Multi‐Level Switching and Reversible Current Driven Domain‐Wall Motion in Single CoFeB/MgO/CoFeB‐Based Perpendicular Magnetic Tunnel Junctions

Abstract

One of the critical issues in spintronics‐based technologies is to increase the data storage density. Current strategy is based on shrinking the devices size down to tens of nanometers, or several nanometers, which is reaching its limit. A new proposal is to use multi‐level cells (MLCs) to store more than two bits in each cell. In this work, the multi‐level switching is realized in CoFeB/MgO/CoFeB based nano‐scale single perpendicular magnetic tunnel junctions (p‐MTJs) with three or four stable resistance states. A large range of writing currents for each state is obtained, accompanying with a good repeatability of set‐reset operations between different states. The developed multi‐domain model perfectly matches the experimental results, reflecting the magnetic behaviors during multi‐level switching. Furthermore, current‐driven domain wall (DW) motion is revealed in the circular p‐MTJs, where the DW position can be reversibly manipulated by applied current. To design high‐performance multi‐level p‐MTJs, the parameter diagrams are calculated, suggesting various feasible strategies to improve the multi‐level switching through materials optimization and devices geometry. In summary, the demonstration of multi‐level switching in single p‐MTJ shows the high potential of realizing the new generation of p‐MTJ‐based multi‐level spintronic devices, such as multi‐level memories and spin‐neuron devices.

Seebeck effect and Joule heating in CoFeB/MgO/CoFeB-based perpendicular magnetic tunnel junctions with low resistance area product

“…We obtain p-TMR = 91%, J c = 2-3 × 10 10 A m −2 and resistance area product (RA) = 7.5 Ωµm 2 , which fit the requirements of the applications of p-STT-MRAMs [2]. A systemetic study of junction size dependent CIS has been reported in our previous study [18]. A small shift of CIS curve center is observed, most likely due to Néel-type and dipole coupling between the RL and FL, which can be affected by the size dependent homogeneous magnetization [19].…”

“…After the nano-fabrication, the p-MTJs were annealed in vacuum conditions (∼1 × 10 −6 Torr) at 300 • C remaining 80 min without magnetic field. The CIS properties of the p-MTJs were characterized in four-probe method, where the DC current (I) was applied in two contacts, while the voltage (V) was measured in two crossed contacts [18].…”

Underlying Mechanisms and Tunability of the Anomalous Hall Effect in NiCo2O4 Films with Robust Perpendicular Magnetic Anisotropy

“…[ 25 , 77 ] Recently, many efforts have been made to develop multiple‐valued memories considering various strategies. [ 78 , 79 , 80 , 81 , 82 , 83 , 84 ] However, a successful design has not been achieved. In this context, our MVL device concept based on NCO films appears particularly promising.…”

Implementation of Highly Reliable and Energy‐Efficient Nonvolatile In‐Memory Computing using Multistate Domain Wall Spin–Orbit Torque Device

“…Some of the reported multistate realizations are based on in-plane magnetic anisotropic structures or geometric device fabrications with domain wall motion (DWM) models, e.g., the experimental demonstration of the two-level device based on DWM in a spin valve, [38] three-level device with the half-ring shape, [39] and four-state MTJ switchable with SOT. [40] Despite the available reports on pure simulation and prototype DW-MTJ devices, [8,[41][42][43][44][45] development is hindered by system integration and operation efficiency limits. Explicitly, to date, few functional implementations exist of SOT-MTJ devices with reliable and switchable multistates in a synthetic, CMOS compatible, and field-free integration.…”