Micro-Electro-Mechanical Transducers

• US 20080197751A1
• Filed: 05/18/2006
• Published: 08/21/2008
• Est. Priority Date: 05/18/2005
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Granted Patent: US 8,120,229 B2
• Time in Patent Office: Days
• US Class Current: 310/311
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• 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: Y10T 29/49005 Acoustic transducer

Abstract

A micro-electro-mechanical transducer (such as a cMUT) is disclosed. The transducer has a substrate, a top plate, and a middle spring layer therebetween. The substrate and the middle spring layer define cavities therebetween sidewalled by standing features. The middle spring layer is anchored by the standing features to create cantilevers over the cavities to enable a vertical displacement of connectors placed on the middle spring layer. The connectors define a transducing space between the middle spring layer and the top plate. The top plate is transported by the vertical displacement of the connectors in a piston-like motion to change the transducing space and to effectuate energy transformation. Various configurations of cantilevers, including single cantilevers, back-to-back double cantilevers and head-to-head double cantilevers (bridges) are possible.

Claims

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

a substrate;

a middle spring layer placed over the substrate, the substrate and the middle spring layer defining a first cavity and a second cavity therebetween, the first cavity and the second cavity sharing a standing feature including a first sidewall bordering the first cavity and an opposing second sidewall bordering the second cavity, wherein the middle spring layer has a first portion connected to the first sidewall and covering at least a part of the first cavity, and a second portion connected to the second sidewall and covering at least a part of the second cavity;

a first connector having a connector height on the first portion of the middle spring layer, the first connector being horizontally distanced from the first sidewall by a sufficient length such that the first portion of the middle spring layer between the first connector and the first sidewall defines a first cantilever anchored at the first sidewall;

a second connector having substantially the same connector height on the second portion of the middle spring layer, the second connector being horizontally distanced from the second sidewall by a sufficient length such that the second portion of the middle spring layer between the second connector and the second sidewall defines a second cantilever anchored at the second sidewall; and

a top plate placed over the first connector and the second connector, the connectors separating the top plate from the middle spring layer to define a transducing space below the top plate,

wherein the first cantilever and the first cavity enable a vertical displacement of the first connector, and the second cantilever and the second cavity enable a vertical displacement of the second connector, the vertical displacements of the connectors transporting the top plate substantially vertically, thus changing the transducing space and activating a transducing member in the transducer for energy transformation.

2. The micro-electro-mechanical transducer of claim 1, wherein the top plate comprises a silicon layer or a polysilicon layer.

3. The micro-electro-mechanical transducer of claim 1, wherein the first cavity and the second cavity are different portions of an extended cavity.

4. The micro-electro-mechanical transducer of claim 1, wherein the first cavity and the second cavity are different portions of an extended cavity, and the first connector and the second connector are different portions of an extended connector.

5. The micro-electro-mechanical transducer of claim 1 wherein the substrate is conductive.

6. The micro-electro-mechanical transducer of claim 1 which is a capacitance micromachined ultrasonic transducer, wherein the transducing member comprises a top electrode and the bottom electrode.

7. The micro-electro-mechanical transducer of claim 6 wherein the top electrode comprises a conductive layer deposited on a surface of the top plate.

8. The micro-electro-mechanical transducer of claim 6 wherein the standing feature of the substrate is conductive and the bottom electrode includes at least a part of the standing feature of the substrate.

9. The micro-electro-mechanical transducer of claim 6 wherein the bottom electrode comprises a separate conductive layer deposited on the middle spring layer.

10. The micro-electro-mechanical transducer of claim 1 which is a pMUT, wherein the transducing member comprises a piezoelectric member disposed on the middle spring layer.

11. The micro-electro-mechanical transducer of claim 1 which is a mMUT, wherein the transducing member comprises a magnetic member disposed on the top plate.

12. The micro-electro-mechanical transducer of claim 1 further comprising an insulation layer disposed between the connector and the top plate.

13. The micro-electro-mechanical transducer of claim 1 wherein the middle spring layer is a contiguous layer placed over the standing feature of the substrate and extending over the sidewall to cover at least part of the cavity.

14. The micro-electro-mechanical transducer of claim 1 wherein the middle spring layer comprises a first region and a second region, and wherein the first region comprises a low doped or intrinsic silicon material, and the second region comprises a highly doped silicon material with increased conductivity.

15. The micro-electro-mechanical transducer of claim 14, wherein the first region is close to the connector and the second region is over the top surface of the standing feature, and the first region and the second region form a PN junction.

16. The micro-electro-mechanical transducer of claim 1 wherein the top plate has a thickness profile having at least two different thicknesses.

17. The micro-electro-mechanical transducer of claim 1 wherein the top plate comprises a first material and a second material different from the first material.

