The Spark Plasma Sintering Of High Density A1N Ceramics And Mechanism Research

The aluminum nitride (AlN), which has some key properties like high thermal conductivity, high electrical resistivity, low dielectric constant and low dielectric loss, is potential material in microelectronic industry. However, AlN is hard to sinter, which constrains its application. The Spark Plasma Sintering (SPS), which is a recently developed densification method and has unique advantage, has potential application in not only facilitating densification of AlN but also reduceing cost.This dissertation studied on the SPS of pure AlN, Y₂O₃-A1N, Sm₂O₃-AlN powders. The SPS process of AlN and the densification mechanism were analyzed, the relationship of composition, structure and thermal conductivity was discussed.The increasing of temperature and lengthening of soak time could accelerate the sintering of samples. The pure AlN sample with 97.5% relative density was fabricated at 1800℃ for 15min. And when doped with additive Y₂O₃/Sm₂O₃, the sintering was greatly accelerated. The samples near to the theoretic density were obtained under the conditions of 100℃/min for increasing temperature rate, 1650℃¹700℃ for sintering temperature, and duration of 5 min, which were over 10% higher than that of pure AlN in the same condition.The observation on SPS process of AlN suggested that there were two stages in the process: at 1600℃¹700℃, additives and Al₂O₃ which was on the surface of AlN powder had solid reaction, thus the grain boundary phase was formed, the sintering was promoted, and the microstructure changed from sparse to dense. When the temperature was higher than 1700℃, the grain boundary phase shifted to the grain junctions. The contacting grain facets became more. The increasing temperature continually promoted the growth of AlN grain. The structure and composition helped to present high thermal conductivity.Study on the thermal conductivity of samples showed that high TC samples were those with low content of Sm₂O₃ as additive, and were sintered at high temperature for longer time. Thus it could attain the structure and composition of high TC. For example, the sample with 150W/mk TC could be obtained when 1.5wt%Sm₂O₃-AlNwas sintered at 1900℃ for 5min.The temperature distribution in SPS was studied. The current distribution, temperature distribution, heat flow were figured out. It suggested that the punch was the most important heat input part, and it was confirmed by watching the sintering process. The plasma and pulse electric/magnetic field maybe occurred in the samples. These two effects can accelerate diffusion, speedup the solid reaction of additives and Al₂O₃ on the surface of AlN powder. As a result, the sintering temperature was reduced and the sintering was promoted.