Middle spring supported micro-electro-mechanical transducers

• US 8,120,229 B2
• Filed: 05/18/2006
• Issued: 02/21/2012
• Est. Priority Date: 05/18/2005
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Primary Examiner(s): TAMAI, KARL I
• Application Number:
  US11/914,608
• Publication Number:
  US 20080197751A1
• Time in Patent Office: 2,105 Days
• Field of Search: 310/309, 381/174, 381/191, 600/459, 600/437, 367/163, 367/181, 735/143.2
• US Class Current: 310/309
• 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 disposed between the substrate and the middle spring layer, the 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 and above or across the middle spring layer, the top plate carrying or including a first electrode,

the top plate being rigid relative to the middle spring layer and supported by the middle spring layer for vertical movement relative to the standing feature, 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 in a piston-like manner relative to the standing feature and the substrate, thus changing the transducing space and activating a transducing member including the first electrode and a second electrode included in or adjacent to the middle spring layer for energy transformation.

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

the top plate comprises a silicon layer or a polysilicon layer;

the substrate comprises a silicon layer or polysilicon layer; and

the middle spring layer is flexible relative to the top plate and the substrate and has a thickness substantially less than thicknesses of the top plate and the substrate.

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 is a capacitor that comprises the first electrode and the second electrode.

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

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

9. The micro-electro-mechanical transducer of claim 1 in which the middle spring layer is flexible relative to the substrate and has a thickness substantially less than a thickness of the substrate.

10. The micro-electro-mechanical transducer of claim 1 in which each of the first and second cavities have a lateral size that is less than a half wavelength of a 1 MHz to 10 MHz acoustic wave.

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

12. 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.

13. 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.

14. The micro-electro-mechanical transducer of claim 13, 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.

15. The micro-electro-mechanical transducer of claim 1 wherein the top plate has a thickness profile having at least two different thicknesses to provide a varied flexibility across the transducing space.

16. 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.

17. The micro-electro-mechanical transducer of claim 16 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.

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

19. The micro-electro-mechanical transducer of claim 18 wherein the holes have a size and location profile optimized for a desired rigidity/mass ratio of the top plate.

20. 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.

21. 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.

22. The micro-electro-mechanical transducer of claim 21 wherein the maximum vertical displacement of the connector is limited by a motion stopper disposed in the cavity.

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

24. 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.

25. 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.

26. The micro-electro-mechanical transducer of claim 25 which is a capacitance micromachined ultrasonic transducer, wherein the transducing member comprises the second electrode below the transducing space and the first electrode above the transducing space, and the second transducing member comprises the first electrode and a third electrode above the third cavity.

27. The micro-electro-mechanical transducer of claim 25 wherein the second standing feature is a circular structure.

28. 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 third electrode below and spaced from the middle spring layer and the second electrode above the first or the second cavity but below the transducing space, the second capacitor including a fourth electrode above the first or the second cavity but below the transducing space and the first electrode above the transducing space.

29. The micro-electro-mechanical transducer of claim 28 wherein the third electrode comprises an electrode layer deposited on a bottom surface of the first cavity or the second cavity.

30. The micro-electro-mechanical transducer of claim 28 wherein the second electrode comprises an electrode layer deposited on the middle spring layer.

31. The micro-electro-mechanical transducer of claim 28 wherein at least a portion of the middle spring layer is conductive, and the second electrode includes the conductive portion of the middle spring layer.

32. The micro-electro-mechanical transducer of claim 28 wherein the second electrode and the fourth electrode are a common electrode shared by the first capacitor and the second capacitor.

33. 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.

34. The micro-electro-mechanical transducer of claim 33 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.

35. The micro-electro-mechanical transducer of claim 33 wherein both the first capacitor and the second capacitor are configured to operate in a transmission mode.

36. The micro-electro-mechanical transducer of claim 33 wherein both the first capacitor and the second capacitor are configured to operate in a receiving mode.

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

a micromachined semiconductor substrate;

a middle spring layer placed over the substrate, the middle spring layer carrying or including a first electrode, 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 disposed between the substrate and the middle spring layer, 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 and above or across the middle spring layer, the top plate being more rigid than the middle spring layer and carrying or including a second electrode,

the middle spring layer supporting the connector and the top plate, wherein the double-cantilever and the cavity enable a vertical displacement of the connector, which transports the top plate substantially vertically relative to the standing features and the substrate, thus changing the transducing space and activating a transducing member including the first electrode and the second electrode for energy transformation.

