Extended RVS characterisation of STT-MRAM devices: Enabling detection of AP/P switching and breakdown

In this work, we detail a novel methodology to extract the magnetisation switching and MgO breakdown characteristics of STT-MRAM devices, from a single d.c. ramped voltage stress (RVS) measurement. This is performed by a two-step process, initially by a robust outlier screening procedure on a piecewise fit to the measured data. Subsequently, these fit results are subjected to k-means cluster analysis to elucidate the magnetisation states present, together with the voltages at which these states change, or breakdown occurs. We validate this methodology by successfully correlating our RVS results with the more widely reported pulsed-breakdown results. An application of this technique examines the impact of scaling MgO tunnel layer thickness. We demonstrate how both the switching and breakdown voltage values reduce with scaling down the MgO tunnel-layer thickness for ultra-thin MgO layers. The switching voltage reduction is more significant than the breakdown voltage reduction, which results in a gain in reliable operation margin on reducing MgO thickness.