Fabrication of magnetic random access memory based on nanoring-type magnetic tunnel junctions and spin-polarized current driving

Nanoring-type magnetic tunnel junctions (NR-MTJs) of Ta/IrMn/CoFe/Ru/CoFeB/Al-O/CoFeB/Ta/Ru were nano-fabricated on the Si/SiO$_2$ substrate. The small NR-MTJs with the outer- and inner-diameter of 100 and 50 nm were nano-fabricated and the corresponding NR-MTJ array integrated above the transistors in CMOS circuit for 4x4 MRAM DEMO devices. The magnetoresistance (R) versus current (I) loops for a spin-polarized current switching were measured and the TMR ratio larger than 20$\%$ at room temperature were observed. The critical switching current for the free CoFeB layer between parallel and anti-parallel magnetization states is smaller than 750 $\mu$A in such NR- MTJs. After each positive and negative pulse writing current the high and low resistance of a NR-MTJ as a MRAM bite were read out using a low read current of between 10 and 20 $\mu$A. It shows that the MRAM fabrication with the density higher than 5 Gbite/inch$^2$ are possible based on 1 NR-MTJ + 1 transistor structure and spin-polarized current switching.