Integration of active MEMS cooling systems into thin computing devices

A cooling system for a computing device is described. The cooling system includes a heat transfer structure. The heat transfer structure includes a heat spreader, a fin structure, and a differential pressure device. The fin structure transfers heat from the heat spreader to a fluid. The differential pressure device generates a low pressure region that draws the fluid from an ingress in the computing device through the fin structure. The heat transfer structure is enclosed in a chamber of the computing device. The chamber includes the ingress and an egress.

BACKGROUND OF THE INVENTION

As computing devices grow in speed and computing power, the heat generated by the computing devices also increases. Various mechanisms have been proposed to address the generation of heat. Active devices, such as fans, may be used to drive air through large computing devices, such as laptop computers or desktop computers. Passive cooling devices, such as heat spreaders, may be used in smaller, mobile computing devices, such as smartphones, virtual reality devices and tablet computers. However, such active and passive devices may be unable to adequately cool both mobile devices such as smartphones and larger devices such as laptops and desktop computers. Moreover, incorporating cooling solutions into computing devices may be challenging. Consequently, additional cooling solutions for computing devices are desired.

DETAILED DESCRIPTION

As semiconductor devices become increasingly powerful, the heat generated during operations also grows. For example, processors for mobile devices such as smartphones, tablet computers, notebook computers, and virtual reality devices as well as for other computing devices such as servers, can operate at high clock speeds, but produce a significant amount of heat. Because of the quantity of heat produced, processors may run at full speed only for a relatively short period of time. After this time expires, throttling (e.g. slowing of the processor's clock speed) occurs. Although throttling can reduce heat generation, it also adversely affects processor speed and, therefore, the performance of devices using the processors. As technology moves to 5G and beyond, this issue is expected to be exacerbated. Further, other components in a computing device may generate heat. Thus, thermal management is increasingly an issue for computing devices.

Larger computing devices, such as laptop computers, desktop computers, or servers, include active cooling systems. Active cooling systems are those in which an electrical signal is used to drive cooling. An electric fan that has rotating blades is an example of an active cooling system, while a heat spreader is an example of a passive cooling system. When energized, the fan's rotating blades drive air through the larger devices to cool internal components. However, space and other limitations in computing devices limit the use of active cooling systems. Fans are typically too large for mobile and/or thinner devices such as smartphones and tablet or notebook computers. Fans also may have limited efficacy because of the boundary layer of air existing at the surface of the components because they provide a limited airspeed for air flow across the hot surface desired to be cooled, and because they may generate an excessive amount of noise. Fans also have a limited backpressure. Space and power limitations may further restrict the ability to provide electrical connection to active cooling systems. For example, if multiple active cooling systems are used, the connections to the active cooling systems may be required to fit within a small area. In addition, the power consumed by such a cooling system may be desired to be small, particularly for mobile devices. Moreover, space limitations may adversely affect the ability to provide a sufficient flow for cooling computing devices. Consequently, active cooling systems face particular challenges when used in computing devices such as active computing devices. Passive cooling solutions may include components such as a heat spreader and a heat pipe or vapor chamber to transfer heat to a heat exchanger. However, passive cooling solutions may be unable to provide a sufficient amount of heat transfer to remove excessive heat generated. Thus, additional cooling solutions are desired.

A cooling system for a computing device is described. The cooling system includes a heat transfer structure. The heat transfer structure includes a heat spreader, a fin structure, and a differential pressure device. The fin structure transfers heat from the heat spreader to a fluid. The differential pressure device generates a low pressure region that draws the fluid from an ingress in the computing device through the fin structure. The heat transfer structure is enclosed in a chamber of the computing device. The chamber includes the ingress and an egress.

In some embodiments, the heat transfer structure restricts flow driven by the differential pressure device such that a pressure differential of at least a one hundred Pascals per cubic feet per minute (cfm) (100 Pa/cfm) is within the chamber. In some such embodiments, the pressure differential is at least four hundred pascals per cfm (400 Pa/cfm). The pressure differential may be at least five hundred pascals per cfm (500 Pa/cfm).

In some embodiments, the differential pressure device generates the low pressure region that draws the fluid from the ingress such that greater than 2 W of heat is ejected from the egress. In some embodiments, at least 6 W of heat is ejected from the egress.

The differential pressure device may include cells, a top cover, and a bottom plate. Each of the cells includes a flow chamber having a vent, an actuator, and a plurality of orifices. Vibrational motion of the actuator draws the fluid into the flow chamber via the vent, directs the fluid around the actuator, and drives the fluid out of the flow chamber through the orifices. The top cover is proximate to the vent and has aperture(s) therein. The bottom plate is proximate to the orifices and coupled with the top cover. The fluid is directed from the orifices toward the bottom plate. In some embodiments, the fluid flows through the differential pressure device and to the egress. A top gap of at least 0.3 mm and not more than 1 mm may be is between the top cover of the differential pressure device and the top of the chamber. The differential pressure device may have a height not exceeding 3.5 millimeters.

A cooling system for a computing device is described. The cooling system includes a heat transfer structure including a heat spreader and a differential pressure device. The differential pressure device generates a low pressure region that draws fluid from an ingress in the computing device through the heat transfer structure. The differential pressure device has a height not exceeding 3.5 millimeters. In some embodiments, the height of the differential pressure device does not exceed 3 millimeters. In some embodiments, the heat transfer structure resides in a chamber of the computing device having a chamber height of at least 2 millimeters and not more than 3.5 millimeters. In some embodiments, the heat transfer structure is enclosed in a chamber of the computing device. The chamber has the ingress and an egress. In such embodiments, the heat transfer structure further includes a fin structure that transfers heat from the heat spreader to the fluid. The low pressure region generated by the differential pressure device draws the fluid through the fin structure. In some embodiments, the heat transfer structure restricts flow driven by the differential pressure device such that a pressure differential of at least a one hundred Pascals per cubic feet per minute (cfm) (100 Pa/cfm) is within the chamber. In some embodiments, the differential pressure device generates the low pressure region such that greater than 2 W of heat is ejected from an egress of the computing device.

The differential pressure device may include cells, a top cover, and a bottom plate. Each of the plurality of cells includes a flow chamber having a vent, an actuator, and orifices. Vibrational motion of the actuator draws the fluid into the flow chamber via the vent, directs the fluid around the actuator, and drives the fluid out of the flow chamber through the orifices. The top cover is proximate to the vent and has at least one aperture therein. The bottom plate is proximate to the orifices and coupled with the top cover. The fluid is directed from the orifices toward the bottom plate.

A method is described. The method includes activating an active component in a differential pressure device to undergo vibrational motion. A computing device includes a heat transfer structure. The heat transfer structure includes the differential pressure device, a fin structure, and a heat spreader. The fin structure transfers heat from the heat spreader to a fluid. The vibrational motion of the active component generates a low pressure region that draws the fluid from an ingress in the computing device through the fin structure. The heat transfer structure is enclosed in a chamber of the computing device. The chamber has the ingress and an egress. In some embodiments, the vibrational motion of the active component generates a low pressure region that draws fluid from an ingress in the computing device such that greater than 2 W of heat is ejected from the egress. In some embodiments, the differential pressure device has a height not exceeding 3.5 millimeters.

FIGS.1A-1Gare diagrams depicting an exemplary embodiment of active MEMS cooling system100usable with heat-generating structure102and including a centrally anchored cooling element120or120′. Although termed a cooling system, MEMS system100and analogous systems described herein may be considered heat transfer systems and/or fluid transfer systems. Cooling element120is shown inFIGS.1A-1Fand cooling element120′ is shown inFIG.1G. For clarity, only certain components are shown.FIGS.1A-1Gare not to scale.FIGS.1A and1Bdepict cross-sectional and top views of cooling system100in a neutral position.FIGS.1C-1Ddepict cooling system100during actuation for in-phase vibrational motion.FIGS.1E-IF depict cooling system100during actuation for out-of-phase vibrational motion. Although shown as symmetric, cooling system100need not be.

Cooling system100includes top plate110having vent112therein, cooling element120, orifice plate130having orifices132and cavities134therein, support structure (or “anchor”)160and chambers140and150(collectively chamber140/150) formed therein. Cooling element120is supported at its central region by anchor160. Although termed a cooling element with respect toFIGS.1A-1G, cooling element120and analogous elements described herein may also be considered actuators, vibrating elements, vibrating components, active components, and/or other terms indicating that the element is configured to undergo vibrational motion when activated (or energized) and/or to drive fluid through a system. Regions of cooling element120closer to and including portions of the cooling element's perimeter (e.g. tip121) vibrate when actuated. In some embodiments, tip121of cooling element120includes a portion of the perimeter furthest from anchor160and undergoes the largest deflection during actuation of cooling element120. For clarity, only one tip121of cooling element120is labeled inFIG.1A. Also shown is pedestal190that connects orifice plate130to and offsets orifice plate130from heat-generating structure102. In some embodiments, pedestal190also thermally couples orifice plate130to heat-generating structure102. In some embodiments, an additional jet channel plate may be present and supported by pedestal190. Thus orifice plate130and/or such a jet channel plate may be part or all of a bottom plate supported by pedestal190. Thus, multiple plates and/or plate(s) having various structures may be used at the bottom plate for cooling system100.

FIG.1Adepicts cooling system100in a neutral position. Thus, cooling element120is shown as substantially flat. For in-phase operation, cooling element120is driven to vibrate between positions shown inFIGS.1C and1D. This vibrational motion draws fluid (e.g. air) into vent112, through chambers140and150and out orifices132at high speed and/or flow rates. For example, the speed at which the fluid impinges on heat-generating structure102may be at least thirty meters per second. In some embodiments, the fluid is driven by cooling element120toward heat-generating structure102at a speed of at least forty-five meters per second. In some embodiments, the fluid is driven toward heat-generating structure102by cooling element120at speeds of at least sixty meters per second. Other speeds may be possible in some embodiments. Cooling system100is also configured so that little or no fluid is drawn back into chamber140/150through orifices132by the vibrational motion of cooling element120.

Heat-generating structure102is desired to be cooled by cooling system100. In some embodiments, heat-generating structure102generates heat. For example, heat-generating structure may be an integrated circuit. In some embodiments, heat-generating structure102is desired to be cooled but does not generate heat itself. Heat-generating structure102may conduct heat (e.g. from a nearby object that generates heat). For example, heat-generating structure102might be a heat spreader or a vapor chamber. Thus, heat-generating structure102may include semiconductor component(s) including individual integrated circuit components such as processors, other integrated circuit(s) and/or chip package(s); sensor(s); optical device(s); one or more batteries; other component(s) of an electronic device such as a computing device; heat spreaders; heat pipes; other electronic component(s) and/or other device(s) desired to be cooled. In some embodiments, heat-generating structure102may be a thermally conductive part of a module containing cooling system100. For example, cooling system100may be affixed to heat-generating structure102, which may be coupled to another heat spreader, vapor chamber, integrated circuit, or other separate structure desired to be cooled.

The devices in which cooling system100is desired to be used may also have limited space in which to place a cooling system. For example, cooling system100may be used in computing devices. Such computing devices may include but are not limited to smartphones, tablet computers, laptop computers, tablets, two-in-one laptops, hand held gaming systems, digital cameras, virtual reality headsets, augmented reality headsets, mixed reality headsets and other devices that are thin. Cooling system100may be a micro-electro-mechanical system (MEMS) cooling system capable of residing within mobile computing devices and/or other devices having limited space in at least one dimension. For example, the total height, h3, of cooling system100(from the top of heat-generating structure102to the top of top plate110) may be less than 2 millimeters. In some embodiments, the total height of cooling system100is not more than 1.5 millimeters. In some embodiments, this total height is not more than 1.1 millimeters. In some embodiments, the total height does not exceed one millimeter. In some embodiments, the total height does not exceed two hundred and fifty micrometers. Similarly, the distance between the bottom of orifice plate130and the top of heat-generating structure102, y, may be small. In some embodiments, y is at least two hundred micrometers and not more than 1.2 millimeter. For example, y may be at least two hundred and fifty micrometers and not more than three hundred micrometers. In some embodiments, y is at least five hundred micrometers and not more than one millimeter. In some embodiments, y is at least two hundred micrometers and not more than three hundred micrometers. Thus, cooling system100is usable in computing devices and/or other devices having limited space in at least one dimension. However, nothing prevents the use of cooling system100in devices having fewer limitations on space and/or for purposes other than cooling. Although one cooling system100is shown (e.g. one cooling cell), multiple cooling systems100might be used in connection with heat-generating structure102. For example, a one or two-dimensional array of cooling cells might be utilized.

