Lithium Niobate Acoustic Wave Electrode Layout for Lower Insertion Loss
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Solution Overview
Problem
Conventional acoustic wave devices using bulk waves in a thickness-shear mode face challenges in reducing filter size and insertion loss, particularly when used in ladder filters.
Innovation Solution
The acoustic wave device incorporates a piezoelectric film made of lithium niobate with a specific electrode structure, including interdigitated electrodes and a third electrode with a meandering shape, along with mass-addition films and through-holes in designated regions to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If acoustic wave resonators are enlarged to increase electrostatic capacitance, then electrostatic capacitance is improved, but filter device size increases
Solution Approach 1:
The patent applies local quality by introducing a third electrode with different potential between the input and output electrodes. This third electrode creates localized electric field regions that enhance capacitance density in specific areas without requiring overall enlargement of the resonator structure. The interdigitated electrode configuration with three electrodes at different potentials creates non-uniform electric field distribution that increases effective capacitance locally.
Solution Approach 2:
The patent utilizes another dimension by adding a third electrode dimension to the traditional two-electrode configuration. This creates a three-electrode system where the third electrode is positioned between the input and output electrodes, adding spatial complexity that increases electrostatic capacitance without proportionally increasing the footprint area. The meandering shape of the third electrode further optimizes space utilization.
2Device complexity
If simple three-electrode structure is adopted, then device complexity is reduced, but insertion loss is not sufficiently reduced
Solution Approach 1:
The patent applies parameter changes by optimizing the potential distribution across the three electrodes. The third electrode is assigned a reference potential that differs from both input and output potentials, creating specific electric field configurations that minimize energy loss. The potential parameters are carefully selected to enhance coupling efficiency and reduce insertion loss while maintaining manageable structural complexity.
Solution Approach 2:
The patent introduces dynamics through the meandering shape of the third electrode fingers. This dynamic configuration optimizes the electric field distribution along the propagation direction, enhancing interaction between electrodes while accommodating wave propagation patterns. The meandering design allows the structure to adapt to acoustic wave patterns, improving energy transfer efficiency and reducing insertion loss.
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 achieves size reduction of filter devices and reduces insertion loss, enabling suitable filter waveforms without enlarging the filter device.
Implementation Method 1
a piezoelectric layer is provided on a support body. Pairs of electrodes are provided on the piezoelectric layer. Each pair of electrodes faces each other on the piezoelectric layer and is connected to different potentials. A bulk wave in the thickness-shear mode is excited by an AC voltage being applied between the electrodes described above.
Data Source
AI summary
An acoustic wave device includes a piezoelectric film including a piezoelectric layer made of lithium niobate, a first interdigitated electrode including a first busbar and first electrode fingers, a second interdigitated electrode including a second busbar and second electrode fingers and interdigitated with the first electrode fingers, and a third electrode including third electrode fingers side by side with the first and second electrode fingers, connected to a potential different from potentials of the first and second interdigitated electrodes and a connection electrode connecting adjacent third electrode fingers to each other. The connection electrode connects ends of adjacent third electrode fingers closer to at least the first busbar. The connection electrode is between at least the first busbar and ends of the second electrode fingers. Mass-addition films are provided in at least a portion of at least one of first, second, and third gap regions.