JP2005072200A - Field effect organic transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect organic transistor equipped with an organic semiconductor layer which is high in mobility and has a high on-off ratio. <P>SOLUTION: A gate electrode 12 is formed on an insulating board 11, a gate insulating layer 13 is formed thereon, a source electrode 15 and a drain electrode 14 are arranged on the gate insulating layer 13, and an organic semiconductor layer 16 and a protective film 17 are arranged over the source electrode 13 and the drain electrode 14 for the formation of the field effect organic transistor, wherein the gate insulating layer 13 is formed of liquid crystal polymer whose dielectric constant is anisotropic. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a field effect organic transistor, and more particularly to a field effect organic transistor having an organic semiconductor layer useful in the electro field such as a display device, an information tag, and an IC.

In order to compete with silicon transistors based on crystalline silicon technology, development of transistors using organic semiconductors has been actively conducted. Organic semiconductors have the characteristics of organic materials, such as light weight, flexibility, diversity, and robustness. They can be formed by low-temperature processes around 100 ° C, and can be manufactured by liquid-phase processes such as printing and spin coating. is there. Therefore, it is possible to manufacture on a plastic substrate and enlarge the screen, which could not be achieved with a crystalline silicon semiconductor, and there is an increasing expectation for application to new devices such as flexible electronic paper and information tags. However, a normal organic semiconductor has a mobility of 10 ⁻⁵ to 10 ⁻² cm ² / Vs, an order of magnitude lower than that of a silicon semiconductor, and a high resistance. Therefore, it is difficult to obtain a large current, and the operating frequency is low. We have problems such as low.

In order to obtain high mobility, it is effective to arrange organic semiconductor layers in an orderly manner so that the overlap of conjugate planes is as large as possible. In Patent Document 1, a fluorine-based amorphous polymer is laminated on an oxide film insulating layer, and organic semiconductors are arranged by rubbing to obtain a mobility of 10 ⁻³ cm ² / Vs level. Patent Document 2 discloses the use of a liquid crystal polymer as an alignment film for arranging organic semiconductors. However, there is no disclosure of a specific structure, and the specific effect is not specified at all.

  On the other hand, the drain current in the saturation region obtained by the field effect organic transistor can be obtained from the following formula (I).

(Where, Id is drain current (A), μ is mobility (cm ² / Vs), W is channel width (cm), L is channel length (cm), and Ci is gate insulating layer capacitance (F / cm ² ), Vg represents the gate voltage (V), Vth represents the threshold voltage (V) of the transistor, and can be obtained by extrapolating the drain current Id = 0 from the relationship between the square root of the drain current and the gate voltage.

That is, in order to obtain a large current, it is effective not only to improve the mobility of the organic semiconductor but also to increase the capacity of the gate insulating layer. In Patent Document 3, an organic polymer having a dielectric constant of 5 or more, such as polyvinyl alcohol or cyanoethyl pullulan, is used to increase the capacity of the gate insulating layer. However, the mobility is still 10 ⁻² cm ² / Vs, which is still sufficient. is not.

When used as a switching device, the ratio of the current flowing between the source / drain electrodes when the transistor is turned on to the current flowing between the source / drain electrodes when the transistor is turned off (on / off ratio) is preferably at least 10 ⁴ or more. 10 ⁶ or more is required. However, in the case of an organic semiconductor, the on-current is small because of low mobility as described above, and a sufficient on-off ratio is not obtained due to the large off-current due to the influence of impurities contained in the organic semiconductor. Accordingly, there is currently no field effect organic transistor using an organic semiconductor that can satisfy practical characteristics.
JP 07-221367 A (page 6) Japanese Patent Laid-Open No. 9-232589 (page 4) Japanese Patent No. 2984370 (page 9)

  The present invention has been made in view of such a background art, solves the problems of the background art described above, and has a high mobility and a high on / off ratio in the electro field such as a display device, an information tag, and an IC. The object is to provide a novel field effect organic transistor having an organic semiconductor layer.

  The present invention provides a field effect organic transistor having improved on-off ratio by improving the mobility of an organic semiconductor by using a liquid crystal polymer having dielectric anisotropy as a gate insulating film.

  That is, the present invention is a field effect organic transistor having three electrodes of a source electrode, a drain electrode, and a gate electrode, and a gate insulating layer and an organic semiconductor layer composed of at least one layer, wherein at least one layer of the gate insulating layer. Is a field effect organic transistor characterized by comprising a liquid crystal polymer having dielectric anisotropy.

