Abstract:
An apparatus includes a plurality of islands each carrying multiple cantilevers. The apparatus also includes a fluidic network having a plurality of channels separating the islands. The channels are configured to provide fluid to the islands, and the fluid at least partially fills spaces between the cantilevers and the islands. Heat from the islands vaporizes the fluid filling the spaces between the cantilevers and the islands to transfer the heat away from the islands while driving the cantilevers into oscillation. The apparatus may also include a casing configured to surround the islands and the fluidic network to create a vapor chamber, where the vapor chamber is configured to retain the vaporized fluid. The islands and the fluidic network could be formed in a single substrate, or the islands could be separate and attached together by a binder located within the channels of the fluidic network.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/961,476 filed on Jul. 20, 2007, which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to thermal management and more specifically to an apparatus and method for thermal management using a vapor chamber. 
       BACKGROUND 
       [0003]    Aggressive advances in electronic device technology, such as for defense and space applications, have created an urgent need for revolutionary thermal management solutions to effectively spread and carry heat dissipated by integrated circuit (IC) chips and multi-chip modules (MCMs). Some conventional thermal solutions use copper alloy heat spreaders, which draw heat away from integrated circuit chips and multi-chip modules and spread the heat over a larger area. However, these thermal solutions are often limited by the thermal conductivity (200 W/mK) and thermal expansion coefficient (TEC) mismatch of the copper alloy heat spreaders. Also, the lack of flexibility of the thermal substrate can limit innovative packaging configurations. 
         [0004]    In other conventional thermal solutions, heat pipes are used to help transport heat generated by electronic systems. By their nature, heat pipes are well suited for both long distance transport and for heat flux transformation (accepting a high heat flux at the source and ejecting it as a low heat flux at some other location, usually with a minimal change in temperature). Most heat pipes used for electronics cooling are made with copper as the envelope material and water as the working fluid. Heat pipes are often made in both cylindrical tube shapes and in low profile cuboids called vapor chamber heat pipes. Heat pipes have a much higher effective thermal conductivity for long-distance transport (compared to copper), but heat pipers are less effective in short-distance transport due to wick thermal resistance. Although the wick thermal resistance can be reduced by using a thinner wick layer or a smaller pore size, this typically leads to reduced capacity to handle heat flux (such as critical heat flux) due to increased liquid flow resistance in the wick capillary. 
       SUMMARY 
       [0005]    This disclosure provides an apparatus and method for thermal management using a vapor chamber. 
         [0006]    In a first embodiment, an apparatus includes a plurality of islands each carrying multiple cantilevers. The apparatus also includes a fluidic network having a plurality of channels separating the islands. The channels are configured to provide fluid to the islands, and the fluid at least partially fills spaces between the cantilevers and the islands. Heat from the islands vaporizes the fluid filling the spaces between the cantilevers and the islands to transfer the heat away from the islands. 
         [0007]    In particular embodiments, the apparatus also includes a casing configured to surround the islands and the fluidic network to create a vapor chamber. The vapor chamber is configured to retain the vaporized fluid. The casing could include a first portion and a second portion sealed together along outer sealing surfaces. 
         [0008]    In other particular embodiments, the islands and the fluidic network are formed in a single substrate. In yet other particular embodiments, the islands include separate islands attached together by a binder located within the channels of the fluidic network. The binder could be selected to provide a desired amount of rigidity or flexibility. 
         [0009]    In still other particular embodiments, the apparatus has an effective thermal conductivity of at least 20,000 watts per meter Kelvin (W/mK) and a critical heat flux of at least 500 watts per square centimeter (W/cm 2 ). 
         [0010]    In additional particular embodiments, the islands include silicon, and the cantilevers represent T-shaped cantilevers and/or zigzag-shaped cantilevers. 
