Buffer influence on magnetic dead layer, critical current and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

摘要

We present a thorough research on Ta/Ru-based buffers and their influence onfeatures crucial from the point of view of applications of MTJs, such ascritical switching current and thermal stability. We investigate devicesconsisting of buffer/FeCoB/MgO/FeCoB/Ta/Ru multilayers for three differentbuffers: Ta 5 / Ru 10 / Ta 3, Ta 5 / Ru 10 / Ta 10 and Ta 5 / Ru 20 / Ta 5 (allthicknesses in nm). In addition, we study systems with a single FeCoB layerdeposited above as well as below the MgO barrier. The crystallographic textureand the roughness of the buffers are determined by means of XRD and atomicforce microscopy measurements. Furthermore, we examine the magnetic domainpattern, the magnetic dead layer thickness and the perpendicular magneticanisotropy fields for each sample. Finally, we investigate the effect of thecurrent induced magnetization switching for nanopillar junctions with lateraldimensions ranging from 1 {\mu}m down to 140 nm. Buffer Ta 5 / Ru 10 / Ta 3,which has the thickest dead layer, exhibits a large increase in the thermalstability factor while featuring a slightly lower critical current densityvalue when compared to the buffer with the thinnest dead layer Ta 5 / Ru 20 /Ta 5.