Thermal Characterization of Ultrathin MgO Tunnel Barriers

Haotian Su; Heungdong Kwon; Fen Xue; Noriyuki Sato; Usha Bhat; Wilman Tsai; Michel Bosman; Mehdi Asheghi; Kenneth E Goodson; Eric Pop; Shan X Wang

doi:10.1021/acs.nanolett.4c02571

Thermal Characterization of Ultrathin MgO Tunnel Barriers

Nano Lett. 2024 Nov 6. doi: 10.1021/acs.nanolett.4c02571. Online ahead of print.

Authors

Haotian Su¹, Heungdong Kwon², Fen Xue¹, Noriyuki Sato¹, Usha Bhat³, Wilman Tsai⁴, Michel Bosman³, Mehdi Asheghi², Kenneth E Goodson^{2

4}, Eric Pop^{1

4

5

6}, Shan X Wang^{1

4}

Affiliations

¹ Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States.
² Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States.
³ Department of Materials Science and Engineering, National University of Singapore, 117575, Singapore.
⁴ Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.
⁵ Department of Applied Physics, Stanford University, Stanford, California 94305, United States.
⁶ Precourt Institute for Energy, Stanford University, Stanford, California 94305, United States.

PMID: 39503294
DOI: 10.1021/acs.nanolett.4c02571

Abstract

Magnetic tunnel junctions (MTJs) with ultrathin MgO tunnel barriers are at the heart of magnetic random-access memory (MRAM) and exhibit potential for spin caloritronics applications due to the tunnel magneto-Seebeck effect. However, the high programming current in MRAM can cause substantial heating which degrades the endurance and reliability of MTJs. Here, we report the thermal characterization of ultrathin CoFeB/MgO multilayers with total thicknesses of 4.4, 8.8, 22, and 44 nm, and with varying MgO thicknesses (1.0, 1.3, and 1.6 nm). Through time-domain thermoreflectance (TDTR) measurements and thermal modeling, we extract the intrinsic (∼3.6 W m^-1 K^-1) and effective (∼0.85 W m^-1 K^-1) thermal conductivities of annealed 1.0 nm thick MgO at room temperature. Our study reveals the thermal properties of ultrathin MgO tunnel barriers, especially the role of thermal boundary resistance, and contributes to a more precise thermal analysis of MTJs to improve the design and reliability of MRAM technologies.

Keywords: MRAM; MTJ; MgO tunnel barrier; TDTR; thermal conductivity.