Capacitive sensor

• US 7,353,711 B2
• Filed: 08/10/2004
• Issued: 04/08/2008
• Est. Priority Date: 08/11/2003
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Hunt, William, Wynne, John M., McCartney, Damien Joseph, O'Dowd, John, Hynes, Eamon, Martin, John R., Crowley, Patrick
• Primary Examiner(s): Allen; Anore J.
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US10/914,909
• Publication Number:
  US 20050229710A1
• Time in Patent Office: 1,337 Days
• Field of Search: 73700-756
• US Class Current: 73/718
• CPC Class Codes: G01L 13/025 using diaphragms
• CPC Class Codes: G01L 19/0076 using buried connections
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: H01L 2224/48091 Arched
• 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 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding

Abstract

A capacitive sensor including a housing having a hermetically sealed cavity, a plate in the cavity, a diaphragm forming a part of the cavity and spaced from the plate, a conductive layer on the first diaphragm, and a second conductive layer on the plate, the first and second conductive layers being the electrodes of a capacitor whose capacitance varies with the position of the diaphragm relative to the plate.

Claims

1. A capacitive sensor comprising:

a housing having a hermetically sealed cavity;

a first plate protruding within said cavity;

a first diaphragm forming a part of said cavity and spaced from said first plate;

a first conductive layer on said first diaphragm; and

a second conductive layer on said first plate, said first and second conductive layers being the electrodes of a capacitor whose capacitance varies with the position of said first diaphragm relative to said first plate.

2. The capacitive sensor of claim 1 in which said first diaphragm is disposed proximate a top surface of said housing.

3. The capacitive sensor of claim 1 in which said first diaphragm is disposed proximate a bottom surface of said housing.

4. The capacitive sensor of claim 1 in which said first diaphragm is disposed proximate a side surface of said housing.

5. The capacitive sensor of claim 1 in which said second conductive layer is disposed proximate a top surface of said first plate.

6. The capacitive sensor of claim 1 in which said second conductive layer is disposed proximate a bottom surface of said first plate.

7. The capacitive sensor of claim 1 in which said second conductive layer is disposed proximate a side surface of said first plate.

8. The capacitive sensor of claim 1 in which said housing includes a material chosen from the group consisting of ceramic, plastic, metal or any combination thereof.

9. The capacitive sensor of claim 1 in which said first plate includes an integrated circuit die.

10. The capacitive sensor of claim 1 in which said first plate includes a printed circuit board.

11. The capacitive sensor of claim 1 in which said first conductive layer is embedded in said first diaphragm.

12. The capacitive sensor of claim 1 in which said second conductive layer is embedded in said first plate.

13. The capacitive sensor of claim 1 in which said first conductive layer is disposed on the outer surface of said first diaphragm.

14. The capacitive sensor of claim 1 in which said first conductive layer is disposed on the inner surface of said first diaphragm.

15. The capacitive sensor of claim 1 in which said first conductive layer is disposed on a portion of said first diaphragm.

16. The capacitive sensor of claim 1 in which said second conductive layer is disposed on a portion of said first plate.

17. The capacitive sensor of claim 1 in which said housing includes a separately attached lid.

18. The capacitive sensor of claim 1 in which said diaphragm is a separately attached lid.

19. The capacitive sensor of claim 18 in which said diaphragm includes a material chosen from the group consisting of:

ceramic, plastic, metal, or any combination thereof.

20. The capacitive sensor of claim 1 in which said diaphragm is comprised of a material different than said housing.

21. The capacitive sensor of claim 18 in which said lid is attached to said housing by soldering said lid to a metal layer fused into said housing.

22. The capacitive sensor of claim 18 in which said lid is attached to said housing by welding said lid to a metal layer fused into said housing.

23. The capacitive sensor of claim 18 in which said lid is attached to said housing with an adhesive material.

24. The capacitive sensor of claim 18 in which said lid is attached to said housing with glass.

25. The capacitive sensor of claim 1 in which said first conductive layer includes a mesh of said conductive material for forming said electrode.

26. The capacitive sensor of claim 1 in which said first conductive layer includes a solid layer of conductive material for forming said electrode.

27. The capacitive sensor of claim 1 in which said first conductive layer includes a solid layer of conductive material with spaced orifices therein.

28. The capacitive sensor of claim 1 in which said second conductive layer includes a mesh of said conductive material for forming said electrode.

