HIGH SENSITIVITY MICROELECTROMECHANICAL SENSOR WITH ROTARY DRIVING MOTION

• US 20090100930A1
• Filed: 09/11/2008
• Published: 04/23/2009
• Est. Priority Date: 09/11/2007
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Coronato, Luca, Zerbini, Sarah, Ludovico, Alessandro Balzelli
• Granted Patent: US 8,042,394 B2
• Time in Patent Office: Days
• US Class Current: 73/504.120
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/14 by making use of gyroscopes gyroscopes per se G01C19/00
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A driving mass of an integrated microelectromechanical structure is moved with a rotary motion about an axis of rotation, and a sensing mass is connected to the driving mass via elastic supporting elements so as to perform a detection movement in the presence of an external stress. The driving mass is anchored to an anchorage arranged along the axis of rotation by elastic anchorage elements. An opening is provided within the driving mass and the sensing mass is arranged within the opening. The elastic supporting and anchorage elements render the sensing mass fixed to the driving mass in the rotary motion, and substantially decoupled from the driving mass in the detection movement. The detection movement is a rotation about an axis lying in a plane. The sensing mass has, in plan view, a non-rectangular shape; in particular, the sensing mass has a radial geometry and, in plan view, the overall shape of a radial annulus sector.

Claims

1. An integrated microelectromechanical structure, comprising:

a driving mass designed to be moved with a rotary motion about an axis of rotation;

an anchorage arranged along said axis of rotation;

elastic anchorage elements anchoring said driving mass to said anchorage;

a first opening provided within said driving mass;

a first sensing mass arranged inside said first opening; and

elastic supporting elements connecting the first sensing mass to said driving mass such that the first sensing mass performs a detection movement in the presence of a first external stress, said elastic supporting elements and said elastic anchorage elements being so configured that said first sensing mass is fixed to said driving mass in said rotary motion, and is substantially decoupled from said driving mass in said detection movement;

wherein said elastic supporting elements define a rotation axis for said sensing mass during said detection movement; and

wherein said sensing mass has a shape so configured to have a centroid that is positioned at a distance farther away from said rotation axis than a centroid of any rectangular-shaped sensing mass inscribable in said driving mass and rotatable about said rotation axis.

2. The structure according to claim 1, wherein said sensing mass has, in plan view, a non-rectangular shape and an arc-shaped outer side.

3. The structure according to claim 1, wherein said sensing mass has a radial geometry and, in plan view, the overall shape of a radial annulus sector.

4. The structure according to claim 1, wherein said first opening has a shape substantially matching the shape of said sensing mass.

5. The structure according to claim 1, wherein said elastic supporting elements define in said sensing mass a first portion and a second portion having a different size than the first portion so that the centroid of said sensing mass is located in said first portion at a distance from said elastic supporting elements;

said first portion having an arc-shaped concave outer side and radially extending lateral sides, and said second portion having an arc-shaped convex outer side and radially extending lateral sides, aligned along the lateral sides of said first portion.

6. The structure according to claim 1, wherein said driving mass has the shape of an annulus extending substantially in a plane;

said axis of rotation being perpendicular to said plane, and said anchorage being arranged substantially at a center of said driving mass in a central aperture defined by said annulus.

7. The structure according to claim 1, wherein said external stress is a Coriolis force acting in a direction perpendicular to a plane in which said driving mass extends, and said detection movement is a rotation outside said plane.

8. The structure according to claim 1, wherein said driving mass extends substantially in a plane and the structure further comprises:

a second sensing mass, which is aligned with said first sensing mass along a first axis of detection lying in said plane and is arranged in a second opening provided within said driving mass, said first and second sensing masses being enclosed in overall dimensions of said driving mass in said plane; and

detection means associated with each of said first and second sensing masses for detecting said detection movement, said detection movement being a rotational movement about an axis lying in said plane and perpendicular to said first axis of detection.

9. The structure according to claim 8, wherein said detection means are configured to implement, in given operating conditions, a differential detection scheme.

10. The structure according to claim 8, wherein said detection means include a first detection electrode and a second detection electrode, which are set facing a respective one of said first and second sensing masses and each have a trapezoidal shape.

11. The structure according to claim 1, further comprising:

a second sensing mass forming with said first sensing mass a first pair of sensing masses, aligned along a first axis of detection lying in a plane on opposite sides with respect to said anchorage; and

a second pair of sensing masses aligned along a second axis of detection lying in said plane and orthogonal to said first axis of detection, on opposite sides of said anchorage.

