BAW Resonator Border Polarization for Spurious Mode Suppression
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Solution Overview
Problem
Bulk Acoustic Wave (BAW) resonators experience degradation in quality factor due to lateral wave spurious modes, which are not effectively eliminated by conventional border rings, leading to increased transmission loss and undesired spurious resonance modes near the main resonance frequency.
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 coefficient, positioned at the periphery and a central portion with higher coupling coefficient, configured to minimize spurious resonance modes by applying a direct current bias voltage to adjust polarization and coupling coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a border ring is added to confine energy and prevent lateral wave spurious modes, then lateral wave spurious modes are reduced, but BO spurious resonance modes are excited due to nonzero electromechanical coupling in the piezoelectric layer at the border region
Solution Approach 1:
The piezoelectric layer is designed with spatially varying properties: the border region has reduced or zero electromechanical coupling coefficient while the central region maintains normal piezoelectric properties. This local differentiation allows the border ring to confine energy without generating spurious resonance modes, as the harmful coupling is eliminated only where needed at the boundaries
Solution Approach 2:
The electromechanical coupling coefficient is modified in the border region through parameter changes in the piezoelectric layer properties. By adjusting the coupling coefficient to zero or reduced values at the border while maintaining normal values in the center, the design eliminates BO spurious resonance modes while preserving energy confinement benefits
2Reliability
If the piezoelectric layer has uniform nonzero electromechanical coupling coefficient, then the resonator provides strong electromechanical coupling for resonance, but the border region generates undesired BO spurious resonance modes
Solution Approach 1:
The piezoelectric layer transitions from uniform coupling to non-uniform coupling with spatially varying properties. The border region has reduced or zero electromechanical coupling while the central region maintains strong coupling, allowing resonance functionality to be preserved locally without generating harmful spurious modes at the boundaries
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 solution effectively eliminates or reduces BO spurious resonance modes while maintaining high Q values and low lateral wave spurious modes, thereby enhancing the performance of BAW resonators by confining energy and reducing transmission loss.
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
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 structure (34), and a ferroelectric layer (36) 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 (40) positioned at a periphery of the ferroelectric layer and a ferroelectric central portion (36_C) surrounded by the ferroelectric BO portion. The ferroelectric BO portion has a first polarization (PBO) and a first electromechanical coupling coefficient, and the ferroelectric central portion has a second polarization (PNON) 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.