Elastic Wave Device Sezawa Wave Suppression
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Solution Overview
Problem
Elastic wave devices using Rayleigh waves suffer from high intensity of Sezawa waves, which are spurious waves, and degradation of electric power handling capability due to the presence of Sezawa waves, particularly in devices with LiNbO3 substrates and silicon oxide films.
Innovation Solution
Incorporating a high-acoustic-velocity dielectric film, such as silicon nitride, aluminum nitride, or aluminum oxide, separated from the IDT electrode by a silicon oxide film, and positioned at a specific distance from the substrate surface to reduce Sezawa wave intensity while maintaining the electric power handling capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide film is used in the elastic wave device, then the electric power handling capability is improved, but the intensity of Sezawa waves increases
Solution Approach 1:
The silicon oxide film is divided into two separate films: a first silicon oxide film and a second silicon oxide film, with a high-acoustic-velocity dielectric film positioned between them. This segmentation allows each film to serve specific functions while the high-acoustic-velocity dielectric film acts as a barrier to reduce Sezawa wave intensity, thus maintaining electric power handling capability while suppressing harmful waves.
Solution Approach 2:
A high-acoustic-velocity dielectric film is introduced as an intermediary layer between the first and second silicon oxide films. This intermediate layer has acoustic velocity characteristics that create impedance mismatch for Sezawa waves, effectively reducing their intensity while allowing the silicon oxide films to maintain their beneficial electrical properties for power handling.
2Object-generated harmful factors
If the high-acoustic-velocity dielectric film is placed close to the IDT electrode, then Sezawa wave intensity is reduced, but the electric power handling capability degrades
Solution Approach 1:
The silicon oxide film is divided into two separate films: a first silicon oxide film and a second silicon oxide film, with a high-acoustic-velocity dielectric film positioned between them. This segmentation allows each film to serve specific functions while the high-acoustic-velocity dielectric film acts as a barrier to reduce Sezawa wave intensity, thus maintaining electric power handling capability while suppressing harmful waves.
Solution Approach 2:
Different regions of the film structure are assigned different material properties: the silicon oxide films provide electrical stability and power handling capability, while the high-acoustic-velocity dielectric film provides acoustic impedance control to suppress Sezawa waves. This local differentiation of material qualities allows simultaneous optimization of both electric and acoustic performance.
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 effectively decreases the intensity of Sezawa waves and prevents degradation of the electric power handling capability of the IDT electrode, enhancing the performance of elastic wave devices by increasing the acoustic velocity of Sezawa waves and improving frequency temperature characteristics.
Implementation Method 1
The high-acoustic-velocity dielectric film propagates longitudinal waves at an acoustic velocity higher than the acoustic velocity of longitudinal waves propagating through the first silicon oxide film
Implementation Method 2
elastic wave devices (surface acoustic wave devices) using Rayleigh waves as the main mode
Implementation Method 3
The elastic wave device of WO 2007/097186 causes generation of Sezawa waves, which are spurious waves for Rayleigh waves, on the high-frequency side of the anti-resonant frequency of Rayleigh waves
Data Source
AI summary
In an elastic wave device, an IDT electrode is provided on a piezoelectric substrate and a first silicon oxide film covers the IDT electrode. A high-acoustic-velocity dielectric film covers the first silicon oxide film. A second silicon oxide film is provided on the high-acoustic-velocity dielectric film. The piezoelectric substrate is made of lithium niobate. The high-acoustic-velocity dielectric film propagates longitudinal waves at an acoustic velocity higher than an acoustic velocity of longitudinal waves propagating through the first silicon oxide film. The high-acoustic-velocity dielectric film is provided at a distance of about (t1+t2)×0.42 or less from a first main surface of the piezoelectric substrate in a thickness direction of the piezoelectric substrate.