. In addition, since the device manufacturing process is performed in a vacuum, an expensive facility is required for the production line, and there is a disadvantage that the cost is increased.

  On the other hand, since most transistors using organic semiconductors can be manufactured at a lower temperature than inorganic semiconductors, plastic substrates and films can be used as substrates, and light-weight and hard-to-break devices are produced. Can do. In recent years, an attempt has been made to give flexibility to the entire element by using a resin as an insulator layer formed on such a plastic substrate. Depending on the type of insulating film, some devices can be manufactured using a solution coating or printing method, and a large-area device can be manufactured at low cost. Furthermore, since there are a wide variety of materials, and it is possible to easily change the material characteristics easily by changing the molecular structure, functions and elements that are impossible with inorganic semiconductors by combining different functions Can also be realized.

  Regarding a transistor using an organic semiconductor as a semiconductor, Patent Document 1 describes a transistor using a conductive polymer and a conjugated polymer, and Patent Document 2 describes a transistor using a low molecular compound. .

  A typical structure of a transistor using an organic semiconductor as a conventional semiconductor is shown in FIGS.

  In the field effect transistor of FIG. 1, a gate electrode 2 is provided on an insulating support substrate 1, and an insulator layer 3 and an organic semiconductor layer 4 are further provided thereon. A source electrode 5 and a drain electrode 6 are provided on the insulator layer 3 so as to be in contact with the organic semiconductor layer 4. This field effect transistor is called a bottom gate / bottom contact type.

  The field effect transistor of FIG. 2 is different from the field effect transistor shown in FIG. 1 in that a source electrode 5 and a drain electrode 6 are provided on an organic semiconductor layer 4 on an insulator layer 3. It is made up of. This field effect transistor is called a bottom gate / top contact type.

  In the field effect transistor shown in FIG. 3, the source electrode 5 and the drain electrode 6 are provided on the insulating support substrate 1, and the organic semiconductor layer 4 and the insulator layer 3 are stacked on the insulating support substrate 1. A gate electrode 2 is provided on the insulator layer 3. This field effect transistor is called a top gate / bottom contact type.

  In such a field effect transistor, when a voltage is applied to the gate electrode 2, the carrier density of the organic semiconductor layer in the vicinity of the interface between the organic semiconductor layer 4 and the insulator layer 3 is changed and the source-drain electrodes 5, 6 are changed. The amount of current flowing between them is changed.

  In addition, studies on the charge transport phenomenon in the organic semiconductor layer of the field effect transistor using such an organic semiconductor have been conducted. For example, in an oligothiophene in which several thiophene rings are connected, the molecular axis is slightly inclined from the perpendicular to the insulator layer, and the π orbitals of the oligothiophene are mutually opposite to the source electrode-drain electrode direction. The arranged oligothiophene molecule layers are stacked in a direction perpendicular to the insulator layer to form an oligothiophene organic semiconductor layer (Non-patent Document 1). Since the induced charge due to the gate electrode moves between the source electrode and the drain electrode through the interacting π orbit, it is desirable to strengthen the π orbit interaction between the oligothiophene molecules in order to obtain high mobility.

  Furthermore, when the bottom contact field effect transistor using the oligothiophene semiconductor layer is operated, the induced charge is moved in one to two or three oligothiophene molecular layers above the insulator layer. It has been suggested (Non-Patent Document 2).

  By the way, as for what conventionally formed the resin-made insulator layer on the plastic substrate of such an organic field effect transistor, the example which used the polyimide as an insulator layer for the board | substrate which consists of a polyethylene terephthalate (PET), for example is used. This is disclosed in Patent Document 3. However, although polyimide is generally excellent in heat resistance and flexibility, it is difficult to achieve flatness when formed on an insulating film, poor in transparency, and requires a high temperature process when forming an insulating film. However, there are problems such as damage to the characteristics of the PET substrate and unfavorable industrial conditions due to severe manufacturing conditions.

  On the other hand, Non-Patent Document 3 discloses a transistor in which polyvinyl alcohol (PVA) is formed as an insulating film on a substrate made of PET. However, PVA has high hygroscopicity and is stable in manufacturing and transistor performance in air. There is a problem with sex.

