Z-axis resonant accelerometer with improved-performance detection structure

Patent metadata

Field	Value
Publication number	US-11933810-B2
Application number	US-202217930689-A
Country	US
Kind code	B2
Filing date	Sep 8, 2022
Priority date	Sep 15, 2021
Publication date	Mar 19, 2024
Grant date	Mar 19, 2024

Abstract

The present disclosure is directed to a detection structure for a vertical-axis resonant accelerometer. The detection structure includes an inertial mass suspended above a substrate and having a window provided therewithin and traversing it throughout a thickness thereof. The inertial mass is coupled to a main anchorage, arranged in the window and integral with the substrate, through a first and a second anchoring elastic element of a torsional type. The detection structure also includes at least a first resonant element having longitudinal extension, coupled between the first elastic element and a first constraint element arranged in the window. The first constraint element is suspended above the substrate, to which it is fixedly coupled through a first auxiliary anchoring element which extends below the first resonant element with longitudinal extension and is integrally coupled between the first constraint element and the main anchorage.

First claim

The invention claimed is:

1. A detection structure for a vertical axis resonant accelerometer, the detection structure comprising:
a substrate;
an inertial mass suspended above the substrate and having a plane of main extension defined by first and second horizontal axes, the vertical axis being transverse to the plane;
a window in the inertial mass, the window extending throughout a thickness of the inertial mass;
a main anchorage coupled to the inertial mass and arranged in the window;
first and second anchoring elastic elements coupled to the main anchorage and the substrate, the first and second anchoring elastic elements being of a torsional type with longitudinal extensions on opposite sides of the main anchorage, the first and second anchoring elastic elements being configured to rotate the inertial mass about a rotation axis parallel to the second horizontal axis;
a first resonant element having a longitudinal extension along the first horizontal axis;
a first auxiliary anchoring element having a longitudinal extension along the first horizontal axis, and extending below the first resonant element; and
a first constraint element in the window, suspended above the substrate, and fixedly coupled to the substrate through the first auxiliary anchoring element, the first auxiliary anchoring element being coupled between the first constraint element and the main anchorage, the first resonant element being coupled between the first anchoring elastic element and the first constraint element.

2. The detection structure according to claim 1 , wherein the first and second anchoring elastic elements are configured to allow the inertial mass an inertial movement of rotation around the rotation axis in response to an external acceleration acting along the vertical axis.

3. The detection structure according to claim 2 , wherein the first resonant element is coupled to the first anchoring elastic element such that the inertial movement of rotation of the inertial mass around the rotation axis causes an axial stress, of compression or traction, on the first resonant element, and causes a consequent variation of a corresponding resonance frequency.

4. The detection structure according to claim 1 , wherein
the first anchoring elastic element has a first thickness along the vertical axis,
the first resonant element has a second thickness along the vertical axis,
the second thickness is smaller than the first thickness, and
the first resonant element is coupled to the first anchoring elastic element and to the first constraint element at a respective top portion of the first resonant element, and is arranged at a distance along the vertical axis with respect to the substrate.

5. The detection structure according to claim 4 , wherein
the first auxiliary anchoring element is coupled to the first constraint element and to the main anchorage at a respective bottom portion of the first auxiliary anchoring element, and
the first auxiliary anchoring element is interposed in a floating manner between the first resonant element and the substrate, with a first gap between the first auxiliary anchoring element and the first resonant element and a second gap between the first auxiliary anchoring element and the substrate.

6. The detection structure according to claim 4 , wherein
the first auxiliary anchoring element has a third thickness along the vertical axis, and
the first thickness is equal to a sum of the second and third thicknesses and of a thickness of a first gap between the first auxiliary anchoring element and the first resonant element.

7. The detection structure according to claim 1 , wherein the first resonant element is coupled to the first anchoring elastic element in proximity to the main anchorage.

8. The detection structure according to claim 1 , further comprising:
a pair of driving electrodes arranged on opposite sides of the first resonant element along the second horizontal axis, and configured to drive the first resonant element in a resonance oscillation movement; and
two pairs of detection electrodes arranged on opposite sides of the pair of driving electrodes along the first horizontal axis, facing opposite sides of the first resonant element along the second horizontal axis, and configured to detect, through a variation of a capacitive coupling with the first resonant element, a variation of a corresponding resonance frequency.

9. The detection structure according to claim 8 , wherein
the driving electrodes and the detection electrodes are arranged above the first auxiliary anchoring element, have respective anchoring portions extending up to and integral with the substrate, and are arranged laterally in the plane with respect to the first auxiliary anchoring element, and
the respective anchoring portions are arranged centrally with respect to the longitudinal extension of the first resonant element and in mutual proximity.

10. The detection structure according to claim 1 , further comprising:
a second resonant element, having a longitudinal extension along the first horizontal axis;
a second auxiliary anchoring element having a longitudinal extension along the first horizontal axis, and extending below the second resonant element; and
a second constraint element in the window, suspended above the substrate, and fixedly coupled to the substrate through the second auxiliary anchoring element, the second auxiliary anchoring element being coupled between the second constraint element and the main anchorage, the second resonant element being coupled between the second anchoring elastic element and the second constraint element.

11. The detection structure according to claim 10 , wherein
the first resonant element is arranged in a first half in which the window is divided by the rotation axis, and
the second resonant element is arranged in a second half of the window on an opposite side of the first resonant element with respect to the rotation axis.

12. The detection structure according to claim 10 , wherein the first and second resonant elements and the first and second auxiliary anchoring elements are arranged in a symmetrical manner with respect to a center of the main anchorage.

13. The detection structure according to claim 1 , wherein the inertial mass has an asymmetrical mass distribution with respect to the rotation axis in such a way that the inertial mass is constrained in an eccentric manner to the main anchorage.

14. A resonant accelerometer, comprising:
a substrate; and
a detection structure configured to detect a linear external acceleration component along a vertical axis, the detection structure including:
an inertial mass suspended above the substrate and having a plane of main extension defined by first and second horizontal axes, the vertical axis being transverse to the plane;
a window in the inertial mass, the window extending throughout a thickness of the inertial mass;
a main anchorage coupled to the inertial mass and arranged in the window;
first and second anchoring elastic elements coupled to the main anchorage and the substrate, the first and second anchoring elastic elements being of a torsional type with longitudinal extensions on opposite sides of the main anchorage, the first and second anchoring elastic elements being configured to rotate the inertial mass about a rotation axis parallel to the second horizontal axis;
a first resonant element having a longitudinal extension along the first horizontal axis;
a first auxiliary anchoring element having a longitudinal extension along the first horizontal axis, and extending below the first resonant element; and
a first

Assignees

• St Microelectronics Srl

Inventors

• Zega Valentina
• Gattere Gabriele
• Frangi Attilio Alberto
• Opreni Andrea
• Riani Manuel

Classifications

• G01P15/097 Primary

  by vibratory elements · CPC title

• G01P15/0802

  Details · CPC title

• G01P15/125

  by capacitive pick-up · CPC title

• G01P15/18

  in two or more dimensions · CPC title

• G01P2015/0831

  the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration · CPC title