Double CoFeB reference layers for optimized PMA and BEOL compatibility of SOT-MRAM

Yuxuan Yao; Siyuan Cheng; Shiyang Lu; Danrong Xiong; Jianing Liang; Wenwen Wang; Xiantao Shang; Kaihua Cao; Daoqian Zhu; Hongxi Liu; Weisheng Zhao

doi:10.1088/1674-4926/26010048

J. Semicond. > Just Accepted

ARTICLES

Double CoFeB reference layers for optimized PMA and BEOL compatibility of SOT-MRAM

Yuxuan Yao^1,, Siyuan Cheng¹, Shiyang Lu^{1, 4}, Danrong Xiong², Jianing Liang², Wenwen Wang², Xiantao Shang², Kaihua Cao², Daoqian Zhu¹, Hongxi Liu^2, and Weisheng Zhao^{1, 3, 4,}

+ Author Affiliations

1. Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, China
2. Truth Memory Corporation, Beijing 100088, China
3. National Key Laboratory of Spintronics, Hangzhou International Innovation Institute, Beihang University, Yuhang District, Hangzhou 311115, China
4. Integrated Circuit and Intelligent Instruments Innovation Center, Qingdao Research Institute of Beihang University, Qingdao 266100, China

Author Bio:

Yuxuan Yao received the Ph.D. degree in microelectronics from Beihang University, China, in 2025. He is currently a Post-Doctoral researcher with School of Integrated Circuit Science and Engineering, Beihang University. His research interests include magnetic multilayers, magnetic tunnel junctions and orbitronics.

Hongxi Liu received the Ph.D. degree in Electronics for Informatics from Hokkaido University, Japan, in 2012. He has worked inacademia and industry for over 10 years, mainly focusing on the research and development of MRAM technology. He is currently in charge of the activities of SOT-MRAM R & D in Truth Memory tech. Corporation, Beijing, China.

Weisheng Zhao received the Ph.D. degree in physics from the University of Paris-Sud, Paris, France, in 2007. In 2009, he joined French National Research Center (CNRS), Paris, as a Tenured Research Scientist. Since 2014, he has been a Distinguished Professor with Beihang University, Beijing, China, where he is currently a Professor with the School of Integrated Circuit Science and Engineering. He has published more than 200 scientific papers in leading journals and conferences. such as Nature Electronics, Nature Communications, Advanced Materials. His current research interests include the MRAM and the hybrid integration of nanodevices with CMOS circuits.

Corresponding author: Yuxuan Yao, yaoyuxuan@buaa.edu.cn; Hongxi Liu, hongxi_liu@tmc-bj.cn; Weisheng Zhao, weisheng.zhao@buaa.edu.cn

DOI: 10.1088/1674-4926/26010048CSTR: 32376.14.1674-4926.26010048

Abstract: Spin-orbit torque (SOT) is widely considered as the key technology for next-generation magnetic random-access memory (MRAM), leveraging ultrafast operating speed and unlimited endurance. However, integrating perpendicular magnetic anisotropy (PMA) SOT-MRAM stacks with the back-end-of-line (BEOL) thermal budget remains a critical challenge, as PMA degradation and Pt-Fe interdiffusion typically occur under 400 °C annealing. Here we propose a double CoFeB reference layer (DCFB) structure to address these issues. The additional CoFeB reference layer and two extra CoFeB/W interfaces significantly enhance the PMA of the reference layers, while improving the crystallization of the overlying Pt/Co multilayers. Furthermore, the DCFB stack effectively acts as a diffusion barrier against Pt-Fe interdiffusion. Consequently, a fabricated magnetic tunnel junction (MTJ) incorporating the DCFB stack achieves a high tunneling magnetoresistance (TMR) of 137% even after annealing at 400 °C. Our work provides a robust, simplified approach for the design of SOT-MRAM stacks with BEOL thermal budget tolerance.

