SAW Filter Dummy Electrode Layout for Transverse Mode Suppression
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Solution Overview
Problem
Existing surface acoustic wave filters struggle to effectively suppress spurious components caused by unnecessary transverse modes in frequency bands higher than the anti-resonance or resonance frequency.
Innovation Solution
The surface acoustic wave filter is designed with a substrate configuration where the acoustic velocity at dummy electrodes is higher than at interdigital transducer (IDT) electrodes, effectively suppressing spurious components in higher frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a low acoustic velocity region is created at the edge portion of IDT electrodes to suppress transverse mode, then spurious components are reduced, but the suppression effect is insufficient in frequency bands higher than anti-resonance frequency
Solution Approach 1:
The electrode structure is segmented into three distinct regions along the propagation direction: a first electrode region with low acoustic velocity, a second electrode region with intermediate acoustic velocity, and a third electrode region with high acoustic velocity. This segmentation allows progressive suppression of transverse modes at different stages of wave propagation, effectively reducing spurious components in high frequency bands where conventional single-region designs fail.
Solution Approach 2:
Different regions of the electrode structure are assigned different acoustic velocity characteristics tailored to their specific functions. The first region (edge portion) has low acoustic velocity to suppress mode conversion, the second region has intermediate velocity to control wave propagation, and the third region has high velocity to maintain signal integrity. This local differentiation of properties enables effective spurious component suppression across the entire frequency range.
2Object-generated harmful factors
If the acoustic velocity at dummy electrodes is increased relative to IDT electrodes, then spurious components in high frequency bands are suppressed, but device complexity increases
Solution Approach 1:
The dummy electrodes are merged with the IDT electrode structure to form a continuous electrode system with varying acoustic velocity. Instead of treating them as separate components, the design integrates the dummy electrodes as extensions of the IDT electrodes, creating a unified structure where the acoustic velocity gradient is naturally established through the electrode geometry and material distribution along the propagation direction.
Solution Approach 2:
The acoustic velocity parameter is systematically changed along the propagation direction by modifying the electrode geometry and material properties. The dummy electrodes are designed with different dimensions or material composition compared to the IDT electrodes, creating a controlled gradient in acoustic velocity that suppresses spurious components without requiring complex additional structures.
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 enhances the filter's ability to suppress spurious components in higher frequency bands, thereby improving the characteristics of high-frequency front-end circuits.
Implementation Method 1
A surface acoustic wave device is an electromechanical device that utilizes an interaction between surface acoustic waves and semiconductor conduction electrons, and use surface acoustic waves transferred to a surface of a piezoelectric crystal.
Implementation Method 2
A surface acoustic wave (SAW) refers to a wave that propagates along a surface of an elastic solid. The surface acoustic wave propagates as energy is concentrated near a surface, and corresponds to a mechanical wave.
Data Source
AI summary
The present disclosure relates to: a surface acoustic wave filter comprising: a substrate on which a support substrate, an energy confinement layer, and a piezoelectric layer are sequentially stacked; a first bus bar and a second bus bar each extending on the substrate in a first direction and spaced apart from each other in a second direction perpendicular to the first direction; a plurality of first interdigital transducer (IDT) electrodes and a plurality of second IDT electrodes alternately disposed to extend from the first and second bus bars in the second direction and spaced apart from each other in the first direction; a second dummy electrode extending from the second bus bar to face an end portion of each of the plurality of first IDT electrodes extending from the first bus bar; and a first dummy electrode extending from the first bus bar to face an end portion of each of the plurality of second IDT electrodes extending from the second bus bar, wherein an acoustic velocity at the first and second dummy electrodes is higher than an acoustic velocity at the plurality of first and second IDT electrodes.