MEMS-BASED ACTIVE COOLING SYSTEM

In various embodiments, a cooling device for dissipating heat generated in an electronic or electrochemical device includes a substrate, multiple benders arranged on the substrate, and supply circuitry for supplying an electric field to actuate the benders for causing movement thereof, thereby producing an air flow.

FIELD OF THE INVENTION

In various embodiments, the present invention relates generally to active cooling systems and methods for manufacturing the active cooling systems using micro-electromechanical system (MEMS) technology.

BACKGROUND

As semiconductor manufacturing technology has evolved to permit ever-greater microprocessor core frequencies and power consumption, heat extraction has emerged as a key factor limiting continued progress. If waste heat cannot be removed from a microprocessor continuously, reliably and without excessive power consumption that would itself contribute to the heat load, the device cannot be used; it would quickly succumb to the heat it generates. Heat removal is even more challenging in mobile environments, which tend to involve thin, light form factors. Indeed, mobile platforms often operate at reduced frequencies precisely to reduce power and limit heat generation. That poses a challenge for manufacturers, as consumers demand more from their mobile devices—sleeker form factors, faster connectivity, richer and bigger displays, and better multimedia capabilities.

Beyond the basic mechanical and thermodynamic challenges of heat removal, consumer acceptance of cooling technologies requires quiet operation; how much noise a user will tolerate depends on the device, but certainly the aggressive noise of a PC fan would be unacceptable in a mobile device used as a phone. Still, fans are widely deployed in many heat-producing devices, often in conjunction with heat sinks or similar designs for increasing the surface area and thermal conductivity of the device to be cooled. For example, fins are often used to improve heat transfer. In electronic devices with severe space constraints, the shape and arrangement of fins must be optimized to maximize the heat-transfer density.

Another cooling approach utilizes synthetic air jets produced by vortices that are generated by alternating brief ejections and suctions of air across an opening such that the net (time-averaged) mass flux is zero. Synthetic jet air movers have no moving parts and are thus maintenance-free. Due to the limited overall flow rates that may be achieved with practical synthetic jet air systems, these are usually deployed at the chip level rather than at the system level.

Electrostatic fluid accelerators (EFAs) represent still another currently used approach to device cooling. An EFA is a device that pumps a fluid (such as air) without any moving parts. Instead of using rotating blades, as in a conventional fan, an EFA uses an electric field to propel electrically charged air molecules. Because air molecules normally have no net charge, the EFA creates some charged molecules, or ions, first. Thus an EFA ionizes air molecules, uses those ions to push many more neutral molecules in a desired direction, and then recaptures and neutralizes the ions to eliminate any net charge. These systems involve high operating voltages and the risk of undesirable electrical events, such as sparking and/or arcing. Unintended contact made with one of the electrodes can result in potentially dangerous physical injury. Accordingly, there is a need for safe and reliable approaches to dissipating heat generated in electronic devices.

SUMMARY

Embodiments of the present invention utilize micro-electromechanical system (MEMS) technology and electroactive polymers (EAPs) to provide flexible benders operable to form, collectively, a cooling system for devices such as computers, smart phones, tablets, lighting systems, batteries, and other applications. In a representative embodiment, the cooling system includes a series of flexible fins or benders that can be repeatedly actuated to create an air flow for dissipating heat. In various embodiments, each bender component includes a fan member, an anchor affixed to a substrate, and a flexible beam connecting the fan member to the anchor. An EAP actuator overlies the beam. In these embodiments, application of an electric field to the EAP actuator causes it to contract, tugging the normally flat beam so that it bends, and consequently causing the fan member to move. The electric fields applied to the various EAP actuators may have the same or different amplitudes, frequencies, and/or phases such that the fan members vibrate with the same or different amplitude, frequencies, and/or phases in a simultaneous, sequential, or any desired manner to collectively produce a desired air flow parameter (e.g., a flow rate or a flow direction). For example, the benders may be actuated at the same amplitude and frequency but at different phases such that the movements thereof collectively form a “wave” travelling along a predetermined direction. Alternatively, a selected subset of the benders may be actuated simultaneously at the same amplitude to achieve a predetermined flow rate and/or flow direction. The cooling systems described herein may thus produce a desired air flow that can efficiently, reliably, and safely dissipate heat generated in the device, thereby optimizing the performance and improving the lifetime thereof. In addition, the use of MEMS technology advantageously allows the cooling system to be manufactured in a sufficiently compact size such that it can be accommodated in devices having severe space constraints.

