JP2018037486A - Thin film transistor manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optimum manufacturing method of a top-contact thin film transistor which achieves easy manufacturing and excellent productivity.SOLUTION: A manufacturing method of a thin film transistor having a source electrode and a drain electrode, a semiconductor layer, an insulator layer and a gate electrode comprises the steps of: forming on a transferred member having a mold release property, an ink drawing line part for forming a source electrode and a drain electrode; dehydrating the ink drawing line part on the transferred member; and performing transfer printing of the ink drawing line part on a printed base material where a semiconductor layer is deposited by using the transferred member as a support medium.SELECTED DRAWING: Figure 1

Description

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

  A transistor in which a source electrode and a drain electrode and a gate electrode made of a semiconductor layer, an insulator layer, and a conductor are stacked is used for a liquid crystal display, electronic paper, an electroluminescence (EL) display device, an RF-ID tag, and the like. Is expected.

  Transistors for these applications have conventionally been produced by forming electrodes and semiconductor layers through a dry process forming process such as vapor deposition and sputtering. In recent years, there has been a strong demand for higher density, smaller size, and improved productivity of transistors, and a method for manufacturing transistors that does not require large-scale and expensive vacuum equipment, which is essential when vapor deposition is used. Has been studied. Recently, wet processes such as printing methods have attracted attention because they can work at lower temperatures, thereby reducing energy consumption, increasing productivity, and enabling higher density and miniaturization. Yes.

  As such a wet process, for example, as a method for manufacturing a transistor having a bottom gate bottom contact type (BGBC type) structure, nano silver ink is spin-coated on a polycarbonate film and baked to form a gate electrode; Forming a gate insulating layer on the gate electrode; forming a line portion corresponding to the source electrode and the drain electrode on the gate insulating layer by performing reverse printing with nano silver ink; firing the line portion to source A method of forming an electrode and a drain electrode; and further forming a semiconductor layer on the source electrode and the drain electrode is known (see Patent Document 1).

  However, the thin film transistor obtained by the wet process described in Patent Document 1 has a low charge injection efficiency and insufficient electrical characteristics at the contact portion between the source / drain electrode and the semiconductor in the channel formation portion. There was a low problem.

  In order to improve the charge injection efficiency, the surface of the source electrode / drain electrode may be treated with a self-assembled monolayer so that the HOMO level or LUMO level of the semiconductor material matches the work function of the electrode. As is known, there is a problem that the process becomes complicated and the productivity is increased.

  On the other hand, by changing the structure of the transistor from the bottom contact type in which the semiconductor layer is formed on the source electrode / drain electrode to the top contact type in which the semiconductor layer is formed under the source electrode / drain electrode, the source electrode / drain is changed. It is known that the charge injection efficiency due to the contact resistance between the electrode and the semiconductor can be improved.

  However, the top contact type has a problem that the underlying semiconductor layer is likely to deteriorate due to physical and chemical stress accompanying the electrode formation, and it is difficult to form the source electrode and the drain electrode by a wet process. A specific method for manufacturing a top contact type thin film transistor is not known. (See Patent Document 2)

WO2010 / 010791 Japanese Patent No. 5135073

  Therefore, the problem to be solved by the present invention is to provide an optimum manufacturing method of a top contact thin film transistor that is easy to manufacture and excellent in productivity.

  As a result of earnest research, the present inventors have suppressed the deterioration of the semiconductor layer due to physical and chemical stress using transfer printing when forming the source electrode and the drain electrode on the semiconductor layer. As a result, the present inventors have found that the above problems can be solved, and have completed the present invention.

  That is, according to the present invention, in a method of manufacturing a thin film transistor including a source electrode and a drain electrode, a semiconductor layer, an insulator layer, and a gate electrode, the source electrode and the drain electrode are formed on a transferred member having releasability. Forming the ink image line portion, drying the ink image line portion on the transferred member, and printing to which the ink image line portion is formed with the semiconductor layer formed on the transfer member as a support And a step of transfer printing on a substrate.

  A releasable transfer member provided with an ink image line portion for forming a source electrode and a drain electrode has a relief plate formed with a convex portion corresponding to the image line of the source electrode and the drain electrode. Using a transferred member having moldability, obtained from a step of applying conductive ink to the entire surface of the transferred member, and a step of pressing the relief plate onto the applied conductive ink surface on the transferred member. The method of manufacturing the thin film transistor, which is a member to be transferred from which a non-image area pressed by a relief plate is removed and an image line corresponding to a source electrode and a drain electrode is formed.

  The method for manufacturing the thin film transistor, wherein the semiconductor layer is made of an organic semiconductor, and the semiconductor layer is formed by a wet process.

  The method for producing a thin film transistor, wherein the semiconductor layer is formed by an inkjet method, a spin coating method, an edge casting method, a dip coating method, or a blade coating method.

