JP2007012986A - Organic semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic semiconductor device which exhibits effectively the respective performances of its flexibility, heat resistance, low-power consuming quality, and high-operating-speed quality, and further, excels in either one of its mobility, ON/OFF ratio, and drifting characteristic. <P>SOLUTION: The organic semiconductor device 1 has on the surface of a base material 2 a gate electrode 3, an gate insulating layer 4, an organic semiconductor layer 5, a source electrode 6, and a drain electrode 7. Hereupon, the gate insulating layer 4 is made of a polyimide hardened at a temperature lower than 300°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic semiconductor device that is excellent in flexibility, heat resistance, low power consumption, high operating speed, and can be manufactured at low cost, and more particularly, to an organic semiconductor device using a predetermined polyimide for a gate insulating layer. .

  An organic semiconductor device such as a field effect transistor (FET) using an organic semiconductor is expected to be applied to a flexible display or the like. An FET used in such a flexible display applies a voltage to a gate electrode sandwiched between an organic semiconductor and a gate insulating layer, modulates a depletion layer of the organic semiconductor layer, and changes a current flowing through the source electrode and the drain electrode. It is driven by this.

Here, the gate insulating layer of the organic semiconductor device has so far been formed using an inorganic material such as SiO ₂ , SiN, or glass. However, a flexible material is preferable for application to a flexible display or the like, and formation of a gate insulating layer using polyvinyl phenol or polyimide as a material has been studied (for example, patents). See references 1 and 2.)

Polyimide has excellent heat resistance, insulation, and coating flatness, so it is widely used as an insulation protection film for semiconductor elements, interlayer insulation films for multilayer wiring, α-ray shield films for memory elements, flexible circuit substrates, etc. It is also expected as a gate insulating layer in organic semiconductor devices.
JP-A-5-110069 JP 2004-200304 A

  However, since the polyimide used so far has a high curing temperature of 300 ° C. or higher and low compatibility with other polymer materials, the materials such as base materials that can be used are limited, and organic The material used for the semiconductor device was insufficient.

  Accordingly, the present invention has been made in view of the above circumstances, and provides an organic semiconductor device capable of effectively exhibiting each performance of flexibility, heat resistance, low power consumption, and high operating speed. It is intended to do.

  As a result of intensive studies and studies to achieve the above object, the present inventors have found that a predetermined polyimide composition achieves the above object, and have completed the present invention.

  That is, the organic semiconductor device of the present invention is an organic semiconductor device having a gate electrode, a gate insulating layer, an organic semiconductor layer, a source electrode, and a drain electrode on the surface of a base material, and the gate insulating layer is less than 300 ° C. It is made of polyimide cured at a temperature.

  According to the organic semiconductor device of the present invention, flexibility, heat resistance, low power consumption, high operating speed, and on / off ratio performance are improved by forming a gate insulating layer using a predetermined polyimide. Can be made.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the configuration of the organic semiconductor device of the present invention.

  As shown in FIG. 1, the organic semiconductor device 1 of the present invention has a gate electrode 3, a gate insulating layer 4, an organic semiconductor layer 5, a source electrode 6 and a drain electrode 7 on the surface of a substrate 2. This configuration is the same as that of a conventional organic semiconductor device.

  Here, as the base material 2, an insulating material, for example, an inorganic material such as glass or an alumina sintered body, or an organic material such as polyimide, polyester, polyethylene, polyphenylene sulfide, polyparaxylene, or polyethylene naphthalate is used. Can be formed.

  The use of a polymer base material in which an organic material is formed into a film is preferable in that a lightweight and flexible organic semiconductor device can be produced, and the organic material is particularly preferably polyethylene naphthalate. Polyethylene naphthalate is excellent in smoothness, has an appropriate stiffness even when formed into a film (for example, a thickness of about 10 μm), has low gas permeability, is an inexpensive material, and has many desirable properties. However, since the heat resistance is 190 ° C., it has not been used so far. However, in the present invention, the combination using polyimide obtained by heating at 190 ° C. or lower is extremely excellent in compatibility.

