Correlation between microstructure and electromagnetic properties in magnetic tunnel junctions with naturally oxidized MgO barrier

Abstract

We investigated the correlation between the microstructure and the electromagnetic properties of magnetic tunnel junctions (MTJs) with MgO barriers fabricated by direct sputtering and natural oxidation of the Mg layers. The MTJ with an oxidized Mg barrier contained amorphous phases in both the barrier and the CoFeB free layer and exhibited large interface fluctuations in both the CoFeB reference/MgO and MgO/CoFeB interfaces This had a significant influence on the low MR ratio and large switching current. Inserting a CoFe seed layer under the oxidized Mg barrier greatly improved the crystallization of the oxidized MgO which ultimately led to a higher MR ratio and lower switching current. In addition to the textured CoFeB/MgO/CoFeB structures, the sharp interface of the MgO barrier, low B content in the MgO barrier, and Fe-rich composition in the free layer are thought to be of key importance for ensuring high magneto-transport properties.