  Thus, at present, an appropriate resin-based insulator layer formed on the PET substrate has not yet been proposed.

  Furthermore, depending on the type of plastic substrate or resin insulating film, the material of wiring and electrodes is also important as a constituent material of organic field-effect transistors or display drive circuits using them, but it can be made flexible at low cost. There have not been sufficient studies on wiring / electrode materials suitable for excellent organic field-effect transistors and their formation processes.

  For example, in the case of ITO, formation by a vacuum process such as sputtering results in high costs as described above, and in wiring / electrode formation by a printing method using ITO fine particles, sufficient electric conductivity is obtained. However, since a high temperature treatment is required after printing, there is a drawback that a plastic substrate cannot be used. In addition, a metal having a small work function such as aluminum is easily oxidized in the air, so that it is formed in an environment where there is no influence of oxygen, and the entire element must be sealed even after formation. Exists.

  Furthermore, in the case of functioning as an organic field-effect transistor having excellent flexibility, the entire element is required when the flexibility of the insulating layer or organic semiconductor layer is poor, even if only the plastic substrate is excellent in flexibility. However, it is considered that the organic field effect transistor excellent in flexibility does not function, but in the past, these have not been sufficiently studied.

JP-A 61-202469 Japanese Patent No. 2984370 JP 2001-230421 A

ADVANCED MATERIALS, Vol. 12, No. 14, pp. 1046-1050, 2000 SCIENCE, Vol.268, No.14, 270-271, 1995 SID 01 DIGEST page 57

  Various studies have been made on the charge transport phenomenon in the organic semiconductor of the organic field effect transistor as described above, and some of the high mobility has been achieved, but in the organic field effect transistor excellent in flexibility at low cost, the substrate, Depending on the type of insulator layer, electrode, wiring, or organic semiconductor, and their various physical properties, the performance as a field effect transistor (mobility, leakage current value, on / off ratio, etc.) is affected and is not constant. It was.

  In addition, by adopting a resin insulator layer for the insulating support substrate, it is possible to give flexibility to the field effect transistor, and it is possible to reduce the cost, diversification, and multifunctionality of the element. Although it is possible, as described above, a resin insulator layer that is excellent in transparency, heat resistance, flatness, and other characteristics has not been provided.

  The present invention has been made in view of the above-described conventional situation. By optimizing the combination of the insulating support substrate and the resin insulator layer, the present invention has flexibility and is low in cost by a simple process. It is an organic field effect transistor that can be manufactured at the same time, and it is an object to provide an organic transistor that can achieve higher mobility and a high on / off ratio and has stable transistor performance.

  The field effect transistor of the present invention includes an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided in contact with the organic semiconductor layer, and an insulating support In the field effect transistor having a substrate, the insulating support substrate is made of polyethylene terephthalate, and the insulator layer is made of polystyrene, polyvinylphenol, polycarbonate, polyester, polyvinyl acetate, polyurethane, polysulfone, (meth) acrylic resin, The main component is one or more resins selected from the group consisting of epoxy resins, hydrocarbon resins having a cyano group, phenol resins, and copolymer resins containing monomer components constituting these resins. It is characterized by.

  As a result of intensive studies on the instability of transistor performance in conventional field effect transistors, the present inventors have found polystyrene, polyvinylphenol, polycarbonate, polyester, polyvinyl acetate, polyurethane, polysulfone, (meth) acrylic resin as an insulator layer, If one or more of epoxy resins, hydrocarbon resins having a cyano group, phenol resins, and copolymer resins containing monomer components constituting these resins are used, transparency, heat resistance, insulating film As a result, the inventors have found that problems such as flatness when formed as a low temperature, low-temperature manufacturing process, and compatibility with conductive oxide electrodes such as ITO electrodes can be solved in a well-balanced manner. In addition, by optimizing flexibility without sacrificing capacitance and insulation when formed as an insulating film, it is possible to suppress cracks and the like from entering the insulator layer when the organic field effect transistor is bent. As a result, the inventors have found that the increase in leakage current can be suppressed, and consequently the reduction in the on / off ratio can be suppressed, and the present invention has been achieved.