         [0011]    In a second embodiment, a system includes a thermal ground plane (TGP) and integrated circuitry. The thermal ground plane includes a plurality of islands each carrying multiple cantilevers and a fluidic network having a plurality of channels separating the islands. The channels are configured to provide fluid to the islands, and the fluid at least partially fills spaces between the cantilevers and the islands. Heat from the integrated circuitry is absorbed by the islands and vaporizes the fluid filling the spaces between the cantilevers and the islands to transfer the heat away from the islands. 
         [0012]    In a third embodiment, a method includes providing a fluid to one or more islands in a thermal ground plane, where the fluid at least partially fills spaces between cantilevers on the islands and the islands. The method also includes absorbing heat at the islands, where the heat is generated by one or more integrated circuit (IC) chips. In addition, the method includes transferring the heat from the islands to the fluid so as to vaporize the fluid in the spaces between the cantilevers and the islands. The vaporized fluid escapes from the spaces and is replaced by additional fluid. 
         [0013]    Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a more complete understanding of this disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0015]      FIG. 1  illustrates an example vapor chamber thermal ground plane according to one embodiment of this disclosure; 
           [0016]      FIG. 2  illustrates additional details of an example vapor chamber thermal ground plane according to one embodiment of this disclosure; 
           [0017]      FIGS. 3A through 3D  illustrate an example operation of a cantilever in a vapor chamber thermal ground plane according to one embodiment of this disclosure; 
           [0018]      FIG. 4  illustrates an example vapor chamber thermal ground plane casing according to one embodiment of this disclosure; 
           [0019]      FIGS. 5A and 5B  illustrate example systems having a vapor chamber thermal ground plane according to one embodiment of this disclosure; and 
           [0020]      FIG. 6  illustrates an example method for thermal management using a vapor chamber thermal ground plane according to one embodiment of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIGS. 1 through 6 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the invention may be implemented in any type of suitably arranged device or system. 
         [0022]      FIG. 1  illustrates an example vapor chamber thermal ground plane  100  according to one embodiment of this disclosure. The embodiment of the vapor chamber thermal ground plane  100  shown in  FIG. 1  is for illustration only. Other embodiments of the vapor chamber thermal ground plane  100  could be used without departing from the scope of this disclosure. 
         [0023]    In this example, the thermal ground plane  100  includes a wick structure having multiple evaporative islands  102  separated from each other by a fluidic network  104 . The evaporative islands  102  allow for high heat-transfer from the island base to the evaporative surface of a fluid. As described in more detail below, the evaporative islands  102  have small features (such as micro- or nano-engineered cantilevers) on their major exposed surfaces. These features facilitate a high fluid evaporation rate. Vapor condensation can take place anywhere within the thermal ground plane  100  where the temperature is lower, such as areas that are away from the heat source or close to an external cooling source. Once condensed, the fluid is transported by the fluidic network  104  back to the evaporative islands  102  by capillary forces. The fluid transported in the fluidic network  104  allows for continuous replenishment of fluid for the evaporative islands  102  and thus helps to sustain a continuous evaporation-condensation cycle. A casing  106  in thermal contact with the evaporative islands  102  encases the evaporative islands  102  and the fluidic network  104 , forming a vapor chamber that contains the vapor produced by the evaporative islands  102 . Note that islands  102  and a fluidic network  104  reside in each portion of the casing  106  as shown in  FIG. 1 . 
         [0024]    As described in more detail below, fluid from the fluidic network  104  covers the evaporative islands  102 . Part of the fluid enters various spaces between the features formed on the evaporative islands  102  (such as the cantilevers) and the evaporative islands  102  themselves. The fluid in those spaces is superheated and experiences explosive evaporation, which helps to pull heat away from the evaporative islands  102 . New fluid then refills the spaces between the features formed on the evaporative islands  102  and the evaporative islands  102  themselves, and the process is repeated. In this way, the thermal ground plane  100  can pull heat away from integrated circuit chips, multi-chip modules, and other heat-generating devices in thermal contact with the casing  106 . 
