Underlayer material influence on electric-field controlled perpendicular magnetic anisotropy in CoFeB/MgO magnetic tunnel junctions

The magnetic properties of the perpendicular storage electrode (buffer/MgO/FeCoB/Cap) were studied as a function of annealing temperature by replacing Ta with W and W/Ta cap layers with variable thicknesses. W in the cap boosts up the annealing stability and increases the effective perpendicular anisotropy by 30% compared to the Ta cap. Correspondingly, an increase in the FeCoB critical thickness characterizing the transition from perpendicular to in-plane anisotropy was observed. Thicker W layer in the W(t)/Ta 1 nm cap layer makes the storage electrode highly robust against annealing up to 570 °C. The stiffening of the overall stack resulting from the W insertion due to its very high melting temperature seems to be the key mechanism behind the extremely high thermal robustness. The Gilbert damping constant of FeCoB with the W/Ta cap was found to be lower when compared with the Ta cap and stable with annealing. The evolution of the magnetic properties of bottom pinned perpendicular magnetic tunnel junctions (p-MTJ) stack with the W2/Ta1 nm cap layer shows back-end-of-line compatibility with increasing tunnel magnetoresistance up to the annealing temperature of 425 °C. The pMTJ thermal budget is limited by the synthetic antiferromagnetic hard layer which is stable up to 425 °C annealing temperature while the storage layer is stable up to 455 °C.

mentioning

confidence: 99%

mentioning

confidence: 99%

Enhanced annealing stability and perpendicular magnetic anisotropy in perpendicular magnetic tunnel junctions using W layer

Chatterjee

Sousa

Perrissin

et al. 2017

“…However, both TMR and PMA were reported to be deteriorated upon annealing at temperatures above 400 C for Ta/CoFeB/MgO junctions. 22,23 Several other underlayers such as Pt (Pd), 24 Hf, [25][26][27] Mo, [28][29][30][31][32] and W 33,34 have been studied to improve thermal stability, TMR, PMA, electric field, and spin orbit torque effects in pMTJs. Furthermore, doping of Ta buffer with nitrogen 35 or using a thin sacrificial Mg layer 36 was also reported to improve PMA and TMR in pMTJs.…”

mentioning

confidence: 99%

Effect of Mo insertion layers on the magnetoresistance and perpendicular magnetic anisotropy in Ta/CoFeB/MgO junctions

Almasi

et al. 2016

The effect of a thin Mo dusting layer inserted at the interface of Ta/CoFeB of perpendicular magnetic tunneling junction with MgO barriers was investigated. Unlike thick Mo layers that exhibited a strong (110) crystalline texture, the inserted Mo layer between Ta/CoFeB had little negative influence on the crystallization of CoFe (001), therefore combining the advantages of Mo as a good thermal barrier and Ta as a good boron sink. For optimized Mo dusting thickness, a large tunneling magnetoresistance of 208% was achieved in perpendicular magnetic tunneling junctions with superior thermal stability at 500 °C.

“…The measurements indicate a transition from in-plane anisotropy to PMA after annealing at 350 C, which is consistent with our earlier work. 21 Next, the AHE of samples with t W ¼ 2 and 4 nm were measured in perpendicular magnetic field (Fig. 2).…”

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confidence: 99%

“…21 The saturation magnetization of CoFeB at room temperature equals l 0 M s ¼ 1.6 T and it increases to 2 T at T ¼ 19 K. Figure 4 presents the effective magnetic fields and spin-orbit torque efficiencies vs. temperature.…”

mentioning

confidence: 99%

Temperature dependence of spin-orbit torques in W/CoFeB bilayers

Skowroński

Cecot

Kanak

et al. 2016

Self Cite

We report on the temperature and layer thickness variation of spin-orbit torques in perpendicularly magnetized W/CoFeB bilayers. Harmonic Hall voltage measurements reveal dissimilar temperature evolutions of longitudinal and transverse effective magnetic field components. The transverse effective field changes sign at 250 K for a 2 nm thick W buffer layer, indicating a much stronger contribution from interface spin-orbit interactions compared to, for example, Ta. Transmission electron microscopy measurements reveal that considerable interface mixing between W and CoFeB is primarily responsible for this effect.