JP2013232683A - Sheet-like structure, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet-like structure using a linear structure of a carbon element, and extremely high in thermal conductivity and electric conductivity.SOLUTION: A sheet-like structure comprises: a plurality of linear structures 16 formed of a carbon element, and comprising a linear structure group 16a and a linear structure group 16b formed adjacently to the linear structure group 16a and having a length different from a length of the linear structure group 16a; and a filling layer 20 formed among the plurality of linear structures 16.

Description

  The present invention relates to a method for producing a sheet-like structure having a linear structure of carbon elements.

  Electronic components used in CPUs (Central Processing Units) of servers and personal computers are required to efficiently dissipate heat generated from semiconductor elements. For this reason, it has a structure in which a heat spreader made of a material having a high thermal conductivity such as copper is arranged through a heat conductive sheet such as an indium sheet provided immediately above the semiconductor element.

  However, the price of indium has soared due to a significant increase in demand for rare metals in recent years, and an alternative material that is cheaper than indium is expected. Moreover, in terms of physical properties, the thermal conductivity (80 W / m · K) of indium is not high, and a material having higher thermal conductivity in order to dissipate the heat generated from the semiconductor element more efficiently. Is desired.

  From such a background, as a material having a higher thermal conductivity than indium, a linear structure made of a carbon element typified by a carbon nanotube has attracted attention. Carbon nanotubes not only have a very high thermal conductivity (1500 W / m · K to 3000 W / m · K), but also are excellent in flexibility and heat resistance, and have a high potential as a heat dissipation material. Yes.

  As a heat conductive sheet using carbon nanotubes, a heat conductive sheet in which carbon nanotubes are dispersed in a resin, or a heat conductive sheet in which a bundle of carbon nanotubes oriented and grown on a substrate is embedded with a resin or the like has been proposed.

JP 2006-186115 A JP 2008-169267 A

  However, the conventional thermal conductive sheet using carbon nanotubes cannot fully utilize the high thermal conductivity of carbon nanotubes.

  An object of the present invention is to provide a sheet-like structure having a very high thermal conductivity and electrical conductivity using a linear structure of carbon element, a method for producing the same, and a high-performance electron using such a sheet-like structure. To provide equipment.

  According to one aspect of the embodiment, the first linear structure group is formed of a carbon element, is provided adjacent to the first linear structure group, and the first linear structure group. A sheet-like structure having a plurality of linear structures including a second group of linear structures having different lengths and a filling layer formed between the plurality of linear structures is provided. .

  According to another aspect of the embodiment, a graphite layer, a plurality of linear structures of carbon elements formed on the graphite layer, and a packed layer formed between the plurality of linear structures, A sheet-like structure is provided.

  Further, according to still another aspect of the embodiment, the heating element, the radiator, and the first linear structure group, which is disposed between the heating element and the radiator, is formed of a carbon element, A plurality of linear structures including a second linear structure group provided adjacent to the first linear structure group and having a length different from that of the first linear structure group; There is provided an electronic apparatus having a sheet-like structure having a filling layer formed between the plurality of linear structures.

  According to still another aspect of the embodiment, a step of forming a catalytic metal film on a substrate, and a first linear shape formed of carbon element on the substrate using the catalytic metal film as a catalyst. Forming a plurality of linear structures including a structure group and a second linear structure group having a length different from that of the first linear structure group; and the plurality of linear structures. In the meantime, there is provided a method for producing a sheet-like structure including a step of forming a filling layer that supports the plurality of linear structures.

  According to the disclosed sheet-like structure and the manufacturing method thereof, in the sheet-like structure having a plurality of linear structures of carbon elements and a filling layer formed between the plurality of linear structures, the first line Since the concavo-convex shape is formed by the end portions of the linear structure group and the second linear structure group, adhesion to the adherend can be improved. Thereby, the contact thermal resistance and contact resistance with respect to a to-be-adhered body can be reduced significantly, and the heat conductivity and electroconductivity through a sheet-like structure can be improved significantly.

FIG. 1 is a schematic cross-sectional view and perspective view showing the structure of the carbon nanotube sheet according to the first embodiment. FIG. 2 is a process cross-sectional view (part 1) illustrating the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 3 is a process cross-sectional view (part 2) illustrating the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 4 is a process cross-sectional view (part 3) illustrating the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 5 is a perspective view (No. 1) showing the method of manufacturing the carbon nanotube sheet according to the first embodiment. FIG. 6 is a perspective view (No. 2) showing the carbon nanotube sheet manufacturing method according to the first embodiment. FIG. 7 is a graph showing the relationship between the thickness of the catalytic metal film and the length of the carbon nanotube. FIG. 8 is a perspective view (No. 1) showing a structure of a carbon nanotube sheet according to a modification of the first embodiment. FIG. 9 is a perspective view (No. 2) showing the structure of the carbon nanotube sheet according to the modification of the first embodiment. FIG. 10 is a perspective view showing an example of the structure of the coating formed on the end of the carbon nanotube. FIG. 11 is a process cross-sectional view illustrating the method for manufacturing the electronic device using the carbon nanotube sheet according to the first embodiment. FIG. 11 is a process cross-sectional view illustrating a method for manufacturing an electronic device using the carbon nanotube sheet of the reference example. FIG. 13 is a schematic cross-sectional view showing the structure of the carbon nanotube sheet according to the second embodiment. FIG. 14 is a schematic cross-sectional view showing the structure of a carbon nanotube sheet according to a modification of the second embodiment. FIG. 15 is a process cross-sectional view (part 1) illustrating the method of manufacturing the carbon nanotube sheet according to the second embodiment. FIG. 16 is a process cross-sectional view (part 2) illustrating the method of manufacturing the carbon nanotube sheet according to the second embodiment. FIG. 17 is a process cross-sectional view (part 3) illustrating the method of manufacturing the carbon nanotube sheet according to the second embodiment. FIG. 18 is a graph showing the relationship between the thickness of the catalytic metal film and the thickness of the graphite layer.

[First Embodiment]
The carbon nanotube sheet and the manufacturing method thereof according to the first embodiment will be described with reference to FIGS.