Accordingly, in one aspect, the invention pertains to a cooling device including a thermally conductive retention member. In various embodiments, the retention member includes a plurality of benders each comprising (i) a support in mechanical and thermal contact with the retention member, (ii) a fan member, (iii) a beam, and (iv) at least one electroactive actuator associated with the beam for transmitting force thereto; and supply circuitry for supplying a time-varying signal to the electroactive actuators, whereby the fan members vibrate at a frequency corresponding to the signal and collectively produce an air flow.

In some embodiments, the retention member, which may be silicon or a polymeric or other suitable material, has a first side for contact with a surface to be cooled, the benders being arranged on a second side of the retention member opposed to the first side. For example, the bender supports may be integral with the retention member. The retention member may take the form of a solid slab, or may be a frame with gaps. In various embodiments, the fan members are cooled by flow around a stagnation region. The electroactive actuator may operate the fan members to achieve minimum displacement and maximum rectilinear velocity.

In another configuration, the fan members depend from the retention member, which includes one or more mounts—e.g., a peripheral frame, interior posts, or both—for mounting to a surface to be cooled.

In another aspect, the invention relates to a method of cooling a system. In various embodiments, the method comprises providing a cooling device comprising a thermally conductive retention member and a plurality of benders arranged on the retention member, each bender comprising (i) a support in mechanical and thermal contact with the retention member, (ii) a fan member, (iii) a beam, and (iv) at least one electroactive actuator associated with the beam for transmitting force thereto; and applying a time-varying signal to the electroactive actuators to cause vibration of the fan members at a frequency corresponding to the signal and collectively produce an air flow. The bender supports may be integral with the retention member.

In various embodiments, the method further comprises the step of fabricating the bender supports with the retention member in a MEMS process. The fan members may be cooled by flow around a stagnation region, and the fan members may be operated so as to achieve minimum displacement and maximum rectilinear velocity.

DETAILED DESCRIPTION

A. Cooling Systems for Heat Dissipation

Refer first toFIGS. 1A and 1B, which illustrate a cooling system100having a series of flexible benders (or fins)102and a power supply104for supplying power (i.e., a voltage or a current) to actuate the benders102. The power supply104may be provided by any appropriate power source, such as an AC mains supply, other conventional AC supply, or a conventional DC supply. The power supply104may also be part of the cooled system100, e.g., the battery of a mobile platform. The benders102may be arranged in an array at the surface of a cooled body106(i.e., a component generating heat that requires cooling) or at positions close thereto. The array may comprise or consist of a single row, a single column or a matrix of the benders102. In some embodiments, each of the benders102in the array has a common orientation such that the air flows produced by each of the benders102are substantially additive. In alternative embodiments, the benders102may be arranged in a pattern or without coordination, i.e., they need not be spaced regularly or arranged in a regular pattern. The array of benders102may be disposed on a planar surface, as illustrated, or a curved or otherwise shaped surface that can be accommodated by the space close to the cooled body106in an electronic device (e.g., a computer, a smart phone, a tablet, a lighting system, a battery, etc.). The dimensions of the bender array may vary, depending on the application, between a few hundred micrometers to a few millimeters.

Referring toFIGS. 1C and 1D, in various embodiments, each bender102includes a fan member108, an anchor110affixed to a common substrate, and a flexible beam114connecting the fan member108to the anchor110. In addition, each bender102may include an EAP actuator116overlaying and mechanically coupled to the beam114for deflecting the bender102. The actuator116may cover a portion (e.g., 50%) of the top surface of the flexible beam114or, in some embodiments, the entire top surface of the beam114. In one embodiment, the beam114itself is an EAP actuator116. In general, the size of the fan member108may range from 100 μm to a few mm (e.g., 1 to 10 mm), and the thickness of the fan member108may vary from a few μm (e.g., less than 10 μm) up to 1 mm.

