Method for constructing an isolate microelectromechanical system (MEMS) device using surface fabrication techniques

• US 20030060051A1
• Filed: 09/26/2001
• Published: 03/27/2003
• Est. Priority Date: 09/26/2001
• Status: Active Grant

• Current Assignee: Longitude Licensing Limited (Vector Capital Corporation)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Kretschmann, Robert J., Harris, Richard D., Lucak, Mark A., Knieser, Michael J.
• Granted Patent: US 6,756,310 B2
• Time in Patent Office: Days
• US Class Current: 438/694
• CPC Class Codes: B81C 1/00357 involving bonding one or several substrates on a non-temporary support, e.g. another substrate
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers
• CPC Class Codes: B81C 2203/0109 Bonding an individual cap on the substrate

Abstract

A method for fabricating an electrically isolated MEMS device is provided that uses surface fabrication techniques to form a conductive stationary MEMS element, and a movable MEMS element spaced apart from the conductive stationary MEMS element. The movable element includes a nonconductive base which provides for electrical isolation between a plurality of conductive members extending from the base. Modifications to the basic process permit the incorporation of a wafer-level cap which provides mechanical protection to the movable portions of the device.

Claims

1. A method of constructing a MEMS device having a first stationary conductive member separated from a second movable conductive member by a variable size gap, the method using exclusively surface fabrication techniques and comprising:

(a) providing a substrate;

(b) depositing sacrificial material onto the substrate to form a sacrificial layer;

(c) depositing insulating material onto the sacrificial layer to form an insulating layer;

(d) after step (c), depositing conductive material onto the insulating layer to form a conductive layer;

(e) etching through a portion of the conductive layer to the insulating layer to form the first and second adjacent conductive structures separated by a variable size gap;

(f) etching through a portion of the insulating layer to provide a base for the second conductive structure; and

(g) etching through at least a portion of the sacrificial layer to release the base and second conductive structure from the substrate.

2. The method as recited in claim 1, further comprising:

depositing a second conductive material onto the conductive layer.

3. The method as recited in claim 1, wherein step (b) further comprises depositing the sacrificial material and patterning it so that it remains on a portion of the substrate that is not in alignment with the first conductive structure.

4. The method as recited in claim 3, wherein step (c) further comprises depositing the insulating material and patterning it so that a portion of it remains directly on the substrate adjacent the sacrificial layer.

5. The method as recited in claim 3, wherein step (c) further comprises depositing insulating material and patterning it so that it remains only on the sacrificial material.

6. The method as recited in claim 5, wherein step (d) further comprises depositing a first portion of the conductive material and patterning it so that it remains on the substrate, and depositing a second portion of the conductive material and patterning it so that it remains on the insulating material, wherein the first portion forms the first conductive member.

7. The method as recited in claim 1, wherein the first conductive member is connected directly to the substrate.

8. The method as recited in claim 1, wherein the first conductive member is connected to the substrate via insulating material.

9. The method as recited in claim 8, wherein the first conductive member is connected to the substrate via sacrificial material.

10. The method as recited in claim 1, further comprising depositing sacrificial material and patterning it to produce a mold having cavities formed therein, wherein step (d) further comprises depositing conductive material so as to cover the surface and fill the cavities and planarizing the surface so as to have the conductive material remain only in the cavities.

11. The method as recited in claim 1, wherein the substrate is a conductive substrate selected from the group consisting of silicon, silicon carbide, and gallium arsenide.

12. The method as recited in claim 1, wherein the substrate is a nonconductive substrate selected from the group consisting of glass, high resistivity silicon, crystalline sapphire, and ceramic.

13. The method as recited in claim 1, wherein the insulating material comprises silicon dioxide.

14. The method as recited in claim 1, wherein the conductive material comprises polycrystalline silicon.

15. The method as recited in claim 1, wherein the sacrificial material comprises silicon nitride.

16. The method as recited in claim 2, wherein the second conductive material comprises a metal.

17. The method as recited in claim 1, further comprising attaching a protective cap to the insulating material to encapsulate the MEMS device.

18. The method as recited in claim 1, wherein the movable conductive member further comprises two conductive elements that are electrically isolated from each other.

19. A method for fabricating an encapsulated MEMS device having a first stationary conductive member separated from a second movable conductive member by a variable size gap, the method using exclusively surface fabrication techniques and comprising:

(a) depositing conductive trace material and patterning it so that it remains on the outer ends of a substrate to form first and second traces;

(b) depositing sacrificial material onto the substrate and patterning it so that it remains between the traces to form a sacrificial layer;

(c) depositing insulating material onto the sacrificial material to form an insulating layer;

(d) depositing additional trace material so as to cover the surface and fill voids formed by the insulating and sacrificial layers aligned with the conductive trace material followed by planarizing the surface so as to form inner and outer trace members with insulating material therebetween;

(e) forming the stationary conductive member in electrical communication with the inner trace member;

(f) etching through a portion of the insulating layer; and

(g) forming the movable conductive member separated by the stationary conductive member by a variable size gap.

20. The method as recited in claim 19, further comprising bonding a cap to the wafer so as to encapsulate the stationary and movable members.

21. The method as recited in claim 20, wherein the cap is bonded to the insulating material disposed between the inner and outer trace members.

22. The method as recited in claim 19, wherein the outer trace member is connectable to the ambient environment to transfer electricity to the stationary conductive member.

23. The method as recited in claim 20, wherein the cap is conductive.

24. The method as recited in claim 20, wherein the cap is nonconductive.

25. The method as recited in claim 19, wherein the movable conductive member further comprises two conductive elements that are electrically isolated from each other.