JP2006165533A - Field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect transistor which comprises an organic semiconductor portion formed by using an organic semiconductor solution and has large current characteristics by increasing the mobility in the organic semiconductor portion. <P>SOLUTION: A field effect transistor comprises a gate insulating portion, an organic semiconductor portion, a source electrode, and a drain electrode. The organic semiconductor portion is formed by using an organic semiconductor solution, and has a mobility of 1.0 cm<SP>2</SP>/Vs or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a field effect transistor, and more particularly to a field effect transistor having an organic semiconductor portion formed using an organic semiconductor.

  In a field effect transistor having a gate electrode and a semiconductor part separated by a gate insulating part on a supporting substrate and a source electrode and a drain electrode provided in contact with the semiconductor part, an organic material is used for the semiconductor part. ing. The organic material can form a semiconductor part by applying a solution, and in addition to the cost advantage as compared to the conventional formation method using a vacuum process using an inorganic material such as silicon, the use of a polymer or the like It is attracting attention because it can be reduced in weight and imparted with impact resistance.

Non-Patent Document 1 proposes a method of forming an organic semiconductor layer by applying a pentacene precursor solution and then converting it to pentacene. However, according to the study by the present inventors, the field effect transistor manufactured by the proposed method has a semiconductor layer mobility of 0.89 cm ² /
It was about (V · s).
Journal of America Chemical Society, 124, p8812-8813 (2004)

  According to the study by the present inventors, the conventional semiconductor has insufficient output current characteristics and cannot be used as an element for a driving circuit for displaying a moving image such as a liquid crystal display. It turned out to be. Therefore, the present invention provides a field effect transistor having an organic semiconductor part formed using an organic semiconductor solution and having high current characteristics by increasing the mobility of the organic semiconductor part. Objective.

The present invention relates to a field effect transistor including a gate insulating part, an organic semiconductor part, and a source electrode and a drain electrode, wherein the organic semiconductor part is formed using an organic semiconductor solution, and the organic semiconductor part is moved A gist is a field effect transistor having a degree of 1.0 cm ² / (V · s) or more.

  According to the present invention, it is possible to provide a field effect transistor having an organic semiconductor part formed using an organic semiconductor solution and having high current characteristics by increasing the mobility of the organic semiconductor part. it can.

Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the invention.
The field effect transistor of the present invention contains at least a gate insulating part, an organic semiconductor part, and a source electrode and a drain electrode. Preferably, it further has a support substrate and a gate electrode. More preferably, the support substrate includes a gate electrode and an organic semiconductor portion separated by a gate insulating portion, and a source electrode and a drain electrode provided in contact with the organic semiconductor portion. In the field effect transistor, when a voltage is applied to the gate electrode, a current flow channel (channel) is formed at the interface between the organic semiconductor portion and the gate insulating portion between the source electrode and the drain electrode. This is a mechanism for controlling the current flowing between the source electrode and the drain electrode by the input voltage applied from the gate electrode.

Hereinafter, each component in the field effect transistor of the present invention will be described.
<Support substrate>
In the field effect transistor of the present invention, as the supporting substrate, those used in conventional field effect transistors can be used.

  The material of the support substrate in the present invention is not limited as long as it can support a field effect transistor and a display element, a display panel and the like produced thereon, and known inorganic materials such as glass, silicon oxide, and metals such as silicon. Examples thereof include organic materials such as materials and various organic polymers. These may be used in combination of two or more types including, for example, a combination of an inorganic material and an organic material such as a substrate in which an organic polymer is coated on the surface of an inorganic material substrate and an insulating layer is formed on the surface. . Examples of the organic polymer include polyester, polycarbonate, polyimide, polyamide, polyether sulfone, epoxy resin, polybenzoxazole, polybenzothiazole, polyparabanic acid, polysilsesquioxane, and polyolefin. Among them, polyesters such as polyethylene terephthalate, polycarbonates, polyimides, polyamides, polybenzoxazoles, polybenzothiazoles, polyparabanic acid and other condensation polymers, and polyvinyl phenols and the like are preferable from the viewpoint of heat resistance and solvent resistance. Polyester, polycarbonate, polyimide, and polybenzoxazole are more preferable, and polyester such as polyethylene terephthalate or polyimide is particularly preferable. In addition, these organic polymers may contain a filler, an additive, etc. as needed.

  The thickness of the substrate made of the substrate material is preferably in the range of 0.01 to 10 mm, particularly preferably in the range of 0.05 to 2 mm. Within these ranges, for example, in the case of an organic polymer substrate, the thickness is preferably about 0.05 to 0.1 mm, and in the case of a glass or silicon substrate, the thickness is preferably about 0.1 to 10 mm. Further, the substrate may be a laminated body composed of a plurality of layers.

  In the present invention, the organic semiconductor portion described later is formed by application using an organic semiconductor solution, and a field effect transistor manufacturing process at a relatively low temperature is employed. Therefore, it is easy to use an organic polymer film having poor heat resistance. In that case, a field-effect transistor that is lighter in weight, superior in flexibility, superior in impact resistance and the like as compared with an inorganic material can be obtained.

  Further, the surface of these substrates may be subjected to a surface treatment for changing the characteristics of the layer formed thereon, for example, by adjusting the balance between hydrophilicity and hydrophobicity. For example, the characteristics of the semiconductor portion vary greatly depending on the state of molecular orientation and the like. Therefore, the molecular orientation at the interface between the substrate and the semiconductor portion is controlled by the surface treatment of the substrate, and the characteristics can be improved. Examples of such substrate surface treatment means include hydrophobization treatment with hexamethyldisilazane, cyclohexene, octadecyltrichlorosilane, etc., acid treatment with hydrochloric acid, sulfuric acid, acetic acid, etc., sodium hydroxide, potassium hydroxide, calcium hydroxide. , Alkali treatment with ammonia, ozone treatment, fluorination treatment, plasma treatment with oxygen, argon, etc., formation treatment of Langmuir-Blodgett film, other thin film formation treatment such as insulator and semiconductor, electrical treatment such as corona discharge And mechanical treatment.

<Gate electrode>
In the field effect transistor of the present invention, as a material of the gate electrode, a conductive material used in a conventional field effect transistor can be used. For example, metals such as platinum, gold, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium and sodium; conductive metal oxides such as InO ₂ , SnO ₂ and ITO; or polyaniline, polypyrrole, polythiophene, Conductive polymers such as polyacetylene; and acids such as hydrochloric acid, sulfuric acid and sulfonic acid; Lewis acids such as PF ₅ , AsF ₅ and FeCl ₃ ; halogen atoms such as iodine; metal atoms such as sodium and potassium; What added a dopant; Furthermore, the conductive composite material etc. with which carbon black, graphite powder, metal fine particles, etc. were disperse | distributed to the binder are mentioned.

  Gate electrodes made of these conductive materials are formed, for example, by patterning a film formed by a vacuum deposition method, a sputtering method, a coating method, a printing method, a sol-gel method or the like into a desired shape as necessary. The As the patterning method, for example, a photolithographic method in which photoresist patterning is combined with etching such as wet etching with an etchant or dry etching with reactive plasma, ink jet printing, screen printing, offset printing, letterpress printing. And a soft lithography technique such as a microcontact printing method and a combination of these techniques. It is also possible to directly form 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 electrodes is preferably 1 nm or more, and particularly preferably 10 nm or more. Moreover, it is preferable that it is 100 nm or less, and it is especially preferable that it is 50 nm or less.

<Source electrode, drain electrode>
The source electrode is an electrode through which an electric current flows from the outside through the wiring, and the drain electrode is an electrode that sends an electric current through the wiring to the outside, and is provided in contact with an organic semiconductor portion described later. In the field effect transistor of the present invention, as a material for the source electrode and the drain electrode, a conductive material used in a conventional field effect transistor can be used. For example, the same material as the material for the gate electrode can be used. Is mentioned.

  In addition, the source electrode and drain electrode are formed from these conductive materials by the same film formation method and patterning method as those described above as the film formation method of the gate electrode and the patterning method as necessary. . Alternatively, a pattern can be formed directly by irradiating an energy beam such as a laser or an electron beam to remove a portion outside the electrode or changing the conductivity of the electrode material. Among these, as a patterning method for the source electrode and the drain electrode, a photolithography method is preferable. As the photolithography method, an electrode material is formed, and a portion outside the electrode of the film is removed by etching, and a pattern is applied to the portion outside the electrode by applying a resist or the like, and then an electrode is formed thereon. There is a method (lift-off method) in which a material is formed, and then the electrode material formed thereon is removed by elution with a solvent that dissolves a resist or the like.

