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

在本研究中，我们提出了几种新的溅射沉积技术来改善饱和磁化强度大于2.2T的Fe、Fe-N和Fe-Co薄膜的软磁性能。1)在液氮温度下沉积薄膜发现，衬底温度从室温降低到液氮温度会显著改善纯铁薄膜的(110)取向。此外，低温离子轰击可以显著减小薄膜的微晶尺寸，从而显著改善薄膜的软磁性能。2)低电压溅射技术降低溅射电压被认为是有效地抑制高能粒子轰击薄膜，从而提高薄膜的结晶度。在本研究中，我们发现在100V以下的低溅射电压和大于10…的大等离子体密度下进行的溅射虽然要在100V以下的低自偏压下产生高密度等离子体，需要50 MHz以上的射频频率，但使用射频-直流耦合溅射技术可以实现更多的等离子体。利用该低压溅射系统对纯铁和Fe-Co薄膜进行了溅射沉积实验。结果表明，随着溅射电压的降低和薄膜压缩应力的降低，薄膜的取向得到了明显的改善。3)脉冲溅射技术在极高等离子体密度下的溅射中，弧光放电引起的辉光放电不稳定是一个亟待解决的重要问题。在本研究中，我们使用了10~100 kHz的直流脉冲电源来抑制这种不稳定性，并展示了它在溅射沉积薄膜中的有效性。这种脉冲溅射技术也适用于二氧化钛薄膜的反应溅射，其中放电的不稳定性更明显。4)面向靶排列的双溅射技术我们提出了面向靶排列的双溅射技术。在该溅射系统中，两个磁控溅射源被布置在相对的位置。与传统的双溅射系统相比，可以在较低的溅射电压下进行溅射沉积，大大减少了高能粒子对薄膜表面的轰击。5)薄膜软磁性能的改善我们证实，在坡莫合金薄膜底层沉积Fe-Co薄膜后，薄膜的微晶尺寸明显减小，这可能是导致薄膜软磁性能改善的原因。沉积在Ta种子层上的坡莫合金底层显著改善了Fe-Co薄膜的(110)择优取向，减小了薄膜的微晶尺寸。较少

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