MEMS SENSOR WITH STRESS ISOLATION AND METHOD OF FABRICATION

• US 20130319117A1
• Filed: 05/29/2012
• Published: 12/05/2013
• Est. Priority Date: 05/29/2012
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: McNeil, Andrew C., Li, Gary G., Zhang, Lisa Z., Lin, Yizhen
• Granted Patent: US 8,925,384 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• 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 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

A MEMS sensor (20, 86) includes a support structure (26) suspended above a surface (28) of a substrate (24) and connected to the substrate (24) via spring elements (30, 32, 34). A proof mass (36) is suspended above the substrate (24) and is connected to the support structure (26) via torsional elements (38). Electrodes (42, 44), spaced apart from the proof mass (36), are connected to the support structure (26) and are suspended above the substrate (24). Suspension of the electrodes (42, 44) and proof mass (36) above the surface (28) of the substrate (24) via the support structure (26) substantially physically isolates the elements from deformation of the underlying substrate (24). Additionally, connection via the spring elements (30, 32, 34) result in the MEMS sensor (22, 86) being less susceptible to movement of the support structure (26) due to this deformation.

Claims

1. A micro electromechanical systems (MEMS) sensor comprising:

a substrate;

a support structure suspended above a surface of said substrate and connected to said substrate via a support element;

a proof mass suspended above said substrate and flexibly connected to said support structure via a flexible support element, said proof mass being adapted for motion about an axis between first and second ends of said proof mass; and

an electrode suspended above said substrate and connected to said support structure, said electrode being spaced apart from said proof mass.

2. A MEMS sensor as claimed in claim 1 wherein said support structure comprises at least one isolation joint, said at least one isolation joint electrically isolating said electrode from said proof mass.

3. A MEMS sensor as claimed in claim 1 wherein:

said electrode is a first electrode;

said proof mass includes a first section formed between said axis and said first end and a second section formed between said axis and said second end, said first electrode being spaced apart from said first section of said proof mass; and

said MEMS sensor further comprises a second electrode suspended above said substrate and connected to said support structure, said second electrode being spaced apart from said second section of said proof mass.

4. A MEMS sensor as claimed in claim 3 wherein said support structure comprises at least one isolation joint, said at least one isolation joint electrically isolating said first electrode from said second electrode.

5. A MEMS sensor as claimed in claim 1 wherein said electrode is disposed beneath said proof mass.

6. A MEMS sensor as claimed in claim 1 wherein said electrode is disposed above said proof mass.

7. A MEMS sensor as claimed in claim 1 wherein said electrode is fixedly attached to said support structure.

8. A MEMS sensor as claimed in claim 1 wherein said flexible support element comprises a torsion spring for enabling said proof mass to rotate about said axis while said electrode connected to said support structure remains substantially nonmovable relative to said proof mass.

9. A MEMS sensor as claimed in claim 1 wherein said support element includes spring elements, and said support structure is a relatively rigid structure as compared to said spring elements.

10. A MEMS sensor as claimed in claim 1 wherein said support structure comprises a frame having a central opening, and said proof mass is positioned in said central opening.

11. A MEMS sensor as claimed in claim 10 wherein:

said frame includes a first frame section laterally displaced from said first end of said proof mass and a second frame section laterally displaced from said second end of said proof mass;

said support element includes a first spring element coupled to said first frame section and a second spring element coupled to said second frame section, said frame being a substantially rigid structure as compared to said first and second spring elements; and

said MEMS sensor further comprises a first anchor connecting said first spring element to said substrate and a second anchor connecting said second spring element to said substrate.

12. A MEMS sensor as claimed in claim 11 wherein:

said support elements further include a third spring element coupled to an intermediate frame section of said frame, said intermediate frame section being located proximate said axis; and

said MEMS sensor further includes a third anchor connecting said third spring element to said substrate; and

said frame includes isolation joints electrically isolating said first, second, and intermediate frame sections from one another so that said first frame section, said first spring element, and said first anchor define a first electrically conductive path for said first electrode, said second frame section, said second spring element, and said second anchor define a second electrically conductive path for said second electrode, and said intermediate frame section, said third spring element, and said third anchor define a third electrically conductive path for said proof mass, each of said first, second, and third conductive paths being electrically isolated from one another.

