Compact MEMS Microphone with Isolated Displacement Sensing
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Solution Overview
Problem
Existing microelectromechanical microphones face challenges with acoustic resistance due to counter-electrodes, leading to degraded detection thresholds and reduced bandwidth, and are bulky due to complex packaging and integration of controlled-atmosphere spaces.
Innovation Solution
A microelectromechanical microphone design that integrates transduction means in a controlled atmosphere within the MEMS structure, using two substrates to form a sealed cavity for the rear volume and measurement space, eliminating the need for post-assembly fabrication and simplifying integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a counter-electrode is used for capacitive measurement, then measurement capability is provided, but acoustic resistance increases degrading detection threshold and bandwidth
Solution Approach 1:
The device is divided into two functionally independent parts: a first part containing the sensitive element and back chamber, and a second part containing the measurement means. This segmentation allows the sensitive element to operate without acoustic resistance from counter-electrodes, while measurement is performed separately on a mechanical copy of the displacement.
Solution Approach 2:
A mechanical transmission means acts as an intermediary, transferring the displacement from the sensitive element to the measurement means. This intermediary mechanism allows indirect measurement without requiring the sensitive element to be in direct contact with counter-electrodes, thereby eliminating acoustic resistance.
2Measurement precision
If transduction means are placed in a controlled atmosphere, then measurement performance improves, but device complexity and packaging difficulty increase
Solution Approach 1:
The device separates the controlled atmosphere environment (containing only the sensitive element and back chamber) from the measurement environment (containing measurement means). This segmentation simplifies packaging by allowing each part to be optimized independently, with the controlled atmosphere space being smaller and easier to seal than previous integrated designs.
Solution Approach 2:
The measurement means are extracted from the controlled atmosphere space and placed in a separate second part. This extraction eliminates the need for complex packaging to accommodate both the controlled atmosphere and measurement equipment together, while still maintaining the performance benefits of controlled atmosphere measurement.
3Ease of manufacture
If traditional separate assembly of sensing element and packaging is used, then manufacturing is straightforward, but final microphone size is bulky
Solution Approach 1:
The first part containing the sensitive element and the second part containing the measurement means are merged into a single integrated device through direct assembly. This merging eliminates the need for separate packaging steps and reduces the overall volume compared to traditional designs where these functions were housed in separate bulky assemblies.
Solution Approach 2:
The measurement means are positioned within the housing structure that also contains the back chamber, creating a nested arrangement where the measurement function is embedded within the overall microphone structure. This nesting optimizes space utilization and reduces the external dimensions of the microphone.
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 design achieves high performance with reduced size and simplified manufacturing, minimizing acoustic resistance and maintaining high bandwidth by isolating the measurement means from the sensitive element.
Implementation Method 1
a piston 4 or pressure-sensitive element... and means for mechanically transmitting the displacement of the piston 8 to the measuring means 12
Implementation Method 2
wherein the measured variable is copied mechanically from the sensitive element to the measuring means 12
Implementation Method 3
the hermetic seal isolates the controlled atmosphere space from the back chamber
Data Source
Figure 1~10
Figure 2A~2D
Figure 2E~2I
AI summary
Microelectromechanical microphone comprising: - a microphone unit made from a first substrate, the microphone unit comprising a movable element capable of moving under the effect of a pressure difference and means for measuring the displacement of the movable element, - a hood made from a second substrate, said hood comprising a first recess, - first means for electrically connecting the measuring means to a control unit, the microphone unit and the hood delimiting between them a vacuum space housing the measuring means and a first cavity, from the first recess, partially closed by the movable element, the vacuum space and the first cavity being hermetically sealed from each other, said microphone comprising mechanical transmission means (8) of the displacement of the movable element (4) to the measuring means (10) and a hermetically sealed insulation element (16) through which the transmission means (8) pass.