  The manufacturing method of the thin film transistor, wherein Ra is 50 nm or less and the thickness of the semiconductor layer is 100 nm or less, where Ra is the arithmetic average roughness of the semiconductor layer surface.

  The method for producing a thin film transistor, wherein an arithmetic average roughness Ra of a surface of a member to be transferred is 10 nm or less.

  The method for producing a thin film transistor according to claim 1, wherein the pressure at the time of transferring and printing the ink image portion on the transferred member onto the substrate to be printed on which the semiconductor layer is formed is 1 MPa or less.

  The method for producing a thin film transistor, wherein an ink image line portion on a member to be transferred is formed using a conductive ink containing water or an alcohol solvent.

The method of manufacturing the thin film transistor is characterized in that the thickness of the source electrode and the drain electrode is 50 nm or more.

According to a method for manufacturing a thin film transistor, in a method for manufacturing a thin film transistor in which a source electrode and a drain electrode are stacked with a gate electrode made of a semiconductor layer, an insulator layer, and a conductor, a source is formed on a transferred member having releasability. A step of forming an ink image portion for forming an electrode and a drain electrode, a step of drying the ink image portion on a member to be transferred, and a semiconductor using the member to be transferred as a support. And a step of performing transfer printing on the substrate to be printed on which the layer is formed, thereby producing a particularly remarkable technical effect that a top contact type thin film transistor excellent in charge injection efficiency can be manufactured with high productivity.

It is sectional drawing of a BGTC type transistor.

In a method of manufacturing a thin film transistor in which a source electrode and a drain electrode and a gate electrode made of a semiconductor layer, an insulator layer, and a conductor are stacked, the source electrode and the drain electrode are formed on a member to be transferred having releasability Forming the ink image line portion, drying the ink image line portion on the transferred member, and printing to which the ink image line portion is formed with the semiconductor layer formed on the transfer member as a support And a step of transfer printing on a substrate.

  In the present invention, a thin film transistor is a transistor in which at least a source electrode and a drain electrode, and a gate electrode made of a semiconductor layer, an insulator layer, and a conductor are stacked on a substrate. The thin film transistor usually has a thickness of 0.1 to 3 μm excluding the substrate serving as a support.

  The thin film transistor in the present invention may be, for example, a thin film transistor having a bottom gate top contact structure (BGTC type) or a top gate top contact structure (TGTC type). FIG. 1 shows a cross-sectional view of a BGTC transistor.

  Since the above thin film transistor structure can increase the contact area between the source / drain electrodes and the semiconductor in the channel formation portion and improve the charge injection efficiency, the bottom contact type structure is difficult. Can be expected to improve transistor characteristics. In particular, the BGTC structure is a structure in which a gate electrode layer and an insulating film layer are formed below the semiconductor layer, and thus is preferable in that deterioration of the semiconductor layer is easily prevented.

  In the thin film transistor of the present invention, a source electrode and a drain electrode made of a conductor, a semiconductor layer, an insulator layer, and a gate electrode made of a conductor are stacked on a substrate so that the function of the transistor is exhibited. It can be manufactured easily.

  A feature of the present invention is that a source electrode and a drain electrode in a thin film transistor are manufactured by a specific manufacturing method. This specific manufacturing method is a method in which the source electrode and the drain electrode are not formed by a dry method such as vapor deposition but manufactured by a wet method.

  There are no limitations on the substrate applicable to the thin film transistor of the present invention. For example, silicon, a thermal oxide film silicon whose surface is oxidized to be an insulating layer, glass, a thin metal plate such as stainless steel on which an insulating layer is formed; polycarbonate (PC) , Polyethylene terephthalate (PET), polyimide (PI), polyethersulfone (PES), polyethylene naphthalate (PEN), liquid crystal polymer (LCP), polyparaxylylene, cellulose and other plastic films; gas barrier layer on these plastic films A composite film or the like provided with a hard coat layer or the like can be used. Among these, a plastic film can be suitably used as the substrate from the viewpoint of making the transistor flexible. Moreover, although there is no restriction | limiting in the thickness of the said board | substrate, it is preferable that thickness is less than 150 micrometers from the point of a softness | flexibility or weight reduction.

Is formed on a member to be transferred having a releasability, and the ink image portion is dried on the member to be transferred, and then the semiconductor layer is formed on the ink image portion using the member to be transferred as a support. The step of transfer printing on the substrate to be printed is included as an essential step. Hereinafter, “a member to be transferred having a releasability provided with ink line portions corresponding to the source electrode and the drain electrode” is referred to as “a member to be transferred having an ink image line portion”. , “The ink line portion corresponding to them for forming the source electrode and the drain electrode” may be referred to as “ink line portion for electrode formation”.

  The method of forming the source electrode and the drain electrode by the printing described above does not require an expensive vacuum device and drastically reduces the production cost including capital investment, compared to the method of obtaining the source electrode and the drain electrode by a dry method such as vapor deposition. Reduction is possible. In addition, the process can be lowered in temperature, and a plastic substrate can be used as the substrate. Therefore, it is preferable for realizing an essential item in the ubiquitous era, that is, flexibility and low cost.

