B-concentration dependence on anisotropy field of CoFeB thin film for gigahertz frequency use

B was added to the high moment CoFe thin films (Co₃₅Fe₆₅, Co₂₅Fe₇₅, and Co₁₅Fe₈₅) using synchronous triple-RF magnetron sputtering to obtain the films with large anisotropy fields greater than 500 Oe. These films required inductor core materials operating at the frequencies of several gigahertz. Magnetic properties and the crystalline structure of the CoFeB films were investigated. It was found that the B addition increased the anisotropy field to 400-700 Oe and that the increase in anisotropy field was associated with changes in the crystalline structure, crystallite sizes, and crystallite orientation. The results indicated that CoFeB films have potential for use in magnetic cores and inductors operating at gigahertz frequencies.