Abstract:
One embodiment of the present invention uses an actuator, which is actuated by electromagnetic microwave. The actuator is used to generate the micro-plasma and ions. The configurations of actuators may be microstrip lines structure, stripline structure, piping structure, multiplayer traces and electrodes structure, waveguide structure, and cavity structure. The generated micro-plasma and ions will induce a local turbulent gas flow and the flow is to carry the heat away from the surfaces of the heat sink fins. The actuators may be coupled to heat sink fins, heat transferring pipes, cooling fans, and heat sources in varied configurations.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to electronic equipment, and more particularly, to apparatus and methods for cooling electronic devices using microwave excited micro-plasma and ions. 
         [0003]    2. Description of the Related Art 
         [0004]    Electronic devices may generate significant heat during operation. High temperatures may reduce the lifespan of these devices, and, therefore, the generated heat may need to be dispersed to keep the operating temperature of the electronic devices within acceptable limits. 
         [0005]    One commonly used cooling device is heat sink. Heat sinks may be coupled to electronic devices to absorb heat through the heat sink base and disperse the heat through their fins. Conventional methods to disperse the heat through the heat sink fins are natural convection and forced convection. Natural convection is to disperse the heat away from the surfaces of heat sink fins without the aid of external forced fluid pumping through heat sink fins. On the other hand, the forced convection cooling is to pump the fluid to flow through heat sink fins, such as the fans to blow the air through the heat sink fins, and therefore enhance the heat transfer between fins and outside ambient. 
         [0006]    With the increasing power density of electronic devices, the pitch or the distance between heat sink fins is becoming smaller, which means more surface area may be used to transport the heat away. However, when the pitch becomes very small, the pressure drop between inlet and outlet of the heat sink fins may become very high, which may results the difficulties to pump the fluid flowing through fins, and as a result, more powerful fans, which consume higher electricity may be needed for the cooling. The invention utilizes microwave excited micro-plasma and ions to induce the gas flow to conduct the convective heat transfer along the heat sink fins and therefore will resolve these issues. 
         [0007]    Another consideration of the electronic device cooling is that, due to size concern, the internal space allowed to put cooling fans and other cooling components, may be limited or not permitted. The invention utilizes the microwave excited micro-plasma and ions gas flow to generate the forced convective heat transfer. Therefore the design is able to improve the heat transfer efficiency and to minimize the required space because microwave excited micro-plasma and ions can be very small. 
         [0008]    Another aspect of using the invention is to lower the required power of the system fans of electronic devices. The micro-plasma and ions driven gas flow excited by the microwave couple with the heat sink fins will induce the local turbulence gas flow near heat sink surfaces. The local turbulence near the heat sink surface will enhance the heat dissipation so a better cooling is achieved. Therefore the system fan doesn&#39;t need to be very powerful and the electricity energy is saved. 
         [0009]    Plasma-driven gas flow has been used either to cool articles or to control and modify the fluid dynamics boundary layer on the wings surfaces of the aerodynamic vehicles. For example, U.S. Pat. No. 3,938,345 used the phenomenon of corona discharge, which is one type of plasma, to do the local cooling of an article. U.S. Pat. No. 4,210,847 designed an apparatus for generating an air jet for cooling application. U.S. Pat. No. 5,554,344 had a gas ionization device to do the cooling of zone producing chamber. U.S. Pat. No. 6,796,532 B2 used a plasma discharge to manipulate the boundary layer and the angular locations of its separation points in cross flow planes to control the symmetry or asymmetry of the vortex pattern. 
         [0010]    However, none of the above patents are coupled to the heat sink, which is a fundamental apparatus for cooling electronic devices. Hence, what are needed are a method and an apparatus, to couple with heat sink fins to cool down electronic devices efficiently. 
       SUMMARY OF THE INVENTION 
       [0011]    One embodiment of the present invention provides a microwave excited micro-plasma and ions couple to heat sink fins to induce the gas flow along the heat sink fins. The induced gas flow will remove the heat away from heat sink fin surface and therefore the heat source is cool down. 
         [0012]    In one embodiment, the cooling system includes heat sink fins assembly and array of the microwave excited micro-plasma and ions devices. The heat sink fin assembly may be composed by a plurality of straight heat sink fins, a plurality of heat sink pins, or other shapes of fin structure. The micro-plasma and ions devices may be composed with different configurations, such as micro-strips, microwave wave guides, and microwave cavities. The micro-plasma and ions may be excited and generated at different locations inside the heat sink fin assembly. 
