Rayleigh Wave Filter Electrode Ratio for Stable Frequency Drift
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Solution Overview
Problem
Elastic wave devices utilizing Rayleigh waves and a lithium niobate substrate with a molybdenum interdigital transducer electrode experience frequency-temperature characteristic degradation due to manufacturing variations in the electrode finger line width, affecting filter performance, especially in frequency bands near the pass band.
Innovation Solution
The elastic wave device incorporates a piezoelectric substrate made of lithium niobate with an interdigital transducer electrode having a molybdenum layer and a silicon oxide dielectric film, with a duty ratio between 0.55 and 0.75, and optionally includes an aluminum electrode layer to reduce electric resistance and manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric film is provided on a lithium niobate substrate with a molybdenum interdigital transducer electrode to improve frequency-temperature characteristics, then frequency-temperature characteristics are improved, but manufacturing variations occur in the electrode finger line width causing frequency variations
Solution Approach 1:
The patent changes the duty ratio parameter of the interdigital transducer electrode from conventional values to specifically 0.55 or higher. This parameter change compensates for the frequency variations caused by manufacturing tolerances in the electrode finger line width, thereby maintaining stable frequency characteristics while preserving the frequency-temperature performance provided by the dielectric film and lithium niobate substrate combination.
2Reliability
If the duty ratio of the interdigital transducer electrode is increased to reduce frequency variations, then frequency stability is improved, but the electrode structure becomes more complex
Solution Approach 1:
The patent achieves frequency stability by adjusting the duty ratio parameter to 0.55 or higher, which optimizes the electrode geometry to be less sensitive to manufacturing variations. This parameter optimization improves frequency stability without requiring additional structural elements or complex multi-layer electrode configurations, thus avoiding increased device complexity.
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 frequency variations and improves frequency-temperature characteristics, enhancing the yield and performance of the elastic wave device, particularly in duplexers and communication apparatuses by maintaining frequency stability across varying conditions.
Implementation Method 1
Rayleigh waves propagating through the piezoelectric substrate are utilized
Implementation Method 2
a piezoelectric substrate that includes a first main surface and a second main surface which face each other; an interdigital transducer electrode that is provided on the first main surface of the piezoelectric substrate
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate that includes first and second main surfaces which face each other, an interdigital transducer electrode that is provided on the first main surface of the piezoelectric substrate and includes a first electrode layer containing molybdenum as a main component, and a dielectric film that is provided on the piezoelectric substrate and covers the interdigital transducer electrode. The piezoelectric substrate is made of lithium niobate. The dielectric film is made of silicon oxide. The elastic wave device utilizes Rayleigh waves propagating through the piezoelectric substrate. The duty ratio of the interdigital transducer electrode is equal to or more than about 0.55 and less than or equal to about 0.75.