Acoustic Wave Filter Busbar Layout for Lower Insertion Loss
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Solution Overview
Problem
Acoustic wave filter devices face challenges in reducing insertion loss due to high electric resistance in interdigital transducer (IDT) electrodes, which is not sufficiently lowered by existing designs.
Innovation Solution
The filter device incorporates a piezoelectric substrate with a high acoustic velocity material layer and a piezoelectric layer, featuring series and parallel arm resonators with IDT electrodes that include specific busbar and electrode finger configurations to create regions of varying acoustic velocities, thereby reducing insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If thin wiring lines are used in the high acoustic velocity region, then the device structure is simplified, but the electric resistance cannot be sufficiently lowered
Solution Approach 1:
The patent applies local quality by creating distinct acoustic velocity regions (high, central, low) at different positions within the IDT electrode structure. The high acoustic velocity region is positioned where wiring lines are present, the central region is in the middle, and the low acoustic velocity region is at the edge. This spatial differentiation of acoustic velocity properties allows the thin wiring lines in the high acoustic velocity region to achieve sufficient current carrying capacity while maintaining structural simplicity, thereby resolving the contradiction between structure simplicity and insertion loss reduction.
2Ease of manufacture
If the IDT electrode uses conventional design, then manufacturing is easier, but insertion loss is not sufficiently reduced
Solution Approach 1:
The patent applies parameter changes by modifying the acoustic velocity distribution parameters within the IDT electrode. Specifically, it changes the acoustic velocity values at different positions (high, central, low regions) and the spatial arrangement of these regions. These parameter changes are implemented through material selection and structural design that can be integrated into conventional manufacturing processes, allowing the IDT electrode to achieve lower insertion loss while maintaining ease of manufacture.
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 insertion loss by optimizing acoustic wave propagation and electric resistance, improving the filter device's performance and reducing spurious signals.
Implementation Method 1
an interdigital transducer (IDT) electrode is provided on a piezoelectric substrate
Implementation Method 2
an acoustic velocity of a bulk wave propagating through the high acoustic velocity material layer is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer
Data Source
AI summary
A filter device includes a piezoelectric substrate including a high acoustic velocity material layer and a piezoelectric layer, and series and parallel arm resonators on the piezoelectric substrate. The parallel arm resonator includes a first IDT electrode on the piezoelectric substrate, and the series arm resonator includes a second IDT electrode on the piezoelectric substrate. First and second busbars of the first IDT electrode include opening formation regions, and an occupancy ratio of areas of openings in the first and second busbars of the first IDT electrode is greater than an occupancy ratio of areas of openings in first and second busbars of the second IDT electrode. In the first and second IDT electrodes, low acoustic velocity regions sandwich a central region. A high acoustic velocity region is provided in the opening formation region of each of the first and second busbars in the first IDT electrode.