Acoustic Wave IDT Layout for Transverse Mode Ripple Suppression
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Solution Overview
Problem
Acoustic wave devices using a piston mode struggle to sufficiently suppress transverse modes due to asymmetrical displacement distribution caused by an inclined crystal axis in the piezoelectric substrate, leading to difficulties in reducing transverse mode ripples.
Innovation Solution
An acoustic wave device design with a piezoelectric layer having a crystal axis inclined relative to the thickness direction, featuring asymmetrical first and second low-acoustic-velocity regions created by mass-adding films on the electrode fingers, which match the transverse mode displacement distribution, effectively reducing or preventing transverse modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a piezoelectric substrate with an inclined crystal axis is used to achieve piston mode operation, then acoustic wave generation is improved, but transverse mode suppression deteriorates due to asymmetrical displacement distribution
Solution Approach 1:
The patent applies asymmetry by creating unequal low-acoustic-velocity regions on opposite sides of the IDT electrode. Specifically, the first low-acoustic-velocity region has a different width than the second low-acoustic-velocity region, which compensates for the asymmetrical displacement distribution caused by the inclined crystal axis. This asymmetrical configuration of mass-adding films allows the device to maintain piston mode operation while suppressing transverse modes that would otherwise be generated by the inherent asymmetry of the crystal structure.
Solution Approach 2:
The patent implements local quality by selectively adding mass only in specific regions where needed. Low-acoustic-velocity regions are created by providing mass-adding films (such as dielectric films) only in the first and second low-acoustic-velocity regions adjacent to the IDT electrode, rather than uniformly across the entire device. This localized mass addition modifies the acoustic velocity distribution precisely where required to suppress transverse modes without affecting other regions of the device.
2Shape
If symmetrical low-acoustic-velocity regions are provided on both sides of the IDT electrode, then device symmetry is maintained, but transverse mode suppression is insufficient due to asymmetrical displacement distribution
Solution Approach 1:
The patent deliberately introduces asymmetry into the low-acoustic-velocity region configuration to counterbalance the asymmetrical displacement distribution inherent in piezoelectric substrates with inclined crystal axes. By making the first low-acoustic-velocity region have a different width than the second low-acoustic-velocity region, the overall asymmetry of the system is adjusted to achieve effective transverse mode suppression, demonstrating that intentional asymmetry can resolve problems caused by unwanted asymmetry.
Solution Approach 2:
The patent changes the parameters of the low-acoustic-velocity regions, specifically their widths, to optimize transverse mode suppression. The first low-acoustic-velocity region is designed with a first width and the second low-acoustic-velocity region with a second width that differs from the first width. This parameter variation allows precise control over the acoustic field distribution to match and counteract the asymmetrical displacement pattern generated by the inclined crystal axis.
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
The design effectively reduces or prevents transverse mode ripples by utilizing asymmetrical low-acoustic-velocity regions that align with the displacement distribution, improving the performance of acoustic wave devices using a piston mode.
Implementation Method 1
an acoustic wave device includes a piezoelectric layer including a crystal axis
Implementation Method 2
these edge regions are located at both ends of the electrode fingers in the extension direction of the electrode fingers inside the region where adjacent electrode fingers of the interdigital transducer (IDT) electrode overlap in the propagation direction of the acoustic waves. The acoustic velocity is reduced in the edge regions by increasing the widths of the electrode fingers in the edge regions or by providing dielectric films for adding extra mass on the electrode fingers in the edge regions
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate including a crystal axis and an IDT electrode. When an acoustic wave propagation direction is a first direction and a direction perpendicular to the first direction is a second direction, the crystal axis of the piezoelectric substrate is inclined toward the second direction with respect to the thickness direction. The IDT electrode includes first and second electrode fingers interdigitated with each other. The portion where the first and second electrode fingers overlap in the first direction is a crossing region. The crossing region includes a center region that is centrally located in the second direction and first and second low-acoustic-velocity regions that are located on both sides of the center region in the second direction and in which the acoustic velocity is lower than the acoustic velocity in the center region. The first and second low-acoustic-velocity regions are asymmetrical.