JP5760360B2 - THIN FILM TRANSISTOR AND METHOD FOR PRODUCING THIN FILM TRANSISTOR - Google Patents

Description

  The present invention relates to a thin film transistor and a method for manufacturing the thin film transistor.

  Due to the remarkable development of information technology, information is frequently sent and received at notebook computers and portable information terminals. It is a well-known fact that in the near future, a ubiquitous society where information can be exchanged regardless of location will come. In such a society, a lighter and thinner information terminal is desired.

  At present, the mainstream of semiconductor materials used for semiconductor elements of information terminals is silicon-based, and as a manufacturing method, there is a method of patterning using photolithography after silicon is formed by a dry method such as sputtering or CVD. It is common.

  By the way, in recent years, printable electronics for producing electronic members using a printing technique which is a wet method using a solvent has attracted attention. By using this printing technique, there are advantages such that the cost of apparatus and manufacturing is lower than that of photolithography, and since a vacuum and high temperature are not required, a plastic substrate can be used.

  In this case, as the semiconductor material, an organic semiconductor material that is soluble in an organic solvent or an oxide semiconductor dispersed in an organic solvent is often used, whereby a semiconductor layer can be formed by a printing method.

Conventionally, for example, a technique for forming a semiconductor layer or the like by a printing method has been proposed.
For example, in Patent Document 1, an organic semiconductor layer is formed by an inkjet method, and a thin film transistor (hereinafter, also referred to as a TFT) using an organic semiconductor material for the semiconductor layer is particularly referred to as an organic TFT. As a member constituting the TFT, there are an electrode and an insulating film in addition to the semiconductor. However, in order to form a low-cost TFT, it is desired that these are also formed using a wet method such as a printing method or a coding technique.

  For example, in Patent Document 2, an electrode is formed using an ink jet method, and in Patent Document 3, for example, a gate insulating film is formed using a spin coating method.

  Furthermore, as a material used when forming an electrode using the wet method, silver is the most common as in Non-Patent Documents 1 and 2, for example. In addition to silver, examples include copper as in Non-Patent Document 3 and a conductive polymer as in Non-Patent Document 4, for example.

Japanese Patent Laid-Open No. 2005-210086 JP 2004-297011 A JP 2007-266355 A

Proceedings of the National Academy of Sciences of the United States of America, Vol. 15 No. 13 (2008) 4976 Applied Physics Letters 95, 253302 (2009) Thin Solid Film Vo. 515 (2007) 7706 Japan Journal of Applied Physics Vol. 44, no. 6A (2005) 3649

  However, as described above, when silver or copper is used for an electrode material, particularly a source / drain electrode, it is known that migration causes a leak or a short circuit between both electrodes.

  Therefore, in order to avoid migration, it is conceivable to use gold as an electrode material. For example, ink containing gold nanoparticles is very expensive, and since the curing temperature is high, application of a flexible substrate is not possible. difficult.

  Furthermore, it is conceivable to use a conductive polymer for the electrode instead of silver or copper. However, since the conductivity is insufficient, there is a drawback that the wiring resistance is increased in a fine wiring pattern.

  The present invention has been made in view of the above circumstances, and even when an electrode is formed by a wet method, a problem due to migration does not occur, wiring resistance is sufficiently small, and a thin film transistor and a thin film transistor having excellent transistor characteristics are manufactured. It is to provide a method.

In order to solve the above problems, according to a first aspect of the present invention, in a thin film transistor having at least a gate electrode, a gate insulating film, a source electrode and a drain electrode, and an organic semiconductor layer on a substrate, the source electrode and the drain electrode are A thin film transistor comprising a three-layered structure, wherein the thickness of the three-layered structure decreases in the order of the first layer, the second layer, and the third layer.

According to a second aspect of the present invention, there is provided the thin film transistor according to the first aspect , wherein the first layer of the three-layer laminate is silver or copper.

A third aspect of the present invention is the thin film transistor according to the first aspect or the second aspect , wherein the second layer of the three-layered laminate is gold.

A fourth aspect of the present invention, among the stack of the three layers, the third layer is the first aspect to any one of the third aspect, which is a self-assembled monolayer The thin film transistor according to item.

