Quartz Acoustic Wave Structure for Higher-Order Mode Suppression
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Solution Overview
Problem
Existing acoustic wave devices struggle to sufficiently suppress higher-order modes, leading to ripple issues in the pass band.
Innovation Solution
The acoustic wave device incorporates a support substrate with a silicon oxide layer having crystallinity, a piezoelectric layer, and an IDT electrode, where the silicon oxide layer thickness is between 0.2λ and 0.4λ, and the piezoelectric layer thickness is less than the silicon oxide layer, effectively suppressing higher-order modes and Rayleigh waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional acoustic wave device structure is used, then the device can operate at the desired frequency, but higher-order modes cannot be sufficiently suppressed, causing ripple in the pass band
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the silicon oxide layer (setting it to 0.2λ or more and 0.4λ or less) and the piezoelectric layer thickness (smaller than the silicon oxide layer). This specific parameter optimization enables effective suppression of higher-order modes across a wide frequency band while maintaining device functionality
Solution Approach 2:
The patent employs a composite multilayer structure consisting of a support substrate, silicon oxide layer, and piezoelectric layer. This composite material approach combines materials with different acoustic and piezoelectric properties to achieve superior higher-order mode suppression compared to single-material structures
2Reliability
If the silicon oxide layer thickness is increased to suppress higher-order modes, then suppression performance improves, but the device structure becomes more complex and manufacturing becomes harder
Solution Approach 1:
The patent defines a specific thickness range (0.2λ to 0.4λ) for the silicon oxide layer that optimizes higher-order mode suppression. By establishing this parameter window rather than requiring a single precise value, the design achieves effective suppression while maintaining manufacturing feasibility and reducing structural complexity
3Reliability
If the piezoelectric layer thickness is reduced to suppress Rayleigh waves, then Rayleigh wave suppression improves, but the piezoelectric effect strength may be reduced
Solution Approach 1:
The patent optimizes the piezoelectric layer thickness by setting it smaller than the silicon oxide layer thickness. This parameter optimization achieves effective Rayleigh wave suppression while maintaining sufficient piezoelectric effect strength for device operation, balancing both requirements through coordinated thickness design
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 achieves suppression of higher-order modes and Rayleigh waves across a wide band, enhancing the device's performance and reducing spurious emissions.
Implementation Method 1
a piezoelectric layer on the silicon oxide layer having crystallinity
Implementation Method 2
a thickness of the silicon oxide layer having crystallinity is about 0.2λ or more and about 0.4λ or less
Data Source
AI summary
An acoustic wave device includes a support substrate, a quartz-crystal layer provided directly or indirectly on the support substrate, a piezoelectric layer on the quartz-crystal layer, and an IDT electrode on the piezoelectric layer. When λ represents a wavelength defined by an electrode finger pitch of the IDT electrode, a thickness of the quartz-crystal layer is about 0.2λ or more and about 0.4λ or less, and the piezoelectric layer has a thickness smaller than the thickness of the quartz-crystal layer.