  Although the thickness of this base material 2 can be used without being specifically limited, in consideration of a case where it is applied to a flexible product such as a flexible display, an electronic artificial skin, a sheet-type scanner, etc., it is 1 to 300 μm. It is preferable that it is 10 to 100 μm.

  Next, the gate electrode 3 may be formed using at least one of a metal and a conductive organic material. In the case of forming a metal film, an existing vacuum film formation method such as vapor deposition or sputtering may be used, and the electrode shape can be formed by a mask film formation method or a photolithographic method. As the material for electrode formation used at this time, metals such as gold, platinum, chromium, palladium, aluminum, indium, molybdenum, nickel, alloys using these metals, polysilicon, amorphous silicon, tin oxide, indium oxide, Inorganic materials such as indium tin oxide (ITO) can be used. Two or more of these materials may be used in combination.

  In the case of forming an electrode using a conductive organic material, a conductive ink such as polyaniline or polythiophene can be applied to form an electrode. In this case, the electrode can be formed by applying an organic material on a substrate and drying it, so that it can be easily and inexpensively performed. Examples of the application method include a spin coating method, a casting method, a pulling method, a transfer method, and an ink jet method.

  The film thickness of the gate electrode 3 is preferably 50 to 1000 nm although it depends on the conductivity of the material. The lower limit of the thickness of the gate electrode varies depending on the conductivity of the electrode material and the adhesion strength with the base substrate. The upper limit of the thickness of the gate electrode is that when a source electrode-drain electrode pair, which will be described later, is provided, an insulating coating with a gate insulating layer is sufficient at the step portion between the base substrate and the gate electrode, and the gate electrode is formed thereon. It is necessary not to cause disconnection in the electrode pattern. In particular, when a flexible substrate is used, it is necessary to consider the balance of stress.

  Next, the gate insulating layer 4 is made of polyimide cured as a material at a temperature of less than 300 ° C., which is a characteristic part of the present invention.

  Until now, when the gate insulating layer is formed of polyimide, the polyamic acid that is the precursor is heated and dehydrated, and the temperature is usually 300 ° C. or higher. However, it was necessary to use a material having high heat resistance, resulting in high costs.

  Moreover, since the characteristics of the organic semiconductor itself are degraded when the high temperature treatment is performed, the use of polyimide as a gate insulating layer has not received much attention at a practical level.

  However, by using polyimide having a curing temperature of less than 300 ° C. as the material of the gate insulating layer, a polyimide film can be formed without exposing other materials to a high temperature of 300 ° C. or higher. Thus, an organic semiconductor can be efficiently produced without causing a decrease in the function.

（但し、式中Ｒ^１は４価の有機基を、Ｒ^２は２価の有機基を表し、Ｒ^１の有機基のうち５０ｍｏｌ％以上が、次の一般式（II）で表されるビフェニルエーテルカルボン酸

に由来する基であり、
Ｒ^２の有機基のうち５０〜９９ｍｏｌ％が、次の一般式（III）で表されるジアミン化合物

（但し、式中、Ｘは−ＣＨ_２−、−Ｏ−、−Ｃ（ＣＨ_３）_２−、−ＳＯ_２−又は−Ｃ（ＣＦ_３）_２−を表し、Ｙは水素原子、ハロゲン原子、炭素数１〜４の脂肪族炭化水素基を表し、ｍは１〜４である。）に由来する基であり、
Ｒ^２の有機基のうち５０〜１ｍｏｌ％が、次の一般式で表されるジアミノシロキサン

（但し、式中、Ｒ^３及びＲ^４は２価の有機基を、Ｒ^５〜Ｒ^８はそれぞれ１価の炭化水素基を表し、ｌは０〜１２の整数を表す。）に由来する基であり、ｎは５〜１００の整数である。）が挙げられる。ここでｎは、１０〜５０の整数であることが好ましい。 As the polyimide having such a curing temperature of less than 300 ° C., for example, a polyimide represented by the following general formula (I)

(In the formula, R ¹ represents a tetravalent organic group, R ² represents a divalent organic group, and 50 mol% or more of the organic groups of R ¹ is represented by the following general formula (II): Ether carboxylic acid

A group derived from
A diamine compound in which 50 to 99 mol% of the organic group of R ² is represented by the following general formula (III)

