Tri-axis accelerometer

• US 20070119252A1
• Filed: 11/16/2006
• Published: 05/31/2007
• Est. Priority Date: 11/22/2005
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: Kionix Incorporated (ROHM Co., Ltd.)
• Inventors: Shen-Epstein, June, Epstein, Keith, Miller, Scott, Adams, Scott
• Granted Patent: US 7,430,909 B2
• Time in Patent Office: Days
• US Class Current: 73/510
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

In an embodiment of the present invention there is provided a micro-electromechanical (MEMS) accelerometer, including a substrate, a first sensor and a second sensor. The first sensor is configured to measure an acceleration along a first axis parallel to a plane of the substrate. The second sensor is configured to measure an acceleration along an axis perpendicular to the plane of the substrate. The second sensor comprises a first beam, a second beam and a single support structure. The single support structure supports the first and second beams relative to the substrate, wherein the first and second beams circumscribe the first sensor.

Claims

1. A micro-electromechanical accelerometer, comprising:

a substrate;

a first sensor configured to measure an acceleration along a first axis parallel to a plane of the substrate; and

a second sensor configured to measure an acceleration along an axis perpendicular to the plane of the substrate, wherein the second sensor comprises a first beam, a second beam and a single support structure, wherein the single support structure supports the first and second beams relative to the substrate, and wherein the first and second beams circumscribe the first sensor.

2. The micro-electromechanical accelerometer of claim 1, wherein the acceleration along the first axis is measured based on a differential capacitance among electrodes of the first sensor.

3. The micro-electromechanical accelerometer of claim 1, wherein the second sensor is configured to measure the acceleration along the axis perpendicular to the plane of the substrate based on an electrical coupling between the first and second beams.

4. The micro-electromechanical accelerometer of claim 3, wherein the first beam moves relative to the second beam in response to the acceleration along the axis perpendicular to the plane of the substrate causing a measurable change in the electrical coupling between the first and second beams.

5. The micro-electromechanical accelerometer of claim 4, wherein the first beam is pliably mounted to the single support structure and the second beam is rigidly mounted to the single support structure.

6. The micro-electromechanical accelerometer of claim 5, wherein the first sensor is supported by and moves with the first beam.

7. The micro-electromechanical accelerometer of claim 5, wherein the first sensor is supported by and moves with the second beam.

8. The micro-electromechanical accelerometer of claim 4, wherein the electrical coupling between the first and second beams comprises a capacitance between a first plurality of electrodes of the first beam and a second plurality of electrodes of the second beam.

9. The micro-electromechanical accelerometer of claim 8, wherein the acceleration along the axis perpendicular to the plane of the substrate is measured by a change in the capacitance between the first plurality of electrodes and the second plurality of electrodes.

10. The micro-electromechanical accelerometer of claim 9, wherein the first plurality of electrodes of the first beam and the second plurality of electrodes of the second beam form an area of overlap that linearly changes with the acceleration along the axis perpendicular to the plane of the substrate.

11. The micro-electromechanical accelerometer of claim 10, wherein a radius of curvature of the first beam is different than a radius of curvature of the second beam, thereby resulting in the area of overlap.

12. The micro-electromechanical accelerometer of claim 10, wherein the first beam comprises an interconnected planar set of beams having a silicon core with a first oxide layer disposed on a top of the first beam, and wherein the second beam comprises an interconnected planar set of beams having a silicon core with a second oxide layer disposed on a top of the second beam.

13. The micro-electromechanical accelerometer of claim 12, wherein a thickness of the first oxide layer is different than a thickness of the second oxide layer, thereby resulting in the area of overlap.

14. The micro-electromechanical accelerometer of claim 1, wherein the second sensor further comprises a nub that confines a range of motion of the first beam.

15. The micro-electromechanical accelerometer of claim 1, wherein the single support structure comprises traces that electrically couple the second sensor to traces on the substrate.

16. The micro-electromechanical accelerometer of claim 1, wherein the single support structure also supports the first sensor relative to the substrate.

17. The micro-electromechanical accelerometer of claim 16, wherein the single support structure comprises traces that electrically couple the first sensor and the second sensor to traces on the substrate.

18. The micro-electromechanical accelerometer of claim 1, further comprising:

a third sensor configured to measure an acceleration along a second axis parallel to a plane of the substrate, wherein the second axis is perpendicular to the first axis; and

a fourth sensor configured to measure an acceleration along the axis perpendicular to the plane of the substrate, wherein the fourth sensor comprises a third beam, a fourth beam and a second single support structure, wherein the second single support structure supports the third and fourth beams relative to the substrate, and wherein the third and fourth beams circumscribe the third sensor.

19. The micro-electromechanical accelerometer of claim 18, wherein the acceleration along the second axis is measured based on a differential capacitance among electrodes of the third sensor.

20. The micro-electromechanical accelerometer of claim 18, wherein the second sensor and fourth sensor are collectively configured to measure the acceleration along the axis perpendicular to the plane of the substrate based on a differential electrical coupling between (i) the first and second beams and (ii) the third and fourth beams.

21. The micro-electromechanical accelerometer of claim 20, wherein the second beam circumscribes the first beam and the second beam is rigidly coupled to the single support structure, thereby restricting movement of the second beam.

22. The micro-electromechanical accelerometer of claim 21, wherein the fourth beam circumscribes the third beam and the third beam is rigidly coupled to the second single support structure, thereby restricting movement of the third beam.

