Micro-electro-mechanical transducer having an optimized non-flat surface

• US 8,975,984 B2
• Filed: 09/09/2011
• Issued: 03/10/2015
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Primary Examiner(s): TRAN, ANH Q
• Application Number:
  US13/229,553
• Publication Number:
  US 20120013218A1
• Time in Patent Office: 1,278 Days
• Field of Search: None
• 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 of the electrostatic type H04R19/005
• 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) having a non-flat surface is disclosed. The non-flat surface may include a variable curve or slope in an area where a spring layer contacts a support, thus making a variable spring model as the spring layer vibrates. The non-flat surface may be that of a non-flat electrode optimized to compensate the dynamic deformation of the other electrode during operation and thus enhance the uniformity of the dynamic electrode gap during operation. Methods for fabricating the micro-electro-mechanical transducer are also disclosed. The methods may be used in both conventional membrane-based cMUTs and cMUTs having embedded springs transporting a rigid top plate.

Claims

1. A micro-electro-mechanical transducer comprising:

a first layer having a first internal surface;

a second layer having a second internal surface opposing the first internal surface of the first layer to define a gap therebetween, wherein at least one of the first internal surface and the second internal surface is non-flat defining, at least in part, a concave curve shape profile having at least a first zone and a second zone, the first zone defining a first width of the gap, and the second zone defining a second width of the gap; and

a transducing member movable with at least one of the first layer and the second layer.

2. The micro-electro-mechanical transducer of claim 1 wherein the first internal surface is non-flat, and the second layer is supported by a contacting portion of the first internal surface in the first zone.

3. The micro-electro-mechanical transducer of claim 2 wherein the second layer comprises a membrane layer supported by a graduated surface of the contacting portion of the first internal surface to form a wedge therebetween, the membrane layer being deformable along the graduated surface, creating a varying contacting surface area in the wedge as the second layer is displaced nearer or closer in relation to the first layer.

4. The micro-electro-mechanical transducer of claim 2 wherein the contacting portion of the first internal surface comprises a substantially smooth surface, rendering the first width of the gap graduating continuously.

5. The micro-electro-mechanical transducer of claim 2 wherein the contacting portion of the first internal surface has a stepped surface rendering the first width of the gap graduating in at least one step.

6. The micro-electro-mechanical transducer of claim 1 wherein the second width of the gap is greater than the first width of the gap.

7. The micro-electro-mechanical transducer of claim 1 wherein the first internal surface is non-flat, the second layer is subject to a deformation during operation of the micro-electro-mechanical transducer, and the non-flat first internal surface has a shape that generally conforms to the deformation of the second layer during operation.

8. The micro-electro-mechanical transducer of claim 7 wherein the second layer is subject to a maximum deformation in the second zone during operation of the micro-electro-mechanical transducer.

9. The micro-electro-mechanical transducer of claim 7 wherein the deformation of the second layer during operation comprises a downward bulge toward the first layer in the second zone, and the first internal surface in the second zone comprises a recess relative to the first internal surface in the first zone, the recess at least partially compensating the deformation of the second layer during operation.

10. The micro-electro-mechanical transducer of claim 1 wherein the first layer comprises a substrate, the second layer comprises a spring layer movable through the gap defined between the first layer and the second layer, and the transducing member comprises a first electrode movable with the spring layer.

11. The micro-electro-mechanical transducer of claim 1 wherein the first layer comprises a mass layer, the second layer comprises a spring layer movable through the gap defined between the first layer and the second layer, the spring layer being connected to a substrate, and the transducing member comprises a first electrode movable with the spring layer.

12. The micro-electro-mechanical transducer of claim 11 wherein the first electrode is disposed on the spring layer, and the transducing member further comprises a second electrode disposed on the substrate.

13. The micro-electro-mechanical transducer of claim 11 wherein the first electrode is disposed on the mass layer, and the transducing member further comprises a second electrode disposed on the spring layer.

14. The micro-electro-mechanical transducer of claim 1 wherein at least one of the first layer and the second layer comprises a resilient membrane.

