Acoustic Wave Filter Resonator Layout for Wide Stop Bands
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Solution Overview
Problem
Acoustic wave filters with multiband functionality face challenges in achieving wide band and high steepness due to narrow adjustable ranges of electromechanical coupling coefficients, leading to insufficient attenuation and increased loss in pass bands.
Innovation Solution
The acoustic wave filter device incorporates series and parallel arm resonators with varying electromechanical coupling coefficients adjusted by films of different thicknesses, ensuring coincident anti-resonant frequencies to widen stop bands and maintain steepness, thereby achieving sufficient attenuation and reduced loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the electromechanical coupling coefficients of series arm resonators are adjusted by adding capacitors through thinning or weighting interdigital transducer electrodes, then the adjustable ranges of the electromechanical coupling coefficient are narrow, but the quality factors at the anti-resonant frequencies decrease
Solution Approach 1:
The patent applies local quality by introducing a specific adjusting film (SiO2 layer) at a precise location between the piezoelectric body and interdigital transducer electrode. This localized structural modification allows independent adjustment of the electromechanical coupling coefficient of the second series arm resonator without affecting other resonators, thereby expanding the adjustable range while maintaining high quality factors through proper film thickness control (5-50 nm).
Solution Approach 2:
The patent employs parameter changes by varying the thickness of the adjusting film (SiO2 layer) to precisely control the electromechanical coupling coefficient. By changing the film thickness parameter within a specific range (5-50 nm), the coupling coefficient can be adjusted to achieve the desired frequency difference between attenuation poles while maintaining optimal quality factors, thus resolving the contradiction between adjustability and reliability.
2Loss of energy
If the adjustable ranges of the electromechanical coupling coefficients of two series arm resonators are narrow, then the difference between the frequencies of two attenuation poles is not increased very much, but the stop band width on the higher side of the pass band is not widened very much, resulting in insufficient attenuation
Solution Approach 1:
The patent applies local quality by selectively adding an adjusting film only to the second series arm resonator, allowing independent control of its electromechanical coupling coefficient. This localized modification enables precise adjustment of the attenuation pole frequency difference, thereby widening the stop band width and improving attenuation performance without requiring broad adjustment ranges for both resonators.
Solution Approach 2:
The patent employs dynamics by making the electromechanical coupling coefficient adjustable through the variable thickness of the adjusting film. This dynamic control capability allows optimization of the frequency difference between attenuation poles to achieve wide stop band width and sufficient attenuation, resolving the contradiction between adjustability and attenuation performance.
3Loss of energy
If the quality factors at the anti-resonant frequencies are low, then a loss in the pass band gets worse
Solution Approach 1:
The patent employs parameter changes by controlling the thickness of the adjusting film within a specific range (5-50 nm) to optimize the electromechanical coupling coefficient. This precise parameter control maintains high quality factors at anti-resonant frequencies while achieving the desired frequency difference between attenuation poles, thereby preventing pass band loss deterioration and resolving the contradiction between quality factor and energy loss.
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 ensures wide stop bands on both sides of the pass band with steepness, providing improved attenuation and reduced loss in the pass band, enhancing the filter's performance.
Implementation Method 1
Each of the first series arm resonator and the second series arm resonator includes at least a piezoelectric body and an interdigital transducer electrode. Of the first series arm resonator and the second series arm resonator, at least the second series arm resonator includes a second adjusting film between the piezoelectric body and the interdigital transducer electrode. The second adjusting film adjusts an electromechanical coupling coefficient.
Data Source
AI summary
An acoustic wave filter includes series arm resonators, and a parallel arm resonator provided in a second path connecting a ground and a node connecting the series arm resonators. Each of the series arm resonators includes a piezoelectric body and an interdigital transducer electrode. One of the series arm resonators includes a second adjusting film that adjusts Ksaw. An anti-resonant frequency of the other one of the series arm resonators is higher than an anti-resonant frequency of the one of series arm resonators. An adjusting film that adjusts Ksaw is not provided in the other one of series arm resonators, or when a first adjusting film that adjusts Ksaw is provided in the other one of the series arm resonators, the first adjusting film is thinner than the second adjusting film.