Ultra-High Density Magnetic Memory Cells

我们研究了亚微米磁存储单元的磁性和磁化过程，以期找到提高MRAM（磁随机存取存储器）密度的突破口。我们已经建立了一种制造矩形存储单元（70 nm x 200 nm）的微加工工艺。对应的内存容量为16gb。(2)用磁力显微镜观察了Ni-Fe(5 nm)/Hf（5 nm）矩形电池和Ni-Fe(5 nm)/Hf(2 nm)/Ni-Fe(5 nm)/Hf（5 nm）矩形电池的磁态。观察结果表明，在Ni-Fe/Hf/Ni-Fe/Hf电池中，磁通量通过两个磁层闭合，闭合的磁通量使Ni-Fe/Hf/Ni-Fe/Hf电池的开关场减小。微磁模拟表明，当电池尺寸为50 nm × 100 nm时，Ni-Fe/Hf/Ni-Fe/Hf电池的开关场约为Ni-Fe/Hf电池的1/2。(3)微磁学模拟表明，不对称环形点（材料：5-20 nm厚Ni-20at%Fe，直径）的磁化方向。500-1000 nm)的外侧面部分为平面的环状点，通过面内磁场控制在顺时针和逆时针之间，即使普通环状点需要垂直电流引起的顺时针和逆时针磁场。

We have investigated magnetic properties and magnetization processes of sub-micron magnetic memory cells in order to find a breakthrough that increases a density of MRAM (magnetic random access memory).(1) We have established a microfabrication process that makes rectangular memory cells (70 nm x 200 nm). The size corresponds a memory volume of 16 Gbits.(2) Magnetic states of the Ni-Fe(5 nm)/Hf(5 nm) rectangular cells and Ni-Fe(5 nm)/Hf(2 nm)/Ni-Fe(5 nm)/Hf(5 nm) rectangular cells were observed using magnetic force microscopy. The observation showed that the magnetic flux closed through the two magnetic layers in the Ni-Fe/Hf/Ni-Fe/Hf cells, and the closed magnetic flux decreased the switching field of the Ni-Fe/Hf/Ni-Fe/Hf cells. The micromagnetics simulation showed that the switching field of the Ni-Fe/Hf/Ni-Fe/Hf cells is about 1/2 of the Ni-Fe/Hf cells for the cell size of 50 nm x 100 nm.(3) The micromagnetics simulation showed that the magnetization direction of the asymmetric ring dots (material: 5-20 nm thick Ni-20at%Fe, diameter. 500-1000 nm) that have partly planed outer sides were controlled between clockwise and counterclockwise by in-plane magnetic fields, even though the ordinary ring dots needed the clockwise and counterclockwise magnetic fields caused by the perpendicular current.