The liquid crystal polymer of the gate insulating layer is preferably a liquid crystal polymer having a negative dielectric anisotropy in which the liquid crystal polymer is homogeneously oriented.
The liquid crystal polymer of the gate insulating layer is preferably a liquid crystal polymer having a positive dielectric anisotropy in which homeotropic alignment is performed.
The liquid crystal polymer of the gate insulating layer is preferably a liquid crystal polymer having at least a nematic liquid crystal phase.
The liquid crystal polymer of the gate insulating layer is preferably a liquid crystal polymer having at least a smectic liquid crystal phase.

The liquid crystal polymer of the gate insulating layer is preferably a liquid crystal polymer having a dielectric anisotropy of 5 or more.
The liquid crystal polymer of the gate insulating layer is preferably a liquid crystal polymer having a dielectric anisotropy of 10 or more.
It is preferable that a substituent selected from a cyano group, a carbonyl group, a halogen group, a nitro group and a hydroxyl group of the liquid crystal polymer of the gate insulating layer is aligned in a direction perpendicular to the substrate.

The organic semiconductor layer is preferably a conjugated polymer compound.
The polymer compound preferably has a weight average molecular weight of 5,000 to 500,000.
The organic semiconductor layer preferably includes an organic compound having a conjugated surface, and the organic compound is an organic semiconductor layer in which the conjugated surface is aligned perpendicular to the charge transfer direction.

  ADVANTAGE OF THE INVENTION According to this invention, the field effect type | mold organic transistor which can be utilized in electro fields, such as a display device, an information tag, and IC, and has a high mobility and a high on / off ratio can be provided.

  The structure of the field effect organic transistor of the present invention is effective in any of the planar type, staggered type, or inverted staggered type, but the structure of the field effect organic transistor of the present invention is shown in FIG. 1 using the planar type as an example. Will be explained.

  FIG. 1 is a schematic cross-sectional view showing an example of a field effect organic transistor of the present invention. In the figure, the field effect organic transistor of the present invention has a gate electrode 12 disposed on an insulating substrate 11, a gate insulating layer 13 disposed thereon, and a source electrode 15 and a drain electrode 14 disposed thereon. The organic semiconductor layer 16 is disposed thereon, and the protective film 17 is disposed on the top.

  The field effect organic transistor of the present invention uses a liquid crystal polymer having dielectric anisotropy as a gate insulating layer, and defines the positive and negative of the dielectric anisotropy and the orientation of the liquid crystal polymer. It has been found that a large current can be obtained by voltage, (2) the mobility of the organic semiconductor is improved, (3) the on / off ratio is improved, and the like.

  In the present invention, the dielectric anisotropy means a value of (dielectric constant in the major axis direction of liquid crystal molecules) − (dielectric constant in the minor axis direction), and the dielectric anisotropy is “negative”. Indicates that the dielectric constant in the major axis direction is smaller than the dielectric constant in the minor axis direction, and that the dielectric anisotropy is “positive”, the dielectric constant in the major axis direction of the liquid crystal molecules is greater than the dielectric constant in the minor axis direction. Indicates big.

The homogeneous alignment refers to an alignment in which the optical axis of liquid crystal molecules is parallel to the substrate, and the homeotropic alignment refers to an alignment in which the optical axis of liquid crystal molecules is perpendicular to the substrate.
Hereinafter, the present invention will be described in detail.

  As shown in the above formula (I), the drain current increases in proportion to the capacitance of the gate insulating layer, that is, the dielectric constant, and the dielectric constant is a dielectric constant component in the film thickness direction of the gate insulating layer. The drain current is not involved no matter how large the dielectric constant in the plane direction. Therefore, it is important not only to use a polymer having a large dielectric constant, but also to align the dielectric constant in the film thickness direction. That is, a liquid crystal polymer having a negative dielectric anisotropy has a uniform dielectric constant in the film thickness direction when the liquid crystal polymer has a negative dielectric anisotropy, and a liquid crystal polymer having a positive dielectric anisotropy has a dielectric constant in the film thickness direction by a homeotropic alignment. The rate increases.

