MEMS Microphone Double Fixed Electrode Design
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Solution Overview
Problem
MEMS microphones based on the capacitance principle suffer from low sensitivity and are sensitive to high sound pressures, with complex and costly manufacturing methods that hinder mass production and reproducibility.
Innovation Solution
A MEMS microphone design featuring a substrate with patterned functional layers, including a bottom and top fixed electrode and a membrane with distinct regions for anchoring and oscillation, allowing for differential capacitance read-out and improved signal-to-noise ratio through symmetrical membrane fixation and DC bias voltage application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a symmetrical double fixed electrode membrane microphone is designed to improve sensitivity and signal-to-noise ratio, then sensitivity is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The membrane is divided into functionally distinct regions: an outer edge anchor region for mechanical fixation and an inner freely oscillating region for sound detection. This segmentation allows the membrane to be vertically fixed at the edges while maintaining freedom of movement in the center, enabling symmetrical differential operation without requiring complex asymmetric structures
Solution Approach 2:
The membrane serves multiple functions simultaneously: it acts as a mechanical anchor point at its edges for vertical fixation, provides electrical connection pathways through its structure, and functions as the active sound-sensitive oscillating element in its central region. This multi-functionality simplifies the overall device design by combining several components into a single integrated structure
2Ease of manufacture
If conventional MEMS microphone design is used, then manufacturing is simple and cost-effective, but sensitivity is low
Solution Approach 1:
By dividing the membrane into anchor and oscillating regions, the invention enables symmetrical differential operation that doubles the output signal, thereby improving sensitivity while maintaining compatibility with standard MEMS manufacturing processes
Solution Approach 2:
The symmetrical arrangement of the membrane between two fixed electrodes creates equipotential conditions that enable differential readout. This symmetrical configuration ensures that both electrodes experience identical mechanical stress and electrical conditions, allowing for enhanced signal output through differential amplification while using conventional manufacturing techniques
3Stability of the object's composition
If membrane is not vertically fixed, then oscillation freedom is maintained, but symmetrical arrangement cannot be stabilized
Solution Approach 1:
The membrane is segmented into an outer edge anchor region that provides vertical fixation and an inner region that maintains oscillation freedom. This spatial segmentation resolves the contradiction by providing stability where needed (at the edges) while preserving movement freedom where required (in the center)
Solution Approach 2:
Different regions of the membrane have different mechanical properties: the outer edge region has fixed vertical position for stability, while the inner region has free vertical movement for sound detection. This local differentiation of mechanical constraints allows the system to simultaneously achieve symmetrical stability and oscillation freedom
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 enhances sensitivity by up to 3 dB, enabling either smaller chip area with the same sensitivity or higher sensitivity with the same chip area, while also improving signal quality and making the microphone suitable for high-end applications.
Implementation Method 1
MEMS microphones usually function according to the capacitance principle, in which the capacitance between fixed electrode and membrane is read out, said capacitance changing with the deflection of the membrane
Implementation Method 2
the membrane is subject to sound pressures which lead to a deflection of the membrane from its rest position
Data Source
AI summary
An improved method for manufacturing an MEMS microphone with a double fixed electrode is specified which results in a microphone which likewise has improved properties.