GHz sandwich strip inductors based on Fe-N Films

TL;DR

This paper reports on the fabrication and characterization of GHz-range sandwich strip inductors using Fe-N magnetic films, demonstrating significant inductance enhancement with external bias and analyzing edge effects on magnetic properties.

Contribution

It introduces a novel fabrication method for GHz inductors with Fe-N films and investigates the impact of magnetic biasing and edge effects on performance.

Findings

70-100% inductance enhancement at 1GHz with biasing

Magnetic layers exhibit high anisotropy up to 1 kOe at large deposition angles

Edge hardening reduces magnetic contribution compared to theoretical predictions

Abstract

Planar strip inductors consisting of two Fe-N films enclosing a conducting film made of Cu, were fabricated on oxidized Si substrates. The inductors were 1mm long, 2 to 100 um wide, with layers of thickness ~0.1 um for the magnetic films and ~0.5 um for the conductor. The soft (Hc=4-8 Oe) magnetic layers were biased during impedance measurement by applying an external field along the strip length thereby facilitating the transverse susceptibility configuration. Biased strips exhibited 70 to 100% inductance enhancement at 1GHz with quality factors Q=4.5 to 3, respectively. The magnetic contribution to the total flux in the narrow devices was less than predicted theoretically, which was attributed to hardening of the magnetic material at the edges of the strip, where the deposition was close to 60 degree incidence. Test films were fabricated on tilted substrates and found to develop a very high anisotropy (up to 1 kOe) for deposition angles larger than 30 degrees. Optimizing the flux closure at the strip edges and using thicker conductor layers is essential for further improving the performance of sandwich strip inductors.