(Wherein, X represents —CH ₂ —, —O—, —C (CH ₃ ) ₂ —, —SO ₂ — or —C (CF ₃ ) ₂ —, Y represents a hydrogen atom, a halogen atom, Represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, and m is 1 to 4).
Diaminosiloxane in which 50 to 1 mol% of the organic group of R ² is represented by the following general formula

Wherein R ³ and R ⁴ represent a divalent organic group, R ^{5 to} R ⁸ each represent a monovalent hydrocarbon group, and l represents an integer of 0 to 12. And n is an integer from 5 to 100. ). Here, n is preferably an integer of 10 to 50.

  Here, the polyimide (I) used in the present invention can be formed by subjecting a predetermined acid component and a diamine component to a polyamic acid by a dehydration condensation reaction and then heating to cause a dehydration reaction.

を全酸成分中に５０ｍｏｌ％以上含有する酸成分を用いることができる。 As this acid component, an acid component represented by the following general formula (II)

An acid component containing 50 mol% or more in the total acid component can be used.

  Examples of the acid component that can be used here include 3,3 ′, 4,4′-biphenyl ether tetracarboxylic acid, 2,3,3 ′, 4′-phenyl ether tetracarboxylic acid, anhydrides thereof, Mainly mentioned are biphenyl ether carboxylic acids such as lower alkyl esters, and these can be used alone or in combination. These biphenyl ether carboxylic acids are preferably used in an amount of 50 mol% or more of the total acid components, and if the amount is less than 50 mol%, the strong acid resistance is lowered.

  Examples of acid components other than the biphenyl ether carboxylic acid component include pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, and 2,3,3 ′, 4′-biphenyltetracarboxylic acid. 3,3 ′, 4,4′-benzophenone tetracarboxylic acid, 2,3,3 ′, 4′-benzophenone tetracarboxylic acid, 2,3,6,7-naphthalene tetracarboxylic acid, 1,4,5, 8-Naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 3,3 ′, 4,4′-diphenylmethanetetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3′4,4′-diphenylsulfonetetracarboxylic acid, 3,4,9,10-tetra Acid components such as ruboxoxyperylene, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] propane, 2,2-bis [4- (3,4-dicarboxyphenoxy) phenyl] hexafluoropropane, The anhydride, the lower alkyl ester, etc. are mentioned, These can be used together with the above-mentioned biphenyl ether carboxylic acid component individually or in mixture.

（但し、式中、Ｘは−ＣＨ_２−、−Ｏ−、−Ｃ（ＣＨ_３）_２−、−ＳＯ_２−又は−Ｃ（ＣＦ_３）_２−を表し、Ｙは水素原子、ハロゲン原子、炭素数１〜４の脂肪族炭化水素基を表し、ｍは１〜４である。）が挙げられ、このＹにおけるハロゲン原子は、フッ素原子、塩素原子、臭素原子等が挙げられる。また、炭素数１〜４の脂肪族炭化水素基としては、メチル、エチル、プロピル、ブチル、イソプロピル等の直鎖状又は分枝鎖状の基が挙げられ、メチル又はエチルであることが好ましい。 Next, as a diamine component used here, the diamine compound represented by the following general formula (III)

(Wherein, X represents —CH ₂ —, —O—, —C (CH ₃ ) ₂ —, —SO ₂ — or —C (CF ₃ ) ₂ —, Y represents a hydrogen atom, a halogen atom, C represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, m is 1 to 4.), and examples of the halogen atom in Y include a fluorine atom, a chlorine atom, and a bromine atom. In addition, examples of the aliphatic hydrocarbon group having 1 to 4 carbon atoms include linear or branched groups such as methyl, ethyl, propyl, butyl, and isopropyl, and methyl or ethyl is preferable.

（但し、式中、Ｒ^３及びＲ^４は２価の有機基を、Ｒ^５〜Ｒ^８はそれぞれ１価の炭化水素基を表し、ｌは０〜１２の整数を表す。）が挙げられる。 The diamine component used here is a diaminosiloxane represented by the following general formula (IV):

(In the formula, R ³ and R ⁴ represent a divalent organic group, R ^{5 to} R ⁸ each represent a monovalent hydrocarbon group, and l represents an integer of 0 to 12).

