High sensitivity microelectromechanical sensor with driving motion

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.

The invention claimed is: 
     
       1. An integrated microelectromechanical structure, comprising:
 a driving mass designed to be moved with a rotary motion about an axis of rotation configured to move in a plane with a driving motion; 
 ana central anchorage arranged along saida central axis of rotationthe structure; 
 elastic anchorage elements anchoring elastically coupling said driving mass to said central anchorage; 
 a first opening provided within said driving mass; 
 a first sensing mass arranged inside said first opening; and 
 first and second elastic supporting elements connectingcoupling the first sensing mass to said driving mass such that the first sensing mass performsis configured to perform a detection movement out of the plane and along a rotation axis in the presence of a first external stressresponse to the structure being rotated, said first and second elastic supporting elements and said elastic anchorage elements being so configured so that said first sensing mass is fixed to said driving mass in said rotary driving motion, and is substantially decoupled from said driving mass in said detection movement; 
 wherein at least one of said first and second elastic supporting elements define a defines said rotation axis for said first sensing mass during said detection movement; and 
 wherein said first sensing mass has a first edge proximate said rotation axis and a second edge proximate a portion of said driving mass farthest from said rotation axis, said first sensing mass having a shape so configured to have that a centroid that of said first sensing mass 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 said first edge than said second edge. 
 
     
     
       2. The structure according to  claim 1 , wherein said first 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 first 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 driving mass has a first opening, and said first mass is arranged inside said first opening has a shape substantially matching the shape of said sensing mass of the driving mass. 
     
     
       5. The structure according to  claim 1 , wherein said elastic supporting elements define in said first sensing mass a first portion and a second portion having a different size than the first portion so that the centroid of said first 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 rotation of the structure causes a Coriolis force acting in a direction perpendicular to a said 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 that is aligned with said first sensing mass along a first axis of, said first axis being parallel to said detection lying in said plane and is arranged in a second opening provided within said driving mass axis, said first and second sensing masses being enclosed in overall dimensions located inward 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 that 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 the 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 said plane, said axis of rotation detection movement 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 having side surfaces enclosed by said driving mass; 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; and 
 a read stage configured to switch a mode of operation of said microelectromechanical structure between a gyroscope mode and an accelerometer mode, 
 wherein said first 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  17, wherein said first sensing mass has an arc-shaped outer side. 
     
     
       20. The sensor device according to claim  18  17, wherein said first 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  17, 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. 
 
     
     
       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 first 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 first sensing mass has a radial geometry and, in plan view, the overall shape of a radial annulus sector. 
 
     
     
       23. The sensor device according to claim  18  17, 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. 
 
     
     
       24. A device, comprising:
 a substrate;   a driving mass configured to move in a plane above the substrate;   elastic elements; and   a non-rectangular first sensing mass coupled to the driving mass by the elastic elements, the first sensing mass configured to be driven by the driving mass in the plane and configured to move out of the plane in response to a rotation of the device about a first rotation axis, the first sensing mass having a shape that places a centroid of the first sensing mass a first distance from an outer edge of the sensing mass and a second distance from an inner edge of the first sensing mass, the second distance being greater than the first distance; and   a non-rectangular second sensing mass coupled to the driving mass, the second sensing mass configured to move with the driving mass in the plane and configured to move out of the plane in response to a rotation of the device about a second rotation axis that is perpendicular to the first rotation axis.   
     
     
       25. The device according to claim 24 wherein first sensing mass has a non-rectangular shape in the plane. 
     
     
       26. The device according to claim 24 wherein the driving mass includes a plurality of electrodes proximate the outer edge of the sensing mass. 
     
     
       27. A device, comprising:
 a substrate;   a driving mass configured to move in a plane above the substrate;   elastic elements; and   non-rectangular first, second, third, and fourth sensing masses coupled to the driving mass by the elastic elements, the first, second, third and fourth sensing masses configured to be driven by the driving mass in the plane and configured to move out of the plane in response to a rotation of the device about one or more rotation axes, the first, second, third and fourth sensing masses having shapes that places a centroid of the sensing masses a first distance from an outer edge of the respective sensing mass and a second distance from an inner edge of the respective sensing mass, the second distance being greater than the first distance.   
     
     
       28. A device, comprising:
 an anchor;   a driving assembly having a first set of driving electrodes on a first side of the driving assembly and a second set of driving electrode on a second side of the driving assembly, the anchor being between the first and second set of driving electrodes; and   four non-rectangular sensing masses positioned around the anchor and between the first set of driving electrodes and the second set of driving electrodes, each of the sensing masses configured to be driven by the driving assembly in a plane and configured to move out of the plane in response to a rotation of the device, an inner edge of each sensing mass being smaller than an outer edge of the same sensing mass, the inner edge being proximate to the anchor and the outer edge being proximate to one of the first or second set of driving electrodes.   
     
     
       29. The device according to claim 28 wherein the inner edge of each sensing mass is nonlinear. 
     
     
       30. The device according to claim 29 wherein the inner edge of each sensing mass is concave. 
     
     
       31. The device according to claim 28 wherein the inner edge has a first dimension and the outer edge has a second dimension that is greater than the first dimension. 
     
     
       32. The device according to claim 28 wherein the four non-rectangular sensing masses includes a first set of sensing mass and a second set of sensing mass, the first set of sensing masses being configured to move out of the plane in response to the rotation of the device along a first axis, the second set of sensing masses being configured to move out of the plane in response to the rotation of the device along a second axis. 
     
     
       33. The device according to claim 32 wherein the second axis is perpendicular to the first axis. 
     
     
       34. The device according to claim 28 wherein the anchor is a central anchor and the driving assembly further includes a driving mass elastically coupled to the central anchor.