Iridium Enabled Field-free Spin-orbit Torque Switching of Perpendicular Magnetic Tunnel Junction Device

Writing magnetic bits by spin-orbit torques (SOTs) arising from spin Hall effect creates new possibilities for ultrafast and low-power magnetoresistive random access memory (MRAM). For perpendicular MRAM, an extra in-plane field is required to break the symmetry for the deterministic SOT writing of the perpendicular storage layer. Although schemes have been demonstrated in external-field-free SOT switching of a perpendicular layer, practically integrating them with perpendicular MTJs still appears to be challenging. Here, we present experimental demonstration of spin-orbit torques (SOTs) switching a perpendicular magnetic tunnel junction (MTJ) device without applying an external magnetic field. An Ir layer is used to serve dual-purpose of both injecting the pure spin current via spin Hall effect and mediating an in-plane exchange field to the perpendicular free layer of the MTJ. Robust field-free SOT switching with pulsed write path current is demonstrated for various MTJ sizes ranging from 50 nm to 500 nm. The effect of MTJ size and pulse width on the critical switching current is studied. Combined micromagnetic simulations are carried out to provide in-depth analysis of the switching dynamics as well as the thermal effect on the switching.