Limited Stochastic Current for Energy-Optimized Switching of Spin-Transfer-Torque Magnetic Random-Access Memory

The switching of spin-transfer-torque magnetic random-access memory (STT MRAM) in the simple macrospin model is determined by the amplitude and pulse duration of the applied current, and it requires a current that is higher than a critical current, Ic. However, this critical current misses one fundamental physical issue for the commercialization of STT MRAM; the so-called nonswitching probability (PNS) or write soft-error rate (WSER), which is influenced by the stochastic nature of the switching process at finite temperature. Herein, we propose a limited stochastic switching (LSS) current, which is another definition for the critical current with the PNS incorporated. The definition of the LSS current and the analytical expressions are obtained by solving the Fokker-Planck equation with a given specific PNS value. Most importantly, by using the LSS current and optimizing it together with the related pulse-duration time, we find the optimum combination of current amplitude and pulse duration, which may reduce the energy consumption of the STT MRAM by up to 75%.