Complementary-Magnetization-Switching Perpendicular Spin-Orbit Torque Random-Access Memory Cell for High Read Performance

Abstract

The read reliability of spin-transfer torque magnetic random-access memory (STT-MRAM) is greatly hindered by a low sensing margin as a result of a small tunneling magnetoresistance ratio. Although the new generation of perpendicular anisotropy spin-orbit torque (SOT)-MRAM offers faster access speed and a longer lifetime than STT-MRAM, its read performance has not improved or even deteriorated because of the additional resistance of the SOT channel in the read path. In this letter, we propose two novel cell structures of SOT-MRAM that consist of one/two transistors, two diodes, and two magnetic tunnel junctions (1T2D2MTJ/2T2D2MTJ) on a shared U-shaped antiferromagnet layer, enabling a self-referencing scheme. Thanks to the bent current channel, the opposite direction of the SOT current below the free layers can one-step switch different data states in compatibility with the existing fabrication process of SOT-MRAM. Combined with the 28 nm tech node and Verilog-A MTJ compact model, the simulation results show that our MRAM cell significantly improves the sensing margin and bit error rate over the conventional two transistors and one MTJ (2T1M) cell, which is expected to become a high read performance solution.