AB-INITIO SIMULATION OF THERMAL-PROPERTIES OF ALN CERAMICS

Aluminum nitride (AlN) ceramics are prospective materials for electronic parts, particularly LSI substrates, because of their excellent mechanical, dielectrical and thermal properties. Their high thermal conductivity is estimated to be about 320 W m(-1)K(-1) from some theoretical and experimental considerations. However, existence of crystalline imperfections such as impurities, lattice defects or a different phase (zincblende phase) practically reduces it to only two-thirds of the theoretically predicted one. In this paper an interatomic potential of AlN which is adequate for molecular dynamics Mo calculation is established on the basis of ab initio molecular orbital Mo analysis of an AlN cluster. Then the thermal conductivity of AlN is estimated by equilibrium Mo simulation, and its dependence on crystallographic structure and lattice defects is examined. We find that the energy difference between two kinds of phase structure in AlN (the wurtzite and zincblende) is so small that they are able to coexist in the realistic material. The thermal conductivity of the zincblende is also found to be much lower than that of the wurtzite.