Elastic Wave Resonator Electrode Structure for Low-Side Attenuation
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Solution Overview
Problem
Existing boundary elastic wave filters using longitudinally-coupled resonators struggle to achieve sufficient attenuation at frequencies lower than the passband while suppressing transverse-mode ripples, which limits their effectiveness as diversity or duplexer filters.
Innovation Solution
The elastic wave device incorporates a configuration with narrow-pitch electrode finger portions and normally-shaped adjacent electrode finger portions, with apodization applied to all other portions, maintaining consistent finger overlap width and a specific ratio of normally-shaped to total electrode fingers, enhancing frequency characteristics and attenuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If apodization is applied to all portions of IDT electrodes to suppress transverse-mode ripples, then passband characteristics are improved, but attenuation at frequencies lower than the passband becomes insufficient
Solution Approach 1:
The patent applies different electrode configurations to different regions of the IDT: the central portion uses apodization to suppress transverse-mode ripples and improve passband characteristics, while the edge portions use normally-shaped electrode fingers with narrow pitch to provide strong attenuation at frequencies below the passband. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Volume of moving object
If the cross width of IDT electrodes is narrowed to downsize the filter, then device size is reduced, but transverse-mode ripples appear in the passband
Solution Approach 1:
The patent maintains narrow electrode cross width for overall filter downsizing but introduces narrow-pitch electrode finger portions at the edges with normal shaping to specifically counteract transverse-mode ripples. This localized structural adjustment allows the filter to remain compact while preventing ripple formation in the passband.
3Volume of moving object
If boundary elastic waves are used instead of surface elastic waves to reduce filter size, then device size is reduced, but transverse-mode ripples enter the passband due to stronger wave confinement
Solution Approach 1:
The patent uses boundary elastic waves for filter miniaturization but introduces normally-shaped electrode finger portions with narrow pitch at the IDT edges to locally compensate for the stronger confinement effect of boundary waves. This localized structural feature suppresses transverse-mode ripples that would otherwise enter the passband, resolving the contradiction between size reduction and passband quality.
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 suppresses transverse-mode ripples and improves passband characteristics, achieving significant attenuations of 43 dB or more at frequencies lower than the passband, ensuring better frequency performance.
Implementation Method 1
a piezoelectric material; a first interdigital transducer (IDT) electrode disposed on the piezoelectric material
Implementation Method 2
The present invention relates to an elastic wave device using boundary elastic waves or surface elastic waves
Implementation Method 3
In addition to surface elastic waves, boundary elastic waves have been used as elastic waves
Data Source
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AI summary
A longitudinally-coupled resonator-type elastic wave device (10) includes first to third IDT electrodes (11-13) disposed on a piezoelectric material and first and second reflectors (14,15) disposed in elastic wave propagation directions. Each of any two IDT electrodes (12,11/11,13) adjacent to each other in the elastic wave propagation directions, of the first to third IDT electrodes, has a narrower-pitch electrode finger portion (121A,112A,113A,131A) at an edge thereof adjacent to the other IDT electrode. Most portions of the first to third IDT electrodes (11-13) are apodized, and the narrower-pitch electrode finger portions (121A,112A,113A,131A) and the electrode finger portions (121B,112B,113B,131B) adjacent thereto are normally shaped.