MEMS Vent Structure with Moveable Flaps for Pressure Equalization

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Solution Overview

Problem

MEMS transducers, such as capacitive microphones, are vulnerable to damage from high pressure impulses, which can cause stress concentration and potential delamination or cracking of the membrane due to rapid deformation and pressure differentials during mechanical shocks, such as when a device is dropped.

Innovation Solution

A vent structure with moveable portions and internal edges featuring protrusions or recesses is introduced, allowing for faster pressure equalization by increasing the initial vent opening speed and reducing stress on the membrane, thereby enhancing the resilience of the transducer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a conventional vent structure is used, then the device is simpler to manufacture, but the pressure equalization speed is slower causing stress concentration on the membrane

Engineering Contradiction:

Improvepressure equalization speedVSAvoidvent structure complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The vent structure is segmented into multiple moveable portions (flaps) that can independently deflect in response to pressure differentials. Each flap is separated from the rest of the membrane by channels, allowing distributed pressure relief across multiple locations rather than a single vent point, thereby increasing overall pressure equalization speed.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The vent structure utilizes the third dimension by having moveable flaps that deflect perpendicular to the membrane plane. The channels extend through the membrane thickness, creating a three-dimensional pressure equalization pathway that allows faster response compared to two-dimensional in-plane venting mechanisms.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Speed

If the moveable portion deflects rapidly to equalize pressure, then stress on the membrane is reduced, but the initial vent opening speed is limited by the edge geometry

Engineering Contradiction:

Improveinitial vent opening speedVSAvoidmembrane stress resistance

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

Protrusions and recesses are added to the internal edges of the moveable flaps, creating curved or non-linear edge geometries. These geometric features increase the effective edge length and provide smoother stress distribution during deflection, enabling faster initial vent opening while reducing stress concentration points that would limit reliability.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The internal edges of the moveable portions are given special geometric treatment with protrusions and recesses at specific locations where stress concentration occurs during rapid deflection. This localized modification of edge geometry enhances the overall vent opening speed without requiring changes to the entire structure, while specifically addressing stress resistance at critical points.

Inventive Principle:

Principle #3Local quality

3Speed

If bleed holes are made larger to equalize pressure faster, then pressure differential is reduced, but acoustic performance deteriorates due to excessive air flow

Engineering Contradiction:

Improvepressure equalization speedVSAvoidacoustic performance degradation

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The vent structure transitions from static bleed holes to dynamic moveable flaps that automatically adjust their opening area based on the pressure differential. At normal operating conditions, the flaps remain closed maintaining good acoustic performance. During high pressure events, the flaps deflect open to provide rapid pressure equalization, thus adapting the venting characteristics to the operational conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

Multiple moveable flap structures are distributed across the membrane surface, each acting as a localized pressure relief mechanism. This distributed arrangement provides sufficient total venting area for rapid pressure equalization during shocks while maintaining acoustically favorable characteristics during normal operation, effectively copying the pressure relief function across multiple locations.

Inventive Principle:

Principle #26Copying

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 modified vent structure facilitates quicker pressure equalization and reduces the likelihood of damage from high pressure events by increasing the initial vent opening speed and distributing the pressure differential force more effectively, improving the transducer's resilience and performance.

Implementation Method 1

a moveable portion which is moveable in response to a pressure differential across the membrane

Methodology Applied

Scientific EffectPressure differential: Pressure Gradient

Implementation Method 2

which can cause stress concentration and potential delamination or cracking of the membrane due to rapid deformation and pressure differentials

Methodology Applied

Scientific EffectStress concentration:

Data Source

PatentUS9926189B2MEMS device and process

Publication Date: 2018.03.27 CIRRUS LOGIC INC

AI summary

The application describes MEMS transducers and associated methods of fabrication. The MEMS transducer has a flexible membrane with a vent structure comprising a moveable portion which opens in response to a differential pressure across the membrane to provide a flow path through the membrane. At least one edge of the moveable portion comprises one or more protrusions and/or recesses in the plane of the moveable portion.