Elastic Wave Resonator Spuriousness Reduction via Local Quality
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Solution Overview
Problem
Conventional elastic wave resonators using lithium niobate substrates suffer from spuriousness in the transverse mode, leading to degraded filtering characteristics and increased size, particularly when apodization is employed, resulting in Q-value degradation, insertion loss, and attenuation issues.
Innovation Solution
The design incorporates a piezoelectric substrate with comb-shaped electrodes featuring a first and second overlapping region, where the second region has a greater electrode finger pitch and width, connected via oblique connection electrodes, and optionally includes a dummy region and a SiO2 thin film, to reduce spuriousness and improve temperature characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If apodization is used in the elastic wave resonator to suppress spuriousness, then spuriousness in the transverse mode is reduced, but the Q-value degrades and the device size increases
Solution Approach 1:
The patent applies local quality by creating two distinct overlapping regions with different characteristics: the first overlapping region has a larger overlapping width and smaller electrode finger pitch for high-Q operation, while the second overlapping region has a smaller overlapping width and larger electrode finger pitch for spuriousness suppression. This local differentiation allows each region to optimize for its specific function without compromising the other.
Solution Approach 2:
The comb-shaped electrode is segmented into multiple overlapping regions with different geometrical parameters. By dividing the electrode structure into distinct segments (first and second overlapping regions), the patent can independently control the acoustic wave generation in each segment, achieving both high Q-value and spuriousness reduction simultaneously.
2Object-generated harmful factors
If apodization is used in the elastic wave resonator to suppress spuriousness, then spuriousness in the transverse mode is reduced, but the device size increases
Solution Approach 1:
The patent uses local quality to concentrate the spuriousness suppression function in a specific localized region (the second overlapping region) rather than requiring uniform apodization across the entire electrode structure. This allows spuriousness reduction without proportionally increasing the overall device size.
Solution Approach 2:
The patent controls spuriousness by adjusting the electrode finger pitch parameter in the lateral dimension rather than extending the electrode length in the propagation direction. This dimensional approach to spuriousness control avoids the size penalty typically associated with conventional apodization techniques.
3Temperature
If the piezoelectric substrate is made of lithium niobate to improve temperature characteristics, then temperature stability is improved, but spuriousness in the transverse mode increases
Solution Approach 1:
The patent combines lithium niobate substrate for temperature stability with locally differentiated overlapping regions where the second region specifically addresses spuriousness. This local quality approach allows the substrate material to provide temperature characteristics while the electrode geometry provides spuriousness control.
Solution Approach 2:
The patent creates a composite structure combining lithium niobate piezoelectric substrate with a specifically designed comb-shaped electrode pattern featuring two overlapping regions. This composite approach leverages the temperature stability of lithium niobate while using the electrode geometry to suppress spuriousness that inherently arises from using this material.
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 results in a downsized elastic wave resonator with reduced spuriousness and improved filtering characteristics, enabling the creation of smaller elastic wave filters and antenna duplexers with enhanced performance and temperature stability.
Implementation Method 1
an elastic wave resonator including a piezoelectric substrate and a comb-shaped electrode provided on an upper surface of the substrate
Implementation Method 2
the elastic wave resonator has comb-shaped electrodes 102 and reflector electrodes 103 that are formed on a piezoelectric substrate 101
Implementation Method 3
providing a silicon oxide film on the IDT electrode so that the temperature characteristic can be improved
Implementation Method 4
an elastic wave resonator having improved characteristics, including less spuriousness, may be advantageously realized
Data Source
AI summary
An elastic wave resonator including a pair of comb-shaped electrodes and a pair of reflector electrodes formed on a piezoelectric substrate. In one example, the pair of comb-shaped electrodes includes first and second overlapping regions in which electrode fingers of the comb-shaped electrodes interdigitate, the second overlapping region being provided on both outside edges of the first overlapping region in an overlapping width direction, an overlapping width of the first overlapping region being greater than an overlapping width of the second overlapping region, the pair of comb-shaped electrodes being configured to excite a first elastic wave in the first overlapping region and to excite a second elastic wave in the second overlapping region, a frequency of the first elastic wave being higher than a frequency of the second elastic wave.