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A 64-kilobit spin–orbit torque magnetic random-access memory based on back-end-of-line-compatible β-tungsten, Nature Electronics volume 8, pages794–802 (2025)
Yen-Lin Huang*, Ming Yuan Song, Chien-Min Lee, Yu-Wei Chen, Ching-Yu Chiang, Shih-Hsiang Chou, Liang-Chao Hsu, Heng-Jui Liu, Guan-Long Chen, Shan-Yi Yang, Yao-Jen Chang, I-Jung Wang, Yu-Chen Hsin, Yi-Hui Su, Jeng-Hua Wei, Fen Xue, Shan X. Wang, and Xinyu Bao
2026/01/27
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%.