JP2006049776A - Field effect type organic transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field effect organic transistor which is improved in on/off ratio and low of threshold voltage. <P>SOLUTION: The field effect organic transistor comprises a source electrode 15, drain electrode 14, gate electrode 12, gate insulating layer 13, and organic semiconductor layer 16. The organic semiconductor layer 16 contains an organic semiconductor compound and such compound as can bond with or include ion. The compound is crown ether compound, alumina compound, silicon compound, or titanium compound. The organic semiconductor compound is conjugated polymer. <P>COPYRIGHT: (C)2006,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.

  An organic transistor using an organic semiconductor can be manufactured on a plastic substrate and have a large screen, which is difficult for a silicon transistor. In particular, those using soluble organic semiconductors can be reduced in cost because they do not require a vacuum process, and are expected to be applied to new devices such as flexible electronic paper and information tags.

However, practical characteristics have not yet been obtained for organic transistors. For example, many problems such as low mobility, low on / off ratio, high threshold voltage, and easy deterioration over time have not been solved. It has been pointed out that the purity of the organic semiconductor is low as one of the causes for deteriorating such characteristics. Therefore, Patent Document 1 and Patent Document 2 disclose that impurities can be removed and characteristics can be improved by purifying an organic semiconductor.
JP 2004-63978 A JP 2004-83650 A

  However, it is impossible to completely remove impurities mixed from raw materials, solvents, catalysts, by-products, glass containers, environments and the like in the synthesis process by a general method. In particular, conjugated polymer compounds are extremely difficult to purify because they cannot be applied to sublimation purification, which is an effective purification method for low molecular compounds. In addition, increasing the number of purification steps or performing special purification leads to an increase in cost.

The present invention has been made in view of such background art, and provides a field effect organic transistor having an improved on / off ratio and a low threshold voltage.
The present invention also provides a low-cost field-effect organic transistor that does not require an advanced method for purifying organic semiconductors.

  That is, the present invention is a field effect organic transistor having a source electrode, a drain electrode, a gate electrode, a gate insulating layer, and an organic semiconductor layer, and the organic semiconductor layer can be combined with or include an organic semiconductor compound and ions. A field effect organic transistor comprising a compound.

Preferably, the compound is a crown ether compound, an alumina compound, a silicon compound, or a titanium compound. More preferably, the compound is a 14-crown-4 ether derivative, 15-crown-5 ether derivative, 18-crown-6 ether derivative, 21-crown-7 ether derivative, 24-crown-8 ether derivative, 4,10- Diaza-12-crown-4 ether derivatives, 4,10-diaza-15-crown-5 ether derivatives, 1-aza-15-crown-5 ether derivatives, 1-aza-18-crown-6 ether derivatives, 4, 13-diaza-18-crown-6 ether derivatives, Al ₂ O _3, a SiO _2, TiO _2.

Moreover, what is 1.0 mass% or less with respect to an organic-semiconductor compound is preferable, and, as for content of the said compound, More preferably, it is 0.1 mass% or less.
The organic semiconductor compound is preferably a conjugated polymer compound, more preferably a polythiophene derivative. The conjugated polymer compound preferably has a weight average molecular weight of 5,000 to 100,000. The conjugated polymer compound is preferably oriented.

According to the present invention, a field effect organic transistor having an improved on / off ratio and a low threshold voltage can be provided.
In addition, since an advanced purification method for an organic semiconductor is not required, a low-cost field effect organic transistor can be provided.

Hereinafter, the present invention will be described in detail.
The field effect organic transistor of the present invention is a field effect organic transistor composed of three electrodes, a source electrode, a drain electrode, and a gate electrode, and a gate insulating layer and an organic semiconductor layer. It contains an organic semiconductor compound and a compound capable of binding or inclusion with ions.

  The present invention has found that the on / off ratio can be improved in the same manner as when impurities are removed by adding a compound that interacts with impurities without removing impurities contained in the organic semiconductor layer. Is. In addition, the inventors have found that the threshold voltage can be lowered.

