Acoustic Wave Ladder Filter Edge Capacitance for Narrower Bandwidth
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Solution Overview
Problem
Existing acoustic wave devices and ladder filters face challenges in reducing fractional band width and increasing steepness, particularly in resonators and band-pass filters.
Innovation Solution
The acoustic wave device incorporates a conductive layer on the piezoelectric layer to overlap with edge regions and busbars of the IDT electrode, creating a capacitance that reduces acoustic velocity and suppresses transverse modes, thereby reducing fractional band width and enhancing steepness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an acoustic velocity adjustment film is not laminated on the IDT electrode, then acoustic velocity can be adjusted with high accuracy and acoustic loss can be suppressed, but the fractional band width cannot be easily reduced
Solution Approach 1:
The IDT electrode overlap region is divided into three segments: a middle region and first and second edge regions. The acoustic velocity adjustment film is selectively laminated only on the first and second edge regions, not on the middle region. This segmentation allows different functional zones within the same electrode structure, enabling fractional band width reduction while preserving the acoustic velocity adjustment accuracy achieved by not covering the entire electrode area.
Solution Approach 2:
The acoustic velocity adjustment film is applied locally to specific regions (edge regions) rather than uniformly across the entire IDT electrode. This local quality approach allows the edge regions to have modified acoustic properties for band width control, while the middle region maintains its original acoustic characteristics for accurate velocity adjustment, thus resolving the contradiction between these two requirements.
2Loss of energy
If an acoustic velocity adjustment film is not laminated on the IDT electrode, then acoustic loss can be suppressed, but the band width cannot be reduced and steepness cannot be increased in band-pass filters
Solution Approach 1:
The overlap region is segmented into middle and edge regions with different film configurations. The acoustic velocity adjustment film is applied only to edge regions, suppressing acoustic loss in these areas while enabling band width reduction. The middle region remains film-free to maintain low acoustic loss, thus achieving both goals simultaneously.
Solution Approach 2:
Different regions of the IDT electrode are given different local properties: edge regions have the acoustic velocity adjustment film for loss suppression and band width control, while the middle region remains unchanged for maintaining low acoustic loss. This local differentiation resolves the contradiction between acoustic loss suppression and band width reduction capability.
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 effectively reduces fractional band width and increases the steepness of filter characteristics in both resonators and band-pass filters.
Implementation Method 1
The acoustic wave device incorporates a conductive layer on the piezoelectric layer to overlap with edge regions and busbars of the IDT electrode, creating a capacitance that reduces acoustic velocity and suppresses transverse modes
Implementation Method 2
a piezoelectric layer provided directly or indirectly on the support substrate, the piezoelectric layer including a first main surface and a second main surface that face away from each other
Data Source
AI summary
In an acoustic wave device, a piezoelectric layer is provided directly or indirectly on a support substrate, an IDT electrode is provided on the piezoelectric layer, an overlap region includes a middle region and first and second edge regions, and first and second conductive layers are provided on a second main surface of the piezoelectric layer to overlap at least some portions of the first and second edge regions in plan view and at least some portions of first and second busbars in plan view.