A novel composite of aluminum nitride and silsesquioxane organic–inorganic hybrid polymer

A novel composite of aluminum nitride (AlN) and vinyl–hydrosilyl–silsesquioxane (VHSQ), an organic–inorganic hybrid polymer with high heat resistance up to approximately 300°C in air, was fabricated by impregnating a porous AlN with liquid VHSQ and then stepwise curing at 120, 180, and 230°C in a vacuum. The fraction of the VHSQ in the composite was systematically varied in the range of 25–45 vol%. The thermal conductivity, elastic modulus at room temperature, average coefficient of linear thermal expansion from room temperature to 300°C, and dielectric breakdown strength at 200°C were studied for the composites to examine their potential application as an electrical insulator substrate for power modules. The thermal conductivity of the composite reached 59.3 W m⁻¹ K⁻¹ at the VHSQ 26 vol%, then decreased with the volume fraction of VHSQ. However, even at 45 vol%, the thermal conductivity stayed at 36.4 W m⁻¹ K⁻¹, and the elastic modulus decreased to 23.5 GPa, less than half of the fully dense AlN, while the average coefficient of linear thermal expansion was slightly higher than that of the dense AlN. On the other hand, the dielectric breakdown strength at 200°C improved with the volume fraction of VHSQ and reached 76 kV mm⁻¹ at 45 vol%. This value was found to be compatible with that of monolithic VHSQ measured at room temperature, indicating the successful retention at 200°C of the intrinsic dielectric breakdown strength of the VHSQ by the efficient heat dispersion via the AlN grain network in the composite system. These results indicate the high potential of the AlN–VHSQ composites for developing high-performance electrical insulator substrates installed in various types of power modules.