JP2007266285A - Field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect transistor having practical mobility of carriers by employing a specific organic compound as a semiconductor material, and having p-type, n-type, and unbipolar-type electric characteristics by selecting a substituted group of a compound. <P>SOLUTION: The field effect transistor employs a compound represented by a formula (1) as a semiconductor material. In the formula (1), X<SB>1</SB>and X<SB>2</SB>each independently denote an oxygen atom, a sulfur atom, or a selenium atom, and R<SB>1</SB>, R<SB>2</SB>, R<SB>3</SB>and R<SB>4</SB>each independently denote a hydrogen atom, a substitutable aliphatic hydrocarbon group, or a substitutable aromatic group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a field effect transistor. More specifically, the present invention relates to a field effect transistor using a specific organic heterocyclic compound as a semiconductor material.

  Field effect transistors generally have a structure in which a semiconductor material on a substrate is provided with a source electrode, a drain electrode, and a gate electrode through these electrodes and an insulator layer. In addition, it is widely used for switching elements. Currently, inorganic semiconductor materials centering on silicon are used for field-effect transistors, and thin film transistors formed on a substrate such as glass using amorphous silicon are used for displays and the like. When such an inorganic semiconductor material is used, it is necessary to process the field effect transistor at a high temperature or in a vacuum, and the cost is very high because it requires expensive equipment investment and a lot of energy for manufacturing. It has become. In these, since the substrate is exposed to a high temperature during the production of the field effect transistor, a substrate having insufficient heat resistance such as a film or plastic cannot be used for the substrate, and its application is limited.

On the other hand, research and development of field effect transistors using organic semiconductor materials that do not require high-temperature processing during the manufacture of field effect transistors have been conducted. By using an organic material, it becomes possible to manufacture at a low temperature process, and the selection of the substrate becomes easy. As a result, it becomes possible to produce a field effect transistor that is excellent in flexibility, lightweight, and hardly broken. Further, in the field effect transistor creation process, a large area field effect transistor may be manufactured at a low cost by employing a technique such as solution coating or ink jet printing. In addition, various compounds can be selected as the compound for the organic semiconductor material, and an expression of an unprecedented function utilizing the characteristics is expected.
As an example of using an organic compound as a semiconductor material, various studies have been made so far. For example, a material using pentacene, thiophene, or an oligomer or polymer thereof has already been used as a material having hole transport (p-type) characteristics. Known (see Patent Documents 1 and 2). Pentacene is an acene-based aromatic hydrocarbon in which five benzene rings are linearly condensed. A field effect transistor using this as a semiconductor material has a charge mobility comparable to amorphous silicon currently in practical use. It has been reported to show (carrier mobility). However, its performance is greatly influenced by the purity of the compound, and further, its purification is difficult, and the production cost is high for use as a transistor material. Furthermore, a field effect transistor using this compound is deteriorated due to the environment and has a problem in stability. In addition, when thiophene compounds are used, there are similar problems, and it is difficult to say that the materials are highly practical.
Further, organic semiconductor materials having electron transport (n-type) characteristics include fluorinated pentacene, fluorinated phthalocyanine, C60, perylenetetracarboxylic acid anhydride and its imide derivative, naphthalenetetracarboxylic acid anhydride and its imide derivative, dicyanopyrazino. Examples include quinoxaline derivatives. However, the research and development of n-type organic semiconductors is still delayed compared to p-type materials, the types are limited, the carrier mobility is generally low, and many problems remain in the cost and stability of the compound itself. ing.
Since n-type organic semiconductors with better characteristics can be obtained, the degree of freedom in circuit design is improved, and organic electronic circuits (complementary integrated circuits: CMOS circuits) with smaller size and lower power consumption are expected to be put to practical use. The
Furthermore, the manufacture of this CMSO circuit becomes very simple by realizing an ambipolar field effect transistor that is driven with both p-type and n-type polarities by changing the polarity of the gate voltage in the same device. Cost reduction is also expected, and the usefulness of the organic field effect transistor is improved.

  On the other hand, diketopyrrolopyrrole (DPP) derivatives of organic pigments are used in paints, inks, color filters, color copy toners, and the like, and are known as coloring materials with excellent durability. Also in the field of electronic materials, it has been reported that it is useful as a dopant in a light emitting layer of an organic EL device (see Patent Document 3).

JP 2001-94107 A JP-A-6-177380 JP-A-2-29691

  An object of the present invention is to provide a field effect transistor having excellent carrier mobility and excellent stability using an organic compound as a semiconductor material.

  As a result of intensive studies to solve the above problems, the present inventors have demonstrated excellent carrier mobility and excellent stability by using a heterocyclic compound having a specific structure as a semiconductor material. It was found that can be obtained. Furthermore, by selecting the substituent of this heterocyclic compound, it exhibits not only p-type and n-type semiconductors but also ambipolar semiconductors having both p-type and n-type characteristics, and has excellent practicality. The inventors have found that the present invention can be applied to high transistor elements and have completed the present invention.

