Low-Pressure MEMS Microphone Diaphragm Backplate

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Solution Overview

Problem

Traditional MEMS microphones face challenges in maintaining sound quality as they miniaturize, experiencing increased viscous and thermal boundary layer losses due to reduced back volume, and require complex signal processing to correct for non-linear relationships, which increases power consumption and noise.

Innovation Solution

A low-pressure MEMS acoustic system with a diaphragm and backplate configuration, where the backplate has voids and the diaphragm has fingers extending into these voids, operates at reduced air pressure to minimize interactions with air particles, reducing noise and energy losses, and uses a constant voltage with a linear relationship between force and capacitor area for improved signal processing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If traditional MEMS microphones are miniaturized to reduce device size, then the device footprint is reduced, but viscous and thermal boundary layer losses increase, degrading sound quality

Engineering Contradiction:

ImproveMEMS microphone sizeVSAvoidboundary layer losses

Core Design Contradiction:

Volume of moving objectVSLoss of energy

Solution Approach 1:

The patent changes the pressure parameter inside the MEMS microphone back volume from atmospheric pressure to a reduced pressure (vacuum or partial vacuum). This parameter change reduces air density and viscosity, thereby minimizing viscous and thermal boundary layer losses while allowing the microphone to maintain small physical dimensions. The capacitance measurement system operates effectively under these modified pressure conditions to detect acoustic signals.

Inventive Principle:

Principle #35Parameter changes

2Volume of moving object

If traditional MEMS microphones are miniaturized, then device size is reduced, but sound quality decreases

Engineering Contradiction:

ImproveMEMS microphone sizeVSAvoidsound quality

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

By reducing the pressure inside the back volume, the patent minimizes energy losses that degrade sound quality, allowing small MEMS microphones to maintain high audio fidelity. The modified pressure environment preserves acoustic signal integrity despite the reduced device size.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a capacitance-based measurement system instead of traditional acoustic measurement methods. The capacitance between the diaphragm and backplate is measured to detect acoustic signals, providing a more reliable measurement mechanism that works effectively in the reduced pressure environment and maintains sound quality in miniaturized devices.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If complex signal processing is applied to correct non-linear relationships in miniaturized MEMS, then measurement accuracy is improved, but power consumption and noise increase

Engineering Contradiction:

Improveacoustic signal accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent linearizes the relationship between acoustic pressure and measurement signal by changing the pressure parameter inside the back volume. This parameter modification creates a more linear response characteristic, reducing the need for complex non-linear correction algorithms in signal processing, thereby lowering power consumption and noise while maintaining measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The capacitance measurement system provides a more direct and linear measurement mechanism compared to traditional acoustic methods. This substitution reduces the complexity of signal processing required to achieve accurate measurements, resulting in lower power consumption and reduced noise in the final audio signal.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enhances sound quality by reducing noise and energy losses, maintaining sound quality in smaller form factors while minimizing power consumption and signal processing complexity.

Implementation Method 1

The diaphragm is configured to move with respect to the backplate in response to changes in the environmental pressure

Methodology Applied

Scientific EffectAcoustic pressure: Acoustics

Implementation Method 2

generate an electrical signal based on a capacitance between the diaphragm and the backplate

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10315912B2Microelectromechanical system microphone

Publication Date: 2019.06.11 KNOWLES ELECTRONICS LLC

AI summary

A microelectromechanical system (MEMS) includes a diaphragm with a first surface and a second surface. The first surface is exposed to an environmental pressure. The second surface comprises a plurality of fingers extending from the second surface. The MEMS also includes a backplate comprising a plurality of voids. Each of the plurality of fingers extends into a respective one of the plurality of voids. The MEMS further includes an insulator between a portion of the diaphragm and a portion of the backplate. The diaphragm is configured to move with respect to the backplate in response to changes in the environmental pressure.