Ti-alloyed β-W heterojunctions exhibiting spin-orbit torque switching at a wide operating temperature range

Abstract

Spin-orbit torque (SOT) switching has gained significant interest, particularly in the context of non-volatile embedded memory for advanced automotive vehicles. The study of temperature-dependent SOT switching, a less explored area, is crucial for developing automotive electronics Grade-0, which requires an ambient operating temperature range from −40 to 150 °C. These SOT devices demand substantial SOT efficiency to ensure a low operating current. Additionally, materials employed in these devices must be compatible with semiconductor fabrication. This study presents the first principles calculations to estimate the spin Hall conductivity (σSH) change of Ti-alloyed β-phase W structures depending on the Ti composition. The calculation predicts the highest σSH value of −1461 (ℏ/e) S/cm at Ti 12.5 at%. In addition, we fabricate β-W-Ti (x at%) 5/Co40Fe40B20 0.9/MgO 1 (in nm) heterojunctions with various Ti compositions to confirm the above result experimentally. Under the controllable experimental condition, we observe the heterojunction with β-W-Ti 11.5 at% exhibits an enhanced damping-like SOT efficiency of 0.54 (compared to 0.30 of pure β-W) with longitudinal resistivity of 149.7 μΩ·cm. The critical current density (Jc) reaches as low as 15.5 cm2. We also demonstrate that SOT switching is possible at ambient temperatures ranging from −55 to +150 °C.