Multilayer Acoustic Wave Structure for Spurious Mode Suppression
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Solution Overview
Problem
Existing acoustic wave devices suffer from Rayleigh mode spurious responses in lower frequency bands and higher-order mode spurious responses in higher frequency bands, which degrade device characteristics.
Innovation Solution
The acoustic wave device incorporates a multilayer body composed of lithium tantalate and lithium niobate piezoelectric layers, with a thickness of 0.66λ or less, and includes a low acoustic velocity film and a high acoustic velocity film to confine acoustic wave energy, reducing spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single piezoelectric layer is used, then the device structure is simple, but Rayleigh mode and higher-order mode spurious responses occur degrading characteristics
Solution Approach 1:
The patent uses a composite piezoelectric layer structure comprising a lithium tantalate piezoelectric layer and a lithium niobate piezoelectric layer laminated together. This composite structure suppresses Rayleigh mode spurious responses in lower frequency bands and higher-order mode spurious responses in higher frequency bands, thereby improving acoustic wave characteristics while maintaining reasonable device complexity
Solution Approach 2:
The piezoelectric layer is segmented into two distinct functional layers: a lithium tantalate layer (0.1λ to 0.3λ thick) that primarily suppresses Rayleigh mode spurious responses, and a lithium niobate layer (0.3λ to 0.5λ thick) that primarily suppresses higher-order mode spurious responses. This segmentation allows each layer to target specific frequency bands and spurious response types
2Reliability
If the piezoelectric layer thickness is increased to improve acoustic wave confinement, then Q factor increases, but device size and complexity increase
Solution Approach 1:
The patent optimizes the thickness parameters of the piezoelectric layers relative to the acoustic wave wavelength λ. The lithium tantalate layer is set to 0.1λ to 0.3λ and the lithium niobate layer to 0.3λ to 0.5λ, achieving effective acoustic wave confinement and high Q factor while controlling overall device thickness to be 0.66λ or less
Solution Approach 2:
The composite piezoelectric structure achieves superior acoustic wave confinement compared to a single layer of equivalent total thickness. The combination of lithium tantalate and lithium niobate with their different acoustic velocities creates effective acoustic impedance matching that enhances confinement without requiring excessive total thickness
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 Rayleigh mode spurious responses in lower frequency bands and higher-order mode spurious responses, enhancing the Q factor and stability of the acoustic wave device.
Implementation Method 1
a lithium tantalate piezoelectric layer and a lithium niobate piezoelectric layer that are laminated
Implementation Method 2
a low acoustic velocity film and a high acoustic velocity film to confine acoustic wave energy
Data Source
AI summary
An acoustic wave device includes a support substrate, a multilayer body, and an IDT electrode. The multilayer body includes a lithium tantalate piezoelectric layer and a lithium niobate piezoelectric layer that are laminated, and is on the support substrate. The IDT electrode is on the multilayer body, and includes electrode fingers. When a wavelength of an acoustic wave determined by a pitch of the electrode fingers is denoted as λ, a thickness of the multilayer body is about 0.66λ or less.