Cooling system100is in communication with a fluid used to cool heat-generating structure102. The fluid may be a gas or a liquid. For example, the fluid may be air. In some embodiments, the fluid includes fluid from outside of the device in which cooling system100resides (e.g. provided through external vents in the device). In some embodiments, the fluid circulates within the device in which cooling system100resides (e.g. in an enclosed device).

Cooling element120can be considered to divide the interior of active MEMS cooling system100into top chamber140and bottom chamber150. Top chamber140is formed by cooling element120, the sides, and top plate110. Bottom chamber150is formed by orifice plate130, the sides, cooling element120and anchor160. Top chamber140and bottom chamber150are connected at the periphery of cooling element120and together form chamber140/150(e.g. an interior chamber of cooling system100).

The size and configuration of top chamber140may be a function of the cell (cooling system100) dimensions, cooling element120motion, and the frequency of operation. Top chamber140has a height, h1. The height of top chamber140may be selected to provide sufficient pressure to drive the fluid to bottom chamber150and through orifices132at the desired flow rate and/or speed. Top chamber140is also sufficiently tall that cooling element120does not contact top plate110when actuated. In some embodiments, the height of top chamber140is at least fifty micrometers and not more than five hundred micrometers. In some embodiments, top chamber140has a height of at least two hundred and not more than three hundred micrometers.

Bottom chamber150has a height, h2. In some embodiments, the height of bottom chamber150is sufficient to accommodate the motion of cooling element120. Thus, no portion of cooling element120contacts orifice plate130during normal operation. Bottom chamber150is generally smaller than top chamber140and may aid in reducing the backflow of fluid into orifices132. In some embodiments, the height of bottom chamber150is the maximum deflection of cooling element120plus at least five micrometers and not more than ten micrometers. In some embodiments, the deflection of cooling element120(e.g. the deflection of tip121), z, has an amplitude of at least ten micrometers and not more than one hundred micrometers. In some such embodiments, the amplitude of deflection of cooling element120is at least ten micrometers and not more than sixty micrometers. However, the amplitude of deflection of cooling element120depends on factors such as the desired flow rate through cooling system100and the configuration of cooling system100. Thus, the height of bottom chamber150generally depends on the flow rate through and other components of cooling system100.

Top plate110includes vent112through which fluid may be drawn into cooling system100. Top vent112may have a size chosen based on the desired acoustic pressure in chamber140. For example, in some embodiments, the width, w, of vent112is at least five hundred micrometers and not more than one thousand micrometers. In some embodiments, the width of vent112is at least two hundred fifty micrometers and not more than two thousand micrometers. In the embodiment shown, vent112is a centrally located aperture in top plate110. In other embodiments, vent112may be located elsewhere. For example, vent112may be closer to one of the edges of top plate110. Vent112may have a circular, rectangular or other shaped footprint. Although a single vent112is shown, multiple vents might be used. For example, vents may be offset toward the edges of top chamber140or be located on the side(s) of top chamber140. Although top plate110is shown as substantially flat, in some embodiments trenches and/or other structures may be provided in top plate110to modify the configuration of top chamber140and/or the region above top plate110.

Anchor (support structure)160supports cooling element120at the central portion of cooling element120. Thus, at least part of the perimeter of cooling element120is unpinned and free to vibrate. In some embodiments, anchor160extends along a central axis of cooling element120(e.g. perpendicular to the page inFIGS.1A-1F). In such embodiments, portions of cooling element120that vibrate (e.g. including tip121) move in a cantilevered fashion. Thus, portions of cooling element120may move in a manner analogous to the wings of a butterfly (i.e. in phase) and/or analogous to a seesaw (i.e. out of phase). Thus, the portions of cooling element120that vibrate in a cantilevered fashion do so in phase in some embodiments and out of phase in other embodiments. In some embodiments, anchor160does not extend along an axis of cooling element120. In such embodiments, all portions of the perimeter of cooling element120are free to vibrate (e.g. analogous to a jellyfish). In the embodiment shown, anchor160supports cooling element120from the bottom of cooling element120. In other embodiments, anchor160may support cooling element120in another manner. For example, anchor160may support cooling element120from the top (e.g. cooling element120hangs from anchor160). In some embodiments, the width, a, of anchor160is at least 0.5 millimeters and not more than four millimeters. In some embodiments, the width of anchor160is at least two millimeters and not more than 2.5 millimeters. Anchor160may occupy at least ten percent and not more than fifty percent of cooling element120.

Cooling element120has a first side distal from heat-generating structure102and a second side proximate to heat-generating structure102. In the embodiment shown inFIGS.1A-1F, the first side of cooling element120is the top of cooling element120(closer to top plate110) and the second side is the bottom of cooling element120(closer to orifice plate130). Cooling element120is actuated to undergo vibrational motion as shown inFIGS.1A-IF. The vibrational motion of cooling element120drives fluid from the first side of cooling element120distal from heat-generating structure102(e.g. from top chamber140) to a second side of cooling element120proximate to heat-generating structure102(e.g. to bottom chamber150). The vibrational motion of cooling element120also draws fluid through vent112and into top chamber140; forces fluid from top chamber140to bottom chamber150; and drives fluid from bottom chamber150through orifices132of orifice plate130. Thus, cooling element120may be viewed as an actuator. Although described in the context of a single, continuous cooling element, in some embodiments, cooling element120may be formed by two (or more) cooling elements. Each of the cooling elements is depicted as one portion pinned (e.g. supported by support structure160) and an opposite portion unpinned. Thus, a single, centrally supported cooling element120may be formed by a combination of multiple cooling elements supported at an edge.

Cooling element120has a length, L, that depends upon the frequency at which cooling element120is desired to vibrate. In some embodiments, the length of cooling element120is at least four millimeters and not more than ten millimeters. In some such embodiments, cooling element120has a length of at least six millimeters and not more than eight millimeters. The depth of cooling element120(e.g. perpendicular to the plane shown inFIGS.1A-1F) may vary from one fourth of L through twice L. For example, cooling element120may have the same depth as length. The thickness, t, of cooling element120may vary based upon the configuration of cooling element120and/or the frequency at which cooling element120is desired to be actuated. In some embodiments, the cooling element thickness is at least two hundred micrometers and not more than three hundred and fifty micrometers for cooling element120having a length of eight millimeters and driven at a frequency of at least twenty kilohertz and not more than twenty-five kilohertz. The length, C, of chamber140/150is close to the length, L, of cooling element120. For example, in some embodiments, the distance, d, between the edge of cooling element120and the wall of chamber140/150is at least one hundred micrometers and not more than five hundred micrometers. In some embodiments, d is at least two hundred micrometers and not more than three hundred micrometers.

Cooling element120may be driven at a frequency that is at or near both the resonant frequency for an acoustic resonance of a pressure wave of the fluid in top chamber140and the resonant frequency for a structural resonance of cooling element120. The portion of cooling element120undergoing vibrational motion is driven at or near resonance (the “structural resonance”) of cooling element120. This portion of cooling element120undergoing vibration may be a cantilevered section in some embodiments. The frequency of vibration for structural resonance is termed the structural resonant frequency. Use of the structural resonant frequency in driving cooling element120reduces the power consumption of cooling system100. Cooling element120and top chamber140may also be configured such that this structural resonant frequency corresponds to a resonance in a pressure wave in the fluid being driven through top chamber140(the acoustic resonance of top chamber140). The frequency of such a pressure wave is termed the acoustic resonant frequency. At acoustic resonance, a node in pressure occurs near vent112and an antinode in pressure occurs near the periphery of cooling system100(e.g. near tip121of cooling element120and near the connection between top chamber140and bottom chamber150). The distance between these two regions is C/2. Thus, C/2=nλ/4, where λ is the acoustic wavelength for the fluid and n is odd (e.g. n=1, 3, 5, etc.). For the lowest order mode, C=λ/2. Because the length of chamber140(e.g. C) is close to the length of cooling element120, in some embodiments, it is also approximately true that L/2=nλ/4, where λ is the acoustic wavelength for the fluid and n is odd. Thus, the frequency at which cooling element120is driven, v, is at or near the structural resonant frequency for cooling element120. The frequency v is also at or near the acoustic resonant frequency for at least top chamber140. The acoustic resonant frequency of top chamber140generally varies less dramatically with parameters such as temperature and size than the structural resonant frequency of cooling element120. Consequently, in some embodiments, cooling element120may be driven at (or closer to) a structural resonant frequency rather than to the acoustic resonant frequency.

Orifice plate130has orifices132and cavities134therein. Although a particular number and distribution of orifices132and cavities134are shown, another number and/or another distribution may be used. Cavities134may be configured differently or may be omitted. In some embodiments, other cavities may be within flow chamber140/150or the jet channel between orifice plate130and heat-generating structure102. For example, cavities may be included in top plate110within flow chamber140/150or in the bottom of orifice plate130. A single orifice plate130is used for a single cooling system100. In other embodiments, multiple cooling systems100may share an orifice plate. For example, multiple cells100may be provided together in a desired configuration. In such embodiments, the cells100may be the same size and configuration or different size(s) and/or configuration(s). Orifices132are shown as having an axis oriented normal to a surface of heat-generating structure102. In other embodiments, the axis of one or more orifices132may be at another angle. For example, the angle of the axis may be selected from substantially zero degrees and a nonzero acute angle. Orifices132also have sidewalls that are substantially parallel to the normal to the surface of orifice plate130. In some embodiments, orifices may have sidewalls at a nonzero angle to the normal to the surface of orifice plate130. For example, orifices132may be cone-shaped. Further, although orifice place130is shown as substantially flat, in some embodiments, trenches and/or other structures may be provided in orifice plate130to modify the configuration of bottom chamber150and/or the region between orifice plate130and heat-generating structure102.

The size, distribution and locations of orifices132are chosen to control the flow rate of fluid driven to the surface of heat-generating structure102. The locations and configurations of orifices132may be configured to increase/maximize the fluid flow from bottom chamber150through orifices132to the jet channel (the region between the bottom of orifice plate130and the top of heat-generating structure102). The locations and configurations of orifices132may also be selected to reduce/minimize the suction flow (e.g. back flow) from the jet channel through orifices132. For example, the locations of orifices are desired to be sufficiently far from tip121that suction in the upstroke of cooling element120(tip121moves away from orifice plate130) that would pull fluid into bottom chamber150through orifices132is reduced. The locations of orifices are also desired to be sufficiently close to tip121that suction in the upstroke of cooling element120also allows a higher pressure from top chamber140to push fluid from top chamber140into bottom chamber150. In some embodiments, the ratio of the flow rate from top chamber140into bottom chamber150to the flow rate from the jet channel through orifices132in the upstroke (the “net flow ratio”) is greater than 2:1. In some embodiments, the net flow ratio is at least 85:15. In some embodiments, the net flow ratio is at least 90:10. In order to provide the desired pressure, flow rate, suction, and net flow ratio, orifices132are desired to be at least a distance, r1, from tip121and not more than a distance, r2, from tip121of cooling element120. In some embodiments, r1is at least one hundred micrometers (e.g. r1≥100 μm) and r2is not more than one millimeter (e.g. r2≤1000 μm). In some embodiments, orifices132are at least two hundred micrometers from tip121of cooling element120(e.g. r1≥200 μm). In some such embodiments, orifices132are at least three hundred micrometers from tip121of cooling element120(e.g. r1≥300 μm). In some embodiments, orifices132have a width, o, of at least one hundred micrometers and not more than five hundred micrometers. In some embodiments, orifices132have a width of at least two hundred micrometers and not more than three hundred micrometers. In some embodiments, the orifice separation, s, is at least one hundred micrometers and not more than one millimeter. In some such embodiments, the orifice separation is at least four hundred micrometers and not more than six hundred micrometers. In some embodiments, orifices132are also desired to occupy a particular fraction of the area of orifice plate130. For example, orifices132may cover at least five percent and not more than fifteen percent of the footprint of orifice plate130in order to achieve a desired flow rate of fluid through orifices132. In some embodiments, orifices132cover at least eight percent and not more than twelve percent of the footprint of orifice plate130.

