Novel design and fabrication of magnetic random access memory based on nano-ring-type magnetic tunnel junctions

Nano-ring-type magnetic tunnel junctions (NR-MTJs) with the layer structure of Ta(5)/Ir₂₂Mn₇₈(10) /Co₇₅Fe₂₅(2)/Ru(0.75) /Co₆₀Fe₂₀B₂₀(3) /Al(0.6)-oxide/Co₆₀Fe₂₀B₂₀(2.5)/ Ta(3)/Ru(5) (thickness unit: nm) were nano-fabricated on the Si(100)/SiO₂ substrate using magnetron sputtering deposition combined with the optical lithography, electron beam lithography (EBL) and Ar ion-beam etching techniques. The smaller NR-MTJs with the inner- and outer-diameter of around 50 and 100 nm and also their corresponding NR-MTJ arrays were nano-patterned. The tunneling magnetoresistance (TMR&R) versus driving current (I) loops for a spin-polarized current switching were measured, and the TMR ratio of around 35% at room temperature were observed. The critical values of switching current for the free Co₆₀Fe₂₀B₂₀ layer relative to the reference Co₆₀Fe₂₀B₂₀ layer between parallel and anti-parallel magnetization states were between 0.50 and 0.75 mA in such NR-MTJs. It is suggested that the applicable MRAM fabrication with the density and capacity higher than 256 Mbit/inch² even 6 Gbite/inch² are possible using both 1 NR-MTJ+1 transistor structure and current switching mechanism based on based on our fabricated 4 × 4 MRAM demo devices.