15. The micro-electro-mechanical transducer of claim 1 wherein the first layer comprises a protruding portion in the first zone, the protruding portion having a tapered surface providing graduated contact with the second layer to support the second layer.

16. The micro-electro-mechanical transducer of claim 1 further comprising a motion stopper disposed in the gap between the first internal surface and the second internal surface.

17. The micro-electro-mechanical transducer of claim 16 wherein the motion stopper is disposed on one of the first internal surface and the second internal surface that is non-flat.

18. The micro-electro-mechanical transducer of claim 16 wherein the motion stopper comprises an insulating material and includes an insulation extension extending into one of the first internal surface and the second internal surface.

19. The micro-electro-mechanical transducer of claim 1 wherein the first layer comprises a substrate and a spring layer placed over the substrate, the substrate and the spring layer defining a cavity therebetween, the cavity being bordered by a sidewall, the spring layer extending from the sidewall to at least partially cover the cavity.

20. The micro-electro-mechanical transducer of claim 19 wherein the spring layer comprises a conductive layer.

21. The micro-electro-mechanical transducer of claim 19 wherein the substrate comprises a conductive material.

22. The micro-electro-mechanical transducer of claim 19 wherein the second layer comprises a top plate with a protruding portion having a tapered surface providing graduated contact with the spring layer, and wherein the protruding portion separates the top plate from the spring layer.

23. The micro-electro-mechanical transducer of claim 22 wherein the top plate comprises a silicon/polysilicon layer.

24. The micro-electro-mechanical transducer of claim 22 wherein the top plate is significantly more rigid than the spring layer and is substantially unbent when transported by a vertical displacement of the protruding portion.

25. The micro-electro-mechanical transducer of claim 1 wherein the first layer comprises a substrate including a spring anchor, and the second layer comprises a spring layer and a mass layer, the mass layer being connected to the spring layer through a spring-mass connector, and the spring layer is anchored at the spring anchor.

26. The micro-electro-mechanical transducer of claim 25 wherein the spring anchor has a sloped shoulder defining the first zone, the sloped shoulder contacting with the spring layer to form a wedge therebetween, and the spring layer being deformable along the sloped shoulder, creating a varying contacting surface area in the wedge as the spring layer is bent nearer or closer in relation to the substrate.

52. The micro-electro-mechanical transducer of claim 1, wherein:

the first layer comprises or is adapted for hosting a bottom electrode;

the second layer comprises or is adapted for hosting a top electrode; and

the first layer is non-flat and includes at least one bent portion defining at least a portion of the shape profile.

53. The micro-electro-mechanical transducer of claim 1, wherein:

the first layer is a base layer including a first electrode; and

the second layer is a spring layer including a second electrode separated from the first electrode to define the electrode gap therebetween, the transducing member comprising the second electrode.

54. The micro-electro-mechanical transducer of claim 53, wherein:

the first internal surface is non-flat;

the second electrode has a deformable area subject to deformation during operation; and

the first electrode includes a non-flat area at least partially conformed to the deformation of the deformable area of the second electrode to increase uniformity of the electrode gap during operation.

55. The micro-electro-mechanical transducer of claim 53, further comprising a support member supporting the spring layer such that the spring layer is adapted for vibration relative to the base layer during transmitting or receiving a signal.

27. A micro-electro-mechanical transducer comprising:

a base layer including a first electrode;

a spring layer including a second electrode separated from the first electrode defining an electrode gap therebetween; and

a support member supporting the spring layer such that the spring layer is adapted for vibration relative to the base layer during transmitting or receiving a signal, wherein one of the first electrode and the second electrode has a deformable area subject to deformation during operation, and the other electrode has a non-flat at least partially concave curved area at least partially conformed to the deformation of the deformable area of the one of the first electrode and the second electrode to increase uniformity of the electrode gap during operation.

28. The micro-electro-mechanical transducer of claim 27 wherein the support member has a graduated surface facing the spring layer, and the spring layer is deformable along the graduated surface of the support member, such that the spring layer has a varying surface area in contact with the support member when the spring layer is displaced nearer or closer in relation to the other layer.

