Acoustic Wave Filter Electrode Layout for Spurious Wave Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Acoustic wave devices using bulk waves in a thickness shear mode often experience deterioration in filter characteristics due to the generation of unnecessary waves, such as plate waves and harmonic waves, which affect their performance.
Innovation Solution
The acoustic wave device incorporates a support substrate with a piezoelectric layer, IDT electrodes, and mass addition films with varying widths on the electrode fingers, where the thickness of the piezoelectric layer and the center-to-center distance between electrode fingers are optimized to reduce or prevent unnecessary waves by dispersing their frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a piezoelectric layer with IDT electrodes is used to generate bulk waves in thickness shear mode, then acoustic wave generation is achieved, but unnecessary waves such as plate waves and harmonic waves are generated causing filter characteristic deterioration
Solution Approach 1:
The patent applies local quality by making the mass addition films have different widths in the electrode finger extending direction. Specifically, the mass addition films have a first width in a first region and a second width in a second region, with the first width being different from the second width. This local variation in mass distribution creates different acoustic impedances in different regions, which selectively suppresses unnecessary waves (plate waves and harmonic waves) while maintaining the desired bulk wave generation in thickness shear mode.
Solution Approach 2:
The patent changes the physical parameter of the mass addition films by varying their width dimension. The mass addition films have different widths (first width vs. second width) in different regions along the electrode finger extending direction. This parameter change in mass distribution modifies the acoustic characteristics of the piezoelectric layer, enabling suppression of spurious modes while maintaining efficient bulk wave generation.
2Ease of manufacture
If uniform mass addition films are provided on all electrode fingers, then manufacturing is simplified, but unnecessary waves cannot be effectively suppressed
Solution Approach 1:
The patent applies segmentation by dividing the mass addition films into different regions along the electrode finger extending direction. The mass addition films are segmented into a first region with a first width and a second region with a second width. This segmentation creates spatially varying mass distribution that suppresses unnecessary waves. The segmentation can be implemented as alternating wide and narrow regions or as distinct zones, providing effective wave suppression while maintaining reasonable manufacturing complexity.
3Measurement precision
If the piezoelectric layer thickness and electrode finger spacing are optimized for bulk wave generation, then thickness shear mode excitation is improved, but plate wave and harmonic wave generation is enhanced
Solution Approach 1:
The patent applies asymmetry by creating an asymmetric mass distribution pattern through mass addition films with different widths in different regions. This asymmetric configuration disrupts the symmetry required for plate wave and harmonic wave generation, while maintaining the conditions for bulk wave excitation in thickness shear mode. The asymmetric mass loading creates different acoustic impedances that selectively filter out spurious modes.
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 unnecessary waves, improving the admittance frequency characteristics and maintaining the integrity of filter characteristics in acoustic wave devices.
Implementation Method 1
a piezoelectric layer on the support, an IDT electrode on the piezoelectric layer... An alternating current voltage is applied between the electrodes to excite the bulk wave in the thickness shear mode
Implementation Method 2
a plurality of mass addition films on the plurality of electrode fingers... a width of at least one of the plurality of mass addition films is different from a width of others of the plurality of mass addition films
Data Source
AI summary
An acoustic wave device includes a support including a support substrate, a piezoelectric layer on the support, an IDT electrode on the piezoelectric layer and including a pair of busbars and electrode fingers, and mass addition films on the electrode fingers. An acoustic reflection portion overlaps at least a portion of the IDT electrode. d/p is about 0.5 or smaller. A region in which adjacent electrode fingers overlap each other is a cross region including a central region, and first and second edge regions. At least a portion of the mass addition films overlap the central region. A width of at least one of the mass addition films is different from a width of other mass addition films.