Microelectromechanical (MEM) fluid health sensing device and fabrication method

• US 20070062261A1
• Filed: 09/22/2005
• Published: 03/22/2007
• Est. Priority Date: 09/22/2005
• Status: Active Grant

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Scientific Licensing LLC (Teledyne Technologies Incorporated)
• Inventors: DeNatale, Jeffrey, Kendig, Martin, Borwick, Robert, Stupar, Philip
• Granted Patent: US 7,328,604 B2
• Time in Patent Office: Days
• US Class Current: 73/54.20
• CPC Class Codes: G01N 11/16 by measuring damping effect upon oscillatory body
• CPC Class Codes: G01N 33/2888 Lubricating oil characteristics, e.g. deterioration lubricating properties G01N33/30

Abstract

A microelectromechanical (MEM) fluid health sensing device comprises a viscosity sensor which provides an output that varies with the viscosity of a fluid in which it is immersed, and at least one other sensor which provides an output that varies with another predetermined parameter of the fluid. The viscosity sensor is preferably a MEM device fabricated by means of a “deep etch” process. The sensors are preferably integrated together on a common substrate, though they might also be fabricated separately and packaged together to form a hybrid device. A data processing means may be included which receives the sensor outputs and provides one or more outputs indicative of the health of the fluid. Sensor types which may be part of the present device include, for example, a temperature sensor, a MEM electrochemical sensor, a MEM accelerometer, a MEM contact switch lubricity sensor, and/or an inductive metallic wear sensor.

Claims

1. A microelectromechanical (MEM) fluid health sensing device, comprising:

a MEM viscosity sensor arranged to, when immersed in a fluid, provide an output which varies with the viscosity of said fluid; and

at least one other sensor arranged to, when immersed in said fluid, provide an output which varies with a predetermined parameter of said fluid, said viscosity and said at least one other sensor integrated together on a common substrate.

2. The device of claim 1, further comprising a data processing means which receives said sensor outputs and is arranged to provide one or more outputs indicative of the health of said fluid.

3. The device of claim 1, wherein said at least one other sensor comprises a temperature sensor arranged to, when immersed in said fluid, provide an output which varies with the temperature of said fluid.

4. The device of claim 3, wherein said temperature sensor comprises a lithographed trace of a material having a known temperature coefficient of electrical resistance.

5. The device of claim 4, wherein said temperature sensor is fabricated directly on said MEM viscosity sensor.

6. The device of claim 1, wherein said at least one other sensor comprises a MEM electrochemical sensor arranged to, when immersed in said fluid, provide an output which varies with one or more electrochemical properties of said fluid.

7. The device of claim 6, wherein said electrochemical properties comprise pH, corrosivity, moisture content, Total Acid Number (TAN), Total Base Number (TBN), oxidation state, conductivity, and/or dielectric constant.

8. The device of claim 6, wherein said electrochemical sensor comprises a plurality of static interdigitated electrodes.

9. The device of claim 1, wherein said at least one other sensor comprises a MEM accelerometer arranged to provide an output which varies with vibration.

10. The device of claim 9, wherein said MEM accelerometer is locally capped to isolate it from said fluid.

11. The device of claim 9, wherein said accelerometer comprises:

a least one proof mass;

at least one anchor member;

compliant flexures coupled between respective ones of said anchor members and proof masses;

a movable comb structure affixed to each of said proof masses; and

fixed comb structures interdigitated with respective ones of said movable comb structures, such that said proof masses move with respect to said anchor members and the capacitance between said movable and fixed comb structures varies with acceleration.

12. The device of claim 1, wherein said at least one other sensor comprises a MEM contact switch lubricity sensor arranged to, when immersed in said fluid, provide an output which varies with said fluid'"'"'s lubricating performance.

13. The device of claim 12, wherein said lubricity sensor includes a pair of switch contacts and said output varies with the applied voltage or force needed to make said switch contacts conduct.

14. The device of claim 1, wherein said at least one other sensor comprises an inductive metallic wear sensor arranged to, when immersed in said fluid, provide an output which varies with said fluid'"'"'s elemental and particulate content.

15. The device of claim 14, wherein said wear sensor includes first and reference plated micromachined 3D coils, said first coil containing fluid to be sensed and said reference coil containing filtered fluid, said coils arranged such that said output varies with the relative inductance of the coils when said coils are energized with an AC current.

