LL-SAW Resonator Reflector Spacing for Spurious Mode Suppression
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Solution Overview
Problem
The existing LL-SAW resonator structure is prone to spurious modes due to strong scattering at the junction between the IDT and the reflector grating electrode, which affects the flatness of the filter's passband.
Innovation Solution
The proposed structure includes a substrate made of SiC, a piezoelectric thin film of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), and an electrode array with an IDT array and a reflector grating electrode array. The center distance between reflector grating electrodes is less than that between IDTs, with a ratio in the range of [0.825, 1), to improve the reflective frequency range and suppress spurious modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the center distance between reflector grating electrodes is made equal to the center distance between IDTs, then the device complexity is reduced, but spurious modes occur due to strong scattering at the junction between IDT and reflector grating electrode
Solution Approach 1:
The patent applies local quality by making the center distance between reflector grating electrodes different from the center distance between IDTs. This creates a localized structural variation at the junction region, which modifies the acoustic field distribution and reduces strong scattering effects that cause spurious modes, while maintaining overall structural simplicity.
Solution Approach 2:
The patent introduces asymmetry by setting the reflector grating electrode center distance to be different from the IDT center distance. This asymmetric configuration breaks the symmetry of the acoustic field at the junction, thereby reducing the scattering strength and suppressing spurious mode generation without significantly increasing device complexity.
2Speed
If the center distance between reflector grating electrodes is reduced, then the reflective frequency range is improved, but the junction scattering between IDT and reflector grating electrode increases
Solution Approach 1:
The patent applies parameter changes by optimizing the center distance between reflector grating electrodes to be different from the IDT center distance. This parameter modification extends the reflective frequency range while simultaneously controlling the junction scattering effects, achieving a balance between frequency performance and scattering reduction.
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
By reducing the center distance between reflector grating electrodes, the reflective frequency range is enhanced, effectively suppressing spurious modes and improving the performance of the LL-SAW resonator and filter.
Implementation Method 1
a piezoelectric thin film provided on the substrate, where the piezoelectric thin film is made of lithium niobate (LiNbO3) or lithium tantalate (LiTaO3)
Implementation Method 2
Because of a high acoustic velocity of the SiC substrate, this structure can effectively excite and confine acoustic field energy of the LL-SAW
Data Source
AI summary
A structure of a longitudinal leaky surface acoustic wave (LL-SAW) resonator and a filter includes a substrate, a piezoelectric thin film provided on the substrate, and an electrode array provided on the piezoelectric thin film, where the electrode array includes an interdigital transducer (IDT) array and a reflector grating electrode array; and a center distance between reflector grating electrodes in the reflector grating electrode array is less than a center distance between IDTs in the IDT array. Based on a nonstandard reflector (NSR) grating structure provided by the embodiments of the present disclosure, by reducing the center distance between the reflector grating electrodes in the reflector grating electrode array, the present disclosure can improve a reflective frequency range of the reflector grating electrode array, thereby suppressing a spurious mode of the LL-SAW, and improving performance of the LL-SAW resonator.