Sunday, October 11, 2009

Heat Sinks: Hot Market for Cool Carbon Nanotubes

Carbon nanotube (CNT) heat sinks could soon be used in billions of new electronic devices annually. With the continually decreasing size of electronic and micromechanical devices, there is an increasing interest in materials that conduct heat efficiently, thus preventing structural damage.

Carbon nanotube heat sinks could be used in wireless mobile phones, a personal digital assistants, pocket PCs, tablet PCs, notebook PCs, desktop computers, set-top boxes, audio/video controllers, DVD players, network routers, network switching devices, or servers. They could be used to cool: main memory, graphics processors, mass storage devices, and input/output modules. Examples of the memory include static random access memory (SRAM) and dynamic random access memory (DRAM). Examples of the mass storage devices include hard disk drives, flash drives, compact disk drives (CD), and digital versatile disk drives (DVD). Examples of the input/output modules include keyboards, cursor control devices, displays, network interfaces, and so forth.

Under normal operation a microprocessor generates heat that must be removed to maintain the device temperature below a critical threshold and thereby maintain reliable operation. If a microprocessor overheats badly during operation it can be permanently damaged. Carbon nanotubes are one of the most thermally conductive materials that are manufactured today.

Intel holds 107 U.S. Patents referencing carbon nanotubes (CNT). Among Intel’s many uses of carbon nanotubes in chip design is as a heat sink to protect microprocessors. Intel Corporation has developed a composite carbon nanotube structures for use as a thermal interface device in packaged integrated circuit devices that is manufactured on the chip. Intel has found the CNT heat sinks can wick away 20% more heat than conventional heat sink material.

In U.S. Patent Application 20090224422, Intel inventor Valery M. Dubin reveals a composite CNT structures that provide high thermal conductivity, high mechanical strength, and good chemical stability. Further, these composite CNT structures may be fabricated to a very thin and uniform thickness. Also, the composite CNT structures may be fabricated using well known, low cost methods semiconductor manufacturing methods (e.g., CVD, PECVD, electroplating, electroless plating, sputtering, etc.). Their fabrication and use as thermal interface devices is compatible with existing assembly and process conditions. The composite carbon nanotube structure may be formed directly on a component, such as an integrated circuit die, a semiconductor wafer, a heat spreader, or a heat sink.

In U.S. Patent 7,335,983, Intel discloses a semiconductor package that includes microchimneys or thermosiphons made of carbon nanotubes to improve the effective thermal conductivity of an integrated circuit die. A thermosiphon is an alternative structure for increasing die effective thermal conductivity. Thermosiphons typically exhibit heat transfer capabilities equivalent to solid materials with high thermal conductivity by taking advantage of a working fluid's latent heat of vaporization and condensation. Microchimneys and thermosiphons have related CNT structures and can be combined to wick heat more quickly from microdevices.

Hon Hai Precision Ind. Co., Ltd. (Taipei Hsien, TW), also known as Foxconn, has also developed carbon nanotube heat sinks, which have high tensile strength, good flexibility and excellent heat conduction coefficients. This ensures good physical and thermal contact between the carbon nanotubes and an electronic device, and improves the heat conduction performance of the heat sink. Secondly, when the heat sink is used with the electronic device, other thermal interface materials such as thermal grease are not needed. Further, the carbon nanotubes have a low height. Therefore not only does the heat sink save on materials, it ensures that the combined electronic device and heat sink has reduced bulkiness and weight. Also the carbon nanotubes are perpendicular to and uniformly formed on the second surface of the semiconductor base, which ensures that the heat sink conducts heat directly and evenly. Finally the area of distribution of the carbon nanotubes can be varied according to need by controlling an area of distribution of the catalyst film.

Nanoconduction Inc. (Menlo Park, CA) has created an “Integrated Circuit Micro-Cooler with the Tubes of a CNT Array.” The heat sink structures employ multi-layers of carbon nanotube or nanowire arrays to reduce the thermal interface resistance between an integrated circuit chip and the heat sink. The nanotubes are cut to essentially the same length over the surface of the structure. Carbon nanotube arrays are combined with a thermally conductive metal filler disposed between the nanotubes. This structure produces a thermal interface with high axial and lateral thermal conductivities.

Lockheed Martin Corporation (Bethesda, MD) has developed carbon nanotube fibers that allow the fabrics to insulate, semi-conduct or super-conduct electrical charges. Additionally, the thermal properties of carbon nanotubes allow thermal energy to flow efficiently between the fabric and a heat sink or source. Additional yarns of materials other than carbon nanotubes can be integrated or woven into the fabric to provide other unique properties for the fabric. These fabrics can be layered to form unique garments or structures. Carbon nanotubes with differing characteristics can be woven together to create unique fabrics. For example, carbon nanotubes that serve to electrically insulate can be combined or layered with highly electrically conductive carbon nanotubes to create garments that shield and protect the wearer from electric shock. Similarly, thermally conductive carbon nanotubes can be woven into materials that when tethered to a heat sink or source, serve to protect a user from intense thermal environments.

Others developing carbon nanotube heat sinks include: The Research Foundation of State University of New York, Sunrgi, Schlumberger-Doll Research, General Electric (GE), Samsung, and Tyco Electronics to name only a few.

1 comment:

  1. I agree with you that Carbon nano tube Heat Sinks used in billions of new electronic devices. Carbon nano tube heat sinks famous because it is mostly use in wireless technology.

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