Abstract
Soft magnetic thin films with high saturation magnetization and resistivity are of great interest in micro-inductor for the magnetic device application. In this study, amorphous Fe–Co–Hf–N thin films with a gradient concentration of Hf doping were fabricated by rf reactive magnetron sputtering. The evaluated magnetic properties and high-frequency characteristics were sensitive to the doping contents. A new technology was used to deposit a series Fe–Co–Hf–N thin films on which gradient concentration of Hf was present. By this new deposition technology, the films existed residual stress, and thus the stress-induced anisotropy field was enhanced. The as-deposited films without post annealing exhibited larger anisotropy field (Hk) of 150 Oe. In addition, coercivity (HC) of less than 5 Oe in both easy and hard axes, and electrical resistivity (ρ) of 500 μΩ-cm were obtained. In addition, nano-composite Fe–Co–Hf–O thin films were developed using dc reactive magnetron sputtering. The influence of oxygen content on the microstructure, high-frequency characteristics and magnetic properties was investigated. With the increase in oxygen content from 31 to 40 at%, the films exhibited high resistivity up to 2600 μΩ-cm. A minimum coercivity (HC) value of 0.8 Oe andρ= 800 μΩ-cm was obtained for the Fe36.5Co17.2Hf9.8O36.5 film with thickness around 1300 nm. The high frequency behavior of Fe–Co–Hf based films was also evaluated. The permeability measurement showed a permeability of Fe–Co–Hf–N films around 100 at 3 GHz and a ferromagnetic resonance frequency (fFMR) in excess of 3 GHz. In addition, the ferromagnetic resonance frequency of Fe–Co–Hf–O film was as high as 2.6 GHz, implying a high cut-off frequency. It is expected that the Fe–Co–Hf based films should be promising for practical applications as a high-frequency ferromagnetic material.