Electromagnetic rebalanced micromechanical transducer

• US 5,331,852 A
• Filed: 12/16/1991
• Issued: 07/26/1994
• Est. Priority Date: 09/11/1991
• Status: Expired due to Term

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Greiff, Paul, Boxenhorn, Burton
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US07/807,726
• Time in Patent Office: 953 Days
• Field of Search: 73/517 B, 73/505, 73/862.61, 73/517 A, 73/517 R, 73/517 AV, 73/862.59, 73/DIG. 1, 73/778, 73/779
• US Class Current: 73/504.09
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

A method and apparatus for electromagnetically rebalancing a micromechanical transducer via a plurality of current carrying electrodes disposed beneath or above the transducer interacting with a current carrying conductor disposed on the transducer. In a first embodiment, the micromechanical transducer comprises a micromechanical accelerometer having electromagnetic rebalance of an asymmetric plate. In an alternative embodiment, the transducer comprises a micromechanical gyroscope having electromagnetic driving of an outer gimbal and electromagnetic rebalance of a sense gimbal.

Claims

1. A micromechanical transducer formed from a mass of semiconductor material, comprising:

a displaceable transducer element having at least one planar surface;

a current carrying conductor disposed on said at least one planar surface;

a plurality of electrodes integral to said mass of semiconductor material and disposed proximate to said displaceable transducer element and proximate to said current carrying conductor; and

at least one current generator providing a fixed current through said current carrying conductor, a first electrode current through one of said plurality of electrodes, and a second electrode current through another of said plurality of electrodes, magnetic fields formed by said first electrode current, said second electrode current and said fixed current, interacting to produce motion of said displaceable transducer element.

2. The micromechanical transducer of claim 1 wherein said displaceable transducer element is selectively etched from silicon.

3. The micromechanical transducer of claim 1 wherein said displaceable transducer element and said plurality of electrodes are constructed in monolithic silicon.

4. The micromechanical transducer of claim 1 wherein said plurality of electrodes are P-type doped silicon electrodes integral to a monolithic mass of N-type silicon from which said displaceable transducer element is selectively etched and said plurality of electrodes are disposed beneath said transducer element.

5. The micromechanical transducer of claim 1 wherein said displaceable transducer is a substantially rectangular planar element fabricated from a mass of silicon and flexibly attached to said mass of silicon by a plurality of linkages.

6. The micromechanical transducer of claim 5 wherein said plurality of linkages comprises two flexures having a slot forming a tension relief beam proximate thereto.

7. The micromechanical transducer of claim 5 wherein said plurality of flexible linkages comprises two linkages between said mass of silicon and said substantially rectangular planar element.

8. The micromechanical transducer of claim 1 wherein said current carrying conductor comprises a first branch and a second branch, and wherein said first electric current flows through each of said first and second branch and said second and third electric currents flow through a first and a second one of said plurality of electrodes.

9. The micromechanical transducer of claim 8 wherein said first electric current is a fixed direct current.

10. The micromechanical transducer of claim 1 wherein said displaceable transducer element is an asymmetric plate flexibly attached to a frame by at least one flexible linkage.

11. The micromechanical transducer of claim 10 wherein said asymmetric plate has a first end and a second end and said first end is longer than said second end.

12. The micromechanical transducer of claim 11 wherein said first end comprises a layer of polysilicon disposed on an insulating layer which is disposed on said displaceable transducer element, said polysilicon layer serving to shift a center of gravity of said displaceable transducer element upwardly to decrease cross axis sensitivity of said displaceable transducer element.

13. The micromechanical transducer of claim 10 wherein said asymmetric plate has a first end and a second end of substantially equal length and said first end has a mass disposed thereon.

14. The micromechanical transducer of claim 1 wherein said displaceable transducer element is a gyroscopic transducer which comprises an outer gimbal flexibly attached to a frame and an inner gimbal flexibly attached to said outer gimbal.

15. The micromechanical transducer of claim 14 wherein said current carrying conductor is disposed on said outer gimbal.

16. The micromechanical transducer of claim 14 wherein said current carrying conductor is disposed on said inner gimbal.

17. The micromechanical transducer of claim 1 wherein said current carrying conductor is a coil configuration.

18. The micromechanical transducer of claim 1 wherein said plurality of electrodes comprises at least two bridge electrodes disposed above said displaceable transducer element.

19. The micromechanical transducer of claim 1 wherein said plurality of electrodes includes at least two buried electrodes disposed beneath said displaceable transducer element.