Electrically decoupled silicon gyroscope

• US 6,626,039 B1
• Filed: 09/13/2000
• Issued: 09/30/2003
• Est. Priority Date: 09/17/1999
• Status: Expired due to Term

• Current Assignee: Konix, Inc., Milli Sensor Systems & Actuators, Inc., Kionix Incorporated (ROHM Co., Ltd.)
• Original Assignee: Milli Sensor Systems & Actuators, Inc.
• Inventors: Cardarelli, Donato, Groves, James, Dauwalter, Charles R., Carroll, Raymond, Adams, Scott G.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US09/660,740
• Time in Patent Office: 1,112 Days
• Field of Search: 735/040.4, 735/040.1, 735/040.2, 735/040.3, 735/040.8, 735/040.9, 735/041.2, 735/10, 735/143.2, 735/142.4
• US Class Current: 73/504.04
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

An oscillatory gyroscope is described with decoupled drive and sense oscillators and reduced cross-axis sensitivity. The gyroscope is fabricated using a plasma micromachining process on standard silicon wafers. The electrical isolation of the drive and sense functions of the gyroscope, contained within the same micromechanical element, reduce cross-coupling while obtaining high inertial mass and high sensitivity.

Claims

1. A silicon angular rate gyroscope comprising:

a substrate,

a movable body comprised of a planar arrangement of high-aspect ratio single-crystal silicon beams forming an open cellular structure, the body comprising;

a torque summing member (TSM) mounted to the substrate by flexures that substantially restrict motion of the TSM to torsional oscillations about an output axis, and

a rotor driven member (RDM) mounted to the TSM by flexures that substantially restrict motion of the RDM to torsional oscillations about a spin axis,

the movable body having a plurality of regions of silicon which are mechanically connected but electrically isolated, forming transducers for sensing the motion of the TSM and driving the motion of the RDM.

2. The gyroscope of claim 1, further comprising an actuator having two sections, a first section mounted on the TSM and a second section mounted on the RDM, at least one of the first section and the second section being an electrically isolated silicon region, such that the RDM may be driven into motion by application of voltage between the first section of the actuator and the second section of the actuator.

3. The gyroscope of claim 1, further comprising a capacitive sensor having two sections, a first section mounted on the RDM and a second section mounted on the TSM, at least one of the first section and the second section being an electrically isolated silicon region, such that the RDM motion can be sensed by changes in capacitance of the capacitive sensor.

4. The gyroscope of claim 1, further comprising a capacitive TSM sensor having two sections, a first section mounted on the TSM and a second section mounted on the substrate, at least one of the first section and the second section being an electrically isolated silicon region, such that the TSM motion can be sensed by changes in capacitance of the capacitive transducer.

5. The gyroscope of claim 4, further comprising an electronic circuit for demodulating a TSM oscillation sensed by the TSM sensor into a signal that is proportional to a rate of rotation of the substrate.

6. The gyroscope of claim 1, further comprising a capacitive RDM sensor having two sections, a first section mounted on the RDM and a second section mounted on the substrate, at least one of the first section and the second section being an electrically isolated silicon region, such that the RDM motion can be sensed by changes in capacitance of the sensor, and the capacitance of the sensor is insensitive to small motions of the TSM.

7. The gyroscope of claim 1, in which the substrate has a recess, and the RDM and TSM are symmetrical structures arranged concentrically in the recess.

8. The gyroscope of claim 7 wherein the TSM is interior to the RDM.

9. The gyroscope of claim 7 wherein the RDM is interior to the TSM.

10. The gyroscope of claim 7, further comprising a plurality of flexible electrical leads, mechanically attaching the body to the substrate, such that electrical signals can be routed into and out of the gyroscope.

11. The gyroscope of claim 1, in which the substrate has a ring-shaped recess with a central projection, and the RSM and TDM are in the form of rings, arranged concentrically in the recess around the central projection.

