A silicon nitride ceramic is prepared by a modified sintering of reaction bonded silicon nitride method (SRBSN). This ceramic has a very high thermal conductivity, high fracture toughness, and a high strength. It is expected to be used as the next‐generation insulating substrate material for high‐power electronic devices and other new applications.

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a b s t r a c tSilicon nitride (Si 3 N 4 ) with high thermal conductivity has emerged as one of the most promising substrate materials for the next-generation power devices. This paper gives an overview on recent developments in preparing high-thermal-conductivity Si 3 N 4 by a sintering of reaction-bonded silicon nitride (SRBSN) method. Due to the reduction of lattice oxygen content, the SRBSN ceramics could attain substantially higher thermal conductivities than the Si 3 N 4 ceramics prepared by the conventional gas-pressure sintering of silicon nitride (SSN) method. Thermal conductivity could further be improved through increasing the ␤/␣ phase ratio during nitridation and enhancing grain growth during post-sintering. Studies on fracture resistance behaviors of the SRBSN ceramics revealed that they possessed high fracture toughness and exhibited obvious R-curve behaviors. Using the SRBSN method, a Si 3 N 4 with a record-high thermal conductivity of 177 Wm −1 K −1 and a fracture toughness of 11.2 MPa m 1/2 was developed. Studies on the influences of two typical metallic impurity elements, Fe and Al, on thermal conductivities of the SRBSN ceramics revealed that the tolerable content limits for the two impurities were different. While 1 wt% of impurity Fe hardly degraded thermal conductivity, only 0.01 wt% of Al caused large decrease in thermal conductivity.

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