Minimizing the effect of 1/ƒ noise with a MEMS flux concentrator

• US 7,195,945 B1
• Filed: 09/15/2005
• Issued: 03/27/2007
• Est. Priority Date: 09/15/2004
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Inventors: Edelstein, Alan S., Pedersen, Michael, Pulskamp, Jeffrey S.
• Primary Examiner(s): LEE, HSIEN MING
• Application Number:
  US11/226,403
• Time in Patent Office: 558 Days
• Field of Search: 438/22, 438/24, 438/25, 438/48, 438/51, 438/53, 438/73, 438/74, 324/244, 324/225, 324/251, 324/252
• US Class Current: 438/48
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/095 extraordinary magnetoresistance sensors

Abstract

A method of fabricating a MEMS device includes forming a magnetic sensor over a SOI wafer which may include an epoxy layer; forming a pair of MEMS flux concentrators sandwiching the magnetic sensor; connecting an electrostatic comb drive to each of the flux concentrators; connecting a spring to the flux concentrators and the comb drive; performing a plurality of DRIE processes on the SOI wafer; and releasing the flux concentrators, the comb drive, and the spring from the SOI wafer. Another embodiment includes forming adhesive bumps and a magnetic sensor on a first wafer; forming a second wafer; forming a pair of MEMS flux concentrators, a pair of electrostatic comb drives, and at least one spring on the second wafer; bonding the second wafer to the adhesive bumps; and compressing the adhesive bumps using non-thermal means such as pressure only.

Claims

1. A method of fabricating a microelectromechanical system (MEMS) device, said method comprising:

forming a magnetic sensor over a silicon on insulator (SOI) wafer, wherein said SOI wafer comprises an epoxy layer;

forming a pair of MEMS flux concentrators sandwiching said magnetic sensor;

connecting an electrostatic comb drive to each of the MEMS flux concentrators;

connecting at least one spring to said pair of MEMS flux concentrators and said electrostatic comb drive;

performing a plurality of deep reactive ion etching (DRIE) processes on said SOI wafer; and

releasing said MEMS flux concentrators, said electrostatic comb drive, and said at least one spring from said SOI wafer.

2. The method of claim 1, wherein said magnetic sensor is formed by:

providing an antiferromagnetic layer;

positioning a first ferromagnetic layer over said antiferromagnetic layer;

positioning a conducting layer over said first ferromagnetic layer; and

positioning a second ferromagnetic layer over said conducting layer.

3. The method of claim 1, wherein said plurality of DRIE processes comprise performing a DRIE process on said SOI wafer to define said MEMS flux concentrators, said electrostatic comb drives, and said at least one spring.

4. The method of claim 1, wherein said MEMS flux concentrators comprise a layer of silicon dioxide thereunder, and wherein said plurality of DRIE processes comprise performing a DRIE process on a handle layer of said SOI wafer to remove said layer of silicon dioxide from beneath said MEMS flux concentrator.

5. The method of claim 1, wherein the releasing of said MEMS flux concentrators, said electrostatic comb drive, and said at least one spring from said SOI wafer is performed using oxygen plasma.

6. The method of claim 1, wherein said MEMS flux concentrators comprise a double layer of Cr and permalloy.

7. A method of fabricating a microelectromechanical system (MEMS) device, said method comprising:

forming a magnetic sensor over a silicon on insulator (SOI) wafer, wherein said SOI wafer comprises a device layer over an intermediate layer over a handle layer;

forming a pair of MEMS flux concentrators sandwiching said magnetic sensor;

connecting an electrostatic comb drive to each of the MEMS flux concentrators;

connecting at least one spring to said pair of MEMS flux concentrators and said electrostatic comb drive;

performing a plurality of deep reactive ion etching (DRIE) processes on said SOI wafer; and

releasing said MEMS flux concentrators, said electrostatic comb drive, and said at least one spring from said SOI wafer.

