MEMS accelerometer with mechanically decoupled proof mass

Patent metadata

Field	Value
Publication number	US-11796560-B2
Application number	US-202117202736-A
Country	US
Kind code	B2
Filing date	Mar 16, 2021
Priority date	Mar 18, 2020
Publication date	Oct 24, 2023
Grant date	Oct 24, 2023

Abstract

The present invention relates to MEMS (microelectromechanical systems) accelerometers, in particular to an accelerometer designed to reduce error in the accelerometer output. The MEMS accelerometer includes a proof mass, which is capable of movement along at least two perpendicular axes and at least one measurement structure. The proof mass is mechanically coupled to the measurement structure along the sense axis of the measurement structure, such that movement of the proof mass along the sense axis causes the moveable portion of the measurement structure to move, and is decoupled from the measurement structures along an axis or axes perpendicular to the sense axis of the measurement structure, such that movement of the proof mass perpendicular to the sense axis of the measurement structure does not cause the moveable portion of the measurement structure to move.

First claim

The invention claimed is:

1. A MEMS accelerometer, the accelerometer comprising:
a substrate, which defines a substrate plane;
at least one in-plane proof mass that is configured to move relative to the substrate along a first axis when the accelerometer undergoes external acceleration in a direction of the first axis and along a second axis when the accelerometer undergoes external acceleration in a direction of the second axis, wherein the first axis and second axis are parallel to the substrate plane and perpendicular to each other;
a first measurement structure for measuring external acceleration upon the in-plane proof mass along a first measurement axis parallel to the first axis by measuring movement of the in-plane proof mass along the first axis, the first measurement structure comprising a first moveable measurement structure, which is moveable relative to the substrate and first fixed measurement structures, which are fixed relative to the substrate, the first moveable measurement structure and the first fixed measurement structures forming two sense comb capacitors which are reflected about the first measurement axis;
a second measurement structure for measuring external acceleration upon the in-plane proof mass along a second measurement axis parallel to the second axis by measuring movement of the in-plane proof mass along the second axis, the second measurement structure comprising a second moveable measurement structure, which is moveable relative to the substrate and a second fixed measurement structure, which is fixed relative to the substrate, the second moveable measurement structure and the second fixed measurement structure forming a sense comb capacitor;
a third measurement structure for measuring external acceleration upon the in-plane proof mass along the second measurement axis parallel to the second axis by measuring movement of the in-plane proof mass along the second axis, the third measurement structure comprising a third moveable measurement structure, which is moveable relative to the substrate and a third fixed measurement structure, which is fixed relative to the substrate, the third moveable measurement structure and the third fixed measurement structure forming a sense comb capacitor;
wherein the sense comb capacitor of the second measurement structure and the sense comb capacitor of the third measurement structure are reflected about the second measurement axis;
wherein the in-plane proof mass extends around the exterior of the first measurement structure, the second measurement structure and the third measurement structure;
wherein the in-plane proof mass is connected to the first moveable measurement structure by at least one spring that mechanically couples the motion of the in-plane proof mass and the first moveable measurement structure along the first axis and mechanically decouples movement of the in-plane proof mass and the first moveable measurement structure along the second axis;
wherein the in-plane proof mass that extends around the exterior of the second measurement structure is connected to the second movable measurement structure by at least one spring that mechanically couples the motion of the in-plane proof mass and the second moveable measurement structure along the second axis and mechanically decouples movement of the in-plane proof mass and the second moveable measurement structure along the first axis;
wherein the in-plane proof mass that extends around the exterior of the third measurement structure is connected to the third moveable measurement structure by at least one spring that mechanically couples the motion of the in-plane proof mass and the third moveable measurement structure along the second axis and mechanically decouples movement of the in-plane proof mass and the third moveable measurement structure along the first axis;
wherein the first moveable measurement structure is an H-shaped structure formed of two longitudinal beams connected by a central transverse beam that extends from the centre of each longitudinal beam, wherein the longitudinal beams are arranged parallel to the first axis and the central transverse beam is arranged parallel to the second axis; and
wherein the central transverse beam of the first moveable measurement structure extends between the second and third measurement structures such that the second and third measurement structures are located on opposite sides of the central transverse beam of the first moveable measurement structure.

2. The MEMS accelerometer of claim 1 , wherein the first moveable measurement structure is connected to at least one first fixed support structure by at least one spring which mechanically couples the motion of the first moveable measurement structure and the at least one first fixed support structure along the second axis and mechanically decouples movement of the first moveable measurement structure and the at least one first fixed support structure along the first axis.

3. The MEMS accelerometer of claim 1 , wherein the first moveable measurement structure comprises first moveable electrodes and the first fixed measurement structures comprise first fixed electrodes, and wherein the first measurement structure is configured to measure the change in capacitance between the first fixed electrodes and first moveable electrodes caused by movement of the in-plane proof mass parallel to the first axis.

4. The MEMS accelerometer of claim 1 , wherein the first fixed measurement structures are located between the longitudinal beams of the first moveable measurement structure.

5. The MEMS accelerometer of claim 4 , wherein the first fixed measurement structures are located such that at least one of the first fixed measurement structures is located on each side of the central beam.

6. The MEMS accelerometer of claim 4 , wherein the first moveable measurement structure is connected to the in-plane proof mass by four springs, wherein each of the four springs is located at one of the ends of the longitudinal beams.

7. The MEMS accelerometer of claim 2 , wherein the first moveable measurement structure is connected to the at least one fixed support structure by four springs, wherein each of the four springs is located at one of the ends of the longitudinal beams.

8. The MEMS accelerometer of claim 1 , wherein the second moveable measurement structure comprises at least one second moveable electrode and the second fixed measurement structure comprises at least one second fixed electrode such that the capacitance of the capacitor formed by the second fixed comb electrode and second moveable comb electrode changes with movement of the in-plane proof mass parallel to the second axis; and
wherein the third moveable measurement structure comprises at least one third moveable electrode and the third fixed measurement structure comprises at least one third fixed electrode such that capacitance of the capacitor formed by the third moveable electrode and third fixed electrode changes with movement of the in-plane proof mass parallel to the second axis.

9. The MEMS accelerometer of claim 1 , wherein the at least one spring comprises a plurality of beam springs, each of which resists compression along its longitudinal axis and permits bending of the spring along a transverse axis parallel to the substrate plane.

10. The MEMS accelerometer of claim 8 , wherein each beam spring also resists bending of the spring along a transverse axis perpendicular to the substrate plane.

11. The MEMS accelerometer of claim 1 , wherein the MEMS accelerometer further comprises one or more stoppers, each fixed to the substrate or a cap wafer, and which restrict movement of a corresponding moveable measurement structur

Assignees

• Murata Manufacturing Co

Inventors

• Liukku Matti
• Blomqvist Anssi
• Vesterinen Hannu

Classifications

• G01P15/125 Primary

  by capacitive pick-up · CPC title

• G01P1/00

  Details of instruments · CPC title

• G01P15/18

  in two or more dimensions · CPC title

• G01P2015/0871

  using stopper structures for limiting the travel of the seismic mass · CPC title

• G01P2015/0822

  for defining out-of-plane movement of the mass · CPC title