Sol–emulsion–gel synthesis of cordierite ceramics for high-frequency multilayer chip inductors

Nano-Cordierite powders used for high frequency chip inductors (MLCIs) were prepared by sol–emulsion–gel method. Effects of precursor concentration and [H2O]/[Si] molar ratio on this material were studied. The sol–emulsion–gel processing of Mg2Al4Si5O18 as well as its dielectric property were investigated. Owing to the better packing efficiency and therefore higher surface energy of the freestanding nano-powder, the pressed pellets made by cordierite powder showed 98.6% theoretical density at 900 °C for 2 h. The additive Bi2O3 was utilized to promote the crystallization or transformation to α-cordierite and sintering. The sol–emulsion–gel-derived cordierite ceramics have low dielectric constant (ε=3.0∼4.0; 18 GHz) and low dielectric loss (tgδ<0.001; 18 GHz) and can be co-fired with high conductivity metals such as Au, Ag/Pd internal electrode at low temperature (900 °C), suggesting that it was an ideal dielectric material for high-frequency multilayer chip inductors.