Preferably, the compound is a crown ether compound, an alumina compound, a silicon compound, or a titanium compound. More preferably, the compound is a 14-crown-4 ether derivative, 15-crown-5 ether derivative, 18-crown-6 ether derivative, 21-crown-7 ether derivative, 24-crown-8 ether derivative, 4,10- Diaza-12-crown-4 ether derivatives, 4,10-diaza-15-crown-5 ether derivatives, 1-aza-15-crown-5 ether derivatives, 1-aza-18-crown-6 ether derivatives, 4, 13-diaza-18-crown-6 ether derivatives, Al ₂ O _3, a SiO _2, TiO _2. For example, the compound of the structure shown below is mentioned.

  In addition, the content of the compound is not particularly limited as long as the effects of the present invention can be obtained, but taking into account that the original characteristics of the organic semiconductor compound are not impaired, 1.0% by mass or less based on the organic semiconductor compound Is preferable, more preferably 0.1% by mass or less, particularly 0.01% by mass to 0.1% by mass. Moreover, it is preferable that the said compound contains not only 1 type but multiple types.

  As the organic semiconductor compound used in the present invention, for example, the following compounds are suitable. (1) 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, conjugated polymer compounds such as polypyridine derivatives having a nitrogen atom, polypyrrole derivatives, polyaniline derivatives, polyquinoline derivatives, (2) oligomers typified by dimethylsexithiophene and quarterthiophene, (3) typified by perylene, tetracene and pentacene Acenes, deposited organic molecules represented by copper phthalocyanine derivatives, (4) discotic liquid crystals represented by triphenylene derivatives, phenylnaphthalene derivatives, and benzothiazole derivatives. Is the smectic liquid crystal, (5) poly (9,9-dialkyl fluorene - bithiophene) is a liquid crystal polymer typified by copolymers thereof are not limited thereto.

  Further, a conjugated polymer compound is preferable, and a polythiophene derivative is particularly preferable. For example, the compound of the structure shown below is mentioned.

(In the formula, R ₁ , R ₂ , R ₃ , and R ₄ represent H, F, an alkyl group having 1 to 20 carbon atoms, an alkoxy group, or a pearl fluoroalkyl group, and 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 100,000 in consideration of solubility in a solvent, film formability and the like. The conjugated polymer compound is preferably oriented. Examples of the alignment method include a rubbing method, a temperature gradient method, a friction transfer method, an alignment method by applying a magnetic field or an electric field, and the like.

  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 gate insulating layer is particularly but not limited to SiO _2, SiN used in the present _{invention, Al 2 O 3, Ta 2} O 5 or the like of inorganic materials, polyimide, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl phenol, polyethylene terephthalate Organic materials such as polyvinylidene fluoride and organic-inorganic hybrid materials can be used. Preferably, an organic compound is preferable from the viewpoint that a liquid phase process leading to low cost can be used.

  The insulating substrate is not particularly limited. For example, in addition to inorganic materials such as glass and quartz, photosensitive polymer compounds such as acrylic, vinyl, ester, imide, urethane, diazo, and cinnamoyl, polyfluoride Organic materials such as vinylidene, 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, ITO (Indium Tin Oxide), SnO _{2 and} other inorganic materials 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 and the gate insulating layer is not particularly limited. However, 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, a micro contact method, a roll coating method. It can be formed by a method, an inkjet 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 inkjet 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.
Example 1
FIG. 2 is a schematic cross-sectional view showing a field effect organic transistor used in an embodiment of the present invention. An n-type highly doped silicon substrate as the gate electrode 21, SiO ₂ as the gate insulating layer 22, gold as the source electrode 24 and drain electrode 23, and poly (3-hexylthiophene) as the organic semiconductor compound forming the organic semiconductor layer 25 (Weight average molecular weight 47,000) is used. The manufacturing procedure is shown below.

A thermal oxide film SiO ₂ (thickness 300 nm) is formed on the silicon substrate. A chromium (5 nm) / gold (100 nm) source / drain electrode having a channel length of 50 μm and a channel width of 50 mm is formed thereon by a lift-off method. 14-crown-4 ether, 15-crown-5 ether and 18-crown-6 ether are added at a ratio of 0.1% by mass to 1 g of poly (3-hexylthiophene) and dissolved in 100 g of chloroform. This solution is applied by spin coating and dried at 120 ° C. for 12 hours to form an organic semiconductor layer. A gold wire of 0.1 mmφ is wired with a silver paste to each of the gate electrode, the drain electrode, and the source electrode to produce a field effect organic transistor element.

