Acoustic Wave Cavity Structure Using Roughness Asymmetry
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Solution Overview
Problem
Acoustic wave devices with a membrane structure and a cavity under a piezoelectric film often experience characteristic degradation due to the excitation of unnecessary waves.
Innovation Solution
The acoustic wave device incorporates a support substrate, a piezoelectric film, and an excitation electrode, with a cavity between the layers, where the surface roughness of one major surface facing the cavity is different from the other, enhancing wave confinement and scattering of unnecessary waves by partially overlapping the excitation electrode with the cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a cavity is provided under a piezoelectric film to create a membrane structure, then device integration and miniaturization are improved, but characteristics are degraded by excitation of unnecessary waves
Solution Approach 1:
The patent applies local quality by creating different surface roughness characteristics at different locations within the cavity. Specifically, the lower surface of the piezoelectric film has a first roughness while the upper surface has a second roughness different from the first. This localized differentiation of surface properties enables selective interaction with acoustic waves, scattering unnecessary waves while maintaining membrane structure benefits for device miniaturization.
Solution Approach 2:
The patent employs asymmetry by making the surface roughness of the piezoelectric film's lower surface (facing the cavity) different from the upper surface (facing away from the cavity). This asymmetric roughness configuration creates unequal acoustic impedance at the two interfaces, which helps scatter spurious waves that would otherwise degrade device characteristics, while preserving the cavity's space-saving function.
2Volume of moving object
If the piezoelectric film is made thin to improve device integration, then miniaturization is achieved, but wave confinement becomes insufficient
Solution Approach 1:
The patent changes the physical parameter of surface roughness to compensate for the reduced thickness of the piezoelectric film. By introducing controlled roughness differences between the upper and lower surfaces of the thin film, the acoustic wave scattering capability is enhanced. This parameter change enables adequate wave confinement even when the film thickness is reduced for better device integration and miniaturization.
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 design effectively prevents characteristic degradation by scattering unnecessary waves and improving wave confinement, maintaining device performance.
Implementation Method 1
a second layer on the first layer and including a piezoelectric film
Data Source
AI summary
An acoustic wave device includes a first layer including a support substrate, a second layer on the first layer and including a piezoelectric film, and a first excitation electrode on the second layer. A cavity is between the first and second layers, and the first excitation electrode at least partially overlaps the cavity in a stacking direction of the first and second layers. A surface roughness of a major surface of the first layer facing the cavity is different from a surface roughness of a major surface of the second layer facing the cavity.