Interdigital Electrode Mass Loading for Transverse-Mode Spurious Control
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Solution Overview
Problem
Elastic wave devices suffer from transverse-mode spurious responses due to the width of low-acoustic-velocity regions, which affect the quality factor and filter characteristics, particularly in the vicinity of the resonant frequency.
Innovation Solution
The design incorporates a piezoelectric substrate with a high-acoustic-velocity member layer and a piezoelectric layer, where the interdigital transducer electrode features mass-adding films with a specific wavelength-normalized film thickness and density product, reducing the effective coupling coefficient in transverse modes and minimizing spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the width of low-acoustic-velocity regions is increased to reduce transverse-mode spurious responses, then the quality factor improves, but the filter characteristics deteriorate due to increased sensitivity to manufacturing variations
Solution Approach 1:
The patent applies parameter changes by precisely controlling the film thickness of mass-adding films in low-acoustic-velocity regions. By optimizing the thickness parameter within a specific range (0.5-2.0 μm), the invention reduces transverse-mode spurious responses while maintaining manufacturing feasibility and filter characteristics, thereby resolving the contradiction between quality factor improvement and manufacturing precision requirements.
2Object-generated harmful factors
If mass-adding films with larger film thickness are used in low-acoustic-velocity regions, then transverse-mode spurious responses are reduced, but the device complexity increases
Solution Approach 1:
The patent applies local quality by selectively adding mass-adding films only in the low-acoustic-velocity regions (edge regions) of the interdigital transducer electrode, rather than uniformly across the entire electrode. This localized approach reduces transverse-mode spurious responses while minimizing the increase in device complexity, as the mass-adding films are applied only where needed to suppress spurious responses.
3Object-generated harmful factors
If the product of wavelength-normalized film thickness and density of mass-adding films is optimized, then transverse-mode spurious responses are reduced, but the ease of manufacture decreases
Solution Approach 1:
The patent applies parameter changes by establishing a specific range for the product of wavelength-normalized film thickness and density of mass-adding films. By optimizing this parameter within defined limits, the invention reduces transverse-mode spurious responses while maintaining ease of manufacture, as the optimized parameters fall within practical deposition capabilities and do not require extreme precision beyond standard manufacturing tolerances.
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 spurious responses, improving the quality factor and filter characteristics by confining elastic wave energy to the piezoelectric layer and maintaining the acoustic velocity gradient.
Implementation Method 1
the first low-acoustic-velocity region and the second low-acoustic-velocity region include mass-adding films disposed on the first electrode fingers and the second electrode fingers
Implementation Method 2
the piezoelectric substrate including a piezoelectric layer and a high-acoustic-velocity member layer
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate and an interdigital transducer electrode on the piezoelectric substrate, the piezoelectric substrate including a piezoelectric layer and a high-acoustic-velocity member layer, the piezoelectric layer being stacked on the high-acoustic-velocity member layer. The piezoelectric layer is made of lithium tantalate. Denoting an elastic wave propagation direction as a first direction, and a direction perpendicular or substantially perpendicular to the first direction as a second direction, a central region, low-acoustic-velocity regions, and high-acoustic-velocity regions are provided in the interdigital transducer electrode in the second direction. The low-acoustic-velocity regions include mass-adding films on electrode fingers. Denoting a film thickness normalized to a wavelength determined by the electrode finger pitch of the interdigital transducer electrode as a wavelength-normalized film thickness (%), a product of the wavelength-normalized film thickness of the mass-adding films and the density (g/cm3) of the mass-adding films is about 13.4631 or less.