Rayleigh Wave Filter Structure to Shift SH Spurious Outside Pass Band
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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 have suppressed SH wave spurious between resonant and anti-resonant frequencies.
Innovation Solution
The design incorporates a piezoelectric substrate with a LiNbO3 layer, an IDT electrode with a main electrode layer made of high-density materials like Pt or W, and specific thickness settings to ensure the SH wave response is outside the pass band, utilizing a Rayleigh wave and optimizing the Euler Angles of the substrate for efficient Rayleigh wave excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple acoustic wave resonators are employed in a bandpass filter, then the filter functionality is improved, but SH wave spurious responses may generate in the pass band
Solution Approach 1:
The patent changes the Euler angles of the LiNbO3 substrate to (0°, 30°, 0°) and adjusts the IDT electrode thickness to 0.061λ or more. These parameter changes shift the SH wave response frequency to be lower than the Rayleigh wave resonant frequency, thereby moving the spurious response outside the pass band while maintaining filter functionality
Solution Approach 2:
Instead of trying to suppress the SH wave response within the pass band, the patent inverts the approach by deliberately positioning the SH wave response on the lower frequency side of the pass band. This is achieved by optimizing the substrate Euler angles and IDT thickness, causing the spurious response to appear where it does not interfere with the filter's pass band operation
2Object-generated harmful factors
If the IDT electrode thickness is increased to suppress SH wave spurious, then the SH wave suppression is improved, but the acoustic velocity difference between SH wave and Rayleigh wave must be precisely controlled
Solution Approach 1:
The patent establishes a specific relationship between IDT electrode thickness and acoustic velocity: the thickness should be 0.061λ or more to ensure the SH wave acoustic velocity is at least 2% slower than the Rayleigh wave. This quantitative parameter specification provides clear manufacturing guidance while achieving effective SH wave suppression
Solution Approach 2:
The patent applies different material properties and structural characteristics to different parts of the system: the LiNbO3 substrate is configured with specific Euler angles (0°, 30°, 0°), the IDT electrode uses high-density material (≥18 g/cm³) with optimized thickness, and the dielectric film covers the IDT. These localized optimizations work together to achieve the desired acoustic velocity difference and SH wave suppression
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
the acoustic wave resonators utilize a Rayleigh wave
Implementation Method 3
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.