  Further, the thickness of the source electrode and the drain electrode is also preferably 1 nm or more, particularly preferably 10 nm or more. Moreover, it is preferable that it is 100 nm or less, and it is especially preferable that it is 50 nm or less. The distance between the source electrode and the drain electrode (channel length L) is preferably 100 μm or less, and particularly preferably 50 μm or less. The channel width W is preferably 2,000 μm or less, particularly preferably 500 μm or less. L / W is preferably formed to be 0.1 or less, particularly preferably 0.05 or less.

<Gate insulation part>
In the field effect transistor of the present invention, the gate insulating portion has a function of maintaining the overlapping region of the source and drain electrodes and the gate electrode, and the channel region on the gate electrode as an electrically insulating region. Here, “electrical insulation” means that the electric conductivity is 10 ⁻⁹ S / cm or less.

In the present invention, the material used for the conventional field effect transistor can be used as the material of the gate insulating portion. For example, organic polymers such as polymethyl methacrylate, polystyrene, polyvinyl phenol, polyvinyl alcohol, polyvinyl acetate, polycarbonate, polyester, polysulfone, polybenzoxazole, polyimide, polyurethane, epoxy resin, phenol resin, polysilsesquioxane, etc. Inorganic materials such as organic materials and oxides such as silicon dioxide, aluminum oxide, and titanium oxide, nitrides such as silicon nitride, and ferroelectric oxides such as SrTiO ₃ and BaTiO ₃ are included. Silicon is preferred.
Among the gate insulating material, an organic material is particularly preferable, and a polymer material is more preferable. The polymer material usually has a number average molecular weight of 5000 or more, preferably 10,000 or more. Among polymer materials, a polyimide material and styrene having excellent solvent resistance and heat resistance are preferable, and a polyimide material containing a fluorine atom with small water absorption is more preferable.
As the organic material, those having a glass transition point of 80 ° C. or higher are preferable from the viewpoint of fluidity when forming a layer as a solution.
The gate insulating material preferably contains 5% by weight or more, more preferably 15% by weight or more, particularly 50% by weight or more, from the viewpoint of brittleness and film strength as the gate insulating part. Preferably, 90% by weight or more is most preferable. A mixture of an organic material and an inorganic material is also used, and examples thereof include the organic polymer in which particles such as the oxide, nitride, and ferroelectric oxide are dispersed.
Water absorption of the insulating portion is preferably low, preferably 1 mg / cm ³ or less, further preferably 0.65 mg / cm ³ or less. If the water absorption rate is too high, when combined with an organic semiconductor, there is a problem that the on / off ratio is low or high mobility cannot be obtained.
In addition, what is soluble in the solvent which does not melt | dissolve a support substrate, and has the solvent resistance which is not corroded by the solvent at the time of formation of the organic-semiconductor part mentioned later is preferable.

  In addition, the gate insulating part is a coating method such as spin coating or blade coating, a vapor deposition method, a sputtering method, a printing method such as screen printing or inkjet, a method of forming an oxide film on a metal such as anodized on aluminum, etc. It can be formed by a method according to the material characteristics.

  Further, the thickness of the gate insulating portion is preferably 0.1 μm or more, particularly preferably 0.2 μm or more, since leakage current may occur if the film thickness is too thin. If it is too large, the capacity as the gate insulating portion is reduced, and the amount of induced carriers when a gate voltage is applied is reduced. Therefore, the thickness is preferably 4 μm or less, and particularly preferably 2 μm or less.

In general, the larger the capacitance of the gate insulating portion, the more advantageous the gate voltage can be driven at a low voltage. This can be dealt with by using an insulating material having a large dielectric constant or by reducing the thickness of the insulating portion. Further, since the gate insulating portion is related to the leakage current to the gate electrode and the low gate voltage driving of the field effect transistor, the electric conductivity at room temperature is 10 ⁻¹² S / cm or less, and further 10 ⁻¹⁴ S / cm. Preferably, the dielectric constant is not more than cm and the relative dielectric constant is not less than 2.0, more preferably not less than 2.5.

<Organic Semiconductor Department>
In the field effect transistor of the present invention, the organic semiconductor portion is 1.0 cm ² / (V · s) or more.

The mobility (μ) of the semiconductor part in the field effect transistor is expressed by the following formula (1) representing the drain current (I _d ) in the pinch-off region where the drain voltage (V _d ) is larger than the gate voltage (V _g ).
I _d = [WC _i / (2L)] μ (V _g −V _t ) ² (1)
[In formula (1), C _i is the capacitance per unit area of the gate insulating portion, L is the distance between the source electrode and the drain electrode (channel length), W is the channel width, V _g is the gate voltage, V _t is a threshold voltage. ]
Based on, to measure the changes in I _d for different V _g, determined as the gradient of the graph plotting the I _d ^1/2 and V _g.

Display in three types of display devices, liquid crystal (LCD), paper display (PD), and digital paper (DP), when a field effect transistor provided with an organic semiconductor portion having a different μ is used as a switching element. The display device is driven unless the value (V / V _on ) of the voltage (V) applied to the display pixel with respect to the pixel driving voltage (V _on ) is sufficiently high, specifically 0.99 or more. It is known that it cannot.

Here, the drain current of the switching element (which is equal to the current passed through the display pixel) I _d is a well-known formula: I _d = C _px · ∂V / ∂t = μ (W / L) C _i ( V _on -V) (V _g -V _t )
Wherein, C _px is the capacitance of the display pixel, V is the voltage applied at the time t on the display pixels, mu is mobility, W is the channel width, L is channel length, C _i is the static gate insulating portion The capacitance, V _g is the voltage applied to the gate insulating part, and V _t is the threshold voltage of the organic semiconductor part. ]
From
∂V / (V _on −V) = μ (W / L) (C _i / C _px ) (V _g −V _t ) ∂t
, And integrating this,
∫ [1 / (V _on −V)] dV = ∫μ (W / L) (C _i / C _px ) (V _g −V _t ) dt
Here, the integration constant is determined from the condition that V = 0 at t = 0, and as a result,
V = V _on [1-exp (−t / τ)]. (2)
In equation (2),
τ = 1 / [μ (W / L) (C _i / C _px ) (V _g −V _t )].