  And, since the surface of the insulator layer formed using such a material is flat, the disorder of the molecular arrangement of the organic semiconductor on the side in contact with the insulator layer is prevented, and this disorder is caused. An element capable of exhibiting good transistor performance without disturbing the arrangement of each layer of organic semiconductor molecules stacked on top of this, the deterioration of π orbital interaction between organic semiconductor molecules, the adverse effect on the movement of induced charges, etc. It was found that can be configured.

  In other words, in the organic field effect transistor of the present invention, the combination of the insulating support substrate and the insulator layer, and the insulating support substrate and the insulator layer are both made of resin, the physical property of flexibility in the flexible display. In addition to satisfying the required characteristics, the manufacturing process is simple and low-cost, and the flatness of the surface of the insulator layer improves the above-mentioned adverse effects on the organic semiconductor, resulting in high mobility and high on-state. Current and low leakage current, high on / off ratio are achieved.

  According to the field effect transistor of the present invention, an organic field effect that is flexible and can be manufactured at a low cost by a simple process by combining a specific plastic substrate and a specific resin insulator layer. A transistor is provided. In the field effect transistor of the present invention, due to the flatness of the surface of the insulator layer, the disorder of the arrangement of organic semiconductor molecules to which the induced charge moves is effectively suppressed, and higher mobility, high on-current and low leakage current are achieved. In addition, a field effect transistor having a high on / off ratio can be provided.

It is sectional drawing which shows the structural example of a field effect transistor. It is sectional drawing which shows the structural example of a field effect transistor. It is sectional drawing which shows the structural example of a field effect transistor. 3 is a graph showing transistor characteristics (voltage-current curve) of the transistor element manufactured in Example 1. FIG. 6 is a graph showing transistor characteristics (voltage-current curve) of the transistor element manufactured in Example 2. 10 is a graph showing transistor characteristics (voltage-current curve) of the transistor element manufactured in Example 3. 10 is a graph showing transistor characteristics (voltage-current curve) of the transistor element manufactured in Example 4. 10 is a graph showing transistor characteristics (voltage-current curve) of the transistor element manufactured in Example 5. 5 is a graph showing transistor characteristics (voltage-current curve) of the transistor element manufactured in Comparative Example 1.

  Embodiments of a field effect transistor according to the present invention will be described below in detail with reference to the drawings.

  The field effect transistor of the present invention has an insulating layer, a gate electrode and an organic semiconductor layer separated by the insulating layer, and a source electrode and a drain electrode provided in contact with the organic semiconductor layer. The structure is provided on the support substrate, and there is no particular limitation on the structure. The bottom gate / bottom contact type shown in FIG. 1, the bottom gate / top contact type shown in FIG. 2, and the top gate / bottom contact type shown in FIG. Etc.

  In the present invention, in such a field effect transistor, a polyethylene terephthalate (PET) substrate is used as the insulating support substrate 1, and the insulator layer 3 is made of polystyrene, polyvinylphenol, polycarbonate, polyester, polyvinyl acetate, polyurethane, polysulfone. , (Meth) acrylic resin, epoxy resin, hydrocarbon resin and phenol resin having a cyano group, and one or more selected from the group consisting of copolymer resins containing monomer components constituting these resins It is comprised with the resin composition which has resin as a main component.

  As the PET substrate, a known resin product such as MYLAR (manufactured by Dupont) can be used. The thickness of the PET substrate is preferably 0.05 mm to 2 mm, more preferably 0.1 mm to 1 mm.

  Polystyrene, polyvinylphenol, polycarbonate, polyester, polyvinyl acetate, polyurethane, polysulfone, (meth) acrylic resin, epoxy resin, hydrocarbon resin having cyano group and phenolic resin constituting the insulator layer should be known ones. Can do. Examples of the hydrocarbon resin having a cyano group include polysaccharides having a cyano group such as cyanopullulan. Moreover, the copolymer which consists of 2 or more types of the monomer component which comprises these resin may be sufficient. Also, two or more of these resins can be used in combination.

