Dependence of tunnel magnetoresistance in MgO based magnetic tunnel junctions on Ar pressure during MgO sputtering

We investigated dependence of tunnel magnetoresistance effect in CoFeB/MgO/CoFeB magnetic tunnel junctions on Ar pressure during MgO-barrier sputtering. Sputter deposition of MgO-barrier at high Ar pressure of 10 mTorr resulted in smooth surface and highly (001) oriented MgO. Using this MgO as a tunnel barrier, tunnel magnetoresistance (TMR) ratio as high as 355% at room temperature (578% at 5 K) was realized after annealing at 325°C or higher, which appears to be related to a highly (001) oriented CoFeB texture promoted by the smooth and highly oriented MgO. Electron-beam lithography defined deep-submicron MTJs having a low-resistivity Au underlayer with the high-pressure deposited MgO showed high TMR ratio at low resistance-area product (RA) below 10 ω μm² as 27% at RA = 1.1 ω μm ², 77% at RA = 1.1 ω μm², 130% at RA = 1.7 ω μm², and 165% at RA = 2.9 ω μm².