18. The micro-electro-mechanical transducer of claim 17 wherein the first material comprises a plurality of segments divided by separation trenches and the second material connects the segments by spanning over the trenches. The second material may fill or partially fill the trenches.

19. The micro-electro-mechanical transducer of claim 1 wherein the top plate comprises holes formed therein.

20. The micro-electro-mechanical transducer of claim 19 wherein the holes have a size and location profile optimized for a desired rigidity/mass ratio of the top plate.

21. The micro-electro-mechanical transducer of claim 1 wherein the top plate is significantly more rigid than the middle spring layer and is substantially unbent when transported by the vertical displacement of the connectors.

22. The micro-electro-mechanical transducer of claim 1 wherein the vertical displacement of the connector is limited to a maximum displacement less than a maximum vertical distance the top plate can be transported through the transducing space.

23. The micro-electro-mechanical transducer of claim 22 wherein the maximum vertical displacement of the connector is limited by a motion stopper disposed in the cavity.

24. The micro-electro-mechanical transducer of claim 1 further comprising an integrated circuit formed in the top plate.

25. The micro-electro-mechanical transducer of claim 1 wherein the substrate comprises a nonconductive wafer and the standing feature is made of a material different from that of the substrate.

26. The micro-electro-mechanical transducer of claim 1 further comprising:

a second standing feature above the top plate, the second standing feature including a third sidewall defining a third cavity above the top plate; and

a membrane covering the third cavity, the membrane having a perimeter fixed on the second standing feature, wherein the membrane is adapted for vibrating upon activation by a second transducing member.

27. The micro-electro-mechanical transducer of claim 26 which is a capacitance micromachined ultrasonic transducer, wherein the transducing member comprises a first electrode below the transducing space and a second electrode above the transducing space, and the second transducing member comprises the second electrode and a third electrode above the third cavity.

28. The micro-electro-mechanical transducer of claim 26 wherein the second standing feature is a circular structure.

29. The micro-electro-mechanical transducer of claim 1 wherein the transducing member comprises a first capacitor and a second capacitor, the first capacitor including a first bottom electrode below and spaced from the middle spring layer and a first top electrode above the first or the second cavity but below the transducing space, the second capacitor including a second bottom electrode above the first or the second cavity but below the transducing space and a second top electrode above the transducing space.

30. The micro-electro-mechanical transducer of claim 29 wherein the first bottom electrode comprises an electrode layer deposited on a bottom surface of the first cavity or the second cavity.

31. The micro-electro-mechanical transducer of claim 29 wherein the first top electrode comprises an electrode layer deposited on the middle spring layer.

32. The micro-electro-mechanical transducer of claim 29 wherein at least a portion of the middle spring layer is conductive, and the first top electrode includes the conductive portion of the middle spring layer.

33. The micro-electro-mechanical transducer of claim 29 wherein the first top electrode and the second bottom electrode are a common electrode shared by the first capacitor and the second capacitor.

34. The micro-electro-mechanical transducer of claim 1 which is a cMUT transducer wherein the transducing member includes a first capacitor, and the cMUT transducer further comprises a second transducing member including a second capacitor stacked on top of the first capacitor.

35. The micro-electro-mechanical transducer of claim 34 wherein the first capacitor is configured to operate in one of a transmission mode and a receiving mode, and the second capacitor is configured to operate in the other of the transmission mode and the receiving mode.

36. The micro-electro-mechanical transducer of claim 34 wherein both the first capacitor and the second capacitor are configured to operate in a transmission mode.

37. The micro-electro-mechanical transducer of claim 34 wherein both the first capacitor and the second capacitor are configured to operate in a receiving mode.

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

a substrate;

a middle spring layer placed over the substrate, the substrate and the middle spring layer defining a cavity therebetween, the cavity being bordered by a first standing feature and a second standing feature, the first standing feature having a first sidewall bordering the cavity and the second standing feature having a second sidewall bordering the cavity on an opposing side, wherein the middle spring layer extends from the first sidewall to the second sidewall to cover the cavity;

a connector having a connector height on the middle spring layer, the connector being horizontally distanced from both the first sidewall and the second sidewall such that the middle spring layer between the first sidewall and the second sidewall defines a double-cantilever anchored at the first sidewall and the second sidewall and connected head-to-head; and

a top plate placed over the connector, which separates the top plate from the middle spring layer to define a transducing space below the top plate, wherein the double-cantilever and the cavity enable a vertical displacement of the connector, which transports the top plate substantially vertically, thus changing the transducing space and activating a transducing member in the transducer for energy transformation.

39. The micro-electro-mechanical transducer of claim 38, wherein the top plate comprises a silicon layer or a polysilicon layer.

40. The micro-electro-mechanical transducer of claim 38, wherein the first standing feature and the second standing feature are different portions of an extended standing feature.

