Development of magnetization reversal technique at low power consumption using a stress-induced magnetic anisotropy for perpendicular MRAM

具有垂直磁各向异性的薄膜作为垂直磁性随机存取存储器(p-MRAM)具有实现高密度单元排列的潜力。我们提出了一种利用应力感生磁各向异性来降低DyFeCo薄膜垂直矫直力的新方法。如果薄膜具有较大的磁致伸缩常数，施加在薄膜面内方向的各向同性应力可以有效地降低写入过程中的垂直磁各向异性。在本研究中，我们成功地在低磁场下实现了磁化反转，其磁化强度低至薄膜原始矫直力的1/6。用反常霍尔效应测量了薄膜的磁化过程，用机械压痕方法测量了薄膜的面内应力。观察到，如果施加面内应力，约500Oe的反向磁场足以完全逆转薄膜的磁化强度，其原始矫顽力为3.3Koe。该技术适用于低功耗、宽写入裕度的p-MRAM的写入工艺。

Thin films with perpendicular magnetic anisotropy have a potential to achieve high-density cell arrangements as a perpendicular magnetic random access memory (p-MRAM). We have demonstrated a new method to reduce perpendicular coercivity of DyFeCo films using a stress-induced magnetic anisotropy. An isotropic stress applied to in-plane direction of the film was so effective to cause reduction of perpendicular magnetic anisotropy during the writing process if the film has large magnetostriction constant. In this study, we have succeeded to cause magnetization reversal at low magnetic field as low as 1/6 of original coercivity of the film. Magnetization processes of the films were measured using anomalous Hall effects and in-plane stress to the films was induced by a mechanical indentation method. It is observed that about 500 Oe of magnetic field in the reverse direction is enough to reverse completely the magnetization of the film which has an original coercivity of 3.3 kOe if the in-plane stress is applied to the film. This technique is applicable to the writing process of p-MRAM with wide writing margin at low power consumption.