JP4700976B2 - Manufacturing method of field effect organic transistor - Google Patents

Description

  The present invention relates to a method for manufacturing a field effect organic transistor, and more particularly to a method for manufacturing 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.

  Field-effect organic transistors using organic semiconductors can be manufactured on a plastic substrate and have a large screen, which is difficult for silicon transistors, and are expected to be applied to new devices such as flexible electronic paper and information tags. Is growing.

A field-effect organic transistor using a process of peeling an organic insulating layer in order to transfer circuit wiring produced on a solid substrate to which photolithography technology can be applied onto an organic material substrate such as plastic without damaging the wiring structure. A manufacturing method is proposed in Patent Document 1.
JP 2003-258264 A

  When forming the organic semiconductor layer, if the surface state of the gate insulating layer forming the organic semiconductor is different, the order of the organic semiconductor is different and the electrical characteristics are also different. In general, in order to improve transistor characteristics from the knowledge of silicon transistors, the gate insulating layer should have a higher dielectric constant. However, generally, when an organic semiconductor layer is formed on a gate insulating layer having a high dielectric constant, the order of the organic semiconductor is lowered as compared with the case where the organic semiconductor layer is formed on a gate insulating layer having a low dielectric constant.

  Therefore, in the method of manufacturing a field effect organic transistor in which an organic semiconductor layer is formed on a high dielectric constant gate insulating layer, it is difficult for the organic semiconductor to have a good ordered structure, and high mobility is obtained. It is also difficult.

  The present invention solves the above-described conventional problems and provides a method for producing a field effect organic transistor having high mobility and small threshold fluctuation.

  The present invention includes a step of forming a source electrode, a drain electrode, and an organic semiconductor layer on a first substrate, and after the second substrate is formed on the organic semiconductor layer, the first substrate is peeled from the organic semiconductor layer And a step of forming a gate insulating layer and a gate electrode on the peeled surface of the organic semiconductor layer.

In the present invention, the gate insulating layer is formed on the separation surface of the organic semiconductor layer, whereby the separation surface of the organic semiconductor having high flatness and a good ordered structure can be used as the interface.
The surface energy density of the first substrate is preferably smaller than the surface energy density of the organic semiconductor layer. The fact that the formed organic semiconductor film is easily peeled off can be used, and since the influence of the interaction of the first substrate is small, the ordering is further improved by the interaction between the molecules of the organic semiconductor.

  The surface roughness Ra of the first substrate is preferably 10 nm or less. The flatness of the first substrate affects the flatness of the peeled surface of the organic semiconductor layer, which is preferable for using the peeled surface as a channel of the transistor.

The organic semiconductor layer preferably has an ordered structure. Since the organic semiconductor layer formed over the first substrate to be peeled has a favorable ordered structure, transistor characteristics are improved.
The gate insulating layer preferably has a dielectric constant of 4 or more. In general, when an organic semiconductor thin film is formed on a gate insulating layer having a high dielectric constant, a good organic semiconductor thin film cannot be formed. However, by using the process of the present invention, such a gate insulating layer having a high dielectric constant can be formed. It can be used.

  The organic semiconductor layer is preferably made of a polymer compound. As the organic semiconductor layer of the transistor, a high molecular compound is preferably used because it can be formed by a wet process.

  According to the present invention, the organic semiconductor has a well-ordered structure regardless of the material of the gate insulating layer, and a field-effect organic having a configuration in which the interface between the organic semiconductor layer and the gate insulating layer having high flatness is used as a channel. Transistors can be manufactured, and there is an effect that transistor characteristics such as high mobility and small threshold fluctuation can be obtained as compared with an element manufactured by forming an organic semiconductor layer over a gate insulating layer.

The best mode of the present invention will be described below with reference to FIG.
FIG. 1 is a process diagram showing one embodiment of a method for producing a field effect organic transistor of the present invention.

In the method for producing a field effect organic transistor of the present invention, first, a source electrode 2 and a drain electrode 3 are formed on a first substrate 1 (see FIG. 1A).
Next, the organic semiconductor layer 4 is formed on the side of the first substrate on which the source electrode 2 and the drain electrode 3 are formed (see FIG. 1B). At this time, since the organic semiconductor layer 4 has a good ordered structure, a field effect organic transistor having a good ordered structure is possible.