23. A micro-electromechanical accelerometer, comprising:

a substrate;

a first sensor comprising a mass and a frame, wherein the mass comprises a first plurality of electrodes and the frame comprises a second plurality of electrodes interdigitated with and electrically coupled to the first plurality of electrodes, wherein the mass moves relative to the frame in response to an acceleration along a first axis parallel to a plane of the substrate causing a measurable change in the electrical coupling between the first and second plurality of electrodes; and

a second sensor comprising a first beam, a second beam and a single support structure, wherein the single support structure supports the first and second beams relative to the substrate, wherein the first beam comprises a third plurality of electrodes and the second beam comprises a fourth plurality of electrodes interdigitated with and electrically coupled to the third plurality of electrodes, wherein the first beam moves relative to the second beam in response to an acceleration along an axis perpendicular to the plane of the substrate causing a measurable change in the electrical coupling between the third and fourth plurality of electrodes, and wherein the first and second beams circumscribe the first sensor.

24. The micro-electromechanical accelerometer of claim 23, wherein a radius of curvature of the first beam is different than a radius of curvature of the second beam, thereby causing the third plurality of electrodes to be offset from the fourth plurality of electrodes.

25. The micro-electromechanical accelerometer of claim 23, wherein the first beam comprises a first oxide layer and the second beam comprises a second oxide layer, a thickness of the first oxide layer being different than a thickness of the second oxide layer, thereby causing the third plurality of electrodes to be offset from the fourth plurality of electrodes.

26. The micro-electromechanical accelerometer of claim 23, wherein the second sensor further comprises a nub that confines a range of motion of the first beam.

27. The micro-electromechanical accelerometer of claim 23, wherein the single support structure comprises traces that electrically couple the second sensor to traces on the substrate.

28. The micro-electromechanical accelerometer of claim 23, wherein the single support structure also supports the first sensor relative to the substrate.

29. The micro-electromechanical accelerometer of claim 28, wherein the single support structure comprises traces that electrically couple the first sensor and the second sensor to traces on the substrate.

30. The micro-electromechanical accelerometer of claim 28, wherein the second sensor further comprises a connector coupled to both the second beam and the single support structure, and wherein the connector restricts movement of the second beam.

31. The micro-electromechanical accelerometer of claim 23, further comprising:

a third sensor comprising a second mass and a second frame, wherein the second mass comprises a fifth plurality of electrodes and the second frame comprises a sixth plurality of electrodes interdigitated with and electrically coupled to the fifth plurality of electrodes, wherein the second mass moves relative to the second frame in response to an acceleration along a second axis parallel to a plane of the substrate causing a measurable change in the electrical coupling between the fifth and sixth plurality of electrodes, wherein the second axis is perpendicular to the first axis; and

a fourth sensor comprising a third beam, a fourth beam and a second single support structure, wherein the second single support structure supports the third and fourth beams relative to the substrate, wherein the third beam comprises a seventh plurality of electrodes and the fourth beam comprises an eighth plurality of electrodes interdigitated with and electrically coupled to the seventh plurality of electrodes, wherein the third beam moves relative to the fourth beam in response to an acceleration along the axis perpendicular to the plane of the substrate causing a measurable change in the electrical coupling between the seventh and eighth plurality of electrodes, and wherein the third and fourth beams circumscribe the third sensor.

32. The micro-electromechanical accelerometer of claim 31, wherein the second sensor and the fourth sensor are configured to measure a difference between (i) the measurable change in the electrical coupling between the third and fourth plurality of electrodes and (ii) the measurable change in the electrical coupling between the seventh and eighth plurality of electrodes.

33. The micro-electromechanical accelerometer of claim 31, wherein the electrical coupling between the third and fourth plurality of electrodes comprises a first capacitance and the electrical coupling between the seventh and eighth plurality of electrodes comprises a second capacitance, and wherein the second sensor and the fourth sensor are configured to measure a difference between the first capacitance and the second capacitance.

34. A method for configuring a micro-electromechanical accelerometer, comprising:

supporting a first sensor relative to a substrate by a single support structure, wherein the first sensor is configured to measure an acceleration along an axis perpendicular to a plane of the substrate, and wherein the first sensor comprises a first beam and a second beam; and

circumscribing a second sensor with the first and second beams of the first sensor, wherein the second sensor is configured to measure an acceleration along a first axis parallel to the plane of the substrate.

35. The method of claim 34, further comprising:

offsetting the first beam relative to the second beam based on an amount of oxide included on each of the first and second beams.

36. The method of claim 34, further comprising:

electrically coupling the second sensor to traces on the substrate by traces included in the single support structure.

37. The method of claim 34, further comprising:

supporting the first sensor relative to the substrate by the single support structure.

38. The method of claim 37, further comprising:

electrically coupling the first sensor and the second sensor to traces on the substrate by traces in the single support structure.

39. The method of claim 37, further comprising:

coupling a connector to both the second beam and the single support structure, thereby restricting movement of the second beam.

40. The method of claim 34, further comprising:

supporting a third sensor relative to the substrate by a second single support structure, wherein the third sensor is configured to measure an acceleration along the axis perpendicular to the plane of the substrate, and wherein the third sensor comprises a third beam and a fourth beam; and

circumscribing a fourth sensor with the third and fourth beams of the third sensor, wherein the fourth sensor is configured to measure an acceleration along a second axis parallel to the plane of the substrate, wherein the second axis parallel to the plane of the substrate is perpendicular to the first axis parallel to the plane of the substrate.

41. The method of claim 40, further comprising:

measuring the acceleration along the axis perpendicular to the plane of the substrate based on a differential electrical coupling between (i) the first and second beams and (ii) the third and fourth beams.