Stacked IDT Acoustic Wave Layout for Compact High Coupling
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Solution Overview
Problem
Existing acoustic wave devices face challenges in reducing size while maintaining high coupling coefficients and resonance characteristics, as increasing the pitch between electrode fingers to achieve a high coupling coefficient often results in larger device sizes.
Innovation Solution
The acoustic wave device incorporates first and second piezoelectric layers with an interdigital transducer (IDT) electrode structure, where the electrode fingers are arranged to overlap in a direction perpendicular to their longitudinal direction, allowing for a reduced center-to-center distance and maintaining high resonance characteristics without the need for reflectors, thus minimizing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pitch between electrode fingers is increased to achieve a high coupling coefficient, then the coupling coefficient is improved, but the device size is enlarged
Solution Approach 1:
The patent transitions from a conventional planar electrode arrangement to a three-dimensional stacked configuration where electrode fingers are arranged in multiple layers (first and second electrode fingers in different planes). This vertical stacking in the thickness direction of the piezoelectric layer allows the electrode fingers to overlap when viewed from the propagation direction, effectively utilizing the third dimension to increase the active electrode area and coupling coefficient without expanding the device footprint in the horizontal plane.
Solution Approach 2:
The patent implements a nested structure where electrode fingers are positioned within and across multiple piezoelectric layers. The first electrode fingers are embedded in the first piezoelectric layer while second electrode fingers are embedded in the second piezoelectric layer, with these layers stacked vertically. This nesting approach allows compact packaging of the electrode structure within the vertical dimension, achieving high coupling coefficients without increasing the horizontal device dimensions.
2Area of stationary object
If the device size is reduced, then the area is decreased, but the resonance characteristics may deteriorate
Solution Approach 1:
By arranging electrode fingers in multiple stacked layers with vertical offset, the patent maintains sufficient electrode overlap and interaction area for strong resonance characteristics while reducing the horizontal footprint. The three-dimensional arrangement ensures that the effective interacting area between electrodes is preserved through vertical stacking rather than horizontal expansion.
Solution Approach 2:
The patent employs a composite structure consisting of multiple piezoelectric layers with different orientations (first piezoelectric layer with first main surface, second piezoelectric layer with second main surface oriented differently). This composite layered structure enables the device to maintain excellent resonance characteristics by optimizing the piezoelectric coupling in each layer while achieving compact overall dimensions through the stacked configuration.
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 excites a bulk wave of the thickness shear primary mode, enabling high resonance characteristics and a high coupling coefficient while reducing the device size, without compromising the Q factor or increasing propagation loss.
Implementation Method 1
first and second piezoelectric layers with an interdigital transducer (IDT) electrode structure, where the electrode fingers are arranged to overlap in a direction perpendicular to their longitudinal direction... effectively excites a bulk wave of the thickness shear primary mode
Data Source
AI summary
An acoustic wave device includes first and second piezoelectric layers and an IDT electrode. The second piezoelectric layer is located above the first piezoelectric layer in a first direction. The IDT electrode includes first and second busbar electrodes and first and second electrode fingers. The first and second busbar electrodes oppose each other. The first electrode finger is provided to the first busbar electrode and extends toward the second busbar electrode. The second electrode finger is provided to the second busbar electrode and extends toward the first busbar electrode. The first and second electrode fingers are sandwiched between the first and second piezoelectric layers in the first direction. The first and second electrode fingers extend in a second direction which intersects with the first direction and are located to overlap each other as seen in a third direction perpendicular or substantially perpendicular to the second direction.