LiNbO3 Acoustic Wave Filter Layout for SH Spurious Isolation
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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, ensuring the SH wave response is outside the pass band by adjusting the thickness and Euler Angles of the substrate, thereby isolating SH wave responses from the filter's pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If acoustic wave resonators are used in a bandpass filter, then the filter can process signals, but SH wave spurious responses may generate in the pass band
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) and optimizing the thickness ratio between the main electrode layer and total IDT electrode to 5-20%. This parameter optimization shifts the SH wave response frequency away from the pass band, resolving the contradiction between signal processing capability and SH wave suppression.
2Reliability
If the SH wave spurious is suppressed in each acoustic wave resonator, then individual resonator performance improves, but SH wave spurious may still generate in the filter pass band
Solution Approach 1:
The patent applies a universal solution across all acoustic wave resonators in the filter by standardizing the IDT electrode material composition and thickness ratio. This ensures that all resonators simultaneously achieve both individual performance optimization and collective SH wave suppression in the pass band, eliminating the need for additional filtering components.
3Object-generated harmful factors
If the IDT electrode thickness is increased to suppress SH wave spurious, then SH wave response moves outside pass band, but device size increases
Solution Approach 1:
The patent optimizes the IDT electrode thickness ratio to a specific range (5-20% of total electrode thickness) and selects high-density materials, achieving effective SH wave suppression without excessive thickness increase. This balanced parameter optimization resolves the contradiction between SH wave suppression and device miniaturization.
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 responses occur on the lower frequency side, thus improving the filter's performance by keeping SH wave spurious outside the desired frequency range.
Implementation Method 1
an IDT (interdigital transducer) electrode is provided on a LiNbO3 substrate
Implementation Method 2
the acoustic wave resonators utilize a Rayleigh wave, and a response of an SH wave excited by one or more of the acoustic wave resonators utilizing the Rayleigh wave is outside a pass band
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.