MEMS SENSOR WITH DUAL PROOF MASSES

• US 20120186347A1
• Filed: 01/24/2011
• Published: 07/26/2012
• Est. Priority Date: 01/24/2011
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: McNeil, Andrew C.
• Granted Patent: US 8,539,836 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• 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: G01P 2015/0837 the mass being suspended so as to only allow movement perpendicular to the plane of the substrate, i.e. z-axis sensor

Abstract

A microelectromechanical systems (MEMS) sensor (20) includes a substrate (26) and suspension anchors (34, 36) formed on a planar surface (28) of the substrate (26). The MEMS sensor (20) further includes a first movable element (38) and a second movable element (40) suspended above the substrate (26). Compliant members (42, 44) interconnect the first movable element (38) with the suspension anchor 34 and compliant members (46, 48) interconnect the second movable element (40) with the suspension anchor (36). The movable elements (38, 40) have an equivalent shape. The movable elements may be generally rectangular movable elements (38, 40) or L-shaped movable elements (108, 110) in a nested configuration. The movable elements (38, 40) are oriented relative to one another in rotational symmetry about a point location (94) on the substrate (26).

Claims

1. A microelectromechanical systems (MEMS) sensor comprising:

a substrate;

a first movable element positioned in spaced apart relationship above a generally planar surface of said substrate; and

a second movable element positioned in spaced apart relationship above said surface of said substrate, said first and second movable elements having a substantially equivalent shape and said second movable element being generally oriented in rotational symmetry relative to said first movable element about a point location on said planar surface of said substrate.

2. A MEMS sensor as claimed in claim 1 wherein said second movable element is located in an orientation that is rotated about said point location approximately one hundred and eighty degrees relative to said first movable element.

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

said first movable element is adapted for rotational motion in a first direction in response to acceleration along an axis perpendicular to said planar surface of said substrate, said rotational motion occurring about a first rotational axis positioned between first and second ends of said first movable element; and

said second movable element is adapted for rotational motion in a second direction in response to said acceleration, said rotational motion occurring about a second rotational axis positioned between third and fourth ends of said second movable element, said second direction being opposite to said first direction.

4. A MEMS sensor as claimed in claim 3 wherein said first and second rotational axes are aligned with one another along a common axis.

5. A MEMS sensor as claimed in claim 4 further comprising:

a first suspension anchor formed on said planar surface of said substrate and approximately centered on said common axis;

a first pair of compliant members interconnecting said first movable element with said first suspension anchor, said first pair of compliant members enabling said rotational motion of said first movable element about said first rotational axis;

a second suspension anchor formed on said surface of said substrate and approximately centered on said common axis; and

a second pair of compliant members interconnecting said second movable element with said second suspension anchor, said second pair of compliant members enabling said rotational motion of said second movable element about said second rotational axis.

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

said first movable element includes a first section between said first rotational axis and said first end and a second section between said first rotational axis and said second end, said first rotational axis being offset between said first and second ends such that a first length of said first section between said first rotational axis and said first end is greater than a second length of said second section between said first rotational axis and said second end; and

said second movable element includes a third section between said second rotational axis and said third end and a fourth section between said second rotational axis and said fourth end, said second rotational axis being offset between said third and fourth ends such that a third length of said third section said between said second rotational axis and said third end is less than a fourth length of said fourth section between said second rotational axis and said fourth end.

7. A MEMS sensor as claimed in claim 6 wherein:

said first length is substantially equivalent to said fourth length; and

said second length is substantially equivalent to said third length.

8. A MEMS sensor as claimed in claim 6 wherein:

said first movable element includes a first lateral extension section extending from a first side of said first section, said first lateral extension section being located proximate said third end of said second movable element; and

said second movable element includes a second lateral extension section extending from a second side of said fourth section, said second lateral extension section being located proximate said second end of said first movable element.

9. A MEMS sensor as claimed in claim 8 wherein:

said first movable element including said first lateral extension section forms a first L-shaped movable element; and

said second movable element including said second lateral extension section forms a second L-shaped movable element, said first and second L-shaped movable elements being arranged in a nested configuration without contact between said first and second L-shaped movable elements.

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

each of said first and second movable elements is adapted for motion about a common rotational axis; and

said MEMS sensor further comprises;

a first sensing element disposed on said substrate beneath each of said first and second movable elements; and

a second sensing element disposed on said substrate beneath said each of said first and second movable elements, each of said first and second sensing elements being displaced away from and on opposite sides of said common rotational axis by a substantially equivalent distance, and said first and second sensing elements being adapted to detect movement of said first and second movable elements about said common rotational axis along an axis perpendicular to said planar surface of said substrate.