From this result, it can be seen how the V / V _on value changes when the field effect transistor having the organic semiconductor portion having different values of μ is used in the driving circuits of the three types of display devices. The result of applying it to an actual display device is shown in FIG. For each of the LCD, PD, and DP, the [frame frequency (Hz) and the number of lines (lines)] are [60, 1000], [60, 1000], and [5, 2000]. According to FIG. 3, it can be seen that the LCD can be driven when μ ≧ 1.0 cm ² / (V · s).
In the present invention, a method for setting the mobility of the organic semiconductor portion to 1.0 cm ² / (V · s) or more will be described. As a factor for reducing the mobility, a shallow trap existing between crystal grains in a polycrystal can be considered. Shallow traps occur for the same reason as the deep traps described above, but they can escape thermally because of their shallow depth and affect mobility because they affect charge transport. That is, the charge trapped in the shallow trap takes time to escape from it, and the mobility becomes slow. Furthermore, if the barrier at the interface between the electrode and the semiconductor is large and sufficient current cannot flow from the semiconductor, the apparent mobility will be lowered, so it is necessary to select the material and shape of the electrode appropriately. is there.
(1) Use a highly pure organic semiconductor material.
Use organic materials with high purity to reduce shallow traps derived from impurities. Preferably, it is 95 wt% or more, more preferably 97 wt% or more.
(2) Increasing the size of crystal grains and reducing the number of particle connection points.
For example, it is conceivable to reduce the number of particle connection points by selecting an organic semiconductor material in which crystal grains are increased or by selecting film forming conditions in which crystal grains are increased. Controls traps that exist between crystal grains.
(3) In an element having a bottom gate structure, an organic polymer is used as an insulating film, and an organic semiconductor is formed thereon.
This is because the wettability and adhesion between the polymer and the organic semiconductor are higher than those between the inorganic insulating film material such as inorganic oxide and the organic semiconductor when the organic semiconductor is formed on the organic polymer insulating film. This is presumably because an organic semiconductor film with few traps is formed. However, it is preferable that the polymer material has a low polarity or a low water absorption. Use an organic polymer for the insulating film. (4) Appropriate electrode combination Combine electrodes that facilitate the injection of charges between the electrode and the semiconductor. For example, materials such as gold, platinum, and ITO having a large work function are selected for hole injection. In addition, patterning by metal etching is preferable to lift-off, in which burrs are easily generated even by photolithography so that there are no raised edges (burrs) in the electrode shape.
The organic semiconductor part of the field effect transistor of the present invention is not particularly limited, but oligothiophenes containing four or more thiophene rings represented by α-sexithiophene and dialkylsexithiophene; or A thiophene ring, a benzene ring, a fluorene ring, a naphthalene ring, an anthracene ring, a thiazole ring, a thiadiazole ring, or a benzothiazole ring in total; a condensed aromatic hydrocarbon 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; naphthalenetetracarboxylic anhydride, Naphthalenetetracarboxylic acid diimide, perylenetetracarboxylic acid anhydride, perylenete Aromatic carboxylic acid anhydrides and imidized products thereof such as lacarboxylic acid diimide; macrocyclic compounds such as phthalocyanine, perfluorophthalocyanine, tetrabenzoporphyrin and metal salts thereof such as copper and zinc; polythiophene, polyfluorene, polythienylene vinylene , Polyphenylene vinylene, polyphenylene, polyacetylene, polypyrrole, polyaniline, particularly those exhibiting self-organization such as regioregular polythiophene, and polymers exhibiting liquid crystallinity represented by polyfluorene and copolymers thereof.
Among these, cyclic azaannulene compounds represented by phthalocyanine, naphthalocyanine, porphyrin, benzoporphyrin, azaporphyrin, thiaporphyrin, oxaporphyrin, confused porphyrin and the like are preferable.
Among these, macrocyclic compounds such as phthalocyanine, perfluorophthalocyanine, tetrabenzoporphyrin and metal salts thereof such as copper and zinc are preferable, and a metal coordination porphyrin compound represented by the following general formula is particularly preferable.

[In the general formula, R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , and R ⁸ are each independently a hydrogen atom, a hydroxyl group, or an optionally substituted amino group. A group, a nitro group, a monovalent organic group, or a halogen atom, and R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² each independently represent a hydrogen atom, a monovalent organic group, or a halogen atom; M represents a metal atom. ]

In the general formula, the substituent of the amino group of R ¹ to R ^8, for example, include alkyl groups of 1 to 10 carbon atoms. Further, the monovalent organic group of R ^{1 to} R ⁸ is preferably one having 1 to 10 carbon atoms. Specifically, for example, an alkyl group, an alkoxy group, an alkylthio group, an acyl group, a carboxyl group And an ester group of C 1-10 alcohol, a formyl group, a carbamoyl group, and the like, and these organic groups may have a substituent. In addition, examples of the halogen atom represented by R ^{1 to} R ⁸ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

Adjacent R ¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ , and R ⁷ and R ⁸ may be bonded to form a ring, in which case the ring formed Examples of the ring include aromatic rings such as a benzene ring, naphthalene ring and anthracene ring; heterocycles such as a pyridine ring, quinoline ring, furan ring and thiophene ring; and alicyclic rings such as a cyclohexene ring.

Examples of the monovalent organic group represented by R ^{9 to} R ¹² include an alkyl group, an alkoxy group, an alkylthio group, an ester group of a carboxyl group and an alcohol having 1 to 10 carbon atoms, an aryl group, and the like. The group may have a substituent. Examples of the halogen atom represented by R ^{9 to} R ¹² include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  The metal atom for M is preferably Cu, Ni, Fe, or Zn, and particularly preferably Cu. In the above general formula, examples of suitable compounds when M is Cu are shown below. In addition, although the thing of the molecular structure with a good symmetry is mainly illustrated, the thing of an asymmetrical structure may be sufficient.

  One of the above metal coordination porphyrin compounds may be used alone, or may be used as a mixture of two or more. Various additives such as an antioxidant may be added to the organic semiconductor portion.

  The organic semiconductor portion in the field effect transistor of the present invention is formed by forming a solution layer using a solution of the organic semiconductor by a coating method, a printing method, or the like and then drying the solution layer.

  The solvent at that time is not particularly limited as long as it can dissolve the organic semiconductor, and any solvent can be used according to the type of the organic semiconductor.

  Also, the method for forming the solution layer is not particularly limited. For example, coating methods such as casting, spin coating, dipping, blade coating, wire bar coating, spray coating, ink jet printing, screen printing, offset printing, letterpress. Examples thereof include a printing method such as printing, and a soft lithography method such as a microcontact printing method. In addition, you may use these methods in combination of 2 or more types suitably. Furthermore, as a method similar to coating, a Langmuir-Blo dgett method in which a monomolecular film of a semiconductor material formed on a water surface is transferred to a substrate and laminated, a liquid crystal or a melted semiconductor material is sandwiched between two substrates, or a capillary tube There is also a method of introducing between two substrates due to a phenomenon.

  In addition, when forming the organic semiconductor part of a metal coordination porphyrin compound by the above method, in addition to a method of applying a solution in which the metal coordination porphyrin compound itself is dissolved in a solvent, the precursor of the metal coordination porphyrin compound is a solvent. It is also possible to take a method of preparing a semiconductor part as a final metal coordinated porphyrin compound by preparing a precursor solution dissolved in, applying the precursor solution, and changing the chemical structure of the precursor . This method is particularly effective when forming an organic semiconductor portion of a metal coordination porphyrin compound that is hardly soluble in a solvent.

  As the precursor when forming the organic semiconductor part of the metal coordinated porphyrin compound using the precursor, for example, the metal coordinated porphyrin compound having the bicyclo structure shown below has an ethylene molecule dissociated by heating, It changes to a benzene ring. The two bonds of the bicyclo structure below and the benzene ring in which the bicyclo structure is changed are bonds connected to porphyrin.

  Since the bicyclo structure is three-dimensionally bulky, the crystallinity is low. Therefore, the molecule having the bicyclo structure has good solubility, and when the solution is applied, the crystallinity is low or an amorphous coating film is formed. Easy to obtain. In addition, when the bicyclo structure is changed to a benzene ring through a heating step, a molecular structure with good planarity is obtained, so that crystallinity is improved. Therefore, by using a chemical change from a precursor having a bicyclo structure, even when an organic semiconductor part is formed from a solution using a porphyrin compound having low solubility in a solvent, it is composed of a porphyrin compound having good crystallinity. The organic semiconductor part can be obtained by coating or the like. The heating for converting the precursor to the final porphyrin compound may also serve other purposes such as distilling off the coating solvent.

In general, in the formation of an organic semiconductor part using a solution, it is said that the film forming property does not become high and it is difficult to obtain an organic semiconductor part with high crystallinity. An organic semiconductor part having excellent characteristics with high crystallinity can be obtained. And the field effect transistor which has the organic-semiconductor part formed in this way has a preferable characteristic that a carrier mobility is high and On / Off ratio is high. In addition, the method using the said precursor is a method applicable not only to a porphyrin compound but other organic-semiconductor materials generally.
The solvent for applying such a precursor is not particularly limited, but aliphatic hydrocarbons such as hexane, heptane, octane, isooctane, nonane, decane; toluene, benzene, xylene, chlorobenzene, tetralin, anisole, etc. Aromatic hydrocarbons; lower alcohols such as methanol, ethanol, propanol and butanol; ketones such as acetone, methyl ethyl ketone, cyclopentanone and cyclohexanone; esters such as ethyl acetate, butyl acetate, methyl lactate and ethyl benzoate Nitrogen-containing organic solvents such as pyridine and quinoline; halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethane, trichloroethane, and trichloroethylene; ethers such as ethyl ether, tetrahydrofuran, dioxane, and dimethoxyethane Dimethylformamide, a solvent of amides such as dimethylacetamide. Among these, aromatic hydrocarbons, ketones, and esters are preferable from the viewpoint of safety, ease of handling, and ease of combination with various coating methods. Moreover, in order to adjust physical properties such as boiling point and viscosity, it is possible to use a mixture of two or more solvents.

