JP2018186131A - Electrode pattern, forming method of electrode pattern, thin film transistor, manufacturing method of thin film transistor, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film transistor capable of obtaining a large drain current with a gate insulating film with high electric capacity while suppressing occurrence of leak current and short circuit.SOLUTION: There is provided an electrode pattern having an uneven structure on the surface. Also, there is provided a forming method of a thin film transistor including a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, a semiconductor layer, and a protective layer, and at least the gate electrode corresponds to the above-described electrode pattern.SELECTED DRAWING: Figure 1D

Description

  The present invention relates to an electrode pattern, a method for forming an electrode pattern, a thin film transistor, a method for manufacturing a thin film transistor, and an image display device.

  Currently, the mainstream of semiconductor materials is silicon (Si). As a method for forming a semiconductor layer using a silicon-based material, a method in which silicon is formed by a dry method such as sputtering or CVD and then patterned using photolithography.

  On the other hand, research on transistors using organic semiconductors (organic transistors) has been actively conducted from the viewpoints of flexibility, weight reduction, and cost reduction. In general, when an organic semiconductor is used, an organic thin film transistor can be manufactured using a printing process which is a wet method. Using printing technology to manufacture organic thin-film transistors reduces the cost of equipment and manufacturing compared to the case of using photolithography, and does not require vacuum or high temperature, so there are advantages such as the availability of plastic substrates. Can be mentioned.

  The field of application of organic thin film transistors manufactured using printing technology is wide, and is not limited to flexible displays such as thin and light electronic paper, but is also expected to be applied to RFID (Radio Frequency Identification) tags and sensors.

  For these reasons, a pattern forming method using a printing technique is currently attracting attention. However, the printing method has a problem that resolution is generally poor and fine patterning is difficult as compared with photolithography.

  On the other hand, there is a reverse offset printing method as a printing method that can cope with a fine pattern (see Patent Document 1).

  In addition, in order to apply an organic thin film transistor to a large screen display, it is necessary not only to pattern a large area but also to increase a drain current.

  It is known that the drain current of a transistor is proportional to the capacitance of the gate insulating film. That is, when the capacitance Q, the area S, the distance (thickness of the gate insulating film) d, and the dielectric constant ε are expressed, Q = εS / d. To increase the drain current, the area S or the gate is increased. It is necessary to reduce the thickness d of the insulating film.

Japanese Patent Publication No. 60-29358

  However, as the pattern becomes higher in definition, it is difficult to increase the area S in order to obtain a large gate insulating film capacitance. In addition, with regard to the film thickness d of the gate insulating film, when the film thickness is reduced, there is a problem that leakage current tends to flow and insulation cannot be maintained.

  If the gate insulating film thickness d is reduced, pinholes may be generated when the gate insulating film is applied, and a short circuit between the lower layer and the upper layer may occur.

  The present invention has been made in view of such problems, and provides a thin film transistor capable of obtaining a large drain current with a gate insulating film having a high capacitance while suppressing the occurrence of a leakage current and a short circuit. For the purpose.

  One aspect of the present invention for solving the above problems is an electrode pattern having a concavo-convex structure on the surface.

  Another aspect of the present invention is a method for forming an electrode pattern as described above, wherein a step of forming an ink film on the surface of a blanket and a protrusion corresponding to the electrode pattern formed on the surface of the relief plate are used as the ink film. An electrode pattern having a concavo-convex structure on the surface by bringing the ink film remaining on the blanket surface into contact with the base material and transferring it onto the base material Forming an electrode pattern.

  Further, the ink film may contain nano silver ink.

  Further, the surface roughness Ra of the electrode pattern formed in the step of forming the electrode pattern may be 10 nm or more and 30 nm or less.

  Another aspect of the present invention is a thin film transistor including a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, a semiconductor layer, and a protective layer, at least the gate electrode being the above-mentioned A thin film transistor which is an electrode pattern.

