Effect of Y2O3 and MoO3 co-doping on the thermal conductivity and flexural strength of black aluminum nitride ceramics

Aluminum nitride (AlN) ceramics are widely used in electronic packaging due to their high thermal conductivity. However, AlN ceramics typically exhibit high reflectance in the visible to near-infrared region, thereby limiting their application in high-power optoelectronic integrated packaging. To address this, black AlN ceramics were fabricated in this study via tape casting and pressureless sintering, using MoO 3 as a coloring agent and Y 2 O 3 as a sintering additive. Mechanistically, Y 2 O 3 promotes densification of the AlN ceramic structure through liquid-phase sintering via the formation of YAlO 3 (YAP), which suppresses phonon scattering and thus enhances thermal conduction. MoO 3 decomposes to form fine and isolated Mo second phase particles that precipitate at triple grain boundaries, exerting a pinning effect that promotes grain refinement and improves the flexural strength of the AlN ceramics. The Mo second phase reduces broadband reflectance through free carrier response and multiple scattering. Density functional theory (DFT) calculations reveal that the solid solution of multivalent Mo and the formation of charge compensating defects introduce defect energy levels within the bandgap. The synergistic effect of these mechanisms enables the black coloration of AlN ceramics. The results show that at a sintering temperature of 1800 °C and a MoO 3 doping content of 1.5 wt%, the black AlN ceramics achieve a thermal conductivity of 173.2 W·m −1 ·K −1 , a flexural strength of 471.8 ± 10.2 MPa, a L value of 42.37, and a reflectance below 15 % in the visible and near-infrared regions.