BAW Resonator Dielectric Flaps for Spurious Mode Suppression
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Solution Overview
Problem
BAW resonators suffer from spurious mode excitation and lower quality factor (Q) due to localized internal laterally acting forces at termination regions, leading to energy loss and spurious signals, which degrade filter performance.
Innovation Solution
Incorporation of dielectric inner-flaps and optional outer-flaps in the resonator termination regions to suppress spurious lateral modes, with the inner-flaps being self-resonant and outer-flaps reflecting energy back constructively, enhancing the quality factor (Q) and electromechanical coupling coefficient (kt²).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional termination regions are used in BAW resonators, then the device structure is simple and easy to manufacture, but spurious mode excitation occurs and quality factor (Q) is reduced
Solution Approach 1:
The termination region is segmented into multiple functional zones: a first termination region with a first electrode pattern, a second termination region with a second electrode pattern, and an optional third termination region with a third electrode pattern. This segmentation allows different electrode configurations to address different aspects of spurious mode suppression while maintaining manufacturing feasibility through systematic layering.
Solution Approach 2:
Different electrode patterns are applied to different termination regions based on their specific requirements. The first termination region uses a first electrode pattern optimized for its location, the second termination region uses a second electrode pattern, and the optional third termination region uses a third electrode pattern. This local optimization suppresses spurious modes at each termination region while maintaining overall device performance.
2Loss of energy
If termination regions are optimized to reduce spurious mode excitation, then energy containment and quality factor (Q) improve, but the device structure becomes more complex
Solution Approach 1:
The termination structure is divided into multiple segments with different electrode patterns arranged in series along the resonator length. Each segment (first, second, and optional third termination regions) is optimized for energy containment at its specific location, collectively improving overall energy containment while maintaining a systematic, manufacturable structure.
Solution Approach 2:
The solution extends from simple planar electrode patterns to three-dimensional stacked electrode patterns across multiple layers. The first, second, and third electrode patterns are arranged in vertical and lateral dimensions, creating a multi-dimensional electrode architecture that enhances energy containment through additional spatial control of acoustic fields.
3Reliability
If multiple electrode patterns are used in termination regions to suppress spurious modes, then electromechanical coupling coefficient (kt²) is enhanced, but manufacturing complexity increases
Solution Approach 1:
The electrode structure is segmented into multiple patterns (first, second, and optional third) that can be manufactured using standard multi-layer thin-film deposition and lithography techniques. Each electrode pattern is formed in its own layer or region, allowing conventional manufacturing processes to be applied systematically without requiring complex single-step patterning.
Solution Approach 2:
The multiple electrode patterns serve multiple functions simultaneously: they provide electrical connections, suppress spurious modes through acoustic field control, and enhance electromechanical coupling. This multi-functionality is achieved through a unified manufacturing approach that forms all electrode patterns using standard semiconductor fabrication processes.
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
Improves the quality factor (Q) from ~1800 to 3000 and enhances the electromechanical coupling coefficient (kt²) from ~6.0 to 6.3% by effectively containing energy within the resonator and reducing spurious signals.
Implementation Method 1
the inner-flaps being self-resonant
Implementation Method 2
outer-flaps reflecting energy back constructively
Implementation Method 3
a piezoelectric layer
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
A high Q acoustic BAW resonator with high coupling and improved spurious mode suppression is given. The BAW resonator comprises an active resonator region (AR) formed by an overlap of the three layers bottom electrode (BE), piezoelectric layer (PL) and top electrode layer (TE). An inner-flap (IF) is formed by a dielectric 3D structure sitting on a marginal region (MR) of the active resonator region (AR) or adjacent thereto, extending inwardly towards the center thereof and having a section that runs in parallel and distant to the top surface of the resonator keeping an inner gap (IG) thereto or an angle Θ.