A fifth aspect of the present invention is the thin film transistor according to the fourth aspect , wherein the self-assembled monolayer is made of a thiol compound.

A sixth aspect of the present invention is the thin film transistor according to any one of the first to fifth aspects , wherein the substrate is a flexible substrate.

According to a seventh aspect of the present invention, in the method of manufacturing a thin film transistor in which at least a gate electrode, a gate insulating film, a source electrode and a drain electrode, and an organic semiconductor layer are formed in this order on a substrate, the source electrode and the drain electrode are 3 A method for manufacturing a thin film transistor, characterized in that a first layer of the three-layer stack is formed by a printing method.

An eighth aspect of the present invention is the method for manufacturing a thin film transistor according to the seventh aspect , wherein the printing method is an inkjet method or a reverse offset printing method.

According to a ninth aspect of the present invention, in the thin film transistor manufacturing method according to the seventh aspect , the second layer of the three-layer laminate is formed by plating.

A tenth aspect of the present invention is the method of manufacturing a thin film transistor according to the seventh aspect , wherein the organic semiconductor layer is formed by a printing method.

An eleventh aspect of the present invention is the method of manufacturing a thin film transistor according to the tenth aspect , wherein the printing method for forming the organic semiconductor layer is an ink jet method or a relief printing method.

  As described above, according to the present invention, the source / drain electrodes are made of a three-layered structure, so that problems due to migration can be eliminated, wiring resistance can be sufficiently reduced, and transistor characteristics (signal conversion characteristics) ) Excellent thin film transistor can be obtained.

The effect of the first aspect of the present invention is that a thin film transistor having excellent transistor characteristics can be obtained by making the source / drain electrodes into a three-layered structure so that migration can be suppressed, wiring resistance can be kept sufficiently small. Can do. Also, by forming the first layer, the second layer, and the third layer in order of decreasing film thickness, the first layer has high conductivity and low cost regardless of the presence or absence of the magnetization. It is possible to use a thin film that reduces the wiring resistance by using a material, covers the first layer with a material that does not cause magnetization on the second layer, and improves the contact with the organic semiconductor layer on the third layer. .

The effect of the second aspect of the present invention is that the first layer is made of silver or copper having high conductivity, so that the wiring resistance can be reduced and firing can be performed at a relatively low temperature. A flexible substrate can be used.

The effect of the 3rd aspect of this invention can eliminate the malfunction by migration by using the gold | metal | money which does not cause a magnetization in the 2nd layer. Further, the second layer only needs to cover the first layer, and since the film thickness is thin, the consumption of gold can be reduced, and thus a low-cost thin film transistor can be obtained.

The effect of the fourth aspect of the present invention is that the contact between the organic semiconductor layer and the source / drain electrodes is improved by using a self-assembled monolayer for the third layer of the three-layered laminate. Thus, a thin film transistor with excellent transistor characteristics can be obtained.

The effect of the fifth aspect of the present invention is that, since the self-assembled monolayer is made of a thiol compound, it can be easily bonded to the gold surface used for the second layer, and is in contact with the source / drain electrodes. Can be easily improved.

The effect of the sixth aspect of the present invention is that since the substrate has flexibility, the thin film transistor can also have flexibility, and a fine pattern is generally formed using an organic semiconductor solution having a relatively low viscosity. Can be obtained.

The effect of the seventh aspect of the present invention is that a low-cost thin film transistor can be manufactured by forming the first layer of the three-layered laminate by a printing method and thus does not require a vacuum device or photolithography.
The effect of the eighth aspect of the present invention is that a fine pattern can be formed by using a relatively low viscosity metal particle ink by using the ink jet method or the reverse offset printing method as the first layer printing method. it can.

The effect of the ninth aspect of the present invention is that the second layer is formed by plating the second layer of the three-layered laminate so as to cover the first layer using a wet method. It can be formed easily.

According to the tenth aspect of the present invention , a low-cost thin film transistor can be obtained by forming the organic semiconductor layer by a printing method.

The effect of the eleventh aspect of the present invention is that a fine pattern is generally obtained using an organic semiconductor solution having a relatively low viscosity by using an inkjet method or a relief printing method as the organic semiconductor layer printing method. Can do.

1 is a schematic cross-sectional view showing an example of an embodiment of a thin film transistor and a method for manufacturing the same according to the present invention. FIG. 6 is a schematic cross-sectional view of a conventional thin film transistor provided with two layers of source / drain electrodes.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a sectional view showing an embodiment of a thin film transistor according to the present invention.

  In this thin film transistor, after a gate electrode 11 is formed on a predetermined substrate 10 by, for example, photolithography and etching, a gate insulating film 12 is formed using a required gate insulating material so as to cover the gate electrode 11 on the substrate 10. . Note that FIG. 1 shows a case of a thin film transistor of a gate gate type, but the thin film transistor of the present invention may be a top gate type, and includes at least a gate electrode, a gate insulating film, a source electrode and a drain electrode, and an organic semiconductor layer. Any thin film transistor can be used.

  The first to third source / drain electrodes 13 to 15 are sequentially formed on the upper surface of the gate insulating film 12, and then the organic semiconductor layer 16 is formed.

  Here, the thickness of each of the three layers forming the source / drain electrodes 13 to 15 is not particularly limited. However, in consideration of wiring resistance and leakage through the gate insulating film 12, the first layer is formed. The source / drain electrode 13 is preferably about 50 nm to 200 nm.

  Next, the source / drain electrode 14 of the second layer is formed so as to cover the surface of the source / drain electrode 13 of the first layer so that migration does not occur, and at least the source / drain electrode 13 of the first layer is formed. It is desirable to form the film so as to be thinner than the thickness of about 5 nm to 20 nm.

  The third-layer source / drain electrode 15 may be improved in contact with the organic semiconductor layer 16 formed on the third-layer source / drain electrode 15, and specifically about 1 nm. desirable. As described above, it is desirable that the thicknesses of the first to third layers be gradually reduced.

  Next, materials used for the source / drain electrodes 13 to 15 of each layer will be described.

  The material of the source / drain electrode 13 of the first layer is not particularly limited, but is selected in consideration of the relationship with the material of the source / drain electrode 14 of the second layer. As the source / drain electrodes 13 of the first layer, for example, metal materials such as gold, silver, copper, aluminum and molybdenum, oxide materials such as indium tin oxide, poly (ethylenedioxythiophene) / polystyrene sulfonate (PEDOT) / PSS) or conductive polymers such as polyaniline can be used.

  When the first layer is formed by a printing method, a solution in which nanoparticles such as silver or copper or a conductive polymer is dispersed can be used. However, when the second layer is formed by plating. It is preferable to use silver or copper.

  Note that the printing method is not particularly limited, and an inkjet method, a reverse offset printing method, a screen printing method, a relief printing method, a gravure printing method, or the like can be used.

  Next, the material of the source / drain electrode 14 of the second layer is not particularly limited, and a metal material such as gold, silver, copper, aluminum, molybdenum, an oxide material such as indium tin oxide, poly ( Conductive polymers such as ethylenedioxythiophene) / polystyrene sulfonate (PEDOT / PSS) and polyaniline can be used, but silver or copper which may cause migration is not preferable, and gold is preferable. When the second layer is formed by plating, electroplating or electroless plating can be used as appropriate.

  Furthermore, the material of the source / drain electrode 15 of the third layer is not particularly limited. However, when gold is used for the second layer, it is easy to use a thiol compound, a disulfide compound, a sulfide compound, or the like. It is desirable to use these compounds because a self-assembled monolayer can be formed. As a treatment method, a wet method using a liquid in which the above-described compound is appropriately dissolved in a solvent, a dry method using vapor of the compound, or the like can be used.

  Examples of compounds include benzenethiol, chlorobenzenethiol, bromobenzenethiol, fluorobenzenethiol, pentafluorobenzenethiol, pentachlorobenzenethiol, nitrothiophenol, 2-mercapto-5-nitrobenzimidazole, perfluorodecanethiol, pentafluoro Examples include thiol compounds such as thiophenol, disulfide compounds such as diphenyl disulfide, and sulfide compounds such as diphenyl sulfide.

