Rigid Diaphragm MEMS Microphone for Parallel Capacitance Detection

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Solution Overview

Problem

Conventional MEMS capacitive microphones with flexible diaphragms suffer from residual stress-induced warping, low sensitivity, and precision issues due to thermal expansion coefficients mismatch, and the flexible diaphragm's non-parallel deformation makes gap variation estimation difficult, leading to inadequate sensitivity and reliability.

Innovation Solution

The use of a rigid diaphragm integrated with an elastic element ensures parallel movement with respect to the back plate, allowing precise capacitance variation detection through the elastic element's deformation, reducing residual stress and enhancing sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a flexible diaphragm is used in conventional MEMS microphones, then the diaphragm can deform under sound pressure to change capacitance, but the residual stress from thermal expansion mismatch causes warping and buckles that reduce detection precision and sensitivity

Engineering Contradiction:

Improvediaphragm deformation capabilityVSAvoiddetection precision

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the physical state of the diaphragm from flexible to rigid, eliminating residual stress warping while maintaining sound detection capability through controlled elastic element deformation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces an elastic element as an intermediary between the rigid diaphragm and back plate, allowing the elastic element to deform and change capacitance while the rigid diaphragm remains stress-free and parallel

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a flexible diaphragm is used, then capacitance variation can be detected, but the non-parallel deformation makes gap variation estimation difficult and reduces sensitivity

Engineering Contradiction:

Improvecapacitance detection capabilityVSAvoidgap variation estimation precision

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the diaphragm from flexible to rigid, ensuring parallel movement relative to the back plate, which simplifies gap variation estimation to a single dimension while maintaining capacitance detection capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent separates the functions of the diaphragm (rigid, parallel movement) and the capacitance changing element (elastic element, deformable), improving measurement precision by isolating the gap variation to a controlled component

Inventive Principle:

Principle #1Segmentation

3Measurement precision

If higher driving voltage is used to enhance sensitivity, then microphone sensitivity increases, but the flexible diaphragm may collapse and attach to the back plate causing failure

Engineering Contradiction:

Improvemicrophone sensitivityVSAvoiddiaphragm structural integrity

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the diaphragm from flexible to rigid, allowing higher driving voltages to be applied without risk of collapse, thereby enhancing sensitivity while maintaining structural integrity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent maintains a constant curvature or parallel geometry of the rigid diaphragm relative to the back plate, preventing collapse under high voltage while the elastic element provides the necessary capacitance variation

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 design achieves higher precision and sensitivity by correlating capacitance variation solely with the gap between the rigid diaphragm and back plate, reducing the risk of diaphragm collapse and improving microphone performance across various frequencies.

Implementation Method 1

the elasticity of the elastic element makes the rigid diaphragm move parallel to the normal of the back plate

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

variation of sound forces the diaphragm to deform correspondingly in a type of acoustic waves. The deformation of the diaphragm induces capacitance variation

Methodology Applied

Scientific EffectCapacitance variation: Capacitance

Data Source

PatentUS8436435B2MEMS capacitive microphone

Publication Date: 2013.05.07 NATIONAL TSING HUA UNIVERSITY

AI summary

The present invention discloses an MEMS capacitive microphone including a rigid diaphragm arranged on an elastic element. When a sound wave acts on the rigid diaphragm, the rigid diaphragm is moved parallel to a normal of a back plate by elasticity of the elastic element. Thereby the variation of the capacitance is obtained between the rigid diaphragm and the back plate.