Acoustic Wave Filter Electrode Layout for Leakage Suppression
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Solution Overview
Problem
Acoustic wave devices suffer from leakage of acoustic waves due to the arrangement direction of electrode fingers.
Innovation Solution
The acoustic wave device includes a piezoelectric layer with specific dimensions and electrode finger configurations, such as varying electrode widths and pitches, to reduce or prevent wave leakage, utilizing bulk waves of the thickness-shear primary mode and a membrane structure with a cavity portion to minimize propagation loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrode fingers are arranged in a conventional uniform pattern, then the device structure is simple and easy to manufacture, but acoustic waves leak in the arrangement direction of electrode fingers
Solution Approach 1:
The patent applies local quality by making the electrode fingers non-uniform: the first electrode finger has a different width from the second electrode finger, and/or the first inter-electrode pitch differs from the second inter-electrode pitch. This local variation in electrode geometry creates different acoustic impedances at different positions, preventing acoustic wave leakage in the arrangement direction while maintaining overall structural simplicity.
2Volume of moving object
If the piezoelectric layer thickness is reduced to enable device miniaturization, then device size is reduced, but acoustic wave leakage increases
Solution Approach 1:
By introducing local variations in electrode finger dimensions and spacing, the patent creates position-dependent acoustic impedance that effectively contains acoustic waves even in thin piezoelectric layers. This allows device miniaturization while preventing the acoustic wave leakage that would otherwise occur with reduced thickness.
3Ease of manufacture
If uniform electrode spacing is used, then manufacturing is simplified, but acoustic wave propagation loss increases due to leakage
Solution Approach 1:
The non-uniform electrode configuration (different widths and/or different inter-electrode pitches) creates local acoustic impedance variations that reflect and contain acoustic waves, reducing propagation loss. While this increases fabrication complexity slightly, the overall manufacturing remains relatively simple compared to the performance benefits achieved.
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 device effectively excites bulk waves, reduces wave leakage, and maintains high resonance characteristics with a wide fractional bandwidth and low spurious emission, even with reduced electrode pairs, thus enhancing performance and size reduction.
Implementation Method 1
a piezoelectric layer including a first main surface and a second main surface opposed to the first main surface, an IDT electrode on at least one of the first main surface and the second main surface of the piezoelectric layer
Implementation Method 2
a support facing the second main surface of the piezoelectric layer and including an acoustic reflection portion toward the second main surface of the piezoelectric layer
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer including first and second main surfaces, an IDT electrode on at least one of the first and second main surfaces and including electrode fingers arranged in a predetermined direction, and a support facing the second main surface and including an acoustic reflection portion toward the second main surface. At least one of a first electrode finger in an outermost portion and a second electrode finger internally adjacent to the first electrode finger differs from central electrode fingers inside the second electrode finger in at least one of a dimension in a direction orthogonal to an extension direction and an inter-center distance to an internally adjacent electrode finger, d/p is about 0.5 or less, where d denotes a thickness of the piezoelectric layer and p denotes the inter-center distance between adjacent electrode fingers.