Analysis and Simulation of Interface Quality and Defect Induced Variability in MgO Spin-Transfer Torque Magnetic RAMs

• Published in: IEEE electron device letters Vol. 42; no. 1; pp. 34 - 37
• Main Authors: Sikder, Bejoy, Lim, Jia Hao, Kumar, Mondol Anik, Padovani, Andrea, Haverty, Michael, Kamal, Uday, Raghavan, Nagarajan, Larcher, Luca, Pey, Kin-Leong, Baten, Md Zunaid
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Electrical resistance measurement; Electron transfer; Energy barrier; Ferromagnetism; Magnesium oxide; Magnetic tunneling; Magnetoresistance; Magnetoresistivity; Mathematical model; Monte Carlo simulation; Resistance; Spatial distribution; STT-MRAM; Temperature measurement; Variability; Voltage measurement
• ISSN: 0741-3106; 1558-0563
• DOI: 10.1109/LED.2020.3040131

Device-to-device variability of CoFeB/MgO based STT-MRAMs is studied based on experiments and simulations taking into account the influence of interface quality, temperature variation and device dimensionality. Metal-induced gap states resulting from electron transfer at the ferromagnet-tunnel barrier interface significantly influence the effective energy barrier height of these devices irrespective of their diameters. Switching voltage and parallel - antiparallel resistance values vary by as much as 43% and 30% respectively for about 13% variation of the energy barrier, whereas the tunneling magnetoresistance remains typically unaffected. WRITE cycles of highly scaled STT-MRAMs are therefore more susceptible to device-to-device variations resulting from microscopic variations in the interface quality, rather than the READ cycles. Such variations are observed to be independent of temperature, as well as spatial distribution of the defects.