Effects of Y2O3 and yttrium aluminates as sintering additives on the thermal conductivity of AlN ceramic substrates

AlN ceramic substrates are prepared by tape casting and presureless sintering at 1850 degrees C for 10 h, with 8 wt% Y2O3 and yttrium aluminates of Y3Al5O12 (YAG), YAlO3 (YAP), and Y4Al2O9 (YAM) as sintering additives. The effects of the sintering additives on the phase assemblage, microstructure, thermal conductivity, and bending strength of the sintered AlN ceramics are discussed. With Y2O3, YAG, YAP, and YAM as sintering additives, the secondary phases in the sintered AlN ceramics are YAM, YAG, YAP + YAG, and YAM + YAP, and the average sizes of AlN grains are 5.5, 3.6, 4.4, and 4.9 mu m, respectively. In the order of sintering additives with decreasing Y2O3/Al2O3 ratio, viz. Y2O3 > YAM > YAP > YAG, both the thermal conductivity and bending strength of the sintered AlN ceramics decrease. With Y2O3 as the sintering additive, the sintered AlN sample shows the maximum thermal conductivity of 205 W/(m K) and bending strength of 295 MPa.