The mechanical relationship between the benders102and the surface of the body to be cooled determines how cooling occurs, including the convection path.FIG. 1Eshows a configuration in which a two-dimensional array of benders102is suspended from a retention member113that may be mounted by a peripheral frame115to the substrate112to be cooled. The retention member113may be thermally conductive and have sufficient contact with the substrate112via the peripheral frame115to transfer by conduction some of the heat to be dissipated; additionally or alternatively, the retention member113may include interior posts in contact with the substrate112for additional thermal conduction. A forced convection regime is created in the narrow air gap between the benders102and the substrate112, removing heat from the surface of the substrate112. In order to achieve convective cooling, the kinetic energy of the aggregate flow produced by the benders102needs to overcome friction between the moving air and the surface of the substrate112in order to produce sufficient lateral velocity inside the gap and parallel to the substrate112.

In the alternative approach shown inFIG. 1F, the benders102are in thermal contact with the substrate112, and hence more directly receive heat to be dissipated by convection. In this embodiment, the benders102are raised above the substrate112by thermally conductive posts or supports102athat are themselves in contact with the substrate. In addition to convective heat removal, the benders102act, collectively, as a heat sink. Of course, the operation of the benders102produces more efficient heat shedding than a stationary heat sink that depends solely on ambient air flow for convective cooling.

Thus, in this configuration, heat flows from the substrate112to the benders102by conduction. To establish steady-state heat conduction and consequent cooling, self-cooling due to movement of the benders102plus the heat-sinking effects of the ambient air flow cool the benders102to an intermediate temperature between the substrate112and the cooler surrounding ambient. In particular, the benders102are cooled by flow around a stagnation region. The moving solid wall of each bender102pushes the stagnant air therebeneath and becomes heated. In this configuration, rather than having to overcome the frictional forces that promote stagnation, the benders102actually exploit the stagnation region to promote forced convective cooling. The convective heat-transfer coefficient in stagnation region flow is proportional to the square root of the bender's velocity.

InFIG. 1F, the benders102are supported on a thermally conductive retention member113; i.e., the supports102aare affixed to, or are fabricated so as to be integral with (i.e., “growing” out of) the retention member. The retention member113may be in the form of a solid slab, in which case it is desirably thin (e.g., 300 μm or thinner) and highly conductive thermally; for example, the retention member113may be silicon, with the benders102and supports102afabricated in accordance with a MEMS process as described below. Alternatively, the retention member113may be in the form of a grating with gaps between adjacent rows or columns of benders102, thereby enabling stagnant air to reach the surface of the substrate112. The retention member113does not significantly contribute to cooling, since it is itself cooled by free convection, which is negligible compared to stagnation-region convective cooling. The retention member113is typically held against the substrate112by a thermal interface material, a thermally conductive epoxy, etc.

The configuration shown inFIG. 1Fbenefits from the high heat conduction afforded by widespread contact with the substrate112, and because the forced convection is not confined to a gap, it need not overcome friction and suffers less damping as a result. Nonetheless, neither design is necessarily superior and relative performance will depend on the specifics of the application.

Optimized movement of the benders102involves minimum displacement and maximum time-averaged rectilinear velocity. As shown inFIG. 1F, the air flow may be analyzed in terms of its rectilinear velocity Rect, which is perpendicular to the substrate112, and its rotational velocity Rot, which is perpendicular to the moving bender and results from bender displacement. Minimum bender displacement maximizes conductive cooling away from the substrate112, while high rectilinear velocity maximizes self-cooling of the benders102by forced convection. In the steady state, the power extracted by conduction is equal to the amount of self-cooling by convection. Maximum reclilinear velocity can be achieved by optimizing the design of the bender. In addition, increasing the total velocity of the bender (e.g., by operating in high-frequencies regimes and improving the electroactive properties of the bender material) will increase its rectilinear component as well.