  Preferable materials constituting the insulator layer are polystyrene, polyvinylphenol, polycarbonate, (meth) acrylic resin (acrylic resin, methacrylic resin), epoxy resin, hydrocarbon resin having a cyano group, and phenolic resin. Furthermore, polystyrene, polyvinylphenol, polycarbonate, (meth) acrylic resin, hydrocarbon resin having a cyano group and phenol resin are preferable, and hydrocarbon resin having a cyano group is particularly preferable from the viewpoint of a high dielectric constant insulating material. Preferably, polyvinylphenol and a phenol resin are preferable from the viewpoint that the substrate and the organic semiconductor layer are attacked in the transistor lamination application step, and the insulating layer is not affected by the substrate and the organic semiconductor layer.

  As a method for forming the insulator layer, there is a formation method that matches the characteristics of the material, such as a coating method such as spin coating or blade coating, a vapor deposition method, a sputtering method, a printing method such as screen printing, ink jet, or electrostatic image development method. Can be adopted.

  In addition, when a photo-curing resin that forms an insulator by applying a monomer as a precursor of the insulator and then curing by irradiation with light is used, the surface average roughness can be easily adjusted to a desired small value. It is preferable in that

Since the insulator layer formed in this manner is related to leakage current to the gate electrode and low gate voltage driving of the field effect transistor, the electrical conductivity at room temperature is 10 ⁻¹² S / cm or less, It is preferable that it is 10 ⁻¹⁴ S / cm or less and the relative dielectric constant is 2.0 or more, more preferably 2.5 or more.

  The thickness of such an insulator layer is preferably 0.1 μm to 4 μm, and more preferably 0.2 μm to 2 μm.

  In the present invention, the average roughness (Ra) of the interface between the insulator layer 3 and the organic semiconductor layer 4 is preferably 50 nm or less, more preferably 40 nm or less, still more preferably 30 nm or less, and particularly preferably 20 nm. Hereinafter, it is particularly preferable that the thickness is 10 nm or less. The average roughness of the interface is preferably as small as possible, but is 0.1 nm or more from the viewpoint of feasibility of the film formation method of the insulator layer 3 and the organic semiconductor layer 4, and is usually 0.2 nm or more. 0.5 nm or more.

  In the present invention, by reducing the average roughness (Ra) of the interface between the insulator layer 3 and the organic semiconductor layer 4 in this way, the organic semiconductor molecules in the region where the induced charges due to the gate electrode 2 move are moved. Prevent disturbance of the array. Therefore, it is sufficient that such average roughness is satisfied at least in a region corresponding to the gate electrode 2 in the interface between the insulator layer 3 and the organic semiconductor layer 4, and the average roughness is not necessarily in the entire surface of the interface. It need not be 50 nm or less.

  Thus, in order to make the average roughness of the interface between the insulator layer 3 and the organic semiconductor layer 4 50 nm or less, the organic semiconductor layer 4 is formed on the insulator layer 3 as shown in FIGS. In the case of the formed field effect transistor, the organic semiconductor layer 4 is formed after the surface average roughness of the upper surface of the insulator layer 3 on which the organic semiconductor layer 4 is stacked is formed to be 50 nm or less. Just do it. In the case of a field effect transistor in which the insulator layer 3 is formed on the organic semiconductor layer 4 as shown in FIG. 3, the surface of the upper surface of the organic semiconductor layer 4 on which the insulator layer 3 is stacked. After the average roughness is 50 nm or less, the insulator layer 3 may be formed.

  Thus, there is no restriction | limiting in particular as a method of controlling the surface average roughness of the upper surface of the insulator layer 3 or the organic-semiconductor layer 4 to 50 nm or less, The film-forming material of an insulator layer or an organic-semiconductor layer, film-forming speed, etc. A smooth surface layer having a small surface average roughness may be formed by appropriately selecting and adjusting the film forming conditions, film thickness, and the like. For example, it is possible to employ a method in which a photocurable resin is used as a material for forming the insulator layer, an uncured coating film is formed, and then the photocurable resin is cured by irradiation with light. Before irradiating with light, a smooth surface transparent plate made of a material having no adhesiveness to the photo-curable resin and good releasability, such as a glass plate, is placed on the coating film and applied in this state. If the method of irradiating the film with light to cure the photocurable resin is adopted, the smooth surface of this plate is transferred to the surface of the resulting cured film, and the surface smooth cured film having a small surface average roughness. Can be formed.

