Piezoelectric MEMS Microphone Feedback Bias for Acoustic Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional piezoelectric MEMS microphones suffer from sensitivity degradation due to residual stress in the piezoelectric thin film, leading to poor low-frequency roll-off control and variability in acoustic resistance.
Innovation Solution
A piezoelectric MEMS microphone design with multilayer cantilever beams and metal electrode layers, where a direct current bias voltage is applied to counteract deflection caused by residual stress, actively controlling the acoustic resistance through a feedback control circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If piezoelectric thin film is used in MEMS microphones, then power consumption is reduced and reliability is improved, but residual stress causes sensitivity degradation and acoustic resistance variation
Solution Approach 1:
The patent applies DC bias voltage to change the electrical state of the piezoelectric film, which compensates for the mechanical deformation caused by residual stress. This parameter change (applying voltage) counteracts the stress-induced sensitivity degradation and stabilizes acoustic resistance, resolving the contradiction between reliability improvement and manufacturing precision maintenance.
Solution Approach 2:
The patent implements feedback control by monitoring the acoustic resistance and adjusting the DC bias voltage accordingly. This feedback mechanism compensates for variations in residual stress effects, maintaining consistent sensitivity and acoustic resistance performance, thus resolving the contradiction between reliability and manufacturing precision.
2Use of energy by moving object
If piezoelectric thin film is used in MEMS microphones, then power consumption is reduced, but residual stress causes poor low-frequency roll-off control
Solution Approach 1:
The patent uses DC bias voltage to change the operational state of the piezoelectric film, which compensates for stress-induced deflection that affects low-frequency roll-off. This parameter adjustment maintains proper frequency response characteristics while preserving the low power consumption advantage, resolving the contradiction between energy efficiency and operational control.
3Ease of manufacture
If cantilever MEMS structure is used, then piezoelectric sensing is achieved, but gap variation due to cantilever deflection causes sensitivity degradation
Solution Approach 1:
The patent applies DC bias voltage that creates an electrostatic force acting as a counterweight to the residual stress-induced deflection. This counteracting force stabilizes the cantilever position and maintains consistent gap dimensions, preventing sensitivity degradation while preserving the ease of manufacture of the cantilever structure.
Solution Approach 2:
The patent changes the electrical parameter (DC bias voltage) to compensate for mechanical parameter variations (gap size) caused by residual stress. This parameter adjustment maintains stable sensitivity performance while keeping the manufacturing process simple, resolving the contradiction between ease of manufacture and manufacturing precision.
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 improves sensitivity and reduces the negative effects of residual stress, maintaining consistent acoustic resistance and performance across varying environmental conditions.
Implementation Method 1
one or more piezoelectric sensors movably coupled to the substrate and including a multilayer cantilever beam... The cantilever beam has a plurality of piezoelectric layers
Implementation Method 2
one or more direct current voltage sources electrically connected to one or more of the plurality of metal electrode layers. The direct current voltage source(s) are configured to apply a direct current bias voltage between at least two of the plurality of metal electrode layers to deflect the cantilever beam
Data Source
AI summary
A piezoelectric MEMS microphone includes a substrate and a piezoelectric sensor movably coupled to the substrate. The piezoelectric sensor includes a multilayer cantilever beam with multiple piezoelectric layers and multiple metal electrode layers. The beam is attached to the substrate and extends to a distal tip at a free unsupported end. A feedback control circuit is electrically connected to one or more of the metal electrode layers and applies a direct current bias voltage between at least two of the metal electrode layers to actively control an acoustic resistance of the piezoelectric sensor.