Key words: magnetic random-access memory, magnetic tunnel junction, perpendicular magnetic anisotropy, tunneling magnetoresistance, spin-orbit torque

References

[1]	Liu L Q, Pai C-F, Li Y, et al. Spin-torque switching with the giant spin Hall effect of tantalum. Science, 2012, 336(6081): 555 doi: 10.1126/science.1218197
[2]	Miron I M, Garello K, Gaudin G, et al. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature, 2011, 476(7359): 189 doi: 10.1038/nature10309
[3]	Fert A, Ramesh R, Garcia V, et al. Electrical control of magnetism by electric field and current-induced torques. Rev Mod Phys, 2024, 96: 015005 doi: 10.1103/RevModPhys.96.015005
[4]	Guo Z X, Yin J L, Bai Y, et al. Spintronics for energy- efficient computing: An overview and outlook. Proc IEEE, 2021, 109(8): 1398 doi: 10.1109/JPROC.2021.3084997
[5]	Zhu D Q, Guo Z X, Du A, et al. First demonstration of three terminal MRAM devices with immunity to magnetic fields and 10 ns field free switching by electrical manipulation of exchange bias. 2021 IEEE International Electron Devices Meeting (IEDM), 2022: 17.5.1
[6]	Jiang C P, Lu S Y, Zhang Z K, et al. Demonstration of 128 kb SOT-MRAM chip with 5 ns write and 15 ns read speed, high endurance over 1010 and low ECC-on bit error rate. 2024 IEEE International Electron Devices Meeting (IEDM), 2025: 1
[7]	Xiong D R, Fan X F, Jiang C P, et al. First CMOS-integrated 128 kb antiferromagnet-based MRAM with immunity to 3 T magnetic fields. 2024 IEEE International Electron Devices Meeting (IEDM), 2025: 1
[8]	Nguyen V D, Rao S, Wostyn K, et al. Recent progress in spin-orbit torque magnetic random-access memory. npj Spintron, 2024, 2: 48 doi: 10.1038/s44306-024-00044-1
[9]	Xiang Y, García-Redondo F, Sharma A, et al. SOT-MRAM bitcell scaling with BEOL read selectors: A DTCO study. IEEE Trans Electron Devices, 2025, 72(12): 6665 doi: 10.1109/TED.2025.3617043
[10]	Worledge D C, Hu G H. Spin-transfer torque magnetoresistive random access memory technology status and future directions. Nat Rev Electr Eng, 2024, 1(11): 730 doi: 10.1038/s44287-024-00111-z
[11]	Edelstein D, Rizzolo M, Sil D, et al. A 14 nm embedded STT-MRAM CMOS technology. 2020 IEEE International Electron Devices Meeting (IEDM), 2021: 11.5.1
[12]	Hatsuda K, Hoya K, Takizawa R, et al. 30.6 a 64Gb DDR4 STT-MRAM using a time-controlled discharge-reading scheme for a. 001681 μm² 1T-1MTJ cross-point cell. 2025 IEEE International Solid-State Circuits Conference (ISSCC). San Francisco, CA, USA. IEEE, 2025: 1
[13]	Hu G, Safranski C, Sun J Z, et al. Double spin-torque magnetic tunnel junction devices for last-level cache applications. 2022 International Electron Devices Meeting (IEDM), 2023: 10.2.1
[14]	Couet S, Rao S, van Beek S, et al. BEOL compatible high retention perpendicular SOT-MRAM device for SRAM replacement and machine learning. 2021 IEEE Symposium on VLSI Technology, 2021: 1
[15]	Garello K, Yasin F, Couet S, et al. SOT-MRAM 300MM integration for low power and ultrafast embedded memories. 2018 IEEE Symposium on VLSI Circuits, 2018: 81
[16]	Ikeda S, Miura K, Yamamoto H, et al. A perpendicular-anisotropy CoFeB–MgO magnetic tunnel junction. Nat Mater, 2010, 9(9): 721 doi: 10.1038/nmat2804
[17]	Razavi A, Wu H, Shao Q M, et al. Deterministic spin–orbit torque switching by a light-metal insertion. Nano Lett, 2020, 20(5): 3703 doi: 10.1021/acs.nanolett.0c00647
[18]	Yu G Q, Upadhyaya P, Fan Y B, et al. Switching of perpendicular magnetization by spin–orbit torques in the absence of external magnetic fields. Nat Nanotechnol, 2014, 9(7): 548 doi: 10.1038/nnano.2014.94
[19]	You L, Lee O, Bhowmik D, et al. Switching of perpendicularly polarized nanomagnets with spin orbit torque without an external magnetic field by engineering a tilted anisotropy. Proc Natl Acad Sci U S A, 2015, 112(33): 10310 doi: 10.1073/pnas.1507474112