         [0013]    In one embodiment, the micro-plasma and ions may be excited and generated with microwave cavities, which have slots, holes, or trench on the surface of the microwave wave guide structure. In a further embodiment, the generated micro-plasma and ions will couple and interact with heat sink fins assembly to do the cooling. 
         [0014]    In one embodiment, the micro-plasma and ions actuators may be configured by one or several micro-strips. In another embodiment, the configurations of the micro-strips may be varied to gain the maximum electrical field at specific regions to induce micro-plasma and ions. 
         [0015]    In one embodiment, the micro-plasma and ions actuators may be composed of microwave wave guides, which have different configurations such as pipe shape, micro-strip shape, rectangular shape, or other shapes. The dielectric layers may couple with microwave wave guides. 
         [0016]    In one embodiment, the applied microwave sources to excite and generate the micro-plasma and ions flow may have varied waveforms, frequencies, amplitude, phase shifts, and may be transient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    A better understanding of the present invention may be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
           [0018]      FIG. 1  illustrates a micro-plasma and ions generating device; 
           [0019]      FIG. 2  illustrates a micro-plasma and ions generating device; 
           [0020]      FIG. 3  illustrates an array of micro-plasma and ions devices; 
           [0021]      FIG. 4  illustrates an array of micro-plasma and ions devices couple to a heat sink fins assembly; 
           [0022]      FIG. 5  illustrates an array of micro-plasma and ions devices couple to a heat sink fins assembly; 
           [0023]      FIG. 6  illustrates an array of micro-plasma and ions devices couple to a heat sink fins assembly; 
           [0024]      FIG. 7  illustrates a micro-plasma and ions device couple to a heat sink fins assembly; 
           [0025]      FIG. 8  illustrates the micro-plasma and ions devices couple to a heat sink fins assembly in varied configurations; 
           [0026]      FIG. 9  illustrates the micro-plasma and ions devices made of micro-strips; 
           [0027]      FIG. 10  illustrates the microwave waveguides coupled with microwave cavities are used to excite and generate micro-plasma and ions; 
           [0028]      FIG. 11  illustrates the microwave waveguides and microwave cavities are used to excite and generate micro-plasma and ions; 
           [0029]      FIG. 12  illustrates the micro-plasma and ions coupled with heat sink fins; 
           [0030]      FIG. 13  illustrates the micro-plasma and ions actuator is used to cool down the heat sources inside an electronic device. 
       
    
    
       [0031]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Furthermore, note that the word “may” is used throughout this application in a permissive sense (i.e., having the potential to, being able to), not a mandatory sense (i.e., must). The term “include”, and derivations thereof, mean “including, but not limited to”. The term “coupled” means “directly or indirectly connected”. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The invention generally relates to apparatus for cooling electronic devices or packages, such as microprocessor and ASIC. Such systems and methods may be used in a variety of applications. A non-exhaustive list of such applications includes the cooling of: a microprocessor chip, a graphics processor chip, an ASIC chip, a video processor chip, a DSP chip, a memory chip, a hard disk drive, a graphic card, a portable testing electronics, a personal computer system. 
         [0033]    Take laptop computer for example, conventional fans use a lot of space and energy. For this reason, the microwave excited micro-plasma and ions cooling represent a way to increase their cooling capacity and make them more reliable and far quieter. Therefore the higher-performance chips that generate too much heat for current laptops can be used. 
         [0034]    As used herein “plasma” is an ionized gas, a gas into which sufficient energy is provided to free electrons from atoms or molecules and to allow both species, ions and electrons, to coexist. Plasma is even common here on earth. A plasma is a gas that has been energized to the point that some of the electrons break free from, but travel with, their nucleus. Gases can become plasmas in several ways, but all include pumping the gas with energy. A spark in a gas will create a plasma. A hot gas passing through a big spark will turn the gas stream into a plasma that can be useful. Plasma torches like that are used in industry to cut metals. 
         [0035]    As used herein “dielectric” is a substance that is a poor conductor of electricity, but an efficient supporter of electrostatic fields. In practice, most dielectric materials are solid. An important property of a dielectric is its ability to support an electrostatic field while dissipating minimal energy in the form of heat. The lower the dielectric loss (the proportion of energy lost as heat), the more effective is a dielectric material. Another consideration is the dielectric constant, the extent to which a substance concentrates the electrostatic lines of flux. Substances with a low dielectric constant include a perfect vacuum, dry air, and most pure, dry gases such as helium and nitrogen. Materials with moderate dielectric constants include ceramics, distilled water, paper, mica, polyethylene, and glass. Metal oxides, in general, have high dielectric constants. 