In some embodiments, cooling element120is actuated using a piezoelectric. Thus, cooling element120may be a piezoelectric cooling element. Cooling element120may be driven by a piezoelectric that is mounted on or integrated into cooling element120. In some embodiments, cooling element120is driven in another manner including but not limited to providing a piezoelectric on another structure in cooling system100. Cooling element120and analogous cooling elements are referred to hereinafter as piezoelectric cooling elements though it is possible that a mechanism other than a piezoelectric might be used to drive the cooling element. In some embodiments, cooling element120includes a piezoelectric layer on substrate. The substrate may include or consist of stainless steel, a Ni alloy, Hastelloy, Al (e.g. an Al alloy), and/or Ti (e.g. a Ti alloy such as Ti6Al-4V). In some embodiments, a piezoelectric layer includes multiple sublayers formed as thin films on the substrate. In other embodiments, the piezoelectric layer may be a bulk layer affixed to the substrate. Such a piezoelectric cooling element120also includes electrodes used to activate the piezoelectric. The substrate functions as an electrode in some embodiments. In other embodiments, a bottom electrode may be provided between the substrate and the piezoelectric layer. Other layers including but not limited to seed, capping, passivation, or other layers might be included in the piezoelectric cooling element. Thus, cooling element120may be actuated using a piezoelectric.

In some embodiments, cooling system100includes chimneys (not shown) or other ducting. Such ducting provides a path for heated fluid to flow away from heat-generating structure102. In some embodiments, ducting returns fluid to the side of top plate110distal from heat-generating structure102. In some embodiments, ducting may instead direct fluid away from heat-generating structure102in a direction parallel to heat-generating structure102or perpendicular to heat-generating structure102but in the opposite direction (e.g. toward the bottom of the page). For a device in which fluid external to the device is used in cooling system100, the ducting may channel the heated fluid to a vent. In such embodiments, additional fluid may be provided from an inlet vent. In embodiments, in which the device is enclosed, the ducting may provide a circuitous path back to the region near vent112and distal from heat-generating structure102. Such a path allows for the fluid to dissipate heat before being reused to cool heat-generating structure102. In other embodiments, ducting may be omitted or configured in another manner. Thus, the fluid is allowed to carry away heat from heat-generating structure102.

Operation of cooling system100is described in the context ofFIGS.1A-1F. Although described in the context of particular pressures, gap sizes, and timing of flow, operation of cooling system100is not dependent upon the explanation herein.FIGS.1C-1Ddepict in-phase operation of cooling system100. Referring toFIG.1C, cooling element120has been actuated so that its tip121moves away from top plate110.FIG.1Ccan thus be considered to depict the end of a down stroke of cooling element120. Because of the vibrational motion of cooling element120, gap152for bottom chamber150has decreased in size and is shown as gap152B. Conversely, gap142for top chamber140has increased in size and is shown as gap142B. During the down stroke, a lower (e.g. minimum) pressure is developed at the periphery when cooling element120is at the neutral position. As the down stroke continues, bottom chamber150decreases in size and top chamber140increases in size as shown inFIG.1C. Thus, fluid is driven out of orifices132in a direction that is at or near perpendicular to the surface of orifice plate130and/or the top surface of heat-generating structure102. The fluid is driven from orifices132toward heat-generating structure102at a high speed, for example in excess of thirty-five meters per second. In some embodiments, the fluid then travels along the surface of heat-generating structure102and toward the periphery of heat-generating structure102, where the pressure is lower than near orifices132. Also in the down stroke, top chamber140increases in size and a lower pressure is present in top chamber140. As a result, fluid is drawn into top chamber140through vent112. The motion of the fluid into vent112, through orifices132, and along the surface of heat-generating structure102is shown by unlabeled arrows inFIG.1C.

Cooling element120is also actuated so that tip121moves away from heat-generating structure102and toward top plate110.FIG.1Dcan thus be considered to depict the end of an up stroke of cooling element120. Because of the motion of cooling element120, gap142has decreased in size and is shown as gap142C. Gap152has increased in size and is shown as gap152C. During the upstroke, a higher (e.g. maximum) pressure is developed at the periphery when cooling element120is at the neutral position. As the upstroke continues, bottom chamber150increases in size and top chamber140decreases in size as shown inFIG.1D. Thus, the fluid is driven from top chamber140(e.g. the periphery of chamber140/150) to bottom chamber150. Thus, when tip121of cooling element120moves up, top chamber140serves as a nozzle for the entering fluid to speed up and be driven towards bottom chamber150. The motion of the fluid into bottom chamber150is shown by unlabeled arrows inFIG.1D. The location and configuration of cooling element120and orifices132are selected to reduce suction and, therefore, back flow of fluid from the jet channel (between heat-generating structure102and orifice plate130) into orifices132during the upstroke. Thus, cooling system100is able to drive fluid from top chamber140to bottom chamber150without an undue amount of backflow of heated fluid from the jet channel entering bottom chamber150. Moreover, cooling system100may operate such that fluid is drawn in through vent112and driven out through orifices132without cooling element120contacting top plate110or orifice plate130. Thus, pressures are developed within chambers140and150that effectively open and close vent112and orifices132such that fluid is driven through cooling system100as described herein.

The motion between the positions shown inFIGS.1C and1Dis repeated. Thus, cooling element120undergoes vibrational motion indicated inFIGS.1A-1D, drawing fluid through vent112from the distal side of top plate110into top chamber140; transferring fluid from top chamber140to bottom chamber150; and pushing the fluid through orifices132and toward heat-generating structure102. As discussed above, cooling element120is driven to vibrate at or near the structural resonant frequency of cooling element120. Further, the structural resonant frequency of cooling element120is configured to align with the acoustic resonance of the chamber140/150. The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element120may be at frequencies from 15 kHz through 30 kHz. In some embodiments, cooling element120vibrates at a frequency/frequencies of at least 20 kHz and not more than 30 kHz. The structural resonant frequency of cooling element120is within ten percent of the acoustic resonant frequency of cooling system100. In some embodiments, the structural resonant frequency of cooling element120is within five percent of the acoustic resonant frequency of cooling system100. In some embodiments, the structural resonant frequency of cooling element120is within three percent of the acoustic resonant frequency of cooling system100. Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used.

Fluid driven toward heat-generating structure102may move substantially normal (perpendicular) to the top surface of heat-generating structure102. In some embodiments, the fluid motion may have a nonzero acute angle with respect to the normal to the top surface of heat-generating structure102. In either case, the fluid may thin and/or form apertures in the boundary layer of fluid at heat-generating structure102. As a result, transfer of heat from heat-generating structure102may be improved. The fluid deflects off of heat-generating structure102, traveling along the surface of heat-generating structure102. In some embodiments, the fluid moves in a direction substantially parallel to the top of heat-generating structure102. Thus, heat from heat-generating structure102may be extracted by the fluid. The fluid may exit the region between orifice plate130and heat-generating structure102at the edges of cooling system100. Chimneys or other ducting (not shown) at the edges of cooling system100allow fluid to be carried away from heat-generating structure102. In other embodiments, heated fluid may be transferred further from heat-generating structure102in another manner. The fluid may exchange the heat transferred from heat-generating structure102to another structure or to the ambient environment. Thus, fluid at the distal side of top plate110may remain relatively cool, allowing for the additional extraction of heat. In some embodiments, fluid is circulated, returning to the distal side of top plate110after cooling. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element120. As a result, heat-generating structure102may be cooled.

FIGS.1E-IF depict an embodiment of active MEMS cooling system100including centrally anchored cooling element120in which the cooling element is driven out-of-phase. More specifically, sections of cooling element120on opposite sides of anchor160(and thus on opposite sides of the central region of cooling element120that is supported by anchor160) are driven to vibrate out-of-phase. In some embodiments, sections of cooling element120on opposite sides of anchor160are driven at or near one hundred and eighty degrees out-of-phase. Thus, one section of cooling element120vibrates toward top plate110, while the other section of cooling element120vibrates toward orifice plate130/heat-generating structure102. Movement of a section of cooling element120toward top plate110(an upstroke) drives fluid in top chamber140to bottom chamber150on that side of anchor160. Movement of a section of cooling element120toward orifice plate130drives fluid through orifices132and toward heat-generating structure102. Thus, fluid traveling at high speeds (e.g. speeds described with respect to in-phase operation) is alternately driven out of orifices132on opposing sides of anchor160. Because fluid is driven through orifices132at high speeds, cooling system100may be viewed as a MEMs jet. The movement of fluid is shown by unlabeled arrows inFIGS.1E and1F. The motion between the positions shown inFIGS.1E and1Fis repeated. Thus, cooling element120undergoes vibrational motion indicated inFIGS.1A,1E, and IF, alternately drawing fluid through vent112from the distal side of top plate110into top chamber140for each side of cooling element120; transferring fluid from each side of top chamber140to the corresponding side of bottom chamber150; and pushing the fluid through orifices132on each side of anchor160and toward heat-generating structure102. As discussed above, cooling element120is driven to vibrate at or near the structural resonant frequency of cooling element120. Further, the structural resonant frequency of cooling element120is configured to align with the acoustic resonance of the chamber140/150. The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element120may be at the frequencies described for in-phase vibration. The structural resonant frequency of cooling element120is within ten percent of the acoustic resonant frequency of cooling system100. In some embodiments, the structural resonant frequency of cooling element120is within five percent of the acoustic resonant frequency of cooling system100. In some embodiments, the structural resonant frequency of cooling element120is within three percent of the acoustic resonant frequency of cooling system100. Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used.

Fluid driven toward heat-generating structure102for out-of-phase vibration may move substantially normal (perpendicular) to the top surface of heat-generating structure102, in a manner analogous to that described above for in-phase operation. Similarly, chimneys or other ducting (not shown) at the edges of cooling system100allow fluid to be carried away from heat-generating structure102. In other embodiments, heated fluid may be transferred further from heat-generating structure102in another manner. The fluid may exchange the heat transferred from heat-generating structure102to another structure or to the ambient environment. Thus, fluid at the distal side of top plate110may remain relatively cool, allowing for the additional extraction of heat. In some embodiments, fluid is circulated, returning to the distal side of top plate110after cooling. In other embodiments, heated fluid is carried away and replaced by new fluid at the distal side of cooling element120. As a result, heat-generating structure102may be cooled.

Although shown in the context of a uniform cooling element inFIGS.1A-IF, cooling system100may utilize cooling elements having different shapes.FIG.1Gdepicts an embodiment of engineered cooling element120′ having a tailored geometry and usable in a cooling system such as cooling system100. Cooling element120′ includes an anchored region122and cantilevered arms123. Anchored region122is supported (e.g. held in place) in cooling system100by anchor160. Cantilevered arms123undergo vibrational motion in response to cooling element120′ being actuated. Each cantilevered arm123includes step region124, extension region126and outer region128. In the embodiment shown inFIG.1G, anchored region122is centrally located. Step region124extends outward from anchored region122. Extension region126extends outward from step region124. Outer region128extends outward from extension region126. In other embodiments, anchored region122may be at one edge of the actuator and outer region128at the opposing edge. In such embodiments, the actuator is edge anchored.

