FeHfN and FeHfNO soft magnetic films for RF applications

Downsizing RF spiral inductors is thought possible with using ferromagnetic material such as high magnetization FeHfN . However, increasing the natural resistivity of FeHfN would be suitable for a better confinement with cancelling the series capacitance with the inductor. Indeed, the magnetic material can be almost in contact to the metal traces, therefore increasing confinement. In this paper, we first detail optimization of FeHfN films combining microstructural investigations and magnetic characterizations. Then, we reveal the effect O incorporation in FeHfN films. Both processes: nitrogenation and oxydation are rather antagonists but combine advantageously. FeHfNO film consists in nanoscale grains scattered in an oxidized matrix. However, it is still difficult to retain saturation magnetization 4πMs above 10 kG with resistivity higher than 10³μΩ cm. Finally, the dual reactive process is promising but requires further investigations.