IDT Electrode Layout for Compact Piston-Mode Elastic Wave Filters
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Solution Overview
Problem
Existing elastic wave devices utilizing the piston mode face challenges in size reduction due to the large area required for high acoustic velocity portions, which increases the size of the device and makes it difficult to miniaturize.
Innovation Solution
The design includes high acoustic velocity portions that are positioned closer to the outside than low acoustic velocity portions, with their widths gradually decreasing from the center to the ends of the IDT electrode, reducing the overall size of the device without increasing loss, and incorporating mass-adding films or dielectric films to manage acoustic velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high acoustic velocity portions are provided on both sides of the intersection width region in the electrode finger direction with sufficient width (at least 1λ), then the piston mode is properly utilized and acoustic performance is improved, but the area of the IDT electrode inside the busbars is increased, making size reduction difficult
Solution Approach 1:
The patent applies local quality by making the width of high acoustic velocity portions position-dependent: they are wider at the center of the IDT electrode in the elastic wave propagation direction and narrower at the end portions. This localized variation in dimension allows the structure to maintain acoustic performance where it is most needed (center region) while reducing overall area (end regions), directly resolving the contradiction between reliability and area.
2Area of stationary object
If the width of high acoustic velocity portions is reduced to achieve size reduction, then device miniaturization is enabled, but the amplitude at the ends may become insufficient, potentially increasing loss
Solution Approach 1:
The patent ensures that high acoustic velocity portions maintain sufficient width at the center region where acoustic amplitude is highest, while reducing width only at end portions where amplitude is already lower. This localized differentiation maintains energy efficiency (preventing loss) in critical regions while enabling size reduction in less critical regions, resolving the contradiction between area and energy 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 allows for a reduction in the size of the elastic wave device while maintaining performance by ensuring that the amplitude is sufficiently small at the ends, thereby minimizing loss and achieving size reduction without compromising device efficiency.
Implementation Method 1
an IDT electrode provided on the piezoelectric substrate
Implementation Method 2
The low acoustic velocity portions are formed by increasing the width of the electrode fingers or by stacked a mass-adding film, which causes a fall in acceleration
Data Source
AI summary
In an elastic wave device, low acoustic velocity portions are provided on both sides of an IDT center portion in an intersection region of an IDT electrode and high acoustic velocity portions are provided outside of the low acoustic velocity portions in an electrode finger direction. Thus, a piston mode is able to be utilized. The widths of the high acoustic velocity portions in end portions of the IDT electrode in an elastic wave propagation direction are relatively smaller than the widths of the high acoustic velocity portions in the center of the IDT electrode in the elastic wave propagation direction.