MEMS multi-axis accelerometer electrode structure

1. An inertial sensor, comprising:

a single proof-mass formed in an x-y plane of a device layer, the single proof-mass including a single, central anchor configured to suspend the single proof-mass above a via wafer;

first and second electrode stator frames formed in the x-y plane of the device layer on respective first and second sides of the inertial sensor, the first and second electrode stator frames symmetric about the single, central anchor, and each separately including:

a central platform; and

an anchor configured to fix the central platform to the via wafer;

wherein the anchors for the first and second electrode stator frames are positioned asymmetrically along the central platforms with respect to the single, central anchor.

2. The inertial sensor of claim 1 , wherein the first and second electrode stator frames include:

first and second inner branches; and

a plurality of stationary fingers coupled to the first and second inner branches.

3. The inertial sensor of claim 2 , wherein the first inner branch is substantially parallel to the second inner branch.

4. The inertial sensor of claim 3 , wherein the first and second inner branches of the first and second electrode stator frames are substantially parallel to the central platforms of the first and second electrode stator frames.

5. The inertial sensor of claim 4 , wherein the central platforms of the first and second electrode stator frames are symmetric about the single, central anchor.

6. The inertial sensor of claim 2 , including:

first and second proof-mass frames formed in the x-y plane of the device layer, each coupled to the single proof-mass and including:

first and second inner branches about and substantially parallel to the central platforms;

first and second outer branches; and

a plurality of moving fingers coupled to the first and second inner and outer branches.

7. The inertial sensor of claim 6 , wherein the first and second electrode stator frames have a first mass, wherein the first and second proof-mass frames have a second mass, and wherein the first mass is less than the second mass.

8. The inertial sensor of claim 6 , wherein at least a portion of the plurality of stationary fingers are interdigitated with at least a portion of the plurality of moving fingers.

9. The inertial sensor of claim 6 , wherein the stationary fingers are substantially perpendicular to the first and second inner branches of the first and second electrode stator frames; and

wherein the moving fingers are substantially perpendicular to the first and second inner and outer branches of the first and second proof-mass frames.

10. The inertial sensor of claim 1 , including:

a single proof-mass 3-axis accelerometer including the single proof-mass and separate x, y, and z-axis flexure bearings; and

wherein the x and y-axis flexure bearings are symmetric about the single, central anchor and the z-axis flexure is not symmetric about the single, central anchor.

11. The inertial sensor of claim 10 , wherein the 3-axis accelerometer includes in-plane x and y-axis accelerometer sense electrodes symmetric about the single, central anchor and out-of-plane z-axis accelerometer sense electrodes; and

wherein the in-plane x-axis accelerometer sense electrodes include the first and second electrode stator frames.

12. The inertial sensor of claim 11 , including:

a single proof-mass 3-axis gyroscope formed in the x-y plane adjacent the 3-axis accelerometer, the single proof-mass 3-axis gyroscope including:

a main proof-mass section suspended about a single, central anchor, the main proof-mass section including a radial portion extending outward towards an edge of the 3-axis gyroscope;

a central suspension system configured to suspend the 3-axis gyroscope from the single, central anchor; and

a drive electrode including a moving portion and a stationary portion, the moving portion coupled to the radial portion, wherein the drive electrode and the central suspension system are configured to oscillate the 3-axis gyroscope about a z-axis normal to the x-y plane at a drive frequency.

13. The apparatus of claim 11 , including:

a cap wafer bonded to a first surface of the device layer; and

wherein the via wafer is bonded to a second surface of the device layer, wherein the cap wafer and the via wafer are configured to encapsulate the single proof-mass 3-axis gyroscope and the single proof-mass 3-axis accelerometer in the same cavity.

14. The inertial sensor of claim 1 , wherein the single, central anchor is not centered on the via wafer; and

wherein the anchors for the first and second electrode stator frames are asymmetric along the central platforms with respect to the single, central anchor to improve temperature performance associated with thermal deformation.

15. An inertial sensor, comprising:

a single proof-mass formed in an x-y plane of a device layer, the single proof-mass including:

a single, central anchor configured to suspend the single proof-mass above a via wafer;

x-axis flexure bearings symmetric about the single, central anchor;

a first proof-mass frame;

a first electrode stator frame on a first side of the single, central anchor, the first electrode stator frame including:

a first central platform;

first and second inner branches;

a plurality of stationary fingers coupled to the first and second inner branches; and

a first anchor configured to fix the first electrode stator frame to the via wafer at a first position along the first central platform; and

a second electrode stator frame on a second side of the single, central anchor, the second electrode stator frame including:

a second central platform;

third and fourth inner branches;

a plurality of stationary fingers coupled to the third and fourth inner branches; and

a second anchor configured to fix the second electrode stator frame to the via wafer at a second position along the second central platform; and

wherein the first position along the first central platform and the second position along the second central platform are asymmetric with respect to the single, central anchor.

16. The inertial sensor of claim 15 , wherein the first and second electrode stator frames are symmetric about the single, central anchor.

17. The inertial sensor of claim 16 , including:

first and second proof-mass frames formed in the x-y plane of the device layer, each coupled to the single proof-mass and including:

first and second inner branches about and substantially parallel to the first and second central platforms;

first and second outer branches; and

a plurality of moving fingers coupled to the first and second inner and outer branches; and

wherein at least a portion of the plurality of stationary fingers are interdigitated with at least a portion of the plurality of moving fingers.