Patent Application
20160138580
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.
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.
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 substrate and multiple benders arranged on the substrate; each bender includes (i) a fan member, (ii) a beam, and (iii) one or more electroactive actuators associated with the beam for transmitting force thereto. In one implementation, the beam is anchored to the substrate, and the fan member and the electroactive actuator(s) are unanchored to the substrate. In addition, the cooling device includes supply circuitry for supplying a time-varying signal to the electroactive actuator(s); the fan members vibrate at a frequency corresponding to the signal and collectively produce an air flow. The electroactive actuator(s) may be mechanically coupled to the beam. In one implementation, the beam is made of an electroactive polymer.
In one embodiment, the benders all have a common orientation on the substrate so that the flows produced by the benders are substantially additive. In another embodiment, at least some of the benders have different orientations on the substrate. Additionally, the vibration of the benders may be synchronized or unsynchronized. The device may further include control circuitry. The control circuitry may selectively operate a subset of the benders to achieve a predetermined flow parameter (e.g., a flow rate or a flow direction) and/or for independently operating each of the benders to achieve the predetermined flow parameter. Some of the time-varying signals applied to the electroactive actuators may have a phase and/or an amplitude difference.
In various embodiments, the control circuitry may group the benders into multiple subsets of the benders and independently operate each subset to achieve the predetermined flow parameter. Vibration of the benders in each subset of the benders may be synchronized. Additionally or alternatively, vibration of the benders between different subsets of the benders may be synchronized. Further, at least some of the time-varying signals applied to the subsets of the electroactive actuators have a phase or an amplitude difference.
Each electroactive actuator may include multiple electroactive layers and multiple conductive layers. Alternatively, each electroactive actuator may include an electroactive layer and multiple conductive lines embedded therein. In one embodiment, the device further includes a flow sensor for detecting a parameter associated with the produced air flow. In another embodiment, the device includes a temperature sensor for detecting the temperature associated with the cooling device, a platform thereof, or an ambient environment.
In another aspect, the invention relates to a method of cooling a system. In various embodiments, the method includes providing a cooling device having a substrate and multiple benders arranged on the substrate, each bender including (i) a fan member, (ii) a beam, and (iii) one or more electroactive actuators associated with the beam for transmitting force thereto, the beam being anchored to the substrate, and the fan member and the electroactive actuator being unanchored to the substrate; and applying a time-varying signal to the electroactive actuator(s) to cause vibration of the fan members at a frequency corresponding to the signal and collectively produce an air flow.
Another aspect of the invention relates to a method of manufacturing a cooling device. In various embodiments, the method includes providing a substrate; and forming, on the substrate, multiple benders, each including (i) a fan member, (ii) a beam, and (iii) one or more electroactive polymers associated with the beam for transmitting force thereto. The benders may be formed utilizing micro-electromechanical system (MEMS) technology. In one implementation, the substrate includes a semi-conductor wafer, metal, glass, quartz, ceramic, and/or a polymer.
In one embodiment, formation of the benders includes the steps of: forming a first electrode layer on a first side of the substrate; forming a hard mask on a second side of the substrate; depositing the electroactive polymer(s) on the first electrode layer; forming a second electrode layer; releasing a portion of the substrate on the second side thereof; releasing the electroactive polymer(s); and separating the benders. The first electrode layer and/or the second electrode layer is formed by a photolithography process, a metal etching process, a lift-off process, and/or a laser cut. In addition, the electroactive polymer(s) is(are) deposited by spin coating, spray coating, rolling and/or nanoimprint lithography.
In another embodiment, formation of the benders includes the steps of: depositing a sacrificial layer on the substrate; forming a polymer sheet layer; forming a first electrode layer; depositing the electroactive polymer(s) on the first electrode layer; forming a second electrode layer; forming a via; separating the benders; and removing the a sacrificial layer to release the benders.