12. The structure according to claim 1, wherein said driving mass has in a plane a circular geometry, having a first axis of symmetry and a second axis of symmetry with an empty space at a center of the driving mass;

wherein the center of the driving mass is in a position corresponding to said anchorage, and said elastic anchorage elements extend within said empty space.

13. The structure according to claim 1, further comprising:

a first external anchorage positioned externally of said driving mass and coupled to a first side of the driving mass by a first external elastic anchorage element; and

a second external anchorage positioned externally of said driving mass and coupled to a second side of the driving mass by a second external elastic anchorage element, the second side being opposite to the first side;

wherein said elastic supporting elements and said first, second and third elastic anchorage elements are so configured that said first sensing mass is fixed to said driving mass in said rotary motion, and is decoupled from said driving mass in said detection movement.

14. The structure according to claim 13, wherein said driving mass has an annular shape extending substantially in a plane, said axis of rotation being perpendicular to said plane, and said anchorage being arranged substantially at a center of said driving mass in a central aperture;

and wherein said second side is opposite to said first side with respect to said central aperture.

15. The structure according to claim 14, wherein said first and second external anchorages are diametrically opposite with respect to said central aperture.

16. The structure according to claim 13, wherein said first and second external elastic anchorage elements comprise respective folded springs.

17. A microelectromechanical sensor device, comprising:

a driving mass designed to be moved with a rotary motion about an axis of rotation;

an anchorage arranged along said axis of rotation;

elastic anchorage elements anchoring said driving mass to said anchorage;

a first opening provided within said driving mass;

a first sensing mass arranged inside said first opening; and

elastic supporting elements connecting the first sensing mass to said driving mass such that the first sensing mass performs a detection movement in the presence of a first external stress, said elastic supporting elements and said elastic anchorage elements being so configured that said first sensing mass is fixed to said driving mass in said rotary motion, and is substantially decoupled from said driving mass in said detection movement;

wherein said sensing mass has, in plan view, a non-rectangular shape.

18. The sensor device according to claim 17, further comprising a read stage configured to switch a mode of operation of said microelectromechanical structure between a gyroscope mode and an accelerometer mode.

19. The sensor device according to claim 18, wherein said sensing mass has an arc-shaped outer side.

20. The sensor device according to claim 18, wherein said sensing mass has a radial geometry and, in plan view, the overall shape of a radial annulus sector.

21. The sensor device according to claim 18, wherein said driving mass extends substantially in a plane and the sensor device further comprises:

a second sensing mass, which is aligned with said first sensing mass along a first axis of detection lying in said plane and is arranged in a second opening provided within said driving mass, said first and second sensing masses being enclosed in overall dimensions of said driving mass in said plane; and

detection means associated with each of said first and second sensing masses for detecting said detection movement, said detection movement being a rotational movement about an axis lying in said plane and perpendicular to said first axis of detection.

23. The sensor device according to claim 18, further comprising:

a second sensing mass, which is aligned with said first sensing mass along a first axis of detection lying in said plane and is arranged in a second opening provided within said driving mass, said first and second sensing masses being enclosed in overall dimensions of said driving mass in said plane; and

detection means associated with each of said first and second sensing masses for detecting said detection movement, said detection movement being a rotational movement about an axis lying in said plane and perpendicular to said first axis of detection.

22. A microelectromechanical gyroscope comprising:

an anchorage;

elastic anchorage elements;

a driving mass operable to move in a rotary motion about an axis of rotation, the driving mass being anchored via the elastic anchorage elements to the anchorage, the anchorage being arranged along the axis of rotation and the driving mass substantially extending in a plane perpendicular to the axis of rotation;

a first opening disposed within the driving mass;

elastic supporting elements;

a first sensing mass disposed within the first opening and coupled to the driving mass via the elastic supporting elements to allow for a detection movement in response to an external stress, the elastic supporting elements and the elastic anchorage elements being configured to fix the sensing mass to the driving mass, and wherein the elastic anchorage elements are substantially decoupled from the driving mass during the first detection movement, and the first detection movement is a rotational movement about a rotation axis lying in the plane;

wherein said sensing mass has a radial geometry and, in plan view, the overall shape of a radial annulus sector.