LiNbO3 Rayleigh Wave Resonator Layout for Low-Spurious RF Filters
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Solution Overview
Problem
Existing elastic wave devices using Rayleigh waves face challenges in miniaturization and spurious noise reduction due to differing propagation directions and silicon oxide film thicknesses in resonators, leading to inefficient arrangement and generation of spurious noise within the pass band.
Innovation Solution
The elastic wave device employs an LiNbO3 substrate with specific Euler angles and dielectric film thicknesses for IDT electrodes, ensuring aligned propagation directions and optimized film thicknesses between series and parallel arm resonators to reduce spurious noise and enhance filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If different propagation directions are used in elastic wave resonators to reduce spurious noise, then spurious noise within the pass band is reduced, but the efficiency in arrangement of resonators on a chip is lowered and device miniaturization becomes difficult
Solution Approach 1:
The patent changes the Euler angle θ of the LiNbO3 substrate to a specific range (25° to 35°) to suppress SH wave generation. This parameter change allows the use of identical propagation directions in all resonators while preventing spurious noise, thereby resolving the contradiction between noise reduction and miniaturization.
2Manufacturing precision
If different thicknesses of silicon oxide films are used in elastic wave resonators to provide steep filter characteristic and wide pass band, then filter performance is improved, but spurious noise other than target spurious noise is generated within the pass band or in a vicinity of the pass band
Solution Approach 1:
The patent modifies the Euler angle θ parameter of the LiNbO3 substrate to a specific range (25° to 35°) which suppresses SH wave generation across different dielectric film thicknesses. This allows the use of different film thicknesses for filter performance optimization without generating spurious noise, resolving the contradiction between filter characteristic and spurious noise reduction.
3Object-generated harmful factors
If a specific relationship between Euler angle θ and electrode thickness is maintained to reduce spurious noise, then spurious noise is reduced, but the relationship holds across a wide range allowing SH wave spurious noise to be generated when thicknesses of silicon oxide differ
Solution Approach 1:
The patent expands the effective range of θ to (25° to 35°) which provides robust suppression of SH wave spurious noise even when dielectric film thicknesses vary. This broader parameter range increases adaptability while maintaining noise suppression, resolving the contradiction between noise reduction and versatility.
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 significantly reduces spurious noise, enables miniaturization, and provides a steep filter characteristic with a wide pass band, suitable for high-frequency front-end circuits and communication apparatuses.
Implementation Method 1
an elastic wave device using a Rayleigh wave
Implementation Method 2
an electrode including an IDT (interdigital transducer) electrode
Data Source
AI summary
An elastic wave device includes an LiNbO3 substrate, a first elastic wave resonator including a first IDT electrode and a first dielectric film, and a second elastic wave resonator including a second IDT electrode and a second dielectric film. A Rayleigh wave travels along at least one surface of the elastic wave device. A thickness of the first dielectric film differs from a thickness of the second dielectric film. A propagation direction of an elastic wave in the first elastic wave resonator coincides with a propagation direction of an elastic wave in the second elastic wave resonator. Euler angles of the LiNbO3 substrate fall within a range of (0°±5°, θ, 0°±10°).