Acoustic Wave Filter Terminal Layout for Isolation on Thin Substrates
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Solution Overview
Problem
Acoustic wave devices experience deterioration in isolation characteristics due to high parasitic capacitance between signal outer electrodes when the piezoelectric substrate is made smaller or thinner, leading to reduced size.
Innovation Solution
The acoustic wave device includes a first piezoelectric substrate with signal and ground electrodes on one surface, insulation layers on the opposite surface, and signal terminals indirectly connected through these layers, with the ground terminal having a contact portion directly on the substrate, reducing capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the piezoelectric substrate is made smaller or thinner to reduce device size, then the device size is reduced, but coupling occurs between signal outer electrodes due to high parasitic capacitance, causing isolation characteristics to deteriorate
Solution Approach 1:
The patent introduces a ground electrode as an intermediary element positioned between signal outer electrodes on the piezoelectric substrate. This ground electrode acts as a mediator to shield and isolate the signal electrodes from each other, preventing parasitic capacitance coupling while allowing the substrate to remain small and thin. The ground electrode serves as a reference potential that blocks unwanted capacitive coupling paths between adjacent signal electrodes.
Solution Approach 2:
The patent applies different functional qualities to different regions of the electrode structure. Signal outer electrodes are designed with specific patterns and positions optimized for signal transmission, while ground electrodes are strategically placed in intermediate positions to provide local shielding. This local differentiation of electrode functions allows small substrate dimensions while maintaining isolation characteristics through localized ground electrode placement between signal paths.
2Volume of moving object
If the piezoelectric substrate is made smaller or thinner to reduce device size, then the device size is reduced, but parasitic capacitance increases causing coupling between signal outer electrodes
Solution Approach 1:
The patent converts the harmful effect of high parasitic capacitance in thin substrates into a beneficial shielding mechanism. By introducing ground electrodes that leverage the inherent capacitance of the thin piezoelectric substrate, the design transforms parasitic capacitance into a useful isolation mechanism. The ground electrodes use the substrate's capacitance to create effective electric field shielding between signal electrodes, turning the harmful parasitic effect into a useful isolation feature.
Solution Approach 2:
Ground electrodes serve as intermediary elements that manage and control parasitic capacitance effects. Positioned between signal electrodes, these ground electrodes provide a controlled capacitance path to ground, preventing uncontrolled parasitic coupling between signal paths. This intermediary structure allows the thin substrate to maintain low device size while the ground electrodes manage the parasitic capacitance to prevent harmful coupling.
3Area of stationary object
If signal outer electrodes are arranged closely to reduce device area, then device area is reduced, but isolation characteristics deteriorate due to coupling through parasitic capacitance
Solution Approach 1:
The patent merges multiple electrode functions into a unified structure on the piezoelectric substrate. Ground electrodes are integrated between signal electrodes, combining signal transmission and isolation functions in a compact arrangement. This merging of functions allows close spacing of signal electrodes to reduce device area while the integrated ground electrodes provide continuous isolation, maintaining reliability despite reduced area.
Solution Approach 2:
Ground electrodes positioned between closely spaced signal electrodes serve as intermediary elements that enable tight packing while maintaining isolation. These intermediary ground electrodes create controlled capacitance barriers that prevent direct coupling between adjacent signal electrodes, allowing the device area to be minimized without sacrificing isolation characteristics.
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 effectively reduces or prevents the deterioration of isolation characteristics by enhancing capacitive coupling, ensuring better signal propagation to the ground terminal and minimizing interference with other signal terminals.
Implementation Method 1
an IDT (Interdigital Transducer) electrode is provided on one of two main surfaces of a piezoelectric substrate
Implementation Method 2
at least one insulation layer on the second main surface of the first piezoelectric substrate
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate, first and second signal electrodes, and a first ground electrode on a first main surface of the piezoelectric substrate, at least one insulation layer on a second main surface of the piezoelectric substrate, first and second signal terminals provided indirectly on the second main surface with the insulation layer interposed therebetween, and a ground terminal on the second main surface. An acoustic wave filter is provided on the piezoelectric substrate. The first signal electrode and the first signal terminal are electrically coupled, the second signal electrode and the second signal terminal are electrically coupled, and the first ground electrode and the ground terminal are electrically coupled. The ground terminal includes a contact portion in contact with the second main surface of the piezoelectric substrate.