Field-free spin–orbit torque devices for logic and neural network applications

Abstract

Robust field-free spin–orbit torque (SOT) switching plays an essential role in realizing practical SOT-based magnetic memories and logic devices. Leveraging the strong interlayer Dzyaloshinskii–Moriya interaction, field-free SOT switching is achieved with a threshold switching current density of 5.4 × 1010 A/m2. By exploiting the advantage of separated read–write paths, we demonstrate fundamental logic operations such as AND, OR, and NOT in a dual-channel SOT Hall bar device. We further explore the application of a digital SOT magnetic random access memory (MRAM) design in addressing the issue of the low ON/OFF ratio of the conventional spin-transfer torque MRAM, highlighting its potential for neural network applications. Our simulation results show that using digital SOT MRAM can achieve a classification accuracy of 92.2% for the MNIST dataset, outperforms the analog SOT MRAM case (<10%), and presents remarkable improvements in power and time efficiencies compared to the SRAM case. These findings establish digital SOT MRAM as a frontrunner for edge artificial intelligence applications and offline inference.