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 /spl Omega/m/sup 2/ 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/Pt/sub 50/Mn/sub 50//Co/sub 70/Fe/sub 30//Ru/Co/sub 60/Fe/sub 20/B/sub 20//MgO (x nm)/Co/sub 60/Fe/sub 20/B/sub 20//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 /spl Aring/. After the film deposition, the MTJs were annealed at 360/spl deg/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 /spl Aring/ and gradually decreases for MgO thickness below 12 /spl Aring/.