Micro-Electro-Mechanical Transducer Having a Surface Plate

• US 20100013574A1
• Filed: 09/28/2009
• Published: 01/21/2010
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Granted Patent: US 7,880,565 B2
• Time in Patent Office: Days
• US Class Current: 333/186
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B81B 3/0027 Structures for transforming mechanical energy, e.g. potential energy of a spring into translation, sound into translation
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: B81C 1/00182 Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• CPC Class Codes: B81C 1/00357 involving bonding one or several substrates on a non-temporary support, e.g. another substrate
• CPC Class Codes: B81C 1/00373 Selective deposition, e.g. printing or microcontact printing
• CPC Class Codes: B81C 1/00523 Etching material
• CPC Class Codes: B81C 1/00626 Processes for achieving a desired geometry not provided for in groups B81C1/00563 - B81C1/00619
• 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 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H02N 1/006 of the gap-closing type H02N1/004 takes precedence
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 9/02259 Driving or detection means
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators
• CPC Class Codes: H03H 9/462 Microelectro-mechanical filters
• CPC Class Codes: H04R 19/005 using semiconductor materials
• CPC Class Codes: H04R 2201/003 Mems transducers or their use
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer

Abstract

A micro-electro-mechanical transducer (such as a cMUT) is disclosed. The transducer has a base, a spring layer placed over the base, and a mass layer connected to the spring layer through a spring-mass connector. The base includes a first electrode. The spring layer or the mass layer includes a second electrode. The base and the spring layer form a gap therebetween and are connected through a spring anchor. The mass layer provides a substantially independent spring mass contribution to the spring model without affecting the equivalent spring constant. The mass layer also functions as a surface plate interfacing with the medium to improve transducing performance. Fabrication methods to make the same are also disclosed.

Claims

1. A micro-electro-mechanical transducer having a movable mechanical part to transform energy, the transducer comprising:

a base including a first electrode;

a spring layer connected to the base through a spring anchor to form a cantilever; and

a mass layer connected to the spring layer through a spring-mass connector, wherein the spring layer or the mass layer includes a second electrode.

2. The micro-electro-mechanical transducer of claim 1 wherein the base has a top surface, the spring layer being disposed over the top surface of the base.

3. The micro-electro-mechanical transducer of claim 1 wherein the spring-mass connector has an area size substantially smaller than that of the mass layer.

4. The micro-electro-mechanical transducer of claim 1 wherein the mass layer is disposed between the spring layer and the base.

5. The micro-electro-mechanical transducer of claim 4 wherein the second electrode is disposed on the mass layer or is an integral part thereof.

6. The micro-electro-mechanical transducer of claim 1 wherein the mass layer is disposed above the spring layer, and the spring layer is disposed between the mass layer and the base.

7. The micro-electro-mechanical transducer of claim 6 wherein the second electrode is disposed on the spring layer or is an integral part thereof.

8. The micro-electro-mechanical transducer of claim 1 wherein the spring anchor comprises a support wall defining a peripheral of a transducer element.

9. The micro-electro-mechanical transducer of claim 1 wherein the spring anchor is integral with the base.

10. The micro-electro-mechanical transducer of claim 1 wherein the mass layer functions as a surface plate to interface with a medium in operation of the transducer.

11. The micro-electro-mechanical transducer of claim 1 wherein the mass layer is significantly more rigid than the spring layer.

12. The micro-electro-mechanical transducer of claim 1 having at least one individually addressed transducer element, each transducer element comprising a plurality of spring anchors.

13. The micro-electro-mechanical transducer of claim 12 wherein the plurality of spring anchors are distributed across the respective transducer element such that there is at least one spring anchor is located away from a peripheral of the transducer element.

14. The micro-electro-mechanical transducer of claim 1 wherein the spring anchor has a minimized footprint.

15. The micro-electro-mechanical transducer of claim 1 wherein the spring-mass connector is located at a position where the spring layer is likely to experience a maximum displacement.

16. The micro-electro-mechanical transducer of claim 1 wherein the base also includes an insulation layer on top of the first electrode.

17. The micro-electro-mechanical transducer of claim 1 wherein the base has a non-flat top surface facing the spring layer.

18. The micro-electro-mechanical transducer of claim 17 wherein the non-flat top surface of the base comprises at least two steps having different heights.

19. The micro-electro-mechanical transducer of claim 17 wherein the non-flat top surface of the base comprises a curved region.

20. The micro-electro-mechanical transducer of claim 1 wherein the base comprises a through wafer interconnection.

21. The micro-electro-mechanical transducer of claim 1 wherein the base comprises a layer having printed circuits.

22. The micro-electro-mechanical transducer of claim 1 wherein the base comprises an integrated circuit.

23. The micro-electro-mechanical transducer of claim 1 wherein the mass layer has a holed structure or a honeycomb structure.