  Another aspect of the present invention is a method for manufacturing the above-described thin film transistor, in which a gate electrode, a gate insulating layer, a source electrode and a drain electrode are sequentially formed on a substrate, and unevenness is formed on the surface of the gate electrode. A method of manufacturing a thin film transistor, including a step of forming a structure, a step of sequentially forming a semiconductor layer and a protective layer.

  Another aspect of the present invention is an image display device including the above-described thin film transistor and an image display medium.

  The image display medium may be an electrophoretic body.

  According to the present invention, it is possible to provide a thin film transistor substrate capable of obtaining a large drain current with a high-capacitance gate insulating film while suppressing occurrence of leakage current and short circuit.

Sectional drawing for demonstrating the formation method of the electrode pattern which concerns on one Embodiment of this invention. Sectional drawing for demonstrating the formation method of the electrode pattern which concerns on one Embodiment of this invention. Sectional drawing for demonstrating the formation method of the electrode pattern which concerns on one Embodiment of this invention. Sectional drawing for demonstrating the formation method of the electrode pattern which concerns on one Embodiment of this invention. Sectional drawing for demonstrating the formation method of the electrode pattern which concerns on one Embodiment of this invention. Sectional drawing for demonstrating the formation method of the electrode pattern which concerns on one Embodiment of this invention. Schematic sectional view of a thin film transistor according to an embodiment of the present invention Cross-sectional view of a thin film transistor according to a comparative example

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating an electrode pattern forming method according to an embodiment of the present invention. Below, each process of the electrode pattern formation method which concerns on this embodiment is demonstrated.

<Electrode pattern forming method>
1A to 1F are diagrams illustrating a method for forming an electrode pattern using a reverse offset printing method, which can be used for forming a gate electrode 2 of a thin film transistor 100 described later. In the following description, a method for forming an electrode pattern will be described for convenience, but this method can also be used for forming a wiring.

  First, the ink 21 is applied to the blanket 11 (FIG. 1A) having a peelable surface to form an ink film (FIG. 1B). Thereafter, at least a part of the solvent contained in the ink 21 is dried to form a transfer product 22 on the surface of the blanket 11 (FIG. 1C).

  Next, after making the removal plate 25 in which the unevenness corresponding to the electrode pattern is formed in close contact with the transfer material 22 on the surface of the blanket 11, this is peeled off. Thereby, a part of the transfer product 22 (transfer product 24 attached to the removal plate 25) adheres to the convex portion of the removal plate 25, and thus the blanket in which the transfer product 23 remaining on the blanket corresponding to the electrode pattern is formed. 11 can be obtained (FIG. 2D).

  Next, after the substrate 1 is brought into close contact with the transfer material 23 remaining on the blanket 11 (FIG. 1E), the transfer material 23 remaining on the blanket 11 is transferred onto the substrate 1 by peeling off the substrate 1. An electrode pattern can be formed (FIG. 1F).

  The material of the blanket 11 is capable of forming a transfer product 22 obtained by drying a part of the ink 21, removing the transfer product 22 from the non-electrode pattern portion by the removal plate 25, and transferring the transfer product 22 to the substrate 5 described later. Things are used. A material with little deformation is preferable, but a certain degree of flexibility is required. As such a material, silicone elastomer, butyl rubber, ethylene propylene rubber and the like can be used. Further, in order to adjust the wettability of the blanket 11 surface, the blanket surface may be subjected to a surface treatment such as application of a fluororesin and silicone, plasma treatment, or UV ozone cleaning treatment.

  Since the blanket 11 is usually supplied as a flexible plate, the blanket 11 can be used by being wound around a cylindrical plate cylinder, or can be fixed to a strong flat plate.

  The material of the ink 21 may be adjusted according to the type of printed matter to be manufactured, and a conductive material obtained by adding various additives as necessary to a dispersion of fine metal particles such as gold, silver, copper, nickel, platinum, palladium, and rhodium. Examples thereof include, but are not limited to, inks. Further, the particle size of the metal fine particles is preferably nano-sized, and specifically, nano-silver can be suitably used. In consideration of swelling of the material of the blanket 11, it is preferable to adjust using water or an alcohol solvent.