  As a means for confirming whether or not the average roughness of the interface between the insulator layer and the organic semiconductor layer is within the above range, the average roughness on the insulator layer or the organic semiconductor layer in the process of producing the field effect transistor is used. May be confirmed to be 50 nm or less, and an insulating layer or an organic semiconductor layer, which is an upper layer formed on the interface of interest in the present invention, is maintained from the manufactured device. However, it may be peeled off and the average roughness may be confirmed. In the case where the insulator layer or organic semiconductor layer, which is the upper layer formed on the interface of interest in the present invention, is a thin film of 1 μm or less, for example, the surface roughness of the upper layer is determined in the present invention. Since the average roughness of the interface of interest is substantially represented, this average roughness of the upper layer can be used as a measure of the roughness of the interface.

  The average roughness (Ra) of the interface between the insulator layer and the organic semiconductor layer is a value measured by the tapping mode of AFM (Atomic Force Microscope). The observation range is between 2 μm square.

  In the present invention, the constituent materials other than the insulating support substrate and the insulator layer of the field effect transistor are not particularly limited, and any of those applied to the conventional field effect transistor can be suitably used.

The constituent material of the gate electrode, the source electrode, and the drain electrode may be any material as long as it exhibits conductivity, and any known material can be used. For example, platinum, gold, aluminum, chromium, nickel, copper, titanium, magnesium Conductive materials such as metals such as calcium, barium and sodium, conductive oxides such as InO ₂ , SnO ₂ and ITO, polyaniline doped with camphorsulfonic acid, polyethylenedioxythiophene doped with paratoluenesulfonic acid, etc. Conductive polymer with good conductivity, doped with conductivity-imparting parts, carbon black, metal fine particles, conductive fine particles such as graphite powder dispersed in binder, etc. Is mentioned.

  Examples of the method for forming the gate electrode, the source electrode, and the drain electrode include a vacuum deposition method, a sputtering method, a coating method, a printing method, a sol-gel method, and the like. Photolithographic methods that combine etching with neutral plasma, printing methods such as ink jet printing, screen printing, offset printing, letterpress printing, soft lithography methods such as microcontact printing methods, and methods that combine these methods. Can be mentioned. 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 changing the conductivity of the material.

  The thickness of these gate electrode, source electrode, and drain electrode is preferably 0.01 μm to 2 μm, and more preferably 0.02 μm to 1 μm.

  The distance between the source electrode and the drain electrode (channel length L) is usually 100 μm or less, preferably 50 μm or less, the channel width W is usually 2000 μm or less, preferably 500 μm or less, and L / W is usually 0.1. Hereinafter, it is preferably 0.05 or less.

  The organic semiconductor that forms the organic semiconductor layer is not particularly limited, and any known one can be used as long as it is a π-conjugated low molecular weight or high molecular weight compound. For example, pentacene, oligothiophene, oligothiophene having a substituent, Bisdithienothiophene, substituted dialkylanthradithiophene, metal phthalocyanine, benzoporphyrin, fluorine-substituted copper phthalocyanine, N, N'-dialkyl-naphthalene-1,4,5,8-tetracarboxylic acid diimide substitution product , Π-conjugated small molecules such as 3,4,9,10-perylenetetracarboxylic acid dianhydride, N, N′-dialkyl-3,4,9,10-perylenetetracarboxylic acid diimide, fullerene, and regioregular poly ( Regioregular poly (3) represented by 3-hexylthiophene) Π-conjugated polymers such as π-conjugated copolymers such as -alkylthiophene) and poly-9,9'-dialkylfluorenecobithiophene.

