Field-free Spin-orbit Torque Switching of Perpendicular Magnetic Tunnel Junction Utilizing Voltage-Controlled Magnetic Anisotropy Pulse Width Optimization

Spin transfer torque magnetic random access memory (STT-MRAM) has been considered as a promising non-volatile memory candidate for next-generation products. The main difficulty of STT-MRAM applications are the write energy consumption, latency, and endurance. Recently, a novel magnetic random access memory: spin-orbit torque MRAM (SOT-MRAM) architecture provides a new method to switch the magnetization direction of the magnetic tunnel junction. SOT-MRAM has the characteristic of short latency, low power, and high endurance, which get rid of the problems encountered by STT-MRAM. The magnetic tunnel junction with perpendicularly magnetized ferromagnetic layers has the advantages of scalability and higher thermal stability. However, the assistance of a magnetic field is essential to switching the magnetization of a perpendicular magnetic tunnel junction deterministically, which is pernicious for real applications. In this paper, a new method is investigated to switch the perpendicular magnetic tunnel junction deterministically without the help of a magnetic field. This method utilizes voltage-controlled magnetic anisotropy (VCMA) to induce an in-plane effective field which substitutes for the external field. The magnetic dynamics and conditions of pulse control of this field-free method are simulated by solving a modified Landau-Lifshitz-Gilbert equation. Our results show that this method is not only field-free but also faster than the typical field-dependent method, which has the potential for high-speed MRAM design.