  The ink 21 may be applied to the blanket 11 as long as a uniform ink film can be formed, and bar coating, die coating, cap coating, spin coating, slit coating, or the like can be used, but is not limited thereto. .

  As the material of the removal plate 25, metals such as glass and stainless steel, various resist materials, and the like are used, but are not limited thereto. Examples of the pattern forming method on the removal plate 25 include sand blasting, photolithography, etching, FIB (focused ion beam), and nanoimprinting.

<Thin film transistor substrate>
The above-described electrode pattern forming method can be suitably used for forming a gate electrode of a thin film transistor. FIG. 2 shows a cross-sectional view of a thin film transistor 100 manufactured using the electrode pattern forming method according to an embodiment of the present invention. The thin film transistor 100 includes a substrate 1, a gate electrode 2, a gate insulating film 3, a source electrode 4, a drain electrode 5, a pixel electrode 6 connected to the drain electrode 5, and a source electrode 4 and a drain electrode 5. The semiconductor layer 7 laminated | stacked between them and the protective layer 8 laminated | stacked on the semiconductor layer 7 are included.

  Note that the gate electrode 2, the source electrode 4, and the drain electrode 5 do not need to be clearly separated from each other in the electrode portion and the wiring portion, and are specifically referred to as electrodes as constituent elements of each thin film transistor 100 in this specification. . When there is no need to distinguish between the electrode and the wiring, they are collectively described as a gate, a source, a drain, and the like.

  Next, a method for manufacturing the thin film transistor 100 will be described.

  First, the gate electrode 2 is formed on the substrate 1. As a material of the substrate 1, polycarbonate, polyethylene sulfide, polyethersulfone, polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyvinyl fluoride film, ethylene-tetrafluoroethylene copolymer resin, weather resistant polyethylene terephthalate, Weatherable polypropylene, glass fiber reinforced acrylic resin film, glass fiber reinforced polycarbonate, polyimide, fluorine resin, cyclic polyolefin resin, glass, quartz glass, and the like can be used, but are not limited thereto. These may be used alone, but two or more kinds may be laminated and used as the substrate 1.

In the case where the substrate 1 is an organic film, a transparent gas barrier layer (not shown) can be formed in order to improve the durability of the thin film transistor 100. Examples of the gas barrier layer include aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), silicon carbide (SiC), and diamond-like carbon (DLC). It is not limited to. These gas barrier layers can also be used by laminating two or more layers. The gas barrier layer may be formed only on one side of the substrate 1 using an organic film, or may be formed on both sides. The gas barrier layer can be formed by using a vacuum deposition method, an ion plating method, a sputtering method, a laser ablation method, a plasma CVD (Chemical Vapor Deposition) method, a hot wire CVD method, a sol-gel method, and the like. Is not to be done.

  The reverse electrode printing described above is used for forming the gate electrode 2. Specifically, the removed plate 25 on which irregularities corresponding to the electrode pattern of the gate electrode 2 are brought into close contact with the transfer material 22 on the surface of the blanket 11, and then peeled off. Thereafter, the substrate 1 is brought into close contact with the transfer material 23 remaining on the blanket 11, and the substrate 1 is peeled off, whereby the electrode pattern of the gate electrode 2 can be formed on the substrate 1.

  The gate electrode 2 is formed so as to have an uneven structure on the surface. The concavo-convex structure is formed so that, for example, the arithmetic average roughness Ra (hereinafter referred to as surface roughness) of the surface is 10 nm or more. The upper limit of the surface roughness is preferably 30 nm or less. If it exceeds 30 nm, the wiring resistance may increase due to the influence of film thickness unevenness.

  Regarding the method for controlling the surface roughness of the gate electrode 2, when the gate electrode 2 uses a precursor of a conductive material, nanoparticles, or the like, the surface roughness can be controlled by heat treatment at the time of forming the gate electrode 2. There is also a method of adjusting the size of the precursor and nanoparticles of the gate electrode 2. There is also a method of controlling by using a heat treatment method such as a hot plate or an oven. In particular, when a nano-sized particle is used, the grain growth is promoted by lengthening the heat treatment, so that the surface roughness is increased. In addition, a dry etching method such as plasma etching or sputter etching may be used, or a method such as corona treatment or atmospheric pressure plasma treatment may be used, but is not limited thereto. The method for defining the surface roughness can be measured using a measuring machine such as an atomic force microscope (AFM).

