Titanium nitride-molybdenum metallizing method for aluminum nitride

A paste containing molybdenum (Mo) and titanium nitride (TiN) powders was printed on aluminum nitride (AlN) substrates and postfired. The adhesion strength of metallized substrates with Ni/Au plate was about 25 kgf/2.5 mm and was unchanged after the thermal cycle test. TiN-Mo does not adhere to the grain boundary phase in AlN substrate, or to the surface oxide layer, but to the AlN grain itself. This method, therefore, seems to be applicable to any kind of AlN substrate, which may have different grain boundary oxide phases and thermal conductivities. This TiN-Mo metallized AlN substrate was tried as a replacement for a beryllium oxide (BeO) heat sink, which has been used for RF power transistors. There was no trouble in assembling the AlN heat sinks into transistors. Thermal resistance and electrical properties for transistors with AlN heat sinks were almost equal to those for transistors with BeO heat sinks. The TiN-Mo metallized AlN substrates were found to be suitable for replacing BeO substrates as the heat sinks for semiconductor devices