  Next, the second substrate 5 is bonded onto the organic semiconductor layer 4 (see FIG. 1C), and the first substrate 1 is peeled from the source electrode 2, the drain electrode 3, and the organic semiconductor layer 4 (FIG. 1). (See (d), (e)).

  Thereafter, a gate insulating layer 6 is formed on the peeling surface of the organic semiconductor layer 4, and a gate electrode 7 is formed on the gate insulating layer 6. Thereafter, the gate insulating layer 6 and the gate electrode 7 are covered with a protective layer 8. Alternatively, the gate electrode 7 is formed on the protective substrate / third substrate 8 and the gate insulating layer 6 is formed on the gate electrode 7, and the peeling surface of the gate insulating layer 6 and the organic semiconductor layer 4 is removed. They may be bonded together (see FIG. 1 (f)).

  Through the above steps, the field effect organic transistor manufactured by the manufacturing method of the present invention has a well-ordered organic semiconductor layer and a highly flat organic semiconductor layer and gate regardless of the material of the gate insulating layer. A channel using an insulating layer interface can be provided.

Note that the ordered structure of the organic semiconductor layer indicates that the molecules of the organic semiconductor are arranged at regular intervals.
The first and second substrates, protective layer, protective layer and third substrate used in the present invention are not particularly limited. For example, in addition to inorganic materials such as silicon, glass and quartz, acrylic and vinyl materials Polymer compounds such as ester, 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.

  As the first substrate, the flatness of the first substrate is such that the surface roughness Ra is 10 nm or less, preferably 0.1 to 1 nm. Moreover, the material from which the organic-semiconductor layer formed on a 1st board | substrate forms a favorable ordered structure is preferable.

  Examples of the method for peeling the first substrate used in the present invention include, but are not limited to, a method for peeling the first substrate, a method for dissolving the first substrate, and the like. In the method of peeling the first substrate, it is preferable that the surface energy density of the first substrate is smaller than the surface energy density of the organic semiconductor layer. In this case, the surface treatment of the first substrate is effective for reducing the surface energy density.

  Examples of the surface treatment method used in the present invention include, but are not limited to, silane coupling agents, titanate coupling agents, plasma treatment, corona discharge, and the like. A silane coupling agent that maintains the flatness of the first substrate to be peeled is preferable. Examples thereof include HMDS, alkyltrichlorosilane, alkyltrimethoxysilane, alkyltriethoxysilane, perfluoroalkylethyltrichlorosilane, aminoalkyltrichlorosilane, hydroxyalkyltrichlorosilane, and phenylalkyltrichlorosilane.

  Moreover, although the method of providing a peeling layer between a 1st board | substrate and an organic-semiconductor layer depending on the case, or using an ultrasonic wave etc. are mentioned, it is not limited to these, if an organic-semiconductor layer is not impaired. Examples of the method for dissolving the first substrate include a method of eroding in a solution, a method of applying a solution, and a method of eroding in a soluble gas.

The source electrode, drain electrode, and gate electrode used in the present invention are not particularly limited as long as they are conductive. For example, Al, Cu, Ti, Au, Pt, Ag, Cr, In, Mo, Pd, Ni, Mg, etc. Inorganic materials such as metal materials and alloys thereof, polysilicon, silicide, ITO (Indium Tin Oxide), and SnO ₂ are also suitable, but conductivity represented by highly doped polypyridine, polyacetylene, polyaniline, polypyrrole, and polythiophene. A conductive ink in which a polymer, carbon particles, silver particles and the like are dispersed 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 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 typified by dimethylsexithiophene and quarterthiophene; acenes typified by perylene, tetracene, and pentacene; typified by copper phthalocyanine derivatives Deposited organic molecules, discotic liquid crystals represented by triphenylene derivatives, smectic liquid crystals represented by phenylnaphthalene derivatives, benzothiazole derivatives Poly (9,9-dialkyl fluorene - bithiophene) liquid crystal polymers typified by a copolymer and the like, but not limited thereto.