  As an example of the precursor in the porphyrin compound, a benzoporphyrin compound in which a benzene ring is condensed with a pyrrole ring can be generated from a precursor having a bicyclo structure. It is advantageous for forming an organic semiconductor part.

  In addition, when forming an organic semiconductor part using a precursor, dissolution of the precursor and the organic semiconductor material can be achieved by repeating the formation process such as application and printing of the precursor solution and the chemical structure change process such as heating. It is possible to form a thick film by making use of the fact that the organic semiconductor parts are not dissolved in the precursor solution by utilizing the difference in properties.

  In addition, as a method for controlling the crystal orientation of the organic semiconductor portion, a method such as an epitaxial growth method or a rubbing after coating can be used. By these methods, it is possible to improve the carrier mobility of the semiconductor layer and reduce the electrical resistivity of the channel.

The organic semiconductor portion may be so-called doped to contain a trace amount of an element, an impurity such as an atomic group, a molecule, or a polymer for the purpose of changing the characteristics of the semiconductor portion. As a doping method at that time, a known method can be arbitrarily used according to the characteristics of the organic semiconductor portion to be formed. Specific examples of the dopant include gases such as oxygen and hydrogen, acids such as hydrochloric acid, sulfuric acid, and sulfonic acid, Lewis acids such as PF ₅ , AsF ₅ , and FeCl ₃ , halogen atoms such as iodine, sodium, potassium, and the like. A metal atom etc. are mentioned. In addition, as a doping method, for example, an organic semiconductor in which the dopant is mixed in an organic semiconductor material or a precursor solution, or in contact with or immersed in a gas or solution of the dopant at the stage of forming the precursor portion. A method of processing before forming the part, a method of processing after forming the organic semiconductor part, such as contacting or immersing the formed organic semiconductor part in a gas or solution of the dopant, or performing an electrochemical treatment, etc. Taken.

  By these doping treatments, effects such as change in electrical conductivity due to increase or decrease in carrier density, change in carrier polarity (p-type or n-type), change in Fermi level, and the like can be obtained.

  Further, the organic semiconductor portion formed in this way can be relaxed, for example, by heat treatment to reduce distortion in the semiconductor portion generated during film formation, or into an oxidizing or reducing gas or liquid such as oxygen or hydrogen. Exposure to induce a characteristic change due to oxidation or reduction, and increase or decrease the carrier density in the semiconductor part, perform a mechanical treatment, or perform an electrical treatment such as corona discharge. May be applied.

  In the field effect transistor of the present invention, the organic semiconductor portion may be formed from a single layer or may be formed from two or more layers. Further, since the thickness of the organic semiconductor portion is likely to increase as the thickness increases, the thickness of the organic semiconductor portion is preferably as thin as possible within a range in which a necessary function can be performed, and is preferably 10 μm or less, and more preferably 1 μm or less. It is preferably 500 nm or less, and most preferably 50 nm or less. Further, it is preferably 1 nm or more, more preferably 5 nm or more, and particularly preferably 10 nm or more.

(Change in threshold voltage of field effect transistor)
In the field effect transistor of the present invention, the threshold voltage changes when a voltage is applied to the gate for 5.0 ± 0.1 hours at 70 ° C. so that the electric field strength in the gate insulating portion is 100 ± 5 MV / m. It is preferably within 5V.
Applying a voltage such that the electric field strength in the gate insulating portion is 100 ± 5 MV / m is applied to the gate by dividing the voltage applied between the source electrode and the drain electrode by the film thickness of the gate insulating film ( It means that the unit V / m) is (100 ± 5) × 10 ⁶ . Although the application time is 5.0 ± 0.1 hours, in order to monitor the change in the threshold voltage during application, it is permissible to examine the FET characteristics within one second after applying for 50 seconds or more.
The threshold voltage can be obtained from the current-voltage characteristics of the field effect transistor. For example, the drain current in the saturation region of the charge effect transistor is given as follows.

(Where, Id is the drain current, W is the electrode width, L is the electrode length, Ci is the capacitance, μ is the mobility, Vg is the gate voltage, and Vt is the threshold voltage.)
From the above equation, plotting against the square root of the drain current in the saturation region and the gate voltage, the mobility is obtained from the slope of the straight line portion, and the voltage at the intercept of the drain current = 0 with the straight line portion extrapolated is obtained as the threshold voltage. be able to. Further, the drain current in a certain gate insulating film is determined by the mobility μ and the threshold voltage Vt unless the electrode shape (W, L) or the capacitance (Ci) of the insulating film changes. If it is confirmed that the mobility μ does not change, the change in the drain current can be reduced to the change in the threshold voltage.
It is desirable that the change in the drain current due to voltage application is small, but this is because the change in the threshold voltage is within 5V, preferably 4V or less, more preferably 3V or less.

  Although the cause of the threshold voltage shift has not been clarified sufficiently, formation of trap levels in the semiconductor is considered, and generally there is a tendency to increase as the temperature is increased. For example, in a transistor using amorphous silicon as a semiconductor part, the threshold voltage shift is expressed by the following empirical formula (TFT / LCD Liquid-Display Displays by Thin-Film Transistors, 1996, p67, T. Tsukada, Gordon and Breach Science Publishers).

Here, β is 1 to 2, γ is 0.3 to 0.4, and Ea is 0.2 to 0.3 eV. The organic semiconductor can also use β = 1.5 and Ea = 0.25 eV assuming temperature dependency and gate voltage dependency close to this.
In general, if the threshold voltage shift at room temperature is within 3 V, it is practically acceptable in view of the lifetime of the display element. If the threshold voltage shift exceeds the allowable range of the external drive circuit due to changes in transistor characteristics, the desired display operation cannot be performed. Therefore, it is preferable that the threshold voltage shift is small, but particularly within 3 V, the gate voltage setting can be reduced, and the power consumption is accordingly reduced, and accordingly, the process / design of the driver circuit IC has a low breakdown voltage. Can be used, and the effect of reducing the cost is remarkable, which is very advantageous in practice.
Usually, when driving a display, a voltage is applied so that an electric field of about 50 MV / m is obtained. In other words, in Equation 2, when the electric field strength in the gate insulating portion becomes 100 MV / m at 70 ° C., it is estimated that the acceleration is about 10 times the threshold voltage shift in the case of room temperature driving.
In addition, since only 1 / vertical number of lines in the vertical direction of the display (1/768 because XGA is 768 lines) is applied, assuming that the lifetime of the display is 20000 hours, the gate voltage is actually applied for about 26 hours. become.

From the above, when a voltage such that the electric field strength in the gate insulating film becomes 100 MV / m at 70 ° C. is applied to the gate for 5 hours, the change in threshold voltage is (3/26) × 10 × 5 = 5. If the condition that the voltage falls within 7 V is satisfied, the generally required characteristics of the operating life at room temperature can be sufficiently satisfied.
Since the liquid crystal display is driven by alternating current, a reverse polarity voltage is also applied to the gate voltage. In this case, a reverse threshold voltage shift occurs, so that the change in all threshold voltages is canceled out, and the voltage of one polarity is It is expected to be smaller than the shift due to application. However, since there are driving methods in which reverse polarity is not applied, such as organic EL and electrophoretic displays, it is desirable that the threshold voltage shift by applying a voltage of one polarity is small as described in the present invention. It is a transistor.
In a pixel circuit of a current drive type display such as an organic EL, a transistor that is normally turned on when selecting a pixel called a switching transistor and a drive transistor of a drive transistor that controls a current to the pixel (organic EL) are used. It is done. In this drive transistor, a gate voltage is always applied to supply current to the organic EL element portion, and a change in threshold voltage becomes more problematic than a switching transistor. For this reason, a circuit that does not depend on the threshold voltage has been devised, but even such a circuit cannot be handled if the threshold voltage changes too much. If the change in threshold voltage is within 3V, it can be used as a drive transistor for organic EL without any problem.

As a factor for increasing the change in the threshold voltage, a deep trap existing in the semiconductor portion can be considered. The charge trapped in the deep trap becomes a non-movable charge, which increases the change in threshold voltage. A normal organic semiconductor film having a relatively high mobility of 0.01 cm ² / Vs or more is often a polycrystal or a polymer structure having an ordered structure, except for a single crystal. Organic single crystals are not practical because they are very difficult to produce and difficult to handle. Causes of deep traps include those due to impurities, those present in the vicinity of connection points between particles, and those due to structural defects in the particles. Therefore, in order to reduce the change in threshold voltage caused by the voltage stress of the organic semiconductor formed by coating, the following method can be mentioned.

