Surface Acoustic Wave Device Spurious Response Suppression
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Solution Overview
Problem
Surface acoustic wave devices experience degradation in frequency characteristics due to unnecessary waves, leading to spurious responses between resonant and anti-resonant frequencies or in passbands.
Innovation Solution
A surface acoustic wave device is designed with a piezoelectric substrate, an IDT electrode, a first dielectric layer of silicon oxide, and a third dielectric layer made of materials like silicon nitride or alumina, which covers the substrate and IDT electrode surfaces, effectively shifting the frequency of spurious responses outside the main frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a SiO2 film is formed on the piezoelectric substrate to cover the IDT electrode, then frequency temperature characteristics are improved, but spurious response is generated due to unnecessary waves
Solution Approach 1:
The dielectric layer is divided into multiple segments with different acoustic velocities arranged in a specific sequence. This segmentation allows different portions of the dielectric layer to serve different functions: some segments suppress unnecessary waves while others maintain frequency temperature characteristics, thereby resolving the contradiction between improved manufacturing precision and reduced spurious response
Solution Approach 2:
The invention uses a composite dielectric layer structure combining materials with different acoustic velocities (such as SiO2, Si3N4, and others). This composite structure leverages the complementary properties of each material to simultaneously achieve good frequency temperature characteristics and suppress spurious responses generated by unnecessary waves
2Object-generated harmful factors
If the thickness of the dielectric layer is increased to suppress unnecessary waves, then spurious response is reduced, but the device structure becomes more complex
Solution Approach 1:
Instead of using a single thick dielectric layer, the invention segments the dielectric layer into multiple thinner layers with different acoustic velocities. This segmentation achieves effective suppression of unnecessary waves through the combined effect of multiple layers, avoiding the need for a single thick layer and thereby reducing structural complexity while maintaining effectiveness in reducing spurious response
Solution Approach 2:
The invention optimizes the thickness and acoustic velocity parameters of each dielectric layer segment to achieve the desired suppression of unnecessary waves. By carefully selecting and adjusting these parameters, the invention achieves effective spurious response reduction without requiring excessive layer thickness or complexity
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 prevents or decreases the degradation in frequency characteristics by positioning spurious responses outside the main frequency band, improving the device's performance and reducing insertion losses.
Implementation Method 1
a surface acoustic wave device that utilizes a surface acoustic wave
Implementation Method 2
spurious response may be disadvantageously generated between a resonant frequency and an anti-resonant frequency or in a passband due to an unnecessary wave
Implementation Method 3
the surface acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2001-44787 has excellent frequency temperature characteristics
Implementation Method 4
when the thickness of the SiN film formed on the SiO2 film is adjusted, the frequency characteristics of the surface acoustic wave device can be adjusted
Data Source
AI summary
A surface acoustic wave device includes a piezoelectric substrate, an IDT electrode provided on the piezoelectric substrate, a first dielectric layer, and a second dielectric layer. The first dielectric layer is provided on the piezoelectric substrate and made of silicon oxide. The second dielectric layer is provided on the first dielectric layer and has an acoustic velocity greater than that of the first dielectric layer. A third dielectric layer is provided between the first dielectric layer and the piezoelectric substrate, and arranged to cover a surface of the piezoelectric substrate and an upper surface and side surfaces of the IDT electrode.