Improvement of Switching Field in Magnetic Tunneling Junction Using Ru/Ta Capping Layer

A Ru/Ta capping layer for magnetic tunneling juctions (MTJs) was used to replace the routinely used Ta capping layer. The MTJs with CoFeB used as the free layer were shaped to ellipses of 0.36
$times$
0.60
$mu$
m. The magnetoresistive (MR) ratio of Ru/Ta capped MTJs was found to be 47.3%, slightly lower than the value of 52.8% of Ta capped MTJs. In the meantime, the switching field of Ru/Ta capped MTJs with 30
$ AA$
of Ru was found to be 37.7 Oe, greatly reduced from 63 Oe of Ta capped MTJs. The switching field varition of Ru/Ta capped MTJs was 6 Oe, also better than the value of 11 Oe of Ta capped MTJs. The different switching behaviors of Ru/Ta and Ta capped MTJs were discussed from the aspects of oxygen diffusion, intermixing, and magnetostriction.