         [0025]    The evaporative islands  102  include any suitable structures on which features can be formed to facilitate superheating and explosive evaporation of a fluid. The evaporative islands  102  could, for example, represent structures formed from silicon. The fluidic network  104  includes any suitable structures allowing transport of fluid to and from the evaporative islands  102 , such as a high mass-transport microfluidic network. The case  106  includes any suitable structure for encasing the evaporative islands  102  and the fluidic network  104 , such as a flexible, robust casing. The case  106  could, for example, represent a structure that offers structural, thermal expansion coefficient (TEC) matching, and electrically isolating properties, which can allow the mounting of integrated circuit chips or other circuitry directly onto the thermal ground plane  100 . In this example, the case  106  includes a top portion and a bottom portion joined along outer sealing surfaces  108  of the two portions. 
         [0026]    Note that there may be no predetermined evaporation or condensation areas of the thermal ground plane  100  since evaporation and condensation can occur anywhere within the thermal ground plane  100 . The locations of evaporation and condensation could be determined by the external placement of heating and cooling elements. For example, a heat-generating device (such as an integrated circuit chip) can be placed anywhere on the external surface of the thermal ground plane  100 , and the islands  102  in thermal contact with the heat source function as the evaporation surface. Likewise, areas of the thermal ground plane  100  in thermal contact with a cooling source (such as a heat sink) could function as condensation surfaces. In typical embodiments, the condensation area may be much larger than the evaporative area. 
         [0027]    In some embodiments, the evaporative islands  102  cover approximately 80% of the total area of the wick structure. The structures formed on the evaporative islands  102  (such as the cantilevers) enable enhanced evaporation and a high capillary pressure. The fluidic network  104  provides long-range fluid transport paths with low resistance. This structured wick design can be optimized to achieve high critical heat flux levels (dry out limit) beyond conventional heat pipe limits. Also, the evaporation enhancement seeks to increase the evaporative mass flux for a given change in temperature (AT) between the base and the evaporative surface, translating to a lower specific thermal resistance (K·cm 2 /W), which in high flux or short-range heat transfers tends to dominate the overall thermal resistance. 
         [0028]    Among other things, this type of thermal ground plane  100  could represent a high performance, thin, and lightweight thermal ground plane, where high effective thermal conductivities (such as 20,000 W/mK) can be achieved and high heat fluxes (such as &gt;500 W/cm 2 ) can be dissipated. Achieving this can involve various aspects of the thermal ground plane  100 , such as materials synthesis, micro- and nano-scale heat transfer and thermal engineering, nanofabrication, microfluidics, multi-phase numerical modeling, and packaging. 
         [0029]    This type of thermal ground plane  100  could be used in a wide variety of applications. For example, the thermal ground plane  100  can address or be used in space electronics systems, where weight and compactness are often critical issues. The thermal ground plane  100  can significantly enhance the packing density of IC chips on multiple MCM boards and enable novel thermal management solutions. As a particular example, one configuration involves allowing vapor transport from multiple individual thermal ground planes  100  to a larger vapor chamber heat sink/condenser, thus eliminating the bulky wedge structure currently used for thermal contact between a sink and copper alloy thermal bridges. In addition to these specified applications, the thermal ground plane  100  could be universally designed to offer significant advantages to address a multitude of other defense or other applications. Among other things, this may help to greatly enhance design flexibility, 2D/3D packing density, weight reduction, and device performance of space-borne systems. This may also enable much more compact and lighter-weight thermal management components, such as those manufactured for commercial computers. These uses are for illustration only. The vapor chamber thermal ground plane  100  could be used with any suitable device or system. 
         [0030]    Although  FIG. 1  illustrates one example of a vapor chamber thermal ground plane  100 , various changes may be made to  FIG. 1 . For example, the thermal ground plane  100  could include any number of evaporative islands  102 , and any suitable fluidic network with any suitable arrangement or pattern could be used. 