11. A device comprising:

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

a substrate;

a first movable element positioned in spaced apart relationship above a generally planar surface of said substrate and adapted for rotational motion about a first rotational axis positioned between first and second ends of said first movable element; and

a second movable element positioned in spaced apart relationship above said surface of said substrate and adapted for rotational motion about a second rotational axis positioned between third and fourth ends of said second movable element, said first and second movable elements having a substantially equivalent shape and said second movable element being generally oriented in rotational symmetry relative to said first movable element about a point location on said planar surface of said substrate, said second movable element being located in an orientation that is rotated about said point location approximately one hundred and eighty degrees relative to said first movable element.

12. A device as claimed in claim 11 wherein:

said first movable element is adapted for said rotational motion about said first rotational axis in a first direction in response to acceleration along an axis perpendicular to said planar surface of said substrate; and

said second movable element is adapted for said rotational motion about said second rotational axis in a second direction in response to said acceleration, said second direction being opposite to said first direction.

13. A device as claimed in claim 11 wherein said first and second rotational axes are aligned with one another along a common axis.

14. A device as claimed in claim 11 wherein:

said first movable element includes a first section between said first rotational axis and said first end and a second section between said first rotational axis and said second end, said first rotational axis being offset between said first and second ends such that a first length of said first section between said first rotational axis and said first end is greater than a second length of said second section between said first rotational axis and said second end; and

said second movable element includes a third section between said second rotational axis and said third end and a fourth section between said second rotational axis and said fourth end, said second rotational axis being offset between said third and fourth ends such that a third length of said third section between said second rotational axis and said third end is less than a fourth length of said fourth section between said second rotational axis and said fourth end.

15. A device as claimed in claim 14 wherein:

said first movable element includes a first lateral extension section extending from a first side of said first section, said first lateral extension section being located proximate said third end of said second movable element; and

said second movable element includes a second lateral extension section extending from a second side of said fourth section, said second lateral extension section being located proximate said second end of said first movable element.

16. A device as claimed in claim 11 wherein:

each of said first and second movable elements is adapted for motion about a common rotational axis; and

said MEMS sensor further comprises;

a first sensing element disposed on said substrate beneath each of said first and second movable elements; and

a second sensing element disposed on said substrate beneath said each of said first and second movable elements, each of said first and second sensing elements being displaced away from and on opposite sides of said common rotational axis by a substantially equivalent distance, and said first and second sensing elements being adapted to detect movement of said first and second movable elements about said common rotational axis along an axis perpendicular to said planar surface of said substrate.

17. A microelectromechanical systems (MEMS) sensor comprising:

a substrate;

a first movable element positioned in spaced apart relationship above a generally planar surface of said substrate;

a second movable element positioned in spaced apart relationship above said surface of said substrate, said first and second movable elements having a substantially equivalent shape and said second movable element being generally oriented in rotational symmetry relative to said first movable element about a point location on said planar surface of said substrate, said second movable element being located in an orientation that is rotated about said point location approximately one hundred and eighty degrees relative to said first movable element, each of said first and second movable elements being adapted for motion about a common rotational axis;

a first sensing element disposed on said substrate beneath each of said first and second movable elements; and

a second sensing element disposed on said substrate beneath said each of said first and second movable elements, each of said first and second sensing elements being displaced away from and on opposite sides of said common rotational axis by a substantially equivalent distance, and said first and second sensing elements being adapted to detect movement of said first and second movable elements about said common rotational axis along an axis perpendicular to said planar surface of said substrate.

18. A MEMS sensor as claimed in claim 17 further comprising:

a first suspension anchor formed on said planar surface of said substrate and approximately centered on said common axis;

a first pair of compliant members interconnecting said first movable element with said first suspension anchor, said first pair of compliant members enabling said rotational motion of said first movable element;

a second suspension anchor formed on said planar surface of said substrate and approximately centered on said common axis; and

a second pair of compliant members interconnecting said second movable element with said second suspension anchor, said second pair of compliant members enabling said rotational motion of said second movable element.

19. A MEMS sensor as claimed in claim 17 wherein:

said first movable element includes first and second ends, a first section between said common axis and said first end, and a second section between said common axis and said second end, wherein a first length of said first section between said common axis and said first end is greater than a second length of said second section between said common axis and said second end; and

said second movable element includes third and fourth ends, a third section between said common axis and said third end, and a fourth section between said common axis and said fourth end, wherein a third length of said third section between said common axis and said third end is less than a fourth length of said fourth section between said common axis and said fourth end.

20. A MEMS sensor as claimed in claim 19 wherein:

said first movable element includes a first lateral extension section extending from a first side of said first section, said first lateral extension section being located proximate said third end of said second movable element; and

said second movable element includes a second lateral extension section extending from a second side of said fourth section, said second lateral extension section being located proximate said second end of said first movable element such that said first and second movable elements are arranged in a nested configuration without contact between said first and second movable elements.