High thermal tolerance synthetic ferrimagnetic reference layer with modified buffer layer by ion irradiation for perpendicular anisotropy magnetic tunnel junctions

A Recent Progress of Spintronics Devices for Integrated Circuit Applications

“…Here, we review our recent progress in the advanced p-MTJs for STT-MRAM. In particular, we describe the material design knowledge of (1) high thermal tolerance by controlling boron composition of CoFeB free layer, (2) damage suppression by sputtering conditions, and (3) thermal tolerance of the reference layer by high-temperature annealing [19,20].…”

“…To obtain high thermal tolerance, one needs to control diffusion of boron from CoFeB to the adjacent layer because boron concentration plays a crucial role in realizing perpendicular easy axis [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. As shown in Figure 2a,c, all the s-MTJs showed an increase of TMR ratio up to a specific temperature, above which the TMR ratio degraded.…”

“…To clarify the origin of the variation of H s , we investigated T a dependence of spontaneous magnetic moment per unit area m s of each layer in reference layer ( Figure 8) and a variation of composition depth profile after annealing at 400 • C. In order to overcome this issue, we have developed surface modification process (SMT) on the Pt buffer layer by ion irradiation [20]. SMT improves crystallinity of the Co/Pt multilayer even after 400 • C annealing, resulting in high perpendicular anisotropy of Co/Pt and suppression of Fe diffusion in the CoFeB reference layer [20].…”