Micro-electromechanical structure with improved insensitivity to thermomechanical stresses induced by the package

• US 20060032310A1
• Filed: 08/10/2005
• Published: 02/16/2006
• Est. Priority Date: 08/13/2004
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Murari, Bruno, Merassi, Angelo, Zerbini, Sarah
• Granted Patent: US 7,322,242 B2
• Time in Patent Office: Days
• US Class Current: 73/514.350
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 7/0048 between the MEMS die and the substrate
• CPC Class Codes: G01P 1/006 used for thermal compensation
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/082 for two degrees of freedom of movement of a single mass

Abstract

In a micro-electromechanical structure, a rotor has a centroidal axis and includes a suspended structure which carries mobile electrodes. A stator carries fixed electrodes facing the mobile electrodes. The suspended structure is connected to a rotor-anchoring region via elastic elements. The stator includes at least one stator element, which carries a plurality of fixed electrodes and is fixed to a stator-anchoring region. One of the rotor-anchoring regions and stator-anchoring regions extends along the centroidal axis and at least another of the rotor-anchoring regions and stator-anchoring regions extends in the proximity of the centroidal axis.

Claims

1. A micro-electromechanical structure comprising:

a rotor having a centroidal axis and including a suspended structure which carries mobile electrodes, said suspended structure being connected to a rotor-anchoring region via elastic elements; and

a stator including fixed electrodes facing said mobile electrodes,

said stator further including at least one stator element, carrying a plurality of said fixed electrodes, said stator element being fixed to a stator-anchoring region; and

wherein one of said rotor-anchoring regions and stator-anchoring regions extends along said centroidal axis and at least another of said rotor-anchoring regions and stator-anchoring regions extends near said centroidal axis.

2. The micro-electromechanical structure according to claim 1 wherein said rotor-anchoring region and said stator-anchoring region are arranged at a minimum distance that can be obtained with the manufacturing processes used for forming the micro-electromechanical structure.

3. The micro-electromechanical structure according to claim 2 wherein said minimum distance is smaller than 10 μ

m .

4. The micro-electromechanical structure according claim 1, wherein said rotor-anchoring region and said stator-anchoring region are integral with a body of semiconductor material.

5. The micro-electromechanical structure according to claim 1 wherein said rotor-anchoring region extends along said centroidal axis, and said stator-anchoring region extends near said centroidal axis and of said rotor-anchoring region.

6. The micro-electromechanical structure according to claim 5 wherein said suspended structure comprises a peripheral region having a generally frame-like shape defining a plurality of sides, arranged opposite to one another two by two, and delimiting at least one window;

said mobile electrodes extending from said suspended mass within said window in a direction parallel to sides of said peripheral region; and

wherein said stator is arranged within said window surrounded by said rotor element, and comprises a plurality of stator elements, each of which carries a respective plurality of said fixed electrodes;

each of said mobile electrodes being capacitively coupled to a respective one of said fixed electrodes.

7. The micro-electromechanical structure according to claim 6wherein said structure is a component of an accelerometer;

wherein said stator comprises a pair of said stator elements for each direction of detection of the accelerometer, said stator elements of said pair being arranged symmetrically with respect to said centroidal axis.

8. The micro-electromechanical structure according to claim 6, further comprising a plurality of stoppers, arranged at respective corners of said peripheral region.

9. The micro-electromechanical structure according to claim 6 a uniaxial linear accelerometer.

10. The micro-electromechanical structure according to claim 9 wherein said elastic elements are connected to said rotor-anchoring region through a suspension body having a rectangular shape, said rotor-anchoring region being formed by a central portion of said suspension body, and said elastic elements extending from a respective extreme edge of said suspension body, parallel to one another and to two opposite sides of said peripheral region.

11. The micro-electromechanical structure according to claim 9 wherein said stator comprises two stator elements having a substantially rectangular shape, arranged on opposite sides with respect to said suspension body and having a first side facing said suspension body and a second side which carries said fixed electrodes.

12. The micro-electromechanical structure according to claim 6 wherein said structure is a component of a biaxial linear accelerometer.

13. The micro-electromechanical structure according to claim 12 wherein said suspended mass comprises four supporting portions carrying said mobile electrodes and aligned to the sides of said peripheral region;

and wherein said stator comprises four stator elements, each of which carries a plurality of fixed electrodes;

said stator elements comprising a first arm facing and parallel to one side of said peripheral region, said plurality of fixed electrodes extending from said first arm parallel to said mobile electrodes.

14. The micro-electromechanical structure according to claim 13 wherein each said supporting portion belongs to a U-shaped projection extending inside said peripheral region at a sharp edge of said peripheral region, and delimiting a respective opening;

and wherein said first arm of said stator element is arranged within said opening and is connected to said stator-anchoring region via a second arm arranged so as to form an L with said first arm;

said mobile electrodes carried by one said supporting portion and said fixed electrodes carried by a respective first arm being housed in a respective opening.

