High Strength with High Thermal Conductivity AlN Ceramics by Low Temperature Sintering

Abstract

Recently, electrical device technology is moving towards higher voltage, larger current, greater power density, and small size. The high power will induce large thermal stresses in the devices, which propose great challenges for the brittle ceramic substrates that provide functions of electrical insulation and heat dissipation. In many occasions, Aluminum Nitride (AlN) is the most promising materials for ceramic substrate due to its outstanding properties: high thermal conductivity, mechanical stability, and electrical resistivity. AlN has been typically densified at high temperature (>1800 oC). However, the high sintering temperature not only increases the production cost of AlN but also causes significant grain growth, which results in a reduction of mechanical strength. In this regard, the research in AlN ceramics has been mainly focused on attaining full densification at low sintering temperature with various sintering additives. In this study, effects of multiple additives on the low temperature sintering of AlN were examined. The additives not only form a liquid phase to enhance densification, but also improve the thermal conductivity by elimination the oxygen from the AlN lattice. Thermal conductivity was characterized by laser flash method and Raman spectroscopy. With Raman spectroscopy, the relative amount of oxygen in AlN lattice can be calculated. Moreover, high mechanical strength of AlN was able to be obtained by suppressing the grain growth which results from lowering sintering temperature.