Dependence of tunnel magnetoresistance effects of MgO based magnetic tunnel junctions on magnetron sputtering parameters

MgO based magnetic tunnel junctions (MTJs) were fabricated by magnetron sputtering single crystal MgO target. The (001) crystal structure of MgO film can be obtained under less than 6 cm parallel distance between MgO target and substrate. Lots of MgO based MTJs have more than 100% TMR values at the distance of 5 cm and annealing temperature 320360 ℃ from the statistical perspective. However, MTJs show almost zero TMR values at the distance ranging from 6 to 10 cm. MTJs deposited with 30° angle and 6 cm distance between MgO target and the substrate have 24-52% TMR values, indicating that the off-axis deposition helps to improve (001) MgO crystal structure. Although the adjustment of RF power (100-220W) and Ar work pressure (12-15 mTorr) can slightly affect TMR values of MTJs, yet the distance between MgO target and substrate is the more sensitive parameter. Therefore, the depositing distance between MgO target and substrate need be carefully considered in the fabrication of MgO based MTJs.