MEMS Microphone Cavity Structure for Lower Viscosity Losses
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Solution Overview
Problem
Microphone assemblies using diaphragm-based capacitive MEMS sensors face issues with lateral velocity gradients and viscosity-induced losses due to the dynamic movement of the diaphragm, limiting the acoustic signal-to-noise ratio (SNR) and the achievable dimensions of the microphone assembly.
Innovation Solution
The implementation of cavities in MEMS sensors, configured with pillars, channels, and rings, reduces lateral air movement by increasing compliance and sensitivity, and the use of a piston-like diaphragm or a rigid IC die to minimize lateral motion and enhance SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diaphragm-based capacitive MEMS sensors are used, then the sensor can detect acoustic pressure waves, but lateral velocity gradients and viscosity-induced losses occur due to dynamic diaphragm movement
Solution Approach 1:
The patent inverts the traditional diaphragm configuration by using a rigid backplate instead of a flexible diaphragm as the moving element. The rigid backplate with cavity structure minimizes lateral motion and viscosity-induced losses while still enabling acoustic pressure detection through controlled air compliance, thereby improving SNR by eliminating the harmful lateral velocity gradients associated with flexible diaphragms.
Solution Approach 2:
The patent changes the physical parameters of the sensor structure by introducing a cavity with specific volume and compliance characteristics. By adjusting the cavity volume and the rigidity of the backplate, the air compliance is optimized to maintain acoustic sensitivity while reducing the impact of viscosity-induced losses, thus resolving the contradiction between measurement precision and energy loss.
2Volume of moving object
If traditional diaphragm structures are used, then acoustic detection is achieved, but the microphone assembly size is constrained by SNR requirements
Solution Approach 1:
By inverting the traditional design and using a rigid backplate with cavity instead of a flexible diaphragm, the patent achieves superior SNR performance in a smaller package. The rigid structure with optimized cavity volume provides the necessary acoustic compliance without requiring large dimensions, thus enabling compact microphone assemblies with high SNR.
Solution Approach 2:
The patent replaces the flexible mechanical diaphragm system with a rigid backplate and air-compliance-based system. This substitution eliminates the need for large flexible membranes while maintaining or improving acoustic detection performance, allowing for smaller overall assembly size without compromising SNR.
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 proposed design reduces noise and increases the acoustic signal-to-noise ratio, allowing for smaller and more compact microphone assemblies with improved performance.
Implementation Method 1
The cavity is configured to increase the compliance of air in the back volume
Implementation Method 2
the use of a piston-like diaphragm or a rigid IC die to minimize lateral motion and enhance SNR
Implementation Method 3
Sensors that include microelectromechanical systems (MEMS) dies convert pressure waves (e.g., resulting from sound) into an electrical signal
Data Source
AI summary
Various implementations of MEMS sensors include an IC die having a cavity that forms at least part of the back volume of the sensor. This arrangement helps to address the problems of lateral velocity gradients and viscosity-induced losses. In some of the embodiments, the cavity is specially configured (e.g., with pillars, channels, and/or rings) to reduce the lateral movement of air. Other solutions (used in conjunction with such cavities) include ways to make a diaphragm move more like a piston (e.g., by adding a protrusion that gives it more “up-down” motion and less lateral motion) or to use a piston (e.g., a rigid piece of silicon such as an integrated circuit die) in place of a diaphragm.