Serrated MEMS resonators
One embodiment of the present invention sets forth a serrated tooth actuator for driving MEMS resonator structures. The actuator includes a fixed drive electrode having a serrated tooth surface opposing a MEMS resonator arm also having a serrated tooth surface, where the MEMS resonator arm is configured to rotate towards the drive electrode when an AC signal is applied to the drive electrode. Such a configuration permits higher amplitude signals to be applied to the drive electrode without the performance of the actuator being compromised by nonlinear effects. In addition, the serrated tooth configuration enables a sufficiently high actuating force to be maintained even though the distance traversed by the MEMS resonator arm during operation is quite small. Further, the serrated configuration allows a MEMS resonator system to withstand larger fluctuations in voltage and larger substrate stresses without experiencing a substantial shift in resonant frequency.
1. A microelectromechanical system (MEMS) for generating a timing signal, the system comprising:
a MEMS resonator including a first member aligned substantially parallel to a first axis when stationary and having a serrated surface comprised of a first plurality of teeth; and
a first drive electrode aligned substantially parallel to the first axis and having a serrated surface comprised of a second plurality of teeth that opposes the serrated surface of the first member, wherein the teeth in the first plurality are interleaved with the teeth in the second plurality, wherein the first member is configured to bend towards the first drive electrode about a second axis that is perpendicular to the first axis when a signal is applied to the first drive electrode,
wherein the teeth in the first plurality of teeth and the teeth in the second plurality of teeth have no surfaces substantially parallel to a third axis that is perpendicular to both the first axis and the second axis, and
wherein a capacitive change across each surface of a tooth in the first plurality of teeth and a corresponding surface of an opposing tooth in the second plurality of teeth results when the first member bends towards the drive electrode.
2. The system of claim 1 , wherein each tooth in the first plurality of teeth is separated from at least one opposing tooth in the second plurality of teeth by a gap when the first member is stationary.
3. The system of claim 2 , wherein the gap between each tooth in the first plurality of teeth and the at least one opposing tooth in the second plurality of teeth is substantially the same for each tooth in the first plurality of teeth.
4. The system of claim 3 , wherein the gap is approximately 400 nanometers.
5. The system of claim 4 , wherein the first member is approximately 200 microns in length.
6. The system of claim 5 , wherein the gaps between the teeth in the first plurality of teeth located proximately to one end of the first member and the opposing teeth in the second plurality of teeth decrease to approximately 200 nanometers when the first member bends towards the drive electrode.
7. The system of claim 1 , wherein the MEMS resonator is fixed to an underlying substrate by only one anchor.
8. The system of claim 1 , wherein the MEMS resonator further includes a second member having a serrated surface comprised of a third plurality of teeth, and further comprising:
a second drive electrode having a serrated surface comprised of a fourth plurality of teeth that opposes the serrated surface of the second member, wherein the teeth in the third plurality are interleaved with the teeth in the fourth plurality when the second member is stationary, and
wherein the second member is configured to bend towards the second drive electrode when the signal is applied to the second drive electrode.
9. The system of claim 8 , wherein the bending of the first member towards the first drive electrode is substantially equal and opposite to the bending of the second member towards the second drive electrode.
10. The system of claim 1 , wherein the first plurality of teeth and the second plurality of teeth are configured such that the capacitance between a first portion of the first member and the first drive electrode is positive and the capacitance between a second portion of the first member and the drive electrode is negative when the first member bends towards the first drive electrode.
11. The system of claim 1 , wherein the serrated teeth in the first plurality and the serrated teeth in the second plurality have a rounded configuration.
12. An electronic device, comprising:
application circuitry; and
a microelectromechanical system (MEMS) for generating a timing signal for the application circuitry, the system comprising:
a MEMS resonator including a first member aligned substantially parallel to a first axis when stationary and having a serrated surface comprised of a first plurality of teeth, and
a first drive electrode aligned substantially parallel to the first axis and having a serrated surface comprised of a second plurality of teeth that opposes the serrated surface of the first member, wherein the teeth in the first plurality are interleaved with the teeth in the second plurality, wherein the first member is configured to bend towards the first drive electrode about a second axis that is perpendicular to the first axis when a signal is applied to the first drive electrode,
wherein the teeth in the first plurality of teeth and the teeth in the second plurality of teeth have no surfaces substantially parallel to a third axis that is perpendicular to both the first axis and the second axis, and
wherein a capacitive change across each surface of a tooth in the first plurality of teeth and a corresponding surface of an opposing tooth in the second plurality of teeth results when the first member bends towards the drive electrode.
13. The electronic device of claim 12 , wherein each tooth in the first plurality of teeth is separated from at least one opposing tooth in the second plurality of teeth by a gap when the first member is stationary.
14. The electronic device of claim 13 , wherein the gap between each tooth in the first plurality of teeth and the at least one opposing tooth in the second plurality of teeth is substantially the same for each tooth in the first plurality of teeth.
15. The electronic device of claim 14 , wherein the gap is approximately 400 nanometers.
16. The electronic device of claim 15 , wherein the first member is approximately 200 microns in length.
17. The electronic device of claim 16 , wherein the gaps between the teeth in the first plurality of teeth located proximately to one end of the first member and the opposing teeth in the second plurality of teeth decrease to approximately 200 nanometers when the first member bends towards the drive electrode.
18. The electronic device of claim 12 , wherein the MEMS resonator is fixed to an underlying substrate by only one anchor.
19. The electronic device of claim 12 , wherein the MEMS resonator further includes a second member having a serrated surface comprised of a third plurality of teeth, and further comprising:
a second drive electrode having a serrated surface comprised of a fourth plurality of teeth that opposes the serrated surface of the second member, wherein the teeth in the third plurality are interleaved with the teeth in the fourth plurality when the second member is stationary, and
wherein the second member is configured to bend towards the second drive electrode when the signal is applied to the second drive electrode.
20. The electronic device of claim 19 , wherein the bending of the first member towards the first drive electrode is substantially equal and opposite to the bending of the second member towards the second drive electrode.
21. The electronic device of claim 12 , wherein the first plurality of teeth and the second plurality of teeth are configured such that the capacitance between a first portion of the first member and the first drive electrode is positive and the capacitance between a second portion of the first member and the first drive electrode is negative when the first member bends towards the first drive electrode.
22. The electronic device of claim 12 , wherein the serrated teeth in the first plurality and the serrated teeth in the second plurality have a rounded configuration.