BAW Resonator Border Structure With Low-Coupling Transduction Layers
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Solution Overview
Problem
Bulk Acoustic Wave (BAW) resonators face issues with undesired border spurious resonance modes due to nonzero electromechanical coupling coefficients, leading to increased transmission loss and degradation of quality factor, particularly at microwave frequencies above 1.5 GHz, which affects their performance in wireless applications.
Innovation Solution
A BAW resonator design utilizing multilayer transduction materials with zero or low electromechanical coupling at the border region, achieved by employing ferroelectric materials with box-shaped polarization-electric field curves and strategically positioning transduction layers with different electromechanical coupling coefficients, allowing for a zero or reduced coupling coefficient in the border section while maintaining a nonzero coupling in the central section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a border ring is introduced to confine energy and prevent lateral wave spurious modes, then lateral wave suppression is improved, but border spurious resonance modes are excited due to nonzero electromechanical coupling
Solution Approach 1:
The patent applies local quality by creating distinct regions within the transduction layer: a border section with zero electromechanical coupling coefficient and a central section with nonzero coupling coefficient. This is achieved by selectively removing or modifying the piezoelectric material at the borders while maintaining it in the central region, allowing each zone to serve its specific function - the border zone suppresses spurious modes through zero coupling while the central zone maintains resonance through nonzero coupling
Solution Approach 2:
The transduction layer is segmented into functionally distinct sections: a border section and a central section. This segmentation allows independent optimization of electromechanical coupling properties in each region, enabling the border section to have zero coupling for spurious mode suppression while the central section maintains nonzero coupling for resonance generation
2Use of energy by moving object
If the border region has nonzero electromechanical coupling coefficient, then transduction efficiency is maintained, but transmission loss increases due to border spurious resonance
Solution Approach 1:
The patent implements local quality by spatially varying the electromechanical coupling coefficient: zero at the borders to eliminate spurious resonance and energy loss, and nonzero in the central region to maintain transduction efficiency. This localized differentiation allows the system to achieve both low transmission loss and high transduction efficiency simultaneously
3Object-affected harmful factors
If a border ring is added to the BAW resonator, then lateral wave confinement is improved, but device complexity increases
Solution Approach 1:
The patent merges the border ring structure with the transduction layer by integrating the zero-coupling border section directly into the transduction layer fabric1ation process. This consolidation eliminates the need for separate border ring components and their associated assembly steps, reducing device complexity while maintaining lateral wave confinement functionality
Solution Approach 2:
The transduction layer becomes a composite structure with different electromechanical coupling properties in different regions - a composite of piezoelectric material in the central section and non-piezoelectric or zero-coupling material in the border section. This composite approach achieves multiple functions within a single integrated layer
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 design effectively eliminates or minimizes border spurious resonance modes, enhancing the quality factor and reducing transmission loss, thereby improving the performance of BAW resonators in wireless devices without increasing production costs.
Implementation Method 1
at least one of which is formed of a first ferroelectric material. Polarization of the first ferroelectric material varies with an electric field across the first ferroelectric material
Implementation Method 2
a multilayer transduction structure sandwiched between the bottom electrode and the top electrode structure. Each transduction layer includes a transduction border portion positioned at a periphery of a corresponding transduction layer
Implementation Method 3
A first electromechanical coupling coefficient of the transduction BO section is smaller than a second (non-zero) electromechanical coupling coefficient of the transduction central section. The transduction central section 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 multilayer transduction structure sandwiched therebetween. Herein, the multilayer transduction structure is composed of multiple transduction layers, at least one of which is formed of a ferroelectric material with a box-shape polarization-electric field curve. Each transduction layer includes a transduction border (BO) portion positioned at a periphery of a corresponding transduction layer and a transduction central portion surrounded by the transduction BO portion. A combination of all transduction BO portions forms a transduction BO section of the multilayer transduction structure, and a combination of all transduction central portions forms a transduction central section of the multilayer transduction structure. An electromechanical coupling coefficient of the transduction BO section is less than an electromechanical coupling coefficient of the transduction central section.