MEMS sensor with movable z-axis sensing element
A MEMS sensor includes a substrate and a MEMS structure coupled to the substrate. The MEMS structure has a mass movable with respect to the substrate. The MEMS sensor also includes a reference structure positioned radially outward from the MEMS structure. The reference structure is used to provide a reference to offset any environmental changes that may affect the MEMS sensor in order to increase the accuracy of its measurement.
1. A MEMS sensor comprising:
a substrate;
a MEMS structure coupled to the substrate and having a mass movable with respect to the substrate; and
a reference structure radially outward from the MEMS structure wherein the reference structure is electrically coupled to the movable mass of the MEMS structure.
2. The MEMS sensor of claim 1 , wherein the reference structure substantially circumscribes the MEMS structure.
3. The MEMS sensor of claim 1 , wherein one surface of the reference structure is substantially coplanar with one surface of the MEMS structure.
4. The MEMS sensor of claim 1 , further comprising a z-plane MEMS electrode formed on the substrate, wherein the MEMS structure is formed substantially above the z-plane MEMS electrode.
5. The MEMS sensor of claim 4 , further comprising a z-plane reference electrode formed on the substrate and coplanar with the z-plane MEMS electrode, the z-plane reference electrode formed substantially beneath the reference structure.
6. The MEMS sensor of claim 1 , further comprising a cap formed above the MEMS structure and the reference structure, the cap encapsulating the MEMS structure and the reference structure.
7. The MEMS sensor of claim 1 , wherein the substrate further includes electronic circuitry formed on or in the substrate.
8. A method of producing a MEMS sensor, the method comprising:
providing a substrate;
forming a MEMS structure coupled to the substrate and having a mass movable with respect to the substrate; and
forming a reference structure radially outward from the MEMS structure wherein the reference structure is electrically coupled to the movable mass of the MEMS structure.
9. The method of claim 8 , wherein the reference structure substantially circumscribes the MEMS structure.
10. The method of claim 8 , wherein one surface of the reference structure is substantially coplanar with one surface of the MEMS structure.
11. The method of claim 8 , further comprising:
forming a z-plane MEMS electrode on the substrate, wherein the MEMS structure is formed substantially above the z-plane MEMS electrode.
12. The method of claim 11 , further comprising:
forming a z-plane reference electrode on the substrate substantially coplanar with the z-plane MEMS electrode, the z-plane reference electrode formed substantially beneath the reference structure.
13. The method of claim 12 , wherein forming the z-plane MEMS electrode and forming the z-plane reference electrode are performed during the same processing step.
14. The method of claim 8 , wherein forming the reference structure and forming the MEMS structure are performed during the same processing step.
15. The method of claim 8 , further comprising:
forming a cap above the MEMS structure and the reference structure, the cap encapsulating the MEMS structure and the reference structure.
16. A method of measuring motion in a z-axis using a MEMS sensor, the method comprising:
providing a substrate having a z-plane MEMS electrode on the substrate;
providing a MEMS structure substantially above the z-plane MEMS electrode, the MEMS structure coupled to the substrate and having a mass movable with respect to the substrate;
providing a reference structure radially outward from the MEMS structure, the reference structure electrically coupled to the movable mass to form a sensing element;
applying a potential to the z-plane MEMS electrode; and
measuring a change in capacitance between the sensing element and the z-plane MEMS electrode using the sensing element.
17. The method of claim 16 , wherein the reference structure substantially circumscribes the MEMS structure.
18. The method of claim 16 , further comprising:
providing a z-plane reference electrode on the substrate substantially coplanar with the z-plane MEMS electrode, the z-plane reference electrode formed substantially beneath the reference structure;
applying a potential to the z-plane reference electrode; and
measuring a change in capacitance between the sensing element and the z-plane reference electrode using the sensing element.