Low temperature processing and electrical properties of embedded ferrite-cored inductor

The inductance of low temperature processable particulate filled polymer matrix composite inductors is constrained by the limited magnetic properties of the polymer matrix. The microstructural and electrical properties of inductors made from amorphous nickel-zinc-iron oxide matrix filled with polycrystalline nickel zinc ferrite (NZF) fillers are investigated in this study. NZF has high resistance, and is essential for high frequency application to reduce eddy current loss. Planar spiral NZF-composite (with 20v% fillers) inductors were fabricated on a glass wafer substrate and heated treated at different temperatures. The electrical properties of the inductors were characterized at frequencies in the MHz range. The inductance is found to increase between 10%-20% for composite inductors after heating at 300°C for 1 hour. The increase is comparable to those reported previously for polymer ferrite composite inductors, albeit the polymer version has significantly higher filler content (90wt%) while the current NZF-composite filler content is markedly less (10-20%). This indicates that the increase is associated with improvement of the matrix´s properties. The changes in matrix microstructures were characterized by X-ray diffraction. The increase in inductance and associated electrical properties are then explained based on the observed microstructural changes. The increase in matrix inductance indicates that the current approach has strong potential for giving a large enhancement in inductance when high filler content is used.