  In the method for manufacturing a thin film transistor in which the source electrode and the drain electrode are formed by a wet process, represented by the printing method as described above of the present invention, the image area is formed by firing ink that forms a conductor (hereinafter, “ The conductive ink is referred to as “conductive ink”. As the conductive ink used in the present invention, any known and commonly used ink can be used. For example, an ink in which a conductive material such as conductive metal particles or a conductive polymer is dissolved or dispersed in a solvent (dispersion medium). Can be used.

Examples of the conductive metal particles include metal particles such as gold, silver, copper, nickel, zinc, aluminum, calcium, magnesium, iron, platinum, palladium, tin, chromium and lead, and these metals such as silver / palladium. Alloys: Thermally decomposable metal compounds that thermally differentiate at relatively low temperatures to give conductive metals such as silver oxide, organic silver, and organic gold; Conductive metal oxides such as zinc oxide (ZnO) and indium tin oxide (ITO) Particles or the like can be used.
As the conductive polymer, for example, polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS), polyaniline, or the like can be used. Furthermore, carbon-based conductive materials such as carbon nanotubes can also be used.

  The type of the solvent (dispersion medium) is not particularly limited, but water or an organic solvent capable of dissolving or dispersing the conductive material can be appropriately selected. Specifically, for example, water; various organic solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones, ethers, esters, and some or all of these intramolecular hydrogens are fluorinated. Can be used. Among these, water or an alcohol-based solvent is preferable in that the residual solvent contained in the electrode forming ink image area hardly affects the deterioration of the semiconductor layer during transfer. These solvents may be used alone or in combination of two or more.

  In addition to the conductive material and solvent (dispersion medium), the conductive ink includes a binder component such as a resin, an antioxidant, various catalysts for promoting film formation, a silicone surfactant, and fluorine as necessary. Various surfactants such as system surfactants, leveling agents, mold release accelerators and the like can be added.

  The conductive ink is a thermosetting ink prepared by mixing a cationic polymerizable compound such as an oxetane compound, an epoxy compound or a vinyl ether compound, or a radical polymerizable compound such as a compound containing a vinyl group or a (meth) acryloyl group. Or an active energy ray-curable ink such as an ultraviolet ray or an electron beam. However, since such a polymerizable compound can expand and contract after polymerization to cause a volume change, it is preferable to use a non-polymerizable compound.

  As the conductive material, an arbitrary image line can be formed with a narrower line width, and a conductor can be formed by firing at a lower temperature. Therefore, it is preferable to use particles of a conductive material on the order of nm.

  In preparing inks using such conductive metal particles of the order of nm, a binder component that is relatively stable near room temperature but can form a conductor by firing at a relatively low temperature such as 150 ° C. or less. It is preferred to use coated conductive metal particles. The binder component may function as a protective agent or dispersant for the conductive metal particles. The material that can be used as such a binder component is preferably a thermoplastic resin having no curability as described above, for example, linear or branched polyethyleneimine, polyethyleneimine-polyalkylene glycol copolymer. , These N-oxidized derivatives, these N-acetylated derivatives, cationic resins such as polyvinyl-2-pyrrolidone, polyalkylene glycol mono (meth) acrylate / (meth) acryloyloxyalkyl acid phosphate copolymer Examples include anionic resins such as coalescence, alkanethiols, and alkylamines.

The electrode forming ink image area is dried on the transfer member, so that a part of the volatile component contained in the conductive ink is removed and becomes semi-solid, and the film quality becomes difficult to deteriorate the semiconductor layer during transfer. .

These drying methods are not particularly limited, and any known and commonly used method can be selected. For example, room temperature drying, suction drying, hot air drying, infrared drying, drying with a flash lamp such as a xenon lamp, UV drying, etc. One or a combination of methods can be applied. Among these, suction drying and hot air drying are preferable because the solvent component contained in the conductive ink forming the ink image line portion can be efficiently volatilized and the semiconductor layer is hardly deteriorated during transfer.

Examples of the method for transferring and printing on the support using the ink image line-shaped member to be transferred include a gravure offset printing method, a microcontact method, and a letterpress reverse printing method. Among these, the letterpress reverse printing method is preferable because it can form a higher-definition ink image area than the gravure offset printing method, can have a larger area than the microcontact method, and is excellent in productivity.