  FIG. 1 is a schematic cross-sectional view and perspective view showing the structure of the carbon nanotube sheet according to the present embodiment. 2 to 4 are process cross-sectional views illustrating the method of manufacturing the carbon nanotube sheet according to the present embodiment. 5 and 6 are perspective views illustrating the method of manufacturing the carbon nanotube sheet according to the present embodiment. FIG. 7 is a graph showing the relationship between the thickness of the catalytic metal film and the length of the carbon nanotube. 8 and 9 are perspective views showing the structure of a carbon nanotube sheet according to a modification of the present embodiment. FIG. 10 is a perspective view showing an example of the structure of the coating formed on the end of the carbon nanotube. FIG. 11 is a process cross-sectional view illustrating the method for manufacturing the electronic apparatus using the carbon nanotube sheet according to the present embodiment.

  First, the structure of the carbon nanotube sheet according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the carbon nanotube sheet 10 according to the present embodiment has a plurality of carbon nanotubes 16 arranged at intervals. A filling layer 20 is formed in the gap between the carbon nanotubes 16, and the carbon nanotubes 16 are supported by the filling layer 20. The carbon nanotube sheet 10 according to the present embodiment forms a sheet-like structure, and the plurality of carbon nanotubes 16 are oriented in the sheet thickness direction, that is, the direction intersecting the sheet surface.

  The plurality of carbon nanotubes 16 include a group formed by a plurality of carbon nanotubes 16a and a group formed by a plurality of carbon nanotubes 16b. The carbon nanotube 16a is longer than the carbon nanotube 16b. The sheet is provided with a region where a plurality of carbon nanotubes 16a are formed and a region where a plurality of carbon nanotubes 16b are formed adjacent to this region. On one surface side (lower side in the drawing) of the sheet, the heights of the carbon nanotubes 16a and the carbon nanotubes 16b are substantially uniform. On the other hand, irregularities corresponding to the difference in length between the carbon nanotubes 16a and 16b are formed on the other surface side (the upper side in the drawing) of the sheet. That is, a surface having an uneven shape is formed by the end portion on the other surface side of the carbon nanotubes 16a and 16b. Each region in which the plurality of carbon nanotubes 16a are formed has a circular shape as shown in FIG. 1B, for example.

  A film 18 is formed on the ends of the carbon nanotubes 16a and 16b on the side where the irregularities are formed. The coating 18 is formed of a material having a higher thermal conductivity than the constituent material of the filling layer 20. The material for forming the film 18 is not particularly limited as long as the material has a higher thermal conductivity than the constituent material of the filling layer 20. When the carbon nanotube sheet 10 is also used for electric conduction, a conductive material such as a metal or an alloy can be applied.

  By providing the coating 18 having high thermal conductivity, the contact area of the carbon nanotube sheet 10 with respect to the adherend (heat radiating body, heating element) can be increased as compared with the case where the coating 18 is not provided. Thereby, the contact thermal resistance between the carbon nanotube 16 and the adherend is reduced, and the thermal conductivity of the carbon nanotube sheet 10 can be increased. When the carbon nanotube sheet 10 is also used as a conductive sheet, the conductivity can be increased. Further, by providing the coating 18, it is possible to ensure thermal conductivity and conductivity in a direction parallel to the surface of the sheet.

  Note that the coating 18 is not necessarily formed. Further, the coating 18 may be provided at both ends of the carbon nanotubes 16a and 16b.

  The constituent material of the filling layer 20 is not particularly limited as long as it shows liquid properties when the carbon nanotubes 16 are embedded and can be cured thereafter. Moreover, you may disperse and mix an additive with the filled layer 20 as needed. As the additive, for example, a substance having high thermal conductivity or a substance having high conductivity can be considered. Thereby, the heat dissipation of a sheet | seat and electroconductivity can further be improved.

  Next, the method for manufacturing the carbon nanotube sheet according to the present embodiment will be explained with reference to FIGS.

  First, the substrate 12 used as a base for forming the carbon nanotube sheet 10 is prepared. As the substrate 12, a semiconductor substrate such as a silicon substrate, an insulator substrate such as an alumina (sapphire) substrate, an MgO substrate, or a glass substrate, or a metal substrate such as stainless steel or aluminum can be used. In addition, a thin film may be formed on these substrates. For example, a silicon substrate having a silicon oxide film with a thickness of about 300 nm can be used. Here, a silicon substrate having a silicon oxide film formed on the surface is used as the substrate 12.

  The substrate 12 is peeled off after the carbon nanotubes 16 are formed. For this purpose, it is desirable that at least the surface in contact with the carbon nanotube 16 is formed of a material that can be easily peeled off from the carbon nanotube 16 as the substrate 12. Alternatively, it is desirable that the carbon nanotube sheet 10 be formed of a material that can be selectively etched.

  Next, an Fe catalytic metal film 14 is formed on the substrate 12 by sputtering, for example. The catalytic metal film 14 is a catalyst for forming the carbon nanotubes 16, and has different film thicknesses in a region where the carbon nanotubes 16a are formed and a region where the carbon nanotubes 16b are formed. A catalytic metal film 14a is formed in a region where the carbon nanotubes 16a are formed, and a catalytic metal film 14b is formed in a region where the carbon nanotubes 16b are formed (FIGS. 2A and 5A).

  In the example of FIG. 5A, an Fe catalytic metal film 14a having a thickness of, for example, 1 nm is formed in a plurality of circular regions on the substrate 12, and an Fe catalytic metal having a thickness of, for example, 5 nm is formed in another region. A film 14b is formed. A method of setting the film thickness of the catalytic metal films 14a and 14b will be described later.

  The method for forming the catalytic metal film 14 having different thicknesses is not particularly limited. For example, using a photoresist film or a metal mask, an Fe film with a thickness of 1 nm is deposited on the formation region of the catalyst metal film 14a, and an Fe film with a thickness of 5 nm is deposited on the formation region of the catalyst metal film 14b. Alternatively, after a 1 nm thick Fe film is deposited on the entire surface, a formation region of the catalytic metal film 14b in which a 1 nm thick Fe film is formed using a photoresist film or a metal mask covering the formation region of the catalytic metal film 14a as a mask. A 4 nm thick Fe film is selectively deposited thereon.