  Further, as a method for orienting the organic semiconductor layer, there is a rubbing method described in Japanese Patent Application Laid-Open No. 07-221367, but this only involves aligning the molecular direction of the organic semiconductor along the groove, and is involved in mobility. A conjugate plane cannot be defined. In the present invention, by arranging the dipoles or substituents of the liquid crystal skeleton in order, not only the molecular direction of the organic semiconductor is aligned, but also the conjugate plane of the organic semiconductor is aligned in one direction by the interaction at the atomic level. It is possible.

  The advantages of using the liquid crystal polymer as the gate insulating layer of the present invention are described as follows: (1) The orientation control of the polymer is easy by having a liquid crystal phase, and (2) the film thickness direction by aligning the dipoles. A large dielectric constant can be obtained. (3) The organic semiconductor can be microscopically arranged by utilizing the interaction in the micro region between the aligned liquid crystal polymer and the organic semiconductor.

  The liquid crystal polymer used in the present invention is not particularly limited as long as it has a liquid crystal phase. Further, a main chain type liquid crystal polymer having a liquid crystal skeleton in the liquid crystal polymer main chain, a side chain type liquid crystal polymer having a liquid crystal skeleton in a side chain, a liquid crystal dendrimer, and the like are exemplified, and the shape is not limited. In addition, examples of the structure of the liquid crystal skeleton include a benzene ring, a pyridine ring, a pyrimidine ring, a cyclohexane ring, and the like. As a substituent, an alkyl group, an alkoxy group, a perfluoroalkyl group, a perfluoroalkoxy group, a fluorine, a cyano group, and a carbonyl group. , A halogen group, a nitro group, a hydroxyl group, a trifluoromethyl group, and the like, but are not limited thereto. Examples of the liquid crystal polymer include, but are not limited to, polyvinyl, polyacrylic, polymethacrylic, and polysiloxane.

The liquid crystal polymer preferably has a weight average molecular weight in the range of 5,000 to 500,000.
Specific examples of liquid crystal polymers having negative dielectric anisotropy in the following structural formulas (Ia) to (IVe), specific examples of liquid crystal polymers having positive dielectric anisotropy in the structural formulas (Va) to (VIe) Indicates.

Note that R in the structural formula of the liquid crystal polymer represents an alkyl group or a perfluoroalkyl group having 1 to 18 carbon atoms. However, one or more methylene groups in the alkyl group may be replaced with CO, O, or S. X represents a single bond, COO, OOC, CH ₂ O or OCH ₂ . m shows the integer of 1-20. n represents an integer of 10 to 1000. A ₁ , A ₂ , and A ₃ each independently represent H, CN, F, Cl, Br, NO ₂ , CF ₃ , CHF ₂ , or CH ₂ F.

  In addition, the method for homogeneously or homeotropically aligning the liquid crystal polymer used in the present invention is not particularly limited, and examples include oblique vapor deposition, rubbing, stretching, magnetic field, electric field, and photoalignment. .

  The method for forming a gate insulating layer comprising the liquid crystal polymer of the present invention comprises a liquid crystal polymer casting method, spin coating method, dip coating method, screen printing method, micro mold method, micro contact method, roll It can be carried out by a method such as a coating method, an ink jet method or an LB method.

In addition, the gate insulating layer used in the present invention may be a single layer or two or more layers, and may be a gate insulating layer by combining a liquid crystal polymer or a liquid crystal polymer with another insulating material. Other insulating materials are not particularly limited, but inorganic materials such as SiO ₂ , SiN, Al ₂ O ₃ , Ta ₂ O ₅ , polyimide, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl phenol, polyethylene terephthalate, polyfluoride. Organic materials such as vinylidene chloride and organic-inorganic hybrid materials can be used.

The organic semiconductor layer used in the present invention is not particularly limited as long as it is a conjugated compound having a conjugated double bond. For example, the following compounds are suitable.
Polyacetylene derivatives, polythiophene derivatives having a thiophene ring, poly (3-alkylthiophene) derivatives, poly (3,4-ethylenedioxythiophene) derivatives, polythienylene vinylene derivatives, polyphenylene derivatives having a benzene ring, polyphenylene vinylene derivatives, nitrogen Conjugated polymer compounds such as polypyridine derivatives having atoms, polypyrrole derivatives, polyaniline derivatives, polyquinoline derivatives:
Oligomers represented by dimethylsexualthiophene and quarterthiophene:
Acenes represented by perylene, tetracene, pentacene, deposited organic molecules represented by copper phthalocyanine derivatives, discotic liquid crystals represented by triphenylene derivatives, smectic liquid crystals represented by phenylnaphthalene derivatives, benzothiazole derivatives, poly (9 , 9-dialkylfluorene-bithiophene) copolymer, a liquid crystal polymer represented by:
However, it is not limited to these.

