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  • Title: Predictive Materials Design of Magnetic Random-Access Memory Based on Nanoscale Atomic Structure and Element Distribution.
    Author: Li X, Sasaki T, Grezes C, Wu D, Wong K, Bi C, Ong PV, Ebrahimi F, Yu G, Kioussis N, Wang W, Ohkubo T, Khalili Amiri P, Wang KL.
    Journal: Nano Lett; 2019 Dec 11; 19(12):8621-8629. PubMed ID: 31697502.
    Abstract:
    Magnetic tunnel junctions (MTJs) capable of electrical read and write operations have emerged as a canonical building block for nonvolatile memory and logic. However, the cause of the widespread device properties found experimentally in various MTJ stacks, including tunneling magnetoresistance (TMR), perpendicular magnetic anisotropy (PMA), and voltage-controlled magnetic anisotropy (VCMA), remains elusive. Here, using high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy, we found that the MTJ crystallization quality, boron diffusion out of the CoFeB fixed layer, and minimal oxidation of the fixed layer correlate with the TMR. As with the CoFeB free layer, seed layer diffusion into the free layer/MgO interface is negatively correlated with the interfacial PMA, whereas the metal-oxides concentrations in the free layer correlate with the VCMA. Combined with formation enthalpy and thermal diffusion analysis that can explain the evolution of element distribution from MTJ stack designs and annealing temperatures, we further established a predictive materials design framework to guide the complex design space explorations for high-performance MTJs. On the basis of this framework, we demonstrate experimentally high PMA and VCMA values of 1.74 mJ/m2 and 115 fJ/V·m-1 with annealing stability above 400 °C.
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