IDT Electrode Gap Layout for Ripple-Suppressed Elastic Wave Filters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Elastic wave devices with piston mode suffer from ripples caused by higher-order transverse modes, which can degrade filter characteristics and loss for the dominant mode, especially when the gap between electrode fingers and busbars is longer than one wavelength.
Innovation Solution
The elastic wave device incorporates a piezoelectric body with interdigital transducer electrodes, where the gap lengths between electrode fingers and busbars are optimized to be between 0.62λ and 0.98λ, and the electrode fingers are thicker in low-acoustic-velocity sections to reduce ripples and maintain filter quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the gap between electrode fingers and busbars is made longer than one wavelength, then the device structure is simplified, but ripples caused by higher-order transverse modes increase
Solution Approach 1:
The patent applies local quality by creating low-acoustic-velocity sections at the end portions of the center region in the intersection of electrode fingers, while maintaining different gap lengths in different regions. The gap lengths are specifically controlled to be about 0.62λ to 0.98λ in these low-acoustic-velocity sections, which locally suppresses higher-order transverse modes without requiring the entire gap to be longer than one wavelength, thus reducing ripples while maintaining structural simplicity.
2Object-generated harmful factors
If the gap between electrode fingers and busbars is reduced to about 0.62λ-0.98λ, then ripples from higher-order transverse modes are reduced, but filter characteristics and loss for the dominant mode may be degraded
Solution Approach 1:
The patent applies local quality by creating low-acoustic-velocity sections at the end portions of the center region in the intersection of electrode fingers, while maintaining different gap lengths in different regions. The gap lengths are specifically controlled to be about 0.62λ to 0.98λ in these low-acoustic-velocity sections, which locally suppresses higher-order transverse modes without requiring the entire gap to be longer than one wavelength, thus reducing ripples while maintaining structural simplicity.
Solution Approach 2:
The patent segments the intersection of electrode fingers into a center region and low-acoustic-velocity sections at the end portions. This segmentation allows different gap length specifications (about 0.62λ-0.98λ) to be applied locally in the low-acoustic-velocity sections, rather than uniformly across the entire structure, enabling ripple reduction while preserving dominant mode characteristics.
3Object-generated harmful factors
If dielectric layers are added on electrode fingers to reduce ripples, then higher-order transverse modes are suppressed, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies parameter changes by controlling the gap lengths between electrode fingers and busbars to be about 0.62λ to 0.98λ in low-acoustic-velocity sections, and by making electrode fingers thicker in these sections. These parameter changes directly suppress higher-order transverse modes without adding dielectric layers or other complex structural elements, maintaining device simplicity while achieving ripple reduction.
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 ripples from higher-order transverse modes while preserving the filter characteristics and loss for the dominant mode, ensuring stable impedance ratios and reduced ripple sizes, allowing the device to function optimally as a filter.
Implementation Method 1
an elastic wave device includes a piezoelectric body and interdigital transducer electrodes on the piezoelectric body
Implementation Method 2
the acoustic velocity is lower than in the center region... where λ denotes the wavelength, which is determined by the finger pitch of the interdigital transducer electrodes
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate and IDT electrodes including first and second busbars and first and second electrode fingers. An intersection of the IDT electrodes includes a center region, and low-acoustic-velocity sections at both end portions of the center region in the direction in which the electrode fingers extend in the center region, sections in which the acoustic velocity is lower than in the center region. The length of the gap between the edge of the first electrode fingers and the second busbar and the length of the gap between the edge of the second electrode fingers and the first busbar are about 0.62λ or more and about 0.98λ or less, where λ denotes the wavelength, which is determined by the finger pitch of the IDT electrodes.