Chi-Feng Pai
Chi-Feng Pai
Research Scientist / Associate Professor
TSMC / National Taiwan University
Research Field: Energy efficient spin transfer torque-magnetoresistive random access memory
Professor Chi-Feng Pai is an IEEE Senior Member and an active researcher/educator in the field of spintronics and magnetism. Prof. Pai received his Ph.D. in Applied & Engineering Physics from Cornell University in 2014. After graduating from Cornell, he worked at Massachusetts Institute of Technology as postdoctoral research associate in Department of Materials Science and Engineering. He is currently a faculty member in the Department of Materials Science and Engineering at National Taiwan University (2016-present), the elected Chair of IEEE Magnetics Society Taiwan Chapter (2022-present), and Research Scientist in the Corporate Research of Taiwan Semiconductor Manufacturing Company (2022-present). He is also the recipient of Asian Union of Magnetics Societies (AUMS) Young Researcher Award in 2016 and the co-author of “Magnetic Memory Technology: Spin-Transfer Torque MRAM and Beyond” published by Wiley-IEEE Press (1st Edition, 2021).
Building Efficient Spin-Orbit MRAMs with Orbital Hall Materials
Chi-Feng Pai a,b, Chen-Yu Hu a, Yu-Fang Chiu a, Chia-Chin Tsai a, Chao-Chung Huang a, Kuan-Hao Chen a,
Cheng-Wei Peng a, Chien-Min Lee b, Ming-Yuan Song b, Yen-Lin Huang b, Shy-Jay Lin b, and Xinyu Bao b
a Department of Materials Science and Engineering, National Taiwan University
b Corporate Research, Taiwan Semiconductor Manufacturing Company
5d transition metals (TMs) such as W and Pt are the classical spin Hall materials for efficient generation of spin-orbit torques (SOTs) in TM/ferromagnetic layer (FM) heterostructures. However, for a long while with tremendous engineering endeavours, the damping-like SOT efficiencies (ξDL) of W, Pt and their alloys are still limited to ξDL < 0.5. In this presentation, I will show that with proper alloying elements, particularly strong orbital Hall effect (OHE) 3d transition metals V and Cr, the strength of the high spin-orbital Hall conductivity of Pt (σSH ∼ 6.45×105(ℏ/2e)Ω−1⋅m−1) can be developed. Especially for the Cr-doped case, an extremely high ξDL ∼ 0.9 in a Pt0.69Cr0.31/Co device can be achieved with a moderate Pt0.69Cr0.31 resistivity of ∼133 μΩ⋅cm. A low critical SOT-driven switching current density of Jc ∼ 3.16×106A⋅cm−2 is also demonstrated. The damping constant (α) of Pt0.69Cr0.31/FM structure is also found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall high σSH, giant ξDL, moderate resistivity, and reduced α of such Pt-Cr/FM heterostructure makes it promising for versatile extremely low power consumption SOT memory applications.