Impact of Spin-Orbit Torque on Spin-Transfer Torque Switching in Magnetic Tunnel Junctions

Abstract

the paper presents our simulated results showing the substantial improvement of both switching speed and energy consumption in a perpendicular magnetic tunnel junction (p-MTJ), a core unit of Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM), by the help of additional Spin-Orbit-Torque (SOT) write pulse current (WP Sot ). An STT-SOT hybrid torque module for OOMMF simulation is implemented to investigate the switching behavior of a 20 nm cell in the p-MTJ. We found that the assistance of WP Sot to STT write pulse current (WP Stt ) have a huge influence on the switching behavior of the free layer in the p-MTJ. For example, we could dramatically reduce the switching time (t SW ) by 80% and thereby reduce the write energy over 70% as compared to those in the absence of the WP Sot . Even a very tiny amplitude of WP Sot (J Sot of the order of 10 2 A/m 2 ) substantially assists to reduce the critical current density for switching of the free layer and thereby decreases the energy consumption as well. It is worth to be pointed out that the energy can be saved further by tuning the WP Sot parameters, i.e., amplitude and duration along at the threshold WP Stt . Our findings show that the proposed STT-SOT hybrid switching scheme has a great impact on the MRAM technology seeking the high speed and low energy consumption.Magnetic Random Access Memory (MRAM) has known to be an outstanding candidate among next-generation memories due to its various advantages, such as non-volatility, high-speed operation, high density and scalability, over other competing memories 1-4 . In particular, spin-transfer torque MRAM (STT-MRAM) composed of perpendicular magnetic tunnel junctions (p-MTJs) has received a significant attention because it offers reduced write current and strong thermal stability 5 . In an MTJ, there are two ferromagnetic (FM) layers separated by an insulating tunneling barrier. One FM layer has a fixed magnetization and another has a variable magnetization (called as a free layer) which can be made to align either parallel (P) or anti-parallel (AP) with respect to the fixed layer. Magnetization of the free layer is used to store the data and can be switched by spin-polarized electrons (equivalently spin current) without a magnetic field. When the spin-polarized current flows through the free layer, the layer absorbs spin angular momentum from the electrons and as a result, its magnetization flips, which is the reason why we call it spin (momentum) transfer torque. STT-MRAM faces various challenges along with its merits such as, the reliability of a tunnel barrier, long write latency and small energy efficiency due to still high write current. Out of these, the most important issue which needs to be counter first is high energy consumption due to high write current and long write latency. The current density for switching of STT-MRAM is relatively large and hence large transistors are inevitable to drive it, which thus significantly limits their future use for memory applications 6,7 . The sustainability of hig...

Critical switching current density of magnetic tunnel junction with shape perpendicular magnetic anisotropy through the combination of spin-transfer and spin-orbit torques

“…Magnetization switching of perpendicularly magnetized MTJ through the interplay of STT and SOT makes deterministic switching possible without an external magnetic field, along with methods of inducing lateral inversion symmetry breaking through the lateral structural asymmetry, generating the exchange field using an antiferromagnetic layer and inducing symmetry breaking through the tilted magnetic easy axis 30,32,34,39,40 . STT-SOT switching of the MTJ with I-PMA has been studied through experiments and micromagnetic simulations [41][42][43] . The current density for magnetization switching decreased as the SOT current density increased.…”

“…In addition, the incubation time of STT-SOT switching was greatly reduced in SOT-dominant switching 41 . In terms of power consumption, the energy efficiency is improved compared with STT switching, and the smaller the radius of the MTJ, the lower the power consumption 42 . Compared with SOT switching with an external magnetic field, STT-SOT switching significantly improves deterministic switching, even when the MTJ is deformed 43 .…”

Tuning the High‐Efficiency Field‐Free Current‐Induced Deterministic Switching via Ultrathin PtMo Layer with Mo Content

“…Zelalem Abebe Bekele, Runze Li, Yucai Li, Yi Cao, Xionghua Liu, and Kaiyou Wang* DOI: 10.1002/aelm.202100528 current intensity injected through the MTJ, leading to a time-dependent degradation of MTJ performance. [5][6][7] The conventional SOT-based MTJ device is composed of the MTJ device deposited above a nonmagnetic heavy metal (HM) layer. [7][8][9] The writing current flows through the low resistance HM layer rather than directly through the MTJ junction, [9][10][11] thereby increasing the opportunity to improve the read stability and energy consumption.…”

“…[1][2][3] Compared with a two-terminal spin-transfer torque (STT) magnetic tunnel junction (MTJ), a three-terminal spin-orbit torque (SOT) based MTJ separates the read and the write paths, which results in a lower integration density of the SOT based magnetic random-access memory (SOT-MRAM) than that of the STT-MRAM. [4][5][6] However, in STT-MRAM, energy efficiency and reliability issues remain a fundamental challenge. [5][6] These challenges come from a large spin hall effect (SHE), which relies on scattering by impurities (or other defects), ascribed to skew scattering and side jump.…”

“…[4][5][6] However, in STT-MRAM, energy efficiency and reliability issues remain a fundamental challenge. [5][6] These challenges come from a large spin hall effect (SHE), which relies on scattering by impurities (or other defects), ascribed to skew scattering and side jump. [28] Based on our previous finding, [11] a high-efficiency field-free SOT switching has been achieved through competing spin currents from opposite θ SHA of Pt and Gd atoms.…”