Silicon Nitride Substrate Microstructure for High Thermal Conductivity
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Solution Overview
Problem
Silicon nitride substrates have low thermal conductivity compared to aluminum nitride substrates, but exhibit high three-point bending strength, making them suitable for thin designs that improve heat dissipation. However, there is a need for enhanced insulation properties at high temperatures and frequencies, and further performance improvements are desired.
Innovation Solution
A highly thermally conductive silicon nitride sintered body is developed with silicon nitride crystal grains and a grain boundary phase, featuring thermal conductivity of at least 80 W/(m·K), controlled solid solution oxygen amounts, and specific crystal grain dimensions and aspect ratios, along with a controlled grain boundary phase content, to enhance thermal conductivity and relative dielectric constant stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If silicon nitride substrate is used instead of aluminum nitride substrate, then three-point bending strength is improved, but thermal conductivity deteriorates
Solution Approach 1:
The invention changes the microstructural parameters of silicon nitride by controlling crystal grain size (1-10 μm) and aspect ratio (2-10), and by precisely controlling solid solution oxygen content (≤0.2 wt%), to achieve a balance between strength and thermal conductivity, reaching ≥80 W/(m·K) while maintaining ≥500 MPa strength
Solution Approach 2:
The invention creates a composite microstructure within silicon nitride by controlling the distribution and characteristics of crystal grains with specific aspect ratios and sizes, forming a composite-like structure that simultaneously provides high strength and improved thermal conductivity compared to conventional silicon nitride
2Temperature
If silicon nitride substrate thickness is reduced to improve heat dissipation, then thermal resistance is reduced, but mechanical strength deteriorates
Solution Approach 1:
By changing the crystal grain parameters (size: 1-10 μm, aspect ratio: 2-10) and solid solution oxygen content (≤0.2 wt%), the invention achieves a microstructure that maintains high strength even in thin substrates, enabling thin design for reduced thermal resistance without sacrificing mechanical integrity
3Reliability
If relative dielectric constant is improved for high-temperature operation, then insulation properties are enhanced, but thermal conductivity deteriorates
Solution Approach 1:
The invention achieves a unique parameter combination where solid solution oxygen is controlled to ≤0.2 wt% and crystal grains have specific size (1-10 μm) and aspect ratio (2-10), which simultaneously improves relative dielectric constant stability at high temperatures and achieves thermal conductivity of ≥80 W/(m·K)
Data Source
AI summary
According to an embodiment, a highly thermally conductive silicon nitride sintered body includes silicon nitride crystal grains and a grain boundary phase. A thermal conductivity of the silicon nitride sintered body is not less than 80 W/(m·K). An average value of solid solution oxygen amounts of the silicon nitride crystal grains existing in a 20 μm×20 μm unit area in any cross section is not more than 0.2 wt %. An average value of major diameters of the silicon nitride crystal grains existing in a 50 μm×50 μm unit area in any cross section is not less than 1 μm and not more than 10 μm. An average of aspect ratios of the silicon nitride crystal grains existing in the 50 μm×50 μm unit area is not less than 2 and not more than 10.