LiNbO3 Elastic Wave Device SH Spurious Suppression
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Solution Overview
Problem
Elastic wave devices using LiNbO3 substrates often experience spurious emission caused by Shear Horizontal (SH) waves in the frequency region between the resonant and anti-resonant frequencies or within the pass band of band pass filters, degrading their characteristics.
Innovation Solution
The elastic wave device incorporates a LiNbO3 substrate with an interdigital transducer (IDT) electrode and a dielectric film, where the IDT electrode is made of metals like Pt, W, Mo, Ta, or Au, with specific film thicknesses and a projection on the dielectric film, ensuring that the SH wave response occurs below the resonant frequency of the Rayleigh wave, and the Euler angles of the substrate are set to reduce SH wave spurious emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an IDT electrode is provided on a LiNbO3 substrate to enable Rayleigh wave operation, then the elastic wave device achieves desired resonance characteristics, but spurious emission caused by SH waves appears in the frequency region between resonant and anti-resonant frequencies
Solution Approach 1:
The patent changes the physical parameters of the IDT electrode by controlling its thickness to be 0.02λ or more (where λ is the acoustic wavelength). This parameter change shifts the SH wave response frequency to be lower than the Rayleigh wave resonant frequency, thereby eliminating spurious emission in the pass band while maintaining resonance characteristics.
2Object-generated harmful factors
If the IDT electrode thickness is increased to suppress SH wave spurious emission, then the SH wave response frequency moves below the resonant frequency, but the device complexity and manufacturing precision requirements increase
Solution Approach 1:
The patent establishes a specific parameter range for the IDT electrode thickness (0.02λ or more) that balances two objectives: suppressing spurious emission by shifting SH wave response frequency below the resonant frequency, and maintaining manufacturability by avoiding excessive thickness requirements. This optimized parameter range resolves the contradiction between performance and manufacturing precision.
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 positions the SH wave spurious emission outside the frequency region of interest, preventing degradation in characteristics and maintaining satisfactory resonance performance.
Implementation Method 1
an IDT electrode provided on the LiNbO3 substrate... the main mode of an elastic wave excited by the IDT electrode uses a Rayleigh wave
Implementation Method 2
Elastic wave devices using a LiNbO3 substrate are widely used... Rayleigh waves are used as elastic waves in the elastic wave device
Data Source
AI summary
An elastic wave device includes a LiNbO3 substrate, an IDT electrode provided on the LiNbO3 substrate, and a dielectric film that is provided on the LiNbO3 substrate so as to cover the IDT electrode and includes a projection on an upper surface of the stated dielectric film. A main mode of an elastic wave excited by the IDT electrode uses a Rayleigh wave, and a thickness of the IDT electrode is set such that a frequency at which a response by an SH wave appears is lower than a resonant frequency of the Rayleigh wave.