Alexander Makarov was born in Volgograd, Russia, in 1985. He studied information technology at the Volgograd State Technical University, where he received the BSc degree in 2006 and MSc degree in 2008. He joined the Institute for Microelectronics in October 2009 and has obtained the doctoral degree in March 2014. He is currently employed as a post-doc researcher. His scientific interests include Monte-Carlo simulations and nonvolatile memory device modeling.
A Novel Method of SOT-MRAM Switching
Three-terminal memory cell structures based on a magnetic tunnel junction (MTJ) are promising candidates for future generations of magnetic memory. In particular, three-terminal devices with spin-orbit torque (SOT) switching have already been proposed. An SOT memory cell is an MTJ fabricated on a heavy metal channel with large spin-orbit interaction, wherein the soft layer is in direct contact with the heavy metal channel. Spin torque is induced by the in-plane current via the spin-orbit coupling effect, such as the Rashba effect and/or the spin Hall effect (SHE). One shortcoming, however, is that an external magnetic field is required to provide deterministic switching. The second shortcoming of this memory type compared to the conventional spin transfer torque memory is that it demands more space and thus leads to a lower area density because of the second transistor required for writing.
In order to overcome these limitations, we propose an external magnetic field free method of soft magnetic layer switching (Fig. 1). In the proposed method the soft magnetic layer switching operation is based on two consecutive orthogonal sub-nanosecond in-plane current pulses. The switching is governed by the torques generated by the SHE. The first pulse is necessary for tilting the magnetization of the soft layer from its stable state and creating a small initial angle (Fig. 1b). The second pulse is used for switching the soft layer to a new state (Fig. 1c).
We investigated the proposed method by means of extensive micromagnetic simulations. Our simulations show an absence of switching when using only one of the two pulses, as this switching is an unwanted event and leads to loss of information in half-selected cells in a cross-point architecture. Furthermore, our analysis of the proposed method reveals a wide range of currents and write pulses’ widths, which could be used for soft magnetic layer switching.
Fig. 1: Schematic illustration of the proposed method of soft magnetic layer switching. In (b) and (c), the direction of the charge current is shown by big arrows, the direction of the electron spin is given by small arrows.