Next, the organic semiconductor layer 16 will be described.
The semiconductor material is not particularly limited, but it is desirable to use an organic semiconductor material or an oxide semiconductor material in order to use a flexible substrate, and particularly when the semiconductor layer 16 is formed using a printing method. An organic semiconductor material is preferable, but an oxide semiconductor material may be used as long as it can be formed by a printing method.

  Organic semiconductor materials include high molecular organic semiconductor materials such as polythiophene, polyallylamine, fluorenebithiophene copolymers, and derivatives thereof, and small molecules such as pentacene, tetracene, copper phthalocyanine, perylene, and derivatives thereof. Organic semiconductor materials can be used. Carbon compounds such as carbon nanotubes or fullerenes, semiconductor nanoparticle dispersions, and the like can also be used as the material for the semiconductor layer. These organic semiconductor materials can be dissolved or dispersed in an aromatic solvent such as toluene and used as an ink-like solution or dispersion. Even if an additive such as a suitable dispersant or stabilizer is added to the solvent. Good.

  As a method for printing the organic semiconductor, known methods such as gravure printing, offset printing, screen printing, and ink jet method can be used. In general, since the organic semiconductor has low solubility in a solvent, it is desirable to use flexographic printing, reverse offset printing, an inkjet method, and a dispenser suitable for printing a low-viscosity solution. In particular, flexographic printing is most preferable because the printing time is short and the amount of ink used is small.

  As the oxide semiconductor material, for example, an oxide containing one or more elements of zinc, indium, tin, tungsten, magnesium, and gallium can be given. Known materials such as zinc oxide, indium oxide, indium zinc oxide, tin oxide, tungsten oxide, and zinc gallium indium oxide (In—Ga—Zn—O) can be mentioned, but are not limited to these materials. The structure of these materials may be single crystal, polycrystal, microcrystal, crystal / amorphous mixed crystal, nanocrystal scattered amorphous, or amorphous.

  As a method for forming the oxide semiconductor layer, after forming a film using a sputtering method, a pulse laser deposition method, a vacuum evaporation method, a CVD method, a sol-gel method, or the like, a pattern is formed using a photolithography method, a lift-off method, or the like. Although it can be formed, it is more preferable to form a dispersion in which an oxide semiconductor material is dispersed in a solvent by a printing method. As the printing method, the same method as described in the organic semiconductor printing method can be used.

  The material of the gate insulating film 12 is not particularly limited, but generally used polymer solutions such as polyvinyl phenol, polymethyl methacrylate, polyimide, polyvinyl alcohol, parylene, fluororesin, epoxy resin, alumina and silica gel And a solution in which particles such as silicon oxide, silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconia oxide, and titanium oxide are used. Moreover, thin film films, such as PET, PEN, and PES, can also be used as an insulating film.

  The method for forming the gate insulating film 12 is not particularly limited, and a vacuum deposition method, a sputtering method, a dry method such as CVD, a wet method such as spin coating or a slit die, or a method such as lamination can be appropriately used. .

  The material used for the substrate 10 is not particularly limited. Examples of commonly used materials include flexible plastics such as polyethylene terephthalate (PET), polyimide, polyethersulfone (PES), polyethylene naphthalate (PEN), and polycarbonate. Materials include glass substrates such as quartz and silicon wafers. However, considering the flexibility of the TFT and the process temperatures in the TFT manufacturing process, it is desirable to use PEN, polyimide, or the like as the substrate.

  Furthermore, the thin film transistor of the present invention can be suitably provided with a sealing layer, a light shielding layer, and the like as necessary. The material for the sealing layer can be selected from the same material as the material for the gate insulating film 12, and the light shielding layer has a light shielding material such as carbon black dispersed in the material described in the gate material 12. Things can be used. Therefore, the same method as that for the gate insulating film 12 can be used for these formation methods.

  Specific examples of the thin film transistor according to the present invention will be described below. Note that the present invention is not limited to each embodiment.

The first embodiment will be described with reference to FIG.
2 is a bottom-gate / bottom-contact thin film transistor shown in FIG.
In this thin film transistor, a polyethylene naphthalate (PEN) film (manufactured by Teijin DuPont) was used for the base substrate 10.

  A gate electrode 11 was fabricated by depositing aluminum with a thickness of 100 nm on the substrate 10 by sputtering and patterning it by photolithography and etching.