[20]	Wang M X, Cai W L, Zhu D Q, et al. Field-free switching of a perpendicular magnetic tunnel junction through the interplay of spin–orbit and spin-transfer torques. Nat Electron, 2018, 1(11): 582 doi: 10.1038/s41928-018-0160-7
[21]	Wang X R, Wu H, Qiu R Z, et al. Room temperature field-free switching of CoFeB/MgO heterostructure based on large-scale few-layer WTe2. Cell Rep Phys Sci, 2023, 4(7): 101468 doi: 10.1016/j.xcrp.2023.101468
[22]	Zhang H C, Ma X Y, Jiang C P, et al. Integration of high-performance spin-orbit torque MRAM devices by 200-mm-wafer manufacturing platform. J Semicond, 2022, 43(10): 102501 doi: 10.1088/1674-4926/43/10/102501
[23]	Vudya Sethu K K, Ghosh S, Couet S, et al. Optimization of tungsten β-phase window for spin-orbit-torque magnetic random-access memory. Phys Rev Appl, 2021, 16(6): 064009 doi: 10.1103/PhysRevApplied.16.064009
[24]	Yao Y X, Zhu D Q, Xia Q T, et al. Orbitronics for energy-efficient magnetization switching. Sci China Inf Sci, 2024, 68(1): 119402 doi: 10.1007/s11432-024-4186-6
[25]	Li K S, Shieh J M, Chen Y-J, et al. First BEOL-compatible, 10 ns-fast, and durable 55 nm top-pSOT-MRAM with high TMR (>130%). 2023 International Electron Devices Meeting (IEDM), 2023: 1
[26]	Swerts J, Liu E, Couet S, et al. Solving the BEOL compatibility challenge of top-pinned magnetic tunnel junction stacks. 2017 IEEE International Electron Devices Meeting (IEDM), 2018: 38.6.1
[27]	Honjo H, Naganuma H, Nguyen T V A, et al. Effect of surface modification treatment on top-pinned MTJ with perpendicular easy axis. AIP Adv, 2021, 11(2): 025211 doi: 10.1063/9.0000047
[28]	Tsou Y J, Chen W J, Shih H C, et al. Thermally robust perpendicular SOT-MTJ memory cells with STT-assisted field-free switching. IEEE Trans Electron Devices, 2021, 68(12): 6623 doi: 10.1109/TED.2021.3110833
[29]	Tsou Y J, Li K S, Shieh J M, et al. First demonstration of interface-enhanced SAF enabling 400°C-robust 42 nm p-SOT-MTJ cells with STT-assisted field-free switching and composite channels. 2021 Symposium on VLSI Technology, 2021: 1
[30]	Yang T Z, Gao J, Cui Y, et al. Thermal stability of SOT-MTJ thin films tuning by multiple interlayer couplings. J Magn Magn Mater, 2021, 529: 167823. doi: 10.1016/j.jmmm.2021.167823
[31]	Honjo H, Tanigawa T, Koike H, et al. 10 nm perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction with over 400°C high thermal tolerance by boron diffusion control. 2015 Symposium on VLSI Technology (VLSI Technology), 2015: T160
[32]	Yakushiji K, Sugihara A, Fukushima A, et al. Very strong antiferromagnetic interlayer exchange coupling with iridium spacer layer for perpendicular magnetic tunnel junctions. Appl Phys Lett, 2017, 110(9): 092406 doi: 10.1063/1.4977565
[33]	Peng S Z, Wang M X, Yang H X, et al. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures. Sci Rep, 2015, 5: 18173 doi: 10.1038/srep18173
[34]	An G G, Lee J B, Yang S M, et al. Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers. Acta Mater, 2015, 87: 259 doi: 10.1016/j.actamat.2015.01.022
[35]	Polishchuk D M, Tykhonenko-Polishchuk Y O, Holmgren E, et al. Thermally induced antiferromagnetic exchange in magnetic multilayers. Phys Rev B, 2017, 96(10): 104427 doi: 10.1103/PhysRevB.96.104427
[36]	Jiang C P, Li J H, Zhang H C, et al. Demonstration of a manufacturable SOT-MRAM multiplexer array towards industrial applications. J Semicond, 2023, 44(12): 122501 doi: 10.1088/1674-4926/44/12/122501
[37]	Huang Y L, Song M Y, Lee C M, et al. A 64-kilobit spin–orbit torque magnetic random-access memory based on back-end-of-line-compatible β-tungsten. Nat Electron, 2025, 8(9): 794 doi: 10.1038/s41928-025-01434-x

