Multi-Layer Piezoelectric Substrate for SAW Filter Isolation
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Solution Overview
Problem
Surface acoustic wave (SAW) filters face challenges in meeting stringent filter specifications due to high frequency drift over temperature, while bulk acoustic wave (BAW) filters are more expensive and larger in size, making them less ideal for mobile communication devices.
Innovation Solution
A multi-layer piezoelectric substrate with a lithium-based piezoelectric layer and a conductive layer positioned between the piezoelectric layer and the substrate, electrically connected to a grounding structure, which improves receive and transmit isolation by attenuating parasitic capacitance and electrical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a surface acoustic wave (SAW) filter is used, then the device size is reduced, but the frequency drift over temperature increases
Solution Approach 1:
The patent employs a multi-layer piezoelectric substrate structure combining lithium niobate and lithium tantalate layers with a conductive layer, creating a composite material system that achieves both compact size and improved thermal stability for SAW filters
Solution Approach 2:
A conductive layer is introduced as an intermediary element between the piezoelectric layer and the substrate, electrically connected to a grounding structure, to attenuate parasitic capacitance and electrical coupling that cause frequency drift
2Stability of the object's composition
If a bulk acoustic wave (BAW) filter is used, then the frequency stability is improved, but the device size and cost increase
Solution Approach 1:
The patent applies local quality modification by introducing a conductive layer at specific positions within the SAW filter structure to locally address parasitic capacitance issues, achieving frequency stability improvements without the need for bulk acoustic wave filter architecture
3Reliability
If a conductive layer is added between the piezoelectric layer and substrate, then the isolation performance is improved, but the device complexity increases
Solution Approach 1:
The conductive layer is merged with the grounding structure to form an integrated electrical connection system that improves isolation performance while minimizing additional structural complexity
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 enhances the isolation performance of acoustic wave filters, reducing frequency drift and improving electrical characteristics, making them suitable for demanding RF filter applications in mobile devices.
Implementation Method 1
A multi-layer piezoelectric substrate with a lithium-based piezoelectric layer and a conductive layer positioned between the piezoelectric layer and the substrate, electrically connected to a grounding structure, which improves receive and transmit isolation by attenuating parasitic capacitance and electrical coupling
Implementation Method 2
The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed
Implementation Method 3
An acoustic wave filter can include a plurality of resonators arranged to filter a radio frequency signal. Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters
Data Source
AI summary
An acoustic wave device is disclosed. The acoustic wave device can include a piezoelectric layer positioned over a substrate. The acoustic wave device can also include an interdigital transducer electrode positioned over the piezoelectric layer. The acoustic wave device can also include a grounding structure positioned over the piezoelectric layer. The acoustic wave device can also include a conductive layer positioned under the substrate such that the substrate is positioned between the conductive layer and the grounding structure. The acoustic wave device can further include an electrical pathway that electrically connects the conductive layer to the grounding structure.