In yet another embodiment, formation of the benders includes the steps of: depositing a sacrificial layer on the substrate; forming a polymer sheet layer; forming a first electrode layer; depositing the electroactive polymer(s) on the first electrode layer; forming a second electrode layer; forming a via; separating the benders; and removing the a sacrificial layer to release the benders.
In some embodiments, formation of the benders includes the steps of: forming a first electrode layer on the substrate; depositing the electroactive polymer(s) on the first electrode layer; forming a second electrode layer; and separating the benders.
As used herein, the terms “approximately,” “roughly,” and “substantially” mean ±10%, and in some embodiments, ±5%. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, with an emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
Refer first to
Referring to
Referring again to
The benders 102 illustrated 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 to
Referring to
When simultaneously applying in-phase power (i.e., φA=φB) at the same frequency to the pair of EAP actuators 402, 404, the motion of the fan member 406 has two degrees of freedom, including deflection in the vertical (z) direction and rotation (or tilting) around the x axis. If, however, the EAP actuators 402, 404 are operated with a phase shift therebetween (e.g., φA and φB have a phase difference of 180°), the motion of the fan member 406 may include an extra degree of freedom—i.e., rotation around the y axis. In one embodiment, the flexible beams 408 includes a highly compliant material (e.g., an AEP) that allows the fan member 406 to 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 to
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 controller 118 may 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 controller 118 may be configured to actuate the benders of the array at the same frequency and amplitude, but at different phases. As a result, with reference to
In one embodiment, the controller 118 groups the fan members 406 into 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 members 406 may 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 controller 118 to repeatedly activate individual fan members 406 or subsets thereof in a synchronized or unsynchronized manner to generate synchronized or unsynchronized vibration. In other embodiments, the controller 118 actuates the benders via a single control circuit 120—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 circuits 120, thereby simplifying the circuitry design.
The controller 118 desirably 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 controller 118 may 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 actuators 116 to the power supply 104. 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 80×86 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 controller 118 may actuate the EAP actuators 116 associated 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 component 106. The thermal gradient may be self-reinforcing as air is forced through the narrow channels beneath the benders.
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 method 500 of manufacturing the benders of the cooling system using hybrid Si-Electroactive polymer MEMS in a wafer-level process is shown in
(a) forming a first electrode layer on a substrate (
(b) forming a hard mask on a backside of the substrate (
(c) depositing an EAP layer on the first electrode layer (
(d) forming a second electrode layer on the EAP layer (
(e) releasing the backside wafer (
(f) releasing the EAP and substrate (
(g) separating the final 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 member 520 may have comparable or larger dimensions than those of the EAP actuator 522.
A second exemplary method 600 of manufacturing the benders of the cooling system using all polymer MEMS is shown in
(a) preparing an interim substrate (
(b) depositing a sacrificial layer on the substrate (
(c) forming a passive polymer sheet layer (
(d) forming a first electrode layer (
(e) depositing an EAP layer on the first electrode layer (
(f) forming a second electrode layer (
(g) forming a via in the EAP layer (
(h) cutting through multiple layers to form a final cooling component (
(i) releasing the final cooling component (
A third exemplary method 700 of manufacturing the benders of the cooling system using an industrial roll-to-roll process 702 is shown in
(a) preparing a polymer sheet layer: this step includes preparation of a polymer (e.g., polyimide) sheet layer 704 that typically has a flat surface.
(b) forming a first electrode layer: this step includes application of a metal contact 706 (including a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the polymer sheet layer 704 formed 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 materials 708 on the first electrode layer 706 using 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 contact 710 (including a material such as Al, Ti, Ta, Au, Cr, Cu, etc.) on the EAP layer 708 using 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 to
The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.
This application claims priority to and the benefit of, and incorporates herein by reference in its entirety, U.S. Provisional Patent Application No. 62/077,626, which was filed on Nov. 10, 2014.
| Number | Date | Country | |
|---|---|---|---|
| 62077626 | Nov 2014 | US |