  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 weight average molecular weight of these conjugated polymer compounds is not particularly limited, but is preferably 5,000 to 500,000 in consideration of solubility in a solvent, film formability, and the like.

Further, the organic semiconductor layer used in the present invention may contain an appropriate dopant in order to adjust its electric conductivity. Acceptable I ₂ , Br ₂ , Cl ₂ , BF ₃ , PF ₅ , H ₂ SO ₄ , FeCl ₃ , TCNQ (tetracyanoquinodimethane), donor-like Li, K, Na, Eu, Examples of the surfactant include alkyl sulfonate and alkyl benzene sulfonate.

SiO _2, is not particularly limited gate insulating layer used in the present invention _{SiNx, Al 2 O 3, Ta} 2 O 5 or the like of inorganic materials, polyimide, polyacrylonitrile, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl phenol, polyethylene Organic materials such as terephthalate and 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. In order to improve transistor characteristics, the dielectric constant of the gate insulating layer is preferably 4 or more.

  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, a spray coating 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.
Example 1
FIG. 1 shows a manufacturing process of the field effect organic transistor of this example.

  A gold (50 nm) source electrode 2 and a drain electrode 3 having a channel length of 50 μm and a channel width of 50 mm were fabricated on a silicon substrate 1 (flatness is surface roughness Ra = 0.13 nm) by a lift-off method. The silicon substrate 1 was dipped in a chloroform solution (0.06 mol / l) of octadecitrichlorosilane for 2 hours and taken out. As a result of measuring the surface energy density of the silicon substrate 1 subjected to the surface treatment, it was confirmed that it was 25 (dyne / cm), which was smaller than the surface energy density 33 (dyne / cm) of poly-3-hexylthiophene.

  A chloroform solution (0.023 g / ml) of poly-3-hexylthiophene was applied on the silicon substrate 1 on the side where the source electrode 2 and the drain electrode 3 were formed, to form an organic semiconductor layer 4. Thereafter, the glass substrate 5 was laminated on the organic semiconductor layer 4 and dried at 200 ° C. for 2 hours. After drying, the silicon substrate 1 was peeled off.

  Thereafter, a 2-propanol solution of polyvinylphenol (0.1 g / ml) was applied to the release surface of the organic semiconductor layer 4 by a spin coating method, and dried at 150 ° C. for 6 hours to form the gate insulating layer 6. Gold (50 nm) was deposited on the gate insulating layer 6 using a mask to form a gate electrode 7. After a 0.1 mmφ gold wire is wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste, a glass substrate is laminated as a protective layer 8 on the wiring, the gate insulating layer 6 and the gate electrode 7 to form a field effect type. An organic transistor element was produced.

Next, the drain current was measured at a gate voltage of 0 V to -50 V and a voltage between the source and drain electrodes of 0 V to -50 V. The threshold voltage Vth is obtained by extrapolating the drain current to 0 from the relationship between the square root of the drain current and the gate voltage, and the threshold voltage is the difference between the threshold voltage of the first measurement and the threshold voltage after repeating the measurement 100 times. The fluctuation of was calculated. The mobility μ was measured by μ = 2 × Id × L / {w × Ci × (Vg−Vth) ² }. At this time, Id is the drain current, L is the channel length, w is the channel width, Ci is the gate capacitance, Vg is the gate voltage, and Vth is the threshold voltage. Each result is shown below.

Mobility μ = 7.2 × 10 ⁻² cm ² / Vs
Threshold fluctuation = 0.1V

Example 2
FIG. 2 shows a manufacturing process of the field effect organic transistor of this example.
A gold (50 nm) source electrode 10 and a drain electrode 11 having a channel length of 100 μm and a channel width of 100 mm were formed on a silicon substrate 9 by an inkjet method. Thereafter, the silicon substrate 9 was immersed in a chloroform solution (0.06 mol / l) of octadecitrichlorosilane for 2 hours and taken out. A chloroform solution (0.023 g / ml) of a polymer semiconductor material poly-3-hexylthiophene is applied to the silicon substrate 9 on the side where the source electrode 10 and the drain electrode 11 are formed by an ink jet method, and the organic semiconductor layer 12 is applied. Formed. Then, the glass substrate 13 was bonded together on the organic semiconductor layer 12, and it dried at 200 degreeC for 2 hours. After drying, the silicon substrate 9 was peeled off.

