Connected Cantilever MEMS Microphone for Bending Mismatch
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Solution Overview
Problem
Cantilevered piezoelectric MEMS microphones face issues due to intrinsic stress from manufacturing, leading to unpredictable bending of beams and increased air path, which decreases sensitivity.
Innovation Solution
The solution involves connecting the cantilevers at a region away from the anchor regions, using a connecting region composed of solid material, piezoelectric film layers, or alternating layers of metal and piezoelectric film, to reduce bending mismatch and enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If cantilevered beams are used in piezoelectric MEMS microphones, then lateral stress in the material is reduced due to freedom of bending, but intrinsic stress from manufacturing causes unpredictable bending of beams leading to mismatch and increased air path, decreasing sensitivity
Solution Approach 1:
Multiple cantilevered beams are connected at their free ends to form a unified structure. This merging ensures that all beams bend together with consistent amplitude, eliminating the mismatch problem caused by individual beam variations while preserving the low lateral stress advantage of cantilevered structures.
Solution Approach 2:
The connecting structure is pre-formed during manufacturing to compensate for intrinsic stress variations. By establishing the connection before final assembly, the design ensures that beams with different intrinsic stresses will still bend together uniformly, predicting the bending behavior in advance rather than dealing with mismatches after fabrication.
2Manufacturing precision
If cantilevers are connected to reduce bending mismatch, then sensitivity and manufacturing precision are improved, but the device complexity increases due to additional connecting structures
Solution Approach 1:
A thin piezoelectric film connects the free ends of the cantilevered beams, forming a continuous flexible structure. This thin film connection provides sufficient mechanical coupling to ensure uniform bending across all beams while adding minimal structural complexity and maintaining the flexibility needed for acoustic response.
Solution Approach 2:
The connecting structure utilizes composite layers of piezoelectric material and metal electrodes. This composite approach provides both mechanical connection functionality and piezoelectric sensing capability within the same structure, reducing overall device complexity by combining multiple functions in a single integrated element.
3Manufacturing precision
If a small connecting region is used, then cantilevers can move more freely improving sensitivity, but the connecting region may be too weak and break
Solution Approach 1:
The connecting region is constructed from composite layers of piezoelectric material and metal, where the metal provides structural strength and the piezoelectric material provides flexibility and sensing functionality. This composite structure achieves both the strength needed to prevent breaking and the flexibility needed for sensitive acoustic response.
Solution Approach 2:
The width of the connecting region is optimized to a specific range (20-50 micrometers) that balances mechanical strength and flexibility. This parameter optimization ensures the connecting region is narrow enough to allow free movement for high sensitivity while being wide enough and structurally sound enough to prevent breaking under normal operating conditions.
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 results in a more predictable sensitivity and reduced acoustic resistance, as the connected cantilevers bend with consistent amplitude, maintaining a constant air gap and improving the microphone's performance.
Implementation Method 1
Piezoelectric MEMS microphones work on the principle of piezoelectric effect, so that they convert acoustic signals to electric signal when sound waves vibrate the piezoelectric sensor. The sound waves bend the piezoelectric film layers of a cantilevered beam or non-cantilevered beam, causing stress and strain, resulting in charges being generated in the piezoelectric film layers.
Data Source
AI summary
A piezoelectric microelectromechanical systems (MEMS) microphone is provided comprising a substrate including walls defining a cavity and at least two of the walls defining a respective anchor region each, a piezoelectric film layer defining at least two beams, each respective beam supported by the substrate at each anchor region, the beams being free along a portion of their respective lengths and also connected at a connecting region away from the respective anchor regions; and an electrode disposed over the piezoelectric film layer. A method of manufacturing such a MEMS microphone is also provided.