Cantilevered Piezoelectric MEMS Microphone With Stress-Compensated Deflection
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Solution Overview
Problem
Conventional piezoelectric MEMS microphones face issues with high residual stress leading to cantilever deflection, sensitivity degradation, and increased manufacturing costs due to complex structures, especially in harsh environments.
Innovation Solution
A piezoelectric microelectromechanical systems microphone design incorporating multiple piezoelectric film layers with differential stress to compensate for intrinsic stress gradients, ensuring the cantilever beam is intentionally bent into the cavity, thereby maintaining performance and reducing sensitivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single piezoelectric film layer is used in the cantilever structure, then the manufacturing process is simple, but the residual stress causes uncontrolled cantilever deflection and sensitivity degradation
Solution Approach 1:
The single piezoelectric film layer is divided into multiple layers with different stress characteristics. The first piezoelectric film layer has compressive stress while the second piezoelectric film layer has tensile stress, allowing the stresses to compensate for each other and achieve controlled cantilever deflection while maintaining manufacturing feasibility through standard deposition processes.
2Manufacturing precision
If multiple piezoelectric film layers with different stresses are used, then cantilever deflection is controlled and sensitivity is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The invention controls the stress parameters of each piezoelectric film layer by adjusting deposition conditions. The first layer is deposited with compressive stress and the second layer with tensile stress, allowing precise control of cantilever deflection through parameter optimization rather than structural complexity. The layers are designed with specific thickness ratios and stress magnitudes to achieve the desired bend into the cavity.
3Stress or pressure
If the cantilever is bent away from the cavity due to residual stress, then the intrinsic stress is reduced, but the gap between cantilevers increases causing sensitivity degradation
Solution Approach 1:
The invention applies preliminary anti-action by intentionally designing the stress distribution in the piezoelectric film layers to counteract the natural tendency of the cantilever to bend away from the cavity. The compressive stress in the first layer and tensile stress in the second layer are engineered to produce a net bending moment that directs the cantilever into the cavity, preventing the harmful gap increase before it can occur.
4Measurement precision
If a complex cantilever structure is used to compensate for stress, then sensitivity can be maintained, but manufacturing costs increase and reliability decreases
Solution Approach 1:
The invention uses a composite structure of multiple piezoelectric film layers with different stress characteristics deposited on a substrate. This composite approach allows stress compensation and cantilever control through material properties rather than geometric complexity. The layered composite structure is simpler to manufacture than complex mechanical compensation structures while achieving the same sensitivity performance.
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 controlled cantilever deflection, enhances sensitivity, and reduces manufacturing complexity, resulting in improved reliability and reduced acoustic resistance, especially in low-frequency ranges.
Implementation Method 1
Piezoelectric MEMS microphones have been used to address the deficiencies of capacitive MEMS microphones. Piezoelectric MEMS microphones offer a constant listening capability while consuming almost no power (e.g., no bias voltage is needed)
Implementation Method 2
Piezoelectric film is commonly made from deposition which suffers from large residual stress after deposition which results in sensitivity degradation and variation
Data Source
AI summary
A piezoelectric microelectromechanical systems (MEMS) microphone is provided comprising a substrate including walls defining a cavity and at least one of the walls defining an anchor region, a piezoelectric film layer supported by the substrate at the anchor region such that the piezoelectric film layer is cantilevered, the piezoelectric film layer being formed to introduce differential stress between a front surface of the piezoelectric film layer oriented away from the cavity and a back surface of the piezoelectric film layer oriented towards the cavity such that the piezoelectric film layer is bent into the cavity, and an electrode disposed over the piezoelectric film layer and adjacent the anchor region. A method of manufacturing such a MEMS microphone is also provided.