Bi-Polar Piezoelectric Border Structure for BAW Spurious Mode Suppression
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Solution Overview
Problem
Current bulk acoustic wave (BAW) resonators face challenges in achieving ideal phase curves due to spurious modes caused by lateral standing waves, which reduce the quality factor and complicate filter design, especially at high frequencies, and the choice of piezoelectric material limits electromechanical coupling optimization across different regions.
Innovation Solution
Incorporating a bi-polar border portion in the piezoelectric layer with sub-portions having opposing polarizations in the border region, which confines lateral acoustic energy without additional mass loading, potentially eliminating the need for border rings and improving spurious mode suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional unipolar piezoelectric layer is used in the border region, then the device structure is simple, but spurious modes are generated due to lateral standing waves
Solution Approach 1:
The piezoelectric layer is divided into distinct regions with different polarization characteristics: a first region with first polarization and a second region with second polarization. This local differentiation allows the border region to have specific piezoelectric properties that suppress lateral standing waves and spurious modes, while the active region maintains its own optimized properties for signal generation.
Solution Approach 2:
The piezoelectric layer is segmented into multiple sub-layers with different polarizations. The first piezoelectric sub-layer has first polarization and the second piezoelectric sub-layer has second polarization, creating a bi-polar structure in the border region that effectively confines acoustic energy and eliminates spurious modes.
2Reliability
If additional mass loading is applied to suppress spurious modes, then spurious mode suppression improves, but the device size and complexity increase
Solution Approach 1:
The invention extracts the spurious mode suppression function from the traditional border ring mass loading structure and integrates it directly into the piezoelectric layer through the bi-polar configuration. The opposing polarizations in the border region inherently suppress lateral standing waves without requiring additional mass loading structures.
Solution Approach 2:
The spurious mode suppression function is merged with the piezoelectric layer itself through the bi-polar border region. Instead of using a separate border ring structure for mass loading, the piezoelectric layer's own polarization structure performs both the piezoelectric function and the spurious mode suppression function simultaneously.
3Ease of manufacture
If uniform piezoelectric material is used across the entire layer, then manufacturing is simplified, but electromechanical coupling cannot be optimized across different regions
Solution Approach 1:
Different regions of the piezoelectric layer are assigned different polarization characteristics to optimize their specific functions. The active region has polarization optimized for signal generation while the border region has bi-polar configuration optimized for acoustic confinement, allowing each region to be optimized for its specific purpose.
Solution Approach 2:
The piezoelectric layer structure is made dynamically adaptable through the bi-polar configuration, allowing the electromechanical coupling to be optimized for different operational requirements in different regions while maintaining a single continuous layer structure that can be manufactured in one process.
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 enhances the quality factor and suppresses spurious modes, allowing for better filter performance and flexibility in electromechanical coupling optimization across different regions of the BAW resonator, enabling more efficient high-frequency filtering.
Implementation Method 1
The piezoelectric material in the active portion has a first polarization. The bi-polar border portion has a first sub-portion and a second sub-portion... The piezoelectric material in the first sub-portion has the first polarization, and the piezoelectric material in the second sub-portion has a second polarization, which is opposite the first polarization.
Data Source
AI summary
An acoustic device includes a foundation structure and a transducer provided over the foundation structure. The foundation structure includes a piezoelectric layer between a top electrode and a bottom electrode. The piezoelectric layer has an active portion within an active region of the transducer, and a bi-polar border portion within a border region of the transducer. The piezoelectric material in the active portion has a first polarization. The bi-polar border portion has a first sub-portion and a second sub-portion, which resides either above or below the first sub-portion. The piezoelectric material in the first sub-portion has the first polarization, and the piezoelectric material in the second sub-portion has a second polarization, which is opposite the first polarization.