Nickel diffusion in base-metal-electrode MLCCs Yongli Wang *, Longtu Li, Jianquan Qi, Zhenwei Ma, Jiangli Cao, Zhilun Gui State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, People’s Republic of China Received 14 June 2002; accepted 15 September 2002 Abstract Nickel is frequently used as an internal electrode in the advanced base-metal-electrode (BME) multilayer ceramic capacitors (MLCCs). The diffusion of nickel element into the non-reducing perovskite dielectric layers plays an important role in the final quality of MLCCs. In this paper, the diffusion of nickel element from internal electrode to the dielectric ceramic layer was investigated by AES and EPMA experiments. It was shown that during sintering, nickel atoms migrate towards the dielectric layer and an interdiffusion region of hundreds of nanometers in thickness is generated near the internal electrode. The difference in dielectric characteristics between MLCC and disk specimens can be attributed to the existence of the interdiffusion region. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Nickel; Diffusion; MLCC; Base metal electrode 1. Introduction Driven towards smaller size, higher performance and lower cost, the manufacturing techniques of multilayer ceramic capacitors (MLCCs) are now undergoing a revolution characterized by the development of MLCCs with base metal internal electrode (BME) and thinner dielectric layers. Great effort has been devoted to optimizing the sintering process and adjusting the dielectric ceramic composition which are considered as two key factors leading to the unwanted failure [1  /3]. The interaction between the internal electrode and the dielectric ceramic layer on the component properties, however, has not been fully understood although it plays an important role in the degradation of MLCCs with precious metal as internal electrode [4,5]. In this paper, the diffusion of nickel element towards the dielectric ceramic layer was studied using AES and EPMA techniques. The dielectric properties of MLCCs and disk samples were measured as a function of temperature and the observations are interpreted on the basis of nickel diffusion. 2. Experimental The dielectric material employed in this work, which satisfies EIA Y5V specifications, is Ba m (Zr x Ti 1x )O 3 , where x /0.16 and m /1.005. The starting powder is thoroughly mixed with an acrylic binder solution containing an appropriate amount of dispersant to form a homogeneous slurry. Doctor-blade art, followed by drying, is then carried out to form green sheets on which Ni electrodes are subsequently printed. These sheets are then laminated, stacked and cut to green chips. The organic binder in the chips is burned off at 320 8C in air at a slow heating rate of 10 8Ch 1 . The chips are then subjected to a two-stage firing program: firstly at 1210  /1250 8C for 2 h in a reducing atmo- sphere of Po 2 /10 11 to 10 13 MPa and then annealing in a weak oxidizing atmosphere (Po 2 /10 8 to 10 10 MPa) at 1050 8C for 3 h. Finally, copper slurry is employed to form external electrodes and to finish the preparation of MLCC specimens. Some disk specimens made up of the same powder, but doped with various doses of metallic Ni, have been prepared as well with the same firing program and electrode coating art. The dielectric measurements are conducted using a HP4192A Impedance/Gain Phase Analyzer controlled by a PC. A PHI-610 scanning auger microprobe (SAM) * Corresponding author. Tel.:  /86-10-6278-4579; fax:  /86-10- 6277-1160. E-mail address: wy198@mails.tsinghua.edu.cn (Y. Wang). Materials Science and Engineering B99 (2003) 378  /381 www.elsevier.com/locate/mseb 0921-5107/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0921-5107(02)00469-5