JP2004319982A - Field effect transistor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect transistor of large field effect mobility which is provided by a simple and easy method. <P>SOLUTION: This field effect transistor comprises an organic semiconductor layer comprising a crystallized film of a benzoporphyrin compound expressed with a formula (2) obtained by converting a coating film of an organic solvent soluble porphyrin compound expressed with a formula (1) by heating at 180-250°C. The organic semiconductor layer has a film thickness of 30-150 nm and a maximum diameter of crystal grain of 1 μm, and has strong absorbency for 660nm or more. In the formula, R<SB>1</SB>and R<SB>2</SB>are a hydrogen atom, a halogen atom, a hydroxyl group or an alkyl group whose carbon number is 1-12, R<SB>3</SB>is the hydrogen atom or an aryl group, and M is two hydrogen atoms or metal atoms, or a metal oxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a field-effect transistor and a method for manufacturing the same, and more particularly to a field-effect transistor using a crystallized film of a benzoporphyrin compound obtained by heating from a coating film of an organic solvent-soluble porphyrin compound, which can be easily manufactured and has a high mobility. Field-effect transistor with high resistance and a method of manufacturing the same.

  2. Description of the Related Art Non-linear optical properties, conductivity, and semiconductivity of organic semiconductor compounds have attracted attention in the fields of organic electronics and optoelectronics, and various devices have been actively developed. Representative examples of organic semiconductor compounds are phthalocyanine-based compounds, porphyrin compounds, and polyacenes. The characteristics such as nonlinear optical properties, conductivity, and semiconductivity required when these compounds are made into a device as an organic material largely depend on not only the purity of the material but also the crystallinity and orientation. However, it has been difficult to achieve high purity because many compounds having an expanded π-conjugated system are insoluble in solvents and easily oxidized in the atmosphere. In addition, a large-scale apparatus was required for film formation, such as performing vacuum deposition to obtain a crystallized film having high orientation.

  In recent years, a field effect transistor (FET) device using an organic semiconductor compound for a semiconductor layer has attracted attention, and the organic semiconductor compound is more flexible than an inorganic material such as silicon. Because of its film properties, it has come to be considered suitable for the production of flexible devices using plastic as a base material.

  However, as described above, pentacene, which is a typical example of an organic semiconductor compound, has high crystallinity and is insoluble in a solvent, and thus a film can be formed on a substrate only by vacuum evaporation. On the other hand, FETs are more easily manufactured by forming a thin film from a solution of an organic semiconductor soluble in an organic solvent by spin coating or the like. As such an example, there is one in which a π-conjugated polymer is used for a semiconductor layer (see Non-Patent Document 1). In the case of a π-conjugated polymer, it is known that the arrangement state of the molecular chains has a great effect on the electric conduction characteristics. It is reported that it largely depends on the arrangement state of molecular chains in a layer (see Non-Patent Document 2).

However, since the arrangement of the molecular chains of the π-conjugated polymer is performed until the solution is applied and dried, there is a possibility that the arrangement state of the molecular chains may significantly change due to environmental changes or differences in the application method. there were. An FET using a film in which a soluble pentacene precursor thin film is formed by coating and converted into pentacene by heat treatment has also been reported (see Non-Patent Document 3). In this case, high-temperature treatment was required for conversion to pentacene, and desorbed components having a large mass had to be removed by reduced pressure.
"Japanese Journal of Applied Physics", Japan Society of Applied Physics, 1991, Vol. 30, p. 596-598 "Nature" Nature Publishing Group, 1999, vol. 401, p. 685-687 "Advanced Materials", WILLEY-VCH Verlag GmbH, 1999, vol. 11, p. 480-483

As described above, conventionally, an FET element using an organic semiconductor has a problem that a complicated process such as vacuum film formation is required, or the FET device is easily affected by the environment.
The present invention has been made to solve this problem, and has an object to provide a field-effect transistor having an organic semiconductor layer formed with a large field-effect mobility and a simple method, and a method for manufacturing the same. I do.

  The present inventors can easily obtain a crystallized film by heat treatment from a coating film obtained when an organic solvent solution of a porphyrin compound represented by the following general formula (1) is applied to a substrate surface. The inventors have found that a field-effect transistor using this crystallized film as an organic semiconductor layer exhibits a field-effect mobility equal to or greater than that of an organic semiconductor layer formed by conventional evaporation.

  That is, the present invention provides the following general formula (1)

(Wherein R ₁ and R ₂ each independently represent at least one selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group) R ₃ represents at least one selected from a hydrogen atom and an aryl group.)
A porphyrin compound coating film represented by the following formula (2) obtained by converting the coating film by heating at 180 to 250 ° C.

(In the formula, R ₂ and R ₃ are the same as described above.)
Having an organic semiconductor layer composed of a crystallized film of a benzoporphyrin compound represented by the formula: wherein the organic semiconductor layer has a thickness of 30 to 150 nm, the maximum diameter of crystal grains is 1 μm or more, and has strong absorption at 660 nm or more. This is a field-effect transistor.

Wherein R ₁ and R ₂ of the porphyrin compound represented by the general formula (1) is a hydrogen atom, and it is preferred that R ₂ of the benzoporphyrin compound represented by the general formula (2) is a hydrogen atom.

Preferably, R _{3 of the} porphyrin compound represented by the general formula (1) and the benzoporphyrin compound represented by the general formula (2) is a hydrogen atom.
The organic semiconductor layer preferably has a field effect mobility of 1 × 10 ⁻³ cm ² / V · s or more and an On / Off ratio of 100 or more.

  Further, the present invention is a method for manufacturing a field effect transistor having an organic semiconductor layer, wherein the organic semiconductor layer is formed by the following general formula (1)

(Wherein R ₁ and R ₂ each independently represent at least one selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group) R ₃ represents at least one selected from a hydrogen atom and an aryl group.)
The following general formula (2) obtained by heating a coating film composed of an organic solvent solution of a porphyrin compound represented by

(In the formula, R ₂ and R ₃ are the same as described above.)
A method for manufacturing a field-effect transistor, comprising a step of forming a crystallized film of a benzoporphyrin compound represented by the formula:

  It is preferable that the organic solvent solution of the porphyrin compound represented by the general formula (1) contains a halogen solvent.

  According to the present invention, a field-effect transistor having a large field-effect mobility can be provided by a much simpler method than in the related art.

Hereinafter, the present invention will be described in detail.
The field effect transistor according to the present invention has the following general formula (1)

(Wherein R ₁ and R ₂ each independently represent at least one selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group) R ₃ represents at least one selected from a hydrogen atom and an aryl group.)
The following general formula (2) obtained by converting a coating film of an organic solvent-soluble porphyrin compound represented by the following formula by heating at 180 to 250 ° C:

(In the formula, R ₂ and R ₃ are the same as described above.)
Having an organic semiconductor layer composed of a crystallized film of a benzoporphyrin compound represented by the formula: wherein the organic semiconductor layer has a thickness of 30 to 150 nm, the maximum diameter of crystal grains is 1 μm or more, and has strong absorption at 660 nm or more. It is characterized by the following.

In the present invention, R ₁ when substituents R ₁ attached to di cyclooctadiene ene ring of the porphyrin compound represented the general formula (1) is converted to the benzoporphyrin compound represented by the general formula (2) by heat treatment -CH = CH-R ₁ to be eliminated. Therefore, R ₁ may be independently at least one selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group. The above may be combined. When the number of carbon atoms exceeds 12, the molecular weight of the desorbed component increases, and the desorbed component remains in the benzoporphyrin film, so that sufficient semiconductor characteristics cannot be obtained. Most preferably, R ₁ is a hydrogen atom.

The substituent R ₂ of the porphyrin compound represented by the general formula (1) remains as a substituent in the benzoporphyrin compound obtained after the heat treatment. Therefore, the substituent R ₂ affects the orientation of the benzoporphyrin. R ₂ may be each independently at least one kind selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group. May be combined. If the number of carbon atoms of R ₂ exceeds 12, the porphyrin ring abundance with respect to the whole molecule decreases, and the porphyrin rings are difficult to orient, and sufficient semiconductor properties cannot be obtained. Most preferably, R ₂ is a hydrogen atom, and stacking between porphyrin rings is more likely to occur, and the crystallinity of the film is improved.

  As a method for forming the organic semiconductor layer, a porphyrin compound represented by the general formula (1) is dissolved in an organic solvent, and then applied to a substrate, and then heated to heat the benzoyl compound represented by the general formula (2). A method for obtaining a crystallized film of a porphyrin compound is preferred.

  The organic solvent used to dissolve the porphyrin compound is not particularly limited as long as the porphyrin compound does not react or precipitate. Further, two or more kinds of organic solvents may be mixed and used. It is preferable to use a halogen solvent in consideration of the smoothness of the coating film surface and the uniformity of the film thickness. Examples of the halogen solvent include chloroform, methylene chloride, dichloroethane, chlorobenzene, 1,2-dichloroethylene and the like. The concentration of the solution is arbitrarily adjusted depending on the desired film thickness, but is preferably 0.01 to 5% by weight.

  Examples of the coating method include a spin casting method, a dipping method, a dropping method, a printing method such as offset or screen, and an ink jet method. In addition, it is desirable that the semiconductor layer is filtered with a membrane filter in advance so that dust and the like are not mixed into the semiconductor layer as much as possible. This is because insoluble matter or dust from outside impedes uniform orientation, causing an increase in off-state current and a decrease in on / off ratio. The benzoporphyrin coating may be pre-dried at 130 ° C. or less.

The porphyrin compound film formed by application causes a retro Diels-Alder reaction by heating, and conversion to a benzoporphyrin compound accompanied by elimination of R ₁ —CH ＝ CH—R ₁ occurs. At the same time as the formation of benzoporphyrin, porphyrin rings are stacked to cause crystal growth, and a crystallized benzoporphyrin film is obtained. The desorption reaction occurs at 150 ° C. or higher, and the heating temperature for obtaining higher field-effect mobility is desirably 180 to 250 ° C., preferably 200 to 230 ° C. If the temperature is lower than 180 ° C., a crystallized film having sufficient crystal growth cannot be obtained. If the temperature exceeds 250 ° C., cracks occur due to rapid film shrinkage.

Heating is performed on a hot plate, in a hot air circulation type oven or in a vacuum oven. In order to obtain uniform orientation, a method of instantaneously heating on a hot plate is preferable.
In order to obtain higher crystallinity, it is preferable to perform a rubbing treatment in which the coating film before heating is lightly rubbed with a cloth or the like. The cloth used for the rubbing treatment includes, but is not limited to, rayon, cotton, silk and the like.

  The thickness of the organic semiconductor layer using the benzoporphyrin alignment film obtained by these operations is desirably 30 to 150 nm, preferably 50 to 120 nm. When the film thickness is less than 30 nm, the uniformity of the film thickness is impaired. On the other hand, when the film thickness exceeds 150 nm, the smoothness of the film surface is impaired, and the field-effect mobility is reduced.

  The growth of the crystal can be confirmed by observation of the film surface using X-ray diffraction, an optical microscope, a laser microscope, or the like, and an ultraviolet-visible absorption spectrum of the film. The maximum diameter of the crystal grains in the organic semiconductor layer is 1 μm or more, preferably in the range of 2 to 50 μm. If it is less than 1 μm, sufficient field effect mobility cannot be obtained.

  In addition, it is preferable that the organic semiconductor layer exhibits strong absorption at 660 nm or more in observation of an ultraviolet-visible absorption spectrum. When the porphyrin ring has no absorption or only weak absorption at 660 nm or more, the stacking between porphyrin rings is weak and the porphyrin rings are not sufficiently oriented, so that the field-effect mobility decreases.

The field effect mobility of the organic semiconductor layer obtained in the present invention is 1 × 10 ⁻³ cm ² / V · s or more. If it is lower than that, the current value between the source and the drain obtained by application of the gate voltage is too small, which is not suitable for driving a liquid crystal element or the like. Further, the On / Off ratio of the organic semiconductor layer is preferably 100 or more.

  FIG. 1 is an enlarged schematic view showing a part of the field effect transistor of the present invention. The field-effect transistor of the present invention includes a gate electrode 1, a gate insulating layer 2, a source electrode 3, a drain electrode 4, and an organic semiconductor layer 4.

  The gate electrode, source electrode, and drain electrode are not particularly limited as long as they are conductive materials. Platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony lead, tantalum, indium, aluminum, zinc, and magnesium , And alloys thereof, conductive metal oxides such as indium tin oxide, or inorganic and organic semiconductors having improved conductivity by doping or the like, for example, silicon single crystal, polysilicon, amorphous silicon, germanium, graphite, Examples include polyacetylene, polyparaphenylene, polythiophene, polypyrrole, polyaniline, polythienylenevinylene, and polyparaphenylenevinylene. Examples of a method for manufacturing an electrode include a sputtering method, an evaporation method, a printing method from a solution or a paste, and an ink-jet method. As the electrode material, among those mentioned above, those having low electric resistance at the contact surface with the semiconductor layer are preferable.