24. The micro-electro-mechanical transducer of claim 1 wherein the spring anchor comprises an insulation extension extending into at least one of the base and the spring layer.

25. A micro-electro-mechanical transducer having a movable mechanical part to transform energy, the transducer comprising:

a base including a first electrode;

a spring layer connected to the base through a first spring anchor and a second spring anchor which separate at least a part of the spring layer from a part of the base to form a gap therebetween; and

a mass layer connected to the spring layer through a spring-mass connector, wherein at least one of the spring layer and the mass layer includes a second electrode, and wherein the spring-mass connector is horizontally distanced from both the first and the second spring anchors to enable a vertical displacement of the spring-mass connector to transport the mass layer substantially vertically.

26. The micro-electro-mechanical transducer of claim 25 wherein the base and the spring layer are connected through a plurality of spring anchors and the mass layer is connected to the spring layer through a plurality of spring-mass connectors, wherein the each spring-mass connector is horizontally distanced from neighboring spring anchors to enable a vertical displacement of the plurality of spring-mass connectors to transport the mass layer substantially vertically.

27. The micro-electro-mechanical transducer of claim 25 wherein the mass layer is disposed above the spring layer and the base is disposed below the spring layer.

28. The micro-electro-mechanical transducer of claim 27 further comprising a supplemental layer below the spring layer and connected to the spring layer.

29. The micro-electro-mechanical transducer of claim 28 wherein the supplemental layer is a conductive layer.

30. The micro-electro-mechanical transducer of claim 28 wherein the supplemental layer is connected to the spring layer through a supplemental connector.

31. The micro-electro-mechanical transducer of claim 25 wherein the spring anchor has an area size substantially smaller than that of the mass layer.

32. The micro-electro-mechanical transducer of claim 25 wherein the second electrode is disposed on the spring layer or is an integral part thereof.

33. The micro-electro-mechanical transducer of claim 25 wherein the spring anchor is integral with the base.

34. The micro-electro-mechanical transducer of claim 25 wherein the spring anchor is integral with the spring layer.

35. The micro-electro-mechanical transducer of claim 25 wherein the spring anchor comprises an electrically insulating material.

36. The micro-electro-mechanical transducer of claim 25 wherein at least one of the first spring anchor and the second spring anchor comprises an insulation extension extending into at least one of the base and the spring layer.

37. The micro-electro-mechanical transducer of claim 25 wherein the mass layer functions as a surface plate to interface with a medium in operation of the transducer.

38. The micro-electro-mechanical transducer of claim 25 wherein the base has a non-flat top surface facing the spring layer.

39. The micro-electro-mechanical transducer of claim 25 wherein the mass layer is significantly more rigid than the spring layer.

40. The micro-electro-mechanical transducer of claim 25 wherein the plurality of spring anchor have a minimized footprint.

41. The micro-electro-mechanical transducer of claim 25 wherein at least one of the first and the second spring anchors is an elongated wall.

42. The micro-electro-mechanical transducer of claim 25, wherein the mass layer comprises a silicon or polysilicon material.

43. The micro-electro-mechanical transducer of claim 25 wherein the base is conductive.

44. The micro-electro-mechanical transducer of claim 25 which is a capacitive micromachined ultrasonic transducer.

45. The micro-electro-mechanical transducer of claim 25 wherein the mass layer is significantly more rigid than the spring layer and is substantially unbent when transported by the vertical displacement of the spring-mass connectors.

46. The micro-electro-mechanical transducer of claim 25 wherein the vertical displacement of the spring-mass connector is limited by a motion stopper disposed between the spring layer and the mass layer.

47. The micro-electro-mechanical transducer of claim 25 wherein the vertical displacement of the spring-mass connector is limited by a smallest separation distance between the mass layer and the spring layer or any intervening layer therebetween.

48. A micro-electro-mechanical transducer having a movable mechanical part to transform energy, the transducer comprising:

a base including a first electrode;

a spring layer connected to the base through a spring anchor which separates at least a part of the spring layer from a part of the base to form a gap therebetween; and

a mass layer connected to the spring layer through a first spring-mass connector and a second spring-mass connector, wherein at least one of the spring layer and the mass layer includes a second electrode, and wherein the first and the second spring-mass connectors are each horizontally distanced from the spring anchor to enable a vertical displacement of the first and the second spring-mass connectors to transport the mass layer substantially vertically.

49. The micro-electro-mechanical transducer of claim 48 wherein the base comprises a conductive layer, and the spring anchor comprises an insulation material extending into the conductive layer to form an insulation extension.