  The catalyst metal is a catalyst for carbon nanotubes such as Fe (Co), Co (cobalt), Ni (nickel), Au (gold), Ag (silver), Pt (platinum), or an alloy containing at least one of these materials. The material can be selected as appropriate. In addition to the metal film, metal fine particles prepared by controlling the size in advance using a differential mobility analyzer (DMA) or the like may be used as the catalyst. In this case, the metal species may be the same as in the case of the thin film.

In addition, as a base film for these catalytic metals, Mo (molybdenum), Ti (titanium), Hf (hafnium), Zr (zirconium), Nb (niobium), V (vanadium), TaN (tantalum nitride), TiSi _x (titanium) Silicide), Al (aluminum), AlO _x (aluminum oxide), TiO _x (titanium oxide), Ta (tantalum), W (tungsten), Cu (copper), Au (gold), Pt (platinum), Pd (palladium) ), A film such as TiN (titanium nitride), or a film made of an alloy including at least one of these materials may be formed.

  The method for depositing the catalytic metal film is not particularly limited. In addition to the sputtering method, an electron beam evaporation (EB) method, a molecular beam epitaxy (MBE) method, or the like may be used.

  The pattern of the region where the catalyst metal film 14a and the catalyst metal film 14b are formed is not limited to the pattern shown in FIG. 5A, and can be selected as appropriate. For example, a checkered pattern as shown in FIG. 8A or a stripe pattern as shown in FIG. 9A may be used.

Next, carbon nanotubes are grown on the substrate 12 by, for example, hot filament CVD using the catalytic metal film 14 as a catalyst. The growth conditions of the carbon nanotube are, for example, a mixed gas of acetylene and argon (partial pressure ratio 1: 9) as a source gas, a substrate temperature of 620 ° C., a total gas pressure in the film formation chamber of 1 kPa, and a hot filament temperature of 1000 ° C. And Thereby, it is possible to grow multi-walled carbon nanotubes having 3 to 6 layers (average of about 4 layers) and diameters of 4 to 8 nm (average of 6 nm). The surface density of the carbon nanotubes 16 formed under the above growth conditions is about 1 × 10 ¹¹ pieces / cm ² .

  At this time, the growth rate of the carbon nanotubes 16 can be changed depending on the thickness of the catalytic metal film 14. For example, when growth is performed for 60 minutes under the above growth conditions, carbon nanotubes having a length of about 250 μm are grown on the catalytic metal film 14a, and carbon nanotubes having a length of about 150 μm are grown on the catalytic metal film 14b. Can grow.

  FIG. 7 is a graph showing an example of the relationship between the thickness of the catalytic metal film and the length of the carbon nanotube. The graph shown in FIG. 7 is obtained by a thermal CVD method using an acetylene / argon mixed gas as a source gas, a growth temperature of 650 ° C., a flow rate of 300 sccm, a total pressure of 1 kPa, a growth time of 60 minutes, and Fe as a catalyst. The measurement result at the time of growing a nanotube is shown.

  As shown in FIG. 7, the growth rate of the carbon nanotubes can be controlled by the thickness of the catalyst metal. Therefore, by forming the catalytic metal film 14 having a different thickness depending on the region on the substrate 12, the carbon nanotubes 12 having different lengths can be grown simultaneously.

  The film thickness of the catalytic metal film 14 is desirably selected as appropriate according to the type of catalytic metal, the length of the carbon nanotube to be formed, the growth conditions of the carbon nanotube, and the like.

  The carbon nanotubes 16 may be formed by other film forming methods such as a thermal CVD method and a remote plasma CVD method. The growing carbon nanotube may be a single-walled carbon nanotube. Moreover, as a carbon raw material, you may use hydrocarbons, such as methane and ethylene other than acetylene, alcohols, such as ethanol and methanol.

  In this manner, a plurality of carbon nanotubes 16 that are aligned (vertically aligned) in the normal direction of the substrate 12 and that include a plurality of carbon nanotubes 16a having a length of 250 μm and a plurality of carbon nanotubes 16b having a length of 150 μm are formed on the substrate 12. It forms (FIGS. 2B and 5B).

  In some drawings of the present application, a state in which the catalytic metal film 14 is formed on the lower end portion of the carbon nanotube 16 is shown. Since the catalytic metal film 14 is aggregated and taken into the carbon nanotubes during the growth of the carbon nanotubes 16, it may not actually remain in the state shown in the figure. Further, the catalytic metal film 14 may be removed at the same time when the substrate 12 is peeled off in a subsequent process.

  When the checkered catalytic metal film 14 as shown in FIG. 8A is formed, the carbon nanotubes 16a and 16b are grown as shown in FIG. 8B, for example. When the catalytic metal film 14 is formed in a stripe pattern as shown in FIG. 9A, the carbon nanotubes 16a and 16b are grown as shown in FIG. 9B, for example.

  The growth rate of the carbon nanotubes 16 can be changed by a method other than the method of changing the film thickness of the catalytic metal film 14.

  For example, the growth rate of the carbon nanotubes 16 can be changed by a base film formed under the catalyst metal film 14. For example, an Al underlayer having a film thickness of, for example, 5 nm is selectively formed in a region on the substrate 12 where the carbon nanotubes 16a are to be formed. For example, an Fe catalyst metal film having a film thickness of 2.5 nm is formed on the entire surface of the substrate 12 on which the Al base film is formed. In the region where the Al underlayer film is formed, the growth rate of the carbon nanotubes 16 is faster than in the region where the Al underlayer film is not formed. Therefore, the carbon nanotubes 16a and 16b having different lengths can be grown simultaneously. . This is presumably because the catalytic metal film is made finer on the surface of the oxide film on aluminum, and in addition, the presence of aluminum or aluminum oxide has a co-catalytic function to activate carbon nanotube growth. .

  By the thermal CVD method, carbon nanotubes 16a, acetylene / argon mixed gas, hydrogen gas, and argon gas are used as source gases, the growth temperature is 650 ° C., each flow rate is 100 sccm each, the total pressure is 1 kPa, and the growth time is 60 minutes. In the experimental example in which 16b was grown, carbon nanotubes 16a having a length of 220 nm and carbon nanotubes 16b having a length of 120 nm could be grown at the same time.

