Tadahiko Hirai

Magnetic tunnel junction device with perpendicular magnetization films for high-density magnetic random access memory

We present here a magnetic tunnel junction device using perpendicular magnetization films designed for magnetic random access memory (MRAM). In order to achieve high-density MRAM, magnetic tunnel junction devices with a small area of low aspect ratio (length/width) is required. However, all MRAMs reported so far consist of in-plane magnetization films, which require an aspect ratio of 2 or more in order to reduce magnetization curling at the edge. Meanwhile, a perpendicular magnetic tunnel junction (pMTJ) can achieve an aspect ratio=1 because the low saturation magnetization does not cause magnetization curling. Magnetic-force microscope shows that stable and uniform magnetization states were observed in 0.3 μm×0.3 μm perpendicular magnetization film fabricated by focused-ion beam. In contrast, in-plane magnetization films clearly show the presence of magnetization vortices at 0.5 μm×0.5 μm, which show the impossibility of information storage. The PMTJ shows a magnetoresistive (MR) ratio larger than 50% w...