Fig. 1. (Color online) Schematic and properties of single CoFeB (SCFB) and double CoFeB (DCFB) reference layer reference layers. (a) Schematic of the top-pinned MTJ with PMA for SOT-MRAM. (b) Schematic of SCFB reference layers. (c) Schematic of DCFB reference layers. (d) PMOKE signal of SCFB reference layers, varying t_CoFeB. (e) PMOKE signal of DCFB reference layers, varying t_CoFeB,upper of the upper CoFeB layer.

DownLoad: Full-Size Img PowerPoint

Fig. 2. (Color online) Magnetic and TMR properties of SCFB and DCFB-based stacks. (a) PMOKE signal of SCFB-based stacks. (b) PMOKE signal of DCFB-based stacks, with the RKKY exchange field (B_ex) labeled. (c) CIPT measurements of SCFB and DCFB-based stacks. For DCFB-based stacks, t_CoFeB,lower layer is varied. (d) TMR-H hysteresis loop of the fabricated MTJ device with DCFB-based stack. The inset shows the microscope image of the MTJ device. The diameter of the MTJ device is 10 μm.

DownLoad: Full-Size Img PowerPoint

Fig. 3. (Color online) Properties of DCFB-based stacks with low RA. (a) CIPT measurements of SCFB and DCFB-based stacks with RA of 150 Ω·μm². (b) PMOKE signal of DCFB-based stack with RA of 50 Ω·μm², when t_CoFeB,lower of the lower CoFeB layer is 1.1 nm, showing the B_ex of ~120 mT.

DownLoad: Full-Size Img PowerPoint

Fig. 4. (Color online) Analyzing crystallization and interdiffusion of SCFB and DCFB-based stacks under different annealing temperatures. (a-c) TEM images of (a) SCFB and (b), (c) DCFB-based stacks after annealing at (a), (b) 350 °C and (c) 400 °C. (d) EDS spectra of SCFB and DCFB-based stacks under different annealing temperatures.

DownLoad: Full-Size Img PowerPoint

Fig. 5. (Color online) Properties of DCFB-based stacks after annealing at 400 °C. (a) PMOKE signal of DCFB-based stacks with different t_CoFeB,lower of the lower CoFeB layer, indicating the reduced B_ex (~50 mT) after 400 °C annealing. (b) TMR-H hysteresis loop of the fabricated MTJ device with DCFB-based stack after annealing at 400 °C, and a TMR value of 137% is achieved.

DownLoad: Full-Size Img PowerPoint

Fig. 6. (Color online) R-H loop and SOT switching characteristics of the DCFB-based MTJ device. (a) R-H hysteresis loop, indicating stable PMA and robust TMR at the device level. (b) Dependence of the critical switching current density (J_c) on pulse width.

