Micro-thermal analysis for advanced silicon nitrides

Microstructures of three grades of gas-pressure-sintered silicon nitride materials, SN-H, SN-L and SN-A, were evaluated with a scanning electron microscopy, an atomic force microscopy and a micro-thermal analyzer. Thermal images corresponding to local thermal conductance distribution were obtained with the micro-thermal analyzer, and the thermal conductivity was confirmed to be higher in silicon nitride grains and lower in grain boundaries. Thermal analyses at particular areas in the microstructures revealed that the local thermal conductivity of silicon nitride grains is higher in SN-L than in SN-H. This seems inconsistent with the bulk thermal conductivities because SN-H exhibited the highest thermal conductivity of 132.3 W/(m K), which is considerably greater than that of SN-L of 104.7 W/(m K). The discrepancy between the grain and bulk thermal conductivities is discussed.