50. A micro-electro-mechanical transducer having a movable mechanical part to transform energy, the transducer comprising at least one addressable transducer element having a periphery defining a transducer element area, wherein the addressable transducer element comprises:

a base including a first electrode;

a spring layer placed over the base, the base and the spring layer being connected through a plurality of spring anchors which separate at least a part of the spring layer from the base to form a gap therebetween; and

a mass layer connected to the spring layer through a plurality of spring-mass connectors, wherein at least one of the spring layer and the mass layer includes a second electrode, and wherein the plurality of spring anchors are each horizontally distanced from the neighboring spring-mass connector to allow the plurality of spring-mass connectors to displace vertically thus transporting the mass layer in the same direction.

51. The micro-electro-mechanical transducer of claim 50 comprising a plurality of addressable transducer elements separated from each other by trenches form through the mass layer.

52. The micro-electro-mechanical transducer of claim 50 wherein each of the plurality of spring-mass connectors defines a spring comprising a cantilever anchored at the neighboring spring anchors, the springs defining an effective spring intensity profile indicating spring strength per area location.

53. The micro-electro-mechanical transducer of claim 52 wherein the effective spring intensity is substantially uniform over the device element area.

54. The micro-electro-mechanical transducer of claim 52 wherein the effective spring intensity is significantly higher at area locations near a perimeter of the device element area than at locations near a center of the device element area.

55. The micro-electro-mechanical transducer of claim 50 wherein the mass layer in the addressable transducer element has a thickness profile including at least two different thicknesses.

56. The micro-electro-mechanical transducer of claim 50 wherein the mass layer comprises holes formed therein.

57. A method for fabricating a micro-electro-mechanical device having a movable mechanical part to transform energy, the method comprising the steps of:

forming at least one spring anchor on either a front side of a substrate wafer or a bottom side of a spring layer;

forming at least one spring-mass connector of a desired height either on the spring layer or on a mass layer; and

joining the substrate wafer, the spring layer and the mass layer such that the spring layer and the substrate wafer are joined through the spring anchor to define a gap therebetween, the mass layer and the spring layer are joined through the spring-mass connector.

58. The method of claim 57 wherein the step of joining the substrate wafer, the spring layer and the mass layer comprises a step using wafer bonding technique.

59. The method of claim 57 wherein the spring-mass connector is horizontally distanced from the spring anchor by a sufficient length to define a cantilever anchored at the spring anchor with an exerting end at the spring-mass connector, the cantilever and the gap enabling a vertical displacement of the spring-mass connector to transport the mass layer substantially vertically with a piston-like motion.

60. The method of claim 57 wherein spring-mass connector is formed on a top side of the spring layer, and the mass layer is connected to the spring-mass connector from the top side of the spring layer opposing the substrate wafer.

61. The method of claim 57 wherein spring-mass connector is formed on the bottom side of the spring layer, and the mass layer is connected to the spring-mass connector from the bottom side of the spring layer.

62. The method of claim 61 wherein the mass layer is disposed in the gap defined by the spring layer and the substrate wafer.

63. The method of claim 57, wherein the step of forming at least one spring anchor comprises:

depositing and patterning a material on the spring layer or the substrate wafer to form the at least one spring anchor.

64. The method of claim 57, wherein the step of forming at least one spring anchor comprises:

growing and patterning an oxide on the spring layer or the substrate wafer to form the at least one spring anchor.

65. The method of claim 57, wherein the step of forming at least one spring anchor comprises:

forming a recess on the spring layer or the substrate wafer; and

growing and patterning an oxide on the spring layer or the substrate wafer to form the at least one spring anchor in the recess, the spring anchor attaching to a bottom of the recess and extending beyond the spring layer or the substrate wafer.

66. The method of claim 57, wherein the step of forming at least one spring-mass connector comprises:

depositing and patterning a material on the mass layer or the spring layer to form the at least one spring-mass connector.

67. The method of claim 57, wherein the step of forming at least one spring-mass connector comprises:

patterning and micromachining the mass layer or the spring layer to form the at least one spring-mass connector on the mass layer.

68. The method of claim 57, wherein the step of forming at least one spring-mass connector comprises:

forming a sacrificial layer on the mass layer or the spring layer, the sacrificial layer defining a negative pattern for the spring-mass connector;

depositing a material over the sacrificial layer and into the negative pattern for the spring-mass connector; and

removing the sacrificial layer to form the spring layer and the spring-mass connector.

69. The method of claim 57 further comprising forming or effectuating a transducing member on the spring layer.

70. The method of claim 69 wherein the transducing member is an electrode.

71. The method of claim 57 wherein the mass layer is disposed between the substrate and the spring layer, the method further comprising forming or effectuating a transducing member on the mass layer.