SAW Interdigital Finger Layout for Transverse Mode Suppression
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Solution Overview
Problem
Existing acoustic wave filters, particularly surface acoustic wave (SAW) devices, face challenges with strong transverse modes that hinder accuracy and stability of oscillators and sensors, causing passband ripples and reduced rejection, despite having high quality factor (Q) and effective electromechanical coupling coefficient (k2eff).
Innovation Solution
The implementation of a multilayer piezoelectric substrate SAW device with a border region featuring a different velocity from the central active region, utilizing structures like multi-hammer head, notch, trench, or multi-thickness steps to suppress transverse modes without significantly degrading k2 or Q.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional uniform interdigital transducer electrodes are used, then the device achieves high quality factor (Q) and effective electromechanical coupling coefficient (k2eff), but strong transverse modes are generated causing passband ripples and reduced rejection
Solution Approach 1:
The patent applies local quality by varying the finger width across different regions of the interdigital transducer. The border region fingers have different widths compared to center region fingers, creating spatially varying acoustic impedance that suppresses transverse modes while maintaining high Q and k2eff in the active region.
Solution Approach 2:
The patent segments the interdigital transducer into distinct regions (border region and center region) with different finger width characteristics. This segmentation allows independent optimization of each region: the border region suppresses transverse modes while the center region maintains high electromechanical coupling.
2Manufacturing precision
If border region structures (multi-hammer head, notch, trench, multi-thickness steps) are implemented to suppress transverse modes, then passband ripples are reduced and rejection is improved, but device complexity increases
Solution Approach 1:
The patent changes the geometric parameters of the interdigital transducer fingers in the border region, specifically varying finger widths to create different acoustic impedance zones. This parameter modification suppresses transverse modes and reduces passband ripples without requiring additional complex 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
The proposed structures effectively suppress transverse modes, enhancing the accuracy and stability of SAW devices by reducing passband ripples and improving rejection, while maintaining high performance in filters and oscillators.
Implementation Method 1
a piezoelectric layer over the support substrate; and an interdigital transducer electrode in electrical communication with the piezoelectric layer, the interdigital transducer electrode generating a surface acoustic wave on a surface of the piezoelectric layer
Data Source
AI summary
A multilayer piezoelectric substrate acoustic wave device including an active region having a center region and a border region is disclosed. The acoustic wave device can include a support substrate, a piezoelectric layer over the support substrate, and an interdigital transducer electrode in electrical communication with the piezoelectric layer. The interdigital transducer electrode includes a bus bar and a finger extending from the bus bar. The finger in the border region has a first portion, a second portion between the center region and the first portion, and a third portion between the center region and the second portion. The first portion and the third portion have liner densities greater than liner densities of the second portion and the finger in the center region.