LiNbO3 Acoustic Wave Filter Electrode Tuning for SH Spurious Suppression
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Solution Overview
Problem
Bandpass acoustic wave filters using Rayleigh waves face challenges in suppressing spurious SH wave responses within the pass band, even when individual acoustic wave resonators' SH wave spurious are suppressed, due to the potential generation of SH waves between resonant and anti-resonant frequencies.
Innovation Solution
The design incorporates a bandpass acoustic wave filter device with a plurality of acoustic wave resonators on a LiNbO3 substrate, featuring an IDT electrode with a main electrode layer made of high-density materials like Pt or W, where the thickness of the main electrode layer is optimized to ensure the SH wave velocity is slower than the Rayleigh wave velocity by at least 2%, positioning the SH wave response outside the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional IDT electrode is used on LiNbO3 substrate, then the resonator can operate at the desired frequency, but SH wave spurious responses appear between resonant and anti-resonant frequencies
Solution Approach 1:
The patent changes the physical parameters of the IDT electrode by using high-density materials (Pt: 21.45 g/cm³, W: 19.3 g/cm³) with specific thicknesses (0.061λ-0.20λ for Pt, 0.090λ-0.20λ for W). This parameter change modifies the acoustic velocity of the SH wave to be at least 2% slower than the Rayleigh wave, shifting the SH wave response outside the pass band and eliminating spurious effects.
Solution Approach 2:
The patent employs composite electrode structures with high-density materials (Pt or W) as the main electrode layer, potentially combined with other materials in multi-layer configurations. This composite approach allows precise control over acoustic wave velocities while maintaining electrical performance, effectively separating the Rayleigh wave and SH wave responses in the frequency domain.
2Reliability
If multiple acoustic wave resonators are employed in a bandpass filter, then the filter can achieve the desired pass band characteristics, but SH wave spurious responses may generate within the pass band
Solution Approach 1:
By uniformly applying the high-density material parameter changes across all resonators in the filter, the patent ensures that SH wave responses from all resonators are consistently shifted to frequencies below the pass band. This prevents any individual resonator from generating spurious responses within the pass band, maintaining clean filter characteristics.
3Reliability
If the IDT electrode thickness is increased to suppress SH wave spurious, then the SH wave response moves outside the pass band, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent identifies specific thickness ranges (0.061λ-0.20λ for Pt, 0.090λ-0.20λ for W) that achieve the required SH wave velocity reduction without excessive thickness. These optimized parameters suppress spurious responses while maintaining manufacturable dimensions and avoiding unnecessary device complexity.
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 eliminates or minimizes the influence of SH wave responses within the pass band, enhancing filter characteristics by ensuring the SH wave response is on the lower frequency side, thus improving the filter's performance by reducing spurious effects.
Implementation Method 1
an IDT (interdigital transducer) electrode is provided on a LiNbO3 substrate
Implementation Method 2
a thickness of the main electrode layer is has a value at which an acoustic velocity of the SH wave is slower than an acoustic velocity of the Rayleigh wave by about 2% or more
Data Source
AI summary
A bandpass acoustic wave filter device includes an IDT electrode and a dielectric film disposed on a piezoelectric substrate including a LiNbO3 layer, and an acoustic wave resonator is defined by the IDT electrode. The acoustic wave resonator utilizes the Rayleigh wave, and a response of an SH wave excited by the acoustic wave resonator is outside a pass band of the acoustic wave filter device.