Extension region126has a thickness (extension thickness) that is less than the thickness of step region124(step thickness) and less than the thickness of outer region128(outer thickness). Thus, extension region126may be viewed as recessed. Extension region126may also be seen as providing a larger bottom chamber150. In some embodiments, the outer thickness of outer region128is the same as the step thickness of step region124. In some embodiments, the outer thickness of outer region128is different from the step thickness of step region124. In some embodiments, outer region128and step region124each have a thickness of at least three hundred twenty micrometers and not more than three hundred and sixty micrometers. In some embodiments, the outer thickness is at least fifty micrometers and not more than two hundred micrometers thicker than the extension thickness. Stated differently, the step (difference in step thickness and extension thickness) is at least fifty micrometers and not more than two hundred micrometers. In some embodiments, the outer step (difference in outer thickness and extension thickness) is at least fifty micrometers and not more than two hundred micrometers. Outer region128may have a width, o, of at least one hundred micrometers and not more than three hundred micrometers. Extension region126has a length, e, extending outward from the step region of at least 0.5 millimeter and not more than 1.5 millimeters in some embodiments. In some embodiments, outer region128has a higher mass per unit length in the direction from anchored region122than extension region126. This difference in mass may be due to the larger size of outer region128, a difference in density between portions of cooling element120, and/or another mechanism.

Use of engineered cooling element120′ may further improve efficiency of cooling system100. Extension region126is thinner than step region124and outer region128. This results in a cavity in the bottom of cooling element120′ corresponding to extension region126. The presence of this cavity aids in improving the efficiency of cooling system100. Each cantilevered arm123vibrates towards top plate110in an upstroke and away from top plate110in a downstroke. When a cantilevered arm123moves toward top plate110, higher pressure fluid in top chamber140resists the motion of cantilevered arm123. Furthermore, suction in bottom chamber150also resists the upward motion of cantilevered arm123during the upstroke. In the downstroke of cantilevered arm123, increased pressure in the bottom chamber150and suction in top chamber140resist the downward motion of cantilevered arm123. However, the presence of the cavity in cantilevered arm123corresponding to extension region126mitigates the suction in bottom chamber150during an upstroke. The cavity also reduces the increase in pressure in bottom chamber150during a downstroke. Because the suction and pressure increase are reduced in magnitude, cantilevered arms123may more readily move through the fluid. This may be achieved while substantially maintaining a higher pressure in top chamber140, which drives the fluid flow through cooling system100. Moreover, the presence of outer region128may improve the ability of cantilevered arm123to move through the fluid being driven through cooling system100. Outer region128has a higher mass per unit length and thus a higher momentum. Consequently, outer region128may improve the ability of cantilevered arms123to move through the fluid being driven through cooling system100. The magnitude of the deflection of cantilevered arm123may also be increased. These benefits may be achieved while maintaining the stiffness of cantilevered arms123through the use of thicker step region124. Further, the larger thickness of outer region128may aid in pinching off flow at the bottom of a downstroke. Thus, the ability of cooling element120′ to provide a valve preventing backflow through orifices132may be improved. Thus, performance of cooling system100employing cooling element120′ may be improved.

Further, cooling elements used in cooling system100may have different structures and/or be mounted differently than depicted inFIGS.1A-1G. In some embodiments, the cooling element may have rounded corners and/or rounded ends but still be anchored along a central axis such that cantilevered arms vibrate. The cooling element may be anchored only at its central region such that the regions surrounding the anchor vibrate in a manner analogous to a jellyfish or the opening/closing of an umbrella. In some such embodiments, the cooling element may be circular or elliptical in shape. In some embodiments, the anchor may include apertures through which fluid may flow. Such an anchor may be utilized for the cooling element being anchored at its top (e.g. to the top plate). Although not indicated inFIGS.1A-1G, the piezoelectric utilized in driving the cooling element may have various locations and/or configurations. For example, the piezoelectric may be embedded in the cooling element, affixed to one side of the cooling element (or cantilevered arm(s)), may occupy some or all of the cantilevered arms, and/or may have a location that is close to or distal from the anchored region. In some embodiments, cooling elements that are not centrally anchored may be used. For example, a pair of cooling elements that have offset apertures, that are anchored at their ends (or all edges), and which vibrate out of phase may be used. Thus, various additional configurations of cooling element120and/or120′, anchor160, and/or other portions of cooling system100may be used.

Using the cooling system100actuated for in-phase vibration or out-of-phase vibration of cooling element120and/or120′, fluid drawn in through vent112and driven through orifices132may efficiently dissipate heat from heat-generating structure102. Because fluid impinges upon the heat-generating structure with sufficient speed (e.g. at least thirty meters per second) and in some embodiments substantially normal to the heat-generating structure, the boundary layer of fluid at the heat-generating structure may be thinned and/or partially removed. Consequently, heat transfer between heat-generating structure102and the moving fluid is improved. Because the heat-generating structure is more efficiently cooled, the corresponding integrated circuit may be run at higher speed and/or power for longer times. For example, if the heat-generating structure corresponds to a high-speed processor, such a processor may be run for longer times before throttling. Thus, performance of a device utilizing cooling system100may be improved. Further, cooling system100may be a MEMS device. Consequently, cooling systems100may be suitable for use in smaller and/or mobile devices, such as smart phones, other mobile phones, virtual reality headsets, tablets, two-in-one computers, wearables and handheld games, in which limited space is available. Performance of such devices may thus be improved. Because cooling element120/120′ may be vibrated at frequencies of 15 kHz or more, users may not hear any noise associated with actuation of cooling elements. If driven at or near structural and/or acoustic resonant frequencies, the power used in operating cooling systems may be significantly reduced. Cooling element120/120′ does not physically contact top plate110or orifice plate130during vibration. Thus, resonance of cooling element120/120′ may be more readily maintained. More specifically, physical contact between cooling element120/120′ and other structures disturbs the resonance conditions for cooling element120/120′. Disturbing these conditions may drive cooling element120/120′ out of resonance. Thus, additional power would need to be used to maintain actuation of cooling element120/120′. Further, the flow of fluid driven by cooling element120/120′ may decrease. These issues are avoided through the use of pressure differentials and fluid flow as discussed above. The benefits of improved, quiet cooling may be achieved with limited additional power. Further, out-of-phase vibration of cooling element120/120′ allows the position of the center of mass of cooling element120/120′ to remain more stable. Although a torque is exerted on cooling element120/120′, the force due to the motion of the center of mass is reduced or eliminated. As a result, vibrations due to the motion of cooling element120/120′ may be reduced. Moreover, efficiency of cooling system100may be improved through the use of out-of-phase vibrational motion for the two sides of cooling element120/120′. Consequently, performance of devices incorporating the cooling system100may be improved. Further, cooling system100may be usable in other applications (e.g. with or without heat-generating structure102) in which high fluid flows and/or velocities are desired.

FIGS.2A-2Bdepict an embodiment of active MEMS cooling system200including a top centrally anchored cooling element.FIG.2Adepicts a side view of cooling system200in a neutral position.FIG.2Bdepicts a top view of cooling system200.FIGS.2A-2Bare not to scale. For simplicity, only portions of cooling system200are shown. Referring toFIGS.2A-2B, cooling system200is analogous to cooling system100. Consequently, analogous components have similar labels. For example, cooling system200is used in conjunction with heat-generating structure202, which is analogous to heat-generating structure102.

Cooling system200includes top plate210having vents212, cooling element220having tip221, orifice plate230including orifices232, top chamber240having a gap, bottom chamber250having a gap, flow chamber240/250, and anchor (i.e. support structure)260that are analogous to top plate110having vent112, cooling element120having tip121, orifice plate130including orifices132, top chamber140having gap142, bottom chamber150having gap152, flow chamber140/150, and anchor (i.e. support structure)160, respectively. Also shown is pedestal290that is analogous to pedestal190. Thus, cooling element220is centrally supported by anchor260such that at least a portion of the perimeter of cooling element220is free to vibrate. In some embodiments, anchor260extends along the axis of cooling element220. In other embodiments, anchor260is only near the center portion of cooling element220. Although not explicitly labeled inFIGS.2A and2B, cooling element220includes an anchored region and cantilevered arms including step region, extension region, and outer regions analogous to anchored region122, cantilevered arms123, step region124, extension region126, and outer region128of cooling element120′. In some embodiments, cantilevered arms of cooling element220are driven in-phase. In some embodiments, cantilevered arms of cooling element220are driven out-of-phase. In some embodiments, a simple cooling element, such as cooling element120, may be used.

Anchor260supports cooling element220from above. Thus, cooling element220is suspended from anchor260. Anchor260is suspended from top plate210. Top plate210includes vent213. Vents212on the sides of anchor260provide a path for fluid to flow into sides of chamber240.

As discussed above with respect to cooling system100, cooling element220may be driven to vibrate at or near the structural resonant frequency of cooling element220. Further, the structural resonant frequency of cooling element220may be configured to align with the acoustic resonance of chamber240/250. The structural and acoustic resonant frequencies are generally chosen to be in the ultrasonic range. For example, the vibrational motion of cooling element220may be at the frequencies described with respect to cooling system100. Consequently, efficiency and flow rate may be enhanced. However, other frequencies may be used.

Cooling system200operates in an analogous manner to cooling system100. Cooling system200thus shares the benefits of cooling system100. Thus, performance of a device employing cooling system200may be improved. In addition, suspending cooling element220from anchor260may further enhance performance. In particular, vibrations in cooling system200that may affect other cooling cells (not shown) may be reduced. For example, less vibration may be induced in top plate210due to the motion of cooling element220. Consequently, cross talk between cooling system200and other cooling systems (e.g. other cells) or other portions of the device incorporating cooling system200may be reduced. Thus, performance may be further enhanced.

FIGS.3A-3Edepict an embodiment of active MEMS cooling system300including multiple cooling cells configured as a module termed a tile, or array.FIG.3Adepicts a perspective view with cover306and spout380removed.FIG.3Bdepicts active MEMS cooling system300with cover306and spout380.FIG.3Cdepicts a side view of a portion of cooling system300.FIGS.3D-3Edepict side views of cooling system300.FIGS.3A-3Eare not to scale. Cooling system300includes four cooling cells301A,301B,301C and301D (collectively or generically301), which are analogous to one or more of cooling systems described herein. More specifically, cooling cells301are analogous to cooling system100and/or200. Tile300thus includes four cooling cells301(i.e. four MEMS jets). Although four cooling cells301in a 2×2 configuration are shown, in some embodiments another number and/or another configuration of cooling cells301might be employed. In the embodiment shown, cooling cells301include shared top plate310having apertures312, cooling elements320, shared orifice plate330including orifices332, top chambers340, bottom chambers350, anchors (support structures)360, and pedestals390that are analogous to top plate110having apertures112, cooling element120, orifice plate130having orifices132, top chamber140, bottom chamber150, anchor160, and pedestal190. In some embodiments, cooling cells301may be fabricated together and separated, for example by cutting through top plate310, side walls between cooling cells301, and orifice plate330. Thus, although described in the context of a shared top plate310and shared orifice plate330, after fabrication cooling cells301may be separated. In some embodiments, tabs (not shown) and/or other structures such as anchors360may connect cooling cells301. Further, tile300includes heat-generating structure (termed a heat spreader hereinafter)302(e.g. a heat spreader, a heat spreader, and/or other structure) that also has sidewalls, or fencing, in the embodiment shown. Cover306having apertures therein is also shown. In some embodiments, a dust filter (not shown) may be provided for the apertures. In such embodiments, dust may be less likely to reach the interior of cooling system300. In some embodiments, a water tight, air porous membrane may be provided for the apertures. Heat spreader302. cover306, and spout380may be part of an integrated tile300as shown or may be separate from tile300in other embodiments. Heat spreader302and cover plate306may direct fluid flow outside of cooling cells301, provide mechanical stability, and/or provide protection. Electrical connection to cooling cells301is provided via flex connector383(not shown inFIGS.3C-3E) which may house drive electronics385. Cooling elements320are driven out-of-phase (i.e. in a manner analogous to a seesaw). Further, as can be seen in FIGS.FIGS.3D-3Ecooling element320in one cell is driven out-of-phase with cooling element(s)320in adjacent cell(s). Cooling element320in cell301C is out-of-phase with cooling element320in cell301D. InFIGS.3D-3E, cooling elements320in a column are driven out-of-phase. Thus, cooling element320in cell301A is out-of-phase with cooling element320in cell301C. Similarly, cooling element320in cell301B is out-of-phase with cooling element320in cell301D. By driving cooling elements320out-of-phase, vibrations in cooling system300may be reduced. Cooling elements320may be driven in another manner in some embodiments.

