CONTACT STRESS SENSOR

• US 20090223299A1
• Filed: 11/19/2008
• Published: 09/10/2009
• Est. Priority Date: 11/17/2004
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Inventors: Kotovsky, Jack
• Granted Patent: US 8,109,149 B2
• Time in Patent Office: Days
• US Class Current: 73/777
• CPC Class Codes: G01L 1/18 using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material

Abstract

A contact stress sensor includes one or more MEMS fabricated sensor elements, where each sensor element of includes a thin non-recessed portion, a recessed portion and a pressure sensitive element adjacent to the recessed portion. An electric circuit is connected to the pressure sensitive element. The circuit includes a thermal compensator and a pressure signal circuit element configured to provide a signal upon movement of the pressure sensitive element.

Claims

1. An apparatus, comprising:

a sensor element that includes a body having a thickness no greater than 280 μ

m, a recessed portion and a pressure sensitive element that extends over said recessed portion; and

an electric circuit operatively connected to said pressure sensitive element, wherein said circuit includes a pressure signal generating circuit element configured to provide a signal when a force is exerted on said pressure sensitive element.

2. The apparatus of claim 1, wherein said sensor element is one of a plurality of sensor elements.

3. The apparatus of claim 1, further comprising a package, wherein said sensor element is located within said package to provide a packaged sensor element, wherein said sensor element together with said package comprises a total thickness no greater than 300 μ

m.

4. The apparatus of claim 2, wherein said plurality of sensor elements is configured in an array selected from the group consisting of a one dimensional array and a two dimensional array.

5. The apparatus of claim 1, wherein said sensor element is manufactured by a microfabrication process.

6. The apparatus of claim 1, wherein said sensor element is processed by attaching it with an adhesive to a handle.

7. The apparatus of claim 6, wherein said adhesive comprises an ethylene vinyl acetate polymer.

8. The apparatus of claim 1, wherein said sensor element comprises silicon.

9. The apparatus of claim 1, wherein said sensor element comprises single crystal silicon.

10. The apparatus of claim 1, wherein said pressure sensitive element comprises a configuration selected from the group consisting of a diaphragm, a cantilever and a doubly supported beam.

11. The apparatus of claim 3, wherein said package comprises a base layer, a mid-layer with an opening for said sensor element, and a capping layer, wherein said mid-layer is between said base layer and said capping layer.

12. The apparatus of claim 11, wherein a conductive trace is located between said base layer and said mid-layer and is in electrical contact with said electrical circuit.

13. The apparatus of claim 12, wherein said base layer, said mid-layer and said capping layer comprise the same material.

14. The apparatus of claim 13, wherein said base layer, said mid-layer and said capping layer comprise polyimide.

15. The apparatus of claim 12, further comprising solder between said conductive trace and said circuit.

16. The apparatus of claim 15, wherein said base layer comprises polymer, wherein said mid-layer and said capping layer each comprise at least one adhesive layer and at least one polymer layer.

17. The apparatus of claim 16, wherein said base layer further comprises a solder shim layer.

18. The apparatus of claim 17, wherein said solder shim layer is configured to uniformly support said sensor element between said sensor element and said conductive trace.

19. The apparatus of claim 11, wherein said base layer comprises means for providing a deterministic solder thickness between said sensor element and said conductive trace.

20. The apparatus of claim 12, wherein said conductive trace is in electrical contact with, but is not adhered or bonded to, said electrical circuit.

21. The apparatus of claim 12, wherein said conductive trace is not bonded to said electric circuit.

22. The apparatus of claim 11, further comprising means for relieving residual stress curl of said package.

23. The apparatus of claim 10, further comprising a sealed reference gas volume beneath said diaphragm.

24. The apparatus of claim 1, further comprising a load amplification element in operative contact with said pressure sensitive element.

25. The apparatus of claim 24, wherein said load amplification element comprises an electro-plated bump.

26. The apparatus of claim 1, wherein said electric circuit comprises implant material implanted into said pressure sensitive element, wherein said pressure sensitive element comprises a substrate selected from the group consisting of an N type substrate, a P type substrate, an N type well in a P type substrate and a P type well in an N type substrate.

27. The apparatus of claim 26, wherein when said substrate comprises an N type substrate, said implant material comprises a P type material, wherein when said substrate comprises a P type substrate, said implant material comprises an N type material.