Among these π-conjugated low molecules and polymers, when an organic semiconductor layer is formed, the electric conductivity in the source electrode-drain electrode direction is 10 ⁻⁴ S / cm or less and 10 ⁻¹² S / cm or more. In particular, those exhibiting 10 ⁻⁶ S / cm or less, 10 ⁻¹¹ S / cm or more, particularly 10 ⁻⁷ S / cm or less, or 10 ⁻¹⁰ S / cm or more are more preferable. Furthermore, among these π-conjugated low molecules and polymers, when an organic semiconductor layer is formed, the carrier density obtained from the field effect mobility, the electric conductivity in the direction of the source electrode and the drain electrode, and the elementary charge amount is 10 ⁷ cm ^-3 or ^more, preferably one showing a 10 18 ^{cm -3} or less, in particular ¹⁰ 8 ^{cm -3} or ^more, more preferably shows a 10 17 ^{cm -3} or less. Among these π-conjugated low molecules and polymers, when the organic semiconductor layer is formed, the activation energy required for charge transfer required from the temperature dependence of the field effect mobility at room temperature or less is 0.2 eV or less. In particular, those showing 0.1 eV or less are more preferred.

  Furthermore, among these π-conjugated low molecular weight molecules having a molecular length of 40 mm or less, when an organic semiconductor layer is formed on the same insulator layer as that used in the field effect transistor, In polarized light absorption measured by inserting incident light from an angle of 60 ° with respect to the normal, the ratio of the p-polarized component and the s-polarized component of the absorption peak intensity derived from the transition moment in the molecular axis direction of these π-conjugated low molecules The p-polarized light component / s-polarized light component having a characteristic of showing 1.5 or more, further 2.0 or more, particularly 3.0 or more is preferable.

  On the other hand, when the organic semiconductor layer is formed on the same insulator layer as the insulator layer used in the field effect transistor in the case of a π-conjugated polymer having a molecular length larger than 40 cm, the light enters the surface of the layer from the vertical direction. In polarized light absorption measured by putting light, the ratio of the source electrode-drain electrode direction component of the absorption peak intensity derived from the transition moment in the main chain direction of these π-conjugated polymers to the source electrode-drain which is the ratio of the vertical direction component thereto Those having a characteristic that the electrode direction component / vertical direction component is 3.5 or more, further 4.5 or more, and particularly 5.0 or more are preferable.

  Furthermore, among these π-conjugated low molecules and polymers, when an organic semiconductor layer is formed on the same insulator layer as the insulator layer used in the field effect transistor, the distance between the nearest neighbor molecules or polymers. Is preferably 3.9 特性 or less, more preferably 3.85 Å or less, and particularly 3.8 示 す or less.

  The film thickness of such an organic semiconductor layer is preferably 1 nm to 10 μm, and more preferably 10 nm to 500 nm.

  As a method of forming an organic semiconductor layer using these organic semiconductors, in the case of a low molecular organic semiconductor, a method of forming by vapor deposition on an insulator layer or an insulating support substrate by vacuum vapor deposition, or dissolving in a solvent. And a method of coating and forming by casting, dipping, spin coating and the like. In the case of a high molecular organic semiconductor, a method in which it is dissolved in a solvent and applied by casting, dipping, spin coating or the like can be used. In addition, a method of forming a layer by the above-described appropriate method using a target low molecular precursor or a target polymer precursor, and then converting it to a target organic semiconductor layer by heat treatment or the like can also be mentioned. Furthermore, since the top gate / bottom contact type field effect transistor shown in FIG. 3 requires the surface smoothness of the upper surface of the organic semiconductor layer as described above, in this case, the deposition is performed under high vacuum particularly in the vacuum deposition method. In the coating method in which vapor deposition is performed with the speed reduced as much as possible, it is effective to form a film by spin coating at high speed rotation after appropriately adjusting the viscosity.

  The basic structure of the field effect transistor of the present invention includes an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, and a source electrode and a drain electrode provided in contact with the organic semiconductor layer. On the insulating support substrate, and the specific structure thereof is as shown in FIGS. 1 to 3, but the field effect transistor of the present invention has the structure shown in FIGS. It is not limited to the field effect transistor, and layers other than those shown in FIGS. 1 to 3 may be formed.

