Unconventional Spin-Orbit Torques (SOT) in Sputtered Materials for High Density High Speed MRAM

Spin orbit torque magnetoresistive random access memory (SOT-MRAM) promises SRAM-like performance at higher bit cell density and energy efficiency. High spin-orbit torques (SOTs) generated by in-plane currents in heavy metals and topological materials and interfaced with a ferromagnetic layer show great potentials of high endurance and robustness for next generation MRAM. From a system perspective, such MRAM is a memory technology well suited for energy efficient in-memory computing (IMC). SOT switching of magnetization is known for ultrafast operation in the nanosecond (ns) and subnanosecond (sub-ns) regimes. An important problem that remains to be solved, though, is that the SOT switching mechanisms still require a stray magnetic field to achieve deterministic switching. To circumvent the above limitation, we and a few other groups are developing unconventional spins generated in MnPd3, IrMn, CuPt and Pt/CoN thin films, among others. Notably, we have demonstrated complete field-free deterministic switching with anti-damping-like SOT due to unconventional spin polarizations. A next-generation high density and high speed MRAM technology is embodied in a 2-terminal SOTMRAM. We find that a 10° unconventional tilt angle in SOT can increase the switching speed by ~4× compared to STT-MRAM.