Acoustic Wave Filter Layout for Reduced Electrode-Finger Leakage
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Solution Overview
Problem
Acoustic wave devices experience leakage of acoustic waves in the arrangement direction of electrode fingers, which affects their performance and efficiency.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer with a specific thickness-to-center distance ratio (d/p ≤ 0.5) and a load film extending over a portion of the electrode fingers, along with a support structure that minimizes wave leakage by reflecting acoustic waves at a defined acoustic reflection plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a load film is provided over all electrode fingers to reduce acoustic wave leakage, then acoustic wave leakage is reduced, but the device size cannot be reduced and propagation loss increases
Solution Approach 1:
The load film is selectively provided only on the inner electrode fingers (not on the outermost electrode fingers in the arrangement direction), creating local differentiation in the structure. This local quality approach allows the load film to reduce acoustic wave leakage where needed while avoiding the drawbacks of providing it on all electrodes, thereby enabling device size reduction without increasing propagation loss.
2Object-affected harmful factors
If the piezoelectric layer thickness d/p is increased to improve acoustic wave confinement, then acoustic wave leakage is reduced, but the Q value decreases and resonance characteristics deteriorate
Solution Approach 1:
The patent optimizes the d/p ratio (piezoelectric layer thickness to electrode finger center distance) to be 0.2 or less, which is a specific parameter change that balances acoustic wave confinement with maintaining high Q value. This parameter optimization, combined with the selective load film placement, achieves both reduced acoustic wave leakage and preserved resonance characteristics.
3Ease of manufacture
If the load film extends over all electrode fingers including outermost ones, then manufacturing is simplified, but acoustic wave leakage occurs and performance deteriorates
Solution Approach 1:
The load film is selectively provided only on inner electrode fingers, creating a differentiated structure where outermost fingers remain without load film. This local quality approach, while slightly increasing manufacturing complexity compared to uniform coverage, effectively prevents acoustic wave leakage at the edges while maintaining overall manufacturing feasibility through standardized fabrication processes.
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 acoustic wave leakage, enhances resonance characteristics, and maintains a high Q value while allowing for size reduction without increasing propagation loss.
Implementation Method 1
a piezoelectric layer including a first main surface and a second main surface opposite to the first main surface in a first direction, an IDT electrode on at least one of the first main surface or the second main surface of the piezoelectric layer
Implementation Method 2
a support facing the second main surface of the piezoelectric layer, and including an acoustic reflection portion at a portion closer to the second main surface of the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer including first and second main surfaces, an IDT electrode on one of the first and second main surfaces, and including electrode fingers, a support facing the second main surface, and including an acoustic reflection portion at a portion closer to the second main surface of the piezoelectric layer, and a load film extending over a region that overlaps, when viewed in plan in the first direction, at least electrode fingers from a fourth one of the electrode fingers from a first outer end in an arrangement direction to a fourth one of the electrode fingers from a second outer end in the arrangement direction. d/p is less than or equal to about 0.5 where d denotes a thickness of the piezoelectric layer, and p denotes a center-to-center distance between adjacent two of the electrode fingers.