  Alternatively, when Co is used as the catalytic metal film, for example, by separately forming TiN and TaN as the base film, a region where the TiN base film is formed and a region where the TaN base film is formed, The growth rate of carbon nanotubes can be changed.

  Alternatively, for example, by using Ti as the base film and separately forming Fe and Co as the catalytic metal film, carbon nanotubes are formed in a region where the Fe catalytic metal film is formed and a region where the Co catalytic metal film is formed. Can change the growth rate.

  In the present embodiment, two types of carbon nanotubes 16a and 16b having different lengths are formed, but three or more types of carbon nanotubes 16 having different lengths may be formed. Also in this case, the length of each carbon nanotube 16 can be controlled by the thickness of the catalytic metal film 14 and the like.

  Next, if necessary, a 10 nm thick titanium (Ti) film and a 300 nm thick gold (Au) film, for example, are deposited on the carbon nanotubes 16 by sputtering, for example. As a result, a film 18 having a laminated structure of Au / Ti is formed on the carbon nanotubes 16.

  The constituent material of the film 18 is not particularly limited as long as it has a higher thermal conductivity than the constituent material of the filling layer 20 to be formed later. When the carbon nanotube sheet 10 is used for electric conduction, a conductive material such as a metal or an alloy can be applied. As a constituent material of the coating 18, for example, copper (Cu), nickel (Ni), gold (Au), indium (In), tin (Sn), gold tin (AuSn), low melting point solder, gold plating, nickel plating Etc. can be used. The coating 14a may have a single layer structure of these metals, or may have a laminated structure of two layers or three or more layers such as a laminated structure of titanium and gold as described above.

  The reason why the Au / Ti laminated structure is used in the above example is that titanium has excellent adhesion to the carbon nanotubes 16. By forming a titanium film between the gold film and the carbon nanotube 16, the contact thermal resistance and the contact resistance between the carbon nanotube 16 and the coating film 18 can be reduced. From the viewpoint of improving adhesion, it is desirable to form a titanium film of about 10 nm or more.

  In the initial stage of growth, the coating 18 is formed so as to cover the tip portions of the carbon nanotubes 16 as shown in FIG. As the growth film thickness increases, the coatings 18 formed on the tip portions of the adjacent carbon nanotubes 16 are connected to each other. Thereby, the coating film 18 is formed so as to bundle the tip portions of the plurality of carbon nanotubes 16 as shown in FIG. 10B, for example. When the growth film thickness of the coating film 18 is further increased, the coating film 18 is completely connected in a two-dimensional direction parallel to the surface of the sheet, and a complete film without gaps is obtained. In order to maintain the permeability of the filling material that forms the filling layer 20 in a later step, it is desirable to control the film thickness so that the coating 18 does not become a complete film.

  Next, a thermoplastic resin (thermoplastic resin film 22) processed into a film shape is placed on the carbon nanotubes 16 on which the coating film 18 is formed (FIGS. 3B and 6A). The film thickness of the thermoplastic resin film 22 is about the thickness of the carbon nanotube sheet 10 to be formed, for example, about 4 to 400 μm. At this time, the carbon nanotubes 16 on which the coating film 18 has been formed in advance may be peeled off from the substrate 12 and placed in an inverted state, and the thermoplastic resin film 22 may be placed on the root portion of the carbon nanotubes 16.

  As a thermoplastic resin of the thermoplastic resin film 22, for example, the following hot melt resin can be applied. Examples of the polyamide-based hot melt resin include “Micromelt 6239” manufactured by Henkel Japan Co., Ltd. Examples of the polyester hot melt resin include “DH598B” manufactured by Nogawa Chemical Co., Ltd. Examples of the polyurethane hot melt resin include “DH722B” manufactured by Nogawa Chemical Co., Ltd. Examples of the polyolefin-based hot melt resin include “EP-90” manufactured by Matsumura Oil Co., Ltd. Examples of the ethylene copolymer hot melt resin include “DA574B” manufactured by Nogawa Chemical Co., Ltd. Examples of the SBR hot melt resin include “M-6250” manufactured by Yokohama Rubber Co., Ltd. Examples of the EVA hot melt resin include “3747” manufactured by Sumitomo 3M Limited. Examples of the butyl rubber hot melt resin include “M-6158” manufactured by Yokohama Rubber Co., Ltd.

  Here, as an example, a case where a thermosetting resin film obtained by processing “Micromelt 6239” manufactured by Henkel Japan Co., Ltd. into a film having a thickness of 200 μm will be described. “Micromelt 6239” has a melting temperature of 135 ° C. to 145 ° C. and a viscosity at the time of melting of 5.5 Pa.s. s to 8.5 Pa. s (225 ° C.) hot melt resin.

  Next, the substrate 12 on which the thermoplastic resin film 22 is placed is heated at a temperature of 195 ° C., for example. As a result, the thermoplastic resin of the thermoplastic resin film 22 is dissolved and gradually penetrates into the gaps between the carbon nanotubes 16.

  Next, the melted thermoplastic resin film is solidified to form a filling layer 20 of the thermoplastic resin (FIG. 4A).

  By processing the thermoplastic resin into a sheet in advance, the amount of filler can be controlled by the thickness of the sheet. The thickness of the thermoplastic resin film that penetrates into the gaps between the carbon nanotubes 16 can be controlled by the heat treatment time.

  The heating temperature and time of the thermoplastic resin film 22 are such that the length of the carbon nanotubes 16, the viscosity when the thermoplastic resin is melted, and the film of the thermoplastic resin film 22 so that the thermoplastic resin film 22 penetrates to a desired position. It is desirable to set appropriately according to the thickness or the like.

  In particular, it is desirable to infiltrate the thermoplastic resin film 22 so that the substrate 12 and the filling layer 20 do not contact when the filling layer 20 is solidified. By preventing the substrate 12 and the filling layer 20 from contacting each other, the substrate 12 can be easily peeled off in a subsequent process.

  The shape of the thermoplastic resin is preferably processed in advance into a film shape, but may be a pellet shape or a rod shape.