  For example, in the case of a field effect transistor exposed by an organic semiconductor layer, such as the field effect transistor shown in FIGS. 1 and 2, further protection is provided on the organic semiconductor layer to minimize the influence of outside air on the organic semiconductor. A film may be formed. In this case, as a material for the protective film, polymers such as epoxy resin, acrylic resin, polyurethane, polyimide, and polyvinyl alcohol, inorganic oxides such as silicon oxide, silicon nitride, and aluminum oxide, nitrides, etc. Is mentioned. Examples of the method for forming the protective film include a coating method and a vacuum deposition method.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Example 1
A 200 μm thick polyethylene terephthalate (PET) film (“SP-976-3” surface roughness 10 nm or less manufactured by Mitsubishi Kasei) was cut into 2.5 × 2.5 cm ² . Using this PET film as a supporting substrate, the top was covered with a shadow mask having a width of 1 mm, and aluminum was added to 1000 liters using a vacuum vapor deposition machine “EX-400” (vacuum degree: 1.3 × 10 ⁻⁴ Pa) manufactured by ULVAC. The gate electrode was formed by vapor deposition to a thickness of.

  Polystyrene (PS): Aldrich (Mw = 280,000 (GPC method)) was dissolved in chloroform at a concentration of 5% by weight and filtered through a 0.45 μm filter. 1 mL of this PS solution was developed on the PET film with a gate electrode produced as described above, and spin coating was performed at 3000 rpm for 120 seconds to form an insulator layer. As a result of measuring the film thickness of this PS insulator layer with a film thickness meter (Alpha-Step 500: manufactured by Tencor), it was 3000 mm.

With respect to this support substrate with an insulator layer, pentacene is used as an organic semiconductor layer from a crucible by using a vacuum vapor deposition machine “EX-400” (vacuum degree: 1.3 × 10 ⁻⁴ Pa) manufactured by ULVAC. Deposition was performed at a rate of sec to a thickness of 1000 mm. In order to produce a source / drain electrode on this organic semiconductor layer, gold was deposited in a thickness of 1000 mm using a channel (L: 1000 μm, W: 50 μm) shadow mask to produce a top contact type organic transistor.

  About this transistor element, the voltage-current curve was calculated | required by measuring using the "semiconductor parameter analyzer 4155" made from Agilent, and the transistor characteristic was evaluated.

  The result was as shown in FIG. Various characteristics of this transistor element were as shown in Table 1.

In Table 1, the measurement method of the average roughness (Ra) and electrical conductivity of the organic semiconductor layer side interface of the insulator layer is as follows.
<Measurement of average roughness (Ra) of organic semiconductor layer side interface>
For the support substrate on which the insulator layer is formed, the surface shape of the insulator layer is observed with an atomic force microscope (AFM) manufactured by Seiko Instruments, the surface roughness is measured, and the average roughness (Ra) is obtained. It was.
<Electrical conductivity measurement>
Using a shadow mask having a width of 1 mm so as to be crossed with respect to the gate electrode, a 1000 mm thick aluminum electrode was applied to a vacuum deposition machine EX-400 (Vacuum degree: 1) .3 × 10 ⁻⁴ Pa), the gap between the electrodes was measured with a semiconductor parameter analyzer 4155 manufactured by Agilent, a voltage-current curve was obtained, and the electric conductivity was calculated.

Example 2
In Example 1, instead of the PS solution, cyanopullulan (CYEPL): Shinetsu co. A transistor element was prepared in the same manner as in Example 1 except that a CIEPL solution obtained by dissolving “Cyanoresin CR-S” manufactured in dimethylformamide (DMF): acetonitrile (1: 1 weight ratio) and filtering was used. Evaluation was performed in the same manner, and the results are shown in FIG.

Example 3
In Example 1, the transistor layer was formed in the same manner as in Example 1 except that polycarbonate (PC): made by Aldrich (Mw = 64000 (GPC method)) was used instead of PS for forming the insulator layer. It produced and evaluated similarly, and the result was shown in FIG.

Example 4
In Example 1, the transistor was formed in the same manner as in Example 1 except that polymethyl methacrylate (PMMA): manufactured by Aldrich (Mw = 996000 (GPC method)) was used instead of PS for forming the insulator layer. An element was fabricated and evaluated in the same manner, and the results are shown in FIG.