The divalent organic group of R ³ and R ⁴ of the diamine component represented by the general formula (IV) is preferably an aliphatic hydrocarbon group having 1 to 6 carbon atoms, such as methylene, ethylene, Examples thereof include linear or branched divalent alkylene groups such as trimethylene, propylene, tetramethylene, pentamethylene, 3,3-dimethyltrimethylene, and hexamethylene.

The monovalent hydrocarbon group R ⁵ to R ^8, is preferably a hydrocarbon group having 1 to 12 carbon atoms, more preferably a hydrocarbon group having 1 to 8 carbon atoms. Specifically, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, etc., cyclopentyl Groups, cycloalkyl groups such as cyclohexyl group and cycloheptyl group, aryl groups such as phenyl group, tolyl group, xylyl group and naphthyl group, aralkyl groups such as benzyl group, phenylethyl group and phenylpropyl group. R ^{5 to} R ⁸ may be the same as or different from each other, and among them, all of them are preferably methyl groups in view of chemical stability and ease of synthesis.

  More specifically, examples of the diamine component represented by the general formula (III) include 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- ( 4-aminophenoxy) phenyl] hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] ether, 2,2-bis [4- (4-aminophenoxy) phenyl] methane, 2, 2-bis [4- (4-aminophenoxy) phenyl] sulfone and the like can be mentioned, and these can be used alone or in combination.

  Examples of the diaminosiloxane represented by the general formula (IV) include bis (γ-aminopropyl) tetramethyldisiloxane, bis (4-aminobutyl) tetramethyldisiloxane, and bis (γ-aminopropyl) tetraphenyldisiloxane. Examples thereof include siloxane and 1,4-bis (γ-aminopropyldimethylsilyl) benzene, and these can be used alone or in combination.

  At this time, the mixing ratio of the diamine component represented by the general formula (III) and the general formula (IV) is 50 to 99 mol% of the diamine compound of the general formula (III) with respect to the total diamine component, and the general formula (IV). The diaminosiloxane is preferably in the range of 50 to 1 mol%. If the proportion of the diamine compound of the general formula (III) is less than 50 mol%, the acid resistance is lowered, and if the proportion of the diaminosiloxane of the general formula (IV) is less than 1 mol%, the adhesion to the surface of the semiconductor element is lowered. End up.

  Although the polyimide used for this invention is obtained by making the acid component mentioned above and the diamine component mentioned above react, these acid components and diamine components may contain block or at random.

  In addition, the polyimide used in the present invention has a logarithmic viscosity at 30 ° C. of 0.2 to 4 when 0.5 g of polyamic acid as a precursor is dissolved in 100 mL of N-methyl-2-pyrrolidone. It is preferably in the range of 0 dl / g, more preferably in the range of 0.3 to 2.0 dl / g.

  The polyamic acid can be obtained by subjecting an approximately equimolar acid component and a diamine component to an addition polymerization reaction in an organic solvent at a reaction temperature of 30 ° C. or lower, preferably 20 ° C. or lower for 3 to 12 hours. Examples of the organic solvent used in this polymerization reaction include N, N′-dimethylsulfoxide, N, N′-dimethylformamide, N, N′-diethylformamide, N, N′-dimethylacetamide, N, N′-. Examples thereof include diethyl tylacetamide, N-methyl-2-pyrrolidone, hexasamethylene phosphoamide and the like, and these can be used alone or in combination.

  After this polyamic acid solution is applied and dried, it is cured by heating at less than 300 ° C., preferably 150 to 250 ° C., more preferably 160 to 200 ° C., to obtain a cured product having a tough polyimide composition with excellent heat resistance. Can do. The polyimide composition of the present invention is particularly excellent in heat resistance, electrical characteristics, chemical resistance and the like. It is preferable that the film thickness of the gate insulating layer 4 formed using the cured product of polyimide is 100 to 1000 nm.

