MEMS sensor with movable Z-axis sensing element

• US 8,939,029 B2
• Filed: 04/02/2012
• Issued: 01/27/2015
• Est. Priority Date: 09/05/2008
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Zhang, Xin, Judy, Michael W.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US13/437,859
• Publication Number:
  US 20120223726A1
• Time in Patent Office: 1,030 Days
• Field of Search: 735/173.2, 361/280
• US Class Current: 73/514.32
• CPC Class Codes: B81B 2203/053 Translation according to an axis perpendicular to the substrate
• CPC Class Codes: B81B 3/0051 For defining the movement, i.e. structures that guide or limit the movement of an element mechanical arrangements for preventing or damping vibration or shock H01H3/60
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0871 using stopper structures for limiting the travel of the seismic mass
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

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 electrically coupled to the mass of the MEMS sensor. 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.

Claims

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 electrically coupled to the movable mass of the MEMS structure, wherein the MEMS structure is radially outward from the reference structure.

2. The MEMS sensor of claim 1, wherein the MEMS structure substantially circumscribes the reference 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 electrically coupled to the movable mass of the MEMS structure, wherein the MEMS structure is radially outward from the reference structure.

9. The method of claim 8, wherein the MEMS structure substantially circumscribes the reference 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 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, wherein the MEMS structure is radially outward from the reference structure.

17. The method of claim 16, wherein the MEMS structure substantially circumscribes the reference 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.