Abstract
Magnetization switching driven by spin–orbit torque could be used to create an energy-efficient form of magnetic random-access memory. Tungsten is a promising heavy metal for such applications and can generate large spin–orbit torques when stabilized in its β-phase. However, the α-phase, which has a lower spin-Hall angle, is more thermodynamically stable. It is thus challenging to integrate metastable β-tungsten into complementary metal–oxide–semiconductor processes while maintaining phase stability under the back-end-of-line thermal constraints (400 °C for extended durations). Here we show that the insertion of thin layers of cobalt can be used to stabilize β-tungsten under back-end-of-line-compatible thermal conditions. Our composite β-tungsten layers can maintain their phase up to 400 °C for 10 h and can withstand 700 °C for 30 min. The film stacks exhibit a spin-Hall conductivity of around 4,500 Ω−1 cm−1, which we measure by means of spin-torque ferromagnetic resonance and harmonic Hall resistance measurements. Using the tungsten composite film stacks, we fabricate a 64-kb spin–orbit torque magnetic random-access memory that offers a spin–orbit torque switching of 1 ns, data retention of more than 10 years and a tunnelling magnetoresistance of 146%.
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Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request. Access to the data may be subject to a data use agreement in compliance with applicable legal and ethical requirements.
Code availability
Codes to perform signal fitting and micromagnetic simulation are available from the corresponding authors upon reasonable request.
References
Makarov, A., Sverdlov, V. & Selberherr, S. Emerging memory technologies: trends, challenges, and modeling methods. Microelectron. Reliab. 52, 628–634 (2012).
Yu, S. & Chen, P.-Y. Emerging memory technologies: recent trends and prospects. IEEE Solid-State Circuits Mag. 8, 43–56 (2016).
Wong, H.-S. P. et al. Phase change memory. Proc. IEEE 98, 2201–2227 (2010).
Qureshi, M. K., Srinivasan, V. & Rivers, J. A. Scalable high performance main memory system using phase-change memory technology. In Proc. of the 36th Annual International Symposium on Computer Architecture 24–33 (ACM, 2009).
Mikolajick, T.,Slesazeck, S., Park, M. H. & Schroeder, U. Ferroelectric hafnium oxide for ferroelectric random-access memories and ferroelectric field-effect transistors. MRS Bull. 43, 340–346 (2018).
Sheikholeslami, A. & Gulak, P. G. A survey of circuit innovations in ferroelectric random-access memories. Proc. IEEE 88, 667–689 (2000).
Wong, H.-S. P. & Salahuddin, S. Memory leads the way to better computing. Nat. Nanotechnol. 10, 191–194 (2015).
Sebastian, A., Le Gallo, M., Khaddam-Aljameh, R. & Eleftheriou, E. Memory devices and applications for in-memory computing. Nat. Nanotechnol. 15, 529–544 (2020).
Roy, K., Jaiswal, A. & Panda, P. Towards spike-based machine intelligence with neuromorphic computing. Nature 575, 607–617 (2019).
Ielmini, D. & Wong, H.-S. P. In-memory computing with resistive switching devices. Nat. Electron. 1, 333–343 (2018).
Zhang, W., Mazzarello, R., Wuttig, M. & Ma, E. Designing crystallization in phase-change materials for universal memory and neuro-inspired computing. Nat. Rev. Mater. 4, 150–168 (2019).
Guo, Z. et al. Spintronics for energy-efficient computing: an overview and outlook. Proc. IEEE 109, 1398–1417 (2021).
Sun, Z. et al. A full spectrum of computing-in-memory technologies. Nat. Electron. 6, 823–835 (2023).
Garello, K. et al. Manufacturable 300mm platform solution for field-free switching SOT-MRAM. In 2019 Symposium on VLSI Circuits T194–T195 (IEEE, 2019).
Couet, S. et al. BEOL compatible high retention perpendicular SOT-MRAM device for SRAM replacement and machine learning. In 2021 Symposium on VLSI Technology 1–2 (IEEE, 2021).
Song, M. et al. High speed (1ns) and low voltage (1.5 V) demonstration of 8Kb SOT-MRAM array. In 2022 IEEE Symposium on VLSI Technology and Circuits (VLSI Technology and Circuits) 377–378 (IEEE, 2022).
Grimaldi, E. et al. Single-shot dynamics of spin–orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions. Nat. Nanotechnol. 15, 111–117 (2020).
Gupta, M. et al. High-density SOT-MRAM technology and design specifications for the embedded domain at 5nm node. In 2020 IEEE International Electron Devices Meeting (IEDM) 24.25. 21–24.25. 24 (IEEE, 2020).
Fukami, S., Anekawa, T., Ohkawara, A., Zhang, C. & Ohno, H. A sub-ns three-terminal spin-orbit torque induced switching device. In 2016 IEEE Symposium on VLSI Technology 1–2 (IEEE, 2016).
Garello, K. et al. Ultrafast magnetization switching by spin-orbit torques. Appl. Phys. Lett. 105, 212402 (2014).
Endoh, T., Honjo, H., Nishioka, K. & Ikeda, S. Recent progresses in STT-MRAM and SOT-MRAM for next generation MRAM. In 2020 IEEE Symposium on VLSI Technology 1–2 (IEEE, 2020).
