BAW Resonator Frame Structure for Spurious Wave Suppression
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Solution Overview
Problem
Bulk acoustic wave resonators (BAW) suffer from spurious acoustic waves due to transverse acoustic waves generated perpendicular to the main acoustic wave, degrading frequency response and performance.
Innovation Solution
The introduction of lower recessed and raised frame regions with varying thicknesses of dielectric and electrode materials on the piezoelectric film to scatter and reflect transverse acoustic waves, preventing them from entering the main active domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transverse acoustic waves are generated in the piezoelectric film, then acoustic wave propagation occurs, but spurious acoustic waves are generated that degrade frequency response and performance
Solution Approach 1:
The patent converts the harmful transverse acoustic waves into a beneficial effect by using them to excite the raised frame regions, which then act as acoustic mirrors to reflect spurious waves away from the active region. The harmful transverse wave energy is transformed into a useful reflection mechanism that improves frequency response and eliminates spurious modes.
Solution Approach 2:
The raised frame regions serve as an intermediary structure between the piezoelectric film and the surrounding environment. These frames act as acoustic mirrors that mediate the interaction between transverse acoustic waves and the active region, reflecting spurious waves and preventing them from degrading performance.
2Power
If the piezoelectric film is made larger to improve performance, then more acoustic energy can be generated, but transverse acoustic waves spread further and generate more spurious modes
Solution Approach 1:
The patent segments the piezoelectric film into a central active region surrounded by raised frame regions. This segmentation allows the active region to generate acoustic energy while the frame regions act as separate acoustic mirrors to contain and reflect spurious waves, preventing them from spreading across the entire structure.
Solution Approach 2:
The patent applies local quality by creating raised frame regions with different thickness and material properties at specific locations around the active region. These localized structures have acoustic mirror properties that are not present in the main active region, allowing selective reflection of spurious waves while maintaining energy generation in the active area.
3Ease of manufacture
If uniform thickness of electrode and dielectric layers is used, then manufacturing is simplified, but acoustic wave control and spurious mode suppression are insufficient
Solution Approach 1:
The patent implements local quality by varying the thickness of electrode and dielectric layers in the raised frame regions compared to the active region. This local variation creates acoustic mirror properties in the frames while maintaining relatively simple uniform layers in the active region, balancing manufacturability with acoustic wave control.
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 suppresses spurious acoustic waves, enhancing the frequency response and performance of BAW resonators by creating a barrier that dissipates and reflects transverse waves, thereby improving signal integrity.
Implementation Method 1
a piezoelectric film having a central region defining a main active domain in which a main acoustic wave is generated during operation
Implementation Method 2
The introduction of lower recessed and raised frame regions with varying thicknesses of dielectric and electrode materials on the piezoelectric film to scatter and reflect transverse acoustic waves, preventing them from entering the main active domain
Data Source
AI summary
A film bulk acoustic wave resonator comprising a piezoelectric film having a central region defining a main active domain in which a main acoustic wave is generated during operation, an upper electrode disposed on a top surface of the piezoelectric film, a lower electrode disposed on a lower surface of the piezoelectric film, a dielectric material layer disposed on a lower surface of the lower electrode, and lower recessed frame regions disposed laterally on opposite sides of the central region, the lower recessed frame regions defined by regions of one of the dielectric material or of the lower electrode having a lesser thickness than the thickness of the one of the dielectric material layer or of the lower electrode in the central region.