29. The capacitive sensor of claim 1 in which said second conductive layer includes a solid layer of conductive material for forming said electrode.

30. The capacitive sensor of claim 1 in which said second conductive layer includes a solid layer of conductive material with spaced orifices therein.

31. The capacitive sensor of claim 1 in which said first plate includes a material chosen from the group consisting of silicon, ceramic, glass, quartz, plastic, epoxy resin and metal.

32. The capacitive sensor of claim 1 in which said first plate includes an electrical sub-system.

33. The capacitive sensor of claim 32 in which said electrical sub-system converts said capacitance to one or more electrical signals.

34. The capacitive sensor of claim 32 in which said electrical sub-system measures said capacitance.

35. The capacitive sensor of claim 32 in which said electrical sub-system includes a transmitter for transmitting said one or more signals representative of said capacitance.

36. The capacitive sensor of claim 35 further including an antenna responsive to said one or more signals.

37. The capacitive sensor of claim 32 further including a receiver for receiving initiation signals.

38. The capacitive sensor of claim 32 in which said electrical sub-system measures the temperature proximate said sub-system.

39. The capacitive sensor of claim 38 in which said electrical sub-system transmits one or more signals representative of said temperature.

40. The capacitive sensor of claim 32 in which said electrical sub-system manages the power consumption of said electrical sub-system.

41. The capacitive sensor of claim 32 in which said electrical sub-system includes an interrogation device for allowing said sub-system to be externally interrogated.

42. The capacitive sensor of claim 32 in which said electrical sub-system receives external commands to manage the power consumption of said sub-system.

43. The capacitive sensor of claim 1 further including an inductor combined with said capacitor formed by said first and second conductive layers to form a resonant circuit.

44. The capacitive sensor of claim 1 in which said first plate includes one or more sensors.

45. The capacitive sensor of claim 44 in which said one or more sensors are chosen from the group consisting of:

an acceleration sensor, a temperature sensor and a motion sensor.

46. The capacitive sensor of claim 45 in which said first plate further includes a transmission device for transmission of one or more output signals of said one or more sensors.

47. The capacitive sensor of claim 1 further including first electrical interconnections disposed in said housing.

48. The capacitive sensor of claim 47 further including second electrical interconnections for connecting said second conductive layer on said first plate to said first electrical interconnections.

49. The capacitive sensor of claim 48 further including third electrical interconnections for connecting said first conductive layer on said diaphragm to said first electrical interconnections.

50. The capacitive sensor of claim 1 in which said capacitance represents pressure.

51. The capacitive sensor of claim 1 in which said capacitance represents the difference in pressure between said cavity and the exterior to said housing.

52. The capacitive sensor of claim 1 further including a proof mass disposed on said diaphragm for varying the position of said diaphragm relative to said plate in response to acceleration.

53. The capacitive sensor of claim 1 in which said second conductive layer includes a conductive spacer for reducing the gap distance between said first conductive layer and said second conductive layer.

54. The capacitive sensor of claim 1 in which said capacitance varies with said position of said diaphragm relative to said plate in response to an external force.

55. The capacitive sensor of claim 1 further including a second plate in said cavity.

56. The capacitive sensor of claim 55 in which said second plate includes an electrical sub-system.

57. The capacitive sensor of claim 56 in which said electrical sub-system converts said capacitance to one or more electrical signals.

58. The capacitive sensor of claim 56 in which said electrical sub-system measures said capacitance.

59. The capacitive sensor of claim 56 in which said electrical sub-system includes a transmitter for transmitting said one or more signals representative of said capacitance.

60. The capacitive sensor of claim 59 further including an antenna responsive to said one or more signals.

61. The capacitive sensor of claim 56 further including a receiver for receiving initiation signals.

62. The capacitive sensor of claim 56 in which said electrical sub-system measures the temperature proximate said sub-system.

63. The capacitive sensor of claim 62 in which said electrical sub-system transmits one or more signals representative of said temperature.

64. The capacitive sensor of claim 56 in which said electrical sub-system manages the power consumption of said electrical sub-system.

65. The capacitive sensor of claim 56 in which said electrical sub-system includes an interrogation device for allowing said sub-system to be externally interrogated.

66. The capacitive sensor of claim 56 in which said electrical sub-system receives external commands to manage the power consumption of said sub-system.

