Electroacoustic Resonator Electrode Layout for Spurious Mode Suppression
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Solution Overview
Problem
Electroacoustic resonators face challenges in suppressing unwanted spurious modes, particularly in materials with high electroacoustic coupling and small distance between main and unwanted modes, leading to issues like dips in passband, group delay ripples, trimming problems, and reduced power durability.
Innovation Solution
The design incorporates interdigital electrodes with specific region configurations and stub fingers to control the velocity of surface acoustic waves, allowing for the suppression of unwanted modes by adjusting the width, height, and length of finger portions, thereby optimizing the resonator's performance without the need for metal dots, which are difficult to produce accurately at high frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional interdigital electrodes are used in materials with high electroacoustic coupling, then the resonator can operate at high frequencies, but spurious modes cannot be suppressed leading to performance degradation
Solution Approach 1:
The electrode fingers are segmented into multiple portions (first portion, second portion, third portion) along the propagation direction. Each portion has different dimensions designed to suppress specific spurious modes while maintaining the main mode operation, thereby resolving the contradiction between high-frequency operation and spurious mode suppression
Solution Approach 2:
Different portions of the electrode fingers have locally optimized dimensions. The first portion has different width/length characteristics than the second and third portions, creating localized impedance variations that selectively suppress spurious modes at specific locations along the electrode structure
2Reliability
If metal dots are added to suppress spurious modes, then mode suppression improves, but fabrication complexity and cost increase due to precise placement requirements
Solution Approach 1:
The invention extracts the spurious mode suppression function from the metal dot approach and integrates it directly into the electrode finger structure itself. The segmented portions of the fingers provide the suppression mechanism through their geometric configuration, eliminating the need for separate metal dot components and their precise placement processes
Solution Approach 2:
The spurious mode suppression functionality is merged with the electrode finger structure. The same electrode fingers that generate the main mode also contain the segmented portions that suppress spurious modes, combining multiple functions into a single integrated structure and simplifying fabrication
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 reduces the velocity of unwanted modes, enhancing the suppression of transversal and polarized modes, improving the resonator's performance and reducing fabrication complexities, while maintaining the accuracy and cost-effectiveness of the production process.
Implementation Method 1
a substrate with a piezoelectric material
Implementation Method 2
an interdigital electrode structure on a top side of the substrate... Both electrodes together define an interdigital transducer
Implementation Method 3
the velocity of a main mode of surface acoustic waves is smaller in the trap regions than in the track region
Data Source
AI summary
An electroacoustic resonator comprises a substrate (3) with a piezoelectric material and an interdigital electrode structure on a top side (33) of the substrate. The electrode structure comprises a first electrode (1) and a second electrode (2) each with a busbar (20) and a plurality of fingers (10). The fingers of both electrodes interdigitate. The region of the top side between the two busbars is subdivided into two barrier regions (113), two trap regions (112) and one track region (111), the trap regions being located between the two barrier regions and the track region being located between the two trap regions. At least some fingers each comprise one barrier portion (13), two trap portions (12) and one track portion (11), wherein the barrier portion is associated with the barrier region closest to the busbar assigned to the finger, the trap portions are each associated with one of the trap regions and the track portion is associated with the track region. The fingers are configured such that the velocity of a main mode of surface acoustic waves is smaller in the trap regions than in the track region. Each electrode comprises a plurality of stub fingers (30) being shorter than the fingers. Each stub finger is associated only with the barrier region closest to the busbar assigned to the stub finger. The electrodes are configured such that a velocity of the main mode in the barrier regions is greater than in the track region.