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

TLDR

High‑density MRAM requires magnetic tunnel junctions with small, low aspect‑ratio areas, but existing in‑plane magnetization devices need aspect ratios ≥2 to suppress edge curling. The study introduces a perpendicular‑magnetization magnetic tunnel junction device intended for use in MRAM. The device employs perpendicular magnetization films fabricated by focused‑ion beam, allowing an aspect ratio of 1 without edge curling. Magnetic‑force‑microscope imaging shows that a 0.3 μm × 0.3 μm perpendicular‑magnetization film exhibits stable, uniform magnetization, whereas a 0.5 μm × 0.5 μm in‑plane film displays vortices, and the pMTJ achieves a >50 % MR ratio with perfect squareness and no MR degradation at 103 Ω μm².

Abstract

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% with a squareness ratio of 1 and no degradation of MR ratio at 103 Ω μm2 ordered junction resistance.