Pai, C.-F. et al. Spin transfer torque devices utilizing the giant spin Hall effect of tungsten. Appl. Phys. Lett. 101, 122404 (2012).
Demasius, K.-U. et al. Enhanced spin–orbit torques by oxygen incorporation in tungsten films. Nat. Commun. 7, 10644 (2016).
Vudya Sethu, K. K. et al. Optimization of tungsten β-phase window for spin-orbit-torque magnetic random-access memory. Phys. Rev. Appl. 16, 064009 (2021).
Takeuchi, Y. et al. Spin-orbit torques in high-resistivity-W/CoFeB/MgO. Appl. Phys. Lett. 112, 192408 (2018).
Rahaman, S. Z. et al. Pulse-width and temperature effect on the switching behavior of an etch-stop-on-MgO-barrier spin-orbit torque MRAM cell. IEEE Electron Device Lett. 39, 1306–1309 (2018).
O’keefe, M. & Grant, J. Phase transformation of sputter deposited tungsten thin films with A‐15 structure. J. Appl. Phys. 79, 9134–9141 (1996).
Shen, Y. & Mai, Y. Influences of oxygen on the formation and stability of A15 β-W thin films. Mater. Sci. Eng. A 284, 176–183 (2000).
Chattaraj, A. et al. Unravelling oxygen driven α to β phase transformation in tungsten. Sci. Rep. 10, 14718 (2020).
Avci, C. O. et al. Interplay of spin-orbit torque and thermoelectric effects in ferromagnet/normal-metal bilayers. Phys. Rev. B 90, 224427 (2014).
Fukami, S., Anekawa, T., Zhang, C. & Ohno, H. A spin–orbit torque switching scheme with collinear magnetic easy axis and current configuration. Nat. Nanotechnol. 11, 621–625 (2016).
Feng, X. & Visscher, P. Sweep-rate-dependent coercivity simulation of FePt particle arrays. J. Appl. Phys. 95, 7043–7045 (2004).
Van Beek, S. et al. Thermal stability analysis and modelling of advanced perpendicular magnetic tunnel junctions. AIP Adv. 8, 055909 (2018).
Li, K.-S. et al. First BEOL-compatible, 10 ns-fast, and Durable 55 nm Top-pSOT-MRAM with High TMR (130%). In 2023 International Electron Devices Meeting (IEDM) 1–4 (IEEE, 2023).
Honjo, H. et al. First demonstration of field-free SOT-MRAM with 0.35 ns write speed and 70 thermal stability under 400° C thermal tolerance by canted SOT structure and its advanced patterning/SOT channel technology. In 2019 IEEE International Electron Devices Meeting (IEDM) 28.25. 21–28.25. 24 (IEEE, 2019).
Sato, N. et al. CMOS compatible process integration of SOT-MRAM with heavy-metal bi-layer bottom electrode and 10ns field-free SOT switching with STT assist. In 2020 IEEE Symposium on VLSI Technology 1–2 (IEEE, 2020).
Acknowledgements
We acknowledge S.-J. Lin, who initiated this project and engaged in constructive discussions at TSMC. We also acknowledge C. Diaz, J. Sun and C.-F. Pai for fruitful discussions. Y.-L.H. acknowledges financial support from the Center for Semiconductor Technology Research from the Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education in Taiwan, and from the National Science and Technology Council, Taiwan, under grant nos. NSTC 110-2634-F-009-027, NSTC 111-2112-M-A49-012-MY3 and NSTC 113-2112-M-A49-029-. Y.-L.H. also acknowledges the Center for Emergent Functional Matter Science of National Yang Ming Chiao Tung University from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education in Taiwan. S.X.W. and F.X. acknowledge that their work at Stanford was supported in part by Precourt Institute for Energy and the SystemX Alliance at Stanford, under NSF grant nos. 2314591 (ACED Fab) and 2328804 (FuSe), and by the SRC GRC Program. Part of this work was performed at the Stanford Nanofabrication Facility (SNF) and Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award ECCS-2026822. We acknowledge the assistance and beam time provided by the Taiwan Photon Source (TPS) 21A X-ray Nanodiffraction beamline at the National Synchrotron Radiation Research Center (NSRRC).
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Y.L.H. supervised the project and wrote the manuscript with input from all authors. Y.L.H. also designed the film stack, performed device fabrication, spin-Hall conductivity measurements and micromagnetic simulations. M.Y.S., C.M.L., G.L.C., S.Y.Y., Y.J.C., I.J.W., Y.C.H., Y.H.S. and J.H.W. were responsible for CMOS-based MTJ integration and device characterization. Y.W.C. and S.H.C. conducted the time- and temperature-dependent annealing experiments and GIXRD analysis. L.C.H. and F.X. contributed to partial device fabrication. C.Y.C. and H.J.L. performed X-ray nanodiffraction measurements. All authors actively discussed the results, contributed to data interpretation and provided feedback throughout the experimental and analytical process.
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Huang, YL., Song, M., Lee, CM. et al. A 64-kilobit spin–orbit torque magnetic random-access memory based on back-end-of-line-compatible β-tungsten. Nat Electron 8, 794–802 (2025). https://doi.org/10.1038/s41928-025-01434-x
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DOI: https://doi.org/10.1038/s41928-025-01434-x
