Lithium Niobate Acoustic Wave Structure for Rayleigh Spur Suppression
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Solution Overview
Problem
Acoustic wave devices using lithium niobate films struggle to suppress Rayleigh mode spurious responses and maintain a small fractional bandwidth, leading to insufficient steepness near the pass band edges, especially when used in filter devices.
Innovation Solution
The acoustic wave device design includes a support substrate with a silicon oxide layer and a lithium niobate layer, where the thickness and density of the IDT electrode, duty ratio, cut-angle of the lithium niobate layer, and silicon oxide layer are optimized within specific ranges to reduce Rayleigh mode spurious responses without increasing the fractional bandwidth, using formulas to determine optimal values for TIDT, ρ, duty, LNcut, and TSiO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lithium niobate film with thickness less than or equal to 0.42λ is used, then the device can operate at the fundamental mode, but Rayleigh mode spurious responses cannot be suppressed sufficiently
Solution Approach 1:
A silicon oxide layer is introduced as an intermediary between the support substrate and the lithium niobate film. This intermediate layer modifies the acoustic wave propagation characteristics and suppresses the generation of Rayleigh mode spurious responses while allowing the fundamental SH mode to operate effectively.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers with different material properties: a support substrate, a silicon oxide layer, and a lithium niobate film. This composite structure leverages the complementary properties of each material to achieve both fundamental mode operation and suppression of spurious Rayleigh mode responses.
2Adaptability or versatility
If the value of the fractional bandwidth is excessively large, then the device has wider bandwidth, but the steepness near the edge portion on the high-frequency or low-frequency side of the pass band is not sufficiently large
Solution Approach 1:
The patent optimizes specific parameters including the thickness of the lithium niobate film (0.06λ to 0.7λ), the thickness of the silicon oxide layer (0λ to 0.6λ), the cut-angle of the lithium niobate layer (25° to 70°), and the IDT electrode characteristics. By carefully controlling these parameters, the device achieves a fractional bandwidth of 12% or less while maintaining sufficiently large steepness near the pass band edges.
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 design effectively reduces Rayleigh mode spurious responses and maintains a small fractional bandwidth, resulting in improved filter characteristics with increased steepness at the pass band edges and reduced influence of spurious responses on filter performance.
Implementation Method 1
an IDT (Interdigital Transducer) electrode is disposed on the lithium niobate film
Implementation Method 2
a thickness of the silicon oxide layer is more than or equal to about 0λ, and when a thickness of the IDT electrode is denoted as TIDT
Data Source
AI summary
An acoustic wave device includes a support substrate a silicon oxide layer on the support substrate, a lithium niobate layer on the silicon oxide layer, and an IDT electrode on the lithium niobate layer. When a wavelength of the IDT electrode is denoted as λ, a thickness of the silicon oxide layer is more than or equal to about 0λ. Values of TIDT, ρ, duty, LNcut, TLN, and TSiO2 are within ranges that enable BW derived from Formula 1 to be about 12% or less and ksaw2 derived from Formula 2 to be about 0.1% or less.