R&D: Two-Terminal Spin–Orbit Torque Magnetoresistive Random Access Memory

Nature Electronics has published an article written by Noriyuki Sato, Department of Electrical Engineering, Stanford University, Stanford, CA, USA, Fen Xue, Department of Electrical Engineering, Stanford University, Stanford, CA, USA , and Department of Electrical Engineering, Tsinghua University, Beijing, China, Robert M. White, Department of Electrical Engineering, Stanford University, Stanford, CA, USA, and Department of Material Science and Engineering, Stanford University, Stanford, CA, USA, Chong Bi, Department of Electrical Engineering, Stanford University, Stanford, CA, USA, and Shan X. Wang, Department of Electrical Engineering, Stanford University, Stanford, CA, USA, and Department of Material Science and Engineering, Stanford University, Stanford, CA, USA.

Abstract : “Spin-transfer torque magnetoresistive random access memory (STT-MRAM) is an attractive alternative to existing random access memory technologies due to its non-volatility, fast operation and high endurance. However, STT-MRAM does have limitations, including the stochastic nature of the STT-switching and a high critical switching current, which makes it unsuitable for ultrafast operation in the nanosecond and subnanosecond regimes. Spin–orbit torque (SOT) switching, which relies on the torque generated by an in-plane current, has the potential to overcome these limitations. However, SOT-MRAM cells studied so far use a three-terminal structure to apply the in-plane current, which increases the size of the cells. Here we report a two-terminal SOT-MRAM cell based on a CoFeB/MgO magnetic tunnel junction pillar on an ultrathin and narrow Ta underlayer. In this device, in-plane and out-of-plane currents are simultaneously generated on application of a voltage, and we demonstrate that the switching mechanism is dominated by SOT.“