Thin film metallisation on AlN substrates

AlN has a good chance of becoming an important substrate material for high-quality hybrid circuits i.e. for HF high power modules because of its good thermal conductivity and its coeffcient of thermal expansion, matching that of Si. Thin film metallisations (NiCr/Ni/Au, NiCr/TiW/Au and TiW/Au) with good adhesion properties could be realised without difficulties by sputtering. Surfaces of AlN ceramics in as-fired quality are to rough for high line resolution. Therefore, polished substrates had been used. On these substrates conducting stripes with 10 mym grid could be achieved. Pores in the surface of the ceramic decreased the number of good samples. NiCi resistors on AlN substrates did not differ from resistors on Al2O3. Changes in resitance and TCR were slightly smaller at AlN after long times of annealing at 300 degree C. The metallisation system NiCr/TiW/Au appeared to be more stable than the NiCr/Ni/Au system after annealing at 400 degree C at air.