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    University - Scholar Department: Electrical Engineering Position: Postdoctoral Scholar

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  • Mail Code: 4045

All Publications

  • Thermal Characterization of Ultrathin MgO Tunnel Barriers. Nano letters Su, H., Kwon, H., Xue, F., Sato, N., Bhat, U., Tsai, W., Bosman, M., Asheghi, M., Goodson, K. E., Pop, E., Wang, S. X. 2024

    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.

    View details for DOI 10.1021/acs.nanolett.4c02571

    View details for PubMedID 39503294

  • On-Device Continual Learning With STT-Assisted-SOT MRAM-Based In-Memory Computing IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS Zhang, F., Sridharan, A., Hwang, W., Xue, F., Tsai, W., Wang, S., Fan, D. 2024; 43 (8): 2393-2404

    View details for DOI 10.1109/TCAD.2024.3371268

    View details for Web of Science ID 001273931700016

  • Thermal optimization of two-terminal SOT-MRAM JOURNAL OF APPLIED PHYSICS Su, H., Kwon, H., Hwang, W., Xue, F., Koroglu, C., Tsai, W., Asheghi, M., Goodson, K. E., Wang, S. X., Pop, E. 2024; 136 (1)

    View details for DOI 10.1063/5.0211620

    View details for Web of Science ID 001260943300007

  • The role of magnetic anisotropy in the magnetoresistance of Cr<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> thin film antiferromagnets AIP ADVANCES Wisser, J. J., Xue, F., Wang, S. X., Suzuki, Y. 2024; 14 (3)

    View details for DOI 10.1063/5.0195641

    View details for Web of Science ID 001181003200006

  • Field-free spin-orbit torque switching assisted by in-plane unconventional spin torque in ultrathin [Pt/Co]N. Nature communications Xue, F., Lin, S. J., Song, M., Hwang, W., Klewe, C., Lee, C. M., Turgut, E., Shafer, P., Vailionis, A., Huang, Y. L., Tsai, W., Bao, X., Wang, S. X. 2023; 14 (1): 3932

    Abstract

    Electrical manipulation of magnetization without an external magnetic field is critical for the development of advanced non-volatile magnetic-memory technology that can achieve high memory density and low energy consumption. Several recent studies have revealed efficient out-of-plane spin-orbit torques (SOTs) in a variety of materials for field-free type-z SOT switching. Here, we report on the corresponding type-x configuration, showing significant in-plane unconventional spin polarizations from sputtered ultrathin [Pt/Co]N, which are either highly textured on single crystalline MgO substrates or randomly textured on SiO2 coated Si substrates. The unconventional spin currents generated in the low-dimensional Co films result from the strong orbital magnetic moment, which has been observed by X-ray magnetic circular dichroism (XMCD) measurement. The x-polarized spin torque efficiency reaches up to -0.083 and favors complete field-free switching of CoFeB magnetized along the in-plane charge current direction. Micromagnetic simulations additionally demonstrate its lower switching current than type-y switching, especially in narrow current pulses. Our work provides additional pathways for electrical manipulation of spintronic devices in the pursuit of high-speed, high-density, and low-energy non-volatile memory.

    View details for DOI 10.1038/s41467-023-39649-1

    View details for PubMedID 37402728

  • Observation of anti-damping spin-orbit torques generated by in-plane and out-of-plane spin polarizations in MnPd3. Nature materials Dc, M., Shao, D. F., Hou, V. D., Vailionis, A., Quarterman, P., Habiboglu, A., Venuti, M. B., Xue, F., Huang, Y. L., Lee, C. M., Miura, M., Kirby, B., Bi, C., Li, X., Deng, Y., Lin, S. J., Tsai, W., Eley, S., Wang, W. G., Borchers, J. A., Tsymbal, E. Y., Wang, S. X. 2023