8. The method of claim 7, wherein said magnetic sensor is formed by:

providing an antiferromagnetic layer;

positioning a first ferromagnetic layer over said antiferromagnetic layer;

positioning a conducting layer over said first ferromagnetic layer; and

positioning a second ferromagnetic layer over said conducting layer.

9. The method of claim 7, wherein said plurality of DRIE processes comprise performing a DRIE process on said device layer of said SOI wafer to define said MEMS flux concentrators, said electrostatic comb drives, and said at least one spring.

10. The method of claim 7, wherein said MEMS flux concentrators comprise a layer of silicon dioxide thereunder, and wherein said plurality of DRIE processes comprise performing a DRIE process on said handle layer of said SOI wafer to remove said layer of silicon dioxide from beneath said MEMS flux concentrator.

11. The method of claim 7, wherein the releasing of said MEMS flux concentrators, said electrostatic comb drive, and said at least one spring from said SOI wafer is performed using oxygen plasma.

12. The method of claim 7, wherein said intermediate layer comprises an epoxy layer.

13. The method of claim 7, wherein said MEMS flux concentrators comprise a double layer of Cr and permalloy.

14. A method of fabricating a microelectromechanical system (MEMS) device, said method comprising:

forming a first wafer;

forming adhesive bumps on said first wafer;

forming a magnetic sensor on said first wafer;

forming a second wafer;

forming a pair of MEMS flux concentrators, a pair of electrostatic comb drives, and at least one spring on said second wafer, wherein said pair of MEMS flux concentrators, said pair of electrostatic comb drives, and said at least one spring is connected to one another, and wherein said pair of MEMS flux concentrators sandwich said magnetic sensor;

bonding said second wafer to said adhesive bumps; and

compressing said adhesive bumps using non-thermal means.

15. The method of claim 14, wherein said adhesive bumps comprise indium.

16. The method of claim 14, wherein said non-thermal means comprises pressure.

17. The method of claim 14, wherein said magnetic sensor is formed by:

providing an antiferromagnetic layer;

positioning a first ferromagnetic layer over said antiferromagnetic layer;

positioning a conducting layer over said first ferromagnetic layer; and

positioning a second ferromagnetic layer over said conducting layer.

18. The method of claim 14, wherein said first wafer comprises a silicon on insulator (SOI) wafer.

19. The method of claim 14, wherein said second wafer comprises Si₃N₄.

20. The method of claim 14, wherein said MEMS flux concentrators comprise a double layer of Cr and permalloy.

21. A method of fabricating a microelectromechanical system (MEMS) device, said method comprising:

forming a magnetic sensor over a silicon on insulator (SOI) wafer, wherein said SOI wafer comprises an epoxy layer;

forming a MEMS flux concentrator proximate said magnetic sensor;

connecting an electrostatic comb drive to the MEMS flux concentrator;

connecting at least one spring to said MEMS flux concentrator and said electrostatic comb drive;

performing a plurality of deep reactive ion etching (DRIE) processes on said SOI wafer; and

releasing said MEMS flux concentrator, said electrostatic comb drive, and said at least one spring from said SOI wafer.

22. The method of claim 21, wherein said magnetic sensor is formed by:

providing an antiferromagnetic layer;

positioning a first ferromagnetic layer over said antiferromagnetic layer;

positioning a conducting layer over said first ferromagnetic layer; and

positioning a second ferromagnetic layer over said conducting layer.

23. The method of claim 21, wherein said plurality of DRIE processes comprise performing a DRIE process on said SOI wafer to define said MEMS flux concentrator, said electrostatic comb drive, and said at least one spring.

24. The method of claim 21, wherein said MEMS flux concentrators comprise a layer of silicon dioxide thereunder, and wherein said plurality of DRIE processes comprise performing a DRIE process on a handle layer of said SOI wafer to remove said layer of silicon dioxide from beneath said MEMS flux concentrator.

25. The method of claim 21, wherein the releasing of said MEMS flux concentrator, said electrostatic comb drive, and said at least one spring from said SOI wafer is performed using oxygen plasma.