ABSTRACT
Aluminum nitride (AlN) has a hexagonal structure of wurtzite type, and combines the following physical properties: high thermal conductivity of 320 W m-1 K-1 (theoretical value) (1) comparable to that of metals, high electrical resistivity of greater than 1014 fi em, and thermal expansion coefficient of 4.1 X 10-6 K-1, matching silicon. These are excellent properties as a substrate material for silicon in very large scale integrated (VLSI) circuits. Both thermal conductivity and electrical resistivity, however, are known to be affected severely by oxygen and metallic impurities included in sintered AlN (2,3). The oxygen inclusion originates mainly in a sintering additive such as CaO, which is necessary for sintering the commercial AlN powder at submicrometer size, and in the residual alumina used as the starting material in carbothermal reduction and nitridation of a-Al20 3 (4). ·
Titanium nitride (Ti-N) has two phases: 8 phase (TiN) with a cubic structure, and e phase(ThN) with a tetragonal one. TiN has a broad composition range from about TiN0.6 to TiNu6 , which reflects the variation of lattice parameter from 0.4217 nm at both border compositions to 0.4240 nm at the stoichiometric composition (5). TiN is a hard refractory material with the melting point of about 3220 K and microhardness of 2450 kg mm - 2, acid and corrosion proof, and with low electrical resistivity, 25.0 J.Lfi em. Furthermore, the high thermal conductivity of about 29 W m-1 K-1 is retained up to about 1900 K (6). These features are widely applied to the metallurgical coating of cutting tools. Ultrafine particles (UFPs) of TiN are often used as reinforcements in metal, ceramic, and polymer matrix composites (7). Hydrogen sorption-desorption characteristics of metal-TiN nanocomposite particles are being studied for use as a new catalyst (8).