Cooling system300also includes spout380having dissipation region386therein. Spout380includes a housing having bottom382and top384, entrance381and exit386. Entrance381is fluidically coupled with orifices332(i.e. egresses from flow chamber340/450). The direction of fluid flow from flow chamber340/450may be seen by the unlabeled arrows inFIG.3C. Spout380operates to smooth pulsations in the pressure waves generated by cooling elements320. Because cooling elements320vibrate, the flow of fluid pulsates. Thus, the pressure of the fluid also pulsates between higher and lower pressures. Flow may also exit orifices332and travel through the jet channel in pulses. The pressure within flow chamber340/350and the jet channel is higher than the pressure of the ambient region. The fluid exits the jet channel and enters spout380at entrance381. The fluid travels through dissipation region386and to exit388. The pulsating pressure in the fluid is dissipated in dissipation region384. Stated differently, the pulsating pressure way may be attenuated such that the pressure equilibrates and approaches (or reaches) the ambient pressure of the ambient region outside of system300. In some embodiments, therefore, the pressure of the fluid at exit388of spout380matches or substantially the boundary conditions for the pressure of the ambient.

Cooling cells301of cooling system300function in an analogous manner to cooling system(s)100,200, and/or an analogous cooling system. Consequently, the benefits described herein may be shared by cooling system300. Because cooling elements in nearby cells are driven out-of-phase, vibrations in cooling system300may be reduced. Because multiple cooling cells301are used, cooling system300may enjoy enhanced cooling capabilities. Further, multiples of individual cooling cells301and/or cooling system300may be combined in various fashions to obtain the desired footprint of cooling cells.

Systems100,200, and300are generally desired to be integrated into devices, such as computing devices, for which cooling is desired. In addition to space and other constraints, cooling systems such as systems100,200, and300are desired to maintain a higher rate of fluid flow, efficiently transfer heat from the heat-generating structure, and reduce the amount of heat transferred back into the device from the cooling systems. Thus, additional control of the fluid flow through the cooling system and the devices in which such systems are incorporated is desired.

Although described as cooling systems, systems100,200and/or300may be considered to be differential pressure devices100,200and/or300. Similarly, cooling elements120/120′,220, and/or320may be considered actuators. As such, the term differential pressure device and cooling system may be used interchangeably herein. Similarly, actuator and cooling element may be used interchangeably. Vibrational motion of actuators120,120′,220, and/or320drive flow through differential pressure devices100,200, and/or300. As a result, pressure differentials are generated not only within the systems100,200, and/or300, but also in the surrounding areas. Thus, flow may be driven through a larger region based on the pressure differentials created by devices100,200, and/or300.FIGS.4-13Bdepict various embodiments of computing devices including heat transfer structures that incorporate one or more of differential pressure devices100,200, and/or300and/or an analogous device.

FIG.4depicts an embodiment of computing device400incorporating heat transfer structure410. Computing device400may be a notebook, laptop, smart phone, gaming device, or other thin computing device. Computing device400may include bottom cover402and top cover404. Top cover404may include a keyboard or display. Alternatively, bottom cover402may include a keyboard or display. Because computing device400is thin, computing device400has a dimension (i.e. a thickness) that is significantly less than the remaining dimensions. For example, the interior of computing device400in which heat transfer structure410resides may have a height, t1, of not more than eight millimeters. In some embodiments, height t1of the interior of computing device400may be not more than five millimeters. In some embodiments, t1is not more than 3.5 millimeters. In some such embodiments, t1is not more than three millimeters. In some embodiments, t1is at least two millimeters. For example, t1may be at least 3.2 millimeters and not more than 3.5 millimeters. The interior of computing device400in which heat transfer structure410resides may be considered to be a chamber. The chamber, and thus computing device400, has ingress401and egress405. Fluid (e.g. air) from exterior to computing device400is drawn into the chamber via ingress401and expelled via egress405. In addition to heat transfer device410, computing device400includes heat-generating structure430and circuit board440. Heat-generating structure430may be one or more processors or other integrated circuit(s) mounted on circuit board440. For simplicity, heat-generating structure430is referred to hereinafter as processor(s)430. Other integrated circuits, such as dynamic random access memory (DRAM) modules (not shown) or other electrical components (not shown) may be mounted on circuit board440.

Heat transfer device410includes heat spreader412, fan structure415, and active MEMS differential pressure device420. Heat spreader412is thermally coupled to processor(s)430, for example via thermal conduction. Thus, heat spreader412is in physical contact with processor(s)430. Heat generated by processor(s)430is conducted to heat spreader412. In some embodiments, heat spreader412is a vapor chamber. In some embodiments, heat spreader412may have another structure.

Fin structure415is thermally coupled to heat spreader412, for example via thermal conduction. Thus, heat from heat spreader412is transferred to fin structure415. Fin structure415includes multiple fins (indicated inFIG.415by horizontal lines). Fins may be horizontal, vertical, or oriented in another manner. Fins increase the surface area exposed to the fluid (e.g. air) drawn through heat transfer device410. Consequently, heat may be more efficiently transferred from fin structure415to the fluid than from heat spreader412to the fluid. The fins of fin structure415are densely packed. In some embodiments, the fins of fin structure415are spaced apart (e.g. the pitch or the distance between a surface of one fin and the surface of an adjacent fin) by not more than two hundred and fifty micrometers. In some embodiments, the fins of fin structure415are not more than one hundred and fifty micrometers apart. In some embodiment, the fins of fin structure415are not more than one hundred micrometers apart. In some such embodiments, the fins are at least fifty micrometers apart.

Differential pressure device420is a differential pressure device analogous to cooling systems100,200, and/or300. In some embodiments, differential pressure device420is most analogous to cooling system300in that multiple cooling cells are present. In some embodiments, differential pressure device420includes three tiles300(i.e. twelve cooling cells301). Differential pressure device420may have a bottom plate analogous to bottom plate302and a cover analogous to cover306. The bottom plate of differential pressure device420is coupled to top cover404. In some embodiments, a thin insulator is between the bottom plate of differential pressure device420and top cover404. This may aid in controlling the skin temperature of computing device400, while allowing for cooling of processor(s)430. As indicated inFIG.4, in some embodiments, the height, t1of the interior of computing device400may be sufficiently small that differential pressure device420is not connected to heat spreader412. Stated differently, heat from heat spreader412may not be transferred to differential pressure device420via thermal conduction.

Differential pressure device420provides a pressure differential that drives fluid flow through heat transfer structure410and, therefore, computing device400. Stated differently, differential pressure device420generates a region of low pressure within computing device400that draws fluid through heat transfer structure410. In some embodiments, this region is proximate to the entrance to differential pressure device420. For example, the region of low pressure may be between fin structure415and differential pressure device420. The direction that fluid (e.g. air) flows through computing device400is indicated by the unlabeled arrows inFIG.4. Fluid is drawn in via ingress401, flows along the gap between heat spreader412and back cover402, around (or through apertures in) heat spreader412and through fin structure415. Heat transfer device410is configured such that the fluid is driven through fin structure415. For example, in the embodiment shown, structure414blocks the flow of the fluid in the gap between heat spreader412and bottom cover402. Thus, most or all of the fluid drawn in through ingress401passes through or around fin structure415and to differential pressure device420. Fluid flows between and along the surfaces of the fins of fin structure415, into differential pressure device420, out of differential pressure device420and out of egress405.

The fluid flow is used to transfer heat from processor(s)430. Heat is transferred from processor(s)430to heat spreader412. Some heat may be transferred from heat spreader412to the fluid passing the surfaces of heat spreader412. However, most or all of the heat is transferred from heat spreader412to fin structure415via thermal conduction. Because of the large surface area of fin structure415, heat is transferred efficiently from fin structure415to the fluid. Heated fluid from fin structure415is drawn into differential pressure device420due to the vibrational motion of actuators therein. In contrast to the discussion with respect to cooling systems100,200, and300, most if not all of the heat transfer to the fluid takes place before the fluid enters differential pressure device420(i.e. primarily via fins415). Fluid, and thus heat, is ejected from differential pressure device420and out of computing device400. In some embodiments, the fluid flowing due to differential pressure device420is such that greater than 2 W of heat is ejected from egress405. In some embodiments, at least 6 W of heat is ejected from the egress405. This may occur where differential pressure device420includes three tiles300. Thus, in this context, differential pressure device420functions to cool processor430by generating a pressure difference with the chamber housing heat transfer structure410that draws fluid through computing device400and, therefore, through fin structure415.

In some embodiments, the heat transfer structure410restricts flow driven by differential pressure device420such that a pressure differential of at least a one hundred Pascals per cubic feet per minute (cfm) (100 Pa/cfm) is within the chamber. In some such embodiments, the pressure differential within the chamber is at least four hundred pascals per cfm (400 Pa/cfm). The pressure differential may be at least five hundred pascals per cfm (500 Pa/cfm). In some embodiments, the majority of the flow restriction is due to fin structure415. Thus, differential pressure device420is configured such that this pressure differential can be achieved. For example, if a flow of 0.5 cfm is provided by differential pressure device420, a pressure difference of 200 Pa, 400 Pa, or 1000 Pa is provided. This pressure difference is primarily across fin structure415in some embodiments.

For example, in some embodiments, differential pressure device420is configured to have a backpressure of at least 1500 Pa. In some embodiments, the backpressure of differential pressure device420is at least 1600 Pa. In some embodiment, the backpressure of differential pressure device420is at least 1700 Pa and not more than 1800 Pa (e.g. nominally 1750 Pa). As used herein, the backpressure of differential pressure device420indicates the pressure at which differential pressure device420can no longer drive flow. The high backpressures described herein may be achieved for differential pressure device420utilizes one or more tiles300including four cells. In some embodiments, a tile300has a backpressure of nominally 1750 Pa (e.g. at least 1700 and not more than 1800 Pa) and provides a flow of at least 0.15 cubic feet per minute (cfm). In some such embodiments, the flow provided is at least 0.2 cfm for tile300. In some embodiments, differential pressure device420includes three such tiles300. Thus, differential pressure device420may provide a flow rate of nominally 0.5 cfm while maintaining the pressure difference of 200 Pa or 400 Pa within the chamber containing heat transfer device410(and in some embodiments across fin structure415). Further, because the backpressure of differential pressure device420may be high, a pressure difference of 200 Pa or 400 Pa within the chamber does not significantly reduce the flow. For example, for 200 Pa of resistance to flow by fin structure415and the remainder of heat transfer structure410(i.e. a pressure difference of at least 200 Pa that is to be provided by differential pressure device420), the fluid flow provided by differential pressure device420may be reduced by approximately eleven percent from the maximum flow.

