Acoustic Wave Filter Electrode Structure for Rayleigh Ripple Control
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Solution Overview
Problem
Existing acoustic wave filters suffer from deteriorated filter characteristics due to transverse mode ripples, particularly in the frequency band on the low frequency side of the pass band, caused by the transverse mode response of the Rayleigh wave in series and parallel arm resonators.
Innovation Solution
The implementation of apodized interdigital transducer electrodes in series arm resonators and the use of intersecting portions with central and low acoustic velocity regions in parallel arm resonators, along with a piezoelectric substrate like LiNbO3, significantly reduces or prevents transverse mode ripples by varying the intersecting width and acoustic velocities, thereby improving filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an interdigital transducer electrode using a piston mode is used in the acoustic wave resonator, then the transverse mode ripple of the Love wave is reduced, but the transverse mode response of the Rayleigh wave appears and causes ripple in the frequency band on the low frequency side of the pass band
Solution Approach 1:
The patent applies local quality by creating regions with different acoustic velocities within the intersecting portion of the interdigital transducer electrode. Specifically, a central region with higher acoustic velocity and side regions with lower acoustic velocity are formed, allowing different parts of the electrode to selectively suppress different transverse modes. This local variation in acoustic velocity properties enables simultaneous suppression of both Love wave and Rayleigh wave transverse mode ripples.
Solution Approach 2:
The patent changes the acoustic velocity parameter across different regions of the intersecting portion by modifying the electrode structure. The central region maintains higher acoustic velocity while the side regions are designed with lower acoustic velocity. This parameter change allows the electrode to control and suppress transverse mode responses at different locations, resolving the contradiction between suppressing Love wave ripple and preventing Rayleigh wave ripple.
2Reliability
If the intersecting width of the interdigital transducer electrode is increased to reduce transverse mode ripple, then the suppression of transverse modes improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent segments the intersecting portion into distinct functional regions: a central region and side regions with different acoustic velocity characteristics. This segmentation allows each region to perform its specific function in suppressing different transverse modes, achieving effective ripple suppression without requiring excessive overall intersecting width. The segmented structure simplifies the design compared to uniformly increasing the entire intersecting width.
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 minimizes transverse mode ripples, leading to improved filter characteristics and reduced deterioration of acoustic wave filter performance, especially in multiplexers and composite filter devices.
Implementation Method 1
acoustic wave resonators including a piezoelectric substrate and an interdigital transducer electrode provided on the piezoelectric substrate
Implementation Method 2
a Love wave is used in the acoustic wave resonator
Data Source
AI summary
An acoustic wave filter device includes at least one series arm resonator and a parallel arm resonator. The series arm resonators and the parallel arm resonator are defined by acoustic wave resonators, an interdigital transducer electrode of the series arm resonators is an apodized interdigital transducer electrode subjected to apodization weighting, in the interdigital transducer electrode of the parallel arm resonator, an intersecting portion includes a central region and low acoustic velocity regions provided at both outer side portions of the central portion, an acoustic velocity of an acoustic wave in the low acoustic velocity region is lower than an acoustic velocity of an acoustic wave in the central region, and a high acoustic velocity region where an acoustic velocity of an acoustic wave is higher than that of the low acoustic velocity region is provided at an outer side portion of each of the low acoustic velocity regions.