Cu IDT SAW Device with SiO2 Films for Spurious Suppression
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Solution Overview
Problem
Existing surface acoustic wave devices with IDT electrodes made of Al or its alloys on LiNbO3 substrates suffer from insufficient reflection coefficients, leading to ripple in resonance characteristics and spurious responses due to negative frequency-temperature coefficients and inadequate power withstanding performance.
Innovation Solution
A surface acoustic wave device with an IDT electrode mainly made of Cu, utilizing SH waves, and featuring a first silicon oxide film of equal thickness to the electrode and a second silicon oxide film covering it, with specific Euler angles and duty ratios to optimize electromechanical coefficients and reduce spurious responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Al or Al-alloy IDT electrode is used on LiNbO3 substrate, then the device structure is simple and easy to manufacture, but the reflection coefficient is insufficient causing ripple in resonance characteristic
Solution Approach 1:
The patent changes the material parameter of the IDT electrode from Al to Cu, which has higher density (8.96 g/cm³ vs 2.70 g/cm³ for Al). This parameter change increases the reflection coefficient by a factor of about 3, eliminating the ripple in resonance characteristic while maintaining manufacturing simplicity
Solution Approach 2:
The patent employs a composite structure with Cu IDT electrode on LiNbO3 substrate, utilizing the high density of Cu and the positive frequency-temperature coefficient of the substrate to achieve both good resonance characteristic and temperature stability
2Reliability
If Cu IDT electrode is used to increase reflection coefficient, then the resonance characteristic improves, but the temperature characteristic deteriorates due to negative frequency-temperature coefficient
Solution Approach 1:
The patent selects LiNbO3 substrate with specific crystal orientation (Y-rotated X-propagating) that has positive frequency-temperature coefficient, which compensates for the temperature drift of Cu electrode, achieving outstanding temperature characteristic
Solution Approach 2:
The positive frequency-temperature coefficient of LiNbO3 substrate acts as a counterweight to the negative temperature coefficient effect, compensating for temperature-induced frequency drift and stabilizing the resonance frequency
3Power
If duty of IDT electrode is reduced to enhance power withstanding performance, then the power withstanding performance improves, but spurious response increases
Solution Approach 1:
The patent optimizes the duty ratio parameter to a specific range (0.4-0.6) that simultaneously achieves good power withstanding performance and suppresses spurious response, rather than simply reducing duty to maximize power handling
Solution Approach 2:
The patent applies different electrode finger width and spacing dimensions locally within the IDT structure to optimize the duty ratio, creating non-uniform local geometry that suppresses spurious modes while maintaining power handling capability
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
The solution enhances the reflection coefficient, improves temperature characteristics, and effectively suppresses spurious responses, achieving superior resonance and filter characteristics while maintaining power withstanding performance.
Implementation Method 1
an IDT electrode and a silicon oxide film are disposed on a LiNbO3 substrate and that utilizes an SH wave
Implementation Method 2
the reflection coefficient of the IDT electrode is sufficiently increased to thereby make it possible to suppress a ripple that occurs in the resonance characteristic
Data Source
AI summary
A surface acoustic wave device has high power withstanding performance and is able to effectively suppress an undesirable spurious response. The surface acoustic wave device includes an LiNbO3 substrate having Euler angles (0°±5°, θ±5°, 0°±10°), an electrode that is disposed on the LiNbO3 substrate and that has an IDT electrode made mainly from Cu, a first silicon oxide film that is disposed in an area other than an area in which the electrode is disposed to have a thickness equal to that of the electrode, and a second silicon oxide film that is disposed so as to cover the electrode and the first silicon oxide film, wherein the surface acoustic wave device utilizes an SH wave, wherein a duty D of the IDT electrode is less than or equal to about 0.49, and θ of the Euler angles (0°±5°, θ±5°, 0°±10°) is set to fall within a range that satisfies the following inequality:−10×D+92.5−100×C≦θ≦37.5×D2−57.75×D+104.075+5710×C2−1105.7×C+45.729D: dutyC: thickness of the IDT electrode normalized using a wavelength λ.