MEMS Sensor with Cap Electrode

• US 20080168838A1
• Filed: 01/11/2008
• Published: 07/17/2008
• Est. Priority Date: 01/11/2007
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Zhang, Xin, Martin, John R.
• Granted Patent: US 8,100,012 B2
• Time in Patent Office: Days
• 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 7/0077 Other packages not provided for in groups B81B7/0035 - B81B7/0074
• CPC Class Codes: B81C 1/00269 Bonding of solid lids or wafers to the substrate
• CPC Class Codes: B81C 99/0045 End test of the packaged device
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

A MEMS sensor includes a substrate having a MEMS structure movably attached to the substrate, a cap attached to the substrate and encapsulating the MEMS structure, and an electrode formed on the cap that senses movement of the MEMS structure.

Claims

1. A MEMS sensor comprising:

a substrate having a MEMS structure movably attached to the substrate;

a cap attached to the substrate, the cap encapsulating the MEMS structure; and

an electrode formed on the cap that senses movement of the MEMS structure.

2. The MEMS sensor of claim 1, further comprising a reference electrode formed coplanar with the MEMS structure and attached to the substrate.

3. The MEMS sensor of claim 1, wherein the substrate comprises an SOI wafer.

4. The MEMS sensor of claim 1, wherein the substrate comprises a silicon wafer.

5. The MEMS sensor of claim 4, further comprising a second electrode formed on the substrate beneath the MEMS structure.

6. The MEMS sensor of claim 5, further comprising a reference electrode formed coplanar with the MEMS structure.

7. The MEMS sensor of claim 1, wherein the electrode is formed from aluminum or an aluminum alloy.

8. The MEMS sensor of claim 1, wherein the electrode is formed from copper, a copper alloy, gold or a gold alloy.

9. The MEMS sensor of claim 1, wherein the cap includes a conductive seal ring formed from aluminum or an aluminum alloy.

10. The MEMS sensor of claim 1, wherein the MEMS sensor is an inertial sensor.

11. The MEMS sensor of claim 1, wherein the MEMS sensor is a pressure sensor, a fluid sensor, or a microphone.

12. The MEMS sensor of claim 1, wherein the substrate further includes electronic circuitry formed on or in the substrate.

13. A method of producing a MEMS sensor that senses motion in the z-axis, the method comprising:

providing a substrate having a MEMS structure movably attached to the substrate;

forming an electrode on a cap; and

attaching the cap to the substrate so that the cap encapsulates the MEMS structure and the electrode senses movement of the MEMS structure.

14. The method of claim 13, further comprising:

forming a reference electrode coplanar with the MEMS structure, wherein the cap encapsulates the MEMS structure and the reference electrode.

15. The method of claim 13 further comprising:

forming a seal ring on the cap, wherein the seal ring is used to attach the cap to the substrate.

16. The method of claim 15, wherein forming the electrode and forming the seal ring are performed during the same processing step.

17. The method of claim 15, wherein the electrode and the seal ring are formed from aluminum or an aluminum alloy.

18. The method of claim 17, wherein attaching the cap comprises:

thermocompression bonding the seal ring on the cap to a corresponding aluminum-based ring on the substrate.

19. The method of claim 13, wherein forming an electrode on the cap comprises:

depositing a layer of aluminum or aluminum alloy on the cap; and

etching the layer to leave a seal ring and the electrode surrounded by the seal ring.

20. The method of claim 13, wherein the substrate comprises an SOI wafer.

21. The method of claim 13, wherein the substrate comprises a silicon wafer.

22. The method of claim 21, further comprising:

forming a second electrode on the substrate beneath the MEMS structure.

23. The method of claim 22, further comprising:

forming a reference electrode coplanar with the MEMS structure, wherein the cap encapsulates the MEMS structure and the reference electrode.

24. The method of claim 13, wherein the substrate further includes electronic circuitry formed on or in the substrate.

25. The method of claim 13, wherein the electrode is formed from copper, a copper alloy, gold or a gold alloy.