Thermal Characterization\nof Ultrathin MgO Tunnel Barriers

Magnetic tunnel junctions (MTJs) with ultrathin MgO tunnel\nbarriers\nare at the heart of magnetic random-access memory (MRAM) and exhibit\npotential for spin caloritronics applications due to the tunnel magneto-Seebeck\neffect. However, the high programming current in MRAM can cause substantial\nheating which degrades the endurance and reliability of MTJs. Here,\nwe report the thermal characterization of ultrathin CoFeB/MgO multilayers\nwith total thicknesses of 4.4, 8.8, 22, and 44 nm, and with varying\nMgO thicknesses (1.0, 1.3, and 1.6 nm). Through time-domain thermoreflectance\n(TDTR) measurements and thermal modeling, we extract the intrinsic\n(∼3.6 W m<sup>–1</sup> K<sup>–1</sup>) and effective\n(∼0.85 W m<sup>–1</sup> K<sup>–1</sup>) thermal\nconductivities of annealed 1.0 nm thick MgO at room temperature. Our\nstudy reveals the thermal properties of ultrathin MgO tunnel barriers,\nespecially the role of thermal boundary resistance, and contributes\nto a more precise thermal analysis of MTJs to improve the design and\nreliability of MRAM technologies.