Referring again toFIGS. 1A and 1B, in various embodiments, the cooling system100includes a controller118and a control circuit120serving to control the power applied by the power supply104to the EAP actuator116. When stimulated by an electric field, the EAP actuator116may exhibit a change in size and/or shape. For example, the electric field may cause the EAP actuator116to contract, in turn causing the normally flat beam114to deflect, and thereby causing the fan member108to move. The controller118may temporally vary the applied power with an operating frequency, f1; as a result, the fan members108may vibrate at a resonance frequency, f2, corresponding to the operating frequency (e.g., f2=f1, f2=2 f1, etc.). This consequently produces an air flow122near the heat-generating component106to dissipate heat. As depicted, the generated flow rate at position124typically increases with the distance D from the heat-generating component106due to viscous effects at the surface. Typically, the applied voltages may range from 1 V to 8000 V and the operating frequencies may range from 1 Hz to 10 KHz. In addition, the cooling system100may include one or more sensors126to provide feedback to the controller118. For example, the sensor126may be a flow sensor that detects a flow parameter (e.g., a flow rate and/or a flow direction) produced by the benders102. If the detected flow parameter reach a predetermined value, the controller118may maintain the amplitudes, frequencies, and/or phases applied to the benders102. If, however, the detected flow parameter does not reach or if it exceeds the predetermined value, the controller118may adjust the applied amplitudes, frequencies, and/or phases until the detected flow parameter satisfies the predetermined value. In some embodiments, the sensor126is a temperature sensor. The controller118adjusts the power applied to the benders102by comparing the detected temperature to a desired temperature to ensure a cooling effect is satisfied.

The benders102illustrated above represent exemplary embodiments only; they may include various configurations that are suitable for producing an air flow in an electronic device for heat dissipation and therefore are within the scope of the present invention. For example, referring toFIG. 2A, the bender202may include a fan member204and a pair of EAP actuators206. When applying power to the pair of EAP actuators206, they may change in size and/or shape and consequently cause the inclination thereof (and/or of the flexible beams208underlying of the actuators206) to change through a range of motion during each actuation cycle (as depicted inFIG. 2B). The movement of the EAP actuators206and/or flexible beams208results in vibration of the fan member204and thereby produces an air flow210.

FIG. 3depicts various alternative bender configurations300in accordance with an embodiment of the present invention, where each fan member302has four actuators304(and/or four flexible beams) for moving the bender. As illustrated, the actuators304can be arranged in various configurations around the fan member302.

Referring toFIG. 4A, in one embodiment, the power applied to each of the EAP actuators402,404is separately controllable, i.e., one of the EAP actuators402,404may be activated at an amplitude, a phase, and/or a frequency that is independent of the amplitude, phase, and/or frequency applied to the other EAP actuators402,404. For n EAP actuators, the controller118may contain n control circuits each comprising a phase-delay circuit and driving one of the EAP actuators with the respective phase. The controller118may split a control signal, typically in the range from 1 Hz to 10 KHz, into n channels for the n control circuits120for separately controlling each of the EAP actuators. For example, the controller118may be configured to activate the individual EAP actuators402,404of the array at the same frequency (i.e., ωA=ωB), but at different phases (i.e., φAand φB, respectively) and different amplitudes (i.e., VAand VB, respectively). In another example, the controller118may activate the EAP actuators402,404at the same frequency (i.e., ωA=ωB) and same amplitude (i.e., VA=VB), but at different phases (i.e., φAand φB, respectively). By adjusting the amplitudes, frequencies and/or phases applied to each actuator402,404, the fan member406may move, including deflecting, twisting, rotating, and/or vibrating, to create a desired flow parameter (e.g., a flow rate or a flow direction).

