JP4816873B2 - Thin film transistor manufacturing method - Google Patents

Description

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

 In recent years, from the viewpoint of flexibility, weight reduction, and cost reduction, research on thin film transistors (printing TFTs) by printing methods has been active, and application to driving circuits such as organic EL and electronic paper and electronic tags is expected. ing. However, in general, the printing method has a lower pattern resolution than the photolithography method, and the coating type organic semiconductor generally has a low carrier mobility. Therefore, the fine formation of various electrodes (gate electrodes and source / drain electrodes) is particularly important and one of the technical problems for the practical use of printed TFTs.

As a method for forming the various electrodes, many examples using screen printing or ink jet have been reported so far, but these printing methods do not have sufficient pattern resolution.
For example, in screen printing, it is difficult to stably form a pattern when the fineness of the pattern is, for example, 20 μm or less in the line space due to the restriction of the fineness of the screen mesh. Also, when the pattern becomes fine, it is necessary to use a printing paste with high viscosity and low fluidity, which causes a problem of surface smoothness such as scumming or surface irregularities remaining in the pattern due to insufficient leveling after printing. .

  On the other hand, inkjet has no problems with the printing plate and surface smoothness is small, but the ink landing accuracy is not sufficient for forming fine patterns, and ink for inkjet is low in viscosity and has high fluidity The pattern resolution is worse than screen printing. On the other hand, there is an example in which a fine pattern is formed by performing various patterning processes for restricting the flow of ink on the surface of the substrate in advance, but the process becomes complicated, so the cost is reduced and the area is increased. Effectiveness is limited.

On the other hand, a reverse offset printing method is known as a method capable of forming a fine pattern. In the reverse offset printing, a transfer material is applied and formed on the entire surface of a printing blanket having a peelable surface, and this printing blanket is brought into close contact with the relief printing plate to remove the portion of the transfer material that has contacted the relief printing plate from the printing blanket. Subsequently, this printing blanket is a printing patterning method in which the transfer material is transferred by bringing the printing blanket into close contact with the transfer object.
Although no example of forming various electrodes of a printed TFT by reverse offset printing has been reported so far, several examples of forming a conductive pattern by offset printing have been reported. In the conductive ink compositions in those formation examples, an organic solvent type is used as a dispersion medium, and metal particles having a particle size of about several μm are used as a conductive material (see Patent Documents 1 to 3).

  When this conventional conductive ink composition is used for reverse offset printing, several problems arise. That is, in the conductive ink composition, since the dispersion medium is an organic solvent, the printing blanket absorbs the solvent and swells to impair the dimensional accuracy and positional accuracy of the printed material. Alignment accuracy will be reduced. Further, since the conductive ink composition has a large particle size of the conductive material, it is impossible to form a fine pattern outline clearly and to obtain sufficient smoothness. In the thin film transistor, an electrode is formed under an insulating layer. However, if the surface smoothness of the electrode is poor, there arises a problem that the insulating property of the gate insulating film is lowered.

Japanese Patent Laid-Open No. 11-305645 JP 2001-093326 A JP 2001-515645 A

  This invention is made | formed in view of this problem, and makes it a subject to provide the formation method of a thin-film transistor which can print-form various electrodes more finely and smoothly.

  The invention according to claim 1 is a method of manufacturing a thin film transistor having a gate electrode, an insulating layer, a source / drain electrode, and a semiconductor layer, wherein any one or more of the gate electrode and the source / drain electrode are average particles. A method of manufacturing a thin film transistor, wherein a conductive ink composition containing metal particles having a diameter of 50 nm or less, an aqueous solvent, and a water-soluble resin is transferred by reverse offset printing and then heat-treated. is there.

  The invention according to claim 2 is characterized in that a mixing ratio of the water-soluble resin and the metal particles is a weight ratio (water-soluble resin / metal particles) = (1/20) to (1/4). It is a manufacturing method of the thin-film transistor of Claim 1.

  The invention described in claim 3 is the method for producing a thin film transistor according to claim 1 or 2, wherein the water-soluble resin is polyethylene oxide.

  The invention according to claim 4 is the method for producing a thin film transistor according to any one of claims 1 to 3, wherein the metal particles contain silver.

  The invention according to claim 5 is the method for manufacturing a thin film transistor according to any one of claims 1 to 4, wherein a heat treatment temperature in the heat treatment is 120 ° C. or higher and 250 ° C. or lower.

  According to the present invention, a finer electrode pattern can be formed in a thin film transistor by a simple method than in a conventional method. Specifically, it is possible to obtain an electrode pattern having a sufficient conductive performance and having a line width of 10 μm or less and a line interval of 5 μm or less.

Hereinafter, the present invention will be described in detail.
The present invention is characterized in that in a thin film transistor having a gate electrode, an insulating layer, a source / drain electrode, and a semiconductor layer, at least one of the gate electrode and the source / drain electrode is formed by a reverse offset printing method. .

