IDT Electrode Layout for Transverse Mode Suppression in Acoustic Waves
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Solution Overview
Problem
Acoustic wave devices with multilayer structures face challenges in suppressing transverse modes due to higher acoustic velocities at the bases or tips of electrode fingers, making it difficult to establish a piston mode and sufficiently reduce ripple.
Innovation Solution
The acoustic wave device incorporates a high-acoustic-velocity material layer, a low-acoustic-velocity film, and a piezoelectric layer made of lithium tantalate, with an IDT electrode design featuring wider edge regions and a specific duty ratio range of 0.62 to 0.73, which reduces acoustic velocity in these regions, establishing a piston mode and minimizing transverse mode ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the duty ratio of wide portions is set to 0.6 to 0.9 as disclosed in prior art, then the acoustic velocity in electrode fingers is reduced, but the acoustic velocity at the bases or tips of electrode fingers becomes higher, making it difficult to establish a piston mode and sufficiently suppress transverse mode
Solution Approach 1:
The patent applies local quality by differentiating the duty ratio settings across different regions of the IDT electrode. Specifically, the central region has a duty ratio of 0.6 to 0.9, while the edge regions have a duty ratio of 0.3 to 0.5. This spatial variation in duty ratio creates different acoustic velocity characteristics in different regions, allowing the central region to suppress transverse mode while the edge regions maintain appropriate acoustic velocity for piston mode establishment.
Solution Approach 2:
The patent segments the IDT electrode into distinct regions: a central region and edge regions. By applying different duty ratio parameters to these segmented regions, the patent addresses the contradiction between transverse mode suppression (requiring high duty ratio) and acoustic velocity control at bases/tips (requiring low duty ratio). The segmentation allows each region to optimize its duty ratio for its specific function.
2Reliability
If a multilayer structure with high-acoustic-velocity support substrate and low-acoustic-velocity film is used, then the acoustic wave propagation characteristics are improved, but the acoustic velocity at electrode finger bases or tips increases, preventing effective piston mode establishment
Solution Approach 1:
The patent combines the multilayer structure with local quality principle by applying region-specific duty ratios. The multilayer structure (high-acoustic-velocity support substrate + low-acoustic-velocity film + piezoelectric layer) provides overall acoustic wave propagation improvement, while the locally varied duty ratio (0.6-0.9 in central region, 0.3-0.5 in edge regions) compensates for the increased acoustic velocity at electrode finger bases/tips, enabling piston mode establishment despite the multilayer structure.
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 transverse mode ripple, enhancing the reliability of the piston mode and improving the acoustic wave device's performance by maintaining low acoustic velocities in edge regions.
Implementation Method 1
a piezoelectric layer on the low-acoustic-velocity film and made of lithium tantalate
Implementation Method 2
An acoustic velocity of bulk waves propagating through the high-acoustic-velocity material layer is higher than an acoustic velocity of acoustic waves propagating through the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a high-acoustic-velocity film, a low-acoustic-velocity film, a piezoelectric layer including lithium tantalate, and an IDT electrode on the piezoelectric layer. The IDT electrode includes first and second busbars and first and second electrode fingers. An intersecting region is a portion where the first and second electrode fingers overlap in an acoustic wave propagation direction. The intersecting region includes a central region and first and second edge regions. The IDT electrode includes first and second gap regions outside the first and second edge regions. The first and second electrode fingers are wider in the first and second edge regions than in the central region. A duty ratio in the first and second edge regions is from about 0.62 to about 0.73.