Layered X-SAW Acoustic Wave Structure for Higher-Order Mode Suppression
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Solution Overview
Problem
Existing acoustic wave devices struggle to effectively reduce or prevent higher-order modes, particularly when using a silicon substrate with a (111) plane orientation.
Innovation Solution
The acoustic wave device incorporates a silicon substrate with a (111) plane orientation, a silicon nitride film, a silicon oxide film, and a piezoelectric layer made of Y-cut X-SAW propagation lithium tantalate. The IDT electrode has a specific electrode finger pitch, and the film thickness of the piezoelectric layer is equal to or less than about 1λ. The Euler angles of the piezoelectric layer are carefully controlled within specific ranges, and the relationship between these angles and the film thickness of the silicon nitride film is defined in tables to achieve effective mode reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon substrate with (111) plane orientation is used, then the Q value is increased, but higher-order modes cannot be sufficiently reduced or prevented
Solution Approach 1:
The patent changes the Euler angles of the piezoelectric layer to specific ranges (θ: 60°≤θ<90° or 90°<θ≤120°, ψ: 0°≤ψ<30° or 60°≤ψ≤90°) to simultaneously achieve high Q value and suppress higher-order modes, resolving the contradiction between these two parameters
Solution Approach 2:
The patent uses a composite structure with silicon substrate, silicon nitride film, silicon oxide film, and piezoelectric layer, where each layer contributes to both maintaining high Q value and suppressing higher-order modes through their combined acoustic velocity differences
2Power
If the film thickness of the piezoelectric layer is increased, then the acoustic wave generation is enhanced, but the higher-order modes become more difficult to control
Solution Approach 1:
The patent optimizes the piezoelectric layer thickness to be 0.2λ≤d≤0.5λ (where λ is the acoustic wavelength) to achieve sufficient acoustic wave generation while effectively controlling higher-order modes through the specific thickness range
3Manufacturing precision
If the Euler angles of the piezoelectric layer are adjusted to suppress higher-order modes, then mode purity is improved, but the acoustic velocity and Q value may be reduced
Solution Approach 1:
The patent identifies specific Euler angle ranges (θ: 60°≤θ<90° or 90°<θ≤120°, ψ: 0°≤ψ<30° or 60°≤ψ≤90°) that simultaneously achieve both high mode purity and maintained acoustic velocity, eliminating the trade-off between these parameters
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 or prevents higher-order modes, ensuring improved performance and efficiency in acoustic wave devices.
Implementation Method 1
a piezoelectric layer on the silicon oxide film and including Y-cut X-SAW propagation lithium tantalate
Implementation Method 2
Y-cut X-SAW propagation lithium tantalate
Data Source
AI summary
An acoustic wave device includes a silicon support substrate, a silicon nitride film on the support substrate, a silicon oxide film on the silicon nitride film, a piezoelectric layer on the silicon oxide film and using Y-cut X-SAW propagation lithium tantalate, and an IDT electrode on the piezoelectric layer. A film thickness of the piezoelectric layer is equal to or less than about 1λ, Euler angles of the piezoelectric layer are (0±5°, θ, 0±5°) or (0±5°, θ, 180±5°), θ in the Euler angles of the piezoelectric layer is about 95.5°≤θ<117.5° or about −84.5°≤θ<−62.5°, and a relationship between θ in the Euler angles of the piezoelectric layer and a film thickness of the silicon nitride film is a combination shown in Table 1 or Table 2.