That is, the configuration of the present invention is as follows.
(1) A field effect transistor using a compound represented by the following formula (1) as a semiconductor material.

(In the formula (1), X ₁ and X ₂ are each independently an oxygen atom, sulfur atom or selenium atom, and R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom or substituted. Each represents an aliphatic hydrocarbon group or an optionally substituted aromatic group.)
(2) The field effect transistor according to (1), wherein X ₁ and X ₂ in formula (1) are each independently an oxygen atom or a sulfur atom.
(3) The field effect transistor according to (1) or (2), wherein R ₁ and R ₂ in formula (1) are both hydrogen atoms.
(4) The field effect transistor according to any one of (1) to (3), wherein R ₃ and R ₄ in formula (1) are aromatic groups that may be substituted together.
(5) The field effect transistor according to any one of (1) to (4), which has a hole transport property.
(6) The field effect transistor according to (5), wherein R ₁ and R ₂ in formula (1) are hydrogen atoms, R ₃ and R ₄ are phenyl groups, and X ₁ and X ₂ are oxygen atoms.
(7) The field effect transistor according to any one of (1) to (4), having electron transport characteristics.
(8) The electrolytic effect according to (7), wherein R ₁ and R ₂ in Formula (1) are hydrogen atoms, R ₃ and R ₄ are halogeno-substituted phenyl groups, and X ₁ and X ₂ are oxygen atoms. Transistor.
(9) The field effect transistor according to any one of (1) to (4), which has ambipolar characteristics.
(10) The field effect transistor according to (9), wherein R ₁ and R ₂ in formula (1) are hydrogen atoms, R ₃ and R ₄ are phenyl groups, and X ₁ and X ₂ are sulfur atoms.
About.

  By using the specific heterocyclic compound represented by the formula (1), an organic field effect transistor having excellent carrier mobility and excellent stability could be provided. Furthermore, by selecting the substituent of this heterocyclic compound, not only the p-type semiconductor, but also the characteristics as an n-type semiconductor and the ambipolar characteristics having both p-type and n-type characteristics, an excellent electric field We were able to provide an effect transistor.

The present invention will be described in detail.
The present invention is an organic field effect transistor using a specific organic compound as a semiconductor material, and a diketopyrrolopyrrole compound represented by the above formula (1) is used as the organic compound. First, the diketopyrrolopyrrole compound represented by the formula (1) will be described.

X ₁ and X ₂ are each independently an oxygen atom, a sulfur atom or a selenium atom, preferably an oxygen atom or a sulfur atom. R _{1 to} R ₄ each independently represent a hydrogen atom, an optionally substituted aliphatic hydrocarbon group or an optionally substituted aromatic group. R ₁ and / or R ₂ are preferably a hydrogen atom or an optionally substituted aliphatic hydrocarbon group, and most preferably a hydrogen atom. Further, preferred as R ₃ and / or R ₄ is an optionally substituted aliphatic hydrocarbon group or an optionally substituted aromatic group, and most preferred is an optionally substituted aromatic group. is there.

In the above, the aliphatic hydrocarbon group of the aliphatic hydrocarbon group which may be substituted in R _{1 to} R ₄ includes a saturated or unsaturated linear, branched or cyclic aliphatic hydrocarbon group, As for carbon number, 1-20 are preferred. Here, examples of the saturated or unsaturated linear or branched aliphatic hydrocarbon group include, for example, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, iso-butyl group, allyl group, t -Butyl group, n-pentyl group, n-hexyl group, n-octyl group, n-decyl group, n-dodecyl group, n-stearyl group, n-butenyl group and the like can be mentioned. Examples of the cyclic aliphatic hydrocarbon group include cycloalkyl groups having 3 to 12 carbon atoms such as a cyclohexyl group, a cyclopentyl group, an adamantyl group, and a norbornyl group.

Examples of the aromatic group of the aromatic group which may be substituted in R _{1 to} R ₄ include aromatic hydrocarbon groups such as phenyl group, naphthyl group, anthryl group, phenanthryl group, pyrenyl group, and benzopyrenyl group. And pyridyl group, pyrazyl group, pyrimidyl group, quinolyl group, isoquinolyl group, pyrrolyl group, indoleenyl group, imidazolyl group, carbazolyl group, thienyl group, furyl group, pyranyl group, pyridonyl group and other heterocyclic groups, benzoquinolyl group, anthraquinolyl group , Condensed heterocyclic groups such as benzothienyl group and benzofuryl group. Of these, preferred are a phenyl group, a naphthyl group, a pyridyl group, and a thienyl group.

