Dopering van platina voor hoogefficiënte spin-orbit torque magnetoweerstand random-access geheugen

Spin-orbit torque magnetoresistive random-access memory (SOT-MRAM) is a promising candidate for replacing non-volatile SRAM. Platinum (Pt) is a favourable SOT material due to its low resistivity and compatibility with back-end-of-line (BEOL) processes in CMOS technology. However, the relatively high write current remains a significant challenge for SOT-MRAM applications. Enhancing the charge-to-spin conversion efficiency of SOT materials while maintaining perpendicular magnetization and BEOL compatibility is therefore crucial. This study explores Pt doping as a strategy to improve SOT efficiency. A comparative analysis of local and global doping reveals that, depending on dopant solubility, Pt alloys (global doping) achieve higher SOT efficiency while preserving sufficient perpendicular magnetic anisotropy (PMA) in the magnetic layer. This improvement is attributed to the formation of binary Pt alloys, which retain intrinsic spin Hall contributions while dopants enhance extrinsic scattering effects. Additionally, these Pt alloys serve as effective seed layers for PtCo alloy formation after BEOL annealing. The most promising Pt-based material, PtCu alloys, was used to fabricate state-of-the-art perpendicular magnetic tunnel junctions (pMTJs) with strong free-layer PMA and stable tunneling magnetoresistance. When patterned into nanoscale SOT-MRAM devices, PtCu alloys reduced the required write current by half, demonstrating their potential for improving SOT-MRAM efficiency through Pt doping.