Acoustic Wave Filter Electrode Thickness for High-Side Attenuation
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Solution Overview
Problem
Frequency variable type acoustic wave devices face deteriorated attenuation characteristics on the higher-frequency side of the pass band due to higher-order mode resonance, which is exacerbated by the impedance increase in parallel arm resonance circuits when varying frequencies, and the need for wider resonance bandwidths.
Innovation Solution
The acoustic wave device incorporates a configuration with a serial arm resonance circuit and a parallel arm resonance circuit, where the parallel arm circuit includes a second acoustic wave resonator with thicker electrode fingers and a frequency variable circuit, such as a capacitance element, to adjust the pass band, ensuring the higher-order mode resonance frequency aligns closer to the fundamental mode, thereby improving attenuation characteristics on the higher-frequency side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the resonance band width is widened by using an acoustic wave resonator with IDT electrode, then the frequency variable width is secured, but the attenuation characteristics on the higher-frequency side deteriorate due to higher-order mode resonance
Solution Approach 1:
The patent applies local quality by making the electrode finger film thickness of the second acoustic wave resonator (parallel arm) different from that of the first acoustic wave resonator (serial arm). Specifically, the second resonator has a larger electrode finger film thickness, which locally modifies its acoustic characteristics to push the higher-order mode resonance frequency higher, thereby improving attenuation in the higher-frequency region while maintaining the required frequency variable width.
Solution Approach 2:
The patent changes the physical parameter of electrode finger film thickness to resolve the contradiction. By increasing the film thickness of the second acoustic wave resonator relative to the first, the higher-order mode resonance frequency is shifted to a higher frequency region, which improves attenuation characteristics on the higher-frequency side while preserving the fundamental mode resonance band width needed for frequency variable operation.
2Adaptability or versatility
If the impedance of the parallel arm resonance circuit is increased to vary frequency, then the frequency variable function is achieved, but the attenuation characteristics deteriorate
Solution Approach 1:
The patent applies local quality by differentiating the electrode finger film thickness between the first and second acoustic wave resonators. The second resonator in the parallel arm has a larger film thickness, which locally enhances its ability to provide frequency variable function through impedance change while simultaneously improving attenuation characteristics by pushing higher-order mode resonances to higher frequencies.
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 enhances attenuation characteristics on the higher-frequency side of the pass band by aligning the higher-order mode resonance frequency with the fundamental mode, reducing insertion loss and steepening the attenuation slope, while allowing for miniaturization and frequency tuning.
Implementation Method 1
an IDT electrode constituted of a plurality of electrode fingers formed on a substrate at least part of which has piezoelectricity
Data Source
AI summary
A variable filter includes a serial arm resonator and a parallel arm resonance circuit, the parallel arm resonance circuit includes a parallel arm resonator and a capacitance element connected to the parallel arm resonator, the serial arm resonator and the parallel arm resonator respectively include IDT electrodes each formed of a plurality of electrode fingers formed on a substrate, and a film thickness of the plurality of electrode fingers of the parallel arm resonator is larger than a film thickness of the plurality of electrode fingers of the serial arm resonator.