BAW Resonator Border Region With Zero Coupling for Spurious Mode Suppression
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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 in wireless applications.
Innovation Solution
A BAW resonator design utilizing a multilayer transduction structure with a ferroelectric material having a box-shaped polarization-electric field curve, where the electromechanical coupling coefficient at the border region is minimized or set to zero, using a combination of ferroelectric and piezoelectric materials with different polarization responses to the electric field, and a DC bias voltage is applied to adjust the coupling coefficients, ensuring the border section has a lower or zero coupling compared to 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 coefficient
Solution Approach 1:
The patent applies local quality by creating distinct regions within the transduction layer: a border section with reduced electromechanical coupling coefficient and a central section with normal coupling. This is achieved by using different materials (ferroelectric material with electric field dependent polarization in border region, piezoelectric material or ferroelectric material without DC bias in central region) to give different functional properties to different parts of the transduction layer, thereby suppressing border spurious modes while maintaining central resonance.
Solution Approach 2:
The patent changes the electromechanical coupling coefficient parameter in the border region by applying DC bias voltage to ferroelectric material, which alters its polarization state. This parameter change reduces the coupling coefficient in the border section compared to the central section, effectively suppressing border spurious resonance modes while preserving the desired central resonance mode.
2Reliability
If a border ring is introduced to eliminate lateral wave spurious modes, then quality factor degradation is reduced, but transmission loss increases due to border spurious resonance
Solution Approach 1:
The patent introduces local quality differentiation by creating a border section with modified electromechanical coupling properties through the use of ferroelectric material with DC bias. This localized modification suppresses border spurious resonance modes that cause transmission loss, while preserving the central section's resonance characteristics that maintain high quality factor.
Solution Approach 2:
The patent changes the electromechanical coupling coefficient in the border region by applying DC bias to ferroelectric material, which modifies the polarization and thereby the coupling strength. This parameter modification eliminates border spurious modes that would otherwise cause transmission loss, while maintaining the central resonance for high Q operation.
3Object-generated harmful factors
If a multilayer transduction structure with ferroelectric material and DC bias is used to reduce border spurious modes, then border spurious resonance is eliminated, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the transduction layer into distinct border and central sections with different material compositions and electrical biasing conditions. The border section uses ferroelectric material with DC bias applied through a border electrode, while the central section uses different material or no bias, creating functionally segmented regions that eliminate border spurious modes.
Solution Approach 2:
The patent uses composite materials by combining ferroelectric material in the border region with piezoelectric material or unbiased ferroelectric material in the central region. This composite structure allows different sections to have different electromechanical coupling coefficients, effectively suppressing border spurious resonance while maintaining overall device functionality.
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 the border spurious resonance mode near the main resonance, maintaining high Q values and reducing transmission loss, while maintaining the energy confinement within the resonator.
Implementation Method 1
at least one of the plurality of transduction layers is formed of a first ferroelectric material, whose polarization varies with an electric field across the first ferroelectric material
Implementation Method 2
a combination of all transduction central portions forms a transduction central section of the multilayer transduction structure... The transduction central section is configured to provide a resonance of the BAW resonator
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
The present disclosure relates to a Bulk Acoustic Wave, BAW, resonator (30), which includes a bottom electrode (32), a top electrode (34) structure, and a multilayer transduction structure (36) sandwiched therebetween. Herein, the multilayer transduction structure is composed of multiple transduction layers (41_1, .... 41_N), 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 (41_BO_1, ... 41_BO_N) positioned at a periphery of a corresponding transduction layer and a transduction central portion (41_C_1,....41_C_N) surrounded by the transduction BO portion. A combination of all transduction BO portions (41_BO_1, ... 41_BO_N) forms a transduction BO section (40) of the multilayer transduction structure (36), and a combination of all transduction central portions (41_C_1,....41_C_N) forms a transduction central section (36_C) of the multilayer transduction structure (36). An electromechanical coupling coefficient of the transduction BO section is less than an electromechanical coupling coefficient of the transduction central section.