Next, the drain current is measured at a gate voltage of 0 V to -50 V and a source-drain electrode voltage of 0 V to -50 V, and it is confirmed that good IV characteristics are obtained.
Next, the threshold voltage Vth is obtained by extrapolating the drain current Id = 0 from the relationship between the square root of the drain current and the gate voltage, and the mobility μ is further calculated from the equation (1).

(Wherein μ is mobility, Id is drain current (A), W is channel width (cm), L is channel length (cm), and Ci is capacitance per unit area of the gate insulating layer (F / cm ² ). , Vg is the gate voltage (V), Vth is the threshold voltage (V))
The on / off ratio is calculated from the ratio of the drain current (off current) when the gate voltage is 0 V and the source-drain electrode is -50 V and the drain current (on current) when the gate voltage is -50 V and the source-drain electrode is -50 V. calculate.

Example 2
Instead of the 14-crown-4 ether and 15-crown-5 ether used in Example 1, 4,10-diaza-12-crown-4 ether and 4,10-diaza-15-crown-5 ether were used. A field effect organic transistor element is produced by the same method as in Example 1 except that.

  It is confirmed that good IV characteristics can be obtained by measuring the drain current when the gate voltage is 0 V to -50 V and the voltage between the source and drain electrodes is 0 V to -50 V. The mobility, on / off ratio, and threshold voltage can be obtained by the same method as in the first embodiment.

Example 3
Similar to Example 1 except that Al ₂ O ₃ , SiO ₂ and TiO ₂ were used instead of 14-crown-4 ether, 15-crown-5 ether and 18-crown-6 ether used in Example 1. A field effect organic transistor element is produced by the method described above.

  It is confirmed that good IV characteristics can be obtained by measuring the drain current when the gate voltage is 0 V to -50 V and the voltage between the source and drain electrodes is 0 V to -50 V. The mobility, on / off ratio, and threshold voltage can be obtained by the same method as in the first embodiment.

Comparative Example 1
Next, as a comparative experiment, a field effect organic transistor was prepared by the same method as in Example 1 except that only poly (3-hexylthiophene) was used as the organic semiconductor layer, and the mobility, The on / off ratio and threshold voltage are obtained. As a result, the field-effect organic transistors produced in Examples 1 to 3 did not change in mobility compared to those produced in Comparative Example 1, but in all cases, the on / off ratio was improved by 2 to 3 digits and the threshold voltage was increased. Is confirmed to be small.

Example 4
FIG. 3 is a schematic cross-sectional view showing a field effect organic transistor used in an embodiment of the present invention. The gate electrode 31 is an n-type highly doped silicon substrate, the gate insulating layer 32 is polyimide, the source electrode 34 and the drain electrode 33 are gold, and the organic semiconductor compound forming the organic semiconductor layer 35 is poly (9,9-dioctylfluorene). -Co-bithiophene) (weight average molecular weight 28,000) is used. The manufacturing procedure is shown below.

  A polyamic acid is applied on a silicon substrate by a spin coating method and baked at 200 ° C. to form a polyimide film. The surface is rubbed with a cloth and rubbed. 0.5% by weight of 14-crown-4 ether and 0.3% by weight of 1-aza-15-crown-5 ether, respectively, per 1 g of poly (9,9-dioctylfluorene-co-bithiophene), 0 Add 2% by weight of 1-aza-18-crown-6 ether and 0.1% by weight of 4,13-diaza-18-crown-6 ether and dissolve in 100 g of dichlorobenzene. On top of this, this solution is applied by spin coating, and dried at 200 ° C. for 6 hours and 280 ° C. for 1 hour to form an organic semiconductor layer. On top of this, gold (50 nm) is vacuum-deposited to produce both source and drain electrodes having a channel length of 50 μm and a channel width of 10 mm. At this time, both the source and drain electrodes are arranged so that the direction of current flow and the rubbing direction are parallel. A gold wire of 0.1 mmφ is wired with a silver paste to each of the gate electrode, the drain electrode, and the source electrode to produce a field effect organic transistor element.