DownLoad: Full-Size Img PowerPoint

[1]	Liu L Q, Pai C-F, Li Y, et al. Spin-torque switching with the giant spin Hall effect of tantalum. Science, 2012, 336(6081): 555 doi: 10.1126/science.1218197
[2]	Miron I M, Garello K, Gaudin G, et al. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature, 2011, 476(7359): 189 doi: 10.1038/nature10309
[3]	Fert A, Ramesh R, Garcia V, et al. Electrical control of magnetism by electric field and current-induced torques. Rev Mod Phys, 2024, 96: 015005 doi: 10.1103/RevModPhys.96.015005
[4]	Guo Z X, Yin J L, Bai Y, et al. Spintronics for energy- efficient computing: An overview and outlook. Proc IEEE, 2021, 109(8): 1398 doi: 10.1109/JPROC.2021.3084997
[5]	Zhu D Q, Guo Z X, Du A, et al. First demonstration of three terminal MRAM devices with immunity to magnetic fields and 10 ns field free switching by electrical manipulation of exchange bias. 2021 IEEE International Electron Devices Meeting (IEDM), 2022: 17.5.1
[6]	Jiang C P, Lu S Y, Zhang Z K, et al. Demonstration of 128 kb SOT-MRAM chip with 5 ns write and 15 ns read speed, high endurance over 1010 and low ECC-on bit error rate. 2024 IEEE International Electron Devices Meeting (IEDM), 2025: 1
[7]	Xiong D R, Fan X F, Jiang C P, et al. First CMOS-integrated 128 kb antiferromagnet-based MRAM with immunity to 3 T magnetic fields. 2024 IEEE International Electron Devices Meeting (IEDM), 2025: 1
[8]	Nguyen V D, Rao S, Wostyn K, et al. Recent progress in spin-orbit torque magnetic random-access memory. npj Spintron, 2024, 2: 48 doi: 10.1038/s44306-024-00044-1
[9]	Xiang Y, García-Redondo F, Sharma A, et al. SOT-MRAM bitcell scaling with BEOL read selectors: A DTCO study. IEEE Trans Electron Devices, 2025, 72(12): 6665 doi: 10.1109/TED.2025.3617043
[10]	Worledge D C, Hu G H. Spin-transfer torque magnetoresistive random access memory technology status and future directions. Nat Rev Electr Eng, 2024, 1(11): 730 doi: 10.1038/s44287-024-00111-z
[11]	Edelstein D, Rizzolo M, Sil D, et al. A 14 nm embedded STT-MRAM CMOS technology. 2020 IEEE International Electron Devices Meeting (IEDM), 2021: 11.5.1
[12]	Hatsuda K, Hoya K, Takizawa R, et al. 30.6 a 64Gb DDR4 STT-MRAM using a time-controlled discharge-reading scheme for a. 001681 μm² 1T-1MTJ cross-point cell. 2025 IEEE International Solid-State Circuits Conference (ISSCC). San Francisco, CA, USA. IEEE, 2025: 1
[13]	Hu G, Safranski C, Sun J Z, et al. Double spin-torque magnetic tunnel junction devices for last-level cache applications. 2022 International Electron Devices Meeting (IEDM), 2023: 10.2.1
[14]	Couet S, Rao S, van Beek S, et al. BEOL compatible high retention perpendicular SOT-MRAM device for SRAM replacement and machine learning. 2021 IEEE Symposium on VLSI Technology, 2021: 1
[15]	Garello K, Yasin F, Couet S, et al. SOT-MRAM 300MM integration for low power and ultrafast embedded memories. 2018 IEEE Symposium on VLSI Circuits, 2018: 81
[16]	Ikeda S, Miura K, Yamamoto H, et al. A perpendicular-anisotropy CoFeB–MgO magnetic tunnel junction. Nat Mater, 2010, 9(9): 721 doi: 10.1038/nmat2804
[17]	Razavi A, Wu H, Shao Q M, et al. Deterministic spin–orbit torque switching by a light-metal insertion. Nano Lett, 2020, 20(5): 3703 doi: 10.1021/acs.nanolett.0c00647
[18]	Yu G Q, Upadhyaya P, Fan Y B, et al. Switching of perpendicular magnetization by spin–orbit torques in the absence of external magnetic fields. Nat Nanotechnol, 2014, 9(7): 548 doi: 10.1038/nnano.2014.94
[19]	You L, Lee O, Bhowmik D, et al. Switching of perpendicularly polarized nanomagnets with spin orbit torque without an external magnetic field by engineering a tilted anisotropy. Proc Natl Acad Sci U S A, 2015, 112(33): 10310 doi: 10.1073/pnas.1507474112