Examples of the substituent that the aliphatic hydrocarbon group and aromatic group of R _{1 to} R ₄ which may be substituted may have, are not particularly limited, but the aliphatic hydrocarbon which may have a substituent Group (for example, a halogen atom, a hydroxyl group, a mercapto group, a carboxylic acid group, a sulfonic acid group, a nitro group, an alkoxyl group, an alkyl-substituted amino group, an aryl-substituted amino group, an unsubstituted amino group, an aryl group, an acyl group, An alkoxycarbonyl group or the like; an aromatic group which may have a substituent (for example, an alkyl group, a halogen atom, a hydroxyl group, a mercapto group, a carboxylic acid group, a sulfonic acid group, a nitro group, an alkoxyl group, an alkyl as a substituent) Substituted amino group, aryl-substituted amino group, unsubstituted amino group, aryl group, acyl group, alkoxycarbonyl group, etc.); cyano group; Group; thiocyanato group; isothiocyanato group; nitro group; nitroso group; acyl group; acyloxy group; halogen atom such as fluorine atom, chlorine atom, bromine atom, iodine atom; hydroxyl group; mercapto group; substituted or unsubstituted amino group; Alkoxyalkyl group; thioalkyl group; aromatic oxy group optionally having substituent; sulfonic acid group; sulfinyl group; sulfonyl group; sulfonic acid ester group; sulfamoyl group; carboxyl group; carbamoyl group; An alkoxycarbonyl group etc. are mentioned. Among them, an aliphatic hydrocarbon group which may have a substituent, an aromatic group which may have a substituent, a cyano group, a nitro group, an acyl group, a halogen atom, a hydroxyl group, a mercapto group, a substituted or non-substituted group A substituted amino group, an alkoxyl group, an aromatic oxy group which may have a substituent, and the like are preferable. More preferable examples include an aliphatic hydrocarbon group which may have a substituent, an aromatic group which may have a substituent, a nitro group, a halogen atom, a substituted or unsubstituted amino group, an alkoxyl group, and the like. Most preferably, an aliphatic hydrocarbon group which may have a substituent or an aromatic group which may have a substituent and a halogen atom may be mentioned.
As the substituent of the aromatic group which may have a substituent, a halogen atom is preferable, and specific examples include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom, a chlorine atom and a bromine atom are preferable. .

Generally, among these substituents, when having a substituent that withdraws electrons (halogen atom, fluorinated alkyl group, cyano group, etc.), it functions as an n-type semiconductor and has a substituent that donates electrons. In many cases (alkoxyl group, substituted or unsubstituted amino group, alkyl group, etc.) function as a p-type semiconductor. Substituents can be selected depending on the intended use as a field effect transistor.
Even in the organic semiconductor materials so far, there have been seen examples in which a tetrafluoromethyl group or all hydrogen atoms are replaced with a fluoro group to act as an n-type field effect transistor. These have high costs, such as the need for multi-step reactions in the production of compounds and high raw materials. However, even in this material, even a derivative having a relatively weak electronegativity, for example, a derivative into which two chlorine atoms are introduced, exhibits n-type characteristics and is expected to be very cost effective.

  The diketopyrrolopyrrole compound represented by the formula (1) can be synthesized by a known method disclosed in US Pat. No. 4,579,949. For example, as shown in the following reaction formula, a basic skeleton can be obtained by condensation-cyclizing a nitrile derivative and a succinate derivative. Furthermore, it can synthesize | combine easily by performing the substitution reaction etc. to sulfur etc. which used N-alkylation reaction, Lawson's reagent, etc. Furthermore, for example, an asymmetric derivative can be synthesized by a method of reacting with a nitrile compound using an enamine compound or a pyrrolinone compound disclosed in US Pat. No. 4,659,775. In the present invention, it is preferable to use a high-purity diketopyrrolopyrrole compound represented by the formula (1).

In the above reaction formula, as described above, X ₁ and X ₂ are each independently an oxygen atom, sulfur atom or selenium atom, and R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom or substituted. Represents a good aliphatic hydrocarbon group or an optionally substituted aromatic group. Moreover, it does not specifically limit as a refinement | purification method of the compound represented by Formula (1), Techniques, such as a column chromatograph and recrystallization known per se, are employable. In order to further increase the purity, vacuum sublimation purification can be performed.

Next, specific examples of the diketopyrrolopyrrole compound represented by the formula (1) are shown. First, Table 1 shows examples (compound No. 1 to compound No. 44) of diketopyrrolopyrrole compounds represented by the following formula (2) among the compounds represented by the formula (1). In Table 1, the phenyl group is abbreviated as Ph, the 4-methylphenyl group as 4-CH3Ph, the naphthyl group as Np, the thienyl group as Th, the pyridyl group as Py, and the cyclohexyl group as Cy. All alkyl groups not specifically mentioned are linear alkyl groups. In addition, the compound of Formula (2) is a compound represented by Formula (1) which is an aromatic group in which both R ₃ and R _{4 in} Formula (1) may be substituted.

