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, I-c. However, this critical current misses one fundamental physical issue for the commercialization of STT MRAM; the so-called nonswitching probability (P-NS) 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 P-Ns incorporated. The definition of the LSS current and the analytical expressions are obtained by solving the Fokker-Planck equation with a given specific P-NS 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%.