MEMS Microphone Vacuum Chamber Electret Layer
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Solution Overview
Problem
Conventional MEMS microphones with large back cavities face limitations in reducing noise and achieving high signal-to-noise ratio due to air viscosity and mechanical sensitivity issues, which restricts their size and reliability.
Innovation Solution
The design incorporates a vacuum chamber between the vibration diaphragm and substrate, utilizing an electret layer to create a high electric field without breakdown, enhancing sensitivity and reducing air viscosity, thereby improving signal-to-noise ratio and allowing for a smaller, more reliable microphone structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large back cavity is designed to ensure air rigidity is much smaller than diaphragm rigidity, then mechanical sensitivity is improved, but the microphone size increases and reliability decreases
Solution Approach 1:
The patent changes the pressure parameter from ambient pressure to vacuum pressure in the back cavity. This parameter change fundamentally alters the air density and viscosity, allowing the system to achieve high mechanical sensitivity without requiring a large cavity volume. The vacuum state eliminates air viscosity effects that would otherwise require large dimensions to overcome.
Solution Approach 2:
The patent replaces the mechanical air cushion system with an electret-based electrostatic field system. Instead of relying on mechanical air pressure differentials in a large cavity, the invention uses electrostatic forces generated by the electret layer to achieve the same sensing function, enabling miniaturization while maintaining sensitivity.
2Stability of the object's composition
If dense perforation holes are designed in the backplate for pressure equalization, then pressure equalization is improved, but air flow resistance increases and signal-to-noise ratio decreases
Solution Approach 1:
The patent replaces the air-filled back cavity with a vacuum environment. This eliminates the harmful effects of air viscosity and air flow resistance entirely, as there is no air to create resistance. Pressure equalization is achieved differently through the vacuum design rather than through air flow through perforation holes.
3Object-affected harmful factors
If a large back cavity is designed, then air viscosity effects are reduced, but device complexity and minimum package size increase
Solution Approach 1:
The patent changes the pressure parameter from ambient to vacuum, which fundamentally eliminates air viscosity effects without requiring large dimensions. This parameter change simplifies the overall device design by removing the need for complex back cavity structures and perforation hole patterns required in ambient pressure designs.
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 approach significantly increases the mechanical sensitivity and signal-to-noise ratio of the MEMS microphone while reducing its overall size and enhancing reliability by minimizing the influence of acoustic resistance and eliminating the need for a large back cavity.
Implementation Method 1
an electret layer providing an electric field between the vibration diaphragm and the lower electrode is provided on the substrate
Implementation Method 2
the high electric field can be provided via the electret layer, and the high electric field can be formed in the vacuum chamber without breakdown
Implementation Method 3
the air viscosity in the vacuum chamber is much lower than the air viscosity at the ambient pressure, thereby reducing an influence of acoustic resistance on a vibration of the vibration diaphragm
Data Source
AI summary
An MEMS microphone is provided, comprising a substrate and a vibration diaphragm supported above the substrate by a spacing portion, the substrate, the spacing portion, and the vibration diaphragm enclosing a vacuum chamber, and a static deflection distance of the vibration diaphragm under an atmospheric pressure being less than a distance between the vibration diaphragm and the substrate, wherein: a lower electrode forming a capacitor structure with the vibration diaphragm is provided on the substrate, and an electret layer providing an electric field between the vibration diaphragm and the lower electrode is provided on the substrate