Optimization of tungsten β -phase window for spin-orbit-torque magnetic random-access memory

International audienceSwitching induced by spin-orbit torque (SOT) is being vigorously explored, as it allows the control of magnetization using an in-plane current, which enables a three-terminal magnetic-tunnel-junction geometry with isolated read and write paths. This significantly improves the device endurance and the read stability, and allows reliable subnanosecond switching. Tungsten in the β phase, β-W, has the largest reported antidamping SOT charge-to-spin conversion ratio (θ AD ≈ −60%) for heavy metals. However, β-W has a limitation when one is aiming for reliable technology integration: the β phase is limited to a thickness of a few nanometers and enters the α phase above 4 nm in our samples when industryrelevant deposition tools are used. Here, we report our approach to extending the range of β-W, while simultaneously improving the SOT efficiency by introducing N and O doping of W. Resistivity and XRD measurements confirm the extension of the β phase from 4 nm to more than 10 nm, and transport characterization shows an effective SOT efficiency larger than −44.4% (reaching approximately −60% for the bulk contribution). In addition, we demonstrate the possibility of controlling and enhancing the perpendicular magnetic anisotropy of a storage layer (Co-Fe-B). Further, we integrate the optimized W(O, N) into SOT magnetic random-access memory (SOT-MRAM) devices and project that, for the same thickness of SOT material, the switching current decreases by 25% in optimized W(O, N) compared with our standard W. Our results open the path to using and further optimizing W for integration of SOT-MRAM technology