BAW Resonator Spurious Mode Suppression via Planarization Border
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators suffer from degradation in quality factor due to lateral acoustic waves leaking from the fundamental thickness mode, leading to spurious resonances and strong ripples in bandpass frequencies, which degrade their performance.
Innovation Solution
Incorporating a border region with a planarization material in the inactive region of the BAW resonator, which changes the mechanical characteristics and decay rate of evanescent waves, ensuring a smoother transition from propagating waves in the active region to evanescent waves in the inactive region, thereby reducing spurious mode resonances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a border ring is added to suppress lateral acoustic waves, then spurious mode resonances are reduced, but device complexity increases
Solution Approach 1:
The patent applies local quality by creating a border region with specifically tailored mechanical properties (different density, stiffness, or acoustic impedance) adjacent to the active region. This localized modification suppresses lateral acoustic wave propagation at the boundaries without altering the entire resonator structure, thereby reducing spurious modes while maintaining overall structural simplicity.
Solution Approach 2:
The border region acts as an intermediary zone between the active region and the inactive region. It provides a gradual transition that prevents abrupt impedance mismatches, thereby suppressing lateral wave leakage and spurious resonances without requiring complex boundary structures.
2Reliability
If the active region size is reduced to suppress lateral waves, then spurious mode resonances are reduced, but the energy containment of the fundamental mode decreases
Solution Approach 1:
The patent maintains a sufficiently large active region for energy containment while introducing a border region with specific mechanical characteristics. This border region locally modifies acoustic wave behavior to suppress lateral propagation and spurious modes, thereby achieving high quality factor without sacrificing the energy containment provided by the larger active region.
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 significantly reduces spurious mode resonances in BAW resonators, resulting in smoother performance in bandpass frequencies and improved overall resonator performance.
Implementation Method 1
changes the mechanical characteristics and decay rate of evanescent waves, enabling a smoother transition of propagating waves in the active region to evanescent waves in the inactive region
Data Source
AI summary
Embodiments provide a solidly-mounted bulk acoustic wave (BAW) resonator and method of making same. In embodiments, the BAW resonator may include a planarization portion in an inactive region of the BAW resonator that is coplanar with a piezoelectric layer of the BAW resonator in an active region of the BAW resonator. Other embodiments may be described and claimed.