In addition to providing a high pressure and a meaningful fluid flow, differential pressure device420has a low profile. In some embodiments, differential pressure device420may have a total height (h1) of not more than 3.5 millimeters. In some embodiments, differential pressure device420may have a total height of not more than 3 millimeters. In some embodiments, the total height, h1, is not more than 2.8 millimeters. In some embodiments, the height of differential pressure device420is at least two millimeters. Moreover, the low profile of differential pressure device420allows for a gap having height g1to be maintained between differential pressure device420and bottom cover402. In some embodiments, g1is at least 0.3 millimeters. In some embodiments, g1is at least 0.4 millimeters. In some such embodiments, g1is at least 0.5 millimeters. Further, g1may be not more than 0.7 millimeters. Because such a gap is between differential pressure device420and bottom cover402, differential pressure device420does not unduly heat bottom cover402. A similar gap is between heat spreader412and bottom cover402. The insulating properties of such gaps are further improved because moving fluid (as opposed to stagnant fluid) is driven through these gaps. As a result, the temperature of bottom cover402may be managed. For example, hot spots may be avoided and the skin temperature (i.e. the external temperature) of bottom cover402may remain within tolerances. For example, the skin temperature of bottom cover may remain not more than forty-five degrees Celsius. In some such embodiments, the skin temperature of bottom cover does not exceed forty degrees Celsius. Although differential pressure device420is coupled to top cover404, an insulator may be interposed between top cover404and differential pressure device420. Thus, top cover404may also have a skin temperature in the same range as that of bottom cover402.

Computing system400may have improved performance. Fin structure415is thermally coupled via conduction to heat spreader412and, therefore, processor(s)430. Thus, heat is efficiently transferred from processor(s)430to fin structure415. Stated differently, the temperature drop between processor(s)430and fin structure415may be small or negligible. Fin structure415provides a significant surface area that can be cooled via fluid flow passing through its fins. Thus, heat may be efficiently transferred from fin structure415to the fluid. Differential pressure device420may provide a significant fluid flow (e.g. at least 0.15 cfm, at least 0.2 cfm, at least 0.4 cfm, or at least 0.5 cfm) through heat transfer structure410despite a high pressure differential for fin structure415. For example, in some embodiments (e.g. where differential pressure device420includes three tiles300), sufficient cooling may be provided that processor430can be run such that processor430consumes at least thirty percent to sixty percent more power while maintaining the desired skin temperature of covers402and/or404. Stated differently, a higher die temperature may be maintained (and performance of processor(s)430improved) for a given skin temperature of computing device400. This cooling is achieved without differential pressure device420being thermally coupled to heat spreader412via conduction. Although heated fluid is ejected from egress405, in some embodiments, this fluid is traveling at a sufficient speed that air in the surrounding environment is entrained. This cooler air rapidly mixes with the heated air from differential pressure device420. Thus, the temperature of the region more than 1-3 millimeters from egress405is not hot enough to burn a user of computing device400. Moreover, the exit (e.g. spout) of differential pressure device420is at or near egress405of computing system. For example, the exit may be flush with or within 1-4 millimeters of the outside of the casing of computing device400. This region may also be sealed, for example using aerogel. Hot fluid exiting differential pressure device420is not recirculated within computing device400. Consequently, cooling efficiency may be improved.

Further, heat transfer structure410provides cooling and improved performance while having a low profile. More specifically, heat transfer structure410, and differential pressure device420, have a sufficiently low profile that they fit within the thickness, t1, of the interior of computing device400. Thus, heat transfer structure410including differential pressure device420may have a total thickness of not more than t1(e.g. 5 millimeters, 3.5 millimeters, or 3 millimeters). Consequently, superior cooling may be provided for thin computing devices, allowing for improved performance of such computing devices.

FIG.5depicts an embodiment of computing device500incorporating heat transfer structure510. Computing device500may be a notebook, laptop, smart phone, gaming device, or other thin computing device. Computing device500may include bottom cover502and top cover504. Top cover504may include a keyboard or display. Alternatively, bottom cover502may include a keyboard or display. Because computing device500is thin, computing device500has a dimension (i.e. a thickness) that is significantly less than the remaining dimensions. For example, the interior of computing device500in which heat transfer structure510resides may have a height, t1, of not more than eight millimeters. In some embodiments, height t1of the interior of computing device500may be not more than five millimeters. In some embodiments, t1is not more than 3.5 millimeters. In some such embodiments, t1is not more than three millimeters. In some embodiments, t1is at least two millimeters. For example, t1may be at least 4.7 millimeters and not more than 5.3 millimeters (i.e. nominally 5 millimeters). The interior of computing device500in which heat transfer structure510resides may be considered to be a chamber. The chamber, and thus computing device500, has ingress501and egress505. Fluid (e.g. air) from exterior to computing device500is drawn into the chamber via ingress501and expelled via egress505. In addition to heat transfer device510, computing device500includes heat-generating structure530and circuit board540. Heat-generating structure530may be one or more processors or other integrated circuit(s) mounted on circuit board540. For simplicity, heat-generating structure530is referred to hereinafter as processor(s)530. Other integrated circuits, such as dynamic random access memory (DRAM) modules (not shown) or other electrical components (not shown) may be mounted on circuit board540.

Heat transfer device510includes heat spreader512and active MEMS differential pressure device520. Heat spreader512is thermally coupled to processor(s)530, for example via thermal conduction. Thus, heat spreader512is in physical contact with processor(s)530. Heat generated by processor(s)530is conducted to heat spreader512. In some embodiments, heat spreader512is a vapor chamber. In some embodiments, heat spreader512may have another structure.

Differential pressure device520is a differential pressure device analogous to cooling systems100,200,300, and/or420. Differential pressure device520is most analogous to differential pressure device420. In some embodiments, multiple cooling cells are present. For example, differential pressure device520may include three tiles300(i.e. twelve cooling cells301). Differential pressure device520may have a bottom plate analogous to bottom plate302and a cover analogous to cover306. The bottom plate of differential pressure device520is coupled to heat spreader512. Therefore, heat from heat spreader512may be transferred to differential pressure device520via thermal conduction.

Differential pressure device520provides a pressure differential that drives fluid flow through heat transfer structure510and, therefore, computing device500. Stated differently, differential pressure device520generates a region of low pressure within computing device500that draws fluid through heat transfer structure510. In some embodiments, this region is proximate to the entrance to differential pressure device520. The direction that fluid (e.g. air) flows through computing device500is indicated by the unlabeled arrows inFIG.5. Fluid is drawn in via ingress501, flows along the gap between circuit board540and top cover504, and into differential pressure device520. The pressure differentials that are capable of being provided as well as the fluid flows described in the context of heat transfer structure410and differential pressure device420may be provided by heat transfer structure510and differential pressure device520. However, the manner in which heat is transferred may differ somewhat.

The fluid flow driven by differential pressure device520is used to transfer heat from processor(s)530. Heat is efficiently transferred from processor(s)530to heat spreader512via conduction. Thus, the temperature of heat spreader512may be at or near that of processor(s)530. Some heat may be transferred from heat spreader512to the fluid passing the surfaces of heat spreader512. However, most or all of the heat is transferred from heat spreader512to differential pressure device520via thermal conduction. Fluid entering differential pressure device520may be heated only slightly as it traverses the chamber of computing device500. Thus, relatively cool fluid enters differential pressure device520. Heat is transferred from differential pressure device520to the fluid in an analogous manner to that described for systems100,200, and/or300. Fluid, and thus heat, is ejected from differential pressure device520and out of computing device500via egress505. In some embodiments, the fluid flowing due to differential pressure device520is such that greater than 2 W of heat is ejected from egress505. In some embodiments, at least 6 W of heat is ejected from the egress505. This may occur where differential pressure device520includes three tiles300. The heated fluid ejected by differential pressure device520may entrain nearby air. This cooler air rapidly mixes with the heated air from differential pressure device520. Thus, the temperature of the region more than 1-3 millimeters from egress505is not hot enough to burn a user of computing device500. Moreover, because the exit (e.g. spout) of differential pressure device520is at or near egress505of computing system, hot fluid is not recirculated within computing device500. Consequently, cooling efficiency may be improved.

In addition to providing improved cooling, differential pressure device520has a low profile. In some embodiments, differential pressure device520may have a total height (h1) that is analogous to that of differential pressure device420. The low profile of differential pressure device520allows for a gap having height g1to be maintained between differential pressure device520and top cover504. In some embodiments, g1for differential pressure device520is analogous to g1for differential pressure device420. Because such a gap is between differential pressure device520and top cover504, differential pressure device520does not unduly heat top cover504. The insulating properties of such a gap are further improved because moving fluid (as opposed to stagnant fluid) is driven through the gap. As a result, the temperature of top cover504may be managed. For example, hot spots may be avoided and the skin temperature (i.e. the external temperature) of top cover504may remain within tolerances. For example, the skin temperature of bottom cover may remain not more than forty-five degrees Celsius. In some such embodiments, the skin temperature of bottom cover does not exceed forty degrees Celsius. A similar gap is between heat spreader512and bottom cover502. Thus, the temperature of bottom cover502may also be managed.

Computing system500may have improved performance. Differential pressure device520may provide a significant fluid flow through heat transfer structure510that differential pressure device520may efficiently transfer heat to the fluid. For example, inlet fluid (e.g. air) at approximately 25 degrees Celsius traveling through computing device500and to differential pressure device520may increase in temperature to approximately 40-45 degrees Celsius (as it removes heat from the processor(s)530and heat spreader512). Differential pressure device520and heat spreader512may be at approximately 70-75 degrees Celsius. Differential pressure device520transfers heat to the fluid drawn into and driven through differential pressure device520. Thus, fluid exiting the differential pressure device520may be at or near 70-75 degrees Celsius. As a result, a higher die temperature may be maintained (and performance of processor(s)530improved) for a given skin temperature of computing device500. Entrained fluid near egress505rapidly lowers the temperature in the region of egress505. The flow of cooler fluid within heat transfer structure510improves the insulating capabilities of the gap between differential pressure device520and top cover504. Thermal management may be improved. Thus, desired temperatures at and near computing device500may be maintained. Further, heat transfer structure510, and differential pressure device520, have a sufficiently low profile that they fit within the thickness, t1, of the interior of computing device500. Thus, heat transfer structure510including differential pressure device520may have a total thickness of not more than t1(e.g. 5 millimeters, 3.5 millimeters, or 3 millimeters). Consequently, superior cooling may be provided for thin computing devices, allowing for improved performance of such computing devices.

FIG.6depicts an embodiment of computing device600incorporating heat transfer structure610. Computing device600may be a notebook or other thin computing device. Computing device600is analogous to computing device500. However, in the embodiment shown, ingress603and egress605are on the same side of computing device600. Computing device600may include bottom housing602and top cover604(or display) analogous to bottom cover502and top cover504. Also shown is top portion607that may include a keyboard. Because computing device600is thin, computing device600has a dimension (i.e. a thickness) that is significantly less than the remaining dimensions. For example, the interior of computing device600in which heat transfer structure610resides may have a height, t1, of nominally five millimeters. Other heights are possible. The interior of computing device600in which heat transfer structure610resides may be considered to be a chamber. Computing device600also includes ingress601, egress605, processor(s)630, and printed circuit board (PCB)640that are analogous to ingress501, egress505, processor(s)530, and circuit board540, respectively. Also shown or labeled are filter603, additional components632, integrated circuits642, lower air gap650, and upper air gap660. Filter603may be utilized to help prevent dust from entering computing system600. For example, filter603may be a MERV 12 or MERV 14 filter. Components632may include a stage and/or thermal interface material that are used to provide good mechanical and thermal connection between heat spreader612and processor(s)630. Integrated circuits642may include dynamic random access memory (DRAM) and/or other components. Thus, components630and642are mounted on both sides of PCB640. Gaps650and660may be used to thermally insulate components within computing device600from covers602and607. In some embodiments, gaps650and660are nominally 0.5 millimeters high.