29. The micro-electro-mechanical transducer of claim 28 wherein the graduated surface of the support member comprises a step having at least two different levels.

30. The micro-electro-mechanical transducer of claim 27 wherein the support member is integral with the base layer or the spring layer.

31. The micro-electro-mechanical transducer of claim 27 wherein the non-flat area includes at least a first zone and a second zone, the first zone defining a first width of the electrode gap, the first width being variable, and the second zone defining a second width of the electrode gap.

32. The micro-electro-mechanical transducer of claim 27 wherein the base layer comprises a mass layer connected to the spring layer through a spring-mass connector.

33. The micro-electro-mechanical transducer of claim 32 wherein the support member comprises a substrate and an anchor standing on the substrate, the spring layer being placed over the anchor to define a cavity between the spring layer and the substrate, the cavity being bordered by the anchor, and the spring layer extending from the anchor to cover the cavity.

34. The micro-electro-mechanical transducer of claim 32 wherein the support member is an integral part of the substrate.

35. The micro-electro-mechanical transducer of claim 27 wherein the base layer comprises a mass layer connected to the spring layer through a spring-mass connector, the mass layer being significantly more rigid than the spring layer and substantially unbent when transported by a vertical displacement of the support members.

36. The micro-electro-mechanical transducer of claim 27 further comprising a motion stopper disposed in the gap between the base layer and the spring layer.

37. The micro-electro-mechanical transducer of claim 36 wherein the motion stopper is disposed on the base layer.

38. The micro-electro-mechanical transducer of claim 36 wherein the motion stopper comprises an insulating material and includes an insulation extension extending into one of the base layer and the spring layer.

56. The micro-electro-mechanical transducer of claim 28 wherein the graduated surface of the support member comprises multiple steps having at least three different levels of three different respective heights.

39. A method for fabricating a micro-electro-mechanical transducer, the method comprising:

growing and patterning a diffusion barrier layer over a surface of a base layer, the diffusion barrier layer having an opening leaving a corresponding part of the surface of the base layer uncovered;

performing a diffusion process over the diffusion barrier layer including the opening such that a diffusion reactivated material reaches a first depth into the base layer at where the opening is located and a second depth into the base layer at positions covered by the diffusion barrier layer, the first depth being greater than the second depth;

removing the diffusion barrier layer and the diffusion reactivated material to form a recess on the surface of the base layer;

forming a cover layer over the recess on the base layer to define a gap therebetween; and

forming a transducing member movable with at least one of the base layer or the cover layer.

40. The method of claim 39 further comprising repeating the growing, performing and removing to form a step on the surface of the base layer.

41. The method of claim 39 further comprising, before forming the cover layer, forming an anchor in the recess of the base layer, the anchor being taller than the recess such that the cover layer is supported by the anchor and clear of the recess of the base layer.

42. The method of claim 39 further comprising forming an insulation layer over the surface of the base layer.

43. The method of claim 39 wherein the base layer comprises a conductive material and includes at least a first zone and a second zone, the first zone defining a first width of the gap, the first width being variable, and the second zone defining a second width of the gap.

44. The method of claim 39 wherein the cover layer comprises a conductive material.

45. The method of claim 39 wherein the forming the cover layer comprises:

bonding an SOI layer carrying the cover layer over the surface of the base layer; and

etching back the SOI layer to leave the cover layer over the surface of the base layer.

46. The method of claim 39 wherein the diffusion barrier layer comprises an oxide layer.

47. The method of claim 39 wherein the diffusion barrier layer comprises a nitride layer.

48. The method of claim 39 wherein the growing and patterning a diffusion barrier layer comprises:

growing and patterning a first diffusion barrier layer over a surface of a base layer; and

growing and patterning a second diffusion barrier layer over the first diffusion barrier layer.

49. The method of claim 39 wherein the cover layer comprises a membrane layer having a perimeter fixed at a support wall on the base layer.

