Capacitive Silicon Microphone Stress Management

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Solution Overview

Problem

Capacitive silicon microphones face challenges with internal stress gradient differences in polycrystalline silicon films, leading to inconsistent performance and increased background noise due to insufficient stress release and limited mechanical vibration range.

Innovation Solution

A capacitive silicon microphone design featuring a substrate with a back cavity, a first dielectric layer, a lower polar plate, a first elastic member, a second dielectric layer, and an upper polar plate with release holes, along with a second elastic member, which helps to uniformly distribute stress and enhance sensitivity by calculating surface stress using specific elastic coefficients and etch-stop layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If polycrystalline silicon films are used for polar plates, then the microphone structure can be fabricated using standard semiconductor processes, but internal stress gradient differences cause inconsistent performance and increased background noise

Engineering Contradiction:

Improvefabrication compatibilityVSAvoidperformance consistency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent segments the originally single polar plate structure into multiple polar plates with different materials. The first polar plate uses polycrystalline silicon for fabrication compatibility, while the second polar plate uses amorphous silicon or silicon nitride to compensate for stress gradients, thereby maintaining manufacturing ease while improving performance consistency

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite material structure by combining different silicon-based materials (polycrystalline silicon, amorphous silicon, silicon nitride) in a multi-layer polar plate configuration. This composite approach allows each material to contribute its beneficial properties while compensating for the weaknesses of individual materials, particularly addressing the internal stress gradient issue

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If polycrystalline silicon film stress is not released sufficiently, then the film structure remains stable, but background noise increases and sensitivity decreases

Engineering Contradiction:

Improvefilm structure stabilityVSAvoidbackground noise

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the material parameters of the polar plates by introducing amorphous silicon or silicon nitride with different stress characteristics. This parameter change allows for stress compensation and release while maintaining overall structural stability, thereby reducing background noise and improving sensitivity without compromising film stability

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If the mechanical vibration range of the vibrating diaphragm is limited, then the device size remains small, but sensitivity of the MEMS microphone decreases

Engineering Contradiction:

Improvedevice sizeVSAvoidacoustic sensitivity

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

The patent uses composite material polar plates where amorphous silicon or silicon nitride layers provide enhanced mechanical properties. This composite structure enables greater vibration range within the same device footprint, improving acoustic sensitivity while maintaining compact dimensions suitable for portable electronics

Inventive Principle:

Principle #40Composite materials

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 design effectively releases structural stress, enhances sensitivity to sound pressure, and reduces overall noise in MEMS microphones by using elastic members to manage stress and improve the flatness of silicon films.

Implementation Method 1

a first elastic member, which has an inner edge and an outer edge, the inner edge thereof being connected with edge of the lower polar plate, and the outer edge thereof being located on the upper surface of the first dielectric layer

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

an upper polar plate as a back electrode of the capacitive silicon microphone, which has a plurality of release holes and is formed above the lower polar plate with an air gap in between

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS9913040B2Capacitive silicon microphone and fabrication method thereof

Publication Date: 2018.03.06 SHANGHAI INTEGRATED CIRCUIT RESEARCH & DEVELOPMENT CENTER CO LTD

AI summary

A capacitive silicon microphone comprises: a first dielectric layer sets on a substrate with a back cavity, a lower polar plate which is located over the back cavity, a first elastic member of which an inner edge is connected with the edge of the lower polar plate and an outer edge is located on the upper surface of the first dielectric layer, a second dielectric layer which is located on the outer edge of the first elastic member and right above the first dielectric layer, an upper polar plate which has a plurality of release holes and is formed above the lower polar plate with an air gap in between, a second elastic member of which an inner edge is connected with the edge of the upper polar plate and an outer edge is located on the upper surface of the second dielectric layer.