BAW Resonator Underlap Structure for Spurious Mode Suppression
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Solution Overview
Problem
Current BAW resonators face challenges in achieving a higher quality factor (Q) due to spurious mode excitation and energy loss, which affects their performance in RF filter applications.
Innovation Solution
The BAW resonator design incorporates a laterally structured layer stack with a reduced thickness in the underlap region relative to the center region, optimized electrode layer thickness adjustments, and the use of a dielectric trimming layer to minimize spurious modes and enhance the Q factor, while maintaining uniform layer thickness and energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the underlap region thickness is reduced to suppress spurious modes, then the Q factor increases, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by creating an underlap region with different thickness characteristics compared to the center region. Specifically, the underlap region has a reduced thickness (dU < dC) while the center region maintains the full design thickness. This localized thickness variation suppresses spurious modes at the edges without affecting the primary resonance in the center, thereby increasing the Q factor while maintaining manufacturability through focused precision requirements only where needed.
2Ease of manufacture
If the layer stack thickness is kept uniform, then the manufacturing complexity is reduced, but the spurious mode suppression is compromised
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through the underlap region structure. The center region maintains uniform thickness for ease of manufacture, while the underlap region introduces localized thickness reduction to suppress spurious modes. This approach allows the majority of the structure to be manufactured with standard uniformity tolerances while achieving spurious mode suppression through the specifically designed underlap zones.
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 suppresses spurious modes, increases the Q factor, and optimizes energy distribution within the resonator, leading to improved performance and frequency accuracy in RF filters.
Implementation Method 1
Due to the piezoelectric effect such resonators convert between RF signals and acoustic waves if an RF signal is applied to the resonator electrodes
Implementation Method 2
An acoustic Bragg mirror is arranged between the sandwich construction of the resonator and the substrate onto which the layer stack is deposited
Implementation Method 3
An acoustic Bragg mirror comprises at least one pair of mirror layers with alternating high and low acoustic impedance
Data Source
AI summary
A BAW resonator comprises a center area (CA), an underlap region (UL) surrounding the center area having a thickness smaller than the thickness dC of the center region and a frame region (FR), surrounding the underlap region having thickness dF greater than dC.