When simultaneously applying in-phase power (i.e., φA=φB) at the same frequency to the pair of EAP actuators402,404, the motion of the fan member406has two degrees of freedom, including deflection in the vertical (z) direction and rotation (or tilting) around the x axis. If, however, the EAP actuators402,404are operated with a phase shift therebetween (e.g., φAand φBhave a phase difference of 180°), the motion of the fan member406may include an extra degree of freedom—i.e., rotation around the y axis. In one embodiment, the flexible beams408includes a highly compliant material (e.g., an AEP) that allows the fan member406to rotate through a large angle (e.g., 45°) around the y axis to enhance the produced air flow.

The benders may be arranged in various configurations. For example, referring toFIGS. 4B and 4C, each fan member406may be affixed to a substrate410on one side only. The fan members406may be oriented parallel to one another, where the same side of each fan member is clamped to the substrate410(FIG. 4B); or the fan members406may be anti-parallel to one another, where the opposite sides of two neighboring fan members406are clamped to the substrate410(FIG. 4C). In the embodiment shown inFIG. 4D, two opposite sides of the fan members406are both attached to the common substrate410. One of ordinary skill in the art will understand that the illustrated bender array may have more configurations, i.e., the benders may be arranged in any manner that is suitable for producing a desired flow parameter(s) (e.g., a desired flow rate and/or a flow direction).

In various embodiments, the power applied to the benders is separately controllable, i.e., each bender may be activated at amplitudes, phases, and/or frequencies that are independent of the amplitudes, phases, and/or frequencies applied to the other benders. For n benders, the controller118may split a control signal into n channels for n control circuits, each control circuit associated with a bender, for separately controlling each of the benders. For example, the controller118may be configured to actuate the benders of the array at the same frequency and amplitude, but at different phases. As a result, with reference toFIG. 4E, the fan members406of the benders may move in the z direction and rotate around the y axis to various degrees, depending on the phases applied thereto, and thereby form a “wave” travelling in the x direction. This design may create an efficient air flow for heat dissipation. Additionally, the “wavelength” of the travelling “wave” may be adjusted by changing, for example, the width of the fan members and/or the number of fans per unit length, to produce a desired flow parameter.

In one embodiment, the controller118groups the fan members406into multiple subsets, each corresponding to fan members separated by a distance corresponding to the wave period; each subset is sequentially activated to produce the illustrated wave-like behavior and thereby achieve a predetermined flow parameter. Alternatively, each subset of the fan members406may be activated randomly or in any desired manner to individually or collectively create an air flow at one or more locations near the heat-generating component. In sum, the present invention provides an approach enabling the controller118to repeatedly activate individual fan members406or subsets thereof in a synchronized or unsynchronized manner to generate synchronized or unsynchronized vibration. In other embodiments, the controller118actuates the benders via a single control circuit120—i.e., the benders are simultaneously activated at the same amplitude with the same frequency and same phase; this obviates the need of multiple control circuits120, thereby simplifying the circuitry design.

The controller118desirably provides computational functionality, which may be implemented in software, hardware, firmware, hardwiring, or any combination thereof, to compute the required frequencies and amplitudes for a desired flow parameter. In general, the controller118may include a frequency generator, phase delay circuitry, and/or a computer (e.g., a general-purpose computer) performing the computations and communicating the frequencies, phases and amplitudes for the individual EAP actuators116to the power supply104. For embodiments in which the functions are provided as one or more software programs, the programs may be written in any of a number of high level languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC, various scripting languages, and/or HTML. Additionally, the software can be implemented in an assembly language directed to the microprocessor resident on a target computer; for example, the software may be implemented in Intel 80x86 assembly language if it is configured to run on an IBM PC or PC clone. The software may be embodied on an article of manufacture including, but not limited to, a floppy disk, a jump drive, a hard disk, an optical disk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gate array, or CD-ROM. Embodiments using hardware circuitry may be implemented using, for example, one or more FPGA, CPLD or ASIC processors. Such systems are readily available or can be implemented without undue experimentation.

