MEMS Microphone Piezoelectric Gap Control
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Solution Overview
Problem
Current MEMS microphones have fixed gaps between vibration and fixed membranes, which affect sensitivity and noise, making reproducibility challenging due to residual stress and sacrificial layer thickness.
Innovation Solution
A microphone design where a piezoelectric electrode is applied to the upper portion of a fixed electrode, allowing the central portion of the fixed electrode to bend in one direction as the vibration electrode vibrates, maintaining a uniform gap between the electrodes, achieved through a structure with a piezoelectric electrode, flexible springs, and sacrificial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed gap is used between vibration and fixed membranes, then the structure is simple, but sensitivity and noise performance deteriorate due to residual stress and sacrificial layer thickness variations
Solution Approach 1:
The patent applies the dynamics principle by making the fixed electrode bendable rather than rigid. The fixed electrode is designed to flex in response to stress changes, allowing it to dynamically adjust its position and maintain a uniform gap with the vibration electrode. This flexibility compensates for residual stress and sacrificial layer thickness variations, resolving the contradiction between structural simplicity and gap uniformity.
Solution Approach 2:
The patent applies parameter changes by allowing the fixed electrode's physical state to change from a rigid fixed position to a flexible, stress-responsive position. The electrode's ability to bend and deform based on applied stress enables the gap parameter to self-regulate, maintaining uniformity despite manufacturing variations in residual stress and sacrificial layer thickness.
2Manufacturing precision
If the gap between vibration and fixed electrodes is varied, then sensitivity changes, but noise performance deteriorates
Solution Approach 1:
The patent uses dynamics to create a self-regulating gap mechanism. The flexible fixed electrode automatically adjusts its position based on stress changes, maintaining a consistent gap that optimizes both sensitivity and noise performance. This dynamic adjustment prevents the gap from varying in a way that would degrade noise performance while still allowing sensitivity control.
Solution Approach 2:
The fixed electrode performs self-adjustment based on residual stress and sacrificial layer thickness variations. The structure automatically compensates for manufacturing variations without external intervention, maintaining optimal gap uniformity that simultaneously optimizes sensitivity and minimizes noise.
3Manufacturing precision
If residual stress varies in the membranes, then gap uniformity deteriorates, but manufacturing complexity increases to compensate
Solution Approach 1:
The patent applies dynamics by designing the fixed electrode to be flexible rather than rigid. This flexibility allows the electrode to dynamically respond to residual stress variations and automatically adjust its position to maintain uniform gap spacing. The dynamic response eliminates the need for complex stress compensation structures while achieving gap uniformity.
Solution Approach 2:
The fixed electrode performs self-compensation for residual stress variations through its inherent flexibility. The structure automatically adjusts to stress changes without requiring external compensation mechanisms, thereby achieving gap uniformity without increasing manufacturing complexity.
4Manufacturing precision
If sacrificial layer thickness varies, then gap uniformity deteriorates, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies dynamics by making the fixed electrode flexible, allowing it to respond to variations in sacrificial layer thickness and automatically adjust its position to maintain uniform gap spacing. This dynamic response compensates for deposition control variations without requiring extremely precise manufacturing tolerances.
Solution Approach 2:
The fixed electrode performs self-adjustment for sacrificial layer thickness variations. The flexible structure automatically compensates for manufacturing variations in the sacrificial layer deposition process, maintaining gap uniformity without requiring high manufacturing precision in that specific step.
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 improves sensitivity by maintaining a uniform gap between the vibration and fixed electrodes, enhancing the microphone's performance indices.
Implementation Method 1
a piezoelectric electrode having a plurality of beams disposed in a radial direction outwards from a center of an upper portion of the fixed electrode and uniformly maintaining a space between the vibration electrode and the fixed electrode by bending the fixed electrode in one direction according to an input voltage
Data Source
AI summary
A microphone includes: a vibration electrode disposed in an upper portion of a substrate which has an acoustic hole; a fixed electrode separated from the upper portion of the vibration electrode by a reference distance and having an insulation membrane on each of an upper surface and a lower surface of the fixed electrode; and a piezoelectric electrode having a plurality of beams disposed in a radial direction outwards from a center of an upper portion of the fixed electrode and uniformly maintaining a space between the vibration electrode and the fixed electrode by bending the fixed electrode in one direction according to an input voltage.