  The method for forming the filling layer 20 is not particularly limited. In addition to the above-described forming method, the gap between the carbon nanotubes 16 may be filled with a filler that becomes the filling layer 20 by, for example, a dipping method, a spin coating method, or the like. For example, the substrate 12 on which the carbon nanotubes 16 are formed is pressed against, for example, a substrate on which a silicone-based resin having a viscosity of 800 mPa · s is spin-coated, for example, at 1000 rpm for 20 seconds. Thereby, the silicone-based resin as the filler can be filled between the carbon nanotubes 16 to almost the same height as the carbon nanotubes 16 by a capillary phenomenon.

  The filler is not particularly limited as long as it exhibits liquid properties at room temperature or by heating and can be cured thereafter. For example, a thermoplastic resin such as a hot melt resin, an acrylic resin, an epoxy resin, a silicone resin, a polyimide resin, or a polyamide resin can be used as the organic filler. Further, as the inorganic filler, a coating type insulating film forming composition such as SOG can be applied. A metal material such as indium, solder, or a metal paste (eg, silver paste) can also be used. In addition, conductive polymers such as polyaniline and polythiophene can also be applied.

  Further, a conductive material such as carbon nanotubes may be dispersed in the filler. By dispersing and mixing an additive having high thermal conductivity in the filled layer 20 portion, the thermal conductivity of the filled layer 20 portion can be improved, and the thermal conductivity of the entire carbon nanotube sheet can be improved. When the carbon nanotube sheet 20 is used as a conductive sheet, the conductivity of the filling layer 20 portion can be improved by dispersing and mixing an additive having high conductivity in the filling layer 18 portion. The electrical conductivity of the entire sheet can be improved. This is particularly effective when an insulating material having low thermal conductivity such as an organic filler is used as the filling layer 20. As the material having high thermal conductivity, carbon nanotube, metal material, aluminum nitride, silica, alumina, graphite, fullerene, or the like can be used. As the highly conductive material, carbon nanotubes, metal materials, and the like can be applied.

  Next, the filler filled between the carbon nanotubes 16 is cured or semi-cured to form the filling layer 20. For example, when a thermoplastic resin such as a hot melt resin is used as the filler, the filler can be cured by returning to room temperature. Moreover, when using photocuring materials, such as an acrylic resin, as a filler, a filler can be hardened by light irradiation. In addition, when a thermosetting material such as an epoxy resin or a silicone resin is used as the filler, the filler can be cured by heat treatment. In the case of an epoxy resin, it can be cured by heat treatment at 150 ° C. for 1 hour, for example. In the case of a silicone resin, it can be cured by heat treatment at 200 ° C. for 1 hour, for example. When a thermosetting or ultraviolet curable material is used, it may be in a semi-cured state in this step and cured at the time of mounting.

  In addition, after the filling layer 20 is cured, when the upper end portion of the carbon nanotube 16 covered with the coating 18 is not sufficiently exposed or covered with the filling layer 20, chemical mechanical polishing or oxygen plasma ashing is performed. Thus, the filling layer 20 on the end of the carbon nanotube 16 may be removed. As the oxygen plasma ashing, for example, a process of power 200 W and 10 minutes can be applied.

  Next, after the filling layer 20 is cured in this manner, the carbon nanotubes 16 and the filling layer 20 are peeled from the substrate 12. For example, in the above example, the carbon nanotubes 16 and the filling layer 20 can be separated from the substrate 12 by removing the silicon oxide film formed on the surface of the substrate 12 by hydrofluoric acid treatment or the like. The carbon nanotubes 16 and the filling layer 20 may be peeled off from the substrate 12.

  Next, if necessary, a film (not shown) is formed at the end of the carbon nanotube 16 on the side peeled off from the substrate 12 in the same manner as the film 18.

  Thus, the carbon nanotube sheet according to the present embodiment is completed (FIGS. 4B and 6B).

  Next, an electronic device manufacturing method using the carbon nanotube sheet 10 according to the present embodiment will be described with reference to FIGS. 11 and 12.

  For example, as shown in FIG. 11, the carbon nanotube sheet 10 according to the present embodiment is provided between a heat generating body 30 and a heat radiating body 32, and dissipates heat for transmitting heat generated by the heat generating body 30 to the heat radiating body 32. It can be used as a sheet (TIM). Examples of the heating element 30 include a semiconductor chip. Examples of the heat radiator 32 include a heat spreader.

  First, the carbon nanotube sheet 10 according to the present embodiment is placed on the radiator 30.

  Next, the filling layer 20 is softened by heating to a temperature equal to or higher than the melting temperature of the thermoplastic resin forming the filling layer 20. Thereby, the filling layer 20 penetrates to the surface of the radiator 30 as shown in FIG.

  Next, the heat radiating body 32 is pressed by applying a load from above. Due to this load, the carbon nanotubes 16 of the carbon nanotube sheet 10 are deformed according to the surface shapes of the heat radiating body 30 and the heat generating body 32.

  At this time, in the carbon nanotube sheet 10 according to the present embodiment, the upper end portion of the carbon nanotube 16 has irregularities, and a gap exists on the carbon nanotube 16b. Therefore, the degree of freedom of bending of the carbon nanotubes 16a increases, and the deformed carbon nanotubes 16a can fall into the gaps on the carbon nanotubes 16b without the carbon nanotubes 16 (see FIG. 11B).

  When the carbon nanotubes 16a are further pushed down to the optimum load position, the carbon nanotubes 16a further fall down, and the radiator 32 and the carbon nanotubes 16a come into contact with each other over a wider area (see FIG. 11C). In other words, one end portion of the carbon nanotube 16a is bent so as to be oriented in the surface direction of the sheet. Thereby, the state between the carbon nanotube 16 and the heat radiating body 32 is close to the surface contact, and the thermal conductivity between the heat generating body 30 and the heat radiating body 32 can be improved.

  On the other hand, in the case of the carbon nanotube sheet 10 of the reference example in which the upper and lower portions of the carbon nanotubes 16 are not formed with the irregularities, for example, as shown in FIG.