50. The method of claim 39 wherein the cover layer comprises a spring layer anchored at a spring anchor on the base layer to form a cantilever.

51. The method of claim 50 wherein the base layer comprises a substrate, the method further comprising forming a mass layer over the spring layer, the mass layer being connected to the spring layer through a spring-mass connector.

57. A method of fabricating a micro-electro-mechanical transducer comprising:

forming a first layer having a first internal surface;

forming a second layer having a second internal surface opposing the first internal surface of the first layer to define a gap therebetween, wherein at least one of the first internal surface and the second internal surface is non-flat defining, at least in part, a concave curve shape profile having at least a first zone and a second zone, the first zone defining a first width of the gap, and the second zone defining a second width of the gap; and

forming a transducing member movable with at least one of the first layer and the second layer.

58. The method of claim 57, wherein the forming the first layer comprises:

forming a non-flat surface on a first wafer, the non-flat surface comprising a first area having a first height and a second area having a second height, the first height being greater than the second height, wherein the first area has a tapered top surface; and

forming the first layer as a membrane layer over the tapered top surface of the first area of the first wafer.

59. The method of claim 57, wherein the forming the first layer comprises:

forming a flexible layer having a desired thickness profile;

placing the flexible layer over a base layer such that the flexible layer is supported by a support wall, the flexible layer and the base layer defining a cavity therebetween; and

bending the flexible layer into a desired shape to form the first layer.

60. The method of claim 57, wherein the forming the first layer comprises:

forming a wall on a substrate, the wall defining a cavity;

placing the first layer over the cavity such that the first layer is supported by the wall on the substrate, the first layer and the substrate together comprising or being adapted for hosting a bottom electrode; and

bending the first layer into a desired shape.

61. The method of claim 60, wherein the first layer comprises a semiconductor material, and the bending the first layer comprises:

selectively doping the first layer using a doping material with doping profile to introduce a desired stress profile in the first layer; and

annealing the first layer at a desired temperature and pressure.

62. The method of claim 57, wherein the forming the first layer comprises:

growing and patterning a diffusion barrier layer over the first internal surface of the first layer, the diffusion barrier layer having an opening leaving a corresponding part of the first internal surface of the first layer uncovered;

performing a diffusion process over the diffusion barrier layer including the opening such that a diffusion reactivated material reaches a first depth into the first layer where the opening is located and a second depth into the first layer at positions covered by the diffusion barrier layer, the first depth being greater than the second depth; and

removing the diffusion barrier layer and the diffusion reactivated material to form a recess on the first internal surface of the first layer.

63. The method of claim 62, wherein the recess defines a first step in the first layer, the method further comprising repeating the growing, the performing and the removing to form a second step in the first internal surface of the first layer.

64. The method of claim 62 further comprising, before forming the second layer, forming an anchor in the recess of the first layer, the anchor being taller than the recess such that the second layer is supported by the anchor and clear of the recess of the first layer.

65. A method for fabricating a micro-electro-mechanical transducer, the method comprising:

oxidizing a surface of a first layer to form an oxide layer;

removing the oxide layer to create a recess in the first layer, wherein at least a portion of the recess includes a concave curve shape; and

forming a second layer over the recess on the first layer to define a gap, the second layer having a deformable area, wherein the recess is at least partially conformed to deformation of the deformable area of the second layer.

66. The method of claim 65 further comprising oxidizing the surface of the first layer and removing oxide to form a step on the surface of the first layer.

67. The method of claim 65 further comprising, before forming the second layer, forming an anchor in the recess of the first layer, the anchor being taller than the recess such that the second layer is supported by the anchor and clear of the recess of the first layer.

68. The method of claim 65 further comprising forming an insulation layer over the recess of the first layer.

69. The method of claim 65 wherein the first layer comprises a conductive material.

70. The method of claim 65 wherein the second layer comprises a conductive material.

71. The method of claim 65 wherein the forming the second layer comprises:

bonding an SOI layer carrying the second layer over the recess of the first layer; and

etching back the SOI layer to leave the second layer over the surface of the first layer.