Texture Control and Thermal Conductivity of Aluminum Nitride Ceramics

Abstract

Aluminum nitride (AlN) is one of typical non-oxide ceramic materials that have intrinsic high thermal conductivities and electrical insulation. Therefore, AlN ceramics have been applied to substrate materials for power devices. AlN is a sintering resistant ceramic due to its high covalence. High temperature and long sintering time with sintering aids are required to obtain dense AlN ceramics. Although sintering temperature of AlN ceramics can be lowered by using low temperature sintering additives and pressure assisted sintering, the low-temperature-sintered AlN ceramics do not show superior thermal conductivity due to the increase of grain boundary caused by the restrained grain growth. To solve these problems, controlling the shape and orientation of AlN grains seems to be useful, as are adjustment of sintering conditions and additives. In this review, we introduce the densities, microstructures, and thermal conductivities of texture controlled AlN ceramics by addition of coarse AlN particles or AlN whiskers. Although the addition of coarse AlN particles or AlN whiskers slightly decreases the relative densities of AlN ceramics, dense textures containing the coarse particles or whiskers are obtained. Samples containing AlN whiskers show an anisotropic thermal conductivity originated from the orientation of AlN whiskers in the samples.