Further, Al ₂ O ₃ (100 nm) was formed as the gate insulating layer 14 on the surface of the n-type highly doped silicon substrate 15 for use as a substrate and gate electrode. Thereafter, the gate insulating layer 14 was bonded to the peeling surface of the organic semiconductor layer 12. 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 element.

Next, evaluation was performed in the same manner as in Example 1, drain current was measured, and fluctuations in mobility and threshold voltage were calculated. The results are shown below.
Mobility μ = 8.5 × 10 ⁻² cm ² / Vs
Threshold fluctuation = 0.3V

Example 3
FIG. 1 shows a manufacturing process of the field effect organic transistor of this example.
A gold (50 nm) source electrode 2 and a drain electrode 3 having a channel length of 100 μm and a channel width of 100 mm were fabricated on a silicon substrate 1 by a lift-off method. Thereafter, the silicon substrate 1 was immersed in a chloroform solution (0.06 mol / l) of octadecitrichlorosilane for 2 hours and taken out. A film of pentacene was formed on the silicon substrate 1 on the side where the source electrode 2 and the drain electrode 3 were formed by a vacuum evaporation method to form an organic semiconductor layer 4. Thereafter, polyimide 5 was laminated on the organic semiconductor layer 4 and only the silicon substrate 1 was peeled off. As a result of observing the peeling surface of the organic semiconductor layer 4 with AFM, the surface roughness Ra = 0.23 nm.

  On the polyethylene terephthalate substrate 8, gold (50 nm) was deposited using a mask to form the gate electrode 7. A 2-propanol solution of polyvinylphenol (0.1 g / ml) was applied by spin coating on the side of the polyethylene terephthalate substrate 8 where the gate electrode was formed, and dried at 120 ° C. for 4 hours to form the gate insulating layer 6. Thereafter, the gate insulating layer 6 was bonded to the peeled surface of the organic semiconductor layer 4. A gold wire of 0.1 mmφ was wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste, and polyimide was formed as a protective layer to produce a field effect organic transistor element.

Next, evaluation was performed in the same manner as in Example 1, drain current was measured, and fluctuations in mobility and threshold voltage were calculated. The results are shown below.
Mobility μ = 6.8 × 10 ⁻¹ cm ² / Vs
Threshold fluctuation = 0.2V

Example 4
FIG. 1 shows a manufacturing process of the field effect organic transistor of this example.
A gold (50 nm) source electrode 2 and a drain electrode 3 having a channel length of 50 μm and a channel width of 50 mm were fabricated on a silicon substrate 1 by a lift-off method. Thereafter, hexamethyldisilazane was applied by spin coating on the silicon substrate 1 on the side where the source electrode 2 and drain electrode 3 were formed, and dried at 200 ° C. for 10 minutes. A chloroform solution (0.023 g / ml) of poly-3-butylthiophene was applied on the silicon substrate 1 on the side where the source electrode 2 and the drain electrode 3 were formed, to form an organic semiconductor layer 4. Thereafter, the glass substrate 5 was laminated on the organic semiconductor layer 4 and dried at 200 ° C. for 2 hours. After drying, the silicon substrate 1 was peeled off. At this time, as a result of X-ray diffraction evaluation of the organic semiconductor layer 4, it was confirmed that there were significant peaks in the vicinity of 2θ = 6.85 °, 13.7 °, and 23.3 °. This suggests an ordered structure.

  Thereafter, a 2-propanol solution of polyvinylphenol (0.1 g / ml) was applied to the release surface of the organic semiconductor layer 4 by a spin coating method, and dried at 150 ° C. for 6 hours to form the gate insulating layer 6. Gold (50 nm) was deposited on the gate insulating layer 6 using a mask to form a gate electrode 7. After a 0.1 mmφ gold wire is wired to each of the gate electrode, the drain electrode, and the source electrode with a silver paste, a glass substrate is laminated as a protective layer 8 on the wiring, the gate insulating layer 6 and the gate electrode 7 to form a field effect type. An organic transistor element was produced.

