Elastic Wave Device Layered Structure for High Frequency and Wide Bandwidth
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Solution Overview
Problem
Existing elastic wave devices using longitudinal wave leaky elastic waves face challenges in achieving a wide band width ratio while maintaining a good impedance ratio and high frequency due to the mode of wave propagation.
Innovation Solution
The elastic wave device incorporates a first medium layer with a larger product of density and elastic constant, a silicon oxide layer, and a piezoelectric film, with an IDT electrode, where the total thickness of the piezoelectric film and silicon oxide layer is kept at or less than a wavelength, and the IDT electrode is made of lightweight metals like Al, Cu, or Mo to achieve high frequencies and wide band width ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If longitudinal wave leaky elastic waves are used to achieve high frequency, then higher frequencies are easily achieved, but it is difficult to realize a wide band width ratio while maintaining a good impedance ratio
Solution Approach 1:
The patent divides the device into multiple functional layers: a piezoelectric layer for generating elastic waves, a first medium layer (with higher ρ×C11) for wave propagation, and a second medium layer (silicon oxide) for impedance control. This segmentation allows each layer to be optimized independently for frequency and bandwidth performance
Solution Approach 2:
The patent changes the physical parameters of the medium layers, specifically selecting materials where the first medium layer has a higher product of density and elastic constant (ρ×C11) than the piezoelectric layer. This parameter change enables control over wave velocity and impedance, achieving both high frequency and wide bandwidth
2Speed
If the total thickness of piezoelectric film and silicon oxide layer is reduced to about 1.0λ or less, then higher frequency is achieved, but Q value degradation may occur
Solution Approach 1:
The patent optimizes the thickness parameters of each layer relative to the wavelength λ, setting the total thickness to about 1.0λ or less for high frequency while maintaining Q value through proper material selection and layer configuration that controls energy loss
3Stability of the object's composition
If a second silicon oxide layer is added to cover the IDT electrode, then temperature characteristics are improved, but device complexity increases
Solution Approach 1:
The second silicon oxide layer acts as an intermediary protective and stabilizing layer over the IDT electrode. It mediates between the electrode and the external environment, providing temperature stability and protection while adding minimal structural complexity
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 higher frequencies and wider band width ratios while maintaining a good impedance ratio, reducing Q value degradation and improving temperature characteristics.
Implementation Method 1
a piezoelectric film stacked on the second medium layer either directly or indirectly
Implementation Method 2
Surface acoustic wave devices that utilize longitudinal wave leaky surface acoustic waves are known... a longitudinal wave leaky elastic wave is utilized
Data Source
AI summary
An elastic wave device that utilizes a longitudinal wave leaky elastic wave includes a first medium layer, a second medium layer stacked on the first medium layer either directly or indirectly and that is a silicon oxide layer, a piezoelectric film stacked on the second medium layer either directly or indirectly, and an IDT electrode disposed on the piezoelectric film either directly or indirectly. In the elastic wave device, ρ1×C11, which is a product of a density ρ1 (kg/m3) of the first medium layer and an elastic constant C11 of the first medium layer, is larger than ρ0×C11, which is a product of a density ρ0 (kg/m3) of the piezoelectric film and an elastic constant C11 of the piezoelectric film.