LiNbO3 Acoustic Wave Filter Layout for Multi-Band Spurious Noise Control
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Solution Overview
Problem
Existing acoustic wave devices face challenges in miniaturization and bandwidth expansion, particularly in forming multiple band pass filters with different pass bands on the same piezoelectric substrate, which leads to unwanted wave interference due to varying electrode finger pitches.
Innovation Solution
The acoustic wave device employs a piezoelectric substrate made of LiNbO3 with multiple IDT electrodes having different electrode finger pitches, where the film thickness and material density ratio of the main electrode layers are optimized, along with a dielectric film, to minimize unwanted waves by controlling the Euler angles and film thickness ratios, ensuring effective reduction of spurious noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple IDT electrodes with different electrode finger pitches are provided on the same piezoelectric substrate, then bandwidth expansion and multi-band filtering capabilities are improved, but unwanted wave interference and spurious noise increase
Solution Approach 1:
The patent applies local quality by providing a dielectric film with specific thickness and material properties only in certain regions above the IDT electrodes. The dielectric film thickness is optimized locally to reduce unwanted waves generated by specific IDT electrodes while maintaining the different electrode finger pitches needed for multi-band operation. This localized modification allows each IDT electrode to have tailored characteristics that minimize its spurious noise contribution.
Solution Approach 2:
The patent changes physical parameters including the dielectric film thickness, material composition, and electrode finger pitch ratios to control unwanted wave generation. By adjusting these parameters within specific ranges and relationships, the device achieves bandwidth expansion while suppressing spurious noise through parameter optimization rather than structural redesign.
2Volume of moving object
If multiple band pass filters are integrated on the same substrate, then device miniaturization is improved, but unwanted wave interference between filters increases
Solution Approach 1:
The patent merges multiple band pass filters onto a single piezoelectric substrate, integrating multiple filtering functions in one compact device. By combining the filters and using a shared dielectric film structure, the patent achieves miniaturization while the dielectric film serves as a common element that helps suppress unwanted waves across all filter operations.
Solution Approach 2:
The dielectric film acts as an intermediary element between the IDT electrodes and the acoustic wave propagation path. This intermediate layer modifies the acoustic field and electromagnetic field interactions, mediating the unwanted wave generation from multiple IDT electrodes and reducing interference between closely spaced band pass filters on the same substrate.
3Adaptability or versatility
If IDT electrodes with different electrode finger pitches are used, then multi-band communication capability is improved, but spurious noise generation increases
Solution Approach 1:
The patent applies local quality by tailoring the dielectric film properties specifically for each IDT electrode region. Each IDT electrode operating at a different band has an associated dielectric film thickness optimized for its frequency range, allowing multi-band communication capability while locally suppressing spurious noise generation at each operating frequency.
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 pitches are used on the same substrate, enhancing the device's frequency-temperature characteristics and bandwidth capabilities.
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... effectively reduce or prevent unwanted waves
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.