Laminated Acoustic Wave Filter Structure for Ripple Suppression
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Solution Overview
Problem
Existing acoustic wave devices experience ripples in frequency characteristics due to unwanted bulk wave signals, which are not effectively mitigated by current designs using piezoelectric substrates like LiNbO3 or LiTaO3, leading to reflection and signal extraction issues.
Innovation Solution
The acoustic wave device incorporates a laminated substrate with specific acoustic impedance relationships between layers, including a dielectric intermediate layer, to control the propagation of transversal waves, thereby reducing or preventing ripples in frequency characteristics by optimizing the thickness and impedance combinations of the piezoelectric, dielectric, and support layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piezoelectric substrate is used to excite Lamb waves, then acoustic wave resonance is achieved, but unwanted bulk waves are excited causing ripples in frequency characteristics
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the piezoelectric substrate and the support substrate. This dielectric layer acts as a mediator that allows the piezoelectric substrate to excite Lamb waves while preventing the excitation of unwanted bulk waves in the support substrate, thereby resolving the contradiction between achieving acoustic wave resonance and eliminating harmful bulk waves.
Solution Approach 2:
The substrate structure is segmented into three distinct layers: a piezoelectric substrate layer, a dielectric layer, and a support substrate layer. This segmentation allows each layer to perform its specific function - the piezoelectric layer generates acoustic waves, the dielectric layer controls wave propagation, and the support layer provides mechanical stability - thereby enabling resonance while preventing harmful bulk wave excitation.
2Ease of manufacture
If wirings connected to different potentials face each other, then electrical connection is achieved, but unwanted bulk wave signals are extracted causing ripples in frequency characteristics
Solution Approach 1:
The dielectric layer serves as an intermediary that prevents unwanted bulk wave signals from being extracted by wirings or busbars. By placing this dielectric layer between the piezoelectric substrate and support substrate, the harmful coupling between electrical connections and bulk wave extraction is eliminated while maintaining necessary electrical connections for device operation.
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 cancels unwanted bulk waves at interfaces, reducing signal extraction and minimizing ripples in frequency characteristics, thereby enhancing the performance of acoustic wave filters.
Implementation Method 1
a piezoelectric layer laminated on the first layer
Implementation Method 2
when an acoustic velocity of a transversal wave propagating through the first layer is defined as v
Implementation Method 3
combinations of a magnitude relationship of acoustic impedances of the piezoelectric layer, the first layer, and the second layer
Data Source
AI summary
An acoustic wave device defining a filter device having a pass band, includes a laminated substrate including first and second layers, a piezoelectric layer laminated on the first layer, and an excitation electrode on the piezoelectric layer. The first layer is a dielectric layer and is included in an intermediate layer laminated on the piezoelectric layer. A thickness of the first layer is defined as td, and combinations of a magnitude relationship of acoustic impedances of the piezoelectric layer and the first and second layers, and the thickness td are as shown in Table 1:TABLE 1MagnitudeRelationship ofAcoustic ImpedanceZp > ZdZp < ZdZs > Zdtd = n (1/2) λtd = (2n − 1) (1/4) λZs < Zdtd = (2n − 1) (1/4) λtd = n (1/2) λ.