  Since the gate electrode 2 has a fine surface concavo-convex structure, it is possible to suppress repelling of the gate insulating film material on the gate electrode 2 when a wet film forming method is used in forming the gate insulating film 3. . Therefore, even when the gate insulating film 3 is thinned, it is possible to suppress the occurrence of pinholes when the gate insulating film 3 is applied.

  Further, since the gate electrode 2 has a fine surface uneven structure, the surface area of the gate electrode 2 can be increased. Therefore, the thin film transistor 100 can increase the electric capacity of the gate insulating film 3 without reducing the thickness of the gate insulating film 3. Thereby, the thin film transistor 100 can increase the drain current.

  Next, a gate insulating film 3 is formed on the substrate 1 and the gate electrode 2. The gate insulating film 3 is formed so as to cover at least the gate electrode 2 of the thin film transistor portion except for the connection portion with the other electrode of the gate electrode 2 and the connection portion with the outside.

  The material of the gate insulating film 3 is an oxide insulating material such as silicon oxide (SiOx), aluminum oxide (AlOx), tantalum oxide (TaOx), yttrium oxide (YOx), zirconium oxide (ZrOx), hafnium oxide (HfOx), etc. Resin materials such as silicon nitride (SiNx), silicon oxynitride (SiON), polyacrylate such as polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyvinylphenol (PVP), polysilsesquioxane (PSQ) Such an organic / inorganic hybrid resin can be used, but is not limited thereto. These may be a single layer or a laminate of two or more layers, or may have a composition inclined toward the growth direction.

The gate insulating film 3 has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more in order to suppress the gate leakage current of the thin film transistor 100.

  About the formation method of the gate insulating film 3, vacuum deposition methods, such as a vacuum evaporation method, an ion plating method, a sputtering method, a laser ablation method, a plasma CVD method, a photo-CVD method, a hot wire CVD method, a spin coat method, A wet film forming method such as a die coating method or a screen printing method can be appropriately used depending on the material.

  Next, the source electrode 4, the drain electrode 5, and the pixel electrode 6 connected to the drain electrode 5 are formed on the gate insulating film 3. Examples of the material for the source electrode 4 and the drain electrode 5 include metal materials such as aluminum (Al), copper (Cu), silver (Ag), gold (Au), and platinum (Pt), indium oxide (InO), and oxidation. Conductive metal oxide materials such as tin (SnO), zinc oxide (ZnO), indium tin oxide (ITO), and indium zinc oxide (IZO) can be used. These materials may be used as a single layer, or may be used as a laminate or an alloy.

  The source electrode 4 and the drain electrode 5 The pixel electrode 6 connected to the drain electrode 5 is preferably formed by a wet film formation method using a precursor of a conductive material or nanoparticles. For example, methods such as an inkjet method, a relief printing method, a planographic printing method, an intaglio printing method, and a screen printing method can be used. Patterning can be performed by, for example, protecting a pattern formation portion with a resist or the like using a photolithography method and removing an unnecessary portion by etching or directly patterning by a printing method, but is not limited thereto. It is not a thing.

  Next, a semiconductor layer 7 is formed on the gate insulating film 3, the source electrode 4, and the drain electrode 5 so as to connect the source electrode 4 and the drain electrode 5. Examples of the material of the semiconductor layer 7 include low molecular organic semiconductor materials such as pentacene, tetracene, phthalocyanine, perylene, thiophene, benzodithiophene, anthradithiophene, and derivatives thereof, and carbon compounds such as fullerene and carbon nanotubes, Polymer organic semiconductor materials such as polythiophene, polyallylamine, fluorenebithiophene copolymer, and derivatives thereof can be used, but are not limited thereto.