         [0036]      FIG. 1  illustrates a configuration of a micro-plasma and ions generating device. The figure shows a microwave  101  is traveling along the axial direction and the wave is between inner cylinder  102  and outer cylinder  103 . The dielectric material  102  is between two cylinders. The dielectric material can be air or other materials. The plasma, as shown in the black color region  104  in the figure, may be excited and generated by the electromagnetic microwave and the plasma may flow out of the nozzle, which is located at the end of outer cylinder. Similarly,  FIG. 2  illustrates another configuration. These configurations act as micro-plasma and ions generators. 
         [0037]    Similar to  FIGS. 1 and 2 , the plasma may be excited and generated by electromagnetic microwave using micro-strip structure as shown in  FIG. 3 . The micro-strips  105  are on one side of the dielectric material  102  and the ground  106  is on the other side. The top micro-strips and bottom ground may have extension on the side wall of the dielectric material as shown in the  FIG. 3 . The gap between top micro-strips  105  and the ground  106  extension may be small in order to have high electrical field distribution when an electromagnetic microwave travels to there. In one embodiment, the micro-plasma and ions actuators may be configured to be an array which has many channels. In another embodiment, the micro-strip may have impedance matching stub, which is not shown here in the figure, to minimize the microwave reflection from the edge of the board. Furthermore, varied micro-strips patterns and different geometries of the micro-strip edge and ground edge may be used. 
         [0038]      FIG. 4  illustrates an array of the circular-pipe shape micro-plasma and ions actuators are assembled on one side of the heat sink fins assembly  201 . The generated micro-plasma and ions will induce local turbulent flow. This turbulent flow may couple with a fan, to enhance the heat removal from the heat sink surface. In one embodiment, besides the circular shape, the micro-plasma and ions actuators may have different configurations, such as rectangular shape. 
         [0039]      FIG. 5  illustrates an array of micro-strip actuators is coupled with the heat sink base  200  and heat sink fins  201  assembly. The micro-plasma and ions generated by micro-strip make the design scaleable and the micro-plasma and ions can easily couple to heat sink fins  201  as shown in the figure. The micro-strips  105  may be deposited on one side of the dielectric  102  board and the other side may be electrically grounded  106 . 
         [0040]      FIG. 6  illustrates another configuration of the micro-strips  105  coupled with heat sink fins  201  and heat sink base  200 . One single micro-strip  105  may couple to a single heat sink fin  201  as shown in the  FIG. 6 . In one embodiment, one micro-strip  105  may couple to several heat sink fins  201  as shown in  FIG. 7 . In another embodiment, the bulk heat sink fins or the micro-channels heat sink fins may be used. 
         [0041]    Not limited by the configurations of the  FIG. 4  to  FIG. 7 , the micro-plasma and ions actuators may be coupled with heat sink fins  201  assembly in varied directions and patterns.  FIG. 8  illustrates the side and top views of the micro-plasma and ions actuators coupled with heat sink fins  201  assembly and heat sink base  200 . The black lines shown are the micro-plasma and ions actuators. In one embodiment, the micro-plasma and ions actuators may be manufactured with flexible materials so they can be bended to fit with specific space and shape requirements, and may be manufactured in a similar way as PCB manufacturing process. In another embodiment, the heat sink fins may be straight as shown in  FIG. 8   a  to  FIG. 8   d,  and the heat sink fins may be configured with fin structure as shown in  FIG. 8   e.  Other geometries and shapes of heat sink fins may be used to couple with micro-plasma and ions actuators and the variation should be considered within the scope of the embodiment here. 
         [0042]      FIG. 9  illustrates some configurations of the micro-strips used to excite and to generate the micro-plasma and ions.  FIGS. 9   a  and  9   b  show the micro-strips  105  are on one side of the dielectric material  102  and the ground metal  106  is on the other side. There is a small gap between top and bottom conductors on the side wall of the dielectric material  102 . The electromagnetic microwave is traveling inside the dielectric material toward the gap region. The high electrical field, which is favorable, will occur at the gap region to ionize the air and therefore the plasma flow is induced. In one embodiment, the configuration of the micro-strips may be varied and the edge patterns may be varied as well. All the variation should be considered within the scope of the invention.  FIG. 9   c  illustrates one configuration of the micro-strip  105  and ground  106  coupled with dielectric material  102 . In another embodiment, the embedded conductive traces and electrodes may be used as shown in  FIG. 9   d.  When electromagnetic interference is concerned, the embedded conductive traces and electrodes may be preferable because it can help shield the electromagnetic wave. In a further embodiment, multi-layers conductive traces and electrodes structures may be used to provide multi-channel capability and  FIG. 9   e  shows one example of the configuration. The electromagnetic microwaves exiting out the openings will ionize the gas at the opening region and induce the turbulent flow.  FIG. 9   e  shows the openings are at in-plane direction. In one embodiment, the openings are not limited to only in-plane direction, but may be also at out-of-plane direction as shown in  FIG. 9   f.    