In the relief printing method, a relief plate having projections corresponding to the inversion patterns of the source electrode and the drain electrode and a member to be transferred having a releasability are used. Applying conductive ink to the entire surface of the member to be transferred, and pressing the relief plate against the applied conductive ink surface on the member to be transferred, corresponding to the reverse pattern of the source electrode and drain electrode Using the transferred member in which the ink image line portion corresponding to the source electrode and the drain electrode is formed by removing the reversal pattern pressed by the relief plate, the step of transferring and removing the ink portion on the relief plate, And a step of performing transfer printing on a support such as a substrate.
By transferring the ink portion corresponding to the reversal pattern of the source electrode and the drain electrode onto the relief plate, the image line portions corresponding to the source electrode and the drain electrode that are not pressed by the relief plate remain on the transferred member. Since the member to be transferred has releasability, a semiconductor layer was previously formed on the member to be transferred having releasability provided with image lines corresponding to the source electrode and the drain electrode. By making contact with the support, the image area is transferred onto the semiconductor layer.

  The image line portion of the conductive ink corresponding to the source electrode and the drain electrode is obtained by heating the source electrode and the drain electrode made of the conductor on the support by, for example, heating in a hot air oven or firing by irradiating with infrared rays. Form. The volatile component contained in the conductive ink is completely removed from the conductor by this baking. Further, when the binder component is decomposed, the binder component also disappears from the formed conductor. However, when the amount of the binder component is extremely small compared to the conductive material, the film of the image area is composed of the image area of the conductive ink and the image area of the conductor obtained after baking before and after baking. No change in thickness or shape. If it is expected that there will be a significant decrease in the film thickness or shape change in the image area before and after firing, the ink image line area should be formed with a thicker film, or the plate shape should be changed in anticipation of these changes. Thus, a source electrode and a drain electrode having a thickness and shape intended as a conductor can be obtained.

  In addition, according to the above method of forming an ink image line portion for electrode formation by transfer printing on a support having a semiconductor layer using an ink image linear transfer member, it has a rectangular electrode shape with no transfer abnormality. A source electrode and a drain electrode are obtained. A thin film transistor having such a source electrode and a drain electrode becomes a thin film transistor with less variation in mobility and threshold voltage when driven.

  Specifically, the source electrode and the drain electrode have the same electrode thickness, both of which are made of a very uniform conductor of 50 nm or more, preferably 100 to 200 nm, and have no abnormalities such as concave and convex shapes. Electrode-shaped source and drain electrodes can be easily obtained. As a result, such a transistor is not only optimal for obtaining a transistor array, an integrated circuit, etc., but also has a stable channel shape. The number of thin film transistors is reduced. Such excellent features are the features of transfer printing described above, which cannot be achieved by conventional printing methods such as screen printing and ink jet printing.

  In order to obtain a thin film transistor with less variation in mobility and threshold voltage, it is also important to form a thin semiconductor layer that is a base uniformly in combination with the above. Specifically, when the arithmetic mean roughness Ra of the semiconductor surface is 50 nm or less and the thickness of the semiconductor layer is 100 nm or less, preferably 10 to 60 nm, the coating film of the ink forming portion for electrode formation laminated on the upper layer Is preferable because uniform layered printing can be performed without breaking.

  Arithmetic average roughness Ra is a roughness curve with the reference length extracted in the direction of the average line, the X-axis in the direction of the average line and the Y axis in the direction of the vertical magnification. When the curve is expressed by y = f (χ), it means a value obtained by the following specific formula expressed in nanometers (nm). This Ra is defined in detail in JIS B 0601 (1994) and JIS B 0031 (1994).

  Such arithmetic average roughness is, for example, an atomic force microscope (commonly known as AFM), for example, manufactured by Nippon Biko Co., Ltd., on the surface of the source electrode or drain electrode on the side where the semiconductor layers are stacked. It can be easily determined using a device such as Nano Scope IIIa. The arithmetic average roughness can be obtained by setting a 1 × 1 μm square range and measuring within that range, for example.

As a semiconductor material used for the semiconductor layer of the thin film transistor, an organic or inorganic semiconductor material can be applied. Examples of organic semiconductor materials include low-molecular organic semiconductors such as phthalocyanine derivatives, porphyrin derivatives, naphthalene tetracarboxylic acid diimide derivatives, fullerene derivatives, pentacene and pentacentriisopropylsilyl (TIPS) pentacene, and various pentacene precursors. Body, anthracene, perylene, pyrene, phenanthrene, coronene and other polycyclic aromatic compounds and derivatives thereof, oligothiophene and derivatives thereof, thiazole derivatives, fullerene derivatives, dinaphthothiophene compounds, carbon nanotubes and other carbon compounds, etc. One or more kinds of various low-molecular semiconductors combined with thiophene such as benzothienobenzothiophene, phenylene, vinylene, and the like, and copolymers thereof can be suitably used.

In addition, as a polymer compound, polythiophene, poly (3-hexylthiophene) (P3HT), polythiophene polymers such as PQT-12, thiophene-thienothiophene copolymers such as B10TTT, PB12TTT, PB14TTT, and fluorenes such as F8T2 Polymers, phenylene vinylene polymers such as paraphenylene vinylene, arylamine polymers such as polytriarylamine, and the like can be suitably used. In addition to these organic semiconductor materials, solution-soluble Si semiconductor precursors that can be modified into inorganic semiconductors by heat treatment, energy beam irradiation such as EB and Xe flash lamps, and oxide semiconductors such as IGZO, YGZO, and ZnO The precursor pair of etc. is applicable.

