Method and apparatus for electrostatic mode-alignment on planar MEMS gyroscopes
A MEMS BAW vibratory planar gyroscope having an in-plane electrode configuration for mode-alignment by utilizing alignment electrodes that have a height less than a full height of the gyroscope resonant body. Such alignment electrodes apply a force component that affects modes with both in-plane and out-of-plane movements. The gyroscope includes a resonant body having a height and a perimeter surface and electrodes disposed adjacent the exterior perimeter surface of the resonant body. At least one of the electrodes is an alignment electrode and has a height less than the height of the resonant body.
1. An apparatus comprising:
a resonant body having a first height dimension value h 1 and an exterior perimeter surface; and
a plurality of electrodes disposed adjacent the exterior perimeter surface of the resonant body,
wherein at least one of the plurality of electrodes is an alignment electrode and has a second height dimension value h 2 that is less than the first height dimension value h 1 of the resonant body,
wherein the first height dimension value h 1 and the second height dimension value h 2 correspond to heights of top surfaces of the respective structures from a reference base.
2. The apparatus of claim 1 , wherein the second height dimension value h 2 is ½ of the first height dimension value h 1 .
3. The apparatus of claim 1 , wherein multiple of the plurality of electrodes are alignment electrodes, each having the second height dimension value h 2 .
4. The apparatus of claim 1 , wherein the resonant body has a vibratory mode characterized by in-plane mode anti-node locations and out-of-plane mode anti-node locations on the resonant body and wherein the at least one alignment electrode is disposed at a location about the exterior perimeter of the resonant body where an in-plane mode antinode location and an out-of-plane mode anti-node location coincide.
5. The apparatus of claim 4 , wherein multiple of the plurality of electrodes are alignment electrodes, each having the second height dimension value h 2 and wherein each of the multiple alignment electrode is disposed at a location about the exterior perimeter of the resonant body where an in-plane mode antinode location and an out-of-plane mode anti-node location coincide.
6. The apparatus of claim 3 , wherein the exterior perimeter surface of the resonant body is substantially circular in shape.
7. The apparatus of claim 6 , wherein pairs of the multiple alignment electrodes are disposed opposite one another about the circular perimeter of the resonant body.
8. An apparatus comprising:
a resonant body defined by a first height dimension value h 1 and an exterior perimeter, the resonant body having a vibratory mode characterized by a plurality of in-plane mode anti-node locations and a plurality of out-of-plane mode anti-node locations on the resonant body; and
at least one electrode disposed at a location about the exterior perimeter of the resonant body where an in-plane mode antinode location and an out-of-plane mode anti-node location coincide,
wherein the at least one electrode is an alignment electrode.
9. The apparatus of claim 8 , wherein the at least one alignment electrode has a second height dimension value h 2 that is ½ of the first height dimension h 1 .
10. The apparatus of claim 9 , wherein a plurality of electrodes are disposed adjacent the exterior perimeter surface of the resonant body.
11. The apparatus of claim 10 , wherein multiple of the plurality of electrodes are alignment electrodes.
12. The apparatus of claim 11 , wherein each of the multiple alignment electrodes is of the second height dimension value h 2 .
13. The apparatus of claim 12 , wherein the second height dimension value h 2 is approximately ½ of the first height dimension value h 1 .
14. The apparatus of claim 11 , wherein each of the multiple alignment electrode is disposed at a location about the exterior perimeter of the resonant body where an in-plane mode antinode location and an out-of-plane mode anti-node location coincide.
15. A method of making a MEMS apparatus, comprising:
A) forming a resonant body having a first height dimension value h 1 and an exterior perimeter surface; and
B) disposing at least one electrode adjacent the exterior perimeter surface of the resonant body,
wherein the at least one of the electrodes is an alignment electrode and has a second height dimension value h 2 that is less than the first height dimension value h 1 of the resonant body,
wherein the first height dimension value h 1 and the second height dimension value h 2 correspond to heights of top surfaces of the respective structures from a reference base.
16. The method of claim 15 , wherein B) comprises:
B1) forming the at least one electrode to have the second height dimension value h 2 be approximately ½ of the first height dimension value h 1 of the resonant body.
17. The method of claim 15 , wherein B) comprises:
B1) forming a plurality of electrodes disposed adjacent the exterior perimeter surface of the resonant body.
18. The method of claim 17 , wherein B1) comprises:
B1a) forming the plurality of electrodes to have a second height dimension value h 2 that is less than the first height dimension value h 1 of the resonant body.
19. The method of claim 17 , wherein the exterior perimeter surface of the resonant body is substantially circular in shape and wherein B1) comprises:
B1a) forming the plurality of electrodes in pairs disposed opposite one another about the circular exterior perimeter surface of the resonant body.
20. A gyroscope, comprising:
a resonant body having a first height dimension value h 1 and an exterior perimeter surface, the resonant body having a vibratory mode characterized by a plurality of in-plane mode anti-node locations and a plurality of out-of-plane mode anti-node locations on the resonant body;
an opening defined in the resonant body;
a first plurality of side electrodes disposed adjacent the resonant body, each side electrode having a same height as the first height dimension value h 1 ;
at least one alignment electrode disposed adjacent the resonant body at a location where an in-plane mode antinode location and an out-of-plane mode antinode location coincide,
wherein the at least one alignment electrode has a second height dimension value h 2 that is less than the first height dimension value h 1 .
21. The gyroscope of claim 20 , wherein the at least one alignment electrode is disposed adjacent the exterior perimeter surface.
22. The gyroscope of claim 20 , wherein the at least one alignment electrode is disposed within the opening of the resonant body.
23. The gyroscope of claim 20 , wherein the second height dimension value h 2 =0.5*h 1 .
24. The gyroscope of claim 20 , wherein the resonant body is a planar resonant body.
25. The gyroscope of claim 20 , wherein the plurality of side electrodes are disposed at the exterior perimeter surface of the resonant body.