  The polyimide described here is excellent in smoothness. When a gate insulating layer is formed of ordinary polyimide, the surface roughness RMS is 0.5 to 10 nm, but it is represented by the general formula (I). With the polyimide to be formed, film formation with a surface roughness RMS of 0.1 to 1.0 nm is possible. By improving the smoothness of the gate insulating layer, the performance of the organic semiconductor can be improved, and the surface roughness RMS is particularly preferably 0.1 to 0.4 nm. Here, the surface roughness RMS was measured by the root mean square roughness when a gate insulating layer was formed on a gate electrode having a surface roughness of 10 to 200 nm by an atomic force microscope (AFM). Is.

  The organic semiconductor layer 5 used in the present invention may be a layer formed using a known organic semiconductor material. Examples of the organic semiconductor material include π-electron conjugated aromatic compounds, chain compounds, organic pigments, It is preferably made of a material such as an organosilicon compound or a charge transfer complex. Specific materials include pentacene, a pentacene derivative having a bicyclo ring introduced between the central benzene rings, tetracene, anthracene, thiophene oligomer derivative, phenylene derivative, phthalocyanine derivative, polyacetylene derivative, polythiophene derivative, cyanine dye, and the like. However, the present invention is not limited to these materials.

  The source electrode 6 and the drain electrode 7 can be used without particular limitation as long as they are known electrodes used for organic semiconductors, but most organic semiconductors are P-type semiconductors in which carriers for transporting charges are holes. For this reason, in order to make ohmic contact with the semiconductor layer, it is preferably formed of a metal having a high work function. Specific examples include gold and platinum.

  The work function here is a potential difference necessary for taking out electrons in the solid to the outside, and is defined as a value obtained by dividing the energy difference between the vacuum level and the Fermi level by the amount of charge. In addition, when a dopant is densely doped on the surface of the semiconductor layer, carriers can tunnel between the metal and the semiconductor and do not depend on the metal material. Therefore, the metal material or the conductive organic material mentioned for the gate electrode Can also be used.

  The organic semiconductor device of the present invention may be formed by a generally manufactured method. For example, a gate made of a metal, a gate made of polyimide cured at less than 300 ° C. on a substrate made of a polymer film, a glass substrate or the like. An insulating layer, an organic semiconductor layer such as pentacene, and a source / drain electrode made of a metal can be laminated in order.

  Furthermore, it is preferable to provide a protective layer for protecting the organic semiconductor layer and the source / drain electrodes from the external environment and maintaining the function of the organic semiconductor device on the surface of the organic semiconductor thus manufactured. As this protective layer, a film may be formed of a polymer organic compound, and examples of the material used at this time include parylene (paraxylylene resin). Parylene is extremely preferable because it has gas barrier properties and pinhole-free properties, is highly pure, and can be vapor-phase grown.

  Furthermore, it is preferable to anneal the organic semiconductor device after forming this protective layer. The annealing treatment may be performed by heat-treating the organic semiconductor device at 80 to 160 ° C. for 1 minute to 20 hours, and it is particularly preferable to perform the heat treatment at 130 to 150 ° C. for 2 to 12 hours. By performing this annealing treatment, it is possible to maintain and improve the characteristics of the organic semiconductor such as mobility and on / off ratio, and suppress drift, and to obtain an organic semiconductor device having more stable operating characteristics. it can.

  EXAMPLES Next, although an Example demonstrates this invention, this invention is not limited by these Examples.

(Synthesis Example 1)
In a flask equipped with a stirrer, a cooler, and a nitrogen introduction tube, 36.9 g (0.09 mol) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane and bis (γ-aminopropyl) 2.49 g (0.01 mol) of tetramethyldisiloxane and 279.1 g of N-methyl-2-pyrrolidone were added, and 3,3 ′, 4,4′-biphenyl ether tetracarboxylic acid dicarboxylate was added in a nitrogen atmosphere at room temperature. 30.38 g (0.098 mol) of anhydride was added in portions while paying attention to an increase in solution temperature, and stirred at room temperature for about 12 hours to prepare a polyamic acid solution.

  A part of this polyamic acid solution was reprecipitated with methanol, and the resulting polyamic acid powder was dissolved in N-methyl-2-pyrrolidone to a concentration of 0.5 g / 100 ml, and the logarithmic viscosity was measured at 30 ° C. .95 dl / g.