  Specifically, a gate electrode, an insulating layer, source / drain electrodes and a semiconductor layer are provided on a base material, a gate electrode on one side of an insulating base material, and a source / drain electrode and a semiconductor on the other side. The structure which provides a layer etc. can be mentioned.

Any base material can be used as long as it can withstand the transfer and heat treatment during the formation of each electrode. However, when the method of the present invention is used, a high conductivity is exhibited even at a temperature of 250 ° C. or lower. Therefore, some plastic substrates can also be used.
For example, soda lime glass, quartz, silicon wafer, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), cycloolefin polymer, polyimide, polyethersulfone (PES), polymethyl methacrylate (PMMA), Polycarbonate, polyallylate and the like can be used.

Next, the conductive ink composition used when forming each electrode will be described.
The conductive ink composition used in the present invention contains at least metal particles having an average particle size of 50 nm or less as a conductive component, an aqueous solvent as a dispersion medium, and a water-soluble resin.
As the metal particles, particles having an average particle size of 50 nm or less are used, and particles having an average particle size of 20 nm or less are preferable. If the particle diameter is larger than 50 nm, the conductivity may be ensured by devising the shape and surface treatment of the particles, but this is not preferable because patterning resolution and surface smoothness are lowered. The particles are preferably 1 nm or more. It is because it is very difficult to actually manufacture if it is smaller than this. In general, in nano-sized metal particles, it is known that when the particle size is reduced, the temperature at which the particles are fused together decreases. When the particles are fused, bulk conductivity is exhibited. Therefore, it is preferable that the particle diameter is within this range, particularly in ensuring conductivity during low-temperature heat treatment. If the particle diameter is in this range, even if it is used as an electrode under the gate insulating layer, the effect of surface smoothness on the insulating properties of the gate insulating film is at a level that does not cause any problem.

The aqueous solvent of the present invention is used as a dispersion medium.
The dispersion medium is preferably an aqueous solvent because it does not swell the printing blanket or is very slight even if it is swollen. As an aqueous solvent, the solvent containing 1 or more types among water and various polar organic solvents can be mentioned. Examples of the polar organic solvent include alcohols such as methanol, ethanol and isopropanol, and ketones such as acetone, but are not limited thereto.

  The metal particles include gold, silver, copper, nickel, platinum, palladium, rhodium and the like as the metal component, but it is preferable that silver is mainly used from the viewpoint of conductivity. The form of the particles may be alloy particles or core-shell particles of the metal in addition to the single component particles of the metal.

  As the metal particles, those commercially available as colloidal dispersions can be used. The particle concentration in the conductive ink composition is not particularly limited, but is usually 50 wt% or less.

The present invention is characterized in that it contains a water-soluble resin in addition to metal particles and an aqueous solvent as a component of the conductive ink composition.
The water-soluble resin is for imparting transferability of the conductive material from the printing blanket to the printing material. By including the water-soluble resin, a fine and sufficient conductive pattern can be formed. .
As the water-soluble resin, those soluble in the metal particle dispersion are used. For example, polyethylene oxide, polypropylene oxide, polyacrylate, polyvinyl pyrrolidone, carboxyvinyl polymer, cellulose, natural polysaccharide, polyvinyl alcohol, hydroxyethyl cellulose, Hydroxypropyl cellulose and the like can be mentioned. In particular, when polyethylene oxide is used, pattern transferability and conductivity are good.

The mixing ratio of the water-soluble resin and the metal particles is (water-soluble resin / metal particles) = (1/20) to (1/4) by weight, preferably (water-soluble resin / metal particles) = (1 / 10) to (1/8). When the addition amount is large, sufficient conductivity is not exhibited in the conductive pattern, and when the addition amount is small, the above-described transferability becomes insufficient and the pattern cannot be formed stably. The molecular weight of the water-soluble resin is not particularly limited, but an appropriate one is selected in consideration of solubility in the colloidal dispersion, transferability, and conductivity after heat treatment.
In addition, the conductive ink composition used in the present invention may be added with a surfactant or a leveling agent as necessary in order to uniformly apply it to a printing blanket.

Next, as an example of forming an electrode pattern by reverse offset printing, a process of forming a gate electrode on a substrate in the formation of a planar thin film transistor will be described with reference to FIG.
First, the conductive ink composition 2 is uniformly applied to the entire surface of the printing blanket 11 having a peelable surface, and then dried to the extent necessary for removal of the transferred material by a relief printing plate described later, whereby the transferred material 31 is formed on the entire surface. A blanket 12 is obtained (FIG. 1a).
Examples of the application method include, but are not limited to, bar coating, die coating, and spin coating. The thickness of the transferred material 31 is usually 10 μm or less, although it depends on the definition of the pattern. If the film thickness is large, the transfer material 31 is liable to cohesively break during transfer, which is not preferable.