15. The micro-electromechanical structure according to claim 13, wherein said elastic elements comprise four springs having a generally T shape;

each of said springs being formed by a stem extending from one side of said rotor-anchoring region towards a facing side of said peripheral region, and by a head connected to said peripheral region and extending transverse to said stem;

said springs extending each within a respective separation trench connected to a central trench surrounding said rotor-anchoring region.

16. The micro-electromechanical structure according to claim 13, wherein each of said stator-anchoring regions is formed by the end of a respective second arm, close to said rotor-anchoring region.

17. The micro-electromechanical structure according to claim 6 wherein said structure is a component of a triaxial linear accelerometer.

18. The micro-electromechanical structure according to claim 17 wherein said peripheral region comprises four peripheral portions, of substantially rectangular shape, each of which carries said plurality of mobile electrodes extending within said window;

and wherein said stator comprises four stator elements, each of which extends approximately from a respective side of said rotor-anchoring region to a facing side of a respective peripheral portion, and which are insulated with respect to said rotor-anchoring region and to said peripheral region;

said stator elements each carrying a plurality of fixed electrodes.

19. The micro-electromechanical structure according to claim 18, further comprising a pair of planar electrodes arranged underneath each of said peripheral portions and forming with said peripheral portions capacitive elements for the detection of a movement component of said peripheral portions parallel to said centroidal axis.

20. The micro-electromechanical structure according to claim 18, wherein said elastic elements comprise a pair of springs having a rectilinear shape extending from each side of said rotor-anchoring region to a respective peripheral portion facing said side;

said springs being configured so as to enable inclination of the respective peripheral portion about an axis intermediate with respect to said springs.

21. A micro-electromechanical device, comprising:

a semiconductor material substrate including a central anchoring region;

a rotor anchor coupled to the substrate at the central anchoring region;

a stator anchor coupled to the substrate at the central anchoring region;

a rotor lying in a spaced-apart relationship with respect to a surface of the substrate and movably coupled to the substrate by a plurality of spring elements extending between the rotor and the rotor anchor, the rotor element being sized and positioned to surround the rotor and stator anchors; and

a stator lying in a spaced-apart relationship with respect to a surface of the substrate and coupled to the substrate by the stator anchor.

22. The device of claim 21 wherein:

the rotor comprises a first plurality of rotor electrodes, each lying parallel to a first axis and extending from the rotor toward the stator from a first side of the rotor, and a second plurality of rotor electrodes, each lying parallel to the first axis and extending from the rotor toward the stator from a second side of the rotor; and

the stator comprises a first plurality of stator electrodes, each lying parallel to the first axis and extending from the stator toward the rotor in a substantially side-by-side relationship with a respective one of the first plurality of rotor electrodes, and a second plurality of stator electrodes, each lying parallel to the first axis and extending from the stator toward the rotor in a substantially side-by-side relationship with a respective one of the second plurality of rotor electrodes.

23. The device of claim 22 wherein the first and second pluralities of rotor electrodes are positioned, relative to the first and second pluralities of stator electrodes, such that translation of the rotor along a second axis, perpendicular to the first axis, will move one of the pluralities of rotor electrodes closer to their respective stator electrodes while moving the other of the pluralities of rotor electrodes farther from their respective stator electrodes.

24. The device of claim 22 wherein the stator comprises first and second stator elements, each coupled to the substrate by a respective stator anchor coupled to the substrate at the central anchoring region and surrounded by the rotor, and to each of which is coupled a respective one of the first or second pluralities of stator electrodes.

25. The device of claim 22 wherein:

the rotor comprises third and fourth pluralities of rotor electrodes, each lying parallel to a second axis, perpendicular to the first axis, and extending from the rotor toward the stator from third and fourth sides of the rotor, respectively; and

the stator comprises third and fourth pluralities of stator electrodes, each lying parallel to the second axis and extending from the stator toward the rotor in a substantially side-by-side relationship with a respective one of the third or fourth plurality of rotor electrodes.

26. The device of claim 21, further comprising a plurality of electrodes positioned between the substrate and the rotor, and wherein the rotor comprises a plurality of rotor elements, each coupled to the substrate by a respective spring element extending between the corresponding rotor element and the rotor anchor or a respective rotor anchor coupled to the substrate at the central anchoring region, and wherein each rotor element is configured to rotate about a respective axis lying substantially parallel to the surface of the substrate,

27. A device comprising:

a semiconductor substrate;

a rotor anchor coupled to the substrate;

a rotor movably coupled to the rotor anchor and having a plurality of rotor electrodes;

a plurality of stator anchors coupled to the substrate substantially equidistant from the rotor anchor;

a stator coupled to the plurality of stator anchors and having a plurality of stator electrodes; and

means for reducing sensitivity of the device to dilatation thereof.

28. The device of claim 27 wherein the reducing means comprises adjacent positioning of the plurality of stator anchors to the rotor anchor.

29. The device of claim 28 wherein each of the plurality of stator anchors is separated from the rotor anchor by less than about 10 μ

m.

30. The device of claim 28 wherein each of the plurality of stator anchors is separated from the rotor anchor by less than about 2 μ

m.