VERTICALLY INTEGRATED 3-AXIS MEMS ACCELEROMETER WITH ELECTRONICS

• US 20080314147A1
• Filed: 06/21/2007
• Published: 12/25/2008
• Est. Priority Date: 06/21/2007
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: Nasiri, Steven S., Seeger, Joseph, Yaralioglu, Goksen
• Granted Patent: US 8,047,075 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• 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 2015/0814 for translational movement of the mass, e.g. shuttle type
• 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 system and method in accordance with the present invention provides for a low cost, bulk micromachined accelerometer integrated with electronics. The accelerometer can also be integrated with rate sensors that operate in a vacuum environment. The quality factor of the resonances is suppressed by adding dampers. Acceleration sensing in each axis is achieved by separate structures where the motion of the proof mass affects the value of sense capacitors differentially. Two structures are used per axis to enable full bridge measurements to further reduce the mechanical noise, immunity to power supply changes and cross axis coupling. To reduce the sensitivity to packaging and temperature changes, each mechanical structure is anchored to a single anchor pillar bonded to the top cover.

Claims

1. An accelerometer comprising:

an actuator substrate;

a reference substrate; and

at least one proof mass substantially on the actuator substrate, anchored to a cover plate at a single point with at least one flexure spring, suspended over the reference substrate;

the at least one proof mass substantially constrained to move only in one direction;

the proof mass having at least one stationary electrode to form a capacitance which changes with the acceleration induced in one direction.

2. The accelerometer of claim 1 wherein the at least one proof mass comprises at least two proof masses.

3. The accelerometer of claim 2 wherein the at least two moving proof masses comprise two proof masses constrained to move in substantially an x-direction to measure acceleration in the x-direction, at least two proof masses constrained to move in substantially for a y-direction to measure acceleration in the y-direction, and at least two proof masses constrained to move in substantially a z-direction to measure acceleration in the z-direction.

4. The accelerometer of claim 1 wherein the at least one electrode forms a parallel plate capacitance.

5. The accelerometer of claim 2 wherein a full bridge configuration is utilized for capacitive measurement of the at least two proof masses.

6. The accelerometer of claim 5, wherein a full bridge configuration is utilized for capacitance measurement of the at least two proof masses constrained to move in the x-direction.

7. The accelerometer of claim 5, wherein a full bridge configuration is utilized for capacitance measurement of the at least two proof masses constrained to move in the y-direction.

8. The accelerometer of claim 5, wherein a full bridge configuration is utilized for capacitance measurement of the at least two proof masses constrained to move in the z-direction.

9. The accelerometer of claim 5, wherein capacitance measurement by the full bridge configuration is proof mass driven.

10. The accelerometer of claim 5, wherein capacitance measurement by the full bridge configuration is electrode driven.

11. The accelerometer of claim 1, which includes at least one damper to suppress the resonance quality factor.

12. The accelerometer of claim 1 which includes an integrated actuator for self-test, wherein the actuator comprises a parallel plate capacitor.

13. The accelerometer of claim 1 which includes travel stoppers in at least one of an x or a y direction.

14. The accelerometer of claim 1 wherein the at least one proof mass is connected electrically to a reference substrate at the anchor.

15. The accelerometer of claim 1 wherein the at least one proof mass is connected electrically to the reference substrate through the at least one flexure.

16. The accelerometer of claim 1 wherein the reference substrate comprises a single crystal silicon wafer.

17. The accelerometer of claim 1 wherein the reference substrate comprises a CMOS integrated circuit.

18. The accelerometer of claim 1 wherein the capacitance measures the displacement of the at least one proof mass.

19. The accelerometer of claim 18 wherein the measurement is provided utilizing a half bridge configuration with the capacitance being in series with a constant capacitance.

20. The accelerometer of claim 18 wherein the measurement is provided utilizing a full bridge configuration with the capacitance being with three other capacitances.

21. The accelerometer of claim 19 wherein the capacitance measurement for the half bridge configuration is proof mass driven.

22. The accelerometer of claim 19 wherein the capacitance measurement for the half bridge configuration is electrode driven.

23. The accelerometer of claim 20 wherein the capacitance measurement for the full bridge configuration is proof mass driven.

24. The accelerometer of claim 20 wherein the capacitance measurement for the full bridge configuration is proof mass driven.

25. The accelerometer of claim 2 wherein a z-axis accelerometer comprises:

a reference substrate;

an actuator substrate;

a first and second structures located on the actuator substrate and including a lever arm, each of the structures being pivoted at a pivot point and including at least three proof mass sections on the lever arm, wherein electrodes are placed under a portion of the plurality of proof mass sections and on the reference substrate to provide a differential measurement, wherein when there is acceleration in the z-direction the lever arm bends around the pivot point.

26. A z-axis accelerometer comprises:

a reference substrate;

an actuator substrate;

first and second structures on the actuator substrate, each of the first and second structures including a lever arm and being pivoted at a pivot point;

each of the structures including at least three proof mass sections on the lesser arm; and

electrodes on the reference substrate, wherein the electrodes are placed under a portion of the plurality of proof mass sections, wherein when there is acceleration in the z-direction the lever arm bends around the pivot point.

27. An accelerometer comprising:

an actuator substrate;

a reference substrate; and

at least two masses substantially on the actuator substrate, and suspended over the reference substrate, the at least two proof masses substantially constrained to move only in one direction;

the at least two proof masses having at least one stationary electrode to form a capacitance which changes with the acceleration induced in one direction.

28. The accelerometer of claim 27 wherein the at least one electrode forms a parallel plate capacitance.

29. The accelerometer of claim 27 therein a full bridge configuration is utilized for capacitive measurement of the at least two proof masses.

30. The accelerometer of claim 29, wherein a full bridge configuration is utilized for capacitance measurement of the at least two proof masses constrained to move in the x-direction.

31. The accelerometer of claim 29, wherein a full bridge configuration is utilized for capacitance measurement of the at least two proof masses constrained to move in the y-direction.

32. The accelerometer of claim 29, wherein a full bridge configuration is utilized for capacitance measurement of the at least two proof masses constrained to move in the z-direction.

33. The accelerometer of claim 29, wherein capacitance measurement by the full bridge configuration is proof mass driven.

34. The accelerometer of claim 29, wherein capacitance measurement by the full bridge configuration is electrode driven.