  Next, the printing blanket 12 having the transfer material 31 formed on the entire surface is brought into close contact with the plate surface of the relief plate 4 and then peeled off (FIG. 1b). As an adhesion method, for example, the printing blanket 12 is slightly inclined on the relief plate 4 so as to be brought into contact with one end side, and in this state, pressure is applied as necessary from the contact side to the non-contact side. There is a method of continuous contact. By this step, the portion of the transfer body 31 that contacts the convex portion of the relief plate 4 is removed from the printing blanket 12. The convex portion of the relief plate 4 is a non-image portion pattern with respect to the desired pattern, and thus the printing blanket 13 on which the transfer product 32 of the desired pattern is formed is obtained.

  As the material of the printing blanket 11, a material that can form the transferred material 31 and can be removed by the relief printing plate 4 and transferred to the base material 5 described later is used. A material having a certain degree of flexibility is preferable. Examples of such materials include silicone elastomers, fluorine elastomers, butyl rubber, and ethylene propylene rubber. Further, the surface of the printing blanket 11 may be subjected to fluorine resin treatment, silicone treatment, or the like.

  The relief printing plate 4 is not particularly limited as long as the transfer product 31 can be removed. Examples of the material include metals such as glass and stainless steel and various resist materials, and include sandblasting, photolithography etching, FIB (focused ion beam). ) And other methods.

  Next, the printing blanket 13 on which the transfer product 32 having a desired pattern is formed is brought into close contact with the substrate 5 and then peeled off (FIG. 1c). As an adhesion method, for example, the same operation as the method of bringing the printing blanket 12 into contact with the relief plate 4 can be mentioned. As a result, the transferred product 32 that has come into contact with the surface of the substrate 5 is removed from the printing blanket 13 and transferred to the substrate 5 to obtain the printed product 52 on which the transferred product 32 is formed. The transfer of the transfer product 32 and the removal of the transfer product 31 are caused by the peeling action of the printing blanket 11.

  Next, the printed material 52 to which the transfer material 32 has been transferred is heat-treated to develop conductivity, and the gate electrode 6 having a desired pattern is obtained (FIG. 1c). The higher the heat treatment temperature, the higher the electrical conductivity tends to be. However, the limitation of the printed material is increased from the viewpoint of heat resistance. For example, when plastic is used as the printed material, it is necessary to be 250 ° C. or lower.

  Note that the reverse offset printing of the present invention can be performed using a general printing apparatus. For example, after the conductive ink composition 2 is applied and dried on a printing blanket 11 wound around a cylindrical roll to form a printing blanket 12 on which a transfer product 31 is formed, the printing blanket roll 12 is applied to the relief plate 4. A printing blanket 13 on which a transfer product 32 is formed by rolling a cylindrical roll on the relief plate 4 in a state of being placed in contact, and then a state in which the printing blanket 13 is placed in contact with the substrate 5 Then, a cylindrical roll is rolled on the substrate 5 to form a transfer 32.

FIG. 2 shows a planar thin film transistor using a base material on which the above-described gate electrode is formed. A gate insulating film 7, a source / drain electrode 8, and a semiconductor layer 9 are sequentially formed on the base material on which the gate electrode is formed. The gate insulating film and the semiconductor layer can be formed by a known printing method, coating method, or the like. The source / drain electrodes can be formed by the same method as that for forming the gate electrode described above.
The gate electrode and the source / drain electrodes are all preferably formed by the reverse offset printing method, but one of them can be formed by the reverse offset printing method and the other can be formed by another patterning method. .

The gate insulating film 7 can be formed using a known material. Specifically, inorganic materials such as SiO ₂ , Ba _x Sr _(1-x) TiO ₃ , BaTi _x Zr _(1-x) O ₃ , polyester / melamine resin paste, polymethyl methacrylate, polyvinyl chloride, Organic materials such as polyvinyl alcohol, polyvinyl phenol, polystyrene, and cyanoethyl pullulan can be used. For forming the gate insulating film, known methods such as spin coating, dip coating, screen printing, letterpress printing, intaglio printing, planographic printing, ink jet, vacuum deposition, and CVD are used. As described above, the base material can also serve as the gate insulating film.

The semiconductor layer 9 can be formed of various known materials. Examples thereof include organic materials such as pentacene, polythiophene, polyallylamine, and fluorenebiothiophene copolymer, carbon compound materials such as carbon nanotubes and fullerenes, and inorganic materials such as cadmium selenide particles. The semiconductor layer 9 can be formed by various known methods. For example, spin coating, dip coating, screen printing, letterpress printing, intaglio printing, planographic printing, ink jet, vacuum deposition, and the like are appropriately selected and used according to the semiconductor material.
The present invention is similarly applicable to staggered TFTs. The staggered TFT of the present invention has a structure in which a source / drain electrode, a semiconductor layer, and a gate insulating film are sequentially formed on a base material, and a gate electrode is further formed on the gate insulating film.

