LiNbO3 Acoustic Wave Layout for Unwanted Wave Suppression
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Solution Overview
Problem
Existing acoustic wave devices struggle to effectively reduce or prevent unwanted waves when multiple IDT electrodes with different electrode finger pitches are used on the same piezoelectric substrate, which is necessary for miniaturization and multi-band communication in mobile information terminals.
Innovation Solution
The acoustic wave device includes a piezoelectric substrate made of LiNbO3, multiple IDT electrodes with different electrode finger pitches, and a dielectric film. The IDT electrodes have main electrode layers with specific film thicknesses and material density ratios, and the dielectric film is made of silicon oxide. The device is designed to satisfy specific relationships between the wavelengths of the IDT electrodes and the Euler angles of the piezoelectric substrate to minimize unwanted waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If multiple IDT electrodes with different electrode finger pitches are provided on the same piezoelectric substrate, then miniaturization and multi-band communication are achieved, but unwanted waves are generated and cannot be effectively reduced or prevented
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Euler angles (φ, θ, ψ) of the LiNbO3 piezoelectric substrate and the film thickness of the dielectric layer to suppress unwanted waves. Specifically, φ is set to 0°±5°, ψ to 0°±10°, and θ to a specific range that satisfies the inequality −A1/(T×r−B1)+C1≤θ≤−A2/(T×r−B2)+C2, where T is the normalized film thickness and r is the density ratio of the electrode material to Pt. This parameter optimization allows multiple IDT electrodes with different pitches to coexist without generating harmful unwanted waves.
Solution Approach 2:
The patent employs composite materials by combining LiNbO3 piezoelectric substrate with a dielectric layer made of silicon oxide (SiO2) or silicon oxynitride (SiON). This composite structure with specific material properties and thickness ratios enables simultaneous achievement of miniaturization and unwanted wave suppression through the interaction between the piezoelectric and dielectric materials.
2Adaptability or versatility
If multiple IDT electrodes with different electrode finger pitches are provided on the same piezoelectric substrate, then multi-band communication capability is improved, but unwanted waves interfere with communication performance
Solution Approach 1:
The patent uses parameter changes by optimizing the Euler angles of the LiNbO3 substrate and the dielectric layer thickness to create a configuration that supports multiple frequency bands while suppressing unwanted waves. The specific parameter ranges (φ=0°±5°, ψ=0°±10°, and θ within a calculated range) enable the device to maintain high reliability for multi-band communication by eliminating wave interference.
3Reliability
If the dielectric layer thickness is increased to cover the IDT electrodes, then electrode protection and electrical isolation are improved, but unwanted waves are not sufficiently reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the dielectric layer thickness T (normalized with respect to the acoustic wavelength) and combining it with specific Euler angles of the LiNbO3 substrate. This optimized parameter combination achieves both adequate electrode protection through the dielectric layer and effective unwanted wave suppression, resolving the contradiction between protection and wave interference.
Solution Approach 2:
The patent uses composite materials by combining the dielectric layer (silicon oxide or silicon oxynitride) with the LiNbO3 piezoelectric substrate in a specific configuration. This composite structure provides both protective coverage for the IDT electrodes and unwanted wave suppression through the synergistic interaction between the dielectric and piezoelectric materials.
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 unwanted waves, even when multiple IDT electrodes with different electrode finger pitches are used on the same substrate, thereby enhancing the performance of acoustic wave devices in miniaturized mobile information terminals.
Implementation Method 1
an acoustic wave device using a Rayleigh wave... a piezoelectric substrate made of LiNbO3... IDT electrodes provided on the piezoelectric substrate
Implementation Method 2
a dielectric film provided on the piezoelectric substrate to cover the plurality of IDT electrodes
Data Source
AI summary
An acoustic wave device includes a piezoelectric substrate made of LiNbO3, and a dielectric film provided on the piezoelectric substrate to cover first and second IDT electrodes on the piezoelectric substrate. The first and second IDT electrodes include main electrode layers. When wave lengths determined by electrode finger pitches of the first and second IDT electrodes are λ1 and λ2, respectively, the average value thereof is λ0, λ1/λ0=1+X, and λ2/λ0=1−X, a relationship of 0.05≤X≤0.65 is satisfied. The wavelength λ1 is the longest, and the wavelength λ2 is the shortest. In Euler angles (φ, θ, ψ) of the piezoelectric substrate, φ is 0°±5°, ψ is 0°±10°, and θ satisfies Expression 1, wherein a relationship of B1<T×r≤0.10λ0 and B2<T×r≤0.10λ0 are satisfied.