  As the gate insulating layer, any material can be used as long as it can uniformly apply a solution of the porphyrin compound soluble in an organic solvent represented by the general formula (1), but a material having a high dielectric constant and a low conductivity is preferable. Examples include inorganic oxides and nitrides such as silicon oxide, silicon nitride, aluminum oxide, titanium oxide, and tantalum oxide, and organic polymers such as polyacrylate, polymethacrylate, polyethylene terephthalate, polyimide, polyether, and siloxane-containing polymers. No. Further, among the insulating materials, those having high surface smoothness are preferable.

  The uniformity of the coating of the solution of the organic solvent-soluble porphyrin compound represented by the general formula (1) on the insulating layer is improved, and the orientation of the film of the benzoporphyrin compound represented by the general formula (2) is improved by heating. For uniformity, only the surface of the insulating layer can be modified. Examples of the method include dry processing using ozone, plasma, and hexamethyldisilazane gas, and wet processing using a solution in which tetraalkoxysilane, trichlorosilane, a surfactant, or the like is dissolved in an organic solvent.

  The structure of the field-effect transistor in the present invention is not limited to a thin film type, but may be a three-dimensional type.

Hereinafter, Synthesis Examples and Examples are shown, but the present invention is not limited to these Examples.
Synthesis Example 1
Synthesis of Bicycloporphyrin Lithium aluminum hydride powder was added to a mixture of 0.109 g (0.5 mmol) of ethyl 4,7-dihydro-4,7-ethano-2H-isoindole-1-carboxylate and 15 mL of THF (tetrahydrofuran). 144 g (3.76 mmol) were added at 0 ° C. After the reaction mixture was stirred at 0 ° C. for 2 hours, it was poured into water and extracted with chloroform. 0.010 g of p-toluenesulfonic acid was added to the extraction solution, and the mixture was stirred at room temperature for 12 hours. Further, 0.150 g (0.61 mmol) of p-chloranil was added, and the mixture was stirred at room temperature for 12 hours. The reaction mixture was washed with a saturated aqueous solution of sodium bicarbonate, pure water and saturated saline in this order, and dried over anhydrous sodium sulfate. After the solution was concentrated, purification was performed by alumina column chromatography and recrystallization to obtain 0.096 g of a bicycloporphyrin crystal represented by the following formula (3).

Example 1
FIG. 1 shows the structure of the field-effect transistor in this embodiment.
First, an N-type silicon substrate was used as the gate electrode 1. A 5000-inch silicon oxide film obtained by thermally oxidizing the surface layer of the silicon substrate was used as the gate insulating layer 2. Then, chromium and gold were vapor-deposited in this order, and a source electrode 3 and a drain electrode 4 were formed by ordinary photolithography. A 1% by weight chloroform solution of bicycloporphyrin synthesized in Synthesis Example 1 was spin-cast on this substrate. Further, the substrate was heated at 200 ° C. to form an organic semiconductor layer 5 composed of a benzoporphyrin thin film represented by the following formula (4). The thickness of the organic semiconductor layer was 60 nm, and as a result of observation using an optical microscope, the maximum diameter of crystal grains was 2 μm.

By the above procedure, a field-effect transistor having a channel length of 50 μm, a channel width of 10 mm, and a semiconductor layer thickness of about 500 ° was prepared. When the Vd-Id curve of the transistor thus formed was measured using a parameter analyzer 4156C (trade name) manufactured by Agilent (product), the result as shown in FIG. 2 was obtained. From the results obtained, this transistor had a field-effect mobility of 2 × 10 ⁻³ cm ² / V · s and an On / Off ratio of 1000.

  Under the same film forming conditions, a benzoporphyrin film was formed on a quartz substrate. When the ultraviolet-visible absorption spectrum of the film was observed using a spectrophotometer U3310 (trade name) manufactured by Hitachi, Ltd., strong absorption having a peak near 690 nm was observed.