[20]	Wang M X, Cai W L, Zhu D Q, et al. Field-free switching of a perpendicular magnetic tunnel junction through the interplay of spin–orbit and spin-transfer torques. Nat Electron, 2018, 1(11): 582 doi: 10.1038/s41928-018-0160-7
[21]	Wang X R, Wu H, Qiu R Z, et al. Room temperature field-free switching of CoFeB/MgO heterostructure based on large-scale few-layer WTe2. Cell Rep Phys Sci, 2023, 4(7): 101468 doi: 10.1016/j.xcrp.2023.101468
[22]	Zhang H C, Ma X Y, Jiang C P, et al. Integration of high-performance spin-orbit torque MRAM devices by 200-mm-wafer manufacturing platform. J Semicond, 2022, 43(10): 102501 doi: 10.1088/1674-4926/43/10/102501
[23]	Vudya Sethu K K, Ghosh S, Couet S, et al. Optimization of tungsten β-phase window for spin-orbit-torque magnetic random-access memory. Phys Rev Appl, 2021, 16(6): 064009 doi: 10.1103/PhysRevApplied.16.064009
[24]	Yao Y X, Zhu D Q, Xia Q T, et al. Orbitronics for energy-efficient magnetization switching. Sci China Inf Sci, 2024, 68(1): 119402 doi: 10.1007/s11432-024-4186-6
[25]	Li K S, Shieh J M, Chen Y-J, et al. First BEOL-compatible, 10 ns-fast, and durable 55 nm top-pSOT-MRAM with high TMR (>130%). 2023 International Electron Devices Meeting (IEDM), 2023: 1
[26]	Swerts J, Liu E, Couet S, et al. Solving the BEOL compatibility challenge of top-pinned magnetic tunnel junction stacks. 2017 IEEE International Electron Devices Meeting (IEDM), 2018: 38.6.1
[27]	Honjo H, Naganuma H, Nguyen T V A, et al. Effect of surface modification treatment on top-pinned MTJ with perpendicular easy axis. AIP Adv, 2021, 11(2): 025211 doi: 10.1063/9.0000047
[28]	Tsou Y J, Chen W J, Shih H C, et al. Thermally robust perpendicular SOT-MTJ memory cells with STT-assisted field-free switching. IEEE Trans Electron Devices, 2021, 68(12): 6623 doi: 10.1109/TED.2021.3110833
[29]	Tsou Y J, Li K S, Shieh J M, et al. First demonstration of interface-enhanced SAF enabling 400°C-robust 42 nm p-SOT-MTJ cells with STT-assisted field-free switching and composite channels. 2021 Symposium on VLSI Technology, 2021: 1
[30]	Yang T Z, Gao J, Cui Y, et al. Thermal stability of SOT-MTJ thin films tuning by multiple interlayer couplings. J Magn Magn Mater, 2021, 529: 167823. doi: 10.1016/j.jmmm.2021.167823
[31]	Honjo H, Tanigawa T, Koike H, et al. 10 nm perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction with over 400°C high thermal tolerance by boron diffusion control. 2015 Symposium on VLSI Technology (VLSI Technology), 2015: T160
[32]	Yakushiji K, Sugihara A, Fukushima A, et al. Very strong antiferromagnetic interlayer exchange coupling with iridium spacer layer for perpendicular magnetic tunnel junctions. Appl Phys Lett, 2017, 110(9): 092406 doi: 10.1063/1.4977565
[33]	Peng S Z, Wang M X, Yang H X, et al. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures. Sci Rep, 2015, 5: 18173 doi: 10.1038/srep18173
[34]	An G G, Lee J B, Yang S M, et al. Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers. Acta Mater, 2015, 87: 259 doi: 10.1016/j.actamat.2015.01.022
[35]	Polishchuk D M, Tykhonenko-Polishchuk Y O, Holmgren E, et al. Thermally induced antiferromagnetic exchange in magnetic multilayers. Phys Rev B, 2017, 96(10): 104427 doi: 10.1103/PhysRevB.96.104427
[36]	Jiang C P, Li J H, Zhang H C, et al. Demonstration of a manufacturable SOT-MRAM multiplexer array towards industrial applications. J Semicond, 2023, 44(12): 122501 doi: 10.1088/1674-4926/44/12/122501
[37]	Huang Y L, Song M Y, Lee C M, et al. A 64-kilobit spin–orbit torque magnetic random-access memory based on back-end-of-line-compatible β-tungsten. Nat Electron, 2025, 8(9): 794 doi: 10.1038/s41928-025-01434-x

