LiNbO3 Elastic Wave Filter Structure for Unwanted Wave Suppression
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Solution Overview
Problem
Existing elastic wave devices face challenges in reducing size while maintaining bandpass characteristics and minimizing unwanted waves, as increasing electrode thickness leads to larger fractional bandwidth of unwanted waves.
Innovation Solution
The elastic wave device incorporates a piezoelectric substrate made of LiNbO3 with interdigital transducer (IDT) electrodes and a silicon oxide dielectric film, using specific metal films (Pt, Cu, Mo, Au, W, Ta) and Euler angles to optimize the thickness and dielectric film combinations, reducing unwanted waves and allowing for size reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the electrode thickness is increased to reduce device size, then the device size is reduced, but the fractional bandwidth of unwanted waves increases
Solution Approach 1:
The patent employs a composite electrode structure consisting of multiple metal films with different properties (e.g., Pt, Cu, Mo, Au, W, Ta) deposited in specific thickness combinations. This composite approach allows optimization of both size and unwanted wave suppression by leveraging the distinct acoustic and electrical characteristics of each metal material.
Solution Approach 2:
The patent systematically varies critical parameters including electrode thickness (hm/λ), dielectric film thickness (hs/λ), and Euler angles (φ, θ, ψ) of the LiNbO3 substrate to achieve optimal performance. By adjusting these parameters within specific ranges, the device achieves size reduction while maintaining control over unwanted wave fractional bandwidth.
2Volume of moving object
If the electrode thickness is increased to reduce device size, then the device size is reduced, but the bandpass characteristics are degraded
Solution Approach 1:
The multi-layer metal film composite structure enables independent optimization of different functional requirements: some layers contribute to size reduction while others maintain electrical conductivity and filter characteristics, thereby preserving bandpass performance despite overall thickness increases.
Solution Approach 2:
The dielectric film made of silicon oxide serves as an intermediary layer between the piezoelectric substrate and the metal electrode films. This intermediate dielectric layer decouples the mechanical stress effects, allowing the electrode thickness to be increased for size reduction while the dielectric layer protects the bandpass characteristics from degradation.
3Manufacturing precision
If different metal materials are used for the first metal film, then the thickness can be optimized, but the material selection complexity increases
Solution Approach 1:
The patent provides specific thickness ranges (hm/λ) for each metal material option (Pt: 6.5-25%, Cu: 13-25%, Mo: 15.5-25%, Au: 6.5-25%, W: 7.5-25%, Ta: 7-25%). These standardized parameter ranges simplify the manufacturing process by providing clear fabrication targets, reducing the complexity of material selection despite offering multiple material choices.
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 enables the elastic wave device to be significantly reduced in size with minimized unwanted waves, maintaining effective bandpass characteristics and high productivity.
Implementation Method 1
a piezoelectric substrate made of LiNbO3; interdigital transducer (IDT) electrodes on the piezoelectric substrate
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate made of LiNbO3, interdigital transducer electrodes on the piezoelectric substrate, and a first dielectric film provided on the piezoelectric substrate and the first dielectric film to cover the IDT electrodes and made of a silicon oxide. The IDT electrodes include a first metal film made of one metal selected from Pt, Cu, Mo, Au, W, and Ta. The Euler angles (ϕ, θ, ψ) of the piezoelectric substrate are (0±5°, −90°≤θ≤−70°, 0°±5°). The metal for the first metal film and the thickness hm/λ (%) match any of the combinations as follows:Metal for the first metal filmThickness hm/λ (%) of the first metal filmPt6.5 ≤ hm/λ≤ 25Cu 13 ≤ hm/λ≤ 25Mo15.5 ≤ hm/λ≤ 25 Au6.5 ≤ hm/λ≤ 25W7.5 ≤ hm/λ≤ 25Ta 7 ≤ hm/λ≤ 25.