Capacitive MEMS Transducer With Separate Sensitive And Transduction Areas
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Solution Overview
Problem
Capacitive MEMS microphones face noise sources such as squeeze film damping and acoustic flow resistance, which degrade their performance and signal-to-noise ratio, and existing solutions either require expensive substrates or complex bonding processes.
Innovation Solution
A capacitive MEMS acoustic transducer design with separate sensitive and transduction areas, where the sensitive membrane is exposed to acoustic waves and the detection membrane operates in a hermetically sealed, low-pressure environment, eliminating viscous damping and thermal noise, and using a double epitaxial layer process for manufacturing to reduce costs and improve mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a movable electrode is used to detect acoustic waves, then acoustic signal detection is enabled, but noise sources such as squeeze film damping and acoustic flow resistance worsen the signal-to-noise ratio
Solution Approach 1:
The patent divides the acoustic transducer into two separate functional areas: a sound collection part with a sensitive membrane exposed to acoustic waves, and a transduction part with a detection membrane operating in a hermetically sealed, low-pressure environment. This segmentation isolates the detection mechanism from noise-generating acoustic flow resistance and squeeze film damping effects while preserving signal detection capability.
Solution Approach 2:
The patent changes the pressure parameter in the transduction chamber to a low-pressure environment, which eliminates viscous damping and thermal noise that plague atmospheric-pressure operation. This parameter change significantly improves the signal-to-noise ratio by removing the harmful noise sources while maintaining acoustic signal detection through the hermetically sealed connection.
2Measurement precision
If expensive substrates like SOI or doped substrates are used to improve performance, then noise reduction is achieved, but manufacturing cost increases and inspection capability is reduced
Solution Approach 1:
The patent replaces expensive specialized substrates (SOI, doped substrates) with a standard silicon substrate that can be manufactured using conventional, cost-effective processes. The hermetically sealed transduction chamber design achieves noise reduction without requiring expensive substrate materials, thereby reducing manufacturing cost while maintaining inspection capability through standard infrared alignment and ultrasound inspection methods.
3Manufacturing precision
If lapping is used to obtain the final thickness of the articulated structure, then thickness control is achieved, but the surface becomes rough with grooves and grinding marks creating mechanical weak points
Solution Approach 1:
The patent replaces the mechanical lapping process with an etching-based thickness control method. This substitution eliminates the mechanical contact that causes surface roughness, grooves, and grinding marks, thereby maintaining manufacturing precision for thickness control while preserving the mechanical strength and surface integrity of the articulated structure.
4Reliability
If metal bonding (e.g., AlGe) is used to assemble components, then hermetic sealing is achieved, but the process becomes complex and costly while losing ultrasound inspectability
Solution Approach 1:
The patent replaces complex metal bonding processes (such as AlGe bonding) with simpler, more cost-effective hermetic sealing methods that maintain sealing reliability. The simplified process restores ultrasound inspectability while achieving the same hermetic sealing function, thereby reducing device complexity and manufacturing cost without sacrificing reliability.
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 solution significantly improves the signal-to-noise ratio by eliminating noise sources and reducing manufacturing costs, while maintaining mechanical stability and flexibility, and allows for a hermetically sealed transduction chamber.
Implementation Method 1
a detection membrane (72) in said transduction chamber (58), said detection membrane being between said substrate region (63) and said fixed structure (62); an articulated structure (67) extending in a first direction between said sensitive membrane (70) and said detection membrane (72); at least one fixed electrode (92, 69C) facing said detection membrane (72) and capacitively coupled thereto
Data Source
AI summary
Capacitive, MEMS-type acoustic transducer, having a sound collection part and a transduction part. A substrate region surrounds a first chamber arranged in the sound collection part and open towards the outside; a fixed structure is coupled to the substrate region; a cap region is coupled to the fixed structure. A sensitive membrane is arranged in the sound collection part, is coupled to the fixed structure and faces the first chamber. A transduction chamber is arranged in the transduction part, hermetically closed with respect to the outside and accommodates a detection membrane. An articulated structure extends between the sensitive membrane and the detection membrane, through the walls of the transduction chamber. A fixed electrode faces and is capacitively coupled to the detection membrane. Conducive electrical connection regions extend above the substrate region, into the transduction chamber.