Heat transfer device610includes heat spreader612and active MEMS differential pressure device620that are analogous to heat spreader512and differential pressure device520. Heat spreader612is thermally coupled to processor(s)630, for example via thermal conduction. Heat generated by processor(s)630is conducted to heat spreader612. In some embodiments, heat spreader612is a vapor chamber. Heat transfer device620may also include thermal interface material614that is used to improve thermal connection between

Differential pressure device620is a differential pressure device analogous to cooling systems100,200,300,420, and/or520. Differential pressure device620is most analogous to and operates in a similar manner to differential pressure device520. In some embodiments, multiple cooling cells are present. For example, differential pressure device620may include three tiles300(i.e. twelve cooling cells301). Differential pressure device620may have a bottom plate (not explicitly labeled) analogous to bottom plate302and a cover (not explicitly labeled) analogous to cover306. The bottom plate of differential pressure device620is coupled to heat spreader612. Therefore, heat from heat spreader612may be transferred to differential pressure device620via thermal conduction. Apertures622in the top cover of differential pressure device620are also shown. Thus, fluid enters differential pressure device620via apertures622.

Differential pressure device620provides a pressure differential that drives fluid flow through heat transfer structure610and, therefore, computing device600. Differential pressure device620operates in an analogous manner to differential pressure device520. The direction that fluid (e.g. air) flows through computing device600is indicated by the unlabeled arrows inFIG.6. Cool fluid is drawn in via ingress601, flows along gap650between heat spreader612and bottom cover602, flows around PCB640, through gap660between integrated circuits642/PCB640and top cover/keyboard607, and into differential pressure device620. As the fluid flows through gap650, some heat is transferred from heat spreader612to the fluid. Some additional heat may be transferred from integrated circuits642and/or PCB640. This somewhat warmer air is drawn into differential pressure device620. Most or all of the heat has been transferred from heat spreader612to differential pressure device620via thermal conduction. Thus, heat is transferred from differential pressure device620to the fluid in an analogous manner to that described for systems100,200, and/or300. Hotter fluid is ejected from differential pressure device620and out of computing device600via egress605. In some embodiments, the fluid flowing due to differential pressure device620is such that greater than 2 W of heat is ejected from egress605. In some embodiments, at least 6 W of heat is ejected from the egress605. The heated fluid ejected by differential pressure device620may entrain nearby air. This cooler air rapidly mixes with the heated air from differential pressure device620. Thus, the temperature of the region more than 1-3 millimeters from egress605is not hot enough to burn a user of computing device600.

As indicated inFIG.6, heat transfer device610is capable of residing in a chamber having a height of not more than five millimeters. In some embodiments, differential pressure device620may have a total height (h1) that is not more than three millimeters. The low profile of differential pressure device620allows for gaps650and660to be maintained between differential pressure device620and covers602and607. The insulating properties of gaps650and660are further improved because moving fluid (as opposed to stagnant fluid) is driven through gaps650and660. As a result, the temperature of covers602and607(e.g. a keyboard) may be managed in a manner analogous to computing device500.

Computing system600may have improved performance analogous to that of computing device500. Differential pressure device620may efficiently transfer heat to the fluid in a manner analogous to differential pressure device520. Entrained fluid near egress605rapidly lowers the temperature in the region of egress605. The flow of cooler fluid within heat transfer structure610improves the insulating capabilities of gaps650and660. Thermal management may be improved. Thus, desired temperatures at and near computing device600may be maintained while performance of processor630may be maintained or improved. Further, heat transfer structure610, and differential pressure device620, have a sufficiently low profile that they fit within the thickness, t1, of nominally five millimeters. Consequently, thermal management for and performance of thin computing device600may be improved.

FIG.7depicts an embodiment of computing device700incorporating heat transfer structure710. Computing device700may be a notebook, laptop, or other thin computing device. Computing device700is analogous to computing device400. Computing device700may include bottom housing702and top cover704(or display) analogous to bottom cover402and top cover404. Also shown is top portion707that may include a keyboard. Because computing device700is thin, computing device700has a dimension (i.e. a thickness) that is significantly less than the remaining dimensions. For example, the interior of computing device700in which heat transfer structure710resides may have a height, t1, of nominally 3.5 millimeters. Other heights are possible. The interior of computing device700in which heat transfer structure710resides may be considered to be a chamber. Computing device700also includes ingress701, egress705, processor(s)730, and printed circuit board (PCB)740that are analogous to ingress401, egress405, processor(s)430, and circuit board440, respectively. Also shown or labeled are filter703, components732, and air gap750. Filter703may be utilized to help prevent dust from entering computing system700. For example, filter703may be a MERV 12 or MERV 14 filter. Components732may include a stage and/or thermal interface material that are used to provide good mechanical and thermal connection between heat spreader712and processor(s)730. Gap750may be used to thermally insulate components within computing device700from cover702. In some embodiments, gap750is nominally 0.5 millimeters high.

Heat transfer device710includes heat spreader712, structure714, fin structure715, and active MEMS differential pressure device720that are analogous to heat spreader412, structure414, fin structure415, and differential pressure device420, respectively. Heat spreader712is thermally coupled to processor(s)730, for example via thermal conduction. Heat generated by processor(s)730is conducted to heat spreader712. In some embodiments, heat spreader712is a vapor chamber. Fin structure715is thermally coupled to heat spreader712via conduction. In some embodiments, fin structure715is nominally two millimeters high. Also shown are insulators716,724, and726. Insulators716and724may be used to thermally insulate top cover707from fin stack715and differential pressure device720, respectively. Insulator726may be used in conjunction with gap750to insulate bottom cover702from differential pressure device720. For example, insulator716may be a graphite panel that is nominally 0.3 millimeter thick. Insulators724and726may each be a graphite panel that is nominally 0.1 millimeter thick.

Differential pressure device720provides a pressure differential that drives fluid flow through heat transfer structure710and, therefore, computing device700. Differential pressure device720generates a region of low pressure proximate to the entrance to differential pressure device720. For example, the region of low pressure may be between fin structure715and differential pressure device720. The direction that fluid (e.g. air) flows through computing device700is indicated by the unlabeled arrows inFIG.7. Cooler fluid (e.g. air) is drawn in via ingress701, flows along gap750, around (or through apertures in) heat spreader712and through fin structure715. Structure714blocks the flow of the fluid in the gap between heat spreader712and bottom cover702so that most or all of the fluid flows through fin structure715. Some heat may be transferred from heat spreader712to the fluid. Thus, somewhat warmer air enters fin structure715. However, most of the heat transfer to the fluid occurs via fin structure715. Thus, hotter air is in the region between fin structure715and differential pressure device720. Fluid is drawn into differential pressure device720, driven out of differential pressure device720, and exits computing device700via egress705.

Heat transfer structure710restricts flow driven by differential pressure device720. For example, fin structure715may have fins that are spaced apart by not more than approximately two hundred and fifty micrometers. As a result, differential pressure device720can provide a pressure differential of at least a one hundred Pascals per cubic feet per minute (cfm) (100 Pa/cfm) within the chamber. In some such embodiments, differential pressure device720provides a pressure differential within the chamber of at least four hundred pascals per cfm (400 Pa/cfm). The differential pressure device720provides a pressure differential within the chamber of at least five hundred pascals per cfm (500 Pa/cfm). For example, if a flow of 0.5 cfm is provided by differential pressure device720, a pressure difference of 200 Pa, 700 Pa, or 1000 Pa is provided. This pressure difference is primarily across fin structure715in some embodiments. Thus, the backpressure, air flows, and pressure differential provided by differential pressure device720may be analogous to that of differential pressure device420.

As indicated inFIG.7, heat transfer device710is capable of residing in a chamber having a height of not more than 3.5 millimeters. In some embodiments, differential pressure device720may have a total height (h1) that is not more than three millimeters. In some embodiments, h1may be not more than 2.8 millimeters. In some embodiments, h1may be not more than 2.5-2.6 millimeters. The low profile of differential pressure device720allows for gap750to be maintained between differential pressure device720and cover702. The insulating properties of gap750are further improved because moving fluid (as opposed to stagnant fluid) is driven through gap750. As a result, the temperature of cover702may be managed. Insulators716,724, and726also aid in thermal management for covers712and707(e.g. a keyboard).

Computing system700may have improved performance analogous to that of computing device400. Differential pressure device720allows for cooling of computing system700without differential pressure device720being thermally coupled to heat spreader712via conduction. Fin structure715efficiently transfers heat to the air flowing between its fins. The flow of through fin structure715is facilitated by the high backpressure and ability of differential pressure device720to generate a high pressure differential. Entrained fluid near egress705rapidly lowers the temperature in the region of egress705. The flow of cooler fluid within heat transfer structure710improves the insulating capabilities of gap750. Thermal management may be improved. Thus, desired temperatures at and near computing device700may be maintained while maintaining or improving performance of processor(s)730. Further, heat transfer structure710, fin structure715, and differential pressure device720, have a sufficiently low profile that they fit within the thickness, t1, of nominally 3.5 millimeters. Consequently, thermal management for and performance of thin computing device700may be improved.

FIG.8depicts an embodiment of computing device800incorporating heat transfer structure810. Computing device800may be a notebook, laptop, or other thin computing device. Computing device800is analogous to computing device(s)400and/or700. Computing device800may include bottom housing802and top cover804(or display) analogous to bottom cover402/702and top cover404/702. Computing device800has a thickness analogous to that of computing device700. For example, the interior of computing device800in which heat transfer structure810resides may have a height of nominally 3.5 millimeters. Other heights are possible.

Heat transfer device810includes heat spreader812, structure814, fin structure815, active MEMS differential pressure device820, and stage832that are analogous to heat spreader412/712, structure414, fin structure415/715, differential pressure device420/720, and components732, respectively. Also shown is differential pressure device drive board823that provides electrical signals to differential pressure device820. The three tiles821(only one of which is labeled) and spout827of differential pressure device820are also shown. Spout827is analogous to spout380for tile300.

Heat transfer device810functions in an analogous manner to heat transfer device410and/or710. Computing system800may have improved performance analogous to that of computing device(s)400and/or700. Differential pressure device820allows for cooling of computing system800without differential pressure device820being thermally coupled to heat spreader812via conduction. Fin structure815efficiently transfers heat to the air flowing between its fins. The flow of through fin structure815is facilitated by the high backpressure and ability of differential pressure device820to generate a high pressure differential. Entrained fluid near the egress of computing system800rapidly lowers the temperature of fluid in the region of the egress. Thus, desired temperatures at and near computing device800may be maintained while maintaining or improving performance of processor(s)830. Further, heat transfer structure810, fin structure815, and differential pressure device820, have a sufficiently low profile that they fit within the thickness (e.g. 3.5 millimeters or less). Consequently, thermal management for and performance of thin computing device800may be improved.

FIG.9depicts an embodiment of computing device900incorporating heat transfer structure910. Computing device900may be a notebook or other thin computing device. Computing device900is analogous to computing device(s)500and/or600. Computing device900may include bottom cover902, top cover904, processor(s)930, PCB940, gaps950and960, ingress901, filter903, and egress905analogous to bottom cover502/602, top cover504/604, processor(s)530/630, circuit board(s)540/640, gaps650and660, ingress501/601, filter603, and egress505/605. A flow seal909that prevents fluid (e.g. air) from entering computing device900from that region is also shown. Further, computing device900is thin. For example, the interior of cooling device900may have a height, t1, of not more than eight millimeters. In some embodiments, height t1of the interior of computing device900may be not more than five millimeters.

Heat transfer device910includes heat spreader912and active MEMS differential pressure device920that are analogous to heat spreader512/612and differential pressure device520/620. Heat spreader912is thermally coupled to processor(s)930, for example via thermal conduction. Heat generated by processor(s)930is conducted to heat spreader912. In some embodiments, heat spreader912is a vapor chamber. Fluid is driven by differential pressure device920, which performs cooling in an analogous manner to differential pressure device(s)520/620. The direction of fluid flow is shown inFIG.9by unlabeled arrows. Thus, fluid may flow around and/or through apertures heat spreader912.

