Recessed Proof Mass MEMS Vibration Sensor Shock Robustness

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Solution Overview

Problem

MEMS vibration sensors face challenges in shock robustness due to potential damage from impacts, which can cause electrode fracture or large deflections leading to collisions with back plates, necessitating measures to limit movement and prevent damage during fabrication and assembly.

Innovation Solution

The MEMS vibration sensor die incorporates a recessed proof mass and lateral support members to limit vertical and lateral travel, preventing damage and enhancing shock robustness, with features like protrusions and displacement-limiting support members to restrict movement and maintain sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the proof mass is made larger to improve vibration detection sensitivity, then the sensitivity is improved, but the risk of damage from shock and impact increases

Engineering Contradiction:

Improvevibration detection sensitivityVSAvoidshock robustness

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The proof mass is segmented into multiple portions (first portion, second portion, third portion) arranged in a distributed configuration. This segmentation allows the proof mass to be more resilient to shock impacts while maintaining sufficient total mass for vibration detection sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the proof mass are positioned at different locations within the aperture, creating local variations in mass distribution. This allows the system to optimize both sensitivity (through total mass) and shock robustness (through distributed placement that prevents concentrated stress points).

Inventive Principle:

Principle #3Local quality

2Ease of operation

If the electrode is made more flexible to accommodate large deflections, then the range of motion is improved, but the risk of electrode fracture during shock increases

Engineering Contradiction:

Improverange of motionVSAvoidelectrode fracture resistance

Core Design Contradiction:

Ease of operationVSStrength

Solution Approach 1:

The recessed proof mass configuration acts as a pre-designed mechanical stop that limits the maximum deflection of the electrode before fracture can occur. During normal operation, the electrode can deflect freely, but during shock events, the recessed structure provides beforehand protection by preventing excessive displacement.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The recessed proof mass structure converts the potentially harmful unbounded deflection into a beneficial limited motion system. The recess acts as a mechanical constraint that transforms what would be a fracture-inducing large deflection into a controlled, bounded motion that protects the electrode.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If lateral support members are added to limit proof mass movement, then shock robustness is improved, but device complexity increases

Engineering Contradiction:

Improveshock robustnessVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The lateral support members are merged with the substrate structure, integrating the support function into the existing substrate rather than adding completely separate components. This integration reduces overall device complexity while still providing the necessary lateral constraint functionality.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The substrate serves multiple functions: it provides mechanical support, electrical connections, and now also incorporates lateral support members for shock protection. This multi-functionality reduces the need for separate dedicated shock protection components, thereby reducing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 effectively reduces the likelihood of damage to the sensor components, enhancing shock robustness and maintaining sensitivity, allowing the sensor to function effectively as both a vibration sensor and accelerometer.

Implementation Method 1

The proof mass can move the first electrode or the second electrode from which it is suspended in response to vibration

Methodology Applied

Scientific EffectInertia: Inertia

Data Source

PatentUS11265641B2Microelectromechanical systems vibration sensor

Publication Date: 2022.03.01 KNOWLES ELECTRONICS LLC

AI summary

A MEMS vibration sensor die can include a substrate having a top portion, a mounting surface, and an aperture extending at least partially through the substrate. The die can include a first electrode coupled to the top portion of the substrate and positioned over the aperture. The die can include a second electrode disposed between the substrate and the first electrode. The second electrode can be spaced apart from the first electrode. The die can include a proof mass that can have a first portion coupled to the first electrode or the second electrode. The proof mass can have a second end opposite the first portion. The second end can be recessed within the aperture relative to the mounting surface of the substrate. The proof mass can be suspended freely within the aperture. The proof mass can move the first electrode or the second electrode from which it is suspended in response to vibration.