Method for manufacturing CNT film and CNT film

Abstract

This invention provides a method for manufacturing a CNT film that allows deposited CNTs to be arranged in a fine pattern and does not require much time to fabricate the arrangement structure. [Solution] A method for producing a CNT film in which CNTs are finely arranged, comprising: a CNT-solubilizer composite preparation step S01 for producing a CNT-solubilizer composite in which CNTs are modified with a solubilizing polymer; and a film formation step S02 for forming a CNT film by applying the CNT-solubilizer composite onto a substrate by spin coating, wherein the water contact angle of the film-forming surface of the substrate is 10° or more and 30° or less, and the rotation speed of the spin coating in the film formation step S02 is 1500 rpm or more and 2500 rpm or less.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a CNT film in which CNTs are finely arranged.

Background Art

[0002] Carbon nanotubes (hereinafter referred to as CNTs) have attracted great attention due to their chemical, electronic, and mechanical properties, and are applied to various nanoscale technologies. In particular, various physical properties such as chemical stability, metallic and semiconductor electrical conductivity, high electron emission ability, high mechanical strength, and high thermal conductivity have been observed. Due to having these physical properties, it can be variously utilized especially in electronic materials such as field effect transistors and conductive thin films.

[0003] The CNT film used in transistors and the like is required to have an ordered structure for improving electrical properties. However, due to its easy aggregation property, it has been conventionally difficult to disperse CNTs and arrange them on a substrate to form a thin film having an ordered structure. Therefore, a technique for arranging CNTs using the self-assembly phenomenon becomes important.

[0004] For example, after immersing a substrate in a solvent and dropping a liquid solution containing s-SWCNT wrapped with a semiconductor-selective polymer dispersed in an organic solvent into the solvent, and then pulling up the substrate, the liquid solution spreads in a layer on the aqueous medium at the air-liquid phase interface, and a technique in which s-SWCNT is deposited in a strip on the substrate (see Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, in recent years, there has been a demand for improving various performance aspects of electronic components such as transistors by increasing the number of carbon nanotubes (CNTs) per unit area through miniaturization. However, the technology described in Patent Document 1 cannot arrange the deposited CNTs in a fine pattern. Furthermore, it takes a long time to create the arranged structure.

[0007] The present invention has been made to solve the problems of the prior art, and aims to provide a method for manufacturing a CNT film in which deposited CNTs can be arranged in a fine pattern, such as parallel or dots, and in which time is not required to fabricate the arrangement structure. Another objective is to provide a CNT film in which CNTs are arranged in a fine pattern. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the method for manufacturing a CNT film according to Embodiment 1 of the present invention is a method for manufacturing a CNT film in which CNTs are finely arranged, and comprises a CNT-solubilizer composite preparation step of preparing a CNT-solubilizer composite by modifying CNTs with a solubilizing polymer, and a film formation step of applying the CNT-solubilizer composite onto a substrate by spin coating to form a CNT film, wherein the water contact angle of the film-forming surface of the substrate is 10° or more and 30° or less, and the rotation speed of the spin coating in the film formation step is 1500 rpm or more and 2500 rpm or less.

[0009] The method for producing a CNT film according to embodiment 1 of the present invention comprises a CNT-solubilizer composite preparation step of preparing a CNT-solubilizer composite in which CNTs are modified with a solubilizing polymer, and a film formation step of applying the CNT-solubilizer composite onto a substrate by spin coating to form a CNT film. Therefore, it does not involve complex steps and can efficiently form a CNT film in which CNTs are arranged in a fine pattern. Furthermore, since the water contact angle of the film-forming surface of the substrate is within the range of 10° to 30°, the interfacial interaction between the solvent of the CNT-solubilizer composite solution and the film-forming surface of the substrate results in an appropriate volatilization rate of the CNT-solubilizer composite solution, enabling the CNTs to self-assemble and be finely arranged. Furthermore, since the spin coating rotation speed in the film deposition process is said to be between 1500 rpm and 2500 rpm, it is possible to obtain a film thickness sufficient for the continuous phase of the CNT-solubilizer composite solution to form and self-assemble (microphase separation).

[0010] The method for producing a CNT film according to aspect 2 of the present invention is characterized in that, in the method for producing a CNT film according to aspect 1 of the present invention, the solubilizing polymer is polyfluorene. According to the method for producing a CNT film of embodiment 2 of the present invention, it is possible to selectively solubilize semiconducting CNTs.

[0011] The method for manufacturing a CNT film according to aspect 3 of the present invention is characterized in that, in the method for manufacturing a CNT film according to aspect 1 or aspect 2 of the present invention, the film-forming surface of the substrate is composed of silicon dioxide. According to the method for producing a CNT film of embodiment 3 of the present invention, since the film-forming surface of the substrate is composed of silicon dioxide, the film-forming surface is reliably hydrophilic, and a CNT film in which CNTs are finely arranged can be formed stably. Furthermore, since silicon dioxide forms a chemically stable insulating film, it becomes possible to construct highly reliable electronic components such as transistors.

