Magnetic tunnel junctions with an Al and Al-Hf-Al oxide barrier formed by ozone oxidation

Abstract

Magnetic tunnel junctions (MTJs) with the barrier oxidized by ozone were studied. Tunnel magnetoresistance (TMR) ratio of about 30 % in the junctions with an ozone oxidized barrier is almost the same as those with plasma oxidized barrier. However, junction resistance of the ozone oxidized specimen was one order magnitude lower than that of plasma oxidized one. The plasma free oxidation process could eliminate the possible structural damage by an oxygen ion bombardment and give improved control over the tunnel barrier. In addition to this, we have modified the oxide barrier by forming Hf oxide layer in the middle of Al oxide. The junctions with Hf-inserted barrier show higher TMR ratio and weaker temperature dependence than those with the conventional Al oxide barrier. The enhancement of TMR by the introduction of Hf layer might be due to the reduction of defects in the barrier.