16. The device of claim 1, wherein said MEM viscosity sensor includes movable and stationary elements, at least one of said movable elements arranged to move in said fluid such that it is subjected to a predominately shear force.

17. The device of claim 16, wherein said at least one of said movable elements is arranged to be displaced laterally relative to at least one of said stationary elements.

18. The device of claim 16, wherein said at least one of said movable elements is arranged to be displaced vertically relative to at least one of said stationary elements.

19. The device of claim 1, wherein said MEM viscosity sensor includes movable and stationary elements, said sensor comprising a silicon-on-insulator (SOI) wafer which includes a silicon device layer, said device layer etched using a deep reactive ion etch (DRIE) to form said movable and stationary elements.

20. A microelectromechanical (MEM) fluid health sensing device, comprising:

a MEM viscosity sensor arranged to sense the viscosity of a fluid in which it is immersed and to provide an output which varies with said viscosity, comprising;

a semiconductor wafer;

a substrate bonded to said wafer and thereby forming a composite structure, portions of said composite structure patterned and etched to form first and second sets of conductive plates spaced apart from each other and having respective parallel surface areas, said first set of plates arranged to interleave with said second set of plates such that their surface areas at least partially overlap to produce a capacitance, one of said sets of plates being a movable element and the other of said sets of plates being a stationary element; and

a drive means for displacing said movable element relative to said stationary element, said viscosity sensor arranged to, when immersed in said fluid, provide an output which varies with the viscosity of said fluid; and

at least one other sensor arranged to, when immersed in said fluid, provide an output which varies with a parameter of said fluid;

said MEM viscosity sensor and said at least one other sensor packaged together in a common housing.

21. The device of claim 20, wherein said MEM viscosity sensor is arranged such that said drive means displaces said movable element laterally relative to said stationary element.

22. The device of claim 20, wherein said MEM viscosity sensor is arranged such that said drive means displaces said movable element vertically relative to said stationary element.

23. The device of claim 20, further comprising an organic adhesive which bonds said substrate to said wafer.

24. The device of claim 20, wherein said wafer and substrate have respective bonding pads which are aligned and mechanically connected such that a thermocompression bond is formed to effect the bonding of said wafer to said substrate.

25. The device of claim 24, wherein said bonding pads are gold (Au) and said thermocompression bond is an Au—

Au thermocompression bond.

26. The device of claim 20, wherein said wafer and substrate have respective bonding pads which are aligned and mechanically connected such that an anodic bond is formed to effect the bonding of said wafer to said substrate.

27. The device of claim 20, wherein said semiconductor wafer is a silicon-on-insulator (SOI) wafer.

28. The device of claim 20, wherein said MEM viscosity sensor and said at least one other sensor are separately fabricated and packaged together in said common housing to form a hybrid device.

29. The device of claim 20, wherein said MEM viscosity sensor and said at least one other sensor are integrated together on a common substrate.

30. The device of claim 20, further comprising a data processing means which receives said sensor outputs and is arranged to provide one or more outputs indicative of the health of said fluid.

31. The device of claim 20, wherein said at least one other sensor comprises one or more sensors selected from a group consisting of:

a MEM electrochemical sensor arranged to, when immersed in said fluid, provide an output which varies with one or more electrochemical properties of said fluid;

a MEM accelerometer arranged to provide an output which varies with vibration;

a MEM contact switch lubricity sensor arranged to, when immersed in said fluid, provide an output which varies with said fluid'"'"'s lubricating performance;

or

a inductive metallic wear sensor arranged to, when immersed in said fluid, provide an output which varies with said fluid'"'"'s elemental and particulate content.

32. The device of claim 20, further comprising a sensing means for sensing said amount of overlap.

33. The device of claim 20, wherein said drive means is selected from a group consisting of an electrostatic actuator, thermal actuator, Lorentz force actuator, or piezoelectric actuator, said actuator coupled to said movable element.

34. A method of determining the health of a fluid, comprising:

providing a microelectromechanical (MEM) fluid health sensing device, comprising;

a MEM viscosity sensor arranged to, when immersed in a fluid, provide an output which varies with the viscosity of said fluid; and

at least one other sensor arranged to, when immersed in said fluid, provide an output which varies with a predetermined parameter of said fluid, said viscosity and said at least one other sensor integrated together on a common substrate;

immersing said sensors in a fluid, the health of which is to be determined; and

processing said sensor outputs to provide one or more outputs indicative of the health of said fluid.

