Acoustic Wave Filter Dielectric Stack for Smaller Stable Resonators
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Solution Overview
Problem
The existing acoustic wave devices, particularly those described in Japanese Patent No. 6766896, face challenges in reducing their size due to the structure of silicon oxide films interposed between the IDT electrode and LiTaO3 film.
Innovation Solution
Incorporating a piezoelectric layer of lithium tantalate or lithium niobate with a dielectric film having a higher dielectric constant than the piezoelectric layer, and using a thicker dielectric film in serial arm resonators compared to parallel arm resonators, along with specific material and thickness combinations to optimize acoustic wave propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide film is interposed between the IDT electrode and LiTaO3 film, then temperature characteristics are improved, but device size cannot be reduced
Solution Approach 1:
The patent changes the dielectric constant parameter by selecting materials with higher dielectric constants (TiO2: 90, SrTiO3: 250, Pb(Zr,Ti)O3: 500-1000) compared to silicon oxide (4.5). This parameter change allows the dielectric film to be thinner while maintaining the same capacitance and temperature compensation effect, thereby reducing device size while preserving temperature characteristics
Solution Approach 2:
The patent uses composite material structures where a thin dielectric film (high dielectric constant material) is combined with the piezoelectric layer and IDT electrode. This composite approach enables achieving both temperature stability and size reduction by leveraging the high dielectric constant property to minimize film thickness while maintaining functional performance
2Volume of moving object
If the dielectric film thickness is increased, then device size is reduced, but filter characteristics may be affected
Solution Approach 1:
The patent optimizes the dielectric film thickness parameter within a specific range (0.01λ to 0.05λ) to achieve the right balance. By changing the dielectric constant parameter and adjusting thickness accordingly, the invention maintains appropriate capacitance values for filter characteristics while minimizing device size
Solution Approach 2:
The patent applies different dielectric film thicknesses to different resonator types within the same filter device. Serial arm resonators use thicker dielectric films while parallel arm resonators use thinner films, optimizing local characteristics for each resonator type while achieving overall size reduction
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 achieves a significant reduction in device size while maintaining suitable filter characteristics and improving temperature stability.
Implementation Method 1
an acoustic wave device according to a preferred embodiment of the present invention includes a piezoelectric layer including lithium tantalate or lithium niobate
Implementation Method 2
the dielectric film including a dielectric material having a higher dielectric constant than that of the lithium tantalate or lithium niobate
Data Source
AI summary
An acoustic wave device includes a piezoelectric layer including lithium tantalate or lithium niobate, a dielectric film on the piezoelectric layer, the dielectric film including a dielectric material having a higher dielectric constant than that of the lithium tantalate or lithium niobate, and an IDT electrode on the dielectric film.