(1) Use a highly pure organic semiconductor material.
In order to reduce deep traps derived from impurities, high-purity organic materials are used. A purity of 95 wt% or more is preferable, and 97 wt% or more is more preferable.
(2) Increasing the size of crystal grains and reducing the number of particle connection points.
For example, by selecting an organic semiconductor material in which crystal grains become large, or by selecting a film forming condition in which crystal grains become large, the number of particle connection points themselves is reduced.
(3) Control traps existing between crystal grains.
For example, it is conceivable that traps between particles are made shallower or eliminated by performing an appropriate overcoat treatment. When overcoat treatment is performed, the overcoat agent reaches the channel formation region in the vicinity of the insulating film of the semiconductor film, which is related to the electrical characteristics of the organic transistor, through the gap between the particles, and directly into the trap part existing between the particles. It acts and can make the trap shallower or disappear. It is necessary to select an appropriate material to be combined depending on the semiconductor material.
(4) In a device having a bottom gate structure, an organic polymer is used for an insulating film, and an organic semiconductor is formed thereon.
This is because the wettability and adhesion between the polymer and the organic semiconductor are higher than those between the inorganic insulating film material such as inorganic oxide and the organic semiconductor when the organic semiconductor is formed on the organic polymer insulating film. This is presumably because an organic semiconductor film with few traps is formed. However, it is preferable that the polymer material has a low polarity or a low water absorption.

(5) Aging the transistor.
If the deep trap is due to a structural defect, the trap can be reduced by sufficiently relaxing the material structure by aging treatment. In this aging treatment, in addition to heating for a long time, it is also effective to leave it for a long time in a state where an electric current is actually passed by passing a current.
These techniques have different effectiveness depending on the material, and in many cases, desired characteristics can be obtained by combining them. It is desirable to combine as many items as possible, but it is also possible to select an appropriate one in consideration of the labor (cost) for that purpose and the other processes for manufacturing the device.
The field effect transistor according to the present invention preferably satisfies both the following (a) and (b).
(A) The threshold voltage changes within 5V when a voltage at which the electric field strength in the gate insulating portion becomes 100 ± 5 MV / m at 70 ° C. is applied to the gate for 5.0 ± 0.1 hours.
(B) The organic semiconductor part is formed using an organic semiconductor solution, and the mobility of the organic semiconductor part is 1.0 cm ² / (V · s) or more.
If the threshold voltage change due to driving is small and the mobility is large, it is preferable because there is a margin in device design. In other words, it is a small (narrow gate width) transistor, and a threshold voltage change correction circuit becomes unnecessary or simple. Furthermore, when driving a voltage-driven element such as an organic EL, in addition to passing a large current, it can be advantageously used for an element in which a voltage is always applied to the gate, unlike a transistor of an active matrix liquid crystal display. Therefore, it is particularly preferable. Further, in order to be used not only for a display but also for a driver circuit, it is preferable to satisfy both (a) and (b). This is because the driver circuit requires faster response and higher stability than the display.
Even if only one of them is satisfied, it may be possible to obtain a practical one by giving a margin to the design of the transistor structure (gate width and length). Reduction, shortening of the service life, or increasing the cost of the peripheral drive circuit, which is disadvantageous.
In order to obtain a field effect transistor that satisfies both (a) and (b), the following means may be mentioned.

As described above, when semiconductors are related to both (a) and (b), traps are related, although there is a difference between the deep and shallow levels. Therefore, since the method for reducing the number of traps and the method for eliminating traps are common, it can be achieved by using them alone or in combination. That is,
・ Use high-purity semiconductor materials. Preferably, a semiconductor material having a purity of 95 wt% or more, more preferably 97 wt% or more is used.
Select a semiconductor material capable of forming large crystal grains or forming a higher order ordered structure.
・ Use an appropriate polymer insulating film.
• Combine appropriate overcoats.
・ Aging processing is performed.
More preferably, the following method is used.
Use a material that converts a precursor film to obtain a crystalline low-molecular semiconductor film.
・ Azaannulene compounds are used as semiconductor materials.
Use a metal electrode patterned by etching.

<Structure of field effect transistor>
The basic structure of the field effect transistor of the present invention will be described with reference to the drawings. FIGS. 1A to 1D are each referred to as a lateral field effect transistor (“FET”) in the field effect transistor of the present invention. FIG. 1A to 1D, a field effect transistor of the present invention includes a gate insulating part 3, a gate electrode 2 and an organic semiconductor part 4 separated by the gate insulating part 3 on a support substrate 1, It has a source electrode 5 and a drain electrode 6 provided in contact with the organic semiconductor portion 4. The structure is not particularly limited. Typically, the bottom gate / bottom contact type shown in FIG. 1 (A), the bottom gate / top contact type shown in FIG. 1 (B), and the structure shown in FIG. And the top gate / bottom contact type shown in FIG. 1D.

  Further, FIG. 2 is a longitudinal sectional view showing an embodiment of an electrostatic induction transistor (referred to as “SIT”) in the field effect transistor of the present invention. In the above-described FET, the source electrode 5 and the drain electrode 6 are arranged in parallel on the support substrate 1 and the direction of current flow is perpendicular to the electric field induced by the gate electrode 2, whereas in SIT, the source The electrode 5 and the drain electrode 6 are arranged in a column on the support substrate 1 with the organic semiconductor part 4 interposed therebetween, and the gate electrode 2 insulated by the gate insulating part 3 (not shown) in the organic semiconductor part 4 therebetween. Is different from the above-described FET in that the current flows in a direction parallel to the electric field induced by the gate electrode 2. .

  In SIT, the channel cross-sectional area, which is the sum of the cross-sectional areas of the plane perpendicular to the source-drain direction of the channel region, can be made larger than that of the FET. It can be moved from the drain electrode to the drain electrode or from the drain electrode to the source electrode, and since the source electrode and the drain electrode are arranged in tandem, the distance between the source electrode and the drain electrode can be reduced, so that the response becomes faster. It is suitable for use in applications where a large current is passed or high-speed switching is performed.

  In SIT, the interval between the gate electrodes 2 is arbitrary, but is usually preferably smaller than the distance between the source electrode 5 and the drain electrode 6 (thickness of the organic semiconductor portion 4). Further, the thickness of the gate electrode 2 is preferably 10 nm or more, particularly preferably 20 nm or more, more preferably 10 μm or less, and particularly preferably 1 μm or less.

  The basic structure of the field effect transistor of the present invention is as described below. However, the field effect transistor of the present invention is not limited to the field effect transistor having the structure shown in FIGS. A layer other than the above-mentioned part may be further formed between the parts or on the outermost part. For example, in the field effect transistor exposed by the organic semiconductor portion 4 like the field effect transistor shown in FIGS. 1A and 1B, the outside air such as moisture is exposed to the organic semiconductor portion 4. In order to minimize the influence or to improve the semiconductor characteristics themselves, it is preferable that a protective layer is further formed thereon. In that case, as a material of the protective layer, for example, a hydrocarbon polymer containing aromatics such as polystyrene, polyvinyl naphthalene, poly (4-methylstyrene), poly (α-methylstyrene), polyacenaphthylene, polymethyl, and the like. Methacrylic resins such as methacrylate and polybenzyl methacrylate, acrylic resins, polyvinyl alcohol, polyvinylidene chloride, polyvinylidene fluoride, polyolefins, polyimide resins, polyurethane resins, polycarbonate resins, epoxy resins, fluorine resins, and other organic polymers or their co-polymers Examples thereof include inorganic substances such as oxides and nitrides such as coalescence, siloxane resin, silicon oxide, aluminum oxide, and silicon nitride. Among these, the protective layer formed in contact with the semiconductor is preferably an organic polymer containing an aromatic ring, more preferably a polymer containing a benzene ring, and particularly preferably polystyrene. Further, these can be laminated to provide a property improving effect and a gas barrier property. Furthermore, characteristics such as carrier mobility and carrier density of the semiconductor film can be controlled by mixing a low molecular weight compound and allowing it to act on the semiconductor film.