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Received: 30 January 2026 Revised: 27 March 2026 Online: Accepted Manuscript: 21 May 2026

Article Navigation > Journal of Semiconductors > 2026 > Accepted Manuscript

Yuxuan Yao, Siyuan Cheng, Shiyang Lu, Danrong Xiong, Jianing Liang, Wenwen Wang, Xiantao Shang, Kaihua Cao, Daoqian Zhu, Hongxi Liu, Weisheng Zhao. Double CoFeB reference layers for optimized PMA and BEOL compatibility of SOT-MRAM[J]. Journal of Semiconductors, 2026, In Press. doi: 10.1088/1674-4926/26010048 ****Y X Yao, S Y Cheng, S Y Lu, D R Xiong, J N Liang, W W Wang, X T Shang, K H Cao, D Q Zhu, H X Liu, and W S Zhao, Double CoFeB reference layers for optimized PMA and BEOL compatibility of SOT-MRAM[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/26010048

Citation:

Y X Yao, S Y Cheng, S Y Lu, D R Xiong, J N Liang, W W Wang, X T Shang, K H Cao, D Q Zhu, H X Liu, and W S Zhao, Double CoFeB reference layers for optimized PMA and BEOL compatibility of SOT-MRAM[J]. J. Semicond., 2026, accepted doi: 10.1088/1674-4926/26010048

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Double CoFeB reference layers for optimized PMA and BEOL compatibility of SOT-MRAM

DOI: 10.1088/1674-4926/26010048

CSTR: 32376.14.1674-4926.26010048

1.
Fert Beijing Institute, School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, China
2.
Truth Memory Corporation, Beijing 100088, China
3.
National Key Laboratory of Spintronics, Hangzhou International Innovation Institute, Beihang University, Yuhang District, Hangzhou 311115, China
4.
Integrated Circuit and Intelligent Instruments Innovation Center, Qingdao Research Institute of Beihang University, Qingdao 266100, China

More Information

Yuxuan Yao received the Ph.D. degree in microelectronics from Beihang University, China, in 2025. He is currently a Post-Doctoral researcher with School of Integrated Circuit Science and Engineering, Beihang University. His research interests include magnetic multilayers, magnetic tunnel junctions and orbitronics
Hongxi Liu received the Ph.D. degree in Electronics for Informatics from Hokkaido University, Japan, in 2012. He has worked inacademia and industry for over 10 years, mainly focusing on the research and development of MRAM technology. He is currently in charge of the activities of SOT-MRAM R & D in Truth Memory tech. Corporation, Beijing, China
Weisheng Zhao received the Ph.D. degree in physics from the University of Paris-Sud, Paris, France, in 2007. In 2009, he joined French National Research Center (CNRS), Paris, as a Tenured Research Scientist. Since 2014, he has been a Distinguished Professor with Beihang University, Beijing, China, where he is currently a Professor with the School of Integrated Circuit Science and Engineering. He has published more than 200 scientific papers in leading journals and conferences. such as Nature Electronics, Nature Communications, Advanced Materials. His current research interests include the MRAM and the hybrid integration of nanodevices with CMOS circuits
Corresponding author: yaoyuxuan@buaa.edu.cn; hongxi_liu@tmc-bj.cn; weisheng.zhao@buaa.edu.cn
Received Date: 2026-01-30
Revised Date: 2026-03-27

Available Online: 2026-05-21

Abstract

Abstract

Spin-orbit torque (SOT) is widely considered as the key technology for next-generation magnetic random-access memory (MRAM), leveraging ultrafast operating speed and unlimited endurance. However, integrating perpendicular magnetic anisotropy (PMA) SOT-MRAM stacks with the back-end-of-line (BEOL) thermal budget remains a critical challenge, as PMA degradation and Pt-Fe interdiffusion typically occur under 400 °C annealing. Here we propose a double CoFeB reference layer (DCFB) structure to address these issues. The additional CoFeB reference layer and two extra CoFeB/W interfaces significantly enhance the PMA of the reference layers, while improving the crystallization of the overlying Pt/Co multilayers. Furthermore, the DCFB stack effectively acts as a diffusion barrier against Pt-Fe interdiffusion. Consequently, a fabricated magnetic tunnel junction (MTJ) incorporating the DCFB stack achieves a high tunneling magnetoresistance (TMR) of 137% even after annealing at 400 °C. Our work provides a robust, simplified approach for the design of SOT-MRAM stacks with BEOL thermal budget tolerance.
- magnetic random-access memory,
- magnetic tunnel junction,
- perpendicular magnetic anisotropy,
- tunneling magnetoresistance,
- spin-orbit torque

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