[0012] The CNT film of embodiment 4 of the present invention is characterized in that the CNTs are arranged in parallel with an average spacing of 10 nm or more and 1000 nm or less. According to the CNT film of embodiment 4 of the present invention, it is possible to realize a CNT arrangement on a scale at least an order of magnitude smaller than conventional methods, thereby improving various characteristics of electronic components such as transistors. [Effects of the Invention]

[0013] It is possible to provide a method for manufacturing a CNT film in which the deposited CNTs can be arranged in a fine pattern and the formation of the arrangement structure does not require time. Further, it is possible to provide a CNT film in which the CNTs are arranged in a fine pattern.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram of a field effect transistor using a CNT film. [Figure 2] It is an explanatory diagram showing a state in which CNTs are arranged in parallel in a CNT film. [Figure 3] It is an explanatory diagram showing a method for manufacturing a CNT film according to Embodiment 1 of the present invention. [Figure 4] It is an explanatory diagram showing a CNT-solubilizer composite preparation step and a film formation step. [Figure 5] It is a schematic explanatory diagram of a procedure for physically adsorbing a solubilizer to CNTs. 1] [Figure 6] [[ID= It is a SEM image of the CNT film produced in Example 1 of the present invention. [Figure 7] It is a SEM image of the CNT film produced in Example 2 of the present invention. [Figure 8] It is a SEM image of the CNT film produced in Comparative Example 1. [Figure 9] It is a SEM image of the CNT film produced in Comparative Example 2.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, a method for manufacturing a CNT film and a CNT film according to an embodiment of the present invention will be described. Hereinafter, based on the accompanying drawings, a method for manufacturing a CNT film and an example of a CNT film according to an embodiment of the present invention will be described in detail. Note that the drawings used in the following description may show, for the sake of clarity, parts that are characteristic by being enlarged for convenience.

[0016] First, the CNT film according to the present embodiment and its application examples will be described using FIGS. 1 and 2. In the CNT film of this embodiment, as shown in FIG. 1, it is formed on the surface of a substrate and used as part of a field effect transistor. A field effect transistor is a basic circuit component in microelectronics technology. It has a gate electrode, a source electrode, and a drain electrode, and further has a channel which is a path for electrons to move between the source electrode and the drain electrode. The CNTs forming the CNT film of this embodiment are superior in terms of the speed of electron movement and the magnitude of the current density that can be passed, compared with silicon. Therefore, the CNT film functions as a channel of a field effect transistor. It is required to arrange CNTs as a fine pattern in the CNT film.

[0017] Therefore, in the CNT film of this embodiment, as shown in FIG. 2, the CNTs are arranged in a fine pattern. For example, the CNTs are arranged parallel to each other with a fine interval. Here, the interval between CNTs refers to the distance from the lower end of the protruding part of one CNT to the lower end of the protruding part of an adjacent CNT. And in the CNT film of this embodiment, the average interval of the CNTs arranged in parallel is within the range of 10 nm or more and 1000 nm or less. In this way, it is possible to realize an arrangement of CNTs having a fine pattern on a scale one digit smaller than before, enabling miniaturization of the transistor. Thereby, an integrated circuit with transistors integrated at a high density can be manufactured to meet the requirements for high performance, miniaturization, or weight reduction of recent electronic devices. Note that the upper limit of the average interval of the CNTs arranged in parallel is preferably 500 nm or less. On the other hand, the lower limit of the average interval of the CNTs arranged in parallel is preferably 20 nm or more.

[0018] Next, the steps of implementing the manufacturing method of the CNT film of this embodiment will be described using FIGS. 3, 4, and 5. In the steps of implementing the manufacturing method of the CNT film of this embodiment, as shown in FIG. 3, it includes a CNT-solubilizing agent composite preparation step S01 and a film formation step S02.

[0019] As shown in Figure 5, the CNT-solubilizer composite fabrication process S01 comprises a mixing step of mixing single-walled carbon nanotubes (WYNA) and a solubilizer, a modification step of modifying the surface of the CNTs with the solubilizer by sonication, and a separation step of separating the CNT-solubilizer composite by centrifugation. By modifying carbon nanotubes (CNTs), which would otherwise aggregate, with a solubilizing agent, the CNTs can be dispersed. The solubilizing agent used to modify the CNTs is not particularly limited and may be any of the following: polyfluorene alternating copolymer, polyfluorene random copolymer, or polyfluorene. Polyfluorene is preferred because it can selectively solubilize semiconducting CNTs.

[0020] For ultrasonic treatment, the ultrasonic output should be 70W. The treatment time should be between 20 and 40 minutes, preferably 30 minutes.

