BAW Resonator Border Polarization to Eliminate BO Spurious Modes
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Solution Overview
Problem
Conventional BAW resonators suffer from undesired BO spurious resonance modes due to nonzero electromechanical coupling in the border region, leading to increased transmission loss and reduced quality factor, while maintaining high Q values and cost-effectiveness remains a challenge.
Innovation Solution
A BAW resonator design incorporating a ferroelectric layer with a ferroelectric border portion featuring antiparallel and parallel polarization parts that cancel each other out, resulting in effectively zero electromechanical coupling at the border region, using materials like scandium aluminum nitride (ScxAl1-xN) with a box-shaped polarization-electric field curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a BO ring is added to confine energy and prevent lateral wave spurious modes, then lateral wave suppression is improved, but BO spurious resonance modes are excited due to nonzero electromechanical coupling in the border region
Solution Approach 1:
The patent changes the electromechanical coupling parameter in the border region by implementing a polarization cancellation structure. The ferroelectric layer is configured with antiparallel polarization directions in the border region, transforming the electromechanical coupling coefficient from nonzero to effectively zero, thereby eliminating BO spurious resonance modes while maintaining energy confinement benefits
Solution Approach 2:
The patent applies different polarization configurations to different regions of the ferroelectric layer. The central region maintains normal piezoelectric coupling for resonance operation, while the border region uses antiparallel polarization to achieve zero coupling. This local differentiation allows the device to simultaneously achieve energy confinement and spurious mode suppression
2Measurement precision
If the BO ring width and position are adjusted to move BO spurious resonance frequency away from main resonance, then frequency separation is improved, but transmission loss increases and quality factor decreases
Solution Approach 1:
The patent fundamentally changes the electromechanical coupling parameter in the border region from nonzero to zero through polarization cancellation. This eliminates the root cause of BO spurious resonance modes, allowing the main resonance to achieve high quality factor without frequency separation compromises
3Ease of manufacture
If conventional piezoelectric materials are used in the border region, then manufacturing simplicity is maintained, but nonzero electromechanical coupling causes BO spurious resonance modes
Solution Approach 1:
The patent uses the same conventional piezoelectric material throughout the ferroelectric layer but changes the polarization parameter in the border region through applied electric fields during fabrication. This approach maintains manufacturing simplicity while achieving zero electromechanical coupling in the border region through polarization reversal
Solution Approach 2:
The patent replaces the traditional mechanical/electrical coupling approach with a field-based polarization control method. By using electric fields during fabrication to reverse polarization in the border region, the patent achieves zero electromechanical coupling without changing the material itself, maintaining ease of manufacture
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 effectively eliminates BO spurious resonance modes, enhances the quality factor, and maintains high Q values by confining energy within the resonator, thereby reducing transmission loss and ensuring cost-effectiveness.
Implementation Method 1
a piezoelectric layer 16 (which is sometimes referred to as a transduction layer) sandwiched between the bottom electrode 12 and the top electrode 14
Implementation Method 2
The first polarization of the antiparallel part and the second polarization of the parallel part at least partially cancel each other out, such that an absolute value of a combined polarization of the ferroelectric BO portion is smaller than an absolute value of a central polarization of the ferroelectric central portion
Implementation Method 3
The ferroelectric central portion is configured to provide a resonance of the BAW resonator
Data Source
AI summary
The present disclosure relates to a bulk acoustic wave (BAW) resonator, which includes a bottom electrode, a top electrode structure, and a ferroelectric layer vertically sandwiched in between. Herein, the ferroelectric layer, which is formed of a ferroelectric material having a box-shape polarization-electric field curve, includes a border portion and a central portion surrounded by the border portion. The border portion includes an antiparallel part having a first polarization and a parallel part having a second polarization in an opposite direction to the first polarization. The first polarization of the antiparallel part and the second polarization of the parallel part at least partially cancel each other out, such that an absolute value of a combined polarization of the border portion is smaller than an absolute value of a central polarization of the central portion. The central portion is configured to provide a resonance of the BAW resonator.