Development of soft magnetic thin films with large saturation magnetization for magnetic recording head by sputter-deposition at liquid nitrogen temperature

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In this research, we proposed several kinds of new sputter-deposition techniques to improve soft magnetic properties of Fe, Fe-N, and Fe-Co thin films with large saturation magnetization above 2.2T.1) Deposition of the film at liquid nitrogen temperatureIt was found that the reduction of the substrate temperature from room temperature to liquid nitrogen temperature leads to a remarkable improvement in the (110) orientation of pure iron films. In addition, ion bombardment at such low temperature can reduce the crystallite size of the films significantly, which results in a remarkable improvement of soft magnetic properties of the film.2) Low voltage sputtering techniqueThe reduction of sputtering voltage is thought to be effective to suppress the high energy particle bombardment of the film, which will lead to an improvement of the crystallinity of the film. In this study, we showed that the sputtering at a low sputtering voltage below 100V and a large plasma density above 10^<11>cm^<-3 … More > can be realized by using rf-dc coupled sputtering technique, although rf frequency of above 50MHz was necessary to produce a high density plasma at low self bias voltage below 100V. Sputter-deposition of pure iron and Fe-Co films were attempted by using this low voltage sputtering system. As a result, it became clear that the orientation of the film is improved by the reduction of sputtering voltages, along with the reduction of compressive film stress. The significant improvement of soft magnetic properties of the film, however, was not observed by the reduction of the sputtering voltage.3) Pulse sputtering techniqueIn the sputtering at a very high plasma density, instability of the glow discharge due to arc discharge was an important problem to be solved. In this study, we used a dc pulse power source of 10 to 100kHz to suppress the instability and showed its effectiveness in the sputter deposition of the films. This pulse sputtering technique was also useful in the reactive sputtering of TiO_2,films, where instability of the discharge was more significant.4) Dual sputtering technique with facing target arrangementWe proposed a new dual sputtering technique with facing target arrangement. In this sputtering system, two magnetron sputtering sources were arranged in an opposed position. Compared with the conventional dual sputtering system, sputter-deposition can be performed at lower sputtering voltages, and high energy particle bombardment to film surface can be reduced markedly.5) Improvement of soft magnetic properties of Fe-Co films deposited on under layerWe confirmed that the crystallite size of the Fe-Co film was decreased significantly by depositing the films on permalloy under layer, which may result in the improvement of soft magnetic properties of the film. Permalloy under layer deposited on Ta seed layer led to a significant improvement of (110) orientation of Fe-Co films along with the reduction of the crystallite size of the film. Less