  Further, from the viewpoint that a liquid phase process can be used preferably, the polymer compound having the above conjugated structure is suitable. For example, the compound of the structure shown below is mentioned.

(Wherein R ₁ , R ₂ , R ₃ and R ₄ represent H, F, or an alkyl group or alkoxy group having 1 to 20 carbon atoms. N represents a positive integer.)
The molecular weight of these conjugated polymer compounds is not particularly limited, but the weight average molecular weight is preferably 5,000 to 500,000 in consideration of solubility in a solvent, film formability and the like.

In addition, the organic semiconductor layer used in the present invention may contain an appropriate dopant in order to adjust its electric conductivity. Acceptant types I ₂ , Br ₂ , Cl ₂ , ICl, BF ₃ , PF ₅ , H ₂ SO ₄ , FeCl ₃ , TCNQ (tetracyanoquinodimethane), donor-type Li, K, Na, Eu, surfactants such as alkyl sulfonates and alkyl benzene sulfonates.

  The field-effect organic transistor of the present invention is preferably manufactured on an insulating substrate, and the insulating substrate is not particularly limited. For example, in addition to inorganic materials such as glass and quartz, acrylic, vinyl, ester, Photopolymer compounds such as imide, urethane, diazo, and cinnamoyl, organic materials such as polyvinylidene fluoride, polyethylene terephthalate, and polyethylene, and organic-inorganic hybrid materials can be used. In addition, two or more layers of these materials can be used, which is effective for increasing the withstand voltage.

Further, the gate electrode, the source electrode and the drain electrode used in the present invention are not particularly limited as long as they are conductors. For example, metal materials such as Al, Cu, Ti, Au, Pt, Ag, Cr, polysilicon, silicide, Inorganic materials such as ITO (Indium Tin Oxide) and SnO ₂ are also suitable, but conductive polymers dispersed in highly doped polypyridine, polyacetylene, polyaniline, polypyrrole, polythiophene, carbon particles, silver particles, etc. are dispersed. Ink or the like can be used. In particular, when used for flexible electronic paper or the like, it is preferable that each electrode is made of a conductive polymer and a conductive ink in which carbon particles, silver particles, and the like are dispersed because the thermal expansion with the substrate can be easily achieved.

  The method for forming each of these electrodes, the gate insulating layer, and the organic semiconductor layer is not particularly limited, but in the case of an organic material, an electrolytic polymerization method, a casting method, a spin coating method, a dip coating method, a screen printing method, a micromold method, and a micro contact method. It can be formed by a method, a roll coating method, an ink jet method, an LB method, or the like. Depending on the material used, vacuum deposition, CVD, electron beam deposition, resistance heating deposition, sputtering, and the like are also effective formation methods.

  These can be patterned into a desired shape by photolithography and etching. In addition, soft lithography and ink jet methods are also effective patterning methods. Moreover, the extraction electrode from each electrode, a protective film, etc. can be formed as needed.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.
Liquid crystal polymer A
First, the liquid crystal polymer A used for the Example of this invention is shown below.

  The liquid crystal polymer A was synthesized according to the synthesis method described in “J. MACROMOL. SCI. CHEM.”, A28 (7), 651 (1991). The weight average molecular weight of the obtained liquid crystal polymer was 8100, and it had a nematic phase at 68 ° C to 105 ° C.

  Next, a pair of glass substrates having a thickness of 1.1 mm on which an ITO film having a thickness of 700 mm was formed as a transparent electrode was prepared. Silica beads having an average particle diameter of 2.4 μm were dispersed as spacers on one substrate on the transparent electrode of the substrate to produce cells having a uniform cell gap. Liquid crystal polymer A was injected into this cell in an isotropic liquid state, and cooled at 20 ° C./h from the isotropic phase while applying an alternating electric field. When the texture of this cell was observed with a polarizing microscope under crossed Nicols, a dark field was obtained, and it was confirmed that the liquid crystal polymer A was homeotropically aligned. The dielectric constant measured in this state was 15. The dielectric constant is a value measured by applying a sine wave of ± 10 mV and 20 KHz.

