Characterisation of Aluminium Nitride Ceramic Substrates

Aluminium nitride (AlN) is currently under investigation as a substrate material for use in microcircuit applications in particular where high thermal conductivity is required. Three commercially available substrate materials have been characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The differences in thermal conductivity between the materials and also the difference from the theoretical thermal conductivity have been correlated to the presence of low thermal conductivity second phase regions between grains, defects within the crystal structure, the presence of oxygen impurities and poor sintering behaviour. The highest thermal conductivity substrate obtainable during this study was 140 W7m K. The substrates were identified as comprising hexagonal AIM having a wurtzite type structure. In addition, oxide and oxynitride phases were detected. The surface morphology of the substrates was also investigated, as it is the nature of the surface that will be of importance in determining the adhesion of applied films.