Bi₂O₃-doping controlled magnetic and dielectric properties of low-temperature co-fired NiCuZn ferrite for high-frequency applications

NiCuZn ferrite, due to its good magnetic properties, is a near optimal material for low-temperature co-fired ceramic (LTCC) filter applications. In this study, low temperature (860 °C and 880 °C) co-fired Ni_0.26Cu_0.22Zn_0.52Fe₂O₄ ferrites with different quantities of Bi₂O₃ (1–11 wt% with an increment of 2 wt%) were synthesized using a solid-state reaction. The effect of the Bi₂O₃ additive on phase formation, microstructure, magnetic permeability, and dielectric permittivity are investigated. The results indicate that a suitable amount of Bi₂O₃ doping can increase both bulk density and the magnetic properties. The superfluous Bi₂O₃ and Fe³⁺ ions form Bi₂₅FeO₃₉, which improves the dielectric properties. More specifically, the sample with 5 wt% Bi₂O₃, sintered at 880 °C, shows excellent magnetic permeability (μ′ ~ 130 @ 1–10 MHz), low magnetic loss (tanδ_μ ~ 0.026), and a high cut-off frequency (~ 100 MHz). The sample with 9 wt% Bi₂O₃, sintered at 880 °C, exhibits excellent dielectric permittivity (ε′ ~ 14.5 @ 1–400 MHz), low dielectric loss (tanδ_ε ~ 0.0075), and a high cut-off frequency (~ 1 GHz). These observations indicate that NiCuZn ferrites, with the right amount of Bi₂O₃, are promising candidate materials for LTCC applications.