Resonator electrode shields
A microelectromechanical system (MEMS) resonator includes a resonant semiconductor structure, drive electrode, sense electrode and electrically conductive shielding structure. The first drive electrode generates a time-varying electrostatic force that causes the resonant semiconductor structure to resonate mechanically, and the first sense electrode generates a timing signal in response to the mechanical resonance of the resonant semiconductor structure. The electrically conductive shielding structure is disposed between the first drive electrode and the first sense electrode to shield the first sense electrode from electric field lines emanating from the first drive electrode.
1. A microelectromechanical system (MEMS) die comprising:
a support region;
a flexure element having a first end secured to the support region and also having a second end;
a resonant structure secured to the second end of the flexure element and capable of mechanically resonant motion in which the flexure element also moves;
a sense electrode to generate a timing signal in response to the mechanically resonant motion of the resonant semiconductor structure; and
an electrically conductive shielding structure disposed between the sense electrode and the flexure element to reduce contribution of flexure element motion to the timing signal.
2. The MEMS die of claim 1 wherein the resonant structure, flexure element, sense electrode and electrically conductive shielding structure are formed within a first semiconductor layer of the MEMS die.
3. The MEMS die of claim 2 wherein the semiconductor layer comprises silicon.
4. The MEMS die of claim 2 wherein the support element, flexure element and resonant structure are integrally formed within the first semiconductor layer.
5. The MEMS die of claim 2 further comprising first and second oxide layers having the first semiconductor layer disposed therebetween, the first and second oxide layers having openings adjacent the resonant structure such that the resonant structure is released from, and free to move relative to, the first and second oxide layers.
6. The MEMS die of claim 5 further comprising an encapsulation layer to encapsulate the resonant structure within the MEMS die.
7. The MEMS die of claim 1 wherein the electrically conductive shielding structure comprises doped silicon.
8. The MEMS die of claim 1 further comprising an electrical sink coupled to the electrically conductive shielding structure.
9. The MEMS die of claim 8 wherein an electrical sink is also coupled to the support region.
10. The MEMS die of claim 8 wherein the electrical sink comprises at least one of a ground contact or a bias voltage contact.
11. A method of fabricating a microelectromechanical system (MEMS) die, the method comprising:
forming a resonant structure capable of mechanically resonant motion and secured to a support region via a flexure element that also moves during mechanically resonant motion of the resonant structure;
forming a sense electrode to generate a timing signal in response to the mechanically resonant motion of the resonant semiconductor structure; and
forming an electrically conductive shielding structure between the sense electrode and the flexure element to reduce contribution of flexure element motion to the timing signal.
12. The method of claim 11 wherein forming the resonant structure capable of mechanically resonant motion and secured to the support region via the flexure element comprises forming the resonant structure, flexure element, and support region within a first semiconductor layer of the MEMS die.
13. The method of claim 12 wherein forming the sense electrode and forming the electrically conductive shielding structure comprise forming the sense electrode and the electrically conductive shielding structure within the first semiconductor layer.
14. The method of claim 12 further comprising disposing the first semiconductor layer between first and second oxide layers of the MEMS die and forming openings in the first and second oxide layers adjacent the resonant structure such that the resonant structure is released from, and free to move relative to, the first and second oxide layers.
15. The method of claim 11 further comprising encapsulating the resonant structure within the MEMS die.
16. The method of claim 11 wherein forming the resonant structure capable of mechanically resonant motion and secured to the support region via the flexure element comprises integrally forming the support element, flexure element and resonant structure.
17. The method of claim 11 wherein forming the electrically conductive shielding structure comprises doping a silicon region in which the electrically conductive shielding structure is formed.
18. The method of claim 11 further comprising coupling the electrically conductive shielding structure to an electrical sink.
19. The method of claim 18 further comprising coupling the support region to the electrical sink.
20. The method of claim 18 wherein coupling the electrically conductive shielding structure to the electrical sink comprises coupling the electrically conductive shielding structure to at least one of a ground contact or a bias voltage contact.