41. The micro-electro-mechanical transducer of claim 38 which is a capacitance micromachined ultrasonic transducer, wherein the transducing member comprises a top electrode and the bottom electrode.

42. The micro-electro-mechanical transducer of claim 41 wherein the bottom electrode comprises a separate conductive layer deposited on the middle spring layer.

43. The micro-electro-mechanical transducer of claim 41 further comprising an insulation layer disposed between the connector and the top plate.

44. The micro-electro-mechanical transducer of claim 38 wherein the middle spring layer comprises a first region and a second region, and wherein the first region comprises a low doped or intrinsic silicon material, and the second region comprises a highly doped silicon material with increased conductivity.

45. The micro-electro-mechanical transducer of claim 44, wherein the first region is close to the connector and the second region is over the top surface of the standing feature, and the first region and the second region form a PN junction.

46. The micro-electro-mechanical transducer of claim 38 wherein the top plate has a thickness profile having at least two different thicknesses.

47. The micro-electro-mechanical transducer of claim 38 wherein the top plate comprises a first material in a plurality of segments separated by separation trenches and a second material which connect the segments by spanning over the trenches.

48. The micro-electro-mechanical transducer of claim 38 wherein the top plate comprises holes formed therein.

49. The micro-electro-mechanical transducer of claim 48 wherein the holes have a size and location profile optimized for a desired rigidity/mass ratio of the top plate.

50. The micro-electro-mechanical transducer of claim 38 wherein the vertical displacement of the connector is limited to a maximum displacement less than a maximum vertical distance the top plate can be transported through the transducing space.

51. The micro-electro-mechanical transducer of claim 50 wherein the maximum vertical displacement of the connector is limited by a motion stopper disposed in the cavity.

52. The micro-electro-mechanical transducer of claim 38 wherein the top plate is significantly more rigid than the middle spring layer and is substantially unbent when transported by the vertical displacement of the connectors.

53. The micro-electro-mechanical transducer of claim 38 further comprising an integrated circuit formed in the top plate.

54. The micro-electro-mechanical transducer of claim 38 further comprising:

a third standing feature above the top plate, the third standing feature including a third sidewall defining a top cavity above the top plate; and

a membrane covering the second cavity, the membrane having a perimeter fixed on the third standing feature, wherein the membrane is adapted for vibrating upon activation by a second transducing member.

55. The micro-electro-mechanical transducer of claim 38 which is a cMUT transducer wherein the transducing member includes a first capacitor, and the cMUT transducer further comprises a second transducing member including a second capacitor stacked on top of the first capacitor.

56. The micro-electro-mechanical transducer of claim 55 wherein the first capacitor is configured to operate in one of a transmission mode and a receiving mode, and the second capacitor is configured to operate in the other of the transmission mode and the receiving mode.

57. The micro-electro-mechanical transducer of claim 55 wherein both the first capacitor and the second capacitor are configured to operate in a transmission mode.

58. The micro-electro-mechanical transducer of claim 55 wherein both the first capacitor and the second capacitor are configured to operate in a receiving mode.

59. The micro-electro-mechanical transducer of claim 38, wherein the middle spring layer comprises a first region of a first thickness, a second region of a second thickness, and a third region of a third thickness, the second region being between the first region and the third region, the second thickness being substantially smaller than the first thickness or the third thickness, wherein the first region forms at least part of the sidewall, the second region and the third region is disposed over the cavity, and the connector is located on the third region.

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

a substrate;

a middle spring layer placed over the substrate, the substrate and the middle spring layer defining a cavity therebetween, the cavity being bordered by a sidewall of a standing feature between the substrate and the middle spring layer, wherein the middle spring layer extends from the sidewall to cover at least part of the cavity, the middle spring layer supporting a connector having a connector height, the connector being horizontally distanced from the sidewall such that the middle spring layer between the connector and the sidewall defines a cantilever anchored at the sidewall; and

a top plate comprising a silicon layer, the top plate being placed over the connector, the connector separating the top plate from the middle spring layer to define a transducing space below the top plate,

wherein the cantilever and the cavity enable a vertical displacement of the connector, which transports the top plate substantially vertically, thus changing the transducing space and activating a transducing member in the transducer.

61. The micro-electro-mechanical transducer of claim 60 wherein the transducing member includes a top electrode above the transducing space.

62. The micro-electro-mechanical transducer of claim 60 wherein the substrate is conductive and the transducing member includes at least a part of the conductive substrate as a bottom electrode.

63. The micro-electro-mechanical transducer of claim 60 further comprising an insulation layer disposed between the connector and the top plate.

64. The micro-electro-mechanical transducer of claim 60 wherein the top plate is significantly more rigid than the middle spring layer and is substantially unbent when transported by the vertical displacement of the connector.