Permeability Enhancement by Multilayer Ferromagnetic Composites for Magnetic-Core On-Chip Inductors

This letter reports about unpatterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip and interposer integrated inductances. The proposed composite structure reduces RF induced currents and thus pushes the permeability cutoff to beyond 3.7 GHz, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. To the best knowledge of the authors, we achieve the highest effective relative permeability of 28 at 1 GHz, highest ferromagnetic resonance frequency and highest inductance enhancement factor above 1 GHz ever reported for devices based on on-chip unpatterned NiFe magnetic cores. A single loop inductor is also implemented as a technology demonstrator, achieving an inductance enhancement of 4.8 and a quality factor enhancement of 4.5 at 400 MHz.