VP12-05 Simulation on Spin-Orbit Torque Switching with Stray Field Assistance
Creators: Jiaxuan Chen
Jiahao Liu
Zhaochun Liu
Weixiang Li
Jiaqi Lu
and Shouzhong Peng
Publisher: name: IEEE
Year: 2025

Spin-orbit torque (SOT) is a key writing technology for magnetic random access memory (MARM) due to fast speed, high reliability, and separation of read and write paths [1-2]. Voltage-controlled magnetic anisotropy (VCMA) lowers the energy barrier during magnetization switching by applying a voltage across the magnetic tunnel junction (MTJ) [3-5]. Integrating multiple MTJs on a shared write line can improve the storage density by using the VCMA effect as a selective mechanism and the SOT effect as a write mechanism. However, SOT-induced switching of deterministic perpendicular magnetization necessitates an in-plane external field, which limits its practical application. Utilizing the in-plane stray field from a magnet under the heavy metal layer is promising to realize field free SOT switching [6-8], while further study is needed in MTJ arrays. In this paper, we simulate spin-orbit torque switching with stray field assistance in a single MTJ and MTJ arrays. First, the stray field of an in-plane magnet with the size of 120nm×60nm×3nm is calculated to be 12.6mT (Fig. 1a). Through Mumax simulation, the single MTJ with the diameter of 60nm can be switched under the cirtical current of 12MA/cm2 with pulse width of 2ns (Fig. 1b). Moreover, in the array of two MTJs, both MTJs can be switched with a critical current of 13MA/cm2. However, the in-plane component of stray field in the MTJ2 is only 0.9 mT in the array of three MTJs (Fig. 2a). The perpendicular component of the magnetic moment oscillates slowly, which takes 10ns to switch with a critical current of 14MA/cm2 (Fig. 2b). Furthermore, in an array of four MTJs, the MTJ2 and MTJ3 cannot be switched due to the small stray field. In conclution, this work demonstrates feasibility of SOT switching with stray filed assistance in a single MTJ and the array with two MTJs, but the arrays with more than three MTJs cannot perform well.References: [1] M. Cubukcu, O. Boulle, M. Drouard, Appl. Phys. Lett., Vol. 104, no. 4, Art. no. 042406(2014) [2] M. Wang, W. Cai, D. Zhu, Nat. Electron., Vol. 1, no. 11, p.582-588(2018) [3] S. Peng, J. Lu, W. Li, in Proc. IEEE Int. Electron Devices Meeting, p.28.6.1-28.6.4(2019) [4] W. Li, Z. Liu, S. Peng, IEEE Electron Device Lett., Vol. 45, no. 5, p.921-924(2024) [5] J. Lu, W. Li, J. Liu, Appl. Phys. Lett., Vol. 122, no. 1, Art. no. 012402(2023) [6] K. Cai, G. Talmelli, K. Fan, in Proc. IEEE Int. Electron Devices Meeting, p.36.2.1-36.2.4(2022) [7] K. Garello, F. Yasin, H. Hody, in Proc. Symp. VLSI Circuits, p.T194-T195(2019) [8] M. Gupta, Y. Xiangt, F. García-Redondo, in Proc. IEEE Int. Electron Devices Meeting, p.1-4(2023).
Spin-orbit torque (SOT) is a key writing technology for magnetic random access memory (MARM) due to fast speed, high reliability, and separation of read and write paths [1-2]. Voltage-controlled magnetic anisotropy (VCMA) lowers the energy barrier during magnetization switching by applying a voltage across the magnetic tunnel junction (MTJ) [3-5]. Integrating multiple MTJs on a shared write line can improve the storage density by using the VCMA effect as a selective mechanism and the SOT effect as a write mechanism. However, SOT-induced switching of deterministic perpendicular magnetization necessitates an in-plane external field, which limits its practical application. Utilizing the in-plane stray field from a magnet under the heavy metal layer is promising to realize field free SOT switching [6-8], while further study is needed in MTJ arrays. In this paper, we simulate spin-orbit torque switching with stray field assistance in a single MTJ and MTJ arrays. First, the stray field of an in-plane magnet with the size of 120nm×60nm×3nm is calculated to be 12.6mT (Fig. 1a). Through Mumax simulation, the single MTJ with the diameter of 60nm can be switched under the cirtical current of 12MA/cm2 with pulse width of 2ns (Fig. 1b). Moreover, in the array of two MTJs, both MTJs can be switched with a critical current of 13MA/cm2. However, the in-plane component of stray field in the MTJ2 is only 0.9 mT in the array of three MTJs (Fig. 2a). The perpendicular component of the magnetic moment oscillates slowly, which takes 10ns to switch with a critical current of 14MA/cm2 (Fig. 2b). Furthermore, in an array of four MTJs, the MTJ2 and MTJ3 cannot be switched due to the small stray field. In conclution, this work demonstrates feasibility of SOT switching with stray filed assistance in a single MTJ and the array with two MTJs, but the arrays with more than three MTJs cannot perform well.References: [1] M. Cubukcu, O. Boulle, M. Drouard, Appl. Phys. Lett., Vol. 104, no. 4, Art. no. 042406(2014) [2] M. Wang, W. Cai, D. Zhu, Nat. Electron., Vol. 1, no. 11, p.582-588(2018) [3] S. Peng, J. Lu, W. Li, in Proc. IEEE Int. Electron Devices Meeting, p.28.6.1-28.6.4(2019) [4] W. Li, Z. Liu, S. Peng, IEEE Electron Device Lett., Vol. 45, no. 5, p.921-924(2024) [5] J. Lu, W. Li, J. Liu, Appl. Phys. Lett., Vol. 122, no. 1, Art. no. 012402(2023) [6] K. Cai, G. Talmelli, K. Fan, in Proc. IEEE Int. Electron Devices Meeting, p.36.2.1-36.2.4(2022) [7] K. Garello, F. Yasin, H. Hody, in Proc. Symp. VLSI Circuits, p.T194-T195(2019) [8] M. Gupta, Y. Xiangt, F. García-Redondo, in Proc. IEEE Int. Electron Devices Meeting, p.1-4(2023).