  A cell was prepared in the same manner, and the liquid crystal polymer A was cooled at 20 ° C./h from the isotropic phase without applying an alternating electric field when injecting the liquid crystal polymer A in the isotropic liquid state. When the texture of this cell was observed with a polarizing microscope under crossed Nicols, it was confirmed that the liquid crystal polymer A was homogeneously oriented. The dielectric constant measured in this state was 3.

Therefore, it was confirmed that the liquid crystal polymer A is a material having a positive dielectric anisotropy.
Liquid crystal polymer B
Next, the liquid crystal polymer B used in the present invention is shown below.

  The liquid crystal polymer B was synthesized according to the synthesis method described in “J. MACROMOL. SCI. CHEM.”, A28 (7), 651 (1991). The obtained liquid crystal polymer had a weight average molecular weight of 9300 and had a nematic phase at 60 to 90 ° C. When the dielectric constants of homeotropic alignment and homogeneous alignment were measured in the same manner as in the case of liquid crystal polymer A, they were 18 and 4, respectively. Therefore, it was confirmed that the liquid crystal polymer B is a material having a positive dielectric anisotropy.

Liquid crystal polymer C
Furthermore, the liquid crystal polymer C used in the present invention is shown below.

  The liquid crystal polymer C was synthesized according to the synthesis method described in “J. Liq. Chromatogr.”, 14 (8), 1519 (1991). The weight average molecular weight of the obtained liquid crystal polymer was 152100, and it had a smectic phase at 35 ° C to 80 ° C and a nematic phase at 80 ° C to 129 ° C. Next, when the dielectric constants of homeotropic alignment and homogeneous alignment were measured in the same manner as in the case of the liquid crystal polymer A, they were 2 and 6, respectively. Therefore, it was confirmed that the liquid crystal polymer B is a material having a negative dielectric anisotropy.

Next, an example in which the above liquid crystal polymer is used for the gate insulating layer is shown.
FIG. 2 is a block diagram showing a field effect organic transistor used in an embodiment of the present invention. An n-type highly doped silicon substrate was used as the gate electrode 21, gold was used as the source electrode 23 and the drain electrode 24, and liquid crystal polymer A was used as the gate insulating layer 22. The following copper phthalocyanine was used as the organic semiconductor layer 25.

  The production procedure is shown below. Hexamethyldisilazane (HMDS) was applied on a silicon substrate by spin coating, and then a liquid crystal polymer A chloroform solution (0.1 g / ml) was applied by spin coating, followed by drying at 80 ° C. for 6 hours. A gate insulating layer was formed. Here, when the liquid crystal polymer A formed on the glass substrate under the same conditions was observed under a polarizing microscope, a dark field in crossed Nicol was obtained, so that this liquid crystal polymer A was homeotropic on the HMDS-treated glass substrate. It was confirmed that it was oriented. Therefore, it is presumed that the liquid crystal polymer A is homeotropically aligned even on the HMDS-treated silicon substrate.

On top of this, gold (50 nm) was vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. Further, copper phthalocyanine was deposited on the sublimation metal board 10 cm away from the vapor deposition substrate under a pressure of 8 × 10 ⁻⁶ torr until the film thickness reached 100 nm at a substrate temperature of 25 ° C. and an average sublimation rate of 0.1 nm / s. An organic semiconductor layer was formed. A 0.1 mmφ gold wire was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste to produce a field effect organic transistor. The dielectric constant of the liquid crystal polymer was calculated from the capacitance of the gate electrode and the source electrode and found to be 13. From this, it was confirmed that the liquid crystal polymer A was homeotropically aligned.

Next, the drain current was measured at a gate voltage of 0 V to −50 V and a source-drain electrode voltage of 0 V to −50 V, and the mobility μ was calculated according to the formula (I). The on / off ratio was calculated as the ratio between the drain current of the gate voltage Vg = -30V and the drain current of Vg = 0 when the voltage between the source and drain electrodes was -30V. The results are shown below.
Mobility μ = 1.2 × 10 ⁻² cm ² / Vs
On-off ratio = 10 ⁶

As a comparative example, an organic semiconductor layer was formed in the same manner as in Example 1 except that polyvinyl alcohol was used for the gate insulating layer. Evaluation was performed in the same manner as in Example 1, and the mobility and on / off ratio were calculated. The results are shown below.
μ = 7.3 × 10 ⁻⁴ cm ² / Vs
On-off ratio = 10 ⁴

  The above results are improved compared to the mobility and on / off ratio of a transistor using conventional copper phthalocyanine. This is because the cyano group, which is a substituent of the homeotropically aligned liquid crystal polymer, is aligned in a direction perpendicular to the substrate, so that a large dielectric constant is obtained, and the conjugate plane of copper phthalocyanine is perpendicular to the drain-source electrode direction. This is probably due to the orientation.