As a semiconductor material used for the semiconductor layer of the thin film transistor, an organic semiconductor is preferable to an inorganic semiconductor because the semiconductor layer can be easily formed at a lower temperature and is easy to handle. Among organic semiconductors, those having a high self-aggregation property and easy to take a crystal structure are preferable because more excellent transistor characteristics can be exhibited.

  Solvents that can be applied to inks of organic and inorganic semiconductor materials only need to be able to dissolve the semiconductor materials at room temperature or slightly heated, have appropriate volatility, and form an organic semiconductor thin film after volatilization of the solvent. , Xylene, chloroform, chlorobenzenes, cyclohexylbenzene, tetralin, N-methyl-2-pyrrolidone, dimethyl sulfoxide, isophorone, sulfolane, tetrahydrofuran, mesitylene, anisole, naphthalene derivatives, benzonitrile, amylbenzene, γ-butyllactone, acetone, methyl ethyl ketone An organic solvent such as can be used.

  In addition, for the purpose of improving ink characteristics, a surface energy adjusting agent such as a polymer such as polystyrene or polymethylmethacrylate or a silicone-based or fluorine-based surfactant can be added to these solutions. In particular, a fluorosurfactant for a crystalline semiconductor solution is preferably used because it can be expected not only to improve the ink characteristics but also to improve the characteristics of the semiconductor film formed by drying the ink, for example, the mobility of the thin film transistor. it can.

  The method for forming the semiconductor layer of the thin film transistor is not particularly limited, and the thin film transistor can be formed by any known and commonly used dry or wet process. Specifically, the vacuum deposition method, molecular beam epitaxial growth method, ion cluster beam method, ion plating method, sputtering method, atmospheric pressure plasma method, dry process represented by CVD method, and printing method as exemplified below A wet process such as the above can be applied. In particular, the wet process is a preferred embodiment of the present invention because a dramatic reduction in manufacturing cost can be expected. Examples of the wet process include an inkjet method, a screen printing method, a spin coating method, a blade coating method, a bar coating method, a slit coating method, an edge casting method, a dip coating method, a spray coating method, a gravure printing method, a flexographic printing method, and a gravure method. An offset printing method, a letterpress offset printing method, a letterpress reverse printing method, and the like are used. Among the wet processes, an inkjet method, a spin coating method, an edge casting method, a dip coating method, and a blade coating method are preferable in terms of excellent material use efficiency.

  In the method for producing a thin film transistor of the present invention, the ink image line-shaped transfer target member is pressed and brought into contact with a support on which a semiconductor layer has been formed in advance, and the electrode image forming ink image area is transferred onto the semiconductor layer. A laminate constituting a part of the thin film transistor is formed, and the pressure during pressing is preferably 1 MPa or less, and more preferably 100 to 500 kPa. If an excessive pressure is applied during transfer printing, the ink image forming area of the electrode formation bites into the semiconductor layer or breaks through the semiconductor layer, causing the transistor to not drive properly, and the mobility and threshold voltage. The variation also increases. On the other hand, when the transfer pressure is too low, transfer unevenness increases, and the variation in transistor characteristics also increases.

Further, in order to suppress variations in transistor characteristics, it is preferable to apply a uniform transfer pressure over the entire support surface with which the member to be transferred contacts, and it is preferable that the surface of the member to be transferred has high smoothness. Specifically, when the arithmetic average roughness Ra of the surface of the transferred member is 10 nm or less, and more preferably Ra is 2 nm or less, a partial area of the ink image forming portion for electrode formation caused by the protrusion on the surface of the transferred member Uneven transfer can be prevented.

The insulator material used for the insulator layer of the thin film transistor of the present invention is not limited as long as it includes an insulating material. For example, polyparaxylene resin, polystyrene resin, polycarbonate resin, polyvinyl alcohol resin, Vinyl acetate resin, polysulfone resin, polyacrylonitrile resin, methacrylic resin, polyvinylidene chloride resin, fluorine resin, epoxy resin, polyimide resin, polyamide resin, polyamideimide resin, polyvinylpyrrolidone resin, polycyanate resin, polyolefin resin , Fluorine resin such as polyterpene resin, polyvinylidene fluoride, polytetrafluoroethylene, organic such as (meth) acrylic resin, diallyl phthalate resin, melamine resin, urethane resin, polyester resin, alkyd resin A silane compound, a silazane compound, a magnesium alkoxide compound, an aluminum alkoxide compound, a tantalum alkoxide compound, an ionic liquid, or an ionic gel that forms an inorganic film by hydrolysis and heat treatment as necessary can be used. . These may be used alone or in combination of two or more. If necessary, oxides such as zirconia, silicon dioxide, aluminum oxide, titanium oxide, and tantalum oxide, ferroelectric oxides such as SrTiO ₃ and BaTiO ₃ , Dielectric fine particles such as nitrides such as silicon nitride and aluminum nitride, sulfides and fluorides can be dispersed.