12. The gyroscope of claim 1, further comprising a plurality of inner flexures connecting the body to the central projection.

13. The gyroscope of claim 1, further comprising a plurality of structures mounted on the RDM to balance inertias of the RDM about the spin and input axes.

14. The gyroscope of claim 1 wherein the substrate forms a plane, and the output axis points out of the plane.

15. The gyroscope of claim 1 wherein the substrate forms a plane, and the input axis points out of the plane.

16. The gyroscope of claim 1 wherein the substrate forms a plane, and the spin axis points out of the plane.

17. The gyroscope of claim 1, wherein the flexures mounting the TSM comprise thick and thin sections, and a relative size of the thick and thin sections are selected to determine an axial stress state and a stiffness of the flexures.

18. The gyroscope of claim 1, in which the electrically isolated regions of silicon are separated by joints formed from a dielectric material that mechanically connect but electrically isolate the said isolate regions of silicon.

19. The gyroscope of claim 1, further comprising:

a) at least one TSM sensor comprising at least one electrically isolated region, for sensing motion of the TSM;

b) at least one RDM sensor comprising at least one electrically isolated region, for sensing motion of the RDM;

c) at least one RDM actuator comprising at least one electrically isolated region, for applying electrostatic force to the RDM; and

d) a signal processing circuit comprising;

i) an oscillator having a carrier signal output, coupled to at least one TSM sensor and to at least one RDM sensor;

ii) a TSM sense circuit having an input coupled to the TSM sensor driven by the oscillator, and an output, the TSM circuit processing a signal from the input and producing a signal at the output which is proportional to a motion of the TSM;

iii) an RDM sense circuit having an input coupled to the RDM sensor driven by the oscillator, and an output, the RDM circuit processing a signal from the input and producing a signal at the output which is proportional to a motion of the RDM;

iv) a rate determining circuit having a first input coupled to the output of the TSM sense circuit and a second input coupled to the output of the RDM sense circuit, and an output, the rate determining circuit combining a signal from the first input and a signal from the second input and providing an output signal at the output which is representative of a rate of movement of the gyroscope; and

v) an RDM drive circuit having an input coupled to the output of the RDM sense circuit and an output coupled to at least one RDM actuator, the RDM drive circuit maintaining a resonance of the RDM by producing a signal at the output which is modified by feedback from a signal at the input.

20. The gyroscope of claim 19, in which the rate determining circuit comprises:

a) a phase adjuster having an input coupled to the output of the RDM sense circuit and an output providing a signal which is approximately 90 degrees phase shifted from a signal present at the input;

b) a multiplier having a first input coupled to the output of the TSM sense circuit, a second input coupled to the output of the phase adjuster, and an output providing a signal which is the product of the signals on the first input and the second input; and

c) a low-pass filter having an input coupled to the output of the multiplier and an output having a low frequency signal,

the output of the low-pass filter being the output of the rate determining circuit.

21. The gyroscope of claim 19, in which the RDM drive circuit comprises:

a) a 90 degree phase shifter having an input coupled to the output of the RDM sense circuit and an output;

b) a voltage limiter having an input coupled to the output of the 90 degree phase shifter, and an output;

the output of the voltage limiter being coupled to the RDM electrostatic levitation actuators through a summing junction with a DC potential.

22. The gyroscope of claim 19, in which the RDM drive circuit further comprises a bias input, such that a DC bias voltage at the bias input applies a DC bias voltage to the RDM actuator, adjusting a resonant frequency of the RDM.

23. The gyroscope of claim 19, in which the signal processing circuit is in the form of an integrated circuit.

24. The gyroscope of claim 23, in which the a first substrate containing the movable body is covered by a second substrate with a seal and a standoff between the first and second substrate provided by a glass frit.

25. the gyroscope of claim 24, in which the integrated circuit and the first and second substrates are packaged together in one hybrid package.

