Elastic Wave IDT Recess Structure for Spurious Mode Suppression
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Solution Overview
Problem
Existing elastic wave devices using a piston mode struggle to sufficiently reduce transverse mode spurious emission and minimize size due to limitations in acoustic velocity differences between edge and center regions, which are not adequately addressed by widening electrode finger widths.
Innovation Solution
The elastic wave device incorporates a piezoelectric substrate with interdigital transducer electrodes, featuring recess portions in the edge regions where the electrode fingers are disposed, made of materials with lower Young's modulus and higher density than the substrate, and grooves with specific cross-sectional shapes to enhance acoustic velocity differences between edge and center regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the widths of the first and second electrode fingers are increased in the edge regions, then the acoustic velocities in the edge regions are lowered, but the device size cannot be reduced and the acoustic velocity difference is not sufficiently achieved
Solution Approach 1:
The patent applies local quality by creating distinct regions with different acoustic velocity characteristics. The edge regions are specifically modified with recess portions and different electrode finger widths compared to the center region, generating localized acoustic velocity differences (V3 > V1 > V2) that suppress transverse mode spurious emission without requiring overall device enlargement
Solution Approach 2:
The patent introduces a vertical dimension by forming recess portions in the piezoelectric substrate at the edge regions. This dimensional change allows the electrode fingers to be positioned at different depths, creating acoustic velocity differences through structural variation rather than simply increasing lateral dimensions, thus achieving the acoustic velocity difference while maintaining compact device size
2Reliability
If the widths of the first and second electrode fingers are increased in the edge regions, then the acoustic velocities in the edge regions are lowered, but it is difficult to reduce the dimension in the elastic wave propagation direction
Solution Approach 1:
The patent modifies only the edge regions with specific electrode finger width variations and recess portions, while keeping the center region unchanged. This localized modification achieves the required acoustic velocity difference without extending the overall device length in the elastic wave propagation direction
Solution Approach 2:
By forming recess portions that extend in the elastic wave propagation direction, the patent utilizes the vertical dimension to create acoustic velocity differences. This allows the device to achieve the required acoustic performance without increasing the lateral dimensions, effectively reducing the device footprint
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 transverse mode spurious emission and allows for a significant reduction in device size while maintaining or improving acoustic performance, with acoustic velocity differences between edge and center regions ranging from 200 to 340 m/sec, thereby minimizing unnecessary wave propagation.
Implementation Method 1
a piezoelectric substrate, and an interdigital transducer (IDT) electrode provided on the piezoelectric substrate
Implementation Method 2
Acoustic velocities in the first and second edge regions are made to be lower than an acoustic velocity in the center region. Acoustic velocities in regions in outer side portions of the intersection region are made to be higher than the acoustic velocities of the first and second edge regions
Data Source
AI summary
An elastic wave device includes an IDT electrode on a piezoelectric substrate, in which the IDT electrode includes first electrode fingers and second electrode fingers, where a portion in which the first electrode fingers and the second electrode fingers overlap with each other in an elastic wave propagation direction is defined as an intersection region including in a direction in which the first and second electrode fingers extend, a center region located on a center side and first and second edge regions respectively located on both sides of the center region, in the first and second edge regions, grooves defining recess portions are provided on the piezoelectric substrate, the first and second electrode fingers are provided inside of the grooves as the recess portions and are disposed on the piezoelectric substrate in the grooves.