Stacked Piezoelectric BAW Resonators for High-Frequency Stability
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Solution Overview
Problem
Current bulk acoustic wave (BAW) resonators face challenges in achieving high resonant frequencies while maintaining mechanical stability and power handling, particularly with thinner layer stacks that are fragile and prone to technical issues like high resistivity and edge losses.
Innovation Solution
The use of stacked piezoelectric layers with alternating polarizations, where at least one layer is formed by atomic layer deposition (ALD) and another by sputtering, to achieve higher resonant frequencies and improved mechanical stability, power handling, and reduced capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If thinner layer stacks are used to achieve higher resonant frequencies, then resonant frequency is improved, but mechanical stability deteriorates
Solution Approach 1:
The piezoelectric layer is divided into multiple thinner sub-layers (first piezoelectric layer, second piezoelectric layer, third piezoelectric layer) with alternating polarizations. This segmentation allows the structure to achieve higher resonant frequencies while maintaining mechanical stability through the distributed architecture and polarization alternation that reduces stress accumulation.
Solution Approach 2:
The patent employs a composite structure combining multiple piezoelectric materials (e.g., aluminum nitride, scandium aluminum nitride) with different properties in a stacked configuration. This composite approach enables optimization of both resonant frequency and mechanical stability by selecting materials with complementary characteristics for different layers.
2Speed
If thinner layer stacks are used to achieve higher resonant frequencies, then resonant frequency is improved, but power handling deteriorates
Solution Approach 1:
The piezoelectric layer is segmented into multiple sub-layers with alternating polarizations, which distributes the electrical and mechanical stress across multiple interfaces. This segmentation enhances power handling capability while maintaining the thin overall structure needed for high resonant frequencies.
Solution Approach 2:
The patent inverts the polarization direction of alternating piezoelectric layers. This inversion creates a push-pull effect that improves power handling by utilizing both tensile and compressive strengths of the piezoelectric materials, enabling higher power operation in thin-layer high-frequency resonators.
3Ease of manufacture
If traditional deposition methods are used for piezoelectric layers, then manufacturing simplicity is maintained, but polarization uniformity and quality deteriorate
Solution Approach 1:
The piezoelectric layer is segmented into multiple sub-layers that can be deposited using standard techniques. Each sub-layer is thin enough to achieve good polarization uniformity, and the alternating polarization structure compensates for any variations, maintaining overall device performance while using manufacturable processes.
Solution Approach 2:
The patent changes the deposition parameters by using atomic layer deposition (ALD) for specific piezoelectric layers to achieve superior polarization uniformity and control over layer thickness and composition. This parameter change in the deposition process enables high-precision manufacturing of the piezoelectric structure.
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 configuration allows for higher resonant frequencies up to 40 GHz, enhanced mechanical stability, and better power handling, suitable for 5G applications, while suppressing non-linearity excitation responses.
Implementation Method 1
In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer
Implementation Method 2
The second piezoelectric layer is formed by atomic layer deposition
Implementation Method 3
The third piezoelectric layer can be formed by sputtering
Data Source
AI summary
Aspects of this disclosure relate to a bulk acoustic wave device with a plurality of piezoelectric layers having at least one polarization inversion. The bulk acoustic wave device can include a plurality of stacked piezoelectric layers. The plurality of stacked piezoelectric layers can include a piezoelectric layer formed by atomic layer deposition. The bulk acoustic wave device can excite an overtone mode as a main mode. Related filters, multiplexers, packaged radio frequency modules, radio frequency front ends, wireless communication devices, and methods are disclosed.