  When the radiator 32 is pressed from above with a load, the carbon nanotubes 16 of the carbon nanotube sheet 10 are deformed by the load. However, in the carbon nanotube sheet 10 having the carbon nanotubes 16 having a uniform length as shown in FIG. 12A, the carbon nanotubes 16 are bent (bent) at the tip or bent in the middle because there is no gap for the carbon nanotubes 16 to collapse. A phenomenon occurs (FIG. 12B).

  Furthermore, even if it pushes in to an optimal load position, only the bending of the carbon nanotube 16 will advance, and it will have only the contact part of an area about a point contact (FIG.12 (c)). As a result, a state close to surface contact as in the case of the carbon nanotube sheet according to the present embodiment is not formed. Moreover, since the filling layer 20 is filled without a gap, it may ooze out when a load is applied.

  When used as a TIM, the carbon nanotube sheet 10 has a thickness of about 10 μm to 300 μm, preferably about 50 μm to 200 μm. When the TIM is sufficiently adhered to the adherend, it is desirable to push in at a maximum of about 50%, that is, several μm to several hundred μm with respect to the entire thickness. Therefore, the difference in height between the carbon nanotubes 16a and 16b is about 50% of the thickness of the carbon nanotube sheet 10 in consideration of the thickness of the TIM to be used and the amount of pushing when mounting, and about 1 μm to 150 μm. Is desirable.

  However, this is not the case when used as a heat dissipation material other than the heat dissipation application directly under the CPU. In order to utilize the high heat dissipation characteristics of the carbon nanotube, the longer the heat dissipation path, the more the characteristics can be exhibited. For example, it can also be used for heat dissipation for servers, heat dissipation for in-vehicle devices, and CPU heat dissipation for personal computers and mobile phones. In these cases, the heat-dissipating sheet can be applied to a thickness of 200 μm or more and a few mm or a few cm or more, and the heat-dissipating sheet has an exception for other purposes.

  In order to bring the carbon nanotubes 16 into contact with the adherend evenly, it is desirable that the area ratio between the concave and convex portions at the upper end of the carbon nanotubes 16 is 1: 1. As the formation region of the carbon nanotubes 16a, for example, a circular pattern as shown in FIG. 1B is adopted. When the circular size is 100 μm in diameter and the pressing amount is 50 μm, the interval between the circular patterns is 100 μm. It is desirable that the degree is more than about.

  Considering the height difference (about 1 μm to 100 μm) between the carbon nanotubes 16a and 16b, it is desirable to provide a distance of about 1 μm to 100 μm in the case of the pattern shown in FIG.

  The maximum TIM shape is about 40 mm, and the period of unevenness when it is assumed to be used as a TIM is approximately 1 μm to 20 mm. Considering the case where the TIM is actually pushed in (about 50 μm), the preferable period is about 50 μm to 10 mm.

  By the carbon nanotube sheet manufacturing method according to the present embodiment described above, a carbon nanotube sheet was manufactured in which carbon nanotubes 16 having a length of 110 μm, 80 μm, and 60 μm were formed stepwise from the end with a width of 3/2 inch. The thermal resistance of the carbon nanotube sheet was about 0.20 [° C./W]. On the other hand, when a carbon nanotube sheet having carbon nanotubes 16 having a uniform length of 120 μm was manufactured, the thermal resistance was about 0.27 [° C./W]. This result suggests the significance of the step shape.

  The unevenness at the upper end of the carbon nanotube 16 has the effect of preventing mounting displacement of the carbon nanotube sheet 10 in addition to the above-described effect. If an uneven shape that fits the unevenness of the upper end portion of the carbon nanotube 16 is formed on the surface of the adherend, the surface unevenness of the carbon nanotube sheet and the surface unevenness of the adherend can be engaged with each other. Thereby, mounting | wearing deviation of the carbon nanotube sheet | seat 10 can be prevented, and adhesiveness between to-be-adhered bodies can also be improved.

  In addition, the carbon nanotube sheet 10 according to the present embodiment can be connected to an adherend through a metal such as AuSn or In, solder, plating, or metal paste as well as a connection by pressure bonding.

  As described above, according to the present embodiment, an uneven shape is provided on the surface formed by the ends of the carbon nanotubes, so that the adhesion to the adherend can be improved when the carbon nanotube sheet is mounted. Thereby, the thermal conductivity and conductivity of the carbon nanotube sheet can be improved.

[Second Embodiment]
The carbon nanotube sheet and the manufacturing method thereof according to the second embodiment will be described with reference to FIGS. Components similar to those of the carbon nanotube sheet and the manufacturing method thereof according to the first embodiment shown in FIGS. 1 to 12 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 13 is a schematic cross-sectional view showing the structure of the carbon nanotube sheet according to the present embodiment. FIG. 14 is a schematic cross-sectional view showing the structure of a carbon nanotube sheet according to a modification of the present embodiment. 15 to 17 are process cross-sectional views illustrating the method of manufacturing the carbon nanotube sheet according to the present embodiment. FIG. 18 is a graph showing the relationship between the thickness of the catalytic metal film and the thickness of the graphite layer.

  First, the structure of the carbon nanotube sheet according to the present embodiment will be explained with reference to FIG.

  As shown in FIG. 13, the carbon nanotube sheet 10 according to the present embodiment has a plurality of carbon nanotubes 16 arranged at intervals. A filling layer 20 is formed in the gap between the carbon nanotubes 16, and the carbon nanotubes 16 are supported by the filling layer 20. The carbon nanotube sheet 10 according to the present embodiment forms a sheet-like structure, and the plurality of carbon nanotubes 16 are oriented in the sheet thickness direction, that is, the direction intersecting the sheet surface.

  A graphite layer 26 is formed on one end (lower side in the drawing) of the carbon nanotube 16.

  A film 18 is formed on the other end (upper side in the drawing) of the carbon nanotube 16. The coating 18 is formed of a material having a higher thermal conductivity than the constituent material of the filling layer 20. The material for forming the coating film 18 is the same as that of the coating film 18 of the first embodiment, and is not particularly limited as long as it has a higher thermal conductivity than the constituent material of the filling layer 20.