26. The gyroscope of claim 1, in which the a first substrate containing the movable body is covered by a second substrate with a seal and a standoff between the first and second substrate provided by a glass frit.

27. A silicon angular rate gyroscope comprising:

a substrate,

a movable body comprising;

a torque summing member (TSM) mounted to the substrate by flexures that substantially restrict motion of the TSM to torsional oscillations about an output axis, and

a rotor driven member (RDM) mounted to the TSM by flexures that substantially restrict motion of the RDM to torsional oscillations about a spin axis,

the movable body having a plurality of electrically isolated regions of silicon which are mechanically connected but electrically isolated by one or more transverse isolation segments formed from a dielectric material, forming transducers for sensing the motion of the TSM and driving the motion of the RDM.

28. The gyroscope of claim 27, further comprising an actuator having two sections, a first section mounted on the TSM and a second section mounted on the RDM, at least one of the first section and the second section being an electrically isolated silicon region which is mechanically connected but electrically isolated by transverse segments formed from a dielectric material, such that the RDM may be driven into motion by application of voltage between the first section of the actuator and the second section of the actuator.

29. The gyroscope of claim 27, further comprising a capacitive sensor having two sections, a first section mounted on the RDM and a second section mounted on the TSM, at least one of the first section and the second section being an electrically isolated silicon region which is mechanically connected but electrically isolated by transverse segments formed from a dielectric material, such that the RDM motion can be sensed by changes in capacitance of the capacitive sensor.

30. The gyroscope of claim 27, further comprising a capacitive TSM sensor having two sections, a first section mounted on the TSM and a second section mounted on the substrate, at least one of the first section and the second section being an electrically isolated silicon region which is mechanically connected but electrically isolated by transverse segments formed from a dielectric material, such that the TSM motion can be sensed by changes in capacitance of the capacitive transducer.

31. The gyroscope of claim 30, further comprising an electronic circuit for demodulating a TSM oscillation sensed by the TSM sensor into a signal that is proportional to a rate of rotation of the substrate.

32. The gyroscope of claim 27, further comprising a capacitive RDM sensor having two sections, a first section mounted on the RDM and a second section mounted on the substrate, at least one of the first section and the second section being an electrically isolated silicon region which is mechanically connected but electrically isolated by transverse segments formed from a dielectric material, such that the RDM motion can be sensed by changes in capacitance of the sensor, and the capacitance of the sensor is insensitive to small motions of the TSM.

33. The gyroscope of claim 27, in which the substrate has a recess, and the RDM and TSM are symmetrical structures arranged concentrically in the recess.

34. The gyroscope of claim 33 wherein the TSM is interior to the RDM.

35. The gyroscope of claim 33 wherein the RDM is interior to the TSM.

36. The gyroscope of claim 33, further comprising a plurality of flexible electrical leads, mechanically attaching the body to the substrate, such that electrical signals can be routed into and out of the gyroscope.

37. The gyroscope of claim 27, in which the substrate has a ring-shaped recess with a central projection, and the RSM and TDM are in the form of rings, arranged concentrically in the recess around the central projection.

38. The gyroscope of claim 27, further comprising a plurality of inner flexures connecting the body to the central projection.

39. The gyroscope of claim 27, further comprising a plurality of structures mounted on the RDM to balance inertias of the RDM about the spin and input axes.

40. The gyroscope of claim 27 wherein the substrate forms a plane, and the output axis points out of the plane.

41. The gyroscope of claim 27 wherein the substrate forms a plane, and the input axis points out of the plane.

42. The gyroscope of claim 27 wherein the substrate forms a plane, and the spin axis points out of the plane.

43. The gyroscope of claim 27, wherein the flexures mounting the TSM comprise thick and thin sections, and a relative size of the thick and thin sections are selected to determine an axial stress state and a stiffness of the flexures.

44. The gyroscope of claim 27, in which the the RDM is formed from an open cellular structure composed of arrangements of high aspect ratio silicon beams.