13. A method of fabricating a microelectromechanical systems (MEMS) sensor isolated from a substrate comprising:

forming a first structural layer on a first sacrificial layer overlying said substrate to produce one of a first element and a second element, said first element including a pair of electrodes and said second element including a support structure and a proof mass torsionally coupled to said support structure;

depositing a second sacrificial layer over said first structural layer;

creating at least one opening through said second sacrificial layer to expose a portion of said one of said first and second elements formed in said first structural layer;

forming a second structural layer over said second sacrificial layer to fill said at least opening and to produce another of said first and second elements, wherein;

when said pair of electrodes is formed in said first structural layer, said support structure and said proof mass are formed in said second structural layer;

when said support structure and said proof mass are produced in said first structural layer, said pair of electrodes is formed in said second structural layer; and

said second structural layer fills said at least one opening to provide at least one junction connecting said pair of electrodes to said support structure; and

removing at least portions of said first and second sacrificial layers to suspend said pair of electrodes, said proof mass, and said support structure above a surface of said substrate and to connect said support structure to said substrate via spring elements.

14. A method as claimed in claim 13 further comprising forming isolation joints in said support structure to electrically isolate each electrode of said pair of electrodes and said proof mass from one another.

15. A method as claimed in claim 13 wherein said removing operation comprises releasing said proof mass to enable said proof mass to pivot about an axis of rotation while said pair of electrodes connected to said support structure remains substantially nonmovable relative to said proof mass.

16. A device comprising:

a microelectromechanical systems (MEMS) sensor, said MEMS sensor including;

a substrate;

a support structure suspended above a surface of said substrate and connected to said substrate via a spring system;

a proof mass suspended above said substrate and flexibly connected to said support structure via a flexible support element, said proof mass being adapted for motion about an axis located between first and second ends of said proof mass, a first section being formed between said axis and said first end and a second section being formed between said axis and said second end;

a first electrode suspended above said substrate and fixedly attached to said support structure, said first electrode being spaced apart from said first section of said proof mass; and

a second electrode suspended above said substrate and fixedly attached to said support structure, said second electrode being spaced apart from said second section of said proof mass.

17. A device as claimed in claim 16 wherein said support structure is a relatively rigid structure as compared to spring elements of said spring system.

18. A device as claimed in claim 16 wherein said axis is an axis of rotation, and said flexible support element comprises a torsion spring for enabling said proof mass to pivot about said axis of rotation while said first and second electrodes connected to said support structure remain substantially nonmovable relative to said proof mass.

19. A device as claimed in claim 16 wherein:

said support structure comprises a frame having a central opening, said proof mass being positioned in said central opening, said frame including a first frame section laterally displaced from said first end of said proof mass and a second frame section laterally displaced from said second end of said proof mass;

said spring system includes a first spring element coupled to said first frame section and a second spring element coupled to said second frame section; and

said MEMS sensor further comprises a first anchor connecting said first spring element to said substrate and a second anchor connecting said second spring element to said substrate.

20. A device as claimed in claim 19 wherein:

said spring system further includes a third spring element coupled to an intermediate frame section of said frame, said intermediate frame section being located proximate said axis;

said MEMS sensor further includes a third anchor connecting said third spring element to said substrate; and

said frame includes isolation joints electrically isolating said first, second, and intermediate frame sections from one another wherein;

said first frame section, said first spring element, and said first anchor define a first electrically conductive path for said first electrode;

said second frame section, said second spring element, and said second anchor define a second electrically conductive path for said second electrode; and

said intermediate frame section, said third spring element, and said third anchor define a third electrically conductive path for said proof mass, each of said first, second, and third conductive paths being electrically isolated from one another.