(Synthesis Example 2)
In a flask equipped with a stirrer, a cooler and a nitrogen introduction tube, 46.6 g (0.09 mol) of 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane and bis (γ-amino) were added. 4.97 g (0.01 mol) of propyl) tetraphenyldisiloxane and 268.3 g of N-methyl-2-pyrrolidone were added, and 3,3 ′, 4,4′-bisphenyl ether tetra was added at room temperature under a nitrogen atmosphere. Carboxylic dianhydride 15.5 g (0.050 mol) and pyromellitic dianhydride 10.46 g (0.048 mol) were added in portions while paying attention to an increase in the solution temperature, and the mixture was stirred at room temperature for about 10 hours. To prepare a polyamic acid solution.

  A part of this polyamic acid solution was reprecipitated with methanol, and the obtained polyamic acid powder was dissolved in N-methyl-2-pyrrolidone to a concentration of 0.5 g / 100 ml, and the logarithmic viscosity was measured at 30 ° C. It was 88 dl / g.

(Synthesis Example 3)
In a flask equipped with a stirrer, a cooler and a nitrogen introduction tube, 18.00 g (0.09 mol) of 4,4′-diaminodiphenyl ether and 2.49 g (0.01 mol) of bis (γ-aminopropyl) tetramethyldisiloxane ) And 167.4 g of N-methyl-2-pyrrolidone, 21.36 g (0.098 mol) of pyromellitic dianhydride is added at room temperature under a nitrogen atmosphere, and the mixture is stirred at room temperature for about 10 hours to be polyamic acid. The solution was adjusted.

  A part of this polyamic acid solution was reprecipitated with methanol, and the obtained polyamic acid powder was dissolved with N-methyl-2-pyrrolidone to a concentration of 0.5 g / 100 ml, and the logarithmic viscosity was measured at 30 ° C. It was 01 dl / g.

(Example 1)
A gate electrode layer was formed by vapor deposition of a chromium layer having a thickness of 5 nm and a gold layer having a thickness of 100 nm on a polyethylene naphthalate substrate having a thickness of 125 μm. Further, the polyamic acid solution obtained in Synthesis Example 1 was applied by spin coating, and heated at 180 ° C. for 60 minutes to form a polyimide film to obtain a gate insulating film. The gate insulating film had a surface roughness RMS of 0.2 nm.

  Next, pentacene is deposited on the gate insulating film by vapor deposition through a metal mask to form a semiconductor layer with a thickness of 50 nm. Finally, gold with a thickness of 30 nm is deposited through the metal mask to form a source / drain electrode layer. An organic transistor was manufactured. The organic transistor had a channel length L of 100 μm and a width W of 1.9 mm.

The performance of the obtained organic transistor alone is a good value when the voltage of −100 V is applied to the gate electrode at room temperature (30 ° C.), the mobility is 1.4 cm ² / Vs, and the on / off ratio is 10 ⁶ or more. It became.

(Example 2)
An organic transistor was manufactured in the same manner as in Example 1 except that the polyamic acid obtained in Synthesis Example 2 was used to form the gate insulating layer. The organic transistor produced here also had the same performance as the organic transistor of Example 1.

Example 3
A protective layer made of parylene was formed by spin coating so as to cover the semiconductor layer and the source / drain electrode layer of the organic transistor manufactured in Example 1, and this was further annealed at 140 ° C. for 12 hours in a nitrogen atmosphere. The organic transistor was manufactured. The organic transistor produced here also had the same performance as the organic transistor of Example 1.

Moreover, the drift characteristic was tested about the obtained organic transistor. Here, the drift characteristic is examined by a change in the current value between the source and the drain when a voltage of −40 V is continuously applied between the source and the drain and between the source and the gate, and the ratio of the current values before and after the application is determined as I / I. _Expressed by _zero . The results are shown in FIG. For comparison, changes in the characteristics of the organic semiconductor (Example 1) that was not annealed and the inorganic semiconductor (gate insulating film: SiO ₂ ) formed on the silicon substrate were also shown.