Heat transfer device910functions in an analogous manner to heat transfer device510and/or610. Computing system900may have improved performance analogous to that of computing device(s)500and/or600. Differential pressure device920may efficiently transfer heat to the fluid in a manner analogous to differential pressure device(s)520and/or620. Entrained fluid near egress905rapidly lowers the temperature in the region of egress905. The flow of cooler fluid within heat transfer structure910improves the insulating capabilities of gaps950and960. Thermal management may be improved. Thus, desired temperatures at and near computing device900may be maintained while performance of processor930may be maintained or improved. Further, heat transfer structure910, and differential pressure device920, have a sufficiently low profile that they fit within the thickness of computing device900. Consequently, thermal management for and performance of thin computing device900may be improved.

FIGS.10A and10Bdepict an exploded view and an air flow (or keyboard) view of an embodiment of computing device1000incorporating heat transfer structure1010. Computing device1000is a thin computing device having an interior height analogous to that described herein. Computing device1000is analogous to computing device(s)500,600, and/or900. Computing device1000may include bottom cover1002, top cover/display1004, keyboard1007, processor(s) (not labeled), PCB1040, ingress1001, and egress1005analogous to bottom cover502/602/902, top cover504/604/904, processor(s)530/630/930, circuit board(s)540/640/940, ingress501/601/901, and egress505/605/905.

Heat transfer device1010includes heat spreader1012and active MEMS differential pressure device1020that are analogous to heat spreader512/612/912and differential pressure device520/620/920. Heat spreader1012is thermally coupled to processor(s), for example via thermal conduction. In some embodiments, heat spreader1012is a vapor chamber. Fluid is driven by differential pressure device1020, which performs cooling in an analogous manner to differential pressure device(s)520/620/920. The direction of fluid flow is shown inFIG.10Bby lighter lines.

The PCB1040and heat spreader1012may also be configured to provide cooling in a low profile form factor. In some embodiments, the PCB1040may include cutouts (as shown) and/or apertures so that the combination of vapor chamber1012, differential pressure devices1020, and PCB1040have a reduced height. Thus, PCB1040and heat transfer structure1010may fit in the interior of a computing device having heights analogous to those described herein. Heat spreader1012may also have an optimized design. The size and the location of the heat spreader1012may be configured to reduce its size. For example, in the embodiment shown, the heat spreader1012includes two larger portions configured to be thermally and mechanically coupled to the differential pressure devices1020. A narrower central region is configured to be coupled to the processor(s) (not shown in this drawing) on PCB1040. Springs (not shown) may be used to ensure good thermal contact with the processor(s). Further, heat spreader1012is substantially flat and may be affixed to PCB1040and/or a stage (not shown) to ensure good thermal contact with the processor(s). In the embodiment shown, cool (e.g. room temperature) air enters through a central ingress1001in the back and exits through egresses1005on the same side of the computing device. Cooler fluid enters through the central inlet travels around PCB1040(transferring some heat and providing improved thermal insulation due to moving fluid). The fluid enters differential pressure devices1020through which significant heat is transferred to the fluid. The fluid exits through the egresses1005.

Heat transfer device1010functions in an analogous manner to heat transfer device510,610, and/or910. Computing system1000may have improved performance analogous to that of computing device(s)500,600, and/or900. Differential pressure device1020may efficiently transfer heat to the fluid in a manner analogous to differential pressure device(s)520and/or620. Entrained fluid near egress1005rapidly lowers the temperature in the region of egress1005. The flow of cooler fluid within heat transfer structure1010may improve the insulating capabilities of air gaps. Thermal management may be improved. Thus, desired temperatures at and near computing device1000may be maintained while performance of processor(s) may be maintained or improved. Further, heat transfer structure1010, and differential pressure device1020, have a sufficiently low profile that they fit within the thickness of computing device1000. Consequently, thermal management for and performance of thin computing device1000may be improved.

FIGS.11A and11Bdepict an exploded view and an air flow view of an embodiment of computing device1100incorporating a heat transfer structure including an active MEMS differential pressure device in. Computing device1100is a thin computing device (i.e. a notebook) having an interior height analogous to that described herein. Computing device1100is analogous to computing device(s)500,600,900, and/or1000. Computing device1100may include bottom cover1102, top cover/display1104, processor(s)1130, PCB1140, ingress1101, and egress1105analogous to bottom cover502/602/902/1002, top cover504/604/904/1004, processor(s)530/630/930, circuit board(s)540/640/940/1040, ingress501/601/901/1001, and egress505/605/905/1005.

Heat transfer device1110includes heat spreader1112and active MEMS differential pressure device1120that are analogous to heat spreader512/612/912/1012and differential pressure device520/620/920/1020. Heat spreader1112is thermally coupled to processor(s)1130, for example via thermal conduction. In some embodiments, heat spreader1112is a vapor chamber. Fluid is driven by differential pressure device1120, which performs cooling in an analogous manner to differential pressure device(s)520/620/920/1020. The direction of fluid flow is shown inFIG.11Bby lighter lines. Thus, cool air is drawn into ingress1101proximate to PCB1140, flows through the interior of computing device1100, is drawn into differential pressure device1120, and driven out via egress1105. Thus, other portions of computing device1100may be cooled by heat transfer structure1110.

Heat transfer device1110functions in an analogous manner to heat transfer device510,610,910, and/or1010. Computing system1100may have improved performance analogous to that of computing device(s)500,600,900, and/or1000. Consequently, thermal management for and performance of thin computing device1100may be improved.

FIGS.12A and12Bdepict exploded and air flow views of an embodiment of computing device1200incorporating heat transfer structure1210. Computing device1200is a hand-held gaming device. Computing device1200is a thin computing device having an interior height analogous to that described herein. Computing device1200is analogous to computing device(s)500,600,900,1000, and/or1100. Computing device1200may include bottom cover1202, top cover/display1204, processor(s) (not explicitly labeled), PCB1240, ingress1201, and egress1205analogous to bottom cover502/602/902/1002/1102, top cover504/604/904/1004/1104, processor(s)530/630/930/1130, circuit board(s)540/640/940/1040/1140, ingress501/601/901/1001/1101, and egress505/605/905/1005/1105.

Heat transfer device1210includes heat spreader1212and active MEMS differential pressure device1220that are analogous to heat spreader512/612/912/1012/1112and differential pressure device520/620/920/1020/1120. Heat spreader1212is thermally coupled to the processor(s), for example via thermal conduction. In some embodiments, heat spreader1212is a vapor chamber. Fluid is driven by differential pressure device1220, which performs cooling in an analogous manner to differential pressure device(s)520/620/920/1020/1120. In some embodiments, eight cooling dells may be present in some embodiments of differential pressure device1220. The direction of fluid flow is shown inFIG.12Bby lighter lines. Thus, cool air is drawn into ingress1201proximate to PCB1240, is drawn into differential pressure device1220, and driven out via egress1205.

Heat transfer device1210functions in an analogous manner to heat transfer device510,610,910,1010and/or1110. Gaming system1200may have improved performance analogous to that of computing device(s)500,600,900,1000, and/or1100. Consequently, thermal management for and performance of gaming device1200may be improved.

FIGS.13A and13Bdepict exploded and air flow views of an embodiment of computing device1300incorporating heat transfer structure1310. Computing device1300is a smart phone. Computing device1300is, therefore, a thin computing device having an interior height analogous to that described herein. Computing device1300is analogous to computing device(s)500,600,900,1000,1100, and/or1200. Computing device1300may include bottom cover1302, top cover/display1304, processor(s) (not explicitly labeled), PCB1340, ingress1301, and egress1305analogous to bottom cover502/602/902/1002/1102/1202, top cover504/604/904/1004/1104/1204, processor(s)530/630/930/1130, circuit board(s)540/640/940/1040/1140/1240, ingress501/601/901/1001/1101/1201, and egress505/605/905/1005/1105/1205.

Heat transfer device1310includes heat spreader1312and active MEMS differential pressure device1320that are analogous to heat spreader512/612/912/1012/1112and differential pressure device520/620/920/1020/1120. Heat spreader1312is thermally coupled to the processor(s), for example via thermal conduction. In some embodiments, heat spreader1312is a vapor chamber. Fluid is driven by differential pressure device1320, which performs cooling in an analogous manner to differential pressure device(s)520/620/920/1020/1120. In some embodiments, eight cooling dells may be present in some embodiments of differential pressure device1320. The direction of fluid flow is shown inFIG.13Bby lighter lines. Thus, cool air is drawn into ingress1301proximate to PCB1340, flows through smart phone1300, is drawn into differential pressure device1320, and driven out via egress1305.

Heat transfer device1310functions in an analogous manner to heat transfer device510,610,910,1010,1110, and/or1210. Smart phone1300may have improved performance analogous to that of computing device(s)500,600,900,1000,1100, and/or1200. Consequently, thermal management for and performance of smart phone1300may be improved.

Thus, various embodiments of systems100,200,300,400,500,600,700,800,900,1000,1100,1200, and1300have been shown. Features of systems100,200,300,400,500,600,700,800,900,1000,1100,1200, and/or1300may be combined in manners not explicitly depicted herein.

FIG.14is a flow chart depicting an exemplary embodiment of method1400for operating a differential pressure device. Method1400may include steps that are not depicted for simplicity. Method1400is described in the context of differential pressure devices100,420and/or520. However, method1400may be used with other cooling systems including but not limited to systems and cells described herein.

One or more of the actuator(s) in a differential pressure device is actuated to vibrate, at1402. At1402, an electrical signal having the desired frequency is used to drive the actuator(s). In some embodiments, the actuators are driven at or near structural and/or acoustic resonant frequencies at1402. The driving frequency may be 15 kHz or higher. In some embodiments, the driving signal may be 20 kHz or higher. If multiple actuators are driven at1402, the cooling actuators may be driven out-of-phase. In some embodiments, the actuators are driven substantially at one hundred and eighty degrees out of phase. Further, in some embodiments, individual actuators are driven out-of-phase. For example, different portions of an actuator may be driven to vibrate in opposite directions (i.e. analogous to a seesaw). In some embodiments, individual actuators may be driven in-phase (i.e. analogous to a butterfly). In addition, the drive signal may be provided to the anchor(s), the actuator(s), or both the anchor(s) and the actuator(s). Further, the anchor may be driven to bend and/or translate.

Feedback from the piezoelectric actuator(s) is used to adjust the driving current, at1404. In some embodiments, the adjustment is used to maintain the frequency at or near the acoustic and/or structural resonant frequency/frequencies of the actuator(s) and/or cooling system. Resonant frequency of a particular actuator may drift, for example due to changes in temperature. Adjustments made at1404allow the drift in resonant frequency to be accounted for.

For example, piezoelectric actuators within differential pressure devices420and/or520may be driven at or near their structural resonant frequency/frequencies, at1402. Such actuators may correspond to cooling element120. This resonant frequency may also be at or near the acoustic resonant frequency for the top chamber140. This may be achieved by driving piezoelectric layer(s) in anchor160and/or piezoelectric layer(s) in actuator120. At1404, feedback is used to maintain actuators120at resonance and, in some embodiments in which multiple actuators are driven, one hundred and eighty degrees out of phase. Thus, the efficiency of actuator120in driving fluid flow through differential pressure device420and/or520may be maintained. In some embodiments,1404includes sampling the current through actuator120and/or the current through anchor160and adjusting the current to maintain resonance and low input power.

Consequently, differential pressure devices420,520,620,720,820,920,1020,1120,1220, and/or1320may be operated to drive fluid through a thin computing device. Thus, thin computing devices may be more efficiently cooled. Thermal management and performance of such thin computing devices may be enhanced.