The planar type thin film transistor shown in FIG. 2 was produced by the following procedures 1) to 5).
(Formation of gate electrode)
Polyethylene oxide (average molecular weight 10,000, manufactured by Aldrich) is added to a silver particle aqueous dispersion (average particle size 20 nm, manufactured by Sumitomo Electric), and the weight ratio of (polyethylene oxide / silver particles / water) = (1/8/31). Then, a conductive ink composition for forming a gate electrode was prepared.
Further, a two-pack type silicone rubber manufactured by Toshiba GE was molded into a thickness of 2 mm and a size of 100 mm × 100 mm was used as a printing blanket.
Further, a concave portion (depth 40 μm) of a square pattern having a side length of 1 mm was provided on a soda lime glass plate by photolithography etching processing to form a relief plate for forming a gate electrode.

  The conductive ink composition was applied to the printing blanket on the entire surface with a bar coater (# 6) and then dried at room temperature for several minutes to obtain a blanket on which the transfer product was formed on the entire surface. Subsequently, the blanket is brought into close contact with the relief plate for forming the gate electrode and then peeled off, and the portion of the transferred material that contacts the protruding portion is removed from the blanket, and the blanket in which the transferred material is formed in the pattern of the gate electrode is removed. Obtained. Subsequently, the blanket was brought into close contact with the glass substrate and then peeled off to transfer the transfer product of the gate electrode pattern onto the glass substrate. Subsequently, this was heat treated at 200 ° C. for 30 minutes to form a gate electrode on the glass substrate.

(Formation of gate insulating film)
Polyvinylphenol (average molecular weight 20,000, manufactured by Aldrich) and a crosslinking agent were dissolved in cyclohexanone to prepare an insulating film forming solution. The insulating film forming solution was spin coated on the gate electrode forming substrate and then thermally cured (200 ° C. for 1 hour) to form a gate insulating film having a thickness of 1 μm.

(Formation of source / drain electrodes)
The conductive ink composition and the printing blanket were the same as those used in the gate electrode formation step. The relief plate for forming the source / drain electrodes has a recess (depth: 0.7 μm) having a pattern in which two rectangles having the same shape (10 μm × 500 μm) are arranged so that the interval between the long sides is 2 μm. It was provided on a soda lime glass plate.
A source / drain electrode was formed on the gate insulating film above the gate electrode in the glass plate on which the gate electrode and the gate insulating film formed in the above were formed by the same method as the gate electrode forming step (channel length 2 μm). , Channel width 500 μm).

(Formation of semiconductor layer)
A poly (3-hexylthiophene) (manufactured by Sigma-Aldrich Japan) solution was applied between the source and drain electrodes by inkjet and then dried to form a semiconductor layer.
Finally, a bonding pad was provided on the source / drain electrodes, and the front surface of the substrate surface excluding the bonding pad was covered with a protective film to complete the TFT. As a result of evaluating the gate voltage dependence of the correlation (V-I characteristic) between the drain voltage V and the drain current I of this TFT, the FET characteristic was confirmed.

It is sectional drawing which shows a part of example of the manufacturing method of the thin-film transistor of this invention to process order. It is sectional drawing of the thin-film transistor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Printing blanket 12 Printing blanket in which transcription | transfer material 31 was formed 13 Printing blanket in which transcription | transfer material 32 was formed 2 Conductive ink composition 31 Transfer material formed in the whole surface of printing blanket 32 Pattern in printing blanket Formed Transfer Material 4 Letterpress 5 Base Material 6 Gate Electrode 7 Gate Insulating Film 8 Source / Drain Electrode 9 Semiconductor Layer

Claims (5)

  A method of manufacturing a thin film transistor having a gate electrode, an insulating layer, a source / drain electrode, and a semiconductor layer, wherein at least one of the gate electrode and the source / drain electrode is formed of metal particles having an average particle diameter of 50 nm or less A method for producing a thin film transistor, comprising: forming a conductive ink composition containing an aqueous solvent and a water-soluble resin by performing a heat treatment after transferring the conductive ink composition by a reverse offset printing method.   2. The thin film transistor according to claim 1, wherein a mixing ratio of the water-soluble resin and the metal particles is a weight ratio (water-soluble resin / metal particles) = (1/20) to (1/4). Production method.   The method for producing a thin film transistor according to claim 1, wherein the water-soluble resin is polyethylene oxide.   The method for producing a thin film transistor according to claim 1, wherein the metal particles contain silver.   The method for manufacturing a thin film transistor according to claim 1, wherein a heat treatment temperature in the heat treatment is 120 ° C. or more and 250 ° C. or less.

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