Thermal conductivity measurement at the micrometer scale of ceramics using thermoreflectance technique —High-thermal-conductivity AlN with reduced amount of grain boundary phase—

High-thermal-conductivity AlN ceramic with eliminated grain boundary phase was prepared by long-term sintering with Y2O3 addition at 1900°C for 100 h in a reducing N2 atmosphere. The thermal conductivity of polished surfaced of obtained ceramic was quantitatively measured at the micrometer-scale by using a thermoreflectance technique with periodic heating. This equipment measures the phase lag, which is the delay between the signal of periodic heating laser and the reflectance signal of detecting laser, to calculate thermal effusivity using the calibration curve obtained from standard materials. The conductivity of polished surface of the ceramic is calculated from obtained thermal effusivity, density and specific heat. The thermal conductivities on the densified and polished surface of the ceramic were ranged from 219 to 318 W/m·°C. Low-thermal-conductivity region (< 20 W/m·°C) relating to presence of hidden pores was observed in thermal conductivity map of the polished surface. Furthermore, high-resolution map of thermal conductivity demonstrated no significant reduction in thermal conductivities due to presence of grain boundaries.