Interface and ionic interdiffusion in cofired ferroelectric/ferrite multilayer composites

Abstract

Recently, the surface mount technology (SMT) has been rapidly developed for miniaturization of electric devices such as multilayer ceramic capacitor (MLCC) and multilayer chip inductor (MLCI). The trend of electronics has been for an increasingly compact design. Some characterizations of cofired devices such as ceramic-filled glass electronic package, and varistorcapacitor cofired multilayer device have been reported [1, 2]. Multilayer chip LC filter, which is combined with several capacitors and inductors by the production process of multilayer chip components, is a type of advanced surface mount devices (SMD). Lead based relaxor ferroelectrics, such as Pb(Mg1/3Nb2/3)O3, Pb(Ni1/3Nb2/3)O3 and Pb(Zn1/3Nb2/3)O3, are being widely used as MLCC due to their high dielectric constant and low sintering temperature [3–5]. And NiCuZn ferrite, which has excellent magnetic permeability and can be densified at low temperature, is an important material using for producing low temperature sintered MLCI [6–8]. They are promising materials for the multilayer chip LC filters. The key issue of manufacturing the multilayer chip LC filters is cofiring the capacitor and inductors together at low temperature. The interfacial interactions such as chemical reaction, ionic interdiffusion, are important for the production of devices. In the present study, the multilayer components were prepared by cofiring Pb(Ni1/3Nb2/3)O3-PbTiO3 (abbreviated as PNNT) ferroelectrics and NiCuZn ferrite. The cofiring interface and ionic interdiffusion between constituents were investigated. According to the diffusioncouple model, the interfacial diffusion coefficient for Pb2+, Nb5+, Ni2+, and Fe3+ had been estimated. The specimens were prepared by the conventional oxide-mixing technique. 99% pure reagent-grade PbO, NiO, Nb2O5, TiO2, Fe2O3, CuO, and ZnO oxides were weighed in the appropriate proportions and used as starting materials. Fe2O3, NiO, CuO and ZnO powders, according to the composition (Ni0.8Cu0.1Zn0.1)Fe2O4, were calcined at 720 ◦C for 4 h to fabricate NiCuZn ferrite. The dielectric material, according to the composition 0.8 Pb(Ni1/3Nb2/3)O3-0.2PbTiO3 with little amount of CuO and ZnO, were calcined at 800 ◦C for 4 h. The calcined mixtures were ground by ball milling for 12 h to a proper surface area. The ground powders were dried and added to PVA for the disk bodies. Firstly, ferroelectic and ferrite disks were separately prepared and sintered at 850–950 ◦C for 2 h, in order to measure characteristics such as phase structure and sintered densities. Secondly, the mixed calcined powders of ferroelectric and ferrite were laminated into a mold and compressed into a plate with the diameter of 12 mm, which was sintered at 950 ◦C for 2 h. The sintered densities were measured by the Archimedes method. The phase structure for the specimens were identified using X-ray diffractometer (XRD). For lead-based ferroelectrics, perovskite phase and pyrochlore phase always coexist. The relative amounts of perovskite and pyrochlore phases were determined by measuring the major X-ray peak intensities for perovskite and pyrochlore phases, i.e. (110) and (222), respectively. The percentage of perovskite phase was calculated by the following equation [9]: