High-Density Spin–Orbit Torque Magnetic Random Access Memory With Voltage-Controlled Magnetic Anisotropy/Spin-Transfer Torque Assist

Abstract

This paper explores an area saving scheme for spinorbit torque (SOT) magnetic random-access memory (MRAM) by sharing the SOT channel and write transistor among multiple magnetic tunnel junctions (MTJs). We use two write mechanisms to selectively write the MTJs; voltage-controlled magnetic anisotropy (VCMA) assisted write in the presence of an external magnetic field and field-free spin-transfer torque (STT) assisted write. Using micromagnetic simulations that are augmented by the rare-event enhancement, we study various tradeoffs among write current, time and energy, write error rate (WER), and the number of MTJs on an SOT channel. We quantify the issue of IR drop on the SOT channel as a function of the SOT layer thickness and number of MTJs. Our results show having more than 4 MTJs on an SOT channel poses major challenges in terms of IR drop and WER. In addition, we evaluate the impact of the proposed scheme on read performance.Index Terms-Magnetic random-access memory (MRAM), spin-transfer torque (STT), spin-orbit torque (SOT), voltagecontrolled magnetic anisotropy (VCMA).

Perpendicular magnetic properties and field-free current-induced switching in W/CoFeB/MgO trilayers with a compensating oblique W underlayer

“…The roughness increases with the tilting angle although the variation is insignificant. We have also fabricated three series control films, W(4)/CoFeB(1.3-3.6)/W(4)/SiO 2 (5), W(+50 • , 4)/CoFeB(1.3-3.6)/W(4)/SiO 2 (5), and MgO(3)/CoFeB(1.3-3.6)/MgO(3)/SiO 2 (5). The nominal magnetic dead layer thickness (t d ) is determined through linear fitting the saturation moment per unit area against CoFeB thickness (t) [28].…”

“…Spin-orbit torque magnetic random access memory (SOT-MRAM) with perpendicular magnetic anisotropy (PMA) has garnered significant interest due to its merits in low power consumption, high-density and fast read-write operation [1][2][3][4][5][6][7]. The typical SOT structure for MRAM devices involves a heavy metal/ferromagnetic metal (HM/FM) bilayer capped by an oxide layer, in which an in-plane current flowing through the HM layer can generate an out-of-plane spin current via the spin Hall effect (SHE) or Rashba effect [8,9].…”

Modeling of spin-orbit torque (SOT) channel and high-density SOT magnetic random-access memory

“…This large ∆ is needed to have sufficient write selectivity for individual MTJs. 16 We assume a field-like to damping-like torque ratio of 0.18 38 and a VCMA coefficient of 100 fJ/V-m. 39 Fig. 5(b) shows the WER as a function of the applied spin current (I s ) for various values of V M T J .…”

“…The details of SPICE simulations along with write voltage/current values are provided in the earlier work. 16 Fig. 7(a) shows the cell area per bit versus N M T J .…”

“…In this invited paper we summarize our prior publications describing the modeling of nanoscale SOT channel 15 and SOT channel sharing schemes for SOT-MRAM. 16 After this introduction, Section II describe the SOT channel modeling and optimization. The SOT channel sharing schemes based on the VCMA effect and STT are presented in Section III.…”