As a result, the inorganic semiconductor, but 10 ⁴ seconds nearly 40% current later had decreased, an organic transistor of the present invention, it is possible to suppress the reduction of about 20%, it is intended to further subjected to annealing treatment The decrease was only about 2%. Therefore, it was found that the organic semiconductor of the present invention has very good drift characteristics.

(Comparative Example 1)
In order to form the gate insulating film, the same procedure as in Example 1 was performed except that the polyamic acid solution obtained in Synthesis Example 3 was spin-coated and heated at 320 ° C. for 30 minutes to obtain a resin film. A transistor was created. The surface roughness RMS of the gate insulating film made of polyimide of this comparative example was 1.0 nm.

The performance of the obtained organic transistor alone was such that when a voltage of −100 V was applied to the gate electrode at room temperature (30 ° C.), the mobility was 0.01 cm ² / Vs or more, and the on / off ratio was 10 ³ and low. It was.

(Test example)
The correlation between the annealing temperature and the change in characteristics when the organic semiconductor device manufactured in Example 3 was annealed was examined. In the annealing treatment, heat treatment was performed in steps of 10 ° C. from 30 ° C. to 220 ° C., and the characteristics of the organic semiconductor device when gradually cooled to room temperature (30 ° C.) were examined. FIG. 4a and FIG. 4b show changes in mobility and on / off ratio when a test is performed by applying a voltage of −40V. As a result, it has been found that the organic semiconductor device of the present invention retains its operating characteristics even by heat treatment at about 160 ° C., and can be applied under high temperature conditions.

In the organic semiconductor device having the same configuration as that of Example 1, when the temperature of heat curing was performed at 320 ° C. when forming the gate insulating film, the mobility was 0.01 cm ² / Vs, and the on / off ratio was It became about 10, and it was also confirmed that the characteristics deteriorated by high-temperature heating.

It is a composition sectional view of the organic semiconductor device of the present invention. It is a structure sectional view of the organic semiconductor device in other modes of the present invention. It is the figure which showed the drift characteristic in the organic semiconductor of this invention. It is the graph which showed the result (relationship between annealing temperature and mobility) of a test example. It is the graph which showed the result (relationship between annealing temperature and on / off ratio) of a test example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic semiconductor device, 2 ... Base material, 3 ... Gate electrode, 4 ... Gate insulating layer, 5 ... Organic semiconductor layer, 6 ... Source electrode, 7 ... Drain electrode, 8 ... Protective layer

Claims (6)

An organic semiconductor device having a gate electrode, a gate insulating layer, an organic semiconductor layer, a source electrode and a drain electrode on the surface of the substrate,
The organic semiconductor device, wherein the gate insulating layer is made of polyimide cured at a temperature of less than 300 ° C.   The organic semiconductor device according to claim 1, wherein the gate insulating layer has a surface roughness RMS of 1.0 nm or less. The polyimide is represented by the following general formula

(In the formula, R ¹ represents a tetravalent organic group, R ² represents a divalent organic group, and 50 mol% or more of the organic groups of R ¹ is represented by the following general formula:

A group derived from
A diamine compound in which 50 to 99 mol% of the organic group of R ² is represented by the following general formula

(Wherein, X represents —CH ₂ —, —O—, —C (CH ₃ ) ₂ —, —SO ₂ — or —C (CF ₃ ) ₂ —, Y represents a hydrogen atom, a halogen atom, Represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, and m is 1 to 4).
Diaminosiloxane in which 50 to 1 mol% of the organic group of R ² is represented by the following general formula

(Wherein R ³ and R ⁴ represent a divalent organic group, R ^{5 to} R ⁸ each represent a monovalent hydrocarbon group, and l represents an integer of 0 to 12). Yes, n is an integer from 5 to 100. The organic semiconductor device according to claim 1, wherein:   The organic semiconductor device according to any one of claims 1 to 3, wherein a protective layer for protecting the organic semiconductor element from an external environment is formed on a surface of the organic semiconductor device.   The organic semiconductor device according to claim 1, wherein the protective layer is made of parylene.   An organic semiconductor device obtained by annealing the organic semiconductor device according to claim 4 or 5.

Images