  Next, the drain current is measured at a gate voltage of 0 V to -50 V and a source-drain electrode voltage of 0 V to -50 V, and it is confirmed that good IV characteristics can be obtained. The mobility, on / off ratio, and threshold voltage can be obtained by the same method as in the first embodiment.

Example 5
Similar to Example 4 except that 21-crown-7 ether and 24-crown-8 ether were used instead of 14-crown-4 ether and 1-aza-15-crown-5 ether used in Example 4. A field effect organic transistor element is produced by the method described above.

  It is confirmed that good IV characteristics can be obtained by measuring the drain current when the gate voltage is 0 V to -50 V and the voltage between the source and drain electrodes is 0 V to -50 V. The mobility, on / off ratio, and threshold voltage can be obtained by the same method as in the first embodiment.

Example 6
Field effect organics were produced in the same manner as in Example 4 except that Al ₂ O ₃ and SiO ₂ were used instead of 14-crown-4 ether and 1-aza-15-crown-5 ether used in Example 4. A transistor element is manufactured.

  It is confirmed that good IV characteristics can be obtained by measuring the drain current when the gate voltage is 0 V to -50 V and the voltage between the source and drain electrodes is 0 V to -50 V. The mobility, on / off ratio, and threshold voltage can be obtained by the same method as in the first embodiment.

Comparative Example 2
Next, as a comparative experiment, a field effect organic transistor was prepared by the same method as in Example 4 except that only poly (9,9-dioctylfluorene-co-bithiophene) was used as the organic semiconductor layer, and the same method as above was used. To find the mobility, on / off ratio, and threshold voltage. As a result, the field effect organic transistors produced in Examples 4 to 6 did not change in mobility compared to those produced in Comparative Example 2, but in any case, the on / off ratio was improved by 2 to 3 digits and the threshold voltage was increased. Is confirmed to be small.

  The field effect organic transistor of the present invention has an improved on-off ratio and a low threshold voltage, and thus can be used for a field effect organic transistor in the electro field such as a display device, an information tag, and an IC. In addition, it is a low-cost field-effect organic transistor because it does not require an advanced purification method for organic semiconductors.

It is a cross-sectional schematic diagram of the field effect type organic transistor of this invention. It is a cross-sectional schematic diagram of the field effect type organic transistor used in an Example. It is a cross-sectional schematic diagram of the field effect type organic transistor used in an Example.

Explanation of symbols

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

Claims (9)

  A field effect organic transistor having a source electrode, a drain electrode, a gate electrode, a gate insulating layer, and an organic semiconductor layer, wherein the organic semiconductor layer contains an organic semiconductor compound and a compound capable of binding or inclusion with ions A field effect organic transistor characterized by that.   2. The field effect organic transistor according to claim 1, wherein the compound is a crown ether compound, an alumina compound, a silicon compound or a titanium compound. The compound is a 14-crown-4 ether derivative, 15-crown-5 ether derivative, 18-crown-6 ether derivative, 21-crown-7 ether derivative, 24-crown-8 ether derivative, 4,10-diaza-12. -Crown-4 ether derivatives, 4,10-diaza-15-crown-5 ether derivatives, 1-aza-15-crown-5 ether derivatives, 1-aza-18-crown-6 ether derivatives, 4,13-diaza 18-crown-6 ether derivatives, Al ₂ O _3, SiO ₂ or field effect type organic transistor according to claim 1 or 2, wherein the TiO _2.   The field effect organic transistor according to any one of claims 1 to 3, wherein the content of the compound is 1.0 mass% or less with respect to the organic semiconductor compound.   The field effect organic transistor according to any one of claims 1 to 3, wherein the content of the compound is 0.1% by mass or less based on the organic semiconductor compound.   The field effect organic transistor according to any one of claims 1 to 5, wherein the organic semiconductor compound comprises a conjugated polymer compound.   The field effect organic transistor according to claim 6, wherein the conjugated polymer compound is a polythiophene derivative.   The field effect organic transistor according to claim 6 or 7, wherein the conjugated polymer compound has a weight average molecular weight of 5,000 to 100,000.   The field effect organic transistor according to any one of claims 6 to 8, wherein the conjugated polymer compound is oriented.

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