IDT Busbar Layout for Ripple-Suppressed Elastic Wave Resonators
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Solution Overview
Problem
Elastic wave devices using a piston mode often experience undesired ripples in their resonance and filter characteristics due to spurious modes occurring in the inner busbar portions and their vicinity.
Innovation Solution
The elastic wave device incorporates offset electrode fingers and wide portions on the busbars, which help mitigate the acoustic velocity differences between the inner busbar portions and their adjacent regions, reducing or preventing ripples by confining the excitation mode to the inner busbar portion and offsetting the reduction in acoustic velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the inner busbar portion is made narrow to confine excitation mode, then transverse modes are suppressed, but acoustic velocity reduction causes ripples in resonance characteristic
Solution Approach 1:
The patent applies local quality by creating edge portions with different acoustic velocity characteristics than the central excitation region. The edge portions have lower acoustic velocity due to their geometric configuration, which locally suppresses transverse modes without affecting the central piston mode operation. This localized differentiation resolves the contradiction by confining excitation to the central region while maintaining overall resonance stability.
Solution Approach 2:
The patent introduces asymmetry by positioning the inner busbar portion offset from the central axis of the IDT electrode. This asymmetric configuration creates a deliberate acoustic velocity gradient across the busbar structure, with the offset inner portion experiencing different acoustic conditions than the central region. This asymmetry enables mode confinement while preventing ripple formation through controlled acoustic velocity distribution.
2Stability of the object's composition
If wide portions are added to suppress transverse modes, then mode purity improves, but device complexity increases
Solution Approach 1:
The patent segments the busbar structure into distinct functional portions: a central busbar portion for primary current conduction, an inner busbar portion for mode confinement, and edge portions for transverse mode suppression. This segmentation allows each portion to be optimized for its specific function while maintaining overall structural integrity. The segmented design achieves mode purity through the inner and edge portions without requiring complete redesign of the entire busbar system.
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 or prevents ripples and transverse modes, improving the resonance and filter characteristics of the elastic wave device.
Implementation Method 1
a piezoelectric layer disposed on the support substrate, and an interdigital transducer (IDT) electrode disposed on the piezoelectric layer
Data Source
AI summary
An elastic wave device includes a support substrate, a piezoelectric layer disposed on the support substrate, and an IDT electrode disposed on a piezoelectric layer and including first and second electrode fingers that are interdigitated. A region where the first and second electrode fingers overlap each other as seen in a direction of propagation of elastic waves is an excitation region. Edge portions where an acoustic velocity is lower than an acoustic velocity in a central portion are disposed on opposite sides of a central portion in the excitation region. A first busbar and second busbar include inner busbar portions, central busbar portions, and outer busbar portions. First and second offset electrode fingers extend from the inner busbar portions toward the leading ends of the second electrode fingers or first electrode fingers.