Example 5
Polyvinylphenol (PVP): Aldrich (Mw = 20000 (GPC method)) and poly (melamine-co-formaldehyde) methacrylate (Aldrich) as a crosslinking agent were mixed at a ratio of 4: 1 (weight ratio). The mixture was dissolved in tetrahydrofuran (THF) at a concentration of 5% by weight and filtered through a 0.45 μm filter. 1 mL of this PVP solution was developed on a PET film with a gate electrode produced in the same manner as in Example 1, and spin coating was performed at 3000 rpm for 120 seconds. Thereafter, a heat treatment was performed at 120 ° C. for 3 minutes, and a transistor element was produced in the same manner as in Example 1 except that a thermally crosslinked PVP film was produced to form an insulator layer. This is shown in FIG. 8 and Table 1.

Comparative Example 1
In Example 1, instead of PS, polyvinyl alcohol (PVA): made by Aldrich (Mw = 31000-50000 (GPC method)) was used to form the insulator layer, and PVA was dissolved in pure water, and after spin coating A transistor element was prepared in the same manner as in Example 1 except that it was dried under reduced pressure at 80 ° C. and 0.13 Pa for 72 hours to obtain an insulator layer. Indicated.

  As is clear from the above results, in Examples 1 to 5, good transistor performance could be obtained, but in Comparative Example 1, the interface with pentacene was affected by moisture absorption of PVA, and transistor performance was reduced. Couldn't get.

DESCRIPTION OF SYMBOLS 1 Insulating support substrate 2 Gate electrode 3 Insulator layer 4 Organic-semiconductor layer 5 Source electrode 6 Drain electrode 7 Interface

Claims (12)

In a field effect transistor having an insulator layer, a gate electrode and an organic semiconductor layer separated by the insulator layer, a source electrode and a drain electrode provided in contact with the organic semiconductor layer, and an insulating support substrate ,
The insulating support substrate is made of polyethylene terephthalate;
The insulator layer constitutes polystyrene, polyvinylphenol, polycarbonate, polyester, polyvinyl acetate, polyurethane, polysulfone, (meth) acrylic resin, epoxy resin, cyano group-containing hydrocarbon resin and phenol resin, and these resins. A field effect transistor comprising, as a main component, one or more resins selected from the group consisting of a copolymer resin containing a monomer component.   2. The field effect transistor according to claim 1, wherein the gate electrode is provided on the insulating support substrate, and an organic semiconductor layer is provided on the gate electrode through an insulator layer.   3. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are in contact with the insulator layer.   3. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are provided on the organic semiconductor layer.   2. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are provided on the insulating support substrate. 6. The electrical conductivity of the organic semiconductor layer in a source electrode-drain electrode direction is 10 ⁻⁴ S / cm or less, 10 ⁻¹² S / cm or more. Field effect transistor. In any one of claims 1 to 6, wherein the field effect mobility of the organic semiconductor layer, a source electrode - the electrical conductivity of the drain electrode direction, and the carrier density obtained based on the elementary charge is 10 ⁷ cm ^{- 3.} A field effect transistor, wherein the field effect transistor is ³ or more and 10 ¹⁸ cm ⁻³ or less.   8. The activation energy required for charge transfer obtained from temperature dependence of the field-effect mobility in the organic semiconductor layer at room temperature or lower is 0.2 eV or lower according to claim 1. Field effect transistor.   9. The field effect transistor according to claim 1, wherein a relative dielectric constant of the insulator layer is 2.0 or more. 10. The field effect transistor according to claim 1, wherein an electric conductivity in the insulator layer is 10 ⁻¹² S / cm or less. 11. 11. The drain electrode according to claim 1, wherein the drain electrode is a metal selected from the group consisting of platinum, gold, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium and sodium, InO ₂ or SnO _2. A field effect transistor comprising: a conductive oxide, a conductive polymer doped with a conductivity-imparting component, or a conductive composite material in which conductive fine particles are dispersed in a binder. 12. The conductive material according to claim 1, wherein the source electrode is a metal selected from the group consisting of platinum, gold, chromium, nickel, copper, titanium, magnesium, calcium, barium, and sodium, or InO ₂ or SnO ₂ . A field-effect transistor comprising a conductive oxide, a conductive polymer doped with a conductivity-imparting component, or a conductive composite material in which conductive fine particles are dispersed in a binder.

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