  FIG. 2 is a block diagram showing a field effect organic transistor used in an embodiment of the present invention. An n-type highly doped silicon substrate was used as the gate electrode 21, gold was used as the source electrode 23 and the drain electrode 24, and a liquid crystal polymer A shown below was used as the gate insulating layer 22. As the organic semiconductor layer 25, the following position-regulated poly-3-hexylthiophene was used.

  The production procedure is shown below. After applying HMDS on a silicon substrate by spin coating, a chloroform solution of liquid crystal polymer A (0.1 g / ml) was also applied by spin coating, and dried at 80 ° C. for 6 hours to form a gate insulating layer. did. On top of this, gold (50 nm) was vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. Further, a toluene solution (0.01 g / ml) of regioregular poly 3-hexylthiophene was applied thereon by a spin coating method to form an organic semiconductor layer 26. A 0.1 mmφ gold wire was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste to produce a field effect organic transistor.

Next, evaluation was performed in the same manner as in Example 1 to calculate mobility and on / off ratio. The results are shown below.
Mobility μ = 7.1 × 10 ⁻² cm ² / Vs
On-off ratio = 10 ⁶

FIG. 3 is a block diagram showing the field effect organic transistor used in the example of the present invention. An n-type highly doped silicon substrate was used as the gate electrode 31, gold was used as the source electrode 34 and drain electrode 35, SiO ₂ was used as the gate insulating layer 32, and liquid crystal polymer B was used as the gate insulating layer 33. The following dimethyl sexithiophene was used as the organic semiconductor layer 36.

For the synthesis of dimethyl secsithiophene, one synthesized according to the synthesis method described in “Advanced Materials”, 5,896, (1993) was used.
The production procedure is shown below. A thermal oxide film SiO ₂ was formed on the silicon substrate. On top of that, HMDS was applied by spin coating, and then a chloroform solution of liquid crystal polymer B (0.1 g / ml) was similarly applied by spin coating and dried at 70 ° C. for 6 hours to form a gate insulating layer. . Here, when the liquid crystal polymer B formed on the glass substrate under the same conditions was observed under a polarizing microscope, a dark field in crossed Nicols was obtained, so that the liquid crystal polymer B was homeotropic on the HMDS-treated glass substrate. It was confirmed that it was oriented. Therefore, it is presumed that the liquid crystal polymer B is homeotropically aligned even on the HMDS-treated silicon substrate.

On top of this, gold (50 nm) was vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. Furthermore, from a board for sublimation metal in which dimethyl secthiothiophene is separated from the vapor deposition substrate by 10 cm under a pressure of 5 × 10 ⁻⁶ torr until the film thickness reaches 100 nm at a substrate temperature of 25 ° C. and an average sublimation rate of 0.1 nm / s. Deposited to form an organic semiconductor layer. A 0.1 mmφ gold wire was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste to produce a field effect organic transistor. It was 16 when the dielectric constant of the liquid crystal polymer B was computed from the capacity | capacitance of a gate electrode and a source electrode. From this, it was confirmed that the liquid crystal polymer B was homeotropically aligned.

Next, evaluation was performed in the same manner as in Example 1 to calculate mobility and on / off ratio. The results are shown below.
Mobility μ = 1.3 × 10 ⁻¹ cm ² / Vs
On-off ratio = 10 ⁷
As a comparative example, an organic semiconductor layer was formed in the same manner as in Example 3 except that polyvinyl alcohol was used for the gate insulating layer. Evaluation was performed in the same manner as in Example 1, and the mobility and on / off ratio were calculated. The results are shown below.
μ = 4.3 × 10 ⁻³ cm ² / Vs
On-off ratio = 10 ⁵

  The above results are improved compared to the mobility and on / off ratio of a transistor using conventional dimethyl succitithiophene. This is because the cyano group, which is a substituent of the homeotropically aligned liquid crystal polymer, is aligned in the direction perpendicular to the substrate, so that a large dielectric constant is obtained, and the conjugated surface of dimethyl sexual thiophene is in the direction of the drain-source electrode. This is thought to be due to the vertical orientation.

