Effects of samarium oxide on thermal and mechanical properties of Y₂O₃-CaCO₃ added aluminum nitride

Aluminum nitride (AlN, hereafter) is one of very important materials in the semiconductor industry because of its high thermal conductivity and low coefficient of thermal expansion. Its dielectric permittivity and mechanical properties are similar to those of aluminum oxide. However, liquid phase sintering is usually adopted because of its high sintering temperature. The resultant microstructural shape in the second phase is known to affect the mechanical properties, thermal properties, and electrical properties of AlN. To control the microstructural shape of the second phase, 1-2 wt% of yttrium oxide and calcium carbonate are added as sintering aids. In addition, 0-5 wt% of samarium oxide is added to prepare various AlN composites with different microstructural shapes. When 1-2 wt% of Sm₂O₃ was added, the second phase appeared as isolated pockets outside along the grain boundaries of AlN. When the amount increased to 3 wt% or higher, the second phase wetted along the grain boundaries as channel-like shapes. The different microstructural shapes of the second phase are thought to be due to the change of kinetic movement of the liquid phase resulted from the different amount of Sm₂O₃. From this study of the effects of the second phase microstructural shape on the density and grain size of AlN, there was no noticeable difference among them in all conditions regardless of additive amounts. The highest thermal conductivity appeared when the second phase existed as isolated pockets, and the value became lower due to phonon scattering when channel-like shapes existed. On the other hand, strength increased in the latter case. The decrease in specific (electrical) resistivity was thought to be caused by the channel-like shapes serving as electron conduction paths.