Effect of annealing on the magnetics of NiFeMo thin films (abstract)

Abstract

NiFeMox thin films, where 0<x<0.1, are considered for usage in high frequency magnetic sensors. Since the device manufacturing process requires that the thin film be exposed to temperatures above 200 °C, its thermal stability is an important criterion for device reliability.1 NiFeMox thin films, with a thickness of 75 nm and 0<x<0.1, were sputter-deposited on single crystal silicon wafers and their magnetic properties were measured after annealing for 2 h at various temperatures up to 350 °C. At lower Mo content, the anisotropy field Hk decreased with annealing temperature,2 whereas at higher Mo content, Hk showed an initial decrease and then an increase above 300 °C. With increasing temperature, the angle of dispersion θk showed a monotonous increase at lower Mo content. At higher Mo content, θk decreased at higher temperatures. At all Mo contents, the magnetostriction increased at higher temperatures. All as-deposited films had a residual tensile stress of about 200 MPa. At temperatures between 250 and 300 °C, the in situ tensile stress sharply increased. Above 300 °C, the stress started decreasing due to grain growth, the amount of decrease being dependent on the Mo content. The films were found to have much higher residual tensile stress (around 2000 MPa) after annealing, depending on the Mo content. The stress was calculated by measuring the wafer curvature with a laser. The microstructure was studied with transmission electron microscopy (TEM). ESCA indicated preferential oxidation of surface iron in NiFeMo during annealing. Changes in magnetics of NiFeMo were correlated to and explained by microstructural and compositional changes.