35. The method of claim 34, wherein said at least one other sensor comprises a temperature sensor arranged to, when immersed in said fluid, provide an output which varies with the temperature of said fluid.

36. The method of claim 34, wherein said at least one other sensor comprises a MEM electrochemical sensor arranged to, when immersed in said fluid, provide an output which varies with one or more electrochemical properties of said fluid.

37. The method of claim 34, wherein said MEM viscosity sensor includes movable and stationary elements, said method further comprising displacing at least one of said movable elements laterally relative to at least one of said stationary elements such that it is subjected to a predominately shear force.

38. The method of claim 34, wherein said MEM viscosity sensor includes movable and stationary elements, said method further comprising displacing at least one of said movable elements vertically relative to at least one of said stationary elements such that it is subjected to a predominately shear force.

39. The method of claim 34, wherein said MEM viscosity sensor comprises:

first and second sets of conductive plates spaced apart from each other and having respective parallel surface areas, said first set of plates arranged to interleave with said second set of plates such that their surface areas at least partially overlap to produce a capacitance, one of said sets of plates being a movable element and the other of said sets of plates being a stationary element; and

a sensing means for sensing said amount of overlap;

said method further comprising;

operating said drive means to displace said movable element relative to said stationary element; and

operating said sensing means to sense said amount of overlap.

40. A method of fabricating a microelectromechanical (MEM) fluid health sensing device, comprising:

providing a semiconductor wafer;

providing a substrate;

bonding said wafer and substrate together to form a composite structure; and

patterning and etching portions of said composite structure to form at least two sensors which, when immersed in a fluid the health of which is to be determined, provide respective outputs which vary with one or more parameters of said fluid.

41. The method of claim 40, wherein at least one of said sensors is a micro-electromechanical (MEM) sensor.

42. The method of claim 40, wherein said MEM sensor is arranged to sense the viscosity of said fluid.

43. The method of claim 42, wherein said patterning and etching of said composite structure form a stationary element and a movable element such that said movable element is mechanically coupled to said stationary element, said movable element and said stationary element conductive and at least partially overlapping so as to produce a capacitance which varies with the amount of overlap.

44. The method of claim 43, wherein said stationary element and a movable element comprise a first set and a second set of conductive plates, respectively, said sets of conductive plates spaced apart from each other and having respective parallel surface areas, said first set of plates arranged to interleave with said second set of plates such that their surface areas at least partially overlap to produce said capacitance.

45. A method of fabricating a microelectromechanical (MEM) fluid health sensing device which includes at least one MEM sensor, each of which has a stationary element and a movable element displaceable relative to the stationary element, comprising:

providing a silicon-on-insulator (SOI) wafer which includes a silicon handle layer and a silicon device layer;

providing a substrate;

etching a recessed area into said substrate;

bonding said wafer to said substrate to form a composite structure;

removing said silicon handle layer from the SOI wafer to expose said silicon device layer;

patterning and etching portions of said composite structure to define the stationary and movable elements of at least one MEM sensor, and at least one other sensor;

depositing, patterning and etching one or more metallization layers on said composite structure to provide electrical interconnections for said sensors; and

releasing said movable elements;

said sensors arranged to provide respective outputs which vary with one or more parameters of a fluid in which they are immersed.

46. The method of claim 45, wherein said device layer is etched using a deep reactive ion etch (DRIE).

47. The method of claim 45, wherein said bonding of said wafer and substrate is effected with an organic adhesive.

48. The method of claim 45, wherein said bonding of said wafer and substrate comprises:

patterning one or more bonding pads on said wafer;

patterning one or more bonding pads on said substrate such that said substrate'"'"'s bonding pads can be aligned with said wafer'"'"'s bonding pads;

aligning said wafer'"'"'s bonding pads with said substrate'"'"'s bonding pads; and

mechanically connecting the bonding pads of said wafer and substrate to produce a mechanical bond which effects said bonding.

49. The method of claim 48, wherein said mechanical bond is a thermocompression bond.

50. The method of claim 48, wherein said mechanical bond is an anodic bond.

51. The method of claim 45, wherein said silicon device layer comprises single crystal silicon.

52. The method of claim 45, wherein said metallization layers comprise a conductive refractory material.