67. The capacitive sensor of claim 55 in which said second plate includes one or more sensors.

68. The capacitive sensor of claim 67 in which said one or more sensors are chosen from the group consisting of:

an acceleration sensor, a temperature sensor and a motion sensor.

69. The capacitive sensor of claim 68 in which said first plate and/or said second plate further includes a transmission device for transmission of one or more output signals of said one or more sensors.

70. The capacitive sensor of claim 55 in which said second plate is disposed on a top surface of said first plate.

71. The capacitive sensor of claim 55 in which said second plate is laterally spaced from said first plate.

72. The capacitive sensor of claim 1 further including a second diaphragm forming said part of said cavity spaced from said first plate.

73. The capacitive sensor of claim 72 further including a third conductive layer on said second diaphragm.

74. The capacitive sensor of claim 73 further including a fourth conductive layer on said first plate, said third and fourth conductive layers being the electrodes of a second capacitor whose capacitance varies with the position of said second diaphragm relative to said first plate.

75. The capacitive sensor of claim 1 further including a second plate having a fourth conductive layer, and a second diaphragm having a third conductive layer forming part of said cavity spaced from said second plate.

76. The capacitive sensor of claim 75 in which said fourth conductive layer on said second plate and said third conductive layer on said second diaphragm form a second capacitor whose capacitance varies with the position of said second diaphragm relative to said second plate.

77. The capacitive sensor of claim 72 in which said first diaphragm is proximate on a top surface of said housing and said second diaphragm is proximate a bottom surface of said housing.

78. The capacitive sensor of claim 72 in which said first and second diaphragms are laterally spaced on said housing.

79. The capacitive sensor of claim 75 in which said first diaphragm and said first plate are proximate a top surface of said housing and said second diaphragm and said second plate are proximate a bottom surface of said housing.

80. The capacitive sensor of claim 75 in which said first plate and said first diaphragm and said second plate and said second diaphragm are laterally spaced in said housing.

81. The capacitive sensor of claim 74 in which each of said first and second diaphragms may be subjected to a different pressure such that the capacitance of said first capacitor represents a difference in pressure between said cavity and the pressure applied to said first diaphragm and the capacitance of said second capacitor represents a difference in pressure between said cavity and the pressure applied to said second diaphragm.

82. The capacitive sensor of claim 76 in which each of said diaphragms may be subjected to a different pressure such that the capacitance of said first capacitor represents a difference in pressure between said cavity and the pressure applied to said first diaphragm and the capacitance of said second capacitor represents a difference in pressure between said cavity and the pressure applied to said second diaphragm.

83. The capacitive sensor of claim 81 wherein said capacitance of said first capacitor and said capacitance of said second capacitor are subtracted to determine a differential pressure.

84. The capacitive sensor of claim 82 wherein said capacitance of said first capacitor and said capacitance of said second capacitor are subtracted to determine a differential pressure.

85. A capacitive sensor comprising:

a housing having a hermetically sealed cavity;

a plate protruding within said cavity;

a conductive diaphragm forming a part of said cavity and spaced from said plate; and

a conductive layer on said plate, said conductive diaphragm and conductive layer on said plate being the electrodes of a capacitor whose capacitance varies with the position of said conductive diaphragm relative to said plate.

86. A capacitive sensor comprising:

a housing having a hermetically sealed cavity;

a conductive plate protruding within said cavity;

a diaphragm forming a part of said cavity and spaced from said conductive plate; and

a conductive layer on said diaphragm, said conductive layer on said diaphragm and said conductive plate being the electrodes of a capacitor whose capacitance varies with the position of said diaphragm relative to said plate.

87. A capacitive sensor comprising:

a housing having a hermetically sealed cavity;

a conductive plate protruding within said cavity; and

a conductive diaphragm forming a part of said cavity and spaced from said conductive plate;

said conductive diaphragm and said conductive plate being the electrodes of a capacitor whose capacitance varies with the position of said diaphragm relative to said plate.

88. A capacitive sensor comprising:

a housing having a hermetically sealed cavity;

a plate protruding within said cavity;

a diaphragm forming a part of said cavity and spaced from said plate;

a first conductive layer on said diaphragm; and

a second conductive layer on said plate, said first and second conductive layers being the electrodes of a capacitor whose capacitance varies with the position of said diaphragm relative to said plate in response to an external force.