Electroosmotic microchannel cooling system

• US 7,131,486 B2
• Filed: 03/10/2003
• Issued: 11/07/2006
• Est. Priority Date: 09/28/2001
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Zeng, Shulin, Santiago, Juan G., Koo, Jae-Mo, Zhang, Lian, Kenny, Thomas W., Huber, David E., Goodson, Kenneth E., Mikkelsen, James C., Jiang, Linan, Laser, Daniel J., Chen, Chuan-Hua, Wang, Evelyn Ning-Yi
• Primary Examiner(s): MCKINNON, TERRELL L
• Application Number:
  US10/385,086
• Publication Number:
  US 20030164231A1
• Time in Patent Office: 1,338 Days
• Field of Search: 165/104.12, 165/185, 165/104.21, 165/104.33, 165/80.4, 361/699, 361/700, 624/77, 624/80, 174/15.2, 257/714, 257/715, 257/716
• US Class Current: 165/80.4
• CPC Class Codes: F04B 19/006 Micropumps F04B43/043 and F04B43/095 take precedence
• CPC Class Codes: F28D 15/00 Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies F28D17/00, F28D19/00, F28D20/00 take precedence
• CPC Class Codes: F28F 2260/02 having microchannels
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/32145 the bodies being stacked
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/45169 Platinum (Pt) as principal constituent
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2225/06562 at least one device in the stack being rotated or offset
• CPC Class Codes: H01L 23/473 by flowing liquids H01L23/4332, H01L23/4338 take precedence
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01322 Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/10158 at the passive surface
• CPC Class Codes: H01L 2924/10253 Silicon [Si]
• CPC Class Codes: H01L 2924/1461 MEMS
• CPC Class Codes: H01L 2924/3011 Impedance

Abstract

Apparatus and methods according to the present invention preferably utilize electroosmotic pumps that are capable of generating high pressure and flow without moving mechanical parts and the associated generation of unacceptable electrical and acoustic noise, as well as the associated reduction in reliability. These electroosmotic pumps are preferably fabricated with materials and structures that improve performance, efficiency, and reduce weight and manufacturing cost relative to presently available micropumps. These electroosmotic pumps also preferably allow for recapture of evolved gases and deposited materials, which may provide for long-term closed-loop operation. Apparatus and methods according to the present invention also allow active regulation of the temperature of the device through electrical control of the flow through the pump and can utilize multiple cooling loops to allow independent regulation of the special and temporal characteristics of the device temperature profiles. Novel microchannel structures are also described.

Claims

1. A cooling system for a heat emitting device, the cooling system operating using a fluid having a liquid phase, the cooling system comprising:

a substrate including at least a portion of a microchannel disposed therein, the substrate adapted to physically connect to the heat emitting device, thereby providing for the transfer of thermal energy from the heat emitting device to the substrate, and the further transfer of thermal energy from the substrate to the fluid disposed within the microchannel, the microchannel configured to provide flow of the fluid therethrough;

a heat exchanger configured to provide flow of the fluid therethrough and the transfer of thermal energy out of the fluid;

a high flow rate electroosmotic pump, the electroosmotic pump creating the flow of the fluid; and

wherein the substrate, the heat exchanger, and the electroosmotic pump are configured to operate together.

2. A method for transferring heat from a heat-generating device to a fluid in a closed-loop cooling system comprising pumping the fluid through the closed-loop at sub-atmospheric pressure by a high flow rate electrokinetic pump.

3. The method for transferring heat of claim 2 wherein the heat is transferred to the fluid in a heat exchanger coupled to the heat-generating device.

4. The method for transferring heat of claim 3 wherein the fluid exits from the heat exchanger at sub-atmospheric pressure.

5. The method for transferring heat of claim 3 wherein the fluid enters the heat exchanger in a liquid phase and exits the heat exchanger in a mixed liquid-vapor phase.

6. The method for transferring heat of claim 2 further comprising decreasing the pressure of the fluid as it transits through the heat exchanger to control a local boiling point of the fluid.

7. The method for transferring heat of claim 2 further comprising controlling a boiling point of the fluid at discrete points in the heat exchanger to cool one region of the coupled heat-generating device at a different rate than in another region.

8. The method for transferring heat of claim 2 further comprising varying the pressure of the fluid as it transits through the heat exchanger to control a boiling point of the fluid.

9. The method of claim 2 wherein the flow rate is greater than 1 ml/min.

10. A method for providing a transfer of heat from a heat-generating device at a sub-atmospheric pressure in a closed loop cooling system, comprising the steps of:

generating a flow of a fluid having a liquid phase using a high flow rate electroosmotic pump;

directing the flow of fluid through a microchannel from a liquid phase at an inlet to a liquid-vapor phase at an outlet, the microchannel configured such that the heated fluid leaves the microchannel at sub-atmospheric pressure;

directing the heated fluid leaving the microchannel to pass through a heat exchanger to create a cooled fluid; and

directing the cooled fluid back to the electroosmotic pump to create a closed loop fluid flow.