         [0031]      FIG. 2  illustrates additional details of an example vapor chamber thermal ground plane  100  according to one embodiment of this disclosure. The additional details of the vapor chamber thermal ground plane  100  shown in  FIG. 2  are for illustration only. Other embodiments of the vapor chamber thermal ground plane  100  could be used without departing from the scope of this disclosure. 
         [0032]    In this example, the vapor chamber thermal ground plane  100  includes or supports a dynamic wick structure, which relies on thermally driven hydrodynamic instability to enhance heat transfer. The dynamic wick structure includes arrays of cantilevers  202  as shown in  FIG. 2 . The cantilevers  202  are formed on the evaporative islands  102 , and fluid travels through the fluidic network  104  between the islands  102  and covers the cantilevers  202 . 
         [0033]    Under each cantilever  202  is a fluid-filled, semi-confined space (which could have a thickness in the submicron to micron scale). A semi-confinement condition due to surface tension, inertia, and flow resistance gives rise to superheating and a highly unstable thin film boiling process (pulsed vaporization). In other words, during heat transfer, the fluid under the cantilevers  202  experiences superheating followed by explosive evaporation. The thin film boiling under the cantilevers  202  is extremely fast due to the small thermal mass of the thin fluid layer and rapid replenishing by capillary pumping. The level of thermal-mechanical energy conversion in this structure is much higher than a free bubble expansion because of the capillary pressurization under the cantilevers  202 . The rapid pulsation caused by the vaporization drives the cantilevers  202  into oscillation at ultrasonic frequencies, which violently agitates the surrounding fluid and gives rise to a dynamically modified surface configuration, leading to significant enhancement of surface evaporation. 
         [0034]    The close spacing between the cantilevers  202  as shown in  FIG. 2  forms local fluid transport channels and provides capillary pumping. The capillary pressure is determined by the spacing between the cantilevers  202 , which can be designed to maximize the mass transfer. The optimal spacing depends on the island dimensions (the larger the island, the larger the spacing). As a particular example, one estimate based on a 1D capillary pumping model suggests that the optimal cantilever spacing is in the micron range for 100-micron islands (where a heat flux well above 500 W/cm 2  can be achieved in this modeled estimate). 
         [0035]    The cantilevers  202  can be fabricated in any suitable manner. For example, the cantilevers  202  can be fabricated on silicon using well-established micro-fabrication processes. In this document, the term “cantilever” refers to a structure defining one or more spaces between itself and another structure, where the cantilever is supported (such as by being coupled to the other structure) at or near one end of each defined space. Additional features may also be added, such as surface treatment to control the nucleation process and the superheating temperature. In some embodiments, this thermal ground plane structure can be monolithically fabricated on silicon substrates, allowing quick testing and evaluation of the evaporator performance. In other embodiments, the evaporator structures can be bonded with a non-silicon casing with pre-fabricated fluidic channels. 
         [0036]    Unlike conventional static wick structures, this dynamic wick structure greatly enhances heat transfer without reducing mass transport capacity (e.g. using a thinner or denser wick). This opens a new route to achieve extremely high effective thermal conductivity at unprecedented heat flux levels. 
         [0037]    The dynamic wick structure illustrated in  FIG. 2  particularly addresses the problem of a limited heat transfer coefficient of the evaporator due to poor thermal conductivity of the working fluid (such as water). The solution offered by the dynamic wick structure works by creating a strong surface agitation, which could attain an extremely high heat transfer coefficient without using ultra small pore sizes that restricts fluid flow, thus both high heat and mass transfer can be achieved. Among other things, the wick structure shown in  FIG. 2  includes or supports:
   Structures that facilitate a much higher degree of thermal-mechanical conversion than free bubble expansion;   Strong surface tension and hydrophilicity in the structures, which creates hydrodynamic instability prohibiting vapor trapping in the wick; and   Dynamic enhancement of heat transfer.   
