MEMS Accelerometer Asymmetric Fulcrum Spurious Mode Compensation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Closed-loop microelectromechanical accelerometers face limitations in sensitivity, noise, and bandwidth due to spurious vibration modes triggered by electrostatic feedback forces, which degrade measurement quality and are difficult to distinguish from inertial forces.

Innovation Solution

A triaxial microelectromechanical accelerometer design with symmetrically arranged sensing and feedback electrodes, where the electrostatic feedback forces have a zero resultant, preventing spurious vibration modes and reducing spurious signal components, while maintaining sensitivity and stability across a wide frequency range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electrostatic feedback forces are applied to maintain the movable mass at equilibrium, then stability and linearity are improved, but spurious vibration modes are triggered that degrade measurement quality

Engineering Contradiction:

ImprovestabilityVSAvoidmeasurement quality

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies asymmetry by positioning the fulcrum axis at a non-barycentric location (offset from the center of mass) and arranging feedback electrodes asymmetrically with respect to the movable mass. This asymmetric configuration creates a feedback torque that counteracts spurious vibrations while maintaining stability, resolving the contradiction between reliability and measurement precision.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent transitions from one-dimensional force feedback to two-dimensional torque feedback by introducing a moment arm through the offset fulcrum. This dimensional change allows the feedback system to address rotational spurious modes that cannot be compensated by simple force feedback alone, thereby improving measurement quality while maintaining stability.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Speed

If feedback control is applied to cancel inertial forces, then bandwidth is extended, but spurious signal components are introduced that degrade measurement quality

Engineering Contradiction:

ImprovebandwidthVSAvoidsignal quality

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent replaces direct mechanical force feedback with electrostatic feedback forces generated by capacitively coupled electrodes. This substitution allows for more precise control of the feedback torque and enables broader bandwidth operation without introducing mechanical resonances that would degrade signal quality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The asymmetric electrode arrangement and offset fulcrum create a feedback mechanism that selectively targets spurious vibration modes while preserving the measurement signal across a wide bandwidth, resolving the contradiction between extended bandwidth and signal quality.

Inventive Principle:

Principle #4Asymmetry

3Adaptability or versatility

If out-of-plane sensing structure is used, then triaxial measurement capability is achieved, but spurious vibration modes are more easily triggered by feedback forces

Engineering Contradiction:

Improvetriaxial measurement capabilityVSAvoidsusceptibility to spurious modes

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent segments the feedback function into two independent components: force feedback through feedback electrodes and torque feedback through the offset fulcrum configuration. This segmentation allows independent optimization of each feedback mechanism to address different types of spurious modes in triaxial operation, improving reliability while maintaining versatility.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution enhances sensitivity, stability, and bandwidth while avoiding spurious vibration modes, resulting in improved measurement quality and cost-effectiveness compared to piezoelectric sensors, and facilitates integration into biaxial or triaxial devices.

Implementation Method 1

A control device applies electrostatic feedback forces FFB, FFB' through the feedback electrodes 5 to bring the movable mass 3 back to the equilibrium position and cancel the displacements

Methodology Applied

Scientific EffectElectrostatic attraction: Electrostatics

Implementation Method 2

the displacements are sesed by the sensing electrodes 4

Methodology Applied

Scientific EffectCapacitive sensing: Capacitance

Data Source

PatentEP4123313B1Closed-loop microelectromechanical accelerometer with compensation of spurious vibration modes and process for manufacturing a microelectromechanical accelerometer

Publication Date: 2024.11.13 STMICROELECTRONICS SRL

Figure 1~3
Figure 4
Figure 5

AI summary

A closed-loop microelectromechanical accelerometer includes a substrate (23) of semiconductor material, an out-of-plane sensing mass (13) and feedback electrodes (17a-17d). The out-of-plane sensing mass (13), of semiconductor material, has a first side (13a) facing the supporting body (11) and a second side (13b) opposite to the first side (13a). The out-of-plane sensing mass (13) is also connected to the supporting body (11) to oscillate around a non-barycentric fulcrum axis (F) parallel to the first side (13a) and to the second side (13b) and perpendicular to an out-of-plane sensing axis (Z). The feedback electrodes (17a-17d) are capacitively coupled to the sensing mass (13) and are configured to apply opposite electrostatic forces (FFB1, FFB2) to the sensing mass (13).