  Thus, the carbon nanotube sheet 10 according to the present embodiment has the graphite layer 26 at one end of the carbon nanotube 16. By providing the graphite layer 26 at one end of the carbon nanotube 16, surface contact is made with the adherend, and contact resistance to the adherend can be reduced.

  When the growth conditions of the carbon nanotubes 16 described in the present embodiment are used, the density (space occupancy) of the carbon nanotubes 16 is about 10 to 20%. Therefore, from the viewpoint of thermal diffusion at one end of the carbon nanotube 16, it can be seen that the thermal diffusibility can be improved by 5 times or more by providing the graphite layer 26.

  The graphite layer 26 is also excellent in thermal conductivity and conductivity in the sheet surface direction, and is useful for diffusing heat from the heating element in the sheet surface direction. Further, providing the graphite layer 26 has an advantage in the manufacturing process. This will be described later.

  The carbon nanotubes formed on the graphite layer 26 are not only the carbon nanotubes 16 having a uniform length as shown in FIG. 13, but also a plurality of types of carbon nanotubes 16a having different lengths as shown in the first embodiment. 16b may be used (see FIG. 14).

  Next, the method for manufacturing the carbon nanotube sheet according to the present embodiment will be explained with reference to FIGS.

  First, the substrate 12 used as a base for forming the carbon nanotube sheet 10 is prepared. As the substrate 12, various substrates as described in the first embodiment can be applied. Here, a silicon substrate having a silicon oxide film formed on the surface is used as the substrate 12.

  Next, an Fe film of, eg, a 30 nm-thickness is formed on the substrate 12 by, eg, sputtering, to form an Fe catalytic metal film 24 (FIG. 15A). The catalytic metal film 24 is a catalyst for forming the graphite layer 26, and has a film thickness necessary for forming graphite.

  The catalyst metal film 24 can be made of the same material as the catalyst metal film 14 of the first embodiment.

  Next, graphite is grown on the substrate 12 by, for example, hot filament CVD using the catalytic metal film 24 as a catalyst. As for the growth conditions of graphite, for example, a mixed gas of acetylene and argon (partial pressure ratio 1: 9) is used as a raw material gas, the substrate temperature is 620 ° C., the total gas pressure in the film forming chamber is 1 kPa, and the hot filament temperature is 1000 ° C. To do. As a result, a graphite layer 26 having a thickness of about 50 to 60 nm is formed on the catalytic metal film 22 (FIG. 15B).

  FIG. 18 is a graph showing the relationship between the thickness of the catalytic metal film and the thickness of the graphite layer.

  As shown in FIG. 18, the thickness of the graphite layer to be grown varies depending on the thickness of the catalytic metal film. The thickness of the catalytic metal film is desirably set as appropriate according to the type of catalyst, the thickness of the graphite layer to be grown, and the like.

  Next, the Fe catalytic metal film 14 is formed on the graphite layer 26 by sputtering, for example (FIG. 15C). The catalytic metal film 14 is a catalyst for forming the carbon nanotubes 16 and has a film thickness necessary for forming the carbon nanotubes. Here, for example, a catalytic metal film 14 of Fe having a thickness of 5 nm is formed.

  In addition, the catalyst metal film 14 of this embodiment can use the same material as the catalyst metal film 14 of 1st Embodiment. In this embodiment, the case where the catalyst metal film 14 having a uniform thickness is formed on the graphite layer 26 is shown. However, as in the first embodiment, the catalyst metal film 14 having a different thickness depending on the region is formed. You may make it (refer FIG. 14).

Next, carbon nanotubes are grown on the graphite layer 26 by, for example, hot filament CVD using the catalytic metal film 14 as a catalyst. The growth conditions of the carbon nanotube are, for example, a mixed gas of acetylene and argon (partial pressure ratio 1: 9) as a source gas, a substrate temperature of 620 ° C., a total gas pressure in the film formation chamber of 1 kPa, and a hot filament temperature of 1000 ° C. And Thereby, it is possible to grow multi-walled carbon nanotubes having 3 to 6 layers (average of about 4 layers) and diameters of 4 to 8 nm (average of 6 nm). The surface density of the carbon nanotubes 16 formed under the above growth conditions is about 1 × 10 ¹¹ pieces / cm ² .

  The length of the carbon nanotube can be arbitrarily set depending on the growth conditions and growth time. When the growth is performed for 60 minutes under the above growth conditions, carbon nanotubes having a length of about 150 μm can be grown on the catalytic metal film 14.

  Thus, a plurality of carbon nanotubes 16 having a length of about 150 μm are formed on the graphite layer 26 in the normal direction of the substrate 12 (vertical alignment) (FIG. 16A).

  Next, a titanium (Ti) film having a thickness of, for example, 10 nm and a gold (Au) film having a thickness of, for example, 300 nm are deposited on the carbon nanotube 16 by, for example, sputtering. As a result, a film 18 having a laminated structure of Au / Ti is formed on the carbon nanotubes 16 (FIG. 16B). A material similar to that of the film 18 of the first embodiment can be used for the film 18 of the present embodiment.

  Next, the filling layer 20 is formed in the gap between the carbon nanotubes 16 in the same manner as in the first embodiment (FIG. 17A). For the filling layer 20 of the present embodiment, the same filler as that of the filling layer 20 of the first embodiment can be used.

  In the present embodiment, since the graphite layer 26 is formed on the base of the carbon nanotube 16, even if the filling layer 20 is filled to the lower end portion of the carbon nanotube 16, it does not become an obstacle to peeling off the substrate 12.

  Next, in the same manner as in the first embodiment, the carbon nanotubes 16 and the filling layer 20 are peeled from the substrate 12 to complete the carbon nanotube sheet according to the present embodiment (FIG. 17B).

  As described above, according to the present embodiment, the graphite layer is provided at one end of the carbon nanotube, so that the adhesion to the adherend can be improved when the carbon nanotube sheet is mounted. Thereby, the thermal conductivity and conductivity of the carbon nanotube sheet can be improved.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications are possible.

