ALD Piezoelectric BAW Stack With Polarization Inversion for 40 GHz
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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 implementation of a bulk acoustic wave device with a plurality of stacked piezoelectric layers, where at least one layer is formed by atomic layer deposition (ALD) with polarization inversion, and additional layers are formed by sputtering, creating a thicker piezoelectric stack that increases mechanical stability and reduces capacitance, thereby achieving higher resonant frequencies up to 40 GHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If thinner piezoelectric layer stacks are used to achieve higher resonant frequencies, then the resonant frequency increases, but the mechanical stability deteriorates and the device becomes fragile
Solution Approach 1:
The piezoelectric layer is divided into multiple discrete layers (first piezoelectric layer, second piezoelectric layer, third piezoelectric layer) with alternating polarizations. This segmentation allows each layer to contribute to the overall mechanical strength while the alternating polarization structure manages stress distribution, enabling high resonant frequencies without sacrificing mechanical stability.
Solution Approach 2:
The device employs a composite structure combining multiple piezoelectric materials with different properties (e.g., aluminum nitride and scandium aluminum nitride) in alternating layers. This composite approach optimizes both mechanical strength and piezoelectric performance, allowing the thin stack to maintain structural integrity while achieving high resonant frequencies.
2Speed
If thinner piezoelectric layer stacks are used to achieve higher resonant frequencies, then the resonant frequency increases, but the power handling capability deteriorates
Solution Approach 1:
The piezoelectric stack is segmented into multiple layers with alternating polarizations, where each layer can be independently optimized for power handling. The segmented structure distributes electrical stress across multiple interfaces, preventing breakdown and enabling higher power operation at high frequencies.
Solution Approach 2:
The invention inverts the polarization direction of alternating piezoelectric layers. This inversion creates a push-pull effect that balances electrical stress and improves power handling capability, allowing the device to operate at high frequencies with enhanced power tolerance.
3Stability of the object's composition
If more piezoelectric layers are stacked to improve mechanical stability, then the mechanical stability improves, but the device complexity increases
Solution Approach 1:
The piezoelectric stack is divided into a repeating pattern of layers with alternating polarizations. This segmented design creates a modular structure where each unit cell (positive polarization layer + negative polarization layer) can be replicated, simplifying the manufacturing process despite the increased number of layers.
Solution Approach 2:
The invention systematically varies the polarization parameter of alternating layers while maintaining consistent material composition and thickness ratios. This parameter-based differentiation allows for simplified manufacturing through standardized deposition processes, reducing complexity despite the multi-layer structure.
4Speed
If polarization inversion is implemented in piezoelectric layers, then the resonant frequency and mechanical stability improve, but the manufacturing precision requirements increase
Solution Approach 1:
The polarization inversion is implemented through discrete segmented layers rather than continuous variation. Each layer's polarization direction is controlled independently through standardized deposition parameters, making the manufacturing process more predictable and precise compared to attempting continuous polarization control.
Solution Approach 2:
The invention controls polarization by changing the deposition parameters (such as precursor sequence, temperature, or pressure) during atomic layer deposition of each piezoelectric layer. This parameter-based control method enables precise polarization inversion through well-established semiconductor manufacturing techniques, achieving high resonant frequency with manageable manufacturing precision.
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 reliable high-frequency operation with improved mechanical stability and power handling, suitable for advanced applications like 5G New Radio, while suppressing non-linearity excitation responses and meeting stringent system level linearity specifications.
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 first piezoelectric layer and a second piezoelectric layer over the first piezoelectric layer. The second piezoelectric layer can be formed by atomic layer deposition. The second piezoelectric layer can have an opposite polarization relative to the first piezoelectric layer. Related filters, multiplexers, packaged radio frequency modules, radio frequency front ends, wireless communication devices, and methods are disclosed.