38. The micro-electro-mechanical transducer of claim 37, wherein:

the top plate comprises a silicon layer or a polysilicon layer; and

the substrate comprises a silicon layer or a polysilicon layer.

39. The micro-electro-mechanical transducer of claim 37, wherein the first standing feature and the second standing feature are different portions of an extended standing feature.

40. The micro-electro-mechanical transducer of claim 37, which is a capacitance micromachined ultrasonic transducer, wherein the transducing member comprises a capacitor that includes the first electrode and the second electrode.

41. The micro-electro-mechanical transducer of claim 40 wherein the first electrode comprises a separate conductive layer deposited on the middle spring layer.

42. The micro-electro-mechanical transducer of claim 40 further comprising an insulation layer disposed between the connector and the top plate.

43. The micro-electro-mechanical transducer of claim 37 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.

44. The micro-electro-mechanical transducer of claim 43, 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.

45. The micro-electro-mechanical transducer of claim 37 wherein the top plate has a thickness profile having at least two different thicknesses to provide a varied flexibility across the transducing space.

46. The micro-electro-mechanical transducer of claim 37 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.

47. The micro-electro-mechanical transducer of claim 37 wherein the top plate comprises holes formed therein.

48. The micro-electro-mechanical transducer of claim 47 wherein the holes have a size and location profile optimized for a desired rigidity/mass ratio of the top plate.

49. The micro-electro-mechanical transducer of claim 37 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.

50. The micro-electro-mechanical transducer of claim 49 wherein the maximum vertical displacement of the connector is limited by a motion stopper disposed in the cavity.

51. The micro-electro-mechanical transducer of claim 37 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.

52. The micro-electro-mechanical transducer of claim 37 further comprising an integrated circuit formed in the top plate.

53. The micro-electro-mechanical transducer of claim 37 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 top 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.

54. The micro-electro-mechanical transducer of claim 37 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.

55. The micro-electro-mechanical transducer of claim 54 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.

56. The micro-electro-mechanical transducer of claim 54 wherein both the first capacitor and the second capacitor are configured to operate in a transmission mode.

57. The micro-electro-mechanical transducer of claim 54 wherein both the first capacitor and the second capacitor are configured to operate in a receiving mode.

58. The micro-electro-mechanical transducer of claim 37, 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.

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

a substrate carrying or including a first electrode;

a middle spring layer placed over the substrate, the middle spring layer being relatively flexible and the substrate being relatively rigid, the substrate and the middle spring layer defining a first cavity and a second cavity therebetween, the first cavity being bordered by a first sidewall of a non-conductive standing feature disposed between the substrate and the middle spring layer, the second cavity being bordered by a second sidewall of the non-conductive standing feature, the first cavity and the second cavity forming a transducing space, wherein;

the middle spring layer extends from the first sidewall to cover at least part of the first cavity and extends from the second sidewall to cover at least part of the second cavity, the middle spring layer carrying or including a second electrode, the first electrode and the second electrode forming a transducing member; and

each of the first and second cavities have a lateral size that is less than a half wavelength of a 1 MHz to 10 MHz acoustic wave;

a first connector and a second connector supported by the middle spring layer and having a connector height, the first connector being horizontally distanced from the first sidewall such that the middle spring layer between the first connector and the first sidewall defines a first cantilever anchored at the first sidewall, the second connector being horizontally distanced from the second sidewall such that 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 first and second connectors separating the top plate from the middle spring layer to define a hollow space below the top plate and above or across the middle spring layer, the top plate and the connectors supported by the middle spring layer such that the first and second cantilevers and the first and second cavities enable a vertical displacement of the connectors and the top plate, which transports the top plate substantially vertically relative to the substrate and the standing feature during a change in the transducing space.

60. The micro-electro-mechanical transducer of claim 59 wherein the substrate is conductive and the transducing member includes at least a part of the conductive substrate as the first electrode.

61. The micro-electro-mechanical transducer of claim 59 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.

62. A micro-electro-mechanical transducer which is a capacitance micromachined ultrasonic 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, and

wherein the transducing member comprises a top electrode and the bottom electrode, the standing feature of the substrate being conductive and the bottom electrode including at least a part of the standing feature of the substrate.