Microelectromechanical resonator with improved electrical features

Patent metadata

Field	Value
Publication number	US-2018339898-A1
Application number	US-201815978958-A
Country	US
Kind code	A1
Filing date	May 14, 2018
Priority date	May 25, 2017
Publication date	Nov 29, 2018
Grant date	—

Abstract

A MEMS resonator is equipped with a substrate, a moving structure suspended above the substrate in a horizontal plane formed by first and second axes, having first and second arms, parallel to one another and extending along the second axis, coupled at their respective ends by first and second transverse joining elements, forming an internal window. A first electrode structure is positioned outside the window and capacitively coupled to the moving structure. A second electrode structure is positioned inside the window. One of the first and second electrode structures causes an oscillatory movement of the flexing arms in opposite directions along the first horizontal axis at a resonance frequency, and the other electrode structure has a function of detecting the oscillation. A suspension structure has a suspension arm in the window. An attachment arrangement is coupled to the suspension element centrally in the window, near the second electrode structure.

First claim

1 . A MEMS resonator, comprising:
a substrate; a moving structure suspended above said substrate and having its main extension in a horizontal plane formed by a first and a second horizontal axis which are orthogonal to one another, the structure comprising a first and a second flexing arm, parallel to one another and extending along the second horizontal axis, said first and second flexing arms being coupled at their respective ends by a first and a second transverse joining element, the first and second transverse joining elements having an extension along the first horizontal axis to forming an internal window with the first and second flexing arms; a first electrode structure positioned outside said window and capacitively coupled in said horizontal plane to the moving structure; a second electrode structure positioned inside said window and capacitively coupled in said horizontal plane to the moving structure, one of said first and second electrode structures having the function of causing an oscillatory movement of said first and second flexing arm in opposite directions along said first horizontal axis, at a corresponding resonance frequency, and the other of said first and second electrode structures having the function of detecting said oscillation; and a suspension structure configured to suspend said moving structure above the substrate, said suspension structure including a suspension arm extending inside said window between said first and second transverse joining elements, and an attachment arrangement coupled to said suspension arm and to said substrate, the attachment arrangement positioned centrally in said window near said second electrode structure.

2 . The MEMS resonator according to claim 1 , wherein said suspension structure is configured in response to forces associated with the oscillatory movement of said moving structure to provide substantially zero energy dissipation towards said substrate at said attachment arrangement.

3 . The MEMS resonator according to claim 2 , wherein said suspension structure has a symmetrical shape with respect to a first and a second axis of symmetry, running, respectively, parallel to the first and to the second horizontal axis, and with respect to a geometric center of said microelectromechanical resonator in said horizontal plane.

4 . The MEMS resonator according to claim 1 , wherein said attachment arrangement comprises a central attachment coupled integrally to a central portion of said suspension arm and to said substrate.

5 . The MEMS resonator according to claim 3 , wherein said attachment arrangement comprises a first and a second attachment, and wherein said suspension structure further comprises connecting elements, positioned inside said window for connecting said suspension arm to said first and second attachments, said first and second attachments being positioned laterally with respect to said suspension arm in alignment along said first horizontal axis.

6 . The MEMS resonator according to claim 3 , wherein said suspension structure comprises a first and a second T-shaped connecting element, each T-shaped connecting element extending from a central portion of said suspension arm, and a first and a second pair of attachments positioned laterally with respect to said suspension arm, said first and second T-shaped connecting elements having their respective ends coupled to the attachments of the first and second pair of attachments, respectively.

7 . The MEMS resonator according to claim 6 , wherein said first and second T-shaped connecting connection elements form a respective double lever coupling between said suspension arm and the respective first and second pair of attachments.

8 . The MEMS resonator according to claim 1 , wherein said attachment arrangement is positioned at a minimum separation distance from respective attachment elements of inner electrodes of said second electrode structure and from respective attachment elements of outer electrodes of said first electrode structure, near a geometric center of said window and of said microelectromechanical resonator in said horizontal plane.

9 . The MEMS resonator as claimed in claim 1 , further comprising a first and a second slide element coupled, respectively, to the first and the second flexing arm of the moving structure at a central portion of the first and the second flexing arm, the first and second slide elements being substantially non-deformable in the presence of the corresponding oscillatory movement of said first and second flexing arm.

10 . The MEMS resonator according to claim 1 , wherein one of said first electrode structure and said second electrode structure comprises a plurality of fixed electrode portions interdigitated with respective moving electrode portions carried by the first and second flexing arm of the moving structure, wherein the fixed electrode portions and the moving electrode portions are positioned parallel to one another along said first horizontal axis.

11 . The MEMS resonator according to claim 10 , wherein there is a separation distance along the first horizontal axis between each fixed electrode portion and each moving electrode portion and a facing portion of one of the respective first and second flexing arm of the moving structure, or of one of the respective first and second electrode structures, is substantially equal to a separation distance along the second horizontal axis between the fixed electrode portion and moving electrode portion interdigitated with one another.

12 . The MEMS resonator according to claim 1 , wherein said moving structure is configured to oscillate in said horizontal plane substantially parallel to an upper surface of said substrate, and wherein said first and second flexing arms are configured to be actuated in an antiphase movement of by one of said first and second electrode structure.

13 . The MEMS resonator according to claim 1 , wherein said resonance frequency is associated with a frequency for a real time clock.

14 . The MEMS resonator of claim 13 further comprising a processing stage for generating a timing signal for a real time clock as a function of said oscillating frequency.

15 . An electronic device, comprising:
a timing circuit is configured to generate a clock signal based on oscillatory movement of first and second flexing arms of a MEMS resonator, the MEMS resonator including:
a substrate;
a moving structure suspended above said substrate and having its main extension in a horizontal plane formed by a first and a second horizontal axis which are orthogonal to one another, the structure comprising a first and a second flexing arm, parallel to one another and extending along the second horizontal axis, said first and second flexing arms being coupled at their respective ends by a first and a second transverse joining element, the first and second transverse joining elements having an extension along the first horizontal axis to forming an internal window with the first and second flexing arms;
a first electrode structure positioned outside said window and capacitively coupled in said horizontal plane to the moving structure;
a second electrode structure positioned inside said window and capacitively coupled in said horizontal plane to the moving structure, one of said first and second electrode structures having the function of causing an oscillatory movement of said first and second flexing arm in opposite directions along said first horizontal axis, at a corresponding resonance frequency, and the other of said first and second electrode structures having the function of detecting said oscillation; and

Assignees

• St Microelectronics Srl

Inventors

• Gattere Gabriele
• Tocchio Alessandro
• Valzasina Carlo

Classifications

• H03H9/02338

  Suspension means · CPC title

• H03H2009/0244

  Anchor loss · CPC title

• H03H9/2431 Primary

  Ring resonators · CPC title

• H03H2009/0248

  Strain · CPC title

• H03H9/2405 Primary

  of microelectro-mechanical resonators · CPC title