Orbital and Spin–Orbit Torque Interplay in Ta/W-Based Magnetic Tunnel Junctions with Vertical Nonlocal Switching

Abstract

Spin–orbit torque (SOT) enables ultrafast, energy-efficient magnetization switching, making it promising for MRAM cache applications. However, current SOT-MRAM devices face write efficiency limitations, with charge-to-spin conversion (ξDL) reaching only ∼ 45%, well below the projected ∼80% required for advanced transistor nodes. Recent advances in orbital current physics offer a route to enhance ξDL. Here, we study the Ta(3–30 nm)/W(1–4 nm) system, revealing a large additional torque contribution from Ta, a 4-fold increase over the spin Hall effect in Ta alone, attributed to the orbital physics. This system exhibits larger ξDL than W-based SOT systems, while maintaining robust perpendicular magnetic anisotropy and 400 °C annealing compatibility. We integrate the Ta/W system into 3-terminal SOT-MTJ devices, demonstrating performance comparable to W-based systems. Our results show that orbital physics offers a viable strategy to enhance SOT-MRAM efficiency. We further propose and demonstrate proof-of-concept vertical nonlocal switching using orbital torques, simplifying bottom-pinned SOT-MRAM fabrication.