  FIG. 2 is a block diagram showing a field effect organic transistor used in an embodiment of the present invention. An n-type highly doped silicon substrate was used as the gate electrode 21, gold was used as the source electrode 23 and the drain electrode 24, and a liquid crystal polymer C was used as the gate insulating layer 22. The following pentacene was used as the organic semiconductor layer 25.

  The production procedure is shown below. A gate insulating layer was formed by applying a chloroform solution of liquid crystal polymer C (0.1 g / ml) on a silicon substrate by spin coating and drying at 80 ° C. for 6 hours. Here, when the liquid crystal polymer C formed on the glass substrate under the same conditions was observed under a polarizing microscope, it was confirmed that the liquid crystal polymer C was homogeneously aligned on the glass substrate. Therefore, it is assumed that the liquid crystal polymer C is homogeneously aligned on the silicon substrate.

On top of this, gold (50 nm) was vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. Further, pentacene was deposited on the sublimation metal board 10 cm away from the vapor deposition substrate under a pressure of 3 × 10 ⁻⁶ torr until the film thickness reached 100 nm at a substrate temperature of 25 ° C. and an average sublimation rate of 0.1 nm / s. A semiconductor layer was formed. A 0.1 mmφ gold wire was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste to produce a field effect organic transistor. The dielectric constant of the liquid crystal polymer was calculated from the capacitance of the gate electrode and the source electrode and found to be 6. From this, it was confirmed that the liquid crystal polymer C was homogeneously aligned.

Next, evaluation was performed in the same manner as in Example 1 to calculate mobility and on / off ratio. The results are shown below.
Mobility μ = 7.1 × 10 ⁻¹ cm ² / Vs
On-off ratio = 10 ⁸

  FIG. 2 is a block diagram showing a field effect organic transistor used in an embodiment of the present invention. An n-type highly doped silicon substrate was used as the gate electrode 21, gold was used as the source electrode 23 and the drain electrode 24, and a liquid crystal polymer C was used as the gate insulating layer 22. Copper phthalocyanine was used as the organic semiconductor layer 25.

The production procedure is shown below. A gate insulating layer was formed by applying a chloroform solution of liquid crystal polymer C (0.1 g / ml) on a silicon substrate by spin coating and drying at 80 ° C. for 6 hours. On top of this, gold (50 nm) was vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. Further, copper phthalocyanine was deposited on the sublimation metal board 10 cm away from the vapor deposition substrate under a pressure of 9 × 10 ⁻⁶ torr until the film thickness reached 100 nm at a substrate temperature of 25 ° C. and an average sublimation rate of 0.1 nm / s. An organic semiconductor layer was formed. A 0.1 mmφ gold wire was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste to produce a field effect organic transistor. Next, evaluation was performed in the same manner as in Example 1 to calculate mobility and on / off ratio. The results are shown below.
Mobility μ = 9.1 × 10 ⁻³ cm ² / Vs
On-off ratio = 10 ⁶

  FIG. 3 is a block diagram showing the field effect organic transistor used in the example of the present invention. An n-type highly doped silicon substrate was used as the gate electrode 31, gold was used as the source electrode 34 and the drain electrode 35, polyimide was used as the gate insulating layer 32, and liquid crystal polymer C was used as the gate insulating layer 33. Pentacene was used as the organic semiconductor layer 36.

  The production procedure is shown below. A polyamic acid was applied on a silicon substrate by a spin coating method and then baked at 200 ° C. to form a polyimide film. The surface was rubbed with a cloth and rubbed. On top of that, a chloroform solution of liquid crystal polymer C (0.1 g / ml) was similarly applied by spin coating, and dried at 70 ° C. for 6 hours to form a gate insulating layer. Here, when the liquid crystal polymer C formed on the glass substrate under the same conditions was observed under a polarizing microscope, it was confirmed that the liquid crystal polymer C was homogeneously aligned on the polyimide film rubbed glass substrate. Therefore, it is presumed that the liquid crystal polymer C is homogeneously aligned even on the polyimide film rubbed silicon substrate.