  For example, in the first and second embodiments, the sheet-like structure (carbon nanotube sheet) using carbon nanotubes is shown, but a linear structure of another carbon element may be used instead of the carbon nanotube. . Examples of the carbon element linear structure include carbon nanowires, carbon rods, and carbon fibers in addition to carbon nanotubes. These linear structures are the same as the carbon nanotubes except that their sizes are different. The present invention can also be applied to a heat dissipation material using these linear structures.

  In addition, the constituent materials and manufacturing conditions described in the above embodiment are not limited to the descriptions, and can be appropriately changed according to the purpose and the like.

  Further, the purpose of using the carbon nanotube sheet is not limited to that described in the above embodiment. The disclosed carbon nanotube sheet is, for example, a CPU heat dissipation sheet, a radio communication base station high output amplifier, a radio communication terminal high output amplifier, an electric vehicle high output switch, a server, a personal computer, etc. Can be applied. Moreover, it is applicable to a vertical wiring sheet and various applications using the high allowable current density characteristic of carbon nanotubes.

  Regarding the above embodiment, the following additional notes are disclosed.

(Additional remark 1) It is formed with a carbon element, is provided adjacent to the first linear structure group and the first linear structure group, and the first linear structure group has a length. A plurality of linear structures including different second linear structures;
A sheet-like structure comprising: a filling layer formed between the plurality of linear structures.

(Supplementary note 2) In the sheet-like structure according to supplementary note 1,
A sheet-like structure characterized by further comprising a coating of a material formed at at least one end of the plurality of linear structures and having a higher thermal conductivity than the filling layer.

(Additional remark 3) In the sheet-like structure of Additional remark 1 or 2,
The uneven structure has a period of 50 μm to 10 mm.

(Appendix 4) In the sheet-like structure according to any one of appendices 1 to 3,
The uneven structure has a step of 1 μm to 150 μm.

(Supplementary note 5) In the sheet-like structure according to any one of supplementary notes 1 to 4,
The plurality of linear structures are oriented in the film thickness direction of the filling layer.

(Appendix 6) In the sheet-like structure according to any one of appendices 1 to 5,
At least one end of each of the plurality of linear structures is exposed from the filling layer.

(Supplementary note 7) In the sheet-like structure according to any one of supplementary notes 1 to 6,
The filling layer is formed of a thermoplastic resin material.

(Appendix 8) In the sheet-like structure according to any one of appendices 1 to 7,
A sheet-like structure further comprising a graphite layer provided at the other end of the plurality of structures.

(Supplementary note 9) Graphite layer,
A plurality of linear structures of carbon elements formed on the graphite layer;
A sheet-like structure comprising: a filling layer formed between the plurality of linear structures.

(Appendix 10) A heating element,
A radiator,
The first line structure group, the first line structure group, and the first line structure group disposed between the heat generating body and the heat dissipating body, formed of a carbon element, and adjacent to the first line structure group. A sheet-like structure having a plurality of linear structures including a second linear structure group having a different length from the linear structure group, and a filling layer formed between the plurality of linear structures And an electronic device.

(Additional remark 11) In the electronic device of Additional remark 10,
The first linear structure group is longer than the second linear structure group, and is bent at one end so as to be oriented in the surface direction of the sheet-like structure. Electronics.

(Supplementary Note 12) A step of forming a catalytic metal film on a substrate;
Using the catalytic metal film as a catalyst, the first linear structure group is formed on the substrate with a carbon element, and the first linear structure group has a different length from the first linear structure group. Forming a plurality of linear structures including a body group;
Forming a filling layer that supports the plurality of linear structures between the plurality of linear structures. A method for producing a sheet-like structure, comprising:

(Additional remark 13) In the manufacturing method of the sheet-like structure of Additional remark 12,
In the step of forming the plurality of linear structures, the first linear structure group and the second line are utilized by utilizing a difference in the growth rate of the linear structures due to a difference in the catalytic metal film. A method for producing a sheet-like structure, comprising growing a group of sheet-like structures simultaneously.

(Additional remark 14) In the manufacturing method of the sheet-like structure of Additional remark 12 or 13,
Prior to the step of forming the catalytic metal film, the method further includes the step of forming a graphite layer on the substrate.

DESCRIPTION OF SYMBOLS 10 ... Carbon nanotube sheet 12 ... Substrate 14, 24 ... Catalytic metal film 16, 16a, 16b ... Carbon nanotube 18 ... Coating 20 ... Filling layer 22 ... Thermoplastic resin film 26 ... Graphite layer

Claims (8)

A second linear structure group formed of carbon element and provided adjacent to the first linear structure group and having a length different from that of the first linear structure group. A plurality of linear structures including a linear structure group;
A sheet-like structure comprising: a filling layer formed between the plurality of linear structures. In the sheet-like structure according to claim 1,
A sheet-like structure characterized by further comprising a coating of a material formed at at least one end of the plurality of linear structures and having a higher thermal conductivity than the filling layer. In the sheet-like structure according to claim 1 or 2,
A sheet-like structure characterized by further comprising a coating of a material formed at at least one end of the plurality of linear structures and having a higher thermal conductivity than the filling layer. In the sheet-like structure according to any one of claims 1 to 3,
A sheet-like structure further comprising a graphite layer provided at the other end of the plurality of structures. A graphite layer;
A plurality of linear structures of carbon elements formed on the graphite layer;
A sheet-like structure comprising: a filling layer formed between the plurality of linear structures. A heating element;
A radiator,
The first line structure group, the first line structure group, and the first line structure group disposed between the heat generating body and the heat dissipating body, formed of a carbon element, and adjacent to the first line structure group. A sheet-like structure having a plurality of linear structures including a second linear structure group having a different length from the linear structure group, and a filling layer formed between the plurality of linear structures And an electronic device. The electronic apparatus according to claim 6.
The first linear structure group is longer than the second linear structure group, and is bent at one end so as to be oriented in the surface direction of the sheet-like structure. Electronics. Forming a catalytic metal film on the substrate;
Using the catalytic metal film as a catalyst, the first linear structure group is formed on the substrate with a carbon element, and the first linear structure group has a different length from the first linear structure group. Forming a plurality of linear structures including a body group;
Forming a filling layer that supports the plurality of linear structures between the plurality of linear structures. A method for producing a sheet-like structure, comprising:

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