[0021] In centrifugal separation, the gravitational acceleration should be within the range of 5000G to 12000G, preferably 10000G. The separation time should be 45 minutes to 75 minutes, preferably 60 minutes. The temperature should be 25°C.

[0022] The concentration of CNTs is preferably 22.5 wt% to 26.5 wt%, and more preferably 25.3 wt%. The concentration of polyfluorene is preferably 35.3 wt% to 45.0 wt%, and more preferably 38.0 wt%.

[0023] In the film formation process S02, as shown in Figure 4, a solution containing a CNT-solubilizer composite is dropped onto a substrate, and a CNT film is formed by spin coating.

[0024] Here, spin coating is a film formation method consisting of a coating liquid discharge step, a rotational processing step, and a drying / curing step. First, in the dispensing process, the object to be coated is fixed on the spin coater stage, and the coating liquid is dripped near the center. Next, in the rotation process, the stage is rotated, and the coating liquid is removed by centrifugal force. As the coating liquid is removed by centrifugal force, its viscosity increases, and the coating liquid stops moving. Finally, in the drying / curing process, a hot air drying oven or ultraviolet curing device is used to remove the solvent or cure it with ultraviolet light, thereby creating a thin film. Thus, spin coating is superior to other film deposition methods in terms of deposition cost and deposition rate.

[0025] In this embodiment, the rotation speed of the spin coating in the film formation process S02 is 1500 rpm or more and 2500 rpm or less. If the rotation speed is 1500 rpm or higher, the formed film thickness is not too thick, and the CNTs do not aggregate. On the other hand, if the rotation speed is 2500 rpm or lower, a film thickness sufficient to create a continuous phase of the solution is formed, preventing the solution from evaporating before the CNTs are aligned parallel due to self-assembly. Here, it is preferable that the upper limit of the spin court's rotation speed is 2200 rpm or less. On the other hand, it is preferable that the lower limit of the spin court's rotation speed is 1800 rpm or more.

[0026] Furthermore, it is preferable that the amount of solution containing the CNT-solubilizer composite added during spin coating be within the range of 5 μL to 100 μL. By adjusting the drop volume of the solution containing the CNT-solubilizer composite to between 5 μL and 100 μL, it becomes possible to deposit CNTs more stably and efficiently by spin coating. Furthermore, the lower limit of the drop volume of the solution containing the CNT-solubilizer complex during spin coating is more preferably 10 μL or more, and even more preferably 25 μL or more. On the other hand, the upper limit of the drop volume of the solution containing the CNT-solubilizer complex during spin coating is more preferably 90 μL or less, and even more preferably 75 μL or less.

[0027] In this embodiment, the water contact angle of the film-forming surface of the substrate is within the range of 10° to 30°. In this embodiment, it is preferable that the upper limit of the water contact angle of the film-forming surface of the substrate is 20° or less. As a result, the interfacial interaction between the solvent in the CNT-solubilizer composite solution and the film deposition surface of the substrate allows the volatilization rate of the CNT-solubilizer composite solution to be optimized, enabling the CNTs to self-assemble and align in parallel.

[0028] In this embodiment, the upper limit of the water contact angle of the film-forming surface of the substrate is preferably 30° or less, and more preferably 25° or less. The lower limit of the water contact angle of the film-forming surface of the substrate is preferably 10° or more. Furthermore, it is preferable that the film-forming surface of the substrate is composed of silicon dioxide (SiO2). The substrate on which the CNT film is deposited is not particularly limited; it is sufficient that its surface has hydrophilic properties. Any substrate may be treated to be hydrophilic so that the water contact angle of the film-deposited surface is between 10° and 30°.

[0029] In this way, a CNT film in which CNTs are arranged in a fine pattern can be manufactured.

[0030] According to the method for manufacturing a CNT film of this embodiment, which has the above configuration, the method comprises a CNT-solubilizer composite preparation step S01 in which CNTs are modified with a solubilizing polymer to produce a CNT-solubilizer composite, and a film deposition step S02 in which the CNT-solubilizer composite is applied to a substrate by spin coating to form a CNT film. As such, a CNT film in which CNTs are finely arranged can be efficiently formed. Furthermore, since the water contact angle of the film-forming surface of the substrate is set to be within the range of 10° to 30°, the interfacial interaction between the solvent of the CNT-solubilizer composite solution and the film-forming surface of the substrate results in an appropriate volatilization rate of the CNT-solubilizer composite solution, enabling the CNTs to self-assemble and finely arrange themselves. Furthermore, since the rotation speed of spin coating in the film forming step S02 is set to be 1500 rpm or more and 2500 rpm or less, it is possible to obtain a film thickness sufficient for the continuous phase of the CNT-solubilizing agent composite solution to form and self-organize (microphase separation).