  Specific examples (compound No. 134 to compound No. 192) other than the diketopyrrolopyrrole compound represented by formula (2) among the diketopyrrolopyrrole compounds represented by formula (1) are shown below.

  Next, the field effect transistor (hereinafter sometimes abbreviated as FET) of the present invention has two electrodes (source electrode and drain electrode) in contact with the semiconductor, and the current flowing between the electrodes is It is controlled by a voltage applied to another electrode called a gate electrode.

  In general, a field-effect transistor often has a structure in which a gate electrode is insulated by an insulating film (Metal-Insulator-Semiconductor: MIS structure). An insulating film using a metal oxide film is called a MOS structure. In addition, there is a structure (MES) in which a gate electrode is formed through a Schottky barrier, but in the case of an FET using an organic semiconductor material, a MIS structure is often used.

Hereinafter, the organic field effect transistor of the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these structures.
FIG. 1 shows some examples of the field effect transistor (element) of the present invention. In each example, 1 represents a source electrode, 2 represents a semiconductor layer, 3 represents a drain electrode, 4 represents an insulator layer, 5 represents a gate electrode, and 6 represents a substrate. In addition, arrangement | positioning of each layer and an electrode can be suitably selected with the use of an element. A to D are called lateral FETs because a current flows in a direction parallel to the substrate. A is called a bottom contact structure, and B is called a top contact structure. C is a structure often used for producing an organic single crystal FET. A source and drain electrodes and an insulator layer are provided on a semiconductor, and a gate electrode is further formed thereon. D has a structure called a top & bottom contact type transistor. E is a schematic diagram of a FET having a vertical structure, a static induction transistor (SIT). According to this SIT structure, since the flow spreads in a plane, a large amount of carriers can move at a time. Further, since the source electrode and the drain electrode are arranged vertically, the distance between the electrodes can be reduced, so that the response is fast. Therefore, it can be preferably applied to uses such as flowing a large current or performing high-speed switching.

Each component in each embodiment will be described.
The substrate 6 needs to be able to hold each layer formed thereon without peeling off. For example, insulating materials such as resin plates and films, paper, glass, quartz, and ceramics, materials in which an insulating layer is formed on a conductive substrate such as metal and alloy by coating, materials made of various combinations such as resin and inorganic materials, etc. Can be used. Examples of the resin film that can be used include polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyamide, polyimide, polycarbonate, cellulose triacetate, polyetherimide, and the like. When a resin film or paper is used, the element can have flexibility, is flexible and lightweight, and improves practicality. The thickness of the substrate is usually 1 μm to 10 mm, preferably 5 μm to 5 mm.

The source electrode 1, the drain electrode 3, and the gate electrode 5 are made of a conductive material. For example, metals such as platinum, gold, silver, aluminum, chromium, tungsten, tantalum, nickel, cobalt, copper, iron, lead, tin, titanium, indium, palladium, molybdenum, magnesium, calcium, barium, lithium, potassium, sodium, etc. And alloys containing them; conductive oxides such as InO ₂ , ZnO ₂ , SnO ₂ , ITO; conductive polymer compounds such as polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene vinylene, polydiacetylene; silicon, germanium, Semiconductors such as gallium arsenide; carbon materials such as carbon black, fullerene, carbon nanotube, and graphite can be used. In addition, the conductive polymer compound or the semiconductor may be doped. As the dopant, for example, 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 lithium, sodium and potassium are used. It is done. In addition, a conductive composite material in which carbon black, metal particles, or the like is dispersed in the above material is also used.
The distance between the source and drain electrodes (channel length) is an important factor that determines the characteristics of the device, but is usually 100 μm or less, preferably 50 μm or less, and the width between the source and drain electrodes (channel width) is usually 2000 μm. Hereinafter, it is preferably 1000 μm or less. The channel width may be longer when the electrode structure is a comb structure.
The structure (shape) of each of the source and drain electrodes will be described. Even if the source and drain electrodes have the same structure. It may be different. Since it has a bottom contact structure, it is generally preferable to use a lithographic method and to form a rectangular parallelepiped. The length of the electrode may be the same as the previous channel width. The width of the electrode is not particularly specified, but is preferably shorter in order to reduce the area of the element within a stable range. Usually, it is 1000 μm or less, preferably 500 μm or less. The thickness of the electrode is usually 1 nm to 1 μm, preferably 5 nm to 0.5 nm, and more preferably 10 nm to 0.2 μm.
A wiring is connected to each of the electrodes 1, 3, and 5, and the wiring is also made of the same material as the electrode.