  As a method for forming the protective layer, various known methods can be arbitrarily used. When the protective layer is made of an organic polymer, for example, a method of applying the solution and then drying to form an organic polymer layer, monomers thereof After coating, a method of polymerizing to a polymer layer, etc. may be mentioned, and after film formation, post-treatment such as cross-linking treatment may be appropriately performed, while laminating in a gas phase typified by parylene and polyimide. A method of forming a film by polymerization is also possible. When the protective layer is made of an inorganic material, for example, a method using a dry process such as a sputtering method, a vapor deposition method, a chemical vapor deposition (CVD) method, a method using a solution typified by a sol-gel method, or the like can be given. It is done.

  In addition, when the material constituting the FET, particularly the organic semiconductor material used in the organic semiconductor portion absorbs light and generates a charge, a desired region, for example, a metal such as chromium, aluminum, silver, gold, etc. A pattern having a low light transmittance (so-called black matrix) can be formed by the above film, a resin film in which a pigment such as carbon black is dispersed, an organic dye film, or the like.

(Voltage application process)
In the present invention, it is preferable to perform a voltage application (aging) process in order to create a field effect transistor having a change in threshold voltage within 5V. This process is performed after forming each part of the field effect transistor. Therefore, the field effect transistor can be processed for a long time by applying a voltage under conditions close to the voltage stress to be actually applied. Processing conditions such as processing temperature, applied voltage, and processing time depend on the semiconductor material used, the gate insulating film material and the layer structure. However, the higher the temperature, the shorter the processing time, 20 ° C. or higher, preferably 40 ° C. or higher, more preferably It is desirable to process at 50 degreeC or more. Since there is a concern about deterioration of the device at a high temperature, 150 ° C. or less, preferably 100 ° C. or less is desirable. The treatment time is preferably 2 hours or more, preferably 10 hours or more, more preferably 50 hours or more for the inorganic insulating film, and preferably 1 minute or more for the polymer insulating film.
The mechanism by the aging process is unknown, but there are components that the threshold voltage shift changes irreversibly and components that change reversibly. By sufficiently reducing the components that change irreversibly due to aging, high drive stability is obtained. It is thought that this is effective. In this aging, it is preferable to apply aging by applying a drain current by applying both gate and drain voltages. The reason is not clear, but it is presumed that there is an effect of removing a portion (for example, a trap or the like) that causes the threshold voltage to become unstable due to the flowing current.
The field effect transistor of the present invention preferably has an On / Off ratio of 800 or more, particularly preferably 1,000 or more.

(Use of field effect transistor)
Field effect transistors are used for display elements driven by an active matrix, and include liquid crystal displays, polymer dispersed liquid crystal displays, electrophoretic displays, toner displays, organic EL displays, inorganic EL displays, light emitting diode displays, etc. Used as a pixel switch.

  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.

<Synthesis Example 1: Synthesis of Bicycloporphyrin Copper Complex>
S. Ito, N .; Ochi, T .; Murashima, H .; Uno, N .; Ono, Heterocycles, vol. According to the method described in 52,399 (2000), a copper bicycloporphyrin complex was synthesized from bicycloporphyrin by the following route. That is, 92.8 mg (0.16 mmol) of bicycloporphyrin having the following structure and 313.6 mg (1.6 mmol) of copper (II) acetate dihydrate were dissolved in a mixture of chloroform 150 mL / methanol 15 mL and stirred for about 1 hour. did. Since it was confirmed by alumina TLC (developing solvent chloroform / hexane = 1/1) that the raw material disappeared and a new compound was formed, water was added to stop the reaction, and the organic solvent was washed with water as it was. The layers were separated. Furthermore, after washing with saturated saline, it was dried over anhydrous sodium sulfate. After the desiccant was filtered through filter paper, the solvent was distilled off, and chromatography was performed on alumina gel (developing solvent chloroform / hexane = 1/1), and only fractions containing only the desired product were collected and concentrated. When methanol was added during the concentration and the concentration was continued further, a precipitate of the desired product was formed. This was filtered off using filter paper and dried in vacuo. The yield of the bicycloporphyrin copper complex thus obtained was 76.5 mg, and the yield was 75%.

  0.8 mg of the obtained bicycloporphyrin copper complex was dissolved in 1.25 g of chloroform and spin-coated on a glass substrate at 2,000 rpm to form a film. The obtained film was heated at 4 ° C./min. The absorption spectrum was measured. The result is shown in FIG. From this, as shown below, it can be seen that the conversion from the bicycloporphyrin copper complex to the benzoporphyrin copper complex occurs between 120 and 180 ° C.

<Synthesis Example 2: Synthesis of bicycloporphyrin>
S. Ito, N .; Ochi, T .; Murashima, H .; Uno, N .; Ono, Heterocycles, vol. According to the method described in 52,399 (2000), bicycloporphyrin was synthesized by the following route.
<Diels-Alder reaction>

Scheme.

Scheme.

Trans-1,2-Diphenylsulfonylethylene (52.74 g, 171 mmol) was placed in a 2 L four-necked flask equipped with a reflux condenser, and dispersed in 1.6 L of toluene. Next, 1,3-Cyclohexadiene (20.52 mL, 205.2 mmol) was added to this solution and refluxed for 5 hours to carry out a thermal Diels-Alder reaction. After completion of the reaction, the reaction mixture was concentrated under reduced pressure with an evaporator and washed with hexane, whereby 72 g (yield 99) of the desired product 2-exo, 3-endo-Bis (phenylsulfonyl) bicyclo [2.2.2] oct-5-ene. %)Obtained. As a measure of completion of the reaction, the raw material trans-1,2-diphenylsulfonylethylene dispersed in toluene was completely dissolved, HPLC (Column: CAPCELL PAK C18 MG S-5 μm, Column size: 4.6 mm I.D. × 250 mm, Eluent: THF 70 vol%; Water 30 vol%), the peak of 1.939 minutes of the raw material disappeared, and the peak of 2.077 minutes of the target product was generated, and the reaction was judged to be complete.
<Pyrroleation reaction>

Scheme .

Scheme.

Add 2-exo, 3-endo-Bis (phenylsulfonyl) bicyclo [2.2.2] oct-5-ene (54.32 g, 140 mmol) to a 2 L four-necked flask and purge with nitrogen, and add 700 mL of dehydrated THF. Dissolved. Isocyanoethylcarboxylate (17.01 g, 154 mmol) was added to this solution and cooled in an ice bath. (The internal temperature at this time is 0 ° C.) To this cooled solution, t-BuOK / THF 1M solution (350 mL, 350 mmol) was slowly added dropwise at a dropping rate of 5 mL / min. (The increase in internal temperature at the time of dropping was about 1 ° C.) After completion of the dropping, the reaction solution was returned to room temperature and stirred for 6 hours. After stirring, 1N hydrochloric acid was added (at this time the internal temperature rose by 3 ° C), extracted with chloroform, washed with water, the organic layer was dried over anhydrous sodium sulfate and purified by silica gel column chromatography (chloroform). As a result, 24 g (yield 79%) of the target product Ethyl4,7-dihydro-4,7-ethano-2H-isoindole-1-carboxylate was obtained. As a measure of completion of the reaction, the peak of the raw material disappeared by HPLC (Column: CAPCELL PAK C18 MG S-5 μm, Column size: 4.6 mm I.D. × 250 mm, Eluent: THF 70 vol%; Water 30 vol%) The end of the reaction was judged by the generation of a peak of minutes.
<Reduction reaction with LiAlH ₄ >

Scheme 1.

Scheme 1.

A 100 mL four-necked flask was purged with nitrogen, and LiAlH ₄ (0.646 g, 17.02 mmol) was measured. To this flask was added 22 mL of THF. At this time, the flask was ice-cooled to 0 ° C. Next, bicyclopyrrole (1 g, 4.60 mmol) was dissolved in 30 mL of THF, and this solution was slowly added and stirred. During this reaction, the temperature returned to room temperature after about 3 hours. After starting stirring, the reaction state was followed by HPLC. After 5 hours, since the peak of the target product appeared, ethyl acetate was added to decompose the remaining LiAlH ₄ to complete the reaction. Then, the organic layer extracted with ammonium chloride aqueous solution and chloroform was dried with magnesium sulfate.
<Cyclization reaction of pyrrole>

Scheme 2.

Scheme 2.

The chloroform solution extracted in the above experiment was further diluted to 1.2 L. P-Toluenesulfonic acid monohydrate (0.368 g, 2.14 mmol) was added to this solution, and cyclization reaction was performed for 24 hours.
<Oxidation reaction>

Scheme 3.