 
         [0041]    Although  FIG. 2  illustrates additional details of one example vapor chamber thermal ground plane  100 , various changes may be made to  FIG. 2 . For example, while  FIG. 2  illustrates two example shapes of the cantilevers  202  (T-shaped and zigzag-shaped), these shapes are for illustration only. In fact, each structure in the thermal ground plane  100  could have any other size or shape. 
         [0042]      FIGS. 3A through 3D  illustrates an example operation of a cantilever  202  in a vapor chamber thermal ground plane  100  according to one embodiment of this disclosure. The cantilever  202  shown in  FIG. 3  is for illustration only. Other cantilevers  202  that operate in the same or similar manner could be used in the vapor chamber thermal ground plane  100  without departing from the scope of this disclosure. 
         [0043]    As shown in  FIG. 3A , the cantilever  202  generally defines a space  302  between itself and its underlying evaporative island  102 . A fluid  304  from the fluidic network  104  covers the cantilever  202  and fills the space  302 . Due to the size and shape of the space  302 , the fluid  304  between the cantilever  202  and the island  102  undergoes superheating during heat transfer. This results in explosive evaporation, which is shown in  FIG. 3B . The explosive evaporation lifts the cantilever  202 , and at least some of the fluid  304  previously in the space  302  escapes as vapor. As shown in  FIGS. 3C and 3D , the cantilever  202  then returns to its resting position, and new fluid  304  enters the space  302 . This process can be repeated numerous times to transfer heat away from the evaporative island  102 . 
         [0044]    Although  FIGS. 3A through 3D  illustrates one example of the operation of a cantilever  202  in a vapor chamber thermal ground plane  100 , various changes may be made to  FIGS. 3A through 3D . For example, the cantilever  202  could have any suitable size or shape. 
         [0045]      FIG. 4  illustrates an example vapor chamber thermal ground plane casing  400  according to one embodiment of this disclosure. The embodiment of the casing  400  shown in  FIG. 4  is for illustration only. Other embodiments of the thermal ground plane casing  400  could be used without departing from the scope of this disclosure. 
         [0046]    As noted above, one common problem with conventional thermal management solutions involves TEC mismatch between an integrated circuit substrate and the thermal ground plane. Although a silicon substrate represents the perfect TEC match with silicon chips, large silicon substrates are rigid, fragile, and hard to handle. In addition, as a low-bandgap semiconductor, it is not suitable for high-voltage insulation and can be lossy for radio frequency (RF) applications. 
         [0047]    As shown in  FIG. 4 , a technique is used to bind the above-described dynamic wick structure (the evaporative islands  102 ) to form a flexible tile casing  400 . In some embodiments, the islands  102  represent silicon islands, thereby forming a flexible tiled silicon casing. 
         [0048]    In this example, the tiled casing  400  is monolithically fabricated with the fluidic network  104  and the evaporative islands  102 . As shown here, the channels between the islands  102  include an adhesive or other binder  402 , such as a polymer binder, that bonds the islands  102  together but leaves sufficient channel depth to meet the capillarity requirements for the fluid in the fluidic network  104 . Also included is a diffusion barrier  404 , such as a dielectric or metal coating, which can be used to help prevent out diffusion of the working fluid. 
         [0049]    The structures in the casing  400  are completely monolithic in this example. This can achieve excellent TEC matching, significant flexibility (such as plastic-like flexibility), good electrical insulation, and toughness and ruggedness (making the thermal ground plane  100  suitable for practical use). The toughness and ruggedness of the tiled structure also enables much smaller wall thickness than using rigid and brittle materials. This results in a thinner thermal ground plane design and smaller thermal resistance across the wall. Using different binders  402 , the casing  400  can be made semi-rigid or extremely flexible for various applications. Because of its compliant nature, the thermal ground plane  100  can be used with chips other than silicon, such as GaAs and GaN, where TEC mismatch will not cause excessive stress. 
         [0050]    Although  FIG. 4  illustrates one example of a vapor chamber thermal ground plane casing  400 , various changes may be made to  FIG. 4 . For example, the cantilevers on the islands  102  could have any suitable size or shape. Also, the islands  102  could have any suitable size or shape. In addition, any suitable technique could be used to bind individual islands  102  together, or the islands  102  could be formed on a single substrate. 
