Sintering behavior of aluminum nitride ceramics with MgO–CaO–Al 2 O 3 –SiO 2 glass additive Hwa-Jun Lee a,b , Sang-Woo Kim b , Sung-Soo Ryu a, ⁎ a Engineering Ceramic Center, Korea Institute of Ceramic Engineering and Technology, Icheon 467-843, Republic of Korea b School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea abstract article info Available online 14 April 2015 Keywords: Aluminum nitride Glass oxide Sintering additive Densification Liquid-phase sintering In this study, MgO–CaO–Al 2 O 3 –SiO 2 (MCAS) glass oxide fabricated by a conventional melting process was used as a sintering additive to prepare dense AlN ceramics at lower temperatures. AlN specimen with 5 wt.% MCAS glass oxide was produced by sintering in a dilatometer and a conventional furnace. The sintering behavior of the glass- doped AlN was investigated by means of dilatometric analysis, X-ray diffraction analysis, and field-emission scanning electron microscopy microstructural observation. Results revealed that the melted glass phase had a significant effect on the densification of the AlN ceramics by a liquid-phase sintering. This led to a reduction in the sintering temperature by 200 °C from the 1800 °C required for conventional AlN–rare earth or –alkaline earth oxide system. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Aluminum nitride (AlN) is considered to be a promising substrate and package material for high-power integrated circuits owing to its high thermal conductivity, low dielectric constant, high electrical resis- tivity, high dielectric breakdown strength, non-toxicity, and thermal ex- pansion coefficient which is close to that of silicon [1,2]. However, AlN is difficult to sinter due to its highly covalent bonding and because it requires a high sintering temperature (≥ 1900 °C) to achieve full density. For full densification, rare earth and/or alkaline earth oxides are often added as sintering aids in the fabrication of AlN ceramics [3–8]. These sintering aids play a double role during the sintering process. One is to help form an aluminate liquid phase that promotes densification through the liquid-phase sintering (LPS) pro- cess. The other is to improve the thermal conductivity by decreasing the oxygen contents in solution in the AlN lattice. Y 2 O 3 is known to be the most common and effective additive to achieve the densified AlN ce- ramics. This additive reacts with the Al 2 O 3 layer on the surface of the AlN particles, thus forming secondary phases that promote the densifi- cation at lower temperatures than AlN without additive [9–14]. Recently, more and more attention has been given to the low- temperature sintering of AlN ceramics as a way of reducing manufactur- ing costs and benefiting from the co-firing of multilayer substrates [15–17]. Watari et al. showed an effective sintering aid in the Y 2 O 3 – CaO–Li 2 O system, which promotes full densification at 1600 °C and high thermal conductivity values (~ 100–172 W/mK) [16]. Qiao et al. have reported that after sintering at 1650 °C, dense AlN ceramics with a thermal conductivity of 148 W/mK were prepared by the simulta- neous addition of 2 wt.% CaF 2 and 2 wt.% Y 2 O 3 [17]. In addition to the sintering aids mentioned above, several attempts have been made to reduce the sintering temperature using glass ceram- ic with low melting temperatures [18–21]. For example, Yang et al. [21] reported that the densification of AlN could be achieved using MgO– CaO–Al 2 O 3 –SiO 2 (MCAS, fabricated by sol-gel method) glass as a sintering aid at lower temperature. However, this report focused on the dielectric properties of the sintered AlN specimen; it did not inves- tigate the sintering behavior of AlN based on the role of the glass oxide as a sintering additive. Glass oxide addition could decrease the thermal conductivity of AlN since SiO 2 element contained in a glass oxide composition deteriorated the thermal conductivity of AlN. However, this work aimed mainly to investigate the effect of the MCAS glass addition on the sintering charac- teristics of the AlN powder rather than on its thermal conductivity by means of dilatometric analysis, which is useful for studying the kinetics of densification during sintering [14,22–24], X-ray diffraction analysis, and field-emission scanning electron microscopy (FE-SEM) microstruc- tural observation. MCAS glass oxide, which was prepared by a conven- tional melting process, was used to fabricate dense AlN ceramics at lower temperature. 2. Experimental procedure Commercially available AlN powder (Grade H, Tokuyama Soda, Japan) was used as a starting material. MgO–CaO–Al 2 O 3 –SiO 2 (MCAS) glass was prepared using a conventional melting process. Reagent Int. Journal of Refractory Metals and Hard Materials 53 (2015) 46–50 ⁎ Corresponding author at: Engineering Ceramic Center, Korea Institute of Ceramic Engineering and Technology, 3321 Gyeongchung Rd., Sindun, Icheon, Gyeonggi 467-843, Republic of Korea. E-mail address: ssryu@kicet.re.kr (S.-S. Ryu). http://dx.doi.org/10.1016/j.ijrmhm.2015.04.013 0263-4368/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM