Microscopic Modeling of MgO Barrier Degradation Due to Interface Oxygen Frenkel Defects in Scaled MTJ Toward High-Density STT-MRAM

Spin-transfer torque magnetic random-access memory (STT-MRAM) is a promising candidate for high-density storage-class memories by using magnetic tunnel junctions (MTJs) with small diameters. However, it is reported that reducing the MTJ diameter can result in resistance drift and degradation of tunnel magnetoresistance (TMR) ratios, which can lead to readout errors. In this study, we investigated the mechanism of the time-dependent degradation of MgO barrier and proposed a method to suppress it. Resistance drift and degradation of TMR ratio were experimentally observed in scaled MTJs under a voltage stress. The degradation can be explained by the current-induced generation of oxygen Frenkel defects at the Fe–MgO interface using microscopic calculations. The reduction of the initial oxygen vacancies in MgO can suppress degradation. Our findings elucidated on the improved reliability in high-density STT-MRAM for storage class memory applications.