CoFeB/MgO/CoFeB magnetic tunnel junctions with high TMR ratio and low junction resistance

A successful attempt in obtaining magnetic tunnel junctions (MTJs) with resistance-area (RA) of 4.7 Ωm² and magneto-resistance (MR) ratio of about 150% at room temperature is reported, in MTJs using CoFeB/MgO/CoFeB. The MTJs consisting of Ta/CuN/Ta/Pt₅₀Mn₅₀/Co₇₀Fe₃₀/Ru/Co₆₀Fe₂₀B₂₀/MgO (x nm)/Co₆₀Fe₂₀B₂₀/Ta/Cu/Ta/Ru were prepared on a thermally oxidized silicon wafer using an ANELVA C-7100 sputtering system. All the metallic films were deposited by using dc magnetron method. The insulating MgO layer was deposited by rf sputtering directly from a sintered MgO target, and the thickness was varied from 6 to 24 Å. After the film deposition, the MTJs were annealed at 360°C for 2 hours in a magnetic field of 8 kOe. It was found that as MgO thickness decreases, RA decreases exponentially, but MR ratio remains constant of about 230% until around 12 Å and gradually decreases for MgO thickness below 12 Å.