There is no limitation on the solvent that can be applied to the ink of the insulating material, and various organic solvents such as water, hydrocarbon, alcohol, ketone, ether, ester, glycol ether, and fluorine can be used. Moreover, antioxidants, leveling agents, mold release accelerators, and various catalysts for promoting film formation can be used as necessary.

The conductive material used for the gate electrode of the thin film transistor of the present invention is not particularly limited as long as it includes a conductive material. For example, gold, silver, copper, nickel, zinc, aluminum, calcium, magnesium, iron, Metals such as platinum, palladium, tin, chromium, lead, etc., and alloys of these metals such as silver / palladium; thermal decomposition that thermally differentiates at relatively low temperatures, such as silver oxide, organic silver, and organic gold, to give conductive metals Conductive metal compounds; conductive metal oxides such as zinc oxide (ZnO) and indium tin oxide (ITO) can be used. As the conductive polymer, for example, polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS), polyaniline, or the like can be used. Furthermore, carbon-based conductive materials such as carbon nanotubes can also be used.

  The insulator layer and the gate electrode layer can be formed by any known and commonly used dry or wet processes. Specifically, the vacuum deposition method, molecular beam epitaxial growth method, ion cluster beam method, ion plating method, sputtering method, atmospheric pressure plasma method, dry process represented by CVD method, and printing method as exemplified below A wet process such as the above can be applied. In particular, the wet process is a preferred embodiment of the present invention because a dramatic reduction in manufacturing cost can be expected. Examples of wet processes include inkjet printing, screen printing, spin coating, bar coating, slit coating, dip coating, spray coating, gravure printing, flexographic printing, gravure offset printing, letterpress offset printing. And letterpress reverse printing are used.

  When an insulating layer such as a gate insulating film is formed by a printing method, the insulating ink used for the insulating layer can be prepared by dissolving or dispersing various known and usual insulating materials in a solvent.

  In order to improve the transistor characteristics, the surface of the insulator layer is formed, for example, by hexamethyldisilazane (HMDS), octyltrichlorosilane (OTS-8), octadecyltrichlorosilane, (OTS-18), dodecyltrichlorosilane (DTS), SAM (self-organized film) treatment can be performed with various silane coupling agents such as fluorine-substituted octatrichlorosilane (PFOTS) and β-phenethyltrichlorosilane.

  In addition, when the affinity of the interface between the insulator layer and the semiconductor layer subjected to the SAM treatment is insufficient, if necessary, in order to improve it and improve the transistor characteristics, a fluorine-based material is used. A surfactant or the like can be used.

  When forming a gate electrode by printing, any conductive ink containing the above various conductive materials that can be used to form a source electrode and a drain electrode is used as the conductive ink used for the gate electrode. it can. The gate electrode, the source electrode, and the drain electrode can be used in combination with conductive inks using different conductive materials in forming the electrodes.

  The thicknesses of the insulating layer and the gate electrode of the thin film transistor of the present invention are not particularly limited, but the thickness of the insulating layer is preferably 5 to 1000 nm from the viewpoint of suppressing variation in the ON / OFF value. The thickness of the gate electrode is preferably 20 to 1000 nm in terms of good followability to a flexible substrate.

In the thin film transistor of the present invention, a protective film layer can be formed on the uppermost layer if necessary. By providing the protective film layer, the influence of outside air can be minimized, and the electrical characteristics of the thin film transistor can be stabilized. The protective film material used for the protective film layer may be any material that can form a film having excellent barrier properties such as light, oxygen, water, ions, etc. by modification treatment by heating, light, electron beam, etc. The same material as the insulator material can be used. When the protective film layer is formed by a wet process, there is no limitation on the applicable solvent as long as it dissolves or disperses the above-described resin. If necessary, various surfactants such as silicone and fluorine can be added to the protective film material.

  The thin film transistor of the present invention can be manufactured by an arbitrary manufacturing method. For example, an ink image line portion obtained by transfer printing on a support is baked using an ink image line shape forming transfer member. Thus, the source electrode and the drain electrode made of a conductor are formed. Further, by forming each layer forming the thin film transistor, that is, the semiconductor layer, the insulator layer, and the gate electrode by printing, the productivity is increased. A thin film transistor that is easy to manufacture a thin film transistor that is high in uniformity and excellent in uniformity can be obtained. Further, the thin film transistors thus obtained can be integrated into a transistor array or an integrated circuit.

