Patent Application
20080298021
1. Field of the Invention
The present invention relates to heat-transfer techniques. More specifically, the present invention relates to the use of a diamond heat spreader to transport heat in computer systems.
2. Related Art
The computational performance of electronic devices has increased significantly in recent years. This increased performance has been accompanied by an increase in power consumption and associated heat generation. Furthermore, this additional heat generation has made it harder to maintain acceptable internal and external operational temperatures in these devices.
Portable devices, such as laptop computers (notebook PCs), cellular telephones, and personal digital assistants have additional design constraints which make it even harder to manage thermal load. In particular, size and weight limitations in such devices can make it difficult to achieve desired operational temperatures. For example, in many portable devices the size and weight of metal heat sinks may be prohibitive. Furthermore, battery life constraints in such devices may limit the available power for active cooling mechanisms, such as fans.
Hence what is needed are cooling mechanisms that overcome the problems listed above.
One embodiment of the present invention provides a device that includes an integrated circuit that is coupled to a heat spreader. This heat spreader includes a first layer of an allotrope of carbon. Note that the allotrope of carbon has an approximately face-centered-cubic crystal structure, which has a thermal conductivity greater than a first pre-determined value and a specific heat greater than a second pre-determined value.
In some embodiments, the allotrope of carbon includes diamond. Furthermore, in some embodiments the diamond is polycrystalline. Note that the diamond may be produced using chemical vapor deposition.
In some embodiments, the first layer includes grains of metal. For example, the metal may include aluminum and/or copper.
In some embodiments, the integrated circuit includes a processor.
In some embodiments, the first pre-determined value facilitates the transfer of steady-state heat from the integrated circuit, and the second pre-determined value facilitates the transfer of transient heat from the integrated circuit.
In some embodiments, the integrated circuit is coupled to the heat spreader using a thermal-interface material. This thermal-interface material may include: solder, thermal grease, and/or a phase-change material. However, in other embodiments the thermal-interface material includes a metal layer, such as: titanium, platinum, and/or gold.
In some embodiments, the device further includes a heat exchanger that is coupled to the heat spreader. Note that the heat exchanger may be configured to passively or actively transfer heat from the integrated circuit. For example, the heat exchanger may include a forced-fluid driver and a heat-coupling-mechanism coupled to the forced-fluid driver. This forced-fluid driver may be configured to pump heat.
Furthermore, in some embodiments the heat-coupling mechanism includes convective-cooling fins. These convective-cooling fins may include a second layer that includes the allotrope of carbon.
Another embodiment provides a computer system that includes the integrated circuit and the heat spreader coupled to the integrated circuit.
Note that like reference numerals refer to corresponding parts throughout the drawings.
The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
Embodiments of a cooling mechanism, a device, and a computer system (such as a desktop computer and/or a laptop or portable computer) that includes the cooling mechanism and/or the device are described. Note that the computer system may include stationary and/or portable electronic devices, such as cellular telephones, personal digital assistants, game consoles, and MP3 players. This cooling mechanism may include a heat spreader that includes an allotrope of carbon (such as single-crystal or polycrystalline diamond). For example, the allotrope of carbon may have an approximately face-centered-cubic crystal structure. In addition, the allotrope of carbon may have a thermal conductivity greater than 1000 W/mK at room temperature and a specific heat greater than 250 J/kgK at room temperature.
In some embodiments, the cooling mechanism is coupled to one or more integrated circuits (such as a processor, a graphics processor, and/or an application-specific integrated circuit) in the device and/or the computer system, for example, using a thermal-interface material, such as: solder, thermal grease, a metal, and/or a phase-change material. Furthermore, the thermal conductivity of the heat spreader may facilitate transfer of steady-state heat from the integrated circuit, and the specific heat may facilitate transfer of transient heat from the integrated circuit.
We now describe embodiments of the cooling mechanism, the device, and the computer system.
In an exemplary embodiment, the heat pipe 114 has a solid copper jacket with a hollow interior. In some embodiments, an inner surface of the jacket may be coated with a thin-wick structure that includes copper powder to increase an effective contact area. In addition, the hollow interior may hold a soft vacuum, i.e., may have reduced air pressure. This reduced pressure may allow water to boil more easily during operation of the computer system 110. The resulting water vapor may be very effective in carrying heat from the integrated circuits 112 to forced fluid drivers 118 (such as fans) that are located at opposite ends of the heat pipe 114. Consequently, the hollow interior of the heat pipe 114 may have an effective thermal conductivity of 5000 W/m/C, which is 100 times larger than that of solid copper.
However, in other embodiments the interior of the heat pipe 114 includes a liquid coolant (i.e., a material with little or no sheer strength). For example, the liquid coolant may include: water, a coolant in an R133 group of coolants, and/or a coolant in an R134 group of coolants. Note that the heat pipe 114 may include two or more metal castings. These castings may include portions of a tube or channel. When the castings are combined, the tube or channel may be formed, thereby providing a path for the liquid coolant. Moreover, in some embodiments these castings may be soldered or welded to each other, thereby hermetically sealing the tube or channel.
Furthermore, in some embodiments an optional pump 116 coupled to the heat pipe 114 circulates the liquid coolant, thereby facilitating heat transfer from a power source in the computer system 110 (such as one of the integrated circuits 112) to the forced-fluid drivers 118.
