Elastic wave device, high-frequency front-end circuit, and communication apparatus
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Solution Overview
Problem
Existing elastic wave devices with interdigital transducer electrodes suffer from degraded resonance and filter characteristics due to insufficient reduction of transverse-mode ripples, which are not adequately addressed by differences in acoustic velocity in central and outer edge regions.
Innovation Solution
The elastic wave device incorporates a high-acoustic-velocity member, a low-acoustic-velocity film, and a piezoelectric film, with an interdigital transducer electrode featuring thicker electrode fingers in inner edge regions made of metals like Cu, Ta, or Au, and a duty ratio adjustment to reduce transverse-mode ripples and enhance resonance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of electrode fingers in inner edge regions is increased to reduce transverse-mode ripples, then the resonance characteristics improve, but the device complexity increases due to multiple region classifications and thickness variations
Solution Approach 1:
The electrode fingers are designed with different thicknesses in different regions: the central region has a first thickness, while the inner edge regions have a second thickness greater than the first. This local variation in thickness creates different acoustic velocities in different regions, which suppresses transverse-mode ripples and improves resonance characteristics without requiring complete redesign of the entire electrode structure.
2Reliability
If multiple regions with different acoustic velocities are created to suppress transverse-mode ripples, then the filter characteristics improve, but the manufacturing precision requirements increase due to precise thickness control needs
Solution Approach 1:
The invention changes the thickness parameter of electrode fingers in inner edge regions to create different acoustic velocity zones. By specifically increasing the thickness in inner edge regions (second thickness > first thickness), the acoustic velocity distribution is modified to suppress transverse-mode ripples. This parameter change approach provides a clear manufacturing guideline that balances performance improvement with fabrication feasibility.
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 ripples, improving resonance and filter characteristics by matching the excitation profile with the displacement profile, thereby maintaining high-frequency performance.
Implementation Method 1
a piezoelectric film stacked on the low-acoustic-velocity film and made of lithium tantalate
Implementation Method 2
the acoustic velocity in the inner edge regions is lower than that in the central region
Data Source
AI summary
An elastic wave device includes a high-acoustic-velocity member, a low-acoustic-velocity film, a piezoelectric film, and am interdigital transducer electrode stacked in this order. The interdigital transducer electrode includes an intersecting region and outer edge regions. The intersecting region includes a central region located in the middle of the intersecting region in the direction in which electrode fingers extend and the inner edge regions located at the respective outer side portions of the central region. The electrode fingers in the inner edge regions have a larger thickness than in the central region. Each electrode finger has an incrased thickness portion. The increased thickness portion is made of a metal having a density d of about 5.5 g/cm3 or more and has a film thickenss equal to or smaller than a wavelength-normalized film thickness represented by T (%)=−0.1458d+4.8654.