Example 2
FIG. 3 shows the structure of the field-effect transistor in this embodiment.
First, an N-type silicon substrate was used as the gate electrode 1. A 5000-inch silicon oxide film obtained by thermally oxidizing the surface layer of the silicon substrate was used as the gate insulating layer 2. A 1% by weight chloroform solution of bicycloporphyrin synthesized in Synthesis Example 1 was spin-cast thereon. Further, the substrate was heated at 200 ° C. to form an organic semiconductor layer 5 composed of a benzoporphyrin thin film represented by the formula (4). The thickness of the organic semiconductor layer was 60 nm, and as a result of observation using an optical microscope, the maximum diameter of crystal grains was 2 μm. Gold was deposited thereon to form a source electrode 3 and a drain electrode 4.

By the above procedure, a field-effect transistor having a channel length of 50 μm, a channel width of 10 mm, and a semiconductor layer thickness of about 500 ° was prepared. When Vd-Id of the transistor thus manufactured was measured, the transistor had a field-effect mobility of 4 × 10 ⁻³ cm ² / V · s and an On / Off ratio of 1000.

Comparative Example 1
A field-effect transistor formed of a benzoporphyrin thin film was manufactured according to Example 1, except that the heating temperature described in Example 1 was 170 ° C. This transistor had a field-effect mobility of 5 × 10 ⁻⁵ cm ² / V · s and an On / Off ratio of 10. The thickness of the organic semiconductor layer was 60 nm, and the maximum diameter of the crystal grain was 0.5 μm or less.

  The organic semiconductor film formed of a benzoporphyrin thin film formed on a quartz plate showed only weak absorption with a peak near 650 nm.

  Since the field-effect transistor of the present invention is a field-effect transistor having a large field-effect mobility, it can be used for a liquid crystal panel, an organic EL panel, electronic paper, a sensor, and the like.

FIG. 2 is a schematic diagram showing an enlarged part of a field-effect transistor according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating electric characteristics of the field-effect transistor according to the first embodiment of the present invention. FIG. 9 is a schematic diagram illustrating a part of a field-effect transistor according to a second embodiment of the present invention in an enlarged manner.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Gate electrode 2 Gate insulating layer 3 Source electrode 4 Drain electrode 5 Organic semiconductor layer

Claims (6)

The following general formula (1)

(Wherein R ₁ and R ₂ each independently represent at least one selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group) R ₃ represents at least one selected from a hydrogen atom and an aryl group.)
A porphyrin compound coating film represented by the following formula (2) obtained by converting the coating film by heating at 180 to 250 ° C.

(In the formula, R ₂ and R ₃ are the same as described above.)
Having an organic semiconductor layer composed of a crystallized film of a benzoporphyrin compound represented by the formula: wherein the organic semiconductor layer has a thickness of 30 to 150 nm, the maximum diameter of crystal grains is 1 μm or more, and has strong absorption at 660 nm or more. A field effect transistor characterized by the above-mentioned. Characterized in that R ₁ and R ₂ of the porphyrin compound represented by the general formula (1) is a hydrogen atom, and R ₂ of the benzoporphyrin compound represented by the general formula (2) is a hydrogen atom The field-effect transistor according to claim 1. _3. The field effect transistor according to claim 1, wherein R _{3 of the} porphyrin compound represented by the general formula (1) and the benzoporphyrin compound represented by the general formula (2) is a hydrogen atom. . 4. The organic semiconductor layer according to claim 1, wherein the organic semiconductor layer has a field-effect mobility of 1 × 10 ⁻³ cm ² / V · s or more and an On / Off ratio of 100 or more. 3. The field-effect transistor according to claim 1. A method for manufacturing a field-effect transistor having an organic semiconductor layer, wherein the organic semiconductor layer is represented by the following general formula (1)

(Wherein R ₁ and R ₂ each independently represent at least one selected from a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group having 1 to 12 carbon atoms, an oxyalkyl group, a thioalkyl group, or an alkyl ester group) R ₃ represents at least one selected from a hydrogen atom and an aryl group.)
The following general formula (2) obtained by heating a coating film composed of an organic solvent solution of a porphyrin compound represented by

(In the formula, R ₂ and R ₃ are the same as described above.)
A method for producing a field-effect transistor, comprising a step of forming a crystallized film of a benzoporphyrin compound represented by the formula:   The method according to claim 5, wherein the organic solvent solution of the porphyrin compound represented by the general formula (1) contains a halogen solvent.

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