THERMAL INTERFACE MATERIAL AND METHOD FOR FABRICATING THE SAME

[0001] 1. Field of the Invention

[0002] The present invention relates to a thermal interface material and a method for fabricating the same, and particularly to a carbon-nanotube-based thermal interface material and a method for fabricating the same.

[0003] 2. Discussion of Related Art

[0004] Electronic components such as semiconductor chips are becoming progressively smaller, while at the same time heat dissipation requirements thereof are increasing. Commonly, a thermal interface material is utilized between the electronic component and an integrated heat spreader in order to efficiently dissipate heat generated by the electronic component. Whereas, the performance of the thermal interface material is restricted by a heat conduction coefficient thereof. The heat conduction coefficient of the thermal interface material is now considered to be too low for many contemporary applications.

[0005] Conventional thermal interface materials are metallic materials. However, the metallic materials disadvantageously tend to have a much higher coefficient of thermal expansion than semiconductor devices. Mechanical stresses are induced during temperature cycling and will tend to overstress the electronic components leading to potential failures when metallic materials are used as a thermal interface material.

[0006] A recently developed thermal interface material is a composite material obtained by diffusing particles in a polymer. The particles can be made of graphite, boron nitride, silicon oxide, alumina, silver, or specially be made of carbon nanotubes. The carbon nanotubes are distributed orderly and provide a heat conduction path in the polymer. Additionally, the carbon nanotubes can protrude from the polymer and contact the electronic components or the integrated heat spreaders. However, the heat conduction coefficient of the polymer is relatively low. As such, performance of the thermal interface material is restricted by the used polymer.

[0007] What is needed, therefore, is to provide a carbon-nanotube-based thermal interface material with high heat conduction coefficient and a method for fabricating the same, in which the above problems are eliminated or at least alleviated.

[0008] In one embodiment, a thermal interface material includes an array of carbon nanotubes with interspaces defined therebetween; and a low melting point metallic material filled in the interspaces.

[0009] In another embodiment, a method for fabricating a thermal interface material, the method includes (a) providing an array of carbon nanotubes with interspaces defined therebetween; and (b) depositing a low melting point metallic material on the carbon nanotubes in the interspaces therebetween to form a metallic layer with the array of carbon nanotubes embedded therein, and thereby, achieving the thermal interface material.

[0010] Other advantages and novel features of the present thermal interface material and method for fabricating the same will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings.

[0015] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one preferred embodiment of the present thermal interface material and related method for fabricating the same, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

[0016] Reference will now be made to the drawings to describe, in detail, embodiments of the present thermal interface material and method for fabricating the same.

[0017] Referring to FIG. 1, a method for fabricating the thermal interface material includes the steps of: (a) providing an array of carbon nanotubes with interspaces defined between the carbon nanotubes, quite suitably, providing a super-aligned array of carbon nanotubes with interspaces defined between the carbon nanotubes; (b) depositing a metallic material in the interspaces between the carbon nanotubes to form a metallic layer with the array of carbon nanotubes embedded therein, and thereby, achieving the thermal interface material.

[0018] In step (a), a given super-aligned array of carbon nanotubes can be formed by the substeps of: (a1) providing a substantially flat and smooth substrate; (a2) forming a catalyst layer on the substrate; (a3) annealing the substrate with the catalyst at a temperature in the approximate range from 700° C. to 900° C. in air for about 30 to 90 minutes; (a4) heating the substrate with the catalyst at a temperature in the approximate range from 500° C. to 740° C. in a furnace with a protective gas therein; and (a5) supplying a carbon source gas into the furnace for about 5 to 30 minutes and growing a super-aligned array of the carbon nanotubes from the substrate.

[0019] In step (a1), the substrate can, beneficially, be a P-type silicon wafer, an N-type silicon wafer, or a silicon wafer with a film of silicon dioxide thereon. Quite usefully, a 4-inch P-type silicon wafer is used as the substrate.

[0020] In step (a2), the catalyst can, advantageously, be made of iron (Fe), cobalt (Co), nickel (Ni), or any alloy thereof.