         [0051]    In various embodiments of the thermal ground plane  100 , the capillary pressure generated by the wick structure may vary inversely with the characteristic pore size of the wick, so available capillary pressure can be increased simply by making features that are smaller than those currently used. This appears well-suited to take advantage of advances in micro- and nano-fabrication technologies that have proliferated in recent years. Simply making the pore size ever smaller does not automatically create structures with improved performance, however, because the fluid experiences higher pressure drop as the pores become smaller. This suggests an optimal pore size exists between making extremely small pores for generation of higher capillary pressure and keeping larger pores that incur less pressure drop on the fluid phase. An optimal design can incorporate multiple pore scales and flow paths that keep the wick supplied with fluid to high heat flux levels. 
         [0052]    Also, reducing the thickness of a vapor space in a vapor chamber may increase the vapor phase pressure drop. For thicknesses below 1 mm, this effect can be very strong and ultimately produce large temperature gradients that degrade the performance of the vapor chamber. To mitigate this problem, a working fluid can be chosen with high vapor density, high heat of vaporization, and low vapor viscosity. 
         [0053]    In addition to being compatible with the working fluid, the envelope (casing  106 ) may be structurally capable of containing the working fluid. In general, this can mean withstanding either positive internal or external pressure, although with water the pressure is usually external in the presence of atmospheric air pressure at temperatures typical of cooling of ordinary silicon-based electronics. 
         [0054]    Without any special features, an open wick may only be able to hold fluid against hydraulic pressure no larger than the capillary pressure of the largest channels (e.g. the channels of the fluidic network  104 ). For example, if the channels are 20 microns wide, it can only hold water against 0.08 bar, while the pressure drop over a 20 cm distance under 20 G is about 0.4 bar. A potential solution is to encapsulate the transport channels and cover the evaporative islands  102  with a gas permeable hydrophobic membrane. In this way, the only possible location for fluid escape is a condenser. However, this can only happen when the hydraulic pressure exceeds the capillary pressure of the evaporator wick or through a cavitation in the fluidic channels. The first possibility can be easily eliminated using sufficient capillary pressure for the evaporative wick. For water, a &lt;4 micron pore or channel size would provide over 0.4 bar holding pressure. The cavitation possibility can be prevented by increasing the gas phase pressure over the fluid surface. 
         [0055]    For metallic casings  106 , soldering or direct low temperature bonding can be used to form a hermetically sealed case. A variety of polymer bonding techniques can also be used to seal polymer structures, such as thermal, adhesive, and chemically assisted bonding. To attain structural requirements for large thermal ground planes, internal supports may also be designed into the casing  106  to reinforce the thermal ground plane to withstand, for example, 20 G accelerations. 
         [0056]    The various elements shown in  FIGS. 1 through 4  could have any suitable size, shape, and dimensions. As a particular example, each of the evaporative islands  102  in the wick structure could be approximately 100 microns by 100 microns or 200 microns by 200 microns. Moreover, the wick structure could be used in defense, space, and other applications. IC chips and MCMs can be hard-bonded to the disclosed structure with minimum thermal resistance. The low profile (thinness) of the structure allows high pack density of electronics, which may be needed for space and other applications. In these or other embodiments, Micro Electro-Mechanical System (MEMS) technology can also be used to fabricate the thermal ground plane. 
         [0057]      FIGS. 5A and 5B  illustrate example systems  500  and  550  having a vapor chamber thermal ground plane according to one embodiment of this disclosure. The embodiments of the systems  500  and  550  shown in  FIGS. 5A and 5B  are for illustration only. Other embodiments of the systems  500  and  550  could be used without departing from the scope of this disclosure. 