An insulating material is used for the insulator layer 4. For example, polymers such as polyparaxylylene, polyacrylate, polymethyl methacrylate, polystyrene, polyvinylphenol, polyamide, polyimide, polycarbonate, polyester, polyvinyl alcohol, polyvinyl acetate, polyurethane, polysulfone, epoxy resin, phenol resin, and combinations thereof Copolymers; oxides such as silicon dioxide, aluminum oxide, titanium oxide and tantalum oxide; ferroelectric oxides such as SrTiO ₃ and BaTiO ₃ ; nitrides such as silicon nitride and aluminum nitride; sulfides; fluorides and the like Or a polymer in which particles of these dielectrics are dispersed can be used. The film thickness of the insulator layer 4 varies depending on the material, but is usually 0.1 nm to 100 μm, preferably 0.5 nm to 50 μm, more preferably 5 nm to 10 μm.

As a material for the semiconductor layer 2, an organic material containing a diketopyrrolopyrrole compound represented by the formula (1) is used. The organic substance may be a mixture, but the organic substance contains a diketopyrrolopyrrole compound represented by the formula (1) in an amount of 50% by weight or more, preferably 80% by weight or more, more preferably 95% by weight or more. Is preferred. In order to improve the characteristics of the field effect transistor or to impart other characteristics, other organic semiconductor materials and various additives may be mixed as necessary. The semiconductor layer 2 may be composed of a plurality of layers.
The thickness of the semiconductor layer 2 is preferably as thin as possible without losing necessary functions. In lateral field effect transistors as shown in A, B, and D, the device characteristics do not depend on the film thickness if the film thickness exceeds a predetermined value, while the leakage current may increase as the film thickness increases. This is because there are many. In order to show a necessary function, it is usually 1 nm to 10 μm, preferably 5 nm to 5 μm, more preferably 10 nm to 3 μm.

In the field effect transistor of the present invention, other layers can be provided between the layers or on the outer surface of the element as necessary. For example, if a protective layer is formed directly on the semiconductor layer or via another layer, the influence of outside air such as humidity can be reduced, and the ON / OFF ratio of the device can be increased. There is also an advantage that the mechanical characteristics can be stabilized.
Although it does not specifically limit as a material of a protective layer, For example, the film | membrane which consists of various resins, such as acrylic resins, such as an epoxy resin and polymethylmethacrylate, polyurethane, polyimide, polyvinyl alcohol, a fluororesin, polyolefin, silicon oxide, aluminum oxide, A film made of a dielectric such as an inorganic oxide film or a nitride film, such as silicon nitride, is preferably used, and a resin (polymer) having a low oxygen or moisture permeability and a low water absorption rate is particularly preferable. In recent years, protective materials developed for organic EL displays can also be used. Although the film thickness of a protective layer can employ | adopt arbitrary film thickness according to the objective, it is 100 nm-1 mm normally.

  In addition, by performing surface treatment on a substrate or an insulator layer on which an organic semiconductor is stacked, it is possible to improve device characteristics. For example, by adjusting the degree of hydrophilicity / hydrophobicity of the substrate surface, the film quality of the film formed thereon can be improved. In particular, the characteristics of organic semiconductor materials can vary greatly depending on the state of the film, such as molecular orientation. Therefore, it is considered that the substrate surface treatment controls the molecular orientation of the interface portion between the substrate and the semiconductor film formed thereafter, and improves characteristics such as carrier mobility. Examples of such substrate treatment include hydrophobization treatment with hexamethyldisilazane, cyclohexene, octadecyltrichlorosilane, acid treatment with hydrochloric acid, sulfuric acid, acetic acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, etc. Electrical treatment such as alkali treatment with ozone, ozone treatment, fluorination treatment, plasma treatment with oxygen or argon, Langmuir / Blodgett film formation process, other insulator or semiconductor thin film formation process, mechanical process, corona discharge, etc. And rubbing treatment using fibers and the like.

  As a method of providing each layer in these embodiments, for example, a vacuum deposition method, a sputtering method, a coating method, a printing method, a sol-gel method, or the like can be appropriately employed.

Next, a method for manufacturing a field effect transistor according to the present invention will be described below with reference to FIG. 2 by taking a bottom contact type field effect transistor (FET) shown in the embodiment example A of FIG.
This manufacturing method can be similarly applied to the field effect transistors of the other embodiments described above.

(Substrate and substrate processing)
It is manufactured by providing necessary layers and electrodes on the substrate 6 (see FIG. 2 (1)). As the substrate, those described above can be used. It is also possible to perform the above-described surface treatment on this substrate. The thickness of the substrate 6 is preferably thin as long as necessary functions are not hindered. Although it varies depending on the material, it is usually 1 μm to 10 mm, preferably 5 μm to 5 mm. If necessary, the substrate may have an electrode function.