[0031] Also, in this embodiment, when the solubilizing polymer is polyfluorene, it is possible to selectively solubilize semiconducting CNTs.

[0032] Furthermore, in this embodiment, when the film forming surface of the substrate is made of silicon oxide, the film forming surface is surely hydrophilic, and it is possible to stably form a CNT film in which CNTs are finely arranged. Also, since silicon oxide becomes a chemically stable insulating film, it is possible to form highly reliable electronic components such as transistors.

[0033] According to the CNT film of this embodiment, it is possible to realize the alignment of CNTs on a scale that is at least one digit smaller than before, and it is possible to improve various characteristics of electronic components such as transistors.

[0034] As described above, the manufacturing method and the CNT film of the CNT film which is an embodiment of the present invention have been described. However, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention. For example, in this embodiment, a parallel alignment film has been described, but the present invention is not limited to this, and an ordered structure film having other structures such as a dot pattern may be used.

Examples

[0035] The results of the verification experiments conducted to confirm the effectiveness of the present invention will be described below.

[0036] (Example 1 of the present invention) <CNT-solubilizing agent composite production process> Six mg of single-walled carbon nanotubes (product name: Signis® SG65i, manufactured by Merck), nine mg of polyfluorene (PFO) (product name: poly(9,9-di-n-dodecylflorenyl-2,7-diyl), manufactured by Merck), and toluene (product name: reagent-grade toluene, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were homogenized by sonication. After mixing, the CNT-PFO complex was extracted from the toluene solution containing CNTs whose surfaces were modified with polyfluorene using a centrifuge (product name: CF18RS, manufactured by himac) to prepare a CNT-solubilizer complex.

[0037] <Film forming process> 30 μL of a CNT-solubilizer composite solution was dropped onto the surface of a silicon dioxide substrate (static contact angle with water: 20°), and the film was deposited using a spin coater (product name: MS-B100, manufactured by Mikasa Corporation) at a rotation speed of 2000 rpm.

[0038] (Example 2 of the present invention) A CNT film was obtained in the same manner as in Example 1 of the present invention, except that the static contact angle of water on the silicon dioxide substrate surface was set to 30° during the film formation process.

[0039] (Comparative Example 1) The CNT film was fabricated in the same manner as in Example 1 of the present invention, except that the rotation speed of the spin coater was set to 3000 rpm.

[0040] (Comparative Example 2) A CNT film was fabricated in the same manner as in Example 1 of the present invention, except that the static contact angle of water on the surface of the silicon dioxide substrate was set to 76.8°.

[0041] Next, the CNT films obtained in Examples 1-2 and Comparative Examples 1-2 were evaluated by the following method.

[0042] The CNT film prepared in Example 1 of the present invention was observed by SEM at a magnification of 100k. The results are shown in Figure 6. A CNT film was obtained having a fine structure in which CNTs are arranged in parallel and the average spacing between them is 98.5 nm.

[0043] The CNT film prepared in Example 2 of the present invention was observed by SEM at a magnification of 13.0k. The results are shown in Figure 7. A CNT film was obtained having a fine structure in which the CNTs are arranged in parallel with an average spacing of 105.2 nm, and a fine structure in which the CNTs are arranged in a dot pattern.

[0044] The CNT film prepared in Comparative Example 1 was observed by SEM at a magnification of 5.00k. The results are shown in Figure 8. A parallel arrangement structure of CNTs was not obtained.

[0045] The CNT film prepared in Comparative Example 2 was observed by SEM at a magnification of 7.00k. The results are shown in Figure 9. Although a parallel arrangement structure of CNTs was obtained, the average spacing was 1163 nm, and a CNT film with a fine structure was not obtained.

[0046] As described above, the present invention has confirmed that, according to the examples, the deposited CNTs can be arranged in a fine pattern, and that a method for manufacturing a CNT film and a CNT film in which the CNTs are arranged in a fine pattern can be provided without requiring time to fabricate the arrangement structure.

Claims

1. A method for manufacturing a CNT film in which CNTs are finely arranged, A CNT-solubilizer composite fabrication step involves creating a CNT-solubilizer composite in which CNTs are modified with a solubilizing polymer, The process includes a film formation step of applying the CNT-solubilizer composite onto a substrate by spin coating to form a CNT film, The water contact angle of the film-forming surface of the substrate is 10° or more and 30° or less. A method for manufacturing a CNT film, characterized in that the rotation speed of the spin coating in the aforementioned film formation step is 1500 rpm or more and 2500 rpm or less.

2. The method for producing a CNT film according to claim 1, characterized in that the solubilizing polymer is polyfluorene.

3. The method for producing a CNT film according to claim 1, characterized in that the film-forming surface of the substrate is composed of silicon dioxide.

4. A CNT film characterized by having CNTs arranged in parallel at an average interval of 10 nm to 1000 nm.

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