On top of this, gold (50 nm) was vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. Further, pentacene was deposited on the sublimation metal board 10 cm away from the vapor deposition substrate under a pressure of 5 × 10 ⁻⁶ torr until the film thickness reached 100 nm at a substrate temperature of 25 ° C. and an average sublimation rate of 0.1 nm / s. A semiconductor layer was formed. A gold electrode of 0.1 mmφ was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste, and a field effect organic transistor was produced. Next, evaluation was performed in the same manner as in Example 1 to calculate mobility and on / off ratio. The results are shown below.
Mobility μ = 9.4 × 10 ⁻¹ cm ² / Vs
On-off ratio = 10 ⁸

As a comparative example, an organic semiconductor layer was formed in the same manner as in Example 6 except that polyvinyl alcohol was used for the gate insulating layer. Evaluation was performed in the same manner as in Example 1, and the mobility and on / off ratio were calculated. The results are shown below.
μ = 5.1 × 10 ⁻² cm ² / Vs
On-off ratio = 10 ⁶

  The above results are improved compared to the mobility and on / off ratio of a transistor using conventional pentacene. This is because the carbonyl groups, which are the substituents of the homogeneously aligned liquid crystal polymer, are aligned in the direction perpendicular to the substrate, so that a large dielectric constant is obtained, and the pentacene conjugate plane is aligned perpendicular to the drain-source electrode direction. It is thought that this is due to

  By using a liquid crystal polymer having dielectric anisotropy as a gate insulating film, the present invention can improve the mobility of an organic semiconductor and provide a field effect organic transistor having an improved on / off ratio. A field effect organic transistor having a high on / off ratio can be applied to the electro field such as a display device, an information tag, and an IC.

It is a cross-sectional schematic diagram which shows an example of the field effect type organic transistor of this invention. It is a block diagram which shows the field effect type organic transistor used for the Example of this invention. It is a block diagram which shows the field effect type organic transistor used for the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Insulating substrate 12 Gate electrode 13 Gate insulating layer 14 Drain electrode 15 Source electrode 16 Organic-semiconductor layer 17 Protective film 21 Gate electrode 22 Gate insulating layer 23 Source electrode 24 Drain electrode 25 Organic-semiconductor layer 31 Gate electrode 32 Gate insulating layer 33 Gate Insulating layer 34 Source electrode 35 Drain electrode 36 Organic semiconductor layer

Claims (11)

  A field effect organic transistor having three electrodes, a source electrode, a drain electrode, and a gate electrode, and at least one gate insulating layer and an organic semiconductor layer, wherein at least one layer of the gate insulating layer has a dielectric anisotropy A field-effect organic transistor comprising a liquid crystal polymer having   The field effect organic transistor according to claim 1, wherein the liquid crystal polymer of the gate insulating layer is a liquid crystal polymer having a negative dielectric anisotropy in which the liquid crystal polymer is homogeneously oriented.   The field effect organic transistor according to claim 1, wherein the liquid crystal polymer of the gate insulating layer is a liquid crystal polymer having a positive dielectric anisotropy in which the liquid crystal polymer is homeotropically aligned.   The field effect organic transistor according to any one of claims 1 to 3, wherein the liquid crystal polymer of the gate insulating layer is a liquid crystal polymer having at least a nematic liquid crystal phase.   The field effect organic transistor according to any one of claims 1 to 3, wherein the liquid crystal polymer of the gate insulating layer is a liquid crystal polymer having at least a smectic liquid crystal phase.   The field effect organic transistor according to any one of claims 1 to 5, wherein the liquid crystal polymer of the gate insulating layer is a liquid crystal polymer having a dielectric anisotropy of 5 or more.   The field effect organic transistor according to any one of claims 1 to 6, wherein the liquid crystal polymer of the gate insulating layer is a liquid crystal polymer having a dielectric anisotropy of 10 or more.   The substituent according to any one of claims 1 to 7, wherein a substituent selected from a cyano group, a carbonyl group, a halogen group, a nitro group, and a hydroxyl group of the liquid crystal polymer of the gate insulating layer is aligned in a direction perpendicular to the substrate. The field effect organic transistor as described.   The field effect organic transistor according to claim 1, wherein the organic semiconductor layer is a conjugated polymer compound.   The field effect organic transistor according to claim 9, wherein the conjugated polymer compound has a weight average molecular weight of 5,000 to 500,000.   11. The organic semiconductor layer according to claim 1, wherein the organic semiconductor layer is an organic semiconductor layer that includes an organic compound having a conjugate plane, and the organic compound is arranged with the conjugate plane aligned in a direction perpendicular to the charge movement direction. The field effect organic transistor as described.

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