(Formation of gate electrode)
A gate electrode 5 is formed on the substrate 6 (see FIG. 2B). The electrode material described above is used as the electrode material. As a method for forming the electrode film, various methods can be used. For example, a vacuum deposition method, a sputtering method, a coating method, a thermal transfer method, a printing method, a sol-gel method, and the like are employed. It is preferable to perform patterning as necessary so as to obtain a desired shape during or after film formation. Various methods can be used as the patterning method, and examples thereof include a photolithography method in which patterning and etching of a photoresist are combined. Patterning can also be performed using a printing method such as ink jet printing, screen printing, offset printing, letterpress printing, soft lithography such as a microcontact printing method, and a combination of these methods. The thickness of the gate electrode 5 varies depending on the material, but is usually 0.1 nm to 10 μm, preferably 0.5 nm to 5 μm, more preferably 1 nm to 3 μm. Moreover, when it serves as a gate electrode and a board | substrate, it may be larger than said film thickness.

(Formation of insulator layer)
An insulating layer 4 is formed over the gate electrode 5 (see FIG. 2 (3)). As the insulator material, those described above are used. Various methods can be used to form the insulator layer 4. For example, spin coating, spray coating, dip coating, casting, bar coating, blade coating, etc., screen printing, offset printing, ink jet printing, vacuum deposition, molecular beam epitaxial growth, ion cluster beam method, ion plating Examples thereof include dry process methods such as a coating method, a sputtering method, an atmospheric pressure plasma method, and a CVD method. In addition, a method of forming an oxide film on a metal such as a sol-gel method or alumite on aluminum is employed.
In the portion where the insulator layer and the semiconductor layer are in contact with each other, a predetermined surface treatment can be performed on the insulator layer in order to satisfactorily orient the semiconductor molecules at the interface between the two layers. As the surface treatment method, the same surface treatment as that of the substrate can be used. The thickness of the insulator layer 4 is preferably as thin as possible without impairing its function. Usually, it is 0.1 nm-100 micrometers, Preferably it is 0.5 nm-50 micrometers, More preferably, it is 5 nm-10 micrometers.

(Formation of source electrode and drain electrode)
The source electrode 1 and the drain electrode 3 can be formed according to the case of the gate electrode 5 (see FIG. 2 (4)).

(Formation of semiconductor layer)
As described above, an organic material containing 50% by weight or more of the diketopyrrolopyrrole compound represented by the formula (1) is used as the semiconductor material. Various methods can be used for forming the semiconductor layer. Formation method in vacuum process such as sputtering method, CVD method, molecular beam epitaxial growth method, vacuum deposition method, coating method such as dip coating method, die coater method, roll coater method, bar coater method, spin coating method, ink jet method In addition, it is roughly classified into formation methods in solution processes such as screen printing, offset printing, and microcontact printing. Hereinafter, a method for forming a semiconductor layer will be described in detail.

First, a method for obtaining an organic semiconductor layer by forming an organic material by a vacuum process will be described.
A method (vacuum deposition method) in which the organic material is heated in a crucible or a metal boat under vacuum and the evaporated organic material is attached (deposited) to a substrate (exposed portions of the insulator layer, the source electrode and the drain electrode). Preferably employed. Under the present circumstances, a vacuum degree is 1.0 * 10 < ^-1 > Pa or less normally, Preferably it is 1.0 * 10 <^-4> Pa or less. Further, since the characteristics of the organic semiconductor film, and hence the field effect transistor, vary depending on the substrate temperature during vapor deposition, it is preferable to select the substrate temperature carefully. The substrate temperature during vapor deposition is usually 0 to 200 ° C, preferably 10 to 150 ° C. The deposition rate is usually 0.001 nm / second to 10 nm / second, preferably 0.01 nm / second to 1 nm / second. The film thickness of the organic semiconductor layer formed from an organic material is usually 1 nm to 10 μm, preferably 5 nm to 1 μm.
Instead of heating and evaporating the organic material for forming the organic semiconductor layer and attaching it to the substrate, a sputtering method in which accelerated ions such as argon collide with the material target to knock out material atoms and attach them to the substrate. It may be used.

  Since the semiconductor material in the present invention is an organic substance and a relatively low molecular compound, such a vacuum process can be preferably used. Although such a vacuum process requires somewhat expensive equipment, there is an advantage that a uniform film can be easily obtained with good film formability.

Next, a method for obtaining an organic semiconductor layer by forming an organic semiconductor material by a solution process will be described.
In this method, the organic material is dissolved or dispersed in a solvent and applied to a substrate (exposed portions of the insulator layer, the source electrode and the drain electrode). Coating methods include casting, spin coating, dip coating, blade coating, wire bar coating, spray coating, and other coating methods, inkjet printing, screen printing, offset printing, letterpress printing, and other micro contact printing methods. The method of soft lithography, etc., or a method combining a plurality of these methods may be employed. Furthermore, as a method similar to the coating method, a Langmuir project method in which a monomolecular film formed on a water surface is transferred to a substrate and laminated, a method in which a liquid crystal or a molten state is sandwiched between two substrates, or introduced between substrates by capillary action, etc. Can also be adopted. The film thickness of the organic semiconductor layer formed by this method is preferably as thin as possible without impairing the function. There is a concern that the leakage current increases as the film thickness increases. The film thickness of the organic semiconductor layer is usually 1 nm to 10 μm, preferably 5 nm to 5 μm, more preferably 10 nm to 3 μm.
When such an organic semiconductor layer is formed, the use of such a solution process has an advantage that a large-area organic field effect transistor can be manufactured with relatively inexpensive equipment.

