SAW Electrode Layout for Piston Mode Without Larger Footprint
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Solution Overview
Problem
Existing surface acoustic wave devices operating in piston mode require longer gap lengths, leading to increased device size due to slower propagation velocities in edge regions compared to alternating regions, which complicates the design and functionality.
Innovation Solution
A surface acoustic wave device with interdigital transducer electrodes and busbars where the propagation velocity in the busbar region is made faster than in the alternating region by varying metal film thickness and density, and using dielectric films with opposite temperature-frequency characteristics to optimize SAW propagation velocities without increasing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gap length dimension in the edge region is increased to achieve piston mode operation, then the surface acoustic wave device achieves high Q-value and reduced spurious responses, but the device size increases
Solution Approach 1:
The patent changes the physical parameters of the electrode fingers in the edge region, specifically reducing the width of electrode fingers connected to the same busbar and increasing the gap length between them. This parameter modification in the edge region creates a reflection effect that enables piston mode operation without requiring the entire device to be larger, thus achieving high Q-value while maintaining compact device size.
2Reliability
If the gap length dimension in the edge region is increased to achieve piston mode operation, then spurious responses are reduced, but the device complexity increases
Solution Approach 1:
The patent applies local quality by creating a specific structure only in the edge region of the IDT electrodes. The electrode fingers in the edge region have different dimensions (reduced width, increased gap) compared to those in the center region. This localized modification generates the necessary reflection effect to suppress spurious responses and achieve piston mode without complicating the entire device structure.
3Reliability
If the propagation velocity in the edge region is made slower to achieve piston mode, then the surface acoustic wave excitation is improved, but the device area increases
Solution Approach 1:
The patent modifies the physical parameters (width and gap length) of electrode fingers in the edge region to change the local propagation characteristics of surface acoustic waves. By reducing the electrode finger width and increasing the gap length in the edge region, the propagation velocity is reduced locally, creating a reflection effect that improves SAW excitation efficiency and enables piston mode operation within a compact device area.
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 solution enables efficient excitation of surface acoustic waves in piston mode with high Q-value and reduced spurious responses, maintaining a compact device size by controlling propagation velocities in edge, alternating, and busbar regions.
Implementation Method 1
a piezoelectric substrate and a pair of interdigital transducer (IDT) electrodes
Data Source
AI summary
A surface acoustic wave device includes a piezoelectric substrate and a pair of interdigital transducer electrodes. The pair of interdigital transducer electrodes include an alternating region as a region where the electrode fingers connected to one busbar and the electrode fingers connected to the other busbar are alternately provided. When a region on an end portion side of the alternating region and a region including distal end portions of the plurality of electrode fingers is referred to as an edge region, a propagation velocity of a surface acoustic wave in the edge region is slower than a propagation velocity of a surface acoustic wave in the alternating region. A propagation velocity of a surface acoustic wave in a busbar region as a region where the busbar is disposed is faster than the propagation velocity of the surface acoustic wave in the alternating region.