Microelectromechanical z-axis detection structure with low thermal drifts
A MEMS detection structure is provided with: a substrate having a top surface, on which a first fixed-electrode arrangement is set; a sensing mass, extending in a plane and suspended above the substrate and above the first fixed-electrode arrangement at a separation distance; and connection elastic elements that support the sensing mass so that it is free to rotate out of the plane about an axis of rotation, modifying the separation distance, as a function of a quantity to be detected along an axis orthogonal to the plane. The MEMS detection structure also includes: a coupling mass, suspended above the substrate and connected to the sensing mass via the connection elastic elements; and an anchoring arrangement, which anchors the coupling mass to the substrate with a first point of constraint, set at a distance from the axis of rotation and in a position corresponding to the first fixed-electrode arrangement.
1. A MEMS structure, comprising:
a substrate having a top surface;
a first fixed-electrode arrangement on the top surface of the substrate;
a mobile mass extending in a plane and suspended above said substrate and said first fixed-electrode arrangement by a separation distance from said first fixed-electrode arrangement;
connection elastic elements configured to support said mobile mass and allow the mobile mass to move out of said plane and modify said separation distance;
a coupling mass suspended above said substrate and connected to said mobile mass via said connection elastic elements; and
an anchoring arrangement configured to couple said coupling mass to said substrate, the anchoring arrangement being coupled to said substrate at a first point of constraint and in a position corresponding to said first fixed-electrode arrangement, wherein said anchoring arrangement includes a first anchoring element rigidly coupled to said substrate at the first point of constraint, and a first supporting elastic element coupling said coupling mass to said first anchoring element.
2. The structure according to claim 1 , wherein said first point of constraint is set within an envelope region of said first fixed-electrode arrangement, with respect to said plane.
3. The structure according to claim 2 , wherein said anchoring arrangement is configured to maintain said coupling mass substantially still, and to generate a displacement of said coupling mass transverse to the plane in response to a displacement of said substrate transverse to the plane at said first point of constraint; and wherein said connection elastic elements are configured to generate a displacement of said mobile mass in response to the displacement of said coupling mass.
4. The structure according to claim 3 , wherein said first anchoring element and first supporting elastic element are configured to define a hinge element at said first point of constraint.
5. The structure according to claim 1 , wherein:
said plane is defined by a first axis and by a second axis, which are mutually orthogonal;
said first point of constraint is set within an envelope region of said first fixed-electrode arrangement, with respect to said plane; and
the position of said first point of constraint substantially corresponds to a median point of said envelope region, along one of said first and second axes.
6. The structure according to claim 1 , wherein said anchoring arrangement includes further points of constraint configured to anchor said coupling mass to said substrate and generate displacements of said coupling mass transverse to the plane in response to displacements of said substrate transverse to the plane.
7. The structure according to claim 1 , wherein said first point of constraint is positioned to reduce a mean deviation between the displacement of said mobile mass and the displacement of said substrate transverse to the plane in a region surrounding said first point of constraint, following upon a deformation of said substrate.
8. The structure according to claim 7 , wherein said first point of constraint is positioned to minimize said mean deviation.
9. The structure according to claim 1 , wherein said first supporting elastic element has, with respect to said connection elastic elements, a greater stiffness.
10. The structure according to claim 1 , wherein said anchoring element is at least in part set within an envelope region of said first fixed-electrode arrangement with respect to said plane.
11. The structure according to claim 1 , wherein:
said plane is defined by a first axis and by a second axis, which are mutually orthogonal; and
said supporting elastic element comprises a first torsional spring having a rectilinear extension along said second axis and being connected to said coupling mass, and a second torsional spring having a rectilinear extension along said first axis and being connected to said anchoring element; said first torsional spring and said second torsional spring having one end in common, in a position that defines said first point of constraint.
12. The structure according to claim 1 , wherein said mobile mass has a through opening, and said coupling mass and said anchoring arrangement are set within said through opening; and wherein said connection elastic elements extend within said through opening and are aligned to define an axis of rotation of said mobile mass.
13. The structure according to claim 1 , further comprising a second fixed-electrode arrangement set on said substrate on an opposite side of said first fixed-electrode arrangement with respect to an axis of rotation of said mobile mass; said mobile mass being set above said substrate in such a way as to form a first detection capacitor and a second detection capacitor respectively with said first fixed-electrode arrangement and said second fixed-electrode arrangement, the detection capacitors having respective capacitance values that vary in a differential way as a function of a quantity to be detected.