    Abstract

    Large spin-orbit torques (SOTs) generated by topological materials and heavy metals interfaced with ferromagnets are promising for next-generation magnetic memory and logic devices. SOTs generated from y spin originating from spin Hall and Edelstein effects can realize field-free magnetization switching only when the magnetization and spin are collinear. Here we circumvent the above limitation by utilizing unconventional spins generated in a MnPd3 thin film grown on an oxidized silicon substrate. We observe conventional SOT due to y spin, and out-of-plane and in-plane anti-damping-like torques originated from z spin and x spin, respectively, in MnPd3/CoFeB heterostructures. Notably, we have demonstrated complete field-free switching of perpendicular cobalt via out-of-plane anti-damping-like SOT. Density functional theory calculations show that the observed unconventional torques are due to the low symmetry of the (114)-oriented MnPd3 films. Altogether our results provide a path toward realization of a practical spin channel in ultrafast magnetic memory and logic devices.

    View details for DOI 10.1038/s41563-023-01522-3

    View details for PubMedID 37012436

  • Energy Efficient Computing With High-Density, Field-Free STT-Assisted SOT-MRAM (SAS-MRAM) IEEE TRANSACTIONS ON MAGNETICS Hwang, W., Xue, F., Zhang, F., Song, M., Lee, C., Turgut, E., Chen, T. C., Bao, X., Tsai, W., Fan, D., Wang, S. X. 2023; 59 (3)

    View details for DOI 10.1109/TMAG.2022.3224729

    View details for Web of Science ID 000963514500004

  • 2-Terminal, High Density, and Magnetic Field Free SOT-MRAM Hwang, W., Xue, F., Tsai, W., Wang, S. X., IEEE IEEE. 2023

    View details for DOI 10.1109/TMRC59626.2023.10264011

    View details for Web of Science ID 001090519000002

  • Performance Benchmarking of Spin-Orbit Torque Magnetic RAM (SOT-MRAM) for Deep Neural Network (DNN) Accelerators Luo, Y., Kumar, P., Liao, Y., Hwang, W., Xue, F., Tsai, W., Wang, S. X., Naeemi, A., Yu, S., IEEE IEEE. 2022: 73-76

    View details for DOI 10.1109/IMW52921.2022.9779279

    View details for Web of Science ID 000869001800019

  • Spin-orbit torques of an in-plane magnetized system modulated by the spin transport in the ferromagnetic Co layer APL MATERIALS Xue, F., Lin, S., Li, P., Hwang, W., Huang, Y., Tsai, W., Wang, S. X. 2021; 9 (10)

    View details for DOI 10.1063/5.0048917

    View details for Web of Science ID 000754460900001

  • Large and robust charge-to-spin conversion in sputtered conductive WTex with disorder MATTER Li, X., Li, P., Hou, V., Mahendra, D. C., Nien, C., Xue, F., Yi, D., Bi, C., Lee, C., Lin, S., Tsai, W., Suzuki, Y., Wang, S. X. 2021; 4 (5): 1639-1653

    View details for DOI 10.1016/j.matt.2021.02.016

    View details for Web of Science ID 000647646400003

  • Micro Electric-field Sensors: Principles and Applications IEEE INDUSTRIAL ELECTRONICS MAGAZINE Han, Z., Xue, F., Hu, J., He, J. 2021

    View details for DOI 10.1109/MIE.2020.3046226

    View details for Web of Science ID 000732888600001

  • Tunable spin-orbit torque efficiency in in-plane and perpendicular magnetized [Pt/Co](n) multilayer APPLIED PHYSICS LETTERS Xue, F., Lin, S., Mahendra, D. C., Bi, C., Li, X., Tsai, W., Wang, S. X. 2021; 118 (4)

    View details for DOI 10.1063/5.0034917

    View details for Web of Science ID 000630477200002

  • Ultrahigh Spin-Orbit Torque Efficiency at Spin Reorientation Transition State in Pt/Co Multilayer Xue, F., Lin, S., Dc, M., Bi, C., Li, X., Tsai, W., Wang, S. X., IEEE IEEE. 2021