45. The gyroscope of claim 27, in which the the TSM is formed from an open cellular structure composed of arrangements of high aspect ratio silicon beams.

46. The gyroscope of claim 27, further comprising:

a) at least one TSM sensor comprising at least one electrically isolated region, for sensing motion of the TSM;

b) at least one RDM sensor comprising at least one electrically isolated region, for sensing motion of the RDM;

c) at least one RDM actuator comprising at least one electrically isolated region, for applying electrostatic force to the RDM; and

d) a signal processing circuit comprising;

i) an oscillator having a carrier signal output, coupled to at least one TSM sensor and to at least one RDM sensor;

ii) a TSM sense circuit having an input coupled to the TSM sensor driven by the oscillator, and an output, the TSM circuit processing a signal from the input and producing a signal at the output which is proportional to a motion of the TSM;

iii) an RDM sense circuit having an input coupled to the RDM sensor driven by the oscillator, and an output, the RDM circuit processing a signal from the input and producing a signal at the output which is proportional to a motion of the RDM;

iv) a rate determining circuit having a first input coupled to the output of the TSM sense circuit and a second input coupled to the output of the RDM sense circuit, and an output, the rate determining circuit combining a signal from the first input and a signal from the second input and providing an output signal at the output which is representative of a rate of movement of the gyroscope; and

v) an RDM drive circuit having an input coupled to the output of the RDM sense circuit and an output coupled to at least one RDM actuator, the RDM drive circuit maintaining a resonance of the RDM by producing a signal at the output which is modified by feedback from a signal at the input.

47. The gyroscope of claim 46, in which the rate determining circuit comprises:

a) a phase adjuster having an input coupled to the output of the RDM sense circuit and an output providing a signal which is approximately 90 degrees phase shifted from a signal present at the input;

b) a multiplier having a first input coupled to the output of the TSM sense circuit, a second input coupled to the output of the phase adjuster, and an output providing a signal which is the product of the signals on the first input and the second input; and

c) a low-pass filter having an input coupled to the output of the multiplier and an output having a low frequency signal,

the output of the low-pass filter being the output of the rate determining circuit.

48. The gyroscope of claim 46, in which the RDM drive circuit comprises:

a) a 90 degree phase shifter having an input coupled to the output of the RDM sense circuit and an output;

b) a voltage limiter having an input coupled to the output of the 90 degree phase shifter, and an output;

the output of the voltage limiter being coupled to the RDM electrostatic levitation actuators through a summing junction with a DC potential.

49. The gyroscope of claim 46, in which the RDM drive circuit further comprises a bias input, such that a DC bias voltage at the bias input applies a DC bias voltage to the RDM actuator, adjusting a resonant frequency of the RDM.

50. The gyroscope of claim 46, in which the signal processing circuit is in the form of an integrated circuit.

51. The gyroscope of claim 50 in which the a first substrate containing the movable body is covered by a second substrate with a seal and a standoff between the first and second substrate provided by a glass frit.

52. the gyroscope of claim 51, in which the integrated circuit and the first and second substrates are packaged together in one hybrid package.

53. The gyroscope of claim 27, in which the a first substrate containing the movable body is covered by a second substrate with a seal and a standoff between the first and second substrate provided by a glass frit.

54. A silicon angular rate gyroscope comprising:

a substrate,

a movable body comprised of a planar arrangement of high-aspect ratio single-crystal silicon beams forming an open cellular structure, the body comprising;

a torque summing member (TSM) mounted to the substrate by flexures that substantially restrict motion of the TSM to torsional oscillations about an output axis, and

a rotor driven member (RDM) mounted to the TSM by flexures that substantially restrict motion of the RDM to torsional oscillations about a spin axis,

the movable body having a plurality of electrically isolated regions of silicon which are mechanically connected but electrically isolated by transverse segments formed from a dielectric material, forming transducers for sensing the motion of the TSM and driving the motion of the RDM.