14. A microelectromechanical device, comprising:
an interface circuit; and
a MEMS structure electrically coupled to the interface circuit and including:
a substrate having a top surface;
a first fixed-electrode arrangement on the top surface of the substrate;
a mobile mass extending in a plane and suspended above said substrate and said first fixed-electrode arrangement at a separation distance from said first fixed-electrode arrangement;
connection elastic elements configured to support said mobile mass and allow the mobile mass to move out of said plane and modify said separation distance;
a coupling mass suspended above said substrate and connected to said mobile mass via said connection elastic elements; and
an anchoring arrangement configured to couple said coupling mass to said substrate, the anchoring arrangement being coupled to said substrate at a first point of constraint and in a position corresponding to said first fixed-electrode arrangement, wherein said anchoring arrangement includes a first anchoring element rigidly coupled to said substrate at the first point of constraint, and a first supporting elastic element coupling said coupling mass to said first anchoring element.
15. The device according to claim 14 , wherein said MEMS structure and said interface circuit form a z-axis accelerometer configured to detect an acceleration directed along an axis orthogonal to said plane.
16. The device according to claim 14 , wherein said anchoring arrangement is configured to maintain said coupling mass substantially still, and to generate a displacement of said coupling mass transverse to the plane in response to a displacement of said substrate transverse to the plane at said first point of constraint; and wherein said connection elastic elements are configured to generate a displacement of said mobile mass in response to the displacement of said coupling mass.
17. An electronic device, comprising:
a microprocessor unit; and
a microelectromechanical device that includes:
an interface circuit electrically coupled to the microprocessor unit; and
a MEMS structure electrically coupled to the interface circuit and including:
a substrate having a top surface;
a first fixed-electrode arrangement on the top surface of the substrate;
a mobile mass extending in a plane and suspended above said substrate and said first fixed-electrode arrangement at a separation distance from said first fixed-electrode arrangement;
connection elastic elements configured to support said mobile mass and allow the mobile mass to move out of said plane and modify said separation distance;
a coupling mass suspended above said substrate and connected to said mobile mass via said connection elastic elements; and
an anchoring arrangement configured to anchor said coupling mass to said substrate, the anchoring arrangement being connected to said substrate at a first point of constraint and in a position corresponding to said first fixed-electrode arrangement, wherein said anchoring arrangement includes a first anchoring element rigidly coupled to said substrate at the first point of constraint, and a first supporting elastic element coupling said coupling mass to said first anchoring element.
18. The electronic device according to claim 17 , wherein said MEMS structure and said interface circuit form a z-axis accelerometer configured to detect an acceleration directed along an axis orthogonal to said plane.
19. The electronic device according to claim 17 , wherein said anchoring arrangement is configured to maintain said coupling mass substantially still, and to generate a displacement of said coupling mass transverse to the plane in response to a displacement of said substrate transverse to the plane at said first point of constraint; and wherein said connection elastic elements are configured to generate a displacement of said mobile mass in response to the displacement of said coupling mass.
20. The electronic device according to claim 17 , wherein:
said plane is defined by a first axis and by a second axis, which are mutually orthogonal; and
said supporting elastic element comprises a first torsional spring having a rectilinear extension along said second axis and being connected to said coupling mass, and a second torsional spring having a rectilinear extension along said first axis and being connected to said anchoring element; said first torsional spring and second torsional spring having one end in common, in a position that defines said first point of constraint.
21. The electronic device according to claim 17 , wherein said anchoring arrangement includes:
second, third, and fourth anchoring elements rigidly coupled to said substrate at second, third, and fourth points of constraint, respectively; and
second, third, and fourth supporting elastic elements coupling the coupling mass to the second, third, and fourth anchoring elements, respectively.
22. The structure according to claim 1 , wherein said anchoring arrangement includes:
second, third, and fourth anchoring elements rigidly coupled to said substrate at second, third, and fourth points of constraint, respectively; and
second, third, and fourth supporting elastic elements coupling the coupling mass to the second, third, and fourth anchoring elements, respectively.
23. The sensor according to claim 14 , wherein said anchoring arrangement includes:
second, third, and fourth anchoring elements rigidly coupled to said substrate at second, third, and fourth points of constraint, respectively; and
second, third, and fourth supporting elastic elements coupling the coupling mass to the second, third, and fourth anchoring elements, respectively.