MICROELECTROMECHANICAL THREE-AXIS CAPACITIVE ACCELEROMETER

• US 20120000287A1
• Filed: 06/15/2011
• Published: 01/05/2012
• Est. Priority Date: 06/15/2010
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: De Masi, Biagio, Simoni, Barbara, Frangi, Attilio
• Granted Patent: US 8,863,575 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 15/18 in two or more dimensions

Abstract

A micromechanical structure for a MEMS three-axis capacitive accelerometer is provided with: a substrate; a single inertial mass having a main extension in a plane and arranged suspended above the substrate; and a frame element, elastically coupled to the inertial mass by coupling elastic elements and to anchorages, which are fixed with respect to the substrate by anchorage elastic elements. The coupling elastic elements and the anchorage elastic elements are configured so as to enable a first inertial movement of the inertial mass in response to a first external acceleration acting in a direction lying in the plane and also a second inertial movement of the inertial mass in response to a second external acceleration acting in a direction transverse to the plane.

Claims

1. A micromechanical structure for a MEMS three-axis capacitive accelerometer, comprising:

a substrate;

a single inertial mass which has a main extension in a plane and is arranged suspended above said substrate;

coupling elastic elements;

anchorages;

anchorage elastic elements;

a frame element, elastically coupled to said inertial mass by the coupling elastic elements, and coupled to the anchorages, fixed with respect to said substrate, by the anchorage elastic elements;

wherein said coupling elastic elements and said anchorage elastic elements are configured so as to enable a first inertial movement of said inertial mass in response to a first external acceleration in a first direction lying in said plane, and to enable a second inertial movement of said inertial mass in response to a second external acceleration in a second direction transverse to said plane.

2. The micromechanical structure according to claim 1, further comprising:

first capacitive-coupling elements, coupled to said inertial mass and configured so as to generate at least a first capacitive variation in response to said first inertial movement; and

second capacitive-coupling elements, coupled to said inertial mass and configured so as to generate at least a second capacitive variation in response to said second inertial movement of said inertial mass.

3. The micromechanical structure according to claim 1, wherein said frame element surrounds said inertial mass in said plane;

and wherein said coupling elastic elements are configured in such a way that said inertial mass is rigidly coupled to said frame element in said first inertial movement and mechanically uncoupled from said frame element in said second inertial movement.

4. The micromechanical structure according to claim 1, wherein said first inertial movement is a movement of translation in the first direction in said plane;

and wherein said coupling elastic elements are configured so as to rigidly couple said inertial mass to said frame element in said movement of translation, and said anchorage elastic elements are configured so as to be compliant to said movement of translation, to enable a relative movement of said frame element with respect to said substrate.

5. The micromechanical structure according to claim 4, wherein said second inertial movement is a movement of rotation out of said plane about a rotation axis defined by said coupling elastic elements;

and wherein said coupling elastic elements are configured so as to be compliant to said movement of rotation, to enable a relative movement of said inertial mass with respect to said frame element.

6. The micromechanical structure according to claim 1, wherein said first external acceleration comprises a first horizontal acceleration component and a second horizontal acceleration component directed along a first horizontal detection axis and, respectively, a second horizontal detection axis, which are mutually transverse and lie in said plane;

and wherein said second external acceleration comprises a vertical acceleration component directed along a vertical detection axis, transverse to said plane and to said first detection horizontal axis and said second detection horizontal axis.

7. The micromechanical structure according to claim 1, wherein said first inertial movement is a movement of translation in said plane;

and wherein said first capacitive-coupling elements comprise a plurality of mobile electrodes fixed with respect to said inertial mass and arranged within a bulk of said inertial mass in said plane, each of said mobile electrodes being set facing and parallel to a first fixed electrode and a second fixed electrode, which are fixed with respect to said substrate, so as to form a first pair of horizontal detection capacitors, configured to undergo a differential capacitive variation in response to said movement of translation, a value of which is a function of the value of said first external acceleration.

8. The micromechanical structure according to claim 7, wherein said first external acceleration comprises a first horizontal acceleration component and a second horizontal acceleration component directed along a first horizontal detection axis and, respectively, a second horizontal detection axis, which are mutually transverse and lie in said plane;

and wherein said first capacitive-coupling elements comprise a plurality of first mobile electrodes extending parallel to said first horizontal detection axis, and a plurality of second mobile electrodes extending parallel to said second horizontal detection axis, said first mobile electrodes and second mobile electrodes being arranged respectively in a first window and a second window, which are arranged within the bulk of said inertial mass and traverse to said inertial mass throughout a thickness thereof along a vertical detection axis, transverse to said plane and to said first horizontal detection axis and said second horizontal detection axis.

