MEMS Diaphragm Spring Suspension for Stiction Prevention

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Solution Overview

Problem

MEMS free plate acoustic transducers face issues with diaphragm sagging and contamination due to stiction, leading to erratic performance, as the diaphragm is not constrained when unpowered and accumulates contaminants in small gaps.

Innovation Solution

Incorporating spring members that suspend the diaphragm between the transducer substrate and back plate when unpowered, preventing sagging and minimizing contamination, while contributing minimally to the diaphragm's compliance when powered.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the diaphragm is simply supported at one point by an electrical lead, then the diaphragm is free to rotate at the posts and can be lightly constrained, but the diaphragm may droop or bend under residual stress or gravity and come in contact with other structural features, leading to stiction and erratic performance

Engineering Contradiction:

Improvediaphragm freedom of movementVSAvoidtransducer performance consistency

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

Spring members are introduced as intermediary elements between the diaphragm and the transducer substrate. These springs provide a compliant support mechanism that prevents the diaphragm from sagging or bending under residual stress or gravity, while still allowing the diaphragm to move freely during operation. The spring members act as a mediator that maintains the diaphragm in a retracted position away from the substrate, preventing stiction and ensuring consistent transducer performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the diaphragm is allowed to move freely when unpowered, then the diaphragm can respond to acoustic signals, but contaminants including condensed vapors, dust, oil, and particles may accumulate in regions around contact points, leading to stiction

Engineering Contradiction:

Improvediaphragm acoustic responseVSAvoidcontaminant accumulation

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The spring members are configured to maintain the diaphragm in a retracted position away from the transducer substrate even before any acoustic signal is applied. This preliminary positioning action prevents contaminants from accumulating in the gap between the diaphragm and substrate by ensuring that the diaphragm does not come into contact with the substrate or other structural features when unpowered, thereby preventing stiction while still allowing full acoustic response capability.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If spring members are added to suspend the diaphragm and prevent sagging, then the diaphragm position is maintained and contamination is minimized, but the device complexity increases

Engineering Contradiction:

Improvediaphragm position stabilityVSAvoidtransducer structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The spring members are implemented as flexible, thin elastic elements that are integrated into the transducer structure. These flexible spring members provide the necessary suspension and positioning functionality while occupying minimal space and adding minimal structural complexity. The spring members can be fabricated using standard MEMS processes, allowing them to be integrated seamlessly into the existing transducer architecture without significantly increasing device complexity.

Inventive Principle:

Principle #30Flexible shells and thin films

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 spring members effectively prevent diaphragm sagging and contamination, ensuring consistent performance by maintaining the diaphragm's position and reducing stiction, thus enhancing the reliability of the MEMS acoustic transducer.

Implementation Method 1

The diaphragm includes a lead structured to suspend the diaphragm over the transducer substrate. The diaphragm also includes a plurality of spring members structured to separate the diaphragm from the transducer substrate and the back plate in the absence of the bias voltage.

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

The diaphragm is structured to move toward the back plate and contact at least one of the protrusions in the presence of a bias voltage.

Methodology Applied

Scientific EffectElectrostatic force: Electrostatics

Implementation Method 3

This may be enhanced by the process of capillary condensation in which condensation happens preferentially in very small gaps.

Methodology Applied

Scientific EffectCapillary condensation: Capillary Condensation

Data Source

PatentUS11197104B2MEMS transducer including free plate diaphragm with spring members

Publication Date: 2021.12.07 KNOWLES ELECTRONICS LLC

AI summary

A microelectromechanical system (MEMS) transducer includes a transducer substrate including an opening; a back plate including a plurality of protrusions oriented substantially perpendicular to the back plate; and a diaphragm between the transducer substrate and the back plate. The diaphragm includes a lead and a plurality of spring members. The lead is structured to suspend the diaphragm over the transducer substrate. The spring members are structured to separate the diaphragm from the transducer substrate and the back plate in the absence of a bias voltage.