  The characteristics of the organic semiconductor layer thus formed (see FIG. 2 (5)) can be further improved by post-processing. For example, the heat treatment can relieve distortion in the film generated during film formation, and can improve and stabilize characteristics. Furthermore, a change in characteristics due to oxidation or reduction can be induced by exposure to an oxidizing or reducing gas or liquid such as oxygen or hydrogen. This can be used for the purpose of increasing or decreasing the carrier density in the film, for example.

In addition, in a technique called doping, characteristics can be changed by adding a trace amount of elements, atomic groups, molecules, and polymers to the organic semiconductor layer. For example, oxygen, hydrogen, hydrochloric acid, sulfuric acid, sulfonic acid and other acids, Lewis acids such as PF ₅ , AsF ₅ and FeCl ₃ , halogen atoms such as iodine, metal atoms such as sodium and potassium, etc. can be doped. This can be achieved by bringing these gases into contact with the organic semiconductor layer, immersing them in a solution, or performing an electrochemical doping treatment. These dopings can be added at the time of synthesizing the material, after the formation of the film, or can be added to the solution in the production process from the solution, or added at the stage of the precursor film. It is also possible to co-deposit materials to be added at the time of vapor deposition, to mix them in the atmosphere at the time of film formation, or to perform doping by accelerating ions in a vacuum and colliding with the film.

  These doping effects include changes in electrical conductivity due to increase or decrease in carrier density, changes in carrier polarity (p-type and n-type), changes in Fermi level, and the like. Such doping is often used in semiconductor devices.

(Protective layer)
When the protective layer 7 is formed on the organic semiconductor layer, there is an advantage that the influence of outside air can be minimized and the electrical characteristics of the organic field effect transistor can be stabilized (see FIG. 2 (6)). The above-mentioned materials are used as the protective layer material.
Although the film thickness of the protective layer 7 can employ | adopt arbitrary film thickness according to the objective, it is 100 nm-1 mm normally.
Various methods can be used to form the protective layer. When the protective layer is made of a resin, for example, a method of applying a resin solution and then drying to form a resin film, or applying or depositing a resin monomer The method of polymerizing after that is mentioned. Cross-linking treatment may be performed after film formation. When the protective layer is made of an inorganic material, for example, a formation method in a vacuum process such as a sputtering method or a vapor deposition method, or a formation method in a solution process such as a sol-gel method can be used.
In the field effect transistor of the present invention, a protective layer can be provided between the layers as necessary in addition to the organic semiconductor layer. These layers help to stabilize the electrical properties of the organic field effect transistor.

  According to the present invention, since an organic material is used as a semiconductor material, it can be manufactured in a relatively low temperature process. Accordingly, flexible materials such as plastic plates and plastic films that could not be used under conditions exposed to high temperatures can be used as the substrate. As a result, it is possible to manufacture a light, flexible, and hard-to-break element, which can be used as a switching element for an active matrix of a display. Examples of the display include a liquid crystal display, a polymer dispersion type liquid crystal display, an electrophoretic display, an EL display, an electrochromic display, a particle rotation type display, and the like. Further, since the field effect transistor of the present invention can be manufactured by a coating method or a printing process, it is also suitable for manufacturing a large area display.

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

  The operating characteristics of the field effect transistor are determined by the carrier mobility of the semiconductor layer, the conductivity, the capacitance of the insulating layer, the element configuration (distance and width between source and drain electrodes, film thickness of the insulating layer, etc.) and the like. As a semiconductor material used for the field effect transistor, the higher the carrier mobility, the better the semiconductor layer. The diketopyrrolopyrrole compound of the formula (1) in the present invention has good film forming properties and large area applicability. In addition, the compound can be produced at a low cost, and has an advantage that it is stable and has a long life even after a thin film is formed. Furthermore, this diketopyrrolopyrrole compound shows not only a p-type semiconductor but also an n-type semiconductor characteristic and an ambipolar characteristic having both p-type and n-type characteristics by selecting the substituent, and is excellent. Field effect transistors can be provided.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated still in detail, this invention is not limited to these examples. In the examples, unless otherwise specified, parts represent parts by mass, and% represents mass%.