9. The micromechanical structure according to claim 1, wherein said second inertial movement is a movement of rotation out of said plane about a rotation axis defined by said coupling elastic elements;

and wherein said second capacitive-coupling elements comprise a first electrode and a second electrode, which are fixed with respect to, and arranged on top of, said substrate underneath said inertial mass, on opposite sides with respect to said rotation axis;

said first electrode and said second electrode being capacitively coupled to said inertial mass to form a pair of vertical-detection capacitors, configured to undergo a differential capacitive variation in response to said movement of rotation, a value of which is a function of the value of said second external acceleration.

10. The micromechanical structure according to claim 9, wherein said inertial mass has an asymmetrical distribution of mass in a direction transverse to said rotation axis in such a way as to have a center of gravity offset with respect to said rotation axis.

11. The micromechanical structure according to claim 10, wherein said inertial mass has, on said rotation axis, a first recess and a second recess, which are set on opposite sides with respect to an axis of symmetry of said inertial mass, transverse to said rotation axis;

and wherein said coupling elastic elements comprise a first elastic element and a second elastic element, each extending within a respective one between said first recess and said second recess, starting from said inertial mass towards said frame element.

12. The micromechanical structure according to claim 1, wherein said frame element is arranged so as to surround said inertial mass in said plane;

and wherein said anchorage elastic elements are arranged outside said frame element and said inertial mass with respect to said plane, each of said anchorage elastic elements coupled to said frame element to a respective anchorage, fixed with respect to said substrate.

13. The micromechanical structure according to claim 1, wherein said coupling elastic elements include torsional springs.

14. A MEMS three-axis capacitive accelerometer, comprising:

a micromechanical structure that includes;

a substrate;

a single inertial mass which has a main extension in a plane and is arranged suspended above said substrate;

coupling elastic elements;

anchorages;

anchorage elastic elements;

a frame element, elastically coupled to said inertial mass by the coupling elastic elements, and coupled to the anchorages, fixed with respect to said substrate, by the anchorage elastic elements;

wherein said coupling elastic elements and said anchorage elastic elements are configured so as to enable a first inertial movement of said inertial mass in response to a first external acceleration in a first direction lying in said plane, and to enable a second inertial movement of said inertial mass in response to a second external acceleration in a second direction transverse to said plane; and

an electronic reading circuit, electrically coupled to said micromechanical structure.

15. The MEMS three-axis capacitive accelerometer of claim 14 wherein the micromechanical structure includes first capacitive-coupling elements coupled to said inertial mass and configured to generate a first capacitive variation in response to said first inertial movement and second capacitive-coupling elements coupled to said inertial mass and configured to generate a second capacitive variation in response to said second inertial movement of said inertial mass.

16. The MEMS three-axis capacitive accelerometer of claim 14 wherein said first inertial movement is a movement of translation in the first direction in said plane;

and wherein said coupling elastic elements are configured to rigidly couple said inertial mass to said frame element in said movement of translation, and said anchorage elastic elements are configured so as to be compliant to said movement of translation, to enable a relative movement of said frame element with respect to said substrate.

17. The MEMS three-axis capacitive accelerometer of claim 16, wherein said second inertial movement is a movement of rotation out of said plane about a rotation axis defined by said coupling elastic elements;

and wherein said coupling elastic elements are configured so as to be compliant to said movement of rotation, to enable a relative movement of said inertial mass with respect to said frame element.

18. An electronic device, comprising:

a MEMS three-axis capacitive accelerometer that includes;

a micromechanical structure that includes;

a substrate;

a single inertial mass which has a main extension in a plane and is arranged suspended above said substrate;

coupling elastic elements;

anchorages;

anchorage elastic elements;

a frame element, elastically coupled to said inertial mass by the coupling elastic elements, and coupled to the anchorages, fixed with respect to said substrate, by the anchorage elastic elements;

wherein said coupling elastic elements and said anchorage elastic elements are configured so as to enable a first inertial movement of said inertial mass in response to a first external acceleration in a first direction lying in said plane, and to enable a second inertial movement of said inertial mass in response to a second external acceleration in a second direction transverse to said plane;

an electronic reading circuit, electrically coupled to said micromechanical structure; and

a digital processing unit coupled to said MEMS three-axis capacitive accelerometer.

19. The electronic device of claim 18 wherein the micromechanical structure includes first capacitive-coupling elements coupled to said inertial mass and configured to generate a first capacitive variation in response to said first inertial movement and second capacitive-coupling elements coupled to said inertial mass and configured to generate a second capacitive variation in response to said second inertial movement of said inertial mass.

20. The electronic device of claim 18 wherein said first inertial movement is a movement of translation in the first direction belonging to said plane;

and wherein said coupling elastic elements are configured to rigidly couple said inertial mass to said frame element in said movement of translation, and said anchorage elastic elements are configured so as to be compliant to said movement of translation, to enable a relative movement of said frame element with respect to said substrate.

21. The electronic device of claim 20, wherein said second inertial movement is a movement of rotation out of said plane about a rotation axis defined by said coupling elastic elements;

and wherein said coupling elastic elements are configured so as to be compliant to said movement of rotation, to enable a relative movement of said inertial mass with respect to said frame element.