Next, evaluation was performed in the same manner as in Example 1, drain current was measured, and fluctuations in mobility and threshold voltage were calculated. The results are shown below.
Mobility μ = 1.1 × 10 ⁻¹ cm ² / Vs
Threshold fluctuation = 0.2V

Example 5
FIG. 2 shows a manufacturing process of the field effect organic transistor of this example.
A source electrode 10 and a drain electrode 11 of gold (50 nm) having a channel length of 50 μm and a channel width of 50 mm were fabricated on a silicon substrate 9 by a lift-off method. The silicon substrate 9 was immersed in a chloroform solution (0.06 mol / l) of octadecitrichlorosilane for 2 hours and taken out. Zexithiophene was deposited on the silicon substrate 9 on the side where the source electrode 10 and the drain electrode 11 were formed by a vacuum vapor deposition method to form an organic semiconductor layer 12. Then, the glass substrate 13 was bonded together on the organic semiconductor layer 12, and it dried at 200 degreeC for 2 hours. After drying, the silicon substrate 9 was peeled off.

  Also, polyvinylidene fluoride (dielectric constant ε = 8.2) was formed as a gate insulating layer 14 on the surface of a silicon substrate 15 highly doped n-type for use as a substrate and gate electrode by spin coating. Thereafter, the gate insulating layer 14 was bonded to the peeling surface of the organic semiconductor layer 12. 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 element.

Next, evaluation was performed in the same manner as in Example 1, drain current was measured, and fluctuations in mobility and threshold voltage were calculated. The results are shown below.
Mobility μ = 4.7 × 10 ⁻¹ cm ² / Vs
Threshold fluctuation = 0.3V

Comparative Example 1
Polyvinylidene fluoride (dielectric constant ε = 8.2) was formed as a gate insulating layer on a silicon substrate surface highly doped in n-type for use as a substrate and gate electrode by a spin coating method. Thereafter, a gold (50 nm) source electrode and drain electrode having a channel length of 50 μm and a channel width of 50 mm were formed on the gate insulating layer by a vacuum evaporation method using a mask. Thereafter, zexithiophene was formed into a film by a vacuum evaporation method 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 element.

Next, evaluation was performed in the same manner as in Example 1, drain current was measured, and fluctuations in mobility and threshold voltage were calculated. The results are shown below.
Mobility μ = 5.8 × 10 ⁻³ cm ² / Vs
Threshold fluctuation = 3V
As is apparent from Example 5 and Comparative Example 1, it can be seen that the field-effect organic transistor obtained by the production method of the present invention has high mobility and small threshold fluctuation.

  INDUSTRIAL APPLICABILITY The present invention can be used for a method of manufacturing a field effect organic transistor that is useful in the electro field such as a display device, an information tag, and an IC and has high mobility and small threshold fluctuation.

It is process drawing which shows one embodiment of the manufacturing method of the field effect type organic transistor of this invention. It is process drawing which shows the other embodiment of the manufacturing method of the field effect type organic transistor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,9 1st board | substrate 2,10 Source electrode 3,11 Drain electrode 4,12 Organic-semiconductor layer 5,13 2nd board | substrate 6,14 Gate insulating layer 7 Gate electrode 8 Protective layer or protective layer 3rd board | substrate 15 Gate electrode and third substrate

Claims (6)

  Forming a source electrode, a drain electrode and an organic semiconductor layer on the first substrate, forming a second substrate on the organic semiconductor layer, and then peeling the first substrate from the organic semiconductor layer; A method for producing a field effect organic transistor, comprising a step of forming a gate insulating layer and a gate electrode on a peeling surface of an organic semiconductor layer.   The manufacturing method according to claim 1, wherein a surface energy density of the first substrate is smaller than a surface energy density of the organic semiconductor layer.   The manufacturing method according to claim 1 or 2, wherein the surface roughness Ra of the first substrate is 10 nm or less.   The manufacturing method according to claim 1, wherein the organic semiconductor layer has an ordered structure.   The manufacturing method according to claim 1, wherein the gate insulating layer has a dielectric constant of 4 or more. The manufacturing method according to claim 1, wherein the organic semiconductor layer is made of a polymer compound.

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