Scheme 3.

  Chloranyl (0.566 g, 2.30 mmol) was added to the chloroform solution subjected to the cyclization reaction in the above experiment, and the oxidation reaction was performed for 24 hours. After completion of the reaction, extraction was performed with saturated aqueous sodium hydrogen carbonate, and the chloroform layer was concentrated with an evaporator to obtain a crude product. The obtained crude product was dissolved in chloroform at a high concentration, separated and purified by silica gel column chromatography (chloroform developing solvent), and recrystallized from chloroform / methanol to obtain bicycloporphyrin. The purity was confirmed by HPLC, MALDI-TOF-MASS, and elemental analysis, and it was found to be highly pure.

<Synthesis Example 3: Synthesis of Bicycloporphyrin Copper Complex>
In the synthesis of the bicycloporphyrin copper complex of Synthesis Example 1, a bicycloporphyrin copper complex was obtained in the same manner as in Synthesis Example 1 except that chromatography with alumina gel was not performed.
(Measurement of purity of organic semiconductor materials)
The purity of each porphyrin material obtained in Synthesis Examples 1 to 3 and pentacene (manufactured by Tokyo Chemical Industry Co., Ltd.) was measured using CHN elemental analysis. In addition, about the pentacene, what was sublimated was used.
The purity of each organic semiconductor was measured by combustion-thermal conductivity detection using a PERKIN ELMER 2400 Series II CHN / O Analyzer as a CHN measuring instrument. As a method for calculating purity, each semiconductor was kept under a vacuum of 10 ⁻⁵ Torr for 3 hours so as not to cause disturbance, and CHN was measured after removing the solvent and moisture. With regard to the obtained analytical value, paying attention to the carbon (C) atom which is an element indispensable for the organic semiconductor and calculating as analytical value / theoretical value × 100 = purity (%), the following purity was obtained.
The results are shown in the table below.

<Synthesis Example 4: Synthesis of Polyamic Acid (Kapton Precursor)>
Under a nitrogen atmosphere at room temperature, 2.0 g (10 mmol) of 4,4′-oxydianiline was dissolved in 42 ml of N-methyl-2-pyrrolidone. To this solution, 2.2 g (10 mmol) of pyromellitic dianhydride was added and a ring-opening polyaddition reaction was performed to polymerize the polyamic acid which is a polyimide precursor. Twelve hours after the start of the polymerization, the polymerization solution was put into 500 ml of methanol and subjected to reprecipitation treatment to obtain a polyamic acid. After drying under reduced pressure, it was dissolved in N-methyl-2-pyrrolidone and reprecipitated with methanol again. This reprecipitation process was repeated twice to obtain a polyamic acid which was a purified kapton precursor.

Example 1
Patterning was performed using a photoresist (Nippon Zeon Co., Ltd.) ZPN1100 on an ITO glass plate (Toyo Sangyo Co., Ltd., 2.5 cm x 2.5 cm), and then 1 wt% iron (II) chloride was dissolved. After etching unnecessary ITO with an aqueous solution of hydrogen chloride, the substrate was washed to produce a gate electrode.
A fluorinated polyimide having the following structure was dissolved in cyclohexanone to a concentration of 10 wt% to prepare a solution. Subsequently, pressure filtration was performed with a 0.2 μm PTFE filter. This solution was spin-coated on an ITO glass substrate at a rotational speed of 1600 rpm and dried at 180 ° C. to form a gate insulating layer made of polyimide. The film thickness measured with a film thickness meter (“Alpha-Step 500” manufactured by Tencor) was 3,100 mm.

  Subsequently, in order to form a source electrode and a drain electrode on this gate insulating layer, it is covered with a shadow mask of a channel (L: 1,000 μm, W: 40 μm), and chromium is 50 mm thick and gold is 1,000 mm thick. The element of the bottom contact structure shown in FIG. 1 was produced by vapor deposition. Next, a 0.7 wt% chloroform solution prepared by dissolving copper tetrabicycloporphyrin having the following molecular structure obtained in Synthesis Example 1 in chloroform at room temperature in a nitrogen atmosphere on an element having a bottom contact structure is 1 After spin-coating at 1,000 rpm and drying to form a layer, it was heated at 180 ° C. for 10 minutes to be converted into a semiconductor layer to form an organic semiconductor layer.

A 10 wt% toluene solution in which polystyrene (manufactured by Aldrich) was dissolved in toluene at room temperature was spin-coated on this semiconductor layer at 2,000 rpm, and heat-treated at 100 ° C. for 10 minutes to form an overcoat layer. A field effect transistor (FET-F) was produced.
The field effect transistor element thus obtained was subjected to a gate voltage stress at 70 ° C. with a gate voltage V _g = −30 V, a source V _s and a drain voltage V _d of 0 V. During this time, the electric field strength in the gate insulating part was 97 MV / m, which could be calculated from V _g / film thickness of the gate part. The drain voltage I _d was measured by applying the drain voltage V _d = −60 V for 60 seconds every 60 seconds, and the threshold voltage V _t was obtained from the value of the I _d . This measurement was repeated for 5 hours, and the change in V _t was measured from the change in I _d during that time. As a result, V _t has changed during the measurement is 2.8V, it can be seen that a very good driving stability.
In addition, the current flowing with respect to the voltage V _d applied between the source electrode and the drain electrode of the obtained field effect transistor element is I _d , the voltage applied to the source electrode and the gate electrode is V _g , and the threshold voltage is V _{Assuming t} , the capacitance per unit area of the gate insulating layer is C _i , the channel length is L, the channel width is W, and the mobility of the organic semiconductor layer is μ, they are expressed by the following equation (1). Measure the change in I _d for different V _g , find the mobility μ as the slope in the graph plotting I _d ^1/2 and V _g, and threshold from the I _d intercept of the graph to determine the voltage V _t.
I _d = [WC _i / (2L)] μ (V _g −V _t ) ² (1)
Further, the voltage V _d applied between the source electrode and the drain electrode is fixed to −30V, and the voltage V _g applied to the source electrode and the gate electrode is set to −50V, + 30V, between the source electrode and the drain electrode. Currents I _d (−50 V) and I _d (+30 V) were measured, and the On / Off ratio was calculated from these ratios I _d (−50 V) / I _d (+30 V).
As a result, the mobility μ of this field effect transistor was 1.19 cm ² / (V · s). The threshold voltage V _t was 17.8 V, and the On / Off ratio was 1.45 × 10 ² .

(Example 2)
On the entire surface of the oxide film of an N-type silicon support substrate (Sb doped, resistivity 0.02 Ωcm or less, manufactured by Sumitomo Metal Industries) having an oxide film having a thickness of 300 nm formed on the surface as a gate insulating part, a thickness of 10 nm is formed by vacuum deposition. Chromium and gold having a thickness of 100 nm are formed in this order, and a gold film other than the source electrode and the drain electrode is removed by etching to have a channel with a length (L) of 10 μm and a width (W) of 500 μm. Thus, a source electrode and a drain electrode were formed. Further, a part of the oxide film at a position different from that of the electrode is etched with a hydrofluoric acid / ammonium fluoride solution, and gold is deposited to a thickness of 100 nm on the exposed silicon support substrate, and this is applied to the gate electrode. Contact point.

Next, in order to avoid the influence of oxygen and humidity, the following film formation and evaluation of electrical properties were all performed in a nitrogen atmosphere, and 0.8 mg of the bicycloporphyrin copper complex obtained in the above synthesis example was added to 1.25 g of chloroform. The solution dissolved in (1) was spin-coated at 1000 rpm on the support substrate on which the electrode was formed, and then placed on a hot plate heated to 120 ° C., and then heated up to 200 ° C. in steps of 10 ° C. every 15 minutes. By heating, an organic semiconductor layer made of a benzoporphyrin copper complex having a thickness of 100 nm was formed. A 10 wt% toluene solution in which polystyrene (Aldrich) is dissolved in toluene at room temperature is spin-coated on this semiconductor layer at 2,000 rpm, and heat-treated at 100 ° C. for 10 minutes to form an overcoat layer of 1 μm. Thus, a field effect transistor FET-B was produced.
The mobility μ of the field effect transistor FET-B was 1.29 cm ² / (V · s). The threshold voltage _{V t} is 15V, On / Off ratio was 1.4 × 10 ^6. Further, when the threshold voltage shift was measured, it was 5.9 V, and the driving stability was lacking.

