AB-INITIO SIMULATION OF THERMAL-PROPERTIES OF ALN CERAMICS

Aluminum nitride (AlN) ceramics are prospective materials for electron ic parts, particularly LSI substrates, because of their excellent mech anical, dielectrical and thermal properties. Their high thermal conduc tivity is estimated to be about 320 W m(-1)K(-1) from some theoretical and experimental considerations. However, existence of crystalline im perfections such as impurities, lattice defects or a different phase ( zincblende phase) practically reduces it to only two-thirds of the the oretically predicted one. In this paper an interatomic potential of Al N which is adequate for molecular dynamics Mo calculation is establish ed on the basis of ab initio molecular orbital Mo analysis of an AlN c luster. Then the thermal conductivity of AlN is estimated by equilibri um Mo simulation, and its dependence on crystallographic structure and lattice defects is examined. We find that the energy difference betwe en two kinds of phase structure in AlN (the wurtzite and zincblende) i s so small that they are able to coexist in the realistic material. Th e thermal conductivity of the zincblende is also found to be much lowe r than that of the wurtzite.