Planarisation of NiFe₂O₄ Thick Film Ferrite Inductors

A variety of thick film planar inductors, designed for applications in the HF range, were printed from conductive PdAg and NiFe₂O₄ ferrite paste on alumina substrate. Pure ferrite powder with a nanometric particle size was used in the NiFe₂O₄ paste preparation. The ferrite thick film layer characterisation was performed on small spirals, after which the following inductor planar geometries were tested together with ferrite layers: meanders, spirals, bispirals and solenoid in plane. Their impedance was analysed with an impedance analyser in the MHz‐GHz range. The results obtained were compared with the properties of the smallest cubic inductors and with the literature data for planar inductors (theoretical and practical). A comparison was made of the L geometries printed. It was observed that better utilisation of the thick ferrite layers was achieved on L geometries with equally distributed windings over the thick ferrite layers.