28. The apparatus of claim 26, wherein when said substrate comprises an N type well in a P type substrate said implant comprises a P type implant and when said substrate comprises a P type well in an N type substrate said implant comprises an N type implant.

29. The apparatus of claim 26, wherein said implant material has been annealed.

30. The apparatus of claim 1, wherein said pressure sensitive element comprises a diaphragm, and further comprises a thermal compensator comprising at least one piezoresistive circuit operatively placed on said diaphragm, wherein said pressure signal circuit element comprises at least one piezoresistive circuit operatively placed on said diaphragm.

31. The apparatus of claim 1, wherein said sensor element comprises single crystal silicon, wherein said single crystal silicon comprises a <

100>

crystalline axis and a <

110>

crystalline axis, wherein a thermal compensator is operatively placed on said <

100>

crystalline axis and wherein said pressure signal circuit element is operatively placed on said <

110>

crystalline axis for p-type piezoresistors in a (100) wafer.

32. The apparatus of claim 31, wherein said thermal compensator comprises a first pair of piezoresistive circuits located about 180 degrees apart and wherein said pressure signal circuit element comprises a second pair of piezoresistive circuits located about 180 degrees apart.

33. The apparatus of claim 8, wherein said pressure sensitive element comprises a diaphragm, wherein said thermal compensator comprises at least one piezoresistive circuit placed on said non-recessed portion, wherein said pressure signal circuit element comprises at least one piezoresistive circuit operatively placed on said diaphragm.

34. The apparatus of claim 17, wherein said polymer comprises polyimide.

35. The apparatus of claim 12, wherein at least one of said base layer, said mid-layer or said capping layer comprises a B-stage polyimide.

36. The apparatus of claim 10, wherein said diaphragm is about 15 μ

m thick, wherein said body has a thickness that is about 50 μ

m.

37. The apparatus of claim 11, further comprising a compliant layer attached to said base layer on the side of said base layer opposite to that of said mid-layer.

38. The apparatus of claim 26, wherein said implant material is electrically connected to a conductor that extends off of said sensor element.

39. The apparatus of claim 26, wherein said implant material is electrically connected, at a bond pad, to a conductor that extends off of said sensor element, wherein said bond pad is stress shielded to prevent damage to said thin-film conductor.

40. The apparatus of claim 2, further comprising means for connecting said plurality of sensor elements together.

41. The apparatus of claim 40, wherein said means for connecting comprise an extensible interconnect that allows complex curvature conformability.

42. The apparatus of claim 41, wherein said flexible interconnect comprises a conductive trace.

43. The apparatus of claim 42, wherein said conductive trace is embedded in polymer.

44. The apparatus of claim 41, wherein said flexible interconnect comprises a metal trace on a silicon spring.

45. The apparatus of claim 1, wherein said plurality of sensor elements are electrically in a row and column configuration.

46. The apparatus of claim 10, wherein said cantilever or beam is formed by a deep reactive ion etch followed by a potassium hydroxide etch.

47. The apparatus of claim 1, further comprising means for providing thermal compensation to said signal.

48. The apparatus of claim 3, wherein said package comprises a material selected from the group consisting of ceramic, metal, and plastic.

49. The apparatus of claim 48, wherein said plastic is selected from the group consisting of hard plastic and epoxy based plastic.

50. The apparatus of claim 3, wherein said package has a thickness no greater than 100 μ

m.

51. The apparatus of claim 3, wherein said package comprises a material selected from the group consisting of polymide, silicone and mylar.

52. The apparatus of claim 1, wherein said sensor element comprises a thickness no greater than 100 μ

m.

53. The apparatus of claim 1, wherein said pressure sensitive element comprises a thickness no greater than 50 μ

m.

54. The apparatus of claim 1, wherein said sensor element has a thickness no greater than 25 μ

m.

55. The apparatus of claim 47, wherein said means for providing thermal compensation are selected from the group consisting of a full wheat-stone bridge, a half wheat-stone bridge, a quarter bridge and a temperature device.

56. The apparatus of claim 1, wherein said pressure sensitive element comprises a circuit comprising a circuit element selected from the group consisting of a piezoresistive circuit element, a piezoelectric circuit element and a capacitive circuit element.