[0021] In step (a4), the protective gas can, beneficially, be made up of at least one of nitrogen (N₂), ammonia (NH₃), and a noble gas. In step (a5), the carbon source gas can, advantageously, be a hydrocarbon gas, such as ethylene (C₂H₄), methane (CH₄), acetylene (C₂H₂), ethane (C₂H₆), or any combination thereof.

[0022] The super-aligned array of carbon nanotubes can, opportunely, be in a height of about 10 microns to 1 millimeter and include a plurality of carbon nanotubes parallel to each other and substantially perpendicular to the substrate. The super-aligned array of carbon nanotubes formed under the above conditions is essentially free of impurities, such as carbonaceous or residual catalyst particles. The carbon nanotubes in the super-aligned array are packed together closely by van der Waals attractive force. The array of carbon nanotubes formed on the substrate has a first surface and a second surface. The second surface of the array of carbon nanotubes contacts the substrate.

[0023] It is to be understood that, the array of carbon nanotubes can be formed by other methods know in the art.

[0024] In step (b), the metallic layer can be deposited on the carbon nanotubes by means of physical vapor deposition (PVD), chemical vapor deposition (CVD), or other methods known in the art. In the present embodiment, quite suitably, the metallic material can be deposited in the interspaces between the carbon nanotubes, and thereby, the metallic layer can be formed by a method of vacuum evaporation. Referring to FIG. 2, a device for depositing the metallic material in the interspaces between the carbon nanotubes includes a vacuum container 20, a source 22, and a heater 24. The source 22 and the heater 24 are disposed in the vacuum container 20. The heater 24 can, suitably, be disposed at a lower side in the vacuum container 20. The source 22 is disposed on the heater 24. A vacuum pump (not shown) can be further connected to the vacuum container 20 to evacuate the air therein. In use, the substrate 28 with the array of carbon nanotubes 26 formed by step (a) can, usefully, be disposed at an upper side in the vacuum container 20 and separated from the source 22. The first surface of the array of carbon nanotubes 26 faces the source 22.

[0025] The material of the source 20 is a low melting point metallic material and can, opportunely, be selected from the group consisting of indium (In), gallium (Ga), an alloy of stibium (Sb) and bismuth (Bi), an alloy of lead and tin, and any combination thereof. The melting point of the metallic material of the source 20 is below 200° C. The degree of vacuum of the vacuum container 20 is above 1 pascal (Pa).

[0026] In step (b), the source 22 can, advantageously, be evaporated or sublimated by the heater 24 to form a metallic vapor in the vacuum container 20. When it meets the array of carbon nanotubes 26, the metallic vapor condenses on the first surface of the array of carbon nanotubes 26 and infiltrates into the interspaces between the carbon nanotubes. As such, a metallic layer with the array of carbon nanotubes 26 embedded therein is formed on the substrate 28.

[0027] After step (b), the metallic layer with the array of carbon nanotubes 26 embedded therein can be peeled from the substrate 28. And, as in step (b), the metallic material can be further deposited on the second surface of the array of carbon nanotubes 26 and infiltrated into the interspaces between the carbon nanotubes.

[0028] Referring to FIG. 3, a thermal interface material 30, formed by the method described above, is shown. Low melting point metallic material 34 is filled into the array of carbon nanotubes 32. In the present embodiment, the thickness of the thermal interface material 30 is in the approximate range from 10 microns to 1 millimeter.

[0029] In use, the thermal interface material 30 of the present embodiment can be disposed between an electronic component and a heat spreader. When temperature is elevated above the melting point, the low melting point metallic material 34 changes to a liquid. The liquid metallic material is capable of filling the gaps between the electronic component and the heat spreader, and as such, reduces the thermal contact resistance therebetween. Further, due to a high thermal conductivity of the metallic material, the thermal interface material has a higher thermal conductivity than a polymer-carbon nanotube composite. Additionally, during temperature cycling, mechanical stress of the metallic material can be reduced by the carbon nanotubes dispersed therein. Further, the method for fabricating the thermal interface material of the present embodiment is simple and can be applied in mass production at a low cost.

[0030] Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.