Low temperature firing of Ni-Cu-Zn ferrites

Ni-Cu-Zn ferrites were prepared by the standard ceramic method. The particle size of the powders was tailored by milling the calcined powders. It is shown that powders with a mean particle size of about 0.5 mum show an enhanced sintering activity and very high densities are obtained after low temperature sintering at 879-900degreesC. The role of sintering aids was investigated: for samples sintered at 900degreesC the density increases with the amount of bismuth oxide and saturates for Bi2O3 concentrations higher than 0.5%. The permeability increases for small bismuth doping, but is reduced for a Bi-content of more than 0.5%. Maximum permeability is observed for intermediate Bi doping with a mu(i) = 900. Starting from ferrite powders, ferrite tapes were prepared by tape casting. These tapes were screen printed with Au or Ag conductors, laminated and sintered. Different types of inductors have been prepared by LTCC techniques and an inductance of up to 90 muH is obtained.