Characterization of NiFe/SiO₂ multilayers for on-wafer inductors operating at radio and low GHz frequencies

Magnetic layers surrounding copper core inductors are studied for use in circuits operating at radio and low GHz frequency ranges in order to address performance issues and quality losses normally observed in miniaturized inductors. Coating an inductor core in a magnetic material has the potential to increase the inductance proportional to the magnetic permeability of the coating. The objective of this research is to identify and construct an appropriate magnetic coating to improve the inductance and quality (Q-factor) of inductors. Permalloy (Py) was selected for these experiments due to its high relative permeability. Py layers, from 10nm to 1μm thick, were grown on silicon wafers using magnetron sputtering. These layers were characterized with SQUID magnetometer and broad-band FMR system. A specific issue we address is that inductor coatings have the potential to decrease the Q-factor due to eddy currents during high frequency operation. A method to reduce eddy current losses is to reduce layer thickness. Therefore, in addition to individual Py layers, multilayer coatings are developed: depositing 5 to 50 identical layers of Py (for total thickness from 150nm to 1.5μm) separated with 5nm layers of SiO₂. Such structures are suitable for high frequency inductor operations.