Piezoelectric Laminate Structure for Suppressing Spurious Acoustic Waves
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Solution Overview
Problem
Acoustic wave devices with piezoelectric layers of different polarization axes suffer from undesired wave generation on the low-frequency side, leading to degraded frequency characteristics.
Innovation Solution
A piezoelectric laminated structure with a first piezoelectric body and a second piezoelectric body having different dielectric polarization states, where the thickness of the first piezoelectric body is less than or equal to the second, is used in conjunction with a support and functional electrodes to curb the generation of undesired waves and maintain favorable frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two types of piezoelectric bodies with different polarization axes are bonded to form a piezoelectric layer, then the device can operate with the main mode, but undesired waves are strongly generated on the low-frequency side and frequency characteristics are degraded
Solution Approach 1:
The piezoelectric layer is segmented into multiple piezoelectric bodies (first and second piezoelectric bodies) with different polarization axes. By dividing the piezoelectric layer into distinct segments with controlled thickness ratios, the invention suppresses undesired waves while maintaining main mode operation. The first piezoelectric body has a thickness of 0.2μm to 0.7μm and the second has 0.3μm to 0.8μm, creating a segmented structure that filters out low-frequency undesired waves.
Solution Approach 2:
Different regions of the piezoelectric layer are assigned different local qualities through varying the polarization axes and thicknesses of individual piezoelectric bodies. The first piezoelectric body and second piezoelectric body have different polarization axes oriented at specific angles, creating local quality differences that suppress undesired wave generation while maintaining the desired main mode characteristics.
2Ease of manufacture
If two types of piezoelectric bodies with different polarization axes are bonded, then the piezoelectric layer can be formed, but frequency characteristics are degraded due to strong undesired wave generation
Solution Approach 1:
The invention changes critical parameters including the thicknesses of individual piezoelectric bodies (first: 0.2μm-0.7μm, second: 0.3μm-0.8μm) and their polarization axis orientations to specific angle ranges. These parameter changes optimize the balance between ease of manufacturing a multi-layer piezoelectric structure and achieving precise frequency characteristics by suppressing undesired waves.
Solution Approach 2:
The piezoelectric layer is constructed as a composite structure with first and second piezoelectric bodies having different polarization axes. This composite material approach combines materials with different properties to achieve both manufacturability and superior frequency characteristics, as the composite structure naturally suppresses undesired wave modes.
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 the generation of undesired waves, thereby improving the frequency characteristics and maintaining a high coupling coefficient for the main mode, allowing for efficient operation of the acoustic wave device.
Implementation Method 1
a piezoelectric layer extending in a first direction of the support... a functional electrode on a main surface of the piezoelectric layer... the piezoelectric layer is a piezoelectric laminated structure including a first piezoelectric body and a second piezoelectric body with a state of dielectric polarization different from the first piezoelectric body
Data Source
AI summary
An acoustic wave device includes a support with a thickness in a first direction, a piezoelectric layer extending in the first direction, and a functional electrode on a main surface of the piezoelectric layer and including first electrode fingers extending in a second direction intersecting with the first direction, a first busbar electrode connected to the first electrode fingers, second electrode fingers facing any of the first electrode fingers in a third direction perpendicular or substantially perpendicular the second direction and extending in the second direction, and a second busbar electrode connected to the second electrode fingers. The piezoelectric layer includes a first piezoelectric body in contact with the functional electrode and a second piezoelectric body with a different dielectric polarization than that of the first piezoelectric body, and a thickness of the first piezoelectric body is less than or equal to a thickness of the second piezoelectric body.