These forced-fluid drivers may circulate a fluid (for example, a gas such as air) via fluid-flow ports 120 (such as vents), i.e., the forced-fluid drivers 118 may drive fluid flows 122. This fluid flow may transfer heat from an interior of the computer system 110 to an external environment. Note that in some embodiments such heat transfer is enhanced by using a heat-coupling mechanism, such as convective-cooling fins. For example, the computer system 110 may include fin stacks 124 (which are discussed further below with reference to
Note that the heat pipe 114 may be a very efficient, passive or active heat-transfer mechanism. In particular, a thermal gradient across the heat pipe 114 may be less than 2 C. Thus, the heat pipe 114 may maintain a temperature inside of the computers system 1O and/or on an outer surface of the computer system 110.
In some embodiments, the fluid-flow ports 122 are tapered such that a cross-sectional area decreases as fluid flows from inside of the computer system 110 to outside. For example, the fluid-flow ports 122 may constitute a Venturi tube. Note that this decrease in area may give rise to a Bernoulli effect in which a partial vacuum at the output of the fluid-flow ports 120-1 and 120-2 (and at the input to fluid-flow port 120-3) reduces and/or eliminates recirculation of the fluid flows 122, thereby reducing the temperature inside of the computer system 110.
Furthermore, in some embodiments the optional pump 116 includes a mechanical pump and/or an electrostatic pump. Alternatively, in some embodiments the pump 116 is configured to circulate the liquid coolant using mechanical vibration (for example, using ultrasonic frequencies) of a membrane.
Note that in some embodiments the computer system 110 (as well as the embodiments discussed below) includes fewer or additional components, two or more components are combined into a single component, and/or a position of one or more components may be changed. For example, in some embodiments there may be more or fewer forced fluid drivers 118 and/or a direction of the fluid flows 122 may be reversed. Furthermore, in some embodiments the liquid coolant includes a refrigerant.
While computer system 110 includes active heat-transfer mechanisms, such as forced-fluid drivers 118 and/or the optional pump 116, in other embodiments (such as in devices having low power consumption) passive cooling techniques are used. This is shown in
We now discuss embodiments of the heat spreader.
In some embodiments, the heat spreader 312-1 includes an allotrope of carbon having an approximately face-centered-cubic crystal structure, such as single-crystal or polycrystalline diamond. This diamond may be produced using chemical vapor deposition (or another fabrication or manufacturing process). In addition to the physical properties discussed previously (including the thermal conductivity and the heat capacity), the heat spreader 312-1 may also have a good match to the thermal-expansion coefficients of the one or more integrated circuits 112 and/or the heat sink 310. Furthermore, the heat spreader 312-1 may have a high strength or stiffness value. In an exemplary embodiment the heat spreader 312-1 is a thin film that has a thickness 316 between 1 and 50 μm. In some embodiments, the heat spreader 312-1 has isotropic thermal properties.
In exemplary embodiments, the heat spreader 312 includes: a film that includes a hybrid of diamond and copper with a coefficient of thermal expansion of 3-8 ppm/K, a density of 4 g/cm3, and a thermal conductivity of 400 W/mK; a film that includes a hybrid of diamond and aluminum with a coefficient of thermal expansion of 5-9 ppm/K, a density of 3 g/cm3, and a thermal conductivity of 650 W/mK; a diamond film with a coefficient of thermal expansion of 1-2 ppm/K, a density of 3.5 g/cm3, and a thermal conductivity of 1000-2000 W/mK; an aluminum film with a coefficient of thermal expansion of 23 ppm/K, a density of 2.7 g/cm3, and a thermal conductivity of 200 W/mK; and/or a copper film with a coefficient of thermal expansion of 17 ppm/K, a density of 9 g/cm3, and a thermal conductivity of 385 W/mK. Note that at room temperature the specific heat of copper is 0.4 J/gK, the specific heat of aluminum of 0.9 J/gK, and the specific heat of diamond is 0.5 J/gK.
Note that the heat spreader 312-1 is sandwiched between one or more conformal and/or insulating layers, such as thermal-interface materials 314. Note that one or both surfaces of the heat spreader 312-1 may be metallized with an over coats (for example, with titanium, platinum, and/or aluminum) to facilitate soldering to either or both of the thermal-interface materials 314.
In an exemplary embodiment, thermal-interface material 314-1 includes: solder (for example, a low melting-point solder), thermal grease, and/or a phase-change material (such as epoxy). Furthermore, thermal-interface material 314-2 may include a metal, such as: titanium, platinum, and/or gold. Note that a reflowed solder (such as one including copper) may be used to thermally couple thermal-interface material 314-2 to the heat spreader 312-1 and/or the heat sink 310.
Moreover, in some embodiments the heat spreader 312-2 is a heterogeneous or hybrid material. For example, the heat spreader 312-2 may include diamond and metal grains (such as aluminum and/or copper). This is shown in
By including one of the heat spreaders 312 (such as diamond), devices and computer systems (such as computer system 110 in
In an exemplary embodiment, the temperature and fluctuation magnitude of a silicon junction (subjected to repeated cycles of thermal-design power for 3.4 s and idle for 1.6 s) was reduced by around 4 C using heat spreaders 312 that include a hybrid of diamond and aluminum or copper and aluminum. In another exemplary embodiment, the temperature and fluctuation magnitude of a silicon junction (subjected to repeated cycles of thermal-design power for 3.4 s and idle for 1.6 s) was reduced by around 2 C using a thin (10-100 μm) diamond film deposited on a copper heat spreader.
Improved materials, such as diamond, may be included in other heat-transfer components. This is shown in
The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.
