Multi‐State Magnetic Tunnel Junction Programmable by Nanosecond Spin‐Orbit Torque Pulse Sequence

Multi-state spin-orbit torque (SOT) switching, particularly in magnetic tunnel junction (MTJ) geometry, is promising hardware for artificial intelligence due to its potential to form artificial neurons and to increase storage density per bit. Here, multi-state switching is demonstrated in Pt/Co40Fe40B20/MgO-based elliptical MTJ, fabricated on a 200 mm wafer platform, using nanosecond spin-orbit torque pulses. Multi-state switching is achieved using MTJs composed of a single ferromagnetic storage layer and without resorting to any domain-wall pinning step. The genesis of the multi-states, rather than the expected bistable states in MTJs, come from the formation and stabilization of metastable domains by the voltage pulse. The persistence and the probability of the mid-states are investigated by two different spin-orbit torque pulse sequences. Additionally, it is reported that size (>domain-wall width), exchange constant (J m(-1)), current density amplitude (approximate to threshold values), and pulse sequence are important considerations for realizing multi-state SOT MTJs. These industry-grade MTJs can be leveraged to accelerate the development of spintronics-based neuromorphic devices.