The configurations of the benders provided herein are for illustration only, and the present invention is not limited to such configurations. One of ordinary skill in the art will understand that any variations are possible and are thus within the scope of the present invention. For example, the number of benders per electronic device, the configuration of the bender array, and/or the size, shape or orientation of the benders may be modified in any suitable manner for generating an air flow to dissipate heat generated in the electronic device. In addition, the controller118may actuate the EAP actuators116associated with the fan members to create movements of the fans simultaneously, sequentially, or in any desired manner to collectively produce a desired flow parameter (e.g., a flow rate and/or a flow direction).

Additionally, the benders may not be necessarily supplied by a power source—i.e., they may be static. In some embodiments, by adjusting the shape, size, and/or orientation of each bender, the density of the bender array (i.e., the number of benders per unit area), and/or the distance between the benders to the heat-generating component, the presence of the bender array itself is sufficient to produce a cooling effect. Without being bound to any particular theory or mechanism, this may be caused by, for example, efficient heat dissipation by the high thermal conductive surface area and varied geometry of the benders and/or bender motion resulting from a thermal gradient across the benders created by the heat-generating component106. The thermal gradient may be self-reinforcing as air is forced through the narrow channels beneath the benders.

B. Materials and Methods of Manufacture

Embodiments of the cooling systems in the present invention may be manufactured utilizing techniques including, but not limited to, MEMS and/or other suitable manufacturing techniques. The use of MEMS technology advantageously allows the cooling system to be manufactured in a sufficiently compact size such to be accommodated in devices having severe space constraints. In one embodiment, the fan member, flexible beam and anchor are fabricated from a single material (using a MEMS fabrication process), and the actuator material is applied thereto by deposition, screening, or other suitable application process. If the substrate is silicon (Si), selective masking and etching steps may be employed to fabricate the fan and beam members directly from the substrate surface. The actuators may include or consist essentially of any materials that exhibit a change in size or shape when stimulated by an electric field, and provide advantages over some traditional electroactive materials such as electro-ceramics for MEMS device applications due to their high strain, light weight, flexibility and low cost. The actuators may be divided into two classes: electrochemical (also known as “wet” or “ionic”) and field-activated (also known as “dry” or “electronic”). Electrochemical polymers use electrically driven mass transport of ions to effect a change in shape (or vice versa). Field-activated polymers use an electric field to effect a shape change by acting on charges within the polymer (or vice versa).

One of the most widely exploited polymers exhibiting ferroelectric behavior is poly(vinylidene fluoride), a family of polymers commonly known as PVDF, and its copolymers. These polymers are partly crystalline and have an inactive amorphous phase. Their Young's moduli are between 1 and 10 GPa. This relatively high elastic modulus offers a correspondingly high mechanical energy density, so that strains of nearly 7% can be induced. Recently, P(VDF-TrFE-CFE) (a terpolymer) has been shown to exhibit relaxor ferroelectric behavior with large electrostrictive strains and high energy densities. All of these materials may be used advantageously in accordance herewith.

Exemplary techniques for manufacturing various components of the cooling system described herein are described below. They generally involve a polymer-based fabrication approach, where a metal layer is first deposited onto a polyimide, silicon or other suitable substrate, and the EAP materials are applied onto the formed metal layer. Thereafter, a second metal layer is applied to the exposed surface of the EAP polymer. The two metal layers serve as electrodes for applying an electric field to actuate the EAP polymer.

A first exemplary method500of manufacturing the benders of the cooling system using hybrid Si-Electroactive polymer MEMS in a wafer-level process is shown inFIGS. 5A-5G. In this embodiment, the bender fabrication process flow includes the steps of:

(a) forming a first electrode layer on a substrate (FIG. 5A): this step includes preparation of a silicon wafer substrate502, deposition of a metal contact504(including a material such as Al, Ti, Ta, Au, Cr, Cu, etc. or a combination thereof) on the top side506of the substrate502, and formation of a desired pattern of the first electrode layer504on the substrate502using a photolithography (PL) process and a metal etching (e.g., wet etching or reactive ion etching (RIE)) process. Alternatively, the metal deposition and photolithography process may be followed by a lift-off process to fabricate the metal pattern. In some embodiments, the metal pattern is created by a laser cut. Further, the first electrode layer504may include conducting polymers (e.g., polyaniline, polypyrrole (Ppy), PEDOT-PSS or the like). Alternatively, the first electrode layer504may include composites of the conducting polymers in combination with metal or with metal seeds.

