Study on spin injection solid state magnetic memories

为了开发高速、非易失性和热稳定的固态存储器，本研究在微细加工的非晶磁性薄膜上进行了热写入和自旋注入写入，利用电子束光刻技术制备了具有较大垂直磁各向异性和中等居里温度的TbFe非晶薄膜。在本研究中，热磁写入是在100Oe的恒磁场下，通过将电流脉冲流入微制造的TbFe窄路径来进行的。在横向尺寸为0.5×0.5μm^2的TbFe上，在0.14 mW、10 0nsec的脉冲电流作用下成功写入。写入成功的临界电流密度随脉冲宽度的减小而增加，并通过数值热模拟再现了其对脉冲宽度的依赖关系。为了利用TbFe存储层作为磁随机存取存储器的元件，需要在TbFe基磁隧道结中表现出高的隧道磁阻(TMR)比。因此，我们试图制备具有TbFe(20 Nm)/CoFe(TnM)/Al-0(1.6 nm)/CoFe(T Nm)/TbFe(20 Nm)结构的磁性隧道结。通过在t=1 nm处插入较薄的CoFe层，得到了高达12%的TMR。通过优化沉积条件和结的结构，有望进一步提高TMR比。

In order to develop high speed, non-volatile, and thermally stable solid-state memory, this research studied thermal writing and spin injection writing on micro-fabricated amorphous magnetic thin films.TbFe amorphous thin films having a large perpendicular magnetic anisotropy and moderate Curie temperature were micro-fabricated by using electron beam lithography technique. In this study, thermomagnetic writing was performed by flowing current pulses into the micro-fabricated TbFe narrow path under a static magnetic field of 100 Oe. The successful writing on TbFe with a lateral size of 0.5 x 0.5 μm^2 was confirmed after the application of the current pulse of 0.14 mW and 100 nsec. The critical current density for the successful writing was increased with decreasing pulse duration, and the dependence on the pulse duration was reproduced by the numerical thermal simulation.It is necessary to exhibit high tunnel magneto-resistance (TMR) ratio in TbFe based magnetic tunnel junctions to utilize the TbFe memory layer as an element of the magnetic random access memory. We, therefore, tried to fabricate magnetic tunneling junctions having the structure of TbFe (20 nm) / CoFe (tnm) / Al-0 (1.6 nm) / CoFe (t nm) / TbFe (20 nm). By inserting thin CoFe layers at t = 1 nm, large TMR ratio of 12% was confirmed. Further improvement of the TMR ratio is expected by optimizing the deposition condition and the structure of the junction.