Capacitive MEMS Accelerometer Self-Test via Segmented Deflection Electrodes

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing three-axis accelerometers face challenges in implementing self-test functionality due to insufficient electrical force provided by rotor/stator electrodes for deflection tests.

Innovation Solution

The implementation of deflection electrodes on a z-axis acceleration sensor with a frame-shaped rotor, where these electrodes are positioned close to the rotor rotation axis, allowing for enhanced electrical force application through differential capacitive measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If rotor/stator electrodes are used for signal readout, then measurement function is achieved, but electrical force is insufficient for self-test deflection

Engineering Contradiction:

Improveself-test functionalityVSAvoidelectrical force

Core Design Contradiction:

ReliabilityVSForce

Solution Approach 1:

The electrode system is segmented into two distinct functional groups: rotor/stator electrodes dedicated to signal readout and measurement, and separate deflection electrodes dedicated to generating electrical force for self-test. This segmentation allows each electrode type to be optimized for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Multiple electrode pairs are combined on the rotor structure, integrating both measurement electrodes and deflection electrodes into a single rotor assembly. This merging allows the rotor to serve dual purposes: capacitive sensing and electrostatic actuation for deflection testing.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If deflection electrodes are added to enable self-test, then self-test functionality is improved, but device complexity increases

Engineering Contradiction:

Improveself-test functionalityVSAvoidelectrode configuration

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The rotor structure is designed with multi-functionality, serving both as a capacitive sensor element and as an actuated component for deflection testing. By incorporating deflection electrodes directly on the rotor, the same structural element performs multiple functions, reducing the need for separate dedicated test mechanisms.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The accelerometer performs self-testing through autonomous deflection tests where the device uses its own deflection electrodes to generate test signals and measures the response through its measurement electrodes. This self-service capability eliminates the need for external testing equipment and integrated circuitry.

Inventive Principle:

Principle #25Self-service

3Force

If deflection electrodes are positioned close to rotor rotation axis, then electrical force is enhanced, but manufacturing precision requirements increase

Engineering Contradiction:

Improveelectrical forceVSAvoidelectrode positioning

Core Design Contradiction:

ForceVSManufacturing precision

Solution Approach 1:

The deflection electrodes are strategically positioned in specific local regions close to the rotor rotation axis where the electric field gradient is maximized. This localized placement optimizes the electrical force generation efficiency while maintaining manufacturability through standard fabrication tolerances.

Inventive Principle:

Principle #3Local quality

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

This configuration enables effective self-test deflection and rotation of the rotor, improving the accelerometer's ability to perform autonomous deflection tests and ensuring proper functionality and reliability.

Implementation Method 1

differential capacitive measurements

Methodology Applied

Scientific EffectCapacitive force: Capacitance

Implementation Method 2

enhanced electrical force application

Methodology Applied

Scientific EffectElectrical force: Electrostatics

Implementation Method 3

rotor which undergoes rotational motion about a rotational axis defined by the torsion springs in response to accelerating movement

Methodology Applied

Scientific EffectInertial motion: Inertia

Implementation Method 4

rotor is attached to one or more torsion springs and undergoes rotational motion about a rotational axis defined by the torsion springs

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS10809279B2Capacitive microelectromechanical accelerometer

Publication Date: 2020.10.20 MURATA MFG CO LTD

AI summary

A micromechanical accelerometer comprises a sensor for measuring acceleration along a vertical axis perpendicular to a substrate plane, and an accelerometer package with at least one inner package plane adjacent and parallel to the substrate plane. The first sensor comprises a rotor which is mobile in relation to the substrate, a rotor suspender and one or more stators which are immobile in relation to the substrate. The rotor is a seesaw frame where longitudinal rotor bar comprise one or more first deflection electrodes, and second deflection electrodes are fixed to the inner package plane above or below each of the one or more first deflection electrodes, so that they overlap. The accelerometer can perform a self-test by applying a test voltage to at least one first deflection electrode and at least one second deflection electrode. A self-test response signal can be read with a measurement between rotor and stator electrodes.