(b) forming a hard mask on a backside of the substrate (FIG. 5B): this step includes deposition of a metal layer508(including a material such as Al, Ti, Ta, Au, Cr, Cu, etc. or a combination thereof) on the backside510of the substrate502, and formation of a hard mask508for back side release purposes using photolithography and metal etching (e.g., wet or RIE) processes. Similar to the formation of the first electrode layer504, the metal etching process here may be replaced by a lift-off process. Alternatively, the metal pattern on the backside may be created by a laser cut. Alternatively, the hard mask may be a photoresist (PR) patterned using PL.

(c) depositing an EAP layer on the first electrode layer (FIG. 5C): this step includes deposition of EAP materials512(e.g., one or more P(VDF-TRFE-CFE) terpolymers) on the first electrode layer504(by spin coating, spray coating, rolling or nanoimprint lithography (NIL)), curing of the EAP materials (in an oven, a belt oven, or on a hot plate), and/or a polling process.

(d) forming a second electrode layer on the EAP layer (FIG. 5D): this step includes deposition of a second layer of metal contact (having a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the EAP layer512formed in step (c), and formation of a desired pattern of the second electrode layer514using photolithography and metal etching (e.g., wet etching or RIE) processes. Similar to the formation of the first electrode layer504, the metal deposition and photolithography processes may be followed by a lift-off process to fabricate the metal pattern of the second electrode layer514. Alternatively, the metal pattern of the second electrode layer514may be created by a laser cut. Again, the second electrode layer514may also include (i) conducting polymers (e.g., polyaniline, PPy, PEDOT-PSS or the like) or (ii) composites of the conducting polymers in combination with metal or with metal seeds.

(e) releasing the backside wafer (FIG. 5E): this step includes release of the backside wafer substrate using, for example, a deep reactive-ion etching (DRIE) process. This step creates the final, desired thickness of the cooling components on the silicon device.

(f) releasing the EAP and substrate (FIG. 5F): this step includes release of the formed EAP and electrodes and the substrate using, for example, an EAP-RIE process followed by a through-silicon etching process516(using e.g., DRIE).

(g) separating the final cooling components (FIG. 5G): this step includes application of a cutting, scribing, cleaving, and/or breaking technique518on the wafer to separate the formed cooling components.

Note that the drawings herein do not necessarily represent the actual scales of various components in the cooling systems. For example, the fan member520may have comparable or larger dimensions than those of the EAP actuator522.

A second exemplary method600of manufacturing the benders of the cooling system using all polymer MEMS is shown inFIGS. 6A-61. In this embodiment, the bender fabrication process flow includes the steps of:

(a) preparing an interim substrate (FIG. 6A): this step includes preparation of an interim substrate602that may include any substrate (such as, semi-conductor wafer, metal, glass, quartz, ceramic, polyimide, or another polymer substrate) having a flat surface.

(b) depositing a sacrificial layer on the substrate (FIG. 6B): this step includes application of a coating layer (using, e.g., OmniCoat or other materials) on the substrate602to form a sacrificial layer604.

(c) forming a passive polymer sheet layer (FIG. 6C): this step includes application of a passive polymer (e.g., polyimide) on the sacrificial layer604by rolling, spin coating, or spray coating to create a passive polymer sheet layer606. Because the passive polymer layer606has a thickness of the final device, it may not be thinned or etched during the fabrication process. Its surface, however, may be modified or functionalized (e.g., modifying the surface energy and/or chemical and physical affinity thereof) to increase the attachment between neighboring layers.

