Microelectromechanical device provided with an anti-stiction structure, and corresponding anti-stiction method

• US 8,354,900 B2
• Filed: 09/30/2009
• Issued: 01/15/2013
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Cazzaniga, Gabriele, Coronato, Luca
• Primary Examiner(s): Rojas, Bernard
• Application Number:
  US12/571,080
• Publication Number:
  US 20100078740A1
• Time in Patent Office: 1,203 Days
• Field of Search: 335/78, 200/181
• US Class Current: 335/78
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2201/0242 Gyroscopes
• CPC Class Codes: B81B 3/0013 Structures dimensioned for mechanical prevention of stiction, e.g. spring with increased stiffness
• CPC Class Codes: B81B 3/0018 Structures acting upon the moving or flexible element for transforming energy into mechanical movement or vice versa, i.e. actuators, sensors, generators

Abstract

An embodiment of a microelectromechanical device having a first structural element, a second structural element, which is mobile with respect to the first structural element, and an elastic supporting structure, which extends between the first and second structural elements to enable a relative movement between the first and second structural elements. The microelectromechanical device moreover possesses an anti-stiction structure, which includes at least one flexible element, which is fixed only with respect to the first structural element and, in a condition of rest, is set at a first distance from the second structural element. The anti-stiction structure is designed to generate a repulsive force between the first and second structural elements in the case of relative movement by an amount greater than the first distance.

Claims

1. A microelectromechanical device comprising:

a first structural element;

a second structural element rotatably coupled to said first structural element;

an elastic supporting structure extending between said first and second structural elements and configured to enable a rotational movement of said second structural element with respect to the first structural element; and

an anti-stiction structure including at least one flexible element fixed to only the first structural element and, in a rest condition thereof, arranged at a first distance from the second structural element, said anti-stiction structure being configured to generate a repulsive force between the first and the second structural elements in the case of a relative movement of an amount greater than said first distance, wherein;

the first structural element comprises a mobile mass, and the second structural element comprises a load-bearing structure, or vice versa;

said load-bearing structure comprises a substrate, said movable mass being suspended above a surface of said substrate and being rotatably movable with respect to said surface, said flexible element having an elongated shape with a first end fixed to said movable mass and a second end provided with a protruding portion facing and arranged at said first distance from said surface; and

said mobile mass has a trench facing a side of the mobile mass and said flexible element extends within said trench.

2. The microelectromechanical device according to claim 1, further comprising a stop element, of a substantially rigid type, fixed only to one of said first and second structural elements wherein, in a rest condition of said device, said stop element being arranged at a second distance from another structural element of said first and second structural elements, said second distance being less than said first distance, and being configured to limit the relative movement between said first and second structural elements.

3. The microelectromechanical device according to claim 2, wherein said stop element is distinct from said flexible element and directly faces an abutment portion of said another structural element between said first and second structural elements.

4. The microelectromechanical device according to claim 1, wherein said flexible element has an elongated shape extending transversely to a direction of movement of the mobile mass and is provided with an end forming an abutment surface facing a portion of said substrate.

5. The microelectromechanical device according to claim 1, wherein said protruding portion comprises a bump extending transversely to said surface.

6. The microelectromechanical device according to claim 1, wherein said protruding portion extends as a prolongation of the flexible element, beyond said side of the mobile mass.

7. The microelectromechanical device according to claim 1, wherein the elastic supporting structure includes a torsional spring coupled to and extending between the first and second structural elements.

8. An apparatus, comprising:

a substrate;

a mass suspended above a surface of said substrate and being rotatably movable with respect to said surface, the mass having a trench facing a side of the mobile mass;

a first elastic member having a first end coupled to the substrate and having a second end coupled to the mass, the first elastic member being configured to enable a rotational movement of the mass with respect to the substrate; and

an anti-stiction structure including an anti-stiction element coupled to the mass and, in a rest condition thereof, arranged at a first distance from the substrate, said anti-stiction structure being configured to generate a repulsive force between the mass and substrate in the case of a relative movement of an amount greater than said first distance, said anti-stiction element having an elongated shape extending in the trench of the mass and having a first end coupled to said movable mass.

9. The apparatus of claim 8 wherein the substrate comprises a semiconductor substrate.

10. The apparatus of claim 8,

wherein the first elastic member comprises a spring.

11. The apparatus of claim 8 wherein the anti-stiction element includes a protuberance extending toward the surface of the substrate from a surface of the anti-stiction element that faces the surface of the substrate.

12. The apparatus of claim 8 wherein the trench is T-shaped and has a first portion extending transversely from the side of the mass and a second portion extending transversely from the first portion, the anti-stiction element extends in the first portion, the anti-stiction further includes a torsional spring coupled to the mass, extending in the second portion, and having a central portion coupled to the anti-stiction element.

13. The apparatus of claim 8, further comprising:

a mass stop extending from the surface of the substrate and spaced from the mass.

14. The apparatus of claim 8, wherein the mass comprises a surface that faces the substrate, the apparatus further comprising:

a mass stop extending from the surface of the mass and spaced from the substrate.

15. The apparatus of claim 8 wherein:

the anti-stiction element has a second end protrudes beyond the side of the mass.

16. The apparatus of claim 8 wherein the mass includes a plate that is substantially parallel to a portion of the substrate.

17. The apparatus according to claim 8, wherein the first elastic element includes a torsional spring coupled to and extending between the mass and substrate.