Abstract
We investigate the effect of the capping layer on the thermal tolerance of magnetic tunnel junctions (MTJs) with free layer of MgO/CoFeB/spacer layer/CoFeB/MgO/capping layers (CoFeB, Ru, or Ta). We observe the largest perpendicular magnetic anisotropy energy density for the free layer with CoFeB capping layer using Ta spacer after annealing at 400°C for 1 h. Energy-dispersive X-ray (EDX) line analysis along film normal direction reveals the absorption of oxygen in MgO by Ta in the stack with Ta capping layer and Ru diffusion into CoFeB free layer in the stack with Ru capping layer, which could cause the reduction of perpendicular magnetic anisotropy. We also evaluate annealing temperature dependence of magnetic properties for the MTJ stacks with different spacer layer. We again observe the largest perpendicular magnetic anisotropy energy density for the MTJ stack using the CoFeB capping layer. The present study reveals that CoFeB capping layer is effective for achieving improved robustness against annealing.
Highlights
Embedded nonvolatile memory is an essential constituent for future electronics as it can achieve significant reduction of standby power, which becomes a more serious issue for advancing technology nodes
The results reveal that Ru atoms in the capping layer diffuse into the free layer region through top MgO layer in the case of Ru capping layer, which could degrade the perpendicular magnetic anisotropy (PMA) of the free layer
We investigate the effect of capping layer material on thermal tolerance of a free layer with a structure of MgO/ CoFeB/spacer layer/CoFeB/MgO/capping layers (CoFeB, Ru, or Ta)
Summary
Embedded nonvolatile memory is an essential constituent for future electronics as it can achieve significant reduction of standby power, which becomes a more serious issue for advancing technology nodes. Much effort has been devoted to achieving the more robust MTJs against annealing; the CoFeB composition and materials adjacent to the CoFeB free layer are the scitation.org/journal/adv important factors.. Much effort has been devoted to achieving the more robust MTJs against annealing; the CoFeB composition and materials adjacent to the CoFeB free layer are the scitation.org/journal/adv important factors.22–25 Both high PMA and robust MTJ stack against annealing are critical for high-performance and highcapacity STT-MRAM, each study has been independently done. In this regard, the effect of the capping layer on the PMA should be studied annealing at 400 ○C
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