LiNbO3 Acoustic Wave Filter Layout for Multi-Band Spurious Suppression
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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, where IDT electrodes with varying finger pitches are required, leading to unwanted wave interference.
Innovation Solution
The acoustic wave device employs a piezoelectric substrate made of LiNbO3 with multiple IDT electrodes having different finger pitches, where the film thickness and material density ratio of the main electrode layers are optimized, along with a dielectric film, to reduce unwanted waves by controlling the Euler angles and film thickness ratios, ensuring effective suppression of spurious noise across varying electrode lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple IDT electrodes with different finger pitches are formed on the same piezoelectric substrate to enable miniaturization and bandwidth expansion, then the device can support multiple bands and wider bandwidth, but unwanted wave interference and spurious noise increase
Solution Approach 1:
The patent applies local quality by providing a dielectric film selectively over specific IDT electrodes (e.g., IDT1 and IDT3) while leaving other IDT electrodes (e.g., IDT2) exposed or differently covered. This localized dielectric coverage modifies the acoustic wave propagation characteristics only in specific regions, allowing different IDT electrodes to operate at different frequencies without mutual interference, thus enabling multi-band capability while suppressing unwanted waves.
Solution Approach 2:
The dielectric film acts as an intermediary element between the IDT electrodes and the acoustic wave propagation medium. By introducing this intermediate layer with specific material properties and thickness, the patent mediates the interaction between electromagnetic signals and acoustic waves, reducing spurious noise and unwanted wave generation while maintaining the multi-band filtering function.
2Adaptability or versatility
If IDT electrodes with largely different electrode finger pitches are formed on the same substrate to widen bandwidth, then bandwidth is expanded, but manufacturing precision and electrode alignment become more difficult
Solution Approach 1:
The patent segments the piezoelectric substrate into multiple regions, each containing IDT electrodes with different finger pitches designed for specific frequency bands. The dielectric film is also segmented to cover only certain IDT electrodes. This segmentation allows each electrode to be optimized independently for its intended frequency range while simplifying the manufacturing process by treating different pitch requirements as separate, manageable units rather than attempting to precision-align all electrodes simultaneously.
3Volume of moving object
If the piezoelectric substrate is miniaturized to reduce device size, then device compactness is improved, but the ability to accommodate multiple IDT electrodes with different pitches is reduced
Solution Approach 1:
The patent utilizes the vertical dimension by introducing a dielectric film layer above the piezoelectric substrate. This third dimension allows the device to accommodate multiple IDT electrodes with different finger pitches in a compact planar footprint while maintaining their individual acoustic wave propagation paths. The dielectric film thickness and material properties provide additional degrees of freedom to optimize performance without increasing the horizontal device area, thus enabling miniaturization while preserving multi-band capability.
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 IDT electrodes with different finger pitches are used on the same substrate, enhancing the miniaturization and bandwidth capabilities of acoustic wave devices while maintaining filter performance.
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
effectively reduce or prevent unwanted waves... relationship of 0.05≤X≤0.65 is satisfied... Euler angles (φ, θ, ψ) of the piezoelectric substrate
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.