BAW Resonator Border Coupling Layout for Spurious Mode Suppression
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Solution Overview
Problem
Bulk Acoustic Wave (BAW) resonators face degradation due to lateral wave spurious modes, leading to increased transmission loss and undesired BO spurious resonance modes, which are not effectively addressed by existing designs while maintaining high Q values and low/no lateral wave spurious modes.
Innovation Solution
A BAW resonator design with a ferroelectric layer having a box-shape polarization-electric field curve, featuring a ferroelectric border portion with zero or low electromechanical coupling, and a central portion with higher coupling, where the border portion is confined under a BO ring, reducing BO spurious resonance modes without affecting the main resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a BO ring is introduced to confine energy and prevent lateral wave spurious modes, then lateral wave spurious modes are eliminated, but BO spurious resonance mode is excited near the main resonance
Solution Approach 1:
The patent applies local quality by creating a border region with distinct piezoelectric properties different from the central region. The border region has reduced or zero electromechanical coupling coefficient, while the central region maintains normal piezoelectric coupling. This local differentiation allows the device to simultaneously suppress BO spurious resonance (by having low coupling at the border) and maintain strong main resonance (by having normal coupling in the center).
2Power
If the piezoelectric layer has uniform electromechanical coupling throughout, then strong main resonance is achieved, but BO spurious resonance mode is excited
Solution Approach 1:
The patent implements local quality by spatially varying the electromechanical coupling coefficient across the piezoelectric layer. The central region maintains strong coupling for powerful main resonance, while the border region has reduced or zero coupling to eliminate BO spurious resonance. This is achieved through controlled removal, doping, or structural modification of the piezoelectric material at the borders.
Solution Approach 2:
The patent segments the piezoelectric layer into functionally distinct regions: a central region for strong electromechanical coupling and border regions for minimal coupling. This segmentation allows independent optimization of each region's properties to achieve both strong main resonance and suppression of spurious modes.
3Reliability
If the border region width is increased to better suppress spurious modes, then lateral wave suppression improves, but the frequency difference between main resonance and BO spurious resonance decreases
Solution Approach 1:
The patent applies parameter changes by modifying the electromechanical coupling coefficient in the border region rather than relying solely on geometric dimensions. By changing the material properties (through doping, removal, or structural modification) to achieve zero or near-zero coupling, the patent can effectively suppress spurious modes without requiring large border region widths, thereby maintaining adequate frequency separation between main and spurious resonances.
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 or reduces BO spurious resonance modes, maintaining high Q values and low/no lateral wave spurious modes, thereby enhancing the performance of BAW filters in wireless applications.
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 ferroelectric layer is formed of a ferroelectric material, which has a box-shape polarization-electric field (P-E) curve
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 sandwiched in between. Herein, the ferroelectric layer is formed of a ferroelectric material, which has a box-shape polarization-electric field (P-E) curve. The ferroelectric layer includes a ferroelectric border (BO) portion positioned at a periphery of the ferroelectric layer and a ferroelectric central portion surrounded by the ferroelectric BO portion. The ferroelectric BO portion has a first polarization and a first electromechanical coupling coefficient, and the ferroelectric central portion has a second polarization and a second electromechanical coupling coefficient. An absolute value of the first polarization is less than an absolute value of the second polarization, and the first electromechanical coupling coefficient is less than the second electromechanical coupling coefficient. The ferroelectric central portion is configured to provide a resonance of the BAW resonator.