High volume spin transfer torque magnetoresistance random access memory (STT-MRAM) for standalone and embedded applications requires a thin perpendicular magnetic tunnel junction (pMTJ) stack (∼10 nm) with a tunnel magnetoresistance (TMR) ratio over 200% after high temperature back-end-of-line (BEOL) processing up to 400 °C. A thin reference layer with low magnetic moment and strong perpendicular magnetic anisotropy (PMA) is key to reduce the total thickness of the full pMTJ stack. We demonstrated strong interfacial PMA and a perpendicular Ruderman-Kittel-Kasuya-Yosida exchange interaction in the Co/Ir system. Owing to the additional high PMA at the Ir/Co interface in combination with a conventional CoFeB/MgO interface in the Ir/Co/Mo/CoFeB/MgO reference layer, the full film pMTJ showed a TMR ratio over 210% after annealing at 400 °C for 150 min. The high TMR ratio can be attributed to the thin stack design by combining a thin reference layer with the efficient compensation by a thin pinned layer. The annealing stability may be explained by the absence of solid solution in the Co-Ir system and the low oxygen affinity of Mo in the reference layer and the free layer. High device performance with a TMR ratio over 210% was also confirmed after subjecting the patterned devices to BEOL processing temperatures of up to 400 °C. This proposed pMTJ design is suitable for both standalone and embedded STT-MRAM applications.
The variation in the magnetic hysteretic properties of rf-sputtered amorphous Tb–Fe thin films as a function of the nominal film thickness was investigated, using Kerr magneto-optic and Hall effect measurements. The results on the thickness dependence of coercivity, polarity of the hysteresis loop, and Curie temperature of films prepared at the same sputtering condition indicate that there is a change in the ‘‘effective’’ film composition. This composition change is believed to be due to microstructure-induced variations in the short-range order during the film growth.
A theoretical analysis of the origin of residual stresses in amorphous wires and their effect on the magnetostrictive properties has been made. The residual stress distribution (compression in the surface and tension in the center) in the wire is attributed to the different cooling rates experienced during solidification by different regions of the wire. Theoretically calculated results agree well with reported experimental data obtained from magnetic measurements.
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