Achieving high spin–orbit torque efficiency and robust thermal stability in the sputter-grown topological bilayer BiSb/Pt

Abstract

Topological insulators (TIs) have emerged as promising candidates for spin–orbit torque (SOT) devices, owing to their high charge-to-spin conversion efficiency. However, integrating TIs, such as polycrystalline Bi0.9Sb0.1, into conventional complementary metal-oxide-semiconductor (CMOS) processes poses significant challenges, as their SOT efficiency is compromised by the elevated thermal budgets required by back-end-of-line (BEOL) processing. In this work, we examine the thermal stability of sputter-grown Bi0.9Sb0.1/Py films. While the system exhibits a high SOT efficiency (ξFMR = 0.83) after annealing at 230 °C, the efficiency decreases by ∼65% when the annealing temperature is increased to 400 °C. To reduce this degradation, a 1.5 nm Pt insertion layer is added to the Bi0.9Sb0.1/Py interface. This engineering approach effectively reduces interfacial intermixing, enabling the stack to maintain a strong SOT efficiency of 0.85 even after annealing at 400 °C. Consequently, our results contribute to the development of BiSb-based spin–orbit torque magnetic random-access memory (SOT-MRAM) and its integration with CMOS technologies.