Control of N atom content in Fe-Fe₃N film with high saturation magnetization and low conductivity

Abstract

Microelectronic devices have a wide range of application prospects. In order to make microelectronic devices that have excellent high-frequency characteristics, developing of soft magnetic films with high saturation magnetization, low coercivity and high resistivity becomes the key to the research. In this work, Fe-Fe₃N soft magnetic films with different numbers of N atoms are prepared by radio-frequency atomic source assisted vacuum thermal evaporation. Among them, the RF atom source provides N atoms with higher chemical activity than N molecules, which reduces the formation energy between Fe atoms and N atoms. The vacuum thermal evaporation is beneficial to accurately controlling the growth rate, impurity concentration and composition ratio of multiple compounds of the film at the atomic level. The combination of the two Fe aom and N atom is easier to form nitrides with Fe atoms. Thus in this way the Fe-N films with stable structure are obtained. In the prepared Fe-Fe₃N soft magnetic film, the introduction of N atoms makes the surface of the film more uniform, resulting in the increase of density. Compared with Fe, surface roughness is reduced by two times, and the crystallinity is obviously enhanced. Owing to the high saturation magnetization, the content of Fe₃N phase is increased by 29% and the (102) orientation of Fe₃N increases to 0.64. Therefore the directionality of the magnetic moment arrangement is improved. Comparing with Fe film, the saturation magnetization of the film is increased by 55.2%, reaching 1705.6 emu/cm³. In addition, with the increase of the (102) orientation of Fe₃N, a large number of lattice mismatches are produced, which impedes the growth of Fe and Fe₃N grains and reduces the grain size and anisotropy of the film. Thus the coercivity of the film decreases. The coercivity (50.3 Oe) is 68.6% lower than that of the Fe film. At the same time, the larger lattice mismatch results in the increase of heterointerface, which promotes the carrier scattering and increases the resistivity of Fe-Fe₃N thin film. The resistivity (8.80 μΩ·m) of Fe-Fe₃N thin film is 7 times higher than that of Fe thin film. Therefore, this research provides a new method for studying and developing soft magnetic films with high saturation magnetization, low coercivity and high resistivity.