Common Ceramic Substrate for BAW-SAW RF Resonators
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Solution Overview
Problem
Current bulk acoustic wave resonators face challenges in achieving high-quality factor (Q) values and maintaining RF performance due to issues like energy leakage and mobilized electrons at the oxide-substrate interface, which affect their characteristics and manufacturing processes.
Innovation Solution
The use of a spinel substrate, such as a polycrystalline magnesium aluminate, for bulk acoustic wave resonators, which reduces tangent loss, enhances mechanical strength, and simplifies manufacturing by forming a sacrificial layer directly over the substrate, thereby minimizing etching and eliminating mobile electrons and holes, and incorporating features like air cavities and passivation layers to improve RF characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional oxide substrate is used for bulk acoustic wave resonators, then the manufacturing process can proceed with standard materials, but energy leakage and mobilized electrons at the oxide-substrate interface reduce the quality factor and RF performance
Solution Approach 1:
The patent changes the substrate material parameter from conventional oxide to spinel ceramic, which fundamentally alters the electrical properties at the interface. This material substitution eliminates mobile electrons and holes at the substrate interface, thereby reducing energy leakage and improving the quality factor of the resonator.
Solution Approach 2:
The patent employs a composite structure consisting of a spinel substrate combined with a piezoelectric layer and sacrificial layer. This composite material approach leverages the unique properties of spinel ceramic to provide both mechanical support and electrical stability, preventing energy loss while maintaining manufacturability.
2Reliability
If a spinel substrate is used to eliminate mobile electrons and improve RF performance, then the quality factor increases, but the manufacturing process requires forming sacrificial layers directly over the substrate
Solution Approach 1:
The patent applies preliminary action by forming the sacrificial layer directly over the spinel substrate before depositing the piezoelectric layer. This sequence is specifically adapted for spinel substrates to enable proper acoustic wave propagation while maintaining the electrical benefits of the spinel material. The preliminary formation of the sacrificial structure simplifies subsequent processing steps.
3Reliability
If air cavities are incorporated into the resonator structure to improve RF characteristics, then the quality factor and acoustic wave propagation are enhanced, but the device structure becomes more complex
Solution Approach 1:
The patent utilizes an air cavity, which can be viewed as a porous or void structure within the resonator. This air cavity allows for improved acoustic wave propagation by providing a low-density region that enhances the mechanical vibration of the piezoelectric layer. The cavity is integrated into the overall device structure in a way that, while adding complexity, provides significant performance benefits.
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 approach results in bulk acoustic wave resonators with improved RF performance, mechanical strength, and simplified processing, achieving better quality factor values and reduced resistivity, while allowing for the implementation of both BAW and SAW resonators on a common substrate.
Implementation Method 1
a piezoelectric layer positioned on the ceramic substrate, first and second electrodes positioned on opposing sides of the piezoelectric layer
Implementation Method 2
acoustic waves propagate in a bulk of a piezoelectric layer
Data Source
AI summary
An acoustic wave component is disclosed. The acoustic wave component can include a bulk acoustic wave resonator and a surface acoustic wave device. The bulk acoustic wave resonator can include a first portion of a ceramic substrate, a first piezoelectric layer positioned on the ceramic substrate, and electrodes positioned on opposing sides of the first piezoelectric layer. The surface acoustic wave device can include a second portion of the ceramic substrate, a second piezoelectric layer positioned on the ceramic substrate, and an interdigital transducer electrode on the second piezoelectric layer.