FeHfN and FeHfNO soft magnetic films for RF applications

Abstract

In this work, recent improvements on high magnetization FeHfN films for RF-use and possibility of very high resistivity with introducing oxygen during deposition are investigated. The films are deposited at room temperature by reactive RF diode sputtering in a mixed Ar + N/sub 2/ atmosphere. N-incorporation leads to lattice expansion and grain size refinement. Up to N /spl sim/ 10 at.%, the films consist of very fine nanostructure, encompassing excellent magnetic properties and retaining relatively high magnetization. The resistivity /spl rho/ increases almost linearly with N but remains at a moderate value for N /spl sim/ 10 at.%. However, the soft magnetic properties rapidly degrade and the 4/spl pi/Ms strongly decreases while the film consists of amorphous-like microstructure with scattered large HfN precipitates. Having 4/spl pi/Ms = 19 kG, Hk = 20 Oe, and /spl rho/ = 130 /spl mu//spl Omega/-cm, a natural ferromagnetic resonance frequency occurs at 1.84 GHz with dc permeability /spl mu/' close to 1000. The insertion of small O/sub 2/ flow rates is instrumental in increasing /spl rho/ above 1000 /spl mu//spl Omega/-cm. A few O/sub 2/ flow rate also allows a soft magnetic behaviour with Hk increasing with O/sub 2/. The N-incorporation in FeHfN results in promoting and increasing Hk, the O/sub 2/ addition seems to compete with the nitrogen effect.