MEMS Microphone Diaphragm Segmentation for Sensitivity
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Solution Overview
Problem
Existing MEMS microphones with a double-membrane structure face reduced sensitivity due to stray capacitance from conductive polysilicon electrodes, which affects their performance.
Innovation Solution
A MEMS device with a substrate and diaphragm having a first and second membrane, where the first membrane is doped with conductive ions for an electrode region and the second membrane is not, and ventilation slots are strategically placed to reduce parasitic capacitance and enhance compliance, while supports and protrusions are used to maintain structural integrity and increase sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the membrane is made of a conductive polysilicon conductor to act as an electrode, then the microphone can function as an electrode, but the sensitivity of the microphone is adversely affected due to stray capacitance between the two membranes
Solution Approach 1:
The membrane is divided into two distinct regions: a first region (central area) made of conductive polysilicon serving as the electrode, and a second region (peripheral area) made of non-conductive polysilicon that does not form stray capacitance with the counter electrode. This segmentation allows the membrane to simultaneously provide electrode functionality and minimize parasitic capacitance effects.
Solution Approach 2:
Different regions of the membrane are assigned different material properties: the central region requires high electrical conductivity for effective signal generation, while the peripheral region requires electrical insulation to avoid stray capacitance. This local differentiation of material properties resolves the contradiction between electrode function and sensitivity.
2Object-affected harmful factors
If pressure in the accommodating space is reduced, then self-noise associated with the counter electrode is significantly reduced, but the structural integrity and compliance of the membranes may be affected
Solution Approach 1:
Multiple support structures are pre-installed between the first and second membranes to provide mechanical reinforcement before the accommodating space pressure is reduced. These supports prevent the membranes from collapsing or deforming excessively when the pressure differential increases, thereby maintaining structural integrity while allowing the pressure reduction needed to minimize self-noise.
3Measurement precision
If the first region is positioned for maximum signal generation, then sensitivity increases, but the electrode region may be positioned near ventilation slots which could affect performance
Solution Approach 1:
The electrode region is deliberately positioned asymmetrically in the central area of the membrane, away from the circumferentially arranged ventilation slots. This asymmetric positioning maximizes the electrode's proximity to the counter electrode for signal generation while minimizing exposure to the ventilation slots, thereby optimizing sensitivity without significant parasitic capacitance effects.
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 configuration increases the sensitivity of the microphone by positioning the electrode region for maximum signal generation and improves compliance without risking delamination, while reducing parasitic capacitance and internal stress.
Implementation Method 1
the first region is formed by doping conductive ions in the semiconductor material
Data Source
AI summary
Provided is a MEMS device. The MEMS device includes: substrate having back cavity passing therethrough; diaphragm connected to the substrate and covers the back cavity, the diaphragm comprises first and second membranes, and accommodating space is formed between the first and second membranes; supports arranged in the accommodating space, and opposite ends of the support are connected to the first and second membranes; counter electrode arranged in the accommodating space, the first and second membranes each include conductive and second regions, the second region is formed by semiconductor material without doping conductive ions. Through design of the first and second membranes as the first region and the second region, respectively, the second region is formed by semiconductor material without doping conductive ions, and the first region is formed by doping conductive ions in the semiconductor material, so that the compliance performance is improved and not at risk of delamination.