Example 1
A resist material is applied on an n-doped silicon wafer (surface resistance 0.02 Ω · cm or less) with 300 nm SiO ₂ thermal oxide film treated with hexamethyldisilazane, exposed to patterning, and 1 nm of chromium and 40 nm of gold. Vapor deposited. Next, the resist was peeled off to form the source electrode (1) and the drain electrode (3) (channel length 25 μm × channel width 4 mm × 19 comb electrodes). The silicon wafer provided with this electrode was placed in a vacuum vapor deposition apparatus and evacuated until the degree of vacuum in the apparatus became 1.0 × 10 ⁻³ Pa or less. This electrode was subjected to compound no. 1 (see Formula (2) and Table 1) was deposited to a thickness of 80 nm at room temperature (25 ° C.) to form a semiconductor layer (2) to obtain a field effect transistor of the present invention. In the field effect transistor in this example, the thermal oxide film in the n-doped silicon wafer with the thermal oxide film has the function of the insulating layer (4), and the n-doped silicon wafer is the substrate (6) and the gate layer (5). It has a function (see FIG. 3).

The obtained field effect transistor was installed in a vacuum prober, depressurized to about 10 ⁻⁴ Pa with a vacuum pump, and semiconductor characteristics were measured using a semiconductor parameter analyzer 4155C (manufactured by Agilent). For semiconductor characteristics, the gate voltage was scanned from 10 V to -100 V in 20 V steps, the drain voltage was scanned from 10 V to -100 V, and the drain current-drain voltage was measured. As a result, current saturation was observed, and from the obtained voltage-current curve, the device showed a p-type semiconductor, and the carrier mobility was 2 × 10 ⁻³ cm ² / Vs. The on / off ratio was 5 × 10 ² .

Example 2
In Example 1, compound no. 1 is compound no. An organic field effect transistor of the present invention was produced in the same manner as in Example 2 except that the number was changed to 42. As for the semiconductor characteristics, the gate voltage was scanned from -10V to 100V in 20V step, the drain voltage was scanned from -10V to 100V, and the drain current-drain voltage was measured. As a result, current saturation was observed, and the obtained voltage current From the curve, the device showed an n-type semiconductor, the carrier mobility was 7 × 10 ⁻⁴ cm ² / Vs, and the on / off ratio was 4 × 10 ² .

Example 3
In Example 1, compound no. 1 is compound no. An organic field effect transistor of the present invention was produced in the same manner as in Example 1 except that the number was changed to 88. As for the semiconductor characteristics, the gate voltage is scanned from -10V to 100V in 20V step, the drain voltage is scanned from -10V to 100V, and the drain current-drain voltage is measured. As a result, current saturation is observed and obtained from the saturation region. The electron mobility was 2 × 10 ⁻⁵ cm ² / Vs. Conversely, the gate voltage is scanned from 10 V to -100 V in 20 V steps, the drain voltage is scanned from 10 V to -100 V, the drain current-drain voltage is measured, and the hole mobility obtained from the saturation region is 4 × 10 ^-4 cm ² / Vs, indicating ambipolar characteristics.

It is the schematic which shows the structural example of the field effect transistor of this invention. It is the schematic of the process for manufacturing the example of 1 aspect of the field effect transistor of this invention. 1 is a schematic view of a field effect transistor of the present invention obtained in Example 1. FIG.

Explanation of symbols

The same number is attached | subjected to the same name in FIGS. 1-3.
1 source electrode 2 semiconductor layer 3 drain electrode 4 insulator layer 5 gate electrode 6 substrate 7 protective layer

Claims (10)

A field effect transistor using a compound represented by the following formula (1) as a semiconductor material.

(In the formula (1), X ₁ and X ₂ are each independently an oxygen atom, sulfur atom or selenium atom, and R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom or substituted. Each represents an aliphatic hydrocarbon group or an optionally substituted aromatic group.) The field effect transistor according to claim _1, wherein X ₁ and X ₂ in formula (1) are each independently an oxygen atom or a sulfur atom. The field effect transistor of claim 1 or claim 2 R ₁ and R ₂ are both hydrogen atoms in the formula (1). The field effect transistor according to any one of claims 1 to 3, wherein R ₃ and R ₄ in the formula (1) are aromatic groups which may be substituted. The field effect transistor according to any one of claims 1 to 4, which has a hole transport property. The field effect transistor according to claim 5, wherein R ₁ and R ₂ in formula (1) are hydrogen atoms, R ₃ and R ₄ are phenyl groups, and X ₁ and X ₂ are oxygen atoms. The field effect transistor according to any one of claims 1 to 4, which has an electron transport property. The field effect transistor according to claim 7, wherein R ₁ and R ₂ in formula (1) are hydrogen atoms, R ₃ and R ₄ are halogeno-substituted phenyl groups, and X ₁ and X ₂ are oxygen atoms. The field effect transistor according to claim 1, which has ambipolar characteristics. The field effect transistor according to claim 9, wherein R ₁ and R ₂ in formula (1) are hydrogen atoms, R ₃ and R ₄ are phenyl groups, and X ₁ and X ₂ are sulfur atoms.

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