  For the semiconductor layer 7, a wet film forming method using a solution or paste in which a semiconductor material or a precursor of the semiconductor material is dissolved and dispersed can be suitably used. For example, methods such as an ink jet method, a relief printing method, a lithographic printing method, an intaglio printing method, and a screen printing method can be used, but the method is not limited to these, and a known general method can be used.

  Next, the protective layer 8 is formed on the semiconductor layer 7. The protective layer 8 is formed to protect the semiconductor layer 7. The protective layer 8 needs to be formed so as to cover at least a region overlapping with the channel portion of the semiconductor layer 6.

  Examples of the material for the protective layer 8 include inorganic materials such as silicon oxide, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconium oxide, and titanium oxide, or polyacrylates such as PMMA (polymethyl methacrylate), Examples thereof include, but are not limited to, insulating materials such as PVA (polyvinyl alcohol), PVP (polyvinylphenol), and fluorine resins.

About the material of the protective layer 8, in order to keep the leakage current of the thin film transistor 100 low, it is desirable that the resistivity is 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more.

  The protective layer 8 is formed by any one of an inkjet method, a relief printing method, a planographic printing method, an intaglio printing method, and a screen printing method using a solution in which the protective layer material or its precursor is dissolved or dispersed. . These protective layers 7 may be used as a single layer, or two or more layers may be laminated. Further, the composition may be inclined in the growth direction.

<Image display device>
By arranging a plurality of thin film transistors 100 in a matrix, a thin film transistor array can be obtained. The thin film transistor array can be used in an image display device in combination with an image display medium. As the image display medium, each image display medium such as an electrophoretic reflective display device, a transmissive liquid crystal display device, a reflective liquid crystal display device, a transflective liquid crystal display device, an organic EL display device, and an inorganic EL display device is used. Can do. The image display device can be used for electronic paper, an organic EL display device, or a liquid crystal display device.

  Thin film transistors according to examples and comparative examples were manufactured and evaluated.

(Example)
First, a 300 mm × 300 mm polyimide film (manufactured by Ube Industries) was prepared as the substrate 1, and the gate electrode 2 was formed thereon by reverse offset printing. The method is shown below.
1) After the conductive ink 21 was applied to the 350 mm × 350 mm blanket 11 using a slit die coater, the ink film 22 was formed on the blanket 11 by drying at room temperature.
2) Using a 350 mm × 350 mm removal plate corresponding to the gate electrode 2, the blanket 11 on which the ink film 22 is formed is brought into close contact with the removal plate 25, and the transfer product 24 in the region corresponding to the convex portion of the removal plate 25 is blanketed. 11 to obtain a blanket 11 on which the gate electrode 2 was formed.
3) Next, the transfer material 24 on the blanket 11 was transferred to the substrate 1 to obtain the gate electrode 2.
3) The substrate 1 on which the gate electrode 2 was formed in the printing process was heated and baked at 200 ° C. for 60 minutes using an oven.
4) Then, when the surface roughness of the gate electrode 2 was measured using AFM, the surface roughness Ra was 20.3 nm.

  Subsequently, polyimide (Mitsubishi Gas Chemical Neoprim) was applied onto a substrate 1 provided with a gate electrode 2 by a die coater, dried at 180 ° C. for 1 hour, and then a 1 μm thick gate insulating film thereon. 3 was formed.

  Subsequently, a silver film having a thickness of 100 nm was formed on the gate insulating film 3 by sputtering, and the source electrode 4, the drain electrode 5, and the pixel electrode 6 were formed by photolithography, etching, and resist removal using a positive resist.

  Subsequently, a semiconductor ink in which 6,13-bis (triisopropylsilylethynyl) pentacene was dissolved in tetralin at a concentration of 2 wt% was applied by a flexographic printing method and dried at 100 ° C. to form a semiconductor layer 7.

  A fluororesin was applied onto the semiconductor layer 7 by a flexographic printing method and dried at 100 ° C. to obtain a protective layer 7.