         [0058]    In  FIG. 5A , various integrated circuit chips  502   a - 502   c  are mounted on the vapor chamber thermal ground plane  100 . The integrated circuit chips  502   a - 502   c  could represent individual chips or chips forming larger multi-chip modules. The integrated circuit chips  502   a - 502   c  could represent any suitable semiconductor chips and can perform any suitable function(s). As particular examples, the integrated circuit chips  502   a - 502   c  could represent central processing units or other data processing devices. The integrated circuit chips  502   a - 502   c  generate heat, which is absorbed and spread by the thermal ground plane  100  as described above. Thermal grease or other conductive material could be placed between the integrated circuit chips  502   a - 502   c  and the thermal ground plane  100  to ensure that a thermal path exists between the thermal ground plane  100  and the integrated circuit chips  502   a - 502   c.    
         [0059]    Also attached to the thermal ground plane  100  is a heat sink  504 . The heat sink  504  generally absorbs heat from the thermal ground plane  100  and dissipates the heat. For example, the heat sink  504  can receive and dissipate the heat from the thermal ground plane  100  into the surrounding environment, typically through a fan structure on the exposed side of the heat sink  504 . The heat sink  504  includes any suitable structure for dissipating heat from the thermal ground plane  100 . 
         [0060]    In  FIG. 5B , multiple vapor chamber thermal ground planes  100  are provided, and integrated circuit chips  552   a - 552   c  are mounted on each of the thermal ground planes  100 . Each of the thermal ground planes  100  is also in thermal contact with a heat sink  554 . The integrated circuit chips  552   a - 552   c  could represent any suitable semiconductor chips and can perform any suitable function(s), and any number of chips could be placed on each thermal ground plane  100 . The heat sink  554  includes any suitable structure for dissipating heat from the thermal ground plane  100 . 
         [0061]    Although  FIGS. 5A and 5B  illustrate two examples of systems  500  and  550  having a vapor chamber thermal ground plane, various changes may be made to  FIGS. 5A and 5B . For example, any integrated circuitry or other structures that require cooling could be used with a thermal ground plane  100 . Also, a thermal ground plane  100  could be used in any other system to cool any other structures or devices. In addition,  FIGS. 5A and 5B  illustrate merely two of many possible configurations or implementations of the thermal ground plane. 
         [0062]      FIG. 6  illustrates an example method  600  for thermal management using a vapor chamber thermal ground plane according to one embodiment of this disclosure. The embodiment of the method  600  shown in  FIG. 6  is for illustration only. Other embodiments of the method  600  could be used without departing from the scope of this disclosure. 
         [0063]    Fluid is transported through a fluidic network in a thermal ground plane at step  602 . This could include, for example, using a high mass-transport fluidic network  104  to transport a cooling fluid (such as water) to various evaporative islands  102  in the thermal ground plane  100 . The fluid from the fluidic network covers cantilevers on the islands at step  604  and fills spaces beneath the cantilevers (between the cantilevers and the islands) at step  606 . Capillary forces could cause movement of the fluid around and under the cantilevers here. 
         [0064]    Heat from one or more devices to be cooled is received at the islands at step  608 . This could include, for example, operating one or more integrated circuit chips, multi-chip modules, or other circuitry. The heat is transported from the chips or other circuitry to the evaporative islands  102 . The fluid beneath the cantilevers is heated by the islands and vaporized at step  610 . This causes the release of vaporized fluid from beneath the cantilevers at step  612  and the transfer of heat away from the islands through the vaporization at step  614 . The vapor is later condensed to transfer heat away from the vapor and reclaim fluid at step  616 . At this point, the method  600  returns to step  606  to again fill the spaces beneath the cantilevers with fluid. 
         [0065]    Although  FIG. 6  illustrates one example of a method  600  for thermal management using a vapor chamber thermal ground plane, various changes may be made to  FIG. 6 . For example, while shown as a series of steps, various steps in  FIG. 6  could overlap or occur in parallel. 
         [0066]    It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. 
         [0067]    While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of the invention, as defined by the following claims.