Study Of ALN Ceramics’ Electrical Properties

Aluminum nitride （AlN） ceramic, which has good comprehensive properties, such ashigh thermal conductivity, high electrical resistivity, low dielectric constant and dielectricloss, thermal expansion coefficient which is close to the silicon and reliable mechanicalperformance at both room temperature and high temperature, non-toxic, etc, is idealmaterial for large scale integrated circuit substrate and high power device packaging andcan be used as optical functional materials, high temperature structural materials andvarious composite materials.As a strong covalent-bonding compound, AlN has a high melting point and a lowself-diffusivity, it is usually difficult for AlN to be sintered densified and less dense AlNceramic can not guarantee good performance, therefore AlN is restricted to be put intoapplication. Spark plasma sintering （SPS） is a kind of new sintering methods, which hasits unique technical advantages such as that the densified sintering temperature is low andsintering time is very short. So SPS technology can be applied in AlN ceramics’ sinteringto enhance the relative density of AlN ceramics and to improve the production efficiency,in order to reduce the cost of AlN ceramics’ fabrication.In this paper，using the method of SPS technology, pure AlN powders, AlN powderswith sintering aids （Y₂O₃, Er₂O₃or Sm₂O₃）, AlN powders with sintering aids （Y₂O₃） andelectrical additives （MoSi₂or TiN） and AlN powders with sintering aids （Er₂O₃or Sm₂O₃）and electrical additives （TiN）, are sintered. AlN ceramics’ SPS sintering process andmechanism are studies, and the relationship of density, electrical properties andmicrostructure are discussed.In this paper，pure AlN ceramic sintered at1700℃for10min reaches to a relativedensity of93.7%. The analysis of microstructure and displacement curve shows that thereis no grain growth phenomenon during the sintering process and it can be inferred that theceramics’ density cannot be further promoted only by prolonging temperature-holdingtime.In this paper, AlN ceramics with three kinds of sintering aids are close to the theoretical density and tend to be fully dense, and the densification process only lasts4min. Phase analysis and micro-area morphology analysis show that there is chemicalreactions in lower temperature between sintering aids and Al₂O₃impurities around AlNparticle surface, generating a solid-phase rare earth aluminate compound. But there is anotable difference between their electrical performance. The electrical resistance of AlNceramic with Sm₂O₃as sintering aid is smaller than those with Er₂O₃or Y₂O₃as sinteringaid in more than two orders of magnitude, but with the increase of the content ofconductive TiN phase, the electrical resistance of these three kinds of AlN/TiN ceramicstend to be similar.With Y₂O₃for sintering additives, the relative density, electrical property andstructure of AlN-based composite ceramics with MoSi₂or TiN as electrical additive wereanalyzed and compared. The electrical resistivity of two kinds of ceramic is decreasing asthe conductive phase content increases, but the conductive performance of AlN ceramicswith TiN as conductive additive is better than those with MoSi₂as conductive additive,and when the adding content is both35wt%, AlN/TiN composite ceramics’ electricalresistivity significantly decreased, while AlN/MoSi₂composite ceramics still appear to bein a insulatingly high-impedance state.For nitrogen atmosphere and vacuum atmosphere in the preparation of Y₂O₃respectively for sintering additives of AlN/MoSi₂composite ceramic density andperformance analysis and comparison of vacuum sintering ceramics density than nitrogenatmosphere sintering ceramics slightly small and two kinds of ceramics are close to fullydense, vacuum sintering ceramics resistivity than the preparation of low nitrogenatmosphere more than two orders of magnitude.In summary，the AlN ceramic SPS sintering process analysis, as well as sinteringadditives types, electrical regulator types and content and sintering atmosphere of AlNceramic density and the influence of the performance for high performance aluminumnitride ceramic preparation for great reference value.