  In the thin film transistor 100 according to the example manufactured as described above, it was confirmed that the surface of the gate electrode 2 has a fine concavo-convex structure, thereby having a high insulating film capacity and a high drain current.

(Comparative example)
As a comparative example, a thin film transistor described below was manufactured. FIG. 3 is a cross-sectional view of a thin film transistor 200 according to a comparative example. The thin film transistor 200 is the same as the embodiment except that the formation method of the gate electrode 9 is different and the surface roughness of the gate electrode 9 is small.

First, a polyimide film (manufactured by Ube Industries) of 300 mm × 300 mm is prepared as the substrate 1, and silver is formed on the substrate 1 by a vacuum evaporation method using an electron beam using a metal mask, and the gate electrode 9 is formed. Formed. The surface roughness of the gate electrode 9 in this comparative example was 2.0 nm.

  Subsequently, polyimide (Neoprim manufactured by Mitsubishi Gas Chemical) was applied onto a substrate 1 provided with a gate electrode 9 by a die coater, dried at 180 ° C. for 1 hour, and then a 0.7 μm-thick gate thereon. An insulating film 3 was formed.

  Subsequently, a silver film having a thickness of 100 nm was formed on the gate insulating film 3 by sputtering, and the source electrode 4, the drain electrode 5, and the pixel electrode 6 were formed by photolithography, etching, and resist removal using a positive resist.

  Subsequently, a semiconductor ink in which 6,13-bis (triisopropylsilylethynyl) pentacene was dissolved in tetralin at a concentration of 2 wt% was applied by a flexographic printing method and dried at 100 ° C. to form a semiconductor layer 7.

  A fluororesin was applied on the semiconductor layer 7 by a flexographic printing method and dried at 100 ° C. to form a protective layer 8.

  In the thin film transistor 200 according to the comparative example manufactured as described above, the surface roughness of the gate electrode 9 is reduced and the electric capacity of the gate insulating film 3 is reduced because the surface roughness of the gate electrode 9 is smaller than that of the example. For this reason, the drain current of the manufactured thin film transistor 200 was 20% smaller than that of the example.

  The present invention is useful for thin film transistors, various image display devices using the same, sensors, and the like.

DESCRIPTION OF SYMBOLS 1 Substrate 2, 9 Gate electrode 3 Gate insulating film 4 Source electrode 5 Drain electrode 6 Pixel electrode 7 Semiconductor layer 8 Protective layer 11 Blanket 21 Ink 22 Pre-dried transfer material (ink film)
23 Transferred material remaining on the blanket 24 Transferred material attached to the removal plate 25 Removal plate 100, 200 Thin film transistor

Claims (8)

  An electrode pattern having a concavo-convex structure on the surface. The electrode pattern forming method according to claim 1,
Forming an ink film on the blanket surface;
A step of contacting a convex portion corresponding to the electrode pattern formed on the surface of a relief plate with the ink film to remove unnecessary portions from the ink film;
Forming an electrode pattern including a step of forming an electrode pattern having a concavo-convex structure on the substrate by bringing the ink film remaining on the blanket surface into contact with the substrate and transferring the ink film onto the substrate. Method.   The method for forming an electrode pattern according to claim 2, wherein the ink film contains nano silver.   The electrode pattern manufacturing method according to claim 2 or 3, wherein a surface roughness Ra of the electrode pattern formed in the step of forming the electrode pattern is 10 nm or more and 30 nm or less. A thin film transistor including a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, a semiconductor layer, and a protective layer,
A thin film transistor, wherein at least the gate electrode is the electrode pattern according to claim 1. A method of manufacturing a thin film transistor according to claim 5,
Sequentially forming a gate electrode, a gate insulating layer, a source electrode and a drain electrode on a substrate;
Forming an uneven structure on the surface of the gate electrode;
A method for manufacturing a thin film transistor, comprising: sequentially forming a semiconductor layer and a protective layer.   An image display device comprising the thin film transistor according to claim 4 and an image display medium.   The image display device according to claim 7, wherein an electrophoretic body is used as the image display medium.