(Production of source and drain electrodes by letterpress reverse printing)
A conductive ink containing ethanol solvent (RAGT-28 manufactured by DIC Corporation, hereinafter referred to as “nanoparticle silver ink”) in which silver particles having an average particle diameter of nanometer order are uniformly dispersed in a liquid medium is used as a film. Apply uniformly to the silicone rubber surface of a transparent blanket with a silicone rubber layer on it using a slit coater and dry it to the extent that tack remains, and then apply a negative pattern of the desired pattern such as the source electrode, drain electrode and gate electrode. The formed glass relief printing plate obtained by wet etching of glass, which was excellent in the precision of the convex acute angle portion (edge), was pressed against the uniform surface of the nanoparticle silver ink to remove unnecessary portions. After the pattern remaining on the blanket was further dried and the solvent in the conductive ink was sufficiently evaporated, the pattern was pressed onto the substrate at a pressure of 150 kPa to transfer the desired pattern onto the substrate. In addition, when the 10 × 1 μm square range was arbitrarily provided over the entire silicone rubber surface of the transparent blanket and the arithmetic average roughness thereof was measured, the average value was 0.8 nm.

(Semiconductor parameter characteristic evaluation)
Thin film transistor test elements shown below were prepared and their characteristics were evaluated. Id-Vg and Id-Vd characteristics were measured using a semiconductor parameter measuring apparatus (4200 manufactured by Keithley), and field effect mobility and ON / OFF value were calculated by known methods.

Example 1
A thin film transistor test element having a BGTC structure was prepared and evaluated by the following procedure.
(1) Formation of gate electrode: After a Cr film having a film thickness of 100 nm is formed on a non-alkali glass having a thickness of 0.7 mm by sputtering, a photoresist is applied, exposed and developed, and Cr film is formed by wet etching. Was patterned to form a gate electrode.
(2) Formation of insulating layer: Polyparaxylylene resin (trade name: Parylene-C, manufactured by Japan Parylene Co., Ltd.) is chemically deposited by CVD on the support on which the source and drain electrodes and the semiconductor layer are formed. An insulating layer having a thickness of 1000 nm was formed.
(3) Formation of semiconductor layer: Blade coating method using a 0.5 wt% mesitylene solution of organic semiconductor 2,7-dioctyl [1] benzothieno [3,2-b] [1] benzothiophene (C8-BTBT) A semiconductor layer was formed on the previously formed insulating layer. Arbitrary five 1 × 1 μm square ranges of the semiconductor layer were provided and their arithmetic average roughness Ra was measured. The average value was 20 nm.
(4) Formation of source electrode and drain electrode: Using the above nanoparticle silver ink on the previously formed semiconductor layer, according to the preparation of the source electrode and the drain electrode by the relief printing method, the channel length is 20 μm, the channel width is 500 μm, A source electrode and a drain electrode pattern were formed so as to have an electrode width of 20 μm, and baked at 80 ° C. for 30 minutes in a clean oven to form a silver electrode having a thickness of 100 nm.

(Comparative Example 1)
A thin film transistor test element was prepared and evaluated in the same manner as in Example 1 except that the method for forming the source electrode and the drain electrode was changed as follows.
Formation of source electrode and drain electrode: An electrode pattern is formed on a previously formed semiconductor layer with a channel length of 100 μm, a channel width of 500 μm, and an electrode width of 100 μm by screen printing using commercially available silver ink for screen printing. A thin film transistor test element was prepared and evaluated in the same manner as in Example 1 except that it was formed.

(Comparative Example 2)
A thin film transistor test element was prepared and evaluated in the same manner as in Example 1 except that the method for forming the source electrode and the drain electrode was changed as follows.
Formation of source electrode and drain electrode: An electrode pattern is formed on a previously formed semiconductor layer using a commercially available silver ink for ink jet so that the channel length is 150 μm, the channel width is 500 μm, and the electrode width is 150 μm. A thin film transistor test element was prepared and evaluated in the same manner as in Example 1 except that.

(Example 2)
A thin film transistor test element was prepared and evaluated in the same manner as in Example 1 except that the method for forming the gate electrode was changed as follows.

  Formation of gate electrode: Using the above nanoparticle silver ink, a gate electrode pattern was formed by a letterpress reverse printing method, and baked in a clean oven at 120 ° C. for 30 minutes to form a silver electrode having a thickness of 100 nm.

(Example 3)
A thin film transistor test element was prepared and evaluated in the same manner as in Example 1 except that the method for forming the semiconductor layer and the method for forming the source and drain electrodes were changed as follows.
Formation of semiconductor layer: An organic semiconductor was used to form a semiconductor layer on the insulating layer previously formed by vacuum deposition. Arbitrary five 1 × 1 μm square ranges of the semiconductor layer were provided and their arithmetic average roughness Ra was measured. The average value was 10 nm.
Formation of source electrode and drain electrode: on the insulating layer formed earlier, the nanoparticle silver ink is used, and according to the preparation of the source electrode and the drain electrode by the relief printing method, the channel length is 20 μm, the channel width is 500 μm, and the electrode width is 20 μm. A source electrode and a drain electrode pattern were formed so as to be and fired in a clean oven at 150 ° C. for 30 minutes to form a silver electrode having a thickness of 100 nm.

(Comparative Example 3)
A thin film transistor test element having a BGBC structure was prepared and evaluated by the following procedure.
(1) Formation of gate electrode: After a Cr film having a thickness of 100 nm is formed on a non-alkali glass having a thickness of 0.7 mm by a sputtering method, a photoresist is applied, exposed and developed, and Cr film is formed by wet etching. Was patterned to form a gate electrode.
(2) Formation of insulating layer: Polyparaxylylene resin (trade name: Parylene-C, manufactured by Japan Parylene Co., Ltd.) is chemically deposited by CVD on the support on which the source and drain electrodes and the semiconductor layer are formed. An insulating layer having a thickness of 1000 nm was formed.
(3) Formation of source electrode and drain electrode: On the insulating layer formed earlier, the nanoparticle silver ink was used, and according to the preparation of the source electrode and the drain electrode by the relief printing method, the channel length was 20 μm, the channel width was 500 μm, A source electrode and a drain electrode pattern were formed so as to have an electrode width of 20 μm, and baked in a clean oven at 150 ° C. for 30 minutes to form a silver electrode having a thickness of 100 nm.
(4) Formation of a semiconductor layer: a source electrode previously formed by vacuum evaporation using organic semiconductor dinaphtho [2,3-b: 2 ′, 3′-f] thieno [3,2-b] thiophene and A semiconductor layer was formed on the drain electrode.

  Table 1 shows the transistor characteristics measured with each test element.

  As can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, in the step of forming the source electrode and the drain electrode, the ink image area is dried on the transfer member using the transfer printing method, and then the semiconductor electrode is formed on the semiconductor layer. When transferred, the transistor is driven even by the top contact type thin film transistor. On the other hand, when the electrode pattern is formed by forming the conductive ink directly on the semiconductor layer without passing through the drying process like the screen printing method or the ink jet method, the transistor is formed. It is clear that field effect mobility cannot be obtained without driving. Further, as can be seen from the comparison between Example 3 and Comparative Example 3, it is clear that excellent field effect mobility cannot be obtained with the BGBC type thin film transistor.

  According to the method for manufacturing a thin film transistor of the present invention, a top contact type thin film transistor by a wet process excellent in productivity can be easily obtained. For example, a backplane or an integrated circuit of an image display device can be easily manufactured.

1 substrate, 2 insulator layer, 3 G gate electrode, 4 source electrode / drain electrode, 5 semiconductor layer, S source electrode, D drain electrode, L channel length

Claims (9)

  In a method for manufacturing a thin film transistor including a source electrode and a drain electrode, and a semiconductor layer, an insulator layer, and a gate electrode, an ink image line portion for forming the source electrode and the drain electrode on a transfer member having releasability A step of forming, a step of drying the ink image area on the transferred member, and a transfer printing of the ink image area on the substrate to be printed on which the semiconductor layer is formed by using the transferred member as a support. And a process for manufacturing the thin film transistor.   A releasable transfer member provided with an ink image line portion for forming a source electrode and a drain electrode has a relief plate formed with a convex portion corresponding to the image line of the source electrode and the drain electrode. Using a transferred member having moldability, obtained from a step of applying conductive ink to the entire surface of the transferred member, and a step of pressing the relief plate onto the applied conductive ink surface on the transferred member. 2. The method for manufacturing a thin film transistor according to claim 1, wherein the thin film transistor is a member to be transferred from which a non-image area pressed by a relief plate is removed and an image line corresponding to a source electrode and a drain electrode is formed.   3. The method of manufacturing a thin film transistor according to claim 1, wherein the semiconductor layer is made of an organic semiconductor, and the semiconductor layer is formed by a wet process.   4. The method for producing a thin film transistor according to claim 1, wherein the semiconductor layer is formed by an ink jet method, a spin coat method, an edge cast method, a dip coat method, or a blade coat method.   The thin film transistor according to any one of claims 1 to 4, wherein Ra is 50 nm or less and the thickness of the semiconductor layer is 100 nm or less when the arithmetic average roughness of the surface of the semiconductor layer is Ra. Manufacturing method.   6. The method of manufacturing a thin film transistor according to claim 1, wherein an arithmetic average roughness Ra of the surface of the member to be transferred is 10 nm or less.   The pressure at the time of transferring and printing the ink image area on the transferred member onto the substrate to be printed on which the semiconductor layer is formed is 1 MPa or less. Manufacturing method of the thin film transistor.   The method for producing a thin film transistor according to any one of claims 1 to 7, wherein the ink image area on the transferred member is formed using a conductive ink containing water or an alcohol solvent. The method of manufacturing a thin film transistor according to any one of claims 1 to 8, wherein the film thickness of the source electrode and the drain electrode is 50 nm or more.

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