  Next, the gate insulating film 12 is formed so as to cover the gate electrode 11. Polyvinylphenol (manufactured by Aldrich) was used as the gate insulating material, and a gate insulating film 12 having a thickness of 1 μm was formed on the substrate 10 including the gate electrode 11 by spin coating.

  Subsequently, source / drain electrodes 13 to 15 having three layers are formed on the gate insulating film 12 in the following order.

  First, the source / drain electrode 13 of the first layer was formed by printing nano silver ink at a predetermined position on the gate insulating film 12 by reverse offset printing and baking at 180 ° C. for 1 hour.

  Next, the source / drain electrode 14 of the second layer was formed so as to cover the source / drain electrode 13 of the first layer by electroless plating.

Next, the source / drain electrode 15 of the third layer is immersed in a solution of pentafluorothiophenol diluted to 1% by weight with isopropyl alcohol for 30 minutes, and self-organized on the source / drain electrode 14 of the second layer. A monolayer was prepared.
Subsequently, an organic semiconductor layer 16 is formed between the source / drain electrodes composed of three layers.

  As the semiconductor material, a solution obtained by dissolving Lisicon SP200 (made by Merck), which is an organic semiconductor material, with tetralin (made by Kanto Chemical Co., Ltd.) so as to be 2% by weight is formed by the inkjet method, and the source / drain electrodes 15 of the third layer The organic semiconductor layer 16 was produced by printing between the source and drain electrodes so as to cover a part of the upper part and drying at 90 ° C. for 3 hours.

  In order to investigate the driving stability of the thin film transistor manufactured as described above, a rectangular wave of plus 20 V to minus 20 V is applied to the gate electrode at a frequency of 50 Hz and a duty ratio of 5%, a voltage of minus 15 V is applied to the drain electrode, When the source current was measured, no short circuit occurred between the source and drain electrodes even after 7 days.

  In Example 2, a thin film transistor was formed in the same manner as in Example 1 except that copper was used as the source / drain electrode 13 of the first layer. In order to investigate the driving stability of the thin film transistor thus fabricated, a rectangular wave of plus 20 V to minus 20 V is applied to the gate electrode at a frequency of 50 Hz and a duty ratio of 5%, a voltage of minus 15 V is applied to the drain electrode, When the current was measured, no short circuit between the source and drain electrodes occurred even after 7 days.

(Comparative Example 1)
On the other hand, in order to compare with the first and second embodiments, the second layer source / drain electrode 14 is not formed as shown in FIG. A thin film transistor was formed in the same manner as in Example 1 except that a self-assembled monomolecular film of pentafluorothiophenol corresponding to the third layer source / drain electrode 15 was formed.

  In order to investigate the driving stability of the thin film transistor thus fabricated, a rectangular wave of plus 20 V to minus 20 V is applied to the gate electrode at a frequency of 50 Hz and a duty ratio of 5%, a voltage of minus 15 V is applied to the drain electrode, When the current was measured, a short circuit occurred between the source and drain electrodes after 12 hours, and silver migration was confirmed by microscopic observation.

  In addition, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the scope of the invention.

  DESCRIPTION OF SYMBOLS 10 ... Substrate, 11 ... Gate electrode, 12 ... Gate insulating film, 13 ... First layer source / drain electrode, 14 ... Second layer source / drain electrode, 15 ... Third layer source / drain electrode 16 ... Organic semiconductor layer.

Claims (5)

In a thin film transistor having at least a gate electrode, a gate insulating film, a source electrode and a drain electrode, and an organic semiconductor layer on a substrate,
The source electrode and the drain electrode are composed of a three-layer laminate, and the thickness of the three-layer laminate is reduced in order of the first layer, the second layer, and the third layer,
The thin film transistor, wherein the first layer of the three-layer stack is silver.   2. The thin film transistor according to claim 1, wherein the second layer of the three-layer stack is gold.   3. The thin film transistor according to claim 1, wherein the third layer of the three-layer stack is a self-assembled monomolecular film. 4.   The thin film transistor according to claim 3, wherein the self-assembled monolayer is made of a thiol compound.   The thin film transistor according to any one of claims 1 to 4, wherein the substrate is a flexible substrate.

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