(Example 3)
On the entire surface of the oxide film of an N-type silicon support substrate (Sb doped, resistivity 0.02 Ωcm or less, manufactured by Sumitomo Metal Industries) having an oxide film having a thickness of 300 nm formed on the surface as a gate insulating part, a thickness of 10 nm is formed by vacuum deposition. Chromium and gold having a thickness of 100 nm are formed in this order, and a gold film other than the source electrode and the drain electrode is removed by etching to have a channel with a length (L) of 10 μm and a width (W) of 500 μm. Thus, a source electrode and a drain electrode were formed. In addition, an oxide film at a position different from that of this electrode was etched with a hydrofluoric acid / ammonium fluoride solution, and gold was deposited to a thickness of 100 nm on the exposed silicon support substrate, and a voltage was applied to the gate electrode through this. .

  Subsequently, in order to avoid the influence of oxygen and humidity, the following film formation and evaluation of electrical properties were all performed in a nitrogen atmosphere, and 0.8 mg of the bicycloporphyrin copper complex obtained in Synthesis Example 1 was added to chloroform 1. A solution dissolved in 25 g was spin-coated at 1000 rpm on the support substrate on which the electrode was formed, and then placed on a hot plate heated to 120 ° C., and then heated up to 200 ° C. in steps of 10 ° C. every 15 minutes. Then, an organic semiconductor layer made of a benzoporphyrin copper complex having a thickness of 100 nm was formed, and a field effect transistor FET-A was produced.

The mobility μ of the obtained field effect transistor was 1.22 cm ² / (V · s), the threshold voltage V _t was 34 V, and the On / Off ratio was 1.8 × 10 ² .
Further, the threshold voltage shift was measured and found to be 12.6 V, and the driving stability was lacking.

Example 4
Using a negative photoresist ZPN1100 (manufactured by ZEON Corporation) on a 4-inch glass mask wafer supporting substrate (surface polishing, manufactured by Universal Corporation), chrome is applied at a degree of vacuum of 10 ^-6 Torr by photolithography (lift-off method). After vapor deposition with a thickness of 100 nm, an unnecessary resist pattern is removed using an organic solvent, and the surface is further subjected to ultrasonic cleaning using an excitran cleaning solution (manufactured by Merck), to obtain a thickness of 100 nm. A chromium gate electrode was patterned.

On top of this, the polyamic acid obtained in Synthesis Example 4 was dissolved in N-methylpyrrolidone at a concentration of 20% by weight, and 2 ml of the polyamic acid solution filtered through a 0.2 μm filter was developed. After spin coating for 120 seconds and forming a film, the film was gradually heated to 300 ° C. in nitrogen to perform imidization to obtain a polyimide gate insulating layer. The film thickness measured with a film thickness meter (“Alpha-Step 500” manufactured by Tencor) was 900 nm. The capacitance of this insulating layer was measured with an electric measuring instrument “4284A” manufactured by Agilent Technologies, and found to be 2.84 × 10 ⁻⁹ F / cm ² .

After a negative photoresist ZPN1100 (manufactured by Nippon Zeon Co., Ltd.) was used again on the gate insulating layer of this polyimide, photolithography was performed to deposit chromium at a thickness of 10 nm and gold at a thickness of 10 ⁻⁶ Torr. Then, the unnecessary resist pattern was removed using an organic solvent and washed to pattern the source electrode and the drain electrode.

Subsequently, a solution obtained by dissolving the bicycloporphyrin copper complex obtained in Synthesis Example 1 in chloroform at 0.7% by weight in chloroform at room temperature under a nitrogen atmosphere on a support substrate on which the electrode is formed at 1,000 rpm. After spin coating, heat treatment is performed at 210 ° C. for 5 minutes to convert to a benzoporphyrin copper complex, and overcoat with a 10% by weight toluene solution of polystyrene, and then dry to form a protective layer. Thus, a field effect transistor FET-C was produced. The mobility μ of the obtained field effect transistor FET-C was 1.12 cm ² / (V · s), and the On / Off ratio was 1.4 × 10 ² .

Comparative Example 1
A field effect transistor FET-D was produced in the same manner as in Example 4 except that the organic semiconductor layer was formed to a thickness of 100 nm by vacuum evaporation of sublimated and purified pentacene (manufactured by Tokyo Chemical Industry Co., Ltd.). The mobility μ of the obtained field effect transistor FET-D was 0.20 cm ² / (V · s).
Thereafter, the threshold voltage shift was measured in the same manner as in Example 1. As a result, it was 15.1 V, and the driving stability was lacking.

Comparative Example 2
As a material for forming an organic semiconductor layer, except that the bicycloporphyrin having the following structure obtained in Synthesis Example 2 was used as a chlorobenzene solution, and was converted to benzoporphyrin by heat treatment at 210 ° C. for 10 minutes, A field effect transistor FET-E was produced in the same manner as in Example 1. The mobility μ of the obtained field effect transistor FET-E was 0.01 cm ² / (V · s).

Comparative Example 3
In Example 4, the formation method of the source electrode and the drain electrode was changed to photolithography (lift-off method) using a negative photoresist ZPN1100 (manufactured by Nippon Zeon Co., Ltd.), and the bicycloporphyrin copper obtained in Synthesis Example 1 was used. A field effect transistor was produced in the same manner as in Example 4 except that the complex was changed to the bicycloporphyrin copper complex obtained in Synthesis Example 3 instead of the complex. The mobility was 0.02 cm ² / (V · s).
The results of the above examples and comparative examples are summarized in the following table.

Further, V / V _on when the field effect transistors A to E obtained in Examples 1 to 4 and Comparative Examples 1 to 2 are used as driving circuits for three types of display devices of LCD, PD, and DP, respectively. Table 1 shows the result of calculating the value using the formula (2). From this result, it is clear that in the field effect transistors A to C and F of Examples 1 to 4, V / V _on ≧ 0.99 is achieved even in LCD driving.

  The field effect transistor of the present invention can be used, for example, in a wide industrial field using an electronic device. Specific examples include an active matrix of a display such as a liquid crystal display element, a polymer dispersed liquid crystal display element, electronic paper, an organic LED display element, an electrophoretic display element, an inorganic EL display element, and an electrochromic element. It can also be used for IC tags, IC chips, sensors and the like.

It is a longitudinal cross-sectional view which shows the Example of the horizontal type field effect transistor (FET) in the field effect transistor of this invention. It is a longitudinal cross-sectional view which shows the Example of the static induction transistor (SIT) in the field effect transistor of this invention. When a field effect transistor having an organic semiconductor portion having a different mobility μ is used in three types of display devices of a liquid crystal (LCD), a paper display (PD), and a digital paper (DP), the driving voltage (V It is a graph which shows the value (V / _Von ) of voltage (V) applied to the display pixel with respect to _on ). 2 is an absorption spectrum of the bicycloporphyrin copper complex used in Example 1 at a temperature of 120 to 180 ° C. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Gate electrode 3 Gate insulation part 4 Organic-semiconductor part 5 Source electrode 6 Drain electrode

Claims (8)

A field effect transistor including a gate insulating part, an organic semiconductor part, and a source electrode and a drain electrode, wherein the organic semiconductor part is formed using an organic semiconductor solution, and the mobility of the organic semiconductor part is 1. A field-effect transistor characterized by being 0 cm ² / (V · s) or more.   The threshold voltage change is within 5 V when a voltage at which the electric field strength in the gate insulating portion becomes 100 ± 5 MV / m at 70 ° C. is applied to the gate for 5.0 ± 0.1 hours. The field effect transistor according to claim 1.   The field effect transistor according to claim 1, wherein the organic semiconductor part contains a cyclic azaannulene compound.   The field effect transistor according to claim 1 or 2, wherein the organic semiconductor portion contains a porphyrin-based or phthalocyanine-based compound.   The field effect transistor according to claim 1, wherein the organic semiconductor portion includes an organic semiconductor converted from an organic semiconductor precursor.   The field effect transistor according to claim 1, further comprising an overcoat layer.   The field effect transistor according to claim 1, wherein the gate insulating part contains a polymer material.   The display element using the field effect transistor as described in any one of Claims 1-7.

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