(d) forming a first electrode layer (FIG. 6D): this step includes deposition of a metal contact (including a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the passive polymer sheet layer606, and formation of the a desired pattern of the first electrode layer608using photolithography and metal etching (e.g., wet etching or RIE) processes. Alternatively, the metal pattern may be created by a laser cut. In some embodiments, the metal pattern includes (i) conducting polymers (e.g., polyaniline, PPy, PEDOT-PSS or the like) or (ii) composites of the conducting polymers in combination with metal or with metal seeds.

(e) depositing an EAP layer on the first electrode layer (FIG. 6E): this step includes deposition of EAP materials610on the first electrode layer608(by spin coating, spray coating, rolling or NIL) and curing of the EAP materials (in an oven, a belt oven, or on a hot plate).

(f) forming a second electrode layer (FIG. 6F): this step includes deposition of a second layer of metal contact (having a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the EAP layer610formed in step (e), and formation of a desired pattern of the second electrode layer612using photolithography and metal etching (e.g., wet etching or RIE) processes. Similar to the formation of the first electrode layer608, the metal pattern of the second electrode layer612may be created by a laser cut. In one embodiment, the second electrode layer612includes (i) conducting polymers (e.g., polyaniline, PPy, PEDOT-PSS or the like) or (ii) composites of the conducting polymers in combination with metal or with metal seeds.

(g) forming a via in the EAP layer (FIG. 6G): this step includes formation of a via614in the EAP layer610using a laser or any other suitable technique.

(h) cutting through multiple layers to form a final cooling component (FIG. 6H): this step includes cutting through multiple layers, including the passive polymer sheet layer606and/or the electrode layer(s), using a laser or any appropriate technique to form a final device.

(i) releasing the final cooling component (FIG. 6I): this step includes removal of the sacrificial layer604from the substrate602to release the final cooling component.

A third exemplary method700of manufacturing the benders of the cooling system using an industrial roll-to-roll process702is shown inFIGS. 7A and 7B. In this embodiment, the bender fabrication process flow includes the steps of:

(a) preparing a polymer sheet layer: this step includes preparation of a polymer (e.g., polyimide) sheet layer704that typically has a flat surface.

(b) forming a first electrode layer: this step includes application of a metal contact706(including a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the polymer sheet layer704formed in step (a) using the roll-to-roll process.

(c) forming an EAP layer on the first electrode layer: this step includes application of EAP materials708on the first electrode layer706using the roll-to-roll process and curing of the EAP materials (in an oven, a belt oven, or on a hot plate).

(f) forming a second electrode layer: this step includes application of a metal contact710(including a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the EAP layer708using the roll-to-roll process.

(g) separating the final cooling components: this step includes application of a selective laser drill to produce the final cooling components.

It should be noted that the methods of manufacturing the cooling systems described herein are presented as representative examples, and any of the cooling systems and/or components thereof may be formed using any of the manufacturing methods described, as appropriate, or other suitable methods. For example, another mode of manufacture may include silicon and polymer cantilever technologies. In a silicon-based approach, the fan and beam members are separated from a silicon substrate in the manner of forming a resonator window (e.g., using a suitable etch), as is well understood by those skilled in MEMS device fabrication, and a well is etched into the beam. Electrodes are deposited onto the well floor, and the well is filled with the EAP materials (which is subsequently cured).

Further, each EAP actuator may include multiple conductive contacts to increase the efficiency thereof. Referring toFIG. 8A, in some embodiments, the EAP actuator802includes multiple EAP layers804and multiple horizontal conductive layers806that are connected to a common port (not shown). The EAP layers804and conductive layers806are interleaved to form a sandwich configuration. The numbers of the EAP layers804and the conductive layers806may be determined based on the thickness thereof, the electro-mechanical properties of the EAP materials, the layout and/or electrical specifications of the electronic devices in which they are deployed, etc. With reference toFIGS. 8B and 8C, in other embodiments, the EAP actuator812includes an EAP layer814having an array of vertical conductive lines816embedded therein. Similarly, the conductive lines816are connected to a common port. The number of conductive lines816in the EAP layer814may, again, be determined based on the thickness and/or electro-mechanical properties of the EAP layer814, the layout and/or electrical specifications of the electronic devices in which they are deployed, etc.