Sialon Composite Substrate for Stable SAW Device Frequency
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Solution Overview
Problem
Existing composite substrates for surface acoustic wave devices face issues with temperature dependence of frequency due to high coefficients of thermal expansion in materials like sapphire and alumina, and poor workability and insulation properties in silicon, leading to reduced performance in high-frequency applications.
Innovation Solution
A composite substrate is developed using a sintered sialon body as the supporting substrate, which has a high acoustic velocity, moderate Young's modulus, and low coefficient of thermal expansion, directly joined with a functional substrate to enhance holding power and reduce temperature dependence, while maintaining high insulation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If sapphire or alumina is used as the supporting substrate, then the coefficient of thermal expansion is reduced, but the temperature dependence of frequency cannot be significantly reduced and the Young's modulus is excessively high causing poor workability
Solution Approach 1:
The patent changes the material parameters by selecting sialon (silicon aluminum oxynitride) with specific compositional ratios, achieving a Young's modulus of 200-350 GPa and coefficient of thermal expansion of 2.0-3.5 ppm/K, which balances mechanical strength and thermal stability for improved workability and frequency stability
Solution Approach 2:
The patent uses composite sialon material combining silicon nitride and aluminum oxynitride phases, achieving optimized properties that neither pure sapphire nor alumina can provide, specifically balancing Young's modulus, thermal expansion coefficient, and acoustic velocity for the supporting substrate
2Stability of the object's composition
If silicon is used as the supporting substrate, then the coefficient of thermal expansion is sufficiently low, but the Young's modulus is low causing curling or cracking and insulation properties are insufficient
Solution Approach 1:
The patent employs composite sialon material with specific Si-Al-O-N composition that provides both high Young's modulus (200-350 GPa) for structural integrity and high resistivity (>10^14 Ωcm) for insulation, overcoming silicon's deficiencies while maintaining low thermal expansion
Solution Approach 2:
The patent optimizes material parameters by controlling the composition ratios in sialon to achieve simultaneous improvement in Young's modulus, resistivity, and thermal expansion coefficient, creating a material that satisfies all required properties for the supporting substrate
3Ease of manufacture
If an adhesive layer is used to join the piezoelectric substrate and supporting substrate, then the substrates are joined together, but the entire composite substrate has excessively low Young's modulus reducing the holding power
Solution Approach 1:
The patent removes the adhesive layer from the composite substrate structure, achieving direct bonding between the piezoelectric substrate and sialon supporting substrate, which eliminates the weak link and maximizes the holding power while maintaining manufacturability through direct joining techniques
4Ease of manufacture
If a thick amorphous layer is used to bond the supporting substrate and functional substrate, then the substrates are joined together, but the entire composite substrate has excessively low Young's modulus reducing the holding power
Solution Approach 1:
The patent eliminates the thick amorphous bonding layer and achieves direct joining between substrates, removing the source of reduced Young's modulus and restoring the full holding power of the sialon supporting substrate while maintaining manufacturing feasibility through direct bonding processes
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 sintered sialon body-based composite substrate enables higher frequency operation with improved workability, reduced curling and cracking, and enhanced resonance characteristics, effectively minimizing temperature-dependent frequency shifts.
Implementation Method 1
The supporting substrate is a sintered sialon body
Data Source
AI summary
A composite substrate includes a supporting substrate and a functional substrate that are directly joined together, the supporting substrate being a sintered sialon body.