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，本研究对微晶非晶磁性薄膜的热写入和自旋注入写入进行了研究。采用电子束光刻技术制备了垂直磁各向异性大、居里温度适中的tfe非晶薄膜。在这项研究中，在100 Oe的静态磁场下，将电流脉冲注入微型制造的tfe窄路中进行热磁写入。在施加0.14 mW和100 nsec的脉冲电流后，证实了在横向尺寸为0.5 x 0.5 μm^2的TbFe上的成功写入。成功写入的临界电流密度随脉冲持续时间的减小而增加，并且通过数值热模拟再现了脉冲持续时间的依赖性。在基于tfe的磁性隧道结中，必须表现出高的隧道磁阻（TMR）比，才能利用tfe存储层作为磁性随机存取存储器的元件。因此，我们试图制造具有TbFe (20 nm) / CoFe (tnm) / Al-0 (1.6 nm) / CoFe (tnm) / 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，证实了较大的TMR比为12%。期望通过优化沉积条件和结的结构进一步提高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.