Numerical Analysis of Deterministic Switching of a Perpendicularly Magnetized Spin-Orbit Torque Memory Cell

Abstract

We propose a magnetic field-free spin-orbit torque switching scheme based on two orthogonal current pulses, for which deterministic switching is demonstrated via numerical simulations. The first current pulse selects the cell, while the second current pulse ensures deterministic switching of the selected cell. 100% switching probability has been obtained for a wide range of amplitudes and durations of the pulses, thus precise timings are not required. This has also been verified considering a variability of ±5% of the saturation magnetization and anisotropy constant. An important feature of the scheme is that the magnitude of the second current is lower than the critical current for spin-orbit torque switching. The lower second current pulse improves the efficiency of the switching, reducing the corresponding pulse power by 75% and the total writing power by 40%, while maintaining the same switching time. Due to the sub-critical current, the corresponding spin-orbit torque is weak and does not disturb the bits of non-selected cells. Therefore, a single additional wire can be routed through several cells in a row, reducing the number of transistors per cell, and simplifying the cell integration in a memory array. Index Terms-Spin-orbit torque MRAM, perpendicular magnetization, magnetic field-free switching, two-pulse switching scheme I. INTRODUCTION S PIN-ORBIT torque (SOT) magnetoresistive random access memory (MRAM) is a promising future nonvolatile memory solution for ultra-fast operation beyond the spintransfer torque MRAM. In particular, it is a viable candidate for a nonvolatile replacement of high-level caches, as it delivers high operation speed and large endurance [1]. However, for deterministic SOT switching of a perpendicularly magnetized free layer (FL) an external magnetic field is required [2], which is cumbersome for large scale integration. In order to circumvent this issue, several field-free schemes have been proposed [3], [4], [5], [6]. Recently, Garello et al. [7], [8] demonstrated a successful integration of a cobalt nanomagnet which provides the required

Optimization of a Spin-Orbit Torque Switching Scheme Based on Micromagnetic Simulations and Reinforcement Learning

“…We consider an alternative field-free scheme, in which a purely electrical control of the switching process is realized by applying current pulses to two orthogonal heavy metal wires [ 24 ]. A proper configuration of the current pulses is able to reverse the perpendicularly magnetized FL [ 25 ]. Nevertheless, an interesting question arises: how can one determine a pulse sequence that leads to optimal switching?…”