MTJ degradation in multi-pillar SOT-MRAM with selective writing

Abstract

In SOT-MRAM, the writing path is decoupled from the reading path and therefore considered robust against MgO breakdown in the MTJ. At operation, high current densities flow through the thin metallic SOT track underneath the MTJ, causing significant heating of both the track and MTJ. At these elevated temperatures, diffusion mechanisms can cause failure of the MTJ. We find that longer tracks heat up more and can sustain less SOT current. Moreover, applying a voltage (VG) on the MTJ during SOT stress can cause MgO breakdown before failure by diffusion occurs. With a failure model, we can predict that breakdown event. This is particularly important in multi-pillar concepts that consist of longer tracks and use VG for selectivity.