Crystallization and microstructural evolution of cordierite-based thick film dielectrics

Microstructural evolution of glass–ceramic dielectric thick films based on a nonstoichiometric cordierite, 2.4MgO·2Al₂O₃·5SiO₂, containing B₂O₃, P₂O₅, and PbO were investigated in conjunction with nucleation and crystal growth. The cordierite thick films were deposited by screen printing on a 96% alumina substrate, and then fired in the temperature range of 850–950°C in a N₂ atmosphere. Surface microstructure characteristics of the thick films depended on PbO content. Heterogeneous nucleation originated predominantly from the interface between the densified thick film and the alumina substrate. The added PbO segregated to the remaining glass during crystallization, and the relative concentration of Pb in the glass was proven to increase with rising temperature. Most of the remaining glass protruded from the film surface at the final temperature of 950°C. Penetration of the alumina substrate by the remaining glass was also observed. The influences of temperature and PbO on the microstructural evolution including nucleation and growth will be discussed with possible explanations for the observed results.