SAW Device LiNbO3 Substrate Euler Angles
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Surface acoustic wave devices with LiNbO3 substrates experience increased insertion loss and spurious responses due to the height difference of SiO2 films and the use of heavy metals like Al for IDT electrodes, which affect the velocity and frequency of acoustic waves, leading to insufficient filter and resonance characteristics.
Innovation Solution
A surface acoustic wave device with a LiNbO3 substrate having specific Euler angles (0°±5°, 180° to 247°, 0°±5°) and an IDT electrode filled with metals like Al, Au, Ta, or Cu, where the SiO2 film is formed to cover the electrode and substrate with a flat surface, optimizing the normalized film thickness and Euler angles to suppress spurious responses and maintain high reflection coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a SiO2 film is formed to cover the IDT electrode to improve temperature characteristics, then the temperature coefficient of resonant frequency is improved, but a height difference is created between portions with IDT fingers and portions without IDT fingers, causing insertion loss to increase
Solution Approach 1:
A first insulator layer is formed between the IDT electrode fingers before forming the SiO2 film. This preliminary layer creates a flat base that allows the SiO2 film to be formed uniformly, preventing height differences that would cause insertion loss while still providing the temperature compensation effect
Solution Approach 2:
The first insulator layer acts as an intermediary between the IDT electrode and the SiO2 film. It mediates the conflict between needing a flat surface for low insertion loss and needing SiO2 coverage for temperature characteristics by providing a uniform base that enables both requirements to be satisfied
2Reliability
If an IDT electrode made of a heavy metal (density at least 1.5 times that of Al) is used to improve the reflection coefficient, then the reflection coefficient is improved, but large variations occur in the velocity and frequency of acoustic waves depending on variations in electrode thickness
Solution Approach 1:
The patent changes the material parameter of the IDT electrode from heavy metals (like Au or Pt) to Al or its alloys. This parameter change reduces the density from at least 1.5 times that of Al to approximately Al's density, thereby reducing the sensitivity of acoustic wave velocity and frequency to thickness variations while maintaining adequate reflection coefficient through optimized electrode geometry and the presence of the insulator layer
3Manufacturing precision
If an IDT electrode made of Al is used to achieve low reflection coefficient and good acoustic wave characteristics, then the acoustic wave velocity and frequency stability is improved, but the reflection coefficient becomes too low for sufficient surface acoustic wave resonator and filter characteristics
Solution Approach 1:
The patent creates a composite structure consisting of the Al-based IDT electrode and the first insulator layer. This composite configuration allows the Al electrode to provide acoustic wave stability while the insulator layer contributes to enhancing the reflection coefficient, achieving both requirements through the combined effect of different materials
Solution Approach 2:
The first insulator layer serves as a mediator that enables the Al electrode to achieve both low sensitivity to thickness variations and adequate reflection coefficient. It works in conjunction with the Al electrode to compensate for the low reflection coefficient issue while preserving the acoustic wave stability benefits of Al
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 effectively suppresses unwanted spurious responses and maintains good resonance and filter characteristics while ensuring a high reflection coefficient and minimal insertion loss, improving the temperature characteristics of the surface acoustic wave device.
Implementation Method 1
LiTaO3 and LiNbO3 have negative values of a temperature coefficient of resonant frequency (TCF). To improve such temperature characteristics, one technique is known in which a SiO2 film having a positive temperature coefficient of resonant frequency is arranged on a piezoelectric substrate to cover an IDT electrode.
Implementation Method 2
Surface acoustic wave devices typically include a piezoelectric substrate made of LiTaO3, LiNbO3, or other suitable material and an IDT electrode thereon.
Implementation Method 3
an IDT electrode formed by filling grooves provided in the upper surface of a piezoelectric substrate with a metal... the electrode has a sufficiently high reflection coefficient
Data Source
AI summary
A surface acoustic wave device includes a LiNbO3 substrate having a plurality of grooves formed in the upper surface thereof, an IDT electrode formed by filling the grooves with a metal, and a SiO2 layer arranged to cover an upper surface of the LiNbO3 substrate and the IDT electrode and having a substantially flat surface. The surface acoustic wave device uses a response of a Rayleigh wave. The LiNbO3 substrate has Euler angles in the range of (0°±5°, 180° to 247°, 0°±5°).