         [0043]    At very high electromagnetic frequencies, the losses due to radiation can be eliminated and the resistive losses can be minimized, by using closed resonant cavities. A cavity resonator stores both magnetic and electric fields, the energy oscillating between the two, losing energy only to the conducting walls if a perfect dielectric fills the space. The resonant frequency of the cavity is determined by the shape of the cavity and the mode, or allowable field distribution, of the electromagnetic energy that the cavity contains. In one embodiment, the micro-plasma and ions may be excited and generated by microwave cavities and varied forms of coupling of the electromagnetic microwave may be utilized.  FIG. 10  illustrates one example of the TE10 wave-guide  301  magnetically  303  coupled to a cylindrical resonator  302 . The top view of the system is shown in  FIG. 10   a  and the side view is shown in  FIG. 10   b.  In this case some of the magnetic field within the cavity leaks through an iris  305  cut into the sides of the wave-guide  301  and the resonator walls, thereby exciting waves in the guide, the larger the iris size, the stronger the degree of coupling. The locations of openings  306  to excite the micro-plasma and ions may be either on a wave-guide structure or on a cavity resonator structure, as long as the electrical field  304  at the locations is high enough to ionize the gas. In practical application, the locations where the maximum electrical field  304  occurs are to be carefully designed. In one embodiment, the shape and the geometry of the microwave wave-guide and cavity structures may be varied. In a further embodiment, varied forms of electromagnetic couplings may be used to excite the micro-plasma and ions, then to induce the turbulent flow. All the variations should be considered within the scope of the invention here. 
         [0044]      FIG. 11  illustrates the slots, holes, and trenches may be made on the wall of wave-guide  307  structure to provide the excitation of the micro-plasma and ions. Different configurations of the wave-guide structure and varied geometries of the holes, slot, and trenches may be used. In another embodiment, different configurations of the microwave cavities  308  may be used to excite the micro-plasma and ions. The location and size and geometry of the opening  309  where maximum electrical field occur may be computationally calculated and experimentally determined. 
         [0045]      FIG. 12  illustrates the coupling between micro-plasma and ions  401  and heat sink fins  402 . In one embodiment, the heat sink fins  402  may have different configurations, such as, straight micro-channel heat sink fins, cylindrical needle-shape pins, and the heat sink fins may have patterns to couple with micro-plasma and ions  401 . As mentioned earlier, the micro-plasma and ions  401  may be excited at the locations where the high electrical field occurs. The coupling of the heat sink fins  402  with microwave may enhance the micro-plasma and ions gas flow and induce the local turbulence flow in the fluid. In another embodiment, the micro-plasma and ions  401  may be excited and generated with electromagnetic microwave from micro-strips, microwave cavities, and microwave thrusters structures. 
         [0046]      FIG. 13  illustrates one example of the micro-plasma and ions cooling device  408  used to cool down the heat sources  405  inside an electronic device  400 . The heat source  405 , such as IC, may couple to micro-channel heat sink fins  407  through a heat transferring pipe  406 , such as heat pipe. In this way, the heat will be dissipated out to a larger area. The micro-plasma and ions cooling device  408  may couple to the micro-channel heat sink fins  407 . The induced plasma gas flow will therefore cool down the micro-channels heat sink fins  407 . In one embodiment, the micro-plasma and ions may couple to a heat sink fan  411 . 
         [0047]    The micro-plasma and ions cooling actuator  408  may be made of wave guide structure, microwave cavity structure, micro-strip structure, and embedded conductive traces and electrodes. The cooling actuator  408  may couple to heat sink fins at the inlet, at the outlet, at the top, at the bottom, or in the middle of the heat sink fins  407 . In one embodiment, all components may couple to a board  410 , such as printed circuit board, so the entire device can be made very small. In another embodiment, the actuators may be made in a bulk scale, a micron meter scale, and a nano meter scale. Furthermore, the actuators may be directly manufactured on a silicon chip structure and the actuators may be manufactured with micro-electro-mechanical wafer processing techniques;