11. The method for providing of claim 10 further comprising determining a location and a plurality of dimensions of the microchannel such that the fluid exits at sub-atmospheric pressure and sufficient thermal energy is transferred to the fluid to maintain the temperature of the particular integrated circuit below an operational limit.

12. The method for providing of claim 11 wherein determining the plurality of dimensions includes selecting a cross section that minimizes a flow resistance through the microchannel.

13. The method for providing claim 12 wherein determining the plurality of dimensions includes selecting a width for the microchannel that provides a lower average wall temperature for a constant cross section.

14. The method for providing of claim 11 wherein determining the plurality of dimensions includes selecting a constant cross section and a variable width for the microchannel, the width being varied between an inlet and an outlet of the microchannel.

15. The method for providing of claim 10 wherein the pressure of the fluid leaving the substrate is in a range from atmospheric pressure to 0.1 pound per square inch.

16. The method for providing of claim 10 wherein the pressure of the fluid leaving the substrate is selected to generate a specific liquid-vapor transition temperature and a specific heat-generating device temperature.

17. The method for providing of claim 10 wherein the fluid is any one of a de-ionized water, an aqueous buffer solution and an organic liquid.

18. The method for providing of claim 10 wherein the fluid comprises at least 10% acetonitrile by mass.

19. The method for providing of claim 10 wherein the fluid comprises at least 10% methanol by mass.

20. A closed loop cooling system for a heat-generating device and using a fluid having both a liquid phase and a liquid-vapor phase, comprising:

a high flow rate electrokinetic pump;

a substrate including at least a portion of a microchannel disposed therein, the substrate disposed on the heat-generating device to transfer thermal energy from the heat-generating device to the substrate, and the further transfer of thermal energy to the fluid disposed within the microchannel; and

wherein the microchannel is configured to provide flow of the fluid therethrough at sub-atmospheric pressure, wherein the fluid is in the liquid phase when entering and in the liquid-vapor phase when exiting the microchannel.

21. The closed loop cooling system for a heat-generating device of claim 20 further comprising a heat exchanger to provide the flow of fluid therethrough and the transfer of thermal energy from the heat exchanger to the surroundings.

22. The closed loop cooling system for a heat-generating device of claim 21 wherein the substrate, heat exchanger and electroosmotic pump operate together to form a closed loop system.

23. The closed loop cooling system for a heat-generating device of claim 20 wherein the microchannel is configured to minimize flow resistance through the microchannel.

24. The closed loop cooling system for a heat-generating device of claim 20 wherein the microchannel is configured to provide a lower average wall temperature for a constant cross section.

25. The closed loop cooling system for a heat-generating device of claim 20 wherein the microchannel has a constant cross section and a width that varies between an inlet and an outlet of the microchannel.

26. The closed loop cooling system for a heat-generating device of claim 20 wherein the sub-atmospheric pressure is in a range from atmospheric pressure to 0.1 pound per square inch.

27. The closed loop cooling system for a heat-generating device of claim 20 wherein the pressure at an exit from the substrate is selected to generate a specific liquid-vapor transition temperature and a specific heat-generating device temperature.

28. The closed loop cooling system for a heat-generating device of claim 20 wherein the fluid is at least one of a de-ionized water, an aqueous buffer solution and an organic liquid.

29. The closed loop cooling system for a heat-generating device of claim 20 wherein the flow rate is greater than 1 ml/min.

30. A method for transferring heat from a heat-generating device to a heat exchanger in a closed loop cooling system including a high-flow rate electrokinetic pump, the heat exchanger including a microchannel that can transfer fluid therethrough, the fluid entering the microchannel in a liquid state and exiting in a liquid-vapor state, the method comprising the steps of:

determining a plurality of dimensions of the microchannel such that the fluid exits at sub-atmospheric pressure and sufficient thermal energy is transferred to the fluid to maintain the temperature of the heat-generating device below an operational limit; and

coupling the microchannel with the determined dimensions to the heat-generating device.

31. The method for transferring heat of claim 30 wherein the step of determining the plurality of dimensions includes selecting a cross section that minimizes a flow resistance through the microchannel.

32. The method for transferring heat of claim 31 wherein the step of determining the plurality of dimensions includes selecting a width for the microchannel that provides a lower average wall temperature for a constant cross section.

33. The method for transferring heat of claim 30 wherein the step of determining the plurality of dimensions includes selecting a constant cross section area and a variable width for the microchannel, the width being varied between an inlet and an outlet of the microchannel.

34. The method for transferring heat of claim 30 wherein the step of determining the plurality of dimensions includes selecting a width and a height that vary with position along the microchannel so as to minimize an overall pressure drop.

35. The method for transferring heat of claim 30 wherein the step of determining the plurality of dimensions includes selecting a width and a height that vary with position along the microchannel so as to minimize the temperature variation along the microchannel.

36. The method for transferring heat of claim 30 wherein the step of determining the plurality of dimensions includes selecting a width and a height for a plurality of microchannels that vary with position along each microchannel, wherein the width and height variations are different for different microchannels so as to minimize the temperature variation across the heat-generating device where the heat-generating device has a non-uniform spatial distribution of heat.

37. The method for transferring heat of claim 30 wherein the exit pressure from the microchannel is in a range from atmospheric pressure to 0.1 pound per square inch.

38. The method for transferring heat of claim 30 wherein the exit pressure is selected to generate a specific liquid-vapor transition temperature and a specific heat-generating device temperature.

39. The method for transferring heat of claim 30 wherein the fluid is at least one of a de-ionized water, an aqueous buffer solution and an organic liquid.

40. The method for transferring heat of claim 30 wherein the fluid comprises at least 10% acetonitrile by mass.

41. The method for transferring heat of claim 30 wherein the fluid comprises at least 10% methanol by mass.

42. The method for transferring heat of claim 30 wherein the flow rate is greater than 1 ml/min.

43. An apparatus for use with a closed loop cooling system, including a high flow rate electroosmotic pump heat exchanger, that operates using a fluid having both a liquid phase and a liquid-vapor phase, comprising:

a heat generating device including a heat generating element;

a substrate physically connected to the heat generating device, the heat generating device and the substrate each containing at least a portion of a microchannel and providing for the transfer of thermal energy to the fluid disposed within the microchannel, the microchannel configured to provide flow of the fluid through the microchannel so as to exit the microchannel at sub-atmospheric pressure, wherein the fluid is in the liquid phase when entering and in the liquid-vapor phase when exiting the microchannel.

44. The apparatus for use with a closed loop cooling system of claim 43 further comprising a heat exchanger configured to provide flow of the fluid therethrough and the transfer of thermal energy out of the fluid.

45. The apparatus for use with a closed loop cooling system of claim 43 further comprising a heat exchanger and an electroosmotic pump that are configured to operate together with the substrate to create a closed loop fluid flow.

46. The apparatus for use with a closed loop cooling system of claim 43 wherein the heat generating device further comprises a temperature control circuit.

47. The apparatus for use with a closed loop cooling system of claim 43 wherein a plurality of dimensions of the microchannel are selected to minimize flow resistance through the microchannel.

48. The apparatus for use with a closed loop cooling system of claim 43 wherein a plurality of dimensions of the microchannel are selected to provide a lower average wall temperature for a constant cross section.

49. The apparatus for use with a closed loop cooling system of claim 43 wherein a constant cross section and a variable width are selected for the microchannel, the width being varied between an inlet and an outlet of the microchannel.

50. The apparatus for use with a closed loop cooling system of claim 43 wherein a width and a height are selected for the microchannel that vary with position along the microchannel so as to minimize an overall pressure drop.

51. The apparatus for use with a closed loop cooling system of claim 43 wherein a width and a height are selected for the microchannel that vary with position along the microchannel so as to minimize the temperature variation along the microchannel.

52. The apparatus for use with a closed loop cooling system of claim 43 wherein a width and a height are selected for the microchannel that vary with position along each microchannel, and wherein the width and height variations are different for different microchannels so as to minimize the temperature variation across the heat-generating device where the heat-generating device has a non-uniform spatial distribution of heat.

53. The apparatus for use with a closed loop cooling system of claim 43 wherein the exit pressure of the fluid from the substrate is in a range from atmospheric pressure to 0.1 pound per square inch.

54. The apparatus for use with a closed loop cooling system of claim 43 wherein the exit pressure of the fluid from the substrate is selected to generate a specific liquid-vapor transition temperature and a specific heat generating device temperature.

55. The apparatus for use with a closed loop cooling system of claim 43 wherein the fluid is at least one of a de-ionized water, an aqueous buffer solution and an organic liquid.

56. The method for transferring heat of claim 43 wherein the flow rate is greater than 1 ml/min.

57. A closed-loop fluid cooling system for a heat-generating device comprising:

a high flow rate electrokinetic pump for pumping the fluid through the closed-loop system;

a microchannel heat exchanger coupled to the heat-generating device for transferring heat to the fluid, the fluid entering the heat exchanger in a liquid state and exiting in a liquid-vapor state;

a second heat exchanger coupled to ambient for transferring heat from the fluid to an external environment; and

wherein the static pressure is below the ambient pressure in at least one location in the closed-loop.

58. The closed-loop fluid cooling system of claim 57 wherein the temperature of the heat-generating device is maintained below 90°

C.

59. The closed-loop fluid cooling system of claim 57 wherein the temperature of the heat-generating device is maintained below 80°

C.

60. The closed-loop fluid cooling system of claim 57 wherein the temperature of the heat-generating device at a location where vapor is generated is maintained in the range between 90°

C. and 50°

C.

61. The closed-loop fluid cooling system of claim 57 wherein the flow rate is greater than 1 ml/min.