Acoustic Wave Device Grating Finger Geometry for Leakage Suppression
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Solution Overview
Problem
Existing acoustic wave devices with IDTs on piezoelectric substrates face challenges in minimizing insertion loss due to acoustic wave leakage in the aperture direction, which is not sufficiently suppressed by conventional gratings on both sides of the IDT.
Innovation Solution
The acoustic wave device incorporates gratings on both sides of the IDT with a concave or convex slowness surface, featuring a larger duty ratio, thickness, or pitch of electrode fingers compared to the IDT, and connected via bended regions, to align the resonant frequency and velocity characteristics, thereby reducing wave leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional gratings are provided on both sides of the IDT, then acoustic wave leakage is partially suppressed, but insertion loss is not sufficiently reduced
Solution Approach 1:
The patent applies parameter changes by modifying the duty ratio, thickness, or pitch of the grating electrode fingers relative to the IDT electrode fingers. Specifically, the grating duty ratio is set to be larger than the IDT duty ratio, or the grating electrode thickness is larger, or the pitch is smaller, which changes the acoustic impedance and velocity characteristics to better suppress wave leakage and reduce insertion loss.
Solution Approach 2:
The patent utilizes the concave shape of the slowness surface of the acoustic wave in the main propagation direction to design the grating structure. This curvature characteristic of the slowness surface is exploited to match the velocity characteristics between the IDT and grating regions, improving the suppression of acoustic wave leakage.
2Loss of energy
If the grating electrode fingers have different duty ratio, thickness, or pitch compared to IDT, then velocity characteristics are matched and wave leakage is suppressed, but device complexity increases
Solution Approach 1:
The patent applies local quality by making the grating electrode fingers have different properties (larger duty ratio, greater thickness, or smaller pitch) specifically in the grating regions compared to the IDT region. This localized differentiation allows velocity characteristic matching for wave leakage suppression without making the entire device complex, as only specific regions are modified.
3Loss of energy
If the resonant frequency of gratings is made substantially the same as IDT, then energy confinement is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent achieves resonant frequency matching between the IDT and gratings by adjusting parameters such as the grating electrode finger dimensions, pitch, or added film thickness. By carefully controlling these parameters during manufacturing, the resonant frequencies are made substantially equal, which improves energy confinement within the IDT area while providing clear fabrication guidelines.
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 acoustic wave leakage, leading to reduced insertion loss and improved performance by matching the velocity characteristics between the IDT and grating regions, ensuring energy confinement within the IDT area.
Implementation Method 1
an IDT that is provided on a piezoelectric substrate and excites an acoustic wave
Implementation Method 2
gratings that are provided on both sides of the IDT in an aperture direction thereof... effectively suppresses acoustic wave leakage... matching the velocity characteristics between the IDT and grating regions, ensuring energy confinement within the IDT area
Data Source
AI summary
An acoustic wave device includes: an IDT provided on a piezoelectric substrate; and gratings provided on both sides of the IDT, wherein: a slowness surface of an acoustic wave has a concave shape; a duty ratio of electrode fingers of the gratings is larger than that of the electrode fingers of the IDT, or a thickness of the electrode fingers of the gratings is larger than that of the electrode fingers of the IDT, or a thickness of an added film provided on the electrode fingers of the gratings is larger than that of an added film provided on the electrode fingers of the IDT; a pitch of the electrode fingers of the gratings is smaller than that of the electrode fingers of the IDT; and a resonant frequency of the gratings is substantially the same as that of the IDT.