Transactions of the Magnetics Society of Japan
Online ISSN : 1884-6726
Print ISSN : 1346-7948
ISSN-L : 1346-7948
On the Improvement of Ferromagnetic Spiral Inductors with using High-Magnetization and High-Resistive FeHf-based Materials
S. CoudercB. VialaA. S. RoyetR. PantelP. Ancey
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2005 Volume 5 Issue 4 Pages 165-170

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Abstract

Significant size reduction for RF spiral inductors is shown possible with using high magnetization (4 π Ms) ferromagnetic material. High 4 π Ms (-19kG) is suitable for realizing high ferromagnetic resonance frequencies FMR (-6GHz) and significant L-enhancements thanks to a high permeability. However, increasing the natural resistivity of FeHfN (-102 μ Ohm.cm) would be also advantageous for a better confinement of the magnetic flux and reducing the series-capacitance with the inductor. Indeed, with a very high resistivity (typically= 103 μ Ohm.cm), the magnetic materials can be almost in contact to the metal traces, therefore reducing the gap between the spiral and the magnetic planes. In a first part, we detail the optimization of FeHfN single layer films and the realization of ferromagnetic spiral inductors integrating this film as a laminated material. The results point out 30% to 130% increase in L over the air-core value which leads to a surface reduction of 25% to 50%. In a second part, we investigate the possibility of coincorporation of oxygen and nitrogen in FeHf films in order to raise the resistivity and to retain a high magnetization. It is shown that nitrogenation and oxidation processes act separately with opposed effects on the microstructures of the films (grain size, lattice parameter.) but combine advantageously. However, the expected compromise with 4 π Ms above-10kg and a resistivity of-103μΩ. cm has not been found yet. Finally, it is concluded that the dual N2-O2-reactive process with FeHf material is promising but requires further investigations.

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