    View details for DOI 10.1109/VLSI-TSA51926.2021.9440118

    View details for Web of Science ID 000680845500054

  • Challenges toward Low-Power SOT-MRAM Lin, S., Huang, Y., Song, M., Lee, C., Xue, F., Chen, G., Yang, S., Chang, Y., Wang, I., Hsin, Y., Su, Y., Wei, J., Pai, C., Wang, S. X., Diaz, C. H., IEEE IEEE. 2021

    View details for DOI 10.1109/IRPS46558.2021.9405127

    View details for Web of Science ID 000672563100039

  • Drive-Current-Free Switch With Internal Transduction in a Magneto Piezo-Electronic Transistor IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS Xue, F., Guo, Y., Sato, N., Ouyang, Y., Han, Z., Wang, S. X., Hu, J., He, J. 2020; 67 (4): 3257–66

    View details for DOI 10.1109/TIE.2019.2910050

    View details for Web of Science ID 000507307000072

  • Piezoelectric-Piezoresistive Coupling MEMS Sensors for Measurement of Electric Fields of Broad Bandwidth and Large Dynamic Range IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS Xue, F., Hu, J., Guo, Y., Han, G., Ouyang, Y., Wang, S. X., He, J. 2020; 67 (1): 551–59

    View details for DOI 10.1109/TIE.2019.2893837

    View details for Web of Science ID 000490858500050

  • Large voltage control of magnetic anisotropy in CoFeB/MgO/OX structures at room temperature APL MATERIALS Xue, F., Sato, N., Bi, C., Hu, J., He, J., Wang, S. X. 2019; 7 (10)

    View details for DOI 10.1063/1.5101002

    View details for Web of Science ID 000501309200002

  • Research on the Protrusions Near Silicon-Glass Interface during Cavity Fabrication. Micromachines Zhang, M., Yang, J., He, Y., Yang, F., Zhao, Y., Xue, F., Han, G., Si, C., Ning, J. 2019; 10 (6)

    Abstract

    Taking advantage of good hermeticity, tiny parasitic capacitance, batch mode fabrication, and compatibility with multiple bonding techniques, the glass-silicon composite substrate manufactured by the glass reflow process has great potential to achieve 3D wafer-level packaging for high performance. However, the difference in etching characteristics between silicon and glass inevitably leads to the formation of the undesired micro-protrusions near the silicon-glass interface when preparing a shallow cavity etched around a few microns in the composite substrate. The micro-protrusions have a comparable height with the depth of the cavity, which increases the risks of damages to sensitive structures and may even trigger electrical breakdown, resulting in thorough device failure. In this paper, we studied the characteristics of the chemical composition and etching mechanisms at the interface carefully and proposed the corresponding optimized solutions that utilized plasma accumulation at the interface to accelerate etching and bridge the gap in etching rates between different chemical compositions. Finally, a smooth transition of 131.1 nm was achieved at the interface, obtaining an ideal etching cavity surface and experimentally demonstrating the feasibility of our proposal. The micromachining solution is beneficial for improving the yield and structural design flexibility of higher performance micro-electromechanical systems (MEMS) devices.

    View details for DOI 10.3390/mi10060420

    View details for PubMedID 31234592

  • Two-terminal spin-orbit torque magnetoresistive random access memory NATURE ELECTRONICS Sato, N., Xue, F., White, R. M., Bi, C., Wang, S. X. 2018; 1 (9): 508–11

    View details for DOI 10.1038/s41928-018-0131-z

    View details for Web of Science ID 000454039700014

  • Linear Control of Magneto-Electric Effect With Small Electric Fields IEEE MAGNETICS LETTERS Xue, F., Hu, J., Wang, S. X., He, J. 2016; 7

    View details for DOI 10.1109/LMAG.2016.2551694

    View details for Web of Science ID 000399976300001

  • Electric Field Sensor Based on Piezoelectric Bending Effect for Wide Range Measurement IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS Xue, F., Hu, J., Wang, S. X., He, J. 2015; 62 (9): 5730-5737

    View details for DOI 10.1109/TIE.2015.2414397

    View details for Web of Science ID 000359560800038